• Alexander, M. A., and C. Deser, 1995: A mechanism for the recurrence of wintertime midlatitude SST anomalies. J. Phys. Oceanogr., 25, 122137, doi:10.1175/1520-0485(1995)025<0122:AMFTRO>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Alexander, M. A., I. Bladé, M. Newman, J. R. Lanzante, N.-C. Lau, and J. D. Scott, 2002: The atmospheric bridge: The influence of ENSO teleconnection on air–sea interaction over the global oceans. J. Climate, 15, 22052231, doi:10.1175/1520-0442(2002)015<2205:TABTIO>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Barnes, E. A., E. Dunn-Sigouln, G. Masato, and T. Woollings, 2014: Exploring recent trends in Northern Hemisphere blocking. Geophys. Res. Lett., 41, 638644, doi:10.1002/2013GL058745.

    • Search Google Scholar
    • Export Citation
  • Barnston, A. G., and R. E. Livezey, 1987: Classification, seasonality, and persistence of low-frequency atmospheric circulation patterns. Mon. Wea. Rev., 115, 10831126, doi:10.1175/1520-0493(1987)115<1083:CSAPOL>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Barriopedro, D., R. García-Herrera, A. R. Lupo, and E. Hernández, 2006: A climatology of Northern Hemisphere blocking. J. Climate, 19, 10421063, doi:10.1175/JCLI3678.1.

    • Search Google Scholar
    • Export Citation
  • Boyle, J. S., and T.-J. Chen, 1987: Synoptic aspects of the wintertime East Asian monsoon. Monsoon Meteorology, C.-P. Chang and T. N. Krishnamurti, Eds., Oxford University Press, 125–160.

  • Chan, J. C. L., and C. Li, 2004: The East Asia winter monsoon. East Asian Monsoon, C.-P. Chang, Ed., World Scientific, 54–106.

  • Chang, C.-P., and K. M. Lau, 1980: Northeasterly cold surges and near-equatorial disturbances over the winter MONEX area during December 1974. II: Planetary-scale aspects. Mon. Wea. Rev., 108, 298312, doi:10.1175/1520-0493(1980)108<0298:NCSANE>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Chang, C.-P., and M.-M. Lu, 2012: Intraseasonal predictability of Siberian high and East Asian winter monsoon and its interdecadal variability. J. Climate, 25, 17731778, doi:10.1175/JCLI-D-11-00500.1.

    • Search Google Scholar
    • Export Citation
  • Chang, C.-P., Z. Wang, and H. Hendon, 2006: The Asian winter monsoon. The Asian Monsoon, B. Wang, Ed., Praxis, 89–127.

  • Chen, T.-C., W.-R. Huang, and J.-H. Yoon, 2004: Interannual variation of the East Asian cold surge activity. J. Climate, 17, 401–413, doi:10.1175/1520-0442(2004)017<0401:IVOTEA>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Chen, W., and T. Li, 2007: Modulation of Northern Hemisphere wintertime stationary planetary wave activity: East Asian climate relationships by the Quasi-Biennial Oscillation. J. Geophys. Res., 112, D20120, doi:10.1029/2007JD008611.

    • Search Google Scholar
    • Export Citation
  • Chen, W., H. Graf, and R. Huang, 2000: The interannual variability of East Asian winter monsoon and its relation to the summer monsoon. Adv. Atmos. Sci., 17, 4860, doi:10.1007/s00376-000-0042-5.

    • Search Google Scholar
    • Export Citation
  • Chen, W., H.-F. Graf, and M. Takahashi, 2002: Observed interannual oscillations of planetary wave forcing in the Northern Hemisphere winter. Geophys. Res. Lett., 29, 2073, doi:10.1029/2002GL016062.

    • Search Google Scholar
    • Export Citation
  • Chen, W., M. Takahashi, and H.-F. Graf, 2003: Interannual variations of stationary planetary wave activity in the northern winter troposphere and stratosphere and their relations to NAM and SST. J. Geophys. Res., 108, 4797, doi:10.1029/2003JD003834.

    • Search Google Scholar
    • Export Citation
  • Chen, W., S. Yang, and R.-H. Huang, 2005: Relationship between stationary planetary wave activity and the East Asian winter monsoon. J. Geophys. Res., 110, D14110, doi:10.1029/2004JD005669.

    • Search Google Scholar
    • Export Citation
  • Chen, W., L. Wang, Y. Xue, and S. Sun, 2009: Variabilities of the spring river runoff system in East China and their relations to precipitation and sea surface temperature. Int. J. Climatol., 29, 13811394, doi:10.1002/joc.1785.

    • Search Google Scholar
    • Export Citation
  • Chen, W., J. Feng, and R. Wu, 2013a: Roles of ENSO and PDO in the link of the East Asian winter monsoon to the following summer monsoon. J. Climate, 26, 622635, doi:10.1175/JCLI-D-12-00021.1.

    • Search Google Scholar
    • Export Citation
  • Chen, W., X. Lan, L. Wang, and Y. Ma, 2013b: The combined effects of the ENSO and the Arctic Oscillation on the winter climate anomalies over East Asia. Chin. Sci. Bull., 58, 13551362, doi:10.1007/s11434-012-5654-5.

    • Search Google Scholar
    • Export Citation
  • Chen, Z., R. Wu, and W. Chen, 2014: Distinguishing interannual variations of the northern and southern modes of the East Asian winter monsoon. J. Climate, 27, 835851, doi:10.1175/JCLI-D-13-00314.1.

    • Search Google Scholar
    • Export Citation
  • Cheung, H. N., W. Zhou, H. Y. Mok, and M. C. Wu, 2012: Relationship between Ural–Siberian blocking and the East Asian winter monsoon in relation to the Arctic Oscillation and the El Niño–Southern Oscillation. J. Climate, 25, 42424257, doi:10.1175/JCLI-D-11-00225.1.

    • Search Google Scholar
    • Export Citation
  • Cheung, H. N., W. Zhou, H. Y. Mok, M. C. Wu, and Y. Shao, 2013a: Revisiting the climatology of atmospheric blocking in the Northern Hemisphere. Adv. Atmos. Sci., 30, 397410, doi:10.1007/s00376-012-2006-y.

    • Search Google Scholar
    • Export Citation
  • Cheung, H. N., W. Zhou, Y. Shao, W. Chen, H. Y. Mok, and M. C. Wu, 2013b: Climatology and characteristics of wintertime atmospheric blocking over Ural–Siberia. Climate Dyn., 41, 6379, doi:10.1007/s00382-012-1587-6.

    • Search Google Scholar
    • Export Citation
  • Chu, E. W. K., 1978: A method for forecasting the arrival of cold surges in Hong Kong. Hong Kong Observatory Tech. Note 43, 31 pp.

  • Cohen, J., M. Barlow, P. J. Kushner, and K. Saito, 2007: Stratosphere-troposphere coupling and links with Eurasian land surface variability. J. Climate, 20, 53355343, doi:10.1175/2007JCLI1725.1.

    • Search Google Scholar
    • Export Citation
  • Cohen, J., M. Barlow, and K. Saito, 2009: Decadal fluctuations in planetary wave forcing moderate global warming in late boreal winter. J. Climate, 22, 44184426, doi:10.1175/2009JCLI2931.1.

    • Search Google Scholar
    • Export Citation
  • Cohen, J., and Coauthors, 2014: Recent Arctic amplification and extreme mid-latitude weather. Nat. Geosci., 7, 627637, doi:10.1038/ngeo2234.

    • Search Google Scholar
    • Export Citation
  • Compo, G. P., G. N. Kiladis, and P. J. Webster, 1999: The horizontal and vertical structure of East Asian winter monsoon pressure surges. Quart. J. Roy. Meteor. Soc., 125, 2954, doi:10.1002/qj.49712555304.

    • Search Google Scholar
    • Export Citation
  • Deser, C., M. A. Alexander, and M. S. Timlin, 2003: Understanding the persistence of sea surface temperature anomalies in midlatitudes. J. Climate, 16, 5772, doi:10.1175/1520-0442(2003)016<0057:UTPOSS>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Ding, Y., 1990: Buildup, air-mass transformation and propagating of Siberian high and its relations to cold surge in East Asia. Meteor. Atmos. Phys., 44, 281292, doi:10.1007/BF01026822.

    • Search Google Scholar
    • Export Citation
  • Ding, Y., 1994: Monsoons over China. Kluwer Academic Publishers, 420 pp.

  • Ding, Y., Z. Wang, Y. Song, and J. Zhang, 2008: Causes of the unprecedented freezing disaster in January 2008 and its possible association with the global warming. Acta Meteor. Sin., 22, 538558.

    • Search Google Scholar
    • Export Citation
  • Ding, Y., X. Jia, Z. Wang, X. Chen, and L. Chen, 2009: A contrasting study of freezing disaster in January 2008 and in winter of 1954/55 in China. Front. Earth Sci. China, 3, 129145, doi:10.1007/s11707-009-0028-2.

    • Search Google Scholar
    • Export Citation
  • Francis, J. A., and S. J. Vavrus, 2012: Evidence linking Arctic amplification to extreme weather in mid-latitudes. Geophys. Res. Lett., 39, L06801, doi:10.1029/2012GL051000.

    • Search Google Scholar
    • Export Citation
  • Hsu, H.-H., 1987: Propagation of low-level circulation features in the vicinity of mountain ranges. Mon. Wea. Rev., 115, 18641892, doi:10.1175/1520-0493(1987)115<1864:POLLCF>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Hsu, H.-H., and J. M. Wallace, 1985: Vertical structure of wintertime teleconnection patterns. J. Atmos. Sci., 42, 16931710, doi:10.1175/1520-0469(1985)042<1693:VSOWTP>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Huang, R., J. Chen, L. Wang, and Z. Lin, 2012: Characteristics, processes, and causes of the spatio-temporal variabilities of the East Asian monsoon system. Adv. Atmos. Sci., 29, 910942, doi:10.1007/s00376-012-2015-x.

    • Search Google Scholar
    • Export Citation
  • Hung, C., and P. Kao, 2010: Weakening of the winter monsoon and abrupt increase of winter rainfalls over northern Taiwan and southern China in the early 1980s. J. Climate, 23, 23572367, doi:10.1175/2009JCLI3182.1.

    • Search Google Scholar
    • Export Citation
  • Jeong, J.-H., T. Ou, H. W. Linderholm, B.-M. Kim, S.-J. Kim, J.-S. Kug, and D. Chen, 2011: Recent recovery of the Siberian high intensity. J. Geophys. Res., 116, D23102, doi:10.1029/2011JD015904.

    • Search Google Scholar
    • Export Citation
  • Jhun, J.-G., and E.-J. Lee, 2004: A new East Asian winter monsoon index and associated characteristics of the winter monsoon. J. Climate, 17, 711726, doi:10.1175/1520-0442(2004)017<0711:ANEAWM>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Joung, C.-H., and M.-H. Hitchman, 1982: On the role of successive downstream development in East Asian polar air outbreaks. Mon. Wea. Rev., 110, 12241237, doi:10.1175/1520-0493(1982)110<1224:OTROSD>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Kalnay, E., and Coauthors, 1996: The NCEP/NCAR 40-Year Reanalysis Project. Bull. Amer. Meteor. Soc., 77, 437471, doi:10.1175/1520-0477(1996)077<0437:TNYRP>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Lam, C. Y., 1976: 500 millibar troughs passing over Lake Baikal and the arrival of surges at Hong Kong. Hong Kong Observatory Tech. Note 31, 22 pp.

  • Lau, K.-M., and M.-T. Li, 1984: The monsoon of East Asia and its global associations—A survey. Bull. Amer. Meteor. Soc., 65, 114125, doi:10.1175/1520-0477(1984)065<0114:TMOEAA>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Lau, K.-M., C.-P. Chang, and P. H. Chan, 1983: Short-term planetary-scale interaction over the tropics and midlatitudes. Part II: Winter-MONEX period. Mon. Wea. Rev., 111, 13721388, doi:10.1175/1520-0493(1983)111<1372:STPSIO>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Lau, N.-C., and K.-M. Lau, 1984: The structure and energetics of midlatitude disturbances accompanying cold-air outbreaks over East Asia. Mon. Wea. Rev., 112, 13091327, doi:10.1175/1520-0493(1984)112<1309:TSAEOM>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Lau, N.-C., and M. J. Nath, 1999: Observed and GCM-simulated westward-propagating, planetary-scale fluctuations with approximately three-week periods. Mon. Wea. Rev., 127, 23242345, doi:10.1175/1520-0493(1999)127<2324:OAGSWP>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Lee, H.-S., and J.-G. Jhun, 2006: Two types of the Asian continental blocking and their relation to the East Asian monsoon during the boreal winter. Geophys. Res. Lett., 33, L22707, doi:10.1029/2006GL027948.

    • Search Google Scholar
    • Export Citation
  • Lejenäs, H., and H. Øakland, 1983: Characteristics of Northern Hemisphere blocking as determined from long time series of observational data. Tellus, 35A, 350362, doi:10.1111/j.1600-0870.1983.tb00210.x.

    • Search Google Scholar
    • Export Citation
  • Li, C., 1990: Interaction between anomalous winter monsoon in East Asia and El Niño events. Adv. Atmos. Sci., 7, 3646, doi:10.1007/BF02919166.

    • Search Google Scholar
    • Export Citation
  • Li, C., and W. Gu, 2010: An analyzing study of the anomalous activity of blocking high over the Ural Mountains in January 2008 (in Chinese). Chin. J. Atmos. Sci., 34, 865874.

    • Search Google Scholar
    • Export Citation
  • Lu, M.-M., and C.-P. Chang, 2009: Unusual late-season cold surges during the 2005 Asian winter monsoon: Roles of Atlantic blocking and the central Asian anticyclone. J. Climate, 22, 52055217, doi:10.1175/2009JCLI2935.1.

    • Search Google Scholar
    • Export Citation
  • Ma, X., Y. H. Ding, H. Xu, and J. He, 2008: The relation between strong cold waves and low-frequency waves during the 2004/2005 winter (in Chinese). Chin. J. Atmos. Sci., 32, 380394.

    • Search Google Scholar
    • Export Citation
  • Mantua, N. J., S. R. Hare, Y. Zhang, J. M. Wallace, and R. C. Francis, 1997: A Pacific interdecadal climate oscillation with impacts on salmon production. Bull. Amer. Meteor. Soc., 78, 10691079, doi:10.1175/1520-0477(1997)078<1069:APICOW>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Nakamura, H., M. Nakamura, and J. L. Anderson, 1997: The role of high- and low-frequency dynamics in blocking formation. Mon. Wea. Rev., 125, 20742093, doi:10.1175/1520-0493(1997)125<2074:TROHAL>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • North, G. R., T. L. Bell, R. F. Cahalan, and F. J. Moeng, 1982: Sampling errors in the estimation of empirical orthogonal functions. Mon. Wea. Rev., 110, 699706, doi:10.1175/1520-0493(1982)110<0699:SEITEO>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Rayner, N. A., D. E. Parker, E. B. Horton, C. K. Folland, L. V. Alexander, E. C. Kent, and A. Kaplan, 2003: Global analyses of sea surface temperature, sea ice, and night marine air temperature since the late nineteenth century. J. Geophys. Res., 108, 4407, doi:10.1029/2002JD002670.

    • Search Google Scholar
    • Export Citation
  • Takaya, K., and H. Nakamura, 2005a: Mechanisms of intraseasonal amplification of the cold Siberian high. J. Atmos. Sci., 62, 44234440, doi:10.1175/JAS3629.1.

    • Search Google Scholar
    • Export Citation
  • Takaya, K., and H. Nakamura, 2005b: Geographical dependence of upper-level blocking formation associated with intraseasonal amplification of the Siberian high. J. Atmos. Sci., 62, 44414449, doi:10.1175/JAS3628.1.

    • Search Google Scholar
    • Export Citation
  • Takaya, K., and H. Nakamura, 2013: Interannual variability of the East Asian winter monsoon and related modulation of the planetary waves. J. Climate, 26, 94459461, doi:10.1175/JCLI-D-12-00842.1.

    • Search Google Scholar
    • Export Citation
  • Tao, S., and J. Wei, 2008: Severe snow and freezing rain in January 2008 in the southern China (in Chinese). Climatic Environ. Res., 13, 337350.

    • Search Google Scholar
    • Export Citation
  • Tibaldi, S., and F. Molteni, 1990: On the operational predictability of blocking. Tellus, 42A, 343365, doi:10.1034/j.1600-0870.1990.t01-2-00003.x.

    • Search Google Scholar
    • Export Citation
  • Trenberth, K. E., 1997: The definition of El Niño. Bull. Amer. Meteor. Soc., 78, 27712777, doi:10.1175/1520-0477(1997)078<2771:TDOENO>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Tyrlis, E., and B. J. Hoskins, 2008: The morphology of Northern Hemisphere blocking. J. Atmos. Sci., 65, 16531665, doi:10.1175/2007JAS2338.1.

    • Search Google Scholar
    • Export Citation
  • Wallace, J. M., and D. S. Gutzler, 1981: Teleconnections in the geopotential height field during the Northern Hemisphere winter. Mon. Wea. Rev., 109, 784812, doi:10.1175/1520-0493(1981)109<0784:TITGHF>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Wang, B., R. Wu, and X. Fu, 2000: Pacific–East Asia teleconnection: How does ENSO affect East Asian climate? J. Climate, 13, 15171536, doi:10.1175/1520-0442(2000)013<1517:PEATHD>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Wang, B., Z. Wu, C. Chang, J. Liu, J. Li, and T. Zhou, 2010: Another look at interannual-to-interdecadal variations of the East Asian winter monsoon: The northern and southern temperature modes. J. Climate, 23, 14951512, doi:10.1175/2009JCLI3243.1.

    • Search Google Scholar
    • Export Citation
  • Wang, C., H. Liu, and S.-K. Lee, 2010: The record-breaking cold temperatures during the winter of 2009/10 in the Northern Hemisphere. Atmos. Sci. Lett., 11, 161168, doi:10.1002/asl.278.

    • Search Google Scholar
    • Export Citation
  • Wang, L., and W. Chen, 2010: Downward Arctic Oscillation signal associated with moderate weak stratospheric polar vortex and the cold December 2009. Geophys. Res. Lett., 37, L09707, doi:10.1029/2010GL042659.

    • Search Google Scholar
    • Export Citation
  • Wang, L., and W. Chen, 2014a: The East Asian winter monsoon: Re-amplification in the 2000s. Chin. Sci. Bull., 59, 430436, doi:10.1007/s11434-013-0029-0.

    • Search Google Scholar
    • Export Citation
  • Wang, L., and W. Chen, 2014b: An intensity index for the East Asian winter monsoon. J. Climate, 27, 23612374, doi:10.1175/JCLI-D-13-00086.1.

    • Search Google Scholar
    • Export Citation
  • Wang, L., W. Chen, W. Zhou, and R. Huang, 2009a: Interannual variations of East Asian trough axis at 500 hPa and its association with the East Asian winter monsoon pathway. J. Climate, 22, 600614, doi:10.1175/2008JCLI2295.1.

    • Search Google Scholar
    • Export Citation
  • Wang, L., R. Huang, L. Gu, W. Chen, and L. Kang, 2009b: Interdecadal variations of the East Asian winter monsoon and their association with quasi-stationary planetary wave activity. J. Climate, 22, 48604872, doi:10.1175/2009JCLI2973.1.

    • Search Google Scholar
    • Export Citation
  • Wang, L., W. Chen, W. Zhou, J. C. L. Chan, D. Barriopedro, and R. Huang, 2010: Effect of the climate shift around mid 1970s on the relationship between wintertime Ural blocking circulation and East Asian climate. Int. J. Climatol., 30, 153158, doi:10.1002/joc.1876.

    • Search Google Scholar
    • Export Citation
  • Wang, X., Z. Gong, B. Shen, and G. Feng, 2013: A comparative study of the climatic characteristics of the periods of frequent occurrence of the regional extreme low temperature events in China in the recent 50 years. Acta Meteor. Sin., 71, 10611073.

    • Search Google Scholar
    • Export Citation
  • Watanabe, M., and T. Nitta, 1999: Decadal changes in the atmospheric circulation and associated surface climate variations in the Northern Hemisphere winter. J. Climate, 12, 494510, doi:10.1175/1520-0442(1999)012<0494:DCITAC>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Wei, K., W. Chen, and W. Zhou, 2011: Changes in the East Asian cold season since 2000. Adv. Atmos. Sci., 28, 6979, doi:10.1007/s00376-010-9232-y.

    • Search Google Scholar
    • Export Citation
  • Wen, M., S. Yang, A. Kumar, and P. Zhang, 2009: An analysis of the large-scale climate anomalies associated with the snowstorms affecting China in January 2008. Mon. Wea. Rev., 137, 11111131, doi:10.1175/2008MWR2638.1.

    • Search Google Scholar
    • Export Citation
  • Wu, M. C., and J. C. L. Chan, 1995: Surface features of winter monsoon surges over South China. Mon. Wea. Rev., 123, 662680, doi:10.1175/1520-0493(1995)123<0662:SFOWMS>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Wu, M. C., and J. C. L. Chan, 1997: Upper-level features associated with winter monsoon surges over South China. Mon. Wea. Rev., 125, 317340, doi:10.1175/1520-0493(1997)125<0317:ULFAWW>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Wu, M. C., and J. C. L. Chan, 2005: Observational relationships between summer and winter monsoons over East Asia, Part I: Basic framework. Int. J. Climatol., 25, 437451, doi:10.1002/joc.1132.

    • Search Google Scholar
    • Export Citation
  • Wu, M. C., and W. H. Leung, 2009: Effect of ENSO on the Hong Kong winter season. Atmos. Sci. Lett., 10, 94101, doi:10.1002/asl.215.

  • Wu, Z., J. Li, Z. Jiang, and J. He, 2011: Predictable climate dynamics of abnormal East Asian winter monsoon: Once-in-a-century snowstorms in 2007/08 winter. Climate Dyn., 37, 16611669, doi:10.1007/s00382-010-0938-4.

    • Search Google Scholar
    • Export Citation
  • Yan, Z. W., J. J. Xia, C. Qian, and W. Zhou, 2011: Changes in seasonal cycle and extremes in China during the period 1960-2008. Adv. Atmos. Sci., 28, 269283, doi:10.1007/s00376-010-0006-3.

    • Search Google Scholar
    • Export Citation
  • Yang, S., K. M. Lau, and K. M. Kim, 2002: Variations of the East Asian jet stream and Asian–Pacific–American winter climate anomalies. J. Climate, 15, 306325, doi:10.1175/1520-0442(2002)015<0306:VOTEAJ>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Zhai, P., Z. Yan, and X. Zou, 2008: Climate extremes and climate-related disasters in China. Regional Climate Studies of China, C. Fu et al., Eds., Springer-Verlag, 313–339.

  • Zhang, Y., K. R. Sperber, and J. S. Boyle, 1997: Climatology and interannual variation of East Asian winter monsoon: Result from the 1979–95 NCEP/NCAR reanalysis. Mon. Wea. Rev., 125, 26052619, doi:10.1175/1520-0493(1997)125<2605:CAIVOT>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Zhou, W., C. Li, and X. Wang, 2007a: Possible connection between Pacific oceanic interdecadal pathway and East Asian winter monsoon. Geophys. Res. Lett., 34, L01701, doi:10.1029/2007GL031061.

    • Search Google Scholar
    • Export Citation
  • Zhou, W., X. Wang, T. Zhou, C. Li, and J. C. L. Chan, 2007b: Interdecadal variability of the relationship between the East Asian winter monsoon and ENSO. Meteor. Atmos. Phys., 98, 283293, doi:10.1007/s00703-007-0263-6.

    • Search Google Scholar
    • Export Citation
  • Zhou, W., J. C. L. Chan, W. Chen, J. Ling, J. G. Pinto, and Y. Shao, 2009: Synoptic-scale controls of persistent low temperature and icy weather over southern China in January 2008. Mon. Wea. Rev., 137, 39783991, doi:10.1175/2009MWR2952.1.

    • Search Google Scholar
    • Export Citation
  • View in gallery

    (a) Number of cold days observed at the Hong Kong Observatory (HKO) Headquarters for the winter period (DJF; NCD) from 1947/48 to 2013/14. The black (gray) dashed line indicates the linear trend for the period 1947/48–2013/14 (1947/48–2003/04) using the least squares fit. (b) The 11-yr (decadal) running mean of the time series in (a).

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    Day-0 composites of prolonged cold spells in Hong Kong. (a) Anomalies of 850-hPa air temperature (shading, °C) and mean sea level pressure (contour, hPa), (b) 500-hPa geopotential height (contour) and its anomaly (shading) (gpm), (c) 250-hPa zonal wind (contour) and its anomaly (shading) (m s−1), and (d) 50-hPa geopotential height (contour) and its anomaly (shading) (gpm). The contour intervals are shown at the bottom right of each panel and negative (nonnegative) contours are shown by broken (solid) lines.

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    (a)–(f) Lag composites of daily 500-hPa geopotential height anomalies (contours with interval of 20 gpm) and surface air temperature anomalies (shading, °C) during the evolution of prolonged cold spells in Hong Kong. Negative (nonnegative) contours are shown by broken (solid) lines.

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    Longitudinal distribution of blocking frequency during the evolution of prolonged cold spells in Hong Kong (colored lines; see legend for description). The gray dashed line and shading indicate the DJF climatology and its half standard deviation, respectively, for the period 1950/51–2009/10. Unit: % of days.

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    Time series of wintertime blocking frequency (% of days) over (a) the Ural sector, (b) the Pacific sector, and (c) the two sectors concurrently, where the bars indicates the value in each winter and the line represents the 11-yr running mean. (d) Standardized time series of the 8-yr low-pass-filtered value of UBI (Ural blocking index; solid line), and the 8-yr low-pass-filtered value of NCD (dashed line).

  • View in gallery

    Regression of NCD anomalies against (a) the 500-hPa geopotential height anomalies (gpm day−1) and (b) the mean sea level pressure anomalies (hPa day−1). (c),(d) As in (a),(b), but for UBI [gpm %−1 in (c); hPa %−1 in (d)]. Shading indicates the 95% confidence level. In (b) and (d), the Tibetan Plateau is dark shaded.

  • View in gallery

    Scatterplot of the standardized anomaly of NCD and UBI in all winters. Dots (crisscrosses) indicate the years with the two variables in the same (opposite) anomaly sign. The rectangle encloses the UBI ranged between −1 and 1.

  • View in gallery

    Regression of NCD anomalies against (a) the 500-hPa geopotential height anomalies (gpm day−1) and (b) the mean sea level pressure anomalies (hPa day−1) in the winters when standardized UBI and NCD have opposite signs. Shading indicates the 95% confidence level. The rectangular box in (a) indicates the domain of the EOF analysis in Fig. 9a.

  • View in gallery

    (a) First leading EOF mode (EOF1) of the 500-hPa geopotential height over 20°–80°N, 90°E–120°W. (b) Time series of negated principal components of EOF1 or −WPI (bar); 11-yr running mean of the time series (solid line); and standardized time series of 11-yr running mean of NCD (dashed line).

  • View in gallery

    (a) Time series of the observed NCD (blue) and the in-sample predicted NCD (red) based on Eq. (2). (b) The 11-yr running mean of the time series shown in (a). The correlation coefficient between the red and blue time series is shown at the top right of each panel.

  • View in gallery

    (a),(b) Regression coefficients of UBI and WPI in the DJF period against the SST anomalies in the preceding SON period. The contour interval is 0.1°C and shading indicates the 95% confidence level. The SST precursors are denoted by SSTUBI and SSTWPI and the related key regions are shown by rectangular boxes. (c),(d) Linear correlation coefficients between UBI and WPI in the DJF period and the SST precursor in different periods. The gray and black dashed lines indicate the 95% and 99% confidence levels, respectively.

  • View in gallery

    (a)–(d) Regression of SSTUBI against the 500-hPa geopotential height anomalies in different periods. The contour interval is 5 gpm and shading indicates the 95% confidence level.

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Interannual and Interdecadal Variability of the Number of Cold Days in Hong Kong and Their Relationship with Large-Scale Circulation

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  • 1 Guy Carpenter Asia-Pacific Climate Impact Centre, School of Energy and Environment, City University of Hong Kong, Hong Kong, China
  • | 2 Hong Kong Observatory, Hong Kong, China
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Abstract

During the past decade (2004/05–2013/14), the number of cold days in Hong Kong (NCD), as a proxy of the temperature of southern China, appeared to have increased from the historical minimum, in contrast to a remarkable decline in the entire postwar period. This is related to the recent apparent changes in the large-scale circulation upstream and downstream of the East Asian winter monsoon (EAWM) region: the increase in Ural blocking (UB) that enhances cold advection from the polar region and reinforces the Siberian high and the decrease in a western Pacific (WP)-like index that corresponds to increasing meridional gradient of geopotential height over the EAWM region. Overall, UB and WP account for 26.4% of the interannual (≤8 yr) variance and 83.7% of the decadal (>8 yr) variance of NCD for the period 1948/49–2013/14, indicating that further study could lead to improvement in the prediction of NCD.

Corresponding author address: Dr. Wen Zhou, School of Energy and Environment, City University of Hong Kong, Tat Chee Ave., Kowloon, Hong Kong 00852, China. E-mail: wenzhou@cityu.edu.hk

Abstract

During the past decade (2004/05–2013/14), the number of cold days in Hong Kong (NCD), as a proxy of the temperature of southern China, appeared to have increased from the historical minimum, in contrast to a remarkable decline in the entire postwar period. This is related to the recent apparent changes in the large-scale circulation upstream and downstream of the East Asian winter monsoon (EAWM) region: the increase in Ural blocking (UB) that enhances cold advection from the polar region and reinforces the Siberian high and the decrease in a western Pacific (WP)-like index that corresponds to increasing meridional gradient of geopotential height over the EAWM region. Overall, UB and WP account for 26.4% of the interannual (≤8 yr) variance and 83.7% of the decadal (>8 yr) variance of NCD for the period 1948/49–2013/14, indicating that further study could lead to improvement in the prediction of NCD.

Corresponding author address: Dr. Wen Zhou, School of Energy and Environment, City University of Hong Kong, Tat Chee Ave., Kowloon, Hong Kong 00852, China. E-mail: wenzhou@cityu.edu.hk

1. Introduction

The East Asian winter monsoon (EAWM) is a complex system involving air–sea interaction between the East Asian continent and the Pacific Ocean, as well as the topographic forcing exerted by the Tibetan Plateau (Hsu 1987; Ding 1994; Chang et al. 2006; Wang and Chen 2014b). Near the surface, the EAWM is characterized by a strong zonal pressure gradient between the Siberian high and the Aleutian low, as well as prevailing northerly geostrophic wind along the East Asian continent. In the middle and upper troposphere, the EAWM is characterized by the East Asian jet stream and the East Asian trough (or the Far East trough) located in the longitude of Japan (Lau and Li 1984; Ding 1994; Chang et al. 2006).

From the late 1980s until the mid-2000s, the aforementioned EAWM features tended to be weak and the winter temperature in China tended to be warmer than normal (Zhai et al. 2008; Wang et al. 2009b; Hung and Kao 2010; Wei et al. 2011). After 18 consecutive warm winters since 1986/87, China experienced its first cold winter in 2004/05 (Ma et al. 2008). Three years later, in the winter of 2007/08, southern China experienced severe snowstorms and extremely low temperatures with a return period of ~20–60 years (Ding et al. 2008; Tao and Wei 2008; Wen et al. 2009; Zhou et al. 2009). Two years later, in the winter of 2009/10, extremely cold weather occurred in the midlatitudes of Eurasia and North America, and northern China had its coldest December since 1979 (Wang and Chen 2010; C. Wang et al. 2010). In the winter of 2010/11, the EAWM was also strong, and the coldest January since 1977 was recorded in eastern China (Wang et al. 2013). These events seem to indicate a reintensification of the EAWM around the mid-2000s (Jeong et al. 2011; Wang and Chen 2014a).

Hong Kong, a coastal city located in southern China with a population of about 7 million, often experiences cold spells in the boreal winter. Hong Kong Observatory (HKO) defined a cold day in Hong Kong as the daily minimum temperature at the HKO Headquarters (22°18′N, 114°10′E) ≤12.0°C [which is about the 25th percentile in the December–February (DJF) period]. In a subtropical city where indoor heating is not a norm, such low temperatures can be a potential health hazard for people with chronic medical conditions, especially the elderly. As can be inferred from Fig. 1, the number of cold days in Hong Kong1 (NCD) appeared to have increased from the late 1990s to the 2000s. Though this number has undergone a remarkable decreasing trend throughout the postwar period, the linear trend increases from −0.281 to −0.179 days yr−1 if the study period is extended from 2003/04 to 2013/14 (Fig. 1a). The increasing NCD in the past decade is also evidenced by the 11-yr (decadal) running mean, where the value increased from the historical minimum of 11.4 days (1992/93–2002/03) (Fig. 1b). The most recent number, 18.5 days (2003/04–2013/14), is comparable to the number in the 1980s. This appears to be consistent with the strengthening tendency of the EAWM in recent years [see Fig. 1 of Wang and Chen (2014a)].

Fig. 1.
Fig. 1.

(a) Number of cold days observed at the Hong Kong Observatory (HKO) Headquarters for the winter period (DJF; NCD) from 1947/48 to 2013/14. The black (gray) dashed line indicates the linear trend for the period 1947/48–2013/14 (1947/48–2003/04) using the least squares fit. (b) The 11-yr (decadal) running mean of the time series in (a).

Citation: Monthly Weather Review 143, 4; 10.1175/MWR-D-14-00335.1

Based on recent observations, we speculate that the increasing NCD in the past decade is related to apparent changes in large-scale circulation. To address this problem, we will first depict the large-scale atmospheric forcing related to prolonged cold spells in Hong Kong, where these events consist of at least seven cold days. Then, we will analyze the long-term variation of the crucial atmospheric factors and identify their precursors.

Cold spells in Hong Kong are usually initiated by the passage of a cold surge across southern China. This is related to the breakdown of the Siberian high associated with the eastward movement of an upper-tropospheric trough and an acceleration of the East Asian jet stream (Lam 1976; Chu 1978; Lau et al. 1983; Boyle and Chen 1987; Ding 1990; Wu and Chan 1995, 1997; Compo et al. 1999; Yan et al. 2011). The intensification and migration of the Siberian high, a semipermanent system of the EAWM (Lau and Lau 1984; Ding 1994; Chang et al. 2006), is closely related to upper- tropospheric forcing upstream and downstream of the Siberian high region (Chang and Lau 1980; Joung and Hitchman 1982; Lau and Lau 1984; Hsu and Wallace 1985; Takaya and Nakamura 2005a,b, 2013). Upstream of the Siberian high, a Rossby wave train propagates eastward from the Euro–Atlantic region (Joung and Hitchman 1982). Such a wavelike signal can be described by the 500-hPa geopotential height anomalies comprising alternating high and low centers of action. When the positive center of action over Ural–Siberia interacts with the transient eddies, a blocking high may form (Nakamura et al. 1997; Takaya and Nakamura 2005b) and it is known as Ural blocking (UB) in the literature.

Tyrlis and Hoskins (2008) and Cheung et al. (2013b) showed that UB is often preceded by a ridge over Europe. Along with cyclogenesis near the Mediterranean Sea, advection of warm and anticyclonic vorticity air from the subtropics to the midlatitudes result in the formation of UB. The strong meridional flow of UB enhances northerly cold advection downstream and reinforces the Siberian high (Takaya and Nakamura 2005a,b; Cheung et al. 2013b). When UB persists or recurs for a prolonged period, such as in the late winter and early spring of 2005 (Lu and Chang 2009) and in January 2008 (Tao and Wei 2008; Ding et al. 2009; Zhou et al. 2009; Li and Gu 2010), recurring development of the Siberian high is accompanied by a series of cold air outbreaks in East Asia. In 2008, the HKO Headquarters recorded 24 consecutive cold days from 24 January to 16 February, which is the longest cold spell since 1968. On interannual and decadal time scales, the frequency of UB is related to the strength of the EAWM (Lee and Jhun 2006; Wu and Leung 2009; L. Wang et al. 2010; Chang and Lu 2012; Cheung et al. 2012).

Downstream of the Siberian high, the East Asian trough and East Asian jet stream are two prominent mid- and upper-tropospheric circulation features of the EAWM (Lau and Li 1984; Yang et al. 2002; Jhun and Lee 2004; Wang et al. 2009a). The intensity of these systems, as well as their spatial features, is related to the temperature variability in the EAWM region (Wang et al. 2009a; Chen et al. 2002, 2003, 2005, 2009; B. Wang et al. 2010; Huang et al. 2012). Associated with a deeper East Asian trough and a southward shift of the East Asian jet stream, the southern part of the EAWM region is cooler (B. Wang et al. 2010). Moreover, cold air outbreaks in East Asia may be attributable to the North Pacific wave train that propagates westward toward East Asia (Lau and Nath 1999; Chen et al. 2004; Chen and Li 2007; Takaya and Nakamura 2005a,b).

In the following, the data and methods will be described in section 2. The prominent circulation features contributing to NCD will be deduced from the prolonged cold spells in section 3. In sections 4 and 5, the contribution of UB and the western Pacific (WP)-like pattern to NCD will be demonstrated. The WP-like pattern in this study was obtained by performing an EOF analysis for the 500-hPa geopotential height over 20°–80°N, 90°E–120°W (Wallace and Gutzler 1981; Barnston and Livezey 1987). In section 6, the combined effect of UB and WP will be assessed. In section 7, the SST precursors of UB and WP will be identified. Finally, the results will be summarized and discussed in section 8.

2. Data and methods

a. Data

The study period is the 66 boreal winters (the DJF period) from 1948/49 to 2013/14. Temperature data were collected from the HKO Headquarters for defining cold days and cold spells. In addition, the NCEP–NCAR reanalysis dataset, a widely used global assimilation product (Kalnay et al. 1996), is used to depict large-scale circulation features. The raw data include air temperature, geopotential height, the zonal and meridional components of wind at 17 isobaric levels (from 1000 to 10 hPa), and mean sea level pressure. The horizontal resolution is 2.5° latitude by 2.5° longitude. Note that none of the above data are detrended in our analyses as it is out of the scope of this study to quantify whether any existing trend is attributable to natural or anthropogenic forcing.

The daily, monthly, and seasonal climatology are obtained using the data from the 60-yr period between 1950/51 and 2009/10. The daily climatological mean is determined by a 11-day running mean (i.e., including 5 days before and after a calendar day).

The 21-point Lanczos filter with a cutoff frequency of eight years is applied to the 66-yr long time series in order to extract its interannual (high pass) and decadal (low pass) components.

b. Cold spells

According to the definition of the HKO, a calendar day is called a cold day when the daily minimum temperature ≤12.0°C. Based on this threshold, we counted NCD in the entire study period (December 1948–February 2014). Afterward, we defined the cold events to be the number of consecutive cold days. When the cold events are separated by less than three days, we grouped these cold events into one “independent” event. The independent cold events are called cold spells. Accordingly, the cold spells comprise consecutive NCD.

Prolonged cold spells are defined as events lasting for at least seven days and beginning in the DJF period. Following the above criteria, 308 cold spells and 61 prolonged cold spells are identified during the entire study period (Table 1). The average number of prolonged cold spells is about one per year, which is thus representative of the strongest cold spell in a year. In addition, NCD due to prolonged cold spells is 631 days and this accounts for 50.3% of all NCD in the study period (1254 days). In the following, the first day of a cold spell is denoted by day 0 and the number of days before and after day 0 is represented by a negative and positive value, respectively.

Table 1.

List of prolonged cold spells in Hong Kong for the period 1948/49–2013/14.

Table 1.

c. Atmospheric blocking

Atmospheric blocking is characterized by a reversal of geopotential height gradient at 500 hPa over the extratropics persisting for at least four consecutive calendar days. A straightforward way to identify blocking is to apply the geopotential height gradient (zonal index) equations (Lejenäs and Øakland 1983; Tibaldi and Molteni 1990). This can be easily achieved by using the global reanalysis datasets:
e1
where
eq1
eq2
eq3
eq4

The algorithm adopted in this study follows the one described in Barriopedro et al. (2006), which has also been used in Cheung et al. (2012, 2013a,b). In a given period, the blocking frequency over a specific sector (e.g., 45°–90°E) is counted as the percentage of days when at least five neighboring longitude grid points (i.e., 12.5° longitude) are blocked.

3. Circulation features of prolonged cold spells

a. Composite analysis

To depict the most pronounced circulation features favorable for a large NCD, the prolonged cold spells are analyzed in this section. The large-scale circulation features of prolonged cold spells in Hong Kong are first depicted by their day-0 composites, as given by Fig. 2. Near the surface, the Siberian high is displaced equatorward along with intense cold air masses. Downstream of the Siberian high is a cyclonic anomaly around Japan, suggesting a stronger zonal pressure gradient in the EAWM region (Fig. 2a).

Fig. 2.
Fig. 2.

Day-0 composites of prolonged cold spells in Hong Kong. (a) Anomalies of 850-hPa air temperature (shading, °C) and mean sea level pressure (contour, hPa), (b) 500-hPa geopotential height (contour) and its anomaly (shading) (gpm), (c) 250-hPa zonal wind (contour) and its anomaly (shading) (m s−1), and (d) 50-hPa geopotential height (contour) and its anomaly (shading) (gpm). The contour intervals are shown at the bottom right of each panel and negative (nonnegative) contours are shown by broken (solid) lines.

Citation: Monthly Weather Review 143, 4; 10.1175/MWR-D-14-00335.1

At 500 hPa, a ridge can be identified upstream and downstream of the East Asian trough. This resembles a typical inverted omega pattern during a severe cold air outbreak in China [Fig. 2b; cf. Fig. 2.7 on p. 98 of Ding (1994)]. These anticyclones are associated with a weaker zonal flow at 250 hPa over the subpolar region of East Asia and the exit region of the East Asian jet stream. The anomalous circulation over the Pacific–North America region consists of a positive center of action over the western North Pacific (~45°N, 165°E), a negative center of action north of Alaska (~75°N, 150°W), and another positive center of action east of Hudson Bay (~70°N, 75°W). This seems to be a downstream influence of the Pacific circulation, but the centers of action are located at higher latitude compared to the Pacific–North American teleconnection pattern [cf. Fig. 17 of Wallace and Gutzler (1981)].

At 50 hPa, two positive height anomaly centers can be observed over the north-central Siberia and the east coast of North America (Fig. 2d). The stratospheric polar vortex is centered near the pole and is displaced toward Eurasia. The positive anomaly centers coincide with the centers in the troposphere, implying an equivalent barotropic structure. Along with a weaker 250-hPa zonal wind over these regions (Fig. 2c), blocking-type circulation likely occurs. Since blocking is characterized by a persistent anticyclone, its occurrence needs to be verified by daily composites on a number of consecutive days and an objective analysis of blocking.

The daily composites of the 500-hPa geopotential height anomalies and the surface air temperature anomalies from day −6 to day +4 are given by Fig. 3. The evolution of cold spells is characterized by a wavenumber-3 pattern in the upper troposphere, where the three positive height anomaly centers are located in the western Atlantic (~60°–45°W), the Ural Mountains and western Siberia (~60°–90°E), and the Pacific (~165°–195°E). The persistence of these positive height anomalies seems to be analogous to the occurrence of blocking over these regions. In particular, surface cold anomalies accumulate downstream of the positive height anomalies over Ural–Siberia. Again, this is a typical precursor signal of severe cold air outbreaks in East Asia.

Fig. 3.
Fig. 3.

(a)–(f) Lag composites of daily 500-hPa geopotential height anomalies (contours with interval of 20 gpm) and surface air temperature anomalies (shading, °C) during the evolution of prolonged cold spells in Hong Kong. Negative (nonnegative) contours are shown by broken (solid) lines.

Citation: Monthly Weather Review 143, 4; 10.1175/MWR-D-14-00335.1

b. Blocking frequency

The blocking frequency over the Northern Hemisphere is presented in Fig. 4. In the winter (DJF) climatology, the blocking frequency attains two peaks, one over the Euro–Atlantic sector (~0°) and one over the Pacific sector (~180°). During the evolution of prolonged cold spells in Hong Kong (day 7 to day 0), the blocking frequency decreases dramatically over Europe and increases substantially over Ural–Siberia and the western Pacific. These peaks in blocking frequency are consistent with the height anomaly centers as shown in Fig. 3.

Fig. 4.
Fig. 4.

Longitudinal distribution of blocking frequency during the evolution of prolonged cold spells in Hong Kong (colored lines; see legend for description). The gray dashed line and shading indicate the DJF climatology and its half standard deviation, respectively, for the period 1950/51–2009/10. Unit: % of days.

Citation: Monthly Weather Review 143, 4; 10.1175/MWR-D-14-00335.1

Based on the results of Figs. 3 and 4, we are curious about the role of simultaneous blocking over Ural–Siberia and the western Pacific in prolonged cold spells as well as interannual and interdecadal variabilities of NCD. Specifically, UB reinforces the Siberian high such that the cold polar air can be advanced southward to East Asia, whereas Pacific blocking favors the cold air masses taking a more southward pathway and exerting a stronger impact on southern China. The blocking frequency over these two sectors will be further investigated in section 4.

4. Role of Ural blocking (UB)

a. Long-term variation

The blocking frequency over the Ural sector and the Pacific sector in a given winter is counted as the percentage of days when a blocking region can be identified in the longitudes between 45° and 90°E and between 120°E and 180°, respectively.2 As shown in Figs. 5a and 5b, the frequency of UB (UBI) underwent a decreasing trend from the late 1960s to the early 1990s, and increased in the 2000s. In contrast, the frequency of Pacific blocking did not decrease in the 1980s and 1990s, nor did it increase in the 2000s.

Fig. 5.
Fig. 5.

Time series of wintertime blocking frequency (% of days) over (a) the Ural sector, (b) the Pacific sector, and (c) the two sectors concurrently, where the bars indicates the value in each winter and the line represents the 11-yr running mean. (d) Standardized time series of the 8-yr low-pass-filtered value of UBI (Ural blocking index; solid line), and the 8-yr low-pass-filtered value of NCD (dashed line).

Citation: Monthly Weather Review 143, 4; 10.1175/MWR-D-14-00335.1

On the other hand, the frequency of simultaneous blocking is counted as the percentage of winter days when blocking regions can be identified in both the Ural and Pacific sectors. In the past few decades, simultaneous blocking in these two sectors has basically followed the variation of UBI (Figs. 5a,c). The 8-yr low-pass-filtered UBI also shows a similar variation to that of NCD, where the linear correlation coefficient between the two time series is 0.821 and the corresponding explained variance is 67.6% (Fig. 5d). Apparently, the decadal variation of UBI is closely related to that of NCD.

b. Relation to NCD

When the unfiltered DJF time sequence of UBI and NCD is regressed against the 500-hPa geopotential height, the two regression patterns seem to resemble a wave train pattern over the North Atlantic and the Eurasian continent (Fig. 6). The centers of action of the 500-hPa geopotential height and the mean sea level pressure nearly coincide, suggesting an equivalent barotropic structure of the wave train pattern. This seems to be similar to the results of Cheung et al. (2012), who showed that the major wintertime blocking patterns over Ural–Siberia (the first two leading EOFs were obtained from the 500-hPa geopotential height over 40°–80°N and 30°–100°E) were related to the quasi-stationary Rossby wave train over the North Atlantic and Eurasia.

Fig. 6.
Fig. 6.

Regression of NCD anomalies against (a) the 500-hPa geopotential height anomalies (gpm day−1) and (b) the mean sea level pressure anomalies (hPa day−1). (c),(d) As in (a),(b), but for UBI [gpm %−1 in (c); hPa %−1 in (d)]. Shading indicates the 95% confidence level. In (b) and (d), the Tibetan Plateau is dark shaded.

Citation: Monthly Weather Review 143, 4; 10.1175/MWR-D-14-00335.1

If the standardized anomaly of NCD is plotted against that of UBI (Fig. 7), it is apparent that the two anomalies are of the same sign in 42 out of 66 (63.6%) winters. The two anomaly signs have a higher agreement when the absolute value of standardized anomaly of UBI is greater than one (17 yr), whereas they are scattered when the standardized anomaly of UBI is small in magnitude. Therefore, the anomaly of NCD is also be related to other atmospheric forcing, especially when the anomalous forcing exerted by UB is not strong.

Fig. 7.
Fig. 7.

Scatterplot of the standardized anomaly of NCD and UBI in all winters. Dots (crisscrosses) indicate the years with the two variables in the same (opposite) anomaly sign. The rectangle encloses the UBI ranged between −1 and 1.

Citation: Monthly Weather Review 143, 4; 10.1175/MWR-D-14-00335.1

5. Role of the western Pacific (WP)-like pattern

a. Western Pacific index (WPI)

We speculate that the winters with an opposite anomaly sign in UBI and NCD as shown in Fig. 7 (24 out of 66 winters) are dominated by other atmospheric forcing. This can be deduced by the regression of the time sequence of the NCD of these winters against the 500-hPa geopotential height. As shown in Fig. 8, a statistically significant signal can be identified over the North Pacific. The north–south-oriented dipole pattern is analogous to the west Pacific teleconnection pattern introduced by Wallace and Gutzler (1981). Indeed, recent studies by Takaya and Nakamura (2013) and Wang and Chen (2014b) also considered the WP-like pattern to be a crucial factor responsible for the interannual variability of the EAWM.

Fig. 8.
Fig. 8.

Regression of NCD anomalies against (a) the 500-hPa geopotential height anomalies (gpm day−1) and (b) the mean sea level pressure anomalies (hPa day−1) in the winters when standardized UBI and NCD have opposite signs. Shading indicates the 95% confidence level. The rectangular box in (a) indicates the domain of the EOF analysis in Fig. 9a.

Citation: Monthly Weather Review 143, 4; 10.1175/MWR-D-14-00335.1

Wallace and Gutzler (1981) defined the west Pacific pattern as the difference in the 500-hPa geopotential height anomaly between 60° and 30°N at 155°E. Because the anomaly centers of Fig. 8a are not located at these two locations, the WP-like index (WPI) in this study is obtained by principal component analysis. An EOF analysis is performed for the correlation matrix of the winter-mean 500-hPa geopotential height enclosing the region of 20°–80°N, 90°E–120°W. The correlation matrix is used instead of the covariance matrix because of the large variance of this field over the central Pacific. The first leading EOF accounts for 28.4% of the total variance and, according to the rule of thumb of North et al. (1982), it is well separated from other EOF modes (figure not shown). As shown in Fig. 9a, this EOF pattern resembles the WP pattern (with the polarity reversed). The principal component time series of this EOF is defined as the WPI and is given in Fig. 9b.

Fig. 9.
Fig. 9.

(a) First leading EOF mode (EOF1) of the 500-hPa geopotential height over 20°–80°N, 90°E–120°W. (b) Time series of negated principal components of EOF1 or −WPI (bar); 11-yr running mean of the time series (solid line); and standardized time series of 11-yr running mean of NCD (dashed line).

Citation: Monthly Weather Review 143, 4; 10.1175/MWR-D-14-00335.1

Specifically, a negative value of the WPI represents a higher height in the high latitudes and a lower height in the low latitudes, which constitutes a stronger meridional height gradient and favors the cold air taking a southward pathway. This is partly contributed by the occurrence of Pacific blocking (120°E–180°; Fig. 5b), where the linear correlation coefficient between the WPI and the Pacific blocking frequency is −0.529 throughout the study period (i.e., more Pacific blocking in the negative phase of WPI). Note that the sign of the WPI is not reversed here in order to be consistent with the WP index defined by Barnston and Livezey (1987) and Wallace and Gutzler (1981).

b. Relation to NCD

Throughout the study period, the unfiltered WPI defined in this study has a linear correlation coefficient of 0.956 with the index of Wallace and Gutzler (1981), suggesting a strong similarity between the two indices. In addition to the unfiltered −WPI time series, Fig. 9b illustrates the 8-yr low-pass-filtered −WPI and standardized NCD. The two time sequences of 11-yr running means are almost in phase throughout the entire study period, attaining a predominant positive (negative) phase before (after) the mid-1980s. Both of them also appear to have undergone an increasing trend in the late 2000s. Thus, besides UB, the decreasing trend of the WP-like pattern partly contributes to the increasing NCD in recent winters.

6. Combined effect of UB and the WP-like pattern

After analyzing the possible relationship between UBI/WPI and NCD, we attempt to analyze how well the combined effect of UBI and WPI can explain the long-term variation of NCD.

A brief look at the combined effect of UBI and WPI is given in Table 2. If the UBI and WPI are of opposite polarity (or the UBI and −WPI are of the same polarity), both of them show a stronger relationship with NCD compared to the correlation in the entire study period. This suggests a coherent forcing for reinforcing or inhibiting the southward intrusion of cold air masses. Conversely, if the UBI and WPI are of the same polarity (or the UBI and −WPI are of opposite polarity), their anomalous forcing tends to oppose each other, and NCD shows a much weaker relationship with the two factors.

Table 2.

Linear correlation coefficient of NCD with the UBI and WPI for the period 1948/49–2013/14, where the p value is given in parentheses. Note that the linear correlations significant at the 99% confidence level are set boldface.

Table 2.

Regarding the UBI and WPI as the predictors and NCD as the predictand, the following equation can be obtained by multiple regression analysis:
e2
The linear correlation coefficient between the predictand and the predictors is 0.544, which corresponds to an explained variance of 29.6%. In other words, though the UBI and WPI are significantly correlated to NCD (Table 2), a significant fraction of the year-to-year variation of NCD is contributed to by other atmospheric forcing. This is evidenced by a smaller year-to-year variation of the predicted time series, as shown in Fig. 10a.
Fig. 10.
Fig. 10.

(a) Time series of the observed NCD (blue) and the in-sample predicted NCD (red) based on Eq. (2). (b) The 11-yr running mean of the time series shown in (a). The correlation coefficient between the red and blue time series is shown at the top right of each panel.

Citation: Monthly Weather Review 143, 4; 10.1175/MWR-D-14-00335.1

A similar result is obtained when the variables are filtered by an 8-yr high-pass filter, where the correlation coefficient would become 0.513 and the corresponding explained variance is 26.4% (figure not shown). On the other hand, if the variables are filtered by an 8-yr low-pass filter, then the correlation coefficient would become 0.915, and the corresponding explained variance would be 83.7%. As can be seen in Fig. 10b, the combined effect of UBI and WPI can well capture the sharp decreasing NCD around the late 1980s and the increasing NCD in the recent years.

7. Precursor SST signals in the preceding autumn

We wonder whether there is any potential predictor of UBI and WPI that would allow a prediction of NCD based on preseason conditions. SST has been regarded as one of the important sources of seasonal predictability, since its forcing tends to persist for several months. The relationship between SST and the EAWM has also been examined thoroughly by many previous studies. On the interannual time scale, this relation can be partly explained by El Niño–Southern Oscillation (ENSO), where an El Niño (La Niña) event tends to be associated with a weaker (stronger) EAWM (Li 1990; Zhang et al. 1997; Chen et al. 2000; Wang et al. 2000; Chan and Li 2004; Wu and Chan 2005). Specifically, the impact of ENSO on the southern part of the EAWM region is stronger (Chen et al. 2013a,b; Chen et al. 2014) where the air temperature tends to be warmer (cooler) in Hong Kong in an El Niño (La Niña) winter (Wu and Leung 2009). On decadal time scales, this relation is related to the Pacific decadal oscillation (PDO; Zhou et al. 2007a,b). Therefore, we speculate that the SST of the Pacific is one of the crucial precursor signals.

To identify the potential predictors of winter UBI and WPI, the two indices are regressed against the three-month running mean of global SST with different time lags. The SST data were obtained from the Hadley Centre and have a horizontal resolution of 1° latitude × 1° longitude (Rayner et al. 2003).

The SST precursors of both UBI and WPI appear to be noticeable in the preceding autumn and persist through the winter. For UBI, the most pronounced signals are the positive and negative SST anomalies located in the central and eastern North Pacific (Fig. 11a). For WPI, positive SST anomalies can be seen over the tropical central and eastern Pacific (Fig. 11b). In short, the apparent precursor signals on the interannual time scale are located mainly over the Pacific basin and not over the Atlantic basin.

Fig. 11.
Fig. 11.

(a),(b) Regression coefficients of UBI and WPI in the DJF period against the SST anomalies in the preceding SON period. The contour interval is 0.1°C and shading indicates the 95% confidence level. The SST precursors are denoted by SSTUBI and SSTWPI and the related key regions are shown by rectangular boxes. (c),(d) Linear correlation coefficients between UBI and WPI in the DJF period and the SST precursor in different periods. The gray and black dashed lines indicate the 95% and 99% confidence levels, respectively.

Citation: Monthly Weather Review 143, 4; 10.1175/MWR-D-14-00335.1

Based on the above results, the unweighted area-averaged SSTs in three key regions of the Pacific are taken as the precursors of UBI and WPI (which are called SSTUBI and SSTWPI hereafter; Figs. 11a,b):
e3
where an overbar on SST denotes the average over specified regions.

From the lead–lag correlations between the three-month-averaged SSTUBI and the UBI (between the three-month-averaged SSTWPI and the WPI) in Fig. 11c (Fig. 11d), the SSTUBI and SSTWPI anomalies likely start to develop in the preceding summer and spring, respectively. Because these anomalies appear to be strong throughout the cool season, they are potential predictors one season ahead of the UBI and WPI, as well as NCD, in winter. This is evidenced by significant correlations among the SST precursors in autumn, the UBI and WPI in winter, and NCD in winter (Tables 3 and 4).

Table 3.

Correlation matrix of the number of cold winter days in Hong Kong (NCD), the winter WPI, and the preceding autumn SST over the Pacific for the period 1948/49–2013/14, where the linear correlations significant at the 99% confidence level are set boldface.

Table 3.
Table 4.

As in Table 3, but for the UBI.

Table 4.

Tables 3 and 4 also present the correlations with two of the well-known SST indices over the Pacific basin; namely, the Niño-3 index (Trenberth 1997) and the PDO index (Mantua et al. 1997). Since the key region of SSTWPI (30°S–25°N, 170°E–100°W) partially overlaps with the Niño-3 region (5°S–5°N, 90°–150°W), a strong interrelationship exists between SSTWPI and the Niño-3 index, and the WPI in winter is significantly correlated with the Niño-3 index in the preceding autumn. Thus, ENSO is related to the West Pacific teleconnection pattern via an “atmospheric bridge,” as suggested by previous studies (Alexander et al. 2002).

The SST precursor signal of UBI, on the other hand, is confined mainly to the extratropical region of the North Pacific (Fig. 11a). Compared to SSTWPI, SSTUBI has a weaker correlation with the Niño-3 index and the PDO index even though the correlations are statistically significant. Lagged regression analysis suggests that the atmospheric response over the Pacific tends to be strong from September–November (SON) to DJF associated with the persistence of SSTUBI (Fig. 12). In SON (Fig. 12a), the regression pattern resembles a quasi-stationary wave train across the central Pacific and North America. Then, another regression center develops over the North Atlantic in October–December (OND) and November–January (NDJ) (Figs. 12b,c). Meanwhile, the regions of positive regression coefficients over the central and eastern North Pacific seem to persist and intensify in DJF (Figs. 12b–d). However, the underlying mechanism responsible for the relationship between UBI and SSTUBI is still unknown and needs to be addressed in future work. Another noteworthy feature is the moderate correlation of the UBI in the current winter and the SSTUBI in both the previous and following winters (Fig. 11c). This is partly related to the “reemergence mechanism” of midlatitude SSTs from one winter to the next (Alexander and Deser 1995; Deser et al. 2003).

Fig. 12.
Fig. 12.

(a)–(d) Regression of SSTUBI against the 500-hPa geopotential height anomalies in different periods. The contour interval is 5 gpm and shading indicates the 95% confidence level.

Citation: Monthly Weather Review 143, 4; 10.1175/MWR-D-14-00335.1

In short, the SSTUBI–UBI–NCD and SSTWPI–WPI–NCD linkages suggest potential predictability of NCD one season ahead.

8. Summary and discussion

In this study, Ural blocking (UB) and Pacific blocking have been identified as the important circulation features associated with the persistent cold spells in Hong Kong for the period 1948/49–2013/14. While UB reinforces the Siberian high, Pacific blocking enhances the southward intrusion of cold air masses during the cold air outbreak. On interannual and decadal time scales, the persistence of high anomalies over the midlatitudes of the aforementioned two blocking sectors is crucial for a higher number of cold days in Hong Kong (NCD). In particular, the high anomaly over the Ural sector is related to the frequency UB and the high anomaly over the Pacific sector is related to the western Pacific-like (WP) teleconnection pattern. Overall, the main findings are summarized as follows:

  • The two dynamic factors account for 26.4% of the interannual variation (<8 yr) and 83.7% of the decadal variation (>8 yr) of NCD;

  • The two dynamic factors appear to be linked to the SST distribution over the Pacific in the preceding autumn;

  • In the past decade, the more frequent occurrence of UB and the falling trend of WPI are indicators for a higher NCD than that in the 1990s and early 2000s. While UB is related to the intensity of the Siberian high (L. Wang et al. 2010; Cheung et al. 2012), WP affects the north–south geopotential height gradient over the Far East and the EAWM region (Takaya and Nakamura 2013; Wang and Chen 2014b). Moreover, WP is negatively correlated to the frequency of Pacific blocking.

The year-to-year variation of NCD, as well as the winter-mean air temperature, is also related to other dynamic and thermodynamic processes that cannot be well explained by UB and WP. Considerable effort should also be made to achieve a better seasonal prediction of NCD. Taking the extreme cold spell of southern China in early 2008 as an example, numerous studies have pinpointed the role of the western North Pacific subtropical high and the moisture supply from the Bay of Bengal in the multiple instances of snow storms and freezing rain (Wen et al. 2009; Zhou et al. 2009; Wu et al. 2011).

In addition, the snow cover and the sea ice have been considered to be a potential predictor of the winter seasonal forecast (Cohen et al. 2014), which should be considered in our future works. Watanabe and Nitta (1999) showed that the reduction of Eurasian snow cover in autumn is followed by a warmer winter in East Asia. Jhun and Lee (2004) further suggested that the autumn snow depth over Siberia may be linked to the EAWM variability. More recently, Cohen et al. (2007, 2009) proposed that the increasing Siberian snow cover in October enhances upward propagation of wave activities into the stratosphere. This results in the weakening of the stratospheric polar vortex and contributes to late-winter cooling, including East Asia. Based on these findings, we need to further investigate the possible linkage among snow cover, blocking and the stratospheric polar vortex, in order to achieve a better predictability of the EAWM on seasonal and even subseasonal time scales.

On the other hand, many recent studies have focused on the consequences of the reduction of Arctic sea ice on the global climate as a result of anthropogenic global warming, including the occurrence of blocking in the Northern Hemisphere and winter temperatures. For instance, Francis and Vavrus (2012) hypothesized that Arctic warming results in the slowdown of eastward-propagating Rossby waves over North America and the North Atlantic, which might in turn increase the occurrence of extreme weather such as cold waves in the midlatitudes. However, a recent study by Barnes et al. (2014) demonstrated that the trend of blocking in most regions of the Northern Hemisphere is not robust across different datasets for the period 1990–2012 when the autumn Arctic sea ice underwent a sharp decline. The only exception is the increasing trend of Asian blocking (60°–120°E). This motivates future works to investigate the relationship among Arctic warming, the occurrence of UB, and the winter temperature in East Asia.

Acknowledgments

The first author is a recipient of a research studentship provided by the City University of Hong Kong. The authors express their gratitude to Mr. C. M. Shun of the Hong Kong Observatory for his advice and valuable comments. The authors also greatly appreciate the constructive comments provided by three anonymous reviewers, which helped improve the clarity of the manuscript. This work is supported by the National Nature Science Foundation of China (Projects 41375096 and 41175079), and CityU strategic research Grant 7004004.

REFERENCES

  • Alexander, M. A., and C. Deser, 1995: A mechanism for the recurrence of wintertime midlatitude SST anomalies. J. Phys. Oceanogr., 25, 122137, doi:10.1175/1520-0485(1995)025<0122:AMFTRO>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Alexander, M. A., I. Bladé, M. Newman, J. R. Lanzante, N.-C. Lau, and J. D. Scott, 2002: The atmospheric bridge: The influence of ENSO teleconnection on air–sea interaction over the global oceans. J. Climate, 15, 22052231, doi:10.1175/1520-0442(2002)015<2205:TABTIO>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Barnes, E. A., E. Dunn-Sigouln, G. Masato, and T. Woollings, 2014: Exploring recent trends in Northern Hemisphere blocking. Geophys. Res. Lett., 41, 638644, doi:10.1002/2013GL058745.

    • Search Google Scholar
    • Export Citation
  • Barnston, A. G., and R. E. Livezey, 1987: Classification, seasonality, and persistence of low-frequency atmospheric circulation patterns. Mon. Wea. Rev., 115, 10831126, doi:10.1175/1520-0493(1987)115<1083:CSAPOL>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Barriopedro, D., R. García-Herrera, A. R. Lupo, and E. Hernández, 2006: A climatology of Northern Hemisphere blocking. J. Climate, 19, 10421063, doi:10.1175/JCLI3678.1.

    • Search Google Scholar
    • Export Citation
  • Boyle, J. S., and T.-J. Chen, 1987: Synoptic aspects of the wintertime East Asian monsoon. Monsoon Meteorology, C.-P. Chang and T. N. Krishnamurti, Eds., Oxford University Press, 125–160.

  • Chan, J. C. L., and C. Li, 2004: The East Asia winter monsoon. East Asian Monsoon, C.-P. Chang, Ed., World Scientific, 54–106.

  • Chang, C.-P., and K. M. Lau, 1980: Northeasterly cold surges and near-equatorial disturbances over the winter MONEX area during December 1974. II: Planetary-scale aspects. Mon. Wea. Rev., 108, 298312, doi:10.1175/1520-0493(1980)108<0298:NCSANE>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Chang, C.-P., and M.-M. Lu, 2012: Intraseasonal predictability of Siberian high and East Asian winter monsoon and its interdecadal variability. J. Climate, 25, 17731778, doi:10.1175/JCLI-D-11-00500.1.

    • Search Google Scholar
    • Export Citation
  • Chang, C.-P., Z. Wang, and H. Hendon, 2006: The Asian winter monsoon. The Asian Monsoon, B. Wang, Ed., Praxis, 89–127.

  • Chen, T.-C., W.-R. Huang, and J.-H. Yoon, 2004: Interannual variation of the East Asian cold surge activity. J. Climate, 17, 401–413, doi:10.1175/1520-0442(2004)017<0401:IVOTEA>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Chen, W., and T. Li, 2007: Modulation of Northern Hemisphere wintertime stationary planetary wave activity: East Asian climate relationships by the Quasi-Biennial Oscillation. J. Geophys. Res., 112, D20120, doi:10.1029/2007JD008611.

    • Search Google Scholar
    • Export Citation
  • Chen, W., H. Graf, and R. Huang, 2000: The interannual variability of East Asian winter monsoon and its relation to the summer monsoon. Adv. Atmos. Sci., 17, 4860, doi:10.1007/s00376-000-0042-5.

    • Search Google Scholar
    • Export Citation
  • Chen, W., H.-F. Graf, and M. Takahashi, 2002: Observed interannual oscillations of planetary wave forcing in the Northern Hemisphere winter. Geophys. Res. Lett., 29, 2073, doi:10.1029/2002GL016062.

    • Search Google Scholar
    • Export Citation
  • Chen, W., M. Takahashi, and H.-F. Graf, 2003: Interannual variations of stationary planetary wave activity in the northern winter troposphere and stratosphere and their relations to NAM and SST. J. Geophys. Res., 108, 4797, doi:10.1029/2003JD003834.

    • Search Google Scholar
    • Export Citation
  • Chen, W., S. Yang, and R.-H. Huang, 2005: Relationship between stationary planetary wave activity and the East Asian winter monsoon. J. Geophys. Res., 110, D14110, doi:10.1029/2004JD005669.

    • Search Google Scholar
    • Export Citation
  • Chen, W., L. Wang, Y. Xue, and S. Sun, 2009: Variabilities of the spring river runoff system in East China and their relations to precipitation and sea surface temperature. Int. J. Climatol., 29, 13811394, doi:10.1002/joc.1785.

    • Search Google Scholar
    • Export Citation
  • Chen, W., J. Feng, and R. Wu, 2013a: Roles of ENSO and PDO in the link of the East Asian winter monsoon to the following summer monsoon. J. Climate, 26, 622635, doi:10.1175/JCLI-D-12-00021.1.

    • Search Google Scholar
    • Export Citation
  • Chen, W., X. Lan, L. Wang, and Y. Ma, 2013b: The combined effects of the ENSO and the Arctic Oscillation on the winter climate anomalies over East Asia. Chin. Sci. Bull., 58, 13551362, doi:10.1007/s11434-012-5654-5.

    • Search Google Scholar
    • Export Citation
  • Chen, Z., R. Wu, and W. Chen, 2014: Distinguishing interannual variations of the northern and southern modes of the East Asian winter monsoon. J. Climate, 27, 835851, doi:10.1175/JCLI-D-13-00314.1.

    • Search Google Scholar
    • Export Citation
  • Cheung, H. N., W. Zhou, H. Y. Mok, and M. C. Wu, 2012: Relationship between Ural–Siberian blocking and the East Asian winter monsoon in relation to the Arctic Oscillation and the El Niño–Southern Oscillation. J. Climate, 25, 42424257, doi:10.1175/JCLI-D-11-00225.1.

    • Search Google Scholar
    • Export Citation
  • Cheung, H. N., W. Zhou, H. Y. Mok, M. C. Wu, and Y. Shao, 2013a: Revisiting the climatology of atmospheric blocking in the Northern Hemisphere. Adv. Atmos. Sci., 30, 397410, doi:10.1007/s00376-012-2006-y.

    • Search Google Scholar
    • Export Citation
  • Cheung, H. N., W. Zhou, Y. Shao, W. Chen, H. Y. Mok, and M. C. Wu, 2013b: Climatology and characteristics of wintertime atmospheric blocking over Ural–Siberia. Climate Dyn., 41, 6379, doi:10.1007/s00382-012-1587-6.

    • Search Google Scholar
    • Export Citation
  • Chu, E. W. K., 1978: A method for forecasting the arrival of cold surges in Hong Kong. Hong Kong Observatory Tech. Note 43, 31 pp.

  • Cohen, J., M. Barlow, P. J. Kushner, and K. Saito, 2007: Stratosphere-troposphere coupling and links with Eurasian land surface variability. J. Climate, 20, 53355343, doi:10.1175/2007JCLI1725.1.

    • Search Google Scholar
    • Export Citation
  • Cohen, J., M. Barlow, and K. Saito, 2009: Decadal fluctuations in planetary wave forcing moderate global warming in late boreal winter. J. Climate, 22, 44184426, doi:10.1175/2009JCLI2931.1.

    • Search Google Scholar
    • Export Citation
  • Cohen, J., and Coauthors, 2014: Recent Arctic amplification and extreme mid-latitude weather. Nat. Geosci., 7, 627637, doi:10.1038/ngeo2234.

    • Search Google Scholar
    • Export Citation
  • Compo, G. P., G. N. Kiladis, and P. J. Webster, 1999: The horizontal and vertical structure of East Asian winter monsoon pressure surges. Quart. J. Roy. Meteor. Soc., 125, 2954, doi:10.1002/qj.49712555304.

    • Search Google Scholar
    • Export Citation
  • Deser, C., M. A. Alexander, and M. S. Timlin, 2003: Understanding the persistence of sea surface temperature anomalies in midlatitudes. J. Climate, 16, 5772, doi:10.1175/1520-0442(2003)016<0057:UTPOSS>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Ding, Y., 1990: Buildup, air-mass transformation and propagating of Siberian high and its relations to cold surge in East Asia. Meteor. Atmos. Phys., 44, 281292, doi:10.1007/BF01026822.

    • Search Google Scholar
    • Export Citation
  • Ding, Y., 1994: Monsoons over China. Kluwer Academic Publishers, 420 pp.

  • Ding, Y., Z. Wang, Y. Song, and J. Zhang, 2008: Causes of the unprecedented freezing disaster in January 2008 and its possible association with the global warming. Acta Meteor. Sin., 22, 538558.

    • Search Google Scholar
    • Export Citation
  • Ding, Y., X. Jia, Z. Wang, X. Chen, and L. Chen, 2009: A contrasting study of freezing disaster in January 2008 and in winter of 1954/55 in China. Front. Earth Sci. China, 3, 129145, doi:10.1007/s11707-009-0028-2.

    • Search Google Scholar
    • Export Citation
  • Francis, J. A., and S. J. Vavrus, 2012: Evidence linking Arctic amplification to extreme weather in mid-latitudes. Geophys. Res. Lett., 39, L06801, doi:10.1029/2012GL051000.

    • Search Google Scholar
    • Export Citation
  • Hsu, H.-H., 1987: Propagation of low-level circulation features in the vicinity of mountain ranges. Mon. Wea. Rev., 115, 18641892, doi:10.1175/1520-0493(1987)115<1864:POLLCF>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Hsu, H.-H., and J. M. Wallace, 1985: Vertical structure of wintertime teleconnection patterns. J. Atmos. Sci., 42, 16931710, doi:10.1175/1520-0469(1985)042<1693:VSOWTP>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Huang, R., J. Chen, L. Wang, and Z. Lin, 2012: Characteristics, processes, and causes of the spatio-temporal variabilities of the East Asian monsoon system. Adv. Atmos. Sci., 29, 910942, doi:10.1007/s00376-012-2015-x.

    • Search Google Scholar
    • Export Citation
  • Hung, C., and P. Kao, 2010: Weakening of the winter monsoon and abrupt increase of winter rainfalls over northern Taiwan and southern China in the early 1980s. J. Climate, 23, 23572367, doi:10.1175/2009JCLI3182.1.

    • Search Google Scholar
    • Export Citation
  • Jeong, J.-H., T. Ou, H. W. Linderholm, B.-M. Kim, S.-J. Kim, J.-S. Kug, and D. Chen, 2011: Recent recovery of the Siberian high intensity. J. Geophys. Res., 116, D23102, doi:10.1029/2011JD015904.

    • Search Google Scholar
    • Export Citation
  • Jhun, J.-G., and E.-J. Lee, 2004: A new East Asian winter monsoon index and associated characteristics of the winter monsoon. J. Climate, 17, 711726, doi:10.1175/1520-0442(2004)017<0711:ANEAWM>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Joung, C.-H., and M.-H. Hitchman, 1982: On the role of successive downstream development in East Asian polar air outbreaks. Mon. Wea. Rev., 110, 12241237, doi:10.1175/1520-0493(1982)110<1224:OTROSD>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Kalnay, E., and Coauthors, 1996: The NCEP/NCAR 40-Year Reanalysis Project. Bull. Amer. Meteor. Soc., 77, 437471, doi:10.1175/1520-0477(1996)077<0437:TNYRP>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Lam, C. Y., 1976: 500 millibar troughs passing over Lake Baikal and the arrival of surges at Hong Kong. Hong Kong Observatory Tech. Note 31, 22 pp.

  • Lau, K.-M., and M.-T. Li, 1984: The monsoon of East Asia and its global associations—A survey. Bull. Amer. Meteor. Soc., 65, 114125, doi:10.1175/1520-0477(1984)065<0114:TMOEAA>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Lau, K.-M., C.-P. Chang, and P. H. Chan, 1983: Short-term planetary-scale interaction over the tropics and midlatitudes. Part II: Winter-MONEX period. Mon. Wea. Rev., 111, 13721388, doi:10.1175/1520-0493(1983)111<1372:STPSIO>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Lau, N.-C., and K.-M. Lau, 1984: The structure and energetics of midlatitude disturbances accompanying cold-air outbreaks over East Asia. Mon. Wea. Rev., 112, 13091327, doi:10.1175/1520-0493(1984)112<1309:TSAEOM>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Lau, N.-C., and M. J. Nath, 1999: Observed and GCM-simulated westward-propagating, planetary-scale fluctuations with approximately three-week periods. Mon. Wea. Rev., 127, 23242345, doi:10.1175/1520-0493(1999)127<2324:OAGSWP>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Lee, H.-S., and J.-G. Jhun, 2006: Two types of the Asian continental blocking and their relation to the East Asian monsoon during the boreal winter. Geophys. Res. Lett., 33, L22707, doi:10.1029/2006GL027948.

    • Search Google Scholar
    • Export Citation
  • Lejenäs, H., and H. Øakland, 1983: Characteristics of Northern Hemisphere blocking as determined from long time series of observational data. Tellus, 35A, 350362, doi:10.1111/j.1600-0870.1983.tb00210.x.

    • Search Google Scholar
    • Export Citation
  • Li, C., 1990: Interaction between anomalous winter monsoon in East Asia and El Niño events. Adv. Atmos. Sci., 7, 3646, doi:10.1007/BF02919166.

    • Search Google Scholar
    • Export Citation
  • Li, C., and W. Gu, 2010: An analyzing study of the anomalous activity of blocking high over the Ural Mountains in January 2008 (in Chinese). Chin. J. Atmos. Sci., 34, 865874.

    • Search Google Scholar
    • Export Citation
  • Lu, M.-M., and C.-P. Chang, 2009: Unusual late-season cold surges during the 2005 Asian winter monsoon: Roles of Atlantic blocking and the central Asian anticyclone. J. Climate, 22, 52055217, doi:10.1175/2009JCLI2935.1.

    • Search Google Scholar
    • Export Citation
  • Ma, X., Y. H. Ding, H. Xu, and J. He, 2008: The relation between strong cold waves and low-frequency waves during the 2004/2005 winter (in Chinese). Chin. J. Atmos. Sci., 32, 380394.

    • Search Google Scholar
    • Export Citation
  • Mantua, N. J., S. R. Hare, Y. Zhang, J. M. Wallace, and R. C. Francis, 1997: A Pacific interdecadal climate oscillation with impacts on salmon production. Bull. Amer. Meteor. Soc., 78, 10691079, doi:10.1175/1520-0477(1997)078<1069:APICOW>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Nakamura, H., M. Nakamura, and J. L. Anderson, 1997: The role of high- and low-frequency dynamics in blocking formation. Mon. Wea. Rev., 125, 20742093, doi:10.1175/1520-0493(1997)125<2074:TROHAL>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • North, G. R., T. L. Bell, R. F. Cahalan, and F. J. Moeng, 1982: Sampling errors in the estimation of empirical orthogonal functions. Mon. Wea. Rev., 110, 699706, doi:10.1175/1520-0493(1982)110<0699:SEITEO>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Rayner, N. A., D. E. Parker, E. B. Horton, C. K. Folland, L. V. Alexander, E. C. Kent, and A. Kaplan, 2003: Global analyses of sea surface temperature, sea ice, and night marine air temperature since the late nineteenth century. J. Geophys. Res., 108, 4407, doi:10.1029/2002JD002670.

    • Search Google Scholar
    • Export Citation
  • Takaya, K., and H. Nakamura, 2005a: Mechanisms of intraseasonal amplification of the cold Siberian high. J. Atmos. Sci., 62, 44234440, doi:10.1175/JAS3629.1.

    • Search Google Scholar
    • Export Citation
  • Takaya, K., and H. Nakamura, 2005b: Geographical dependence of upper-level blocking formation associated with intraseasonal amplification of the Siberian high. J. Atmos. Sci., 62, 44414449, doi:10.1175/JAS3628.1.

    • Search Google Scholar
    • Export Citation
  • Takaya, K., and H. Nakamura, 2013: Interannual variability of the East Asian winter monsoon and related modulation of the planetary waves. J. Climate, 26, 94459461, doi:10.1175/JCLI-D-12-00842.1.

    • Search Google Scholar
    • Export Citation
  • Tao, S., and J. Wei, 2008: Severe snow and freezing rain in January 2008 in the southern China (in Chinese). Climatic Environ. Res., 13, 337350.

    • Search Google Scholar
    • Export Citation
  • Tibaldi, S., and F. Molteni, 1990: On the operational predictability of blocking. Tellus, 42A, 343365, doi:10.1034/j.1600-0870.1990.t01-2-00003.x.

    • Search Google Scholar
    • Export Citation
  • Trenberth, K. E., 1997: The definition of El Niño. Bull. Amer. Meteor. Soc., 78, 27712777, doi:10.1175/1520-0477(1997)078<2771:TDOENO>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Tyrlis, E., and B. J. Hoskins, 2008: The morphology of Northern Hemisphere blocking. J. Atmos. Sci., 65, 16531665, doi:10.1175/2007JAS2338.1.

    • Search Google Scholar
    • Export Citation
  • Wallace, J. M., and D. S. Gutzler, 1981: Teleconnections in the geopotential height field during the Northern Hemisphere winter. Mon. Wea. Rev., 109, 784812, doi:10.1175/1520-0493(1981)109<0784:TITGHF>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Wang, B., R. Wu, and X. Fu, 2000: Pacific–East Asia teleconnection: How does ENSO affect East Asian climate? J. Climate, 13, 15171536, doi:10.1175/1520-0442(2000)013<1517:PEATHD>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Wang, B., Z. Wu, C. Chang, J. Liu, J. Li, and T. Zhou, 2010: Another look at interannual-to-interdecadal variations of the East Asian winter monsoon: The northern and southern temperature modes. J. Climate, 23, 14951512, doi:10.1175/2009JCLI3243.1.

    • Search Google Scholar
    • Export Citation
  • Wang, C., H. Liu, and S.-K. Lee, 2010: The record-breaking cold temperatures during the winter of 2009/10 in the Northern Hemisphere. Atmos. Sci. Lett., 11, 161168, doi:10.1002/asl.278.

    • Search Google Scholar
    • Export Citation
  • Wang, L., and W. Chen, 2010: Downward Arctic Oscillation signal associated with moderate weak stratospheric polar vortex and the cold December 2009. Geophys. Res. Lett., 37, L09707, doi:10.1029/2010GL042659.

    • Search Google Scholar
    • Export Citation
  • Wang, L., and W. Chen, 2014a: The East Asian winter monsoon: Re-amplification in the 2000s. Chin. Sci. Bull., 59, 430436, doi:10.1007/s11434-013-0029-0.

    • Search Google Scholar
    • Export Citation
  • Wang, L., and W. Chen, 2014b: An intensity index for the East Asian winter monsoon. J. Climate, 27, 23612374, doi:10.1175/JCLI-D-13-00086.1.

    • Search Google Scholar
    • Export Citation
  • Wang, L., W. Chen, W. Zhou, and R. Huang, 2009a: Interannual variations of East Asian trough axis at 500 hPa and its association with the East Asian winter monsoon pathway. J. Climate, 22, 600614, doi:10.1175/2008JCLI2295.1.

    • Search Google Scholar
    • Export Citation
  • Wang, L., R. Huang, L. Gu, W. Chen, and L. Kang, 2009b: Interdecadal variations of the East Asian winter monsoon and their association with quasi-stationary planetary wave activity. J. Climate, 22, 48604872, doi:10.1175/2009JCLI2973.1.

    • Search Google Scholar
    • Export Citation
  • Wang, L., W. Chen, W. Zhou, J. C. L. Chan, D. Barriopedro, and R. Huang, 2010: Effect of the climate shift around mid 1970s on the relationship between wintertime Ural blocking circulation and East Asian climate. Int. J. Climatol., 30, 153158, doi:10.1002/joc.1876.

    • Search Google Scholar
    • Export Citation
  • Wang, X., Z. Gong, B. Shen, and G. Feng, 2013: A comparative study of the climatic characteristics of the periods of frequent occurrence of the regional extreme low temperature events in China in the recent 50 years. Acta Meteor. Sin., 71, 10611073.

    • Search Google Scholar
    • Export Citation
  • Watanabe, M., and T. Nitta, 1999: Decadal changes in the atmospheric circulation and associated surface climate variations in the Northern Hemisphere winter. J. Climate, 12, 494510, doi:10.1175/1520-0442(1999)012<0494:DCITAC>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Wei, K., W. Chen, and W. Zhou, 2011: Changes in the East Asian cold season since 2000. Adv. Atmos. Sci., 28, 6979, doi:10.1007/s00376-010-9232-y.

    • Search Google Scholar
    • Export Citation
  • Wen, M., S. Yang, A. Kumar, and P. Zhang, 2009: An analysis of the large-scale climate anomalies associated with the snowstorms affecting China in January 2008. Mon. Wea. Rev., 137, 11111131, doi:10.1175/2008MWR2638.1.

    • Search Google Scholar
    • Export Citation
  • Wu, M. C., and J. C. L. Chan, 1995: Surface features of winter monsoon surges over South China. Mon. Wea. Rev., 123, 662680, doi:10.1175/1520-0493(1995)123<0662:SFOWMS>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Wu, M. C., and J. C. L. Chan, 1997: Upper-level features associated with winter monsoon surges over South China. Mon. Wea. Rev., 125, 317340, doi:10.1175/1520-0493(1997)125<0317:ULFAWW>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Wu, M. C., and J. C. L. Chan, 2005: Observational relationships between summer and winter monsoons over East Asia, Part I: Basic framework. Int. J. Climatol., 25, 437451, doi:10.1002/joc.1132.

    • Search Google Scholar
    • Export Citation
  • Wu, M. C., and W. H. Leung, 2009: Effect of ENSO on the Hong Kong winter season. Atmos. Sci. Lett., 10, 94101, doi:10.1002/asl.215.

  • Wu, Z., J. Li, Z. Jiang, and J. He, 2011: Predictable climate dynamics of abnormal East Asian winter monsoon: Once-in-a-century snowstorms in 2007/08 winter. Climate Dyn., 37, 16611669, doi:10.1007/s00382-010-0938-4.

    • Search Google Scholar
    • Export Citation
  • Yan, Z. W., J. J. Xia, C. Qian, and W. Zhou, 2011: Changes in seasonal cycle and extremes in China during the period 1960-2008. Adv. Atmos. Sci., 28, 269283, doi:10.1007/s00376-010-0006-3.

    • Search Google Scholar
    • Export Citation
  • Yang, S., K. M. Lau, and K. M. Kim, 2002: Variations of the East Asian jet stream and Asian–Pacific–American winter climate anomalies. J. Climate, 15, 306325, doi:10.1175/1520-0442(2002)015<0306:VOTEAJ>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Zhai, P., Z. Yan, and X. Zou, 2008: Climate extremes and climate-related disasters in China. Regional Climate Studies of China, C. Fu et al., Eds., Springer-Verlag, 313–339.

  • Zhang, Y., K. R. Sperber, and J. S. Boyle, 1997: Climatology and interannual variation of East Asian winter monsoon: Result from the 1979–95 NCEP/NCAR reanalysis. Mon. Wea. Rev., 125, 26052619, doi:10.1175/1520-0493(1997)125<2605:CAIVOT>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Zhou, W., C. Li, and X. Wang, 2007a: Possible connection between Pacific oceanic interdecadal pathway and East Asian winter monsoon. Geophys. Res. Lett., 34, L01701, doi:10.1029/2007GL031061.

    • Search Google Scholar
    • Export Citation
  • Zhou, W., X. Wang, T. Zhou, C. Li, and J. C. L. Chan, 2007b: Interdecadal variability of the relationship between the East Asian winter monsoon and ENSO. Meteor. Atmos. Phys., 98, 283293, doi:10.1007/s00703-007-0263-6.

    • Search Google Scholar
    • Export Citation
  • Zhou, W., J. C. L. Chan, W. Chen, J. Ling, J. G. Pinto, and Y. Shao, 2009: Synoptic-scale controls of persistent low temperature and icy weather over southern China in January 2008. Mon. Wea. Rev., 137, 39783991, doi:10.1175/2009MWR2952.1.

    • Search Google Scholar
    • Export Citation
1

Note that the number of cold days (NCD) in this study only includes the December–February period. Throughout the study period from 1948/49 to 2013/14, the averaged NCD in the DJF period is 19.00 days and the averaged NCD in other months (November/March/April) is 2.36 days. Thus, NCD in the DJF period includes 89.0% of the total NCD in all months.

2

The blocking frequency of a sector is larger than the blocking frequency of any longitude grid within that sector.

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