The Role of Bay of Bengal Convection in the Onset of the 1998 South China Sea Summer Monsoon

Yimin Liu State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics (LASG), Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, and Laboratory for Atmospheric Research, Department of Physics and Materials Science, City University of Hong Kong, Hong Kong, China

Search for other papers by Yimin Liu in
Current site
Google Scholar
PubMed
Close
,
Johnny C. L. Chan Laboratory for Atmospheric Research, Department of Physics and Materials Science, City University of Hong Kong, Hong Kong, China

Search for other papers by Johnny C. L. Chan in
Current site
Google Scholar
PubMed
Close
,
Jiangyu Mao State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics (LASG), Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China

Search for other papers by Jiangyu Mao in
Current site
Google Scholar
PubMed
Close
, and
Guoxiong Wu State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics (LASG), Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China

Search for other papers by Guoxiong Wu in
Current site
Google Scholar
PubMed
Close
Restricted access

Abstract

Assimilated analysis fields from the South China Sea Monsoon Experiment and the outgoing longwave radiation data from the National Center for Atmospheric Research (NCAR) have been employed to describe the large-scale and synoptic features of the subtropical circulation during the Bay of Bengal (BOB; 6°–20°N, 80°–100°E) and South China Sea (SCS; 7°–20°N, 110°–120°E) monsoon onsets in 1998. The results show that the Asian monsoon onset during May 1998 exhibited a typical eastward development from the BOB region to the SCS domain. The weakening and retreat of the subtropical anticyclone from the SCS were preceded by the intrusion of westerlies and the development of convective activities over the northern part of the SCS (NSCS; 15°–20°N, 110°–120°E). As the vertical shear of zonal wind changes in sign, the ridge surface of the subtropical anticyclone tilted northward and the summer pattern was established over the SCS. Based on these observational results, version 4 of the NCAR climate model (CCM3) is used to investigate the physical link between the convection associated with the BOB monsoon vortex and the SCS summer monsoon onset, as well as the mechanism of the evolution of the low-level subtropical anticyclone over the SCS.

Introduction of heating over the BOB results in vigorous convection over the BOB, and the BOB monsoon onset, as well as the development of westerlies and vertical ascent over the NSCS region due to an asymmetric Rossby wave response. Together with the low-level moisture advection, convection is induced over the NSCS. It is the condensation heating over the NSCS that causes the overturning of the meridional gradient of temperature over the SCS. Consequently the subtropical anticyclone in the lower troposphere over the SCS weakened gradually. Eventually as convection develops over the entire SCS domain, the subtropical anticyclone moves out of the region.

Corresponding author address: Dr. Yimin Liu, LASG, Institute of Atmospheric Physics, Chinese Academy of Sciences, P.O. Box 9804 Beijing 100029, China. Email: lym@lasg.iap.ac.cn

Abstract

Assimilated analysis fields from the South China Sea Monsoon Experiment and the outgoing longwave radiation data from the National Center for Atmospheric Research (NCAR) have been employed to describe the large-scale and synoptic features of the subtropical circulation during the Bay of Bengal (BOB; 6°–20°N, 80°–100°E) and South China Sea (SCS; 7°–20°N, 110°–120°E) monsoon onsets in 1998. The results show that the Asian monsoon onset during May 1998 exhibited a typical eastward development from the BOB region to the SCS domain. The weakening and retreat of the subtropical anticyclone from the SCS were preceded by the intrusion of westerlies and the development of convective activities over the northern part of the SCS (NSCS; 15°–20°N, 110°–120°E). As the vertical shear of zonal wind changes in sign, the ridge surface of the subtropical anticyclone tilted northward and the summer pattern was established over the SCS. Based on these observational results, version 4 of the NCAR climate model (CCM3) is used to investigate the physical link between the convection associated with the BOB monsoon vortex and the SCS summer monsoon onset, as well as the mechanism of the evolution of the low-level subtropical anticyclone over the SCS.

Introduction of heating over the BOB results in vigorous convection over the BOB, and the BOB monsoon onset, as well as the development of westerlies and vertical ascent over the NSCS region due to an asymmetric Rossby wave response. Together with the low-level moisture advection, convection is induced over the NSCS. It is the condensation heating over the NSCS that causes the overturning of the meridional gradient of temperature over the SCS. Consequently the subtropical anticyclone in the lower troposphere over the SCS weakened gradually. Eventually as convection develops over the entire SCS domain, the subtropical anticyclone moves out of the region.

Corresponding author address: Dr. Yimin Liu, LASG, Institute of Atmospheric Physics, Chinese Academy of Sciences, P.O. Box 9804 Beijing 100029, China. Email: lym@lasg.iap.ac.cn

Save
  • Boville, B. A., and P. R. Gent, 1998: The NCAR climate system model, version one. J. Climate, 11 , 11151130.

  • Chan, J. C. L., Y. G. Wang, and J. J. Xu, 2000: Dynamic and thermodynamic characteristics associated with the onset of the 1998 South China Sea summer monsoon. J. Meteor. Soc. Japan, 78 , 367380.

    • Search Google Scholar
    • Export Citation
  • Chang, C. P., and G. T. J. Chen, 1995: Tropical circulation associated with southwest monsoon onset and westerly surges over the South China Sea. Mon. Wea. Rev., 123 , 32543267.

    • Search Google Scholar
    • Export Citation
  • Chen, P., M. P. Hoerling, and R. M. Dole, 2001: The origin of the subtropical anticyclones. J. Atmos. Sci., 58 , 18271835.

  • Ding, Y. H., and C. Y. Li, Eds.,. 1999: Onset and Evolution of the South China Sea Monsoon and Its Interaction with the Ocean. Chinese Meteorological Press, 422 pp.

    • Search Google Scholar
    • Export Citation
  • Ding, Y. H., and Y. Liu, 2001: Onset and the evolution of the summer monsoon over the South China Sea during SCSMEX Field Experiment in 1998. J. Meteor. Soc. Japan, 79 , 255276.

    • Search Google Scholar
    • Export Citation
  • Ertel, H., 1942: Ein neuer hydrodynamische wirbdsatz. Meteor. Z. Braunschweig, 59 , 277281.

  • Fong, S. K., and A. Y. Wang, 2001: Climatological Atlas for Asian Summer Monsoon. Macau Foundation, 318 pp.

  • Gill, A. E., 1980: Some simple solutions for heat-induced tropical circulation. Quart. J. Roy. Meteor. Soc., 106 , 447662.

  • Hack, J. J., 1994: Parameterization of moist convection in the National Center for Atmospheric Research Community Climate Model (CCM2). J. Geophys. Res., 99 , 55515568.

    • Search Google Scholar
    • Export Citation
  • Hoskins, B. J., 1996: On the existence and strength of the summer subtropical anticyclones. Bull. Amer. Meteor. Soc., 77 , 12871292.

  • Kiehl, J. T., J. J. Hack, G. B. Bonan, B. A. Boville, B. P. Briegleb, D. L. Williamson, and P. J. Rasch, 1996: Description of the NCAR Community Climate Model (CCM3). NCAR Tech. Note NCAR/TN-420+STR, 152 pp. [Available from NCAR, P.O. Box 3000, Boulder, CO 80307.].

    • Search Google Scholar
    • Export Citation
  • Krishnamurti, T. N., P. Ardanuy, Y. Ramanathan, and R. Pasch, 1981: On the onset vortex of the summer monsoon. Mon. Wea. Rev., 109 , 344363.

    • Search Google Scholar
    • Export Citation
  • Lau, K. M., H. T. Wu, and S. Yang, 1998: Hydrologic processes associated with the first transition of the Asian summer monsoon: A pilot satellite study. Bull. Amer. Meteor. Soc., 79 , 18711882.

    • Search Google Scholar
    • Export Citation
  • Lau, K. M., and Coauthors. 2000: A report of the field operations and early results of the South China Sea Monsoon Experiment (SCSMEX). Bull. Amer. Meteor. Soc., 81 , 12611270.

    • Search Google Scholar
    • Export Citation
  • Li, C. Y., and X. Qu, 1999: Characteristics of atmospheric circulation associated with summer monsoon onset in the South China Sea. Onset and Evolution of the South China Sea Monsoon and Its Interaction with the Ocean, Y. Ding and C. Li, Eds., China Meteorological Press, 200–209.

    • Search Google Scholar
    • Export Citation
  • Lin, P-H., M-D. Chou, S-C. Tsay, and G. R. Liu, 1998: Surface radiation budget analysis at Dongsha during SCSMEX. Proc. IX Pacific Science Inter-Congress, Asian Pacific Monsoon and Typhoon Meteorology Symp., Taipei, Taiwan, 87–89. [Available from linpo@atmos.as.ntu.edu.tw.].

    • Search Google Scholar
    • Export Citation
  • Liu, Y. M., G. X. Wu, H. Liu, and P. Liu, 2001a: Condensation heating of the Asian summer monsoon and the subtropical anticyclone in the Eastern Hemisphere. Climate Dyn., 17 , 327338.

    • Search Google Scholar
    • Export Citation
  • Liu, Y. M., R. C. Yu, and X. Liu, 2001b: Thermal adaptation, overshooting, dispersion, and subtropical anticyclone. II: Horizontal inhomogeneous heating and energy dispersion. China J. Atmos. Sci., 25 , 317328. [Available in Chinese with English abstract from lym@lasg.iap.ac.cn.].

    • Search Google Scholar
    • Export Citation
  • Mao, J. Y., G. X. Wu, Y. Liu, P. Liu, and W. Li, 2002: Study on modal variation of subtropical high and its mechanism during seasonal transition. Part I: Climatological features of subtropical high structure. . Acta Meteor. Sin., 60 , 19. [Available in Chinese with English abstract from lym@lasg.iap.ac.cn.].

    • Search Google Scholar
    • Export Citation
  • Reynolds, R. W., and T. M. Smith, 1994: Improved global sea surface temperature analyses using optimum interpolation. J. Climate, 7 , 929948.

    • Search Google Scholar
    • Export Citation
  • Rodwell, M. R., and B. J. Hoskins, 1996: Monsoons and the dynamics of deserts. Quart. J. Roy. Meteor. Soc., 122 , 13851404.

  • Rodwell, M. R., . 2001: Subtropical anticyclones and summer monsoons. J. Climate, 14 , 31923211.

  • Tao, S. Y., and L. X. Chen, 1987: A review of recent research on the East Asia summer monsoon in China. Monsoon Meteorology, C. P. Chang and T. N. Krishnamurti, Eds., Oxford University Press, 60–92.

    • Search Google Scholar
    • Export Citation
  • Wu, G. X., and Y. S. Zhang, 1998: Tibetan Plateau forcing and the timing of the monsoon onset over south Asia and the South China Sea. Mon. Wea. Rev., 126 , 913927.

    • Search Google Scholar
    • Export Citation
  • Wu, G. X., Y. M. Liu, and P. Liu, 1999: The effect of spatially non-uniform heating on the formation and variation of subtropical high. Part I: Scale analysis. Acta Meteor. Sin., 57 , 257263. [Available in Chinese with English abstract from lym@lasg.iap.ac.cn.].

    • Search Google Scholar
    • Export Citation
  • Wu, K. W., and J. C. L. Chan, 2000: Intraseasonal and interannual variabilities of the South China Sea summer monsoon. Proc. Int. Conf. on Climate and Environment Variability and Predictability, Shanghai, China, 69. [Available from lym@lasg.iap.ac.cn.].

    • Search Google Scholar
    • Export Citation
  • Xu, J., and J. C. L. Chan, 2001: First transition of the Asian summer monsoon in 1998 and the effect of the Tibet–Tropical ocean thermal contrast. J. Meteor. Soc. Japan, 79 , 241253.

    • Search Google Scholar
    • Export Citation
  • Zhang, G. J., and N. A. McFarlane, 1995: Sensitivity of climate simulations to the parameterization of cumulus convection in the Canadian Climate Centre General Circulation Model. Atmos.–Ocean, 33 , 407446.

    • Search Google Scholar
    • Export Citation
  • Zhang, Y. S., and G. X. Wu, 1998: Diagnostic investigations of mechanism of onset of Asian summer monsoon and abrupt seasonal transitions over Northern Hemisphere, Part I. Acta Meteor. Sin., 56 , 513527. [Available in Chinese with English abstract from lym@lasg.iap.ac.cn.].

    • Search Google Scholar
    • Export Citation
All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 535 246 11
PDF Downloads 290 108 9