Exceptional Warmth in the Northern Hemisphere during January–March of 2020: The Roles of Unforced and Forced Modes of Atmospheric Variability

Siegfried D. Schubert aGlobal Modeling and Assimilation Office, NASA GSFC, Greenbelt, Maryland
bScience Systems and Applications, Inc., Lanham, Maryland

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Yehui Chang aGlobal Modeling and Assimilation Office, NASA GSFC, Greenbelt, Maryland
cMorgan State University, Baltimore, Maryland

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Anthony M. DeAngelis aGlobal Modeling and Assimilation Office, NASA GSFC, Greenbelt, Maryland
bScience Systems and Applications, Inc., Lanham, Maryland

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Randal D. Koster aGlobal Modeling and Assimilation Office, NASA GSFC, Greenbelt, Maryland

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Young-Kwon Lim aGlobal Modeling and Assimilation Office, NASA GSFC, Greenbelt, Maryland
dUniversity of Maryland, Baltimore County, Baltimore, Maryland

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Hailan Wang eClimate Prediction Center, NCEP/NWS/NOAA, College Park, Maryland

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Abstract

Much of northern Eurasia experienced record high temperatures during the first three months of 2020, and the eastern United States experienced a significant heat wave during March. In this study, we show that the above episodes of extraordinary warmth reflect to a large extent the unusual persistence and large amplitude of three well-known modes of atmospheric variability: the Arctic Oscillation (AO), the North Atlantic Oscillation (NAO), and the Pacific–North American (PNA) pattern. We employ a “replay” approach in which simulations with the NASA GEOS AGCM are constrained to remain close to MERRA-2 over specified regions of the globe in order to identify the underlying forcings and regions that acted to maintain these modes well beyond their typical submonthly time scales. We show that an extreme positive AO played a major role in the surface warming over Eurasia, with forcing from the tropical Pacific and Indian Ocean regions acting to maintain its positive phase. Forcing from the tropical Indian Ocean and Atlantic regions produced positive NAO-like responses, contributing to the warming over eastern North America and Europe. The strong heat wave that developed over eastern North America during March was primarily associated with an extreme negative PNA that developed as an instability of the North Pacific jet, with tropical forcing providing support for a prolonged negative phase. A diagnosis of the zonally symmetric circulation shows that the above extratropical surface warming occurred underneath a deep layer of tropospheric warming, driven by stationary eddy-induced changes in the mean meridional circulation.

© 2022 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).

Corresponding author: Siegfried Schubert, siegschu2002@yahoo.com

Abstract

Much of northern Eurasia experienced record high temperatures during the first three months of 2020, and the eastern United States experienced a significant heat wave during March. In this study, we show that the above episodes of extraordinary warmth reflect to a large extent the unusual persistence and large amplitude of three well-known modes of atmospheric variability: the Arctic Oscillation (AO), the North Atlantic Oscillation (NAO), and the Pacific–North American (PNA) pattern. We employ a “replay” approach in which simulations with the NASA GEOS AGCM are constrained to remain close to MERRA-2 over specified regions of the globe in order to identify the underlying forcings and regions that acted to maintain these modes well beyond their typical submonthly time scales. We show that an extreme positive AO played a major role in the surface warming over Eurasia, with forcing from the tropical Pacific and Indian Ocean regions acting to maintain its positive phase. Forcing from the tropical Indian Ocean and Atlantic regions produced positive NAO-like responses, contributing to the warming over eastern North America and Europe. The strong heat wave that developed over eastern North America during March was primarily associated with an extreme negative PNA that developed as an instability of the North Pacific jet, with tropical forcing providing support for a prolonged negative phase. A diagnosis of the zonally symmetric circulation shows that the above extratropical surface warming occurred underneath a deep layer of tropospheric warming, driven by stationary eddy-induced changes in the mean meridional circulation.

© 2022 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).

Corresponding author: Siegfried Schubert, siegschu2002@yahoo.com
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  • Ambaum, M. H. P., B. J. Hoskins, and D. B. Stephenson, 2001: Arctic Oscillation or North Atlantic Oscillation? J. Climate, 14, 34953507, https://doi.org/10.1175/1520-0442(2001)014<3495:AOONAO>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Bader, J., and M. Latif, 2005: North Atlantic Oscillation response to anomalous Indian Ocean SST in a coupled GCM. J. Climate, 18, 53825389, https://doi.org/10.1175/JCLI3577.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Bloom, S. C., L. L. Takacs, A. M. da Silva, and D. Ledvina, 1996: Data assimilation using incremental analysis updates. Mon. Wea. Rev., 124, 12561271, https://doi.org/10.1175/1520-0493(1996)124<1256:DAUIAU>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Bosilovich, M. G., R. Lucchesi, and M. Suarez, 2015: GMAO Office Note No. 9 (version 1.1): MERRA-2: File specification. NASA, 73 pp., http://gmao.gsfc.nasa.gov/pubs/office_notes.

    • Search Google Scholar
    • Export Citation
  • Chang, E. K. M., 1995: The influence of Hadley circulation intensity changes on extratropical climate in an idealized model. J. Atmos. Sci., 52, 20062024, https://doi.org/10.1175/1520-0469(1995)052<2006:TIOHCI>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Chang, Y., S. D. Schubert, R. D. Koster, A. M. Molod, and H. Wang, 2019: Tendency bias correction in coupled and uncoupled global climate models with a focus on impacts over North America. J. Climate, 32, 639661, https://doi.org/10.1175/JCLI-D-18-0598.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Ciavarella, A., and Coauthors, 2021: Prolonged Siberian heat of 2020 almost impossible without human influence. Climatic Change, 166, 9, https://doi.org/10.1007/s10584-021-03052-w.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Collow, A. B. M., N. P. Thomas, M. G. Bosilovich, Y.-K. Lim, S. D. Schubert, and R. D. Koster, 2022: Seasonal variability in the mechanisms behind the 2020 Siberian heatwaves. J. Climate, https://doi.org/10.1175/JCLI-D-21-0432.1, in press.

    • Search Google Scholar
    • Export Citation
  • Douville, H., S. Bielli, C. Cassou, M. Déqué, N. M. J. Hall, S. Tyteca, and A. Voldoire, 2011: Tropical influence on boreal summer mid-latitude stationary waves. Climate Dyn., 37, 17831798, https://doi.org/10.1007/s00382-011-0997-1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Edmon, H. J., Jr., B. J. Hoskins, and M. E. McIntyre, 1980: Eliassen-Palm cross sections for the troposphere. J. Atmos. Sci., 37, 26002616, https://doi.org/10.1175/1520-0469(1980)037<2600:EPCSFT>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Eliassen, A., and E. Palm, 1961: On the transfer of energy in stationary mountain waves. Geofys. Publ., 22 (3), 123.

  • Feldstein, S. B., 2000: The timescale, power spectra, and climate noise properties of teleconnection patterns. J. Climate, 13, 44304440, https://doi.org/10.1175/1520-0442(2000)013<4430:TTPSAC>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Feldstein, S. B., 2003: The dynamics of NAO teleconnection pattern growth and decay. Quart. J. Roy. Meteor. Soc., 129, 901924, https://doi.org/10.1256/qj.02.76.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Feldstein, S. B., and C. Franzke, 2006: Are the North Atlantic Oscillation and the northern annular mode distinguishable? J. Atmos. Sci., 63, 29152930, https://doi.org/10.1175/JAS3798.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Gelaro, R., and Coauthors, 2017: The Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2). J. Climate, 30, 54195454, https://doi.org/10.1175/JCLI-D-16-0758.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Guirguis, K., A. Gershunov, D. R. Cayan, and D. W. Pierce, 2018: Heat wave probability in the changing climate of the Southwest US. Climate Dyn., 50, 38533864, https://doi.org/10.1007/s00382-017-3850-3.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Hoerling, M. P., J. W. Hurrell, and T. Y. Xu, 2001: Tropical origins for recent North Atlantic climate change. Science, 292, 9092, https://doi.org/10.1126/science.1058582.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Hoskins, B. J., I. N. James, and G. H. White, 1983: The shape propagation and mean flow interaction of large-scale weather systems. J. Atmos. Sci., 40, 15951612, https://doi.org/10.1175/1520-0469(1983)040<1595:TSPAMF>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Hurrell, J. W., 1995: Decadal trends in the North Atlantic oscillation: Regional temperatures and precipitation. Science, 269, 676679, https://doi.org/10.1126/science.269.5224.676.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Hurrell, J. W., Y. Kushnir, G. Ottersen, and M. Visbeck, 2003: An overview of the North Atlantic Oscillation. The North Atlantic Oscillation: Climatic Significance and Environmental Impact, Geophys. Monogr., Vol. 143, Amer. Geophys. Union, 135, https://doi.org/10.1029/134GM01.

    • Search Google Scholar
    • Export Citation
  • Lawrence, Z. D., J. Perlwitz, A. H. Butler, G. L. Manney, P. A. Newman, S. H. Lee, and E. R. Nash, 2020: The remarkably strong Arctic stratospheric polar vortex of winter 2020: Links to record-breaking Arctic Oscillation and ozone loss. J. Geophys. Res. Atmos., 125, e2020JD033271, https://doi.org/10.1029/2020JD033271.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Leathers, D. J., B. Yarnal, and M. A. Palecki, 1991: The Pacific/North American teleconnection pattern and United States climate. Part I: Regional temperature and precipitation associations. J. Climate, 4, 517528, https://doi.org/10.1175/1520-0442(1991)004<0517:TPATPA>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Lee, S. H., Z. D. Lawrence, A. H. Butler, and A. Y. Karpechko, 2020: Seasonal forecasts of the exceptional Northern Hemisphere winter of 2020. Geophys. Res. Lett., 47, e2020GL090328, https://doi.org/10.1029/2020GL090328.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Limpasuvan, V., and D. L. Hartmann, 2000: Wave-maintained annular modes of climate variability. J. Climate, 13, 44144429, https://doi.org/10.1175/1520-0442(2000)013<4414:WMAMOC>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Molod, A. M., L. Takacs, M. Suarez, and J. Bacmeister, 2015: Development of the GEOS-5 atmospheric general circulation model: Evolution from MERRA to MERRA2. Geosci. Model Dev., 8, 13391356, https://doi.org/10.5194/gmd-8-1339-2015.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • NOAA, 2020: State of the climate: Global climate report, NOAA/NCEI, accessed 1 March 2021, https://www.ncdc.noaa.gov/sotc/global-regions/2020.

    • Search Google Scholar
    • Export Citation
  • Overland, J. E., and M. Wang, 2021: The 2020 Siberian heat wave. Int. J. Climatol., 41 (Suppl. 1), E2341E2346, https://doi.org/10.1002/joc.6850.

  • Reichle, R. H., R. D. Koster, G. J. M. De Lannoy, B. A. Forman, Q. Liu, S. P. P. Mahanama, and A. Touré, 2011: Assessment and enhancement of MERRA land surface hydrology estimates. J. Climate, 24, 63226338, https://doi.org/10.1175/JCLI-D-10-05033.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Richman, M. B., 1986: Rotation of principal components. J. Climatol., 6, 293335, https://doi.org/10.1002/joc.3370060305.

  • Rivière, G., and M. Drouard, 2015: Dynamics of the northern annular mode at weekly time scales. J. Atmos. Sci., 72, 45694590, https://doi.org/10.1175/JAS-D-15-0069.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Schubert, S. D., and Y.-K. Lim, 2013: Climate variability and weather extremes: Model-simulated and historical data. Extremes in a Changing Climate: Detection, Analysis and Uncertainty, A. Schubert et al., Eds., Springer, 239285, https://doi.org/10.1007/978-94-007-4479-0.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Schubert, S. D., M. J. Suarez, Y. Chang, and G. Branstator, 2001: The impact of ENSO on extratropical low-frequency noise in seasonal forecasts. J. Climate, 14, 23512365, https://doi.org/10.1175/1520-0442(2001)014<2351:TIOEOE>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Schubert, S. D., A. Borovikov, Y.-K. Lim, and A. Molod, 2019a: Ensemble generation strategies employed in the GMAO GEOS-S2S forecast system. NASA Tech. Rep. NASA/TM-2019-104606, Vol. 53, 75 pp.

    • Search Google Scholar
    • Export Citation
  • Schubert, S. D., Y. Chang, H. Wang, R. D. Koster, and A. M. Molod, 2019b: A systematic approach to assessing the sources and global impacts of errors in climate models. J. Climate, 32, 83018321, https://doi.org/10.1175/JCLI-D-19-0189.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Schubert, S. D., Y. Chang, A. M. DeAngelis, H. Wang, and R. D. Koster, 2021: On the development and demise of the fall 2019 southeast U.S. flash drought: Links to an extreme positive IOD. J. Climate, 34, 17011723, https://doi.org/10.1175/JCLI-D-20-0428.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Seager, R., N. Harnik, Y. Kushnir, W. Robinson, and J. Miller, 2003: Mechanisms of hemispherically symmetric climate variability. J. Climate, 16, 29602978, https://doi.org/10.1175/1520-0442(2003)016<2960:MOHSCV>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Simmons, A. J., J. M. Wallace, and G. Branstator, 1983: Barotropic wave propagation and instability, and atmospheric teleconnection patterns. J. Atmos. Sci., 40, 13631392, https://doi.org/10.1175/1520-0469(1983)040<1363:BWPAIA>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Thompson, D. W. J., and J. M. Wallace, 1998: The Arctic oscillation signature in the wintertime geopotential height and temperature fields. Geophys. Res. Lett., 25, 12971300, https://doi.org/10.1029/98GL00950.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Thompson, D. W. J., and J. M. Wallace, 2001: Regional climate impacts of the Northern Hemisphere annular mode. Science, 293, 8589, https://doi.org/10.1126/science.1058958.

    • Crossref
    • 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, https://doi.org/10.1175/1520-0493(1981)109<0784:TITGHF>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • WMO, 2021: State of the global climate 2020: Unpacking the indicators. World Meteorological Organization, https://public.wmo.int/en/our-mandate/climate/wmo-statement-state-of-global-climate.

    • Search Google Scholar
    • Export Citation
  • Wu, R., and B. P. Kirtman, 2004: Impacts of the Indian Ocean on the Indian summer monsoon–ENSO relationship. J. Climate, 17, 30373054, https://doi.org/10.1175/1520-0442(2004)017<3037:IOTIOO>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
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