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Eun-Pa Lim, Harry H. Hendon, Amy H. Butler, David W. J. Thompson, Zachary D. Lawrence, Adam A. Scaife, Theodore G. Shepherd, Inna Polichtchouk, Hisashi Nakamura, Chiaki Kobayashi, Ruth Comer, Lawrence Coy, Andrew Dowdy, Rene D. Garreaud, Paul A. Newman, and Guomin Wang

Abstract

This study offers an overview of the low-frequency (i.e., monthly to seasonal) evolution, dynamics, predictability, and surface impacts of a rare Southern Hemisphere (SH) stratospheric warming that occurred in austral spring 2019. Between late August and mid-September 2019, the stratospheric circumpolar westerly jet weakened rapidly, and Antarctic stratospheric temperatures rose dramatically. The deceleration of the vortex at 10 hPa was as drastic as that of the first-ever-observed major sudden stratospheric warming in the SH during 2002, while the mean Antarctic warming over the course of spring 2019 broke the previous record of 2002 by ∼50% in the midstratosphere. This event was preceded by a poleward shift of the SH polar night jet in the uppermost stratosphere in early winter, which was then followed by record-strong planetary wave-1 activity propagating upward from the troposphere in August that acted to dramatically weaken the polar vortex throughout the depth of the stratosphere. The weakened vortex winds and elevated temperatures moved downward to the surface from mid-October to December, promoting a record strong swing of the southern annular mode (SAM) to its negative phase. This record-negative SAM appeared to be a primary driver of the extreme hot and dry conditions over subtropical eastern Australia that accompanied the severe wildfires that occurred in late spring 2019. State-of-the-art dynamical seasonal forecast systems skillfully predicted the significant vortex weakening of spring 2019 and subsequent development of negative SAM from as early as late July.

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Sharon Stammerjohn, Ted A. Scambos, Susheel Adusumilli, Sandra Barreira, Germar H. Bernhard, Deniz Bozkurt, Seth M. Bushinsky, Kyle R. Clem, Steve Colwell, Lawrence Coy, Jos De Laat, Marcel D. du Plessis, Ryan L. Fogt, Annie Foppert, Helen Amanda Fricker, Alex S. Gardner, Sarah T. Gille, Tessa Gorte, Bryan Johnson, Eric Keenan, Daemon Kennett, Linda M. Keller, Natalya A. Kramarova, Kaisa Lakkala, Matthew A. Lazzara, Jan T. M. Lenaerts, Jan L. Lieser, Zhi Li, Hongxing Liu, Craig S. Long, Michael MacFerrin, Michelle L. Maclennan, Robert A. Massom, David Mikolajczyk, Lynn Montgomery, Thomas L. Mote, Eric R. Nash, Paul A. Newman, Irina Petropavlovskikh, Michael Pitts, Phillip Reid, Steven R. Rintoul, Michelle L. Santee, Elizabeth H. Shadwick, Alessandro Silvano, Scott Stierle, Susan Strahan, Adrienne J. Sutton, Sebastiaan Swart, Veronica Tamsitt, Bronte Tilbrook, Lei Wang, Nancy L. Williams, and Xiaojun Yuan
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E. Povl Abrahamsen, Sandra Barreira, Cecilia M. Bitz, Amy Butler, Kyle R. Clem, Steve Colwell, Lawrence Coy, Jos de Laat, Marcel D. du Plessis, Ryan L. Fogt, Helen Amanda Fricker, John Fyfe, Alex S. Gardner, Sarah T. Gille, Tessa Gorte, L. Gregor, Will Hobbs, Bryan Johnson, Eric Keenan, Linda M. Keller, Natalya A. Kramarova, Matthew A. Lazzara, Jan T. M. Lenaerts, Jan L. Lieser, Hongxing Liu, Craig S. Long, Michelle Maclennan, Robert A. Massom, François Massonnet, Matthew R. Mazloff, David Mikolajczyk, A. Narayanan, Eric R. Nash, Paul A. Newman, Irina Petropavlovskikh, Michael Pitts, Bastien Y. Queste, Phillip Reid, F. Roquet, Michelle L. Santee, Susan Strahan, Sebastiann Swart, and Lei Wang
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