For questions about GML seminars, contact
Julie Singewald, Phone: (303) 497-6074
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The Role of the Atmosphere During Marine Heatwaves
Lauren Schmeisser Dr. Lauren Schmeisser is a new CIRES postdoc working in the Global Radiation and Aerosols group of GML. Lauren recently completed her PhD in Atmospheric Sciences at theUniversity of Washington as an NSF IGERT fellow. Lauren also has Bachelor and Masters degrees in Environmental Engineering from the University of Colorado at Boulder, and a Masters degree in Earth Science from the University of Amsterdam, which she earned while on a Rotary Ambassadorial Scholarship to the Netherlands
Marine heatwaves (MHWs) are events of abnormally warm sea surface temperatures (SSTs) that last for an extended period of time. MHWs have devastating impacts on marine ecosystems and coastal economies, and thus there is motivation to better understand these extreme events and forecast their evolution in order to improve the adaptive capacity of communities experiencing these impacts. Although MHWs are extreme oceanic events, both the atmosphere and the ocean affect the buildup, maintenance, and decay of MHWs. This talk focuses on the role of the clouds and radiative fluxes during the maintenance phase of MHWs. There are robust patterns in SST-cloud and SST-heat flux relationships that show important geographical differences in atmosphere-ocean interactions during MHWs. Because of these regional differences, we do not expect MHWs to evolve the same way in all regions. Some regions that have climatologically positive net heat flux feedbacks are shown to be especially prone to persistent MHWs. These new insights into the role of the atmosphere during MHWs are key for properly modelling and forecasting these extreme events.
The 2019 Southern Hemisphere polar stratospheric warming and its impacts
Eun-Pa Lim, Australian Bureau of Meteorlogy Eun-Pa Lim is a senior scientist in the Research Program of the Australian Bureau of Meteorology. She received her PhD and a Bachelor's degree from the University of Melbourne, and a Bachelor's degree from Ewha Womans University in Korea. Dr. Lim is an expert in seasonal climate prediction, associated large-scale ocean and atmosphere circulations, and the links between the stratosphere and troposphere for subseasonal to seasonal forecasts.
This study offers an overview of the mechanism and predictability of a rare Southern Hemisphere (SH) stratospheric warming that occurred in austral spring 2019 and its impacts on the SH surface climate. From late August to mid-September, the stratospheric westerly jet suddenly weakened and Antarctic stratospheric temperatures dramatically rose. The deceleration of the vortex observed 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 mid-stratosphere. This event was preconditioned by a poleward shift of the SH winter jet near the stratopause, which was followed by record strong planetary wave-one activity propagating from the troposphere in August that acted to dramatically weaken the polar vortex. The weakened wind and enhanced temperature signals moved downward to the surface in October to December, promoting a record strong swing of the Southern Annular Mode (SAM) to its negative phase for the season. The resulting record negative SAM was the primary driver of the extreme hot and dry conditions over subtropical eastern Australia in late spring 2019 that, in turn, were conducive for the severe wildfires that occurred at that time. State-of-the-art dynamical sub-seasonal to seasonal forecast systems skilfully predicted the significant vortex weakening of spring 2019 and subsequent development of negative SAM from late July.