报告题目： Intensification of Arctic Cyclone Activity

讲座简介：

Intense cyclones have become more frequently observed in the Arctic, with obvious links to the occurrence of Arctic extreme events. The increase in cyclone activity may also strengthen atmosphere-sea ice-ocean interactions to further amplify long-term Arctic climate change. Therefore, an imperative question to answer is: how have Arctic cyclones changed and how will they change in the future? While previous studies have suggested intensification of Arctic cyclone activity, inconsistencies have also emerged when using different analysis metrics and analyzing different datasets. In this study, we employed an improved, integrative index to analyze variability of and changes in Arctic cyclone activity in multiple state-of-the-art reanalysis datasets. The index aggregates information on cyclone frequency, intensity, and duration. The results indicate that Arctic cyclone activity has intensified during past seven decades. Dynamic mechanism analysis suggests that increased lower troposphere baroclinicity in the Arctic and changes in the large-scale upper tropospheric/stratospheric circulations jointly contributed to the cyclone intensification.

主讲人简介：

Dr. Xiangdong Zhang is a senior scientist at the North Carolina Institute for Climate Studies and a research professor at the Department of Marine, Earth and Atmospheric Sciences, North Carolina State University. He has conducted integrative research, aiming to improve systematic understanding of the Arctic and Northern Hemisphere climate variability and changes. One of his current responsibilities is to provide scientific input and leadership in the Technical Support Unit and to the National Coordination Office in support the U.S. National Climate Assessment. He is also serving as a member of the CliC-CLIVAR Northern Oceans Region Panel (NORP) and a member of the International Advisory Board of the EU H2020 project PolarRES.

报告题目： Blowing-Snow Enhanced Surface-Air Interactions during Extreme Weather Events from the Arctic to Midlatitudes

讲座简介：

The occurrence of extreme winter weather events has ostensibly increased in both the Arctic and midlatitudes. These events often bring snowfall and strong winds to the impacted area – resulting in blowing snow. Drifted snow can complicate the surface–air interactions and feedback to further strengthen the extreme event, particularly over some specific heterogeneous surfaces such as Arctic sea ice/polynya or a midlatitude urban/lake area. To better understand and compare the blowing snow effects on the surface-air interactions in the Arctic and midlatitudes, we apply a snow/ice-enhanced version of the Weather Research and Forecasting model to conduct simulations on two extreme weather events. The first event occurred in the Arctic during February 22-26, 2018, when extremely strong surface winds (>25 m/s) and an unprecedented polynya off the north coast of Greenland developed due to a synergistic effect of an intense cyclone centered to the north of the Canadian Arctic Archipelago and a strong anticyclone northeast/east of Iceland. The second event is a winter blizzard in the Great Lakes area during December 22-25, 2022. The blizzard brought strong winds (>20 m/s), a 40-year record cold temperatures, and snowfall to the area, resulting in white-out conditions by the blowing snow. The modeling results reveal significant thermodynamic effects of blowing snow sublimation, which can be further enhanced by the presence of an Arctic polynya or a midlatitude urban environment. Moreover, the blowing snow sublimation effect also contributes to a continuing development of the polynya in the Arctic and a stronger lake-effect snow in the Great Lakes area.

主讲人简介：

Jing Zhang is a professor of atmospheric sciences at Department of Physics, North Carolina A&T State University (NCAT). Her research interests lie in regional weather and climate studies by the means of numerical modeling and data analysis. Specifically, her recent and ongoing research studies include mesoscale modeling of downslope winds for wildfire study; urban modeling; glacier/ice-sheet surface mass balance modeling; Arctic cyclone modeling; regional reanalysis for the Arctic coast of Alaska; land/ice/snow surface processes and interactions with the atmosphere; and real-time weather forecast.

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