Monday (9-18) MEAS seminar

Abstract: Arctic climate system has experienced rapid changes, showing an amplified surface/lower tropospheric warming and an accelerated sea ice decrease. Behind the generally documented mean state changes, intense synoptic-scale cyclones have become more frequently observed in the Arctic region, driving the occurrence of extreme events. The increase in cyclone activity may also strengthen atmosphere-sea ice-ocean interactions to further increase the long-term Arctic climate state changes. Therefore, imperative questions to answer arise: how have Arctic cyclones changed and how do they influence Arctic sea ice? To address the first question, we employed an improved cyclone tracking algorithm and 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 the 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 Arctic cyclone intensification. To understand cyclone influence on sea ice, we also conducted a summer field observational study. We found that intense cyclones induce Ekman upwelling to bring the Pacific-origin, intermediate layer warmer water to the upper mixing layer. At the same time, the cyclone also enhances ocean mixing, increasing the turbulent heat flux from ocean-to-the bottom of sea ice and, therefore, causing an acceleration of summer sea ice melt.