Asymmetric Patterns in the Atmosphere and Sea Ice During Polar Cyclones and Their Changes Under Global Warming

• Main Author: Clancy, Robin
• Other Authors: Bitz, Cecilia M
• Format: Thesis
• Language: English
• Published: 2022
• Subjects: Antarctic; Arctic; Cyclones; Polar; Sea ice; Atmospheric sciences; Southern Ocean; Antarc*; Global warming
• Online Access: http://hdl.handle.net/1773/48813

Thesis (Ph.D.)--University of Washington, 2022 The spatial structure of polar cyclones is often considered to be largely symmetrical and distinct from that of midlatitude cyclones, however we use ERA5 reanalysis and a cyclone-centered compositing method to show that polar cyclones display clear asymmetries in their atmospheric structure much like those in midlatitude cyclones, including a warm, moist sector to the east, a cold dry sector to the west, and frontal uplift. Antarctic and Arctic cyclones share many similarities in their spatial structure, however the geography of the Southern Ocean results in a more equatorward storm track and larger perturbations to atmospheric fields. The same cyclone-centered compositing method is applied to satellite sea ice concentration data and output from the CICE5 sea ice model to show that the response of sea ice to polar cyclones is not one of uniform gain or loss of concentration and thickness, but more of a redistribution, as both Arctic and Antarctic cyclones drive sea ice concentration and thickness decreases to the east of the cyclone center, but increases to the west of the cyclone center. A primarily dynamic mechanism is demonstrated to drive the east-west difference in sea ice response to cyclones, with the combination of cyclonic sea ice advection and meridional gradients in the sea ice playing a key role. As is the case for atmospheric fields, the sea ice response to Antarctic cyclones is slightly larger and more consistent across seasons than for Arctic cyclones. We extend this analysis to evaluate how the influence of Arctic cyclones on sea ice may change under global warming using projections from the CESM1 large ensemble. Large reductions in the meridional gradient of sea ice thickness under global warming result in a reduced influence of Arctic cyclones on sea ice thickness, while sea ice concentration gradients change much less, and therefore changes in the influence of Arctic cyclones on sea ice concentration are also much smaller. Many of the noted ...