Past research by the PI has identified meteorological conditions favorable to the development of tropopause polar vortices (TPV) in the Arctic. These atmospheric features can be broad ((o) 10^3km) and persistent (days to months), thus potentially influencing large-scale circulation and sea ice movement. Vortex intensity is linked to atmospheric water vapor content and latent heat availability, which, in a warming, ice-free Arctic, are predicted to increase significantly. Using the Weather Research and Forecasting (WRF) model, several sensitivity studies will be run to investigate the influence of surface conditions, including varied sea ice cover, sea surface temperature, turbulent flux, and dynamical scenarios, on vortex intensification. A second set of experiments will focus on understanding the changes in near-surface atmospheric circulation, predicted by the Community Atmosphere Model (CAM), in relation to TPVs, using the WRF model in combination with CAM forcings resulting from projected reductions in sea ice. The combined set of modeling activities will provide a bottom-up and top-down view of the connection between these common, but largely unexplored, upper tropospheric features and the complex motion of sea ice. Idealized warming scenarios will provide further insight into the potential intensification of these vortices.

Project Report

The Arctic has been experiencing substantial sea ice loss over the past decades, which has become more pronounced in recent years. While Arctic sea ice loss will not have a significant impact on sea levels, the impact on the atmospheric circulation and extratropical storm tracks is not well understood. Changes in extratropical storm tracks are important with regard to water resources and agricultural practices due to the shifting precipitation and temperature patterns that would follow. Sea ice blocks heat that is stored in the ocean from entering the atmosphere, which can otherwise enter the atmosphere without sea ice. This study examined the impact that reductions in Arctic sea ice will have on the atmosphere and whether these changes could alter typical extratropical cyclone tracks, with an emphasis on understanding the physical mechanisms that cause these changes. A numerical sensitivity approach was used, where a high-resolution state-of-the-art numerical weather prediction model was used to create two simulated climatologies: one with 20th Century sea ice and one with projected 21st Century sea ice. Since the only difference between the two numerically simulated climatologies was sea ice, these experiments were designed to isolate the effects of sea ice from all other changes occurring in the Earth's climate system, such as increases in greenhouse forcings. The results of this study indicate that reductions in sea ice shifts the climatological low pressure near Iceland poleward to the Barents Sea. Additionally, the strength of the mean cyclone is weaker. This implies that there are considerable changes in extratropical storm tracks, and that on average, cyclone intensities are weaker (see Figure 1). These changes are seen in association with changes in upper-level vortices that are maintained over higher latitudes. These upper-level vortices are an important precursor that initiates cyclone development at the surface. Cold atmospheric temperatures and low moisture content are crucial for the maintenance of upper-level vortices over the Arctic. The additional heat and moisture in the atmosphere have considerable impacts at both lower- and upper-atmospheric levels and on the characteristics and locations of the upper-level vortices, in-turn affecting the most probable locations of surface cyclone development.

National Science Foundation (NSF)
Division of Polar Programs (PLR)
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Erica L. Key
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Cavallo, Steven M
United States
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