Sarah Borg-December 6

Observed Characteristics of Tropopause Polar Vortices over Summit Station, Greenland

Tropopause Polar Vortices (TPVs) are long-lived, coherent vortices that are identified by closed material contours of potential temperature on the tropopause. These potential vorticity anomalies spend most of their lifetime in the Arctic and can impact their surrounding environment by introducing variability in sea ice, generating surface cyclones, and intensifying midlatitude weather systems when carried equatorward by the Polar jet stream. While several studies have modeled the structure and climatology of TPVs, there is much to be discovered in terms of their evolution, intensification, and genesis. Past studies have used results of a water-shed based tracking algorithm of TPVs on the 2 PVU surface in the NCEP-NCAR reanalysis dataset to model TPV composite structure and intensity changes. Case studies from these model runs have shown that changes in TPV intensity can be attributed to local factors such as radiative cooling and latent heating, while cloud top radiative cooling had the most influence on increasing potential vorticity. However, due to the sparse nature of observations in the Arctic, no observation-based studies have focused on TPV characteristics to compare to these model results. This study uses observations to investigate if liquid or mixed-phase clouds contribute more significantly to TPV intensification by radiative cooling than ice-only clouds or clear-sky conditions.

As part of the Integrated Characterization of Energy, Clouds, Atmospheric State, and Precipitation at Summit (ICECAPS) project, observations of tropospheric and cloud properties at Summit, Greenland have been collected since 2010. Using temperature and humidity profiles from soundings, we compare the TPV composite characteristics from previous modeling studies to the observed data. With ground-based instruments such as a vertically pointing polarization sensitive lidar, millimeter cloud radar, and microwave radiometer, we also consider what cloud characteristics are associated with TPVs passing over Summit. Additionally, sounding data in conjunction with the stand-alone version of the Rapid Radiative Transfer Model are used to analyze shortwave and longwave radiative contributions to TPV diabatic intensity changes from both clouds and clear-sky water vapor effects.