Tropopause polar cyclone intensity sensitivity to surface boundary conditions

Tropopause polar vortices (TPVs) are coherent, tropopause-based structures, frequently observed in high latitudes. Horizontal scales can range up to 2000 km, and with lifetimes occasionally reaching months, TPVs can potentially influence the large-scale atmospheric circulation. Cyclonic TPVs are radiatively maintained due to both isolation from the stronger shear associated with the midlatitude jet stream, and relatively low latent heating rates in the Arctic. While cyclonic TPVs can play an important role in the formation of surface cyclones, it is unclear whether the surface boundary conditions have a significant influence on TPVs. In particular, as declining sea ice gives way to more open water, air-sea gradients will increase and more water vapor will evaporate into the atmosphere, potentially increasing latent heating rates. Here, the sensitivity of TPV intensity with changes to surface boundary conditions is examined in a series of idealized numerical modeling experiments with the expectation that higher latent heating rates will reduce vortex intensification.

Results show that the elimination of sea ice has a considerable effect on TPV intensity. When the surface is completely covered by sea ice, upward latent heat fluxes are relatively small, and the downward intrusion of the tropopause in the vortex core results in radiative intensification from an enhanced vertical water vapor gradient. Without sea ice, increases in the latent heat flux increase the vertical water vapor gradient, however this leads to more cloud cover and precipitation, ultimately reducing the radiative mechanism of vortex intensification. The relationship of these feedbacks to the lower atmospheric circulation will also be discussed.