The Impacts of Tropopause Vortex-Vortex Interactions on Arctic Cyclones

Tropopause polar vortices (TPVs) are small-scale vortices commonly found in high latitudes, characterized by radii up to ~1000 km and lifetimes of up to several months. While TPVs are an essential precursor to Arctic cyclones (ACs), the processes that control the size and longevity of Arctic Cyclones (ACs) remain unclear, with some ACs reaching diameters of up to 5000 km and lifetimes sometimes over two weeks. The size and longevity of ACs are far larger than expected for balanced flows from theory based on the Rossby radius, where theory predicts smaller, subsynoptic-scale cyclones that are more consistent with polar lows. The Arctic environment is predominantly characterized by vortices, differing from the midlatitudes where waves are favored, while TPV maintenance is favored in the Arctic given colder environmental temperatures allowing radiative processes to dominate over latent heating. Given the large frequency of TPVs and their significant role in the development and evolution of ACs, this study investigates the hypothesis that AC evolution is frequently impacted by multiple TPV interactions rather than just one single interaction, which may be a mechanism responsible for the long lifetimes of some ACs.

First, an analysis will examine the statistical frequency and characteristics of observed AC and TPV interactions. ERA5 data with TPVTrack (TPV tracker) and Sprenger et al. 2017 (surface cyclone tracker) will be used to match TPVs to ACs from 1979-2019. Results show that most ACs interact with at least one TPV, and nearly half of ACs interact with multiple TPVs. Next, a numerical modeling study will be presented for the Great Arctic Cyclone of 2012 (AC12) using the Model for Prediction Across Scales (MPAS). A series of experiments are designed to weaken particular TPVs by imposing artificial heating rates near the tropopause that offset a TPV’s known physical strengthening mechanism. The results of these experiments quantify the isolated impacts of two TPVs on the strength and evolution of AC12.