A Multiscale Analysis and Predictability Study of a Polar Low Linked to a Tropopause Polar Vortex

The purpose of this study is to 1) analyze the evolution of a polar low that is linked to a tropopause polar vortex (TPV), and 2) investigate factors influencing the predictability of the evolution of the polar low. Polar lows are intense, mesoscale cyclones that often form within a cold air mass or along an Arctic front at the leading edge of a cold air mass moving over relatively warmer sea surfaces in high latitudes. Polar lows may be associated with strong winds, large waves, and heavy precipitation, posing hazards to shipping and infrastructure. TPVs are coherent vortices in the vicinity of the tropopause that may act as precursors for the formation of polar lows. TPVs may also be accompanied by cold surges that have the potential to influence the evolution and position of Arctic fronts and consequently the evolution of polar lows. It is anticipated that uncertainties in the position and strength of TPVs and associated cold surges may influence the predictability of the evolution of polar lows.

An existing database of TPVs constructed using the ERA-Interim will first be compared to the Sea Surface Temperature and Altimeter Synergy for Improved Forecasting of Polar lows database of polar lows in the Nordic Seas. Based on the spatial and temporal proximity of the polar lows to the TPVs, polar lows that are linked to TPVs will be identified. Polar lows that are linked to TPVs will be ranked by intensity and longevity, and a multiscale analysis will be performed on a relatively intense and long-lived polar low. The multiscale analysis will be carried out using the Arctic System Reanalysis version 2 and/or the ERA5 to identify factors and diagnose processes contributing to the evolution of the polar low. The 51-member ECMWF Ensemble Prediction System from TIGGE will be utilized to evaluate forecast skill associated with the prediction of the evolution of the polar low. The ensemble forecasts will be separated in two groups: the most and least accurate members in terms of track and intensity errors of the polar low. Composite differences between the two groups will be computed for selected atmospheric quantities, which will enable determining the degree to which the position and strength of the TPV and associated cold surge influence the predictability of the evolution of the polar low.