Characteristics and Lifecycles of Anticyclonic Tropopause Polar Vortices

Abstract

Tropopause polar vortices (TPVs) are sub-synoptic, long-lived, closed circulation features located in the upper-troposphere and lower-stratosphere region. Although TPV circulations can be cyclonic or anticyclonic, most previous studies have focused only on cyclonic TPVs, especially due to their direct influence on weather systems, including Arctic cyclones, but also cold air outbreaks and severe convection in middle latitudes. Cyclonic TPV longevity is unique to polar regions due to the relatively limited role of latent heating and the more dominant role of longwave radiative cooling. TPVs are also important to global circulations as recent studies have shown that cyclonic TPVs can exit the Arctic and interact with the polar jet, causing the initiation of Rossby wave packets on the polar jet. Rossby wave initiation and subsequent Rossby wave breaks (RWBs) and blocking patterns cause high-impact weather from droughts and floods to heatwaves and cold air outbreaks. However, current models have low skill when forecasting RWBs and blocking patterns, especially in the sub-seasonal to the seasonal timeframe.

This study aims to determine if anticyclonic TPVs are associated with RWBs and impact the development and persistence of blocking patterns. It is hypothesized that anticyclonic TPVs form from poleward RWBs and are important potential vorticity anomalies that aid in the maintenance of blocking patterns. It is also hypothesized that examining the lifecycles and characteristics of anticyclonic TPVs can improve understanding and forecasting of RWBs and blocking patterns. ERA5 data are used to create cyclonic and anticyclonic TPV and block tracks. The characteristics and lifecycles of all three are compared. Results show that anticyclonic TPVs have significantly shorter lifetimes than their cyclonic counterparts while decreasing in maximum intensity on average throughout their lifetime. Anticyclonic TPVs have less seasonal variability than cyclonic TPVs. The maxima in anticyclonic TPV genesis locations overlap the maxima in RWB and blocking frequencies. Anticyclonic TPVs are found to be in close spatial and temporal proximity to known blocks. Composites of multiple blocking and RWB indices show that ATPVs are most commonly associated with cyclonically sheared, poleward RWBs.