Examining the Relationship between Tropopause Polar Vorticies and Stratospheric Variability

Tropopause polar vortices (TPVs) are long lived, tropopause-based cyclonic features that exist within the polar regions. In the Northern Hemisphere, TPVs are known not only to be precursors to Arctic cyclones, but also known to interact with the midlatitude jet stream, resulting in high-impact weather. Thus, understanding the variability in the distribution and frequency of these long-lived features can have implications on the ability to make extended range forecasts for the polar regions. The analysis is motivated by the fact that anomalous conditions in the high-latitude lower-stratospheric flow are known to persist on timescales of 30-60 days in the vicinity of the tropopause and can influence weather in the troposphere. Given the overlap in the timescales of TPV lifespan and stratospheric high-latitude variability, the goal of this study is to diagnose the variability in TPVs that is associated with the variability of stratospheric circulation.

The analysis examines the relationship between TPV tracks and amplitudes, the stratospheric polar vortex, and the QBO. The extreme stratospheric conditions are quantified using data from the ERA-Interim reanalysis to calculate 10-hPa zonal mean winds at 60 ̊N and ellipses that represent the stratospheric polar vortex. The magnitude of the high-latitude stratospheric flow is correlated to the quasi-biennial oscillation (QBO), which is defined as the downward propagation of zonal wind anomalies within the tropical stratosphere. The QBO can modulate extratropical planetary waves which are dynamically associated with high-latitude stratospheric variability. The analysis also considers the phase of the QBO at 30 hPa and the QBO shear in the 30-50 hPa layer to examine TPV variability, using NOAA/CPC data. TPV tracks and amplitudes are also calculated with ERA-Interim data using a well-established TPV tracking algorithm. Preliminary results suggest that polar vortex extremes are associated with anomalous tracks of TPVs. In particular, TPVs appear to track more frequently across the Northern Atlantic during strong vortex periods. This work is presented in the context of known relationships between extreme stratospheric conditions and changes in the midlatitude storm tracks.