Tropospheric and stratospheric polar vortex variability and winter surface weather

Winter surface weather during the cold season is frequently discussed in relation to polar vortex variability, particularly in the stratosphere. However, winter weather events characterised by cold outbreaks, snowfall, and blizzard conditions exhibit substantial variability in surface expression across different circulation settings. This motivates a detailed diagnostic analysis of how tropospheric and stratospheric polar vortex variability relate to winter surface weather.

In this study, several winter periods over the Northern Hemisphere are analysed using ERA5 reanalysis data, with the objective of examining the relationship between vortex variability and surface weather characteristics. The analysis focuses on the correspondence between tropospheric circulation regimes, the vertical structure of vortex variability, and the resulting diversity of winter surface weather outcomes.

The analysis follows a troposphere-first approach, in which surface and lower-tropospheric circulation is examined prior to assessing the stratospheric state. Winter surface weather is described in terms of near-surface temperature, snowfall-related precipitation, and associated large-scale circulation regimes.

Tropospheric dynamics are diagnosed using sea-level pressure, 500 hPa geopotential height, 850 hPa temperature advection, upper-tropospheric jet structure, and potential vorticity near the dynamical tropopause, providing a framework for identifying jet displacement, blocking, and cyclone pathways. Stratospheric variability is examined using zonal-mean zonal wind at 60°N and 10 hPa, polar-cap temperature, geopotential height, and potential vorticity across multiple stratospheric levels (10–50 hPa), together with eddy heat flux diagnostics to characterise wave forcing and vertical structure.

By explicitly contrasting cases with similar stratospheric signatures but differing tropospheric configurations, the findings underline the importance of considering tropospheric circulation regimes when interpreting stratospheric polar vortex variability in relation to surface weather.