Connection of predictability of major stratospheric sudden warmings to polar vortex geometry

Abstract

This study explores a possible connection between predictability variations of major stratospheric sudden warmings (MSSWs) during Northern winter and the geometry of the polar vortex. We compare 1-month hindcasts from 1979 to 2012 of the Japan Meteorological Agency to the Japanese 55-year Reanalysis data. Results show that error variations of medium range (≈14day) forecasts of 21 actual MSSWs do depend on the observed geometry of the polar vortex: the errors are larger for vortex split MSSWs when the polar vortex is highly stretched as characterized by a high aspect ratio and an amplified zonal wavenumber 2 component.