Features of vortex split MSSWs that are problematic to forecast

Abstract

AbstractA companion paper demonstrated that it is more difficult to forecast major stratospheric sudden warmings (MSSWs) of the vortex split type on medium range time scales of about 2 weeks than other MSSWs. As its extension, this study further investigates more specific features of planetary waves for the greater difficulty through a composite analysis using the Japanese 55‐year reanalysis data and the Japan Meteorological Agency 1‐month hindcast data. Results show that the hindcast data of about two week lead times to the MSSWs largely underestimate the vortex stretching and split at 10 hPa, and the forcing and propagation of planetary wave of zonal wavenumber 2 to the stratosphere. The underestimation in the wave forcing largely reflects a deficiency in simulating a nonlinear, or quadratic, term in wave anomalies (meridional wind and temperature) from the climatology.