Observational evidence of a stratospheric influence on the troposphere by planetary wave reflection

Abstract

Recent studies have pointed out the impact of the stratosphere on the troposphere by dynamic coupling. In the present paper, observational evidence for an effect of downward planetary wave reflection in the stratosphere on Northern Hemisphere tropospheric waves is given by combining statistical and dynamical diagnostics. A time-lagged singular value decomposition analysis is applied to daily tropospheric and stratospheric height fields recomposed for a single zonal wavenumber. A wave geometry diagnostic for wave propagation characteristics that separates the index of refraction into vertical and meridional components is used to diagnose the occurrence of reflecting surfaces. For zonal wavenumber 1, this study suggests that there is one characteristic configuration of the stratospheric jet that reflects waves back into the troposphere-when the polar night jet peaks in the high-latitude midstratosphere. This configuration is related to the formation of a reflecting surface for vertical propagation at around 5 hPa as a result of the vertical curvature of the zonal-mean wind and a clear meridional waveguide in the lower to middle stratosphere that channels the reflected wave activity to the high-latitude troposphere.