Eliassen–Palm Fluxes of the 2-Day Wave

Abstract

High-Resolution Doppler Imager (HRDI) winds and temperatures are used to diagnose a 2-day wave event detected in the Southern Hemisphere during January 1994. A novel aspect of this study is the focus upon the wave fluxes throughout the 65?100-km range, and their relationship to the background state. A wave ?packet? composed of zonal wavenumbers 2, 3, and 4 propagates westward with a phase speed near 60 m s?1. The periods associated with zonal wavenumbers 2, 3, and 4 are 3.5, 2.1, and 1.7 days, respectively. The morphology of the 2-day temperature and wind fields is consistent with that of a developing baroclinic wave. The divergence of the Eliassen?Palm flux of zonal wavenumbers 2?4 is dominated by the vertical convergence of meridional heat flux. The wave driving (or Eliassen?Palm flux divergence per unit mass) is predominantly westward, with magnitudes on the order of 5 m s?1 day?1. A steady-state quasigeostrophic model of the mean meridionaI circulation is used to estimate the mean wind response. The January 1994 event induces weak equatorward flow (less than 1 m s?1), together with westward winds on the order of 20 m s?1.