Stationary planetary waves inferred from WINDII wind data taken within altitudes 90-120 km during 1991-96

A climatology of stationary planetary waves (SPWs) in horizontal winds at l atitudes 70 degrees S-70 degrees N and altitudes 90-120 km is obtained from Wind-Imaging Interferometer (WINDII) green line measurements in December-J anuary and March-April of 1991-96. The observed solstitial SPW fields are r elatively stronger and dominated by zonal wavenumber-1 variations. In contr ast, the equinoctial SPW fields are weaker and characterized by zonal waven umber-2 variations. The zonal amplitude maxima of 10-25 m s(-1) are general ly centered at the midlatitudes of 35 degrees-40 degrees in both hemisphere s around 96 km, with the eastward perturbation velocity maxima around 90 de grees E for wavenumber 1 and 60 degrees and 240 degrees E for wavenumber 2. The meridional amplitude maxima are about 5-15 m s(-1) and show more varia bilities in their latitude-height distributions. The meridional phases indi cated that Eliassen-Palm (EP) fluxes were downward-poleward for the winter maxima, vertically varying poleward for the summer maxima, and more variabl e during March-April. The hemispheric-seasonal-interannual variations in am plitude and phase are of 10 m s(-1) and 30 degrees, respectively. In partic ular, a distinguishable local summer maximum with an amplitude of 10-20 m s (-1) is found to exist in the wavenumber-1 variation of zonal wind componen t. The hemispheric asymmetry is also characterized by the nodal phase (or p hase jump) lines shifted toward the winter hemisphere by 10 degrees-30 degr ees. Wave penetrations across the equator are observed with amplitudes of 5 m s(-1) at 97-100 km. While the summer maximum of the wavenumber-1 compone nt persisted during the four years, large variability is found in the winte r hemisphere where the wavenumber-2 component became significant at the 90- 105-km region during December 1992-January 1993 and December 1993-January 1 994 and at the 105-120-km region during December 1991-January 1992. The exc itation due to in situ forcing of atonal gravity wave drag, which varies lo ngitudinally, is thought to be largely responsible for the observed SPW par ticularly for the summer maximum, while the leakage of upward propagating S PW from the lower to the higher atmosphere also plays a role, especially in the winter and the equinoctial periods.