Spectroscopic Observations of Winds on Venus

Abstract

We have measured the differential Doppler shift between various points on Venus using a high-resolution PEPSIOS interferometer (three Fabry-Perot etalons in series). Using both a CO2 line and a Fraunhofer line we find a mean zonal wind velocity near the equator of ?83 ± 10 m s?1 (retrograde); the velocity appears to vary from about ?2 to ?125 m s?1, with a time scale of greater than one week. Meridional velocities are measured to be weak (on the order of 30 m s?1 or less). The equatorial zonal velocity appears to be smaller (?73 m s?1) in the ?morning? than in the ?afternoon? (?111 m s?1) where the times of day are for retrograde rotation. A comparison with reported velocities of the ultraviolet dark markings reveals general agreement in that both find the motion to be retrograde, variable, and accelerated during the day. A new potential source of systematic error in all spectroscopic determinations of the differential Doppler shift of nonuniformly illuminated objects is pointed out.