RADIO SCINTILLATIONS IN VENUSS ATMOSPHERE - APPLICATION OF A THEORY OF GRAVITY-WAVE GENERATION

Radio scintillations in Pioneer Venus radio occultation data are simul ated assuming that the index of refraction fluctuations in Venus's atm osphere responsible for the scintillations are directly caused by grav ity wave fluctuations. The gravity waves are created by a global conve ction layer between 50- and 55-km altitude in Venus's atmosphere and p ropagate vertically. The authors compare the simulated scintillations with data from Pioneer Venus. These gravity waves can explain the spec tral shape and amplitude of the radio scintillations. The shape at hig h frequencies is controlled by wave breaking, which yields a saturated spectrum. The amplitude is subject to parameters such as the intensit y of the convection, the angle between the zonal winds and the beam pa th, and the zonal wind profile at polar latitudes. To match the observ ed amplitude of the scintillations, the velocity variations of the ene rgy-bearing eddies in the convection must be at least 2 m s(-1). This value is consistent with the Venus balloon results of Sagdeev et al. a nd is in the middle of the range considered by Leroy and Ingersoll in their study of convectively generated gravity waves. The latter study, combined with the lower bound on velocity from the present study, the n yields lower bounds on the vertical fluxes of momentum and energy in the Venus atmosphere.