Physics
Scientific paper
Jan 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994phdt........25l&link_type=abstract
PhD Dissertation, California Inst. of Tech. Pasadena, CA United States
Physics
Convection, Gravity Waves, Momentum Transfer, Scintillation, Venus Atmosphere, Radio Spectra, Planetary Waves, Middle Atmosphere, Venus (Planet), Atmospheric Circulation, Radio Occultation, Wind Profiles
Scientific paper
We investigate the emission of internal gravity waves from dry convection in Venus's atmosphere, how they might support Venus's atmospheric superrotation, and how they manifest themselves in radio scintillation data. Firstly, we calculate the emission of gravity waves from dry convection between 50 and 55 km altitude in Venus's atmosphere. We assume order of magnitude estimates for nonlinear terms in the anelastic equations of motion when in the convection and subsequently track the waves as they propagate out of the convection. We assume an atmosphere with realistic zonal wind and stability profiles. Waves are damped by reabsorption by the convection, wavebreaking in the stable atmosphere, critical layer absorption, and wave radiation to space. The westward propagating carry enough momentum to support the westward superrotation between the convection and the cloud-tops; however, the bulk of the wave momentum flux is critically absorbed and deposited within a kilometer of the convection because most of the waves propagate slowly in the horizontal. The eastward propagating waves are found to exert decelerations in excess of 20 m/s/day above the zonal wind maximum. A layer of wavebreaking adjacent to the convection is required to maintain the linear stability of waves emitted from the convection. Secondly, we simulate radio scintillations as they would appear in Pioneer Venus radio occultation data assuming that the index of refraction fluctuations in Venus's atmosphere responsible for the scintillations are the fluctuations of gravity waves emitted from the convection. The simulations can explain the shape and amplitude of the radio scintillation variance spectra in frequency. The shape of such spectra is nearly a direct result of the saturated spectrum of breaking gravity waves. The overall amplitude, however, is subject to parameters such as the intensity of the convection, the angle between the zonal winds and the beam path, and the zonal wind profile at polar latitudes. Nonetheless, we find that the convection in Venus's middle atmosphere, even in polar regions, must transport 1 W/m2 to create gravity waves strong enough to break. This result is dependent on the amplitude of the zonal winds in polar latitudes.
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