Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p53b1515t&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #P53B-1515
Physics
[6295] Planetary Sciences: Solar System Objects / Venus
Scientific paper
In Venusian atmosphere, there are waves with various scales and they compose turbulence. Undertstanding the distribution and kinetic energy transportation of turbulence is important to find out about Venusian atmospheric structure. The cloud top(~70km altitude), observable under ultraviolet, is in the superrotation, so studying the energy transport and diccipation of turbulence at this altitude is especially significant. According to the classical turbulence theory, power spectral intensity at the wavenumber k is expressed as follows: P(k)= Ckk-n. In this equation, the index -n corresponds to the slope in the logarithmic plot and characterizes the power spectrum. Enstrophy and energy cascade between the turbulence would occur in the case of n=3 and 5/3, respectively. Earlier studies have derived the power spectra of the turbulence from the Venusian cloud images obtained by earlier spacecrafts in the low latitude. However, the details of the power spectrum in the high latitude have been unknown well. Venus Express, which is the spacecraft launched in 2005, is in the elliptical orbit and closely observing the polar region in the South hemisphere. In this study, we obtained power spectra from the cloud brightness distribution of the ultraviolet images at the cloud top by Venus Monitoring Camera (VMC) onboard Venus Express, compared the slope of the spectra with the predicted value from the classical turbulence theory. And then we determined latitudinal dependence of the slope and the wavenumber at the inflection point. The obtained spectra show that the slope in the longer wavelength range is steeper than that in the shorter wavelength range. The result suggests that the enstrophy and energy cascade are dominant in the longer wavelength range and the shorter wavelength range, respectively. The obtained slopes have any temporal and latitudinal variations but the slope in the shorter wavelength range has relatively small latitudinal variation. This result reflects the little rotational effect. And the scale of the inflection point of spectra has small dependence on latitude, we think that the turbulence motion shift from 2 dimension to 3 dimension can make the inflection. Therefore we studied the correlation between Rossby number and the inflection point. In this presentation, we will show analysis result and discuss the features of the spectra, energy injection and the energy and enstrophy flows.
Hoshino N.
Kasaba Yasumasa
Markiewicz Wojciech J.
Matsuda Yuichi
Takahashi Yoshiyuki
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