Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009dps....41.1013c&link_type=abstract
American Astronomical Society, DPS meeting #41, #10.13
Astronomy and Astrophysics
Astronomy
Scientific paper
We analyze and compare the power-law slopes of energy spectra of Jupiter's cloud albedos and atmospheric kinetic energy from a common Cassini imaging data set. We assembled near-infrared images into mosaics, and used image pairs separated by short time intervals within this data set to measure winds with an automated cloud feature tracker. Sufficient coverage is present for four high-resolution full-longitudinal image and wind vector mosaics. We employ zonal and meridional FFT scans of these mosaics to assess the power spectra of the underlying quantities. We determine that the typical zonal power spectrum of the cloud albedo and the kinetic energy are broadly similar but contain some differences. The typical zonal spectrum is characterized by two regions with distinct slopes. At low wavenumbers, the slopes of the zonal kinetic energy spectra are steeper than the slopes of the cloud albedo spectra and approach the expected Kolmogorov value of -5/3. Furthermore, the slopes are markedly different at high wavenumbers, with the kinetic energy spectra much steeper compared to the spectra calculated from the images, though both spectra imply the presence of enstrophy transfer taking place in the atmosphere. The transition between the two slopes for both the cloud albedos and kinetic energies occurs at approximately planetary wavenumber 100, implying a half-wavelength of approximately 2000 km. We find little variation in the slope as a function of latitude, with the exception of low wavenumber slopes of the zonal cloud albedo power spectra, which appear to become slightly steeper with decreasing latitude. Our meridional power spectra reveal a strong anisotropy in the energy transfer, with slopes approaching -5, similar to previous studies. Overall, our analysis provides further observational evidence that an inverse energy cascade is occurring in Jupiter's atmosphere.
This work is supported by a NASA Earth and Space Science Fellowship, #NNX08AW01H.
Choi David S.
Showman Adam P.
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