Astronomy and Astrophysics – Astronomy
Scientific paper
Oct 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007dps....39.6102b&link_type=abstract
American Astronomical Society, DPS meeting #39, #61.02; Bulletin of the American Astronomical Society, Vol. 39, p.538
Astronomy and Astrophysics
Astronomy
Scientific paper
We have obtained simultaneous infrared images and spectra of the nightside of Venus for 10 consecutive nights from the NASA IRTF. Using the SpeX spectrograph, 2.3 μm images were obtained each evening and image cubes from 0.8 to 2.5 μm were obtained most evenings from July 21 to July 30, 2007. Carlson et al. (1993) used the nightside fluxes at 1.74 and 2.3 μm obtained during the Galileo flyby of Venus to distinguish particle size populations in the middle and lower clouds. We use our high spatial resolution ( 250 km) ground-based images and spectral image cubes with a similar technique to Carlson et al. to map the relative contributions of different size modes in the Venus clouds over 10 days. Since the scattering and absorption properties of different aerosol size modes result in differences in 1.74 and 2.3 μm fluxes, the relative contribution of mode 2’ (rave = 1.5 μm) and mode 3 (rave = 3 μm) can be mapped on the nightside as a function of time.
We use a radiative transfer model to compute the 1.74 and 2.3 μm radiances that would be expected for variations in mode 2’ and mode 3 particles in the upper, middle and lower clouds. We compare regions of differing aerosol distributions with total cloud opacity as derived from our 2.3 μm images. In addition to helping understand the Venus cloud motions as a function of time, these efforts are valuable for understanding the altitudes of sources of opacity in the 2.3 μm cloud silhouette images. With estimates of the altitudes of cloud opacities, we are able to derive more complete wind velocities using cloud tracking algorithms (Tavenner et al. 2007), as well as identify possible regions of upwelling and downwelling.
This work was supported by NASA's Planetary Atmpospheres and Planetary Astronomy Programs.
Bullock Mark Alan
Tavenner Tanya
Young Eliot Fisher
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