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R. West (JPL/Caltech), A. Del Genio (NASA/GISS), A. McEwen (Univ. Arizona), J. Barbara (NASA/GISS), E. P. Turtle, J. Perry (Univ. Arizona), C. C. Porco (Space Science Institute), Cassini ISS Team
We observed the evolution of a cumulus methane cloud field near Titan’s south pole over an 8-hour period on July 2, 2004 with an image scale approaching 2 km/pixel. During this period individual clouds were seen to form and dissipate, making wind measurements problematic. One measurement of positional differences yielded a zonal wind of 8 m/s prograde at latitude -81 degrees, if differences in the images can indeed be attributed to motion. Clouds are seen best in the 938-nm continuum filter which also shows surface contrast. Clouds are also seen with diminished contrast at shorter-wavelength continuum and methane filters where no surface contrast is apparent. Views with different filters suggest that cloud tops are located in the upper troposphere. Quantitative radiative transfer analysis will follow. We may also be able to assess altitudes from stereo pairs. Low-resolution images during the approach phase establish that these clouds preferentially appear in late afternoon. A few images also show an occasional cloud near latitude -38 degrees with an apparent motion of 34 m/s prograde and possibly with a measurable meridional component as well. Additional observations and measurements are needed to assess these very preliminary results. Surface contrast diminishes with view angle. Quantitative analysis of these data is expected to provide estimates of haze optical depth. A detached stratospheric haze is apparent in near-ultraviolet images, and less so at longer wavelengths. Preliminary measurements indicate that the detached haze is significantly higher than that reported from Voyager images. A dark polar hood is not seen in near-ultraviolet images at 338 nm.
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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.