Near Infrared Observations of the Latitudinal Variation of Vertical Cloud Structure in Uranus’ Atmosphere Prior to its Equinox

Details Near Infrared Observations of the Latitudinal Variation of Vertical Cloud Structure in Uranus’ Atmosphere Prior to its Equinox Near Infrared Observations of the Latitudinal Variation of Vertical Cloud Structure in Uranus’ Atmosphere Prior to its Equinox

Oct 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007dps....39.0905i&link_type=abstract

American Astronomical Society, DPS meeting #39, #9.05; Bulletin of the American Astronomical Society, Vol. 39, p.424

Astronomy and Astrophysics

Astronomy

Scientific paper

With Uranus approaching its northern spring equinox in December 2007 there is great international interest in observing the near-infrared spectrum of Uranus to monitor any changes in cloud structure that are widely anticipated to occur.
Near-infrared spectra of Uranus were observed in August/September 2006 and June 2007 using the UIST instrument on the United Kingdom Infrared Telescope (UKIRT). Spectra were recorded between 1 and 2.5 microns with the instrument in Long Slit mode and with the slit aligned with the planet's central meridian to determine the North-South variations of Uranus' cloud structure. In addition, context images were also recorded to monitor the position of discrete mid-latitude clouds. The last time the complete near-IR spectrum of Uranus was observed was in 1975, and then only disc-integrated spectra could be observed. Hence, these appear to be the first latitudinally-resolved complete 1-2.5 micron spectra of Uranus ever obtained.
We present initial studies of the latitudinal variation of Uranus' vertical cloud structure from these data using new methane absorption coefficients and a multiple scattering correlated-k model. In the 1.3 and 1.6 micron methane windows a clear North-South asymmetry is observed, with a clear increase in albedo at southern mid-latitudes, especially in the southern circumpolar collar at 45S. However, an unexpected discovery is that while the shortwave side of the 1.06 micron peak shows the same N-S asymmetry, complete symmetry is seen on the longwave side. We find that these data are best fitted with two cloud layers, one at 2bars, which has a N-S asymmetry in albedo, being most reflective at 45S and a second cloud at 8 bars, whose reflectivity decreases symmetrically towards both poles. We are grateful to the United Kingdom Science and Technology Facilities Council for funding this research.

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