Physics
Scientific paper
May 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agusm.p34a..01k&link_type=abstract
American Geophysical Union, Spring Meeting 2008, abstract #P34A-01
Physics
5405 Atmospheres (0343, 1060), 5410 Composition (1060, 3672), 6295 Venus
Scientific paper
Venus was observed at 2.4 and 3.7 μm using a long-slit high-resolution spectrograph CSHELL at NASA IRTF (Hawaii). The instrument resolving power is ν/δν=40,000. The observations cover the latitude range of ±60° at local time of 8:00. The Doppler shift corresponds to velocity of 12.5 km/s. The observed reflectivity at 2.4 μm shows a weak limb brightening which is fitted by a cloud layer with τ=20, 1- ω=0.01, and g=0.75 superimposed by an absorbing layer with τ=0.09. The observed absorption lines are analyzed using the standard equivalent width technique and a simple reflection model. The atmosphere is divided in 30 layers from 60 to 90 km using the temperature profile from VIRA. A line shape is divided in 300 points, and the equivalent width is calculated by integration over wavenumber and altitude using the Voigt formulation and then compared with the observed width. The CO2 R32 and R34 lines at 4443.11 and 4444.81 cm-1 show the effective abundance varying from 100 mbar at low latitudes to 50 mbar at ±60° near the limb. The relevant altitudes are 64 and 68 km, respectively. A CO mixing ratio is retrieved from the observed CO P21 line at 4164.84 cm-1. The measured ratio is rather constant at 70 ppm with local variations of ~eq10%. The HF R3 line at 4109.94 cm-1 is used to measure the HF abundance which is also rather constant at 3.5 ppb with the values at the northern latitudes smaller than those at the southern latitudes by ~eq10%. Spectra at 4089 to 4115 cm-1 have been observed to search for OCS in the upper cloud layer. These spectra are corrected for the nightside emission in this range by subtracting the nightside spectra observed at the similar geometry. Absorption of OCS is revealed by summing of spectral intervals at the expected positions of 50 OCS lines. The retrieved OCS mixing ratio varies from 5.5 ppb at 64 km to 2.2 ppb at 68 km and may be given as fOCS(ppb)= (P/P0)1.3 where P0 = 27 mbar. Hence the OCS scale height is smaller than that of the atmosphere by a factor of 2.3. The observed OCS abundance is significant and presents a main source of free sulfur in the middle atmosphere. H2S lines near 2689 cm-1 are used for sensitive search of this species.
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