Temperatures in Venus upper Atmosphere from mid infrared heterodyne Spectroscopy of CO2 around 10 μm Wavelength

Details Temperatures in Venus upper Atmosphere from mid infrared heterodyne Spectroscopy of CO2 around 10 μm Wavelength Temperatures in Venus upper Atmosphere from mid infrared heterodyne Spectroscopy of CO2 around 10 μm Wavelength

Sep 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008epsc.conf...24s&link_type=abstract

European Planetary Science Congress 2008, Proceedings of the conference held 21-25 September, 2008 in Münster, Germany. Online a

Computer Science

Scientific paper

We report observations of temperatures in the Venus upper Mesosphere/lower Thermosphere. Data was acquired between 22 and 24 October 2007 at the NASA Infrared Telescope Facility on Mauna Kea, Hawaii using the NASA Goddard Space Flight Center Heterodyne Instrument for Planetary Wind and Composition (HIPWAC). The receiver is based on a CO2 laser local oscillator which allows operation between 9 and 12 μm using various isotopes of CO2. Fully resolved non-thermal emission (non-LTE) lines in the 10.6 μm band of CO2 from various rotational levels were used to study rotational and kinetic temperatures on the Venus dayside. A typical spectrum is shown in Fig. 1. Shown is the P(16) line observed at 45° East (45E) of central meridian longitude (CML) and the equator. From models the emission is assumed to originate in the range of 100-120 km altitude. Rotational temperatures were derived from the intensity distribution of the CO2 lines measured at the equator/45E, mid-latitudes (45N and 45S)/45E, and 70S/30E. Retrieved values (171-236 K) disagree with the observed kinetic temperatures in all but one point (45N/45E). In addition the measured intensities show a large dispersion originating most likely in the Venus atmosphere. Information on kinetic temperatures was extracted from the widths of the emission lines. Temperature values range from 224 to 236 K and were retrieved at the equator/45° East, mid-latitudes (45N and 45S)/45E, and 70S/30E, and along the equator at various longitudes with an accuracy of up to 2 K. The longitudinal scan (Fig. 2) shows kinetic temperatures of ~230-250 K from the sub solar point to 40° offset from the terminator followed by a decrease to ~120 K close to the terminator. This values are higher than the Venus International Reference Atmosphere model predicts. The rotational and kinetic temperatures retrieved from ultra-high heterodyne spectral resolution mid-infrared observations of CO2 on the dayside thermosphere and mesosphere of Venus will be useful for improving our understanding of the Venus thermal structure, non- LTE emission processes, and possible temporal and spatial variability. Reasons for apparent measured differences in the rotational and kinetic temperatures at 45S and the possible mid-latitude North-South rotational temperature asymmetry need to be investigated further especially the possibility of temporal changes on time scales of a few hours impeding the retrieval.

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