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| Titel |
Spatial and Temporal distribution of CO2 4.3μm NLTE Emission from nadir VIRTIS-H/Venus Express observations |
| VerfasserIn |
Javier Peralta, Miguel Angel Lopez-Valverde, Gabriella Gilli, Pierre Drossart, Giuseppe Piccioni |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250041638
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| Zusammenfassung |
| Non-Local Thermodynamic Equilibrium (non-LTE) emissions are known to play a key role in
the radiative heating and cooling of the Venus mesosphere and lower thermosphere
(Dickinson, JAS, 1973; Roldan et al., Icarus, 2000). In the case of the Venusian atmosphere,
CO2 vibrational-rotational emissions at 4.3 μm and 2.7 μm were predicted to give intense
emissions, and since they are originated between 80 and 150 km, their observation might give
information on the atmospheric parameters at those altitudes, depending on sensitivity and
spectral resolution. The VIRTIS spectrometer on board Venus Express allows for the
first time the systematic sounding of these bands in the Venus atmosphere, both in
nadir and limb observing geometries. The limb data by VIRTIS has been recently
studied by our team (Gilli et al., JGR, 2009; López-Valverde et al., 2010 submitted;
Gilli et al., 2010 submitted), focusing on its vertical distribution and the validation
of non-LTE models, but an exhaustive study of nadir observations has not been
presented so far, except for the detection of gravity waves by García et al. (2008;
2009). In this work, we have used the nadir observations to study the horizontal
distribution of the CO2 non-LTE emissions at 4.3 μm, mainly originated at altitudes
about ~110 km. The analyzed dataset comprises the whole nadir measurements
with VIRTIS-H (the highest spectral resolution channel) obtained up to September
2009, covering nearly 900 days of observations and more than 140,000 spectra.
Similarly to the case of limb data, it was found that the nadir radiance depends not only
on the Solar Zenith Angle, but also on the Emission Angle, as predicted by our
non-LTE model. After careful radiance averages, the small dispersion found in the
mean emission of this band suggests that the Venus lower thermosphere is more
stable than expected, with scarce episodes of significant variation during the studied
period. Since the spectral resolution of VIRTIS-H allows separating different CO2
isotopic and hot bands, this dataset implies a valuable test for non-LTE models.
Therefore, a revision of some key rate coefficients for collisional relaxation of CO2
vibrational energy levels is also carried out, by means of a systematic comparison
between radiance ratios measured by VIRTIS-H and the ones obtained with our
non-LTE radiative transfer model. Conclusions will be briefly discussed at the meeting. |
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