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| Titel |
Meridional trends in the radiative energy balance of the Venus mesosphere |
| VerfasserIn |
Y. J. Lee, D. Titov, N. Ignatiev, S. Tellmann, M. Paetzold, G. Piccioni |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250059064
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| Zusammenfassung |
| The Venus clouds play an important role in the radiative energy balance. Thermal cooling to
space occurs from the cloud tops. Also almost half of the solar energy received
by Venus is deposited at about the same altitude by the unknown UV absorber.
Observations revealed the latitudinal trend in the aerosol structure with cloud top
altitude decreasing from ~68 km in low latitudes to ~62 km in polar region and
aerosol scale height changing from ~4 km to ~1-2 km. This results in significant
changes in the radiative energy balance at the cloud tops and the mesosphere as
well as global energy balance of the planet. Here we present calculations of the
thermal flux in the 0-99 km altitude range using the latitude dependent cloud top
structure. Aerosol and temperature profiles are based on the radio science experiment
(VeRa) and the thermal spectrometer (VIRTIS) onboard Venus Express [1]. We
used radiative transfer model merged with a fast line-by-line routine to calculate
thermal fluxes in the broad wavenumber range from 50 to 2590 cm-1 (=3.86-200.0
μm).
The cloud layers are responsible for thermal cooling below ~70 km altitude. The
meridional changes in the upper clouds result in cooling rate variation 6-10 K/day along the
latitude. Contribution of the CO2 emission to the outgoing flux becomes dominant above 70
km altitude. The outgoing flux shows maxima at equator (164 W/m2) and pole (171 W/m2)
and a minimum (133 W/m2) in the “cold collar” region (50-60Ë S). The earlier studies of the
solar heating rate were used to derive a meridional trend of the radiative energy balance. The
comparison shows dominant thermal cooling in high latitudes and strong solar heating at low
latitudes suggesting radiative disequilibrium, that implies a need for another, possibly
dynamical, mechanism to maintain the observed temperature and cloud structure
[2,3].
References
[1] Lee et al. (2011) Vertical structure of the Venus cloud top from the VeRa and VIRTIS
observations onboard Venus Express, Icarus
[2] Crisp (1989) Radiative Forcing of the Venus Mesosphere II. Thermal Fluxes, Cooling
Rates, and Radiative Equilibrium Temperatures, Icarus, 77, p.391-413
[3] Titov et al. (2007) Radiation in the Atmosphere of Venus, Geophysical Monograph
Series 176, AGU, p.121-138 |
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