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Martian mesospheric CO2 clouds: OMEGA and HRSC data, the LMD-MGCM and possibility for mesospheric convection

Määttänen, Anni and Montmessin, Franck and Gondet, Brigitte and Hoffmann, Harald and Scholten, Frank and González-Galindo, Francisco and Spiga, Aymeric and the, Martian-CO2 cloud Team (2010) Martian mesospheric CO2 clouds: OMEGA and HRSC data, the LMD-MGCM and possibility for mesospheric convection. EGU General Assembly 2010, 02 – 07 May 2010, Vienna, Austria.

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Official URL: http://meetingorganizer.copernicus.org/EGU2010/oral_programme/2113

Abstract

We will present 3 Martian years (Mars Years 27-29) of high-altitude CO2 cloud data from MEx/OMEGA and se- lected results from Mex/HRSC. OMEGA observed these clouds on 51 and HRSC in 28 orbits with 11 simultaneous observations. The 3-year dataset shows that the cloud activity starts latest at Ls=0° (with the earliest occurrence ob- served at the end of MY 29 at Ls=330°), and continues until Ls=60° when ceasing for a period before the summer solstice. The activity starts again at or after Ls=90°, and after Ls=120° the equatorial clouds are nearly absent in our dataset. Three cases of midlatitude autumn/winter clouds have been observed: one in the northern hemisphere and two in the southern. The spatial distribution of the clouds is limited in a latitude range of 20°S-20°N (with the exceptions of the midlatitude clouds) and a longitude range -120 – 30°E (3 exceptions). The HRSC stereo observations enable accurate cloud altitude measurements, yielding values between 60 and 85 km (+/-2 km) for the near-equatorial clouds. The clouds speeds, related to the prevailing east-west winds, range from 15 to 107 m/s (+/-15 m/s). Two cloud shadow observations show that cloud opacities can go up to =0.6 and the cloud particle effective radii are mainly in the range reff=1-2 µm. A comparison with the LMD Mars Global Climate Model shows a good agreement between the model-predicted winds and those observed by the HRSC. The LMD-MGCM predicts a strong diurnal variation of temperature at the cloud observation altitudes due to the propagation of the diurnal thermal tide. The coldest temperatures in the near-equator cloud altitude range (60-85 km) are observed towards the end of the afternoon, whereas the warmest temperatures are found in the early morning hours. Most of the observed clouds are cirrus-type, filamented clouds, but in some OMEGA observations the clouds exhibit round, clumpy structures that have been suggested to be of convective origin. We assess the plausibility of the hypothesis of mesospheric convection in light of the observations and theoretical Convective Available Potential Energy calculations. Estimates of convective potential and vertical velocities based on observed cloud properties suggest that the convective clouds could most likely be clusters of smaller scale convective updrafts. To attain the estimated values of CAPE and vertical velocity, most probably only moderate deviations from saturation are required. Based on nucleation modeling, such deviations may imply cloud formation via heterogeneous nucleation onto small condensation nuclei.

Item URL in elib:https://elib.dlr.de/67436/
Document Type:Conference or Workshop Item (Speech)
Title:Martian mesospheric CO2 clouds: OMEGA and HRSC data, the LMD-MGCM and possibility for mesospheric convection
Authors:
AuthorsInstitution or Email of AuthorsAuthors ORCID iD
Määttänen, AnniLaboratoire Atmosphères, Milieux, Observations Spatiales, CNRS/IPSL/UVSQ/UPMC, BP 3, Guyancourt 78280, FranceUNSPECIFIED
Montmessin, FranckLaboratoire Atmosphères, Milieux, Observations Spatiales, CNRS/IPSL/UVSQ/UPMC, BP 3, Guyancourt 78280, FranceUNSPECIFIED
Gondet, BrigitteInstitut d’Astrophysique Spatiale (IAS), Orsay 91405, France, Planetary and Space ScienceUNSPECIFIED
Hoffmann, Haraldharald.hoffmann (at) dlr.deUNSPECIFIED
Scholten, Frankfrank.scholten (at) dlr.deUNSPECIFIED
González-Galindo, FranciscoLaboratoire de météorologie dynamique, CNRS/UPMC, 4 place Jussieu, 75252 Paris cedex 05, FranceUNSPECIFIED
Spiga, AymericDepartment of Physics and Astronomy, The Open University, Milton Keynes, United KingdomUNSPECIFIED
the, Martian-CO2 cloud TeamUNSPECIFIEDUNSPECIFIED
Date:2010
Refereed publication:No
Open Access:No
Gold Open Access:No
In SCOPUS:No
In ISI Web of Science:No
Volume:Vol. 12
Series Name:Geophysical Research Abstracts
Status:Published
Keywords:Mars, mesospheric CO2 clouds, HRSC, OMEGA
Event Title:EGU General Assembly 2010
Event Location:Vienna, Austria
Event Type:international Conference
Event Dates:02 – 07 May 2010
Organizer:European Geoscience Union
HGF - Research field:Aeronautics, Space and Transport (old)
HGF - Program:Space (old)
HGF - Program Themes:W EW - Erforschung des Weltraums
DLR - Research area:Space
DLR - Program:W EW - Erforschung des Weltraums
DLR - Research theme (Project):W - Projekt MARS-EXPRESS / HRSC (old)
Location: Berlin-Adlershof
Institutes and Institutions:Institute of Planetary Research
Deposited By: Scholten, Dipl.-Ing. Frank
Deposited On:04 Jan 2011 22:46
Last Modified:04 Jan 2011 22:46

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