Strategy of meteorological study in Venus Climate Orbiter mission. T. Imamura, M. Nakamura Institute of Space and Astronautical Sciences. Venus Climate Orbiter (Planet-C) project: Status and schedule. The VCO mission was approved by the Space Development Committee of the government in 2001.
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T. Imamura, M. Nakamura
Institute of Space and Astronautical Sciences
General circulation of terrestrial planetary atmospheres: how they work?
Angular momentum flux how they work?
Viscosity?Super-rotation of Venus’ atmosphere
Although the period of planetary rotation is 243 days, the atmosphere near the cloud top circles around the planet once every 4 days.
Strong zonal wind
Large contrifugal force
Weak zonal wind
Small contrifugal force
These two torques are balanced each other.
Brightness temperature (K)
S.Pole EQ N.Pole
？ how they work?
Direct or indirect cells?
Momentum carrier?A hypothesis for super-rotation: Gierasch’s mechanism
Hadley celltransports angular momentum upward at low latitudes and downward at high latitudes
Horizontal viscositytransports angular momentum equatorward
Net transport of angular momentum : UPWARD
Meridional circulation how they work?
Shaded: ClockwiseWhite: Anti-clockwise
Venus .. ?
Winter Pole EQ Summer Pole
Earth: 3-cells exist in each hemisphere
Motion of the sun relative to cloud layer how they work?
Excitation of eastward-propagating tidal wave accelerates the cloud layer westward.
Acceleration by thermal tide
Vertical structure of semi-diurnal tide (Takagi, 2001)
SOLUTION: Continuoushigh-resolutionglobal imaging from a meteorological satellite (like METEOSAT!)
Leakage of thermal emission from the hot lower atmosphere
2.3mm (Galileo flyby)
Altitude regions to be covered how they work?
Angular momentum transport
SO /Unknown absorber （UV）
CO absorption （Near-IR)
Cloud top temperature （Long-IR)
Lower cloud (Near-IR)
0 50 100
Wind speed (m s-1)
12 deg FOV, 1000x1000 pixels
detect small deviations of atmospheric motion from the background zonal flow
Angle from apoapsis (deg)
Air motion at 50 km altitude
300 km x 13 Venus radii
Orbital period = 30 h
Example: Earth cloud movie
Derivation of wind field how they work?
Continuous global viewing Cloud motion vectors
Movement with time
Cloud tracked winds on the Earth
Morphology of lower clouds
2.3mm Images byGround-based observation (Crisp et al. 1991)
Cameras (1) how they work?
IR2 thermal test model how they work?
Venus image taken with IR2 test filter (Okayama Astronomical Observatory)
Cameras (2) how they work?
280, 320 nm
PVO (North pole)
12 deg FOV
Development/decay of planetary-scale features in both hemispheres
Precise mapping of each pixel onto planetary surface
To the earth
Temperature, H2SO4 vapor （Radio occultation）
SO2, Unknown absorber (UV）
Cloud top temperature（Mid-IR）
Cloud top height （Near-IR）
Lower clouds （Near-IR）
Cloud motion vectors
Optical sounding of ground surface how they work?
Chemical species related with cloud formation (VEX) how they work?
Spatial correlation between cloud top height and UV contrast (VCO)
Model predictions for “horizontal viscosity” how they work?
Two-dimensional turbulence in Venus-like mechanical model (Iga, 2001)
Phase velocity-latitude cross section of meridional momentum flux u’v’ in Venus-like GCM (Yamamoto and Takahashi, 2003)
Venus? how they work?
Disturbance potential energy
Axi-symmetric potential energy
Disturbance kinetic energy
Axi-symmetric kinetic energy
Planetary waves driving the circulation how they work?
Meridional transport of trace gases
Meridional transport of trace gases
Gravity waves at low latitude (radio occult.)
Gravity waves at high latitude (radio occult.)
Polar collar Polar dipole
H2SO4 vapor at high latitude by radio occult.
H2SO4 vapor at low latitude by radio occult.
Meridional drift velocity at low latitude
Meridional drift velocity at high latitude