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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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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
Venus Climate Orbiter (Planet-C) project:Status and schedule
  • The VCO mission was approved by the Space Development Committee of the government in 2001.
  • Budget request for the prototype model study in 2003 is being made.
  • The spacecraft will be launched in 2008 and arrive at Venus in 2009.
  • The mission life will be more than than 2 earth years.
earth and venus
Earth and Venus
  • They have almost the same size and mass.
  • Surface environments are completely different.
  • How does the climate system depend on planetary parameters?

Thermal structures of Earth and Venus


H2SO4 Cloud

Altitude (km)


Pressure (atm)


Temperature (K)

super rotation of venus atmosphere

Angular momentum flux


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.

cyclostrophic balance of venus atmosphere
Cyclostrophic balance of Venus’ atmosphere



Strong zonal wind


Large contrifugal force

Weak zonal wind

Small contrifugal force




These two torques are balanced each other.

similar wind system in titan s stratosphere
Similar wind system in Titan’s stratosphere?

Brightness temperature (K)

  • Rotation period= 16 days
  • Assuming cyclostrophic balance, the rotation period of the upper atmosphere is 4 days.

S.Pole EQ N.Pole

a hypothesis for super rotation gierasch s mechanism

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

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


Tidal wave


Tidal wave


Excitation of eastward-propagating tidal wave accelerates the cloud layer westward.

Acceleration by thermal tide

Cloud layer

Heating region

model prediction for thermal tide
Model prediction for thermal tide

Zonal wind


Meridional wind


Vertical structure of semi-diurnal tide (Takagi, 2001)

Vertical wind


goals of the mission
Goals of the mission


  • Mechanism of super-rotation
  • Structure of meridional circulation
  • Hierarchy of atmospheric motion
  • Lightning
  • Cloud physics
  • Plasma environment
  • Detection of active volcanism


requirements for meteorological study
Requirements for meteorological study
  • Determination of wind field below cloud top
  • Covering both dayside and nightside  Zonally-averaged circulation and momentum flux
  • Multiple altitude levels including sub-cloud region  Vertical structure
  • Covering from meso-scale to planetary-scale  Cross-scale coupling

SOLUTION: Continuoushigh-resolutionglobal imaging from a meteorological satellite (like METEOSAT!)

near ir windows
Near-IR windows


Leakage of thermal emission from the hot lower atmosphere

2.3mm (Galileo flyby)


Altitude regions to be covered

Angular momentum transport

Zonal wind

Sounding region









Airglow (Visible)

Cloud layer

SO /Unknown absorber (UV)

CO absorption (Near-IR)

Cloud top temperature (Long-IR)



Lower cloud (Near-IR)

Radio occultation


CO (Near-IR)

0 50 100

Wind speed (m s-1)

platform for imaging observation
Platform for imaging observation


Solar cell

500N thruster



360 deg

±10 deg


12 deg FOV, 1000x1000 pixels


synchronization with the super rotation
Synchronization with the super-rotation

 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

Inclination 172°

Spacecraft motion

Orbital period = 30 h

Example: Earth cloud movie

Time (hours)


Derivation of wind field

Continuous global viewing  Cloud motion vectors

100-300 km

Movement with time

Cloud tracked winds on the Earth


What can be seen in high-resolution lower-cloud movie?

  • Synoptic/planetary-scale waves
  • Cloud organization
  • Gravity waves
  • Other meso-scale phenomena

Morphology of lower clouds

2.3mm Images byGround-based observation (Crisp et al. 1991)


Cameras (1)

  • Near IR camera 1 (IR1)
  • 1.0 mm (near-IR window)
  • 1024 x 1024 pixels, FOV 12deg, SiCCD
  •  Cloud distribution, fine structure of lower cloud (dayside)
  •  Surface emission including active volcanism (nightside)
  • Near IR camera 2 (IR2)
  • 1.7, 2.3, 2.4 mm (near-IR window), 2.0 mm (CO2 absorption)
  • 1040 x 1040 pixels, FOV 12deg, PtSi
  •  Cloud distribution and particle size (nightside)
  •  Cloud top height (dayside, 2.0mm)
  •  Carbon monooxide (nightside)

Galileo (2.3mm)


IR2 thermal test model


Filter wheel

Detector housing


Stirling cooler

Dayside Nightside

Venus image taken with IR2 test filter (Okayama Astronomical Observatory)


Cameras (2)

  • UV camera (UVI)

280, 320 nm

  • 1024 x 1024 pixels, FOV 12deg, SiCCD
  •  SO2 and unknown UV absorber near the cloud top (dayside)
  • Longwave IR camera (LIR)
  • 9-11 mm
  • 240 x 240 pixels, FOV 12deg, Uncooled bolometer
  •  Cloud top temperature (day/night)
  • Lightning and Airglow camera (LAC)
  • 777, 551, 558 nm
  • 8 x 8 pixels, FOV 12deg, Photo diode
  •  High-speed sampling of lightning flashes (nightside)
  •  O2 / O airglows (nightside)

Mariner 10

PVO (North pole)

operation of cameras
Operation of cameras

12 deg FOV

  • Whole disk in the field of view over 70% of the orbital period

 Development/decay of planetary-scale features in both hemispheres

 Precise mapping of each pixel onto planetary surface

  • Acquisition every few minutes- few hours (nominal: 2 hours)
  • Spatial resolution is <16 km
  • Near-IR (dayside)
  • Ultraviolet
  • Long-IR
  • Near-IR (nightside)
  • Lightning/Airglow
radio occultation uso
Radio occultation (USO)
  • Temperature profiles at two opposite longitudes in the low latitude
  •  Zonal propagation of planetary-scale waves
  • H2SO4 vapor profile
  • Ionosphere

To the earth


Spacecraft motion


3 d viewing
3-D viewing



Temperature, H2SO4 vapor (Radio occultation)

Airglow (Visible)

90 km

SO2, Unknown absorber (UV)

Cloud top temperature(Mid-IR)

Cloud top height (Near-IR)

70 km

Lower clouds (Near-IR)

50 km

CO (Near-IR)

35-50 km

Cloud motion vectors

0 km

Lightning (Visible)

Surface (Near-IR)


Optical sounding of ground surface

  • Search for hot lava erupted from active volcano by taking global pictures at 1.0mm every half a day
  • Emissivity distribution of the ground surface
  • The spacecraft will be launched in 2008, arrive at Venus in 2009, and observe meteorological processes more than 2 years.
  • The mission is optimized for observing atmospheric dynamics in the low/mid-latitudes.
  • Science payloads will be multi-wavelength cameras covering wavelengths from UV to IR, USO, plasma detectors, and magnetometer.
  • Collaboration with complementary VEX measurements is strongly needed.
vex and vco
  • Optimization: Spectroscopy  Imaging
  • Orbit: Polar  Equatorial
  • Global images: High latitudes  Low latitudes
possible collaboration
Possible collaboration
  • Complementary information on the general circulation and cloud chemistry

Chemical species related with cloud formation (VEX)

Spatial correlation between cloud top height and UV contrast (VCO)

  • Origin of ultraviolet contrast
    • Cloud height or UV absorber
    • Mechanism of producing inhomogeneity
possible collaboration1
Possible collaboration
  • Complementary information on the general circulation and cloud chemistry
  • Cloud morphology in both low and high latitudes
  • To constrain the VCO sounding region using the VEX spectroscopic data
  • Collaboration in receiving downlink (Radio science)
  • Mutual comparison of the tools for data analysis
    • Radiative transfer code
    • Cloud tracking algorithm
    • General circulation model
  • European instruments onboard VCO

Model predictions for “horizontal viscosity”

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)

energy cycle of earth climate system


Energy cycle of Earth climate system

Disturbance potential energy

15.6x105 J/m2

Axi-symmetric potential energy

33.5x105 J/m2

1.5 W/m2

Solar energy

0.7 W/m2

Solar energy

1.5 W/m2

2.2 W/m2

0.2 W/m2


1.9 W/m2


0.1 W/m2

Disturbance kinetic energy

8.8x105 J/m2

Axi-symmetric kinetic energy

3.6x105 J/m2

0.3 W/m2


Planetary waves driving the circulation

Equatorial waves

Meridional transport of trace gases

Meridional transport of trace gases


Forbes (2002)

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