Strategy of meteorological study in Venus Climate Orbiter mission
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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

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Strategy of meteorological study in venus climate orbiter mission

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.


Science background

SCIENCE BACKGROUND


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?


Strategy of meteorological study in venus climate orbiter mission

Thermal structures of Earth and Venus

Earth

H2SO4 Cloud

Altitude (km)

Haze

Pressure (atm)

Venus

Temperature (K)


Strategy of meteorological study in venus climate orbiter mission

General circulation of terrestrial planetary atmospheres: how they work?

Earth

Venus


Super rotation of venus atmosphere

Angular momentum flux

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.


Cyclostrophic balance of venus atmosphere

Cyclostrophic balance of Venus’ atmosphere

Pole

Pole

Strong zonal wind

Cool

Large contrifugal force

Weak zonal wind

Small contrifugal force

Hot

EQ

EQ

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


Strategy of meteorological study in venus climate orbiter mission

Meridional circulation

Shaded: ClockwiseWhite: Anti-clockwise

Venus .. ?

Winter Pole EQ Summer Pole

Earth: 3-cells exist in each hemisphere


Strategy of meteorological study in venus climate orbiter mission

Motion of the sun relative to cloud layer

Acceleration

Tidal wave

Acceleration

Tidal wave

Acceleration

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

Temperature

Meridional wind

T×√p

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

Vertical wind

Phase


Goals of the mission

Goals of the mission

Meteorology

  • Mechanism of super-rotation

  • Structure of meridional circulation

  • Hierarchy of atmospheric motion

  • Lightning

  • Cloud physics

  • Plasma environment

  • Detection of active volcanism

Others


Strategy

STRATEGY


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

Visible-UV

Leakage of thermal emission from the hot lower atmosphere

2.3mm (Galileo flyby)


Strategy of meteorological study in venus climate orbiter mission

Altitude regions to be covered

Angular momentum transport

Zonal wind

Sounding region

(km)

100

80

60

40

20

0

Viscosity?

Airglow (Visible)

Cloud layer

SO /Unknown absorber (UV)

CO absorption (Near-IR)

Cloud top temperature (Long-IR)

2

2

Lower cloud (Near-IR)

Radio occultation

Lightning

CO (Near-IR)

0 50 100

Wind speed (m s-1)


Platform for imaging observation

Platform for imaging observation

North

Solar cell

500N thruster

MGA

HGA

360 deg

±10 deg

cameras

12 deg FOV, 1000x1000 pixels

South


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

Orbit:

300 km x 13 Venus radii

Inclination 172°

Spacecraft motion

Orbital period = 30 h

Example: Earth cloud movie

Time (hours)


Strategy of meteorological study in venus climate orbiter mission

Derivation of wind field

Continuous global viewing  Cloud motion vectors

100-300 km

Movement with time

Cloud tracked winds on the Earth


Strategy of meteorological study in venus climate orbiter mission

  • 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)


Instruments

INSTRUMENTS


Strategy of meteorological study in venus climate orbiter mission

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)


Strategy of meteorological study in venus climate orbiter mission

IR2 thermal test model

Optics

Filter wheel

Detector housing

Aperture

Stirling cooler

Dayside Nightside

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


Strategy of meteorological study in venus climate orbiter mission

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

Pole

Spacecraft motion

Atmosphere


3 d viewing

3-D viewing

Dayside

Nightside

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)


Strategy of meteorological study in venus climate orbiter mission

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


Summary

Summary

  • 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

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


Strategy of meteorological study in venus climate orbiter mission

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


Strategy of meteorological study in venus climate orbiter mission

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

Venus?

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

Dissipation

1.9 W/m2

Dissipation

0.1 W/m2

Disturbance kinetic energy

8.8x105 J/m2

Axi-symmetric kinetic energy

3.6x105 J/m2

0.3 W/m2


Strategy of meteorological study in venus climate orbiter mission

Planetary waves driving the circulation

Equatorial waves

Meridional transport of trace gases

Meridional transport of trace gases

VEX VCO

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


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