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Transcript
Exosphere Temperature Variability
at Earth, Mars and Venus
due to Solar Irradiation
Jeffrey M. Forbes
Department of Aerospace Engineering Sciences
University of Colorado, Boulder, Colorado, USA
Sean L. Bruinsma
Department of Terrestrial and Planetary Geodesy
Centre Nationale D'Etudes Spatiales,Toulouse, France
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International Conference on Comparative Planetology: Venus – Earth – Mars, 11-15 May 2009, ESA-ESTEC
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International Conference on Comparative Planetology: Venus – Earth – Mars, 11-15 May 2009, ESA-ESTEC
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Exosphere Temperature Variability
at Earth, Mars and Venus
Earth
Solar Irradiation
& Planetary Rotation
• In-situ
Mars
Venus
200-400K
50-120K
200 K
20-50K
> 20-50K ?
?
800K
180K
40K
• Solar Rotation
50-100K
20-40K
20K
• Day-to-day
20-40K
?
?
Solar Wind Interaction
20-200K
?
?
• Solar Tides Propagating
from Below
Solar Radiation Variability
• Long-term
International Conference on Comparative Planetology: Venus – Earth – Mars, 11-15 May 2009, ESA-ESTEC
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81-DAY MEAN EXOSPHERE DENSITY AT MARS,
Normalized to 390 km and Derived from Precise Orbit Determination of MGS
(370 x 437 km orbit; perigee -40º to -60º latitude, 1400 LT)
81-day mean
F10.7 solar
flux at Mars
(1.37-1.66 AU)
81-day mean
F10.7 solar
flux at 1 AU
Equinox
Equinox
S.
N.
Hemis.
Hemis.
Summer
Summer
81-day mean density
Note: Each density determination is made over 3-5 Mars days, and is a longitude average, so there
is no possibility to derive longitude variability, e.g., as seen in MGS accelerometer data.
International Conference on Comparative Planetology: Venus – Earth – Mars, 11-15 May 2009, ESA-ESTEC
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Least-Squares Fit to Exosphere Temperature Derived from
Observed Densities and DTM-Mars (Lemoine and Bruinsma, 2002)
S. Equinox
N.
Equinox
Hemis.
Hemis.
Summer
Summer
T  130.7  1.53F10.7
1.14 cos Ls  13.5sin Ls 
(R  .98)
zonal mean
dust optical
depth ±30o
latitude avg.
Fit for density (10-18 cm-3):
390  3.72  0.28F10.7  1.4 cos Ls  4.3sin Ls 
(R  .96)
International Conference on Comparative Planetology: Venus – Earth – Mars, 11-15 May 2009, ESA-ESTEC
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Mars
Earth
T
 1.5
F10.7
Venus
T
 2.9
F10.7
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T
 4.2
F10.7
T
 .31
F10.7
International Conference on Comparative Planetology: Venus – Earth – Mars, 11-15 May 2009, ESA-ESTEC
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Exosphere Temperature Variability due to the Sun’s Rotation
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Forbes, J.M., Bruinsma, S., Lemoine, F.G., Bowman, B.R., and A. Konopliv, Variability of the Satellite Drag Environments of Earth, Mars and
Venus due to Rotation of the Sun, J. Spacecraft & Rockets, 44, 1160-1164, 2007.
International Conference on Comparative Planetology: Venus – Earth – Mars, 11-15 May 2009, ESA-ESTEC
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Solar Irradiation
& Planetary Rotation
In-situ Thermal Tides
at Mars & Earth
Niemann et al., Earth Planets
Space, 50, 785-792, 1998.
Mars
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SSMAX T ~ 120K
SSMIN T ~ 40K
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SSMAX T ~ 400K
Earth
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SSMIN T ~ 200K
International Conference on Comparative Planetology: Venus – Earth – Mars, 11-15 May 2009, ESA-ESTEC
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Exosphere Temperature Variability due to Sun-Synchronous
Semidiurnal Solar Tides Propagating from Below
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Mars
low dust
Ls = 270
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Mars
low dust
Ls = 270
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Earth
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International Conference on Comparative Planetology: Venus – Earth – Mars, 11-15 May 2009, ESA-ESTEC
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Topographic/land-sea Modulation of Periodic Solar Radiation
Absorption Gives Rise to Longitude-Dependent Tidal perturbations
Diurnally-varying solar radiation
≈ 25 K
max-min
variation
with
longitude
0
12
local time
24
Diurnal amplitude of latent heating due to tropical convection
International Conference on Comparative Planetology: Venus – Earth – Mars, 11-15 May 2009, ESA-ESTEC
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Mars Thermosphere Densities at 120 km, 1500 LT, Kg/m3
Longitudinal Structures Due to Vertically-Propagating
Thermal Tides Modulated by Topography
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MGS Accelerometer
Mars GCM, Moudden & Forbes, 2008
International Conference on Comparative Planetology: Venus – Earth – Mars, 11-15 May 2009, ESA-ESTEC
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Conclusions Concerning Exosphere Temperature
Responses of the Terrestrial Planets to Changes in
Solar Irradiation
These exosphere temperature responses are determined by
• Magnitude of incoming solar radiation (i.e., orbit) & heating
efficiency
• CO2 content, i.e., cooling efficiency
• Dynamics, i.e., adiabatic cooling (ion drag on Earth)
• Rotation rate of the planet
• Solar radiative absorption and heating at lower altitudes, i.e.,
upward-propagating thermal tides
• Modulating topography
International Conference on Comparative Planetology: Venus – Earth – Mars, 11-15 May 2009, ESA-ESTEC
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