International Conference on Comparative Planetology: Venus – Earth – Mars, 11-15 May 2009, ESA-ESTEC 1
Exosphere Temperature Variability at Earth, Mars and Venus
due to Solar Irradiation
Jeffrey M. ForbesDepartment of Aerospace Engineering SciencesUniversity of Colorado, Boulder, Colorado, USA
Sean L. BruinsmaDepartment 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 2
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International Conference on Comparative Planetology: Venus – Earth – Mars, 11-15 May 2009, ESA-ESTEC 3
Exosphere Temperature Variability at Earth, Mars and Venus
Earth Mars Venus
Solar Wind Interaction
Solar Irradiation & Planetary Rotation
• In-situ
• Solar Tides Propagating from Below
Solar Radiation Variability
• Long-term
• Solar Rotation
• Day-to-day
200-400K 50-120K 200 K
20-50K ?
800K 180K 40K
50-100K 20-40K 20K
??20-40K
> 20-50K ?
20-200K ? ?
International Conference on Comparative Planetology: Venus – Earth – Mars, 11-15 May 2009, ESA-ESTEC 4
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 density
81-day meanF10.7 solar flux at 1 AU
81-day meanF10.7 solar flux at Mars
Note: Each density determination is made over 3-5 Mars days, and is a longitude average, so thereis no possibility to derive longitude variability, e.g., as seen in MGS accelerometer data.
N. Hemis.
Summer
Equinox EquinoxS.
Hemis.Summer
(1.3
7-1.
66 A
U)
International Conference on Comparative Planetology: Venus – Earth – Mars, 11-15 May 2009, ESA-ESTEC 5
T∞ =130.7 +1.53F10.7
−1.14cos Ls( )−13.5sin Ls( )(R=.98)
zonal mean dust optical depth ±30o
latitude avg.
ρ390 = 3.72 + 0.28F10.7 − 1.4 cos Ls( ) − 4.3sin Ls( ) (R = .96)Fit for density (10-18 cm-3):
N. Hemis.
Summer
Equinox EquinoxS. Hemis.
Summer
Least-Squares Fit to Exosphere Temperature Derived fromObserved Densities and DTM-Mars (Lemoine and Bruinsma, 2002)
International Conference on Comparative Planetology: Venus – Earth – Mars, 11-15 May 2009, ESA-ESTEC 6
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Mars Venus
ΔTΔF10.7
= 4.2
ΔTΔF10.7
= .31
ΔTΔF10.7
= 1.5
ΔTΔF10.7
= 2.9
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Earth
International Conference on Comparative Planetology: Venus – Earth – Mars, 11-15 May 2009, ESA-ESTEC 7
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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 8
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Niemann et al., Earth Planets Space, 50, 785-792, 1998.
Solar Irradiation & Planetary RotationIn-situ Thermal Tides
at Mars & Earth
SSMIN ΔT ~ 40K
SSMAX ΔT ~ 120K
SSMIN ΔT ~ 200K
SSMAX ΔT ~ 400K
Mars
Earth
International Conference on Comparative Planetology: Venus – Earth – Mars, 11-15 May 2009, ESA-ESTEC 9
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Exosphere Temperature Variability due to Sun-SynchronousSemidiurnal Solar Tides Propagating from Below
Marslow dustLs = 270
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Earth
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Marslow dust Ls = 270
International Conference on Comparative Planetology: Venus – Earth – Mars, 11-15 May 2009, ESA-ESTEC 10
Topographic/land-sea Modulation of Periodic Solar Radiation Absorption Gives Rise to Longitude-Dependent Tidal perturbations
≈ 25 Kmax-min variation
with longitude
Diurnally-varying solar radiation
12local time
0 24
Diurnal amplitude of latent heating due to tropical convection
International Conference on Comparative Planetology: Venus – Earth – Mars, 11-15 May 2009, ESA-ESTEC 11
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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
MGS Accelerometer Mars GCM, Moudden & Forbes, 2008
International Conference on Comparative Planetology: Venus – Earth – Mars, 11-15 May 2009, ESA-ESTEC 12
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