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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 QuickTime™ and a decompressor are needed to see this picture. International Conference on Comparative Planetology: Venus – Earth – Mars, 11-15 May 2009, ESA-ESTEC 1 QuickTime™ and a decompressor are needed to see this picture. International Conference on Comparative Planetology: Venus – Earth – Mars, 11-15 May 2009, ESA-ESTEC 2 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 3 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 4 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 5 Mars Earth T 1.5 F10.7 Venus T 2.9 F10.7 QuickTime™ and a decompressor are needed to see this picture. T 4.2 F10.7 T .31 F10.7 International Conference on Comparative Planetology: Venus – Earth – Mars, 11-15 May 2009, ESA-ESTEC 6 Exosphere Temperature Variability due to the Sun’s Rotation QuickTime™ and a decompressor are needed to see this picture. QuickTime™ and a decompressor are needed to see this picture. 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 7 Solar Irradiation & Planetary Rotation In-situ Thermal Tides at Mars & Earth Niemann et al., Earth Planets Space, 50, 785-792, 1998. Mars QuickTime™ and a decompressor are needed to see this picture. SSMAX T ~ 120K SSMIN T ~ 40K QuickTime™ and a decompressor are needed to see this picture. SSMAX T ~ 400K Earth QuickTime™ and a decompressor are needed to see this picture. SSMIN T ~ 200K International Conference on Comparative Planetology: Venus – Earth – Mars, 11-15 May 2009, ESA-ESTEC 8 Exosphere Temperature Variability due to Sun-Synchronous Semidiurnal Solar Tides Propagating from Below QuickTime™ and a decompressor are needed to see this picture. Mars low dust Ls = 270 QuickTime™ and a decompressor are needed to see this picture. Mars low dust Ls = 270 QuickTime™ and a decompressor are needed to see this picture. Earth QuickTime™ and a decompressor are needed to see this picture. International Conference on Comparative Planetology: Venus – Earth – Mars, 11-15 May 2009, ESA-ESTEC 9 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 10 Mars Thermosphere Densities at 120 km, 1500 LT, Kg/m3 Longitudinal Structures Due to Vertically-Propagating Thermal Tides Modulated by Topography QuickTime™ and a decompressor are needed to see this picture. MGS Accelerometer Mars GCM, Moudden & Forbes, 2008 International Conference on Comparative Planetology: Venus – Earth – Mars, 11-15 May 2009, ESA-ESTEC 11 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 12
