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Comparative Planetary Study: How do the Exosphere Temperatures of Earth, Mars and Venus Respond to Long-Term Solar Cha

F 10.7 : 81-day mean solar flux received at the planet, proxy for EUV solar flux : change in exosphere temperature per unit change in F 10.7. Comparative Planetary Study: How do the Exosphere Temperatures of Earth, Mars and Venus

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Comparative Planetary Study: How do the Exosphere Temperatures of Earth, Mars and Venus Respond to Long-Term Solar Cha

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  1. F10.7 : 81-day mean solar flux received at the planet, proxy for EUV solar flux : change in exosphere temperature per unit change in F10.7 Comparative Planetary Study: How do the Exosphere Temperatures of Earth, Mars and Venus Respond to Long-Term Solar Change? Jeffrey M. Forbes, U. of Colorado Frank G. Lemoine, NASA/GSFC Sean Bruinsma, CNES Michael D. Smith, NASA/GSFC Xiaoli Zhang, U. of Colorado ……and acknowledging significant motivation and insight into interpretations provided by Comparative General Circulation Model Results of Stephen Bougher (Bougher et al., 1997, 1999, 2000, 2006) Fall AGU 2007

  2. May be Nonlinear Relation between F10.7 and EUV (Balan et al., 1994) Jacchia (1970) MSISE00, NRLMSISE00 Mars Venus Earth MGS Drag Analysis Kasprzak et al. (1997) PVO, Magellan Fall AGU 2007

  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) Equinox Equinox S. Hemis. Summer N. Hemis. Summer 81-day mean F10.7 solar flux at 1 AU 81-day mean F10.7 solar flux at Mars (1.37-1.66 AU) 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. Fall AGU 2007

  4. Fit for density (10-18 cm-3): Least-Squares Fit to Exosphere Temperature Derived from Observed Densities and DTM-Mars (Lemoine and Bruinsma, 2002) S. Hemis. Summer Equinox N. Hemis. Summer Equinox zonal mean dust optical depth ±30o latitude avg. Fall AGU 2007

  5. Venus Mars Earth MGS Drag Analysis Fall AGU 2007

  6. Probably dominates response at Venus compared to Earth May be playing an important role in relative response between Earth and Mars, at least on dayside Factors Affecting Planetary Response to Solar Flux Received at the Planet (e.g., Bougher et. al, 1999, 2000, 2006) • Heating efficiency • Infrared cooling, e.g., CO2 and O/CO2 ratio • Thermal conductivity (eddy & molecular) • Large-scale circulation (adiabatic heating & cooling) • and plasma-neutral coupling Fall AGU 2007

  7. Adiabatic cooling Adiabatic cooling Adiabatic cooling EUV Heating EUV Heating EUV Heating Adiabatic cooling Global Circulation Inhibited by Enhanced Ion Drag EUV Heating Plasma-Neutral Coupling (“Ion Drag”) may act to Amplify the Thermal Response at Earth by Limiting Adiabatic Cooling (Hagan and Oliver, 1985) in Contrast to Mars (Bougher et al., 1999,2000) Solar Maximum Solar Minimum Large-scale circulation Mars Large-scale circulation Earth Fall AGU 2007

  8. Conclusions Concerning Exosphere Temperature Responses of the Terrestrial Planets to Long-Term Changes in Solar Flux • Venus is about 10% as responsive to solar flux changes as Earth • Mars is about 36-50% as responsive as Earth • Plasma-neutral coupling in Earth’s atmosphere may be playing an important role in regulating its response in comparison to Mars’. • Further understanding of the role of plasma-neutral coupling in the energetic response of Earth’s atmosphere is required. • Definitive interpretations concerning Mars require careful comparisons with the MTGCM, wherein the latitude and local time sampling of the drag experienced by MGS are replicated. Fall AGU 2007

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