Earth's Thermosphere under extreme solar EUV radiation environment

Details Earth's Thermosphere under extreme solar EUV radiation environment Earth's Thermosphere under extreme solar EUV radiation environment

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufmsa33c..05t&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #SA33C-05

Other

0325 Evolution Of The Atmosphere (1610, 8125), 0358 Thermosphere: Energy Deposition (3369), 3369 Thermospheric Dynamics (0358), 5749 Origin And Evolution

Scientific paper

It has been suggested that the exobase temperature of early terrestrial planetary atmosphere could have reached over 10,000 K (Kulikov et al. 2006) due to the extreme (up to 100 times that of today) solar EUV energy flux from the young Sun during the early stage of planetary evolution. Such high exobase temperature should have caused the dominant species at the exobase to escape at significant rate. Extremely fast escape of major gases in planetary atmospheres will lead to deviation from hydrostatic equilibrium. A newly developed 1-D, multi-component, hydrodynamic model has been used to investigate the response of Earth's thermosphere/ionosphere to extreme solar EUV conditions (Tian et al. 2007). We found that Earth's thermosphere/ionosphere could experience the transition from a hydrostatic equilibrium regime into a hydrodynamic regime when exposed to solar EUV fluxes exceeding certain critical level. In this regime, adiabatic cooling related to the hydrodynamic flow must be taken into the energy consideration. Due to extreme solar EUV fluxes, atomic nitrogen may have been the dominant species in upper thermosphere instead of atomic oxygen. In this work, we couple the hydrodynamic thermosphere model with an expanded GLOW model (including the electron impact ionization and excitation of nitrogen atoms) to investigate the contributions of photoelectrons and secondary electrons to thermospheric energetics under extreme conditions. The combined model provides self- consistent heating efficiency estimates for the Earth's atmosphere under extreme conditions. Implications of the simulation results to other early planetary atmospheres and their evolutions will be discussed.

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