Thermosphere

Abstract

The thermosphere consists of neutral- composition as O, O₂ and N₂ which absorb solar radiation for heating, ionization, excitation and dissociation. The composition density widely varies in distribution accompanying the solar activity.

Kinematic viscosity is so large in the thermosphere that turbulence mixing of the atmosphere stops above about 100 km, and the atmosphere tends to be in diffusive equilibrium. Precise mechanism of the cessation of the turbulence mixing remains open to question. Other important dynamics of the thermosphere is of tides and gravity waves (GW) which have been studied for long time. Tides are being studied now with sophisticated GCM (General Circulation Model) simulation reproducing the real complex situation. GW are related to TID (traveling ionospheric disturbance). Certain peculiar behaviors of TID, as showing geomagnetic conjugacy, have recently been discovered, requiring novel understanding of TID which may imply inconsistency with simple manifestation of GW as understood so far. Thermosphere global winds are little known observationally but GCM simulation now presents a plausible model. Intense vertical motion as highly fluctuating and with large amplitudes is sometimes observed in the polar thermosphere, showing nonhydrostatic motion, requiring new approaches. Observations have given remarkable successes in recent thermosphere studies. Besides with incoherent scatter radars, observation with Imager and Fabry-Perot interfermeter at many ground-stations can elucidate precise dynamic behaviors of the mesopause and lower thermosphere; observation with satellites can give global snapshots of these regions as done by UARS et al.; and innovative is observation with GPS.