Global model of longitude/UT variations in thermospheric composition and temperature based on mass spectrometer data

Measurements of N2, O, He, and Ar densities from neutral gas mass spectrometers on four satellites (Ogo 6, Aeros A, AE‐C, and AE‐D) and inferred O2 and H densities from an ion mass spectrometer on AE‐C have been combined to produce a model of longitude/universal time (UT) variations in thermospheric neutral temperature and composition. The longitude/UT model is an extension of the mass spectrometer‐incoherent scatter thermospheric model and uses spherical harmonic terms dependent on geographic latitude, longitude, and universal time. The terms which depend only on longitude indicate a temperature enhancement of about 30°K somewhat equatorward of the magnetic poles. The temperature varies also in universal time, the greatest enhancement being about 30°K near 2130 UT in the northern hemisphere and about 70°K near 0930 UT in the southern hemisphere. The extrapolated 120‐km variations are generally in phase for Ar and O2 and out of phase for He, O, and H. Changes during magnetic storms are relatively small. The combined longitude and UT variations reflect the influence of the earth's magnetic field but indicate that the variations may not be simply represented in magnetic coordinates. The longitude/UT model helps reduce differences in the local time variation between the incoherent scatter stations.