Variations of thermospheric composition according to AE-C data and CTIP modelling

摘要

Data from the Atmospheric Explorer C satellite, taken at middle and low latitudes in1975-1978, are used to study latitudinal and month-by-month variations of thermospheric composition. Theparameter used is the "compositional -parameter", related to the neutral atomic oxygen/molecularnitrogen concentration ratio. The midlatitude data show strong winter maxima of the atomic/molecular ratio,which account for the "seasonal anomaly" of the ionospheric F2-layer. When the AE-C data arecompared with the empirical MSIS model and the computational CTIP ionosphere-thermosphere model,broadly similar features are found, but the AE-C data give a more molecular thermosphere than do themodels, especially CTIP. In particular, CTIP badly overestimates the winter/summer change ofcomposition, more so in the south than in the north. The semiannual variations at the equator and insouthern latitudes, shown by CTIP and MSIS, appear more weakly in the AE-C data. Magnetic activityproduces a more molecular thermosphere at high latitudes, and at mid-latitudes in summer. Atmospheric composition and structure (thermosphere– composition and chemistry)