Ionospheric sporadic E layer is thin irregularity with much higher plasma density in the ionospheric E region (~90-120 km). Morphology of sporadic E intensity is investigated by using the COSMIC radio occultation data during 2007-2012. Maximum gradient value of total electron content fluctuation is defined as S max index, and it shows good linear relationship with the sporadic E intensity parameter (ordinary critical frequency, foEs) in the low-latitude and midlatitude regions. By using this S max index as the sporadic E layer intensity, distribution of sporadic E intensity is obtained. Some known features are confirmed such as the hemisphere summer enhancement, diurnal and semidiurnal behavior, and intensity depression anomaly regions. New findings are also obtained, especially the different behavior pattern in the low-latitude region. (1) Both positive and negative correlations exist between sporadic E intensity and solar activity, and this correlation also shows complex magnetic latitude dependency. (2) Weaker seasonal variation is found in the low-latitude region. Besides, hemisphere asymmetries of sporadic E intensity/location are also found during the equinox. (3) Longitudinal wave number-4 feature of sporadic E intensity is prominent in the lower latitude region, which may be related to the diurnal eastward wave number-3 tide. In a word, it is feasible to investigate the sporadic E layer intensity distribution based on radio occultation data, which also allows for a global morphology analysis.
In this study, the effective exospheric temperature, named as T∞, derived from thermospheric densities measured by the CHAMP satellite during 2002–2010 was utilized to develop an exospheric temperature model (ETM) with the aid of the NRLMSISE‐00 model. In the ETM, the temperature variations are characterized as a function of latitude, local time, season, and solar and geomagnetic activities. The ETM is validated by the independent GRACE measurements, and it is found that T∞ and thermospheric densities from the ETM are in better agreement with the GRACE data than those from the NRLMSISE‐00 model. In addition, the ETM captures well the thermospheric equatorial anomaly feature, seasonal variation, and the hemispheric asymmetry in the thermosphere.
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