Morphology of Ionospheric Sporadic E Layer Intensity Based on COSMIC Occultation Data in the Midlatitude and Low-Latitude Regions

Ionospheric sporadic E layer is thin irregularity with much higher plasma density in the ionospheric E region (similar to 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.