The topside ionosphere scale height extracted from two empirical models are compared in the paper. The Topside Sounder Model (TSM) provides directly the scale height (HT), while the incoherent scatter radar ionospheric model (ISRIM) provides electron density profiles and its scale height (HR) is determined by the lowest gradient in the topside part of the profile. HTand HRare presented for 7 ISR locations along with their dependences on season, local time, solar flux F10.7, and geomagnetic index ap. Comparison reveals that HTvalues are systematically lower than respective HRvalues as the average offset for all 7 stations is 55 km. For the midlatitude stations Arecibo, Shigaraki, and Millstone Hill this difference is reduced to 43 km. The range of variations of HRis much larger than that of HT, as the HTrange overlaps the lower part of the HRrange. Dependences on ap, DoY and LT are much stronger in the ISRIM than in TSM. This results in much larger values of HRat higher ap. Diurnal amplitude of HRis much larger than that of HT, with large maximum of HRat night. The present comparison yields the conclusion that the ISR measurements provide steeper topside Ne profiles than that provided by the topside sounders. © 2012 COSPAR. Published by Elsevier Ltd. All rights reserved.
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