Midlatitude ionospheric plasma temperature climatology and empirical model based on Saint Santin incoherent scatter radar data from 1966 to 1987

Ionospheric plasma temperature variations have recently been studied based on incoherent scatter radar (ISR) observations at a lower midlatitude site, Shigaraki, in East Asia [Otsuka et al., 1998] and Millstone Hill, a typical subauroral midlatitude site in North America [Zhang and Holt, 2004]. The French Saint Santin ISR, with a geographic latitude slightly higher but an apex latitude 14° lower than Millstone, collected bistatic and quadristatic measurements for over two solar cycles beginning in September 1965. A database of these data, containing observations between 1966 and 1987, has been used in this study in order to establish the midlatitude ionospheric climatology, in particular that of the upper atmosphere thermal status, as well as empirical models for space weather applications. This paper presents, in comparison with the Millstone Hill results, variations of ion and electron temperatures (Ti and Te) with solar activity, season, time of the day, and altitude. The F2 region Te at St. Santin is found to be lower than at Millstone between March and July, when the St. Santin electron density Ne is relatively higher. The midday Te below 300 km increases with F10.7, as at Millstone Hill. Above 300 km it tends to decrease with F10.7 at St. Santin, while it increases in summer at Millstone Hill. Ti between 250 and 350 km peaks midway between spring and summer. We have also created St. Santin ionospheric models for Ne, Te, and Ti using a bin-fit technique similar to that used for the Millstone Hill models. Comparisons with corresponding IRI predications indicate good agreement in Ti at high solar activity, and above the F2 peak, Te from the IRI tends to be higher than both the St. Santin and Millstone Hill models.

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