Abstract
Abstract. Long-term incoherent scatter radar (ISR) observations are used to study ionospheric variability for two midlatitude sites, Millstone Hill and St. Santin. This work is based on our prior efforts which resulted in an empirical model system, ISR Ionospheric Model (ISRIM), of climatology (and now variability) of the ionosphere. We assume that the variability can be expressed in three terms, the background, solar activity and geomagnetic activity components, each of which is a function of local time, season and height. So the background variability is ascribed mostly to the day-to-day variability arising from non solar and geomagnetic activity sources. (1) The background variability shows clear differences between the bottomside and the topside and changes with season. The Ne variability is low in the bottomside in summer, and high in the topside in winter and spring. The plasma temperature variability increases with height, and reaches a minimum in summer. Ti variability has a marked maximum in spring; at Millstone Hill it is twice as high as at St. Santin. (2) For enhanced solar activity conditions, the overall variability in Ne is reduced in the bottomside of the ionosphere and increases in the topside. For Te, the solar activity enhancement reduces the variability in seasons of high electron density (winter and equinox) at altitudes of high electron density (near the F2-peak). For Ti, however, while the variability tends to decrease at Millstone Hill (except for altitudes near 200 km), it increases at St. Santin for altitudes up to 350 km; the solar flux influence on the variability tends to be stronger at St. Santin than at Millstone Hill.
Highlights
Studies of ionospheric climatology and variability have been pursued by many prior workers
Zhang and Holt (2007) reported on a study based on long-term databases of multiple incoherent scatter radars (ISRs) that resulted in the ISR ionospheric model (ISRIM) system
The difference is squared and goes into the same modeling system as used to produce the Ionospheric Model (ISRIM) climatology, i.e., 1) bin data according to local time and month, 2) represent the height variation by a piecewise-linear function, and represent the solar and magnetic dependence using a linear function with F10.7p and ap terms, i.e
Summary
Studies of ionospheric climatology and variability have been pursued by many prior workers. Zhang and Holt (2007) (hereafter Paper I) reported on a study based on long-term databases of multiple incoherent scatter radars (ISRs) that resulted in the ISR ionospheric model (ISRIM) system. This system contains two models: (1) the local ISRIM is constructed for each of the seven ISR sites around the world, i.e., Svalbard, Tromsø, Sondrestrom, Millstone Hill, St. Santin, Arecibo and Shigaraki, based on its long-term dataset. Unlike other studies, this work pays attention to (1) various ionospheric parameters (not just electron density), (2) variations in a large height range (not just the F2-peak), and (3) two mid-latitude sites with similar geographic but different geomagnetic latitudes. Further discussion and a summary of this research are given in the last section
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