Modeling of Ionospheric Responses to the Solar Flux Change Based on Millstone Hill Incoherent Scatter Radar

In order to develop ionospheric empirical models of electron density Ne, plasma temperatures (Te and Ti) and ion drifts based on Millstone Hill incoherent scatter radar observations, we investigate an important issue of ionospheric responses to the solar flux changes that have to be quantitatively represented. The representation is associated with selecting a mathematical function where a suitable solar flux index at a proper time ahead the observing time has to be determined. Traditionally, the solar 10.7 cm flux F107 for the previous day is applied, and a linear function is used. However, the non-linear feature of Ne responses to the solar flux was discovered previously. This paper shows the development of the non-linear feature with altitude, season and local time, and also indicates the non-linear feature for the Te and Ti responses. A mathematical function is proposed. We also discuss the use of other solar flux indices, in addition to F107.