Dependence of the electromagnetic and precipitating particle energy inputs to the ionosphere upon the sunlit/shade condition of the ionosphere

Fujii, R.1, Handa, H.1, Nozawa, S.1 and Ogawa, Y.2

1 STEL/Nagoya University, Nagoya, Japan
2 National Institute of Polar Research, Tokyo, Japan

Based on an analysis of EISCAT CP-1 data obtained from January 1987 to November 2004, we have statistically determined the dependence of the electromagnetic energy and the kinetic energy of precipitating particles from the magnetosphere into the ionosphere and then thermosphere upon the sunlit/shade condition of the ionosphere. The energy deposition by precipitating particles can be derived from the ion-electron pair production rate that is obtained from the recombination rate using measured electron density in the E-region. Since the neutral atmosphere is ionized not only by particle precipitation but also by solar irradiation, however, in order to obtain the electron density due to particle precipitation, we have first estimated the electron density due to the solar irradiation and expressed it as a function of solar zenith angle by using data where we do not see any significant ionizations by particle precipitation. We have thus successfully estimated the precipitating particle energy deposition even in the sunlit ionosphere on all available CP-1 data. The present study shows that not only the electromagnetic energy but also the precipitating particle energy deposition in the dark ionosphere tends to be larger in the sunlit ionosphere, indicating that ionospheric conditions actively control the magnetosphere-ionosphere (M-I) coupling.