Global 30-240 keV proton precipitation in the 17-18 April 2002 geomagnetic storms: 3. Impact on the ionosphere and thermosphere

NOAA Polar Orbiting Environmental Satellites 30-240 keV proton precipitation measurements in the 17-18 April 2002 geomagnetic storms are used with a Monte Carlo ion transport model to obtain ionization and heating rates that are subsequently fed into the Global Ionosphere Thermosphere Model to investigate the proton impact on the ionosphere and thermosphere. Simulation results show that after the addition of proton precipitation in a moderate geomagnetic storm (specifically, the one during mid-April 2002), there are places at low altitudes (100-120 km) on the nightside undergoing significant increases in electron and nitric oxide (NO) densities. The enhancement can be as large as several factors or even by an order of magnitude. Moreover, the temporal profiles of the enhancement in ionospheric electron densities demonstrate a direct correlation with proton precipitation imposed on the topside boundary, and there is no integral effect. This is in contrast with a continuous buildup process illustrated in the time variation of the thermospheric NO density enhancement because NO at these altitudes has a long lifetime. In addition, by including high-energy precipitating protons in a global ionosphere thermosphere coupled model, significant changes take place in the ion convection (locally around +/- 20%) and in the neutral winds (locally around +/- 40%). This study represents the first attempt to understand the global influence of proton precipitation on the ionosphere and thermosphere using in situ observational data.