Study of ionospheric variation during the eclipse of July 22, 2009 using NICT Space Weather Simulator

It has been suggested that the ionosphere is significantly affected by a solar eclipse. Previous studies have indicated that decrease of solar EUV and X-ray radiations during solar eclipses reduces electron densities of the ionosphere locally and temporarily. Furthermore, some studies reported that decrease of neutral temperatures drives neutral winds and atmospheric waves, which also affects the ionosphere. However, no convincing results on the effects of solar eclipse on the ionosphere have been obtained. The solar eclipse on July 22, 2009 passed near Japan where there are a number of observation facilities of the ionosphere and the atmosphere. On the same day, a magnetic storm also occurred simultaneously. A large number of data on the ionosphere obtained by various instruments provided us with useful information on the ionospheric processes as well as space weather forecast. National Institute of Information and Communications Technology (NICT) has developed a magnetosphere-ionosphere-thermosphere coupled model for space weather forecast. The model was used to study ionospheric variations during the solar eclipse. The simulation results indicate that the electron density significantly decreases as the solar eclipse begins, followed by an increase of the electron density caused by ionospheric storm. The results are consistent with GPS/TEC results.