Variations of the electron density in the low and middle latitude ionosphere due to high-speed solar wind streams observed by the DEMETER satellite

Earth's ionosphere varies very dynamically according to the geomagnetic activities and solar irradiance. Recently it has been studied that the plasma and neutral densities in the thermosphere and ionosphere show periodic oscillations with respect to the solar wind speed and Kp index during the declining phase of the solar cycle. In this study, we investigate the relationship between the electron density and the solar wind speed during the declining phase of the solar cycle using the observation from the Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions (DEMETER) satellite at the altitude of 660 km. The electron density near the dip equator tends to increase with the solar wind speed from January to April, but there is no clear tendency in the other times. Also, the electron density shows good relationship with the solar wind speed at the magnetic longitudes from 240 to 300 degrees. However, there is poor relationship in the other longitudes. We will discuss the seasonal and longitudinal dependences of the electron density on the solar wind speed in the low and middle latitude ionosphere.