[P-EM15] Dynamics in magnetosphere and ionosphere

[PEM15-P09] Nightside Ultra-Low-Frequency waves observed in the topside ionosphere by the DEMETER satellite

*Xinyan Ouyang¹ (1.Institute of Earthquake Forecasting, China Earthquake Administration)

キーワード：topside ionosphere, ultra-low-frequency oscillations, electron density perturbations

We study Ultra-Low-Frequency waves (ULF) at frequencies 17-100 mHz observed in the topside ionosphere by the DEMETER satellite in a ~5-year period from January 2006 to November 2010. Our results show that two types of ULF oscillations occur on the nightside in the L<2 region. These two kinds of ULF oscillations are separated based on cross-covariance analysis between electric field in the DC/ULF range and electron density. Type I ULF oscillations, accompanied by electron density perturbations (average |δNe/Ne₀|>5%), are found to lag behind density variations; and the longitudinal distribution of type I ULF oscillations is quite similar to the distribution of plasma irregularities at solar minimum. These signatures suggest that type I ULF oscillations are related to plasma irregularities that are common phenomena in the nightside F region ionosphere. The characteristics of type II ULF oscillations (without significant electron density perturbations) agree well with those features of mid-latitude ionospheric electric field fluctuations, which are not thought to be related to magnetospheric origins.