Ionospheric perturbations observed by the low altitude satellite DEMETER and possible relation with seismicity

摘要

The high-altitude ionospheric perturbations around the equatorial anomalies (EA) are often observed by DEMETER spacecraft on the nighttime orbits. The ionospheric perturbations are recognized as an enhancement of the electric field in the ELF frequency range in the satellite coordinate. Clear perturbations are mostly recognized on the dayside of the satellite orbit and the peak perturbation intensity tends to increase with increasing magnetic latitude based on around 1000 perturbation events observed in the year of 2005. The perturbation intensities are examined in relation with major seismic activities. As a result, most importantly higher perturbation intensity persists for the time periods around the occurrence days of the land earthquakes rather than those for the sea earthquakes and without major earthquakes nearby. However, the difference of the observed perturbation intensity between above-mentioned three cases are rather small due to relatively large variability indicative of the weak correlation of seismicity with the high altitude ionospheric perturbations near EA.