Shufan Zhao

Ionospheric perturbations of electron density before the Wenchuan Earthquake

Based on electron density data recorded by the Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions (DEMETER) satellite of France, the phenomena of disturbed electron density in the ionosphere before the Wenchuan Earthquake of magnitude 8.0 on 12 May 2008, were analysed. The results showed that the anomalies concentrated 3 days prior to the earthquake, especially the variation on 9 May, when the electron density reduced above the northeast epicentral area, and the peak values moved to the equator. Compared with the variations in the geomagnetic indexes and other parameters related to solar activity, the geomagnetic condition and solar activity were all quiet from 7 to 12 May, so the variation on 9 May might be related to this strong earthquake. In addition, the geomagnetic field observed at the surface was analysed, and the Z component data at stations near the epicentral area showed apparent aberrations of daily variation compared with those at stations in eastern China. All these phenomena illustrate that obvious perturbations in the ionosphere and at the surface might be related to the preparation process of the Wenchuan Earthquake.

Plasma perturbations HF-induced in the topside ionosphere

Three plasma perturbations induced by SURA HF (high-frequency) heating have been selected and analyzed in detail with the DEMETER satellite observing data by instruments of Langmuir probe and ion analyzer. Some common features are revealed, such as (1) electron density and electron temperature both increased during the heating period; (2) both O+ density and ion temperature also increased generally, while H+ varied negatively with O+ density; (3) the ions were accelerated in upward and northward directions, resulting from the thermal pressure gradient, which also caused the variations in ULF (ultralow-frequency) electric field due to V⇀×B⇀ effects; and (4) the simulation results verify the electron density and temperature enhancement at the topside ionosphere due to the ohmic heating process and thermal self-focusing instability over the heating region, which is consistent with the observing phenomena by the DEMETER satellite.