Changes in the ultra-low frequency wave field during the precursor phase to the Sichuan earthquake: DEMETER observations

Electromagnetic phenomena observed in association with increases in seismic activity have been studied for several decades. These phenomena are generated during the precursory phases of an earthquake as well as during the main event. Their occurrence during the precursory phases may be used in short-term prediction of a large earthquake. In this paper, we examine ultra-low frequency (ULF) electric field data from the DEMETER satellite during the period leading up to the Sichuan earthquake. It is shown that there is an increase in ULF wave activity observed as DEMETER passes in the vicinity of the earthquake epicentre. This increase is most obvious at lower frequencies. Examination of the ULF spectra shows the possible occurrence of geomagnetic pearl pulsations, resulting from the passage of atmospheric gravity waves generated in the vicinity of the earthquake epicentre

Oxygen Cyclotron Harmonic Waves in the Deep Plasmasphere During Magnetic Storms

A new approach to the generation of storm{associated ULF waves with discrete spectra (ion cyclotron harmonic waves) observed in the equatorial plasmasphere is presented. It is proposed that the appearance of waves with phase velocities smaller than the Alfven velocity is connected with a strong dispersion of magnetosonic waves near the bi{ion frequency occurring in the presence of oxygen ions of ionospheric origin. The waves are generated by an instability involving hot oxygen ions with loss cone or ring like distributions. Such ions are found in the magnetosphere during magnetic storms. A simple analytical model of this instability is elaborated. It is shown that ULF wave observations on board Akebono satellite are in a reasonable agreement with the present theoretical approach. 2 1

Ionospheric Response to Natural and Man Made Impacts

International audienceThe problem of energy transfer from the Earth’s solid mantles to the atmosphere and surrounding space is of essential importance for the fundamental geophysics and applied studies. These processes can largely govern the structure and dynamics of the phenomena developing in the near Earth space. Moreover, the consequences of such impacts as earthquakes, hurricanes, etc. upon the Earth’s electromagnetic field and ionosphere can become an extra factor in monitoring the processes involved in the upcoming large-scale seismic and meteorological catastrophes. The acoustic-gravity waves (comprising acoustic and gravity waves and hereafter referred to as AGW) are one of the most efficient ways to transport over the ionosphere the energy of the dynamic processes developing in the low atmosphere. The early experiments of the 1950’s and 60’s on Doppler sounding even showed that the ionosphere can serve as a sensitive indicator of natural and man made disturbances. The Doppler sounding of the ionosphere revealed impulse and wave disturbances excited by powerful sources of infrasound, such as: a) megaton nuclear explosions in the atmosphere, kiloton ground industrial explosions, b) earthquakes and volcano eruptions, c) thunderstorms, tornadoes and tsunamis, d) bolides and meteorites, e) rocket launches and flights of supersonicjets, f) aurora and solar eclipse