Search

Thermal ion measurements from the French Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions micro-satellite have been used to study the climatology of nighttime Medium-scale traveling ionospheric disturbances (MSTIDs) in the topside ionosphere at 650 km altitude during the 6 years of the satellite operation, from 2005 to 2010. This period encompasses the declining phase of solar cycle 23, the deep solar minimum of 2008–2009 and the early rise of solar cycle 24. MSTIDs were detected from the quasi-periodic variations of the density of the dominant ionospheric O+ ions. Mostly present between ∼15° and ∼40° invariant latitudes with a small number of events in equatorial regions, the MSTIDs exhibit, on the average, larger occurrence rates in the Southern hemisphere with a peak in the Eastern Pacific-South America longitude sector. The dependence of MSTID activity on solar activity appears more complex than the previously reported simple anti-correlation. In addition to year-to-year variations, our study has, in particular, put in evidence a noticeable hemispheric asymmetry in the seasonal variations during the deep solar minimum of 2008–2009. These statistical observations provide a remarkable observational support to the key role of sporadic Es layers and the conjugate mapping of the associated electric fields. Yet, improved theoretical and numerical models, taking into account the actual inter-hemispheric differences of the seasonal and solar activity variations of thermospheric and ionospheric processes, are needed for a better understanding of the highly complex MSTID phenomena. [ABSTRACT FROM AUTHOR]

Based on the results of the experiments performed in 2005–2010 within the framework of the Sura—DEMETER program, we analyze the features of the precipitations of energetic electrons (with energies E ≈ 100 keV) from the Earth's radiation belt. The modification of the ionospheric F2 region was conducted by means of high-power HF O-mode radio waves radiated in the CW regime. The precipitations were detected using the equipment onboard DEMETER, a French microsatellite. The conditions of precipitation appearance were determined, and it was found that the electron precipitation region was stretched along the geomagnetic meridian to a distance of 1300 km; the size of the region in the transverse direction is about 400 km. It was shown by ionosonde measurements that such precipitations lead to increased absorption of radio waves in the lower ionosphere. It is assumed that the mechanism for precipitation of electrons from the Earth's radiation belt is determined by the interaction of energetic electrons with VLF radio waves, which are generated due to the interaction of the amplitude-unmodulated O-mode pump wave with the ionospheric plasma near the wave reflection height. [ABSTRACT FROM AUTHOR]

The analysis of the VLF signals radiated by ground transmitters and received on board of the French DEMETER satellite, reveals a drop of the signals (scattering spot) connected with the occurrence of large earthquakes. The extension of the "scattering spots" zone is large enough (1000-5000 km) and, probably, it increases with the magnitude of the "relative" earthquake. A possible model to explain the phenomenology, based on the acoustic gravity waves and the ionosphere turbulence, is proposed. The method of diagnostics applied to this study has the advantage to be a global one due to the world wide location of the powerful VLF transmitters and of the satellite reception. However, a specific disadvantage exists because the method requires rather a long time period of analysis due to the large longitudinal displacements among the successive satellite orbits. At the moment, at least, one month seems to be necessary. [ABSTRACT FROM AUTHOR]

Abstract: In the present paper, plasma probe data taken from DEMETER and DMSP-F15 satellites were used to study the ion density and temperature disturbances in the morning topside ionosphere, caused by seismic activity at low latitudes. French DEMETER (Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions) micro-satellite mission had been especially designed to provide global scale observations in the topside ionosphere over seismically active regions. Onboard the DEMETER satellite, the thermal plasma instrument called “Instrument Analyser de Plasma” (IAP) provides ion mass and densities, ion temperature, three component ion drift and ion density irregularities measurements. As a part of “Defense Meteorological Satellite Program”, DMSP-F15 satellite is on orbit operation since 1999. It provides ionospheric plasma diagnostics by means of the “Special Sensor-Ion, Electron and Scintillations” (SSIES-2) instrument. We examined few examples of possible seismic effects in the equatorial ionosphere, probably associated with seismic activity during December month in the area of Sumatra Island, including main shock of giant Sumatra event. It is found that the localized topside ionospheric disturbances appear close to the epicenters of certain earthquakes in the Sumatra region. In two cases, ion H+/O+ ratio rises more than one hour before the main shock, due to the O+ density decrease at the winter side of the geomagnetic equator, with longitudinally closest location to the epicenter of the earthquakes. These anomalous depletions in O+ density do exist in all cases of SSIES-2 data. Particularly for Sumatra main event, more than one hour after the main shock, we observe large-scale depletion in O+ density northward of the geomagnetic equator at winter side hemisphere. Associated with O+ depletion, ion temperature latitudinal profile around the geomagnetic equator shows enhanced asymmetry with minimum at the summer side and maximum in positive Ti deviation from mean value at the winter side. This disturbance lasted for more than three hours, later in time observed at the same place by IAP/DEMETER. [Copyright &y& Elsevier]