Midlatitude propagation of VLF to MF waves through nighttime ionosphere above powerful VLF transmitters

International audience[1] Midlatitude nighttime observations made by the DEMETER satellite in the very low frequency (VLF) to medium frequency (MF) bands (3 kHz to 3 MHz) have demonstrated the propagation of radio waves from the bottom of ionosphere up to the satellite altitude (~700 km). Propagation characteristics derived from the magneto-ionic theory [Budden, 1985] are used to explain the absence of wave observations between ~1 and 2 MHz. Under hypotheses made for the Appleton and Hartree (or Appleton and Lassen) formula, studies of the vertical variations of the real and imaginary parts of the refractive index are performed to point out modifications in the propagation characteristics of the waves: (i) at the crossing of the plasma cutoffs regions, (ii) at the crossing of the ordinary and extraordinary mode resonance regions, and (iii) in the region where the product of the collision frequency (n) and the electronic density (Ne) is maximum. It is shown that enhancements in the collision frequencies, produced by powerful VLF transmitters in the region where the product of n and Ne is maximum, open the half angle of the MF wave transmission cones and increase the power densities of those waves at the DEMETER altitude. Citation: Lefeuvre F., J. L. Pinc¸n , and M. Parrot (2013), Midlatitude propagation of VLF to MF waves through nighttime ionosphere above powerful VLF transmitters

TARANIS — Scientific payload and mission strategy

International audienceOn December 2010 the implementation phase of the TARANIS micro-satellite was authorized by the French space agency. TARANIS is dedicated to the study of impulsive transfers of energy between the Earth atmosphere and the space environment, and more precisely to the physics of the Transient Luminous Events (TLEs) and of the Terrestrial Gamma ray Flashes (TGFs). By 2015 TARANIS will provide combined Nadir observations of TLEs and TGFs, high resolution measurements of energetic electrons, and wave field measurements. The strategy adopted to maximize the scientific return of the data is presented

Temporal and spatial analyses on seismo-electric anomalies associated with the 27 February 2010 M = 8.8 Chile earthquake observed by DEMETER satellite

International audienceThis paper studies seismo-electromagnetic anomalies observed by the French satellite DEMETER (Detection of ElectroMagnetic Emissions Transmitted from Earthquake Regions) during the 27 February 2010 M = 8.8 Chile earthquake. The nighttime electron density (N e), electron temperature (T e), ion density (N i), ion temperature (T i) and whistler counts (C w) are investigated. A statistical analysis of the box-and-whisker method is applied to see if data of two or more groups under study are significantly different. A cross-examination of temporal variations before and after shows that N e and N i (C w) increases (decreases) appear 10–20 days before the earthquake. A comparison of data over the epicenter and those over its reference area can be employed to discriminate the earthquake-related anomalies from global effects. Results prove that anomalous enhancements of N e , N i , and T i occur specifically around the epicenter area. The intersection of the temporal and spatial results confirms that N e and N i are useful and sensitive detecting anomalous related to the 2010 M = 8.8 Chile earthquake

Particle energization in space plasmas : towards a multi-point, multi-scale plasma observatory

This White Paper outlines the importance of addressing the fundamental science theme "How are charged particles energized in space plasmas" through a future ESA mission. The White Paper presents five compelling science questions related to particle energization by shocks, reconnection, waves and turbulence, jets and their combinations. Answering these questions requires resolving scale coupling, nonlinearity, and nonstationarity, which cannot be done with existing multi-point observations. In situ measurements from a multi-point, multi-scale L-class Plasma Observatory consisting of at least seven spacecraft covering fluid, ion, and electron scales are needed. The Plasma Observatory will enable a paradigm shift in our comprehension of particle energization and space plasma physics in general, with a very important impact on solar and astrophysical plasmas. It will be the next logical step following Cluster, THEMIS, and MMS for the very large and active European space plasmas community. Being one of the cornerstone missions of the future ESA Voyage 2050 science programme, it would further strengthen the European scientific and technical leadership in this important field.Peer reviewe

Compton Large Area Silicon Timing Tracker for Cosmic Vision M3

International audienceProposed in response to the ESA call for the third Medium size mission (M3), CAPSiTT is a small mission designed for a 3-year survey of the non-thermal high energy sky from an equatorial LEO orbit. With a large effective area and a very wide field of view, its single instrument, a silicon tracker, provides good imaging, spectroscopic and polarimetric capabilities with a sensitivity 10-100 times better than COMPTEL. Nucleosynthesis and particle acceleration mechanisms in various sites are the main scientific topics addressed by CAPSiTT

The COBRAT project (Coupled Observations from Balloon Related to Asim and Taranis)

International audienceWithin a few years the TARANIS (Tool for the Analysis of RAdiations from lightNIngs and Sprites) mission from CNES and the ASIM (Atmosphere-Space Interactions Monitor) from ESA will be operating in space. They are dedicated to the study of TLEs and TGFs and their potential consequences. Both phenomena are observed above thunderstorms and are supposed to be generated in the altitude range [10 km - 80 km]. Accordingly, coordinated measurements from balloons (in the vicinity of the generation regions) will be needed to identify unambiguously the generation mechanisms and the importance of the atmospheric effects. The aim of the COBRAT (Coupled Observations from Balloon Related to Asim and Taranis) project is to maximize the scientific return of the TARANIS and ASIM missions. It is based on the development and the operation of Zero Pressure Balloons (ZPB) that can reside in the middle stratosphere (altitudes in the 20-40 km range) above stormy areas for more than one week and can carry heavy poly-instrumented gondolas (up to 150 kg). We present and discuss the strategy adopted by the COBRAT project

The COBRAT project (Coupled Observations from Balloon Related to Asim and Taranis)

International audienceWithin a few years the TARANIS (Tool for the Analysis of RAdiations from lightNIngs and Sprites) mission from CNES and the ASIM (Atmosphere-Space Interactions Monitor) from ESA will be operating in space. They are dedicated to the study of TLEs and TGFs and their potential consequences. Both phenomena are observed above thunderstorms and are supposed to be generated in the altitude range [10 km - 80 km]. Accordingly, coordinated measurements from balloons (in the vicinity of the generation regions) will be needed to identify unambiguously the generation mechanisms and the importance of the atmospheric effects. The aim of the COBRAT (Coupled Observations from Balloon Related to Asim and Taranis) project is to maximize the scientific return of the TARANIS and ASIM missions. It is based on the development and the operation of Zero Pressure Balloons (ZPB) that can reside in the middle stratosphere (altitudes in the 20-40 km range) above stormy areas for more than one week and can carry heavy poly-instrumented gondolas (up to 150 kg). We present and discuss the strategy adopted by the COBRAT project

Is There an Earthquake Weather?

International audienceThe aim of this study is to check if there is a relationship between the seismic activity and the whistlers observed by the micro-satellite DEMETER. Whistlers are the waves emitted by lightning strokes during thunderstorm activity. They use to propagate in the Earth-ionosphere waveguide but also in the ionosphere and the magnetosphere mainly along the magnetic field lines. Due to this reason we have checked the whistler occurrence not close to earthquake epicenters but close to the magnetically conjugate point of these epicenters at the satellite altitude. The number of whistlers is given by a neural network in operation onboard the satellite. It appears that the whistler amplitude is attenuated at the satellite altitude around the magnetic equator. It is why we have removed the earthquakes occurring at low geomagnetic latitudes in the statistic. The whistler rate is normalized with a background value to take into account the seasons and the epicenter locations. A superposed epoch method is used to display the results between −15 and +5 days around the earthquake day and up to 1000 km from the conjugate point of the epicenters. It is shown that the whistler rate is higher the day before the earthquake at a distance less than 200 km. It would be unrealistic to believe in the possibility to use this study for earthquake prediction because everyday thunderstorm activity reliably masks seismic effects. But it is further evidence that there is a lithosphere-atmosphere-ionosphere coupling at the time of the seismic activity