DEMETER observations of an intense upgoing column of ELF/VLF radiation excited by the HAARP HF heater

International audienceDEMETER spacecraft observations of ELF signals generated by the recently upgraded High-Frequency Active Auroral Research Program (HAARP) HF facility (3.6 MW) reveal three distinctive regions characterizing upgoing ELF waves. These regions are classified by signal intensity and the minimum lateral distance d between the magnetic footprint of the satellite at 75-km altitude (D layer) and the point at 75-km altitude immediately above HAARP where the source is located. The first large region within d ' 900 km contains waves which propagate in the Earth-ionosphere waveguide and then leak upward to the spacecraft. The second region of d ' 200-300 km contains waves propagating to the spacecraft from the ionospheric source region without reflection from the ground. The third region contains waves of very high intensity (E ' 350 mV/m, B ' 20 pT) within a narrow cylindrical column of $10-20 km radius, also observed once before on the ISIS 1 spacecraft. The observed intense columnar radiation is consistent with predictions of a recent full-wave model of ELF radiation from HF-heater-produced ionospheric source currents

DEMETER observations of ionospheric heating by powerful VLF transmitters

International audience[1] We report DEMETER spacecraft observations of iono-spheric heating produced above powerful VLF transmitters by their intense radiated electromagnetic (EM) signals. We compare the heating effects of signals from the 1 MW NWC transmitter in Australia with those produced by signals from the 885 kW NAA transmitter in Maine. Significant observable effects include perturbations in plasma density and thermal electron temperature, and the production of quasi‐electrostatic (QE) VLF plasma wave bands, both over the transmitters, and, in the case of NWC, also in the magnetically conjugate region. In the regions in which the QE wave bands were observed, they were invariably accompanied by a band of ELF turbulence with maximum intensity below 300 Hz. Such turbulence has in the past been associated with the presence of small scale plasma density irregularities. This association suggests that heating effects due to NWC are far‐reaching and extend along B o into the conjugate hemisphere where they are expressed in part as small scale plasma density fluctuations

DEMETER satellite observations of lightning-induced electron precipitation

International audienceDEMETER spacecraft detects short bursts of lightninginduced electron precipitation (LEP) simultaneously with newly-injected upgoing whistlers, and sometimes also with once-reflected (from conjugate hemisphere) whistlers. For the first time causative lightning discharges are definitively geo-located for some LEP bursts aboard a satellite. The LEP bursts occur within <1 s of the causative lightning and consist of 100-300 keV electrons. First in-situ observations of large regions of enhanced background precipitation are presented. The regions are apparently produced and maintained by high rate of lightning within a localized thunderstorm

Modeling of Doppler-shifted terrestrial VLF transmitter signals observed by DEMETER

International audienceObservations of signals from a terrestrial very low frequency (VLF) transmitter made by the DEMETER spacecraft inside the plasmasphere are modeled using a three-dimensional wave propagation code. The simulation results agree well with the satellite measurements, predicting both the incidence and frequency offset of Doppler-shifted signals resulting from non-ducted interhemispheric propagation paths through the plasmasphere. The observed Doppler shifts are similar to those which can result from linear mode coupling as VLF transmitter signals scatter from small-scale plasma density irregularities. Thus care must be taken to differentiate the two effects when studying the power loss of VLF waves through the ionosphere. The agreement shown between predictions and observation demonstrates the utility of the models used for understanding the wave energy distribution in the plasmasphere from terrestrial transmitters

DEMETER observations of transmitter-induced precipitation of inner radiation belt electrons

International audienceNear loss cone energetic electron flux increases induced by ground-based very low frequency (VLF) transmissions are observed directly via satellite-based detection. In 2 years of experiments ranging from 27 March 2006 through 2 April 2008 with the 21.4-kHz transmitter NPM in Lualualei, Hawaii, and the French satellite DEMETER (detection of electromagnetic emissions transmitted from earthquake regions), only a few cases of detection of individual pulses of transmitter-induced precipitation of inner radiation belt electrons have been realized. Analysis of the specific cases of detection allow comparison of precipitating flux with predictions based on ray-tracing analyses of wave propagation and test particle modeling of the wave-particle interaction. Results indicate that the precipitated flux of >100 keV electrons induced by the NPM transmitter peaks at L ' 1.9 and, in the rare cases of detection, may be at higher energies than the $100 keV peak predicted by the model. The low detection rate is attributed to the orientation of the DEMETER particle detector, which is mostly overwhelmed by the trapped population at the location of detection

DEMETER observations of the ionospheric trough over HAARP in relation to HF heating experiments

International audiencePlasma density variations observed aboard the DEMETER satellite in the topside ionospheric F layer are analyzed in relation to high-frequency transmitter operations. The main interest is the high-latitude region. One hundred cases with operating and nonoperating High Frequency Active Auroral Research Program HF transmitter during day and night are examined. It is found that most large-scale variations can be attributed to the presence of the main ionospheric trough and that such natural variations complicate the detection of HF transmitter effects on a case-by-case basis. From statistics, no correlation between the HF transmissions and the presence of the irregularities has been established. A comparison of our observations with two recent works on electron density ducts created by HF transmitters and detected by DEMETER shows that in those works the main ionospheric trough is the major factor in density variations, and it is not clear how to distinguish density variations created by the HF heater from natural variations in such cases. Finally, possible experimental techniques for duct formation by HF heaters are discussed

Spatial Power Distribution of ELF Radiation Induced by HF Heating of the Ionosphere

International audienceThe High Frequency Active Auroral Research Program (HAARP) transmitter array (3.6 MW, 2.8 - 10 MHz) is used to generate Extremely Low Frequency (ELF, 300 - 3000 Hz) waves through periodic heating of the ionospheric D-layer and subsequent modulation of the conductivity of the auroral electrojet. The generated ELF waves can be used in various manners depending on whether the part of energy which penetrates into the space, or the other part which propagates into the Earth-ionosphere waveguide, is considered. One application of ELF waves in space is the study of wave-particle interactions which occur in the Earth’s magnetosphere between waves of this frequency range and energetic electrons in the range of about 10 - 500 keV. One of the most important applications of ELF waves in the Earth-ionosphere waveguide is maritime communication over long distances. In all situations, the knowledge of ELF power distribution as a function of the distance from the source is required. The spatial power distribution depends on many factors. Some of them can be controlled: the ELF and HF frequencies, direction, and modulation techniques of an HF transmitter. Other parameters are natural and can not be directly affected: strength of the electrojet current, absorption of the waves in the ionosphere, and so on. The distribution of the ELF power can be effectively studied using a low-earth-orbit (LEO) satellite which passes through a large region of electromagnetic radiation in several minutes. This allows to keep most of the parameters constant during a single experiment. The waves propagating up into the space can be directly measured by such a satellite. As was shown in Piddyachiy et al., 2008, the waves observed in space at the horizontal distances of more than 300 km from the source are directly leaking from the Earth-ionosphere waveguide and therefore their power is a direct indication of the power in the waveguide at long distances. In this work we use the LEO DEMETER satellite (altitude of 670 km) in conjunction with HAARP to study the spatial power distribution of ELF waves radiated by HAARP. Initial studies were conducted on a case by case basis, but now they are complemented by a statistical study of many experiments conducted over 4 years. Case studies show that the signal distribution in space can be more variable in specific situations than predicted from theoretical modeling using a stratified ionosphere. Ionospheric density irregularities are deemed to be the main factor of an abrupt signal variation in space for specific examples. That is why the comparison of theoretical results with not only specific observations, but also with average power distributions over multiple passes, is need to increase the accuracy of modeling and adjust the techniques of ELF generation

Spatial Power Distribution of ELF Radiation Induced by HF Heating of the Ionosphere

International audienceThe High Frequency Active Auroral Research Program (HAARP) transmitter array (3.6 MW, 2.8 - 10 MHz) is used to generate Extremely Low Frequency (ELF, 300 - 3000 Hz) waves through periodic heating of the ionospheric D-layer and subsequent modulation of the conductivity of the auroral electrojet. The generated ELF waves can be used in various manners depending on whether the part of energy which penetrates into the space, or the other part which propagates into the Earth-ionosphere waveguide, is considered. One application of ELF waves in space is the study of wave-particle interactions which occur in the Earth’s magnetosphere between waves of this frequency range and energetic electrons in the range of about 10 - 500 keV. One of the most important applications of ELF waves in the Earth-ionosphere waveguide is maritime communication over long distances. In all situations, the knowledge of ELF power distribution as a function of the distance from the source is required. The spatial power distribution depends on many factors. Some of them can be controlled: the ELF and HF frequencies, direction, and modulation techniques of an HF transmitter. Other parameters are natural and can not be directly affected: strength of the electrojet current, absorption of the waves in the ionosphere, and so on. The distribution of the ELF power can be effectively studied using a low-earth-orbit (LEO) satellite which passes through a large region of electromagnetic radiation in several minutes. This allows to keep most of the parameters constant during a single experiment. The waves propagating up into the space can be directly measured by such a satellite. As was shown in Piddyachiy et al., 2008, the waves observed in space at the horizontal distances of more than 300 km from the source are directly leaking from the Earth-ionosphere waveguide and therefore their power is a direct indication of the power in the waveguide at long distances. In this work we use the LEO DEMETER satellite (altitude of 670 km) in conjunction with HAARP to study the spatial power distribution of ELF waves radiated by HAARP. Initial studies were conducted on a case by case basis, but now they are complemented by a statistical study of many experiments conducted over 4 years. Case studies show that the signal distribution in space can be more variable in specific situations than predicted from theoretical modeling using a stratified ionosphere. Ionospheric density irregularities are deemed to be the main factor of an abrupt signal variation in space for specific examples. That is why the comparison of theoretical results with not only specific observations, but also with average power distributions over multiple passes, is need to increase the accuracy of modeling and adjust the techniques of ELF generation

Microwave Radiometer for Spectral Observations of Mesospheric Carbon Monoxide at 115 GHz Over Kharkiv, Ukraine

We present the results of the development of high sensitivity microwave radiometer designed for observation of the atmospheric carbon monoxide (CO) emission lines at 115 GHz. The receiver of this radiometer has the double-sideband noise temperature of 250 K at a temperature of 10A degrees C. To date, this is the best noise performance for uncooled Schottky diode mixer receiver systems. The designed radiometer was tested during the 2014-2015 period at observations of the carbon monoxide emission lines over Kharkiv, Ukraine (50A degrees N, 36.3A degrees E). These tests have shown the reliability of the receiver system, which allows us in the future to use designed radiometer for continuous monitoring of carbon monoxide. The first observations of the atmospheric carbon monoxide spectral lines over Kharkiv have confirmed seasonal changes in the CO abundance and gave us reasons to assume the spread of the influence of the polar vortex on the state of the atmosphere up to the latitude of 50A degrees N where our measurement system is located