Imperial College London


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Publication Type

128 results found

Lilensten J, Galand M, 1998, Proton-electron precipitation effects on the electron production and density above EISCAT (Tromsø) and ESR, Annales Geophysicae, Vol: 16, Pages: 1299-1307, ISSN: 0992-7689

The suprathermal particles, electrons and protons, coming from the Sun and precipitating into the high-latitude atmosphere are an energy source for the Earth's ionosphere. They interact with the ambient thermal gas through inelastic and elastic collisions. Most of the physical quantities perturbed by the precipitation, such as the electron production rate, may be evaluated by solving the stationary Boltzmann transport equation, which yields the particle fluxes as a function of altitude, energy, and pitch angle. This equation has been solved for the three different suprathermal species (electrons, protons and hydrogen atoms). We first compare the results of our theoretical code to a coordinated DMSP/EISCAT experiment, and to another approach. Then, we show the effects that pure proton precipitation may have on the ionosphere, through primary and secondary ionization. Finally, we compare the effects of proton precipitation and electron precipitation in some selected cases above EISCAT (Tromsø) and ESR.

Journal article

Galand M, Lilensten J, Kofman W, Sidje RBet al., 1997, Proton transport model in the ionosphere .1. Multistream approach of the transport equations, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 102, Pages: 22261-22272

Journal article

Nilsson H, Kirkwood S, Lilensten J, Galand Met al., 1997, Enhanced incoherent scatter plasma lines, Annales Geophysicae, Vol: 14, Pages: 1462-1472, ISSN: 0992-7689

Detailed model calculations of auroral secondary and photoelectron distributions for varying conditions have been used to calculate the theoretical enhancement of incoherent scatter plasma lines. These calculations are compared with EISCAT UHF radar measurements of enhanced plasma lines from both the E and F regions, and published EISCAT VHF radar measurements. The agreement between the calculated and observed plasma line enhancements is good. The enhancement from the superthermal distribution can explain even the very strong enhancements observed in the auroral E region during aurora, as previously shown by Kirkwood et al. The model calculations are used to predict the range of conditions when enhanced plasma lines will be seen with the existing high-latitude incoherent scatter radars, including the new EISCAT Svalbard radar. It is found that the detailed structure, i.e. the gradients in the suprathermal distribution, are most important for the plasma line enhancement. The level of superthermal flux affects the enhancement only in the region of low phase energy where the number of thermal electrons is comparable to the number of suprathermal electrons and in the region of high phase energy where the suprathermal fluxes fall to such low levels that their effect becomes small compared to the collision term. To facilitate the use of the predictions for the different radars, the expected signal-to-noise ratios (SNRs) for typical plasma line enhancements have been calculated. It is found that the high-frequency radars (Søndre Strømfjord, EISCAT UHF) should observe the highest SNR. but only for rather high plasma frequencies. The VHF radars (EISCAT VHF and Svalbard) will detect enhanced plasma lines over a wider range of frequencies, but with lower SNR.

Journal article

Carpenter DL, Galand M, Bell TF, Sonwalkar VS, Inan US, LaBelle J, Smith AJ, Clark TDG, Rosenberg TJet al., 1997, Quasiperiodic similar to 5-60 s fluctuations of VLF signals propagating in the Earth-ionosphere waveguide: A result of pulsating auroral particle precipitation?, JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS, Vol: 102, Pages: 347-361

Journal article

Nilsson H, Kirkwood S, Lilensten J, Galand Met al., 1996, Enhanced incoherent scatter plasma lines, ANNALES GEOPHYSICAE-ATMOSPHERES HYDROSPHERES AND SPACE SCIENCES, Vol: 14, Pages: 1462-1472, ISSN: 0992-7689

Journal article

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