Mid-latitude electron precipitation into the atmosphere and related geophysical phenomena



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Balloon observations of the X-ray flux of photons with energies greater than 25 keV, measured at an atmospheric depth of 8 g/cm at Roberval, Quebec (1=4.2) and satellite observations of the flux of electrons with energies greater than 35 keV in the dawn sector from L=4.2 to 1=5.3 were analyzed. The substorm-associated electron flux during the most disturbed time was estimated to be close to the theoretical upper limit imposed upon the trapped electron flux by the self-sustained cyclotron resonance wave-particle interaction. The pitch angle diffusion was found not to be at the strong diffusion limit. The pitch angle distribution was not isotropic. A cross-correlation study of the X-ray intensities for various energy channels was performed to examine the relative arrival time of electrons with different energies. During the time period between the two substorms, the cross-correlation curve was found to have a peak at zero lag whenever there was a change in the average X-ray counting rate. A differently structured cross-correlation curve was found during the first five minutes immediately after the onset of enhancement of the X-ray intensity. The technique of power spectral analysis was used to investigate periodicities in the flux. A dominant peak at the period of 0.83 second was found in the power spectral density of the counting rate of the greater than 200 keV channel during a relatively quiet-period of time from the point of view of electron precipitation. The precipitation of intermediate energy (250-500 keV) electrons responsible for the greater than 200 keV X rays was modulated at the bounce period of low energy (65-90 keV) electrons. The mechanism for the precipitation was pitch angle diffusion due to the electron-whistler mode wave interaction. Waves generated by low energy electrons in the equatorial region propagated outside of the region of growth. These waves could interact with higher energy electrons and modulate the flux of these electrons. A correlation study of the enhancement seen in the low energy channels of the S[raised 3] satellite electron detector with the enhancement of X-ray fluxes during a substorm was made. The satellite data were used to locate where and when the injections occurred. Two sets of enhancements observed by the satellite were found to be injectedat different local times at the same time which was within a few minutes of the onset of geomagnetic bays at several near-midnight ground stations. A model based on convection due to a static westward electric field and azimuthal drift due to the gradient and curvature of B was used to explain the energy dispersion and time delay of the substormassociated observations.