Satellite observations of Bremsstrahlung from widespread energetic electron precipitation events

Abstract

This is a preliminary report of the first satellite observations that have been made of the intensities and energy spectra of the bremsstrahlung >50 keV produced in the atmosphere by intense widespread precipitations of energetic electrons from the outer radiation belt. The measurements afford the opportunity to investigate nearly simultaneously the energetic electron behavior on a worldwide scale during magnetic disturbances. With such a technique, one may study different features of the precipitation processes than those covered by satellite‐borne particle detectors, which can provide more detailed particle information in a local region but without simultaneous measurements from many satellites can provide worldwide particle precipitation information only from long‐term statistical studies. The observations are made with a 50‐cm³ Ge(Li) gamma ray spectrometer that was launched aboard the spin‐stabilized satellite 1972–076B into a nearly circular polar orbit at 750‐km altitude on October 2, 1972. Correlative measurements of precipitating electrons are also made with an energetic electron spectrometer on board the same satellite. The longitude and hence local time extents of the precipitations are derived by least square fitting techniques from the gamma ray spectrometer responses at various spin angle orientations and satellite locations. The observations indicate the occurrence of nearly simultaneous precipitations over a wide range of local times. Significant variations occur in the intensity versus local time, but in the limited number of cases studied to date the intensities near noon are generally greater than those in the early morning hours.

Review of radiation belt relativistic electron losses

“…Anderson and Milton (1964) and Barcus and Rosenberg (1966). Observations of the bremsstrahlung X-rays up to $500 keV were also carried out from spacecraft which allowed for the separation of temporal and spatial variations (Imhof et al, 1974, Imhof et al, 1975a.…”

Correlated observations of auroral arcs, electrons, and X rays from a DMSP satellite

“…Therefore, x-ray measurements by satellites provide an attractive means of obtaining true global coverage of particle precipitation phenomena. Imhof and his coworkers, in the first of an extensive list of papers on satellite x-ray measurements (Imhof et aL, 1974;Imhof, 1975;Imhof et 81., 1975a;1975b) have pointed out potential applications of this technique. However, their x-ray measurements were at energies above 50 key and therefore outside the 1-10 keY energy range of primary Interest In aurora!…”

Coordinated measurements of ELF transmission anomalies and the precipitation of energetic particles into the ionosphere

“…New techniques could profitably be employed for measuring the spatial distributions of the precipitating electron intensities and energy spectra simultaneously over a broad spatial region. One promising approach involves the measurement from a satellite of the bremsstrahlung X rays produced in the atmosphere by the precipitating electrons [Imhof et al, 1974a]. In the meantime, before more detailed coordinated measurements are performed, the data and computations reported here should serve to indicate both the importance and the complexity of the effects of energetic electron precipitation events on ELF wave propagation.…”