Hard X ray survey of energetic electrons from low‐Earth orbit

Abstract

Hard X ray and neutron emissions measured in low-Earth orbit are surveyed to develop a global overview of lightning-related energetic-electron precipitation and acceleration processes. Comparison of geographic intensity maps shows the dominance of enhanced hard X ray intensities measured when the satellite was above the continental United States and above the southern Indian Ocean between Madagascar and Australia. This emission is most enhanced during the northern summer months. Lesser although significant enhancements are seen between the Middle East and the Tibetan Plateau, a stretch of ocean off the east Asian coast between the Philippines and Korea, a stretch of equatorial Africa from the Ivory Coast to Mozambique, a region of the eastern equatorial Pacific just west of Columbia, and a patch of the Indian Ocean stretching between the southern tip of India and Indonesia. Although emissions from many of these regions are generally enhanced during the northern summer and fall seasons, none show any regularity relative to local time of day. Many but not all of these enhancements support natural interpretations in terms of lightning-induced energetic-electron precipitation from the terrestrial trapped radiation belts. Electron scattering induced by radio waves from VLF transmitters most likely contributes to this precipitation.

Dynamics of the Earth’s Particle Radiation Environment

“…The electromagnetic energy originating in lightning discharges escapes into the magnetosphere and propagates as a whistler mode wave, which pitch-angle scatters (and thus precipitates) energetic electrons, thereby generating hard X-rays through bremsstrahlung (Feldman et al 1996;. Furthermore, precipitating electrons cause localized ionization and changes of ionospheric plasma conductivity (Demirkol et al 1999).…”

Space Weather: Physics, Effects and Predictability

“…Precipitating energetic electrons stimulate the high frequency whistler mode emissions via the incoherent Cerenkov radiation process (Rothkaehl and Parrot 2005). Precipitating energetic electrons also generate hard X-rays through bremsstrahlung radiation (Feldman et al 1996;Bucík et al 2006). A LEO satellite detected enhanced (by about 28 dB) high frequency emissions over the Euro-Asia region (Klos et al 1997); these are thought to be caused by high energy (0.5-1.5 MeV) precipitating charged particles from the radiation belt (Rothkaehl and Klos 2003).…”

Experimental simulation of satellite observations of 100 kHz radio waves from relativistic electron beams above thunderclouds

“…The primary electrons can reach relativistic energies with a mean of ∼7 MeV and a standard deviation of ∼6 MeV (Roussel-Durpé et al, 2008) prior to escaping into near-Earth space (Inan, 2005;Lehtinen et al, 2000Lehtinen et al, , 1996. It is indeed possible to observe terrestrial relativistic electrons in space with particle detectors on satellites (Carlson et al, 2009;Dwyer et al, 2008;Feldman et al, 1996Feldman et al, , 1995Burke et al, 1992), but the direct association with individual intense lightning discharges remains to be made.…”