Energy deposition and middle atmosphere electrodynamic response to a highly relativistic electron precipitation event Journal Article uri icon

Overview

abstract

  • Rocket data have been used to evaluate the characteristics of precipitating relativistic electrons and their effects on the electrodynamic structure of the middle atmosphere. These data were obtained at Poker Flat, Alaska, on May 13 and 14, 1990, during a midday, highly relativistic electron (HRE) precipitation event. Solid state detectors were used to measure the electron fluxes and their energy spectra. An X ray scintillator was included on each flight to measure brems Strahlung X rays produced by energetic electrons impacting on the upper atmosphere. However, these were found to be of negligible importance for this particular event. The energy deposition by the electrons has been determined from the flux measurements and compared with in situ measurements of the atmospheric electrical response. The electrodynamic measurements were obtained by the same rockets and additionally on May 13, with an accompanying rocket. The impacting flux was highly irregular, containing short‐lived bursts of relativistic electrons, mainly with energies below 0.5 MeV and with fluxes most enhanced between pitch angles of 0°–20°. Although the geostationary counterpart of this measured event was considered to be of relatively low intensity and hardness, energy deposition peaked near 75 km with fluxes approaching an ion pair production rate in excess of 100/cm3 s. This exceeds peak fluxes in relativistic electron precipitation (REP) events as observed by us in numerous rocket soundings since 1976. Conductivity measurements from a blunt probe showed that negative electrical conductivities exceeded positive conductivities down to 50 km or lower, consistent with steady ionization by precipitating electrons above 1 MeV. These findings imply that the electrons from the outer radiation zone can modulate the electrical properties of the middle atmosphere to altitudes below 50 km. During the decline and activity minimum of the current solar cycle, we anticipate the occurrence of similar events but with fluxes 1–2 orders of magnitude above that reported here, based on studies of earlier solar cycles (e.g., Baker et al., 1993).

publication date

  • October 20, 1994

has restriction

  • closed

Date in CU Experts

  • February 21, 2014 12:31 PM

author count

  • 0

Other Profiles

International Standard Serial Number (ISSN)

  • 0148-0227

Additional Document Info

start page

  • 21071

end page

  • 21081

volume

  • 99

issue

  • D10