Energetic Electron Precipitation During a Magnetospheric Substorm and Its Relationship to Wave Particle Interaction

Energetic electron precipitation was observed via X ray measurements from three simultaneously flown balloons in a region conjugate to the location of the geosynchronous satellite GEOS 2. Data from the particle, wave, and field experiments on this satellite were used to investigate the relationship between magnetospheric processes in the equatorial plane and the electron precipitation. A large part of the electron precipitation during a substorm on July 3, 1979, was accompanied by VLF waves at whistler frequencies and had a temporal structure grossly similar to the intensity variations of the equatorial electron fluxes. Some precipitation also occurred in the absence of VLF waves. During the wave associated precipitation the equatorial electrons were anisotropically distributed with maximum fluxes perpendicular to the geomagnetic field. The anisotropy was larger than the critical anisotropy and thus enabled wave growth. The growth rate itself was determined numerically from the observations and turned out to have a frequency dependence similar to that of the observed waves. The interaction of the electrons with the waves led to strong pitch angle diffusion. The temporal variations of the electron flux in the loss cone were similar to those of the electron precipitation observed with a balloon near the conjugate point to GEOS 2. It is concluded that most of the electron precipitation during this substorm was caused by wave particle interaction.

[1]  A. Korth,et al.  Experimental study of the relationship between energetic electrons and ELF waves observed on board GEOS: A support to quasi‐linear theory , 1985 .

[2]  Wolfgang Baumjohann,et al.  Latitude-integrated Joule and particle heating rates during the Energy Budget Campaign , 1985 .

[3]  Y. Kamide,et al.  Total current of the auroral electrojet estimated from the IMS Alaska meridian chain of magnetic observatories , 1982 .

[4]  I. B. Iversen,et al.  Coordinated balloon‐satellite observations of energetic particles at the onset of a magnetospheric substorm , 1982 .

[5]  E. W. Hones,et al.  Near‐equatorial, high‐resolution measurements of electron precipitation at L ≃6.6 , 1981 .

[6]  Wolfgang Baumjohann,et al.  A two-dimensional magnetometer array for ground-based observations of auroral zone electric currents during the international magnetospheric study /IMS/ , 1979 .

[7]  E. W. Hones,et al.  Strong electron pitch angle diffusion observed at geostationary orbit , 1979 .

[8]  H. I. West,et al.  Ground‐satellite correlations during presubstorm magnetic field configuration changes and plasma sheet thinning in the near‐Earth magnetotail , 1978 .

[9]  G. Kremser,et al.  On the morphology of energetic (≥30keV) electron precipitation during the growth phase of magnetospheric substorms , 1976 .

[10]  P. Tanskanen,et al.  On the morphology of energetic (≥30keV) electron precipitation at the onset of negative magnetic bays , 1976 .

[11]  V. Jentsch.  Electron precipitation in the morning sector of the auroral zone , 1976 .

[12]  P. Tanskanen,et al.  On the morphology of auroral-zone X-ray events—IV. Substorm-related electron precipitation in the local morning sector , 1975 .

[13]  M. Ashour‐Abdalla,et al.  Wave-Particle Interactions Near the Geostationary Orbit , 1974 .

[14]  A. Roux,et al.  A self‐consistent theory of magnetospheric ELF hiss , 1973 .

[15]  M. Kivelson,et al.  Satellite studies of magnetospheric substorms on August 15, 1968: 5. Energetic electrons, spatial boundaries, and wave‐particle interactions at Ogo 5 , 1973 .

[16]  G. Maral,et al.  On the morphology of auroral-zone X-ray events—III. Large-scale observations in the midnight-to-morning sector , 1973 .

[17]  P. Tanskanen,et al.  On the morphology of auroral-zone X-ray events—II. Events during the early morning hours , 1973 .

[18]  G. Parks,et al.  BEHAVIOR OF OUTER RADIATION ZONE AND A NEW MODEL OF MAGNETOSPHERIC SUBSTORM. , 1972 .

[19]  K. Saeger,et al.  On the morphology of auroral-zone X-ray events—I Dynamics of midnight events , 1971 .

[20]  G. Parks.  The acceleration and precipitation of Van Allen outer zone energetic electrons , 1970 .

[21]  G. Parks,et al.  Simultaneous observations of 5‐ to 15‐second period modulated energetic electron fluxes at the synchronous altitude and the auroral zone , 1969 .

[22]  G. Parks,et al.  Acceleration of energetic electrons observed at the synchronous altitude during magnetospheric substorms. , 1968 .

[23]  Charles F. Kennel,et al.  LIMIT ON STABLY TRAPPED PARTICLE FLUXES , 1966 .