Wind Spacecraft Observations of Solar Impulsive Electron Events Associated with Solar Type III Radio Bursts

Abstract

We present W ind spacecraft observations of solar impulsive electron events associated with locally generated Langmuir waves during solar type III radio bursts. The solar impulsive electrons had energies from D600 eV to greater than 300 keV. Local Langmuir emissions associated with these Ñuxes generally coincided with the arrival of 2È12 keV electrons. A survey of 27 events over 1 yr shows that there were few occurrences of electron distributions (D96 s averaged) that were unstable to Langmuir waves and none that had a substantial growth rate ([3 ] 10~2 s~1) or endured for more than 96 s. Intense solar impulsive electron events that occurred on 1995 April 2 are studied in detail. Marginally stable (plateaued) distributions occasionally coincided with a periods of local Langmuir emissions, but the electron distributions were otherwise stable. These observations suggest that kinetic processes were modifying the electron distribution but also suggest that processes other than one-dimensional quasilinear relaxation were involved. We Ðnd that solar impulsive electron distributions were often unstable to oblique waves, such as quasi-electrostatic whistler waves or electromagnetic ion cyclotron waves, suggesting that competition between Langmuir and oblique emissions may be important. There are several other features in the W ind spacecraft solar impulsive electron observations that are noteworthy. Nondis-persive Ñux modulations were visible in many of the events (also visible in the published ISEE 3 data) in D1È4 keV electrons, suggesting that a local hydromagnetic instability may have accompanied the lowest energy solar impulsive electron Ñuxes. The W ind data di †er from the ISEE 3 data in the energy spectra of the electron events. ISEE 3 recorded few events with only high-energy ([10 keV) electron Ñuxes, whereas a survey of the W ind events shows a substantially higher ratio of high-energy events. The high-energy events were often associated with solar Ñares that could not have been magnetically well connected with the satellite.