Solar Energetic Electrons Research Articles

Tracing of high‐latitude magnetic field lines by solar particles

Recent measurements of solar particles in the energy interval between hundreds of keV and a few MeV have shown that a direct connection exists between a portion of the high‐latitude geomagnetic field and the interplanetary magnetic field. The access window for 300‐keV solar protons that reach the center of the polar cap may be as near as 150 RE in the downstream magnetotail. Solar protons that precipitate into the atmosphere at latitudes near the geomagnetic cutoff enter through the flanks of the magnetosphere and the nearby neutral sheet, possibly within 30 RE of the earth. Comparison of the patterns of auroral particle precipitation with the zones of access of energetic solar electrons and protons indicates that a substantial fraction of the aurora originates on field lines connected to the interplanetary field.

Solar energetic particles and wide-band continuum storms from metric to hectometric frequencies

In association with solar flares accompanying type IV radio bursts of U-shaped spectrum, solar cosmic rays (MeV) and energetic electrons (keV) were generated. After acceleration, they were first stored in or near the flare regions and then gradually emitted into outer space. It seems that the streams of keV electrons generated the continuum radio emissions from metric to hectometric frequencies while passing through the outer coronal regions.

Location of the electron acceleration region in solar flares

Observations of impulsive solar flare X-rays ≳ 10 keV by the OGO-5 satellite and the measurements of energetic solar electrons made with the Explorer-35 and Explorer-41 (IMP-5) satellites during the period March 1968–September 1969 have been analyzed in order to determine the ion density in the X-ray source region as well as the location of the electron acceleration region in the solar atmosphere. If we assume that the efficiency of escape of the accelerated electrons into interplanetary space is ∼ 10−3, the observations are found to be consistent with the following interpretation: (i) the ion density in the X-ray source region varies from event to event and lies between 109 and 1011 ions cm−3 for those events in which the impulsive X-ray emission could be detected; (ii) for those events in which no impulsive emission was detected above threshold, the ion density in the X-ray source was < 109 ions cm−3; (iii) at least in some small solar flares the region where the electrons are accelerated during the flash phase is located in the lower corona.

Determination of the coronal magnetic field and the radio-emitting electron energy from a Type IV solar radio burst

The intensity and frequency spectrum of gyro-synchrotron emission from energetic solar electrons radiating in coronal magnetic fields are calculated. These calculations, based on a recent study of the generation of gyro-synchrotron emission in a magnetoactive plasma, are applied to a Type IV radio burst originating at a high altitude in the solar corona. It is shown that the observed frequency spectrum of the burst, which exhibits very sharp low and high frequency cutoffs, can be best understood in terms of gyro-synchrotron emission in an ionized medium and that from the observed frequency spectrum and the ambient coronal density it is possible to deduce both the magnetic field at the site of the emission and the range of electron energies responsible for the burst.