No abstract

An investigation has been made of electron and associated ion precipitation spikes near the plasmapause that are narrow in L shell and in which relativistic electrons are favored. The electron energy spectra during the spikes sometimes had equivalent e fold energies in excess of 500 keV. In approximately 31% of these spike events observed from the low‐altitude polar orbiting satellites P72‐1, P78‐1, and S81‐1, nearly simultaneous precipitation was measured in energetic ions above ∼30 keV at about the same L value. Several of the precipitation spikes occurred primarily in the drift loss cone, but in some cases, significant precipitation (∼10−2 ergs/cm² s) was also observed in the bounce loss cone. The electron spikes occurred preferentially in the evening sector, and all of the associated narrow ion spikes were in that local time interval. Narrow relativistic electron spikes were observed on less than 1% of the crossings of the plasmapause. From the set of S81‐1 events a search was made for those also observed on the NOAA 6 spacecraft. On rare occasions, nearly simultaneous (<2000 s) narrow spikes with hard electron spectra were found at approximately the same L value from both spacecraft and at longitudes differing by 8°–47°. These findings suggest a patchy profile, sometimes with an arc structure which may extend over longitude intervals as great as 25° and time intervals as long as 2000 s. From consideration of the AE index for 17 events, 12 were found to occur close to the times of substorms. The spike precipitation is interpreted in terms of cyclotron resonance wave‐particle interactions involving radiation belt particles, the narrow widths being associated with fine structure in the cold plasma density profiles near the plasmapause and the energy selectivity associated with an upper frequency cutoff in the waves.

Radiation belt electrons precipitated by controlled injection of VLF signals from a ground based transmitter have been directly observed for the first time. These observations were part of the SEEP (Stimulated Emission of Energetic Particles) experiment conducted during May ‐ December 1982. Key elements of SEEP were the controlled modulation of VLF transmitters and a sensitive low altitude satellite payload to detect the precipitation. An outstanding example of time‐correlated wave and particle data occurred from 8680 to 8740 seconds U.T. on 17 August 1982 when the satellite passed near the VLF transmitter at Cutler, Maine (NAA) as it was being modulated with a repeated ON (3‐s)/OFF (2‐s) pattern. During each of twelve consecutive pulses from the transmitter the electron counting rate increased significantly after start of the ON period and reached a maximum about 2 seconds later. The measured energy spectra revealed that approximately 15 to 50 percent of the enhanced electron flux was concentrated near the resonant energies for first order cyclotron interactions occurring close to the magnetic equator with the nearly monochromatic waves emitted from the transmitter.

The temporal and spectral shape and the absolute flux level of particle pulses precipitated by a VLF transmitter are examined from a theoretical point of view. A test‐particle model of the gyroresonant wave‐particle interaction is applied to the parameters of the observed cases for calculating the precipitation characteristics. The temporal shapes of the precipitation pulses are found to be controlled (1) by the pitch angle dependence of the particle distribution near the edge of the loss cone and (2) by the multiple interaction of the particles with the waves due to significant atmospheric backscatter.

The spatial extent and the ionization profiles within the extended oval‐shaped regions irradiated by the intense solar particle events (SPE) of August 1972 have been derived from high‐energy proton data obtained with the 1971‐089A polar‐orbiting satellite and from several balloon flights. The particle ionization during the most intense 10‐hour period of the event on August 4 greatly enhanced the concentrations of short‐lived HOx and long‐lived NOx constituents, which in turn were responsible for the creation of a polar ozone cavity (POC) that has been identified and tracked with the backscattered ultraviolet (BUV) ozone sensors on the Nimbus 4 satellite. At the end of the peak irradiation period the ozone concentrations within the northern hemisphere POC were reduced by 46, 16, and 4% at altitudes of 49.5, 41, and 32 km, respectively. The total columnar ozone is estimated to have been reduced by ∼2% at this time. Above ∼45 km the ozone recovered on the time scale of several days. At 38.7 km in the northern hemisphere, however, the POC persisted and rotated as a semirigid mass in an east‐to‐west direction for some 53 days until the autumnal changes in wind patterns finally prevented further tracking. Time‐dependent chemistry calculations have been performed to explain the cause, magnitude, and temporal features of the ozone reductions. Using the calculated diurnal and particle‐induced behavior of the ozone during the SPE, the changes in heating rate and temperature expected in the stratosphere have been estimated. As a result of the initial large HOx‐caused ozone reduction, the temperature at 45 km should have decreased by ∼4°K several days after the event. Attempts to verify the predicted temperature changes have been unsuccessful due to limitations in the temperature measurement techniques.