Balloon observations of auroral zone X rays in conjugate regions: 2. Microbursts and pulsations

Abstract

Simultaneous balloon observations of X‐ray pulsations in the 5–10 second range made from Fairbanks, Alaska, and Macquarie Island, Australia, showed no detailed correlation in time or amplitude. Observations in the northern hemisphere, with two balloon instruments separated by about 150 km in the east‐west direction, showed no obvious correlation, but when the separation was reduced to about 100 km in the north‐south direction, X‐ray pulsations showed in‐phase variations. Observations with two balloon instruments separated by 150 km in the east‐west direction showed time coincidences for about one‐third of the microbursts; the other two‐thirds were observed on one balloon or the other. From the small scale size of microburst electron precipitation it is suggested that magnetospheric plasma instabilities are responsible for the electron bombardment of the auroral zone atmosphere. Similar considerations are suggested for pulsating electron precipitation.

Review of radiation belt relativistic electron losses

“…The generation mechanism of plasmaspheric hiss is not yet fully understood. Some observations and theoretical modeling are consistent with generation in the equatorial plane by the electron-cyclotron instability (Church and Thorne, 1983;Huang and Goertz, 1983;Meredith et al, 2004). Higher frequency observations indicate a geographic control on emission intensities which is consistent with lightning-generated whistlers as a source, particularly at low L-values (Green et al, 2005;Meredith et al, 2006b).…”

“…Occasionally, a sawtooth pattern of precipitation is observed, indicating a packet of bouncing electrons that is depleted on each bounce. Blake et al (1996) constrain the size of most microbursts to less than a few tens of electron gyroradii ðp10 kmÞ, however, balloon observations indicate a correlation in temporal structure over 100 km for o150 keV microbursts (Brown et al, 1965).…”

“…This dimensionless parameter which controls the resonance condition, depends on the magnetic field strength and cold plasma density, N. There is an abrupt decrease in a à to typical values between 0.05 and 0.1 on entry into the dense plasmasphere. The decrease in a à leads to a lowering of electron resonant energies and a corresponding increase in wave amplification (Church and Thorne, 1983).…”

The acceleration and precipitation of Van Allen outer zone energetic electrons

“…This event and the event shown in Figure 4 consisted of easily -7 discernible rapid fluctuations in precipitated fluxes, including microbursts (Anderson and Milton, 1964) and 5-15 second modulated fluxes (Brown et al, 1965). The modulated structures have now been shown to occur also in equatorial electron fluxes, and details concerning this analysis are reported in Parks and Winckler (1969).…”

Balloon Observations of Electron Precipitation in Conjugate Regions of the Auroral Zone

“…During the 1964 conjugate series (Brown et al, 1965b) Brown, and Rosenberg, 1966), further examples of pulsating precipitation in the 5-to 15-s period range were obtained. Temporal features of these events, drawn from power spectrum analyses, were found to be nonstationary; in addition, from simultaneous balloon flights in one hemisphere, features of the spatial distribution of pulsating electron precipitation were established, showing a horizontal extent of the order of 100 km.…”