Electron fluxes and correlations with quiet time auroral arcs

An Isis 2 pass is singled out for a detailed examination of the particle fluxes, optical emissions, and ionospheric parameters observed during a quiescent period (late recovery) between two substorms. This pass was chosen because it was part of a coordinated data acquisition period between the Air Force Geophysics Laboratory (AFGL) Airborne Ionospheric Observatory, Isis 2, and DMSP (Defense Meteorological Satellite Program). As a result, both long‐duration measurements (aircraft) and transient, snapshot (spacecraft) data are available. This allows, on a macroscopic level, the separation of space and time effects. On the basis of the joint data set it was established that the latitudinal morphology observed by the satellite is basically spatial in nature. It is concluded that the observed particle fluxes are most easily understood in terms of precipitation from the quiet time plasma sheet without intervening acceleration. The observed optical emissions and ionospheric parameters are found to be in good qualitative and quantitative agreement (within experimental error) with the electron fluxes, although establishment of this point has required careful determination of the viewing direction of the optical instruments, removal of scattered light (albedo) from underlying cloud and snow, and consideration of the effects of photon‐counting statistics on contour plots of the optical data.

Section: Discussionmentioning

confidence: 99%

A case study of the aurora, high‐latitude ionosphere, and particle precipitation during near‐steady state conditions

Winningham¹,

Anger²,

Shepherd³

et al. 1978

“…The aperture of the electron analyzer is always pointed in the local zenith direction. A more detailed description is given by Mizera et al [1975] and Meng [1976].…”

Section: Msp Satellite Datamentioning

confidence: 99%

The spatial relationship of field-aligned currents and auroral electrojets to the distribution of nightside auroras

Kamide¹,

Rostoker

1977

In this paper, nearly simultaneous sets of ground-based magnetometer data, magnetic perturbations recorded at 800-km altitude by the polar-orbiting Triad satellite and auroral imagery and information on precipitating electr6ns in the energy range 200 eV < E < 20 keV obtained from the DMSP satellites are analyzed for intervals of moderate magnetospheric activity during which substorms were in progress. It is found that the boundaries of intense (>2 kR at 5577,4,) auroral features coincide with the boundaries of field-aligned current regions defined by the Triad data. In the morning sector the downward field-aligned current flows in the poleward portion of the auroral oval, and the intensity of this current appears not to be a function of the intensity of the related auroral features. These results suggest that the current is carried by upgoing thermal electrons from the ionosphere. On the equatorward side of the oval the region of the upward field-aligned current coincides with the bright aurora regime and is probably carried by precipitating energetic electrons. In the evening sector, regions of intense upward field-aligned currents are found to coincide with discrete auroral arcs and fluxes of precipitating electrons with energies peaked at several keV in the region immediately poleward of the eastward electrojet. This region is thought to coincide with the extension of the westward electrojet from the morning sector, and precipitating electrons in the bright auroral forms are thought to carry the upward field-aligned current in this region. In a narrow latitudinal area poleward of the upward current where no auroral luminosity is detected, downward field-aligned current is often observed, indicating the importance of ionospheric thermal electrons carrying the downward current. This current is thought to be connected to the equatorward Pedersen current of the equatorward electric field that is dominant in the westward electrojet region. In the equatorward half of the evening auroral oval the diffuse aurora is located in the region of the downward field-aligned current and, in general, collocated with the eastward electrojet. Paschmannet al., 1972; Berko, 1973; Fairfield, 1973]. The possible connection between the auroral electrojets and the field-aligned currents has also been discussed theoretically ]. Further detailed studies of the gross Birkeland current configuration have yielded important information on the character of the currents and their relationship to both auroral luminosity and auroral electrojet flow. Yasuhara et al. [1975], Sugiura and Potemra [1976], lijima and Potemra [1976], and Kamide and Akasofu [1976a] have reported that the current flow is often unbalanced in the morning and evening sectors, excess current flowing into the auroral oval in the morning sector and out of the oval in the evening ;ector. Kamide et al. [1976a] have shown that in the morning ;ector the field-aligned current region coincides with the region of the westward electrojet, while Armstrong et al. [1975] have presented e...

“…However, only semi-qualitative estimates of the total precipitating electron population could be inferred, even when direct electron measurements were made on the same satellite (Mizera et aL , 1975;Meng, 1976;Liu et al, 1977).…”

Section: Introductionmentioning

confidence: 99%

Correlated observations of auroral arcs, electrons, and X rays from a DMSP satellite

Mizera¹,

Luhmann²,

Kolasinski³

et al. 1978

Self Cite

The first simultaneous observations made from a single DMSP satellite of visible auroral arcs, precipitating primary electrons, and atmospheric bremsstrahlung X rays are presented for a magnetically disturbed auroral event. Measured electron fluxes were used to compute absolute X ray distributions expected at the satellite altitude. The agreement between the calculated and measured X ray spectra is sufficiently good to suggest that the primary electron spectra, which produce structured auroral arcs, can be inferred with an orbiting X ray spectrometer.