A 12-hour case study of auroral phenomena in the midnight sector: Electrojet and precipitating particle characteristics

Abstract

Airborne observations of auroral activity at midnight were conducted for a period of 9 hours by employing an ionospheric sounder and all‐sky cameras. During the observation period, two substorms occurred. The first substorm was associated with a compression of the magnetosphere (as measured by Dst) and with oscillations of the earth's bow shock. At this time, auroral activity was characterized by a series of poleward and equatorward motions and by the absence of a breakup phase. Magnetic disturbances were confined to a small region in the midnight sector. The second auroral substorm displayed many of the features associated with a large‐scale polar magnetic substorm. For selected times the locations of the eastward and westward electrojets were inferred from a number of high‐latitude magnetic records. All‐sky photographs and ionosonde data indicate that the poleward edge of the westward electrojet was bounded by a westward moving auroral surge accompanied by a strong sporadic E ionization. The equatorward electrojet boundary was less well defined by visual auroral forms. Soft particle spectrometer measurements from the Isis 2 satellite were made in conjunction with the aircraft measurements and indicate that large fluxes of field‐aligned electrons gave rise to the bright auroral surge, more isotropic fluxes of less energetic electrons contributing to the auroral E layer.

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

“…Data from the AFGL NKC-135 all-sky camera and scanning photometer provide evidence of quiet stable auroral conditions (see Pike et al [1977] and Weber et al [1977] for a more complete discussion of the aircraft data). Figuratively speaking, it is the lull between storms.…”

Satellite Particle Observations and Coincident Auroral-E Ionization.

“…A number of scientific results of the study have been published Weber et al, 1977;Pike et al, 1977;and Winningham et al, 1978), so the geophysical events of the day are well documented.…”

“…Associated with this diffuse, often subvisual aurora is a relatively thick band of E-region ionization known as auroral-E, apparently caused by the same particles which produce the diffuse aurora (Whalen et al, 1971;Whalen et al, 1977;and Weber et al, 1977). In spite of the fact that a clear association between the diffuse aurora and auroral-E ionization has been made, a detailed investigation of the properties of the incident particle spectrum, and its relation to the properties of aurora.l-E as measured by an ionosphere sounder, has not been previously undertaken.…”

Comparison of D-region Doppler drift winds measured by the SuperDARN Finland HF radar over an annual cycle using the Kiruna VHF meteor radar

“…Outside the auroral oval, they are predominantly summer phenomena and are especially prevalent in the daytime. During intense geomagnetic activity, sporadic-E can be seen at night due to increased precipitation of electrons from the solar wind (see, for example, Weber et al, 1977).…”