Particle and auroral observations from the ESRO I/AURORAE satellite

This paper reports results of the first detailed study of simultaneous low‐energy electron precipitation and optical auroral observations during quiet geomagnetic conditions in the evening side of the auroral oval, observed by the DMSP 32 satellite. The precipitation characteristics are different for different types of quiet auroral arcs. (1) Inside a faint diffuse aurora, equatorward of the oval, the six‐point differential energy spectrum is characterized by nearly constant differential fluxes from 0.2 to about 8 keV with a sharp cutoff above 8 keV; the precipitated energy flux is about 0.1 erg/cm² s sr between 0.2 and 20 keV. (2) A faint discrete arc is characterized by a spectral peak (about 108–109 el/cm² s sr keV) near 0.5 or 1.2 keV superposed on a soft spectrum and an energy flux of a fraction of 1 erg/cm² s sr. (3) Inside a bright discrete quiet arc a distinct spectral peak near 3.2 keV with fluxes between 107 and 108 el/cm² s sr keV on a hard spectrum is observed; the precipitated energy flux is a few ergs/cm² s sr.

Section: Introductionmentioning

confidence: 63%

Simultaneous observations of low-energy electron precipitation and optical auroral arcs in the evening sector by the DMSP 32 satellite

Meng¹

1976

“…It is thus of great interest to examine the corresponding features in the pattern of precipitation of auroral particles. The precipitation patterns of auroral electrons along magnetic meridian lines have been studied by Frank and A ckerson [1971], Hoffman and Burch [1973], Deehr et al [1973], and most recently by Winningham et al [1975]. In general, the latitudinal profiles have suggested that one can distinguish at least two precipitation regions.…”

Section: Introductionmentioning

confidence: 99%

Simultaneous observations of discrete and diffuse auroras by the Isis 2 satellite and airborne instruments

Deehr

Winningham²,

Yasuhara

et al. 1976

All-sky camera and photometric data were obtained by airborne instrumentation as a function of latitude and time during the course of an auroral substorm. During the substorm recovery phase the Isis 2 satellite passed within 60 km of the aircraft zenith. The discrete and diffuse auroral regions were identified from the airborne all-sky camera data. Satellite and photometric observations of the corresponding incoming particles led to the following conclusions: (1) The diffuse and the discrete auroras seen in the allsky camera data correspond to the two different particle precipitation regions observed from satellites and referred to as CPS and BPS, respectively (Winningham et al., 1975). (2) The diffuse auroral region is associated with high-energy stably trapped energetic electrons, and the discrete aurora is poleward of the stable electron trapping boundary. (3) The latitudinal distribution of characteristic particle energies does not change in a relative sense during the poleward expansion, but expands 'accordionlike.' (4) The heightintegrated intensity ratio of the red (6300 •) to green (5577 A) emissions of atomic oxygen is a good indicator of the characteristic energy of the incoming particle spectrum.

“…The UVI experiment provided images with an unprecedented combination of temporal and spatial resolution and sensitivity. Auroras were detected in both the sunlit and dark hemispheres by the twin camer• of the imager which responded to two Previous quantitative comparisons of satellite optical and particle data have typically used measurements from two instruments aboard the same satellite (e.g., ESRO 1/AURORAE [Deehr et al, 1973], ISIS 2 [ Winningham et al, 1978], AE-C [Kasting and Hays, 1977;Rees and Abreu, 1984]. Particle measurements in a flux tube and optical observations of the auroral emissions from the foot of the flux tube were obtained nearly simultaneously and could be easily correlated.…”

Section: Introductionmentioning

confidence: 99%

On the possibility of auroral remote sensing with the Viking ultraviolet imager

Steele¹,

McEwen

Murphree

1992

An investigation was carried out to assess the value of ultraviolet auroral images for remote sensing of electron precipitation. We compared auroral images, obtained by both cameras of the Viking Ultraviolet Imager during April and early May 1986, with simultaneous measurements of electron precipitation from the DMSP F7 and HiLat satellites at low altitudes above the auroral zone. The camera signals in the pixels that viewed the low‐altitude satellite footprint were corrected for various instrumental and nonauroral background contributions and were converted to the equivalent signals for vertical viewing from Viking. The electron data were averaged over the image pixels and were used to normalize the imager signals to unit electron energy flux. The resulting quantity, here termed the “effective sensitivity,” showed large scatter about the mean values for both cameras that tended to mask any energy dependence except a decrease at electron energies above 6 keV. The mean effective sensitivities were 11.3 ± 1.1 digitization numbers (DN)/(erg cm−2 s−1) for the Lyman‐Birge‐Hopfield (LBH) camera and 15.9 ± 2.5 DN/(erg cm−2 s−1) for the 1304 camera. These values correspond to 39 and 55 DN per kR of λ 4278 (N2+ first negative (1 N) (0,1) band), respectively, for the two cameras and are nearly independent of electron energy below about 6 keV. A published model calculation of the LBH camera response overestimates the effective sensitivity by about 40%. The signal ratio in simultaneous images from both cameras was insensitive to electron energy in the two cases examined, consistent with the weak energy dependences of the effective sensitivities. Unusually high LBH camera effective sensitivities of 45–60 DN/(erg cm−2 s−1) were obtained during several orbits on May 2 and 3. These observations could not be accounted for by thermospheric composition changes during the geomagnetic storm on May 1 and 2 or by changes in the intrinsic gain of the camera. Some of the scatter in the measured effective sensitivities resulted from approximations required in comparing the images and particle data, which differed significantly in spatial scale. We conclude that images from either Viking camera may be used to infer the instantaneous distribution of electron energy deposition, with roughly 50% accuracy.