Size of the auroral oval: UV ovals and precipitation boundaries compared

Kauristie, K.; Weygand, J. M.; Pulkkinen, Tuija; Murphree, J. S.; Newell, P. T.

doi:10.1029/1998ja900046

Cited by 57 publications

(68 citation statements)

References 22 publications

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“…The UVI signature, however, appears to expand only as far as 70°, whereas the enhanced electron temperatures, presumably resulting from softer precipitation than the required for a signi®cant UVI intensity, expand to 72°. This disparity between the ESR and UVI data is consistent with the statistical o set found between Viking UV images and particle precipitation boundaries derived from 32 eV±30 keV particles measured by the DMSP spacecraft observed by Kauristie et al (1999).…”

Section: Discussionsupporting

confidence: 69%

Combined CUTLASS, EISCAT and ESR observations of ionospheric plasma flows at the onset of an isolated substorm

et al. 2000

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Abstract. On August 21st 1998, a sharp southward turning of the IMF, following on from a 20 h period of northward directed magnetic ®eld, resulted in an isolated substorm over northern Scandinavia and Svalbard. A combination of high time resolution and large spatial scale measurements from an array of coherent scatter and incoherent scatter ionospheric radars, ground magnetometers and the Polar UVI imager has allowed the electrodynamics of the impulsive substorm electrojet region during its ®rst few minutes of evolution at the expansion phase onset to be studied in great detail. At the expansion phase onset the substorm onset region is characterised by a strong enhancement of the electron temperature and UV aurora. This poleward expanding auroral structure moves initially at 0.9 km s )1 poleward, ®nally reaching a latitude of 72.5°. The optical signature expands rapidly westwards at 6 km s )1 , whilst the eastward edge also expands eastward at 0.6 km s )1 . Typical¯ows of 600 m s )1 and conductances of 2 S were measured before the auroral activation, which rapidly changed to 100 m s )1 and 10±20 S respectively at activation. The initial¯ow response to the substorm expansion phase onset is a¯ow suppression, observed up to some 300 km poleward of the initial region of auroral luminosity, imposed over a time scale of less than 10 s. The high conductivity region of the electrojet acts as an obstacle to the¯ow, resulting in a region of low-electric ®eld, but also low conductivity poleward of the high-conductivity region. Rapid¯ows are observed at the edge of the high-conductivity region, and subsequently the high¯ow region develops,¯owing around the expanding auroral feature in a direction determined by the¯ow pattern prevailing before the substorm intensi®cation. The enhanced electron temperatures associated with the substorm-disturbed region extended some 2°further poleward than the UV auroral signature associated with it.

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Section: Discussionsupporting

confidence: 69%

Combined CUTLASS, EISCAT and ESR observations of ionospheric plasma flows at the onset of an isolated substorm

et al. 2000

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“…Since in both cases the required power must be imparted to the particles by local acceleration, it is useful to consider the terrestrial case as an analog. Kauristie et al (1999) compare electron precipitation measurements from the V iking spacecraft with Defense Meteorological Satellite Program UV observations. They Ðnd that the correspondence between the boundaries of the UV and the electron precipitation is signiÐcant but by no means perfect and that di †erences can occur.…”

Section: T Errestrial Analogmentioning

confidence: 99%

Excitation of the Ganymede Ultraviolet Aurora

Eviatar

Strobel

Wolven

et al. 2001

ApJ

100

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We analyze the ultraviolet aurorae observed on Ganymede by means of the Hubble Space T elescope and compare them to similar phenomena on Earth. We Ðnd that the tenuous nature of GanymedeÏs atmosphere precludes excitation of the aurora by high-energy electrons and requires a local acceleration mechanism. We propose the following as plausible mechanisms for generating both the continuous background emission and the intense auroral bright spots :1. Birkeland-type currents and associated magnetic ÐeldÈaligned electric Ðelds. 2. The stochastic heating of plasma electrons by the Landau damping of electron plasma oscillations generated by precipitated energetic electrons.We conclude that the electron density in the bright regions may attain local values as high as 105 cm~3.

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“…Previous comparisons between in-situ particle measurements and space-based observations of the UV aurora have revealed a discrepancy of a few degrees of latitude between the OCB and the poleward boundary of UV auroral emission (e.g. Kauristie at al., 1999;Baker et al, 2000), with the largest discrepancy in the 05:00 MLT sector (Carbary et al, 2003). We note that these studies have generally utilised wideband UV auroral imagery, typically corresponding to the Lyman-Birge-Hopfield (LBH) region of the UV spectrum (∼140-180 nm).…”

Section: Introductionmentioning

confidence: 99%

The location of the open-closed magnetic field line boundary in the dawn sector auroral ionosphere

et al. 2004

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Abstract. As a measure of the degree of coupling between the solar wind-magnetosphere-ionosphere systems, the rate at which the size of the polar cap (the region corresponding to ionospheric termini of open magnetic flux tubes) varies is of prime importance. However, a reliable technique by which the extent of the polar cap might be routinely monitored has yet to be developed. Current techniques provide particularly ambiguous indications of the polar cap boundary in the dawn sector. We present a case study of spaceand ground-based observations of the dawn-sector auroral zone and attempt to determine the location of the polar cap boundary using multi-wavelength observations of the ultraviolet aurora (made by the IMAGE FUV imager), precipitating particle measurements (recorded by the FAST, DMSP, and Cluster 1 and 3 satellites), and SuperDARN HF radar observations of the ionospheric Doppler spectral width boundary. We conclude that in the dawn sector, during the interval presented, neither the poleward edge of the wideband auroral UV emission (140-180 nm) nor the Doppler spectral width boundary were trustworthy indicators of the polar cap boundary location, while narrow band UV emissions in the range 130-140 nm appear to be much more reliable.

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Size of the auroral oval: UV ovals and precipitation boundaries compared

Cited by 57 publications

References 22 publications

Combined CUTLASS, EISCAT and ESR observations of ionospheric plasma flows at the onset of an isolated substorm

Combined CUTLASS, EISCAT and ESR observations of ionospheric plasma flows at the onset of an isolated substorm

Excitation of the Ganymede Ultraviolet Aurora

The location of the open-closed magnetic field line boundary in the dawn sector auroral ionosphere

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