Radar measurements of the latitudinal variation of auroral ionization

Vondrak, R. R.; Baron, M. J.

doi:10.1029/rs011i011p00939

Cited by 70 publications

(48 citation statements)

References 17 publications

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“…Considering the rapid changes with time it is speculated whether the 630 nm line is a good observable in this case. This atomic oxygen line is an emission from a forbidden transition from the metastable O( 1 D) state which has a lifetime of about 100 s. The spectral information is, therefore, also obtained from riometer and 427.8 nm photometer data using an extended version (a description is given by Aksnes et al, 2002) of an original model developed by Vondrak and Baron (1976) and validated by Vondrak and Sears (1978). The model is based on the techniques described by Rees (1963).…”

Section: Electron Energy Spectrummentioning

confidence: 99%

Conjugate high-intensity energetic electron precipitation at high latitude

et al. 2003

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Abstract.On 6 August 1998 an intense precipitation event occurring at high latitude in the evening sector was observed by X-ray and far-ultraviolet imagers on board the Polar satellite and by several ground-based instruments. The precipitation region was centred at approximately 19:00 MLT at 74 • MLAT (at an L-shell of about 13). The event started at 22:59 UT and lasted about 10 minutes. It happened during the late expansion phase of a substorm after two hours of strongly southward IMF. Imaging riometers at geomagnetically conjugate sites recorded strong absorption levels which exceeded 7 dB at 38 MHz in a transient and localized intensification occurring within a poleward moving arc-like feature. The temporal and spatial similarities between the recordings from the two conjugate regions are remarkable. The arc-like precipitation region progressed poleward with a velocity of 1.5 km/s. Ground magnetometers co-located with the imaging riometers observed disturbances consistent with poleward moving westward currents. In X-ray and riometer images which are sensitive only to energetic electrons (above 5-10 keV) the event seems isolated, but in UV images the event is seen to occur on the poleward edge of the rapidly poleward expanding evening side aurora. The energy spectrum of precipitating electrons was subject to a temporary hardening which peaked at a mean energy of about 20 keV when the event was at its most intense at 23:02 UT. The event is likely to have been caused by an accelerating mechanism at some height above the ionosphere or by an earthward flow burst in the magnetotail, or possibly both.

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Section: Electron Energy Spectrummentioning

confidence: 99%

Conjugate high-intensity energetic electron precipitation at high latitude

et al. 2003

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“…Their computer code is based on the TANGLE code (Vondrak and Baron, 1976;Vondrak and Robinson, 1985). By giving the electron spectra derived from the PIXIE and UVI measurements as input, this code can estimate the conductivities.…”

Section: Deriving Conductance Values From the Energy Spectramentioning

confidence: 99%

Effects of energetic electrons on the electrodynamics in the ionosphere

Aksnes

Stadsnes

et al. 2004

Ann. Geophys.

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Abstract. From the observations by the PIXIE and UVI cameras on board the Polar satellite, we derive global maps of the precipitating electron energy spectra from less than 1 keV to 100 keV. Based on the electron spectra, we generate instantaneous global maps of Hall and Pedersen conductances. The UVI camera provides good coverage of the lower electron energies contributing most to the Pedersen conductance, while PIXIE captures the high energy component of the precipitating electrons affecting the Hall conductance. By characterizing the energetic electrons from some tens of keV and up to about 100 keV using PIXIE X-ray measurements, we will, in most cases, calculate a larger electron flux at higher energies than estimated from a simple extrapolation of derived electron spectra from UVI alone. Instantaneous global conductance maps derived with and without inclusion of PIXIE data have been implemented in the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) procedure, to study the effects of energetic electrons on electrodynamical parameters in the ionosphere. We find that the improved electron spectral characterization using PIXIE data most often results in a larger Hall conductance and a smaller inferred electric field. In some localized regions the increase in the Hall conductance can exceed 100%. On the contrary, the Pedersen conductance remains more or less unaffected by the inclusion of the PIXIE data. The calculated polar cap potential drop may decrease more than 10%, resulting in a reduction of the estimated Joule heating integrated over the Northern Hemisphere by up to 20%. Locally, Joule heating may decrease more than 50% in some regions. We also find that the calculated energy flux by precipitating electrons increases around 5% when including the PIXIE data. Combined with the reduction of Joule heating, this results in a decrease in the ratio between Joule heating and energy flux, sometimes exceeding 25%. An investigation of the relationship between Joule heating and the AE index shows a nearlyCorrespondence to: A. Aksnes (Arve.Aksnes@fi.uib.no) linear correspondence between the two quantities, in accordance with previous studies. However, we find lower proportionality factors than reported by others when taking geomagnetic conditions into account, ranging between 0.13 and 0.23 GW/nT. We also find that the contribution from auroral particles to the energy budget is more important than most previous studies have reported.

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“…We use a computer code developed by University of Maryland based on the TANGLE code (for more details on TAN-GLE, see Vondrak and Baron, 1976;Vondrak and Robinson, 1985). The code models the ionospheric effects of energy deposition into the atmosphere by energetic particles.…”

Section: Deriving the Conductance Values From The Energy Spectramentioning

confidence: 99%

Instantaneous ionospheric global conductance maps during an isolated substorm

et al. 2002

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Abstract. Data from the Polar Ionospheric X-ray Imager (PIXIE) and the Ultraviolet Imager (UVI) on board the Polar satellite have been used to provide instantaneous global conductance maps. In this study, we focus on an isolated substorm event occurring on 31 July 1997. From the PIXIE and the UVI measurements, the energy spectrum of the precipitating electrons can be derived. By using a model of the upper atmosphere, the resulting conductivity values are generated. We present global maps of how the 5 min timeaveraged height-integrated Hall and Pedersen conductivities vary every 15 min during this isolated substorm. The method presented here enables us to study the time development of the conductivities, with a spatial resolution of ∼700 km. During the substorm, a single region of enhanced Hall conductance is observed. The Hall conductance maximum remains situated between latitudes 64 and 70 corrected geomagnetic (CGM) degrees and moves eastward. The strongest conductances are observed in the pre-midnight sector at the start of the substorm expansion. Toward the end of the substorm expansion and into the recovery phase, we find the Hall conductance maximum in the dawn region. We also observe that the Hall to Pedersen conductance ratio for the regions of maximum Hall conductance is increasing throughout the event, indicating a hardening of the electron spectrum. By combining PIXIE and UVI measurements with an assumed energy distribution, we can cover the whole electron energy range responsible for the conductances. Electrons with energies contributing most to the Pedersen conductance are well covered by UVI while PIXIE captures the high energetic component of the precipitating electrons affecting the Hall conductance. Most statistical conductance models have derived conductivities from electron precipitation data below approximately 30 keV. Since the intensity of the shortest UVI-wavelengths (LBHS) decreases significantly at higherCorrespondence to: A. Aksnes (arve.aksnes@fi.uib.no) electron energies, the UVI electron energy range is more or less comparable with the energy ranges of the statistical models. By calculating the conductivities from combined PIXIE and UVI measurements to compare with the conductivities from using UVI data only, we observe significant differences in the Hall conductance. The greatest differences are observed in the early evening and the late morning sector. We therefore suggest that the existing statistical models underestimate the Hall conductance.

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Radar measurements of the latitudinal variation of auroral ionization

Cited by 70 publications

References 17 publications

Conjugate high-intensity energetic electron precipitation at high latitude

Conjugate high-intensity energetic electron precipitation at high latitude

Effects of energetic electrons on the electrodynamics in the ionosphere

Instantaneous ionospheric global conductance maps during an isolated substorm

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