Instantaneous ionospheric global conductance maps during an isolated substorm

Aksnes, A.; Stadsnes, J.; Bjordal, Jan Magnus; Østgaard, Nikolai; Vondrak, R. R.; Detrick, D. L.; Rosenberg, T. J.; Germany, G. A.; Chenette, D. L.

doi:10.5194/angeo-20-1181-2002

Cited by 35 publications

(51 citation statements)

References 38 publications

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“…The temporal resolution of the UVI conductance estimate (the time required to take both LBHS and LBHL images) is 184 s for this specific event. Aksnes et al (2002) have shown that conductance estimates derived from only UVI data may underestimate the Hall conductance by several tens of percent. This is caused by the limited sensitivity to precipitating electrons with energies over 20 keV, which contribute to the Hall conductance.…”

Section: Uvi Conductance Estimatesmentioning

confidence: 99%

Electrodynamics of an omega-band as deduced from optical and magnetometer data

et al. 2009

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Abstract.We investigate an omega-band event that took place above northern Scandinavia around 02:00-02:30 UT on 9 March 1999. In our analysis we use ground based magnetometer, optical and riometer measurements together with satellite based optical images. The optical and riometer data are used to estimate the ionospheric Hall and Pedersen conductances, while ionospheric equivalent currents are obtained from the magnetometer measurements. These data sets are used as input in a local KRM calculation, which gives the ionospheric potential electric field as output, thus giving us a complete picture of the ionospheric electrodynamic state during the omega-band event.The overall structure of the electric field and field-aligned current (FAC) provided by the local KRM method are in good agreement with previous studies. Also the E×B drift velocity calculated from the local KRM solution is in good qualitative agreement with the plasma velocity measured by the Finnish CUTLASS radar, giving further support for the new local KRM method. The high-resolution conductance estimates allow us to discern the detailed structure of the omega-band current system. The highest Hall and Pedersen conductances, ∼50 and ∼25 S, respectively, are found at the edges of the bright auroral tongue. Inside the tongue, conductances are somewhat smaller, but still significantly higher than typical background values. The electric field shows a converging pattern around the tongues, and the field strength drops from ∼40 mV/m found at optically dark regions to ∼10 mV/m inside the areas of enhanced conductivity. Downward FAC flow in the dark regions, while upward currents flow inside the auroral tongue. Additionally, sharp conductance gradients at the edge of an auroral tongue are associated with narrow strips of intense FACs, so that a strip of downCorrespondence to: H. Vanhamäki (heikki.vanhamaki@fmi.fi) ward current flows at the eastern (leading) edge and a similar strip of upward current is present at the western (trailing) edge. The Joule heating follows the electric field pattern, so that it is diminished inside the bright auroral tongue.

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Section: Uvi Conductance Estimatesmentioning

confidence: 99%

Electrodynamics of an omega-band as deduced from optical and magnetometer data

et al. 2009

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“…During the recovery phase, PIXIE showed a precipitation maximum in the morning sector which was not seen by UVI. Many studies have reported such a maximum in the energetic electron precipitation in the dawn region, including substorm studies (Jelly and Brice, 1967;Berkey et al, 1974;Østgaard et al, 2001;Aksnes et al, 2002) and statistical studies involving different geomagnetic conditions (Hartz and Brice, 1967;McDiarmid et al, 1975;Wallis and Budzinski, 1981;Spiro et al, 1982;Hardy et al, 1985;Hardy et al, 1987). Østgaard et al (1999) used models of the gradient and curvature drift of electrons to estimate the energy of eastward drifting electrons causing the X-rays seen by PIXIE.…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

“…A study by Aksnes et al (2002) showed that the calculation of an accurate Hall conductance depends strongly on measurements of energetic electrons up to 100 keV. Aksnes et al (2002) also used Polar data from the PIXIE and UVI cameras, in order to provide instantaneous global conductance maps. By calculating the conductivities from combined PIXIE and UVI measurements, to compare with the conductivities from using UVI data only, they found significant differences in the Hall conductance.…”

Section: Introductionmentioning

confidence: 99%

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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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“…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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Instantaneous ionospheric global conductance maps during an isolated substorm

Cited by 35 publications

References 38 publications

Electrodynamics of an omega-band as deduced from optical and magnetometer data

Electrodynamics of an omega-band as deduced from optical and magnetometer data

Effects of energetic electrons on the electrodynamics in the ionosphere

Conjugate high-intensity energetic electron precipitation at high latitude

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