Auroral electron distributions derived from combined UV and X‐ray emissions

Østgaard, Nikolai; Stadsnes, J.; Bjordal, Jan Magnus; Vondrak, R. R.; Parks, G. K.; Cummer, Steven A.; Chenette, D. L.; Pronko, J.G.

doi:10.1029/2001ja000031

Cited by 45 publications

(42 citation statements)

References 24 publications

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“…The X rays measured by PIXIE are produced by electrons from ∼3 keV to 100 keV. Detailed descriptions of the data processing from PIXIE is given by Østgaard et al [1999] and details on deriving four‐parameter electron spectra from PIXIE measurements are given by Østgaard et al [2000] and Østgaard et al [2001].…”

Section: Instrumentation and Data Processingmentioning

confidence: 99%

“…By combining the measurements from UVI and PIXIE it is possible to derive 5 min‐average electron distributions from 100 eV to 100 keV with a spatial resolution of ∼700 km in the Northern Hemisphere when Polar is at 6–8 R E . A validation of the method by comparing with directly measured electron spectra by low‐altitude satellites is given by Østgaard et al [2001]. The time resolution of 15 min (5 min‐average every 15 min) is determined by the duty cycling of the front chamber of PIXIE and the spatial resolution is basically determined by the pinhole size of the PIXIE instrument.…”

Section: Instrumentation and Data Processingmentioning

confidence: 99%

“…In this study we have used the combined measurements from the Polar Ionospheric X‐ray Imaging Experiment (PIXIE) [ Imhof et al , 1995] and the Ultraviolet Imager (UVI) [ Torr et al , 1995] to derive the 5 min average precipitating electron energy distribution from 100 eV to ∼100 keV with a spatial resolution of ∼700 km on a global scale during 7 substorms. This method was examined by Østgaard et al [2001] and was found to give a fairly precise estimate of the energy deposition by auroral electrons. The focus of the study in this paper is twofold.…”

Section: Introductionmentioning

confidence: 99%

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Energy analysis of substorms based on remote sensing techniques, solar wind measurements, and geomagnetic indices

Østgaard

Stadsnes

Vondrak

2002

Journal of Geophysical Research: Space Physics

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[1] Observations from the Polar Ionospheric X-ray Imaging Experiment (PIXIE) and the Ultraviolet Imager (UVI) on board the Polar satellite have been used to examine the energy deposition in the Northern Hemisphere by precipitating electrons for seven substorms during 1997. By combining the results from these two remote sensing techniques we derive the 5 min average electron energy distributions from 100 eV to 100 keV with a spatial resolution of $700 km. During growth phase we find that most of the energy is carried by electrons below 10 keV. The study shows that the maximum intensity of the substorm is mostly defined by the flux of electrons below 10 keV. In contrast, the electrons above 10 keV show a greater intensification at substorm onset and are more confined azimuthally during the expansion phase. By using the most appropriate parameterized methods to estimate the energy increase of the ring current (U R ) and the Joule heating rate in both hemispheres (U J ) and by adding the rate of energy deposition in both hemispheres by precipitating electrons (U A ), we estimate the total energy dissipation rate during substorms (U T ). Our estimate of U A is a factor 2-4 larger than that reported in earlier studies. We find that the contributions to the total time-integrated energy dissipation over the duration of the substorm, W(U T ), from W(U R ), W(U J ), and W(U A ) on average are 15%, 56%, and 29%. Comparing W(U T ) and the time-integrated parameter, W(), which approximates the solar wind input due to dayside reconnection, we find that the parameter does not always provide enough energy into the magnetosphere to balance W(U T ). An additional energy transfer mechanism is needed to balance the energy budget. We find that a viscous interaction that transfers 0.17% of the solar wind kinetic energy in addition to the energy transfer due to dayside reconnection, estimated by the parameter, is sufficient to balance the total energy dissipation U T .INDEX TERMS: 2784 Magnetospheric Physics: Solar wind/ magnetosphere interactions; 2736 Magnetospheric Physics: Magnetosphere/ionosphere interactions; 2455 Ionosphere: Particle precipitation; 2716 Magnetospheric Physics: Energetic particles, precipitating; KEYWORDS: energy budget of substorms, X-ray and UV imaging, particle precipitation, Joule heating, ring current, solar wind Citation: Østgaard, N., G. Germany, J. Stadsnes, and R. R. Vondrak, Energy analysis of substorms based on remote sensing techniques, solar wind measurements, and geomagnetic indices,

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Section: Instrumentation and Data Processingmentioning

confidence: 99%

Section: Instrumentation and Data Processingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Energy analysis of substorms based on remote sensing techniques, solar wind measurements, and geomagnetic indices

Østgaard

Stadsnes

Vondrak

2002

Journal of Geophysical Research: Space Physics

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“…A number of com-parison studies exist in the literature (e.g. Basu and Jasperse, 1987;Vondrak et al, 1988;Senior, 1991;Watermann et al, 1993;Doe et al, 1997;Germany et al, 1997;Dymond et al, 2001;Østgaard et al, 2001). Such studies are complicated when the stochastical processes operate on different scales.…”

Section: Introductionmentioning

confidence: 99%

Ionospheric conductances derived from satellite measurements of auroral UV and X-ray emissions, and ground-based electromagnetic data: a comparison

Aksnes

Amm²,

Stadsnes³

et al. 2005

Ann. Geophys.

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Abstract. Global instantaneous conductance maps can be derived from remote sensing of UV and X-ray emissions by the UVI and PIXIE cameras on board the Polar satellite. Another technique called the 1-D method of characteristics provides mesoscale instantaneous conductance profiles from the MIRACLE ground-based network in Northern Scandinavia, using electric field measurements from the STARE coherent scatter radar and ground magnetometer data from the IM-AGE network. The method based on UVI and PIXIE data gives conductance maps with a resolution of ∼800 km in space and ∼4.5 min in time, while the 1-D method of characteristics establishes conductances every 20 s and with a spatial resolution of ∼50 km. In this study, we examine three periods with substorm activity in 1998 to investigate whether the two techniques converge when the results from the 1-D method of characteristics are averaged over the spatial and temporal resolution of the UVI/PIXIE data.In general, we find that the calculated conductance sets do not correlate. However, a fairly good agreement may be reached when the ionosphere is in a state that does not exhibit strong local turbulence. By defining a certain tolerance level of turbulence, we show that 14 of the 15 calculated conductance pairs during relatively uniform ionospheric conditions differ less than ±30%. The same is true for only 4 of the 9 data points derived when the ionosphere is in a highly turbulent state. A correlation coefficient between the two conductance sets of 0.27 is derived when all the measurements are included. By removing the data points from time periods when too much ionospheric turbulence occurs, the correlation coefficient raises to 0.57. Considering the two very different techniques used in this study to derive the conductances, with different assumptions, limitations and scale sizes, our results indicate that simple averaging of mesoscale results allows a continuous transition to large-scale results.Correspondence to: A. Aksnes (arve.aksnes@ift.uib.no) Therefore, it is possible to use a combined approach to study ionospheric events with satellite optical and ground-based electrodynamic data of different spatial and temporal resolutions. We must be careful, though, when using these two techniques during disturbed conditions. The two methods will only give results that systematically converge when relatively uniform conditions exist.

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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%

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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Auroral electron distributions derived from combined UV and X‐ray emissions

Cited by 45 publications

References 24 publications

Energy analysis of substorms based on remote sensing techniques, solar wind measurements, and geomagnetic indices

Energy analysis of substorms based on remote sensing techniques, solar wind measurements, and geomagnetic indices

Ionospheric conductances derived from satellite measurements of auroral UV and X-ray emissions, and ground-based electromagnetic data: a comparison

Effects of energetic electrons on the electrodynamics in the ionosphere

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