Cause of the localized maximum of X‐ray emission in the morning sector: A comparison with electron measurements

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

doi:10.1029/1999ja000354

Cited by 26 publications

(22 citation statements)

References 28 publications

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“…On July 31 the energy input to the magnetosphere as well as the energy deposition into the ionosphere is high and the flux of injected quasi‐trapped energetic particles is probably high. This implies that wave‐particle interaction, which is the most probable mechanism for the morning maximum can last as long as the flux level is high enough [ Østgaard et al , 2000, and references therein]. For the July 24 event, the flux of injected quasi‐trapped particles is probably much lower and soon decreases below the threshold level for the wave‐particle interaction to occur.…”

Section: Discussionmentioning

confidence: 99%

“…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%

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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: Discussionmentioning

confidence: 99%

Section: Instrumentation and Data Processingmentioning

confidence: 99%

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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“…The entire terrestrial auroral oval has been imaged from several Earth radii by orbiting spacecraft, including Dynamics Explorer 1 (DE1), Polar, and IMAGE, in the far ultraviolet (FUV), visible, and X-ray spectral regions. This approach is the only way to obtain snapshots of the particle input over entire auroral regions and permits inference of the time variability of the total hemispheric auroral particle power (e.g., Østgaard et al 2000, 2001. In situ particle measurements acquired over many years have been used to derive statistical patterns of the particle energy input (e.g., Fuller-Rowell and Evans 1987;Hardy et al 1989;Brautigam et al 1991).…”

Section: Relevance Of Auroral Emission Analysismentioning

confidence: 99%

Energy Deposition in Planetary Atmospheres by Charged Particles and Solar Photons

2008

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We discuss here the energy deposition of solar FUV, EUV and X-ray photons, energetic auroral particles, and pickup ions. Photons and the photoelectrons that they produce may interact with thermospheric neutral species producing dissociation, ionization, excitation, and heating. The interaction of X-rays or keV electrons with atmospheric neutrals may produce core-ionized species, which may decay by the production of characteristic X-rays or Auger electrons. Energetic particles may precipitate into the atmosphere, and their collisions with atmospheric particles also produce ionization, excitation, and heating, and auroral emissions. Auroral energetic particles, like photoelectrons, interact with the atmospheric species through discrete collisions that produce ionization, excitation, and heating of the ambient electron population. Auroral particles are, however, not restricted to the sunlit regions. They originate outside the atmosphere and are more energetic than photoelectrons, especially at magnetized planets. The spectroscopic analysis of auroral emissions is discussed here, along with its relevance to precipitating particle diagnostics. Atmospheres can also be modified by the energy deposited by the incident pickup ions with energies of eV's to MeV's; these particles may be of solar wind origin, or from a magnetospheric plasma. When the modeling of the energy deposition of the plasma is calculated, the subsequent modeling of the atmospheric processes, such as chemistry, emission, and the fate of hot recoil particles produced is roughly independent of the exciting radiation. However, calculating the spatial distribution of the energy deposition versus depth into the atmosphere produced by an incident plasma is much more complex than is the calculation of the solar excitation profile. Here, the nature of the energy deposition processes by the incident plasma are described as is the fate of the hot recoil particles produced by exothermic chemistry and by knock-on collisions by the incident ions.

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“…The best electron energy coverage and spectral calculation is probably done by Gjerloev and Hoffman (2000b), detecting electrons with energies up to 32 keV. Nevertheless, even Gjerloev and Hoffman are not able to capture in full the high energy tail of the auroral spectrum which is reported in several papers (Meng et al, 1979;Goldberg et al, 1982;Miller and Vondrak, 1985;Østgaard et al, 2000). In this paper, we will show that these hard spectra have a significant influence on determining the correct value of the Hall conductance.…”

Section: Introductionmentioning

confidence: 97%

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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Cause of the localized maximum of X‐ray emission in the morning sector: A comparison with electron measurements

Cited by 26 publications

References 28 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

Energy Deposition in Planetary Atmospheres by Charged Particles and Solar Photons

Instantaneous ionospheric global conductance maps during an isolated substorm

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