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

Østgaard, Nikolai; Stadsnes, J.; Vondrak, R. R.

doi:10.1029/2001ja002002

Cited by 76 publications

(88 citation statements)

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“…The data base for this study is the U A derived from UV and X‐ray emissions during 7 isolated substorms which also have been used for another study of the total energy budget of isolated substorms [ Østgaard et al , 2002]. The two imagers, UVI and PIXIE as well as the technique used to derive the electron distribution from 100 eV to 100 keV with a spatial resolution of ∼700 km and a time resolution of 15 min (5 min‐average every 15 min) are described in the companion paper; Østgaard et al [2002] and in Østgaard et al [2001]. To see the time development of U A in different energy ranges as well as the total U A we refer to the companion paper.…”

Section: Datamentioning

confidence: 99%

“…In a companion paper [ Østgaard et al , 2002] we show how we can derive the 5 min‐average hemispherically integrated precipitating electron energy distribution from 100 eV to 100 keV ( U A ) using the combined measurements from the imagers on board the Polar spacecraft; the Polar Ionospheric X‐ray Imaging Experiment (PIXIE) [ Imhof et al , 1995] and the Ultraviolet Imager (UVI) [ Torr et al , 1995]. As we believe that the U A derived from UVI and PIXIE gives a fairly precise estimate of the energy deposition by auroral electrons [ Østgaard et al , 2001] the motivation of this study is to contribute with a more accurate estimate of the relation between U A and the geomagnetic indices AE , AL and AU .…”

Section: Introductionmentioning

confidence: 99%

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A relation between the energy deposition by electron precipitation and geomagnetic indices during substorms

Østgaard

Vondrak

Gjerloev

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 derive the total energy dissipation (U A ) in the Northern Hemisphere by electron precipitation in the energy range from 100 eV to 100 keV. Comparing with geomagnetic indices, we find that during substorms, U A is linearly related to the quick look AE QL 1/2 and AL QL 1/2 indices. The best correlation (0.86) is found between the energy flux above 10 keVand the AL QL index, which reflects that the energetic electron precipitation modulates the westward electrojet intensity by affecting the Hall conductance. The AU QL index which reflects the eastward electrojet intensity shows poor correlation with U A , either for soft or energetic electrons. This is consistent with an electric field dominance in the dusk sector and a minor role for auroral conductance in the eastward electrojet. On the basis of ionospheric electrodynamics, we argue that a nonlinear relation between U A and AE (and AL) is more appropriate than a linear relation. We show that the linear relations reported by others do not fit our data set and that they provide U A values which are too low. For the total electron energy flux (0.1-100 keV) we find the best fit to be U A [GW] = 4.4 AL QL 1/2 À 7.6, with a correlation coefficient of 0.83, which is slightly better than that for the AE QL index (0.77). By time-integrating the U A derived from AL QL , we obtain estimates of the total deposited energy during substorms within ±20% of the time-integrated U A derived from UV and X rays. INDEX TERMS: 2455Ionosphere: Particle precipitation; 2716 Magnetospheric Physics: Energetic particles, precipitating; 2409 Ionosphere: Current systems (2708); 2411 Ionosphere: Electric fields (2712); KEYWORDS: geomagnetic indices, particle precipitation, substorms, X-rays, UV emissions, imaging Citation: Østgaard, N., R. R. Vondrak, J. W. Gjerloev, and G. Germany, A relation between the energy deposition by electron precipitation and geomagnetic indices during substorms,

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Section: Datamentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

A relation between the energy deposition by electron precipitation and geomagnetic indices during substorms

Østgaard

Vondrak

Gjerloev

2002

Journal of Geophysical Research: Space Physics

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“…The role of Joule heating rate in the global energy budget has been estimated even as 50-60% (Tanskanen et al, 2002;Østgaard et al, 2002). The global Joule heating rate estimates are typically calculated using different proxy formulas, based e.g.…”

Section: Introductionmentioning

confidence: 99%

Statistical properties of Joule heating rate, electric field and conductances at high latitudes

Aikio

Selkälä

2009

Ann. Geophys.

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Abstract. Statistical properties of Joule heating rate, electric field and conductances in the high latitude ionosphere are studied by a unique one-month measurement made by the EISCAT incoherent scatter radar in Tromsø (66.6 cgmlat) from 6 March to 6 April 2006. The data are from the same season (close to vernal equinox) and from similar sunspot conditions (about 1.5 years before the sunspot minimum) providing an excellent set of data to study the MLT and K p dependence of parameters with high temporal and spatial resolution.All the parameters show a clear MLT variation, which is different for low and high K p conditions. Our results indicate that the response of morning sector conductances and conductance ratios to increased magnetic activity is stronger than that of the evening sector. The co-location of Pedersen conductance maximum and electric field maximum in the morning sector produces the largest Joule heating rates 03-05 MLT for K p ≥ 3. In the evening sector, a smaller maximum occurs at 18 MLT. Minimum Joule heating rates in the nightside are statistically observed at 23 MLT, which is the location of the electric Harang discontinuity.An important outcome of the paper are the fitted functions for the Joule heating rate as a function of electric field magnitude, separately for four MLT sectors and two activity levels (K p < 3 and K p ≥ 3). In addition to the squared electric field, the fit includes a linear term to study the possible anticorrelation or correlation between electric field and conductance. In the midday sector, positive correlation is found as well as in the morning sector for the high activity case. In the midnight and evening sectors, anticorrelation between electric field and conductance is obtained, i.e. high electric fields are associated with low conductances. This is expected to occur in the return current regions adjacent to auroral arcsCorrespondence to: A. T. Aikio (anita.aikio@oulu.fi) as a result of ionosphere-magnetosphere coupling, as discussed by Aikio et al. (2004). In addition, a part of the anticorrelation may come from polarization effects inside highconductance regions, e.g. auroral arcs. These observations confirm the speculated effect of small scale electrodynamics, which is not included in most of the global modeling efforts of Joule heating rate.

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“…One of the fundamental questions in space physics involves the energy coupling between the solar wind and the Earth's magnetosphere. The energy budget during magnetic storms and substorms has been evaluated and presented in several papers in the literature (Akasofu, 1981;Harel et al, 1981;Stern, 1984;Tsurutani and Gonzalez, 1995;Lu et al, 1995Lu et al, , 1998Knipp et al, 1998;Østgaard et al, 2002a). The studies agree that the most important forms of energy dissipation in the near-Earth space are the magnetospheric ring current injection, atmospheric Joule heating and the energy flux carried by precipitating particles.…”

Section: Effects On Energy Budgetmentioning

confidence: 70%

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

Cited by 76 publications

References 44 publications

A relation between the energy deposition by electron precipitation and geomagnetic indices during substorms

A relation between the energy deposition by electron precipitation and geomagnetic indices during substorms

Statistical properties of Joule heating rate, electric field and conductances at high latitudes

Effects of energetic electrons on the electrodynamics in the ionosphere

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