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See detailContributions of the driven process and the loading-unloading process during substorms: A study based on the IMAGE-SI12 imager
Blockx, Caroline ULg; Gérard, Jean-Claude ULg; Coumans, Valérie ULg et al

in Journal of Geophysical Research (2009), 114

Substorm energetics has been shown to have two components, the "loading-unloading'' component releasing energy previously stored in the tail and the "directly driven'' component dissipating simultaneously ... [more ▼]

Substorm energetics has been shown to have two components, the "loading-unloading'' component releasing energy previously stored in the tail and the "directly driven'' component dissipating simultaneously fed solar wind energy. Previous studies disagree about the relative importance of each process. The SI12 spectral imager onboard the IMAGE satellite provides images of the Doppler-shifted Lyman alpha auroral emission at 121.8 nm every 2 min. It has been used to determine the auroral intensity during substorms, which may be compared to the solar wind characteristics and interplanetary magnetic field components before and/or after substorm onsets. In this study, we analyze 256 substorms between June 2000 and December 2002, which satisfy criteria relative to the viewing conditions. We compare the mean nightside intensity during the expansion phase with the magnetic open flux, the epsilon parameter, and other coupling functions (used as proxies of transfer of solar wind energy to the magnetosphere) integrated over the growth phase or the expansion phase. The mean auroral intensity during the expansion phase correlates well with coupling functions integrated over the growth phase. We also find that the correlation between the auroral precipitation during the expansion phase and the coupling functions integrated over the expansion phase is lower but still significant. This implies that, even though both mechanisms contribute to the energy precipitated during substorms, the loading-unloading process is statistically dominant. [less ▲]

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See detailEL - a possible indicator to monitor the magnetic field stretching at global scale during substorm expansive phase: Statistical study
Meurant, M.; Gérard, Jean-Claude ULg; Blockx, Caroline ULg et al

in Journal of Geophysical Research. Space Physics (2007), 112

An interesting open question of magnetospheric physics is the understanding of the dynamics of the magnetotail. The question of the field stretching is even more challenging during substorm periods ... [more ▼]

An interesting open question of magnetospheric physics is the understanding of the dynamics of the magnetotail. The question of the field stretching is even more challenging during substorm periods, mainly because of the short time scales involved during such explosive events. In this study, we asses the ability of global scale proton auroral imaging to provide information on the tail stretching during active periods. We base our investigation on more than 250 isolated substorms observed by IMAGE-SI12 between 2000 and 2002. Applying the algorithm proposed by Donovan et al. (2003) for ground based observations to IMAGE-SI12 data, we determine the Equatorial Limit (EL) of the oval and propose to use it as an indicator of the tail stretching. Simultaneous comparison with GOES-8 allows us to estimate how strong is the relationship between the EL position deduced from SI12 and the magnetic field stretching. The EL indicator is shown to be consistent with previous studies (Sergeev and Gvozdevsky (1995) and Blockx et al. (2005)) and is found to be located in average ~1 degree equatorward of the limit deduced from DMSP measurements. The time evolution of the EL magnetic latitude is also presented for different local times relative to the onset position. This evolution of the EL index presents an asymmetric shape following the time of onset, suggesting a more important stretching of the tail duskward of the onset position. This asymmetric stretching is consistent with GOES-8 in situ measurements. [less ▲]

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See detailA comparison between FUV remote sensing of magnetotail stretching and the T01 model during quiet conditions and growth phases
Blockx, Caroline ULg; Gérard, Jean-Claude ULg; Coumans, Valérie ULg et al

in Annales Geophysicae [= ANGEO] (2007), 25(1), 161-170

In a previous study, Blockx et al. (2005) showed that the SI12 camera on board the IMAGE spacecraft is an excellent tool to remotely determine the position of the isotropy boundary (IB) in the ionosphere ... [more ▼]

In a previous study, Blockx et al. (2005) showed that the SI12 camera on board the IMAGE spacecraft is an excellent tool to remotely determine the position of the isotropy boundary (IB) in the ionosphere, and thus is able to provide a reasonable estimate of the amount of stretching of the magnetic field lines in the magetotail. By combining an empirical model of the magnetospheric configuration with Sergeev's criterion for non-adiabatic motion, it is also possible to obtain a theoretical position of IB in the ionosphere, for known conditions in the solar wind. Earlier studies have demonstrated the inadequacy of the Tsyganenko-1989 (T89) model to quantitatively reproduce the field line stretching, particularly during growth phases. In this study, we reexamine this question using the T01 model which considers the time history of the solar wind parameters. We compare the latitude of IB derived from SI12 global images near local midnight with that calculated from the T01 model and the Sergeev's criterion. Observational and theoretical results are found to frequently disagree. We use in situ measurements of the magnetic field with the GOES-8 satellite to discriminate which of the two components in the calculation of the theoretical position of the IB (the T01 model or Sergeev's criterion) induces the discrepancy. For very quiet magnetic conditions, we find that statistically the T01 model approximately predicts the correct location of the maximum proton precipitation. However, large discrepancies are observed in individual cases, as demonstrated by the large scatter of predicted latitudes. For larger values of the AE index, the model fails to predict the observed latitude of the maximum proton intensity, as a consequence of the lack of consideration of the cross-tail current component which produces a more elongated field configuration at the location of the proton injection along the field lines. We show that it is possible to match the observed location of the maximum proton precipitation by decreasing the current sheet half-thickness D parameter. We thus conclude that underestimation of the field line stretching leads to inadequately prediction of the boundary latitude of the non-adiabatic proton precipitation region. [less ▲]

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See detailMagnetotail topology around substorm onset time
Meurant, M.; Donovan, E. F.; Gérard, Jean-Claude ULg et al

Conference (2006, December 01)

The time evolution of the magnetotail topology during minutes preceding and following substorm onset is an important question of the magnetospheric dynamic. The substorm onset is a local and explosive ... [more ▼]

The time evolution of the magnetotail topology during minutes preceding and following substorm onset is an important question of the magnetospheric dynamic. The substorm onset is a local and explosive phenomenon, which makes it difficult to describe with in situ data. In this study, we investigate this problem thanks the remote sensing data provided by the FUV camera onboard the IMAGE spacecraft. In the first part of this study, we use a set of IMAGE-FUV and GOES-8 simultaneous observations obtained during substorms periods to develop a model of the magnetic field elevation angle at geosynchronous orbit. In the second part, we use a set of 259 substorms observed by the IMAGE spacecraft between 2000 and 2002. Taking advantage of the global scale of the observations provided by IMAGE-FUV, we describe the time evolution of the magnetotail topology provided by the model. An interesting result shows that the field is symmetrically stretched around the onset position before the onset time and this symmetry is broken after onset, with a more important stretching duskward to the onset. [less ▲]

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See detailGlobal auroral proton precipitation observed by IMAGE-FUV: Noon and midnight brightness dependence on solar wind characteristics and IMF orientation
Coumans, Valérie ULg; Gérard, Jean-Claude ULg; Hubert, Benoît ULg et al

in Journal of Geophysical Research. Space Physics (2006), 111(A5),

The brightness of proton aurora observed near solar maximum at summer and winter solstices with the FUV-SI12 global imager on board the IMAGE satellite has been correlated with the solar wind and the ... [more ▼]

The brightness of proton aurora observed near solar maximum at summer and winter solstices with the FUV-SI12 global imager on board the IMAGE satellite has been correlated with the solar wind and the interplanetary magnetic field characteristics measured by ACE satellite instruments. By contrast to the electron aurora, we find a strong correlation both on nightside and dayside between the proton precipitated power and the solar wind dynamic pressure calculated with 1-hour averaged solar wind data. For both southward and northward IMF, the proton power increases with \B-z\, but much more rapidly on the nightside for southward IMF orientation. Correlations for the nightside aurora were also calculated with a series of solar wind-magnetosphere coupling functions. We find highest correlation coefficients for expressions containing the dynamic pressure or involving the solar wind electric field in the Y-Z plane. The influence of the solar wind dynamic pressure on the proton aurora is tentatively explained by the effect of the pressure on the shape of the magnetosphere, generating stretching of the magnetotail and proton precipitation but also by other coupling processes between the solar wind and the magnetosphere. Adding FUV-WIC and SI13 electron aurora images in the study, we determine how proton and electron precipitations simultaneously react to solar wind and IMF characteristics and Kp. Results shows that protons are more reactive to dynamic pressure variations than electrons when B-z is positive, while the influence on of both types of particles is similar for negative B-z. The precipitating proton flux is found proportionally larger compared with the electron flux when the total auroral flux increases for low activity level. Instead, for high activity level, the proportion of the proton and the electron powers are similar when auroral power increases. Consequently, it is suggested that similar mechanisms cause proton and electron auroral precipitation for high activity levels, while they appear somewhat decoupled for lower activity conditions. [less ▲]

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See detailEL-a possible indicator to monitor the magnetic field stretching at global scale during substorm expansive phase: case study
Meurant, M.; Blockx, Caroline ULg; Spanswick, E. et al

in Syrjasuo, M.; Donovan, E. (Eds.) Substorms VIII (2006, March)

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See detailFar ultraviolet remote sensing of the isotropy boundary and magnetotail stretching
Blockx, Caroline ULg; Gérard, Jean-Claude ULg; Meurant, M. et al

in Journal of Geophysical Research. Space Physics (2005), 110(A11),

Several studies have attempted to identify the isotropy boundary (IB) defining the limit between the adiabatic and nonadiabatic trajectories of the trapped protons along closed magnetic field lines. This ... [more ▼]

Several studies have attempted to identify the isotropy boundary (IB) defining the limit between the adiabatic and nonadiabatic trajectories of the trapped protons along closed magnetic field lines. This boundary is an indicator of the amount of magnetic field line stretching in the magnetotail. Previous studies were based on in situ measurements, resulting in spatially and temporally restricted samples. To overcome these limitations, we propose to use global data obtained with the FUV spectrographic proton auroral imager (SI12) on board the IMAGE satellite. We determine at each magnetic local time the position of an optical boundary related to the IB and thereby to the stretching of the magnetic field lines. We show that the correspondence between the latitude of the maximum proton precipitation observed by SI12 and the IB measured by Defense Meteorological Satellite Program satellites is statistically established and depends on the magnetic local time. The relation between the position of the maximum proton precipitation as well as the intensity of this maximum and the magnetic field distortion is determined by comparison with GOES 8 data. We suggest that SI12 images can be used as a tool to globally determine the isotropy boundary and to monitor the level of stretching in the magnetotail. [less ▲]

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See detailComparison of intense nightside shock-induced precipitation and substorm activity
Meurant, M.; Gérard, Jean-Claude ULg; Blockx, Caroline ULg et al

in Journal of Geophysical Research. Space Physics (2005), 110(A7),

[1] Sudden variations of the solar wind dynamic pressure frequently induce dayside enhancements of auroral activity with features such as high-latitude arcs, low-latitude proton flashes, and enhancement ... [more ▼]

[1] Sudden variations of the solar wind dynamic pressure frequently induce dayside enhancements of auroral activity with features such as high-latitude arcs, low-latitude proton flashes, and enhancement of auroral precipitation propagating dawnward and duskward from noon to the night sector. In some cases, these shocks also induce enhanced activity during which the power precipitated into the night sector may reach values as high as observed during substorms. Several studies have shown that the triggering of nightside-enhanced precipitation is more likely during periods of southward interplanetary magnetic field (IMF) components. Early works showed that substorm-like activity is not frequent after a shock and suggested that shocks may not be considered as substorm triggers. We examine up to what point substorm-like nightside activity triggered by a shock is comparable to an isolated substorm. For this purpose, we analyze three events morphologically similar to substorms and occurring within less than 20 min after the arrival of a pressure pulse on the front of the magnetosphere. Different features of these events such as the mean energy of precipitated electrons, the latitudinal motion of boundaries before and after onset, and the power precipitated into the nightside sector are compared with isolated substorms. We conclude that the characteristics of shock-induced substorms appear very similar to those of isolated substorms. Shocks are able to trigger substorms when they hit an unstable magnetosphere. The interpretation is that the perturbation due to the shock induces a substorm by closure of the plasma sheet magnetic field. For the events presented in this study, the instability result from a period of southward IMF or stretching of the magnetic tail induced by a previous shock. [less ▲]

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See detailFUV remote sensing of the isotropic boundary and magnetotail stretching
Blockx, Caroline ULg; Gérard, Jean-Claude ULg; Meurant, M. et al

Conference (2004, December 01)

Several studies attempted to identify the Isotropic Boundary (IB) defining the limit between the adiabatic and non-adiabatic trajectories of the trapped protons along closed magnetic field lines. This ... [more ▼]

Several studies attempted to identify the Isotropic Boundary (IB) defining the limit between the adiabatic and non-adiabatic trajectories of the trapped protons along closed magnetic field lines. This boundary is an indicator of the amount of magnetic field lines' stretching in the magnetotail. These studies are based on in situ measurements, resulting in spatially and temporally restricted samples. To avoid this limitation, we propose to use global data obtained with the FUV-SI12 proton imager on board IMAGE spacecraft. We determine at each magnetic local time the position of an optical boundary equivalent to IB and thereby the stretching of the magnetic field lines. We show that the correspondence between the latitude of the maximum proton precipitation observed by SI12 and the IB measured by DMSP satellites is statistically established and depends on the magnetic local time. The relation between the position of the maximum proton precipitation as well as the intensity of this maximum and the magnetic field's distortion is determined by comparison with GOES-8 data. We thus suggest that SI12 can be used as a tool for the global determination of the isotropic boundary and to monitor the amount of stretching in the magnetotail. [less ▲]

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See detailComparison of intense nightside shock induced aurora and substorms activity
Meurant, M.; Gérard, Jean-Claude ULg; Blockx, Caroline ULg et al

Conference (2004, December 01)

Variations of the solar wind dynamic pressure induce perturbation of magnetospheric processes. These perturbations frequently induce dayside enhancements of activity with particular features such as low ... [more ▼]

Variations of the solar wind dynamic pressure induce perturbation of magnetospheric processes. These perturbations frequently induce dayside enhancements of activity with particular features such as low latitude proton flash, low latitude arcs and aurora propagating eastward and westward from noon to the night sector. In some cases, these shocks may also induce an enhancement of the nightside activity during which the power precipitated in the night sector may reach values as high as observed during substorms. Various studies have shown that high precipitated powers are more likely during period of negative values of the North - South IMF components. Liou et al (2003) have shown that substorm-like activity is not frequent after a shock and they concluded that a shock may not be considered as a substorm trigger. The question addressed in this study is to know up to what point the substorm like nightside activity triggered by a shock is comparable to a classical substorm. For this purpose, we analyze four events presenting nightside activity morphologically similar to substorms and occurring within a short time (less than 20 minutes) after the arrival of a pressure pulse on the front of the magnetosphere. Different features of these events such as the mean energy of precipitated electrons, the motion of boundaries before and after onset and the power precipitated in the nightside region are compared to typical substorms. Except for the absence of southward motion of activity before onset, shock induced substorms appear very similar to isolated substorms. We investigate the ability of a shock to trigger a substorm during periods characterized by particular conditions. We suggest that the sign of B[SUB]z[/SUB] plays an important role as well as the history of solar wind and interplanetary magnetic field and the resulting state of the magnetosphere. [less ▲]

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See detailPropagation of electron and proton shock-induced aurora and the role of the interplanetary magnetic field and solar wind
Meurant, M.; Gérard, Jean-Claude ULg; Blockx, Caroline ULg et al

in Journal of Geophysical Research. Space Physics (2004), 109

Shock-induced aurora observed with satellite-borne ultraviolet imagers shows distinct characteristics from the more common and extensively studied aurora generated during magnetospheric substorms. It is ... [more ▼]

Shock-induced aurora observed with satellite-borne ultraviolet imagers shows distinct characteristics from the more common and extensively studied aurora generated during magnetospheric substorms. It is initiated in the noon sector immediately following dynamic pressure pulses associated with the arrival of enhanced solar wind plasma at the front of the magnetosphere. The auroral brightening rapidly propagates toward the dawn and dusk sectors and may eventually trigger the development of an auroral substorm on the nightside. The FUV imaging system on board the IMAGE satellite has the ability to discriminate between proton and electron precipitation. This feature has been used to study the morphology and dynamics of the electron and proton precipitation following pulse-induced magnetospheric perturbations. A different dynamic is observed for aurora caused by electron and proton precipitation, as well as the important role played by the north-south component of the interplanetary magnetic field. The propagation from the noon to the night sector mainly occurs through the afternoon region for proton precipitation and the morning sector for electron aurora, as expected from azimuthal drift of newly injected plasma. The asymmetry of the precipitation distribution around the noon-midnight axis is more pronounced during negative B[SUB]z[/SUB] periods, when activity is the most important. The magnitude of both the interplanetary magnetic field and the solar wind speed appears well correlated with the precipitated power, by contrast with the solar wind density and the magnitude of the dynamic pressure, which appear to play a minor role. It is suggested that adiabatic compression and plasma waves play an important role on the locations of electron and proton precipitation in the dayside. [less ▲]

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See detailSolar wind control of auroral substorm onset locations observed with the IMAGE-FUV imagers
Gérard, Jean-Claude ULg; Hubert, Benoît ULg; Grard, Aline ULg et al

in Journal of Geophysical Research. Space Physics (2004), 109

The FUV imagers on board the IMAGE satellite provide multispectral snapshots of the polar region every 2 min. The combination of the Wide-Angle Imaging Camera (WIC) with SI12 (Doppler shifted Lyman-alpha ... [more ▼]

The FUV imagers on board the IMAGE satellite provide multispectral snapshots of the polar region every 2 min. The combination of the Wide-Angle Imaging Camera (WIC) with SI12 (Doppler shifted Lyman-alpha) and SI13 (135.6 nm) spectral imagers is used to discriminate between the electron and the proton aurora. We describe a statistical study of the location of 78 substorms observed close to the 2000-2001 winter solstice. The latitudinal distribution of the onsets observed with WIC is asymmetric with a median at 65.6° MLAT and a full width at half maximum (FWHM) of 3.5°. Their local time distribution is concentrated between 2000 and 0200 MLT with a median at 23.4 +/- 0.3 hours MLT and a FWHM of 1.8 hours. No statistically significant difference is found in the spatial distribution of the proton and electron onsets. All onsets take place within a region of preexisting proton precipitation, indicating that substorm initiation occurs in regions of stretched but dipole-like field lines that cross the equatorial plane close to the Earth. Latitudes of substorm onsets are located at a variable distance from the poleward FUV auroral boundary but remain at a nearly constant distance from the equatorward limit of both proton and electron auroral ovals. The magnetic latitudes of the onsets are correlated with some of the solar wind plasma properties measured by the ACE satellite prior to the substorm breakup. In particular, a clear anticorrelation is found between the onset MLAT and the 1-hour averaged solar wind dynamic pressure. A decrease of the onset latitude is also observed for larger B intensity values. No dependence of the onset MLT on the solar wind speed is observed, in contrast to the relationship expected from the thermal catastrophe model for substorm initiation. Our results are in agreement with models locating the initial instability in the near magnetosphere such as the near-Earth current disruption models. [less ▲]

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See detailGlobal auroral conductance distribution due to electron and proton precipitation from IMAGE-FUV observations
Coumans, Valérie ULg; Gérard, Jean-Claude ULg; Hubert, Benoît ULg et al

in Annales Geophysicae [= ANGEO] (2004), 22(5), 1595-1611

The Far Ultraviolet (FUV) imaging system on board the IMAGE satellite provides a global view of the north auroral region in three spectral channels, including the SI 12 camera sensitive to Doppler shifted ... [more ▼]

The Far Ultraviolet (FUV) imaging system on board the IMAGE satellite provides a global view of the north auroral region in three spectral channels, including the SI 12 camera sensitive to Doppler shifted Lyman-alpha emission. FUV images are used to produce instantaneous maps of electron mean energy and energy fluxes for precipitated protons and electrons. We describe a method to calculate ionospheric Hall and Pedersen conductivities induced by auroral proton and electron ionization based on a model of interaction of auroral particles with the atmosphere. Different assumptions on the energy spectral distribution for electrons and protons are compared. Global maps of ionospheric conductances due to instantaneous observation of precipitating protons are calculated. The contribution of auroral protons in the total conductance induced by both types of auroral particles is also evaluated and the importance of proton precipitation is evaluated. This method is well adapted to analyze the time evolution of ionospheric conductances due to precipitating particles over the auroral region or in particular sectors. Results are illustrated with conductance maps of the north polar region obtained during four periods with different activity levels. It is found that the proton contribution to conductance is relatively higher during quiet periods than during substorms. The proton contribution is higher in the period before the onset and strongly decreases during the expansion phase of substorms. During a substorm which occurred on 28 April 2001, a region of strong proton precipitation is observed with SI 12 around 14:00MLT at similar to75degrees MLAT. Calculation of conductances in this sector shows that neglecting the protons contribution would produce a large error. We discuss possible effects of the proton precipitation on electron precipitation in aurora] arcs. The increase in the ionospheric conductivity, induced by a former proton precipitation can reduce the potential drop along field lines in the upward field-aligned currents by creating an opposite polarization electric field. This feedback mechanism possibly reduces the electron acceleration. [less ▲]

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See detailRemote sensing of the proton aurora characteristics from IMAGE-FUV
Bisikalo, D. V.; Shematovich, V. I.; Gérard, Jean-Claude ULg et al

in Annales Geophysicae [= ANGEO] (2003), 21

The combination of simultaneous global images of the north polar region obtained with the IMAGE-FUV imaging system makes it possible to globally map the properties of the electron and proton auroral ... [more ▼]

The combination of simultaneous global images of the north polar region obtained with the IMAGE-FUV imaging system makes it possible to globally map the properties of the electron and proton auroral precipitation. The SI12 imager, which observes the Doppler-shifted Lyman-a [less ▲]

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See detailDynamics of global scale electron and proton precipitation induced by a solar wind pressure pulse
Meurant, M.; Gérard, Jean-Claude ULg; Hubert, Benoît ULg et al

in Geophysical Research Letters (2003), 30(20),

[1] On April 28 2001, simultaneous global images of electron and proton aurora were obtained by IMAGE- FUV following a sudden increase of solar wind dynamic pressure. The local time and intensity ... [more ▼]

[1] On April 28 2001, simultaneous global images of electron and proton aurora were obtained by IMAGE- FUV following a sudden increase of solar wind dynamic pressure. The local time and intensity distribution of both types of precipitation are examined and compared. It is found that the electron and the proton precipitation both start in the post noon sector and expand concurrently, but the expansion into the nightside starts sooner for the protons than for the electrons. The characteristic rise time in the onset sector is on the order of 6 minutes. A distinct dynamics and morphology of electron and proton precipitation is observed in the nightside sector. DMSP electron measurements in the afternoon sector indicate that the shock has a significant effect on the electron spectral characteristics. It is suggested that the various Alfven frequencies generated by the shock account for the two different speeds of propagation of the disturbance. [less ▲]

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See detailCharacterization and dynamics of the auroral electron precipitation during substorms deduced from IMAGE-FUV
Meurant, M.; Gérard, Jean-Claude ULg; Hubert, Benoît ULg et al

in Journal of Geophysical Research. Space Physics (2003), 108(A6),

[1] The FUV imager on board the IMAGE satellite provides simultaneous images of the north polar aurora every 2 min in three spectral channels. The Wideband Imaging Camera (WIC) responds primarily to the N ... [more ▼]

[1] The FUV imager on board the IMAGE satellite provides simultaneous images of the north polar aurora every 2 min in three spectral channels. The Wideband Imaging Camera (WIC) responds primarily to the N-2 LBH bands while one of the Spectral Imagers (SI13) includes the OI 135.6 nm emission and nearby LBH bands. The third channel (SI12) is sensitive to Doppler-shifted Lyman-alpha emission at 121.8 nm generated by proton precipitation. The relative magnitude of the WIC and SI13 signals depends on the altitude distribution of the energy deposition, in response to the differential O-2 absorption and the altitude dependence of the neutral composition. The ratio of simultaneous images from WIC and SI13 is used to derive the spatial distribution of the characteristic energy of the precipitating auroral electrons and the energy flux they carry. The method is described and the uncertainties introduced by possible perturbations of the neutral composition known to occur in the auroral thermosphere are discussed. The first part of this study describes a validation of this method performed by comparing precipitation characteristics derived from FUV with in situ measurements from two coincident passes of the NOAA-16 satellite. They are shown to agree within about 45%. The second part applies this ratio method to analyze the time evolution of auroral activity which occured during two substorms on 28 October 2000. The time evolution is displayed in the form of magnetic local time and magnetic latitude keograms. It is shown that the pattern of the electron average energy distribution exhibits both spatial and temporal changes. Comparison with FAST in situ electron spectrograms confirms the ability of IMAGE to detect precipitation events with a similar to200 km spatial scale. However the characteristics of the physical process leading to electron acceleration cannot be identified with FUV. The highest values of the average energy are colocated in time and space with the largest electron precipitation fluxes. A dawnward motion of bright features is observed in the postmidnight at speeds on the order of 5 magnetic local time hours/UT hour. [less ▲]

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See detailElectron and proton shock aurora observed by IMAGE-FUV
Meurant, M.; Gérard, Jean-Claude ULg; Hubert, Benoît ULg et al

in EGS - AGU - EUG Joint Assembly (2003, April 01)

The FUV instrument on the IMAGE (Imager for Magnetopause-to-Aurora Global Exploration) satellite monitors the aurora in three different spectral regions. The Wideband Imaging Camera (WIC) observes the ... [more ▼]

The FUV instrument on the IMAGE (Imager for Magnetopause-to-Aurora Global Exploration) satellite monitors the aurora in three different spectral regions. The Wideband Imaging Camera (WIC) observes the molecular N_2 LBH and the atomic NI emissions at 140-180 nm. The two channels of the Spectrographic Imager (SI) observe the Doppler shifted Lyman-α emission at 121.8 nm due to precipitating protons (SI12) and the electron auroral emission of OI at 135.6 nm (SI13). Three simultaneous snapshots are recorded each 2 minutes. In this study, the FUV instrument allows a global viewing of the aurora with a high temporal resolution both in proton and electron. It is used to study the shock aurora resulting from the disturbance caused by the arrival of a coronal mass ejection on the front of the magnetosphere. A comparison between electron and proton injection features at global scale is performed for different isolated events with positive and negative interplanetary B_z. A correlation with IMF and solar wind parameters is presented as well as a description of the magnetosphere morphology given by the Tsyganenko model in the shock aurora period. [less ▲]

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See detailElectron and proton shock aurora observed by IMAGE-FUV
Meurant, M.; Gérard, Jean-Claude ULg; Hubert, Benoît ULg et al

in EGS - AGU - EUG Joint Assembly (2003, April 01)

The FUV instrument on the IMAGE (Imager for Magnetopause-to-Aurora Global Exploration) satellite monitors the aurora in three different spectral regions. The Wideband Imaging Camera (WIC) observes the ... [more ▼]

The FUV instrument on the IMAGE (Imager for Magnetopause-to-Aurora Global Exploration) satellite monitors the aurora in three different spectral regions. The Wideband Imaging Camera (WIC) observes the molecular N_2 LBH and the atomic NI emissions at 140-180 nm. The two channels of the Spectrographic Imager (SI) observe the Doppler shifted Lyman-α emission at 121.8 nm due to precipitating protons (SI12) and the electron auroral emission of OI at 135.6 nm (SI13). Three simultaneous snapshots are recorded each 2 minutes. In this study, the FUV instrument allows a global viewing of the aurora with a high temporal resolution both in proton and electron. It is used to study the shock aurora resulting from the disturbance caused by the arrival of a coronal mass ejection on the front of the magnetosphere. A comparison between electron and proton injection features at global scale is performed for different isolated events with positive and negative interplanetary B_z. A correlation with IMF and solar wind parameters is presented as well as a description of the magnetosphere morphology given by the Tsyganenko model in the shock aurora period. [less ▲]

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See detailSeasonal effects on the proton auroral precipitation observed by IMAGE-FUV
Coumans, Valérie ULg; Gérard, Jean-Claude ULg; Hubert, Benoît ULg et al

in EGS - AGU - EUG Joint Assembly (2003, April 01)

The statistical approach of the auroral electron precipitation has shown a summer/winter dissymmetry. Electron energy flux in the 1900-0300 MLT sector increases from summer to winter. The frequency of ... [more ▼]

The statistical approach of the auroral electron precipitation has shown a summer/winter dissymmetry. Electron energy flux in the 1900-0300 MLT sector increases from summer to winter. The frequency of occurrence of intense aurora (with electron energy flux above 5 erg cm[SUP]-2[/SUP] s[SUP]-1[/SUP]) in the dusk-to-midnight sector was observed to be 3 times higher under winter conditions (or conditions of local darkness) than under summer conditions (or in sunlight). On board the IMAGE satellite the FUV instruments monitor the aurora in three different spectral regions and especially one of them only images the auroral proton precipitation. The Wideband Imaging Camera (WIC) observes the molecular N_2 LBH and the atomic NI emissions between 140 and 180 nm. The two channels of the Spectrographic Imager (SI) respond to the Doppler shifted Lyman-α emission at 121.8 nm due to precipitating protons (SI12) and the electron auroral emission of OI at 135.6 nm (SI13). The auroral proton and electron energy fluxes are calculated from the IMAGE-FUV data, relying on energy degradation and auroral emission models. We will discuss possible seasonal asymmetry in the auroral proton precipitation. A statistical study is made with FUV data from 2 successive solstices to minimize effects due to the solar activity variations. [less ▲]

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See detailA Comparison of FUV Auroral Emissions During the April 2002 Events as seen by the IMAGE/FUV and TIMED/GUVI Instruments
Gladstone, G.; Retherford, K.; Solomon, S. et al

Conference (2002, December 01)

The auroral emissions that resulted from the series of solar particle events and magnetic storms during 14-24 April 2002 provide an excellent data set for the cross-comparison of the IMAGE/FUV and TIMED ... [more ▼]

The auroral emissions that resulted from the series of solar particle events and magnetic storms during 14-24 April 2002 provide an excellent data set for the cross-comparison of the IMAGE/FUV and TIMED/GUVI auroral imagers. The IMAGE/FUV instrument comprises the SI spectral imager (121.8 nm and 135.6 nm) and the WIC imaging photometer (LBH) and observes the entire Earth from high Earth orbit. The TIMED/GUVI spectral imager (121.6 nm, 130.4 nm, 135.6 nm, LBH short, and LBH long) scans a nadir-to-limb swath from low Earth orbit. Although there is a large difference in spatial resolution, preliminary comparison of simultaneously-observed diffuse auroral emissions indicates fairly good agreement between the calibrated brightnesses determined for common spectral features. We will present a detailed simulation of one or more of the April 2002 events as seen by each imager to determine if a single description of the auroral precipitation can self-consistently account for the proton- and electron-generated FUV emissions observed from the two spacecraft. [less ▲]

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