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See detailOn the origin of the 2-3 minutes quasi-periodicity in the Jovian magnetosphere
Bonfond, Bertrand ULg; Vogt, Marissa F.; Gérard, Jean-Claude ULg et al

Poster (2011, October 05)

Several kinds of periodicities have been observed at Jupiter since the first probes fly-by. However, pre- vious investigations mainly focused on the longer timescales, such as the 40 minutes (QP40) or the ... [more ▼]

Several kinds of periodicities have been observed at Jupiter since the first probes fly-by. However, pre- vious investigations mainly focused on the longer timescales, such as the 40 minutes (QP40) or the 2- 3 days quasi-periodicity. Here we describe the recent finding of the 2-3 minutes quasi-periodic occurrence of UV flares in the active region of the polar aurora. These observations are then compared to other measurements of such quasi-periodic behaviors in electron and magnetic field data and their probably common origin is discussed. [less ▲]

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See detailQuasi-periodic polar flares at Jupiter: A signature of pulsed dayside reconnections?
Bonfond, Bertrand ULg; Vogt, M. F.; Gérard, Jean-Claude ULg et al

in Geophysical Research Letters (2011), 38

The most dynamic part of the Jovian UV aurora is located inside the main auroral oval. This region is known to regularly show localized but dramatic enhancements on timescales of several tens of seconds ... [more ▼]

The most dynamic part of the Jovian UV aurora is located inside the main auroral oval. This region is known to regularly show localized but dramatic enhancements on timescales of several tens of seconds, called polar flares. They have often been associated with the polar cusp, based on their location in the polar cap. The present study is based on the longest high-time resolution image sequences ever acquired by the Space Telescope Imaging Spectrograph aboard the Hubble Space Telescope. We report the first observations of a regularity in the occurrence of these flares, with a timescale of 2-3 minutes. We use a magnetic flux mapping model to identify the region corresponding to these emissions in the equatorial plane: the radial distance ranges from 55 to 120 Jovian radii and the local times are between 10: 00 and 18: 00. The analogy with similar phenomena observed at Earth suggests that these quasi-periodic auroral flares could be related to pulsed reconnections at the dayside magnetopause. Indeed, the flares' projected location in the equatorial plane and their rate of re-occurrence show some similarities with the properties of the flux transfer events observed by the Pioneer and Voyager probes. [less ▲]

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See detailJupiter's ultraviolet polar emission: a statistical study
Coumans, Valérie ULg; Bonfond, Bertrand ULg; Grodent, Denis ULg et al

Conference (2010, September)

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See detailJupiter's ultraviolet polar auroral emissions
Coumans, Valérie ULg; Bonfond, Bertrand ULg; Grodent, Denis ULg et al

Conference (2009, September)

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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 detailSeasonal, Kp, solar wind, and solar flux variations in long-term singlepass satellite estimates of electron and ion auroral hemispheric power
Emery, Barbara A; Coumans, Valérie ULg; Evans, David S et al

in Journal of Geophysical Research (2008), 113(A6),

Electron auroral energy flux is characterized by electron hemispheric power (Hpe) estimated since 1978 from National Oceanic and Atmospheric Administration (NOAA) and Defense Meteorological Satellite ... [more ▼]

Electron auroral energy flux is characterized by electron hemispheric power (Hpe) estimated since 1978 from National Oceanic and Atmospheric Administration (NOAA) and Defense Meteorological Satellite Program (DMSP) satellites after the estimates were corrected for instrumental problems and adjusted to a common baseline. Similarly, intersatellite adjusted ion hemispheric power (Hpi) estimates come from one MetOp and four NOAA satellites beginning in 1998. The hemispheric power (Hp) estimates are very crude, coming from single satellite passes referenced to 10 global activity levels, where the Hpi estimates are the difference between the total and the electron Hp (Hpi = Hpt-Hpe). However, hourly averaged NOAA/DMSP Hpe and Hpi estimates correlate well with hourly Polar Ultraviolet Imager (UVI) Hpt and Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) far ultraviolet (FUV) Hpe and Hpi estimates. Hpe winter values were larger than summer values similar to 65% of the time (when geomagnetic activity was moderate or higher), and Hpe were larger in the summer similar to 35% of the time (typically for low geomagnetic activity). Hpe was similar to 40% larger at winter solstice than summer solstice for the largest Hp from mostly nightside increases, and Hpe was similar to 35% larger in summer than winter for the smallest Hp owing to dayside auroral enhancements. Ion precipitation differed from electron precipitation because it was almost always larger in summer than winter. Hpe and Hpi increased with Kp, solar wind speed (Vsw), and negative Interplanetary Magnetic Field (IMF) B-z, similar to previous studies. Hpi also increased strongly with positive Bz. For quiet conditions, Hpe increased with increasing 10.7-cm solar flux (Sa), while Hpi increased with Sa up to Sa similar to 115 for all conditions. [less ▲]

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See detailGlobal morphology of substorm growth phases observed by the IMAGE-SI12 imager
Coumans, Valérie ULg; Blockx, Caroline ULg; Gérard, Jean-Claude ULg et al

in Journal of Geophysical Research (2007), 112(A11),

We present case studies and a statistical summary of optical observations of proton precipitation made during substorm growth phases. Our analysis is based on observations of the Doppler-shifted Lyman ... [more ▼]

We present case studies and a statistical summary of optical observations of proton precipitation made during substorm growth phases. Our analysis is based on observations of the Doppler-shifted Lyman-alpha auroral emission obtained with the SI12 Spectrographic Imager on board the IMAGE satellite. These images are used to determine the morphology and dynamics of the auroral oval and of the polar cap boundary on a global scale, as well as the total open magnetic flux and its time evolution. We also investigate the relationship with the solar wind and the interplanetary magnetic field ( IMF) characteristics measured by the ACE satellite and with the magnetic elevation angle measured by GOES-8. The statistical study shows that the sector of maximum proton precipitation during the growth phase is on average centered around 2200 MLT and rapidly shifts in local time by about 1.2 h toward midnight at the time of the onset. The open magnetic flux increases by 33% on average during the growth phase. The mean value of the open flux immediately before the substorm onset is about 0.66 GWb for substorms triggered by a northward turning of B-z and 0.74 GWb for nontriggered substorms. The averaged open flux at the substorm onset is smallest when the substorm is triggered by a sudden reversal of B-z, suggesting that the accumulation of energy by the magnetosphere is perturbed by changes in B-z. The open magnetic flux continues to increase during the 20 min following the onset, for a large number of events. The rate of equatorward displacement of the auroral oval boundaries during growth phase is typically similar to 3 deg/h. It is statistically correlated (r=0.40) with the magnitude of the Bz component of the IMF measured by the ACE satellite. It is also correlated, with higher coefficient (r=0.54), with functions describing the efficiency of solar wind energy transfer involving the transverse electric field carried by the solar wind. The equatorward motion may be global, restricted to local time sectors or a combination of both. At no nightside local time sector does the motion of the equatorial boundary appear more pronounced than at others, but the maximum displacement of the polar boundary is statistically located around midnight MLT. [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 detailGlobal morphology of substorm growth phases observed by the IMAGE-SI12 imager
Blockx, Caroline ULg; Gérard, Jean-Claude ULg; Coumans, Valérie ULg et al

Poster (2007)

Growth phases are observed to start from less than 30 minutes to over an hour before the substorm onset. The sector of maximum proton precipitation during the growth phase is generally located around 2200 ... [more ▼]

Growth phases are observed to start from less than 30 minutes to over an hour before the substorm onset. The sector of maximum proton precipitation during the growth phase is generally located around 2200 MLT. It rapidly moves in local time by about 1.2 hour toward midnight at the time of the onset. The open magnetic flux increases by as much as a 33% during the growth phase. The mean value of the open flux at the end of the growth phase, immediately preceding the substorm, onset is about 0.74. GWb for substorms triggered by external (solar wind) factors and 0.67 GWb for non-triggered substorms. The open magnetic flux generally drops following the onset of triggered substorms but continues to increase for non-triggered events. We interpret this behavior as an indication that the rate of opening of closed field lines on the dayside can exceed that of the nightside reconnection after the onset in non-triggered substorms. By contrast, flux closure is more efficient while the flux opening rate drops in the case of externally triggered onset, so that the closure rate exceeds that of field line opening on the dayside. The rate of equatorward displacement is typically ~ 3 deg/hour. It is statistically correlated with the magnitude of the southward Bz component of the IMF measured by the ACE satellite. It is also correlated with transfer functions describing the efficiency of solar wind energy transfer which involve the transverse electric field carried by the solar wind. The equatorward motion may be global, restricted to local time sectors or a combination of both. No nightside local time sector appears favored where the motion of the equatorial boundary would be more pronounced. The maximum displacement of the polar boundary is statistically located around midnight MLT. [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 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 detailMorphology and seasonal variations of global auroral proton precipitation observed by IMAGE-FUV
Coumans, Valérie ULg; Gérard, Jean-Claude ULg; Hubert, Benoît ULg et al

in Journal of Geophysical Research. Space Physics (2004), 109(A12),

Observations with the FUV imagers on board the IMAGE satellite have been used to map the auroral electron and proton energy fluxes during the summer and winter solstices of 2000, in order to construct a ... [more ▼]

Observations with the FUV imagers on board the IMAGE satellite have been used to map the auroral electron and proton energy fluxes during the summer and winter solstices of 2000, in order to construct a statistical view of the global auroral proton precipitation. The distribution for electrons compare well both in morphology and in magnitude with those obtained previously with the Polar-UVI instruments and with an empirical auroral precipitation model based on DMSP data. The proton morphology also closely resembles the statistical ion oval derived from DMSP data, showing a "C-shaped'' morphology with a minimum located in the morning sector. The precipitation proton auroral power is on the order of 2.2 GW for an average Kp value of 2, also in close agreement with the values of the DMSP empirical model. The FUV data also reveal the presence of seasonal effects in the proton precipitation. Specifically, the latitudinal width of the proton oval is larger in summer than in winter so that the globally precipitated proton power is 1.5 times higher in summer than in winter. The occurrence probability of intense proton auroras (with energy flux >0.5 mW m(-2)) is also shown to be nearly three times higher in summer than in winter. This seasonal effect in the proton precipitation contrasts with those observed for electrons, where intense electron events occur more often in winter than in summer. We discuss a mechanism that may account for these results based on the presence of field-aligned potential drops which accelerate auroral electrons downward in regions of upward directed field-aligned current, while suppressing the precipitating magnetospheric proton flux. The presence of such field-aligned potentials is dependent on the differing solar illumination in winter and summer. [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 detailOn the Characteristics and Source Regions of Dayside Proton Precipitation
Chua, D. H.; Dymond, K. F.; Budzien, S. A. et al

Conference (2004, December 01)

The source regions of precipitating protons on the dayside and their dependence on solar wind conditions are studied using far-ultraviolet (FUV) spectral observations and imaging. The High-resolution ... [more ▼]

The source regions of precipitating protons on the dayside and their dependence on solar wind conditions are studied using far-ultraviolet (FUV) spectral observations and imaging. The High-resolution Ionospheric and Thermospheric Spectrograph (HITS) aboard the Advanced Research and Global Observation Satellite (ARGOS) observes Doppler-shifted H Lyman-α emissions from precipitating protons with a spectral resolution of 1.5 Angstroms. The shapes of these Doppler spectra are indicative of the energy and pitch angle distributions of the proton precipitation. Global images of H Lyman-α emissions obtained by the SI-12 instrument on the IMAGE spacecraft are examined to relate the spectral observations to the dayside morphology of the proton aurora. During periods of sustained southward interplanetary magnetic field (IMF), the dayside proton aurora spectra exhibit broad Doppler shifts and are similar to those observed on the nightside with inferred mean energies typical of plasma sheet protons of magnetospheric origin. Global images of proton aurorae under these conditions show continuous regions of H Lyman-α emissions across the dayside extending from the nightside. In contrast, during periods of northward or variable IMF, proton aurora emissions on the dayside often appear in an isolated spot in the noon to late afternoon MLT sector. The Doppler-spectra of the proton emissions in these regions are narrow, indicating precipitation with low mean energies and from a different origin than that observed in the southward IMF cases. These spectra may be indicative of magnetosheath protons that have direct access to the ionosphere through high-latitude dayside reconnection. This study further quantifies the characteristics of dayside proton precipitation under various states of the magnetosphere and highlights the importance of IMF orientation on the coupling between the high-latitude, dayside ionosphere and its plasma sources at higher altitudes. [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 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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