Substorm related changes in precipitation in the dayside auroral zone – a multi instrument case study

Kavanagh, A. J.; Honary, F.; McCrea, I. W.; Donovan, E.; Woodfield, E. E.; Manninen, J.; Anderson, P. C.

doi:10.5194/angeo-20-1321-2002

Cited by 13 publications

(14 citation statements)

References 45 publications

(35 reference statements)

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“…This is consistent with the effects of gradient-curvature drift, which predicts that particles on a higher L-shell should reach a particular longitude earlier than particles of the same energy at lower L-shells (e.g. Kavanagh et al, 2002, and references therein). The spike-like enhancements in CNA in the dayside ionosphere are not the same phenomenon as night-side spikes related to the substorm onset/injection.…”

Section: Dayside Absorption (Finnish Sector)supporting

confidence: 70%

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Energetic electron precipitation during sawtooth injections

Kavanagh

Donovan

et al. 2007

Ann. Geophys.

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Abstract. We present simultaneous riometer observations of cosmic noise absorption in the nightside and dawn-noon sectors during sawtooth particle injections during 18 April 2002. Energetic electron precipitation (>30 keV) is a feature of magnetospheric substorms and cosmic radio noise absorption acts as a proxy for qualitatively measuring this precipitation. This event provides an opportunity to compare the absorption that accompanies periodic electron injections with the accepted paradigm of substorm-related absorption. We consider whether the absorption is consistent with the premise that these injections are quasi-periodic substorms and study the effects of sustained activity on the level of precipitation. Four consecutive electron injection events have been identified from the LANL (Los Alamos National Laboratory) geosynchronous data; the first two showing that additional activity can occur within the 2-4 h sawtooth periodicity. The first three events have accompanying absorption on the nightside that demonstrate good agreement with the expected pattern of substorm-absorption: discrete spike events with poleward motion at the onset followed by equatorward moving structures and more diffuse absorption, correlated with optical observations. Dayside absorption is linked to gradient-curvature drifting electrons observed at geostationary orbit and it is shown that low fluxes can lead to a lack of absorption as precipitation is suppressed; precipitation begins when the drifting electron flux surpasses some critical level following continuous injections of electrons from the magnetotail. In addition it is shown that the apparent motion of absorption determined from an azimuthal chain of riometers exhibits an acceleration that may be indicative of an energisation of the drifting electron population.

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Section: Dayside Absorption (Finnish Sector)supporting

confidence: 70%

“…It is probable that this is linked with the motion of the injection region, but also the electrons will gradient-curvature drift eastward towards dawn (e.g. Kavanagh et al, 2002, and references therein). The electrons are quasi-trapped and experience pitch-angle scattering through whistler mode wave interactions (e.g.…”

Section: Introductionmentioning

confidence: 99%

Energetic electron precipitation during sawtooth injections

Kavanagh

Donovan

et al. 2007

Ann. Geophys.

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“…This result disagrees with those of Nielsen (1980) and del Pozo et al (2002), who presented several examples demonstrating a significant difference between the absorption and E×B drift velocities, but one has to keep in mind that their observations were performed near magnetic midnight during the substorm expansion phase, while ours refer to a different MLT sector, for which the E×B drift mechanism seems to be dominating (Kavanagh et al, 2002).…”

Section: Summary and Discussioncontrasting

confidence: 55%

“…These authors concluded that the narrow absorption regions appeared to move with a velocity that was consistent with the E×B drift. A similar conclusion was also reached in several case studies that used the data from the Imaging Riometer for Ionospheric Studies (IRIS) in Kilpisjärvi, Finland (Nielsen and Honary, 2000;Kavanagh et al, 2002;del Pozo et al, 2002). In the latter study, however, it was demonstrated that this conclusion seemed to hold only for relatively stable auroral arcs and that during the substorm expansion phase the absorption drift velocity was significantly different from that of convection, as observed by the European Incoherent Scatter (EISCAT) radar facility, a result similar to that of Nielsen (1980).…”

Section: R a Makarevitch Et Al: Imaging Riometer Observations Of Dmentioning

confidence: 48%

Imaging riometer observations of drifting absorption patches in the morning sector

et al. 2004

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Abstract.Observations by a 7×7-beam imaging riometer in Kilpisjärvi, Finland (∼66 • MLAT) of the drifting cosmic noise absorption (CNA) structures in the morning sector near the zonal drift reversals are presented. The examination of the absorption intensity images revealed several regions with enhanced CNA (absorption patches) slowly drifting through the riometer field of view (FoV). The absorption patches were found to vary in shape, orientation (for elongated arc-like patches), and drift direction. The latter was calculated from the regression lines to positions of the absorption maxima in the FoV images and compared with the direction of electrojet plasma flow from horizontal magnetic perturbations and (for one event) tristatic ion drift velocities in the F-region. A reasonable agreement was found between these directions both in point-by-point comparisons and in terms of direction reversal timings. The absorption patches of lower intensity appear to have smaller drift velocities and to be associated with weaker magnetic perturbations. These results are consistent with the notion that relatively slow motions of the auroral absorption near the zonal drift reversals are associated with the E×B drift of the entire magnetic flux tube as opposed to the gradient-curvature drift of energetic electrons injected into the ionosphere at the substorm onset. The absorption drift velocity magnitude, on the other hand, was found to be substantially lower than that of the plasma flow based on the results of limited comparison with tristatic ion drift measurements. A comparison of the drift directions with those of the patch elongation showed that a considerable number of patches had these directions close to each other. Using this observation, we demonstrate a satisfactory agreement between the patch drift velocities (both in direction and magnitude) as determined from the absorption images and keograms under the assumption that some patches were propagating in a direction that was significantly different from the perpendicularity to elongation.

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“…Absorption in the pre-midnight sector is attributed to the precipitation of electrons directly associated with substorm activity (e.g. Ansari, 1964;Ranta et al, 1981), and the precipitation in the morning sector has often been associated with the eastward drift of electrons (Kavanagh et al, 2002 and references therein) following substorm injection. Thus, it is the absorption around midnight that is considered to be of premier geophysical importance, however, for practical purposes (e.g.…”

Section: Diurnal Variationmentioning

confidence: 99%

The statistical dependence of auroral absorption on geomagnetic and solar wind parameters

et al. 2004

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Abstract. Data from the Imaging Riometer for Ionospheric Studies (IRIS) at Kilpisjärvi, Finland, have been compiled to form statistics of auroral absorption based on seven years of observations. In a previous study a linear relationship between the logarithm of the absorption and the K p index provided a link between the observations of precipitation with the level of geomagnetic activity. A better fit to the absorption data is found in the form of a quadratic in K p for eight magnetic local time sectors. Past statistical investigations of absorption have hinted at the possibility of using the solar wind velocity as a proxy for the auroral absorption, although the lack of available satellite data made such an investigation difficult. Here we employ data from the solar wind monitors, WIND and ACE, and derive a linear relationship between the solar wind velocity and the cosmic noise absorption at IRIS for the same eight magnetic local time sectors. As far as the authors are aware this is the first time that in situ measurements of the solar wind velocity have been used to create a direct link with absorption on a statistical basis. The results are promising although, it is clear that some other factor is necessary in providing reliable absorption predictions. Due to the substorm related nature of auroral absorption, this is likely formed by the recent time history of the geomagnetic activity, or by some other indicator of the energy stored within the magnetotail. For example, a dependence on the southward IMF (interplanetary magnetic field) is demonstrated with absorption increasing with successive decreases in B z ; a northward IMF appears to have little effect and neither does the eastward component, B y .

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Substorm related changes in precipitation in the dayside auroral zone – a multi instrument case study

Cited by 13 publications

References 45 publications

Energetic electron precipitation during sawtooth injections

Energetic electron precipitation during sawtooth injections

Imaging riometer observations of drifting absorption patches in the morning sector

The statistical dependence of auroral absorption on geomagnetic and solar wind parameters

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