A study of substorm-associated nightside spike events in auroral absorption using imaging riometers at South Pole and Kilpisjärvi

Hargreaves, J. K.; Browne, S. E.; Ranta, H.; Ranta, A.; Rosenberg, T. J.; Detrick, D. L.

doi:10.1016/s1364-6826(96)00061-2

Cited by 25 publications

(22 citation statements)

References 13 publications

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“…In this case they would not be spike events in the classical sense (e.g. Hargreaves et al, 1997); rather they are the direct precipitation of short-lived injection bursts from the tail.…”

Section: Nightside Absorption (Canadian Sector)mentioning

confidence: 99%

“…Kavanagh et al: Energetic electron precipitation during sawtooth injections 1975, 1997Pytte el al., 1976;Ranta et al, 1981;Ranta et al, 1999). Riometers provide a simple means of monitoring the precipitation of energetic electrons (energy greater than ∼30 keV) via measurements of the cosmic radio noise absorption (CNA), which has been recognised as a substorm phenomenon (Akasofu, 1968).…”

Section: Introductionmentioning

confidence: 99%

“…Neilsen and Axford, 1977). Observations with imaging riometers have shown that the spike event is actually localised in nature with typical dimensions of 190×80 (167×74) km at L∼6 (∼13) (Hargreaves et al, 1997). The spikes typically display a poleward motion at the start of an event with speeds from hundreds to thousands of ms −1 .…”

Section: Introductionmentioning

confidence: 99%

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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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“…In this case they would not be spike events in the classical sense (e.g. Hargreaves et al, 1997); rather they are the direct precipitation of short-lived injection bursts from the tail.…”

Section: Nightside Absorption (Canadian Sector)mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Energetic electron precipitation during sawtooth injections

Kavanagh

Donovan

et al. 2007

Ann. Geophys.

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“…Night-time spike events, which seem to have a close link with substorm onsets (Hargreaves et al, 1997), have had their various properties identified and studied since then. The spike event is identified as a sudden high intensity increase in absorption followed by a rapid decrease within few minutes.…”

Section: Introductionmentioning

confidence: 99%

Characteristics of night-time absorption spike events

et al. 2006

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Abstract. Sudden increases in cosmic radio noise absorption, known as spike events, have been identified as signatures of substorms in the previous studies. Using data from the IRIS (Imaging Riometer for Ionospheric Studies) at Kilpisjärvi, Finland (L ∼6) more than 450 night-time spike events between 1994 and 2003 have been identified. Spike events fall into four distinct categories based on their structure and the background magnetic activity as indicated by a local westward electrojet (IL index) derived from the IM-AGE (International Monitor for Auroral Geomagnetic Effects) magnetometer network as well as Pi2 magnetic pulsations from SAMNET (The UK Sub-Auroral Magnetometer Network). Classifying the types of absorption spikes allows for identification of phenomena such as multiple onsets and pseudobreakups from riometer data. In addition we have studied the statistical variation of absorption spikes and their sub-classes. This includes examining the magnetic local time (MLT) distribution and the seasonal and solar-cycle variation in spike occurrence.Those that seem to represent substorm onsets show a decidedly different MLT variation to those isolated spikes that represent pseudobreakups. The occurrence of spikes during different levels of geomagnetic activity is examined using the K p index.Wavelet analysis has been used for studying the temporal structure of spikes; also the direction of motion of spike events and localisation of spikes are presented for all events and each sub-class and results are compared with previous studies.Statistical studies are supported with X-ray images of aurora from PIXIE (The Polar Ionospheric X-ray Imaging Experiment) when available.

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“…The oblique beams are considerably wider. The eighth riometer is connected to a wide-beam antenna at the site which covers a circle with a radius of 50 km at the 90 km level (Hargreaves et al, 1991(Hargreaves et al, , 1997Detrick and Rosenberg, 1990).…”

Section: Observationsmentioning

confidence: 99%

Estimates of the field-aligned current density in current-carrying filaments using auroral zone ground-based observations

2001

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Abstract.We described the ground signatures of dynamic substorm features as observed by the imaging riometer, magnetometers and all-sky camera (ASC) at Kilpisjärvi, Finland on 5 and 25 October 1999 during the late evening hours. The magnetometer data was consistent with the motion of upward field-aligned currents (FACs) associated with absorption patches moving within the field of view of the riometer. We used riometer data in order to estimate the intensity of FACs associated with these local current-carrying filaments. It is shown that during these events, the estimated FAC intensity exceeds a threshold value that corresponds to the excitation of the low-frequency turbulence in the upper ionosphere. As a result, a quasi-oscillating regime of anomalous resistivity on the auroral field lines can give rise to the burstlike electron acceleration responsible for simultaneously observed auroral forms and bursts of Pi1B pulsations.

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A study of substorm-associated nightside spike events in auroral absorption using imaging riometers at South Pole and Kilpisjärvi

Cited by 25 publications

References 13 publications

Energetic electron precipitation during sawtooth injections

Energetic electron precipitation during sawtooth injections

Characteristics of night-time absorption spike events

Estimates of the field-aligned current density in current-carrying filaments using auroral zone ground-based observations

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