The development of the substorm in auroral radio absorption

Hargreaves, J. K.; Chivers, H.J.A.; Axford, W. I.

doi:10.1016/0032-0633(75)90177-4

Cited by 42 publications

(29 citation statements)

References 5 publications

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“…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%

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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: Introductionmentioning

confidence: 99%

“…CNA manifests in various time-dependent structures during the phases of a substorm both on the night and dayside. During the growth phase an equatorward drifting arc forms (Hargreaves et al, 1975;Ranta et al, 1981); this can contain pulsating forms (Ranta et al, 1999) and is linked to optical arcs (e.g. Jussila et al, 2004).…”

Section: Introductionmentioning

confidence: 99%

Energetic electron precipitation during sawtooth injections

Kavanagh

Donovan

et al. 2007

Ann. Geophys.

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“…The development of auroral absorption substorms has been studied in several papers (Hargreaves et al, 1975;Pytte et al, 1976;Ranta et al, 1981;Pellinen et al, 1982;Ranta and Ranta, 1984;Ranta et al, 1999). Studies show a pre-onset absorption bay that often precedes an onset of a substorm.…”

Section: Introductionmentioning

confidence: 99%

Cosmic radio noise absorption events associated with equatorward drifting arcs during a substorm growth phase

et al. 2004

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Abstract. Cosmic radio noise absorption (CNA) events associated with equatorward drifting arcs during a substorm growth phase are studied by using simultaneous optical auroral, IRIS imaging riometer and EISCAT incoherent scatter radar measurements. The CNA is generally attributed to energetic particle precipitation in the D-region. However, it has been argued that plasma irregularities or enhanced electron temperature (T e ) in the E-region could also produce CNA. Both of the latter mechanisms are related to intense electric fields in the ionosphere. We present two events which occur during a substorm growth phase in the evening MLT sector. In both of the events, an auroral arc is drifting equatorward, together with a region of CNA (auroral absorption bay) located on the equatorward side and outside of the arc. Both of the events are associated with enhanced D-region electron density on the equatorward side of the auroral arc, but in the second event, a region of intense electric field and enhanced electron temperature in the E-region is also located on the equatorward side of the arc. We show that in the studied events neither plasma instabilities nor enhanced T e play a significant role in producing the measured CNA, but the CNA in the vicinity of the equatorward drifting arcs is produced by D-region energetic electron precipitation.

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“…Speiser and Ness, 1967) and most workers have made the connection at 8 or 10 R E . The closer distance of 5 R E has been used here because observations indicate that the substorm in auroral absorption in the night sector begins at about L=5 (Hargreaves et al, 1975). However, the value is tapered from zero at 5 R E to the full value at 8 R E .…”

Section: A Basic Explanationmentioning

confidence: 99%

Seasonal variations in the incidence of auroral radio absorption events at very high latitude, and the influence of the magnetotail

Hargreaves

2007

Ann. Geophys.

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Abstract.A statistical analysis has been made of the incidence of auroral radio absorption events at South Pole, and of its dependence on basic geophysical parameters such as season, time of day, and magnetic activity level. It is found that at low and moderate levels of activity the incidence of events in the winter season is at least twice that in the summer. However, at high activity no events at all occurred during the local summer night, which appears to be explicable as the effect of the magnetotail and the consequent distortion of the magnetosphere when the southern polar region is tilted strongly towards the Sun. Previous results from even higher latitudes show the effect in an even more exaggerated form, in that both the day and night periods of absorption activity exhibit strong seasonal variations.

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The development of the substorm in auroral radio absorption

Cited by 42 publications

References 5 publications

Energetic electron precipitation during sawtooth injections

Energetic electron precipitation during sawtooth injections

Cosmic radio noise absorption events associated with equatorward drifting arcs during a substorm growth phase

Seasonal variations in the incidence of auroral radio absorption events at very high latitude, and the influence of the magnetotail

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