Auroral radio absorption as an indicator of magnetospheric electrons and of conditions in the disturbed auroral D-region

Collis, P. N.; Hargreaves, J. K.; Korth, A.

doi:10.1016/0021-9169(84)90041-2

Cited by 29 publications

(21 citation statements)

References 32 publications

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“…On the other hand, a nearly isotropic pitch angle distribution was observed during 17:20:20-17:20:48 UT. The anisotropic pitch angle distribution in this figure is consistent with the previous studies (Parthasarathy et al, 1966;Fritz, 1970;Rossberg, 1978;Collis et al, 1983Collis et al, , 1984. Parthasarathy et al (1966) have shown, using measurements from a low-altitude satellite, that the trapped electron flux with energy >40 keV observed in the auroral region is typically greater by one to two orders of magnitude than the precipitating electron flux.…”

Section: Discussionsupporting

confidence: 90%

“…So far, several authors have reported a good correlation between the CNA observed with broad-beam riometers and precipitating medium-energy electrons, by comparing with data from the low-altitude satellites (Maehlum and O'Brien, 1963;Hargreaves and Sharp, 1965;Parthasarathy et al, 1966;Jelly and Brice, 1967) and from a geostationary satellite (Collis et al, 1983(Collis et al, , 1984Collis and Korth, 1985). Some of them have also shown an empirical relationship between CNA and precipitating medium-energy electrons measured at low altitude (Hargreaves and Sharp, 1965;Parthasarathy et al, 1966) and at geosynchronous orbit (Collis et al, 1983).…”

Section: Introductionmentioning

confidence: 93%

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Comparison between CNA and energetic electron precipitation: simultaneous observation by Poker Flat Imaging Riometer and NOAA satellite

et al. 2005

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Abstract. The cosmic noise absorption (CNA) is compared with the precipitating electron flux for 19 events observed in the morning sector, using the high-resolution data obtained during the conjugate observations with the imaging riometer at Poker Flat Research Range (PFRR; 65.11 • N, 147.42 • W), Alaska, and the low-altitude satellite, NOAA 12. We estimate the CNA, using the precipitating electron flux measured by NOAA 12, based on a theoretical model assuming an isotropic pitch angle distribution, and quantitatively compare them with the observed CNA. Focusing on the eight events with a range of variation larger than 0.4 dB, three events show high correlation between the observed and estimated CNA (correlation coefficient (r 0 )>0.7) and five events show low correlation (r 0 <0.5). The estimated CNA is often smaller than the observed CNA (72% of all data for 19 events), which appears to be the main reason for the low-correlation events. We examine the assumption of isotropic pitch angle distribution by using the trapped electron flux measured at 80 • zenith angle. It is shown that the CNA estimated from the trapped electron flux, assuming an isotropic pitch angle distribution, is highly correlated with the observed CNA and is often overestimated (87% of all data). The underestimate (overestimate) of CNA derived from the precipitating (trapped) electron flux can be interpreted in terms of the anisotropic pitch angle distribution similar to the loss cone distribution. These results indicate that the CNA observed with the riometer may be quantitatively explained with a model based on energetic electron precipitation, provided that the pitch angle distribution and the loss cone angle of the electrons are taken into account.

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Section: Discussionsupporting

confidence: 90%

Section: Introductionmentioning

confidence: 93%

Comparison between CNA and energetic electron precipitation: simultaneous observation by Poker Flat Imaging Riometer and NOAA satellite

et al. 2005

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“…This latter observation is consistent with the findings of Collis et al (1984), who predicted that spectra during noon-time absorption events would indeed be harder than for the morning sector.…”

Section: Flux-energy Spectra Of Precipitating Electronssupporting

confidence: 92%

A localised co-rotating auroral absorption event observed near noon using imaging riometer and EISCAT

1996

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Abstract. An isolated region of energetic electron precipitation observed near local noon in the auroral zone has been investigated using imaging riometer (IRIS) and incoherent-scatter radar (EISCAT) techniques. IRIS revealed that the absorption event was essentially co-rotating with the Earth for about 2 h. The spatial and temporal variations in D-region electron density seen by EISCAT were able to be interpreted within a proper context when compared with the IRIS data. EISCAT detected significant increases in electron density at altitudes as low as 65 km as the event drifted through the radar beam. The altitude distribution of incremental radio absorption revealed that more than half of the absorption occurred below 75 km, with a maximum of 67 km. The energy spectrum of the precipitating electrons was highly uniform throughout the event, and could be described analytically by the sum of three exponential distributions with characteristic energies of 6, 70 and 250 keV. A profile of effective recombination coefficient that resulted in self-consistent agreement between observed electron desities and those inferred from an inversion procedure has been deduced. The observations suggest a co-rotating magnetospheric source region on closed dayside field lines. However, a mechanism is required that can sustain such hard precipitation for the relatively long duration of the event.

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“…These methods are advantageous and a valuable compliment to in situ measurements due to availability of dense arrays of ground-based instruments and relative ease of higher resolution analysis than satellitebased studies. One such instrument is the riometer, a common tool for observing fluctuations in auroral zone radio absorption during substorms [Fjordheim and Henriksen, 1974;Baker et al, 1982;Collis et al, 1984;Rosenberg and Dudeney, 1986;Spanswick et al, 2005]. Riometer absorption measurements are sensitive to enhanced D and lower E region electron density associated with the high particle precipitation [Hargreaves et al, 1979].…”

Section: Introductionmentioning

confidence: 99%

GPS TEC technique for observation of the evolution of substorm particle precipitation

et al. 2011

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[1] One of the signatures of magnetospheric substorms is the precipitation of high energy particles into the high latitude ionosphere. In this paper, we introduce a new method of tracking substorm particle precipitation using GPS Total Electron Content (TEC) and provide some preliminary observations of precipitation signatures from application of this method. Using TEC measurements from several GPS receivers, we examined particle precipitation signatures associated with two separate substorm events (4 October 2008 and 29 October 2008) and monitored the expansion of the high energy precipitation regions with a higher temporal and spatial resolution than previously available. For each event we have observed TEC signatures associated with substorm particle precipitation along 20 to 25 separate GPS raypaths from up to 7 GPS receivers located in the Canadian Arctic. This is in addition to particle injection signatures found in CLUSTER satellite data and precipitation signatures in ground based riometer data. Signature timing on different raypaths from different stations indicates a mainly northward (tailward) expansion of the precipitation (injection) region with a smaller westward (azimuthal) component for the events studied. By applying a triangulation method, we also calculated propagation velocity of the precipitation boundary in regions covered by our GPS receivers. For each substorm, expansion velocity ranged from 0.3-2 km/s northward and 0-1 km/s westward, and tended to decrease in magnitude at higher latitudes.

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Auroral radio absorption as an indicator of magnetospheric electrons and of conditions in the disturbed auroral D-region

Cited by 29 publications

References 32 publications

Comparison between CNA and energetic electron precipitation: simultaneous observation by Poker Flat Imaging Riometer and NOAA satellite

Comparison between CNA and energetic electron precipitation: simultaneous observation by Poker Flat Imaging Riometer and NOAA satellite

A localised co-rotating auroral absorption event observed near noon using imaging riometer and EISCAT

GPS TEC technique for observation of the evolution of substorm particle precipitation

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