Polar patches observed by ESR and their possible origin in the cusp region

Smith, A. M.; Pryse, S. E.; Kersley, L.

doi:10.1007/s005850000273

Cited by 5 publications

(6 citation statements)

References 9 publications

(11 reference statements)

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“…Note that intense summertime electron density enhancements around magnetic noon have also been reported in recent case studies (Smith et al, 2000;Sims et al, 2005). In a case with southward IMF conditions, Smith et al (2000) concluded that the origin of electron density enhancements observed by ESR was soft-particle precipitation in the cusp region.…”

Section: Soft Particle Precipitation In Cusp Regionsupporting

confidence: 62%

“…In a case with southward IMF conditions, Smith et al (2000) concluded that the origin of electron density enhancements observed by ESR was soft-particle precipitation in the cusp region. In another event also under southward IMF conditions, however, Sims et al (2005) argued that plasma convection may play a more important role than soft-particle precipitation in the formation of the summertime Tongue-ofIonization (TOI).…”

Section: Soft Particle Precipitation In Cusp Regionmentioning

confidence: 95%

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Climatological features of electron density in the polar ionosphere from long-term observations of EISCAT/ESR radar

Cai

Fan

et al. 2007

Ann. Geophys.

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Abstract. In this paper, climatological features of the polar F2-region electron density (N e ) are investigated by means of statistical analysis using long-term observations from the European Incoherent Scatter UHF radar (called EISCAT in the following) and the EISCAT Svalbard radar (ESR) during periods of quiet to moderate geomagnetic activity. Fieldaligned measurements by the EISCAT and ESR radars operating in CP-1 and CP-2 modes are used in this study, covering the years 1988-1999 for EISCAT and 1999-2003 for ESR. The data are sorted by season (equinox, summer and winter) and solar cycle phase (maximum, minimum, rising and falling). Some novel and interesting results are presented as follows: (1) The well-known winter anomaly is evident during the solar maximum at EISCAT, but it dies out at the latitude of the ESR; (2) The daytime peaks of N e at EISCAT for all seasons during solar maximum lag about 1-2 h behind those at ESR, with altitudes about 10-30 km lower. (3) In addition to the daytime peak, it is revealed that there is another peak just before magnetic midnight at ESR around solar maximum, especially in winter and at equinox. The daytime ionization peak around magnetic noon observed by ESR can be attributed to soft particle precipitation in the cusp region, whereas the pre-midnight N e maximum seems likely to be closely related to substorm events which frequently break out during that time sector, in particular for the winter case. (4) Semiannual variations are found at EISCAT during solar minimum and the falling phase of the solar cycle; at the rising phase, however, the EISCAT observations show no obvious seasonal variations.

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Section: Soft Particle Precipitation In Cusp Regionsupporting

confidence: 62%

Section: Soft Particle Precipitation In Cusp Regionmentioning

confidence: 95%

Climatological features of electron density in the polar ionosphere from long-term observations of EISCAT/ESR radar

Cai

Fan

et al. 2007

Ann. Geophys.

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“…MacDougall, private communication, 2002). They are created either in the sunlit F-region equatorward of the cusp or by precipitation in the cusp and are subsequently convected across the polar cap [Lockwood and Carlson, 1992;Valladares et al, 1994;McEwen et al, 1995;Ma and Schunk, 1997;Walker et al, 1999;Smith et al, 2000]. The patches have been studied by using both ground-based instruments (such as optical imagers [Steele and Cogger, 1996] and radars ) and satellite-based in situ detectors [Coley and Heelis, 1998].…”

Section: Introductionmentioning

confidence: 99%

Interplanetary magnetic field control of polar patch velocity

2003

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[1] Polar patch drift speed and direction have been investigated using oxygen 630 nm images recorded by an all-sky imager at Eureka (89°CGM), Canada over an extended period, January and December 1998. Statistical studies showed that (1) the interplanetary magnetic field (IMF, from the WIND satellite) B z component linearly controls the patch speed when B z is between À7.5 nT and 0 nT. The speed tends to saturate when B z is less than À7.5nT due to nonlinear coupling between the solar wind and the magnetosphere. The average patch speed of 600 m/s is in agreement with results from earlier studies; (2) The IMF B y or the IMF clock angle has a clear control of the patch drift direction as determined by the drift azimuth angle. When jB y j is less than 7.5nT, the drift azimuth angle is linearly and positively correlated with B y . For a large jB y j (>7.5 nT), the positive correlation is replaced by a negative correlated linear relation and the azimuth angle tends to turn towards 180 degrees; that is, the patches drift in an antisunward direction. These IMF B y effects can be qualitatively explained by the northern winter polar ionospheric convection models developed by Weimer [1995] and Hairston and Heelis [1990]. Results from our quantitative study on the IMF control of polar patch speed and drift direction provide constraints for the development of future polar ionospheric convection models.

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“…Valladares et al, 1994;Walker et al, 1999;Smith, et al, 2000). Most of these observations, however, are not related to magnetic storms.…”

Section: Introductionmentioning

confidence: 98%

Positive storm effects in the dayside polar ionospheric F-region observed by EISCAT and ESR during the magnetic storm of 15 May 1997

Cai

Liu

et al. 2002

Ann. Geophys.

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Abstract. EISCAT/ESR radar data and in situ FAST and PO-LAR satellite observations are coordinately analyzed to investigate positive ionospheric storm effects in the dayside upper F-region in both the polar cap and the auroral oval during the magnetic storm of 15 May 1997. An ionization enhancement, lasting for about 2.5 h, appeared first over the EIS-CAT site around magnetic noon; about one hour later, a similar ionization enhancement was also seen over ESR. During the concerned time period ion energy spectra measured on board FAST show clearly continuous energy-latitude dispersion when the satellite passed by over the EISCAT latitude. This implies that EISCAT was located under the polar cusp region which was highly active, and expanded greatly equatorwards due to magnetopause reconnections during longlasting southward IMF. Simultaneously, soft particles of the magnetosheath precipitated into the F-region ionosphere and caused the positive storm effects over EISCAT. The coincident increase in electron temperature at EISCAT gives additional evidence for soft particle precipitation. Consistently, POLAR UV images show strong dayside aurora extending to as low as 62 • N magnetic latitude. The ionization enhancement over ESR, however, seems not to be caused by local particle precipitation, evidenced by a lack of enhanced electron temperature. The observed plasma convection velocity and data-fitted convection patterns by AMIE suggested that it is likely to be a polar patch originating from the cusp region and traveling to the ESR site.

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Polar patches observed by ESR and their possible origin in the cusp region

Cited by 5 publications

References 9 publications

Climatological features of electron density in the polar ionosphere from long-term observations of EISCAT/ESR radar

Climatological features of electron density in the polar ionosphere from long-term observations of EISCAT/ESR radar

Interplanetary magnetic field control of polar patch velocity

Positive storm effects in the dayside polar ionospheric F-region observed by EISCAT and ESR during the magnetic storm of 15 May 1997

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