Drifting F-Layer Patches over the Magnetic Pole.

McEwen, D. J.; Harris, D. P.; MacDougall, J. W.; Grant, I. F.

doi:10.5636/jgg.47.527

Cited by 16 publications

(9 citation statements)

References 11 publications

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“…As seen in Figure 1, the observatory is approximately 2 ø of magnetic latitude farther from the dayside cusp at 0600 UT than it is 12 hours later at 1800 UT because of its offset from the magnetic pole. This increased distance is equivalent to some 10-20 min of patch travel time, assuming drift speeds from 200-400 m/s [McEwen et al, 1995]. Schunk and Sojka [1987] calculate the total lifetime of such ionospheric structures in the winter polar cap to be about 11 hours (considering an ionization patch initially 10 times the background density and its decay to be only 10% above background).…”

Section: Temporal Trends In Intensitymentioning

confidence: 99%

Occurrence patterns of F layer patches over the north magnetic pole

McEwen¹,

Harris²

1996

Radio Science

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An analysis of some 523 F layer patches observed over Eureka, Northwest Territories, Canada (89° corrected geomagnetic latitude) during the four winters from 1990–1991 to 1993–1994 has given some definitive results on their occurrence patterns and characteristics. They are observed on average about 25% of the time and are seen at all hours of the day but with more present in the local evening hours than the morning hours. For the 182 patches for which interplanetary magnetic field data were available, 143 of the patches occurred with Bz negative and 39 with Bz positive. In most of the latter cases, Bz was either near zero or had changed to positive only 30–120 min prior to the patch observation. The average optical emission intensity of the patches over the 4‐year period was 150 R of 630 nm and 55 R of 558 nm. The excitation is by dissociation recombination of the oxygen ion with a branching ratio O[1S]/O[1D] of 0.37. They were on average less bright during the midnight hours (by about 50 R) than through the midday, a fact perhaps due to the offset of the Eureka station from the magnetic pole. The average patch intensity has decreased from 190 R in 1990–1991 to 120 R in 1993–1994 as solar activity has declined. While patch sizes in the dawn‐dusk direction varied up to >2000 km, the average cross‐sectional dimension was 500–600 km.

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Section: Temporal Trends In Intensitymentioning

confidence: 99%

Occurrence patterns of F layer patches over the north magnetic pole

McEwen¹,

Harris²

1996

Radio Science

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“…The term "polar patch" denotes a discrete plasma density enhancement in the polar F region, of order 100-1000 km in horizontal extent, that convects through the polar cap under the influence of the magnetospheric electric field and may be variously observed by means of scintillation of transionospheric radio signals [Weber et al, 1984;Basu et al, 1994], radiowave probing [Buchau et al, 1985;l/alladares et al, 1994;Rodger et al, 1994], in situ plasma density measurements by satellite-borne sensors [Coley and Heelis, 1994], and [Oil optical emission at 630.0 nm and 557.7 nm [Weber et al, 1984[Weber et al, , 1986McEwen et al, 1995]. Suggested sources of the enhanced plasma densities include the sunlit F region equatorward of the cusp [Anderson et al, 1988;Lockwood and Carlson, 1992] and the precipitating particle impact-induced ionization in the cusp [Rodger et al, 1994].…”

Section: Introductionmentioning

confidence: 99%

Polar patches and the “tongue of ionization”

Steele¹,

Cogger²

1996

Radio Science

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Optical images of [O I] 630.0‐nm emission from drifting F region polar patches acquired with a sensitive all‐sky imager have been analyzed to infer the ionospheric convection velocity over a period of 9 hours on December 8, 1993. The drift vectors agree well in both direction and magnitude with simultaneous measurements from a nearby digital ionosonde. The delay between interplanetary magnetic field By changes measured at IMP 8 and changes in the convection direction at the pole is estimated. A montage of the optical emission from the patches observed over the period is presented to illustrate the range of optical patch shapes, sizes, and spacings observed.

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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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Drifting F-Layer Patches over the Magnetic Pole.

Cited by 16 publications

References 11 publications

Occurrence patterns of F layer patches over the north magnetic pole

Occurrence patterns of F layer patches over the north magnetic pole

Polar patches and the “tongue of ionization”

Interplanetary magnetic field control of polar patch velocity

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