Production of polar cap electron density patches by transient magnetopause reconnection

Lockwood, Mike; Carlson, H. C.

doi:10.1029/92gl01993

Cited by 191 publications

(257 citation statements)

References 6 publications

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“…The authors believe that this is probably related to the fact that the IMF B y component was positive for 71% of the intervals presented in this study (see Provan et al, 1999), but further discussion on this subject is beyond the scope of our current study, and will await improved data coverage. It is possible that the observed seasonal variation of PIFs is related to the creation of polar cap patches of enhanced plasma density during¯ux transfer events (Lockwood and Carlson, 1992). Such polar cap patches are produced by solar photoionisation on the dayside and would thus exhibit variations with solar luminosity.…”

Section: Seasonal Variationsmentioning

confidence: 99%

Statistical observations of the MLT, latitude and size of pulsed ionospheric flows with the CUTLASS Finland radar

Provan

Yeoman

1999

Ann. Geophys.

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Abstract. A study has been performed on the occurrence of pulsed ionospheric¯ows as detected by the CUTLASS Finland HF radar. These¯ows have been suggested as being created at the ionospheric footprint of newly-reconnected ®eld lines, during episodes of magnetic¯ux transfer into the terrestrial magnetosphere (¯ux transfer events or FTEs). Two years of both hightime resolution and normal scan data from the CUT-LASS Finland radar have been analysed in order to perform a statistical study of the extent and location of the pulsed ionospheric¯ows. We note a great similarity between the statistical pattern of the coherent radar observations of pulsed ionospheric¯ows and the traditional low-altitude satellite identi®cation of the particle signature associated with the cusp/cleft region. However, the coherent scatter radar observations suggest that the merging gap is far wider than that proposed by the Newell and Meng model. The new model for cusp low-altitude particle signatures, proposed by Lockwood and Onsager and Lockwood provides a uni®ed framework to explain the dayside precipitation regimes observed both by the low-altitude satellites and by coherent scatter radar detection.

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Section: Seasonal Variationsmentioning

confidence: 99%

Statistical observations of the MLT, latitude and size of pulsed ionospheric flows with the CUTLASS Finland radar

Provan

Yeoman

1999

Ann. Geophys.

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“…Plasma density gradients drive the E x B instability thought to be responsible for the scintillation-producing smaller-scale density irregularities associated with patches [Weber et al, 1984;Tsunoda, 1988, and references therein] and have been used as a criterion for patch identification [Coley and Heelis, 1995]. Observations of plasma density gradients at patch edges and in other regions of the highlatitude ionosphere have also been used to examine the feasibility of some proposed patch creation scenarios, such as polar cap expansion across the terminator region [Lockwood and Carlson, 1992 . � �\ � :…”

Section: Introductionmentioning

confidence: 99%

Incoherent scatter radar observations of horizontal F region plasma structure over Sondrestrom, Greenland, during polar cap patch events

Pedersen¹,

Fejer²,

Doe³

et al. 1998

Radio Science

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Abstract. Horizontal profiles of F region plasma density from the Sondrestrom incoherent scatter radar facility (66.99øN latitude, 50.95øW longitude) are used to determine the large-scale structure and statistical distribution of ionospheric plasma during polar cap patch events. Largescale latitudinal gradients in average electron density were observed coincident with primarily meridional flow, suggesting the plasma decayed with time constants of the order of 1 hour. Plasma density distributions for each of the five nights in the data set were characterized by peaks at low plasma densities representing the background plasma, with the presence of patches typically resulting in a "tail" in the high-density regime of the distribution. Observed patch sizes averaged -400 km, with a most probable value in the 200-to 300-km range. Patch edges were found to be characterized by gradient scale lengths of-100 km, significantly smaller than the typical 400-km scale length of background gradients. Gradients interior to patches were intermediate in magnitude, with average scale lengths of-275 km. The general characteristics of the patches in these data, including their occurrence in latitude and local time, are consistent with an origin in a tongue of ionization. The observed distributions of patch scale sizes and density enhancement ratios verify the general features of earlier results from satellite measurements. The relatively short decay time constants inferred from this data set suggest that patches do not survive long enough to make multiple passes through the convection pattern and that their impact as a source of auroral zone blobs may be mostly limited to the nightside ionosphere.

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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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Production of polar cap electron density patches by transient magnetopause reconnection

Cited by 191 publications

References 6 publications

Statistical observations of the MLT, latitude and size of pulsed ionospheric flows with the CUTLASS Finland radar

Statistical observations of the MLT, latitude and size of pulsed ionospheric flows with the CUTLASS Finland radar

Incoherent scatter radar observations of horizontal F region plasma structure over Sondrestrom, Greenland, during polar cap patch events

Interplanetary magnetic field control of polar patch velocity

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