Patches in the polar ionosphere: UT and seasonal dependence

Sojka, J. J.; Bowline, M. D.; Schunk, R. W.

doi:10.1029/93ja03327

Cited by 102 publications

(154 citation statements)

References 29 publications

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“…This study extends the work of Bowline et al [ 1993] and Sojka et al [1993aSojka et al [ , 1994 by presenting the UT and seasonal dependence of patches as might be seen via an observer's localized view from a ground station rather than the theoretical "global" presentation made in the earlier two papers. Three stations are considered: Eureka (Canada), Sondrestrom (Greenland), and NyAlesund (Svalbard).…”

Section: Paper Number 96rs00236supporting

confidence: 74%

“…Our prior patch studies [Sojka et al, 1993a[Sojka et al, , 1994 showed that the F region polar cap patches were associated with the tongue of ionization, which was the plasma source for the patches. In these studies the chopping of the tongue into patches was due to temporal changes in the convection electric field; these changes in turn were associated with IMF By.…”

Section: Patch-to-background Ratiomentioning

confidence: 99%

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Relationship of theoretical patch climatology to polar cap patch observations

Bowline¹,

Sojka²,

Schunk³

1996

Radio Science

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Abstract. During a southward orientation of the interplanetary magnetic field (IMF), patches are often observed moving antisunward across the polar cap. In saying "patches" we refer to structures in which the F region electron densities are enhanced relative to lower background levels; we do not in this paper consider patches which are observed optically (see J. J. Sojka et al., Ambiguity in identificiation of polar cap F region patches, submitted to the Journal of Atmospheric and Terrestrial Physics, 1995). The patches can be modeled by a process which involves the "chopping up" of the tongue of ionization (TOI) [Sojka et al., 1993a]. Various mechanisms for chopping the TOI have been suggested; our preferred method is to introduce temporal changes in the convection electric field pattern. In any case the present study is quite independent of any particular mechanism, so long as the TOI is considered to be the source of the patches. In this study we have used the Utah State University Time-Dependent Ionospheric Model (TDIM) to model the TOI for various IMF By orientations. In our simulations the location of the TOI in the polar cap is mainly determined by the IMF By component, and hence the patch locations are also expected to be By dependent. This suggests that a polar ground-based instrument may not see patches even when they are present in the polar ionosphere. This is because the typical field of view of a ground-based instrument, such as an all-sky camera, covers less than 10% of the polar region. The TDIM simulation results were used to predict the By dependence of patches that different ground-based sites would observe. Eureka (Canada) at the magnetic pole is predicted not to observe patches for southward IMF conditions if the By component is strongly negative. Sondrestrom (Greenland) and NyAlesund (Svalbard), although at similar cusp latitudes, are expected to see quite different diurnal responses to patches. At Sondrestrom, patches are seen at noon in winter; both sites should see them in the premidnight sector. These model predictions are the "groundwork" for detailed patch observation-model comparisons at all three sites. IntroductionBuchau et al. [1983] have shown that polar F region density structures come in two main forms, that is, patches and sun-aligned arcs. The patches were found to correlate with times of strong geomagnetic activity. Today we also know that the patches form under southward interplanetary magnetic field (IMF) conditions. Weber et al. [1984] showed that the patches were transported into the polar cap rather than formed locally by precipitation. These observations show that the patches convect across the polar cap at the prevailing convection speed. This convection is predominantly antisunward for southward IMF conditions. The convection can be traced backward, through the cusp, into a dayside region equatorward of the auroral ionosphere. Hence the origin of the patches could be equatorward of the cusp region, in the cusp region, or a combination of both. Weber et al. [1984, ...

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Section: Paper Number 96rs00236supporting

confidence: 74%

Section: Patch-to-background Ratiomentioning

confidence: 99%

Relationship of theoretical patch climatology to polar cap patch observations

Bowline¹,

Sojka²,

Schunk³

1996

Radio Science

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“…They have been observed in summer and winter (Buchau and Reinisch, 1991) and have been seen to form in geomagnetically conjugate regions (Rodger et al, 1994a). The modelling study of Sojka et al (1994) indicated the presence of patches in all seasons with their occurrence modulated by UT. Pederson et al (1998) observed patch structures on horizontal scales of some 200±300 km using the Sondrestrom incoherent scatter radar, while Walker et al (1999) imaged a patch-like structure of latitudinal dimension some 2.5°using radio tomography.…”

Section: Introductionmentioning

confidence: 95%

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

2000

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Abstract. Observations by the EISCAT Svalbard radar in summer have revealed electron density enhancements in the magnetic noon sector under conditions of IMF Bz southward. The features were identi®ed as possible candidates for polar-cap patches drifting anti-Sunward with the plasma¯ow. Supporting measurements by the EISCAT mainland radar, the CUTLASS radar and DMSP satellites, in a multi-instrument study, suggested that the origin of the structures lay upstream at lower latitudes, with the modulation in density being attributed to variability in soft-particle precipitation in the cusp region. It is proposed that the variations in precipitation may be linked to changes in the location of the reconnection site at the magnetopause, which in turn results in changes in the energy distribution of the precipitating particles.

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“…For example, Sojka et al (1993Sojka et al ( , 1994 showed that the TOI can be modulated by season and UT and broken up into discrete patches by temporal changes in the plasma convection pattern due to variations in the IMF B y . Early modelling work by Robinson et al (1985) indicated that the evening side boundary blob may be formed by polar cap plasma drifting out of the polar cap and into the nightside sector where it is drawn into a latitudinally confined but longitudinally extended enhancement.…”

Section: Introductionmentioning

confidence: 99%

Modelling the tongue-of-ionisation using CTIP with SuperDARN electric potential input: verification by radiotomography

et al. 2009

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Abstract. Electric potential patterns obtained by the SuperDARN radar network are used as input to the Coupled Thermosphere-Ionosphere-Plasmasphere model, in an attempt to improve the modelling of the spatial distribution of the ionospheric plasma at high latitudes. Two case studies are considered, one under conditions of stable IMF B z negative and the other under stable IMF B z positive. The modelled plasma distributions are compared with sets of wellestablished tomographic reconstructions, which have been interpreted previously in multi-instrument studies. For IMF B z negative both the model and observations show a tongueof-ionisation on the nightside, with good agreement between the electron density and location of the tongue. Under B z positive, the SuperDARN input allows the model to reproduce a spatial plasma distribution akin to that observed. In this case plasma, unable to penetrate the polar cap boundary into the polar cap, is drawn by the convective flow in a tongue-of-ionisation around the periphery of the polar cap.

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Patches in the polar ionosphere: UT and seasonal dependence

Cited by 102 publications

References 29 publications

Relationship of theoretical patch climatology to polar cap patch observations

Relationship of theoretical patch climatology to polar cap patch observations

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

Modelling the tongue-of-ionisation using CTIP with SuperDARN electric potential input: verification by radiotomography

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