Hook-shaped arcs in dayside polar cap and their relation to the IMF

Gusev, M.G.; Трошичев, О. А.

doi:10.1016/0032-0633(86)90087-5

Cited by 34 publications

(25 citation statements)

References 19 publications

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“…Bending arcs form such that the dayside part of the arc moves poleward, while the nightside end does not show a considerable motion such that this auroral feature resembles a hook‐shaped arc sometime after its formation. Note that Kullen et al 's [] bending arcs should not be confused with so‐called hook‐shaped transpolar arcs that have been reported occasionally [e.g., Meng and Akasofu , ; Ismail and Meng , ; Gusev and Troshichev , ], or the bending arc reported by Fear and Milan []. None of those reported cases show the characteristic development of the bending arcs identified in Kullen et al [] and are thus most probably not the same auroral feature.…”

Section: Introductionmentioning

confidence: 93%

The statistical difference between bending arcs and regular polar arcs

et al. 2015

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In this work, the Polar UVI data set by Kullen et al. (2002) of 74 polar arcs is reinvestigated, focusing on bending arcs. Bending arcs are typically faint and form (depending on interplanetary magnetic field (IMF) By direction) on the dawnside or duskside oval with the tip of the arc splitting off the dayside oval. The tip subsequently moves into the polar cap in the antisunward direction, while the arc's nightside end remains attached to the oval, eventually becoming hook‐shaped. Our investigation shows that bending arcs appear on the opposite oval side from and farther sunward than most regular polar arcs. They form during By‐dominated IMF conditions: typically, the IMF clock angle increases from 60 to 90° about 20 min before the arc forms. Antisunward plasma flows from the oval into the polar cap just poleward of bending arcs are seen in Super Dual Auroral Radar Network data, indicating dayside reconnection. For regular polar arcs, recently reported characteristics are confirmed in contrast to bending arcs. This includes plasma flows along the nightside oval that originate close to the initial arc location and a significant delay in the correlation between IMF By and initial arc location. In our data set, the highest correlations are found with IMF By appearing at least 1–2 h before arc formation. In summary, bending arcs are distinctly different from regular arcs and cannot be explained by existing polar arc models. Instead, these results are consistent with the formation mechanism described in Carter et al. (2015), suggesting that bending arcs are caused by dayside reconnection.

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Section: Introductionmentioning

confidence: 93%

The statistical difference between bending arcs and regular polar arcs

et al. 2015

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“…These arcs are about 100 km wide, extend 1000-2000 km in the sunward direction, and have an intensity range of about 50 to 1000 R, although most are ∼100 R. These arcs occur under similar IMF conditions as the moving arcs and the oval-aligned arcs discussed above and have a strong dependence on positive IMF B z . The motion of these small-scale Sun-aligned arcs is controlled by IMF B y in the same way as large-scale transpolar arcs (Gusev and Troshichev, 1986;Cumnock et al, 1997;Kullen et al, 2002). It has been proposed that small-scale Sun-aligned arcs are embedded in polar rain and thus occur on open field lines (e.g., Carlson and Cowley, 2005, and references therein).…”

Section: Polar Arcs During Northward Imfmentioning

confidence: 99%

“…They are hook-shaped poleward-moving arcs where one end of the arc separates from the main oval and moves toward the other side of the oval whereas the other end remains fixed (Ismail and Meng, 1982;Murphree et al, 1982;Gusev and Troshichev, 1986). Bending arcs occur during average IMF conditions with IMF B z fluctuating around zero and for slightly higher solar wind velocities than average.…”

Section: Polar Arcs During Northward Imfmentioning

confidence: 99%

Small-scale characteristics of extremely high latitude aurora

et al. 2009

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Abstract. We examine 14 cases of an interesting type of extremely high latitude aurora as identified in the precipitating particles measured by the DMSP F13 satellite. In particular we investigate structures within large-scale arcs for which the particle signatures are made up of a group of multiple distinct thin arcs. These cases are chosen without regard to IMF orientation and are part of a group of 87 events where DMSP F13 SSJ/4 measures emissions which occur near the noonmidnight meridian and are spatially separated from both the dawnside and duskside auroral ovals by wide regions with precipitating particles typical of the polar cap. For 73 of these events the high-latitude aurora consists of a continuous region of precipitating particles. We focus on the remaining 14 of these events where the particle signatures show multiple distinct thin arcs. These events occur during northward or weakly southward IMF conditions and follow a change in IMF B y . Correlations are seen between the field-aligned currents and plasma flows associated with the arcs, implying local closure of the FACs. Strong correlations are seen only in the sunlit hemisphere. The convection associated with the multiple thin arcs is localized and has little influence on the large-scale convection. This also implies that the sunward flow along the arcs is unrelated to the overall ionospheric convection.

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“…Thus in a more general context the sharpness of the inner edges (i.e., the "bars") of a horse-collar aurora will depend on the size of the gradients in the electric field; and on the dawnside, the magnitude of the gradient will determine the brightness of the emission feature at the edge. Some observations (GUSEV and TROSCHICHEV, 1986) and modeling (CORNWALL, 1985;REIFF and BURCH,1985) have associated dawnside polar cap arcs in the northern (southern) hemisphere with negative (positive) IMF By. Our observations of the dawn edge feature as well as the feature observed at "l421 UT are consistent with these findings.…”

Section: Large Scale Convection Patternmentioning

confidence: 99%