On the possible role of cusp/cleft precipitation in the formation of polar-cap patches

Walker, I. K.; Moen, J.; Kersley, L.; Lorentzen, D. A.

doi:10.1007/s005850050857

Cited by 37 publications

(48 citation statements)

References 23 publications

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“…In addition, there are many other types of localized aurora at high latitude separated from the auroral oval. Polar‐cap patches drift in the anti‐sunward direction [see, e.g., Walker et al , 1999]. Poleward moving auroral forms separate from the dayside auroral oval, move poleward for several minutes, and disappear inside the polar cap [ Sandholt et al , 1986].…”

Section: Introductionmentioning

confidence: 99%

Seasonal dependence of localized, high‐latitude dayside aurora (HiLDA)

et al. 2004

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[1] The FUV instrument on the IMAGE spacecraft frequently observes intense ultraviolet (UV) emissions from a localized High Latitude Dayside Aurora (HiLDA) poleward of the general auroral oval location [Frey et al., 2003a]. It has been shown that this aurora is entirely created by high-energy precipitating electrons, which have probably been accelerated in a quasi-static field-aligned electric potential. Here we extend the previous case study to an investigation of the HiLDA occurrence in the Northern Hemisphere over more than 2 years and compare it with the averaged solar wind plasma and interplanetary magnetic field (IMF) properties. HiLDA occurrence is strongly biased toward low solar wind density and IMF with positive B z , strong positive B y (clock angles around 70°), and negative B x components. Such IMF conditions are favorable for lobe reconnection in the Northern Hemisphere, and the creation of a dominating dusk convection cell with an upward field-aligned current in its center. Additionally, we investigate the seasonal occurrence of this phenomenon, which shows a maximum in the Northern Hemisphere during sunlit summer months and an almost complete absence in the dark winter. In contrast to the daylight-suppressed aurora in the auroral oval, the HiLDA cannot be the result of ionospheric feedback due to the stronger ionospheric conductance in sunlight. Instead, in agreement with ionospheric convection models, it is caused by the asymmetry of field-aligned currents in different seasons, which result from the different dipole tilt angles in summer and winter. We further discuss two scenarios for how the low solar wind density can enhance the field-aligned parallel potential over the dusk convection cell.

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Section: Introductionmentioning

confidence: 99%

Seasonal dependence of localized, high‐latitude dayside aurora (HiLDA)

et al. 2004

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“…Many different types of localized aurora at high latitude in the polar cap have been described. Polar‐cap patches occur predominantly during southward IMF, show enhanced optical red‐line emission from soft particle precipitation, and drift in the anti‐sunward direction [see, e.g., Walker et al , 1999]. Sandholt et al [1986] identified the ionospheric signatures of plasma transfer from the solar wind to the magnetosphere creating poleward moving auroral forms (PMAF).…”

Section: Introductionmentioning

confidence: 99%

Properties of localized, high latitude, dayside aurora

Frey

Immel

et al. 2003

J. Geophys. Res.

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[1] The FUV instrument on the IMAGE spacecraft frequently observes intense ultraviolet (UV) emission from a localized dayside region poleward of the general auroral oval location. One type of these emissions has been described as the signature of direct proton precipitation into the cusp after lobe reconnection during northward interplanetary magnetic field (IMF) and high solar wind dynamic pressure periods . Here we describe a completely different type of high latitude aurora, which does not show any signature of precipitating protons. It also occurs during northward IMF conditions however, only during periods of very low solar wind dynamic pressure. It occurs at a much higher geomagnetic latitude than the normal cusp location and only during periods of positive IMF B y . The intensity of the UV emission is somewhat anti-correlated with the solar wind dynamic pressure, much in contrast to the cusp emission. The brightness of the localized emission changes rapidly on time scales between 30 and 70 minutes without corresponding changes in solar wind properties. Coincident measurements by the FAST spacecraft verify that this is not the cusp, that ion precipitation is absent in these regions, and that strong precipitation of field-aligned accelerated electrons causes the aurora. We interpret this aurora as the optical signature of electron precipitation in the upward leg of a current system which closes the downward leg of the current system into the cusp in the ionosphere.

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“…However, our understanding of patch creation processes remains insufficient. A number of processes have been considered to explain the generation of patches on the dayside [ Carlson , ]: (1) the large‐scale reorientation of plasma convection near the cusp due to changes in the interplanetary magnetic field (IMF) B y and B z [ Anderson et al , ; Sojka et al , ]; (2) plasma reduction due to convection jets through frictional heating [ Rodger et al , ; Valladares et al , , ]; (3) the capturing of dense plasma in the sunlit region due to the expansion/contraction of the open/closed field line boundary by transient reconnection [ Lockwood and Carlson , ; Carlson et al , , ]; and (4) localized plasma enhancement through impact ionization due to cusp precipitation [ Walker et al , ; Smith et al , ; Oksavik et al , ]. However, it is still unclear as to which of these mechanisms is dominant.…”

Section: Introductionmentioning

confidence: 99%

Periodic creation of polar cap patches from auroral transients in the cusp

2016

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On 24 November 2012, an interval of polar cap patches was identified by an all‐sky airglow imager located near the dayside cusp. During the interval, the successive appearance of poleward moving auroral forms (PMAFs) was detected, which are known to represent ionospheric manifestations of pulsed magnetic reconnections at the dayside magnetopause. All of the patches observed during the interval appeared from these transient auroral features (i.e., there was a one‐to‐one correspondence between PMAFs and newly created baby patches). This fact strongly suggests that patches can be directly and seamlessly created from a series of PMAFs. The optical intensities of the baby patches were 100–150 R, which is slightly lower than typical patch luminosity on the nightside and may imply that PMAF‐induced patches are generally low density. The generation of such patches could be explained by impact ionization due to soft particle precipitation into PMAFs traces. In spite of the faint signature of the baby patches, two coherent HF radars of the SuperDARN network observed backscatter echoes in the central polar cap, which represented signatures of plasma irregularities associated with the baby patches. These indicate that patches created from PMAFs have the potential to affect the satellite communications environment in the central polar cap region.

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On the possible role of cusp/cleft precipitation in the formation of polar-cap patches

Cited by 37 publications

References 23 publications

Seasonal dependence of localized, high‐latitude dayside aurora (HiLDA)

Seasonal dependence of localized, high‐latitude dayside aurora (HiLDA)

Properties of localized, high latitude, dayside aurora

Periodic creation of polar cap patches from auroral transients in the cusp

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