Dayside reconnection under interplanetary magnetic field By‐dominated conditions: The formation and movement of bending arcs

Carter, Jennifer; Milan, S. E.; Fear, R. C.; Kullén, Anita; Hairston, M. R.

doi:10.1002/2014ja020809

Cited by 23 publications

(12 citation statements)

References 32 publications

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“…This model was augmented by Milan et al (2005) to show how magnetotail reconnection within a twisted tail (B Z > 0, B Y ≠ 0) could give rise to tongues of closed magnetic flux intruding into the polar cap from the nightside to form transpolar arcs. Carter et al (2015) explained how low-latitude magnetopause reconnection occurring for B Y -dominated IMF (B Z ≈ 0, B Y ≠ 0) gives rise to a class of polar cap auroras known as bending arcs. We have now elucidated the dynamics during purely northward IMF, completing our understanding of the ECPC response of the magnetosphere to solar wind coupling under all IMF clock angle regimes.…”

Section: Discussionmentioning

confidence: 99%

“…Østgaard et al, 2003). "Bending arcs" are auroral features that protrude into the polar cap from the dawnside or duskside auroral oval and progress over time toward the nightside, which are now thought to be created by low-latitude magnetopause reconnection, in a manner similar to poleward-moving auroral forms associated with flux transfer events, during B Y -dominated IMF (Carter et al, 2015;Kullen et al, 2002Kullen et al, , 2015. Finally, polar cap arcs have also been identified as the poleward edge of a thickened plasma sheet in the dawn and/or dusk sectors (Meng, 1981;Newell et al, 2009), that is, at the polar cap boundary of the HCAs, the subject of this paper.…”

Section: Introductionmentioning

confidence: 99%

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Dual‐Lobe Reconnection and Horse‐Collar Auroras

et al. 2020

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We propose a mechanism for the formation of the horse-collar auroral configuration during periods of strongly northward interplanetary magnetic field (IMF), invoking the action of dual-lobe reconnection (DLR). Auroral observations are provided by the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) satellite and spacecraft of the Defense Meteorological Satellite Program (DMSP). We also use ionospheric flow measurements from DMSP and polar maps of field-aligned currents (FACs) derived from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE). Sunward convection is observed within the dark polar cap, with antisunward flows within the horse-collar auroral region, together with the NBZ FAC distribution expected to be associated with DLR. We suggest that newly closed flux is transported antisunward and to dawn and dusk within the reverse lobe cell convection pattern associated with DLR, causing the polar cap to acquire a teardrop shape and weak auroras to form at high latitudes. Horse-collar auroras are a common feature of the quiet magnetosphere, and this model provides a first understanding of their formation, resolving several outstanding questions regarding the nature of DLR and the magnetospheric structure and dynamics during northward IMF. The model can also provide insights into the trapping of solar wind plasma by the magnetosphere and the formation of a low-latitude boundary layer and cold, dense plasma sheet. We speculate that prolonged DLR could lead to a fully closed magnetosphere, with the formation of horse-collar auroras being an intermediate step. Plain Language Summary During quiet geomagnetic conditions, the global distribution of auroras can acquire a "horse-collar" configuration, in which regions of weak auroral emission appear at dawn and dusk poleward of the main auroral oval. We propose a new model to explain the formation of this configuration, which provides new insights into magnetospheric dynamics during periods of northward-directed interplanetary magnetic field. To support our proposal, we use observations of the auroras, ionospheric convection, and estimations of the pattern of electrical currents flowing between the ionosphere and magnetosphere from a suite of spacecraft. Our proposed model resolves a 40-year-old question regarding the nature of the horse-collar auroras and many other aspects of magnetospheric dynamics.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Dual‐Lobe Reconnection and Horse‐Collar Auroras

et al. 2020

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“…Similarly, studies of the distribution of FTE signatures in the ionosphere [e.g., Lockwood and Davis, 1996;Provan et al, 1999;Milan et al, 2000;Wild et al, 2005;Fear et al, 2008Fear et al, , 2009Fear et al, , 2012Carter et al, 2015] have demonstrated that reconnection signatures can be observed over a wide range of magnetic local times (MLT) and that there appears to be an IMF B Y control of the location. Such studies have also shown that the FTE signatures can differ considerably in local time extent, from small scales of order a few 100 km [e.g., Oksavik et al, 2004Oksavik et al, , 2005 to larger scales encompassing 4-5 h of MLT [e.g., Lockwood et al, 1990].…”

Section: 1002/2015ja022012mentioning

confidence: 98%

What controls the local time extent of flux transfer events?

et al. 2016

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Flux transfer events (FTEs) are the manifestation of bursty and/or patchy magnetic reconnection at the magnetopause. We compare two sequences of the ionospheric signatures of flux transfer events observed in global auroral imagery and coherent ionospheric radar measurements. Both sequences were observed during very similar seasonal and interplanetary magnetic field (IMF) conditions, though with differing solar wind speed. A key observation is that the signatures differed considerably in their local time extent. The two periods are 26 August 1998, when the IMF had components BZ≈−10 nT and BY≈9 nT and the solar wind speed was VX≈650 km s−1, and 31 August 2005, IMF BZ≈−7 nT, BY≈17 nT, and VX≈380 km s−1. In the first case, the reconnection rate was estimated to be near 160 kV, and the FTE signatures extended across at least 7 h of magnetic local time (MLT) of the dayside polar cap boundary. In the second, a reconnection rate close to 80 kV was estimated, and the FTEs had a MLT extent of roughly 2 h. We discuss the ramifications of these differences for solar wind‐magnetosphere coupling.

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“…Northern Hemisphere summer is taken for all values that occur during May, June, and July, and winter results compose of values that occur in November, December, and January. A similar method was employed in Carter et al (2015) to parameterize FACs, as obtained from the Active Magnetosphere and Planetary Electrodynamic Response Experiment (AMPERE). We examine the parameterized SSUSI products with respect to the FACs.…”

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confidence: 99%

Height‐Integrated Ionospheric Conductances Parameterized By Interplanetary Magnetic Field and Substorm Phase

et al. 2020

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An understanding of ionospheric conductances is important for models of large-scale dynamics in the Earth's magnetosphere. We parameterize height-integrated Pedersen and Hall conductances in the ionosphere, derived from images of auroral emissions obtained by the Defense Meteorological Satellite Programme low-altitude orbiting spacecraft, under different interplanetary and solar wind conditions. For the dayside, conductances are parameterized by interplanetary magnetic field clock angle and magnitude, and by season. These dayside conductances are compared to distributions of field-aligned currents determined from measurements of the Active Magnetosphere and Planetary Electrodynamic Response Experiment. We use these currents to spatially determine a return flow region. We find that the return flow regions exhibit marginally larger conductances than those observed in the polar cap. Conductances in summer exceed those in winter for both the return flow and polar cap regions, on average by a factor of 1.2. On the nightside, we track changes in height-integrated conductance across the Southern Hemisphere polar regions during an average substorm, following a substorm onset list derived from the SuperMAG database. Mean conductances peak approximately 0.75 hr after substorm onset, with maximum conductances seen in the 23 hr magnetic local time sector. Plain Language Summary Low-altitude spacecraft are able to build up images of aurora in the polar regions with low temporal resolution. Using a combination of these images taken in different wavebands, and after applying a model of atmospheric conditions, we can derive parameters such as ionospheric conductance, integrated along the line of sight from the spacecraft. Knowledge of conductances in the high-latitude polar regions is important for our understanding of the large-scale dynamics of the Earth's magnetosphere. We divide our results into two sections. The first section explores conductances in the dayside Northern Hemisphere under the effects of the incoming solar wind and interplanetary magnetic field. We compare these conductances to large-scale patterns of ionospheric currents derived from a separate constellation of satellites. The currents can be used to define certain polar regions, and we compare conductances between these regions. The second section examines conductances under different phases of a substorm, when the magnetosphere is rearranged under the influence of particular driving conditions in the incoming solar wind. The behavior of the conductances is consistent with known patterns of substorm progression, and we show that peak conductances are seen half an hour after substorm onset.

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Dayside reconnection under interplanetary magnetic field B_y‐dominated conditions: The formation and movement of bending arcs

Cited by 23 publications

References 32 publications

Dual‐Lobe Reconnection and Horse‐Collar Auroras

Dual‐Lobe Reconnection and Horse‐Collar Auroras

What controls the local time extent of flux transfer events?

Height‐Integrated Ionospheric Conductances Parameterized By Interplanetary Magnetic Field and Substorm Phase

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