High spatial and temporal resolution observations of the ionospheric cusp
TL;DR: In this article, the Halley PACE HF radar has been operated in a new mode to provide very high time (10 s) and space (15 km) resolution measurements of the iono-spheric signatures of the cusp and the low-latitude boundary layer.
Abstract: The Halley PACE HF radar has been operated in a new mode to provide very high time (10 s) and space (15 km) resolution measurements of the iono-spheric signatures of the cusp and the low-latitude boundary layer. The first data show that the iono-spheric signature of flux transfer events occur up to 300 km equatorward of regions showing the HF characteristics of the ionospheric cusp. Whilst larger flux transfer events are seen, on average, every 7 min, many much smaller and short-duration events have been identified. On one occasion DMSP data have been used to show that at least four flux transfer events are occurring simultaneously at the edge of the cusp over 2 h of MLT. There is strong, but not conclusive evidence, that reconnection at the magnetopause is both intermittent and patchy. These data also suggest that flux transfer events can be a significant contributor to the cross-polar cap potential.
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Natural Environment Research Council1, University of Leicester2, University of Saskatchewan3, Johns Hopkins University Applied Physics Laboratory4, La Trobe University5, Nagoya University6, University of KwaZulu-Natal7, National Institute of Polar Research8, Centre national de la recherche scientifique9
TL;DR: The Super Dual Auroral Radar Network (SuperDARN) as discussed by the authors has been operating as an international co-operative organization for over 10 years and has been successful in addressing a wide range of scientific questions concerning processes in the magnetosphere, ionosphere, thermosphere, and mesosphere, as well as general plasma physics questions.
Abstract: The Super Dual Auroral Radar Network (SuperDARN) has been operating as an international co-operative organization for over 10 years. The network has now grown so that the fields of view of its 18 radars cover the majority of the northern and southern hemisphere polar ionospheres. SuperDARN has been successful in addressing a wide range of scientific questions concerning processes in the magnetosphere, ionosphere, thermosphere, and mesosphere, as well as general plasma physics questions. We commence this paper with a historical introduction to SuperDARN. Following this, we review the science performed by SuperDARN over the last 10 years covering the areas of ionospheric convection, field-aligned currents, magnetic reconnection, substorms, MHD waves, the neutral atmosphere, and E-region ionospheric irregularities. In addition, we provide an up-to-date description of the current network, as well as the analysis techniques available for use with the data from the radars. We conclude the paper with a discussion of the future of SuperDARN, its expansion, and new science opportunities.
690 citations
Cites background from "High spatial and temporal resolutio..."
...Early studies estimated the typical recurrence time between bursts as being *7–8 mins (Pinnock et al. 1995; Provan et al. 1998) closely matching what had been identified as the average recurrence time for magnetopause FTEs (Rijnbeek et al. 1984; Lockwood and Wild 1993)....
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...Numerous SuperDARN studies have shown that convection flow enhancements of this type are a regular feature of the dayside cusp ionosphere (Pinnock et al. 1995; Rodger and Pinnock 1997; Provan and Yeoman 1999; Provan et al. 1999)....
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TL;DR: Recently, new ground-based observations, combined with in situ satellite measurements, have led the way in reinterpreting cusp signatures, which have stimulated new interest in the solar wind-magnetosphere-ionosphere coupling chain this paper.
Abstract: Earth's cusps are magnetic field features in the magnetosphere associated with regions through which plasma from the Sun can have direct access to the upper atmosphere. Recently, new ground-based observations, combined with in situ satellite measurements, have led the way in reinterpreting cusp signatures. These observations, combined with theoretical advances, have stimulated new interest in the solar wind-magnetosphere-ionosphere coupling chain. This coupling process is important because it causes both momentum and energy from the solar wind to enter into the near-Earth region. Here we describe the current ideas concerning the cusps and the supporting observational evidence which have evolved over the past 30 years. We include discussion on the plasma entry process, particle motion between the magnetopause and ionosphere, ground optical and radar measurements, and transient events. We also review the important questions that remain to be answered.
194 citations
01 Jul 2000
TL;DR: In this article, the first spacecraft-borne imager observations of the auroral manifestation of transient magnetic flux transfer at the magnetopause were presented, during an interval of interplanetary magnetic field Bz ≈ −10 nT and By ≈ 10 nT, and solar wind dynamic pressure and velocity Psw ≈ 5 nPa and vsw vw ≈ 650 km s−1, Polar Ultraviolet Imager (UVI) images show a sequence of events, each of which begins as a bifurcation of the main auroral oval in
Abstract: We present the first spacecraft-borne imager observations of the auroral manifestation of transient magnetic flux transfer at the magnetopause. During an interval of interplanetary magnetic field Bz ≈ −10 nT, By ≈ 10 nT, and solar wind dynamic pressure and velocity Psw ≈ 5 nPa and vsw ≈ 650 km s−1, Polar Ultraviolet Imager (UVI) images show a sequence of events, each of which begins as a bifurcation of the main auroral oval in the 14 to 16 magnetic local time (MLT) sector which subsequently progresses antisunward (eastward) at 2 km s−1 toward the 19 MLT sector. The poleward portion of the bifurcation is interpreted as a poleward-moving auroral form (PMAF) as has previously been observed by ground-based optical instrumentation and identified as the auroral signature of flux transfer events. Ground-based measurements of the associated plasma drift, made with the Cooperative U.K. Twin Located Auroral Sounding System (CUTLASS) Finland HF radar, show poleward (1 km s−1) and westward (1 km s−1) convection flow, consistent with the By tension force, as well as poleward-moving regions of backscatter. International Monitor for Auroral Geomagnetic Effects (IMAGE) magnetometers within the radar field of view observe poleward-progressing, 10 min period, X component magnetic deflections, which are consistent with the effect of Hall currents associated with the plasma flow. The combined radar and optical observations suggest that the PMAFs can be 3500 km or 7 hours of MLT in length. The antisunward motion of the bifurcation of the auroral oval is interpreted as an expansion of the reconnection X line along the flank of the magnetopause.
179 citations
TL;DR: In this paper, the polar cap patches are formed by transient magnetic reconnection events and the shears become the dominant plasma structuring mechanism until the initial magnetic tension force is relaxed.
Abstract: [1] Since polar cap patches were discovered, their nature, physics, and impact on navigation and communication signals has been repeatedly addressed. Both terminology and inference of physical processes from diverse instruments have introduced confusion. Poleward moving auroral form is a morphological descriptor but cannot be equated to an island of high-density plasma. Particle precipitation produces low-density patches, but high-density patches derive from solar produced plasma. The challenge of patches is finding the dominant mechanism for chopping entering ionization into islands (∼100–1000 km in size). Velocity-dependent recombination physics is valid in principle but not relevant to patches formed in at least the European sector. Most patches are formed by transient magnetic reconnection events. While the plasma is at too high an altitude for the strong velocity shears to erode plasma densities, the shears become the dominant plasma structuring mechanism until the initial magnetic tension force is relaxed. Initial patch structuring is not by gradient drift as believed for decades but rather by the shear driven instability, impacting mitigation techniques. Large-scale shears, driven to 2–3 km/s, impact satellite drag through thermospheric heating. The study here is intended to sharpen understanding of patches for future research and development of techniques for mitigation of their effects on navigation and other systems dependent on receiving radio frequency signals from satellites and understanding reconnection driven impact on thermospheric density and satellite drag.
129 citations
TL;DR: In this paper, the SuperDARN convection model is used to track polar cap ionosphere patches backward and forward in time, which can be used to forecast its destination in the future.
Abstract: This paper presents research on polar cap ionosphere space weather phenomena conducted during the European Cooperation in Science and Technology (COST) action ES0803 from 2008 to 2012. The main part of the work has been directed toward the study of plasma instabilities and scintillations in association with cusp flow channels and polar cap electron density structures/patches, which is considered as critical knowledge in order to develop forecast models for scintillations in the polar cap. We have approached this problem by multi-instrument techniques that comprise the EISCAT Svalbard Radar, SuperDARN radars, in-situ rocket, and GPS scintillation measurements. The Discussion section aims to unify the bits and pieces of highly specialized information from several papers into a generalized picture. The cusp ionosphere appears as a hot region in GPS scintillation climatology maps. Our results are consistent with the existing view that scintillations in the cusp and the polar cap ionosphere are mainly due to multi-scale structures generated by instability processes associated with the cross-polar transport of polar cap patches. We have demonstrated that the SuperDARN convection model can be used to track these patches backward and forward in time. Hence, once a patch has been detected in the cusp inflow region, SuperDARN can be used to forecast its destination in the future. However, the high-density gradient of polar cap patches is not the only prerequisite for high-latitude scintillations. Unprecedented high-resolution rocket measurements reveal that the cusp ionosphere is associated with filamentary precipitation giving rise to kilometer scale gradients onto which the gradient drift instability can operate very efficiently. Cusp ionosphere scintillations also occur during IMF B Z north conditions, which further substantiates that particle precipitation can play a key role to initialize plasma structuring. Furthermore, the cusp is associated with flow channels and strong flow shears, and we have demonstrated that the Kelvin-Helmholtz instability process may be efficiently driven by reversed flow events.
120 citations
Cites background from "High spatial and temporal resolutio..."
...FTEs are associated with flow channels (Van Eyken et al. 1984; Goertz et al. 1985; Lockwood et al. 1993; Pinnock et al. 1993, 1995; Moen et al. 1995; Provan et al. 1998, 2002; Neudegg et al. 1999, 2000; Provan & Yeoman 1999; Chisham et al. 2000; McWilliams et al. 2000; Oksavik et al. 2004a, Rinne…...
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