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J Moen - One of the best experts on this subject based on the ideXlab platform.
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space weather challenges of the Polar Cap ionosphere
arXiv: Space Physics, 2017Co-Authors: J Moen, K Oksavik, Lucilla Alfonsi, Yvonne Daabakk, V Romano, Luca SpogliAbstract: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... (continued)
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Polar Cap hot patches enhanced density structures different from the classical patches in the ionosphere
Geophysical Research Letters, 2017Co-Authors: Qinghe Zhang, P. T. Jayachandran, J Moen, Mike Lockwood, Shunrong Zhang, Yongliang Zhang, J C Foster, Yong Wang, David R Themens, B C ZhangAbstract:Based on in situ and ground-based observations, a new type of “Polar Cap hot patch” has been identified that is different from the classical Polar Cap enhanced density structure (cold patches). Comparing with the classical Polar Cap patches, which are transported from the dayside sunlit region with dense and cold plasma, the Polar Cap hot patches are associated with particle precipitations (therefore field-aligned currents), ion upflows, and flow shears. The hot patches may have the same order of density enhancement as classical patches in the topside ionosphere, suggesting that the hot patches may be produced by transported photoionization plasma into flow channels. Within the flow channels, the hot patches have low-energy particle precipitation and/or ion upflows associated with field-aligned currents and flow shears. Corresponding Global Navigation Satellite System (GNSS) signal scintillation measurements indicate that hot patches may produce slightly stronger radio signal scintillation in the Polar Cap region than classical patches.
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interhemispheric study of Polar Cap patch occurrence based on swarm in situ data
Journal of Geophysical Research, 2017Co-Authors: Andres Spicher, Yaqi Jin, L B N Clausen, W J Miloch, Victoria Lofstad, J MoenAbstract:The Swarm satellites offer an unprecedented opportunity for improving our knowledge about Polar Cap patches, which are regarded as the main space weather issue in the Polar Caps. We present a new robust algorithm that automatically detects Polar Cap patches using in situ plasma density data from Swarm. For both hemispheres, we compute the spatial and seasonal distributions of the patches identified separately by Swarm A and Swarm B between December 2013 and August 2016. We show a clear seasonal dependency of patch occurrence. In the Northern Hemisphere (NH), patches are essentially a winter phenomenon, as their occurrence rate is enhanced during local winter and very low during local summer. Although not as pronounced as in the NH, the same pattern is seen for the Southern Hemisphere (SH). Furthermore, the rate of Polar Cap patch detection is generally higher in the SH than in the NH, especially on the dayside at about 77° magnetic latitude. Additionally, we show that in the NH the number of patches is higher in the postnoon and prenoon sectors for interplanetary magnetic field (IMF) By 0, respectively, and that this trend is mirrored in the SH, consistent with the ionospheric flow convection. Overall, our results confirm previous studies in the NH, shed more light regarding the SH, and provide further insight into Polar Cap patch climatology. Along with this algorithm, we provide a large data set of patches automatically detected with in situ measurements, which opens new horizons in studies of Polar Cap phenomena.
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Polar Cap patch transportation beyond the classic scenario
Journal of Geophysical Research, 2016Co-Authors: K A Mcwilliams, J Moen, Qinghe Zhang, Mike Lockwood, I W Mccrea, Beichen Zhang, Qiugang Zong, Shunrong Zhang, Michael J RuohoniemiAbstract:We report the continuous monitoring of a Polar Cap patch, encompassing its creation and a subsequent evolution that differs from the classic behviour. The patch was formed from the storm enhanced density (SED) plume, by segmentation associated with a subauroral Polarization stream (SAPS) generated by a substorm. Its initial anti-sunward motion was halted due to a rapidly changing of interplanetary magnetic field (IMF) conditions from strong southward to strong eastward with weaker northward components and the patch subsequently very slowly evolved behind the duskside of a lobe reverse convection cell in afternoon sectors, associated with high-latitude lobe reconnection, much of it fading rapidly due to an enhancement of the ionization recombination rate. This differs from the classic scenario where Polar Cap patches are transported across the Polar Cap along the streamlines of twin-cell convection pattern from day to night. This observation provides us new important insights into patch formation and control by the IMF, which has to be taken into account in F-region transport models and space weather forecasts.
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earth s ion upflow associated with Polar Cap patches global and in situ observations
Geophysical Research Letters, 2016Co-Authors: Qinghe Zhang, M. R. Hairston, J Moen, Mike Lockwood, I W Mccrea, Beichen Zhang, Qiugang Zong, R A Heelis, Jun Liang, Shunrong ZhangAbstract:We report simultaneous global monitoring of a patch of ionization and in situ observation of ion upflow at the center of the Polar Cap region during a geomagnetic storm. Our observations indicate strong fluxes of upwelling O+ ions originating from frictional heating produced by rapid antisunward flow of the plasma patch. The statistical results from the crossings of the central Polar Cap region by Defense Meteorological Satellite Program F16–F18 from 2010 to 2013 confirm that the field-aligned flow can turn upward when rapid antisunward flows appear, with consequent significant frictional heating of the ions, which overcomes the gravity effect. We suggest that such rapidly moving patches can provide an important source of upwelling ions in a region where downward flows are usually expected. These observations give new insight into the processes of ionosphere-magnetosphere coupling.
Alice K Harding - One of the best experts on this subject based on the ideXlab platform.
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full Polar Cap cascade scenario gamma ray and x ray luminosities from spin powered pulsars
The Astrophysical Journal, 2000Co-Authors: Bing Zhang, Alice K HardingAbstract:Canonical Polar Cap cascade models involve curvature radiation (CR) or inverse Compton scattering (ICS) of the primary particles and synchrotron radiation (SR) of the higher generation pairs. Here we modify such a cascade picture to include the ICS of the higher generation pairs. In such a ii full-cascade ˇˇ scenario, not only the perpendicular portion of the energy of the pairs goes to high-energy radiation via SR, but the parallel portion of the energy of the pairs can also contribute to high-energy emission via ICS with the soft thermal photons from either the full neutron star surface or the hot Polar Cap. The efficiency of converting particleskinetic energy to radiation by ICS is very high if the scatterings occur in the ii resonant ˇˇ regime. As a result, almost 100% of the energy input from the pulsar inner acceler- ators could be converted to high-energy emission. An important output of such a scenario is that the soft tail of the ICS spectrum can naturally result in a nonthermal X-ray component that can contribute to the luminosities observed by ROSAT and ASCA. Here we present an analytic description of such a full Polar Cap cascade scenario using the recursion relationships between adjacent generations following the approach —rst proposed by Lu et al., but we develop it to be able to delineate the complex full- cascade process. The acceleration model we adopted is the space-chargelimited —ow model proposed by Harding & Muslimov. We present the theoretical predictions of the c-ray luminosities, the thermal and nonthermal X-ray luminosities for the known spin-powered X-ray pulsars (eight of them are also c-ray pulsars) and compare them with the observations from CGRO, ROSAT , and ASCA. We estimate the nonthermal X-ray luminosity by including all the possible ICS branches contributing to a certain energy band and estimate both the full surface and hot Polar Cap thermal X-ray luminosities by adopting a standard neutron star cooling scenario, and by treating self-consistent Polar Cap heating in the Harding & Muslimov model, respectively. Our results show that the observed diUerent dependences of the high- energy luminosities on the pulsar spin-down luminosities, i.e., and are well L c P (L sd )1@2 L X D 10~3L sd , reproduced. We found that, for normal pulsars, both the hard (ASCA band) and the soft (ROSAT band) X-ray luminosities are dominated by the nonthermal X-rays of ICS origin, although for some pulsars, thermal components due to either neutron star cooling or Polar Cap heating can have comparable lumi- nosities so that they are detectable. For the millisecond pulsars, our predicted upper limits of the thermal luminosities due to Polar Cap heating are usually higher than the ICS-origin nonthermal components if there are no strong multiPolar magnetic —eld components near the neutron star surface; thus, the pulsed soft X-rays in the ROSAT band from most of the millisecond pulsars might be of thermal origin. Subject headings: gamma rays: theorypulsars: generalradiation mechanisms: nonthermal ¨ X-rays: stars
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full Polar Cap cascade scenario gamma ray and x ray luminosities from spin powered pulsars
arXiv: Astrophysics, 1999Co-Authors: Bing Zhang, Alice K HardingAbstract:We modify Polar Cap cascade picture to include the ICS of the higher generation pairs. In such a ``full-cascade'' scenario, not only the perpendicular portion of the energy of the pairs goes to high energy radiation via SR, but the parallel portion of the energy of the pairs can also contribute to high energy emission via ICS with the soft thermal photons from either the full neutron star surface or the hot Polar Cap. An important output of such a scenario is that the soft tail of the ICS spectrum can naturally result in a non-thermal X-ray component which can contribute to the luminosities observed by ROSAT and ASCA. Here we present an analytic description of such a full Polar Cap cascade scenario within the framework of Harding & Muslimov acceleration model. We present the theoretical predictions of the $\gamma$-ray luminosities, the thermal and non-thermal X-ray luminosities for the known spin-powered X-ray pulsars. Our results show that the observed different dependences of the high energy luminosities on the pulsar spin-down luminosities, i.e., $L_\gamma \propto (L_{\rm sd})^{1/2}$ and $L_x \sim 10^{-3} L_{\rm sd}$, are well reproduced. Our model predicts that the {\em pulsed} soft X-rays in the ROSAT band from most of the millisecond pulsars might be of thermal origin if there is no strong multipole field components near the surfaces of these pulsars.
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gamma ray pulsars emission from extended Polar Cap cascades
The Astrophysical Journal, 1996Co-Authors: J K Daugherty, Alice K HardingAbstract:We have used a Monte Carlo simulation of a Polar Cap (PC) model of gamma-ray pulsars to estimate light curves and phase-resolved spectra for sources whose rotational and magnetic axes are oriented so that only one of the magnetic poles produces emission directed at the Earth. In this Single Polar Cap (SPC) scenario, even sources whose light curves have two distinct peaks (Crab, Vela, Geminga, PSR B1951+32) are due to emission concentrated near the rim of a single PC. If the inclination alpha is comparable to the half-width of the PC gamma-beam, alpha ~ theta_{b}, the peak-to-peak phase separation can have the large values (0.4 - 0.5) observed from these sources. In the model presented here we attribute the observed interpeak emission to pair cascades above the PC interior. Our simulation assumes the physics of conventional PC models, in which the gamma rays are due to photon-pair cascades initiated by curvature radiation from the acceleration of electrons above the PCs. In this work we assume that the acceleration occurs over a finite region which may extend up to several radii above the neutron star surface. We find that the combined effects of moderately enlarged PC dimensions and extended acceleration zones resolve a major difficulty with earlier PC models, namely their small beam widths (and hence small detection probabilities). Our best fits to the observed light curves are obtained from models in which the accelerated electrons have a uniform surface density over the PC interior and a sharp density increase of 3 - 5 near the rim.
Mike Lockwood - One of the best experts on this subject based on the ideXlab platform.
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Polar Cap hot patches enhanced density structures different from the classical patches in the ionosphere
Geophysical Research Letters, 2017Co-Authors: Qinghe Zhang, P. T. Jayachandran, J Moen, Mike Lockwood, Shunrong Zhang, Yongliang Zhang, J C Foster, Yong Wang, David R Themens, B C ZhangAbstract:Based on in situ and ground-based observations, a new type of “Polar Cap hot patch” has been identified that is different from the classical Polar Cap enhanced density structure (cold patches). Comparing with the classical Polar Cap patches, which are transported from the dayside sunlit region with dense and cold plasma, the Polar Cap hot patches are associated with particle precipitations (therefore field-aligned currents), ion upflows, and flow shears. The hot patches may have the same order of density enhancement as classical patches in the topside ionosphere, suggesting that the hot patches may be produced by transported photoionization plasma into flow channels. Within the flow channels, the hot patches have low-energy particle precipitation and/or ion upflows associated with field-aligned currents and flow shears. Corresponding Global Navigation Satellite System (GNSS) signal scintillation measurements indicate that hot patches may produce slightly stronger radio signal scintillation in the Polar Cap region than classical patches.
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Polar Cap patch transportation beyond the classic scenario
Journal of Geophysical Research, 2016Co-Authors: K A Mcwilliams, J Moen, Qinghe Zhang, Mike Lockwood, I W Mccrea, Beichen Zhang, Qiugang Zong, Shunrong Zhang, Michael J RuohoniemiAbstract:We report the continuous monitoring of a Polar Cap patch, encompassing its creation and a subsequent evolution that differs from the classic behviour. The patch was formed from the storm enhanced density (SED) plume, by segmentation associated with a subauroral Polarization stream (SAPS) generated by a substorm. Its initial anti-sunward motion was halted due to a rapidly changing of interplanetary magnetic field (IMF) conditions from strong southward to strong eastward with weaker northward components and the patch subsequently very slowly evolved behind the duskside of a lobe reverse convection cell in afternoon sectors, associated with high-latitude lobe reconnection, much of it fading rapidly due to an enhancement of the ionization recombination rate. This differs from the classic scenario where Polar Cap patches are transported across the Polar Cap along the streamlines of twin-cell convection pattern from day to night. This observation provides us new important insights into patch formation and control by the IMF, which has to be taken into account in F-region transport models and space weather forecasts.
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earth s ion upflow associated with Polar Cap patches global and in situ observations
Geophysical Research Letters, 2016Co-Authors: Qinghe Zhang, M. R. Hairston, J Moen, Mike Lockwood, I W Mccrea, Beichen Zhang, Qiugang Zong, R A Heelis, Jun Liang, Shunrong ZhangAbstract:We report simultaneous global monitoring of a patch of ionization and in situ observation of ion upflow at the center of the Polar Cap region during a geomagnetic storm. Our observations indicate strong fluxes of upwelling O+ ions originating from frictional heating produced by rapid antisunward flow of the plasma patch. The statistical results from the crossings of the central Polar Cap region by Defense Meteorological Satellite Program F16–F18 from 2010 to 2013 confirm that the field-aligned flow can turn upward when rapid antisunward flows appear, with consequent significant frictional heating of the ions, which overcomes the gravity effect. We suggest that such rapidly moving patches can provide an important source of upwelling ions in a region where downward flows are usually expected. These observations give new insight into the processes of ionosphere-magnetosphere coupling.
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direct observations of the evolution of Polar Cap ionization patches
Science, 2013Co-Authors: Qinghe Zhang, Michael J Ruohoniemi, J Moen, Mike Lockwood, Beichen Zhang, Shunrong Zhang, Eg Thomas, Huigen Yang, Ruiyuan Liu, K A McwilliamsAbstract:Patches of ionization are common in the Polar ionosphere, where their motion and associated density gradients give variable disturbances to high-frequency (HF) radio communications, over-the-horizon radar location errors, and disruption and errors to satellite navigation and communication. Their formation and evolution are poorly understood, particularly under disturbed space weather conditions. We report direct observations of the full evolution of patches during a geomagnetic storm, including formation, Polar Cap entry, transPolar evolution, Polar Cap exit, and sunward return flow. Our observations show that modulation of nightside reconnection in the substorm cycle of the magnetosphere helps form the gaps between patches where steady convection would give a “tongue” of ionization (TOI).
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on the importance of interplanetary magnetic field by on Polar Cap patch formation
Journal of Geophysical Research, 2011Co-Authors: Qinghe Zhang, J Moen, Mike Lockwood, Beichen Zhang, R Y Liu, M W Dunlop, H G Yang, S L Liu, I W MccreaAbstract:[1] A number of poleward moving events were observed between 1130 and 1300 UT on 11 February 2004, during periods of southward interplanetary magnetic field (IMF), while the steerable antenna of the European Incoherent Scatter (EISCAT) Svalbard radar (ESR) and the Tromso VHF radar pointed nearly northward at low elevation. In this interval, simultaneous SuperDARN CUTLASS Finland radar measurements showed poleward moving radar aurora forms (PMRAFs) which appeared very similar to the density enhancements observed by the ESR northward pointing antenna. These events appeared quasiperiodically with a period of about 10 min. Comparing the observations from the above three radars, it is inferred that there is an almost one-to-one correspondence between the poleward moving plasma concentration enhancements (PMPCEs) observed by the ESR and the VHF radar and the PMRAFs measured by the CUTLASS Finland radar. These observations are consistent with the interpretation that the Polar Cap patch material was generated by photoionization at subauroral latitudes and that the plasma was structured by bursts of magnetopause reconnection giving access to the Polar Cap. There is clear evidence that plasma structuring into patches was dependent on the variability in IMF ∣By∣. The duration of these events implies that the average evolution time of the newly opened flux tubes from the subauroral region to the Polar Cap was about 33 min.
K A Mcwilliams - One of the best experts on this subject based on the ideXlab platform.
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Polar Cap patch transportation beyond the classic scenario
Journal of Geophysical Research, 2016Co-Authors: K A Mcwilliams, J Moen, Qinghe Zhang, Mike Lockwood, I W Mccrea, Beichen Zhang, Qiugang Zong, Shunrong Zhang, Michael J RuohoniemiAbstract:We report the continuous monitoring of a Polar Cap patch, encompassing its creation and a subsequent evolution that differs from the classic behviour. The patch was formed from the storm enhanced density (SED) plume, by segmentation associated with a subauroral Polarization stream (SAPS) generated by a substorm. Its initial anti-sunward motion was halted due to a rapidly changing of interplanetary magnetic field (IMF) conditions from strong southward to strong eastward with weaker northward components and the patch subsequently very slowly evolved behind the duskside of a lobe reverse convection cell in afternoon sectors, associated with high-latitude lobe reconnection, much of it fading rapidly due to an enhancement of the ionization recombination rate. This differs from the classic scenario where Polar Cap patches are transported across the Polar Cap along the streamlines of twin-cell convection pattern from day to night. This observation provides us new important insights into patch formation and control by the IMF, which has to be taken into account in F-region transport models and space weather forecasts.
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swarm in situ observations of f region Polar Cap patches created by cusp precipitation
arXiv: Space Physics, 2016Co-Authors: L V Goodwin, Stephan Buchert, L B N Clausen, Johnathan Burchill, D J Knudsen, B Iserhienrhien, David M Miles, S Patra, C Van Der Meeren, K A McwilliamsAbstract:High-resolution in situ measurements from the three Swarm spacecraft, in a string-of-pearls configuration, provide new insights about the combined role of flow channel events and particle impact ionization in creating $\textit{F}$ region electron density structures in the northern Scandinavian dayside cusp. We present a case of Polar Cap patch formation where a reconnection-driven low-density relative westward flow channel is eroding the dayside solar-ionized plasma but where particle impact ionization in the cusp dominates the initial plasma structuring. In the cusp, density features are observed which are twice as dense as the solar-ionized background. These features then follow the Polar Cap convection and become less structured and lower in amplitude. These are the first in situ observations tracking Polar Cap patch evolution from creation by plasma transport and enhancement by cusp precipitation, through entrainment in the Polar Cap flow and relaxation into smooth patches as they approach the nightside auroral oval.
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Polar Cap precursor of nightside auroral oval intensifications using Polar Cap arcs
Journal of Geophysical Research, 2015Co-Authors: Ying Zou, K Shiokawa, Y Nishimura, L R Lyons, E Donovan, Michael J Ruohoniemi, K A Mcwilliams, Nozomu NishitaniAbstract:Recent radar and optical observations suggested that localized fast flows in the Polar Cap precede disturbances within the nightside auroral oval. However, how commonly this connection occurs has been difficult to examine due to limited coverage of radar flow measurements and diffuse and dim nature of airglow patches. Polar Cap arcs are also associated with fast flows in the Polar Cap and appear much brighter than patches, allowing evaluation of the interaction between Polar Cap structures and nightside aurora more definitively. We have surveyed data during six winter seasons and selected quasi-steady Polar Cap arcs lasting >1 h. Thirty-four arcs are found, and for the majority (~85%) of them, as they extend equatorward from high latitude, their contact with the nightside auroral poleward boundary is associated with new and substantial intensifications within the oval. These intensifications are localized (< ~1 h magnetic local time (MLT)) and statistically occur within 10 min and ±1 h MLT from the contact. They appear as poleward boundary intensifications in a thick auroral oval or an intensification of the only resolvable arc within a thin oval, and the latter can also exhibit substantial poleward expansion. When radar echoes are available, they corroborate the association of Polar Cap arcs with localized enhanced antisunward flows. That the observed oval intensifications are major disturbances that only occur after the impingement of Polar Cap arcs and near the contact longitude suggest that they are triggered by localized fast flows coming from deep in the Polar Cap.
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localized Polar Cap flow enhancement tracing using airglow patches statistical properties imf dependence and contribution to Polar Cap convection
Journal of Geophysical Research, 2015Co-Authors: Ying Zou, K Shiokawa, Y Nishimura, L R Lyons, E Donovan, Michael J Ruohoniemi, K A Mcwilliams, N NishitaniAbstract:Recent radar observations have suggested that Polar Cap flows are highly structured and that localized flow enhancements can lead to nightside auroral disturbances. However, knowledge of these flows is limited to available echo regions. Utilizing wide spatial coverage by an all-sky imager at Resolute Bay and simultaneous Super Dual Auroral Radar Network measurements, we statistically determined properties of such flows and their interplanetary magnetic field (IMF) dependence. We found that narrow flow enhancements are well collocated with airglow patches with substantially larger velocities (≥200 m/s) than the weak large-scale background flows. The flow azimuthal widths are similar to the patch widths. During the evolution across the Polar Cap, the flow directions and speeds are consistent with the patch propagation directions and speeds. These correspondences indicate that patches can optically trace localized flow enhancements reflecting the flow width, speed, and direction. Such associations were found common (~67%) in statistics, and the typical flow speed, propagation time, and width within our observation areas are 600 m/s, tens of minutes, and 200–300 km, respectively. By examining IMF dependence of the occurrence and properties of these flows, we found that they tend to be observed under By-dominated IMF. Flow speeds are large under oscillating IMF clock angles. Localized flow enhancements are usually observed as a channel elongated in the noon-midnight meridian and directed toward premidnight (postmidnight) for +By (−By). The potential drops across localized flow enhancements account for ~10–40% of the cross Polar Cap potential, indicating that they significantly contribute to Polar Cap plasma transport.
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swarm in situ observations of f region Polar Cap patches created by cusp precipitation
Geophysical Research Letters, 2015Co-Authors: L V Goodwin, Stephan Buchert, L B N Clausen, Johnathan Burchill, D J Knudsen, B Iserhienrhien, David M Miles, S Patra, C Van Der Meeren, K A McwilliamsAbstract:High-resolution in situ measurements from the three Swarm spacecraft, in a string-of-pearls configuration, provide new insights about the combined role of flow channel events and particle impact ionization in creating F region electron density structures in the northern Scandinavian dayside cusp. We present a case of Polar Cap patch formation where a reconnection-driven low-density relative westward flow channel is eroding the dayside solar-ionized plasma but where particle impact ionization in the cusp dominates the initial plasma structuring. In the cusp, density features are observed which are twice as dense as the solar-ionized background. These features then follow the Polar Cap convection and become less structured and lower in amplitude. These are the first in situ observations tracking Polar Cap patch evolution from creation by plasma transport and enhancement by cusp precipitation, through entrainment in the Polar Cap flow and relaxation into smooth patches as they approach the nightside auroral oval.
Qinghe Zhang - One of the best experts on this subject based on the ideXlab platform.
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Polar Cap hot patches enhanced density structures different from the classical patches in the ionosphere
Geophysical Research Letters, 2017Co-Authors: Qinghe Zhang, P. T. Jayachandran, J Moen, Mike Lockwood, Shunrong Zhang, Yongliang Zhang, J C Foster, Yong Wang, David R Themens, B C ZhangAbstract:Based on in situ and ground-based observations, a new type of “Polar Cap hot patch” has been identified that is different from the classical Polar Cap enhanced density structure (cold patches). Comparing with the classical Polar Cap patches, which are transported from the dayside sunlit region with dense and cold plasma, the Polar Cap hot patches are associated with particle precipitations (therefore field-aligned currents), ion upflows, and flow shears. The hot patches may have the same order of density enhancement as classical patches in the topside ionosphere, suggesting that the hot patches may be produced by transported photoionization plasma into flow channels. Within the flow channels, the hot patches have low-energy particle precipitation and/or ion upflows associated with field-aligned currents and flow shears. Corresponding Global Navigation Satellite System (GNSS) signal scintillation measurements indicate that hot patches may produce slightly stronger radio signal scintillation in the Polar Cap region than classical patches.
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Polar Cap patch transportation beyond the classic scenario
Journal of Geophysical Research, 2016Co-Authors: K A Mcwilliams, J Moen, Qinghe Zhang, Mike Lockwood, I W Mccrea, Beichen Zhang, Qiugang Zong, Shunrong Zhang, Michael J RuohoniemiAbstract:We report the continuous monitoring of a Polar Cap patch, encompassing its creation and a subsequent evolution that differs from the classic behviour. The patch was formed from the storm enhanced density (SED) plume, by segmentation associated with a subauroral Polarization stream (SAPS) generated by a substorm. Its initial anti-sunward motion was halted due to a rapidly changing of interplanetary magnetic field (IMF) conditions from strong southward to strong eastward with weaker northward components and the patch subsequently very slowly evolved behind the duskside of a lobe reverse convection cell in afternoon sectors, associated with high-latitude lobe reconnection, much of it fading rapidly due to an enhancement of the ionization recombination rate. This differs from the classic scenario where Polar Cap patches are transported across the Polar Cap along the streamlines of twin-cell convection pattern from day to night. This observation provides us new important insights into patch formation and control by the IMF, which has to be taken into account in F-region transport models and space weather forecasts.
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earth s ion upflow associated with Polar Cap patches global and in situ observations
Geophysical Research Letters, 2016Co-Authors: Qinghe Zhang, M. R. Hairston, J Moen, Mike Lockwood, I W Mccrea, Beichen Zhang, Qiugang Zong, R A Heelis, Jun Liang, Shunrong ZhangAbstract:We report simultaneous global monitoring of a patch of ionization and in situ observation of ion upflow at the center of the Polar Cap region during a geomagnetic storm. Our observations indicate strong fluxes of upwelling O+ ions originating from frictional heating produced by rapid antisunward flow of the plasma patch. The statistical results from the crossings of the central Polar Cap region by Defense Meteorological Satellite Program F16–F18 from 2010 to 2013 confirm that the field-aligned flow can turn upward when rapid antisunward flows appear, with consequent significant frictional heating of the ions, which overcomes the gravity effect. We suggest that such rapidly moving patches can provide an important source of upwelling ions in a region where downward flows are usually expected. These observations give new insight into the processes of ionosphere-magnetosphere coupling.
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direct observations of the evolution of Polar Cap ionization patches
Science, 2013Co-Authors: Qinghe Zhang, Michael J Ruohoniemi, J Moen, Mike Lockwood, Beichen Zhang, Shunrong Zhang, Eg Thomas, Huigen Yang, Ruiyuan Liu, K A McwilliamsAbstract:Patches of ionization are common in the Polar ionosphere, where their motion and associated density gradients give variable disturbances to high-frequency (HF) radio communications, over-the-horizon radar location errors, and disruption and errors to satellite navigation and communication. Their formation and evolution are poorly understood, particularly under disturbed space weather conditions. We report direct observations of the full evolution of patches during a geomagnetic storm, including formation, Polar Cap entry, transPolar evolution, Polar Cap exit, and sunward return flow. Our observations show that modulation of nightside reconnection in the substorm cycle of the magnetosphere helps form the gaps between patches where steady convection would give a “tongue” of ionization (TOI).
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on the importance of interplanetary magnetic field by on Polar Cap patch formation
Journal of Geophysical Research, 2011Co-Authors: Qinghe Zhang, J Moen, Mike Lockwood, Beichen Zhang, R Y Liu, M W Dunlop, H G Yang, S L Liu, I W MccreaAbstract:[1] A number of poleward moving events were observed between 1130 and 1300 UT on 11 February 2004, during periods of southward interplanetary magnetic field (IMF), while the steerable antenna of the European Incoherent Scatter (EISCAT) Svalbard radar (ESR) and the Tromso VHF radar pointed nearly northward at low elevation. In this interval, simultaneous SuperDARN CUTLASS Finland radar measurements showed poleward moving radar aurora forms (PMRAFs) which appeared very similar to the density enhancements observed by the ESR northward pointing antenna. These events appeared quasiperiodically with a period of about 10 min. Comparing the observations from the above three radars, it is inferred that there is an almost one-to-one correspondence between the poleward moving plasma concentration enhancements (PMPCEs) observed by the ESR and the VHF radar and the PMRAFs measured by the CUTLASS Finland radar. These observations are consistent with the interpretation that the Polar Cap patch material was generated by photoionization at subauroral latitudes and that the plasma was structured by bursts of magnetopause reconnection giving access to the Polar Cap. There is clear evidence that plasma structuring into patches was dependent on the variability in IMF ∣By∣. The duration of these events implies that the average evolution time of the newly opened flux tubes from the subauroral region to the Polar Cap was about 33 min.
