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Статті в журналах з теми "Polar magnetic substorm"
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DeJong, A. D., X. Cai, R. C. Clauer, and J. F. Spann. "Aurora and open magnetic flux during isolated substorms, sawteeth, and SMC events." Annales Geophysicae 25, no. 8 (August 29, 2007): 1865–76. http://dx.doi.org/10.5194/angeo-25-1865-2007.
Повний текст джерелаАнотація:
Abstract. Using Polar UVI LBHl and IMAGE FUV WIC data, we have compared the auroral signatures and polar cap open flux for isolated substorms, sawteeth oscillations, and steady magnetospheric convection (SMC) events. First, a case study of each event type is performed, comparing auroral signatures and open magnetic fluxes to one another. The latitude location of the auroral oval is similar during isolated substorms and SMC events. The auroral intensity during SMC events is similar to that observed during the expansion phase of an isolated substorm. Examination of an individual sawtooth shows that the auroral intensity is much greater than the SMC or isolated substorm events and the auroral oval is displaced equatorward making a larger polar cap. The temporal variations observed during the individual sawtooth are similar to that observed during the isolated substorm, and while the change in polar cap flux measured during the sawtooth is larger, the percent change in flux is similar to that measured during the isolated substorm. These results are confirmed by a statistical analysis of events within these three classes. The results show that the auroral oval measured during individual sawteeth contains a polar cap with, on average, 150% more magnetic flux than the oval measured during isolated substorms or during SMC events. However, both isolated substorms and sawteeth show a 30% decrease in polar cap magnetic flux during the dipolarization (expansion) phase.
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Yagova, Nadezda, Natalia Nosikova, Lisa Baddeley, Olga Kozyreva, Dag A. Lorentzen, Vyacheslav Pilipenko, and Magnar G. Johnsen. "Non-triggered auroral substorms and long-period (1–4 mHz) geomagnetic and auroral luminosity pulsations in the polar cap." Annales Geophysicae 35, no. 3 (March 8, 2017): 365–76. http://dx.doi.org/10.5194/angeo-35-365-2017.
Повний текст джерелаАнотація:
Abstract. A study is undertaken into parameters of the polar auroral and geomagnetic pulsations in the frequency range 1–4 mHz (Pc5∕Pi3) during quiet geomagnetic intervals preceding auroral substorms and non-substorm background variations. Special attention is paid to substorms that occur under parameters of the interplanetary magnetic field (IMF) conditions typical for undisturbed days (non-triggered substorms). The spectral parameters of pulsations observed in auroral luminosity as measured by a meridian scanning photometer (Svalbard) in the polar cap and near the polar boundary of the auroral oval are studied and compared with those for the geomagnetic pulsations measured by the magnetometer network IMAGE in the same frequency range. It is found that Pc5∕Pi3 power spectral density (PSD) is higher during pre-substorm time intervals than for non-substorm days and that specific variations of pulsation parameters (substorm precursors) occur during the last 2–4 pre-substorm hours.
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Provan, G., M. Lester, S. B. Mende, and S. E. Milan. "Statistical study of high-latitude plasma flow during magnetospheric substorms." Annales Geophysicae 22, no. 10 (November 3, 2004): 3607–24. http://dx.doi.org/10.5194/angeo-22-3607-2004.
Повний текст джерелаАнотація:
Abstract. We have utilised the near-global imaging capabilities of the Northern Hemisphere SuperDARN radars, to perform a statistical superposed epoch analysis of high-latitude plasma flows during magnetospheric substorms. The study involved 67 substorms, identified using the IMAGE FUV space-borne auroral imager. A substorm co-ordinate system was developed, centred on the magnetic local time and magnetic latitude of substorm onset determined from the auroral images. The plasma flow vectors from all 67 intervals were combined, creating global statistical plasma flow patterns and backscatter occurrence statistics during the substorm growth and expansion phases. The commencement of the substorm growth phase was clearly observed in the radar data 18-20min before substorm onset, with an increase in the anti-sunward component of the plasma velocity flowing across dawn sector of the polar cap and a peak in the dawn-to-dusk transpolar voltage. Nightside backscatter moved to lower latitudes as the growth phase progressed. At substorm onset a flow suppression region was observed on the nightside, with fast flows surrounding the suppressed flow region. The dawn-to-dusk transpolar voltage increased from ~40kV just before substorm onset to ~75kV 12min after onset. The low-latitude return flow started to increase at substorm onset and continued to increase until 8min after onset. The velocity flowing across the polar-cap peaked 12-14min after onset. This increase in the flux of the polar cap and the excitation of large-scale plasma flow occurred even though the IMF Bz component was increasing (becoming less negative) during most of this time. This study is the first to statistically prove that nightside reconnection creates magnetic flux and excites high-latitude plasma flow in a similar way to dayside reconnection and that dayside and nightside reconnection, are two separate time-dependent processes.
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Andalsvik, Y., P. E. Sandholt, and C. J. Farrugia. "Substorms and polar cap convection: the 10 January 2004 interplanetary CME case." Annales Geophysicae 30, no. 1 (January 6, 2012): 67–80. http://dx.doi.org/10.5194/angeo-30-67-2012.
Повний текст джерелаАнотація:
Abstract. The expansion-contraction model of Dungey cell plasma convection has two different convection sources, i.e. reconnections at the magnetopause and in the magnetotail. The spatial-temporal structure of the nightside source is not yet well understood. In this study we shall identify temporal variations in the winter polar cap convection structure during substorm activity under steady interplanetary conditions. Substorm activity (electrojets and particle precipitations) is monitored by excellent ground-satellite DMSP F15 conjunctions in the dusk-premidnight sector. We take advantage of the wide latitudinal coverage of the IMAGE chain of ground magnetometers in Svalbard – Scandinavia – Russia for the purpose of monitoring magnetic deflections associated with polar cap convection and substorm electrojets. These are augmented by direct observations of polar cap convection derived from SuperDARN radars and cross-track ion drift observations during traversals of polar cap along the dusk-dawn meridian by spacecraft DMSP F13. The interval we study is characterized by moderate, stable forcing of the magnetosphere-ionosphere system (EKL = 4.0–4.5 mV m−1; cross polar cap potential (CPCP), Φ (Boyle) = 115 kV) during Earth passage of an interplanetary CME (ICME), choosing an 4-h interval where the magnetic field pointed continuously south-west (Bz < 0; By < 0). The combination of continuous monitoring of ground magnetic deflections and the F13 cross-track ion drift observations in the polar cap allows us to infer the temporal CPCP structure on time scales less than the ~10 min duration of F13 polar cap transits. We arrived at the following estimates of the dayside and nightside contributions to the CPCP (CPCP = CPCP/day + CPCP/night) under two intervals of substorm activity: CPCP/day ~110 kV; CPCP/night ~50 kV (45% CPCP increase during substorms). The temporal CPCP structure during one of the substorm cases resulted in a dawn-dusk convection asymmetry measured by DMSP F13 which is opposite to that expected from the prevailing negative By polarity of the ICME magnetic field, a clear indication of a nightside source.
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Sandholt, P. E., C. J. Farrugia, and W. F. Denig. "M–I coupling across the auroral oval at dusk and midnight: repetitive substorm activity driven by interplanetary coronal mass ejections (CMEs)." Annales Geophysicae 32, no. 4 (April 9, 2014): 333–51. http://dx.doi.org/10.5194/angeo-32-333-2014.
Повний текст джерелаАнотація:
Abstract. We study substorms from two perspectives, i.e., magnetosphere–ionosphere coupling across the auroral oval at dusk and at midnight magnetic local times. By this approach we monitor the activations/expansions of basic elements of the substorm current system (Bostrøm type I centered at midnight and Bostrøm type II maximizing at dawn and dusk) during the evolution of the substorm activity. Emphasis is placed on the R1 and R2 types of field-aligned current (FAC) coupling across the Harang reversal at dusk. We distinguish between two distinct activity levels in the substorm expansion phase, i.e., an initial transient phase and a persistent phase. These activities/phases are discussed in relation to polar cap convection which is continuously monitored by the polar cap north (PCN) index. The substorm activity we selected occurred during a long interval of continuously strong solar wind forcing at the interplanetary coronal mass ejection passage on 18 August 2003. The advantage of our scientific approach lies in the combination of (i) continuous ground observations of the ionospheric signatures within wide latitude ranges across the auroral oval at dusk and midnight by meridian chain magnetometer data, (ii) "snapshot" satellite (DMSP F13) observations of FAC/precipitation/ion drift profiles, and (iii) observations of current disruption/near-Earth magnetic field dipolarizations at geostationary altitude. Under the prevailing fortunate circumstances we are able to discriminate between the roles of the dayside and nightside sources of polar cap convection. For the nightside source we distinguish between the roles of inductive and potential electric fields in the two substages of the substorm expansion phase. According to our estimates the observed dipolarization rate (δ Bz/δt) and the inferred large spatial scales (in radial and azimuthal dimensions) of the dipolarization process in these strong substorm expansions may lead to 50–100 kV enhancements of the cross-polar-cap potential due to inductive electric field coupling.
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Safargaleev, Vladimir V., Alexander E. Kozlovsky, and Valery M. Mitrofanov. "Polar substorm on 7 December 2015: preonset phenomena and features of auroral breakup." Annales Geophysicae 38, no. 4 (July 28, 2020): 901–18. http://dx.doi.org/10.5194/angeo-38-901-2020.
Повний текст джерелаАнотація:
Abstract. Comprehensive analysis of a moderate 600 nT substorm was performed using simultaneous optical observations inside the auroral oval and in the polar cap, combined with data from satellites, radars, and ground magnetometers. The onset took place near the poleward boundary of the auroral oval that is not typical for classical substorms. The substorm onset was preceded by two negative excursions of the interplanetary magnetic field (IMF) Bz component, with a 1 min interval between them, two enhancements of the antisunward convection in the polar cap with the same time interval, and 15 min oscillations in the geomagnetic H component in the auroral zone. The distribution of the pulsation intensity along meridian has two local maxima, namely at the equatorial and poleward boundaries of the auroral oval, where pulsations occurred in the out-of-phase mode resembling the field line resonance. At the initial stage, the auroral breakup developed as the auroral torch stretched and expanded poleward along the meridian. Later it took the form of the large-scale coiling structure that also distinguishes the considered substorm from the classical one. Magnetic, radar, and the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) satellite data show that, before the collapse, the coiling structure was located between two field-aligned currents, namely downward at the poleward boundary of structure and upward at the equatorial boundary. The set of GEOTAIL satellites and ground data fit to the near-tail current disruption scenario of the substorm onset. We suggest that the 15 min oscillations might play a role in the substorm initiation.
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Brogl, S., R. E. Lopez, M. Wiltberger, and H. K. Rassoul. "Studies of magnetotail dynamics and energy evolution during substorms using MHD simulations." Annales Geophysicae 27, no. 4 (April 8, 2009): 1717–27. http://dx.doi.org/10.5194/angeo-27-1717-2009.
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Abstract. We examine the distribution and propagation of energy in the plasma sheet and lobes using observations and simulations for three substorms. The substorms occurred on 9 March 1995, 10 December 1996, and 27 August 2001 and have been simulated using the Lyon-Fedder-Mobarry magneto-hydrodynamic code. All three events occur over North America and show a clear substorm current wedge over the ground magnetometer chains of Alaska, Canada, and Greenland. The three simulations show the thinning of the plasma sheet during the growth phase of the event and an increase in the relative amount of thermal energy due to the compression of the plasma sheet. Generally, the total lobe energy, polar cap flux, and lobe magnetic field strength simultaneously increase during the growth phase, and polar cap flux and total lobe energy only start dropping at substorm onset, as measured by the CANOPUS magnetometer chain. Starting at time of onset and continuing throughout the expansion phase a transfer of magnetic energy from the lobes into the plasma sheet occurs, with the increase in the plasma sheet energy ranging from 30–40% of the energy that is released from the lobes.
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Shue, J. H., P. T. Newell, K. Liou, C. I. Meng, M. R. Hairston, and F. J. Rich. "Ionospheric characteristics of the dusk-side branch of the two-cell aurora." Annales Geophysicae 24, no. 1 (March 7, 2006): 203–14. http://dx.doi.org/10.5194/angeo-24-203-2006.
Повний текст джерелаАнотація:
Abstract. The two-cell aurora is characterized by azimuthally elongated regions of enhanced auroral brightness over extended local times in the dawn and dusk sectors. Its association with the convection, particle precipitation, and field-aligned currents under various phases of substorms has not been fully understood. With Polar Ultraviolet Imager auroral images in conjunction with Defense Meteorological Satellite Program (DMSP) F12 spacecraft on the dusk-side branch of the two-cell aurora, we are able to investigate an association of the auroral emissions with the electric fields, field-aligned currents, and energy flux of electrons. Results show that the substorm expansion onset does not significantly change the orientation of the dusk-side branch of the two-cell aurora. Also, the orientation of the magnetic deflection vector produced by the region 1 field-aligned current changed from 73±1° to the DMSP trajectory during the substorm growth phase, to 44±6° to the DMSP trajectory during the substorm expansion phase. With a comparison between the orientation of the dusk-side branch of the two-cell aurora and the orientation of the magnetic deflection vector, it is found that the angular difference between the two orientations is 28±5° during the substorm growth phase, and 13±6° during the substorm expansion phase.
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Forsyth, C., M. Lester, R. C. Fear, E. Lucek, I. Dandouras, A. N. Fazakerley, H. Singer, and T. K. Yeoman. "Solar wind and substorm excitation of the wavy current sheet." Annales Geophysicae 27, no. 6 (June 19, 2009): 2457–74. http://dx.doi.org/10.5194/angeo-27-2457-2009.
Повний текст джерелаАнотація:
Abstract. Following a solar wind pressure pulse on 3 August 2001, GOES 8, GOES 10, Cluster and Polar observed dipolarizations of the magnetic field, accompanied by an eastward expansion of the aurora observed by IMAGE, indicating the occurrence of two substorms. Prior to the first substorm, the motion of the plasma sheet with respect to Cluster was in the ZGSM direction. Observations following the substorms show the occurrence of current sheet waves moving predominantly in the −YGSM direction. Following the second substorm, the current sheet waves caused multiple current sheet crossings of the Cluster spacecraft, previously studied by Zhang et al. (2002). We further this study to show that the velocity of the current sheet waves was similar to the expansion velocity of the substorm aurora and the expansion of the dipolarization regions in the magnetotail. Furthermore, we compare these results with the current sheet wave models of Golovchanskaya and Maltsev (2005) and Erkaev et al. (2008). We find that the Erkaev et al. (2008) model gives the best fit to the observations.
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Hoffman, R. A., J. W. Gjerloev, L. A. Frank, and J. W. Sigwarth. "Are there optical differences between storm-time substorms and isolated substorms?" Annales Geophysicae 28, no. 5 (May 28, 2010): 1183–98. http://dx.doi.org/10.5194/angeo-28-1183-2010.
Повний текст джерелаАнотація:
Abstract. We have performed an extensive analysis of auroral optical events (substorms) that occurred during the development of the main phase of magnetic storms. Using images from the Earth Camera on the Polar spacecraft (Frank et al., 1995), we compared the optical emission features of substorms occurring during 16 expansion phases of magnetic storms with the features of isolated substorms occurring during non-storm times. The comparison used two techniques, visual inspection and statistical comparisons. The comparisons were based on the common characteristics seen in isolated substorms that were initially identified by Akasofu (1964) and quantified by Gjerloev et al. (2008). We find that when auroral activity does occur during main phase development the characteristics of the aurora are very dissimilar to those of the classical isolated substorm. The primary differences include the lack of a surge/bulge, lack of bifurcation of the aurora, much shorter expansion phases, and greater intensities. Since a surge/bulge and bifurcation of the aurora are characteristics of the existence of a substorm current wedge, a key component of the magnetosphere-ionosphere current system during substorms, the lack of this component would indicate that the classical substorm model does not apply to the storm time magnetosphere-ionosphere current system. Rather several of the analyses suggest that the storm-time substorms are associated more closely with the auroral oval, at least spatially, and, therefore, probably with the plasma sheet dynamics during the main phase development. These results then must call into question the widely held assumption that there is no intrinsic difference between storm-time substorms and classical isolated substorms.
Дисертації з теми "Polar magnetic substorm"
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Wissing, Jan Maik. "Analysis of Particle Precipitation and Development of the Atmospheric Ionization Module OSnabrück - AIMOS." Doctoral thesis, 2011. https://repositorium.ub.uni-osnabrueck.de/handle/urn:nbn:de:gbv:700-201108318300.
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The goal of this thesis is to improve our knowledge on energetic particle precipitation into the Earth’s atmosphere from the thermosphere to the surface. The particles origin from the Sun or from temporarily trapped populations inside the magnetosphere.
The best documented influence of solar (high-) energetic particles on the atmosphere is the Ozone depletion in high latitudes, attributed to the generation of HOx and NOx by precipitating particles (Crutzen et al., 1975; Solomon et al., 1981; Reid et al., 1991). In addition Callis et al. (1996b, 2001) and Randall et al. (2005, 2006) point out the importance of low-energetic precipitating particles of magnetospheric origin, creating NOx in the lower thermosphere, which may be transported downwards where it also contributes to Ozone depletion.
The incoming particle flux is dramatically changing as a function of auroral/geomagnetical activity and in particular during solar particle events. As a result, the degree of ionization and the chemical composition of the atmosphere are substantially affected by the state of the Sun. Therefore the direct energetic or dynamical influences of ions on the upper atmosphere depend on solar variability at different time scales.
Influences on chemistry have been considered so far with simplified precipitation patterns, limited energy range and restrictions to certain particle species, see e.g. Jackman et al. (2000); Sinnhuber et al. (2003b, for solar energetic protons and no spatial differentiation), and Callis et al. (1996b, 2001, for magnetospheric electrons only). A comprehensive atmospheric ionization model with spatially resolved particle precipitation including a wide energy range and all main particle species as well as a dynamic magnetosphere was missing.
In the scope of this work, a 3-D precipitation model of solar and magnetospheric particles has been developed. Temporal as well as spatial ionization patterns will be discussed. Apart from that, the ionization data are used in different climate models, allowing (a) simulations of NOx and HOx formation and transport, (b) comparisons to incoherent scatter radar measurements and (c) inter-comparison of the chemistry part in different models and comparison of model results to MIPAS observations. In a bigger scope the ionization data may be used to better constrain the natural sources of climate change or consequences for atmospheric dynamics due to local temperature changes by precipitating particles and
their implications for chemistry. Thus the influence of precipitating energetic particles on the composition and dynamics of the atmosphere is a challenging issue in climate modeling. The ionization data is available online and can be adopted automatically to any user specific model grid.
Книги з теми "Polar magnetic substorm"
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United States. National Aeronautics and Space Administration., ed. Waves in space plasmas: Final report. [Washington, DC: National Aeronautics and Space Administration, 1994.
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United States. National Aeronautics and Space Administration., ed. Ion drift meter research: Final report 1 January 1992 - 31 December 1993. Richardson, TX: The University of Texas at Dallas, 1994.
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Akasofu, Syun-Ichi. Polar and Magnetospheric Substorms. Springer, 2011.
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Akasofu, Syun-Ichi. Polar and Magnetospheric Substorms. Springer, 2012.
Знайти повний текст джерелаЧастини книг з теми "Polar magnetic substorm"
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Akasofu, Syun-Ichi. "Realizing the Dream of Our Pioneers: Polar Magnetic Substorms and the Associated Current System." In Astrophysics and Space Science Library, 79–95. New York, NY: Springer New York, 2007. http://dx.doi.org/10.1007/0-387-45097-1_3.
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Kennel, Charles F. "The Reconnection Substorm." In Convection and Substorms. Oxford University Press, 1996. http://dx.doi.org/10.1093/oso/9780195085297.003.0010.
Повний текст джерелаАнотація:
The reconnection model of magnetospheric substorms was designed 20 years ago to rationalize the time-dependent changes in the magnetospheric structure associated with auroral substorms. By 1970, it was becoming apparent that there was a characteristic sequence of events prior to auroral onset: The dayside magnetopause moved earthward, the inner edge of the cross-tail current sheet approached the earth, the field strength in the tail lobes increased, and the magnetic flux in the polar caps and tail lobes increased, all while the evening side aurora were migrating equatorward prior to onset. The increase in lobe magnetic field clearly suggested that the growth phase commenced with an increase in the dayside reconnection rate. By the early 1980s, studies quantitatively correlating the ionospheric electric field with southward interplanetary field had confirmed that the changes in structure accompanied enhanced convection as had been suspected all along. Both were related somehow to substorms. There was no other choice in the reconnection model but to spotlight its two reconnection events, at the dayside magnetopause and in the plasma sheet on the nightside, as the “main events” in the magnetospheric substorm. Dayside reconnection clearly initiated the growth phase, and tail reconnection had to follow with some delay. It seemed natural to associate tail reconnection with the onset of the auroral substorm. Sections 7.2 through 7.6 are devoted to growth-phase phenomenology. Section 7.2 deals with the changes in magnetopause position that follow a single isolated southward shift of the interplanetary field, and Section 7.3 deals with the changes in the geomagnetic tail that occur as a result. These changes take place as the rate of convection builds up in the ionosphere (Section 7.4) and the dayside magnetosphere (Section 7.5). A growth phase that begins with enhanced dayside reconnection has to lead to enhanced tail reconnection—the second key event in the reconnection model of substorms. In an MHD model, the time and place where the new reconnection event takes place is determined by the propagation of waves along the characteristics connecting the dayside reconnection region to the tail lobes (Section 7.6).
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Kennel, Charles F. "The Nightside Auroral Oval." In Convection and Substorms. Oxford University Press, 1996. http://dx.doi.org/10.1093/oso/9780195085297.003.0014.
Повний текст джерелаАнотація:
The basic structure of the auroral oval was pieced together from relatively local magnetometer measurements and all-sky photographs taken on the ground. The all-sky cameras picked out relatively intense features whose intensities exceeded roughly one kilorayleigh. Their fields of view had a 500-1000 km radius at auroral altitudes, and so extended over 5-10 degrees of latitude and about 90 minutes of local time. Had the aurora been stationary and time-independent, this would have been enough, and it was enough to spot the existence of substorms. It was not enough to solve the substorm problem. As the instruments to study auroral phenomena grew in sophistication and comprehensiveness, so also did our understanding of the concept of the auroral oval. This chapter is dedicated to communicating some of this modern understanding as a prelude to the discussion of substorms in the next chapter. Ground instruments can follow the time development of events within their fields of view but have difficulty separating changes in space and time on scales longer than an hour of universal time or local time, because the observing station rotates with the earth to a local time sector where the aurora may differ. This difficulty can be offset to some extent by airplane flights that remain at a constant local time. However, the real breakthrough came with auroral imaging from space. In the 1970s, optical wavelength imaging from low-altitude polar orbit provided snapshots of the aurora over several thousand kilometer scale portions of the oval on each polar pass of the spacecraft (Shepherd et al., 1973; Anger et al., 1973; Lui and Anger, 1973; Pike and Whalen, 1974; Snyder and Akasofu, 1974). And the spacecraft could detect the precipitating particles responsible for the auroral light emitted from the magnetic footprint of the field lines along its path. The results from the first generation of auroral imaging experiments have been summarized in excellent reviews (Akasofu, 1974, 1976; Hultquist, 1974; Burch, 1979). Ultraviolet imaging allows one to see the dayside aurora.
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Kennel, Charles F. "The Reconnecting Magnetosphere." In Convection and Substorms. Oxford University Press, 1996. http://dx.doi.org/10.1093/oso/9780195085297.003.0008.
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Dungey’s (1961a) pattern of internal magnetospheric convection was similar to that of Axford and Hines (1961). However, his model made testable statements about the structure of the magnetosphere that were not contained in the viscous convection model. It predicted that solar wind plasma enters the magnetosphere over the polar caps, that open field lines connect the polar caps directly to the interplanetary magnetic field, and that these field lines are stretched into a long, low-density magnetic tail. There would be a current layer separating the two lobes of the tail, and surrounding it, a sheet of relatively dense, hot, earthward-convecting plasma confined by closed field lines. A second magnetic neutral line would terminate the earthward flow region (Levy et al., 1964; Axford et al., 1965; Petschek, 1966; Axford, 1969). To preserve the steady state, reconnection at the tail neutral line had to have the same rate as at the dayside magnetopause. Clearly, the two reconnection regions ought to be major drivers of magnetospheric activity. Yet unambiguous proof of the existence of magnetopause reconnection was not found until 1979, 18 years after the reconnection model was proposed, and no one knew where to look for tail reconnection, because Dungey’s model did not say how far away the tail neutral line was. However, the closure of the slow expansion fans carrying solar wind plasma into the tail lobes was a natural way to force tail reconnection (Coroniti and Kennel, 1979). This closure point is fifty to one hundred earth radii downstream of earth. Twenty-four years were to pass before the average location of the tail neutral line could be established, because no spacecraft until ISEE-3 spent enough time that far downtail. In retrospect, it is a testament to the power of the paradigm that so many would search for so long for direct evidence of dayside and nightside reconnection without jettisoning Dungey’s model altogether. Faith in Dungey’s model was sustained by its collateral predictions. The access of energetic particles of solar origin to the polar cap ionosphere confirmed that reconnection occurs.
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Kennel, Charles F. "Bursty Magnetopause Reconnection and its Consequences." In Convection and Substorms. Oxford University Press, 1996. http://dx.doi.org/10.1093/oso/9780195085297.003.0011.
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There is at least one way in which the reconnection model of substorms is unrealistic. Rarely if ever will the interplanetary field rotate southward, stay southward, and remain constant. Even on those infrequent occasions when it does do so, steady reconnection may not be established on the dayside: We will see that dayside reconnection proceeds in bursts even then. How likely is it then that steady convection will be established on the nightside? In the next two chapters, we will fit together observations of bursty convection at the magnetopause, in the polar cap and auroral ionosphere, at various distances downtail in the plasma sheet, and beyond the average position of the neutral line in the deep tail. In this chapter, we deal with unsteady magnetopause reconnection. We start with one simple observation: The magnetopause is a source of escaping particles with energies higher than can be generated by the average convection potential across the ionosphere (Section 8.2). This, together with the fact that high-speed magnetopause flows can turn on and off between successive magnetopause crossings only minutes apart, suggests that the rate of reconnection is high for short periods of time and low for longer intervals. When the reconnection events are shorter than or comparable to MHD wave propagation times to the ionosphere, we call the reconnection “bursty.” We then let observation define the properties of bursty magnetopause reconnection. First, we discuss “flux transfer events” (FTEs), the traveling magnetic perturbations near the magnetopause (Section 8.3) that are signatures of bursty reconnection elsewhere on the magnetopause (Section 8.4). The magnitudes of the fluxes reconnected in FTEs are estimated in Section 8.5. Next, we discuss some of the ionospheric signatures of flux transfer events that might be expected on general theoretical grounds (Section 8.6). Variable dayside reconnection could be responsible for ULF magnetic activity in the polar cusp region (Section 8.7). We expect sudden magnetopause reconnection events to send Alfven waves (Section 8.8) and velocity-dispersed ions along field lines towards the polar cusp ionosphere (Section 8.9).
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A. Troshichev, Oleg. "The Polar Cap Magnetic Activity (PC Index) as a Tool of Monitoring and Nowcasting the Magnetospheric Disturbances." In Magnetosphere and Solar Winds, Humans and Communication. IntechOpen, 2022. http://dx.doi.org/10.5772/intechopen.103165.
Повний текст джерелаАнотація:
PC index was originally introduced as a characteristic of the polar cap magnetic activity generated by geoeffective solar wind coupling with the magnetosphere. Subsequent researches showed that the PC index follows changes of the solar wind electric field EKL through the field-aligned current system (R1 FAC) responding to variations of the solar wind parameters. Appearance of magnetospheric disturbances is specified by the PC index value (with a typical threshold level ~ 1.5 ± 0.5 mV/m) and by the PC index growth rate. The disturbance progression strongly follows the PC index variations, the intensity of substorms (AL) and magnetic storms (Dst) being linearly related to the PC magnitude. In view of these statistically justified relationships, the PC index is regarded at present as a proxy of the solar wind energy input into the magnetosphere. A great advantage of the PC index application over other methods, based on the satellite measurements, is a permanent on-line availability of information on the magnetic activity in both northern (PCN) and southern (PCS) polar caps, providing a means for monitoring the magnetosphere state and for nowcasting the magnetic disturbances development.
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Kennel, Charles F. "Convection For Northward Interplanetary Field." In Convection and Substorms. Oxford University Press, 1996. http://dx.doi.org/10.1093/oso/9780195085297.003.0013.
Повний текст джерелаАнотація:
Besides common sense, a number of results suggest that we can learn more about the slow “viscous” flow state by studying the magnetosphere during northward interplanetary field conditions. In particular, statistical studies have consistently identified a “residual” state of magnetospheric and ionospheric convection in northward field conditions. The integrated potential across the high latitudeionosphere does not drop below a certain resting value of about 20 kV even when the interplanetary field has been due north for several hours. There appears to be a similar residual component of geomagnetic activity that is independent of the direction of the interplanetary field (Scurry and Russell, 1991). Its correlation with the dynamic pressure of the solar wind strengthens our suspicion that it is related to viscosity. Will we be able to prove the convection in this residual state is driven by viscosity? Does the flow in northward field conditions resemble the underlying irregular flow state of the plasma sheet found at other times? Does the magnetosphere approach the teardrop configuration during prolonged intervals of northward interplanetary field? These are but a few of the questions that whet our interest in convection during northward field conditions. One does not arrive at the state of pure viscous convection immediately after the interplanetary field swings northward. Dungey (1963) was the first of many to argue that a northward magnetosheath field line will reconnect with an open tail lobe field line to create one that is connected to the ionosphere at one end and draped over the dayside magnetopause at the other. The sudden reconfiguration of stress will lead to sunward convection on the newly reconnected field lines. In the ionosphere, this superposes a “reverse” two-cell convection pattern in the central polar cap upon the two “direct” convection cells. If and when the draped reconnected field line finds a partner in the opposite tail lobe with which to reconnect, a newly closed field line will form. Dungey had imagined that the same magnetosheath field line would reconnect simultaneously with both tail lobes, in which case the rate at which open magnetic flux is closed depends upon the rate of tail-lobe reconnection.
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"Realizing the Dream of Our Pioneers: Polar Magnetic Substorms and the Associated Current System." In Exploring the Secrets of the Aurora, 89–132. Dordrecht: Springer Netherlands, 2002. http://dx.doi.org/10.1007/0-306-47970-2_3.
Повний текст джерелаЗвіти організацій з теми "Polar magnetic substorm"
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BARKHATOV, NIKOLAY, and SERGEY REVUNOV. A software-computational neural network tool for predicting the electromagnetic state of the polar magnetosphere, taking into account the process that simulates its slow loading by the kinetic energy of the solar wind. SIB-Expertise, December 2021. http://dx.doi.org/10.12731/er0519.07122021.
Повний текст джерелаАнотація:
The auroral activity indices AU, AL, AE, introduced into geophysics at the beginning of the space era, although they have certain drawbacks, are still widely used to monitor geomagnetic activity at high latitudes. The AU index reflects the intensity of the eastern electric jet, while the AL index is determined by the intensity of the western electric jet. There are many regression relationships linking the indices of magnetic activity with a wide range of phenomena observed in the Earth's magnetosphere and atmosphere. These relationships determine the importance of monitoring and predicting geomagnetic activity for research in various areas of solar-terrestrial physics. The most dramatic phenomena in the magnetosphere and high-latitude ionosphere occur during periods of magnetospheric substorms, a sensitive indicator of which is the time variation and value of the AL index. Currently, AL index forecasting is carried out by various methods using both dynamic systems and artificial intelligence. Forecasting is based on the close relationship between the state of the magnetosphere and the parameters of the solar wind and the interplanetary magnetic field (IMF). This application proposes an algorithm for describing the process of substorm formation using an instrument in the form of an Elman-type ANN by reconstructing the AL index using the dynamics of the new integral parameter we introduced. The use of an integral parameter at the input of the ANN makes it possible to simulate the structure and intellectual properties of the biological nervous system, since in this way an additional realization of the memory of the prehistory of the modeled process is provided.