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Yagova, Nadezda, Natalia Nosikova, Lisa Baddeley, Olga Kozyreva, Dag A. Lorentzen, Vyacheslav Pilipenko i 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, nr 3 (8.03.2017): 365–76. http://dx.doi.org/10.5194/angeo-35-365-2017.
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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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Guineva, Veneta, Irina Despirak, Rolf Werner, Rumiana Bojilova i Lyubomira Raykova. "Mid-latitude effects of “expanded” geomagnetic substorms: a case study". EPJ Web of Conferences 254 (2021): 01004. http://dx.doi.org/10.1051/epjconf/202125401004.
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The goal of this work is to examine the effects of the “expanded” or “high-latitude” substorms at mid-latitudes. These substorms are generated at auroral latitudes and propagate up to geomagnetic latitudes above ∼70° GMLat. They are usually observed during reccurent high-speed streams (HSS) from coronal holes. To identify the substorm activity, data from the networks IMAGE, SuperMAG and INTERMAGNET, and data from the all-sky cameras in Lovozero were used. To verify the interplanetary and geomagnetic conditions, data from the CDAWeb OMNI and from the WDC for geomagnetism at Kyoto were taken. We analyzed one substorm event on 20 February 2017 at ∼18:40 UT, it developed during HSS, in non-storm conditions. Some features of mid-latitude positive bays (MPB) at the European and Asian stations, and in particular at the Scandinavian meridian have been studied: the bay sign conversion from negative to positive values, the longitudinal and latitudinal extent of the MPB. The central meridian of the substorm was determined.
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Lu, Li, Qinglong Yu, Shuai Jia, Zhong Xie, Jian Lan i Yuan Chang. "Simulation of Dynamic Evolution of Ring Current Ion Flux by a Lunar Base Energetic Neutral Atom (ENA) Imaging". Astronomy 2, nr 3 (22.08.2023): 153–64. http://dx.doi.org/10.3390/astronomy2030011.
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The distribution of energetic ion flux in the ring current region, such as a meteorological cumulonimbus cloud, stores up the particle energy for a geomagnetic substorm. It is helpful to study the geomagnetic substorm mechanism by using a lunar base ENA imaging simulation of the dynamic evolution of the ring current, and establishing the corresponding relationship between key node events of the substorm. Based on the previous observation experience and our simulation results of the dynamic evolution of the ring current, we propose a macroscopic model of substorms related to the dynamic evolution of ring currents and present the possibility of confirming the causal sequence of some of those critical node events of substorms with the lunar base ENA imaging measurement. IBEX, operating in the ecliptic plane, may even give examples of the telemetry of ring current ion fluxes through ENA measurements during substorms/quiets.
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Iyemori, T., i D. R. K. Rao. "Decay of the Dst field of geomagnetic disturbance after substorm onset and its implication to storm-substorm relation". Annales Geophysicae 14, nr 6 (30.06.1996): 608–18. http://dx.doi.org/10.1007/s00585-996-0608-3.
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Abstract. In order to investigate the causal relationship between magnetic storms and substorms, variations of the mid-latitude geomagnetic indices, ASY (asymmetric part) and SYM (symmetric part), at substorm onsets are examined. Substorm onsets are defined by three different phenomena; (1) a rapid increase in the mid-latitude asymmetric-disturbance indices, ASY-D and ASY-H, with a shape of so-called `mid-latitude positive bay\\'; (2) a sharp decrease in the AL index; (3) an onset of Pi2 geomagnetic pulsation. The positive bays are selected using eye inspection and a pattern-matching technique. The 1-min-resolution SYM-H index, which is essentially the same as the hourly Dst index except in terms of the time resolution, does not show any statistically significant development after the onset of substorms; it tends to decay after the onset rather than to develop. It is suggested by a simple model calculation that the decay of the magnetospheric tail current after substorm onset is responsible for the decay of the Dst field. The relation between the IMF southward turning and the development of the Dst field is re-examined. The results support the idea that the geomagnetic storms and substorms are independent processes; that is, the ring-current development is not the result of the frequent occurrence of substorms, but that of enhanced convection caused by the large southward IMF. A substorm is the process of energy dissipation in the magnetosphere, and its contribution to the storm-time ring-current formation seems to be negligible. The decay of the Dst field after a substorm onset is explained by a magnetospheric energy theorem.
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Belova, E., S. Kirkwood i H. Tammet. "The effect of magnetic substorms on near-ground atmospheric current". Annales Geophysicae 18, nr 12 (31.12.2000): 1623–29. http://dx.doi.org/10.1007/s00585-001-1623-z.
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Abstract. Ionosphere-magnetosphere disturbances at high latitudes, e.g. magnetic substorms, are accompanied by energetic particle precipitation and strong variations of the ionospheric electric fields and currents. These might reasonably be expected to modify the local atmospheric electric circuit. We have analysed air-earth vertical currents (AECs) measured by a long wire antenna at Esrange, northern Sweden during 35 geomagnetic substorms. Using superposed epoch analysis we compare the air-earth current variations during the 3 h before and after the time of the magnetic X-component minimum with those for corresponding local times on 35 days without substorms. After elimination of the average daily variation we can conclude that the effect of substorms on AEC is small but distinguishable. It is speculated that the AEC increases observed during about 2 h prior to the geomagnetic X-component minimum, are due to enhancement of the ionospheric electric field. During the subsequent 2 h of the substorm recovery phase, the difference between "substorm" and "quiet" atmospheric currents decreases. The amplitude of this "substorm" variation of AEC is estimated to be less than 50% of the amplitude of the diurnal variation in AEC during the same time interval. The statistical significance of this result was confirmed using the Van der Waerden X-test. This method was further used to show that the average air-earth current and its fluctuations increase during late expansion and early recovery phases of substorms.Key words: Ionosphere (electric fields and currents) · Magnetospheric physics (storms and substorms) · Meteorology and atmospheric dynamics (atmospheric electricity)
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Куражковская, Надежда, Nadezhda Kurazhkovskaya, Борис Клайн i Boris Klain. "Effect of geomagnetic activity, solar wind and parameters of interplanetary magnetic field on regularities in intermittency of Pi2 geomagnetic pulsations". Solnechno-Zemnaya Fizika 1, nr 3 (27.09.2015): 11–20. http://dx.doi.org/10.12737/11551.
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We present the results of investigation of the influence of geomagnetic activity, solar wind and parameters of the interplanetary magnetic field (IMF) on properties of the intermittency of midlatitude burst series of Pi2 geomagnetic pulsations observed during magnetospheric substorms on the nightside (substorm Pi2) and in the absence of these phenomena (nonsub-storm Pi2). We considered the index α as a main characteristic of intermittency of substorm and nonsubstorm Pi2 pulsations. The index α characterizes the slope of the cumulative distribution function of Pi2 burst amplitudes. The study indicated that the value and dynamics of the index α varies depending on the planetary geomagnetic activity, auroral activity and the intensity of magnetospheric ring currents. In addition, the forms of dependences of the index α on the density n, velocity V, dynamic pressure Pd of the solar wind and IMF Bx-component are different. The behavior of the index α depending on the module of B, By- and Bz-components is similar. We found some critical values of V, Pd, B, By- and Bz-components, after reaching of which the turbulence of the magnetotail plasma during substorm development is decreased. The revealed patterns of the intermittency of Pi2 pulsations can be used for qualitative assessment of turbulence level in the magnetotail plasma depending on changing interplanetary conditions.
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Wild, J. A., E. E. Woodfield i S. K. Morley. "On the triggering of auroral substorms by northward turnings of the interplanetary magnetic field". Annales Geophysicae 27, nr 9 (25.09.2009): 3559–70. http://dx.doi.org/10.5194/angeo-27-3559-2009.
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Abstract. Some studies over the last decade have indicated that the instability responsible for substorm expansion phase onset may require an external trigger such as a northward turning of the interplanetary magnetic field (IMF). Statistical investigations have lead to contrasting interpretations regarding the relationship between proposed solar wind triggers and substorm onsets identified from geomagnetic data. We therefore present the results of a study into the possible triggering of 260 substorms between 2001–2005, exploiting data from the Cluster and IMAGE satellite missions. We find that only a small fraction (<25%) of the substorms studied are associated with northward turnings of the IMF. However, the majority of the observed onsets are associated with a growth phase characterised using a subset of the criteria employed to define northward-turning IMF triggers. Based upon a case-by-case investigation and the results of an analysis using the statistics of point processes, we conclude that northward-turning structures in the IMF, while sometimes coinciding with the initial phase of individual substorms, are not required to trigger the magnetospheric instability associated with substorm expansion phase onset.
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Wang, H., i H. Lühr. "The efficiency of mechanisms driving Subauroral Polarization Streams (SAPS)". Annales Geophysicae 29, nr 7 (20.07.2011): 1277–86. http://dx.doi.org/10.5194/angeo-29-1277-2011.
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Abstract. We have investigated the seasonal and diurnal variation of SAPS (Subauroral Polarization Streams) occurrence based on 3663 SAPS events identified in DMSP ion drift observations in the Northern Hemisphere during July 2001 and June 2003. Their relationships with high latitude convection electric field, substorm, and ionospheric conductivity have been addressed. SAPS occurrences show a clear seasonal and diurnal variation with the occurrence rates varying by a factor of 5. It is found that the convection electric field might play a dominant role in association with SAPS occurrence. Peak convection electric fields mark the occurrence maximum of SAPS. Substorm might play a secondary role related to SAPS occurrence. It account for the secondary maximum in SAPS occurrence rate during December solstice. Our work demonstrates that the substorm induced electric field can develop SAPS during relatively low global convection. Somewhat low fluxtube-integrated conductivity is favorable for SAPS to develop. Another topic is the temporal relationship between SAPS and substorm phases. SAPS can occur at substorm onset, substorm expansion and recovery phases. Most probably SAPS tend to occur 60 min/45 min after substorm onset during quiet/more disturbed geomagnetic activity, respectively. This indicates that enhanced global convection helps SAPS to develop quicker during substorms. The peak plasma velocity of SAPS is increased on average only by 5–10 % by the substorm process.
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Guineva, Veneta, Irina Despirak i Natalia Kleimenova. "Substorms manifestation at high and mid-latitudes during two large magnetic storm". Aerospace Research in Bulgaria 31 (2019): 27–39. http://dx.doi.org/10.3897/arb.v31.e03.
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The dynamics of magnetic substorms at high and middle latitudes during two severe geomagnetic storms: on 17March 2015 and on 22–23 June2015has been analyzed. The storms were rather similar: both storms were a result of the solar wind Sheath impact and both storms were characterized by a strong intensity (SYM/Hmin<–200nT). We studied the magnetic substorms during these storms on the base of the INTERMAGNET and IMAGE networks data. The attendant solar wind and Interplanetary Magnetic Field (IMF) parameters were taken from the OMNI data base. The spatial-temporal dynamics of three substorms was studied in detail: at 17:29 UT and at 22:55 UT during the first storm and at 18:33 UT during the second storm. The substorms on 17.03.2015originated during the main storm phase, and the onset of the substorm on 22.06.2015 followed the storm sudden commencement (SSC) of the second storm. All three substorms were characterized by a sharp poleward expansion of the westward electrojet simultaneously with a slower motion to lower latitudes. They were observed also at middle and low latitudes as positive magnetic bays. The westward electrojet reached ~71°CGMLat during the first two substorms and surpassed 75°CGMLat during the third substorm. Therefore, the first two events were “classical” substorms, and the third one –an “expanded” substorm. We suggested that this behavior is related to the different solar wind conditions: the “classical” substorms developed under magnetic cloud (MC) conditions, and the “expanded” –under the Sheath region effect.
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Pulkkinen, A., A. Thomson, E. Clarke i A. McKay. "April 2000 geomagnetic storm: ionospheric drivers of large geomagnetically induced currents". Annales Geophysicae 21, nr 3 (31.03.2003): 709–17. http://dx.doi.org/10.5194/angeo-21-709-2003.
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Abstract. Geomagnetically induced currents (GIC) flowing in technological systems on the ground are a direct manifestation of space weather. Due to the proximity of very dynamic ionospheric current systems, GIC are of special interest at high latitudes, where they have been known to cause problems, for example, for normal operation of power transmission systems and buried pipelines. The basic physics underlying GIC, i.e. the magnetosphere – ionosphere interaction and electromagnetic induction in the ground, is already quite well known. However, no detailed study of the drivers of GIC has been carried out and little is known about the relative importance of different types of ionospheric current systems in terms of large GIC. In this study, the geomagnetic storm of 6–7 April 2000 is investigated. During this event, large GIC were measured in technological systems, both in Finland and in Great Britain. Therefore, this provides a basis for a detailed GIC study over a relatively large regional scale. By using GIC data and corresponding geomagnetic data from north European magnetometer networks, the ionospheric drivers of large GIC during the event were identified and analysed. Although most of the peak GIC during the storm were clearly related to substorm intensifications, there were no common characteristics discernible in substorm behaviour that could be associated with all the GIC peaks. For example, both very localized ionospheric currents structures, as well as relatively large-scale propagating structures were observed during the peaks in GIC. Only during the storm sudden commencement at the beginning of the event were large-scale GIC evident across northern Europe with coherent behaviour. The typical duration of peaks in GIC was also quite short, varying between 2–15 min.Key words. Geomagnetism and paleo-magnetism (geomagnetic induction) – Ionosphere (ionospheric disturbances) – Magnetospheric physics (storms and substorms)
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Moldwin, Mark B., i W. Jeffrey Hughes. "Geomagnetic substorm association of plasmoids". Journal of Geophysical Research: Space Physics 98, A1 (1.01.1993): 81–88. http://dx.doi.org/10.1029/92ja02153.
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Guineva, V., I. Despirak, R. Werner, R. Bojilova i L. Raykova. "STUDY OF MID-LATITUDE POSITIVE BAYS DURING SUBSTORMS OVER SCANDINAVIA – A CASE STUDY". PHYSICS OF AURORAL PHENOMENA 44 (2021): 28–31. http://dx.doi.org/10.51981/2588-0039.2021.44.006.
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The purpose of this work is to study the midlatitude effects during substorms observed in different interplanetary conditions over Scandinavia. To identify the substorm disturbances, data from the magnetometer networks IMAGE, SuperMAG and INTERMAGNET in the range 31.8° - 75.25° CGMLat and 92° - 104° CGMLon were used. To verify the interplanetary and geomagnetic conditions, data from the CDAWeb OMNI (http://cdaweb.gsfc.nasa.gov/), the catalog of large-scale solar wind phenomena (ftp://ftp.iki.rssi.ru/omni/) and from the WDC for geomagnetism at Kyoto (http://wdc.kugi.kyoto-u.ac.jp/index.html) were taken. Two isolated substorms were chosen, with different intensity: ALmin values ~ -270 nT and ~ -1300 nT, respectively. The first substorm occured on 6 February 2018, at 21:25 UT, under quiet conditions: during slow solar wind streams. The second substorm, at 19:10 UT on 27 September 2020, originated under moderately disturbed conditions: during a high-speed stream (HSS) in the solar wind, just after the passage of EJECTA by the Earth. It was found out, that the latitude of the bay sign conversion from negative to positive values in the case of quiet solar wind conditions, appeared at latitude, 7° higher than the one in the case of disturbed conditions. In both cases, the amplitude of the positive bays, after a maximum near the sign conversion latitude decreased gradually towards the lower latitudes, with a difference between the minimal and maximal amplitude of about 50%. The magnetic bays kept their duration throughout the whole latitudinal range, ~115 min. for the first case and ~ 60 min. for the second one. It was ascertained, that the mean positive bays amplitude in the case of disturbed conditions was 4 times higher than the amplitude during quiet conditions.
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Pierrard, V., i J. Cabrera. "Comparisons between EUV/IMAGE observations and numerical simulations of the plasmapause formation". Annales Geophysicae 23, nr 7 (14.10.2005): 2635–46. http://dx.doi.org/10.5194/angeo-23-2635-2005.
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Abstract. Simulations of plasmapause formation described in Pierrard and Lemaire (2004) predict the shape and equatorial distance of the plasmapause as a function of the geomagnetic activity index Kp. The equatorial positions predicted by this model are compared with the observations of EUV/IMAGE during the geomagnetic storm of 24 May 2000, substorm events of 10 June 2001 and 25 June 2000, and also during a prolonged quiet period (2 May 2001) when the plasmasphere was very extended. The formation of structures, like plumes and shoulders observed during periods of high geomagnetic activity, is quite well reproduced by the simulations. These structures are directly related to specific time sequences of Kp variations. The radial distances of the plasmapause are also reproduced, on average, by the model. Keywords. Magnetospheric physics (Plasmasphere; Storms and substorms; Solar wind magnetosphere interactions)
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Niehof, J. T., S. K. Morley i R. H. W. Friedel. "Association of cusp energetic ions with geomagnetic storms and substorms". Annales Geophysicae 30, nr 12 (6.12.2012): 1633–43. http://dx.doi.org/10.5194/angeo-30-1633-2012.
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Abstract. Energetic ions observed in the cusp have been explained as a result of processes within the magnetosphere, but also proposed as a driver of some of those same processes. This study assesses potential connections between energetic ions observed in the cusp and geomagnetic storm and substorm activity. These connections may suggest sources of cusp energetic particles (CEPs), or imply effects of these particles on magnetospheric dynamics. We identify CEPs from six years of cusp crossings by the Polar satellite, relating them to storm and substorm onsets. CEPs showed no significant dependence on storms but did show a weak, statistically significant, increase after substorm onsets. CEPs had no significant association with subsequent storm or substorm onsets. We conclude that substorm acceleration may contribute to CEPs but CEPs are unlikely to contribute to global magnetospheric dynamics.
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Sharma, Rahul, Nandita Srivastava i D. Chakrabarty. "Role of filament plasma remnants in ICMEs leading to geomagnetic storms". Proceedings of the International Astronomical Union 8, S300 (czerwiec 2013): 493–94. http://dx.doi.org/10.1017/s1743921313011708.
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AbstractWe studied three interplanetary coronal mass ejections associated with solar eruptive filaments. Filament plasma remnants embedded in these structures were identified using plasma, magnetic and compositional signatures. These features when impacted the Earth's terrestrial magnetosphere - ionosphere system, resulted in geomagnetic storms. During the main phase of associated storms, along with high density plasma structures, polarity reversals in the Y-component (dawn-to-dusk) of the interplanetary electric field seem to trigger major auroral substorms with concomitant changes in the polar ionospheric electric field. Here, we examine the cases where plasma dynamics and magnetic structuring in the presence of the prompt penetration of the electric field into the equatorial ionosphere affected the space weather while highlighting the complex geomagnetic storm-substorm relationship.
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Belakhovsky, Vladimir B., Yaqi Jin i Wojciech J. Miloch. "Influence of different types of ionospheric disturbances on GPS signals at polar latitudes". Annales Geophysicae 39, nr 4 (20.07.2021): 687–700. http://dx.doi.org/10.5194/angeo-39-687-2021.
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Abstract. The comparative research of the influence of different types of auroral particle precipitation and polar cap patches (PCPs) on the global positioning system (GPS) signals disturbances in the polar ionosphere was done. For this purpose, we use the GPS scintillation receivers at Ny-Ålesund and Skibotn, operated by the University of Oslo. The presence of the auroral particle precipitation and polar cap patches was determined by using data from the EISCAT 42m radar on Svalbard. The optical aurora observations in 557.7 and 630.0 nm spectrum lines on Svalbard were used as well for the detection of ionospheric disturbances. The cusp identification was done with using SuperDARN (Hankasalmi) data. We consider events when the simultaneous EISCAT 42m and GPS data were available for the years 2010–2017, and in this paper we present, in detail, typical examples describing the overall picture, and we present the statistics for 120 events. We considered the dayside/cusp precipitation, substorm precipitation, daytime and nighttime PCPs, and precipitation associated with the interplanetary shock wave arrival. We demonstrate that substorm-associated precipitation (even without PCPs) can lead to a strong GPS phase (σϕ) scintillations up to ∼ 1.5–3 radians, which is much stronger than those usually produced by other types of considered ionosphere disturbances. The value of the substorm-phase scintillations in general correlate with the value of the geomagnetic field disturbance. But sometimes even a small geomagnetic substorm, when combined with the PCPs, produces quite strong phase scintillations. Cusp phase scintillations are lower than dayside PCPs scintillations. PCPs can lead to stronger ROT (rate of total electron content) variations than other types of ionosphere disturbances. So our observations suggest that the substorms and PCPs, being different types of the high-latitude disturbances, lead to the development of different types and scales of ionospheric irregularities.
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Milan, S. E., A. Grocott, C. Forsyth, S. M. Imber, P. D. Boakes i B. Hubert. "A superposed epoch analysis of auroral evolution during substorm growth, onset and recovery: open magnetic flux control of substorm intensity". Annales Geophysicae 27, nr 2 (11.02.2009): 659–68. http://dx.doi.org/10.5194/angeo-27-659-2009.
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Abstract. We perform two superposed epoch analyses of the auroral evolution during substorms using the FUV instrument on the Imager for Magnetopause-to-Aurora Global Explorer (IMAGE) spacecraft. The larger of the two studies includes nearly 2000 substorms. We subdivide the substorms by onset latitude, a measure of the open magnetic flux in the magnetosphere, and determine average auroral images before and after substorm onset, for both electron and proton aurora. Our results indicate that substorms are more intense in terms of auroral brightness when the open flux content of the magnetosphere is larger, and that magnetic flux closure is more significant. The increase in auroral brightness at onset is larger for electrons than protons. We also show that there is a dawn-dusk offset in the location of the electron and proton aurora that mirrors the relative locations of the region 1 and region 2 current systems. Superposed epoch analyses of the solar wind, interplanetary magnetic field, and geomagnetic indices for the substorms under study indicate that dayside reconnection is expected to occur at a faster rate prior to low latitude onsets, but also that the ring current is enhanced for these events.
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LI Shiyou, XIE Rong i XIAO Yang. "Statistical Study on the Geomagnetic Substorm". Chinese Journal of Space Science 40, nr 6 (2020): 1000. http://dx.doi.org/10.11728/cjss2020.06.1000.
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Simmons, D. A. R., F. Sigernes i K. Henriksen. "Geomagnetic storm and substorm aurora observed from Spitsbergen". Polar Record 31, nr 179 (październik 1995): 375–88. http://dx.doi.org/10.1017/s0032247400027352.
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ABSTRACTThe present study confirms that the auroras of the nightside oval population consist of two main types, namely storm and substorm aurora. Storm-type aurora, which is relatively infrequent, results from bombardment of the upper ionosphere by fast particle streams generated in the solar wind by cataclysmic solar events related to coronal mass ejections. The associated turbulent plasma that is injected into the magnetosphere produces great magnetic storms of world-wide dimensions that may last for days. In contrast, substorm aurora is a frequent (almost daily) occurrence that lasts for an hour or two around geomagnetic midnight. It is generated by the impulsive release of stored magnetospheric energy from the substorm onset region in the Earth's magnetotail and is associated with localised negative magnetic bays in the H (horizontal)-component of the Earth's magnetic field in the vicinity of the auroral oval.
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Selvamurugan, Raman, B. M. Pathan, A. N. Hanchinal i A. Dhar. "Geomagnetic pulsation over conjugate locations during geomagnetic storms and substorm". Advances in Space Research 48, nr 10 (listopad 2011): 1591–99. http://dx.doi.org/10.1016/j.asr.2011.07.011.
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Varlamov, Ilya, Stanislav Parnikov, Igor Ievenko, Dmitry Baishev i Kazuo Shiokawa. "Registration of synchronous geomagnetic pulsations and proton aurora during the substorm on March 1, 2017". EPJ Web of Conferences 254 (2021): 02012. http://dx.doi.org/10.1051/epjconf/202125402012.
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Data of synchronous geomagnetic pulsations and proton aurora registrations were analyzed during the substorm on March 1, 2017 at Zhigansk (L=4.5, induction magnetometer), Maimaga (L=4, all-sky imager and Yakutsk (L = 3.3, induction magnetometer) stations, simultaneously with satellite measurement of EMIC waves. Ground-based registration of proton aurora is very difficult due to the fact that their intensity is much lower than the aurora intensity caused by precipitations of electrons, but in the event of substorm activity at the zenith of Maimaga station, a narrow (1 degree in latitude) proton arc was observed. Irregular pulsations of the diminishing periods (IPDPs) in the range of Pc1 geomagnetic pulsations associated with the injection of energetic protons were recorded simultaneously at Zhigansk and Yakutsk stations. This is the first report when STEVE (Strong Thermal Emission Velocity Enhancement) was observed in the course of a substorm with the onset at 12:45 UT after the decay of Pc1-associated proton arc. It is shown that the proton arc and geomagnetic pulsations are a consequence of ion-cyclotron instability in the area of the outer plasmasphere overlapping by energetic protons.
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Namuun, B., Battuulai Tsegmed, L. Y. Li i G. M. Leghari. "Differences in the response to CME and CIR drivers of geomagnetic disturbances". Solar-Terrestrial Physics 9, nr 2 (29.06.2023): 31–36. http://dx.doi.org/10.12737/stp-92202304.
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Utilizing 1-minute resolution data on the geomagnetic indices SYM-H, AE, solar wind parameters (velocity Vsw and density Np), and z-component Bz of the interplanetary magnetic field (IMF) during solar cycles 23 and 24, we have statistically analyzed the correlations between geomagnetic activity (storms and substorms), Vsw, Np, Bz, and energy coupling functions of solar wind and Earth’s magnetosphere. For the selected 131 CME-driven storms, SYM-H stronger depends on Vsw and B than other parameters, whereas the selected 161 CIR-driven storms have nearly the same dependence on the solar wind electric field, the rate of open magnetic flux dφ/dt, and the reconnection electric field Ekl. Thus, the solar wind electric field and the dayside magnetic reconnection are likely to have different contributions for storms of the two types. During storms of different types, the substorm intensity AE relies mainly on the IMF Bz, rate of open magnetic flux and reconnection electric field.
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Lopez, Ramon E., i Daniel N. Baker. "Evidence for Particle Acceleration During Magnetospheric Substorms". International Astronomical Union Colloquium 142 (1994): 531–39. http://dx.doi.org/10.1017/s0252921100077770.
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AbstractMagnetospheric substorms represent the episodic dissipation of energy stored in the geomagnetic tail that was previously extracted from the solar wind. This energy release produces activity throughout the entire magnetosphere-ionosphere system, and it results in a wide variety of phenomena such as auroral intensifications and the generation of new current systems. All of these phenomena involve the acceleration of particles, sometimes up to several MeV. In this paper we present a brief overview of substorm phenomenology. We then review some of the evidence for particle acceleration in Earth’s magnetosphere during substorms. Such in situ observations in this most accessible of all cosmic plasma domains may hold important clues to understanding acceleration processes in more distant astrophysical systems.Subject headings: acceleration of particles — Earth — solar wind
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Safargaleev, Vladimir V., Alexander E. Kozlovsky i Valery M. Mitrofanov. "Polar substorm on 7 December 2015: preonset phenomena and features of auroral breakup". Annales Geophysicae 38, nr 4 (28.07.2020): 901–18. http://dx.doi.org/10.5194/angeo-38-901-2020.
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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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Barkhatov, N. A., A. B. Vinogradov, A. E. Levitin i E. A. Revunova. "Geomagnetic substorm activity associated with magnetic clouds". Geomagnetism and Aeronomy 55, nr 5 (wrzesień 2015): 596–602. http://dx.doi.org/10.1134/s0016793215050023.
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Santarelli, L., S. Lepidi i L. Cafarella. "Propagation of low frequency geomagnetic field fluctuations in Antarctica: comparison between two polar cap stations". Annales Geophysicae 25, nr 11 (29.11.2007): 2405–12. http://dx.doi.org/10.5194/angeo-25-2405-2007.
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Abstract. We conduct a statistical analysis of the coherence and phase difference of low frequency geomagnetic fluctuations between two Antarctic stations, Mario Zucchelli Station (geographic coordinates: 74.7° S, 164.1° E; corrected geomagnetic coordinates: 80.0° S, 307.7° E) and Scott Base (geographic coordinates: 77.8° S 166.8° E; corrected geomagnetic coordinates: 80.0° S 326.5° E), both located in the polar cap. Due to the relative position of the stations, whose displacement is essentially along a geomagnetic parallel, the phase difference analysis allows to determine the direction of azimuthal propagation of geomagnetic fluctuations. The results show that coherent fluctuations are essentially detectable around local geomagnetic midnight and, in a minor extent, around noon; moreover, the phase difference reverses in the night time hours, indicating a propagation direction away from midnight, and also around local geomagnetic noon, indicating a propagation direction away from the subsolar point. The nigh time phase reversal is more clear for southward interplanetary magnetic field conditions, suggesting a relation with substorm activity. The introduction, in this analysis, of the Interplanetary Magnetic Field conditions, gave interesting results, indicating a relation with substorm activity during nighttime hours. We also conducted a study of three individual pulsation events in order to find a correspondence with the statistical behaviour. In particular, a peculiar event, characterized by quiet magnetospheric and northward interplanetary magnetic field conditions, shows a clear example of waves propagating away from the local geomagnetic noon; two more events, occurring during southward interplanetary magnetic field conditions, in one case even during a moderate storm, show waves propagating away from the local geomagnetic midnight.
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Uritsky, V. M., i M. I. Pudovkin. "Low frequency 1/<i>f</i>-like fluctuations of the AE-index as a possible manifestation of self-organized criticality in the magnetosphere". Annales Geophysicae 16, nr 12 (31.12.1998): 1580–88. http://dx.doi.org/10.1007/s00585-998-1580-x.
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Abstract. Low frequency stochastic variations of the geomagnetic AE-index characterized by 1/f b-like power spectrum (where f is a frequency) are studied. Based on the analysis of experimental data we show that the Bz-component of IMF, velocity of solar wind plasma, and the coupling function of Akasofu are insufficient factors to explain these behaviors of the AE-index together with the 1/f b fluctuations of geomagnetic intensity. The effect of self-organized criticality (SOC) is proposed as an internal mechanism to generate 1/f b fluctuations in the magnetosphere. It is suggested that localized spatially current instabilities, developing in the magnetospheric tail at the initial substorm phase can be considered as SOC avalanches or dynamic clusters, superposition of which leads to the 1/f b fluctuations of macroscopic characteristics in the system. Using the sandpile model of SOC, we undertake numerical modeling of space-localized and global disturbances of magnetospheric current layer. Qualitative conformity between the disturbed dynamics of self-organized critical state of the model and the main phases of real magnetospheric substorm development is demonstrated. It is also shown that power spectrum of sandpile model fluctuations controlled by real solar wind parameters reproduces all distinctive spectral features of the AE fluctuations.Key words. Magnetospheric physics (MHD waves and instabilities; solar wind · magnetosphere interactions; storms and substroms).
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Namuun, B., Battuulai Tsegmed, L. Y. Li i G. M. Leghari. "Differences in the response to CME and CIR drivers of geomagnetic disturbances". Solnechno-Zemnaya Fizika 9, nr 2 (29.06.2023): 35–40. http://dx.doi.org/10.12737/szf-92202304.
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Utilizing 1-minute resolution data on the geomagnetic indices SYM-H, AE, solar wind parameters (velocity Vsw and density Np), and z-component Bz of the interplanetary magnetic field (IMF) during solar cycles 23 and 24, we have statistically analyzed the correlations between geomagnetic activity (storms and substorms), Vsw, Np, Bz, and energy coupling functions of solar wind and Earth’s magnetosphere. For the selected 131 CME-driven storms, SYM-H stronger depends on Vsw and B than other parameters, whereas the selected 161 CIR-driven storms have nearly the same dependence on the solar wind electric field, the rate of open magnetic flux dφ/dt, and the reconnection electric field Ekl. Thus, the solar wind electric field and the dayside magnetic reconnection are likely to have different contributions for storms of the two types. During storms of different types, the substorm intensity AE relies mainly on the IMF Bz, rate of open magnetic flux and reconnection electric field.
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Milan, S. E., T. B. Jones, M. Lester, E. M. Warrington i G. D. Reeves. "Substorm correlated absorption on a 3200 km trans-auroral HF propagation path". Annales Geophysicae 14, nr 2 (29.02.1996): 182–90. http://dx.doi.org/10.1007/s00585-996-0182-8.
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Abstract. A high-frequency transmitter located at Clyde River, NWT, Canada, and a receiver located near Boston, USA, provide a 3200 km trans-auroral, near-meridional propagation path over which the propagation characteristics have been measured. Out of the fourteen frequencies in the HF band sampled every hour for the duration of the experimental campaign (16 January–8 February 1989), the signal level measurements of 6.800 MHz transmissions were selected in order to determine the extent and occurrence of auroral absorption. The median level of auroral absorption along the path is found to increase with geomagnetic activity, quantified by the index Kp, with the increase being greater in the post-midnight sector than in the pre-midnight sector. This asymmetric behaviour is attributed to the precipitation of high energy electrons into the midnight and morning sector auroral D region. The measured diurnal variation in the median level of absorption is consistent with previous models describing the extent and magnitude of auroral absorption and electron precipitation. Individual substorms, identified from geosynchronous satellite data, are found to cause short-lived absorption events in the HF signal level of ~30 dB at 6.800 MHz. The occurrence of substorm correlated auroral absorption events is confined to the midnight and morning sectors, consistent with the location of the electron precipitation. The magnitude of absorption is related to the magnetotail stress during the substorm growth phase and the magnetotail relaxation during the substorm expansion phase onset. The absorption magnitude and the occurrence of substorms during the period of the campaign increase at times of high Kp , leading to an increase in median auroral absorption during disturbed periods.
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Benkevitch, L. V., W. B. Lyatsky, A. V. Koustov, G. J. Sofko i A. M. Hamza. "Substorm onset times as derived from geomagnetic indices". Geophysical Research Letters 29, nr 10 (15.05.2002): 134–1. http://dx.doi.org/10.1029/2001gl014386.
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Keiling, A., F. S. Mozer, H. Rème, I. Dandouras, E. Lucek, M. Fujimoto, H. Hasegawa i G. D. Reeves. "Periodic traveling compression regions during quiet geomagnetic conditions and their association with ground Pi2". Annales Geophysicae 26, nr 11 (21.10.2008): 3341–54. http://dx.doi.org/10.5194/angeo-26-3341-2008.
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Abstract. Recently, Keiling et al. (2006) showed that periodic (~90 s) traveling compression regions (TCRs) during a substorm had properties of Pi2 pulsations, prompting them to call this type of periodic TCRs "lobe Pi2". It was further shown that time-delayed ground Pi2 had the same period as the lobe Pi2 located at 16 RE, and it was concluded that both were remotely driven by periodic, pulsed reconnection in the magnetotail. In the study reported here, we give further evidence for this association by reporting additional periodic TCR events (lobe Pi2s) at 18 RE all of which occurred in succession during a geomagnetically very quiet, non-substorm period. Each quiet-time periodic TCR event occurred during an interval of small H-bay-like ground disturbance (<40 nT). Such disturbances have previously been identified as poleward boundary intensifications (PBIs). The small H bays were superposed by Pi2s. These ground Pi2s are compared to the TCRs in the tail lobe (Cluster) and both magnetic pulsations and flow variations at 9 RE inside the plasma sheet (Geotail). The main results of this study are: (1) Further evidence is given that periodic TCRs in the tail lobe at distances of 18 RE and ground Pi2 are related phenomena. In particular, it is shown that both had the same periodicity and occurred simultaneously (allowing for propagation time delays) strongly suggesting that both had the same periodic source. Since the TCRs were propagating Earthward, this source was located in the outer magnetosphere beyond 18 RE. (2) The connection of periodic TCRs and ground Pi2 also exists during very quiet geomagnetic conditions with PBIs present in addition to the previous result (Keiling et al., 2006) which showed this connection during substorms. (3) Combining (1) and (2), we conclude that the frequency of PBI-associated Pi2 is controlled in the outer magnetosphere as opposed to the inner magnetosphere. We propose that this mechanism is pulsed reconnection based on previous results which combined modeled results and observations of substorm-related periodic TCRs and ground Pi2. (4) We show that TCRs with small compression ratios (ΔB/B<1%) can be useful in the study of magnetotail dynamics and we argue that other compressional fluctuations with ΔB/B<1% (without having all of the characteristic signatures of TCRs) seen in the tail lobe could possibly be related to the same mechanism that generates TCR with ΔB/B>1% (which are more commonly studied). (5) Finally, it is noted that both quiet time and substorm-related periodic TCRs had remarkably similar periods in spite of the drastically different geomagnetic conditions prevailing during the events which poses the important question of what causes this periodicity under these different conditions.
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Ugai, M. "Conditions for substorm onset by the fast reconnection mechanism". Annales Geophysicae 26, nr 12 (2.12.2008): 3875–83. http://dx.doi.org/10.5194/angeo-26-3875-2008.
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Abstract. The fast reconnection mechanism, involving slow shocks and Alfvénic fast plasma jets, is most responsible for the explosive conversion of magnetic energy associated with geomagnetic substorms and solar flares. In this paper, the spontaneous fast reconnection model is applied to well-known phenomena of substorms. When the east-west width of the tail current sheet becomes 3–4 times larger than its north-south thickness, the fast reconnection mechanism can fully be established, which may lead to substorm onset. The resulting Alfvénic jet can exactly explain, both qualitatively and quantitatively, the in-situ satellite observations of the traveling compression regions (TCRs) associated with large-scale plasmoids propagating down the tail. Also, the earthward fast reconnection jet causes drastic magnetic field dipolarization, so that the sheet current ahead of the magnetic loop of closed field lines suddenly turns its direction toward the loop footpoint and a large-scale current wedge is formed according to the growth of field-aligned currents. It is demonstrated that an MHD generator arises ahead of the magnetic loop and drives the current wedge to distinctly enhance the current density in a pair of thin layers of the loop footpoint, giving rise to drastic heating in the form of two ribbons.
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Meredith, N. P., R. B. Horne, D. Summers, R. M. Thorne, R. H. A. Iles, D. Heynderickx i R. R. Anderson. "Evidence for acceleration of outer zone electrons to relativistic energies by whistler mode chorus". Annales Geophysicae 20, nr 7 (31.07.2002): 967–79. http://dx.doi.org/10.5194/angeo-20-967-2002.
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Abstract. We use plasma wave and electron data from the Combined Release and Radiation Effects Satellite (CRRES) to investigate the viability of a local stochastic electron acceleration mechanism to relativistic energies driven by gyroresonant interactions with whistler mode chorus. In particular, we examine the temporal evolution of the spectral response of the electrons and the waves during the 9 October 1990 geomagnetic storm. The observed hardening of the electron energy spectra over about 3 days in the recovery phase is coincident with prolonged substorm activity, as monitored by the AE index and enhanced levels of whistler mode chorus waves. The observed spectral hardening is observed to take place over a range of energies appropriate to the resonant energies associated with Doppler-shifted cyclotron resonance, as supported by the construction of realistic resonance curves and resonant diffusion surfaces. Furthermore, we show that the observed spectral hardening is not consistent with energy-independent radial diffusion models. These results provide strong circumstantial evidence for a local stochastic acceleration mechanism, involving the energisation of a seed population of electrons with energies of the order of a few hundred keV to relativistic energies, driven by wave-particle interactions involving whistler mode chorus. The results suggest that this mechanism contributes to the reformation of the relativistic outer zone population during geomagnetic storms, and is most effective when the recovery phase is characterised by prolonged substorm activity. An additional significant result of this paper is that we demonstrate that the lower energy part of the storm-time electron distribution is in steady-state balance, in accordance with the Kennel and Petschek (1966) theory of limited stably-trapped particle fluxes.Key words. Magnetospheric physics (storms and substorms, energetic particles, trapped) – Space plasma physics (wave-particle interactions)
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Blagoveshchensky, D. V., M. Lester, V. A. Kornienko, I. I. Shagimuratov, A. J. Stocker i E. M. Warrington. "Observations by the CUTLASS radar, HF Doppler, oblique ionospheric sounding, and TEC from GPS during a magnetic storm". Annales Geophysicae 23, nr 5 (28.07.2005): 1697–709. http://dx.doi.org/10.5194/angeo-23-1697-2005.
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Abstract. Multi-diagnostic observations, covering a significant area of northwest Europe, were made during the magnetic storm interval (28–29 April 2001) that occurred during the High Rate SolarMax IGS/GPS-campaign. HF radio observations were made with vertical sounders (St. Petersburg and Sodankyla), oblique incidence sounders (OIS), on paths from Murmansk to St. Petersburg, 1050 km, and Inskip to Leicester, 170 km, Doppler sounders, on paths from Cyprus to St. Petersburg, 2800 km, and Murmansk to St. Petersburg, and a coherent scatter radar (CUTLASS, Hankasalmi, Finland). These, together with total electron content (TEC) measurements made at GPS stations from the Euref network in northwest Europe, are presented in this paper. A broad comparison of radio propagation data with ionospheric data at high and mid latitudes, under quiet and disturbed conditions, was undertaken. This analysis, together with a geophysical interpretation, allow us to better understand the nature of the ionospheric processes which occur during geomagnetic storms. The peculiarity of the storm was that it comprised of three individual substorms, the first of which appears to have been triggered by a compression of the magnetosphere. Besides the storm effects, we have also studied substorm effects in the observations separately, providing an improved understanding of the storm/substorm relationship. The main results of the investigations are the following. A narrow trough is formed some 10h after the storm onset in the TEC which is most likely a result of enhanced ionospheric convection. An enhancement in TEC some 2–3 h after the storm onset is most likely a result of heating and upwelling of the auroral ionosphere caused by enhanced currents. The so-called main effect on ionospheric propagation was observed at mid-latitudes during the first two substorms, but only during the first substorm at high latitudes. Ionospheric irregularities observed by CUTLASS were clearly related to the gradient in TEC associated with the trough. The oblique sounder and Doppler observations also demonstrate differences between the mid-latitude and high-latitude paths during this particular storm. Keywords. Ionosphere (Ionospheric disturbances) – Magnetospheric physics (Storms and substorms) – Radio science (Ionospheric propagation)
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Turnbull, K. L., J. A. Wild, F. Honary, A. W. P. Thomson i A. J. McKay. "Characteristics of variations in the ground magnetic field during substorms at mid latitudes". Annales Geophysicae 27, nr 9 (1.09.2009): 3421–28. http://dx.doi.org/10.5194/angeo-27-3421-2009.
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Abstract. Substorms are known to cause geomagnetically induced currents (GIC) in power transmission lines through variations in the ground magnetic field. An improved knowledge and understanding of how the different phases of substorms affect the ground magnetic field will ultimately help to better understand how GIC arise. Although usually associated with high latitude power transmission networks, GIC potentially pose a risk to mid latitude networks such as the UK's National Grid. Using a list of substorm expansion phase onsets derived from auroral observations by the IMAGE-FUV satellite, this study examines 553 individual onsets. In order to cover mid latitudes, ground magnetometer data from the UK Sub-Auroral Magnetometer Network (SAMNET) are exploited. These high time resolution (5 s) data are used to study the ground magnetic field for an hour after onset, in particular the time derivative of the horizontal magnetic field, H. The data covers the period from 2000 to 2003 (just after solar maximum). Results are compared with a previous study of magnetic field variations at higher latitudes, using data with a much lower (1 min) cadence during substorms identified from geomagnetic indices during a period just after solar minimum.
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Feldstein, Y. I., L. I. Gromova, A. E. Levitin i A. Grafe. "Conjugacy of geomagnetic disturbances and the substorm current wedge". Geophysical Research Letters 25, nr 16 (15.08.1998): 3083–86. http://dx.doi.org/10.1029/98gl02323.
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Ding, Weizhen, Jinbin Cao i Aimin Du. "Statistical Analysis of Substorm Onsets Determined by Geomagnetic Indices". Chinese Journal of Space Science 30, nr 1 (2010): 17. http://dx.doi.org/10.11728/cjss2010.01.017.
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Рахматулин, Равиль, Ravil Rakhmatulin, Александр Пашинин i Aleksandr Pashinin. "Polarization dynamics of Pi2 pulsations at midlatitudes during development of substorms in the auroral zone". Solar-Terrestrial Physics 4, nr 3 (28.09.2018): 46–51. http://dx.doi.org/10.12737/stp-43201807.
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We examine the changes in the orientation of the major axis of the polarization ellipse of irregular geomagnetic pulsations Pi2, observed at midlatitudes during a substorm disturbance developing in the auroral zone of the Russian Arctic sector. We have found the dependence of the polarization ellipse orientation on the longitude of a corresponding substorm. The results of current studies are compared with earlier results of similar studies using materials on the North American continent. We have concluded that the results are similar in general, with a slight discrepancy which may be due to peculiarities of the geological structure of the earth crust in the Russian Arctic sector.
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Рахматулин, Равиль, Ravil Rakhmatulin, Александр Пашинин i Aleksandr Pashinin. "Polarization dynamics of Pi2 pulsations at midlatitudes during development of substorms in the auroral zone". Solnechno-Zemnaya Fizika 4, nr 3 (28.09.2018): 61–67. http://dx.doi.org/10.12737/szf-43201807.
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We examine the changes in the orientation of the major axis of the polarization ellipse of irregular geomagnetic pulsations Pi2, observed at midlatitudes during a substorm disturbance developing in the auroral zone of the Russian Arctic sector. We have found the dependence of the polarization ellipse orientation on the longitude of a corresponding substorm. The results of current studies are compared with earlier results of similar studies using data on the North American continent. We have concluded that the results are similar in general, with a slight discrepancy which may be due to peculiarities of the geological structure of the earth crust in the Russian Arctic sector.
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Blagoveshchenskaya, N. F., V. A. Kornienko, A. V. Petlenko, A. Brekke i M. T. Rietveld. "Geophysical phenomena during an ionospheric modification experiment at Tromsø, Norway". Annales Geophysicae 16, nr 10 (31.10.1998): 1212–25. http://dx.doi.org/10.1007/s00585-998-1212-5.
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Abstract. We present an analysis of phenomena observed by HF distance-diagnostic tools located in St. Petersburg combined with multi-instrument observation at Tromsø in the HF modified ionosphere during a magnetospheric substorm. The observed phenomena that occurred during the Tromsø heating experiment in the nightside auroral Es region of the ionosphere depend on the phase of substorm. The heating excited small-scale field-aligned irregularities in the E region responsible for field-aligned scattering of diagnostic HF waves. The equipment used in the experiment was sensitive to electron density irregularities with wavelengths 12–15 m across the geomagnetic field lines. Analysis of the Doppler measurement data shows the appearance of quasiperiodic variations with a Doppler frequency shift, fd and periods about 100–120 s during the heating cycle coinciding in time with the first substorm activation and initiation of the upward field-aligned currents. A relationship between wave variations in fd and magnetic pulsations in the Y-component of the geomagnetic field at Tromsø was detected. The analysis of the magnetic field variations from the IMAGE magnetometer stations shows that ULF waves occurred, not only at Tromsø, but in the adjacent area bounded by geographical latitudes from 70.5° to 68° and longitudes from 16° to 27°. It is suggested that the ULF observed can result from superposition of the natural and heater-induced ULF waves. During the substorm expansion a strong stimulated electromagnetic emission (SEE) at the third harmonic of the downshifted maximum frequency was found. It is believed that SEE is accompanied by excitation of the VLF waves penetrating into magnetosphere and stimulating the precipitation of the energetic electrons (10–40 keV) of about 1-min duration. This is due to a cyclotron resonant interaction of natural precipitating electrons (1–10 keV) with heater-induced whistler waves in the magnetosphere. It is reasonable to suppose that a new substorm activation, exactly above Tromsø, was closely connected with the heater-induced precipitation of energetic electrons.Key words. Ionosphere (active experiments; ionosphere · magnetosphere interactions). Radio science (nonlinear phenomena).
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Despirak, I. V., P. V. Setsko, Ya A. Sakharov i V. N. Selivanov. "GICS IN THE MAIN TRANSMISSION LINE “NORTHERN TRANSIT” IN RUSSIA AND IN THE MÄNTSÄLÄ FINLAND PIPELINE: A CASE STUDY". PHYSICS OF AURORAL PHENOMENA 44 (2021): 20–23. http://dx.doi.org/10.51981/2588-0039.2021.44.004.
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Geomagnetically induced currents (GICs), arising both on power lines and on pipelines, may have strong negative impact on the technological networks up to accidents ("blackouts"). Magnetospheric disturbances are one of the factors in the appearance of GICs, however there is no unambiguous relationship between substorm and presence of currents. In this paper, we consider two intense cases of GIC (15March 2012 and 17 March 2013), registered on two different technological networks: 1) on the "Nothern Transit" power line (Vykhodnoy, Revda and Kondopoga stations) located in the auroral zone, 2) on the Finnish natural gas pipeline near Mäntsälä located in the subauroral zone. Both GIC cases are compared with substorm development in the auroral zone, using data from IMAGE magnetometers network and MAIN camera system in Apatity. We found a good correlation between the GIC appearance and variations of geomagnetic indexes: IL – index, which characterized of westward electrojet intensity on the IMAGE meridian and Wp - index, which describes the wave activity of the substorm. Besides, it was shown also a good correlation between GICs and the thin spatio-temporal structure of the substorm development (the appearance and the propagation to the pole of substorm activations), which is appeared both in the magnetic data and in the all sky camera images.
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Nikolaev, A. V., V. A. Sergeev, N. A. Tsyganenko, M. V. Kubyshkina, H. Opgenoorth, H. Singer i V. Angelopoulos. "A quantitative study of magnetospheric magnetic field line deformation by a two-loop substorm current wedge". Annales Geophysicae 33, nr 4 (29.04.2015): 505–17. http://dx.doi.org/10.5194/angeo-33-505-2015.
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Abstract. Substorm current wedge (SCW) formation is associated with global magnetic field reconfiguration during substorm expansion. We combine a two-loop model SCW (SCW2L) with a background magnetic field model to investigate distortion of the ionospheric footpoint pattern in response to changes of different SCW2L parameters. The SCW-related plasma sheet footprint shift results in formation of a pattern resembling an auroral bulge, the poleward expansion of which is controlled primarily by the total current in the region 1 sense current loop (I1). The magnitude of the footprint latitudinal shift may reach ∼ 10° corrected geomagnetic latitude (CGLat) during strong substorms (I1= 2 MA). A strong helical magnetic field around the field-aligned current generates a surge-like region with embedded spiral structures, associated with a westward traveling surge (WTS) at the western end of the SCW. The helical field may also contribute to rotation of the ionospheric projection of narrow plasma streams (auroral streamers). Other parameters, including the total current in the second (region 2 sense) loop, were found to be of secondary importance. Analyzing two consecutive dipolarizations on 17 March 2010, we used magnetic variation data obtained from a dense midlatitude ground network and several magnetospheric spacecraft, as well as the adaptive AM03 model, to specify SCW2L parameters, which allowed us to predict the magnitude of poleward auroral expansion. Auroral observations made during the two substorm activations demonstrate that the SCW2L combined with the AM03 model nicely describes the azimuthal progression and the observed magnitude of the auroral expansion. This finding indicates that the SCW-related distortions are responsible for much of the observed global development of bright auroras.
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Fox, N. J., M. Lockwood, S. W. H. Cowley, M. P. Freeman, E. Friis-Christensen, D. K. Milling, M. Pinnock i G. D. Reeves. "EISCAT observations of unusual flows in the morning sector associated with weak substorm activity". Annales Geophysicae 12, nr 6 (31.05.1994): 541–53. http://dx.doi.org/10.1007/s00585-994-0541-2.
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Abstract. A discussion is given of plasma flows in the dawn and nightside high-latitude ionospheric regions during substorms occurring on a contracted auroral oval, as observed using the EISCAT CP-4-A experiment. Supporting data from the PACE radar, Greenland magnetometer chain, SAMNET magnetometers and geostationary satellites are compared to the EISCAT observations. On 4 October 1989 a weak substorm with initial expansion phase onset signatures at 0030 UT, resulted in the convection reversal boundary observed by EISCAT (at ~0415 MLT) contracting rapidly poleward, causing a band of elevated ionospheric ion temperatures and a localised plasma density depletion. This polar cap contraction event is shown to be associated with various substorm signatures; Pi2 pulsations at mid-latitudes, magnetic bays in the midnight sector and particle injections at geosynchronous orbit. A similar event was observed on the following day around 0230 UT (~0515 MLT) with the unusual and significant difference that two convection reversals were observed, both contracting poleward. We show that this feature is not an ionospheric signature of two active reconnection neutral lines as predicted by the near-Earth neutral model before the plasmoid is "pinched off", and present two alternative explanations in terms of (1) viscous and lobe circulation cells and (2) polar cap contraction during northward IMF. The voltage associated with the anti-sunward flow between the reversals reaches a maximum of 13 kV during the substorm expansion phase. This suggests it to be associated with the polar cap contraction and caused by the reconnection of open flux in the geomagnetic tail which has mimicked "viscous-like" momentum transfer across the magnetopause.
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Kauristie, K., M. V. Uspensky, N. G. Kleimenova, O. V. Kozyreva, M. M. J. L. Van De Kamp, S. V. Dubyagin i S. Massetti. "Equivalent currents associated with morning-sector geomagnetic Pc5 pulsations during auroral substorms". Annales Geophysicae 34, nr 4 (7.04.2016): 379–92. http://dx.doi.org/10.5194/angeo-34-379-2016.
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Abstract. Space and time variations of equivalent currents during morning-sector Pc5 pulsations (T ∼ 2–8 min) on 2 days (18 January and 19 February 2008) are studied in the context of substorm activity with THEMIS and MIRACLE ground-based instruments and THEMIS P3, P5, and P2 probes. These instruments covered the 22:00–07:00 magnetic local time during the analyzed events. In these cases abrupt changes in the Pc5 amplitudes, intensifications and/or weakenings, were recorded some minutes after auroral breakups in the midnight sector. We analyze three examples of Pc5 changes with the goal to resolve whether substorm activity can have an effect on Pc5 amplitude or not. In two cases (on 19 February) the most likely explanation for Pc5 amplitude changes comes from the solar wind (changes in the sign of interplanetary magnetic field Bz). In the third case (on 18 January) equivalent current patterns in the morning sector show an antisunward-propagating vortex which replaced the Pc5-related smaller vortices and consequently the pulsations weakened. We associate the large vortex with a field-aligned current system due to a sudden, although small, drop in solar wind pressure (from 1 to 0.2 nPa). However, the potential impact of midnight substorm activity cannot be totally excluded in this case, because enhanced fluxes of electrons with high enough energies (∼ 280 keV) to reach the region of Pc5 within the observed delay were observed by THEMIS P2 at longitudes between the midnight and morning-sector instrumentation.
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Dewhurst, J. P., C. J. Owen, A. N. Fazakerley i A. Balogh. "Thinning and expansion of the substorm plasma sheet: Cluster PEACE timing analysis". Annales Geophysicae 22, nr 12 (22.12.2004): 4165–84. http://dx.doi.org/10.5194/angeo-22-4165-2004.
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Abstract. The storage and subsequent removal of magnetic flux in the magnetotail during a geomagnetic substorm has a dramatic effect on the thickness of the cross-tail plasma sheet. The near-Earth plasma sheet is thought to thin during the growth phase and then rapidly expand after onset of the substorm. The direction of propagation, whether earthward or tailward along the GSM-X direction in the near-Earth tail, may suggest the time ordering of current-disruption and near-Earth reconnection, both of which are key to the substorm process. Cluster's Plasma Electron And Current Experiment (PEACE) allows 4-point observations of electrons at the plasma sheet - lobe boundary as this interface passes over the Cluster tetrahedron. The relative timings of the boundary passage at each spacecraft allow a determination of this boundary's speed and direction of motion, assuming this is planar on the scale of the Cluster separation scale. For those boundaries corresponding to the expansion of the plasma sheet, this direction is fundamental to determining the direction of expansion. We present an example of isolated thinning and expansion of the plasma sheet, as well as a multiple thinning-expansion event that occurs during a more active substorm. Data from the 2001 and 2002 tail passes have been analysed and the average plasma sheet – lobe boundary normal vectors and normal component velocities have been calculated. A total of 77 crossings, typically between 10 and 20 RE downtail, correspond to substorm associated expansion of the plasma sheet over the spacecraft. These had normal vectors predominantly in the GSM-YZ plane and provided no clear evidence for the formation of the near-Earth neutral line occurring before current disruption or vice versa. The expansions of the plasma sheet generally exhibit the appropriate GSM-Z direction expected for the given lobe, and tend to have GSM-Y components that support onset occurring near the origin of the GSM-YZ plane. This result is noteworthy in that it indicates a homogeneous plasma sheet expansion. These expansions have an average velocity along their normal of 60±37kms–1. Conversely we find an average thinning velocity of 43±32kms–1 from 66 substorm-associated thinnings. The normal vectors of the thinning plasma sheet vary considerably in the GSM-YZ plane across the entire magnetotail, suggesting that more complex dynamics govern this process.Key words. Magnetospheric physics (Magnetotail; Plasma sheet; Storms and substorms)bk\\rasphone.
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Švanda, Michal, Didier Mourenas, Karla Žertová i Tatiana Výbošt’oková. "Immediate and delayed responses of power lines and transformers in the Czech electric power grid to geomagnetic storms". Journal of Space Weather and Space Climate 10 (2020): 26. http://dx.doi.org/10.1051/swsc/2020025.
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Eruptive events of solar activity often trigger abrupt variations of the geomagnetic field. Through the induction of electric currents, human infrastructures are also affected, namely the equipment of electric power transmission networks. It was shown in past studies that the rate of power-grid anomalies may increase after an exposure to strong geomagnetically induced currents. We search for a rapid response of devices in the Czech electric distribution grid to disturbed days of high geomagnetic activity. Such disturbed days are described either by the cumulative storm-time Dst or d(SYM-H)/dt low-latitude indices mainly influenced by ring current variations, by the cumulative AE high-latitude index measuring substorm-related auroral current variations, or by the cumulative ap mid-latitude index measuring both ring and auroral current variations. We use superposed epoch analysis to identify possible increases of anomaly rates during and after such disturbed days. We show that in the case of abundant series of anomalies on power lines, the anomaly rate increases significantly immediately (within 1 day) after the onset of geomagnetic storms. In the case of transformers, the increase of the anomaly rate is generally delayed by 2–3 days. We also find that transformers and some electric substations seem to be sensitive to a prolonged exposure to substorms, with a delayed increase of anomalies. Overall, we show that in the 5-day period following the commencement of geomagnetic activity there is an approximately 5–10% increase in the recorded anomalies in the Czech power grid and thus this fraction of anomalies is probably related to an exposure to GICs.
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Longden, N., F. Honary, A. J. Kavanagh i J. Manninen. "The driving mechanisms of particle precipitation during the moderate geomagnetic storm of 7 January 2005". Annales Geophysicae 25, nr 9 (2.10.2007): 2053–68. http://dx.doi.org/10.5194/angeo-25-2053-2007.
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Abstract. The arrival of an interplanetary coronal mass ejection (ICME) triggered a sudden storm commencement (SSC) at ~09:22 UT on the 7 January 2005. The ICME followed a quiet period in the solar wind and interplanetary magnetic field (IMF). We present global scale observations of energetic electron precipitation during the moderate geomagnetic storm driven by the ICME. Energetic electron precipitation is inferred from increases in cosmic noise absorption (CNA) recorded by stations in the Global Riometer Array (GLORIA). No evidence of CNA was observed during the first four hours of passage of the ICME or following the sudden commencement (SC) of the storm. This is consistent with the findings of Osepian and Kirkwood (2004) that SCs will only trigger precipitation during periods of geomagnetic activity or when the magnetic perturbation in the magnetosphere is substantial. CNA was only observed following enhanced coupling between the IMF and the magnetosphere, resulting from southward oriented IMF. Precipitation was observed due to substorm activity, as a result of the initial injection and particles drifting from the injection region. During the recovery phase of the storm, when substorm activity diminished, precipitation due to density driven increases in the solar wind dynamic pressure (Pdyn) were identified. A number of increases in Pdyn were shown to drive sudden impulses (SIs) in the geomagnetic field. While many of these SIs appear coincident with CNA, SIs without CNA were also observed. During this period, the threshold of geomagnetic activity required for SC driven precipitation was exceeded. This implies that solar wind density driven SIs occurring during storm recovery can drive a different response in particle precipitation to typical SCs.
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Бархатова, Оксана, Oksana Barhatova, Наталия Косолапова, Natalia Kosolapova, Николай Бархатов, Nikolay Barhatov, Сергей Ревунов i Sergey Revunov. "Synchronization of geomagnetic and ionospheric disturbances over Kazan station". Solar-Terrestrial Physics 3, nr 4 (29.12.2017): 58–66. http://dx.doi.org/10.12737/stp-34201706.
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The phenomena which accompany synchronization of night-time ionospheric and geomagnetic disturbances in an ULF range with periods 35–50 min near the mid-latitude station Kazan during a global magnetically quiet period have been analyzed. The comparison between dynamic spectra and wavelet patterns of these disturbances has revealed that spectral features of simultaneous disturbances of the F2-layer critical frequency and H, D, Z geomagnetic field components are similar. By studying spectral features of the F2-layer critical frequency over Kazan and disturbances of the H and D geomagnetic field components at magnetic stations which differ from Kazan station in longitude and latitude, we have established that the disturbances considered belong to the class of fast magnetosonic waves. The analysis of solar wind parameters, inter-planetary magnetic field (IMF), and values of the auro-ral index AL in the period under study has shown that this event is associated with IMF Bz component disturb-ances and occurs during substorm development.
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Wood, A. G., S. E. Pryse i J. Moen. "Modulation of nightside polar patches by substorm activity". Annales Geophysicae 27, nr 10 (13.10.2009): 3923–32. http://dx.doi.org/10.5194/angeo-27-3923-2009.
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Abstract. Results are presented from a multi-instrument study showing the influence of geomagnetic substorm activity on the spatial distribution of the high-latitude ionospheric plasma. Incoherent scatter radar and radio tomography measurements on 12 December 2001 were used to directly observe the remnants of polar patches in the nightside ionosphere and to investigate their characteristics. The patches occurred under conditions of IMF Bz negative and IMF By negative. They were attributed to dayside photoionisation transported by the high-latitude convection pattern across the polar cap and into the nighttime European sector. The patches on the nightside were separated by some 5° latitude during substorm expansion, but this was reduced to some 2° when the activity had subsided. The different patch separations resulted from the expansion and contraction of the high-latitude plasma convection pattern on the nightside in response to the substorm activity. The patches of larger separation occurred in the antisunward cross-polar flow as it entered the nightside sector. Those of smaller separation were also in antisunward flow, but close to the equatorward edge of the convection pattern, in the slower, diverging flow at the Harang discontinuity. A patch repetition time of some 10 to 30 min was estimated depending on the phase of the substorm.
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Aksnes, A., J. Stadsnes, J. Bjordal, N. Østgaard, R. R. Vondrak, D. L. Detrick, T. J. Rosenberg, G. A. Germany i D. Chenette. "Instantaneous ionospheric global conductance maps during an isolated substorm". Annales Geophysicae 20, nr 8 (31.08.2002): 1181–91. http://dx.doi.org/10.5194/angeo-20-1181-2002.
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Abstract. Data from the Polar Ionospheric X-ray Imager (PIXIE) and the Ultraviolet Imager (UVI) on board the Polar satellite have been used to provide instantaneous global conductance maps. In this study, we focus on an isolated substorm event occurring on 31 July 1997. From the PIXIE and the UVI measurements, the energy spectrum of the precipitating electrons can be derived. By using a model of the upper atmosphere, the resulting conductivity values are generated. We present global maps of how the 5 min time-averaged height-integrated Hall and Pedersen conductivities vary every 15 min during this isolated substorm. The method presented here enables us to study the time development of the conductivities, with a spatial resolution of ~ 700 km. During the substorm, a single region of enhanced Hall conductance is observed. The Hall conductance maximum remains situated between latitudes 64 and 70 corrected geomagnetic (CGM) degrees and moves eastward. The strongest conductances are observed in the pre-midnight sector at the start of the substorm expansion. Toward the end of the substorm expansion and into the recovery phase, we find the Hall conductance maximum in the dawn region. We also observe that the Hall to Pedersen conductance ratio for the regions of maximum Hall conductance is increasing throughout the event, indicating a hardening of the electron spectrum. By combining PIXIE and UVI measurements with an assumed energy distribution, we can cover the whole electron energy range responsible for the conductances. Electrons with energies contributing most to the Pedersen conductance are well covered by UVI while PIXIE captures the high energetic component of the precipitating electrons affecting the Hall conductance. Most statistical conductance models have derived conductivities from electron precipitation data below approximately 30 keV. Since the intensity of the shortest UVI-wavelengths (LBHS) decreases significantly at higher electron energies, the UVI electron energy range is more or less comparable with the energy ranges of the statistical models. By calculating the conductivities from combined PIXIE and UVI measurements to compare with the conductivities from using UVI data only, we observe significant differences in the Hall conductance. The greatest differences are observed in the early evening and the late morning sector. We therefore suggest that the existing statistical models underestimate the Hall conductance.Key words. Ionosphere (auroral ionosphere, particle precipitation) – Magnetospheric physics (storms and substorms)