Wave structure of magnetic substorms at high latitudes

Geomagnetism and Aeronomy, 2011

A complex of geophysical phenomena (geomagnetic pulsations in different frequency ranges, VLF emissions, riometer absorption, and auroras) during the initial phase of a small recurrent magnetic storm that occurred on February 27-March 2, 2008, at a solar activity minimum has been analyzed. The difference between this storm and other typical magnetic storms consisted in that its initial phase developed under a pro longed period of negative IMF B z values, and the most intense wave like disturbances during the storm initial phase were observed in the dusk and nighttime magnetospheric sectors rather than in the daytime sector as is observed in the majority of cases. The passage of a dense transient (with Np reaching 30 cm -3 ) in the solar wind under the southward IMF in the sheath region of the high speed solar wind stream responsible for the discussed storm caused a great (the AE index is ~1250 nT) magnetospheric substorm. The appearance of VLF chorus, accompanied by riometer absorption bursts and Pc5 pulsations, in a very long longitudinal interval of auroral latitudes (L ~ 5) from premidnight to dawn MLT hours has been detected. It has been concluded that a sharp increase in the solar wind dynamic pressure under prolonged negative values of IMF Bz resulted in the global (in longitude) development of electron cyclotron instability in the Earth's magnetosphere.

EPJ Web of Conferences, 2021

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 o...

Aerospace Research in Bulgaria

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

Journal of Geophysical Research, 2003

This paper presents simultaneous observations of 6-mHz magnetic pulsations in the nightside high-latitude plasma sheet, inner plasma sheet at the geosynchronous distance, and auroral region on the ground in association with substorm onset. We study an isolated substorm (AE $ 300 nT) onset on 19 October 1999 at $0145 UT. The Polar spacecraft was located in the plasma sheet near the plasma sheet boundary and was magnetically conjugate with the Greenland west coast magnetometer chain. Polar measured large-amplitude transverse magnetic (10 nT; toroidal) and electric (20 mV m À1) field oscillations ($6 mHz) during the early development of the negative bay (300 nT) in Greenland. On the ground, pulsations (50 nT) with the same frequency were superimposed on the negative bay. The geostationary GOES 8 spacecraft was located 2 hours west of Greenland. It observed compressional magnetic field oscillations (1 nT and $6 mHz). At Polar the pulsations were initiated $3 min before the first outward propagating substorm signature, an abrupt enhancement of the plasma sheet electron fluxes. Such a rich data set allows us to study in detail the spatial origin of the pulsations, their timing with respect to the negative bay onset, and their role in initiation of the substorm current wedge. It is concluded that the pulsations were initiated between the plasma sheet boundary and the tailward expanding region of the enhanced plasma sheet electron fluxes. The pulsations were then later observed on the ground and at GOES 8. It can also be argued that the pulsations were an integral part of the formation of the substorm current wedge. Finally, we suggest that the pulsations were generated by periodic variations in the rate of the current diversion from the braking region of the earthward flows generated by reconnection at the near-Earth neutral line.

Geomagnetism and Aeronomy, 2006

The spatial dynamics of geomagnetic variations and pulsations, auroras, and riometer absorption during the development of the main phase of the extremely strong magnetic storm of November 7-8, 2004, has been studied. It has been indicated that intense disturbances were observed in the early morning sector of auroral latitudes rather than in the nighttime sector, as usually takes place during magnetic storms. The unusual spatial dynamics was revealed at the beginning of the storm main phase. A rapid poleward expansion of disturbances from geomagnetic latitudes of 65°-66° to 74°-75° and the development of the so-called polar cap substorm with a negative bay amplitude of up to 2500 nT, accompanied by precipitation of energetic electrons (riometer absorption) and generation of Pi2-Pi3 pulsations, were observed when IMF B z was about -45 nT. The geomagnetic activity maximum subsequently sharply shifted equatorward to 60°-61° . The spatial dynamics of the westward electrojet, Pi2-Pi3 geomagnetic pulsations, and riometer absorption was similar, which can indicate that the source of these phenomena is common. PACS numbers: 94.30.Lr, 94.30.Ms

Geomagnetism and Aeronomy, 2006

Based on the observations in six pairs of almost conjugate high-latitude stations in the Arctic and Antarctic regions, the spectral and spatial-temporal structures of long-period geomagnetic pulsations (f = 2-5 mHz) during the magnetic storm of April 16-17, 1999, which is characterized by a high (up to 20 nPa) solar wind dynamic pressure, have been studied. It has been indicated that the magnetic storm sudden commencement is accompanied by a symmetrical excitation of np pulsations near the dayside polar cusps with close amplitudes. Under the conditions when IMF B z > 0 and B y < 0, strong magnetic field variations with the periods longer than 15-20 min were observed only in the northern polar cap. When IMF B z and B y became close to zero, geomagnetic pulsation bursts in both hemispheres were registered simultaneously but differed in the spectral composition and spatial distribution. In the Northern Hemisphere, pulsations were as a rule observed in a more extensive latitude region than in the Southern Hemisphere. In the Northern Hemisphere, the oscillation amplitude maximum was observed at higher latitudes than in the Southern Hemisphere. The pulsation amplitude at geomagnetic latitude lower than 74° was larger in the Arctic Regions than in the Antarctic Regions. This can be explained by sharply different geographic longitudes in the polar cap and latitudes in the auroral zone, which results in a different ionospheric conductivity affecting the amplitude of geomagnetic pulsations.

Annales Geophysicae, 2009

This study is focused on the problem of the localization of substorm expansion onset. In this context, the high latitude topology of transverse magnetospheric currents has been analyzed. This study has included the radial distribution of plasma pressure near noon, obtained using the THEMIS-B satellite data, the daytime compression of magnetic field lines and the existence of magnetic field minima far from the equatorial plane, given by all geomagnetic field models. As a result, the dayside integral transverse currents at the geocentric distances 7-10 R E has been estimated. It is suggested, that nightside transverse currents at geocentric distances ∼7-10 R E are closed inside the magnetosphere and with dayside transverse currents form surrounding the Earth current system (cut ring current or CRC) which topologically is the high latitude continuation of ordinary ring current. A possibility of localization of substorm expansion onset at the nighside CRC region is analyzed using the experimental evidences that the onset is localized at geocentric distances <10 R E .

2018

Based on the IMAGE magnetometer network data, OMNI database of the solar wind and Interplanetary Magnetic Field (IMF) parameters, and the catalog of the large-scale solar wind types (ftp://ftp.iki.rssi.ru/omni/), the comparative analysis of the interplanetary conditions of the high-latitude substorm appearance has been carried out. We analyzed substorms observed at the meridional chain (TAR-NAL) of IMAGE magnetometer stations in 1995-1996, and 1999-2000. According to our previous study (Despirak et al., 2014; 2016; 2017), we divided the considered substorms into two types. First type-the substorms which propagate from the auroral latitudes (<70º CGC) to polar geomagnetic ones (>70º CGC) (so called "expanded" substorms); the second type-the substorms which are observed only at the latitudes higher ~70º CGC under the absence of simultaneous geomagnetic disturbances at the latitudes below 70° (so called "polar" substorms). The 202 "expanded" and 186 "polar" substorms have been selected during the four considered years. It is shown that the "expanded" substorms are mainly (in 74.7% of the events) observed while the high-speed recurrent streams (FAST) and the regions of the plasma compression before these streams (CIR) occur. For 18.3% of the events, such substorms are observed during the interplanetary displays of coronal mass ejections (SHEATH and EJECTA). Contrary to that, the "polar" substorms occur mainly (in 67.2% of the events) during the slow flows and heliospheric current sheet (SLOW and HCS); and for 18.8% of the events, they occur during the SHEATH, EJECTA and MCs, which were observed in the background of the slow solar wind. Thus, the space weather conditions control the type of the developed highlatitude magnetic substorms in the Earth's magnetosphere.

The high latitude geomagnetic events that occurred under extreme space weather conditions dur ing the non typical development of the main phase of the strong magnetic storm of November 24, 2001 were studied. The development of the main phase was or ceased by a sharp turn of the IMF to the north and the appearance of extremely high (up to about 60 nT) positive IMF Bz values; in this period, high alternating IMF By values were observed (from +40 to -40 nT) against a high dynamic pressure of the solar wind, with sharp bursts up to 50-70 nPa. This resulted in the cessation of nighttime substorms. Magnetic disturbances were recorded on the Earth's surface only in the daytime sector of polar latitudes as a very strong magnetic bay with amplitude of about 2000 nT. According to model calculations, a sharp intensification of field aligned currents of the NBZ system was noted in that region. The onset of the daytime polar magnetic bay was accompanied by an auroral burst and strong local geomagnetic pulsations in the ~(2-7) mHz band. Bursts of fluctuations in the solar wind and IMF were not accompanied by simultaneous bursts in ground based high latitude geo magnetic pulsations, that is, the direct penetration of solar wind and IMF pulsations into the magnetosphere was unlikely to occur. The daytime polar geomagnetic pulsations observed on the Earth's surface could be caused by variations in high latitude field aligned currents, which were excited in a turbulent daytime bound ary layer as a result of interaction with solar wind inhomogeneities.

Journal of Geophysical Research, 1994

In contrast to the extensively studied growth and expansion phases of magnetospheric substorms, the substorm recovery phase has not received much attention in the published literature. It has generally been considered as a period in which all disturbances caused by the previous two phases decay, the magnetosphere "recovers" to reach a quiet state again. Using mainly groundbased data, we show that the "recovery phase" contains a number of features which are qualitatively different from the expansion phase, that is, not just a decay of previously excited forms of energy release. Typical recovery phase phenomena include intense electrojet activity in the morning sector, high-energy particle precipitation, the development of large-scale auroral vortex streets (so-called f/bands and associated magnetic Ps 6 pulsations), and very often new eastward expanding active auroral phenomena, not unlike evening-sector expansion phase features but concentrated to the morning sector of the auroral oval. Such features must be associated with the substorm mechanism itself. We suggest that our observations during the substorm recovery phase are explained by the magnetospheric reorganization after the ejection of a plasrnoid. We show that a more detailed investigation of the late substorm features can increase our understanding of the physical processes leading to the complete cycle of magnetospheric energy release. the pioneering work of Akasofu and Chapman [1961]. Later Akasofu [1964, 1977] laid the basis for substorm terminology by exactly defining the various development stages of a magnetospheric substorm with the help of auroral images at first from ground and later mainly from the DMSP satellites. This descriptive picture of the auroral substorm was then combined with ground-based observations of ionospheric currents and various in-situ observations of changes in the configuration of the magnetospheric field and plasma acceleration. The result was the generally accepted definition of a substorm that we have today [see Rostoker et al., 1980]. However, 30 years after the recognition of the phenomenon itself, and more than 10 years after a general agreement on the logical time sequence of magnetospheric observations, we still lack a satisfying theory explaining the basic physical processes and the causal relationship between the observed disturbances in the magnetospheric plasma. A number of quite different theories claim to be able to explain most of the observations during the substorm growth phase and expansion phase equally well (see, for example, Lui [1991] and Rostoker [1991] for recent reviews).