On magnetic storms and substorms

Geoscience Letters

The history of geomagnetism is more than 400 years old. Geomagnetic storms as we know them were discovered about 210 years ago. There has been keen interest in understanding Sun-Earth connection events, such as solar flares, CMEs, and concomitant magnetic storms in recent times. Magnetic storms are the most important component of space weather effects on Earth. We give an overview of the historical aspects of geomagnetic storms and the progress made during the past two centuries. Super magnetic storms can cause life-threatening power outages and satellite damage, communication failures and navigational problems. The data for such super magnetic storms that occurred in the last 50 years during the space era is sparce. Research on historical geomagnetic storms can help to create a database for intense and super magnetic storms. New knowledge of interplanetary and solar causes of magnetic storms gained from spaceage observations will be used to review the super magnetic storm of September 1-2, 1859. We discuss the occurrence probability of such super magnetic storms, and the maximum possible intensity for the effects of a perfect ICME: extreme super magnetic storm, extreme magnetospheric compression, and extreme magnetospheric electric fields.

Universe

An accurate understanding of dissimilarities in geomagnetic variability between quiet and disturbed periods has the potential to vastly improve space weather diagnosis. In this work, we exploit some recently developed methods of dynamical system theory to provide new insights and conceptual ideas in space weather science. In particular, we study the co-variation and recurrence statistics of two geomagnetic indices, SYM-H and AL, that measure the intensity of the globally symmetric component of the equatorial electrojet and that of the westward auroral electrojet, respectively. We find that the number of active degrees of freedom, required to describe the phase space dynamics of both indices, depends on the geomagnetic activity level. When the magnetospheric substorm activity, as monitored by the AL index, increases, the active number of degrees of freedom increases at high latitudes above the dimension obtained through classical time delay embedding methods. Conversely, a reduced nu...

Journal of Atmospheric and Solar-terrestrial Physics, 2010

Tremendous amount of solar energy is hurled into the space by transient sporadic emissions occurring within the Sun. A fraction of this energy is transferred into the Earth's magnetosphere by the magnetic reconnection process. Interplanetary magnetic field plays a crucial role in the excitation of geomagnetic storms and their subsequent evolution. The present study attempts to determine the influence of postshock duration of southward B z on the development and intensification of intense (Dst r À200 nT) geomagnetic storms. The study presents 18 big storm events that occurred during the solar cycle 23. In all the cases under study, the interplanetary shocks were driven by the interplanetary coronal mass ejections (ICMEs). The ICME structures may contain southward magnetic fields within the sheath, the magnetic cloud or both in succession, which can lead to the development of intense geomagnetic storms. In addition, dependence of storm strength on the total energy influx into the magnetosphere (E) and ring current (E RC ) energy is also assessed. Geomagnetic storm characteristics are examined at a lowlatitude station, Alibag (geographic lat. 18:63 3 N, long. 72:87 3 E; geomagnetic lat. 10:02 3 N, long. 145:97 3 ), using high resolution digital data. The minimum duration of southward B z for strengthening the storms is $ 1:25 h. All intense storms are found to have minimum values of southward directed B z to be r À18 nT and interplanetary electric field E y 4 12 mV=m. Intensity of geomagnetic storms at lowlatitudes follows a fairly linear dependence on the ring current energy.

Journal of Atmospheric and Solar-Terrestrial Physics, 2010

Tremendous amount of solar energy is hurled into the space by transient sporadic emissions occurring within the Sun. A fraction of this energy is transferred into the Earth's magnetosphere by the magnetic reconnection process. Interplanetary magnetic field plays a crucial role in the excitation of geomagnetic storms and their subsequent evolution. The present study attempts to determine the influence of postshock duration of southward B z on the development and intensification of intense (Dst r À200 nT) geomagnetic storms. The study presents 18 big storm events that occurred during the solar cycle 23. In all the cases under study, the interplanetary shocks were driven by the interplanetary coronal mass ejections (ICMEs). The ICME structures may contain southward magnetic fields within the sheath, the magnetic cloud or both in succession, which can lead to the development of intense geomagnetic storms. In addition, dependence of storm strength on the total energy influx into the magnetosphere (E) and ring current (E RC ) energy is also assessed. Geomagnetic storm characteristics are examined at a lowlatitude station, Alibag (geographic lat. 18:63 3 N, long. 72:87 3 E; geomagnetic lat. 10:02 3 N, long. 145:97 3 ), using high resolution digital data. The minimum duration of southward B z for strengthening the storms is $ 1:25 h. All intense storms are found to have minimum values of southward directed B z to be r À18 nT and interplanetary electric field E y 4 12 mV=m. Intensity of geomagnetic storms at lowlatitudes follows a fairly linear dependence on the ring current energy.

Space Weather, 2018

Interactions between the solar wind and the Earth's magnetosphere manifest many important space weather phenomena. In this paper, magnetosphere-ionosphere drivers of intense dB∕dt produced during geomagnetic storms that occurred on 9 March 2012 and 17 March 2015 are analyzed. A multi-instrument approach combining Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission space-borne and ground-based observations was adopted to examine the magnetosphere-ionosphere signatures associated with the dB∕dt extremes during each storm. To complement the THEMIS measurements, ground-based magnetometer recordings and All-Sky Imager observations, equivalent ionospheric currents derived from magnetometer chains across North America and Greenland, and geosynchronous observations from the Los Alamos National Laboratory Synchronous Orbit Particle Analyzer are also examined. Our results show that the most extreme dB∕dt variations are associated with marked perturbations in the THEMIS magnetospheric measurements, poleward expanding discrete aurora passing over the magnetometer sites (seen by the ground-based THEMIS All-Sky Imagers), intense Pc5 waves, rapid injection of energetic particles, and intense auroral westward currents. Substorms are considered as the major driver with a possible contribution from magnetospheric waves. The findings of this study strongly suggest that the localization of extreme dB∕dt variations is most likely related to the mapping of magnetosphere currents to local ionospheric structures.

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.

Journal of Space Weather and Space Climate, 2014

Extreme geomagnetic storms are considered as one of the major natural hazards for technology-dependent society. Geomagnetic field disturbances can disrupt the operation of critical infrastructures relying on space-based assets, and can also result in terrestrial effects, such as the Quebec electrical disruption in 1989. Forecasting potential hazards is a matter of high priority, but considering large flares as the only criterion for early-warning systems has demonstrated to release a large amount of false alarms and misses. Moreover, the quantification of the severity of the geomagnetic disturbance at the terrestrial surface using indices as Dst cannot be considered as the best approach to give account of the damage in utilities. High temporal resolution local indices come out as a possible solution to this issue, as disturbances recorded at the terrestrial surface differ largely both in latitude and longitude. The recovery phase of extreme storms presents also some peculiar features which make it different from other less intense storms. This paper goes through all these issues related to extreme storms by analysing a few events, highlighting the March 1989 storm, related to the Quebec blackout, and the October 2003 event, when several transformers burnt out in South Africa.

Space Weather, 2010

1992

Unclassified 2a 5EC.ýWTY CLASSFCA7 0\ Ak.'-'OR;T'f 3-' 87 0% 1A VA L 4 L 2b." CLASS; FiCATON• OO04\GRADOG SC"ED•.E Unlimited 4 PERFORMING ORGAVZA-'_O• :2;•ORT 7 ._MSsR!-) 5 VON iCRNiG ORGA,. ZA-% TC1. 1'4"W77 6a. NAME OF PERFORMING ORGANiZATION 6b OF~iCE SYMBOL 7A NAME OF MONITORAG ORGANIZATýOt (if aP04K•bl) Southwest Research Institute SwRI APOSR/f•L.. 6c. ADDRESS (City, State. and ZIPCotie) 7b ADDRESS(City. Stare. and ZIP Code) Abstract 'Fis project has demonstrated that one class of magnetic pulsations knowl; as stormtime Pc 5 waves is correlated with ssubstorin onsets. Stormitime Pc ; waves observed by geostationary satellites in the afternoon sector is characterized by oscillations of magnetic field with a period from '2 to 10 minutes. easiiv detected by magnetometers on communication or weather satellites. The es-Table of Contents L til ntroduction 1[, Remote Diagnostic of Substorm Onsets A. Method j B. Data Analysis Riesults

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