DYNAMICS OF THE GEOMAGNETIC STORM
Geomagnetic storms, trapped particles, solar wind, ionospheric gases
TRAPPED PARTICLE↗
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Flares, Forbush decreases, and geomagnetic storms.
Geomagnetic storms and Forbush decreases accounted for by interplanetary solar corpuscular streams effects described by interplanetary magnetic field structure, noting independence of flares
Ballif, J. R.↗
Electrodynamics of the magnetosphere - Geomagnetic storms.
Geomagnetic and auroral storms provide information on interaction of solar plasma flows and magnetosphere
MAGNETOSPHERE↗
A study of the propagation of solar particles in interplanetary space - the center-limb effect of the magnitude of cosmic-ray storms and of geomagnetic storms.
Magnitude of cosmic ray storms and geomagnetic storms as function of central meridian distance of corresponding solar flares
FORBUSH EFFECT↗
Large decreases in ionospheric total electron content as a result of thermospheric composition changes during geomagnetic storms
The geomagnetic storms of April 17-21,2002 and May 29-30,2003 caused large decreases in the O/N2 column density ratio in the thermosphere. For these storms, ON2 column density decreases of greater than 50% were observed to extend to mid-to-low latitudes with the FUV sensitive Earth Camera of the Visible Imaging System (VIS) on the Polar spacecraft. Simultaneously in these same regions, the ground-based GPS network observed approximately 80% reductions in the Total Electron Content (TEC) of the ionosphere. The reduction in the Om2 column density ratio is due mainly to increases in the molecular species that have welled-up into the thermosphere from the lower levels of the atmosphere due to auroral heating. The geomagnetic-storm driven increase in molecular densities at typical ionospheric heights rapidly charge exchange with the ambient ionized atoms and subsequently dissociatively recombine with the ionospheric electrons leading to a reduction in the total charge density. The transition boundaries between high and low regions of O/N2 as well as TEC can be tracked in the images and the thermospheric winds can be determined from the motion of the boundaries. The motion of these boundaries during the development of the geomagnetic storm will be discussed.
Sigwarth, J. B.↗
The Dynamics of Thermospheric Composition and Ionospheric Total Electron Content During Geomagnetic Storms
The geomagnetic storms of April 17-21,2002 and May 29-30,2003 caused large decreases in the O/N2 column density ratio in the thermosphere. For these storms, O/N2 column density decreases of greater than 50% were observed to extend to mid-to-low latitudes with the FUV sensitive Earth Camera of the Visible Imaging System (VIS) on the Polar spacecraft. Simultaneously in these same regions, the ground-based GPS network observed approximately 80% reductions in the Total Electron Content (TEC) of the ionosphere. The reduction in the O/N2 column density ratio is due mainly to increases in the molecular species that have welled-up into the thermosphere from the lower levels of the atmosphere due to auroral heating. The geomagnetic-storm driven increase in molecular densities at typical ionospheric heights rapidly charge exchange with the ambient ionized atoms and subsequently dissociatively recombine with the ionospheric electrons leading to a reduction in the total charge density. The transition boundaries between high and low regions of O/N2 as well as TEC can be tracked in the images and the thermospheric winds may be inferred from the motion of the boundaries. The motion of these boundaries during the development of the geomagnetic storm will be discussed.
Sigwarth, John B.↗
Evolution of the ring current during two geomagnetic storms
Two geomagnetic storms in September 1984 were studied to examine the progressive changes in the radial profiles of particle pressure, plasma beta, and electric currents of the ring current region during the course of geomagnetic storms. It is shown that enhancements in the particle pressure occur initially in the outer region and reach the inner region in the late phase of the storm. Structures suggestive of multiple particle injections are seen in the pressure profile. The leading and trailing edges of the particle injection structures are respectively associated with the depressions and enhancements of the westward current densities of the ring current. The location of the maximum ring current particle pressure can be several earth radii from where the most intense westward ring current flows.
Lui, A. T. Y.↗
Interplanetary field and plasma during initial phase of geomagnetic storms
Twenty-three geomagnetic storm events during 1966 to 1970 were studied by using simultaneous interplanetary magnetic field and plasma parameters. Explorer 33 and 35 field and plasma data were analyzed on large-scale (hourly) and small-scale (3 min.) during the time interval coincident with the initial phase of the geomagnetic storms. The solar-ecliptic Bz component turns southward at the end of the initial phase, thus triggering the main phase decrease in Dst geomagnetic field. The By component also shows large fluctuations along with Bz. When there are no clear changes in the Bz component, the By shows abrupt changes at the main phase onset. On the small-scale, behavior of the magnetic field and electric field were studied in detail for the three events; it is found that the field fluctuations in By, Bz and Ey and Ez are present in the initial phase. In the large-scale, the behavior field remains quiet because the small-scale variations are averaged out. It appears that large as well as small time scale fluctuations in the interplanetary field and plasma help to alter the internal electromagnetic state of the magnetosphere so that a ring current could causing a geomagnetic storm decrease.
Patel, V. L.↗
Effects of orbit progression on the radiation exposures from solar proton fluxes in low Earth orbit under geomagnetic storm conditions
The present study examines the effects of orbit progression on the exposures within a Space Station Freedom module in a 51.6-degree inclined orbit at 450 km. The storm evolution is modeled after the November 1960 event, and the solar proton flux evolution is taken from the August 1972 solar proton event. The effects of a strong magnetic shock, such as was observed during the October 1989 event, is also modeled. The statistics on hourly average storm fields for the last forty years reveal that the largest geomagnetic storms geomagnetic storms approach a Dst value of -500 nanotesla at the storm peak. Similarly, one of the largest satellite-measured proton flux (greater than 10 MeV) for space exposures is the event of August 1972. The effects of orbit progression (advance of the line of nodes) is examined for the above conditions to study the variation of exposures under differing times of occurrence of the solar proton peak intensity, attainment of geomagnetic storm maximum, and the location of the line of nodes of the last geomagnetically protected orbit. The impact of the inherent inhomogeneity of the space station module is examined as a limiting factor on exposure with regard to the need of additional parasitic shielding.
Nealy, J. E.↗
A study of geomagnetic storms
Twenty-one geomagnetic storm events during 1966 and 1970 were studied by using simultaneous interplanetary magnetic field and plasma parameters. Explorer 33 and 35 field and plasma data were analyzed on large-scale (hourly) and small-scale (3 min.) during the time interval coincident with initial phase of the geomagnetic storms. The solar-ecliptic Bz component turns southward at the end of the initial phase, thus triggering the main phase decrease in Dst geomagnetic field. When the Bz is already negative, its value becomes further negative. The By component also shows large fluctuations along with Bz. When there are no clear changes in the Bz component, the By shows abrupt changes at the main phase onet. On the small-scale behavior of the magnetic field and electric field (E=-VxB) studied in details for the three events, it is found that the field fluctuations in By, Bz and Ey and Ez are present in the initial phase. These fluctuations become larger just before the main phase of the storm begins. In the largescale behavior field remains quiet because the small scale variations are averaged out.
Patel, V. L.↗
A search for the interplanetary quantity controlling the development of geomagnetic storms
An historical account is presented concerning the evolution of our present concept of geomagnetic storms. The present concept was formulated by Chapman (1927) in his magnetic data statistical studies of 'the initial rise' (now termed the initial phase) 'and subsequent larger decrease' (now termed the main phase) in H, followed by 'slow recovery'. The concept introduced by Alfven in 1940 of guiding center motions of a charged particle in a nonuniform magnetic field (ring currents) is also discussed. By 1963 it became quite certain that the ring current, namely a storm-time Van Allen belt, is formed in the magnetosphere during the storm's main phase. The search then began for the solar wind quantity controlling the development of the main phase. The author then gives a personal account of how our concept of geomagnetic storms has advanced and how new findings based on satellite and ground-based observations have made it possible to arrive at a first-approximation expression for the interplanetary quantity controlling the development of geomagnetic storms. Since a geomagnetic storm is a magnetic manifestation of a magnetospheric storm, which is a nonlinear superposition of intense magnetospheric substorms, the main emphasis is shifted toward the understanding of magnetospheric substorms in order to arrive at the parameters controlling the development of geomagnetic storms.
Akasofu, S.-I.↗
Geomagnetic storms at ATS 1
Geomagnetic storms at ATS 1 in 1967, discussing storm-time disturbance field and associated pulsations
Coleman, P. J., Jr.↗
Analysis of the Heliospheric Conditions Leading to the February 2022 Geomagnetic Storm Event
The February 2022 geomagnetic storm was a moderate but extended event that may have been associated with two interplanetary coronal mass ejection (ICME) arrivals. The first of these coronal mass ejections (CMEs) was first visible in SOHO LASCO C2 coronagraph imagery on 29 January and may be associated with the arrival of an interplanetary shock at L1 late on 1 February, followed by the separate arrival of a flux rope at L1 approximately one day afterward. The second CME was first visible in SOHO LASCO C2 coronagraph imagery on 1 February and may be associated with the arrival of a weaker interplanetary shock at L1 late on 3 February, just hours after the SpaceX launch. While the second arrival was relatively weak, it further enhanced geomagnetic conditions that had resulted from the first arrival. This work analyzes the two CMEs, their propagation into interplanetary space, and their associated geomagnetic impacts.
Coronal Mass Ejection↗
Adiabatic betatron acceleration by a geomagnetic storm.
Reversible betatron acceleration mechanism during geomagnetic storm
ADIABATIC EQUATION↗
Interplanetary field and plasma during initial phase of geomagnetic storms
A study has been conducted of a large number of geomagnetic storms occurring during the period from 1966 to 1970. Questions of data selection are discussed and the large-scale interplanetary magnetic field during the initial phase is examined. Small-scale interplanetary fields during the initial phase are also considered, taking into account important features of small-scale variations in the interplanetary field and plasma for three storms. Details concerning 23 geomagnetic storms and the interplanetary magnetic field are presented in a table. A study of the initial phase of these storms indicates that in most of these events, the solar-ecliptic Z component of the interplanetary magnetic field turns southward when the main phase decrease begins.
Patel, V. L.↗
Recurrent geomagnetic storms and the solar wind.
Recurrent geomagnetic storms and structure of solar wind consisting of fast M-region stream embedded in slower ambient wind
SOLAR WIND↗
Moderate Geomagnetic Storms: Interplanetary Origins and Coupling Functions (ISEE3 Data)
Geomagnetic storms are related to the ring current intensification, which is driven by energy injection primarily during energetic solar wind-magnetosphere coupling due to reconnection at the magnetopause. This work identified the interplanetary origins of moderate geomagnetic storms (-100nT is less or equal to Dst(sub peak) is less than or equal to -50 nT) and analyzed the coupling processes during the storm main phase at solar maximum (1978-1979).
Mendes, Odim, Jr.↗
A source for the geomagnetic storm main phase ring current
The paper considers a proposed source for the geomagnetic storm main phase ring current. It is shown that the flux increases of trapped ions and electrons observed by Explorer 45 at L below 4 during two large geomagnetic storms can be explained by inward radial displacement of the preexisting trapped particle distribution. The proposed source requires only the acceleration of the previously entrapped particle population by inward displacement under conservation of the first two adiabatic invariants. It is suggested that a significant difference between large geomagnetic storms and typical substorm activity may be the inward convection occurring over a large longitude range during storms, but only over a small longitude range during typical substorms.
Lyons, L. R.↗