Major Geomagnetic Disturbances Research Articles

Phase Space Density Analysis of Outer Radiation Belt Electron Energization and Loss During Geoeffective and Nongeoeffective Sheath Regions

AbstractCoronal mass ejection driven sheath regions are one of the key drivers of drastic outer radiation belt responses. The response can however be significantly different based on the sheath properties and the associated inner magnetospheric wave activity. We performed two case studies on the effects of sheaths on outer belt electrons of various energies using data from the Van Allen Probes. One sheath caused a major geomagnetic disturbance and the other had only a minor impact. We especially investigated the phase space density (PSD) of seed, core, and ultrarelativistic electrons to determine the dominant energization and loss processes taking place during the events. Both sheaths produced substantial variation in the electron fluxes from tens of kiloelectronvolts up to ultrarelativistic energies. The responses were however the opposite: the geoeffective sheath mainly led to enhancement, while the nongeoeffective one caused a depletion throughout most of the outer belt. The case studies highlight that both inward and outward radial transport driven by ultra‐low frequency waves played an important role in both electron energization and loss. Additionally, PSD radial profiles revealed a local peak that indicated significant acceleration to core energies by chorus waves during the geoeffective event. The distinct responses and different mechanisms in action during these events were related to the timing of the peaked solar wind dynamic pressure causing magnetopause compression, and the differing levels of substorm activity. The most remarkable changes in the radiation belt system occurred in key sheath sub‐regions near the shock and the ejecta leading edge.

Field‐Aligned Current and Polar Cap Potential and Geomagnetic Disturbances: A Review of Cross‐Correlation Analysis

AbstractPolar cap potential (PCV) is an important parameter used for determining what kind of interaction takes place between solar wind and magnetosphere. Highly energetic particles from Sun driven by solar wind constantly bombard with Earth's magnetosphere–ionosphere system that results into a phenomenon like auroras, and major geomagnetic disturbances. Solar wind electron deposition determines the magnitude of field‐aligned current (FAC) and ultimately leads to PCV variation. Several studies found that increase in magnitude of IMF‐Bz causes an electric field of cross magnetosphere to increase, and it leads to increase in magnitude of ionospheric cross‐polar cap potential (PCV). Moreover, PCV was found to be a linear function of Vsw. In this research, we aim to study how field‐aligned current (FAC), for example, region 1 current and PCV, is related during different forms of geomagnetic disturbances. In all events, FAC and PCV are found to have corresponding fluctuations—especially at times of significant variation of IMF‐Bz (negative Bz interval) following the linearity of equation suggested by Moon in Moon (2012, https://doi.org/10.5140/JASS.2012.29.3.259). We found one‐to‐one correspondence between FAC and PCV. We did CWT analysis and found that FAC and PCV have more or less same spectral behaviors for each event considered. The cross‐correlation analysis shows a high and positive correlation between FAC and PCV at 0‐min time lag for all geomagnetic activity. The CWT analysis clearly supports the result of cross correlation between FAC and PCV. We found that FAC and Vsw, FAC‐B, and FAC and AE are also positively correlated with high‐correlation coefficient at lag 0 min for all geomagnetic storm. However, FAC‐Bz, FAC‐By, and FAC‐SYM (H) have varying correlation in different events. For a particular storm and substorm, the parameters Bz and By may not necessarily be varied with FAC in regular sequence but IMF (B) always show positive correlation with FAC for all geomagnetic activity. This paper presents a clear relation between FAC and PCV. This result will help to identify some of the outstanding issues in determining the causal mechanism of PCV variation, a crucial thing to understanding the coupling between the solar wind and M‐I system.

Plasma Interactions with the Space Environment in the Acceleration Region: Indications of CME-trailing Reconnection Regions

Abstract Coronal mass ejections (CMEs) are sources of major geomagnetic disturbances. On 2013 May 10, a CME crossed the signal path between the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft and Earth. Using the MESSENGER signal, characteristics of the density, velocity, and magnetic field properties of the crossing plasma were measured. An anomalously strong event occurred in the plasma trailing the CME’s passage that correlated with a wave mode conversion, indicating a potential reconnection region. We determine that the plasma following CMEs should be considered when studying how CMEs evolve in interplanetary space and the severity of their geomagnetic impact.

Searching for Carrington-like events and their signatures and triggers

The Carrington storm in 1859 is considered to be the major geomagnetic disturbance related to solar activity. In a recent paper, Cid et al. (2015) discovered a geomagnetic disturbance case with a profile extraordinarily similar to the disturbance of the Carrington event at Colaba, but at a mid-latitude observatory, leading to a re- interpretation of the 1859 event. Based on those results, this paper performs a deep search for other 'Carrington-like' events and analyses interplanetary observations leading to the ground disturbances which emerged from the systematic analysis. The results of this study based on two Carrington-like events (1) reinforce the awareness about the possibility of missing hazardous space weather events as the large H-spike recorded at Colaba by using global geomagnetic indices, (2) argue against the role of the ring current as the major current involved in Carrington-like events, leaving field- aligned currents (FACs) as the main current involved, and (3) propose abrupt southward reversals of IMF along with high solar wind pressure as the interplanetary trigger of a Carrington-like event.

Methodology for simulation of geomagnetically induced currents in power systems

To assess the geomagnetic hazard to power systems it is useful to be able to simulate the geomagnetically induced currents (GIC) that are produced during major geomagnetic disturbances. This paper examines the methodology used in power system analysis and shows how it can be applied to modelling GIC. Electric fields in the area of the power network are used to determine the voltage sources or equivalent current sources in the transmission lines. The power network can be described by a mesh impedance matrix which is combined with the voltage sources to calculate the GIC in each loop. Alternatively the power network can be described by a nodal admittance matrix which is combined with the sum of current sources into each node to calculate the nodal voltages which are then used to calculate the GIC in the transmission lines and GIC flowing to ground at each substation. Practical calculations can be made by superposition of results calculated separately for northward and eastward electric fields. This can be done using magnetic data from a single observatory to calculate an electric field that is a uniform approximation of the field over the area of the power system. It is also shown how the superposition of results can be extended to use data from two observatories: approximating the electric field by a linear variation between the two observatory locations. These calculations provide an efficient method for simulating the GIC that would be produced by historically significant geomagnetic storm events.

Traffic accidents and environmental physical activity

Environmental physical activity (EPA) is considered as one of main regulators of human homeostasis. Evidence is growing that components of this activity through the "human factor" (i.e., changing human physiological and psychological status) can affect the dynamics of traffic accidents (TA)-the modern life epidemic. This paper presents results of studies conducted in order to reveal the potential influence of EPA [solar (SA), geomagnetic (GMA) and cosmic ray (CRA) activities] on the number of TA and related casualties in the years of the maximum and declining phase of SA cycle 23 (2000-2005). We selected the 7,160 most severe TA and their related 7,558 deaths and 1,647 severe injuries, registered in the Grand Baku Area (Azerbaijan, middle latitudes), for analysis. A significant increase of TA and victims was observed during the whole year and also during the last months of the year. The monthly numbers of TA and victims were inversely related to SA (probability p = 0.0002), and non-significantly to background GMA, but were significantly affected by major geomagnetic disturbances and storms. A strong correlation between CRA variations (cosmic ray intensity measured by ground-based neutron monitors on the Earth's surface) and the number of TA (p = 0.001) has been observed. It was found that the number of TA which occur within a month depends significantly on the particular month of the year, the CRA, and the SA levels (inverse correlation). The increase of the number of TA is also significantly linked to geomagnetic storms, but not to steady GMA. These effects can be related to changes in human functional and behavioral markers provoked by EPA influences.

A statistical link between tropical cyclone intensification and major geomagnetic disturbances

Se encuentra una relación estadísticamente significante entre la actividad geomagnética y la intensificación de ciclones tropicales sobre el Atlántico tropical donde se forman la mayoría de los huracanes. El trabajo es congruente con un estudio previo relativo a la conexión entre actividad geomagnética y la intensidad de ciclones tropicales. Se amplían los resultados anteriores dirigiendo el enfoque hacia la intensificación en lugar de intensidad y el empleo de datos horarios. El resultado es de mayor generalidad, en el sentido de que no hay necesidad de separar los ciclones tropicales por categoría para interpretación.

Solar cycle changes, geomagnetic variations, and energetic particle properties in the inner magnetosphere

The causes and effects of geospace variability during recent years have been studied using coordinated measurements from an international constellation of Sun–Earth spacecraft. Particular emphasis is placed on long-term, homogeneous data sets from recent NASA spacecraft missions. It is found that even for modest geomagnetic storms, radiation belt electron fluxes can be rapidly enhanced within the Earth's inner magnetosphere. Remote-sensing solar data identify the eruptive or recurrent coronal features that produce the upstream drivers that, in turn, cause episodes of intense geomagnetic activity. Continuous solar wind data allow study of the principal drivers of magnetospheric acceleration processes. The Earth's radiation belts and inner magnetosphere show pronounced differences in their characteristics as the interplanetary magnetic field and solar wind properties change over the 11-year solar cycle. Solar coronal holes produce regular, recurrent solar wind streams, almost invariably enhancing highly relativistic electrons when solar wind speeds exceed 500 km/s. These phenomena are characteristic of the several-year approach to solar minimum. This contrasts with major geomagnetic disturbances associated with aperiodic coronal mass ejections that occur most frequently around solar maximum. As a practical consequence of Sun–Earth connection events, it is found that many adverse space weather episodes have contributed significantly to spacecraft operational anomalies and failures. We discuss how present and future space missions can address International Living With a Star (ILWS) goals and improve space weather forecasts.

Ionospheric plasma blobs observed by OI 630 nm all‐sky imaging in the Brazilian tropical sector during the major geomagnetic storm of April 6–7, 2000

This paper presents first observations of plasma blobs (localized plasma density enhancements) associated with large‐scale plasma density depletions (plasma bubbles) in the nighttime low‐latitude F‐region during a major geomagnetic disturbance. Ground‐based observations of the OI 630 nm all‐sky images obtained at Cachoeira Paulista (22.7°S, 45.0°W), Brazil, in the Appleton anomaly region, showed the presence of plasma blobs during the major geomagnetic storm of April 6–7, 2000 (ΣKp = 38 −/40+; ∣Dst∣max = 288 nT). The OI 630 nm emission images were used to map the spatial and temporal locations of plasma blobs and bubbles in the bottomside of the F‐region. The F‐region parameters, presented in this work, were obtained from ionosondes operating near the same site and also at Sao Luis (2.6°S, 44.4°W), Brazil. Ionospheric plasma blobs and bubbles zonal drift velocities, measured by the all‐sky imaging system, showed that both the plasma blobs and the bubbles moved westward (normally the plasma drift is eastward during nighttime) on this magnetically disturbed night. Furthermore, the plasma blobs showed typically east‐west and north‐south extensions in the range of 110–160 km and 200–450 km, respectively. It appears that the DMSP‐15 satellite, orbiting at about 850 km altitude, passed through one of the blobs detected by the ground‐based observations on this night while crossing the Brazilian sector. This indicates the enormous altitude extent [from about 275 km (OI 630.0 nm emission) to 850 km (DMSP satellite) altitude] of the localized plasma density enhanced regions. In this work, we present and discuss several features related to the dynamics of the localized plasma density enhancements and large‐scale plasma density depletions during this major geomagnetic disturbance.

Substorms: Fundamental observational features, distinction from other disturbances, and external triggering

Fundamental observational signatures of substorms and other auroral zone disturbances are summarized in this review. It is shown that at least three distinct types of major geomagnetic disturbance have been identified in the auroral zones, and it is suggested that care should be taken in distinguishing substorms from the other types of disturbance when reaching observational conclusions concerning substorms. Substorms can be uniquely identified by the formation of the current wedge and by the associated westward electrojet and region of active aurora that move poleward within the ionosphere during the expansion phase. Periods of enhanced convection have been observed to continue without substorms for as long as the interplanetary magnetic field (IMF) remains stably southward. They can have AL signatures that look very much like intense substorms, but these signatures result from strong DP 2 ionospheric currents driven by enhanced convection rather than from a nightside, westward electrojet. A third type of disturbance is characterized by short intervals of enhanced equatorward flow within the ionosphere and enhanced auroral emissions. These enhancements move equatorward from near the polar cap boundary, and they may be associated with several‐minute‐long enhancements of earthward flow within the plasma sheet. Studies that have examined the triggering of substorm expansions by IMF changes are also reviewed. When considered together, and substorms are distinguished from the other disturbances, these studies imply that most, and perhaps all, expansions are triggered by IMF changes. These changes include both northward turnings and reductions in the magnitude of the y component. If most substorms are indeed externally triggered as suggested here, then substorms must generally not be the result of an internal magnetospheric instability.

The response of the thermosphere and ionosphere to magnetospheric forcing

During the past six years, rapid advances in three observational techniques (groundbased radars, optical interferometers and satellite-borne instruments) have provided a means of observing a wide range of spectacular interactions between the coupled magnetosphere, ionosphere and thermosphere system. Perhaps the most fundamental gain has come from the combined data-sets from the NASA Dynamics Explorer (DE) Satellites. These have unambiguously described the global nature of thermospheric flows, and their response to magnetospheric forcing. TheDEspacecraft have also described, at the same time, the magnetospheric particle precipitation and convective electric fields which force the polar thermosphere and ionosphere. The response of the thermosphere to magnetospheric forcing is far more complex than merely the rare excitation of 1 km s-1wind speeds and strong heating; the heating causes large-scale convection and advection within the thermosphere. These large winds grossly change the compositional structure of the upper thermosphere at high and middle latitudes during major geomagnetic disturbances. Some of the major seasonal and geomagnetic storm-related anomalies of the ionosphere are directly attributable to the gross windinduced changes of thermospheric composition; the mid-latitude ionospheric storm ‘negative phase’, however, is yet to be fully understood. The combination of very strong polar wind velocities and rapid plasma convection forced by magnetospheric electric fields strongly and rapidly modify F-region plasma distributions generated by the combination of local solar and auroral ionization sources. Until recently, however, it has been difficult to interpret the observed complex spatial and timedependent structures and motions of the thermosphere and ionosphere because of their strong and nonlinear coupling. It has recently been possible to complete a numerical and computational merging of the University College London (UCL) global thermospheric model and the Sheffield University ionospheric model. This has produced a self-consistent coupled thermospheric-ionospheric model, which has become a valuable diagnostic tool for examining thermospheric-ionospheric interactions in the polar regions. In particular, it is possible to examine the effects of induced winds, ion transport, and the seasonal and diurnal U.T. variations of solar heating and photoionization within the polar regions. Polar and high-latitude plasma density structure at F-region altitudes can be seen to be strongly controlled by U.T., and by season, even for constant solar and geomagnetic activity. In the winter, the F-region polar plasma density is generally dominated by the effects of transport of plasma from the dayside (sunlit cusp). In the summer polar region, however, an increase in the proportion of molecular to atomic species, created by the global seasonal circulation and augmented by the geomagnetic forcing, controls the plasma composition and generally depresses plasma densities at all U.Ts. A number of these complex effects can be seen in data obtained from ground-based radars, Fabry-Perot interferometers and in the combinedDEdata-sets. Several of these observations will be used, in combination with simulations using the UCL-Sheffield coupled model, to illustrate the major features of large-scale thermosphere-ionosphere interactions in response to geomagnetic forcing.

Comparisons of theoretical models and observations of the thermosphere and ionosphere during extremely disturbed geomagnetic conditions during the last solar cycle

During the last solar cycle, a series of major geomagnetic disturbances, at times of moderate to high solar activity, were well observed by a combination of ground-based and space-borne instruments capable of observing both thermospheric and ionospheric structure, dynamics and their responses to geomagnetic inputs. A wide range of information is now available describing the major geomagnetic driving processes, and their magnitudes and large-scale variations during major disturbances, as a result of concerted experimental programmes of the past 6 to 8 years. Using these data, some of the largest geomagnetic disturbances recorded during the past 30 years have been simulated. Observations from Dynamics Explorer and ESRO IV, in addition to those from ground-based Fabry-Perot interferometers, provide detailed thermospheric data against which these simulated disturbances can be compared. These are presented as several case studies. The simulations provide a considerable insight into the behaviour of the thermosphere during extreme events, in addition to a valuable body of data for examination of extreme conditions of the thermospheric and ionospheric environment for spacecraft operations.

The response of the high-latitude thermosphere to geomagnetic activity

The past three years have seen a wealth of new data from satellite and ground-based instrumentation describing the structure and dynamics of the thermosphere and its response to geomagnetic activity. In this review, data obtained from sampling the middle latitude and polar regions during disturbed geomagnetic periods will be surveyed for evidence of the major sources of geomagnetic energy and momentum forcing. It is not feasible to present a unique description of the storm-like phenomena induced in the thermosphere during major geomagnetic disturbances. The winter and the summer hemisphere respond differently due to the contrast in solar EUV heating and photo-ionisation in the polar regions. Geomagnetic disturbances causing similar magnetic effects may create quite different thermospheric perturbations. Certain of these latter differences may be associated with the structure of the Interplanetary Magnetic Field (IMF) before and during the event. By comparison of observational data with the predictions of numerical models, it is possible to place some quantitative limits on the total energy transferred from the solar wind via the magnetosphere and deposited in the polar ionosphere and thermosphere during some recent major events. It is also possible to assess the energy and momentum contributions of the major geophysical processes in particular regions.

The Doppler Imaging System: Initial observations of the auroral thermosphere

During December 1982, a novel Fabry-Perot interferometer—a Doppler Imaging System (DIS)— was used at Kiruna Geophysical Institute (KGI), Sweden (67.8°N, 21.2°E) to complement a series of coordinated observations of global thermospheric dynamics utilizing a number of conventional ground-based Fabry-Perot interferometers and the NASA Dynamics Explorer satellite. The DIS is an interferometer with two unique attributes : it has a luminosity or étendue more than one hundred times that of the conventional Fabry-Perot interferometer, and it is also capable of deducing a two-dimensional velocity field of a suitable line-emitting areal source by independently measuring the Doppler shift at a large number of points within the field of view. On 17 December 1982, a very large geomagnetic Storm Sudden Commencement (08.05 U.T.) preceded a major geomagnetic disturbance. During this disturbance, Northern Scandinavia was influenced by a strong eastward auroral electrojet for an extended period (10–19 U.T.). The DIS was able to observe the dynamical response of the upper thermosphere to this event in conjunction with a second Fabry-Perot interferometer (FPI) at KGI. Westward thermospheric winds of about 900 m s −1 occurred during the disturbance and, at the peak of the disturbance, the combined DIS and FPI observations indicate that the thermospheric flow was quite chaotic. Fluctuations of the order of ± 150 m s −1, associated with spatial scales of the order of 100 or 200 km occurred within the mean westward flow inside the 800 km diameter region observed from Kiruna.

Ferromagnetic resonance in thin films: A. van Herbeek and J. Witters, J. Physique, 24 (5), May 1963, 315–318

During December 1982, a novel Fabry-Perot interferometer—a Doppler Imaging System (DIS)— was used at Kiruna Geophysical Institute (KGI), Sweden (67.8°N, 21.2°E) to complement a series of coordinated observations of global thermospheric dynamics utilizing a number of conventional ground-based Fabry-Perot interferometers and the NASA Dynamics Explorer satellite. The DIS is an interferometer with two unique attributes : it has a luminosity or étendue more than one hundred times that of the conventional Fabry-Perot interferometer, and it is also capable of deducing a two-dimensional velocity field of a suitable line-emitting areal source by independently measuring the Doppler shift at a large number of points within the field of view. On 17 December 1982, a very large geomagnetic Storm Sudden Commencement (08.05 U.T.) preceded a major geomagnetic disturbance. During this disturbance, Northern Scandinavia was influenced by a strong eastward auroral electrojet for an extended period (10–19 U.T.). The DIS was able to observe the dynamical response of the upper thermosphere to this event in conjunction with a second Fabry-Perot interferometer (FPI) at KGI. Westward thermospheric winds of about 900 m s−1 occurred during the disturbance and, at the peak of the disturbance, the combined DIS and FPI observations indicate that the thermospheric flow was quite chaotic. Fluctuations of the order of ± 150 ms−1, associated with spatial scales of the order of 100 or 200 km occurred within the mean westward flow inside the 800 km diameter region observed from Kiruna.