Large Geomagnetic Storms Research Articles

On the origins and timescales of geoeffective IMF

AbstractSouthward interplanetary magnetic field (IMF) in the geocentric solar magnetospheric (GSM) reference frame is the key element that controls the level of space weather disturbance in Earth's magnetosphere, ionosphere, and thermosphere. We discuss the relation of this geoeffective IMF component to the IMF in the geocentric solar ecliptic (GSE) frame, and using the almost continuous interplanetary data for 1996–2015 (inclusive), we show that large geomagnetic storms are always associated with strong southward, out‐of‐ecliptic field in the GSE frame: Dipole tilt effects, which cause the difference between the southward field in the GSM and GSE frames, generally make only a minor contribution to these strongest storms. The time‐of‐day/time‐of‐year response patterns of geomagnetic indices and the optimum solar wind coupling function are both influenced by the timescale of the index response. We also study the occurrence spectrum of large out‐of‐ecliptic field and show that for 1 h averages it is, surprisingly, almost identical in ICMEs (interplanetary coronal mass ejections), around CIRs/SIRs (corotating and stream interaction regions) and in the “quiet” solar wind (which is shown to be consistent with the effect of weak SIRs). However, differences emerge when the timescale over which the field remains southward is considered: for longer averaging timescales the spectrum is broader inside ICMEs, showing that these events generate longer intervals of strongly southward average IMF and consequently stronger geomagnetic storms. The behavior of out‐of‐ecliptic field with timescale is shown to be very similar to that of deviations from the predicted Parker spiral orientation, suggesting the two share common origins.

Using citizen science reports to define the equatorial extent of auroral visibility

AbstractAn aurora may often be viewed hundreds of kilometers equatorward of the auroral oval owing to its altitude. As such, the NOAA Space Weather Prediction Center (SWPC) Aurora Forecast product provides a “view line” to demonstrate the equatorial extent of auroral visibility, assuming that it is sufficiently bright and high in altitude. The view line in the SWPC product is based upon the latitude of the brightest aurora, for each hemisphere, as specified by the real‐time oval variation, assessment, tracking, intensity, and online nowcasting (OVATION) Prime (2010) aurora precipitation model. In this study, we utilize nearly 500 citizen science auroral reports to compare with the view line provided by an updated SWPC aurora forecast product using auroral precipitation data from OVATION Prime (2013). The citizen science observations were recorded during March and April 2015 using the Aurorasaurus platform and cover one large geomagnetic storm and several smaller events. We find that this updated SWPC view line is conservative in its estimate and that the aurora is often viewable further equatorward than is indicated by the forecast. By using the citizen reports to modify the scaling parameters used to link the OVATION Prime (2013) model to the view line, we produce a new view line estimate that more accurately represents the equatorial extent of visible aurora. An OVATION Prime (2013) energy flux‐based equatorial boundary view line is also developed and is found to provide the best overall agreement with the citizen science reports, with an accuracy of 91%.

A case study of electron precipitation fluxes due to plasmaspheric hiss

AbstractWe find that during a large geomagnetic storm in October 2011 the trapped fluxes of >30, >100, and >300 keV outer radiation belt electrons were enhanced at L = 3–4 during the storm main phase. A gradual decay of the trapped fluxes was observed over the following 5–7 days, even though no significant precipitation fluxes could be observed in the Polar Orbiting Environmental Satellite (POES) electron precipitation detectors. We use the Antarctic‐Arctic Radiation‐belt (Dynamic) Deposition–VLF Atmospheric Research Konsortium receiver network to investigate the characteristics of the electron precipitation throughout the storm period. Weak electron precipitation was observed on the dayside for 5–7 days, consistent with being driven by plasmaspheric hiss. Using a previously published plasmaspheric hiss‐induced electron energy e‐folding spectrum of E0 = 365 keV, the observed radio wave perturbation levels at L = 3–4 were found to be caused by >30 keV electron precipitation with flux ~100 el cm−2 s−1 sr−1. The low levels of precipitation explain the lack of response of the POES telescopes to the flux, because of the effect of the POES lower sensitivity limit and ability to measure weak diffusion‐driven precipitation. The detection of dayside, inner plasmasphere electron precipitation during the recovery phase of the storm is consistent with plasmaspheric hiss wave‐particle interactions and shows that the waves can be a significant influence on the evolution of the outer radiation belt trapped flux that resides inside the plasmapause.

Short-term variability of the Sun-Earth system: an overview of progress made during the CAWSES-II period

This paper presents an overview of results obtained during the CAWSES II period on the short term variability of the Sun and how it affects the near Earth space environment. CAWSES II was planned to examine the behavior of the solar terrestrial system as the solar activity climbed to its maximum phase in solar cycle 24. After a deep minimum following cycle 23, the Sun climbed to a very weak maximum in terms of the sunspot number in cycle 24 (MiniMax24), so many of the results presented here refer to this weak activity in comparison with cycle 23. The short term variability that has immediate consequence to Earth and geospace manifests as solar eruptions from closed field regions and high speed streams from coronal holes. Both electromagnetic (flares) and mass emissions (coronal mass ejections, CMEs) are involved in solar eruptions, while coronal holes result in high speed streams that collide with slow wind forming the so called corotating interaction regions (CIRs). Fast CMEs affect Earth via leading shocks accelerating energetic particles and creating large geomagnetic storms. CIRs and their trailing high speed streams (HSSs), on the other hand, are responsible for recurrent small geomagnetic storms and extended (days) of auroral zone activity, respectively. The latter lead to the acceleration of relativistic magnetospheric killer electrons. One of the major consequences of the weak solar activity is the altered physical state of the heliosphere that has serious implications for the shock-driving and storm causing properties of CMEs. Finally, a discussion is presented on extreme space weather events prompted by the 2012 July 23 super storm event that occurred on the backside of the Sun. Many of these studies were enabled by the simultaneous availability of remote-sensing and in situ observations from multiple vantage points with respect to the Sun Earth line.

No Major Solar Flares but the Largest Geomagnetic Storm in the Present Solar Cycle

No Major Solar Flares but the Largest Geomagnetic Storm in the Present Solar Cycle

Fractal and wavelet analysis evaluation of the mid latitude ionospheric disturbances associated with major geomagnetic storms

Variations of the total electron content (TEC) of the ionosphere are mainly associated with major geomagnetic storms occurring with the arrival of coronal mass ejections (CMEs) to the Earth environment. The purpose of this paper is to show results of the analysis we made of the impact of all major geomagnetic storms (Dst<-200nT) on the ionosphere at mid latitudes, which have occurred since 2000. The analysis consists in the calculation of TEC of the ionosphere using data from several Mexican GPS stations, with the purpose of quantifying the impact into the ionosphere to these latitudes, through the variations in amplitude, Hurst index, that is roughness, and wavelet transform of the time series of TEC. Indeed, during the geomagnetic storms of April 7, 2000, July 16, 2000, October 30, 2003, November 20, 2003 and November 8, 2004, major ionospheric disturbances at mid latitudes took place with changes in amplitude of TEC going from 3.29 to 8.82 sigmas. These ionospheric disturbances were probably associated with prompt penetration electric fields (PPEFs) and equatorward neutral winds. On the other hand, during four geomagnetic storms (August 12, 2000, March 31, 2001, April 11, 2001 and May 15, 2005), there were negative ionospheric storms that pushed the TEC to significantly lower values. This has been interpreted as the presence of regions in which the neutral composition is changed. Also, in some cases during the disturbed days, the Hurst values were smaller than during the undisturbed days, i.e. during these geomagnetic storms, the roughness of the time series of TEC increased. The wavelet analysis showed a strong influence of the diurnal variation on TEC values (periodicities of 12h), and periodicities characteristics of ionospheric disturbances of 1–8h. It is found that large geomagnetic storms produce significant ionospheric disturbances at mid latitudes, as shown by the wavelet analysis and, in some cases, changes in the roughness of the time series of TEC as shown by the Hurst exponent.

Global simulation of extremely fast coronal mass ejection on 23 July 2012

The July 23, 2012 CME was an extremely fast backside event, reaching ∼1AU (STEREO-A) within 20h as compared to ∼3–6 days for typical CME events. Here, we present results from a simulation study of the CME and its driven shock using a combined kinematic and magnetohydrodynamic (MHD) simulation model, H3DMHD. In general, the model results match well with in situ measurements in the arrival time of the CME-driven shock and the total magnetic field strength, assuming an initial CME speed of 3100km/s. Based on extrapolation of an empirical model, the fast CME and its large magnetic field (|B|∼120nT) are capable of producing an extremely large geomagnetic storm (Dst∼−545nT), comparable to the well-known Halloween storm in 2003, if the CME had made a direct impact to the Earth. We investigated the effect of the adiabatic index (γ). It is found that the shock tends to arrive slightly later for a smaller γ value, and γ=5/3 provides the best agreement for the shock arrival time. We also demonstrate that the strength (the Mach number) of the CME-driven fast-mode shock is not the largest at the “nose” of the CME. This is mainly due to the manifestation of fast-mode wave speed upstream of the shock.

Storm-time meridional flows: a comparison of CINDI observations and model results

Abstract. During a large geomagnetic storm, the electric field from the polar ionosphere can expand far enough to affect the mid-latitude and equatorial electric fields. These changes in the equatorial zonal electric field, called the penetration field, will cause changes in the meridional ion flows that can be observed by radars and spacecraft. In general this E × B ion flow near the equator caused by the penetration field during undershielding conditions will be upward on the dayside and downward on the nightside of the Earth. Previous analysis of the equatorial meridional flows observed by CINDI instrument on the C/NOFS spacecraft during the 26 September 2011 storm showed that all of the response flows on the dayside were excess downward flows instead of the expected upward flows. These observed storm-time responses are compared to a prediction from a physics-based coupled model of thermosphere–ionosphere–inner-magnetosphere in an effort to explain these observations. The model results suggest that the equatorial downward flow could be attributed to a combined effect of the overshielding and disturbance dynamo processes. However, some discrepancy between the model and observation indicates a need for improving our understanding of how sensitive the equatorial electric field is to various model input parameters that describe the magnetosphere–ionosphere coupling processes.

Variations of nitric oxide in the mesosphere and lower thermosphere over Antarctica associated with a magnetic storm in April 2012

We report extreme enhancements of the nitric oxide (NO) column density observed with the ground-based millimeter-wave spectroscopic radiometer installed at Syowa Station, Antarctica, during a large geomagnetic storm in April 2012. From the NO spectrum line shape and NO column density relationship with solar radiation, we concluded that the NO was emitted in the altitude range between 75 km and 100 km. The column density of NO gradually increased during the recovery phase. In addition to variations on a time frame of several days, we found diurnal variations. The increase of NO was related to precipitated electrons in the energy range of 30–300 keV observed by Polar-orbiting Operational Environmental Satellite (POES)/The Meteorological Operational (METOP). We found a rapid response (within 1 h) and a one-to-one correspondence between them. For the first time, we show that a remarkable increase of the column density of NO is caused by dawn-dusk asymmetry of the plasma sheet electrons.

Large magnetic storms as viewed by TWINS: A study of the differences in the medium energy ENA composition

AbstractDuring large geomagnetic storms (Dst ≤−100 nT), oxygen can become a significant component of the energetic particles of the inner magnetosphere. Until recently, there were no available global observations of the medium energy (&lt;50 keV) oxygen populations. Using observations from the Two Wide‐angle Imaging Neutral‐atom Spectrometers (TWINS) Energetic Neutral Atom (ENA) imagers we present a study of nine large storms of solar cycle 24 as a function of storm phase. For these storms we observe that the H and O ENA fluxes and their temperatures increase in tandem during the storm's initial phase. However, there is no increase in the O+/H+ ratio in the inner magnetosphere until the storm main phase. Also seen during the main phase is an energy dispersion with higher‐energy (32 keV) H ENAs seen before the arrival of O ENAs of the same energy. The O ENAs take longer to return to prestorm levels during the recovery phases. This longer recovery time is likely because of the large difference between the storm time and prestorm O populations compared to H (i.e., there is always some prestorm H in the inner magnetosphere, but effectively no O prestorm). These results imply that medium‐energy O ENAs evolve over long time scales (hours to days) as opposed to the shorter substorm time scales of the higher‐energy (&gt;52 keV) O ENAs.

Magnetotail current contribution to the Dst Index Using the MT Index and the WINDMI model

In this paper, we have improved the capabilities of a low dimensional nonlinear dynamical model called WINDMI to determine the state of the global magnetosphere by employing the magnetotail (MT) index as a measurement constraint during large geomagnetic storms. The MT index is derived from particle precipitation measurements made by the NOAA/POES satellites. This index indicates the location of the nightside ion isotropic boundary, which is then used as a proxy for the strength of the magnetotail current in the magnetosphere. In Asikainen et al. (2010), the contribution of the tail current to the Dst index is estimated from an empirical relationship based on the MT index. Here the WINDMI model is used as a substitute to arrive at the tail current and ring current contribution to the Dst index, for comparison purposes. We run the WINDMI model on 7 large geomagnetic storms, while optimizing the model state variables against the Dst index, the MT index, and the AL index simultaneously. Our results show that the contribution from the geotail current produced by the WINDMI model and the MT index are strongly correlated, except during some periods when storm time substorms are observed. The inclusion of the MT index as an optimization constraint in turn increases our confidence that the ring current contribution to the Dst index calculated by the WINDMI model is correct during large geomagnetic storms.

Reduction of the field-aligned potential drop in the polar cap during large geomagnetic storms

[1] We have studied photoelectron flows and the inferred field-aligned potential drop in the polar cap during five large geomagnetic storms, which occurred in the periods when the photoelectron observations in the polar cap are available near the apogee of the Fast Auroral SnapshoT satellite (~4000 km) at solar maximum, and the footprint of the satellite paths in the polar cap was under sunlit conditions most of the time. In contrast to the ~20 V potential drop during geomagnetically quiet periods at solar maximum identified by Kitamura et al. (2012), the field-aligned potential drop frequently became smaller than ~5 V during the main and early recovery phases of the large geomagnetic storms. This result indicates that the acceleration of ions by a field-aligned potential drop in the polar cap and the lobe region is smaller during the main and early recovery phases of large geomagnetic storms compared to during geomagnetically quiet periods. Since ions with large flux originating from the cusp/cleft ionosphere convect into the polar cap during geomagnetic storms, the net escaping electron number flux should increase to balance the enhanced ion outflows under small field-aligned current conditions. The magnitude of the field-aligned potential drop would be reduced to let larger part of photoelectrons escape.

Vertical and meridional equatorial ion flows observed by CINDI during the 26 September 2011 storm

AbstractThe equatorial ionosphere is generally shielded from outside electrical fields except during large geomagnetic storms. During these storms, the polar region electric fields can temporarily extend to the equatorial regions in what is called a penetration field. During the subsequent recovery period, a disturbance dynamo is produced with an enhanced electric field with the opposite orientation relative to the penetration field. The penetration electric field would be oriented toward the east on the dayside causing an excess upward E × B motion of the equatorial ionospheric ions. The disturbance dynamo electric field would have the opposite orientation, westward on the dayside, producing an excess downward E × B motion of the equatorial ionospheric ions. The moderate storm (minimum Dst = −103 nT) on 26 September 2011 is examined using ion flow data from the Coupled Ion‐Neutral Dynamics Investigation (CINDI) thermal plasma instrument package on the Communication/Navigation Outage Forecast System (C/NOFS) spacecraft on the dayside and early evening local times to look for examples of these flows. Despite what should have been a large enough storm to produce penetration fields and upward flows, a detailed examination of the observed flows from this storm shows only enhanced downward flows before the storm, during the main phase, and through the recovery.

Variation of proton radiation belt deduced from solar cell degradation of Akebono satellite

We have analyzed the degradation of the solar cells of the Akebono satellite due to various space radiations, and found a signature of a deformed proton radiation belt in 1991. The output current of the solar cells decreased slowly from 13A in 1989 to about 7A in 2009, with a quasi-periodic oscillation. By comparing the decrease rate with the solar proton flux measured by GOES satellites and the flux of trapped radiations from NASA’s models (AP8MAX and AE8MAX), we found a fair correlation between the decrease rate of the solar cell output current and the trapped proton flux between 1989 and 1992. However, we also found an interval of inconsistency after a large solar proton event and geomagnetic storm in March 1991. Modified models of trapped proton flux distribution with a second peak around L = 2.3 lead to a better coincidence during the interval, indicating that the deformation of the proton radiation belt terminated around the end of 1991 or early 1992. The result provides further evidence for the proton radiation belt, usually thought as being quite stable, changing drastically on special occasions.

Study of large geomagnetic storms (GMSs) and their association with different solar source activities observed during solar cycle 23

Geomagnetic storms (GMSs) are stimulated by higher solar wind flow speed (VSW) and by a southward-directed interplanetary magnetic field (IMF Bz). Two kinds of flows dominate the large scale structure of solar wind: corotating flows and transient disturbances. Corotating flows are associated with spatial variability in coronal expansion and solar rotation, whereas transient disturbances are associated with episodic ejections of material into interplanetary space from coronal regions. The high speed streams originated from coronal interaction regions (CIRs) and transient disturbances are mostly caused by fast coronal mass ejections (CMEs). CMEs are the crucial link between solar activity and transient interplanetary disturbances and are responsible for major GMSs. CMEs eject magnetic flux into interplanetary space that produces abrupt increase in the northward component of Earth's magnetic field. There are two types of geomagnetic field variations termed as long-time variation and storm-time variations. The long-term variations are very useful to solar cyclical study of geomagnetic field variation as well as change in polarity of the Sun, climate change, plants growth rate and geological change of Earth's pole. The storm time variations also known as geomagnetic storm deals the various characteristics of GMSs and their connection with solar source activities and interplanetary magnetic fields. These variations are directly affect us and shows adverse effect in satellites, communication system and power losses. In the present study, we have analysed large geomagnetic storms (GMSs) associated with storm time index (D st ) decrease of more than 100 nT observed during solar cycle 23

Observations of geomagnetically induced currents in the Australian power network

AbstractInfrastructures such as pipelines and power networks at low‐middle latitude regions have historically been considered relatively immune to geomagnetically induced currents (GICs). Over the past decade there have been an increasing number of investigations into the impact of GICs in long grounded conductors at these latitudes. The Australian region power network spans thousands of kilometers from low to middle latitudes. The approaching maximum of solar cycle 24 and recent findings of studies into power networks located at similar latitudes have stimulated the Australian power industry to better understand this phenomenon in their region. As a result, a pilot study to compare space weather activity with in situ GIC monitors at strategic locations within the power network was initiated. This paper provides some results from the first of these operational GIC monitors during a modest geomagnetic storm, showing the first observational evidence of space weather well correlated with GICs measured in the Australian power network. Transformer neutral currents show a high degree of similarity with the geoelectric field derived from the closest available geomagnetic observatory. Current maxima of 4–5 amperes were observed in association with geoelectric field values of ~0.06–0.07 volts per kilometer. This paper also discusses the GIC measurements obtained during this storm in terms of the space weather drivers and the considerably larger geoelectric field values anticipated during larger geomagnetic storms.

On the multi-scale nature of large geomagnetic storms: an empirical mode decomposition analysis

Abstract. Complexity and multi-scale are very common properties of several geomagnetic time series. On the other hand, it is amply demonstrated that scaling properties of geomagnetic time series show significant changes depending on the geomagnetic activity level. Here, we study the multi-scale features of some large geomagnetic storms by applying the empirical mode decomposition technique. This method, which is alternative to traditional data analysis and is designed specifically for analyzing nonlinear and nonstationary data, is applied to long time series of Sym-H index relative to periods including large geomagnetic disturbances. The spectral and scaling features of the intrinsic mode functions (IMFs) into which Sym-H time series can be decomposed, as well as those of the Sym-H time series itself, are studied considering different geomagnetic activity levels. The results suggest an increase of dynamical complexity and multi-scale properties for intermediate geomagnetic activity levels.

Satellite observations of banded VLF emissions in conjunction with energy‐banded ions during very large geomagnetic storms

Frequency‐banded electromagnetic VLF waves up to 2000 Hz are observed concurrently with warm (10 s to 10,000 s of eV) energy‐banded ions in the low latitude auroral and sub‐auroral zones during every large geomagnetic storm encountered by the FAST and DEMETER satellites. The banded ions and waves persist for several FAST or DEMETER orbits, lasting up to 12 h, in both dawn and dusk sectors, in both the northern and southern hemispheres. If the waves are generated at harmonics of the proton gyrofrequency, the inferred source region would be ∼4000 km altitude. Previous investigations have shown that such waves can propagate from this source region to the locations of both spacecraft. An investigation into the growth of waves at harmonics of fci in the inferred source region suggests that these emissions could be generated by ion bands similar to those observed at the same time as the waves. Magnetospheric waves such as these play a role in energy transfer between distinct particle populations and may contribute to ion heating and ion outflow as well as electron energization. All of these phenomena occur during the strongest magnetic storms. The appearance of the banded ions and associated wave activity suggests that there may be distinct changes in the geospace system that characterize large magnetic storms.

The source of the steep plasma density gradient in middle latitudes during the 11–12 April 2001 storm

A steep plasma density gradient has been observed in the middle‐latitude F region during large geomagnetic storms. This phenomenon can be understood as a special form of the middle‐latitude ionization trough (hereafter trough), but its causal linkage has not yet been clarified. We investigate the association of the steep density gradient and the trough by comparing their morphologies and occurrence locations using the satellite and ground observation data during the 11–12 April 2001 storm. Steep density gradients are detected in the dusk sector at the equatorward edges of the aurora by the Defense Meteorological Satellite Program (DMSP) F13 spacecraft. The locations of the steep density gradients coincide with the locations of the ionospheric footprints of the plasmapause identified by the Imager for Magnetopause‐to‐Aurora Global Exploration satellite. These observations demonstrate that the steep density gradient is created at the typical location of the trough. However, the steep density gradient is not produced by the formation of an intense trough during the storm. The temporal evolution of the total electron content maps shows that the steep density gradient observed at dusk by DMSP is associated with the plasma density enhancement in the dayside and its corotation into the dusk sector. The severe plasma density enhancement in middle latitudes, in combination with the trough and presumably the plasma depletion in high latitudes by the neutral composition change, produces the steep density gradient in the subauroral region during the storm.

Bayesian prediction of geomagnetic storms: Wind data, 1996–2010

The feature‐based Bayesian method previously developed by Chen et al. (1996, 1997) to predict the occurrence, severity, and duration of large geomagnetic storms has been run on a daily basis on the Wind/Magnetic Fields Investigation (MFI) data from January 1996 until March 2010. The algorithm uses as input real‐time solar wind magnetic field data obtained at the L1 Lagrange point, and the output is the probability prediction of the magnetic field structure of the upstream solar wind that has yet to arrive, and its geoeffectiveness, where geoeffectiveness is measured by the traditional Dst index. The performance characteristics of the method are evaluated using a four‐level contingency table: nonstorm disturbances (−80 nT &lt; Dst ≤ − 50 nT), weak storms (−120 nT &lt; Dst ≤ − 80 nT), moderate storms (−160 nT &lt; Dst ≤ − 120 nT), and strong storms (Dst ≤ − 160 nT). It is found that the greater the level of disturbances, the more accurate the prediction is. With moderate and strong storms combined, the algorithm correctly predicted 30 out of 37 storms (81%). The false negatives are caused by solar wind structures with short durations (≲ 1–2 hrs) of strong southward magnetic field (say, Bz ≲ −30 nT), which are sparsely represented in the probability distribution functions constructed using prior solar wind data (OMNI data set from 1973–1981). The algorithm does not predict the storm onset time, but the results of the present and previous tests show that the average warning time ranges from a few hours to a maximum of 10–15 hours.