Geomagnetic Storm Time Research Articles

Effect of Coronal Mass Ejection on Earth’s Magnetic Field during Ascending Phase of Solar Cycles 23-24

We have studied the width and speed of coronal mass ejections (CMEs) and geomagnetic disturbance storm time (Dst) Index during ascending phase of solar cycles 23 and 24. We have classified total CMEs according to angular width and speed for the ascending period 1996-2002 and 2008-2014. We have found that the width of 62% CMEs is narrow, and 3% are Halo for the solar cycle 23 and 73% CMEs are narrow, and 2% CMEs are Halo for the solar cycle 24. The speed distribution of 65% CMEs has speed ≤ 500 km/sec and 4% CMEs has speed > 1000 km/sec for solar cycle 23 and 84% CMEs has speed ≤ 500 km/sec and 1% CMEs has speed > 1000 km/sec in cycle 24. The relationship between width and speed is more pronounced for fast ejecta (>1000 km/sec.), while slower ejecta shows more astronomically immense scatter. We have reported that the correlation between Dst and CMEs for ascending phase of solar cycle 24 is less than as compare to ascending phase of solar cycle 23.

Diversity of threshold phenomena in geophysical media

The sample analysis of threshold phenomena in the lithosphere, atmosphere, and magnetosphere is conducted. The phenomena due to the flow of electric current and pore fluid in the rocks are considered, the scenario of wind-driven generation of atmospheric electricity is suggested, and the model of the geomagnetic storm time Dst variation is analyzed. An important general conclusion consists in the fact that in the geophysical media there is a wide class of threshold phenomena that are affine with phase transitions of the second kind. These phenomena are also related to the critical transitions in self-oscillatory systems with soft self-excitation. The integral representation of bifurcation diagrams for threshold phenomena is suggested. This provides a simple way to take into account the influence of the fluctuations on the transition of a system through the threshold. Fluctuations remove singularity at the threshold point and, generally, lead to a certain shifting of the threshold. The question concerning the hard transition through the threshold and several aspects of modeling the blow-up instability which is presumed to occasionally develop in the geophysical media are discussed.

Statistical analysis of the mid-latitude trough position during different categories of magnetic storms and different storm intensities

The ionospheric mid-latitude trough minimum position as a function of geomagnetic storm time is identified and investigated statistically in terms of the category and the intensity of storms. The data of ion density derived from DMSP and DEMETER satellites were used to extract the trough position. The variations of mid-latitude trough in 41 moderate magnetic storms and 88 intense magnetic storms in the 23rd solar cycle were studied. The results show that the trough moves toward the equator as Dst index decreases and toward the pole as Dst index increases. Compared with the ICME, MC and CIR storms, in sheath storms the trough shifts to lower latitude at the end of the main phase, although the average storm intensity is weak. During the storm recovery phase, the rapid recovery of the trough position can be seen at the start of the recovery phase for moderate CIR storms. We also calculated the correlation between the minimum latitude of the trough position and the storm magnitude as well as other related main phase parameters during all storms. We found that the minimum latitude of the trough position exhibits a strong correlation with the storm magnitude during magnetic storms. However, the correlation coefficients between the trough position and other related main phase parameters are very low.

The geomagnetic storm time response of GPS total electron content in the North American sector

AbstractOver the last two decades, maps of GPS total electron content (TEC) have improved our understanding of the large perturbations in ionospheric electron density which occur during geomagnetic storms. However, previous regional and global studies of ionospheric storms have performed only a limited separation of storm time, local time, longitudinal, and seasonal effects. Using 13 years of GPS TEC data, we present a complete statistical characterization of the ionospheric response to geomagnetic storms for midlatitudes in the North American sector where dense ground receiver coverage is available. The rapid onset of a positive phase is observed across much of the dayside and evening ionosphere followed by a longer‐lasting negative phase across all latitudes and local times. Our results show clear seasonal variations in the storm time TEC, such that summer events tend to be dominated by the negative storm response while winter events exhibit a stronger initial positive phase with minimal negative storm effects. We find no discernable difference between spring and fall equinox events with both being equivalent to the average storm time response across all seasons. We also identify a prominent magnetic declination effect such that stronger dayside positive storm effects are observed in regions of negative declination (i.e., eastern North America). On the nightside, asymmetries in the TEC response are observed near the auroral oval and midlatitude trough which may be attributed to thermospheric zonal winds pushing plasma upward/downward along field lines of opposite declination.

Sub-ionospheric VLF signal anomaly due to geomagnetic storms: a statistical study

Abstract. We investigate quantitatively the effect of geomagnetic storms on the sub-ionospheric VLF/LF (Very Low Frequency/Low Frequency) propagations for different latitudes based on 2-year nighttime data from Japanese VLF/LF observation network. Three statistical parameters such as average signal amplitude, variability of the signal amplitude, and nighttime fluctuation were calculated daily for 2 years for 16–21 independent VLF/LF transmitter–receiver propagation paths consisting of three transmitters and seven receiving stations. These propagation paths are suitable to simultaneously study high-latitude, low-mid-latitude and mid-latitude D/E-region ionospheric properties. We found that these three statistical parameters indicate significant anomalies exceeding at least 2 times of their standard deviation from the mean value during the geomagnetic storm time period in the high-latitude paths with an occurrence rate of anomaly between 40 and 50 % presumably due to the auroral energetic electron precipitation. The mid-latitude and low-mid-latitude paths have a smaller influence from the geomagnetic activity because of a lower occurrence rate of anomalies even during the geomagnetically active time period (from 20 to 30 %). The anomalies except geomagnetic storm periods may be caused by atmospheric and/or lithospheric origins. The statistical occurrence rates of ionospheric anomalies for different latitudinal paths during geomagnetic storm and non-storm time periods are basic and important information not only to identify the space weather effects toward the lower ionosphere depending on the latitudes but also to separate various external physical causes of lower ionospheric disturbances.

Statistical storm time examination of MLT‐dependent plasmapause location derived from IMAGE EUV

AbstractThe location of the outer edge of the plasmasphere (the plasmapause) as a function of geomagnetic storm time is identified and investigated statistically in regard to the solar wind driver. Imager for Magnetopause‐to‐Aurora Global Exploration (IMAGE) extreme ultraviolet (EUV) data are used to create an automated method that locates and extracts the plasmapause. The plasmapause extraction technique searches a set range of possible plasmasphere densities for a maximum gradient. The magnetic local time (MLT)‐dependent plasmapause results are compared to manual extraction results. The plasmapause results from 39 intense storms are examined along a normalized epoch storm timeline to determine the average plasmapause L shell as a function of MLT and storm time. The average extracted plasmapause L shell follows the expected storm time plasmapause behavior. The results show that during the main phase, the plasmapause moves earthward and a plasmaspheric drainage plume forms near dusk and across the dayside during strong convection. During the recovery phase, the plume rejoins the corotationally driven plasma while the average plasmapause location moves farther from the Earth. The results are also examined in terms of the solar wind driver. We find evidence that shows that the different categories of solar wind drivers result in different plasmaspheric configurations. During magnetic cloud‐driven events the plasmaspheric drainage plume appears at the start of the main phase. During sheath‐driven events the plume forms later but typically extends further in MLT.

Information measures based analysis of complex solar wind—magnetosphere interaction dynamics during geomagnetic storms

By calculating the complexity measures such as approximate entropy, sample entropy, algorithmic complexity and permutation entropy of auroral and polar cap index time series, it can be determined whether or not these show similar regularity of underlying solar wind—magnetosphere interaction dynamics. The complexity profiles of magnetospheric indices and coupling coefficients for 45 geomagnetic storm time events of solar cycle 23 using a correlation-based characterisation in the nonlinear regime are explored. Using a sliding window method, we study the variation in permutation entropy of magnetospheric response, which exhibits a high degree of dynamical complexity associated with different features during calm and storm periods.

Geomagnetic Disturbances and Its Impact on Ionospheric Critical Frequency (foF2) at High, Mid and Low Latitude Region

A geomagnetic storm is a major disturbance of Earth's magnetosphere that occurs when there is a very efficient exchange of energy from the solar wind into the space environment surrounding Earth. During solar and geomagnetic activities, critical frequency of F2 layer (foF2) varies in a great extent. In this Study, our main aim is to examine the effect of solar and geomagnetic activities on the critical frequency (foF2) during January 2014 to April 2014 respectively. One magnetic intense storm occurred on 19 February with (Dst -112) and other moderate storm occurred on 12 April 2014 with (Dst -80). In our study, we have analyzed these effects on critical frequency of F2 layer for ionospheric monitoring. We have used ionospheric data at Low, mid and high latitude station. The absorption and ionization of the ionospheric medium depends on solar activity. The value of foF2 increased from their normal value at all the three latitudes. This is due to geomagnetic storms that occurred around the same time. A very interesting feature that can be seen in the figures is that the increase of foF2 at Low latitude is much more intense as compare to high and mid latitude. Comparison among all the latitudes shows that the values of foF2 at high latitude are quite less as compared to low and mid latitude. We have found that the effect of solar and geomagnetic storm disturbances is strongest at the low latitude and weakest at the high latitude during the geomagnetic storm time.

The Anemomilos prediction methodology for Dst

AbstractThis paper describes new capabilities for operational geomagnetic Disturbance storm time (Dst) index forecasts. We present a data‐driven, deterministic algorithm called Anemomilos for forecasting Dst out to a maximum of 6 days for large, medium, and small storms, depending upon transit time to the Earth. This capability is used for operational satellite management and debris avoidance in Low Earth Orbit (LEO). Anemomilos has a 15 min cadence, 1 h time granularity, 144 h prediction window (+6 days), and up to 1 h latency. A new finding is that nearly all flare events above a certain irradiance threshold, occurring within a defined solar longitude/latitude region and having sufficient estimated liftoff velocity of ejected material, will produce a geoeffective Dst perturbation. Three solar observables are used for operational Dst forecasting: flare magnitude, integrated flare irradiance through time, and event location. Magnitude is a proxy for ejecta quantity or mass and, combined with speed derived from the integrated flare irradiance, represents the kinetic energy. Speed is estimated as the line‐of‐sight velocity for events within 45° radial of solar disk center. Storms resulting from high‐speed streams emanating from coronal holes are not modeled or predicted. A new result is that solar disk, not limb, observable features are used for predictive techniques. Comparisons between Anemomilos predicted and measured Dst for every hour over 25 months in three continuous time frames between 2001 (high solar activity), 2005 (low solar activity), and 2012 (rising solar activity) are shown. The Anemomilos operational algorithm was developed for a specific customer use related to thermospheric mass density forecasting. It is an operational space weather technology breakthrough using solar disk observables to predict geomagnetically effective Dst up to several days at 1 h time granularity. Real‐time forecasts are presented at http://sol.spacenvironment.net/~sam_ops/index.html?

TEC Enhancement due to Energetic Electrons Above Taiwan and the West Pacific

The energetic electrons of the inner radiation belt during a geomagnetic disturbance can penetrate in the forbidden range of drift shells located at the heights of the topside equatorial ionosphere (< 1000 km). A good correlation was previously revealed between positive ionospheric storms and intense fluxes of quasi-trapped 30-keV electrons at ~900 km height in the forbidden zone. In the present work, we use statistics to validate an assumption that the intense electron fluxes in the topside equatorial ionosphere can be an important source of the ionization in the low-latitude ionosphere. The data on the energetic electrons were obtained from polar orbiting satellites over the periods of the 62 strong geomagnetic storms from 1999 to 2006. Ionospheric response to the selected storms was determined using global ionospheric maps of vertical total electron content (VTEC). A case-event study of a major storm on 9 November 2004 provided experimental evidence in support to the substantial ionization effect of energetic electrons during positive ionospheric storms at the low latitudes. Statistical analysis of nine magnetic storms indicated that the VTEC increases coincided with and coexisted with intense 30-keV electron fluxes irrespective of local time and phase of geomagnetic storm. We concluded that extremely intense fluxes of the 30-keV electrons in the topside low-latitude ionosphere can contribute ~ 10 30 TECU to the localized positive ionospheric storms.

On the effects of geomagnetic storms and pre storm phenomena on low and middle latitude ionospheric F2

This paper presents some features of the ionospheric response observed in equatorial and mid-latitudes region to two strong geomagnetic storms, occurring during Oct. 19–23, 2001 and May 13–17, 2005 and to understand the phenomena of pre-storm that lead to very intense geomagnetic storms. The result point to the fact that pre-storm phenomena that leads to intense ionospheric storm are; large southward turning of interplanetary magnetic field Bz, high electric field, increase in flow speed stream, increase in proton number density, high pressure ram and high plasma beta. The magnitude of Bz turning into southward direction from northward highly depends upon the severity of the storm and the variation in F2 layer parameter at the time of geomagnetic storm are strongly dependent upon the storm intensity. A detailed analysis of the responses of the ionosphere shows that during the storm periods, foF2 values depleted simultaneously both in the equatorial and mid latitude. Observation also shows that low to moderate variations in ionospheric F2 at the pre-storm period may signal the upcoming of large ionospheric disturbances at the main phase. The ionospheric F2response for low and mid latitude does not show any significant differences during the storm main phase and the pre-storm period. The ionospheric response during the pre-storm period is thought very puzzling. The period is observed to be depleted throughout with low-moderate effect across all the stations in the low and mid latitude.

Comment on the existence of a long range correlation in the geomagnetic disturbance storm time (Dst) index

Very recently (Banerjee et al. in Astrophys. Space, doi:1007/s10509-011-0836-1, 2011) the statistics of geomagnetic Disturbance storm (Dst) index have been addressed, and the conclusion from this analysis suggests that the underlying dynamical process can be modeled as a fractional Brownian motion with persistent long-range correlations. In this comment we expose several misconceptions and flaws in the statistical analysis of that work. On the basis of these arguments, the former conclusion should be revisited.

On the existence of a long range correlation in the Geomagnetic Disturbance storm time (Dst) index

The Dst (Disturbance storm time) index is a measurement of earth geomagnetic activity and is widely used to characterize the geomagnetic storm. It is calculated on the basis of the average value of the horizontal component of the earth’s magnetic field at four observatories, namely, Hermanus (33.3° south, 80.3° in magnetic dipole latitude and longitude), Kakioka (26.0° north, 206.0°), Honolulu (21.0° north, 266.4°), and San Juan (29.9° north, 3.2°) and is expressed in nano-Teslas. The strength of the low-latitude surface magnetic field is inversely proportional to the energy content of the ring current around earth caused by solar protons and electrons, which increases during geomagnetic storms. Thus a negative Dst index value indicates that the earth’s magnetic field is weakened which is specifically the case during solar storms. Predicting Dst index is a difficult task due to its structural complexity involving a variety of underlying plasma mechanism. For characterizing and forecasting this complex time series, a formal model must be established to identify the specific pattern of the series. Persistent demand for a fool proof model of Geomagnetic Dst index prompted us to investigate the Dst Time Series mechanism with a very recent technique called Visibility Algorithm and it is observed that the Dst time series follows the same model that of a Stochastic Fractional Brownian motion having long range correlation.

Analyzing the variation of embedding dimension of solar and geomagnetic activity indices during geomagnetic storm time

Abstract Cyclic solar activity as one of the natural chaotic phenomena has significant effects on Earth, climate, and satellites. Rapid changes in the near-Earth space environment can affect the performance and reliability of both spacecraft and ground-based systems. This can imply major problems due to communication and satellite operational anomalies. Therefore, it is meaningful to analyze solar activity and geomagnetic indices to elicit the behavior of sun as the origin of most of these chaotic phenomena. One of the most important tools for analyzing the chaotic trends is the “Embedding Dimension” (ED). In this paper, the variation of ED for solar activity indices especially during storm time for two well-known storms is considered. The first storm is the super-storm on 13 March 1989, which shuts down the power supply system in Québec, Canada and the second one is the storm caused by Coronal Mass Ejection on 11 January 1997 which causes the failure of Telstar 401 satellite. The method of this paper is based on the fact that the reconstructed dynamics of an attractor should be a smooth map, i.e. with no self intersection in the reconstructed attractor. It is shown that the Embedding Dimension (and other chaotic characteristics) of some solar and geomagnetic activity indices during these storms varies rapidly.

An empirical model of the Earth's horizontal wind fields: HWM07

The new Horizontal Wind Model (HWM07) provides a statistical representation of the horizontal wind fields of the Earth's atmosphere from the ground to the exosphere (0–500 km). It represents over 50 years of satellite, rocket, and ground‐based wind measurements via a compact Fortran 90 subroutine. The computer model is a function of geographic location, altitude, day of the year, solar local time, and geomagnetic activity. It includes representations of the zonal mean circulation, stationary planetary waves, migrating tides, and the seasonal modulation thereof. HWM07 is composed of two components, a quiet time component for the background state described in this paper and a geomagnetic storm time component (DWM07) described in a companion paper.

Spectral features of geomagnetic low point displacement and its mechanism

In this paper, Changli station in Hebei Province was taken as an example, in which the minute data of geomagnetic Z component was used to analyze the spectral values of its main frequencies during normal time, geomagnetic storm time and low point displacement time interval respectively. After fitting of ten high spectral values to logarithmic functions, it is found that, by using same length of data, the spectral values at geomagnetic storm time increase apparently compared with those at normal time, especially at the high frequency segment. While low point displacement occurred, the spectral values at high frequency are approximate to those at normal time, but at period above 4 hours they are mostly lower than those at normal time. Comparison of accumulating of some FFT results at low point displacement and normal time shows that, spectral values at periods of 8.5 and 13.7 hours increase at low point displacement time relative to those at normal time. Compared with the images of Ne observed at DEMETER satellite, it is illustrated that the occurrence of geomagnetic low point displacement is well corresponding with the increase of Ne in ionosphere. Finally it was discussed about those spectral features and the occurrence mechanism of geomagnetic low point displacement.

Large geomagnetic storms of extreme solar event periods in solar cycle 23

During extreme solar events such as big flares or/and energetic coronal mass ejections (CMEs) high energy particles are accelerated by the shocks formed in front of fast interplanetary coronal mass ejections (ICMEs). The ICMEs (and their sheaths) also give rise to large geomagnetic storms which have significant effects on the Earth’s environment and human life. Around 14 solar cosmic ray ground level enhancement (GLE) events in solar cycle 23 we examined the cosmic ray variation, solar wind speed, ions density, interplanetary magnetic field, and geomagnetic disturbance storm time index ( D st). We found that all but one of GLEs are always followed by a geomagnetic storm with D st ⩽ −50 nT within 1–5 days later. Most(10/14) geomagnetic storms have D st index ⩽ −100 nT therefore generally belong to strong geomagnetic storms. This suggests that GLE event prediction of geomagnetic storms is 93% for moderate storms and 71% for large storms when geomagnetic storms preceded by GLEs. All D st depressions are associated with cosmic ray decreases which occur nearly simultaneously with geomagnetic storms. We also investigated the interplanetary plasma features. Most geomagnetic storm correspond significant periods of southward B z and in close to 80% of the cases that the B z was first northward then turning southward after storm sudden commencement (SSC). Plasma flow speed, ion number density and interplanetary plasma temperature near 1 AU also have a peak at interplanetary shock arrival. Solar cause and energetic particle signatures of large geomagnetic storms and a possible prediction scheme are discussed.

Solar activity, Earth’s rotation rate and climate variations in the secular and semi-secular time scales

By applying the wavelet formalism to sudden storm commencements and aa geomagnetic indices and solar total irradiation, as a proxy data for solar sources of climate-forcing, we have searched the signatures of those variables on the Northern Hemisphere surface temperature. We have found that cyclical behaviour in surface temperature is not clearly related to none of these variables, so we have suggested that besides them surface temperature might be related to Earth’s rotation rate variations. Also it has been suggested that in the long-term Earth’s rotation rate variations might be excited by geomagnetic storm time variations which, in turn, depends on solar activity. The study of these phenomena and its relationships is addressed in the present paper. With this purpose we perform an analysis of the evolution during the last 350 years of the signals that conform the 11-year sunspot cycle maxima envelope for different time scales. The result is applied to analyze the relationship between long-term variations in sunspot number and excess of length of day; and to unearth the signature in surface temperature of this last from that of sudden storm commencement and aa geomagnetic indices and total solar irradiation. As solar dynamo experiments transient processes in all the time scales from seconds to centuries, Fourier analysis and its requirement for the process to be stationary is likely to produce spurious periodicities. We resort instead to wavelet formalism. By this representation we found that sunspot maxima envelope for the last 350 years may be described by means of the superposition of two cycles – a decadal and a semi-secular one – and a secular trend. And that the changing amplitude and phase of the cycles are well reconstructed using the superposition of two wavelets with nearby periods. The strong temporal changes in amplitude of the cycles facilitate to detect its phase in a given time series. It is found that a strong semi-secular cycle in the sunspot maxima envelope that started during the 1705 chaotic transition having its maximum amplitude at the Dalton minimum, was mapped 94 years later in Earth’s rotation rate and simultaneously in surface temperature. Also, there was a decrease (increase) of 0.022 °C for each millisecond of decrease (increase) in the Earth’s rotation period for the semi-secular cycle as well as the secular trend.

Energy transport and dissipation in the magnetosphere during geomagnetic storms

Major geomagnetic storms represent a significant dissipation of energy by the magnetosphere. The energy is derived from the solar wind flow and the subsequent powerful conversion of that energy takes several different forms. Ring current injection and decay, ionospheric Joule heating, particle precipitation into the atmosphere, and several related physical processes are exhibited clearly in large storm events. The modern-day constellation of operating spacecraft gives an unprecedented opportunity to study magnetic storm processes and energetics. This paper focuses on recent coronal mass ejection (CME) events that have been well-observed near the sun. These disturbances are followed from the sun to their arrival in near-Earth space. The reconfiguration of the magnetosphere under the driving influence of CME/magnetic cloud events is examined and the energetics of various forms of input and output are assessed. It is concluded that the present observations in the ISTP era, along with modern modeling techniques, have given us new insights into geomagnetic stormtime energy dissipation. Ionospheric Joule heating and auroral particle precipitation account for a substantial majority of energy dissipation during CME-driven storms (i.e., ≳70%). However, ring current energy injection due to moderate energy ions is also a key. Direct in situ observations of such ions are found to be crucially important because indices such as D st may be contaminated by many other effects.

Equatorial electrojet as part of the global circuit: a case-study from the IEEY

Abstract. Geomagnetic storm-time variations often occur coherently at high latitude and the day-side dip equator where they affect the normal eastward Sq field. This paper presents an analysis of ground magnetic field and ionospheric electrodynamic data related to the geomagnetic storm which occured on 27 May 1993 during the International Equatorial Electrojet Year (IEEY) experiment. This storm-signature analysis on the auroral, mid-latitude and equatorial ground field and ionospheric electrodynamic data leads to the identification of a sensitive response of the equatorial electrojet (EEJ) to large-scale auroral return current: this response consists in a change of the eastward electric field during the pre-sunrise hours (0400-0600 UT) coherently to the high-, mid-, and equatorial-latitude H decrease and the disappearance of the EEJ irregularities between the time-interval 0800-0950 UT. Subsequent to the change in h'F during pre-sunrise hours, the observed foF2 increase revealed an enhancement of the equatorial ionization anomaly (EIA) caused by the high-latitude penetrating electric field. The strengthening of these irregularities attested by the Doppler frequency increase tracks the H component at the equator which undergoes a rapid increase around 0800 UT. The ∆H variations observed at the equator are the sum of the following components: SR, DP, DR, DCF and DT.Keywords. Equatorial electrojet · Magnetosphere-ionosphere interactions · Electric fields and currents · Auroral ionosphere · Ionospheric disturbances