Dawn-dusk Electric Field Research Articles

Statistical Analysis of the Correlation between Geomagnetic Storm Intensity and Solar Wind Parameters from 1996 to 2023

The occurrence of space weather events, notably geomagnetic storms driven by various solar wind structures, can significantly alter Earth’s electromagnetic environment. In this study, we examined the interplanetary origins and statistical distribution of 384 geomagnetic storms (Dstmin ≤ −50 nT) that occurred from September 1996 to December 2023. We statistically analyzed the correlations between storm intensity and solar wind parameters (SWPs) across different subsets. The results indicate that (1) the solar activity level, indicated by the sunspot number (SSN), and the number of geomagnetic storms during the first four years of the 25th solar cycle were intermediate, compared to the first four years of the 23rd and 24th solar cycles. Specifically, ICME-related structures caused 80% of the strong storms (Dstmin ≤ −100 nT) and 34% of the moderate storms (−100 nT < Dstmin ≤ −50 nT) from 2020 to 2023. (2) The storm intensity correlated with the peak and/or time-integral values of the southward interplanetary magnetic field (IMF Bs), the dawn–dusk electric field (Ey), the Akasofu’s function (ε), and dynamic pressure (Psw) to varying extents. Strong storms exhibited higher correlation levels than moderate ones and ICME-related storms showed larger correlation levels compared to those driven by other sources. (3) Compared with the storms from 1996-09 to 2000-08, the storms that occurred from 2020 to 2023 had lower correlations with the peak values of the IMF Bs and Ey but higher correlations with the peak value of ε and the time-integral values of the IMF Bs, Ey, Psw, and ε. (4) Among the 174 events that featured continuous southward IMF during the storm’s main phase, the duration of southward IMF during about 66.7% of moderate storms and 51.5% of strong storms were less than 13 h. Continuous southward IMF resulted in more direct and efficient energy coupling, enhancing the correlation between the peak values of SWPs and storm intensity but weakening the relationships with the time-integral values of SWPs. Notably, when the southward IMF persisted for a longer duration (e.g., ∆t > 13 h), the continuous energy input further enhanced correlations with both peak and integral values of SWPs, leading to stronger overall correlations with storm intensity. This analysis sheds light on the intricate relationships between geomagnetic storms and their solar wind drivers, emphasizing the significant influence of ICME-related structures and the duration of southward IMF on storm intensity.

Transient particle acceleration by a dawn–dusk electric field in a current sheet

The influence of a dawn–dusk electric field Ey on transient particles in a 1D current sheet (CS), characterized by the normal (Bz) and tangential (Bx) components of the magnetic field, is studied. The motion and energization of particles injected at the edges of a CS are investigated within the framework of the trajectory method. The analytical treatment reveals that in the case of uniform Bz and Ey, the dynamics of transient particles are described by magnetic flux conservation on specific segments of the trajectory, which allows prediction of some specific properties of the velocity space inside the CS. Verification of the analytical treatment by means of test-particle numerical modeling demonstrates good agreement. In particular, it is shown that the CS can play the role of a converging lens that focuses particles to pitch-angle values close to θ∼π. At the same time, the analysis reveals that the particle energy gain stays within the range of ΔW∈2m[(Ey/Bz)2,(Ey/Bz)(v0+Ey/Bz)], where m is the particle mass and v0 is the initial particle speed (i.e., v0=v·v). The limits of the range depend only weakly on the CS half-thickness. The analysis reveals that for the typical parameters of Ey and Bz in the stationary terrestrial magnetotail, protons with v0≃450 km/s (before CS crossing) can be accelerated along the CS up to vx≃1800 km/s.

Importance of Shock Compression in Enhancing ICME’s Geoeffectiveness

Abstract Shock embedded interplanetary coronal mass ejections (ICMEs) are of great interest in the solar and heliosphere physics community due to their high potential to cause intense geomagnetic storms. In this work, 18 moderate to intense geomagnetic storms caused by shock-ICME complex structures are analyzed in order to show the importance of shock compression in enhancing ICMEs’ geoeffectiveness. Based on the characteristics of the shocks inside ICMEs, including the shock velocity, shock normal direction, and the density compression ratio, we recover the shocked part in the ICME to the uncompressed state by using a recovery model developed by Wang et al. according to the Rankine–Hugoniot relationship. Comparing the observational data and the recovered parameters, we find that the maximum southward magnetic field in the ICME is doubled and the dawn–dusk electric field is increased 2.2 times due to the shock compression. Then, the parameters of the observed and recovered solar wind and magnetic field are, respectively, introduced into various Dst prediction models. The prediction results show that, on average, the shock compression can enhance the intensity of the geomagnetic storm by a factor of 1.4. Without shock compression, the geoeffectiveness of these ICMEs would be markedly reduced. Moreover, there is a significant correlation between the shock density compression ratio and the shock’s capacity of strengthening geomagnetic storms. The larger the shock density compression ratio is, the more obvious Dst index decrease is caused.

Contrasting dynamics of electrons and protons in the near-Earth plasma sheet during dipolarization

Abstract. The fortunate location of Cluster and the THEMIS P3 probe in the near-Earth plasma sheet (PS) (at X ∼ −7–−9 RE) allowed for the multipoint analysis of properties and spectra of electron and proton injections. The injections were observed during dipolarization and substorm current wedge formation associated with braking of multiple bursty bulk flows (BBFs). In the course of dipolarization, a gradual growth of the BZ magnetic field lasted ∼ 13 min and it was comprised of several BZ pulses or dipolarization fronts (DFs) with duration ≤ 1 min. Multipoint observations have shown that the beginning of the increase in suprathermal (> 50 keV) electron fluxes – the injection boundary – was observed in the PS simultaneously with the dipolarization onset and it propagated dawnward along with the onset-related DF. The subsequent dynamics of the energetic electron flux was similar to the dynamics of the magnetic field during the dipolarization. Namely, a gradual linear growth of the electron flux occurred simultaneously with the gradual growth of the BZ field, and it was comprised of multiple short (∼ few minutes) electron injections associated with the BZ pulses. This behavior can be explained by the combined action of local betatron acceleration at the BZ pulses and subsequent gradient drifts of electrons in the flux pile up region through the numerous braking and diverting DFs. The nonadiabatic features occasionally observed in the electron spectra during the injections can be due to the electron interactions with high-frequency electromagnetic or electrostatic fluctuations transiently observed in the course of dipolarization. On the contrary, proton injections were detected only in the vicinity of the strongest BZ pulses. The front thickness of these pulses was less than a gyroradius of thermal protons that ensured the nonadiabatic acceleration of protons. Indeed, during the injections in the energy spectra of protons the pronounced bulge was clearly observed in a finite energy range ∼ 70–90 keV. This feature can be explained by the nonadiabatic resonant acceleration of protons by the bursts of the dawn–dusk electric field associated with the BZ pulses. Keywords. Magnetospheric physics (Magnetotail; plasma sheet) – Space plasma physics (Transport processes)

Void structure of O+ ions in the inner magnetosphere observed by the Van Allen Probes

AbstractThe Van Allen Probes Helium Oxygen Proton Electron instrument observed a new type of enhancement of O+ ions in the inner magnetosphere during substorms. As the satellite moved outward in the premidnight sector, the flux of the O+ ions with energy ~10 keV appeared first in the energy‐time spectrograms. Then, the enhancement of the flux spread toward high and low energies. The enhanced flux of the O+ ions with the highest energy remained, whereas the flux of the ions with lower energy vanished near apogee, forming what we call the void structure. The structure cannot be found in the H+ spectrogram. We studied the generation mechanism of this structure by using numerical simulation. We traced the trajectories of O+ ions in the electric and magnetic fields from the global magnetohydrodynamics simulation and calculated the flux of O+ ions in the inner magnetosphere in accordance with the Liouville theorem. The simulated spectrograms are well consistent with the ones observed by Van Allen Probes. We suggest the following processes. (1) When magnetic reconnection starts, an intensive equatorward and tailward plasma flow appears in the plasma lobe. (2) The flow transports plasma from the lobe to the plasma sheet where the radius of curvature of the magnetic field line is small. (3) The intensive dawn‐dusk electric field transports the O+ ions earthward and accelerates them nonadiabatically to an energy threshold; (4) the void structure appears at energies below the threshold.

Study of the geoeffectiveness of coronal mass ejections, corotating interaction regions and their associated structures observed during Solar Cycle 23

The interplanetary coronal mass ejections (ICMEs) and the corotating interaction regions (CIRs) are the two most important structures of the interplanetary medium affecting the Earth and the near-Earth space environment. We study the solar wind-magnetosphere coupling during the passage of ICMEs and CIRs, in the Solar Cycle 23 (Jan. 1995–Dec. 2009), and their relative geoeffectiveness. We utilize the timings of different features of these structures, their arrival and duration. As geomagnetic parameter, we utilize high time resolution data of Dst and $\mathit{AE}$ indices. In addition to these geomagnetic indices, we utilize the simultaneous and similar time resolution data of interplanetary plasma and field, namely, solar wind velocity, interplanetary magnetic field, its north-south component and dawn-dusk electric field. We apply the method of superposed epoch analysis. Utilizing the properties of various structures during the passage of ICMEs and CIRs, and variations observed in plasma and field parameters during their passage along with the simultaneous changes observed in geomagnetic parameters, we identify the interplanetary conditions, plasma/field parameters and their relative importance in solar wind-magnetosphere coupling. Geospace consequences of ICMEs and CIRs, and the implications of these results for solar wind-magnetosphere coupling are discussed.

Plasma transport between the ionosphere and plasmasphere in response to solar wind dynamic pressure pulsation

The plasma transport between the plasmasphere and the ionosphere in response to the interplanetary conditions is still not fully understood until now. Simultaneous observations of the plasmasphere and ionosphere from the newly developed Chinese Meridian Project provide a new opportunity for understanding the characteristic of the plasma transport and the coupling mechanism between these two regions. We investigate the response of the plasmasphere (L≈2) and ionosphere to the solar wind dynamic pressure pulse during geomagnetically quiet period of 21–27 March 2011. The response of the plasmasphere shows a significant depletion. The plasmaspheric density nearly decreases by half in response to the solar wind dynamic pressure pulse, and subsequently recovers to the original level in 1–2 d. Meanwhile, the maximum electron density of the ionospheric F2 layer (NmF2) and the total electron content (TEC) increase by 13% and 21%, respectively, and then gradually recover, which is opposite to the behavior during magnetic storms. Preliminary analysis shows that the plasmaspheric depletion may be mainly caused by the southward interplanetary magnetic field and changing dawn-dusk electric field. The plasmaspheric density variations seem to be controlled by both the IMF and ionospheric conditions.

Effects of a magnetic cloud simultaneously observed on the equatorial ionosphere in midday and midnight sectors

An impact of a magnetic cloud on the Earth’s magnetosphere occurred at 1636 UT on 25 June, 1998, associated with a sudden increase of the solar wind density and velocity, as well as a sudden increase of the zenithal component of the interplanetary magnetic field (IMF-Bz). Following the impact of the magnetic cloud, IMF-Bz was northward (10 nT) and remained steadily strong (about 15 nT) for the next six hours. IMF-Bz turned southward at 2330 UT on 25 June, 1998, and remained strongly southward (−15 nT) for the next four hours. During the positive phase of IMF-Bz, both the Auroral index and ring current index SYM/H remained steadily low indicating complete isolation of the Earth’s magnetosphere from the solar wind and no significant changes were observed in the equatorial ionosphere. After the southward turning, the steady southward IMF-Bz permitted solar wind energy to penetrate the magnetosphere and caused the generation of a magnetic storm associated with strong auroral electrojet activity (AE index). Strong southward IMF-Bz corresponds to the dawn-dusk interplanetary electric field (eastward on the dayside and westward on the night side). The ionograms at Jicamarca (night side) showed strong spread-F and at Thumba (dayside) showed an absence of equatorial type of sporadic-E, indicating a dusk-to-dawn electric field. Thus, the observations point to an electric field opposite in direction to that expected by the prompt penetration of the interplanetary electric field. An abnormally-large Auroral index (AE) associated with the start of the storm suggests that the cause of the equatorial electric field changes is due to the disturbance dynamo effect.

Suprathermal electron acceleration during reconnection onset in the magnetotail

Abstract. We study one event of reconnection onset associated to a small substorm on 27 September 2006 by using Cluster observations at inter-spacecraft separation of about 10 000 km. We focus on the acceleration of suprathermal electrons during different stages of reconnection. We show that several distinct stages of acceleration occur: (1) moderate acceleration during reconnection of pre-existing plasma sheet flux tubes, (2) stronger acceleration during reconnection of lobe flux tubes, (3) production of the most energetic electrons within dipolarization fronts (magnetic pile-up regions). The strongest acceleration is reached at the location of Bz maxima inside the magnetic pile-up region where the reconnection jet stops. Very strong localized dawn-dusk electric field are observed within the magnetic pile-up regions and are associated to most of the magnetic flux transport.

Contribution of magnetotail reconnection to the cross-polar cap electric potential drop

[1] Since the work of Dungey (1961), the global circulation pattern with two (dayside and nightside) reconnection regions has become a classic concept. However, the contributions of dayside and nightside sources to the cross-polar cap potential (PCP) are not fully understood, particularly, the relative role and specifics of the nightside source are poorly investigated both in quantitative and qualitative terms. To fill this gap, we address the contributions of dayside and nightside sources to the PCP by conducting global MHD simulations with both idealized solar wind input and an observed event input. The dayside source was parameterized by solar wind–based “dayside merging potential” Φd = LeffVBt sin4(θ/2), whereas to characterize the nightside source we integrated across the tail the dawn-dusk electric field in the plasma sheet (to obtain the “cross-tail potential” Φn). For the idealized run we performed simulations using four MHD codes available at the Community Coordinated Modeling Center to show that contribution of the nightside source is a code-independent feature (although there are many differences in the outputs provided by different codes). Particularly, we show that adding a nightside source to the linear fit function for the ionospheric potential (i.e., using the fit function Φfit = KdΦd + KnΦn + Φ0) considerably improves the fitting results both in the idealized events as well as in the simulation of an observed event. According to these simulations the nightside source contribution to the PCP has a fast response time (<5 min) and a modest efficiency (potential transmission factor from tail to the ionosphere is small, Kn < 0.2), which is closely linked to the primarily inductive character of strong electric field generated in the plasma sheet. The latter time intervals are marked by strongly enhanced nightside (lobe) reconnection and can be associated with substorm expansion phases. This association is further strengthened by the simulated patterns of precipitation, the R1-type field-aligned substorm current wedge currents and Hall electrojet currents, which are consistent with the known substorm signatures.

A consistent understanding of the ribbon structure for the Io plasma torus at the Voyager 1, 1991 ground-based, and Galileo J0 epochs

[1] A new four-dimensional (three spatial and local time) empirical model for the Io plasma torus is presented that includes several System III longitude asymmetries and a dawn-dusk electric field with variable direction and magnitude. The model is used to analyze and compare observations for the peak density structure of the plasma torus acquired at the 1979 Voyager 1, the 1991 ground-based, and the 1995 Galileo J0 epochs. The mean magnitude of the dawn-dusk electric field is determined to be much smaller at the 1991 ground-based epoch than at the Voyager 1 and Galileo J0 epochs. A consistent understanding of the radial structure for the density peaks in the plasma torus may then be achieved for these epochs if the dawn-dusk electric field departs by ∼20° from the true dawn-dusk direction and if account is taken of absolute density changes. The ratio of the electron density in the inner and outer plasma torus varies significantly for the three epochs and indicates different temporal evolutions in the balance of the plasma torus production and loss processes. The undisturbed electron density at Io's position in the plasma torus is calculated and has significantly different values at the three epochs; it is shown for each epoch to undergo large variations as Io changes its location in heliocentric phase angle and System III longitude. These large variations provide a wide variety of changing upstream plasma conditions for Io's atmospheric formation, local aurora and distant footprint emissions, and electrodynamic interaction.

On the energization of protons interacting with 3-D time-dependent electromagnetic fields in the Earth's magnetotail

[1] A test particle simulation has been performed in order to reproduce the interaction between protons and time-dependent electromagnetic fluctuations in the magnetotail current sheet. The three-dimensional model takes into account a dawn-dusk electric field component E0y, a magnetic field reversal Bx(z), and a constant component Bn along the z direction. Electromagnetic perturbations are generated by random oscillating “clouds” moving in the (x, y) plane. The simultaneous presence of stochastic time-dependent fluctuations and 3-D large-scale fields gives rise to a rich variety of phenomena that are studied by varying the size and shape of the oscillating clouds. The main findings are as follows: (1) the efficiency of the Fermi-like interaction between test particles and moving clouds is largest close to z = 0, where the large-scale magnetic field is weakest; (2) in times of 1–2 min protons can reach energy values up to 50–70 keV, which is beyond the maximum potential drop due to the presence of E0y; (3) the ion energization grows with the size of the magnetic clouds, while it is slightly influenced by the thickness of the clouds along z, confirming that the main acceleration takes place in the quasi-neutral sheet; and (4) assuming parameters of the model corresponding to those of the Earth's magnetotail, it is found that many observed features, such as the formation of a beam in velocity space and non-Gaussian velocity distributions, can be reproduced.

Comparing Solar Minimum 23/24 with Historical Solar Wind Records at 1 AU

Based on the variations of sunspot numbers, we choose a 1-year interval at each solar minimum from the beginning of the acquisition of solar wind measurements in the ecliptic plane and at 1 AU. We take the period of July 2008 - June 2009 to represent the solar minimum between Solar Cycles 23 and 24. In comparison with the previous three minima, this solar minimum has the slowest, least dense, and coolest solar wind, and the weakest magnetic field. As a result, the solar wind dynamic pressure, dawn-dusk electric field, and geomagnetic activity during this minimum are the weakest among the four min- ima. The weakening trend had already appeared during solar minimum 22/23, and it may continue into the next solar minimum. During this minimum, the galactic cosmic ray inten- sity reached the highest level in the space age, while the number of solar energetic proton events and the ground level enhancement events were the least. Using solar wind measure- ments near the Earth over 1995 - 2009, we have surveyed and characterized the large-scale solar wind structures, including fast-slow stream interaction regions (SIRs), interplanetary coronal mass ejections (ICMEs), and interplanetary shocks. Their solar cycle variations over the 15 years are studied comprehensively. In contrast with the previous minimum, we find that there are more SIRs and they recur more often during this minimum, probably because more low- and mid-latitude coronal holes and active regions emerged due to the weaker so- lar polar field than during the previous minimum. There are more shocks during this solar minimum, probably caused by the slower fast magnetosonic speed of the solar wind. The SIRs, ICMEs, and shocks during this minimum are generally weaker than during the pre- vious minimum, but did not change as much as did the properties of the undisturbed solar wind.

Modeling of the turbulent plasma sheet during quiet geomagnetic conditions

Recent studies have shown the importance of turbulent processes in the Earth magnetosphere dynamics, including the plasma sheet stability. In this study, turbulent eddy-diffusion coefficients were derived using the Cluster satellite data. The corresponding values of dawn–dusk electric field potential were obtained from the SuperDarn measurements. These results confirm the theory of the turbulent plasma sheet formation proposed by Antonova and Ovchinnikov (1996, 1999, 2001). According to this theory, a compact and comparatively stable turbulent plasma sheet is formed when the regular plasma transport related to the dawn–dusk electric field across the plasma sheet is compensated by the eddy-diffusion turbulent transport. Our results have shown that this theory reproduces the dynamics of the turbulent plasma sheet, including its thickness.

On the Geoeffectiveness Structure of Solar Wind-Magnetosphere Coupling Functions during Intense Storms

The geoeffectiveness of some coupling functions for the Solar Wind-Magnetosphere Interaction had been studied. 58 storms with peak Dst &lt; −100 nT were used. The result showed that the interplanetary magnetic field Bz appeared to be more relevant with the magnetic field B (which agreed with previous results). However, both the V (solar wind flow speed) and Bz factors in the interplanetary dawn-dusk electric field (V×Bz) are effective in the generation of very intense storms (peak Dst &lt; −250 nT) while “intense” storms (−250 nT ≤ peak Dst &lt; −100 nT) are mostly enhanced by the Bz factor alone (in most cases). The southward Bz duration BT seems to be more relevant for Dst &lt; −250 nT class of storms and invariably determines the recovery phase duration. Most of the storms were observed to occur at midnight hours (i.e., 2100–0400 UT), having a 41.2% incidence rate, with high frequency between 2300 UT and 0000 UT. 62% of the events were generated as a result of Magnetic Cloud (MC), while 38% were generated by complex ejecta. The B-Bz relation for the magnetic cloud attained a correlation coefficient of 0.8922, while it is 0.7608 for the latter. Conclusively, Bz appears to be the most geoeffective factor, and geoeffectiveness should be a factor that depends on methods of event identification and classification as well as the direction of event correlation.

Changes in the response of the AL Index with solar cycle and epoch within a corotating interaction region

Abstract. We use observations in the solar wind and on the ground to study the interaction of the solar wind and interplanetary magnetic field with Earth's magnetosphere. We find that the type of response depends on the state of the solar wind. Coupling functions change as the properties of the solar wind change. We examine this behavior quantitatively with time dependent linear prediction filters. These filters are determined from ensemble arrays of representative events organized by some characteristic time in the event time series. In our study we have chosen the stream interface at the center of a corotating interaction region as the reference time. To carry out our analysis we have identified 394 stream interfaces in the years 1995–2007. For each interface we have selected ten-day intervals centered on the interface and placed data for the interval in rows of an ensemble array. In this study we use Es the rectified dawn-dusk electric field in gsm coordinates as input and the AL index as output. A selection window of width one day is stepped across the ensemble and for each of the nine available windows all events in a given year (~30) are used to calculate a system impulse response function. A change in the properties of the system as a consequence of changes in the solar wind relative to the reference time will appear as a change in the shape and/or the area of the response function. The analysis shows that typically only 45% of the AL variance is predictable in this manner when filters are constructed from a full year of data. We find that the weakest coupling occurs around the stream interface and the strongest well away from the interface. The interface is the time of peak dynamic pressure and strength of the electric field. We also find that coupling appears to be stronger during recurrent high-speed streams in the declining phase of the solar cycle than it is around solar maximum. These results are consistent with the previous report that both strong driving (Es) and high dynamic pressure (Pdyn) reduce the coupling efficiency. Although the changes appear to be statistically significant their physical cause cannot be uniquely identified because various properties of the solar wind vary systematically through a corotating interaction region. It is also possible that the quality of the propagated solar wind data depends on the state of the solar wind. Finally it is likely that the quality of the AL index during the last solar cycle may affect the results. Despite these limitations our results indicate that the Es-AL coupling function is 50% stronger outside a corotating interaction region than inside.

Particle acceleration by stochastic fluctuations and dawn-dusk electric field in the Earth’s magnetotail

This work is devoted to investigate the interaction between protons and stochastic time-dependent electromagnetic fields generated by oscillating clouds of finite size, randomly positioned in the x–y-plane. The geometry of the system is two-dimensional and, beside the time-dependent electromagnetic fluctuations, a steady-state, dawn-dusk electric field, E y , has been added along the y-direction. The simultaneous presence of the stochastic time-dependent fluctuations and of the constant electric field component in the same system gives rise to two types of acceleration mechanisms operating on test particles: a second order Fermi-like process and a direct acceleration. By performing a parametric study, we extensively study the contribution of the two processes to proton acceleration. The energy values reached by test particles in this simple model are in good agreement with those observed in the Earth’s magnetotail region. Possible applications to the problem of particle acceleration in the terrestrial magnetosphere are widely discussed, and guidelines for future works are drawn.

Energy balance during intense and super-intense magnetic storms using an Akasofu ε parameter corrected by the solar wind dynamic pressure

Geomagnetic storms are large disturbances in the Earth's magnetosphere caused by enhanced solar wind–magnetosphere energy transfer. One of the main manifestations of a geomagnetic storm is the ring current enhancement. It is responsible for the decrease in the geomagnetic field observed at ground stations. In this work, we study the ring current dynamics during two different levels of magnetic storms. Thirty-three events are selected during the period 1981–2004. Eighteen out of 33 events are very intense (or super-intense) magnetic storms ( Dst ⩽−250 nT) and the remaining are intense magnetic storms (−250< Dst ⩽−100 nT). Interplanetary data from spacecraft in the solar wind near Earth's orbit (ACE, IMP-8, ISEE-3) and geomagnetic indices ( Dst and Sym-H) are analyzed. Our aim is to evaluate the interplanetary characteristics (interplanetary dawn–dusk electric field, interplanetary magnetic field component B S), the ε parameter, and the total energy input into the magnetosphere ( Wε) for these two classes of magnetic storms. Two corrections on the ε energy coupling function are made: the first one is an already known correction in the magnetopause radius to take into account the variation in the solar wind pressure. The second correction on the Akasofu parameter, first proposed in this work, accounts for the reconnection efficiency as a function of the solar wind ram pressure. Geomagnetic data/indices are also employed to study the ring current dynamics and to search for the differences in the storm evolution during these events. Our corrected ε parameter is shown to be more adequate to explain storm energy balance because the energy input and the energy dissipated in the ring current are in better agreement with modern estimates as compared with previous works. For super-intense storms, the correction of the Akasofu ε is on average a scaling factor of 3.7, whilst for intense events, this scaling factor is on average 3.4. The injected energy during the main phase using corrected ε can be considered a criterion to separate intense from very intense storms. Other possibilities of cutoff values based on the energy input are also investigated. A threshold value for the input energy is much more clear when a new classification on Dst=−165 nT is considered. It was found that the energy input during storms with Dst<−165 nT is double of the energy for storms with Dst>−165 nT.

Response of Earth's Ionosphere to Interplanetary Shocks

AbstractThis paper presents three‐dimensional, global numerical simulations of the dynamic response of the Earth's ionosphere to interplanetary shocks. The background interplanetary magnetic field is spiral with a vanishing south‐north component, the initial ionosphere is dominated by the region I field‐aligned current (FAC) and the corresponding dawn‐dusk electric field, and the interplanetary shock collides with the Earth along the Sun‐Earth line. It is shown that with the impact of interplanetary shocks, the region I current moves towards the midnight sector, accompanied by a successive occurrence of two FAC structures: an anomalous FAC pair of opposite direction to the region I current and a new region I current of the same direction. The anomalous FAC pair creates a transient dusk‐dawn electric field over the polar cap, tailing behind the original region I current and drifting towards the night side until it falls into oblivion. In the meantime, the new region I current keeps increasing and expanding towards the night and equator side, and it eventually replaces the original region I current, so the polar cap returns to a state similar to the original with a dawn‐dusk electric field. Such a response depends on the strength of the interplanetary shock. For a stronger shock, the new region I current gets stronger, extends for a longer distance towards the equator, and reaches a lower latitude. These results agree with the observations associated with traveling convection vortices and midday sub‐auroral patches.

Formation of an F3 layer in the equatorial ionosphere: A result from strong IMF changes

We analyzed ionospheric observations made with digisondes in Jicamarca, Ramey, Wallops Island, Ascension Island, and Kwajalein Island during the major magnetic storm of November 9–10, 2004, which was associated with rapid interplanetary magnetic field (IMF) Bz changes. The strongest ionospheric responses to the southward IMF Bz turning were observed at the dip equator at Jicamarca where during the magnetic disturbance a dramatic F2 peak density depletion occurred at around 15:00 local time, accompanied by a fast upward motion of the plasma. In this process, an additional ionospheric layer, the F3 layer, formed with peak densities NmF3 exceeding NmF2. This observation may be considered evidence of an equatorial plasma fountain enhancement caused by the magnetic field disturbance. Responses were observed in a large range of latitudes and local times. The best indicator of the responses appears to be the peak height of the F layer, since competing processes determine the peak densities. The observed responses at low latitude locations in the morning and dusk sectors pose challenges to the simple penetrating electric field model because the upward motion is inconsistent with the E× B drift associated with a dawn–dusk electric field. Clear responses in the Jicamarca local time sector occurred at latitudes as high as 28°, at Ramey, Puerto Rico. This latitude range appears to be beyond the range of the flux tube corresponding to the 900 km F3 layer peak height at Jicamarca, indicating a more extended uplifting of flux tubes.