Moderate Storm Research Articles

Simulations of inner magnetosphere dynamics with an expanded RAM‐SCB model and comparisons with Van Allen Probes observations

Simulations from our newly expanded ring current‐atmosphere interactions model with self‐consistent magnetic field (RAM‐SCB), now valid out to 9 RE, are compared for the first time with Van Allen Probes observations. The expanded model reproduces the storm time ring current buildup due to the increased convection and inflow of plasma from the magnetotail. It matches Magnetic Electron Ion Spectrometer (MagEIS) observations of the trapped high‐energy (>50 keV) ion flux; however, it underestimates the low‐energy (<10 keV) Helium, Oxygen, Proton, and Electron (HOPE) observations. The dispersed injections of ring current ions observed with the Energetic particle, Composition, and Thermal plasma (ECT) suite at high (>20 keV) energy are better reproduced using a high‐resolution convection model. In agreement with Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) observations, RAM‐SCB indicates that the large‐scale magnetic field is depressed as close as ∼4.5 RE during even a moderate storm. Regions of electromagnetic ion cyclotron instability are predicted on the duskside from ∼6 to ∼9 RE, indicating that previous studies confined to geosynchronous orbit may have underestimated their scattering effect on the energetic particles.

Contrasting patterns of nutrient dynamics during different storm events in a semi-arid catchment of northern China.

Nutrient discharge during storm events is a critical pathway for nutrient export in semi-arid catchments. We investigated nutrient dynamics during three summer storms characterized by different rainfall magnitude in 2012 in a semi-arid catchment of northern China. The results showed that, in response to storm events, nutrient dynamics displayed big variation in temporal trends of nutrient concentration and in nutrient concentration-flow discharge relationships. Nutrient concentrations had broader fluctuations during an extreme storm than during lesser storms, whereas the concentration ranges of the a moderate storm were no broader than those of a smaller one. The different concentration fluctuations were caused by storm magnitude and intensity coupled with the antecedent rainfall amount and cumulative nutrients. Correlation coefficients between nutrient concentrations and flow discharge varied from positive to negative for the three different events. There were no consistent hysteresis effects for the three different events, and no hysteresis effects were observed for any of the variables during the moderate storm (E2). Our findings provide useful information for better understanding nutrient loss mechanisms during storm events in semi-arid areas of a monsoon climate region.

Ionospheric response to magnetic activity at low and mid-latitude stations

The F2-layer response to the moderate storm of 5–7 April 2010 was investigated using data from two equatorial stations (Ilorin: lat. 8.5°N, 4.5°E; Kwajalein: lat. 9°N, long. 167.2°E) and mid-latitude (San Vito: lat. 40.6°N, long. 17.8°E; Pruhonice: lat. 50°N, long. 14.6°E). Before storm commencement, enhancement, and depletion of NmF2 values were observed in the equatorial and mid-latitude stations, respectively, indicating the latitudinal dependence of the pre-storm event. All the stations with the exception of Kwajalein show positive phase in NmF2 response at the storm onset stage. Positive phase in NmF2 continues over Ilorin and appears on the daytime ionosphere of Kwajalein on 6 April, whereas negative phase suppressed the positive feature in Pruhonice and San Vito until the recovery condition. The differences in the response of F2-layer to the storm for the two equatorial stations were attributed to their longitudinal differences. On the average, both the AE and D st indices revealed poor correlation relationship. More studies are required to ascertain this finding.

Two-step forecast of geomagnetic storm using coronal mass ejection and solar wind condition.

To forecast geomagnetic storms, we had examined initially observed parameters of coronal mass ejections (CMEs) and introduced an empirical storm forecast model in a previous study. Now we suggest a two-step forecast considering not only CME parameters observed in the solar vicinity but also solar wind conditions near Earth to improve the forecast capability. We consider the empirical solar wind criteria derived in this study (Bz ≤ −5 nT or Ey ≥ 3 mV/m for t≥ 2 h for moderate storms with minimum Dst less than −50 nT) and a Dst model developed by Temerin and Li (2002, 2006) (TL model). Using 55 CME-Dst pairs during 1997 to 2003, our solar wind criteria produce slightly better forecasts for 31 storm events (90%) than the forecasts based on the TL model (87%). However, the latter produces better forecasts for 24 nonstorm events (88%), while the former correctly forecasts only 71% of them. We then performed the two-step forecast. The results are as follows: (i) for 15 events that are incorrectly forecasted using CME parameters, 12 cases (80%) can be properly predicted based on solar wind conditions; (ii) if we forecast a storm when both CME and solar wind conditions are satisfied (∩), the critical success index becomes higher than that from the forecast using CME parameters alone, however, only 25 storm events (81%) are correctly forecasted; and (iii) if we forecast a storm when either set of these conditions is satisfied (∪), all geomagnetic storms are correctly forecasted.

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.

Predicting the location of polar cusp in the Lyon‐Fedder‐Mobarry global magnetosphere simulation

In this paper we compare observations of the high‐latitude cusp from DMSP data to simulations conducted using the Lyon‐Fedder‐Mobarry (LFM) global magnetosphere simulation. The LFM simulation is run for the 31 August 2005 to 02 September 2005 moderate storm, from which the solar wind data exhibits a wide range of conditions that enable a statistical representation of the cusp to be obtained. The location of the cusp is identified using traditional magnetic depression and plasma density enhancement at high altitude. A new diagnostic using the parallel ion number flux is also tested for cusp identification. The correlation of the cusp latitude and various solar wind interplanetary magnetic field (IMF) coupling functions is explored using the three different cusp identification methods. The analysis shows (1) the three methods give approximately the same location and size of the simulated cusp at high altitude and (2) the variations of the simulated cusp are remarkably consistent with the observed statistical variations of the low‐altitude cusp. In agreement with observations, a higher correlation is obtained using other solar wind coupling functions such as the Kan‐Lee electric field. The magnetic local time (MLT) position of the simulated cusp is found to depend upon the IMF By component, with a lower linear correlation. The width of the simulated cusp in both latitude and MLT is also examined. The size of the cusp is found to increase with the solar wind dynamic pressure with saturation seen when the dynamic pressure is greater than 3 nPa.

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.

Oxygen‐hydrogen differentiated observations from TWINS: The 22 July 2009 storm

The 22 July 2009 magnetic storm is the first significant storm during the emergence of the recent prolonged solar cycle minimum. This moderate storm (minimum Dst approximately ≤ −78 nT) has received a good deal of attention in the community. We present here global observations of the H and O populations in the inner magnetosphere using Energetic Neutral Atom (ENA) observations from the TWINS mission. We develop and provide the methodology for separating H and O ENAs, based on mass dependent differences in the pulse height distributions of the microchannel plate (MCP) based detectors. We present the first composition separated H and O ENA images at central energies of 16 and 32 keV. We also show that TWINS has sufficient angular resolution to separate the High Altitude Emissions (HAEs) from the Low Altitude Emissions (LAEs). We observe that all ENA emissions in this energy range quickly rise, but the O ENAs have a larger relative increase, and stay at elevated levels much longer, well into the recovery phase.

Can a Moderate-Resolution Limited-Area Data Assimilation System Add Value to the Global Analysis of Tropical Cyclones?

AbstractThis study investigates the benefits of employing a limited-area data assimilation (DA) system to enhance lower-resolution global analyses in the northwest Pacific tropical cyclone (TC) basin. Numerical experiments are carried out with a global analysis system at horizontal resolution T62 and a limited-area analysis system at resolutions from 200 to 36 km. The global and limited-area DA systems, which are both based on the local ensemble transform Kalman filter algorithm, are implemented using a unique configuration, in which the global DA system provides information about the large-scale analysis and background uncertainty to the limited-area DA system. The limited-area analyses of the storm locations are, on average, more accurate than those from the global analyses, but increasing the resolution of the limited-area system beyond 100 km has little benefit. Two factors contribute to the higher accuracy of the limited-area analyses. First, the limited-area system improves the accuracy of the location estimates for strong storms, which is introduced when the background is updated by the global assimilation. Second, it improves the accuracy of the background estimate of the storm locations for moderate and weak storms. Improvements in the steering flow analysis as a result of increased resolution are modest and short lived in the forecasts. Limited-area track forecasts are more accurate, on average, than global forecasts, independently of the strength of the storms up to five days. This forecast improvement is due to the more accurate analysis of the initial position of storms and the better representation of the interactions between the storms and their immediate environment.

Sediment transport along the Cap de Creus Canyon flank during a mild, wet winter

Abstract. Cap de Creus Canyon (CCC) is known as a preferential conduit for particulate matter leaving the Gulf of Lion continental shelf towards the slope and the basin, particularly in winter when storms and dense shelf water cascading coalesce to enhance the seaward export of shelf waters. During the CASCADE (CAscading, Storm, Convection, Advection and Downwelling Events) cruise in March 2011, deployments of recording instruments within the canyon and vertical profiling of the water column properties were conducted to study with high spatial-temporal resolution the impact of such processes on particulate matter fluxes. In the context of the mild and wet 2010–2011 winter, no remarkable dense shelf water formation was observed. On the other hand, the experimental setup allowed for the study of the impact of E-SE storms on the hydrographical structure and the particulate matter fluxes in the CCC. The most remarkable feature in terms of sediment transport was a period of dominant E-SE winds from 12 to 16 March, including two moderate storms (maximum significant wave heights = 4.1–4.6 m). During this period, a plume of freshened, relatively cold and turbid water flowed at high speeds along the southern flank of the CCC in an approximate depth range of 150–350 m. The density of this water mass was lighter than the ambient water in the canyon, indicating that it did not cascade off-shelf and that it merely downwelled into the canyon forced by the strong cyclonic circulation induced over the shelf during the storms and by the subsequent accumulation of seawater along the coast. Suspended sediment load in this turbid intrusion recorded along the southern canyon flank oscillated between 10 and 50 mg L−1, and maximum currents speeds reached values up to 90 cm s−1. A rough estimation of 105 tons of sediment was transported through the canyon along its southern wall during a 3-day-long period of storm-induced downwelling. Following the veering of the wind direction (from SE to NW) on 16 March, downwelling ceased, currents inside the canyon reversed from down- to up-canyon, and the turbid shelf plume was evacuated from the canyon, most probably flowing along the southern canyon flank and being entrained by the general SW circulation after leaving the canyon confinement. This study highlights that remarkable sediment transport occurs in the CCC, and particularly along its southern flank, even during mild and wet winters, in absence of cascading and under limited external forcing. The sediment transport associated with eastern storms like the ones described in this paper tends to enter the canyon by its downstream flank, partially affecting the canyon head region. Sediment transport during these events is not constrained near the seafloor but distributed in a depth range of 200–300 m above the bottom. Our paper broadens the understanding of the complex set of atmosphere-driven sediment transport processes acting in this highly dynamic area of the northwestern Mediterranean Sea.

First solar-terrestrial storms in cycle 24 of solar activity

The dynamics of the occurrence frequency and intensity of solar-terrestrial storms at the current solar cycle (cycle 24) onset (2007–2011) is considered. The storms were identified based on the moving semidiurnal average planetary index of activity, beginning from Ap* ≥ 30. It has been established that 12, 11, and 2 only moderate storms (Ap* = 30–49), which were randomly distributed during the year, were successively observed in the first three years. After a prolonged period without storms (August 2009–March 2010), a series of storms with mixed or only moderate activity, which were regularly distributed over the seasons (ecliptic longitudes) from April to August, started appearing beginning from the storm of April 1–6, 2010. This period followed the tendency toward the transformation of the slowly rotating four-sector structure (Large-Scale Open Solar Magnetic Field, LOSMF) from the two-sector structure (March 2010). The first storm in the new cycle (April 2010) was very powerful and originated owing to the successive destabilization of the complex of two magnetic filamentary ropes. It is interesting that the origination of a new LOSMF sector was associated with a 27-day interval, during which thermal neutrons appeared at Kamchatka and volcanoes erupted in Iceland, and a strong earthquake occurred in March 2011 in Japan when the Earth was located precisely in this sector.

Pc3 geomagnetic pulsations at near-equatorial latitudes at the initial phase of the magnetic storm of April 5, 2010

An analysis of sampled 1-s observational data on geomagnetic pulsations within the Pc3 range on the INTERMAGNET network of near-equatorial and low-latitude observatories spaced over longitude during the initial phase of a moderate magnetic storm (April 5–7, 2010) was carried out for the first time. The obtained results were compared with magnetic observations at the low-latitude Chambon-la-Foret (CLF) and subauroral Kerguelen (PAF) observatories, as well as with observations at six Australian observatories located at low and middle latitudes. Two time intervals were studied in detail: the sudden commencement (SC) of the storm and the onset of the great global substorm. In the first interval, maximal amplitudes of near-equatorial pulsations were observed in the near-noon sector; in the second interval, in the near-midnight sector. The dynamics of the spectral structure of Pc3 pulsations in the considered events was shown to be different in spite of the fact that in both cases an amplification of waves was observed in two close spectral bands of the Pc3 spectrum: ∼20–30 and ∼30–40 mHz. The considered Pc3 pulsations were characterized by very small azimuthal wavenumbers (0.5 and less). Possible generation mechanisms for the observed Pc3 pulsations are discussed.

Geomagnetic storm decreases the coherence of electric oscillations in the human brain during work on computer

A study was made of the influence of geomagnetic storms at the latitude of Moscow on the electric activity of the human cerebral cortex. By electroencephalographic measurements it was shown that when volunteers aged 18–23 were performing tasks on a computer during moderate magnetic storm or within 24 h after it, the values of the coherence function for electric oscillations in the frontal-polar and occipital areas of the brain in the 4.0–7.9 Hz range (theta rhythm) decreased by a factor of two or more (relative to quiet geomagnetic conditions), whereas the arterial blood pressure, respiratory rate and the electrocardiogram registered in parallel did not deviate from the norm.

Solar and geomagnetic activity effects on heart rate variability

Investigation into possible space weather hazards on cardiovascular system has been performed. A group of 14 healthy volunteers was examined in the spring of 2009 and 2 healthy persons performed electrocardiograph records for a period of 1 year everyday in the morning and in the evening. Results revealed that heart rate variability (HRV) parameters of the group varied strongly from the day before till 3 days after the registered weak storms during the time of investigation. Blood pressure and subjective psychophysiological complaints increased statistically significantly from 0 day till +2nd day. Heart rate (HR) of the group showed a trend for decrease. It was established that morning measurements were more sensitive to space weather variations in comparison with evening measurements. Both persons with prolonged registrations for a period of year did not reveal graded response to geomagnetic storms with different intensities. Both of them decreased HR during moderate storms, but they increased HR during major storms and on the days before and after these storms. HRV parameters varied significantly on these days.

Variability of turbulent quantities in the tidal bottom boundary layer: Case study in the eastern English Channel

Tidal current structure and turbulent quantities within a tidal bottom boundary layer (BBL) have been examined using an upward-looking acoustic Doppler current profiler (ADCP). The instrument was deployed on the seafloor, off the north-eastern French coast in the eastern English Channel over 12 tidal cycles and covered the period of the transition from mean spring to neap tide. Forcing regimes varied from calm to moderate storm conditions during the deployment. For the study of turbulent quantities in the BBL, we have chosen a calm period, when an effect of surface waves on the velocity structure was negligible. Stresses were found to vary regularly with the predominantly semidiurnal tidal flow, with the along-shore stress being generally greater during the flood flow (∼3.0Pa) than during the ebb flow (∼−1.5Pa). The turbulent kinetic energy (TKE) production rate, P, TKE density, Q, and its dissipation rate, ε, followed a nearly regular cycle with close to quarter-diurnal period. Near the seabed, peak values of P, Q and ε were found to be 0.5Wm−3, 0.5m2s−2 and, 0.04Wm−3, respectively, during the flood while, during the ebb, these quantities reached lesser values: 0.1Wm−3, 0.1m2s−2 and 0.03Wm−3, respectively. Near the bottom, eddy viscosity, Az, peak ranged from about 0.1m2s−1 during the flood to 0.03m2s−1 during the ebb flow. Away from the bottom, Az increased to reach a maximum near the mid-depth. Time–depth variation of the P/ε ratio indicated that the turbulence in the BBL, most of the time, was at a non-equilibrium state (P/ε≠1). The largest deviation from the equilibrium occurred during the flood, when P/ε exceeded about one decade near the bottom. During the ebb, P/ε was close to the equilibrium state, slightly decreasing with height above the bottom. Results are found to be in a good agreement with those of the other researches working on direct measurements of turbulence in tidal flows.

Evidence for potential and inductive convection during intense geomagnetic events using normalized superposed epoch analysis

AbstractThe relative contribution of storm‐time ring current development by convection driven by either potential or inductive electric fields has remained an unresolved question in geospace research. Studies have been published supporting each side of this debate, including views that ring current buildup is entirely one or the other. This study presents new insights into the relative roles of these storm main phase processes. We perform a superposed epoch study of 97 intense (DstMin < –100 nT) and 91 moderate (–50 nT > DstMin > –100 nT) storms using OMNI solar wind and ground‐based data. Instead of using a single reference time for the superpositioning of the events, we choose four reference times and expand or contract each phase of every event to the average length of this phase, creating a normalized timeline for the superposed epoch analysis. Using the bootstrap method, we statistically demonstrate that timeline normalization results in better reproduction of average storm dynamics than conventional methods. Examination of the Dst reveals an inflection point in the intense storm group consistent with two‐step main phase development, which is supported by results for the southward interplanetary magnetic field and various ground‐based magnetic indices. This two‐step main‐phase process is not seen in the moderate storm timeline and data sets. It is determined that the first step of Dst development is due to potential convective drift, during which an initial ring current is formed. The negative feedback of this hot ion population begins to limit further ring current growth. The second step of the main phase, however, is found to be a more even mix of potential and inductive convection. It is hypothesized that this is necessary to achieve intense storm Dst levels because the substorm dipolarizations are effective at breaking through the negative feedback barrier of the existing inner magnetospheric hot ion pressure peak.

Atmospheric light extinction reconstructed from the size-resolved aerosol composition using PIXE analysis

Intensive visibility monitoring was performed in the urban atmosphere of Seoul from 2007 to 2009. Using optical and chemical measurement data and the well-known reconstruction light extinction equations, contributions of size-resolved aerosols to light extinction were calculated. Composite variables for visibility impairing aerosols were reconstructed with elemental and ionic concentrations determined by particle induced X-ray emission and ion chromatography methods. Three types of reconstruction equations were introduced in this study. The first equation is the early reconstruction equation mainly based on fine particles. The second equation considers light scattering by sulfates and sea salt aerosol components in the coarse particle regime. The third equation provides information on light scattering by sulfates, nitrates, and organics for PM1.0 and particles between PM1.0 and PM2.5 and the hygroscopic function of sea salt aerosol. Visibility conditions were classified into four categories of clear, moderate, hazy, and Asian dust storm event. The contributions of sulfates and nitrates particles to light extinction increased significantly under the hazy event. The light extinction budget for sulfate particles, including coarse sulfates, increased approximately 1.5% compared to the results from the first equation. Sulfates, nitrates, and organic aerosols in the large particle size mode were responsible for 18.7 ∼ 28.6%, 3.2 ∼ 5.1%, and 6.4 ∼ 8.4% of total light extinction, and they were 1.8, 1.3, and 1.5 times larger than those in the small particles size mode, respectively. During Asian dust storm events, they were 59.1, 9.1, and 1.3%, respectively. The major visibility impairing aerosol species of sulfates, nitrates, organics, and elemental carbon accounted for 77.1 ∼ 78.2% of the total light extinction according to estimation resulting from the three reconstruction equations.

Forecasting the Earth’s radiation belts and modelling solar energetic particle events: Recent results from SPACECAST

High-energy charged particles in the van Allen radiation belts and in solar energetic particle events can damage satellites on orbit leading to malfunctions and loss of satellite service. Here we describe some recent results from the SPACECAST project on modelling and forecasting the radiation belts, and modelling solar energetic particle events. We describe the SPACECAST forecasting system that uses physical models that include wave-particle interactions to forecast the electron radiation belts up to 3 h ahead. We show that the forecasts were able to reproduce the >2 MeV electron flux at GOES 13 during the moderate storm of 7–8 October 2012, and the period following a fast solar wind stream on 25–26 October 2012 to within a factor of 5 or so. At lower energies of 10 – a few 100 keV we show that the electron flux at geostationary orbit depends sensitively on the high-energy tail of the source distribution near 10 RE on the nightside of the Earth, and that the source is best represented by a kappa distribution. We present a new model of whistler mode chorus determined from multiple satellite measurements which shows that the effects of wave-particle interactions beyond geostationary orbit are likely to be very significant. We also present radial diffusion coefficients calculated from satellite data at geostationary orbit which vary with Kp by over four orders of magnitude. We describe a new automated method to determine the position at the shock that is magnetically connected to the Earth for modelling solar energetic particle events and which takes into account entropy, and predict the form of the mean free path in the foreshock, and particle injection efficiency at the shock from analytical theory which can be tested in simulations.

Interplanetary origins of moderate (−100 nT < Dst ≤ −50 nT) geomagnetic storms during solar cycle 23 (1996–2008)

The interplanetary causes of 213 moderate‐intensity (−100 nT < peak Dst ≤ −50 nT) geomagnetic storms that occurred in solar cycle 23 (1996–2008) are identified. Interplanetary drivers such as corotating interaction regions (CIRs), pure high‐speed streams (HSSs), interplanetary coronal mass ejections (ICMEs) of two types [those with magnetic clouds (MCs) and those without (nonmagnetic cloud or ICME_nc)], sheaths (compressed and/or draped sheath fields), as well as their combined occurrence were identified as causes of the storms. The annual rate of occurrence of moderate storms had two peaks, one near solar maximum and the other in the descending phase, around 3 years later. The highest rate of moderate storm occurrence was found in the declining phase (25 storms year−1). The lowest occurrence rate was 5.7 storms year−1 and occurred at solar minimum. All moderate‐intensity storms were associated with southward interplanetary magnetic fields, indicating that magnetic reconnection was the main mechanism for solar wind energy transfer to the magnetosphere. Most of these storms were associated with CIRs and pure HSSs (47.9%), followed by MCs and noncloud ICMEs (20.6%), pure sheath fields (10.8%), and sheath and ICME combined occurrence (9.9%). In terms of solar cycle dependence, CIRs and HSSs are the dominant drivers in the declining phase and at solar minimum. CIRs and HSSs combined have about the same level of importance as ICMEs plus their sheaths in the rising and maximum solar cycle phases. Thus, CIRs and HSSs are the main driver of moderate storms throughout a solar cycle but with variable contributions from ICMEs, their shocks (sheaths), and combined occurrence within the solar cycle. This result is significantly different than that for intense (Dst ≤ −100 nT) and superintense (Dst ≤ −250 nT) magnetic storms shown in previous studies. For superintense geomagnetic storms, 100% of the events were due to ICME events, while for intense storms, ICMEs, sheaths, and their combination caused almost 80% of the storms. CIRs caused only 13% of the intense storms. The typical interplanetary electric field (Ey) criteria for moderate magnetic storms were identified. It was found that ~80.1% of the storms follow the criterion of Ey ≥ 2 mV m−1 for intervals longer than 2 h. It is concluded that southward directed interplanetary magnetic fields within CIRs/HSSs may be the main energy source for long‐term averaged geomagnetic activity on Earth.

Transport of the plasma sheet electrons to the geostationary distances

AbstractThe transport and acceleration of low‐energy electrons (50–250 keV) from the plasma sheet to the geostationary orbit were investigated. Two moderate storm events, which occurred on 6–7 November 1997 and 12–14 June 2005, were modeled using the Inner Magnetosphere Particle Transport and Acceleration model (IMPTAM) with the boundary set at 10 RE in the plasma sheet. The output of the IMPTAM was compared to the observed electron fluxes in four energy ranges (50–225 keV) measured by the Synchronous Orbit Particle Analyzer instrument onboard the Los Alamos National Laboratory spacecraft. It was found that the large‐scale convection in combination with substorm‐associated impulsive fields is the drivers of the transport of plasma sheet electrons from 10 RE to geostationary orbit at 6.6 RE during storm times. The addition of radial diffusion had no significant influence on the modeled electron fluxes. At the same time, the modeled electron fluxes are one (two) order(s) smaller than the observed ones for 50–150 keV (150–225 keV) electrons, respectively, most likely due to inaccuracy of electron boundary conditions. The loss processes due to wave‐particle interactions were not considered. The choice of the large‐scale convection electric field model used in simulations did not have a significant influence on the modeled electron fluxes, since there is not much difference between the equipotential contours given by the Volland‐Stern and the Boyle et al. (1997) models at distances from 10 to 6.6 RE in the plasma sheet. Using the TS05 model for the background magnetic field instead of the T96 model resulted in larger deviations of the modeled electron fluxes from the observed ones due to specific features of the TS05 model. The increase in the modeled electron fluxes can be as large as two orders of magnitude when substorm‐associated electromagnetic fields were taken into account. The obtained model distribution of low‐energy electron fluxes can be used as an input to the radiation belt models. This seed population for radiation belts will affect the local acceleration up to relativistic energies.