Southward Interplanetary Magnetic Field Research Articles

Revisiting the Superstorm on 6–7 April 2000 Caused by an Extraordinary Corotating Interaction Region (With an Embedded Coronal Jet?)

AbstractThe 6–7 April 2000 superstorm of SYM‐H intensity = −319 nT discussed in Meng et al. (2019; https://doi.org/10.1029/2018JA026425) was misidentified as being due to an interplanetary coronal mass ejection associated with a solar flare. The interplanetary cause was a highly unusual corotating interaction region (CIR) bounded by a strong fast forward shock (FS) with magnetosonic Mach number Mms = 4.6 and a fast reverse shock (RS) with Mms = 1.9. The exceptionally strong FS caused a ∼3‐factor interplanetary magnetic field (IMF) magnitude amplification in the leading half of the CIR with peak southward IMF Bz = −27 nT causing the superstorm. A plasma region between a tangential discontinuity and the stream interface had a scale size of ∼0.096 AU. We hypothesize that this is the first detection of a coronal jet at 1 AU. The jet/Gold magnetic tongue (1959; https://doi.org/10.1029/JZ064i011p01665) was embedded within the CIR, contained the southward Bz and caused the magnetic storm. We hypothesize that a shrinking coronal hole and magnetic reconnection caused the formation and release of the jet.

Giant Kelvin‐Helmholtz (KH) Waves at the Boundary Layer of the Coronal Mass Ejections (CMEs) Responsible for the Largest Geomagnetic Storm in 20 Years

AbstractStarting in the evening of 10 May 2024 the Earth's magnetosphere was hit by the coronal mass ejections (CMEs) creating the largest geomagnetic storm in 20 years. The CME encounter was characterized by variations of plasma number density and magnetic field. Here, I present the ARTEMIS observations at the lunar orbit during this event. The IMF ranged from −60 to +40 nT both with hour to minutes periodicity with plasma jets propagating in ‐direction within multi‐scale wave structures. Similar signature has been recently reported at the magnetopause by MMS spacecraft (Li et al., 2023, https://doi.org/10.1029/2023GL105539; Nykyri, 2024, https://doi.org/10.1029/2024GL108605) during a strongly southward IMF. Here, I show that the CME boundaries were KH unstable leading to multi‐scale density and magnetic field fluctuations including reconnection jets. The wavelengths varied from 60 to 270 , suggesting that the magnetosphere was periodically exposed to successive intervals of strongly northward and southward IMF leading to enhanced mass and magnetic flux loading.

The Global Characteristics of Electrons Near the Inner Edge of the Inner Radiation Belt

AbstractEnergetic electrons around the inner edge of the inner radiation belt (L1.3) have not been studied to the extent of the rest of the inner belt and certainly not to that of the outer radiation belt. Yet, the behavior of electrons at the inner edge of the inner belt could improve our understanding of important dynamics deep within Earth's magnetosphere. Previous work has analyzed these electrons during either isolated events or via significantly limited statistical studies, and it remains unclear what the particular drivers of electron flux enhancements in this region may be. Here, we present a broad statistical study of electrons around the inner edge of the inner radiation belt, utilizing the 7‐year data set of the MagEIS particle detectors aboard both Van Allen Probes spacecraft. Moreover, we separate electron flux measurements into stably trapped and quasi‐trapped electrons and directly compare their behavior. We find both populations to be variable in L and energy, as well as showing a clear magnetic local time (MLT) asymmetry. Potential drivers are also explored, where we demonstrate an association between increased electron fluxes in this region and heightened solar wind speed, Sym‐H, dynamic pressure, southward IMF and most prominently with the AU and AL indices.

Impact of the Out‐Of‐Plane Flow Shear on Magnetic Reconnection at the Flanks of Earth's Magnetopause

AbstractMagnetic reconnection changes the magnetic field topology and facilitates the energy and particle exchange at magnetospheric boundaries such as the Earth's magnetopause. The flow shear perpendicular to the reconnecting plane prevails at the flank magnetopause under southward interplanetary magnetic field conditions. However, the effect of the out‐of‐plane flow shear on asymmetric reconnection is an open question. In this study, we utilize kinetic simulations to investigate the impact of the out‐of‐plane flow shear on asymmetric reconnection. By systematically varying the flow shear strength, we analyze the flow shear effects on the reconnection rate, the diffusion region structure, and the energy conversion rate. We find that the reconnection rate increases with the upstream out‐of‐plane flow shear, and for the same upstream conditions, it is higher at the dusk side than at the dawn side. The diffusion region is squeezed in the outflow direction due to magnetic pressure which is proportional to the square of the Alfvén Mach number of the shear flow. The out‐of‐plane flow shear increases the energy conversion rate , and for the same upstream conditions, the magnitude of is larger at the dusk side than at the dawn side. This study reveals that out‐of‐plane flow shear not only enhances the reconnection rate but also significantly boosts energy conversion, with more pronounced effects on the dusk‐side flank than on the dawn‐side flank. These insights pave the way for better understanding the solar wind‐magnetosphere interactions.

Interplanetary Causes and Impacts of the 2024 May Superstorm on the Geosphere: An Overview

The recent superstorm of 2024 May 10–11 is the second largest geomagnetic storm in the space age and the only one that has simultaneous interplanetary data (there were no interplanetary data for the 1989 March storm). The May superstorm was characterized by a sudden impulse (SI+) amplitude of +88 nT, followed by a three-step storm main-phase development, which had a total duration of ∼9 hr. The cause of the first storm main phase with a peak SYM-H intensity of −183 nT was a fast-forward interplanetary shock (magnetosonic Mach number M ms ∼ 7.2) and an interplanetary sheath with a southward interplanetary magnetic field component B s of ∼40 nT. The cause of the second storm's main phase with an SYM-H intensity of −354 nT was a deepening of the sheath B s to ∼43 nT. A magnetosonic wave (M ms ∼ 0.6) compressed the sheath to a high magnetic field strength of ∼71 nT. Intensified B s of ∼48 nT were the cause of the third and most intense storm main phase, with an SYM-H intensity of −518 nT. Three magnetic cloud events with B s fields of ∼25–40 nT occurred in the storm recovery phase, lengthening the recovery to ∼2.8 days. At geosynchronous orbit, ∼76 keV to ∼1.5 MeV electrons exhibited ∼1–3 orders of magnitude flux decreases following the shock/sheath impingement onto the magnetosphere. The cosmic-ray decreases at Dome C, Antarctica (effective vertical cutoff rigidity <0.01 GV) and Oulu, Finland (rigidity ∼0.8 GV) were ∼17% and ∼11%, respectively, relative to quiet-time values. Strong ionospheric current flows resulted in extreme geomagnetically induced currents of ∼30–40 A in the subauroral region. The storm period is characterized by strong polar-region field-aligned currents, with ∼10 times intensification during the main phase and equatorward expansion down to ∼50° geomagnetic (altitude-adjusted) latitude.

Крупномасштабные связи геомагнитных индексов SYM-H и ASY-H с северо-южной компонентой ММП и бета-параметром солнечного ветра

Using annual average values, the relationships are examined of the geomagnetic indices SYM-H, ASY-H, and Dst with solar wind parameters in 1981–2015. The data used was divided into two samples according to the sign of the north-south component Bn of the interplanetary magnetic field (IMF). Variations in the annual average values of each of the Dst, SYM-H, and ASY-H indices for southward and northward IMF have been found to be similar and their linear correlation coefficients r to be high: 0.871, 0.863, and 0.943 respectively. The similarity between variations of the indices with different signs of Bn is probably due to their connection with the number of sunspots. It has been established that Dst, SYM-H, and ASY-H depend on the solar wind parameter β: their absolute values decrease with increasing β, regardless of Bn sign. The decrease in the indices with increasing β is likely to be caused by the transition of the magnetosphere to a quiet state due to the increasing predominance of thermal pressure over magnetic one in the solar wind and a decrease in the level of solar wind turbulence. SYM-H and ASY-H have been found to reveal the closest relationships with β, whereas SYM-H more strongly depends on β for southward IMF (r=0.744) than for northward IMF (r=0.677). On the contrary, for ASY-H r=–0.741 at northward IMF and r=–0.719 at southward IMF. Similar to SYM-H, Dst (to a lesser extent) significantly correlates with β at southward IMF (r=0.629) and weaker at northward IMF (r=0.456).

Large-scale relationships of the geomagnetic indices SYM-H and ASY-H with the north-south IMF component and the solar wind beta parameter

Using annual average values, the relationships are examined of the geomagnetic indices SYM-H, ASY-H, and Dst with solar wind parameters in 1981–2015. The data used was divided into two samples according to the sign of the north-south component Bn of the interplanetary magnetic field (IMF). Variations in the annual average values of each of the Dst, SYM-H, and ASY-H indices for southward and northward IMF have been found to be similar and their linear correlation coefficients r to be high: 0.871, 0.863, and 0.943 respectively. The similarity between variations of the indices with different signs of Bn is probably due to their connection with the number of sunspots. It has been established that Dst, SYM-H, and ASY-H depend on the solar wind parameter β: their absolute values decrease with increasing β, regardless of Bn sign. The decrease in the indices with increasing β is likely to be caused by the transition of the magnetosphere to a quiet state due to the increasing predominance of thermal pressure over magnetic one in the solar wind and a decrease in the level of solar wind turbulence. SYM-H and ASY-H have been found to reveal the closest relationships with β, whereas SYM-H more strongly depends on β for southward IMF (r=0.744) than for northward IMF (r=0.677). On the contrary, for ASY-H r=–0.741 at northward IMF and r=–0.719 at southward IMF. Similar to SYM-H, Dst (to a lesser extent) significantly correlates with β at southward IMF (r=0.629) and weaker at northward IMF (r=0.456).

A Multi‐Scale Particle‐In‐Cell Simulation of Plasma Dynamics From Magnetotail Reconnection to the Inner Magnetosphere

AbstractDuring magnetospheric substorms, plasma from magnetic reconnection in the magnetotail is thought to reach the inner magnetosphere and form a partial ring current. We simulate this process using a fully kinetic 3D particle‐in‐cell (PIC) numerical code along with a global magnetohydrodynamics (MHD) model. The PIC simulation extends from the solar wind outside the bow shock to beyond the reconnection region in the tail, while the MHD code extends much further and is run for nominal solar wind parameters and a southward interplanetary magnetic field. By the end of the PIC calculation, ions and electrons from the tail reconnection reach the inner magnetosphere and form a partial ring current and diamagnetic current. The primary source of particles to the inner magnetosphere is bursty bulk flows (BBFs) that originate from a complex pattern of reconnection in the near‐Earth magnetotail at to . Most ion acceleration occurs in this region, gaining from 10 to 50 keV as they traverse the sites of active reconnection. Electrons jet away from the reconnection region much faster than the ions, setting up an ambipolar electric field allowing the ions to catch up after approximately 10 ion inertial lengths. The initial energy flux in the BBFs is mainly kinetic energy flux from the ions, but as they move earthward, the energy flux changes to enthalpy flux at the ring current. The power delivered from the tail reconnection in the simulation to the inner magnetosphere is W, which is consistent with observations.

The Influence of Ionospheric Conductance on Magnetospheric Convection During the Southward IMF

The Influence of Ionospheric Conductance on Magnetospheric Convection During the Southward IMF

Time‐Lagged Effects of Ionospheric Response to Severe Geomagnetic Storms on GNSS Kinematic Precise Point Positioning

AbstractThis paper investigates time‐lag effects of ionospheric response to two severe geomagnetic storms (Kp = 8) on the degradation of kinematic precise point positioning (PPP) solutions, utilizing over 5500 Global Navigation Satellite Systems (GNSS) stations distributed worldwide. Focusing on these two severe geomagnetic storms that occurred during solar cycle 24, the study employs an open‐source positioning software package, namely RTKLIB, to derive the PPP solutions. The findings reveal significant variations in time lags across different magnetic latitudes. These variations are driven by ionospheric responses to a southward interplanetary magnetic field and subsequent decreases in the SMY‐H index during the 2015 St. Patrick's Day Storm and the 2017 September 7–8 Storm. Specifically, at high latitudes, PPP degradation primarily manifests during the main phase of the storm, resulting in delays spanning from several minutes to 1–2 hr after the sudden onset of the storm. In contrast, mid‐ and low latitudes exhibit a wider range of delays extending up to tens of hours. Notably, rapid positioning degradation is observed predominantly at the magnetic local time noon and midnight sectors. The study discusses these time lag effects concerning the intensity of various ionospheric disturbances triggered by the interactions among the solar wind, magnetosphere, and ionosphere during geomagnetic storms. The insights obtained from this research have the potential to be integrated into physics‐based and machine‐learning models to enhance forecasting capabilities of space weather impacts.

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 &lt; 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 &gt; 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.

Seasonal and Interhemispheric Variations of the Afternoon Auroral Responses to the Interplanetary Magnetic Field By Polarity

AbstractThis work investigates seasonal and interhemispheric variations of the afternoon auroral responses to the interplanetary magnetic field (IMF) By effects. The auroral observations are adopted from the global ultraviolet imager instrument on board the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite during 2002–2007. The results show that in both summer and winter solstices, the stronger afternoon auroral intensity is associated with negative IMF By (By &lt; 0) in the northern hemisphere, and with By &gt; 0 in the southern hemisphere. This suggests stronger contributions from the upward field‐aligned currents (FACs), which can be induced by the By‐associated north‐south oriented electric field and the By‐associated flow shear in the ionosphere. In addition, the strongest afternoon aurora occurs in summer in each hemisphere. In summer, the absolute difference between the auroral peak intensity under the two By polarities is greater and occurs earlier than in winter, which may be related to changes in FACs and conductivity from winter to summer. Differently, in equinoxes stronger auroral intensity favors By conditions associated with more frequent occurrence of southward IMF Bz, such as By &lt; 0 and By &gt; 0 conditions in March and in September, respectively. Therefore, in equinoxes the effects of the favorable By, which were seen in solstices, are masked. We suggest that these are caused by the Russell‐McPherron effect, which leads to more southward Bz conditions, resulting in more energy deposited and subsequent stronger aurora in polar ionosphere. These results contribute to our deeper understanding of the asymmetrical phenomena in the Earth's magnetosphere‐ionosphere induced by IMF By.

Plasma Mixing During Active Kelvin‐Helmholtz Instability Under Different IMF Orientations

AbstractWhen the velocity shear between the two plasmas separated by Earth's magnetopause is locally super‐Alfvénic, the Kelvin‐Helmholtz (KH) instability can develop. A crucial role is played by the interplanetary magnetic field (IMF) orientation, which can stabilize the velocity shear. Although, in a linear regime, the instability threshold is equally satisfied during both northward and southward IMF orientations, in situ measurements show that KH instability is preferentially excited during the northward IMF orientation. We investigate this different behavior by means of a mixing parameter which we apply to two KH events to identify both boundaries and the center of waves/vortices. During the northward orientation, the waves/vortex boundaries have stronger electrons than ions mixing, while the opposite is observed at their center. During the southward orientation, instead, particle mixing is observed predominantly at the boundaries. In addition, stronger local ion and electron non‐thermal features are observed during the northward than the southward IMF orientation. Specifically, ion distribution functions are more distorted, due to field‐aligned beams, and electrons have a larger temperature anisotropy during the northward than the southward IMF orientation. The observed kinetic features provide an insight into both local and remote processes that affect the evolution of KH structures.

Geomagnetically induced currents (GICs) during strong geomagnetic activity (storms, substorms, and magnetic pulsations) on 23–24 April 2023

We analyzed intense geomagnetically induced currents (GICs) recorded during a complex space weather event observed on 23–24 April 2023. Two geomagnetic storms characterized by SYM/H intensities of −179 nT and −233 nT were caused by southward interplanetary magnetic field (IMF) Bz component of −25 nT in the sheath fields, and −33 nT in the magnetic cloud (MC) fields, respectively. GIC observations were divided into two local time sectors: nighttime (1700–2400 UT on 23 April) GICs observed during the interplanetary sheath magnetic storm, and morning sector (0200–0700 UT on 24 April) GICs observed during the MC magnetic storm. By using the direct measurements of GICs on several substations of Karelian-Kola power line (located in the north-west portion of Russia) and gas pipeline station near Mäntsälä (south of Finland), we managed to trace the meridional profile of GIC increases at different latitudes. It was shown that the night sector GIC intensifications (∼18–42 A) occurred in accordance with poleward expansion of the westward electrojet during a substorm. On the other hand, the intense morning sector GICs (∼12–46 A) were caused by Ps 6 magnetic pulsations. In addition, a strong local morning GIC (∼44 A) was associated with a local substorm-like disturbance caused by a high-density solar wind structure, possibly a coronal loop portion of an interplanetary coronal mass ejection.

Time Sequence of Magnetospheric Responses to a Southward IMF Turning

AbstractWe use MHD simulations to study the time sequence of magnetospheric responses to a synthetic event with a southward interplanetary magnetic field (IMF) turning. The onset of dayside magnetopause reconnection launches a weak rarefaction wave and sunward flow in the equatorial magnetosphere simultaneously with a tailward flow through the polar cap. This convection results in the accumulation of magnetic flux in the tail lobes and thinning of the tail current layer which provides favorable conditions for the onset of nightside reconnection. The onset of nightside reconnection about 40 min later closes the Dungey convection cycle, resulting in a second increase in the sunward flow in the equatorial plane. Variations of the magnetopause standoff distance as well as the size of the polar cap (PC) may indicate the onsets of the dayside and nightside reconnections. We compare the results of two MHD models and discuss their differences.

IMF Bx, By, and Bz dependence of energetic particle precipitation in the magnetosphere

The orientation of Interplanetary Magnetic Field (IMF B) components plays a major role in magnetospheric Energetic Particles Precipitation (EPP). This is because the IMF B components in the Geocentric Solar Magnetospheric (GSM) coordinate system control magnetic reconnection at the subsolar magnetopause. This study intends to unravel the dependence of the preceding conditions of the orientations of IMF B components that drove geomagnetic storms on the EPPs produced in the Van Allen radiation belt. We classified the geomagnetic storms based on their drivers and IMF Bz orientations prior to the storms’ onset. Energetic particle fluxes, IMF B, and solar wind data were used. The study showed that electrons are more reactive to solar wind speed than protons. Additionally, storms with southward IMF Bz orientation caused more EPP enhancement than with northward orientation. Our results also showed that protons are more influenced by magnetospheric compression than electrons at the northward orientation of IMF Bz. In fact, at this point, the proton’s motion violates adiabatic invariants. As particles interact with electric fields, a significant population of EPPs is produced by pitch angle diffusion. Generally, IMF Bx and IMF By are often anticorrelated. The preceding conditions of orientations of the IMF Bx indicated weaker dependence on auroral indices, and invariably on energetic particles precipitation than the IMF By.

Statistical Properties of Whistler-mode Waves in the Dayside Terrestrial Space: MMS Observations

Whistler-mode waves have been extensively observed and investigated in terrestrial space. In this study, we present the dynamic response of whistler-mode waves to different solar wind conditions in the dayside terrestrial space based on Magnetospheric Multiscale (MMS) data. Statistical results show that the occurrence rate, amplitudes, and corresponding electron temperature anisotropy of whistler-mode waves increase with P sw in the dayside terrestrial space, which is attributed to the compression of magnetic fields in these magnetosheath and outer magnetosphere. Furthermore, whistler-mode waves under the southward interplanetary magnetic fields (IMFs) show a higher occurrence rate than that under the northward IMFs, mostly corresponding to T e⊥/T e∥ > 1, and have a higher occurrence rate during quasi-radial IMFs. These results present that whistler-mode waves in these magnetosheath and outer magnetosphere are also modulated by the solar wind as clearly as the inner magnetosphere. This work advanced our understanding in the solar–terrestrial interaction.

Comparison of Solar Wind Interaction with Mars and Earth: Energy Transfer

Using a global magnetohydrodynamics numerical simulation, this work compares the interaction of the solar wind with Mars and Earth from the perspective of energy transfer under north–south interplanetary magnetic fields (IMFs). Mars lacks a global dipole magnetic field like Earth’s and instead has a small-scale crustal magnetic field near highlands in the southern hemisphere. Unlike Earth’s magnetopause reconnection (at the subsolar point or tail under a southward IMF, or behind the cusp under a northward IMF), the reconnection of the Martian magnetic pileup boundary (MPB) occurs near solar zenith angle (SZA) ≈ 45° (SZA ≈ 30° and 60°) for a southward (northward) IMF, resulting in asymmetric energy transfer between the northern and southern hemispheres. The Martian outflow of mechanical energy appears near SZA ≈ 45° (SZA ≈ 30° and 60°) under a southward (northward) IMF, accompanied by an inflow due to the process of “solar wind pickup.” For energy transfer across the MPB, whether the IMF is northward or southward, the input of electromagnetic energy is twice as large as the input of mechanical energy, which is similar to Earth’s magnetopause for a southward IMF, but opposite to it for a northward IMF. The energy transfer rate of the MPB is slightly higher in a northward IMF than in a southward one, whereas the energy transfer rate of Earth’s magnetopause is far higher in a southward IMF than in a northward one.

Analysis of global ionospheric scintillation and GPS positioning interference triggered by full-halo CME-driven geomagnetic storm: A case study

Currently, the 25th solar activity peak has commenced, driving frequent geomagnetic storms and causing irregular disturbances in the global ionosphere, leading to the scintillation of Global Positioning System (GPS) signals, consequently decreasing the accuracy of GPS positioning. Analyzing the patterns of global ionospheric scintillation and changes in GPS positioning accuracy caused by geomagnetic storms is crucial to mitigate the adverse effects of GPS positioning. Current research has primarily concentrated on analyzing the effects of geomagnetic storms on ionospheric scintillation disturbances and GPS positioning interference. However, there is a notable gap in studying the holistic impact of coronal mass ejections (CMEs)-driven geomagnetic storms on GPS performance as an integrated event complex. This study investigates the conditions under which a CME drives a severe geomagnetic storm to elucidate the space weather phenomena associated with CME-driven geomagnetic storms. The ionospheric scintillation induced by the geomagnetic storm is analyzed, while we also examine the accuracy variability in kinematic precision point positioning (PPP) and its possible leading reasons. The research findings suggest that factors such as a high-speed full-halo CME, a southward interplanetary magnetic field (IMF) Bz, and high-speed solar wind contribute to the onset of this geomagnetic storm. Ionospheric scintillation and the decrease in positioning accuracy in low-latitude regions are less pronounced compared to mid- and high-latitude areas. Geomagnetic-storm-induced scintillation increases cycle slips, leading to a decrease in PPP accuracy. Even in the cases where geomagnetic storms do not induce ionospheric scintillation, positioning accuracy can still be affected by cycle slips, deterioration of the precision of the GPS measurements, data outages, and the decrease in the number of available satellites.

Influences of Solar Wind Parameters on Energetic Electron Fluxes at Geosynchronous Orbit Revealed by the Deep SHAP Method

AbstractSolar wind is an intermediary in energy transfer from the Sun into the Earth's magnetosphere, and is considered as a decisive driver of energetic electron dynamics at the geosynchronous orbit (GEO). Based on machine learning technology, several models driven by solar wind parameters have been established to predict GEO electron fluxes. However, the relative contributions of different solar wind parameters on GEO electron fluxes are still unclear. Recently, a feature attribution method, Deep SHapley Additive exPlanations (Deep SHAP) is proposed to open black boxes of machine learning models. In this study, we use the Deep SHAP method to quantify contributions of different solar wind parameters with an artificial neural network (ANN) model. Backpropagating the prediction results of this ANN model from 2011 to 2020, SHAP values for four solar wind parameters (interplanetary magnetic field (IMF) BZ, solar wind speed, solar wind dynamic pressure, and proton density) are calculated and comprehensively analyzed. The results suggest that solar wind speed with a lag of 1 day is the most important driver. We further investigate relative roles of different parameters in three specific electron fluxes variation events (corresponding to electron fluxes reaching a local maximum, a local minimum, and unchanged, respectively). The results suggest that high solar wind speed and southward IMF BZ (high dynamic pressures) facilitate increases (decreases) of electron fluxes. These findings help reveal the underlying physical mechanisms of GEO electron dynamics and help develop more accurate prediction models for GEO electron fluxes.