Impact Of Coronal Mass Ejection Research Articles

Validation of EUHFORIA cone and spheromak coronal mass ejection models

We present validation results for calculations of arrival times and geomagnetic impact of coronal mass ejections (CMEs) using the cone and spheromak CME models implemented in EUropean Heliospheric FORecasting Information Asset (EUHFORIA). Validating numerical models is crucial for ensuring their accuracy and performance with respect to real data. We compared CME plasma and magnetic field signatures measured in situ by satellites at the L1 point with the simulation output of EUHFORIA. The validation of this model was carried out using two datasets in order to ensure a comprehensive evaluation. The first dataset focuses on 16 CMEs that arrived at Earth, offering specific insights into the model's accuracy in predicting arrival time and geomagnetic impact. Meanwhile, the second dataset encompasses all CMEs observed over eight months within Solar Cycle 24, regardless of whether or not they arrived at Earth, covering periods of both solar minimum and maximum activity. This second dataset enables a more comprehensive evaluation of the model's predictive precision in term of CME arrivals and misses. Our results show that EUHFORIA provides good estimates in terms of arrival times, with root mean square error (RMSE) values of 9 hours. Regarding the number of correctly predicted ICME arrivals and misses, we find a 75<!PCT!> probability of detection in a 12 hour time window and 100<!PCT!> probability of detection in a 24 hour time window. The geomagnetic impact forecasts measured by the $K_p$ index provide different degrees of accuracy ranging from 31<!PCT!> to 69<!PCT!>. These results validate the use of cone and spheromak CMEs for real-time space weather forecasting.

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.

The spheroid CME model in EUHFORIA

Predictions of coronal mass ejection (CME) propagation and impact in the heliosphere, in either research or operational settings, are usually performed by employing magnetohydrodynamic (MHD) models. Within such simulations, the CME ejecta is often described as a hydrodynamic pulse that lacks an internal magnetic field and is characterized by a spherical geometry – leading to the so-called cone CME model. White-light observations of CMEs in the corona, however, reveal that the morphology of these structures resembles more closely that of a croissant, i.e., exhibiting an elongated cross-section of their front. It follows that, in space weather forecasts, the assumption of a spherical geometry may result in erroneous predictions of CME impacts in the heliosphere in terms of hit/miss and arrival time/speed, especially in the case of flank encounters. A spheroid CME model is expected to provide a more accurate description of the elongated morphology that is often observed in CMEs. In this paper, we describe the implementation and initial validation of the spheroid CME model within the MHD EUropean Heliospheric FORecasting Information Asset (EUHFORIA) code. We perform EUHFORIA simulations of an idealized CME as well as a “real” event to compare the spheroidal model with the traditional cone one. We show how the initial ejecta geometry can lead to substantially different estimates in terms of CME impact, arrival time/speed, and geoeffectiveness, especially with increasing distance to the CME nose.

Estimating Geomagnetically Induced Currents in High‐Voltage Power Lines for the Territory of Kazakhstan

AbstractExtreme solar events, such as powerful solar flares are accompanied by the release of strong solar disturbances, such as coronal mass ejections (CMEs). The impact of CMEs on the Earth's magnetosphere causes geomagnetic storms, which trigger geomagnetic effects measurable in the ionosphere, upper atmosphere, and on and in the ground. During extreme cases, rapidly changing geomagnetic fields generate intense geomagnetically induced currents (GICs), which can cause dramatic effects on man‐made technological systems, including transmission lines and pipelines. In countries with large territories such as Kazakhstan, long power lines contribute to high values of induced currents during periods of extreme geoeffective solar events. It is of interest to estimate the values of GICs in an extensive network of power lines on the territory of Kazakhstan. However, there are no estimations of induced currents in power lines in Kazakhstan, and most estimation techniques are made difficult because of absence of field measurements of Earth conductivity. This study aims to model geoelectric fields on the surface of the Earth for Kazakhstan and to estimate the values of the GICs in 500 kV power lines. This study also compares between two methods for calculating induced voltages in power lines: one based on linear paths and the other based on curvilinear paths between substations of transmission power lines.

Rotation of a Stealth CME on 2012 October 5 Observed in the Inner Heliosphere

Coronal mass ejections (CMEs) are subject to changes in their direction of propagation, tilt, and other properties. This is because CMEs interact with the ambient solar wind and other large-scale magnetic field structures. In this work, we report on the observations of the 2012 October 5 stealth CME using coronagraphic and heliospheric images. We find clear evidence of a continuous rotation of the CME, i.e., an increase in the tilt angle, estimated using the graduated cylindrical shell (GCS) reconstruction at different heliocentric distances, up to 58 R ⊙. We find a further increase in the tilt at L1 estimated from the toroidal and cylindrical flux rope fitting on the in situ observations of interplanetary magnetic field (IMF) and solar wind parameters. This study highlights the importance of observations of Heliospheric Imager (HI), on board the Solar Terrestrial Relations Observatory. In particular, the GCS reconstruction of CMEs in the HI field of view promises to bridge the gap between the near-Sun and in situ observations at the L1. The changes in the CME tilt have significant implications for the space weather impact of stealth CMEs.

A Time-efficient, Data-driven Modeling Approach for Predicting the Geomagnetic Impact of Coronal Mass Ejections

To understand the global-scale physical processes behind coronal mass ejection (CME)–driven geomagnetic storms and predict their intensity as a space weather forecasting measure, we develop an interplanetary CME flux rope–magnetosphere interaction module using 3D magnetohydrodynamics. The simulations adequately describe CME-forced dynamics of the magnetosphere including the imposed magnetotail torsion. These interactions also result in induced currents, which are used to calculate the geomagnetic perturbation. Through a suitable calibration, we estimate a proxy of geoeffectiveness—the Storm Intensity index (STORMI)—that compares well with the Dst/SYM-H index. Simulated impacts of two contrasting CMEs quantified by the STORMI index exhibit a high linear correlation with the corresponding Dst and SYM-H indices. Our approach is relatively simple, has fewer parameters to be fine-tuned, and is time efficient compared to complex fluid-kinetic methods. Furthermore, we demonstrate that flux rope erosion does not significantly affect our results. Thus our method has the potential to significantly extend the time window for predictability—an outstanding challenge in geospace environment forecasting—if early predictions of near-Earth CME flux rope structures based on near-Sun observations are available as inputs. This study paves the way for early warnings based on operational predictions of CME-driven geomagnetic storms.

A Comparison of the Impacts of CMEs and CIRs on the Martian Dayside and Nightside Ionospheric Species

AbstractMeasurements from the Mars Atmosphere and Volatile EvolutioN spacecraft orbiting Mars are used for investigating the impact of coronal mass ejections (CMEs) and corotating interaction regions (CIRs) on Martian ionospheric species. We have chosen 15 CME and 15 CIR events (2015–2020) at Mars from the existing catalogs. We have extensively analyzed the Martian dayside and nightside profiles of ionospheric species during each of the CME and CIR events. We have selected those orbit plasma density profiles which showed significant differences from the mean quiet‐time profile during each event. The primary focus of this paper is to provide a comparative average scenario of the variation of Martian ionospheric species during CME and CIR events. A significant difference can be observed in the profiles of the Martian dayside and nightside ionospheric species (O+, O2+, CO2+, NO+, C+, N+, & OH+) during CMEs and CIRs in comparison to mean quiet‐time profile. The difference is more prominent on the nightside compared to the dayside ionosphere. During CIRs, the nightside ion density is nearly one order of magnitude less (above 250 km) in comparison to CMEs. The mean peak altitude and density of the lighter ions (O+, C+, N+, & OH+) were at lower altitudes during the CIRs compared to CMEs. Therefore, this study suggests that during the declining phase of solar cycle (SC 24), the impact of CIRs on the Martian ionospheric species is more prominent compared to CMEs.

Interior Heating of Rocky Exoplanets from Stellar Flares with Application to TRAPPIST-1

Many stars of different spectral types with planets in the habitable zone are known to emit flares. Until now, studies that address the long-term impact of stellar flares and associated coronal mass ejections (CMEs) assumed that the planet’s interior remains unaffected by interplanetary CMEs, only considering the effect of plasma/UV interactions on the atmosphere of planets. Here, we show that the magnetic flux carried by flare-associated CMEs results in planetary interior heating by ohmic dissipation and leads to a variety of interior–exterior interactions. We construct a physical model to study this effect and apply it to the TRAPPIST-1 star whose flaring activity has been constrained by Kepler observations. Our model is posed in a stochastic manner to account for uncertainty and variability in input parameters. Particularly for the innermost planets, our results suggest that the heat dissipated in the silicate mantle is both of sufficient magnitude and longevity to drive geological processes and hence facilitate volcanism and outgassing of the TRAPPIST-1 planets. Furthermore, our model predicts that Joule heating can further be enhanced for planets with an intrinsic magnetic field compared to those without. The associated volcanism and outgassing may continuously replenish the atmosphere and thereby mitigate the erosion of the atmosphere caused by the direct impact of flares and CMEs. To maintain consistency of atmospheric and geophysical models, the impact of stellar flares and CMEs on atmospheres of close-in exoplanetary systems needs to be studied in conjunction with the effect on planetary interiors.

Medium-term prediction of the fluence of relativistic electrons in geostationary orbit using solar wind streams forecast based on solar observations

The new approaches to the modelling of the Sun-solar wind-magnetosphere-radiation belts chain and their implementation at MSU's Space weather center (Space Monitoring Data Center, SMDC) are presented. The main idea is to use data from medium-term (3–5 days) forecasts of the speed of quasi-stationary solar wind streams based on data obtained from solar images in the UV wavelength range to improve the quality of forecasts of the magnetospheric factors of the space environment. An operational model for predicting the daily fluence of relativistic electrons (>2 MeV) in the Earth's outer radiation belt has been developed, with the extended set of input parameters that include the forecast of the solar wind velocity. To validate the model, the period from October 11, 2016 to February 18, 2017 was considered, during which the Sun made several revolutions and it was possible to observe the evolution of coronal holes and the development of solar sporadic phenomena. The arrival of high-speed solar wind streams from coronal holes to the Earth's magnetosphere, as well as, as impact of coronal mass ejections, provoked geomagnetic disturbances of various intensity, and caused significant variations of the electron fluxes of the Earth's outer radiation belt. SMDC website implements solar wind model based on the data of solar observations by the AIA instrument of the SDO space observatory at wavelengths of 19.3 and 21.1 nm that forecasts the daily fluence of relativistic electrons (E > 2 MeV) in geostationary orbit. It is shown that the use of the results of medium-term forecasting of the solar wind speed as an input parameter in the daily electron fluence forecast model can significantly improve its quality with a forecast horizon of up to 4 days.

The impact of coronal mass ejections and flares on the atmosphere of the hot Jupiter HD189733b

ABSTRACT High-energy stellar irradiation can photoevaporate planetary atmospheres, which can be observed in spectroscopic transits of hydrogen lines. For the exoplanet HD189733b, multiple observations in the Ly α line have shown that atmospheric evaporation is variable, going from undetected to enhanced evaporation in a 1.5-yr interval. Coincidentally or not, when HD189733b was observed to be evaporating, a stellar flare had just occurred 8 h prior to the observation. This led to the question of whether this temporal variation in evaporation occurred due to the flare, an unseen associated coronal mass ejection (CME), or even the simultaneous effect of both. In this work, we investigate the impact of flares (radiation), winds, and CMEs (particles) on the atmosphere of HD189733b using three-dimensional radiation hydrodynamic simulations that self-consistently include stellar photon heating. We study four cases: first, the quiescent phase including stellar wind; secondly, a flare; thirdly, a CME; and fourthly, a flare that is followed by a CME. Compared to the quiescent case, we find that the flare alone increases the evaporation rate by only 25 per cent, while the CME leads to a factor of 4 increments. We calculate Ly α synthetic transits and find that the flare alone cannot explain the observed high blueshifted velocities seen in the Ly α. The CME, however, leads to an increase in the velocity of escaping atmospheres, enhancing the blueshifted transit depth. While the effects of CMEs show a promising potential, our models are not able to fully explain the blueshifted transit depths, indicating that they might require additional physical mechanisms.

Impact of CME and HSSW driven geomagnetic storms on thermosphere and ionosphere as observed from mid-latitudes

The present paper reports magnetospheric-thermospheric-ionospheric interactions, observed during geomagnetically disturbed periods in 2015–2016 from mid-latitude stations located in the US-Pacific longitudes (~120°W geographic). These interactions have been analyzed for a series of Coronal Mass Ejection (CME) and High Speed Solar Wind (HSSW) driven geomagnetic storms during the moderate solar activity periods. The geomagnetically disturbed periods under consideration in this paper have an interesting feature of the occurrences of one or more HSSW events following an intense CME driven intense geomagnetic storm. Correlations were observed between the solar and geomagnetic parameters, hemispherically integrated Joule heating, changes in O/N2 ratio, corresponding changes in neutral wind velocities and mid-latitude Vertical Total Electron Content (VTEC) in most of the cases. Prolonged effects of neutral wind driven equatorward plasma transport process were noticed during the period of the summer solstice (June 23–26, 2015) which was correlated with the hemispherically integrated Joule heating and ionospheric conductivities. The effects of storm onset were observed during March 17–18, 2015. The influences of the ‘super-fountain effect’ in terms of Prompt Penetration Electric Field (PPEF) were seen during the main phases of the geomagnetic storms from these mid-latitude stations. This is correlated with the strength of Equatorial Electrojet (EEJ).

The impact of a stealth CME on the Martian topside ionosphere

ABSTRACT Solar cycle 24 is one of the weakest solar cycles recorded, but surprisingly the declining phase of it had a slow coronal mass ejection (CME) that evolved without any low coronal signature and is classified as a stealth CME that was responsible for an intense geomagnetic storm at Earth (Dst = −176 nT). The impact of this space weather event on the terrestrial ionosphere has been reported. However, the propagation of this CME beyond 1 au and the impact of this CME on other planetary environments have not been studied so far. In this paper, we analyse the data from the Sun–Earth L1 point and from the Martian orbit (near 1.5 au) to understand the characteristics of the stealth CME as observed beyond 1 au. The observations near Earth are using data from the Solar Dynamics Observatory (SDO) and the Advanced Composition Explorer (ACE) satellite located at L1 point, whereas those near Mars are from the instruments for plasma and magnetic field measurements onboard Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. The observations show that the stealth CME has reached 1.5 au after 7 d of its initial observations at the Sun and caused depletion in the nightside topside ionosphere of Mars, as observed during the inbound phase measurements of the Langmuir Probe and Waves (LPW) instrument onboard MAVEN. These observations have implications on the ion escape rates from the Martian upper atmosphere.

Testing the impact of coronal mass ejections on cosmic-ray intensity modulation with algorithm selected Forbush decreases

ABSTRACT The relationship between coronal mass ejections (CMEs) and Forbush decreases (FDs) has been investigated in the past. But the selection of both solar events are difficult. Researchers have developed manual and automated methods in efforts to identify CMEs as well as FDs. While scientists investigating CMEs have made significant advancement, leading to several CME catalogues, including manual and automated events catalogues, those analyzing FDs have recorded relatively less progress. Till date, there are no comprehensive manual FD catalogues, for example. There are also paucity of automated FD lists. Many investigators, therefore, attempt to manually select FDs which are subsequently used in the analysis of the impact of CMEs on galactic cosmic-ray (GCR) flux depressions. However, some of the CME versus FD correlation results might be biased since manual event identification is usually subjective, unable to account for the presence of solar-diurnal anisotropy which characterizes GCR flux variations. The current paper investigates the relation between CMEs and FDs with emphasis on accurate and careful Forbush event selection.

The Impact of Coronal Mass Ejections on the Seasonal Variation of the Ionospheric Critical Frequency f0F2

We investigated the relations between the monthly average values of the critical frequency (f0F2) and the physical properties of the coronal mass ejections (CMEs), then we examined the seasonal variation of f0F2 values as an impact of the several CMEs properties. Given that, f0F2 were detected by PRJ18 (Puerto Rico) ionosonde station during the period 1996–2013. We found that the monthly average values of f0F2 are varying coherently with the sunspot number (SSN). A similar trend was found for f0F2 with the CMEs parameters such as the CME energy (linear correlation coefficient R = 0.73), width (R = 0.6) and the speed (R = 0.6). The arrived CMEs cause a plasma injection into the ionosphere, in turn, increasing the electron density, and consequently, f0F2 values. This happens in the high latitudes followed by the middle and lower latitudes. By examining the seasonal variation of f0F2, we found that the higher correlation between f0F2 and CMEs parameters occurs in the summer, then the equinoxes (spring and autumn), followed by the winter. However, the faster CMEs affect the ionosphere more efficiently in the spring more than in the summer, then the winter and the autumn seasons.

Recurrent Solar Energetic Particle Flux Enhancements Observed near Earth and Mars

Abstract The period 2016 August 1 to November 15 was characterized by the presence of corotating interaction regions (CIRs) and a few weak coronal mass ejections (CMEs) in the heliosphere. In this study we show recurrent energetic electron and proton enhancements observed near Earth (1 au) and Mars (1.43–1.38 au) during this period. The observations near Earth use data from instruments on board the Advanced Composition Explorer, the Solar and Heliospheric Observatory, and Solar Dynamics Observatory and those near Mars are from the Solar Energetic Particle, Solar Wind Ion Analyzer, and Magnetometer instruments on board the Mars Atmosphere and Volatile EvolutioN (MAVEN). During this period, the energetic electron fluxes observed near Earth and Mars showed prominent periodic enhancements over four solar rotations, with major periodicities of ∼27 days and ∼13 days. Periodic radar blackouts/weakenings of radar signals at Mars were observed by the Mars Advanced Radar for Subsurface and Ionosphere Sounding/Mars Express, and are associated with these solar energetic electron enhancements. During this period, a weak CME and a high-speed stream (HSS)-related interplanetary shock could have interacted with the CIR and enhance energetic proton fluxes near 1.43–1.38 au, causing ∼27 days periodicity in proton fluxes to be significantly diminished at 1.43–1.38 au. These events also have an unexpected impact on the Martian topside ionosphere, such as topside ionospheric depletion and compression observed by the Langmuir Probe and Waves and Neutral Gas and Ion Mass Spectrometer on board MAVEN. These observations are unique not only because of the recurring nature of electron enhancements seen at two vantage points, but also because they reveal the unexpected impact of the weak CME and interplanetary shock on the Martian ionosphere, which provides new insights into the impact of CME–HSS interactions on the Martian plasma environment.

Improving Predictions of High‐Latitude Coronal Mass Ejections Throughout the Heliosphere

AbstractPredictions of the impact of coronal mass ejections (CMEs) in the heliosphere mostly rely on cone CME models, whose performances are optimized for locations in the ecliptic plane and at 1 AU (e.g., at Earth). Progresses in the exploration of the inner heliosphere, however, advocate the need to assess their performances at both higher latitudes and smaller heliocentric distances. In this work, we perform 3‐D magnetohydrodynamics simulations of artificial cone CMEs using the EUropean Heliospheric FORecasting Information Asset (EUHFORIA), investigating the performances of cone models in the case of CMEs launched at high latitudes. We compare results obtained initializing CMEs using a commonly applied approximated (Euclidean) distance relation and using a proper (great circle) distance relation. Results show that initializing high‐latitude CMEs using the Euclidean approximation results in a teardrop‐shaped CME cross section at the model inner boundary that fails in reproducing the initial shape of high‐latitude cone CMEs as a circular cross section. Modeling errors arising from the use of an inappropriate distance relation at the inner boundary eventually propagate to the heliospheric domain. Errors are most prominent in simulations of high‐latitude CMEs and at the location of spacecraft at high latitudes and/or small distances from the Sun, with locations impacted by the CME flanks being the most error sensitive. This work shows that the low‐latitude approximations commonly employed in cone models, if not corrected, may significantly affect CME predictions at various locations compatible with the orbit of space missions such as Parker Solar Probe, Ulysses, and Solar Orbiter.

Radial Evolution of Coronal Mass Ejections Between MESSENGER, Venus Express, STEREO, and L1: Catalog and Analysis

AbstractOur knowledge of the properties of coronal mass ejections (CMEs) in the inner heliosphere is constrained by the relative lack of plasma observations between the Sun and 1 AU. In this work, we present a comprehensive catalog of 47 CMEs measured in situ measurements by two or more radially aligned spacecraft (MESSENGER, Venus Express, STEREO, Wind/ACE). We estimate the CME impact speeds at Mercury and Venus using a drag‐based model and present an average propagation profile of CMEs (speed and deceleration/acceleration) in the inner heliosphere. We find that CME deceleration continues past Mercury's orbit but most of the deceleration occurs between the Sun and Mercury. We examine the exponential decrease of the maximum magnetic field strength in the CME with heliocentric distance using two approaches: a modified statistical method and analysis from individual conjunction events. Findings from both the approaches are on average consistent with previous studies but show significant event‐to‐event variability. We also find the expansion of the CME sheath to be well fit by a linear function. However, we observe the average sheath duration and its increase to be fairly independent of the initial CME speed, contradicting commonly held knowledge that slower CMEs drive larger sheaths. We also present an analysis of the 3 November 2011 CME observed in longitudinal conjunction between MESSENGER, Venus Express, and STEREO‐B focusing on the expansion of the CME and its correlation with the exponential falloff of the maximum magnetic field strength in the ejecta.

The impact of CMEs on the critical frequency of F2-layer ionosphere (foF2)

AbstractThe ionospheric critical frequency (foF2) from ionosonde measurements at geographic high, middle, and low latitudes are analyzed with the occurrence of coronal mass ejections (CMEs) in long term variability of the solar cycles. We observed trends of monthly maximum foF2 values and monthly averaged values of CME parameters such as speed, angular width, mass, and kinetic energy with respect to time. The impact of CMEs on foF2 is very high at high latitudes and low at low latitudes. The time series for monthly maximum foF2 and monthly-averaged CME speed are moderately correlated at high and middle latitudes.

Geoelectric Field Evaluation During the September 2017 Geomagnetic Storm: MA.I.GIC. Model

AbstractThe space environment near Earth is constantly subjected to changes in the solar wind flow generated at the Sun. Examples of this variability are the occurrence of powerful solar disturbances, such as coronal mass ejections (CMEs). The impact of CMEs on the Earth's magnetosphere perturbs the geomagnetic field causing the occurrence of geomagnetic storms. Such extremely variable geomagnetic fields trigger geomagnetic effects measurable not only in the geospace but also in the ionosphere, upper atmosphere, and on the ground. For example, during extreme events, rapidly changing geomagnetic fields generate intense geomagnetically induced currents (GICs). In recent years, GIC impact on the power networks at middle and low latitudes has attracted attention due to the expansion of large‐scale power networks into these regions. This paper presents a new model, called MA.I.GIC. (Magnetosphere‐Ionosphere‐Ground‐Induced Current), to derive the geoelectric field used to determine the magnitude of GICs. In addition, we discuss the results of the MA.I.GIC. model applied to the September 2017 Geomagnetic Storm with particular focus on the two sudden impulses occurring on 6 and 7 September 2017, and the two main phases on 7 and 8 September 2017.

GUMICS-4 analysis of interplanetary coronal mass ejection impact on Earth during low and typical Mach number solar winds

Abstract. We study the response of the Earth's magnetosphere to fluctuating solar wind conditions during interplanetary coronal mass ejections (ICMEs) using the Grand Unified Magnetosphere-Ionosphere Coupling Simulation (GUMICS-4). The two ICME events occurred on 15–16 July 2012 and 29–30 April 2014. During the strong 2012 event, the solar wind upstream values reached up to 35 particles cm−3, speeds of up to 694 km s−1, and an interplanetary magnetic field of up to 22 nT, giving a Mach number of 2.3. The 2014 event was a moderate one, with the corresponding upstream values of 30 particles cm−3, 320 km s−1 and 10 nT, indicating a Mach number of 5.8. We examine how the Earth's space environment dynamics evolves during both ICME events from both global and local perspectives, using well-established empirical models and in situ measurements as references. We show that on the large scale, and during moderate driving, the GUMICS-4 results are in good agreement with the reference values. However, the local values, especially during high driving, show more variation: such extreme conditions do not reproduce local measurements made deep inside the magnetosphere. The same appeared to be true when the event was run with another global simulation. The cross-polar cap potential (CPCP) saturation is shown to depend on the Alfvén–Mach number of the upstream solar wind. However, care must be taken in interpreting these results, as the CPCP is also sensitive to the simulation resolution.