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Based on decades of single-spacecraft measurements near 1 au as well as data from heliospheric and planetary missions, multi-spacecraft simultaneous measurements in the inner heliosphere on separations of 0.05-0.2 au are required to close existing gaps in our knowledge of solar wind structures, transients, and energetic particles, especially coronal mass ejections (CMEs), stream interaction regions (SIRs), high speed solar wind streams (HSS), and energetic storm particle (ESP) events. The Mission to Investigate Interplanetary Structures and Transients (MIIST) is a concept for a small multi-spacecraft mission to explore the near-Earth heliosphere on these critical scales. It is designed to advance two goals: (a) to determine the spatiotemporal variations and the variability of solar wind structures, transients, and energetic particle fluxes in near-Earth interplanetary (IP) space, and (b) to advance our fundamental knowledge necessary to improve space weather forecasting from in situ data. We present the scientific rationale for this proposed mission, the science requirements, payload, implementation, and concept of mission operation that address a key gap in our knowledge of IP structures and transients within the cost, launch, and schedule limitations of the NASA Heliophysics Small Explorers program.

Understanding and predicting the geoeffectiveness of solar activity on Earth is crucial for space weather. Therefore, predicting the impact of coronal mass ejections (CMEs) and their associated interplanetary (IP) shocks on Earth is essential. Observations of CMEs near the Sun can be used for these prediction and to study their propagation and evolution in IP space. Commonly used international models do not accurately predict whether and when IP shocks would reach Earth, thus failing to meet the demands of space weather forecasting. This study investigated the geoeffectiveness of solar-IP disturbance events, focusing on type II radio bursts from 1996 to 2019 (solar cycles 23 and 24). The study results showed that during this period, Wind/WAVES detected 623 type II bursts and 541 IP shocks at the L1 point, where 181 type II bursts were associated with L1 shocks. Approximately 29% of the IP shocks associated with type II bursts reached Earth, and approximately 34% of the IP shocks at the L1 point were accompanied by these bursts. IP type II radio bursts and their cutoff frequencies can serve as indicators of the geoeffectiveness of CMEs towards Earth. IP shocks accompanied by type II radio bursts cause stronger geomagnetic responses than those without the associated type II radio bursts. Lower cutoff frequencies of type II radio bursts increase the probability that the corresponding shocks reaching Earth, intensifying the geomagnetic response of the shock. Consequently, the presence of IP type II radio bursts and can serve as indicators of geoeffectiveness of the Earth-directed CMEs. Further, they help improve the accuracy of forecasting the geoeffectiveness of CME/shock events towards Earth. [ABSTRACT FROM AUTHOR]

Solar eruptive activities, mainly including solar flares, coronal mass ejections (CME), and solar proton events (SPE), have an important impact on space weather and our technosphere. The short-term solar eruptive activity prediction is an active field of research in the space weather prediction. Numerical, statistical, and machine learning methods are proposed to build prediction models of the solar eruptive activities. With the development of space-based and ground-based facilities, a large amount of observational data of the Sun is accumulated, and data-driven prediction models of solar eruptive activities have made a significant progress. In this review, we briefly introduce the machine learning algorithms applied in solar eruptive activity prediction, summarize the prediction modeling process, overview the progress made in the field of solar eruptive activity prediction model, and look forward to the possible directions in the future. [ABSTRACT FROM AUTHOR]

We report a rare regime of Earth's magnetosphere interaction with sub‐Alfvénic solar wind in which the windsock‐like magnetosphere transforms into one with Alfvén wings. In the magnetic cloud of a Coronal Mass Ejection (CME) on 24 April 2023, NASA's Magnetospheric Multiscale mission distinguishes the following features: (a) unshocked and accelerated low‐beta CME plasma coming directly against Earth's dayside magnetosphere; (b) dynamical wing filaments representing new channels of magnetic connection between the magnetosphere and foot points of the Sun's erupted flux rope; (c) cold CME ions observed with energized counter‐streaming electrons, evidence of CME plasma captured due to by reconnection between magnetic‐cloud and Alfvén‐wing field lines. The reported measurements advance our knowledge of CME interaction with planetary magnetospheres, and open new opportunities to understand how sub‐Alfvénic plasma flows impact astrophysical bodies such as Mercury, moons of Jupiter, and exoplanets close to their host stars. Plain Language Summary: Like supersonically fast fighter jets creating sonic shocks in the air, planet Earth typically moves in the magnetized solar wind at super‐Alfvénic speeds and generates a bow shock. Here we report unprecedented observations of Earth's magnetosphere interacting with a sub‐Alfvénic solar wind brought by an erupted magnetic flux rope from the Sun, called a coronal mass ejection (CME). The terrestrial bow shock disappears, leaving the magnetosphere exposed directly to the cold CME plasma and the strong magnetic field from the Sun's corona. Our results show that the magnetosphere transforms from its typical windsock‐like configuration to having wings that magnetically connect our planet to the Sun. The wings are highways for Earth's plasma to be lost to the Sun, and for the plasma from the foot points of the Sun's erupted flux rope to access Earth's ionosphere. Our work indicates highly dynamic generation and interaction of the wing filaments, shedding new light on how sub‐Alfvénic plasma wind may impact astrophysical bodies in our solar and other stellar systems. Key Points: MMS observed a rare regime of magnetosphere interaction with unshocked low‐beta CME plasmaWing filaments represent dynamical channels of magnetic connection between the magnetosphere and foot points of the Sun's erupted flux ropeCold CME ions observed on closed field lines, likely generated by dual‐wing reconnection [ABSTRACT FROM AUTHOR]

Updated summaries of the August 1972 and March 1989 space weather events have been constructed. The features of these two events are compared to the Carrington 1859 event and a few other major space weather events. It is concluded that solar active regions release energy in a variety of forms (X‐rays, EUV photons, visible light, coronal mass ejection (CME) plasmas and fields) and they in turn can produce other energetic effects (solar energetic particles (SEPs), magnetic storms) in a variety of ways. It is clear that there is no strong one‐to‐one relationship between these various energy sinks. The energy is often distributed differently from one space weather event to the next. Concerning SEPs accelerated at interplanetary CME (ICME) shocks, it is concluded that the Fermi mechanism associated with quasi‐parallel shocks is relatively weak and that the gradient drift mechanism (electric fields) at quasi‐perpendicular shocks will produce harder spectra and higher fluxes. If the 4 August 1972 intrinsic magnetic cloud condition (southward interplanetary magnetic field instead of northward) and the interplanetary Sun to 1 au conditions were different, a 4 August 1972 magnetic storm and magnetospheric dawn‐to‐dusk electric fields substantially larger than the Carrington event would have occurred. Under these special interplanetary conditions, a Miyake et al. (2012), https://doi.org/10.1038/nature11123‐like extreme SEP event may have been formed. The long duration complex 1989 storm was probably greater than the Carrington storm in the sense that the total ring current particle energy was larger. Plain Language Summary: All the main information for the August 1972 and March 1989 space weather events have been gathered together for the readership. Various features of these two events have been compared and contrasted to the Carrington event and several other recent major events. It is thought that major energetic MeV to GeV particle acceleration occurs at interplanetary shocks instead of acceleration at the solar flare site. Two popular mechanisms for shock particle acceleration are: (a) Fermi acceleration between waves upstream and downstream of a shock, and (b) particle gradient drift in the direction of an electric field along the shock surface. The second mechanism is concluded to form a harder particle spectrum with higher fluxes. If the intrinsic conditions of the 4 August 1972 coronal mass ejection were different (southward interplanetary magnetic fields) and that propagated to the Earth without major evolution or distortion, a magnetic storm equal to or more intense than the Carrington event would have occurred. We have also constructed a scenario involving altered interplanetary space for the August 1972 event which could lead to a high Mach number quasiperpendicular shock and possibly a solar particle event comparable to the Miyake et al. (2012, https://doi.org/10.1038/nature11123) tree ring event. Key Points: The August 1972 and March 1989 space weather events are summarized and compared to the Carrington plus a few other recent eventsWith different solar and interplanetary conditions, the August 1972 ICME could have caused a storm greater than the Carrington stormThe complex March 1989 storm was a "stealth magnetic storm", probably greater ring‐current energy‐wise than the Carrington storm [ABSTRACT FROM AUTHOR]

When a magnetic storm hits a power transmission system, quasi-stationary geomagnetically induced currents (GIC) are generated in the high-voltage part of the system. These currents cause semi-saturation of the magnetic circuits of power transformers, which induces current overload in their high-voltage windings and subsequently thermal overload, which can lead to system failures. This rather complex phenomenon was described in [11] by a system of nonlinear differential equations and subsequently solved. This very challenging method is replaced in the present work by a simple approach. It allows not only predicting the imminent danger of system collapse, but gives transformer designers valuable information on how they can counteract this danger. [ABSTRACT FROM AUTHOR]

We report a study of major solar energetic particle (SEP) and ground level enhancement (GLE) events that occurred during the first 62 months of the rising phase of the 24th solar cycle. Our objective is to comprehend the key factors that influence the severity and occurrence of such events. The coronal mass ejection (CME) speed (serves as or is) is a reliable indicator of SEP and GLE events, as it consistently supports the shock acceleration mechanism. Some very fast CMEs, which are likely to have accelerated particles up to GeV energies, may not have resulted in a GLE event due to poor latitudinal connectivity. We have emphasized that the CME speed, magnetic connectivity to Earth, and ambient conditions are the main or primary factors that contribute to the lack of high-energy particle events during cycle 24. Furthermore, we observed that even well-connected fast CMEs that did not seem to have accelerated high-energy particles due to potentially unfavourable prevailing conditions such as high Alfven speed and overall reduction in acceleration efficiency in cycle 24. These conclusions are generally supported by insights gleaned from the observation of the time series of SW-IMF parameters on the flare day. [ABSTRACT FROM AUTHOR]

Type II radio emissions are events mostly found to be associated with coronal mass ejections (CMEs) and accelerated by the CME-driven shock in the heliosphere. This study reports on the estimation of the CME-shock standoff distance at the commencement of metric type II radio emissions by combining the CME-deprojected speed and spectral features of radio bursts using a robust TensorFlow Deep-Learning Sequential (TFDLS) technique. The dataset of 96 CMEs at the commencement of type II radio bursts was used between Solar cycle 24 and the ascending phase of Solar Cycle 25. The measured root mean squared error (RMSE) was 0.145 (Rs), with an average height difference of 0.096 Rs between the observed and predicted CME-shock heights. Five (5) CMEs/radio bursts energetic events associated with solar flares were selected from the test data, and the CME shock stand-off heights were forecasted using the TFDLS and flare-onset (FL) methods. The data were used to compare the leading-edge (LE) and dynamic spectra (DS) methods. The RMSE measured between the FL and LE was 0.35 Rs, and the RMSE estimated between the TFDLS and LE approaches was 0.04 Rs. The RMSE between FL and DS was 0.34. Rs, and the RMSE between the TFDLS and the DS was 0.04 Rs. We also used the findings gained from the five selected events and compared them to the 3D shock-fitting (3D-SF) approach. The RMSE found between the TFDLS and the 3D-SF was 0.18 Rs, while the RMSE estimated between the FL and the 3D-SF was 0.23 Rs. This shows that the TFDLS has satisfactory performance and can be used as an alternative technique. [ABSTRACT FROM AUTHOR]

Detection of weak signals remains challenging in astrophysics. This is particularly applicable in the investigation of Forbush events. There is thus, a paucity of catalogs of small-amplitude Forbush decreases (FDs). Detail investigations of the space-weather implications of small FDs are, thus, lacking in the literature. Recently, large catalogs of weak FDs, for the first time, have been published. This work employs the newly created lists of small-amplitude FDs to investigate the statistical link between small FDs and solar-geomagnetic variables. The solar-geomagnetic variables were obtained from the OMNI database. A simple coincident R software code was employed in matching the related solar-geomagnetic variables with the weak Forbush events. The FD dates were taken as the input signal. Scatter plots of FDs against interplanetary magnetic field (IMF), solar wind speed (SWS), planetary K-index (Kp) and planetary A-index (Ap) reveal a negative relationship, while that of FDs against disturbance storm time index (Dst) shows a positive relationship. Statistical significance of these relations were tested. The small-amplitude FDs and solar-geomagnetic variables at Potchefstroom (PTFM) station register statistically significant relations. Non-statistically significant correlation between the small-amplitude FDs and solar-geomagnetic variables were obtained at South Pole (SOPO) station, with the exception of FD-SWS that reveals statistically significant correlation. The differences in the correlation results obtained at the two stations (PTFM and SOPO) could be attributed to the differences in the characteristics of the NM stations. These results suggest that geomagnetic storm indices play important role in the evolution of FDs. [ABSTRACT FROM AUTHOR]

Solar cycle 24 began in December 2008 and ended in December 2019. Maximum of solar cycle 24 occurred in April 2014. Magnetic field intensity has been reported via data from the Wilcox Solar Observatory. Sunspot numbers are reported via the data from WDC-SILSO, Royal Observatory of Belgium. Sunspot area distribution was determined using the data from the Max Planck Institute. Flare Index intensity is indicated, and the data recorded by the Kandilli Observatory at Bogazici University is presented. Hemisphere asymmetries in terms of sunspots and solar flare index are calculated. The number of solar flares that occur at the highest intensity (X-class) during this cycle are presented, the data for which from the NOAA/SWPC. The characteristics of Coronal Mass Ejections are given, as determined using the LASCO coronagraph operating on the SOHO mission. Solar radio flux distribution and comparison with previous cycles was studied using data from Space Weather Canada. [ABSTRACT FROM AUTHOR]

Understanding and predicting the geoeffectiveness of solar activity on Earth is crucial for space weather. Therefore, predicting the impact of coronal mass ejections (CMEs) and their associated interplanetary (IP) shocks on Earth is essential. Observations of CMEs near the Sun can be used for these prediction and to study their propagation and evolution in IP space. Commonly used international models do not accurately predict whether and when IP shocks would reach Earth, thus failing to meet the demands of space weather forecasting. This study investigated the geoeffectiveness of solar-IP disturbance events, focusing on type II radio bursts from 1996 to 2019 (solar cycles 23 and 24). The study results showed that during this period, Wind/WAVES detected 623 type II bursts and 541 IP shocks at the L1 point, where 181 type II bursts were associated with L1 shocks. Approximately 29% of the IP shocks associated with type II bursts reached Earth, and approximately 34% of the IP shocks at the L1 point were accompanied by these bursts. IP type II radio bursts and their cutoff frequencies can serve as indicators of the geoeffectiveness of CMEs towards Earth. IP shocks accompanied by type II radio bursts cause stronger geomagnetic responses than those without the associated type II radio bursts. Lower cutoff frequencies of type II radio bursts increase the probability that the corresponding shocks reaching Earth, intensifying the geomagnetic response of the shock. Consequently, the presence of IP type II radio bursts and can serve as indicators of geoeffectiveness of the Earth-directed CMEs. Further, they help improve the accuracy of forecasting the geoeffectiveness of CME/shock events towards Earth.

Abstract We report a rare regime of Earth's magnetosphere interaction with sub‐Alfvénic solar wind in which the windsock‐like magnetosphere transforms into one with Alfvén wings. In the magnetic cloud of a Coronal Mass Ejection (CME) on 24 April 2023, NASA's Magnetospheric Multiscale mission distinguishes the following features: (a) unshocked and accelerated low‐beta CME plasma coming directly against Earth's dayside magnetosphere; (b) dynamical wing filaments representing new channels of magnetic connection between the magnetosphere and foot points of the Sun's erupted flux rope; (c) cold CME ions observed with energized counter‐streaming electrons, evidence of CME plasma captured due to by reconnection between magnetic‐cloud and Alfvén‐wing field lines. The reported measurements advance our knowledge of CME interaction with planetary magnetospheres, and open new opportunities to understand how sub‐Alfvénic plasma flows impact astrophysical bodies such as Mercury, moons of Jupiter, and exoplanets close to their host stars.

This study addresses the limitations of single‐viewpoint observations of Coronal Mass Ejections (CMEs) by presenting results from a 3D catalog of 360 CMEs during solar cycle 24, fitted using the Graduated Cylindrical Shell (GCS) model. The data set combines 326 previously analyzed CMEs and 34 newly examined events, categorized by their source regions into active region (AR) eruptions, active prominence (AP) eruptions, and prominence eruptions (PE). Estimates of errors are made using a bootstrapping approach. The findings highlight that the average 3D speed of CMEs is ∼1.3 times greater than the 2D speed. PE CMEs tend to be slow, with an average speed of 432 km s−1. AR and AP speeds are higher, at 723 and 813 km s−1, respectively, with the latter having fewer slow CMEs. The distinctive behavior of AP CMEs is attributed to factors like overlying magnetic field distribution or geometric complexities leading to less accurate GCS fits. A linear fit of projected speed to width gives a gradient of ∼2 km s−1 deg−1, which increases to 5 km s−1 deg−1 when the GCS‐fitted 'true' parameters are used. Notably, AR CMEs exhibit a high gradient of 7 km s−1 deg−1, while AP CMEs show a gradient of 4 km s−1 deg−1. PE CMEs, however, lack a significant speed‐width relationship. We show that fitting multi‐viewpoint CME images to a geometrical model such as GCS is important to study the statistical properties of CMEs, and can lead to a deeper insight into CME behavior that is essential for improving future space weather forecasting. Plain Language Summary: Space weather refers to the changing conditions in space, largely influenced by massive eruptions from the Sun. We call these eruptions "Coronal mass ejections" or "CMEs." Earth‐directed CMEs produce geomagnetic storms that affect our satellites, communication systems, and power grids, causing disruptions in our technology and infrastructure. Hence, how fast CMEs move and how wide they are in 3D space is crucial to predicting their arrival on Earth. To trace these eruptions in 3D, we use a geometrical model on a large set of CMEs during low and high solar activity from different angles, like figuring out the path of a flying bird from different angles. Derived 3D characteristics such as speed and width (size) compared to the values obtained from one angle (like watching the bird from only one spot) gives us a better idea of how fast they are going. Some eruptions were slow, while others were faster. The bigger the eruption, the faster it tends to be. Our results highlight that the 3D aspect of CMEs is crucial for issuing timely warnings and taking necessary precautions to safeguard our technology and prevent potential damages caused by space weather events. Key Points: Presents a large multi‐viewpoint data set containing 3D (true) speeds, 3D (true) widths, locations, and source regions of 360 Coronal Mass Ejections (CMEs) observed during the solar cycle 24Statistical analysis of true speed and width of CMEs with and without source region separation is compared to the projected valuesCorrected speed and width to be used as initial conditions in space weather forecasting models for better arrival time predictions at Earth [ABSTRACT FROM AUTHOR]

The polytropic behavior describes the relationship between macroscopic properties of plasma species and provides useful information in understanding physical mechanisms in space plasma. Through the value of the polytropic index, which governs the polytropic relationship, we can identify the energy transfer in plasma systems. In this paper, we determine the polytropic index of proton plasma within an Interplanetary Coronal Mass Ejection (ICME), which has been observed by three different spacecraft at ∼ 1 AU, each separated by ∼ 20 ∘ degrees in longitude during the analyzed observations. By performing this multi-spacecraft analysis, we provide evidence that the polytropic index does not vary significantly across the structure of the observed ICME. This may imply that the ICME evolution process is nearly coherent. Moreover, the polytropic index values we derive here can set boundary conditions in existing and future ICME evolution models. [ABSTRACT FROM AUTHOR]

Interplanetary scintillation (IPS) is a useful tool for detecting coronal mass ejections (CMEs) throughout interplanetary space. Global magnetohydrodynamic (MHD) simulations of the heliosphere, which are usually used to predict the arrival and geo-effectiveness of CMEs, can be improved using IPS data. In this study, we demonstrate an MHD simulation that includes IPS data from multiple stations to improve CME modelling. The CMEs, which occurred on 09–10 September 2017, were observed over the period 10–12 September 2017 using the Low-Frequency Array (LOFAR) and IPS array of the Institute for Space-Earth Environmental Research (ISEE), Nagoya University, as they tracked through the inner heliosphere. We simulated CME propagation using a global MHD simulation, SUSANOO-CME, in which CMEs were modeled as spheromaks, and the IPS data were synthesised from the simulation results. The MHD simulation suggests that the CMEs merged in interplanetary space, forming complicated IPS g-level distributions in the sky map. We found that the MHD simulation that best fits both LOFAR and ISEE data provided a better reconstruction of the CMEs and a better forecast of their arrival at Earth than from measurements when these simulations were fit from the ISEE site alone. More IPS data observed from multiple stations at different local times in this study can help reconstruct the global structure of the CME, thus improving and evaluating the CME modelling. [ABSTRACT FROM AUTHOR]

Observations of interplanetary scintillation (IPS – the scintillation of compact radio sources due to density variations in the solar wind) enable the velocity of the solar wind to be determined, and its bulk density to be estimated, throughout the inner heliosphere. A series of observations using the Low Frequency Array (LOFAR - a radio telescope centred on the Netherlands with stations across Europe) were undertaken using this technique to observe the passage of an ultra-fast CME which launched from the Sun following the X-class flare of 10 September 2017. LOFAR observed the strong radio source 3C147 at an elongation of 82 degrees from the Sun over a period of more than 30 h and observed a strong increase in speed to 900 km s−1 followed two hours later by a strong increase in the level of scintillation, interpreted as a strong increase in density. Both speed and density remained enhanced for a period of more than seven hours, to beyond the period of observation. Further analysis of these data demonstrates a view of magnetic-field rotation due to the passage of the CME, using advanced IPS techniques only available to a unique instrument such as LOFAR. [ABSTRACT FROM AUTHOR]

Type II radio bursts arise due to shocks typically driven by coronal mass ejections (CMEs). When these shocks propagate outward from the Sun, their associated radio emissions drift down in frequency as excited particles emit at the local plasma frequency, creating the usual type II patterns. In this work, we use dynamic spectra from the Wind/WAVES Thermal Noise Receiver (TNR) to identify type II radio emissions in the kilometric wavelength range (kmTIIs, f < 300 kHz ) between 1 January 2000 and 31 December 2012, i.e., over a solar cycle. We identified 134 kmTII events and compiled various characteristics for each of them. The finding of 45 kmTII events not reported by the official Wind/WAVES catalog (based on RAD1 and RAD2 data) is particularly important. We search for associations with interplanetary structures and analyze their main characteristics to reveal distinctive attributes that may correlate with the occurrence of kmTII emission. We find that the fraction of interplanetary coronal mass ejections (ICMEs) classified as magnetic clouds (MCs) that are associated with kmTIIs is roughly similar to that of MCs not associated with kmTIIs. Conversely, the fraction of ICMEs with bidirectional electrons is significantly larger for those ICMEs associated with kmTIIs (74% vs. 48%). Likewise, on average, ICMEs associated with kmTIIs are 23% faster. The disturbance storm time (Dst) mean value is almost twice as large for kmTII-associated ICMEs, indicating that they tend to produce intense geomagnetic storms. In addition, the proportion of ICMEs producing moderate to intense geomagnetic storms is twice as large for the kmTII-associated ICMEs. After this investigation, TNR data proved to be valuable not only as complementary data for the analysis of kmTII events but also for forecasting the arrival of shocks at Earth. [ABSTRACT FROM AUTHOR]

The magnetosphere is the outermost part of the Earth, formed by the interaction of the Earth's dipole magnetic field and the solar wind. Solar wind conditions depend on solar activity, which can affect space weather. One of the solar activities that significantly impact space weather is Coronal Mass Ejection (CME). The magnetosphere is observed using satellites in space-based and using a magnetometer on earth-based. However, these observations are limited to a specific location and time. In this work, we are interested in employing magnetohydrodynamics (MHD) to investigate the interaction of solar wind in the magnetosphere. The MHD has four equations: transfer of mass, momentum, magnetic, and thermal energy, which explain the four main parameters of the solar wind: density, velocity, magnetic field, and pressure, respectively. From these four parameters, the response of Earth's magnetosphere can be identified. Here, we used both analytical and numerical calculation via the SHASTA-FCT. The results show that the positive interplanetary magnetic field merges to Earth's magnetic field. However, the negative interplanetary magnetic field does not merge with Earth's magnetic field. We also observed that the higher solar wind speed results in the shorter simulation time. The bow shock as a result of the interaction of the solar wind and the Earth's magnetic field is formed at a distance of ∼ 50 , 000 km , and the magnetopause as a result of the equilibrium of the solar wind pressure and the pressure of the Earth's magnetic field has a thickness of ∼ 5000 km . In addition, we also discuss Alfvén velocity represents the motion of the magnetic field. [ABSTRACT FROM AUTHOR]

This study investigates the ionospheric response to a geomagnetic storm triggered by a Coronal Mass Ejection (CME) during 6–9 September 2017, across GPS stations located in diverse geographical regions. We analyze the changes in the magnetic field component (ΔH), the Prompt Penetration Electric Fields (PPEF), and the Total Electron Content (TEC). We find that ΔH exhibits latitude-dependent responses during the storm, with high-latitude stations experiencing more significant reductions compared to low-latitude stations. The PPEF behavior is found to be directly correlated with solar wind disturbances. Particularly during the main phase of the storm, fluctuations in PPEF were clearly associated with negative values in the Dst index. The KIRU station, located at a high latitude, shows the most pronounced PPEF effects, indicating the increased susceptibility of high-latitude regions to solar wind interactions. The time series plot of TEC, covering a full month at different stations, shows a distinct diurnal pattern driven by solar ionization. Equatorial stations such as HYDE, BOU, HON (HNLC), and DODM exhibit the highest daily TEC values. During the geomagnetic storm, TEC disturbances are evident across all stations, with significant disturbances and varying trends in TEC depletion rate observed at different locations. The TEC values differ by 5–25 TECU during the storm period, suggesting intricate ionospheric responses to geomagnetic storms at different stations. This highlights the importance of considering different geographical regions to fully understand the ionospheric dynamics related to solar activities.

Diffusion and electromagnetic mechanisms determine the formation of sporadic Forbush decreases. The diffusion mechanism affects the Forbush decrease amplitude in the turbulent layer, and the part of the coronal mass ejection preceding the magnetic cloud, and its efficiency depends on the level of magnetic field turbulence. The electromagnetic mechanism works in a magnetic cloud, and its efficiency depends on the intensity of regular magnetic and electric fields. We analyze solar wind parameters and cosmic ray density, using the superposed epoch analysis. In 1996–2006, 23 strong Forbush decreases (amplitude >5 %) were detected. The average amplitude of 7 % is equally formed by both mechanisms. The events can be divided into 2 groups depending on the contribution of the mechanisms to Forbush decrease amplitude. Group 1 includes the strongest Forbush decreases (amplitude=8.5 %), formed by both diffusion and electromagnetic mechanisms. The diffusion mechanism forms 0.26 amplitude, and the electromagnetic mechanism is responsible for 0.74 one. In group 2, the averege amplitude Forbush decrease =5.7 %, the diffusion mechanism forms 0.79 of amplitude; and the electromagnetic one, 0.21. The spatial distributions of the mean values of the medium parameters in the region of disturbances in the groups differ. This difference can be explained by the fact that Forbush decrease amplitude in groups 1 and 2 are formed in the central and peripheral parts of coronal mass ejection respectively.

We examine the Forbush decreases (FDs) associated with solar flares and coronal mass ejections (CMEs) from January 2008 to December 2019, covering the whole of Solar Cycle 24, and we compare them to our earlier study of Solar Cycle 23 (Bhatt and Chandra, Adv. Space Res. 71, 1098, 2023). On a sample of 56 events, we conducted a statistical analysis using solar and geomagnetic parameters to examine their effect on interplanetary space and the decrease in the galactic cosmic rays (GCR). Our research concentrated on an in-depth analysis of the two most significant events. The first event with an FD magnitude of 11.2% on 8 March 2012 and the second with an FD magnitude of 7.7% on 7 September 2017, respectively. We discovered that compared to other latitude bands, the northern 11 – 20° latitude band had the highest number of FD-associated flare events. We conducted a statistical analysis of FD magnitude, geomagnetic Dst-index, solar and interplanetary parameters. [ABSTRACT FROM AUTHOR]

We report ground-based measurements of the atmospheric electric field (Ez = −potential gradient (PG)) and current density (Jz) that were conducted at two locations in Israel. One is at the Emilio Segre cosmic ray station located on Mt. Hermon (34.45° N, 2020 m AMSL) in northern Israel near the Syrian-Lebanon border, and the other is at the Wise astronomical observatory in the Negev desert highland plateau of southern Israel (31.18° N, 870 m AMSL). We searched for possible effects of strong, short-term solar events on the potential gradient and the vertical current density, as disruptions to the global electric circuit are often observed following strong solar events. The first case study (St. Patrick's Day, 17 March 2015) was classified as the strongest event of 2015. The second case study (8 September 2017) was categorized as the strongest event of 2017 and one of the twenty strongest events on record to date. The results show that the electrical parameters measured at ground level at both stations were not affected during the two massive proton events and the ensuing geomagnetic storms. The magnetospheric shielding in lower latitudes is strong enough to shield against the flux of energetic particles from solar events, obscuring any impact that may be noticeable above the local daily variations induced by local meteorological conditions (aerosol concentrations, clouds, high humidity, and wind speed), which were investigated as well. [ABSTRACT FROM AUTHOR]

The solar surface activity produces space weather. Solar flares, coronal mass ejections (CMEs), and coronal holes are examples of solar activity phenomena that can compress the magnetosphere and cause a geomagnetic storm. Previous studies have indicated that these solar events disturb the near-Earth region. This study examines the behavior of the terrestrial geomagnetic field (H-component) and focuses on how the geomagnetic index (SYM/H) responds to solar wind parameters related to solar activity. Results showed that on September 9, 2017, a powerful geomagnetic storm (SYM/H = 200 nT) was observed that was brought on by powerful solar flares, CMEs, and coronal holes that happened on September 7 and 8, 2017, which generated significant alterations in the magnetosphere's solar wind. On October 3 and 18, 2017, a moderate geomagnetic storm occurred, which resulted in a strong southbound situation with a high solar wind pressure that blasted high-density plasma due to CME associated with a coronal hole event into the magnetosphere. A moderate geomagnetic storm (SYM/H = 80 nT) on November 14, 2017, was triggered, according to findings, by a wider direction and high speed of CME with CIR event occurrence implies the accelerated large-scale solar wind that exacerbated the reconnection of the flowing interplanetary magnetic field into the inner magnetosphere. There were fewer injections of ions and energetic solar particles into the magnetosphere on December 12, 2017, which were thought to be a source of a weak geomagnetic storm(SYM/H = 49 nT). Additionally, the response of solar wind parameters and geomagnetic storm due to solar flare, CMEs and coronal holes to the modest drop in the ground geomagnetic field resulted in H-component reading at the RAN and DLT station. This study has contributed to the study of earthquake precursors in ultra-low frequency (ULF) emission with the effect of solar wind. [ABSTRACT FROM AUTHOR]

We explore the correlation between different parameters of space weather events associated with intense geomagnetic disturbances that occurred during the solar cycles (SCs) 23 and 24 (1996–2019). The space weather events under this study are the Solar Flares (SFs), Coronal Mass Ejections (CMEs), Geomagnetic Storms (GSs), Solar Energetic Protons (SEPs) and Electrons (SEEs), respectively. The severity of the GSs is identified based on the Dst ⩽ - 100 nT and a list of 111 GSs with their associated space weather counterparts is obtained over the pre-selected time period. The utilized association procedure between the different space weather events is described and their observed properties are listed. For the performed analysis, Pearson correlation metrics is employed. The results are summarized and discussed. [ABSTRACT FROM AUTHOR]

The ionospheric total electron content (TEC) response during the St. Patrick's Day geomagnetic storm of 2015 (max Kp = 8) is an interest of study in the field of space weather since it is the strongest geomagnetic storm of Solar Cycle 24. The cause of this storm is a coronal mass ejection (CME) from the Sun on 15 Mar 2015 recorded by SOHO/LASCO and arrived at ~ 05:00 UT 17 Mar 2015. The CME speed is estimated at ~ 668 km/s. At the initial phase of the storm, the disturbance storm time (Dst) index rose from 15 nanoteslas nT at 03:21-56 nT at 05:31 UT. The main phase of the storm caused the Dst index to drop to the minimum value of -223 nT from 05:31-22:33 UT on 17 Mar 2015. In the Philippine-Taiwan sector, TEC during the main phase was enhanced by ~ 25 TECU on 10 GNSS receiver stations and was depleted afterward with a maximum depletion of ~ 33 TECU on PBAS. The recovery phase showed a TEC depletion on all stations for the whole day. The minimum dTEC (differential TEC) is observed at PBAS (Basco, Batanes, Philippines), and the maximum percent depletion is observed at TWTF (Taoyuan, Taiwan) during the early hours of photoionization. Results from this study verified that GNSS TEC measurements along Asian sectors dropped significantly during St. Patrick's geomagnetic storm. [ABSTRACT FROM AUTHOR]

The unexpected observation of a sudden expulsion of mass through the solar corona in 1971 opened up a new field of interest in solar and stellar physics. The discovery came from a white-light coronagraph, which creates an artificial eclipse of the Sun, enabling the viewing of the faint glow from the corona. This observation was followed by many more observations and new missions. In the five decades since that discovery, there have been five generations of coronagraphs, each with improved performance, enabling continued understanding of the phenomena, which became known as Coronal Mass Ejection (CME) events. The conceptualization of the CME structure evolved from the elementary 2-dimensional loop to basically two fundamental types: a 3-dimensional magnetic flux rope and a non-magnetic eruption from pseudo-streamers. The former persists to 1 AU and beyond, whereas the latter dissipates by 15 R⊙. Historically, most of the studies have been devoted to understanding the CME large-scale structure and its associations, but this is changing. With the advent of the fourth and fifth coronagraph generations, more attention is being devoted to the their internal structure and initiation mechanisms. In this review, we describe the evolution of CME observations and their associations with other solar and heliospheric phenomena, with one of the more important correlations being its recognition as a driver of space-weather. We conclude with a brief overview of open questions and present some ideas for future observations.

SiRGraF Integrated Tool for Coronal dynaMics (SITCoM) is based on the Simple Radial Gradient Filter used to filter the radial gradient in the white-light coronagraph images and bring out dynamic structures. SITCoM has been developed in Python and integrated with SunPy and can be installed by users with the command pip install sitcom. This enables the user to pass the white-light coronagraph data to the tool and generate radially filtered output with an option to save in various formats as required. We implemented the functionality of tracking the transients such as coronal mass ejections, outflows, and plasma blobs, using height–time plots and deriving their kinematics. In addition, SITCoM also supports oscillation and wave studies such as for streamer waves. This is performed by creating a distance–time plot at a user-defined location (artificial slice) and fitting a sinusoidal function to derive the properties of waves, such as time period, amplitude, and damping time (if any). We provide the option to manually or automatically select the data points to be used for fitting. SITCoM is a tool to analyze some properties of coronal dynamics quickly. We present an overview of the SITCoM with the applications for deriving coronal dynamics’ kinematics and oscillation properties. We discuss the limitations of this tool along with prospects for future improvement.

Predicting non‐recurrent geomagnetic storms caused by Coronal Mass Ejection (CME) is important and necessary for space weather forecasting. Previous studies have shown that it is feasible to predict non‐recurrent geomagnetic storms by reconstructing precursors from cosmic ray intensity (CRI) in the frequency domain. However, the difficulty lies in predicting the minor storms, the moderate storms, and the storms accompanying ground level enhancement (GLE). This study proposes a new method that includes the spectral whitening method and CEEMDAN‐CWT for predicting non‐recurrent geomagnetic storms. The method was applied to 229 CME‐driven events, including 166 events with Kp ≥ 5 and 63 events with Kp < 5, during the solar cycles 23 and 24. This study analyzed 166 geomagnetic storm events and found that 129 of them were accurately predicted, resulting in a recall rate of 77.7%. Additionally, the study found that as the Kp index increased, the amplitude of the precursor detected by this method also increased, while the time interval between the onset of CME and the maximum amplitude of the precursor decreased. Plain Language Summary: The cosmic ray traveling in interplanetary will be modulated by Coronal Mass Ejections (CMEs), which could trigger non‐recurrent geomagnetic storms. Previous works have proved that the variation of cosmic ray intensity (CRI) in the frequency domain caused by CME could indicate the onset of non‐recurrent geomagnetic storms. However, the weaker variations of CRI in the frequency domain will be masked by the periodic signal of CRI and the influence of GLE so that some non‐recurrent geomagnetic storms can't be predicted. This paper presents a new method to investigate 229 CME‐driven events during the 23rd and 24th solar activity cycles. The new method is found to be effective in predicting non‐recurrent geomagnetic storms, regardless of the strength of geomagnetic storms and the influence of GLE. In addition, the amplitude of precursor extract using this method varies with the Kp index, indicating the strength of the non‐recurrent geomagnetic storms. Key Points: A new method was proposed to predict non‐recurrent geomagnetic storms caused by coronal mass ejections (CME)We have investigated 229 CME‐driven events, and 129 events were successfully predicted among 166 geomagnetic storm eventsWith the increase of the geomagnetic activity index, the amplitude of the precursor increased [ABSTRACT FROM AUTHOR]

In order to advance our understanding of the dynamic interactions between coronal mass ejections (CMEs) and the magnetized solar wind, we investigate the impact of magnetic erosion on the well-known aerodynamic drag force acting on CMEs traveling faster than the ambient solar wind. In particular, we start by generating empirical relationships for the basic physical parameters of CMEs that conserve their mass and magnetic flux. Furthermore, we examine the impact of the virtual mass on the equation of motion by studying a variable-mass system. We next implement magnetic reconnection into CME propagation, which erodes part of the CME magnetic flux and outer-shell mass, on the drag acting on CMEs, and we determine its impact on their time and speed of arrival at 1 AU. Depending on the strength of the magnetic erosion, the leading edge of the magnetic structure can reach near-Earth space up to ≈ three hours later, compared to the non-eroded case. Therefore, magnetic erosion may have a significant impact on the propagation of fast CMEs and on predictions of their arrivals at 1 AU. Finally, the modeling indicates that eroded CMEs may experience a significant mass decrease. Since such a decrease is not observed in the corona, the initiation distance of erosion may lie beyond the field-of-view of coronagraphs (i.e. 30 R ⊙ ). [ABSTRACT FROM AUTHOR]

We have studied and compared kinematic characteristics of the motion of coronal mass ejections (CMEs) in three-dimensional (3D) space for three groups of CMEs for the period 2008–2014. These CME groups include: (i) stealth CMEs, (ii) CMEs that originate on the front side of the Sun (for an observer on Earth) and are associated with X-ray flares and filament eruption, (iii) all CMEs registered during the given period. Stealth CMEs are CMEs that emerge on the front side of the Sun and are unrelated to X-ray flares, as well as to filament eruption. We compare kinematic and some physical characteristics of these CMEs with those of a separate group of CMEs, classified as stealth in [D’Huys et al., 2014]. After comparing the characteristics of the three CME groups (i)–(iii), we concluded that stealth CMEs have, on average, the lowest velocity, kinetic energy, mass and angular size, central position angle, and also the angle φ between the direction of CME motion in the ecliptic plane and the Sun–Earth line and the angle λ between the direction of CME motion in 3D space and the ecliptic plane. We also discuss distributions of CMEs of different types by kinematic characteristics.

The efficacy of coronal mass ejection (CME) observations as a key input to space weather forecasting is explored by comparing on and off Sun‐Earth line observations from the ESA/NASA SOHO and NASA STEREO spacecraft. A comparison is made of CME catalogs based on L1 coronagraph imagery and off Sun‐Earth line coronagraph and heliospheric imager observations, for the year 2011. Analysis reveals inconsistencies in the identification of a number of potentially Earth‐directed CMEs. The catalogs reflect our ability to identify and characterize CMEs, so any discrepancies can impact our prediction of Earth‐directed CMEs. We show that 15 CMEs, which were observed by STEREO, that had estimated directions compatible with Earth‐directed events, had no identified halo/partial halo counterpart listed in the L1 coronagraph CME catalog. In situ data confirms that for 9 of these there was a consistent L1 Interplanetary CME (ICME). The number of such "discrepant" events is significant compared to the number of ICMEs recorded at L1 in 2011, stressing the need to address space weather monitoring capabilities, particularly with the inclusion of off Sun‐Earth line observation. While the study provides evidence that some halo CMEs are simply not visible in near‐Earth coronagraph imagery, there is evidence that some halo CMEs viewed from L1 are compromised by preceding CME remnants or the presence of multiple‐CMEs. This underlines (a) the value of multiple vantage point CME observation, and (b) the benefit of off Sun‐Earth line platform heliospheric imaging, and coronagraph imaging, for the efficient identification and tracking of Earth‐directed events. Plain Language Summary: Coronal Mass Ejections (CMEs) can impact human activities and technological assets and are continuously monitored by dedicated space weather operations centers. This study identifies inconsistencies between the identification of potentially Earth‐directed CMEs in observations made from a near Earth vantage point and those made from off the Sun‐Earth line. Almost a third of a set of potentially Earth‐directed CMEs that were identified in an off Sun‐Earth line heliospheric imager catalog from 2011, which were subsequently evidenced as Interplanetary CMEs (ICMEs) in in situ data near Earth, were not cataloged as halo or partial halo events in near Earth coronagraph imagery. Given the number of such discrepant events, compared to the total number of ICMEs recorded near Earth in 2011, it is important to understand the inconsistencies and to ensure that future space weather monitoring strategies cater for them. Key Points: The identification of Earth‐directed coronal mass ejections (CMEs) is compared for observations from L1 and off the Sun‐Earth line, for 2011We show a number of CMEs identified as Earth directed, with consistent in situ Interplanetary CME (ICME) data, with no identification from L1 dataGiven the number of ICMEs recorded at L1 in 2011, the number of inconsistent events is of concern [ABSTRACT FROM AUTHOR]

This research aims to examine the multiscale‐multifractal correlation properties between the geomagnetic storm and coronal mass ejection (CME) occurrences by analyzing the CME linear speed and Planetary K‐index time series data. The relevant data for both CME and geomagnetic storm occurrences were obtained from the Solar and Heliospheric Observatory mission's LASCO and the NOAA Space Weather Prediction Center, respectively, for the same period (February 1999 to December 2007). We performed MultiFractal cross‐correlation Detrended Fluctuation Analysis (MFXDFA) and Multifractal cross‐correlation Detrending Moving average Analysis (MFXDMA) to investigate and quantify the possible cross‐correlation between the two natural events. The MFXDFA technique is also compared to the backward MFXDMA algorithm's performance. The change in the degree of cross‐correlation over time has been investigated, and the findings are quantitatively analyzed. The existence of significant power‐law cross‐correlations has been discovered within all scaling orders. Furthermore, we also find evident persistence of cross‐correlation with substantial Hurst exponents. In addition, it has been observed that long‐term cross‐correlation has a more considerable degree of multifractality and persistence than short‐term cross‐correlation. [ABSTRACT FROM AUTHOR]

Interpreting multi-spacecraft heliospheric observations of the evolving solar wind (SW) streams with propagating and interacting coronal mass ejections (CMEs) is challenging. Numerical simulations can provide global context and suggest what may and may not be observed. The heliospheric three-dimensional (3D) magnetohydrodynamic (MHD) ENLIL model can provide a near-real-time prediction of heliospheric space weather, and it is used at NASA Community Coordinated Modeling Center (CCMC), NOAA Space Weather Prediction Center (SWPC), and UK Meteorological Office (MetOffice). However, this version does not show its full potential, especially in the case of multi-CME events observed by various spacecraft. We describe tools developed to interpret remote observations and in-situ measurements better and apply them to multi-CME events observed by ACE, STEREO-A, Parker Solar Probe (PSP), BepiColombo, and Solar Orbiter. We present some results on 1) global structures of the SW speed and density at the ecliptic, 2) the evolution of SW parameters at the spacecraft, 3) magnetic field connectivity at the spacecraft, 4) automatic detection of shock parameters and alert plots, and 5) synthetic white-light (WL) imaging. This paper is not on model initialization or analyzing specific CME events, but it describes features not used at space weather prediction centers and provided by NASA/CCMC Run-On-Request service. This paper advertises new tools and shows their benefits when applied to selected heliospheric space weather events observed at near-Earth, PSP, Solar Orbiter, and STEREO-A spacecraft.

In the early hours of 2021 April 25, the Solar Probe Cup on board Parker Solar Probe registered the passage of a solar wind structure characterized by a clear and constant He2+/H+ density ratio above 6% during three hours. The He2+ contribution remained present but fainting and intermittent within a twelve-hour window. Solar Orbiter and Parker Solar Probe were in nearly perfect quadrature, allowing for optimal observing configuration in which the material impacting the Parker Solar Probe was in the Solar Orbiter plane of the sky and visible off the limb. In this work, we report the journey of the helium-enriched plasma structure from the Sun to the Parker Solar Probe by combining multi-spacecraft remote-sensing and in situ measurements. We identify an erupting prominence as the likely source, behind the Sun relative to the Earth, but visible to multiple instruments on both the Solar-Terrestrial Relations Observatory-A and Solar Orbiter. The associated CME was also observed by coronagraphs and heliospheric imagers from both spacecrafts before reaching the Parker Solar Probe at 46 R⊙, 8 h after the spacecraft registered a crossing of the heliospheric current sheet. Except for extraordinary helium enhancement, the CME showed ordinary plasma signatures and a complex magnetic field with an overall strength enhancement. The images from the Wide-field Imager for Solar Probe (WISPR) aboard Parker Solar Probe show a structure entering the field of view a few hours before the in situ crossing, followed by repetitive transient structures that may be the result of flying through the CME body. We believe this to be the first example of a CME being imaged by WISPR directly before and during being detected in situ. This study highlights the potential of combining the Parker Solar Probe in situ measurements in the inner heliosphere with simultaneous remote-sensing observations in (near) quadrature from other spacecrafts.

Interplanetary scintillation (IPS) refers to random fluctuations in radio intensity of distant small-diameter celestial object, over time periods of the order of 1 s. The scattering and scintillation of emergent radio waves are ascribed to turbulent density irregularities transported by the ubiquitous solar wind streams. The spatial correlation length of density irregularities and the Fresnel radius of radio diffraction are two key parameters in determining the scintillation pattern. Such a scintillation pattern can be measured and correlated between multi-station radio telescopes on the Earth. Using the “phase-changing screen” scenario based on the Born approximation, the bulk-flow speed and turbulent spectrum of the solar wind streams can be extracted from the single-station power spectra fitting and the multi-station cross-correlation analysis. Moreover, a numerical computer-assisted tomography (CAT) model, iteratively fit to a large number of IPS measurements over one Carrington rotation, can be used to reconstruct the global velocity and density structures in the inner heliosphere for the purpose of space weather modelling and prediction. In this review, we interpret the underlying physics governing the IPS phenomenon caused by the solar wind turbulence, describe the power spectrum and cross correlation of IPS signals, highlight the space weather application of IPS-CAT models, and emphasize the significant benefits from international cooperation within the Worldwide IPS Stations (WIPSS) network.

One of the goals of Space Weather studies is to achieve a better understanding of impulsive phenomena, such as Coronal Mass Ejections (CMEs), to improve our ability to forecast their propagation characteristics and mitigate the risks to our technologically driven society. The essential part of achieving this goal is to assess the performance of forecasting models. To this end, the quality and availability of suitable data are of paramount importance. In this work, we merged publicly available data of CMEs from both in-situ and remote observations in order to build a dataset of CME properties. To evaluate the accuracy of the dataset and confirm the relationship between in-situ and remote observations, we have employed the Drag-Based Model (DBM) due to its simplicity and modest consumption of computational resources. In this study, we have also explored the parameter space for the drag parameter and solar wind speed using a Monte Carlo approach to evaluate how efficiently the DBM determines the propagation of CMEs for the events in the dataset. The geoeffective CMEs selected as a result of this work are compliant with the hypothesis of DBM (isolated CME, constant solar wind speed beyond 20 R⊙) and also yield further insight into CME features such as arrival time and arrival speed at L1 point, lift-off time, speed at 20 R⊙ and other similar quantities. Our analysis based on the acceptance rate in the DBM inversion procedure shows that almost 50% of the CME events in the dataset are well described by DBM as they propagate in the heliosphere. The dataset includes statistical metrics for the DBM model parameters. The probability distribution functions (PDFs) for the free parameters of DBM have been derived through a Monte Carlo-like inversion procedure. Probability distribution functions obtained from this work are comparable to PDFs employed in previous works. The analysis showed that there exist two different most probable values (median values) of solar wind speed for DBM input based on slow (wslow ≈ 386 km/s) and fast (wfast ≈ 547 km/s) solar wind type. The most probable value for the drag parameter (γ ≈ 0.687 × 10−7 km−1) in our study is somewhat higher than the values reported in previous studies. Using a data-driven approach, this procedure allows us to present a homogeneous, reliable, and robust dataset for the investigation of CME propagation. Additionally, possible CME events are identified where the DBM prediction is not valid due to model limitations and higher uncertainties in the input parameters. These events require further thorough investigation in the future.

The shape and dynamics of coronal mass ejections (CMEs) vary significantly based on the instrument and wavelength used. This has led to significant debate about the proper definitions of CME/shock fronts, pile-up/compression regions, and core observations in projection in optically thin vs. optically thick emission. Here we present an observational analysis of the evolving shape and kinematics of a large-scale CME that occurred on May 7, 2021 on the eastern limb of the Sun as seen from 1 AU. The eruption was observed continuously, consecutively by the Atmospheric Imaging Assembly (AIA) telescope suite on the Solar Dynamics Observatory (SDO), the ground-based COronal Solar Magnetism Observatory (COSMO) K-coronagraph (K-Cor) on Mauna Loa, and the C2 and C3 telescopes of the Large Angle Solar Coronagraph (LASCO) on the Solar and Heliospheric Observatory (SoHO). We apply the updated multi-instrument version of the recently developed Wavetrack Python suite for automated detection and tracking of coronal eruptive features to evaluate and compare the evolving shape of the CME front as it propagated from the solar surface out to 20 solar radii. Our tool allows tracking features beyond just the leading edge and is an important step towards semi-automatic manufacturing of training sets for training data-driven image segmentation models for solar imaging. Our findings confirm the expected strong connection between EUV waves and CMEs. Our novel, detailed analysis sheds observational light on the details of EUV wave-shock-CME relations that lacking for the gap region between the low and middle corona.

Coronal mass ejection (CME) is a kind of space weather phenomenon caused by the intense activity of the sun. Important issues of concern to the space weather community include understanding the propagation and evolution of a particular CME in the corona and interplanetary space, forecasting whether and when it will reach the earth orbit, and predicting the change of solar wind state in near-earth space. CME always carries a vast amount of energy. When it reaches space near the earth, it will cause a severe disturbance, and trigger catastrophic space weather events, such as the geomagnetic storm. In order to utilize space resources and develop space science more deeply, avoid the damage of severe space weather caused by CME, it is important to improve the accuracy and efficiency of CME forecasting. Numerical simulation is one of the practical tools for the study and prediction of CME's propagation.This review introduces the different models used in the CME propagation simulations and their latest research progress. Firstly, we summarize the various CME propagation simulation models including background solar wind models, CME initialization models, and coronal magnetic field reconstruction models. The outline of the application and research progress of these models in the propagation simulation is also presented. Then, we review the simulation studies on the deflection of CME, including the deflection in the corona and its interaction with CIR. The relationship between CMEs and their simulation is then discussed. Finally, based on this research, we propose the problems that need to be solved in the CME propagation simulation research and give a few prospects.

Analysis of seven near-limb coronal mass ejections (CMEs) has shown that at distances R

From 29 January to 7 February 2022, the heliosphere was structured with large-scale interacting substructures that appeared with significant dissimilarities at distant observations separated longitudinally by ∼34°. Probing the complexity of the structured heliosphere with multi-point in situ and imaging observations by using a fleet of spacecraft has revealed many unknown facts on the dynamics of large-scale structures in the heliosphere. In this paper, we investigate a complex-structured heliosphere by analyzing the Sun, solar corona, and solar wind with remote and in situ observations aided by heliospheric modeling. We identified multiple flux ropes (FRs) associated with large expulsions of magnetized plasma-coronal mass ejections, from the same solar source in a three-day interval, an interplanetary wave shock, and a sheath in front of the FRs. In situ observations displayed a stream interaction region behind FRs formed due to the overtaking of different-speed solar winds. This high-speed stream originated from a coronal hole located southeast of the coronal mass ejection solar source. We find evidence of merging FRs, FR deflection due to the presence of the nearby coronal hole, and FR’s unalike structural appearance at distant multi-point observations obtained at 1 au. This complex-structured heliosphere resulted in multiple G1-class geomagnetic storms when interacting with Earth’s magnetosphere. Thus, the study focuses on the reconstruction of the structured heliosphere based on observations and modeling. It highlights the importance of multi-point observations in understanding the global configuration and disparity in the local nature of a structured heliosphere.

There continue to be open questions regarding the solar wind and coronal mass ejections (CMEs). For example: how do magnetic fields within CMEs and corotating/stream interaction regions (CIRs/SIRs) evolve in the inner heliosphere? What is the radially distributed magnetic profile of shock-driving CMEs? What is the internal magnetic structure of CMEs that cause magnetic storms? It is clear that these questions involve the magnetic configurations of solar wind and transient interplanetary plasma structures, for which we have limited knowledge. In order to better understand the origin of the magnetic field variability in steady-state structures and transient events, it is necessary to probe the magnetic field in Earth-directed structures/disturbances. This is the goal of the Multiview Observatory for Solar Terrestrial Science (MOST) mission (Gopalswamy et al., 2022). For MOST to answer the aforementioned questions, we propose the instrument concept of the Faraday Effect Tracker of Coronal and Heliospheric structures (FETCH), a simultaneous quad-line-of-sight polarization radio remote-sensing instrument. With FETCH, spacecraft radio beams passing through the Sun–Earth line offer the possibility of obtaining information of plasma conditions via analysis of radio propagation effects such as Faraday rotation and wave dispersion, which provide information of the magnetic field and total electron content (TEC). This is the goal of the FETCH instrument, one of ten instruments proposed to be hosted on the MOST mission. The MOST mission will provide an unprecedented opportunity to achieve NASA’s heliophysics science goal to “explore and characterize the physical processes in the space environment from the Sun” (Gopalswamy et al., 2022).

The predictions of plasma parameters in the interplanetary medium are the core of space weather forecasts, and the magnetohydrodynamics (MHD) numerical simulation is an important tool in the prediction of plasma parameters. Operational space weather forecasts are commonly produced by a heliosphere model whose inner boundary is set at 18 Rs or beyond. Such predictions typically use empirical/physics-based inner boundary conditions to solve the MHD equations for numerical simulation. In recent years, significant progress has been made in the numerical modeling of the inner heliosphere. In this paper, the numerical modeling of solar wind and coronal mass ejection in the inner heliosphere is reviewed. In particular, different inner boundary conditions used in the simulation are investigated since the MHD solutions are predetermined by the treatment of the inner boundary conditions to a large extent. Discussion is made on further development of the heliosphere model.

Magnetic flux ropes manifest as twisted bundles of magnetic field lines. They carry significant amounts of solar mass in the heliosphere. This paper underlines the need to advance our understanding of the fundamental physics of heliospheric flux ropes and provides the motivation to significantly improve the status quo of flux rope research through novel and requisite approaches. It briefly discusses the current understanding of flux rope formation and evolution, and summarizes the strategies that have been undertaken to understand the dynamics of heliospheric structures. The challenges and recommendations put forward to address them are expected to broaden the in-depth knowledge of our nearest star, its dynamics, and its role in its region of influence, the heliosphere.

We report Forbush decreases (FD) in cosmic ray intensity from January 1996 to December 2008, the whole Solar Cycle 23rd. Statistical analysis is done for only 152 events for which associated solar flare position, flare classes, and Coronal Mass Ejections (CME) speed are given. We applied FD parameters taken from the Forbush Effects and Interplanetary Disturbances databases maintained by the Pushkov Institute of Terrestrial Magnetism, Ionosphere, and Radiowave Propagation (IZMIRAN), obtained by processing the data of the worldwide neutron monitor network using the global survey method (GSM) (A. Belov et al., 2018). For the said number of events, we examine their effect on interplanetary space and the decrease of the galactic cosmic rays (GCR) near Earth. We found that the 11–20° latitudinal belt shows more FD- associated flare events than the other latitudinal belts, and on this belt, the Southern hemisphere is more active. The results reveal that FDs and solar flares are well correlated. Statistical analysis is carried out for the magnitude of the CR decrease with solar and geomagnetic parameters. [ABSTRACT FROM AUTHOR]

Coronal mass ejection (CME) is the large scale magnetized plasmoid ejected from the Sun, which brings huge amount of magnetic flux and plasma into interplanetary space. An earthward CME will interact with the magnetosphere of the Earth, and invokes the substorm and the other phenomena of the space weather as it approaches to the Earth. The 2-dimensional data provided by the current observational techniques cannot describe the true magnetic structure and the plasma distribution of CMEs comprehensively. We need to look into the 3-dimensional structure and the associated three components of CME speeds in order to predict the time when an ICME (Interplanetary CME) reaches the Earth, and the potential consequent impact on the Earth and the nearby environment. In this paper, 3D reconstruction methods of CME based on existing imaging observations are introduced, including two kinds of reconstruction methods based on coronagraph data and heliosphere imager data, and CME-driven shock wave 3D reconstruction methods with high correlation with CME imaging reconstruction. Each method shows apparent advantages in dealing with specific events, but its weakness and necessary constrains to its applications exist as well. Results obtained via various methods are compared in this work, and we found that CME velocities and moving directions deduced from these methods are fairly close to one another, which shows high reliability of these methods. Finally, the hot topics related to the 3-dimensional reconstruction of CME (ICME) and the relevant development in reconstructing methods are also discussed. [ABSTRACT FROM AUTHOR]