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The launch of new spacecraft such as Parker Solar Probe or Solar Orbiter allow us to measure in-situ at different radial distances the physical magnitudes of ICMEs. With that, we are able to quantify the evolution of ICMEs and their substructures at a specific radial distance in order to better understand the interaction processes that occur with the background solar wind.Using multiple spacecraft covering the inner heliosphere, we extract plasma and magnetic field parameters from several ICMEs to relate the physical processes responsible for the formation of the different substructures. We present ICME case studies that prepare for a large statistical analysis.

The primary condition to produce eruptive solar flare events and solar energetic particles is the opening of magnetic field lines into interplanetary space. In that respect, real-time radio spectra cover important observational information with substantial lead time for space weather warnings. For Space Weather forecasting an objective detection of radio type III and type II bursts is key. We present an algorithm using multiple e-CALLISTO radio stations to detect a) type III bursts, distinguishing between confined and eruptive flares and b) type II bursts, identifying shocks produced by fast coronal mass ejections. We present statistical results for the detection rates and an outlook of the implementation of the algorithm to the e-CALLISTO station at the University of Graz in Austria as well as to the entire international network.

Parker Solar Probe (PSP) and Solar Orbiter (SolO) observe the Sun from unprecedented close-in orbits out of the Sun-Earth line. In combination with EUV imagery from STEREO and SDO, these unique and high-resolution data from different vantage points will give us new insights into the early evolution of coronal mass ejections (CMEs) in the low corona and inner heliosphere. For a case study, we apply 3D CME reconstruction methods to relate different CME substructures as observed in white-light coronagraphs like WISPR aboard PSP, to EUV off-limb structures for an erupting event. We interpret the results in terms of projection and Thomson scattering effects.

With a view to the rising solar cycle 25 (maximum expected to be 2025/26) the solar activity level will steadily increase, which implies that the Earth’s atmosphere is expanding, and higher drag forces are acting on near-Earth satellites. To avoid earlier re-entries of satellite missions it is mandatory to monitor and at best accurately forecast extreme space weather conditions. We investigated different kinds of coronal mass ejections (CMEs) which had divergent effects on the trajectories of low Earth orbiting satellites. A special focus is given to the interaction of sequentially occurring CME events (e.g., 2021/11/03). So called multiple events lead to multiple field compressions and a capable to increase the severity of the impact on the near-Earth environment. Furthermore, we investigated the predominant chemical composition of Earth atmosphere based on satellite observation from the TIMED satellite (SEE, SABER). Additionally, we explored identified diverging behavior of various CMEs by simulating the events with the Kompot code, a 1D first-principles hydrodynamic upper atmosphere model. We found that for some of the selected events the atmospheric exobase and density profile shows some significant expansion mainly based on the increased XUV flux from the Sun. However, we also found that the sole effect of the incident XUV flux might only partially explain NO production, and the structure of the upper atmosphere.

The COSPAR iSWAT (international Space Weather Action Teams) initiative is a global hub for collaborations addressing challenges across the field of space weather. We present the COSPAR Space Weather Roadmap update for the iSWAT clusters H1+H2 covering interplanetary space and its characteristics, with focus on large-scale corotating and transient structures impacting Earth. We review the physical background of different solar wind streams together with coronal mass ejections and the considerable efforts that have been made to model these phenomena. We outline the limitations coming from observations with rather large uncertainties, making reliable predictions of the structures impacting Earth difficult. Moreover, in the wake of the upcoming solar cycle 25, the increased complexity of interplanetary space with enhanced solar activity poses a challenge to models. The current paper presents the efforts and progress achieved in recent years, identifies open questions, and gives an outlook for the next 5-10 years.

Coronal mass ejections (CMEs) are the major eruptive phenomena that cause various space weather effects. CMEs can be deflected by coronal holes (CH) away or towards the Sun-Earth line depending on their relative location, and also the high speed streams from CH can influence CME propagation. Coronal dimmings which are away or toward the CH may also cause CME deflection. The main aim of our study is to analyse the deflection/rotation of CMEs by tracking them in COR1 and COR2 field of view of STEREO onboard SECCHI with the help of 3D reconstruction Graduated cylindrical shell (GCS) model. We analyse 60 Earth-directed CMEs and their associated low coronal signatures observed in SDO/AIA. In addition, with the help of CATCH tool we study the nearby coronal hole parameters. Furthermore, we analyze the associated coronal dimmings by considering the movement of secondary dimmings towards or away the nearby CH. Out of 60 events, 31 events show deflection/rotation, as we track them from 1.76R☉ to 20.8R☉. A small fraction of (11%) events show deflection in longitude, and a significant fraction of events show deflection in latitude (38%) and rotation (40%). We discuss these results with respect to the vicinity and direction of coronal holes.

Large scale solar wind (SW) structures called Coronal Mass Ejections (CMEs) and Stream Interaction Regions (SIRs) propagate through the interplanetary medium, where they might impact Earth and cause jet-like disturbances in the magnetosheath. Such jets are short scale structures characterized by an enhancement in dynamic pressure that propagate through the Earth’s magnetosheath (EMS) transporting mass, momentum and energy being able to affect and perturb the Earth’s magnetosphere.Jets have been studied for 20 years, but how different SW conditions triggered by CMEs and SIRs affect jet production is a topic that has only recently begun to be studied. In this work we characterize jets observed by THEMIS during a CME and a SIR passage. We find clear differences in number and size between the jets associated with the CME regions arriving at the EMS as well as in comparison with the characteristics of jets associated with the SIR passage. Comparing WIND and THEMIS data we discuss how these differences are linked to the SW conditions in the context of a recent statistical study (Koller et al. 2022) and with different jet generation mechanisms.

Geomagnetic storms are capable of triggering thermospheric density variations which in turn have an influence on the trajectory of low Earth orbiting satellites (LEO). The strongest of these disturbances of the thermosphere are caused by interplanetary coronal mass ejections (ICMEs). Due to increases in the neutral mass density during such ICME induced geomagnetic storms the altitude of satellites will decrease. Therefore, ICME induced orbit decays are important for long-term orbit prediction as well as short-term as the prominent example of the so called ‘Starlink’ event of February 2022 showed where 40 satellites reentered the atmosphere. In order to calculate the ICME induced orbit decay we calculated the thermospheric neutral mass density through the deceleration due to drag. This is done either with an observation approach using the high orbiting global navigation satellite system (GNSS) or calibrated data from onboard accelerometers. We then relate the solar wind plasma and magnetic field measurements taken at L1 from the ACE (Advanced Composition Explorer) and the DSCOVR (Deep Space Climate Observatory) satellites to the calculated ICME induced orbit decays. 299 ICMEs occurred during the operation of the GRACE (Gravity Recovery And Climate Experiment) satellite which orbits at an altitude of around 490 km. Analysis of the ICME induced orbit decays and the interplanetary magnetic field at L1 show a strong correlation as well as a time delay between the ICME and the associated thermospheric response of around 15 hours on average. This correlation is implemented in the real time forecasting tool SODA (Satellite Orbit DecAy). Because the ICME induced orbit decay strongly depends on the altitude we additionally processed data from the CHAMP (CHAllenging Minisatellite Payload) satellite mission to cover the range of 400 km altitude. The GRACE focused forecast algorithm SODA is part of the project SWEETS and ESPRIT, which will be implemented in the ESA Space Safety Program (Ionospheric Weather Expert Service Center) in 2023.

We present the ESA service STEREO+CH which forecasts the solar wind speed for Earth, based on persistence modeling from STEREO in situ measurements combined with multi-viewpoint EUV observational data. By comparing the fractional areas of coronal holes (CHs) extracted from EUV data of STEREO and SoHO/ SDO, we add an uncertainty level derived from changes in the CH areas, and apply those changes to the predicted solar wind speed profile at Earth (see Temmer, Hinterreiter, and Reiss, 2018). In principle, the service was developed to work with in situ and EUV data from the location behind Earth (e.g., future Vigil mission) providing a lead time of solar wind speed forecast for a couple of days. As STEREO-A will switch its location to ahead of Earth, we perform additional statistical studies and upgrade the service by adding co-latitude information of the CHs and dynamic thresholding for CH extraction to keep the performance level up. With that we make the ESA service ready for solar cycle 25.

Large-scale solar wind (SW) structures like coronal mass ejections (CMEs) and stream interaction regions (SIRs) significantly alter the plasma within the Earth’s magnetosheath and change the foreshock region. Thus, they modulate the number and the parameters of dynamic pressure transients in the magnetosheath, which we call magnetosheath jets. We use THEMIS spacecraft data from 2008 to 2022 to detect these jets in the magnetosheath and OMNI data for the SW within the same time range. We investigate which properties in each SW structure primarily influence the jet occurrence. We find that CMEs cause a reduction in jet occurrence due to the mix of high magnetic field strength, high plasma beta, low Mach number, and high cone angles. These conditions most likely disrupt the building of a proper foreshock region and thus hinder the major generation mechanism for jets in the magnetosheath. On the other hand, high speed streams in SIRs show favorable conditions for jet generation in all plasma parameters, most importantly due to the high probability for low cone angles, the low density, high velocity, and low magnetic field strength. We analyze how the jet parameters differ in each type of SW structure and discuss how this influences the geoeffectiveness of jets.

Since the 1970s it has been empirically known that the area of solar coronal holes a ects the properties of high-speed solar windstreams (HSSs) at Earth. We derive a simple analytical model for the propagation of HSSs from the Sun to Earth and thereby showhow the area of coronal holes and the size of their boundary regions a ect the HSS velocity, temperature, and density near Earth.We assume that velocity, temperature, and density profiles form across the HSS cross section close to the Sun and that these spatialprofiles translate into corresponding temporal profiles in a given radial direction due to the solar rotation. These temporal distributionsdrive the stream interface to the preceding slow solar wind plasma and disperse with distance from the Sun. The HSS properties at1AU are then given by all HSS plasma parcels launched from the Sun that did not run into the stream interface at Earth distance.We show that the velocity plateau region of HSSs as seen at 1AU, if apparent, originates from the center region of the HSS closeto the Sun, whereas the velocity tail at 1AU originates from the trailing boundary region. Small HSSs can be described to entirelyconsist of boundary region plasma, which intrinsically results in smaller peak velocities. The peak velocity of HSSs at Earth furtherdepends on the longitudinal width of the HSS close to the Sun. The shorter the longitudinal width of an HSS close to the Sun, themore of its “fastest” HSS plasma parcels from the HSS core and trailing boundary region have impinged upon the stream interfacewith the preceding slow solar wind, and the smaller is the peak velocity of the HSS at Earth. As the longitudinal width is statisticallycorrelated to the area of coronal holes, this also explains the well-known empirical relationship between coronal hole areas and HSSpeak velocities. Further, the temperature and density of HSS plasma parcels at Earth depend on their radial expansion from the Sunto Earth. The radial expansion is determined by the velocity gradient across the HSS boundary region close to the Sun and gives thevelocity-temperature and density-temperature relationships at Earth their specific shape. When considering a large number of HSSs,the assumed correlation between the HSS velocities and temperatures close to the Sun degrades only slightly up to 1AU, but thecorrelation between the velocities and densities is strongly disrupted up to 1AU due to the radial expansion. Finally, we show howthe number of particles of the piled-up slow solar wind in the stream interaction region depends on the velocities and densities of theHSS and preceding slow solar wind plasma.

On March 12, 2012, a Coronal Mass Ejection (CME) was released from the Sun with a speed of ~2000 km/s. The CME source region was surrounded by three different coronal holes (CHs), located to the East (negative polarity), South-West (positive polarity) and West (positive polarity). Its interplanetary counterpart (ICME) impacted Earth and was in-situ measured by the Advanced Composition Explorer (ACE) / Wind at L1 and the Solar TErrestrial RElations Observatory Ahead (STEREO)-A on March 15th. During this period, the angular separation between the two locations was greater than 100 degrees. Nevertheless, the in-situ measurements revealed almost identical profiles with clear markers of ICME signatures, which is evidence of one of the widest reported multi-spacecraft detection of an ICME, having STEREO-A crossing the west flank and Earth the east flank. Supra-thermal electrons show signatures of bidirectionality and isotropy/simple strahl as the ICME crosses the different spacecraft, providing information about the eroded parts of the ICME. Certain parts might have been eroded, possibly due to the interaction with the fast solar wind produced by the nearby CHs. We analysed the propagation of the ICME structure using remote-sensing observations from both STEREOs and Earth together with different in-situ instrumentation at ~1 au, and performed a comparison between the physical properties derived at multiple spacecraft. This study shows the importance of multi-spacecraft observations to understand the large-scale structures of ICMEs, their evolution and interaction, as well as their implications for the space-weather discipline.

The empirical solar wind forecast (ESWF) model in its current version 2.0 runs as a space safety service in the frame of ESA’s Heliospheric Weather Expert Service Centre. The ESWF model forecasts the solar wind speed at Earth with a leadtime of 4 days. The algorithm uses an empirical relation found between the area of solar coronal holes (CHs), as observed in EUV within a 15° meridional slice, and the in-situ measured solar wind speed at 1 AU. This relation however, forecasts Gaussian type speed profiles, as the CH rotates in and out of the meridional slice, causing some discrepancy in the timing between forecasted and observed solar wind speed. With adaptations to the ESWF 2.0 algorithm we improve the precision and accuracy of the ESWF speed profiles. For that we implement compression and rarefaction effects occurring between solar wind streams of different velocities in interplanetary space. By considering the propagation times for plasma parcels between the Sun and Earth and their interactions, we achieve the asymmetrical shape of the speed profile that is characteristic of highspeed streams (HSS). By further implementing CH segmentation, co-latitude information and dynamic thresholding, we find that the newly developed ESWF 3.2 performs significantly better than ESWF 2.0. For a sample of 294 different HSSs, we derive a relative increase in hits of the timing and peak velocity by 13.9%. The Pearson correlation coefficient increases by 14.3% from cc = 0.35 to cc = 0.40.

We investigated the interaction of a coronal mass ejection (CME) and a coronal hole (CH) in its vicinity using remote-sensing and 1 AU in situ data. We used extreme-ultraviolet images and magnetograms to identify coronal structures and coronagraph images to analyze the early CME propagation. The Wind spacecraft and the Advanced Composition Explorer (ACE) provide plasma and magnetic field data of near-Earth interplanetary space. We applied various diagnostic tools to the images and to the time-series data. We find that the CME erupts under a streamer and causes the evacuation of material at its far end, which is observable as dimming and subsequent CH formation. The CME is likely deflected in its early propagation and travels southwest of the Sun-Earth line. In situ data lack signatures of a large magnetic cloud, but show a small flux rope at the trailing edge of the interplanetary CME (ICME), followed by an Alfvénic wave. This wave is identified as exhaust from a Petschek-type reconnection region following the successful application of a Walén test. We infer that the two spacecraft at 1 AU most likely traverse the ICME leg that is in the process of reconnection along the heliospheric current sheet that separates the ICME and the high-speed stream outflowing from the CH.

Since the 1970s it has been empirically known that the area of solar coronal holes affects the properties of high-speed solar wind streams (HSSs) at Earth. We derive a simple analytical model for the propagation of HSSs from the Sun to Earth and thereby show how the area of coronal holes and the size of their boundary regions affect the HSS velocity, temperature, and density near Earth. We assume that velocity, temperature, and density profiles form across the HSS cross section close to the Sun and that these spatial profiles translate into corresponding temporal profiles in a given radial direction due to the solar rotation. These temporal distributions drive the stream interface to the preceding slow solar wind plasma and disperse with distance from the Sun. The HSS properties at 1 AU are then given by all HSS plasma parcels launched from the Sun that did not run into the stream interface at Earth distance. We show that the velocity plateau region of HSSs as seen at 1 AU, if apparent, originates from the center region of the HSS close to the Sun, whereas the velocity tail at 1 AU originates from the trailing boundary region. Small HSSs can be described to entirely consist of boundary region plasma, which intrinsically results in smaller peak velocities. The peak velocity of HSSs at Earth further depends on the longitudinal width of the HSS close to the Sun. The shorter the longitudinal width of an HSS close to the Sun, the more of its “fastest” HSS plasma parcels from the HSS core and trailing boundary region have impinged upon the stream interface with the preceding slow solar wind, and the smaller is the peak velocity of the HSS at Earth. As the longitudinal width is statistically correlated to the area of coronal holes, this also explains the well-known empirical relationship between coronal hole areas and HSS peak velocities. Further, the temperature and density of HSS plasma parcels at Earth depend on their radial expansion from the Sun to Earth. The radial expansion is determined by the velocity gradient across the HSS boundary region close to the Sun and gives the velocity-temperature and density-temperature relationships at Earth their specific shape. When considering a large number of HSSs, the assumed correlation between the HSS velocities and temperatures close to the Sun degrades only slightly up to 1 AU, but the correlation between the velocities and densities is strongly disrupted up to 1 AU due to the radial expansion. Finally, we show how the number of particles of the piled-up slow solar wind in the stream interaction region depends on the velocities and densities of the HSS and preceding slow solar wind plasma.

Plasma jets in the magnetosheath are identified as strong local enhancements in dynamic pressure. Being created at the bow shock, they are able to traverse the entire magnetosheath and impact the magnetopause. There, they can severely indent the boundary, set up waves on it, and trigger magnetic reconnection. They are a key yet heavily underexplored element in the solar wind – magnetosphere coupling. Jets are mostly (but not exclusively) observed downstream of the quasi-parallel shock. Consequently, they have been observed significantly more often under low interplanetary magnetic field cone angle conditions.In this study, we revisit the occurrence of jets, this time taking into account the whole space of parameters of solar wind input conditions. We answer the question where in this space jet occurrences cluster and how the emerging patterns change when the solar wind input becomes significantly different in nature, e.g., under the influence of coronal mass ejections or stream interaction regions.

Localized enhancements in dynamic pressure observed in the Earth’s magnetosheath (EMS) have been studied since 20 years ago. These structures known as jets can propagate through the EMS transporting mass, momentum and energy being able to reach and perturb the Earth’s magnetopause. Large scale solar wind (SW) structures called Coronal Mass Ejections (CMEs) travel through the interplanetary medium and depending on their direction they may impact the Earth. How the different SW conditions triggered by the CMEs (upstream side – shock/sheath – magnetic ejecta) change the production of jets in the EMS is a topic that is just beginning to be explored. In this case study we characterize jets observed by THEMIS A, E and D during a CME passage. We find clear differences in number and size between the jets associated with the different CME regions arriving at the EMS. Comparing WIND and THEMIS data we discuss how these differences are associated with the SW conditions and with different jet generation mechanisms.

The FFG funded project SWEETS (space weather effects on low Earth orbiting satellites) covers the analysis of a large sample of more than 300 ICMEs (interplanetary coronal mass ejections) from 2002 to 2017 and how they relate to the orbit decay of satellites. Based on the results by Krauss et al. (2018, 2020), we investigate the correlation between the interplanetary magnetic field of ICMEs and the variation of the neutral density in the thermosphere. So far, the satellite drops were calculated from either accelerometer measurements or kinematic orbits for the satellite GRACE at a height of approximately 490 km. Presently, we are working on constructing kinematic orbits for satellites in various heights so we will be able to cover altitudes between 300 to 800 km and a wider timeframe. The algorithm is also going to be improved with respect to multiple ICME events and the calculation of a so-called “effective Bz” component and its duration.With the correlation and the real-time in-situ magnetic field data from satellites at L1 we were able to construct a nowcast. The nowcast algorithm is the basis of a new service called SODA (Satellite Orbit DecAy) which will be implemented in the ESA Space Safety Program (Ionospheric Weather Expert Service Center).

Low earth orbiting (LEO) satellites can be affected by space weather events like coronal mass ejections (CMEs) in such a way that the drag force acting on the spacecraft is enhanced due to increasing atmospheric neutral density. As a consequence, this leads to an additional storm induced orbit decay. LEO satellites equipped with accelerometers offer the possibility to deduce information on the current state of the atmospheric neutral mass density based on the measurements of non-gravitational forces acting on the spacecraft. However, satellites with suitable onboard accelerometers are extremely rare. An alternative method to derive atmospheric densities along a satellite trajectory can be realized through the usage of global navigation satellite system (GNSS) based kinematic orbit information. This approach offers the advantage that that theoretically almost every LEO satellite mission which is tracked by GNSS can be used for the evaluation. In addition, through the increasing number of analysable satellites the explorable altitude range can be expanded to 300 km - 800 km. Thus, a tomography of the upper Earth’s atmosphere is feasible and the impact of a solar event on a satellite can be estimated as a function of its orbital altitude. In this study, we present density estimates based on kinematic orbits during quiet and active solar periods. The results are compared to state-of-the-art thermosphere models like the NRLMSIS 2.0, JB2008 and HASDM. In the case of extreme solar events the investigations are extended by estimating the storm induced orbit decay for different altitudes and satellites.

Drag-Based Ensemble Model (DBEM) is a probabilistic model for heliospheric propagation of Coronal Mass Ejections (CMEs) that predicts the CME hit chance, most probable arrival times and speeds, quantify the prediction uncertainties and calculate the confidence intervals. DBEM is based on the 2D analytical Drag-based Model (DBM) with very short computational time. By using CME cone geometry with flattening DBM calculates the CME arrival time and speed at Earth or any other given target in the solar system. DBEM considers the variability of model input parameters by making an ensemble of n different input parameters to obtain the distribution and significance of the DBM results. As an important tool for space weather forecasters, DBM/DBEM web application is integrated as one of the ESA Space Situational Awareness portal services (https://swe.ssa.esa.int/current-space-weather). Important requirement to perform DBM calculations is to assume that two input parameters namely background solar wind speed and the drag parameter γ are constant in order to have the analytical solution and fast computational times. However, this assumption is not always valid in more complex heliospheric conditions. Thus, to further increase the accuracy of CME propagation forecast we developed the new DBEMv4 version that calculates CME propagation in more steps with variable solar wind speeds. This allows also to employ as DBEMv4 input the dynamic solar wind data in real-time taken from simple persistence model under consideration of the CME propagation direction.

Magnetosheath jets are dynamic pressure enhancements frequently observed in the Earth’s magnetosheath. They are significant coupling elements between the solar wind and the magnetosphere of the Earth and they can be geoeffective. Jets travel anti-sunward through the magnetosheath and can impact the magnetopause. The generation of these jets is generally linked to processes at the quasi-parallel bow shock and the foreshock. We analyzed how the appearance of these jets is linked to large-scale solar wind (SW) structures, in particular coronal mass ejections (CMEs) and stream interaction regions (SIRs) and their associated high speed streams (HSSs). In our statistical analysis, we use magnetosheath jets detected by the THEMIS spacecraft between 2008 to 2020. We found that the number of detected jets is lower during the passing of CMEs. Significantly more jets are observed during SIRs and HSSs. We analyze the difference in conditions during each SW structure and compare them to the SW conditions measured during the detection of jets. We focus on SW Alfvénic Mach number and IMF cone angle, which affect the presence of the foreshock and the position of the quasi-parallel shock front. We find that jets are unlikely to appear during a mix of low Alfvénic Mach numbers and high cone angles, which are SW conditions often found during CMEs and their associated sheaths.

The empirical solar wind forecast (ESWF) model is an ESA service to forecast the solar wind speed at Earth with 4 days lead time. The model uses a simple empirical relation between the area of coronal holes (CHs) as measured in meridional slices in EUV at the Sun and the in-situ measured solar wind speed at 1 AU (Vršnak, Temmer, Veronig, 2007). The relation has the drawback that Gaussian type speed profiles are produced as the CH rotates in and out of the meridional slice. With adaptations to the ESWF algorithm we aim to improve the precision of the ESWF speed profile by implementing compression and rarefaction effects occurring between SW streams of different velocities in the interplanetary space. By considering the propagation times for plasma parcels between the Sun and Earth and their interactions, we achieve the asymmetrical shape of the speed profile that is characteristic of high-speed streams (HSS). We present a statistical analysis for the period 2012 - 2019 showing that our adaptions improve the ability to predict HSS speed profiles as well as smaller structures with higher precision.

Helios 1 and 2 data, covering the distance range from 0.3-1au, have been analysed to derive the characteristics of various substructures of interplanetary coronal mass ejections (ICMEs). We have investigated a data sample of 40 events observed by the Helios 1/2 spacecraft during the time period 1974-1981 with respect to the characteristics of different ICME features, such as sheath regions, leading edges and the magnetic ejecta (ME) themselves. For comparison and to investigate events at distances even closer to the Sun, we add a sample of 5 ICMEs observed with Parker Solar Probe during 2018-2021. We study the sheath density variations over distance and relate those to the ambient solar wind speed. The results show that the sheath region is moderately anti-correlated with the solar wind speed ahead of the disturbance. We further find that the sheath density becomes dominant over the ME density beyond about 0.2au and that its spatial extent constantly increases with distance. The results are important for better understanding the CME mass evolution due to sheath enlargements. Based on these analyses we derive an empirical relation between the sheath density and the local solar wind plasma speed upstream of the ICME shock. The empirical results can be used to model the sheath structure and help improve our understanding about CME propagation in the inner heliosphere.

We observe a long-lived CIR recurring in 27 consecutive Carrington rotations 2057-2083 in the time period from June 2007 - May 2009. We characterize the in situ measurements of this long-lived CIR as well as the corresponding depression in the GCR count observed by SOHO/EPHIN, and analyze them throughout different rotations. We find that the inverted GCR count time-profile correlates well with that of the flow speed throughout different rotations. We perform a statistical analysis and find the GCR count amplitude correlated to the peak in the magnetic field and flow speed, as expected based on previous statistical studies. In order to characterize a generic CIR profile for modelling purposes, we perform the superposed epoch analysis using relative values of the key parameters. Based on the observed properties we propose a simple analytical model starting from the basic Fokker-Planck equation. We employ a convection-diffusion GCR propagation model and apply it to the solar wind and interplanetary magnetic field properties observed for the analyzed long-lived CIR. Our analysis demonstrates a very good match of the model results and observations.

The interaction of interplanetary coronal mass ejections (ICMEs) and stream interaction regions (SIRs) gives rise to complex heliospheric plasma and magnetic field conditions. Considering the different magnetic configurations of both phenomena as well as the source regions in the solar corona, there is also the possibility of magnetic reconnection either at coronal heights or farther out in the heliosphere.The event of February 7th, 2014 shows clear signatures of a qualitative alteration of the ICME structure in ACE plasma and magnetic field data. There is a significant drop of the magnetic field strength inside the FR simultaneously to an enhancement in temperature and a high variability of speed. The flow angle reversal expected to take place at the stream interface sharply coincides with the onset of the ICME magnetic field rotations and drop of temperature below expected temperature. The speed inside the flux rope, yet showing the aforementioned variations, overall features a decline from the front to the rear of the ICME. The launch site of the ICME is derived from SDO AIA data, showing its location to be 30° West from a N-S elongated coronal hole.These results imply a deterioration of the FR due to magnetic reconnection, either caused by the proximity of CH and CME eruption site and favorable magnetic configurations, or the heliospheric interaction of the associated SIR and ICME. WSA-ENLIL simulations suggest that the ICME catches up with the SIR close to Earth, which, along with the in-situ signatures, implies the simultaneous occurrence of stream interface and flux rope onset. The declining speed profile that is characteristic for quiescent ICME spatial evolution suggests no high-speed stream is inhibiting expansion from behind. Due to its complexity, this event provides a great opportunity to study the interaction of ICMEs and SIRs.

Context: In this paper we present a validation scheme to investigate the quality of coronal magnetic field models, which is based upon comparisons with observational data from multiple sources. Aims: Many of these coronal models may use a range of initial parameters that produce a large number of physically reasonable field configurations. However, that does not mean that these results are reliable and comply with the observations. With an appropriate validation scheme the quality of a coronal model can be assessed. Methods: The validation scheme is developed on the example of the EUropean Heliospheric FORecasting Information Asset (EUHFORIA) coronal model. For observational comparison we use EUV and white-light data to detect coronal features on the surface (open magnetic field areas) and off-limb (streamer and loop) structures from multiple perspectives (Earth view and the Solar Terrestrial Relations Observatory - STEREO). The validation scheme can be applied to any coronal model that produces magnetic field line topology. Results: We show its applicability by using that validation scheme on a large set of model configurations, which can be efficiently reduced to an ideal set of parameters that matches best with observational data. Conclusions: We conclude that by using a combined empirical visual classification with a mathematical scheme of topology metrics a very efficient and rather objective quality assessment for coronal models can be performed., Accepted for publication in A&A

Configuration of the interplanetary magnetic field and related ambient solar wind features in the ecliptic and meridional planes are different. Therefore, one can expect that the coronal mass ejection (CME) inclination influences the propagation of the CME itself. This study aims to investigate the non-radial flow in the sheath region of the interplanetary CME (ICME) in order to provide the first proxy to relate the ICME orientation with its propagation. We investigated isolated CME-ICME events from the period 1997-2018. We obtained the CME tilt in the “near-Sun” environment by performing the ellipse fitting technique to the CME outer front as determined from the SOHO/LASCO coronagraph. In the “near-Earth” environment, we obtained the orientation of the corresponding ICME using in-situ plasma and field data and we investigated the non-radial flow in its sheath region. Most of the CME-ICME pairs under investigation were found to be characterized by a low inclination. For the majority of CME-ICME pairs, we obtain consistent estimations of the dominant inclination from remote and in situ data. The observed non-radial flows in the sheath region show a greater y-direction to z-direction flow ratio for high-inclination events, indicating that the CME orientation could have an impact on the CME propagation.

The configuration of the interplanetary magnetic field and features of the related ambient solar wind in the ecliptic and meridional plane are different. Therefore, one can expect that the orientation of the flux rope axis of a coronal mass ejection (CME) influences the propagation of the CME itself. However, the determination of the CME orientation remains a challenging task to perform. This study aims to provide a reference to different CME orientation determination methods in the near-Sun environment. Also, it aims to investigate the non-radial flow in the sheath region of the interplanetary CME (ICME) in order to provide the first proxy to relate the ICME orientation with its propagation. We investigated 22 isolated CME-ICME events in the period 2008-2015. We first determined the CME orientation in the near-Sun environment using a 3D reconstruction of the CME with the graduated cylindrical shell (GCS) model applied to coronagraphic images provided by the STEREO and SOHO missions. The CME orientation in the near-Sun environment was determined using an ellipse fitting technique to the CME outer front as determined from the SOHO/LASCO coronagraph. In the near-Earth environment, we obtained the orientation of the corresponding ICME using in-situ plasma and field data and also investigated the non-radial flow in its sheath region. The ability of GCS and ellipse fitting to determine the CME orientation is found to be limited to only distinguishing between the high or low inclination of the events. Most of the CME-ICME pairs under investigation were found to be characterized by a low inclination, and regardless of whether their inclination was high or low, the CME-ICME pairs maintained their inclination during interplanetary propagation. The observed non-radial flows in the sheath region show a greater y-direction to z-direction flow ratio for low-inclination events which suggests that there is a connection between the orientation and propagation of the observed CME-ICME pairs.

Coronal mass ejections (CMEs) are generally considered magnetic structures in which the magnetic field spirals around a central axis (flux rope, FR). The FR axis can be oriented at any angle to the ecliptic. The dynamics of the CME in interplanetary (IP) space is determined primarily by the magnetohydrodynamic (MHD) drag force, i.e., the interaction of the CME with the interplanetary magnetic field (IMF) and the ambient solar wind (SW). The configuration of IMF and SW is neither homogeneous nor isotropic in IP space. For this very reason, we expect the occurrence of variations in the dynamics of the CME with respect to the orientation of its FR axis. In other words, we expect some difference in the propagation of CMEs with a FR axis parallel to the ecliptic plane (CMEs with low inclination) and CMEs with a FR axis perpendicular to the ecliptic plane (CMEs with high inclination). We study isolated Earth-directed CMEs during 1997- 2018. We obtain the inclination of the CME in the "near-Sun" environment by applying the ellipse fitting technique to the outer front of the CME determined with the SOHO /LASCO coronagraph. In the "near-Earth" environment, we determined the orientation of the corresponding ICME using in situ plasma and magnetic field data. We also investigate the non-radial flows (NRFs) in the sheath region of ICME. Most of the CME-ICME associations studied have low inclination. For most CME-ICME pairs, we have obtained consistent estimates of the dominant inclination from remote sensing and in situ data. The observed NRFs in the sheath region show a larger ratio between y- and z-directions for high inclination events, suggesting that the orientation of the CME likely has an impact on its propagation. In addition, we discuss the effects of CME orientation on MHD drag in IP space. These results provide new insights into CME dynamics, the understanding of which is critical for improving space weather forecasting.

Magnetosheath jets constitute a significant coupling effect between the solar wind (SW) and the magnetosphere of the Earth. In order to investigate the effects and forecasting of these jets, we present the first-ever statistical study of the jet production during large-scale SW structures like coronal mass ejections (CMEs), stream interaction regions (SIRs) and high speed streams (HSSs). Magnetosheath data from Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft between January 2008 and December 2020 serve as measurement source for jet detection. Two different jet definitions were used to rule out statistical biases induced by our jet detection method. For the CME and SIR + HSS lists, we used lists provided by literature and expanded on incomplete lists using OMNI data to cover the time range of May 1996 to December 2020. We find that the number and total time of observed jets decrease when CME-sheaths hit the Earth. The number of jets is lower throughout the passing of the CME-magnetic ejecta (ME) and recovers quickly afterward. On the other hand, the number of jets increases during SIR and HSS phases. We discuss a few possibilities to explain these statistical results.