The solar wind is an uninterrupted flow of highly ionised plasma that fills interplanetary space and is crossed by strong transient perturbations such as coronal mass ejections (CMEs), (corotating) stream interaction regions (SIRs), and solar energetic particles (SEPs). These phenomena are capable of driving large disturbances at Earth as well as at the other planets. Remote-sensing observations from multiple vantage points, in-situ measurements from multiple well-separated locations, and novel modelling efforts have been employed systematically to study the properties of the solar wind plasma and of solar transients in general, from their formation to their arrival at different planets throughout the inner heliosphere. However, despite the number of past and current spacecraft missions distributed throughout the heliosphere, it is still difficult to fully understand the properties of these transients phenomena, including their 3D structure and their evolution with heliocentric distance.

The recently launched Parker Solar Probe, the imminent launch of Solar Orbiter, current and planned planetary missions, as well as potential future missions at L1, L5, and over the solar poles, will provide us with the perfect opportunity to test, validate, and refine the current knowledge of these physical phenomena and their interactions at different heliocentric distances. Accordingly, the aim of this session is to showcase the latest observational and modelling efforts regarding the evolution of the solar wind and solar transients during their propagation throughout the heliosphere as seen from multiple vantage points, and to foresee future developments. Potential improvements to our current space weather forecasting capabilities will be highlighted.

Convener: Rui Pinto | Co-conveners: David BarnesECSECS, Erika PalmerioECSECS
| Attendance Wed, 06 May, 10:45–12:30 (CEST)

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Chat time: Wednesday, 6 May 2020, 10:45–12:30

D2864 |
| solicited
Mathew Owens

Atmospheric science and forecasting, concerned with a volume ~1013 m3, is underpinned by an extensive observational network; point measurements at 10k land-based stations, 4k ships and buoys, and around 1k dedicated balloon launches and aircraft; remote sensing from hundreds of radars and 10 dedicated operational satellites providing independent “look directions” through the atmosphere. By comparison, the heliosphere is a vastly under-sampled system. In the ~1028 m3 volume contained within Earth orbit, there has been a maximum of 5 simultaneous point measurements and remote sensing from (at most) 3 simultaneous vantage points. This makes it difficult to reliably interpret observations in terms of the 3-dimensional structure and extent of solar wind transients. Solar Orbiter, Parker Solar Probe, STEREO-A and L1 monitors (and a possible future L5 monitor), as well as more limited solar wind measurements from planetary/cometary missions, will shortly provide unprecedented observational coverage and thus a unique opportunity to better understand solar wind transients. Nevertheless, sampling will remain sparse and connecting point observations and interpreting remote sensing observations will remain ambiguous. Global models of the solar wind can aid greatly in this regard. This talk will summarise how observations and models can be best combined to exploit the strengths of both, and what we can learn about solar wind transients.

How to cite: Owens, M.: Connecting the dots: Multi-point observations for solar wind science and forecasting, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2643, https://doi.org/10.5194/egusphere-egu2020-2643, 2020.

D2865 |
| solicited
Nada Al-Haddad and Noé Lugaz

The structure of coronal mass ejections (CMEs) has been the center of numerous studies over the past few decades. Defining the magnetic field orientation locally and globally has proven to be a challenging problem, due to the limited nature of observations that we have, as well as our reliance on the current paradigm of highly-twisted flux ropes. Studies suggest that not all CMEs measured in situ fit within the simple twisted and well-organized flux rope topology. Additionally, many of the events that can be well fitted by existing static flux rope models, do not have as simple a structure as that assumed by the models. This is clear from remote observations and multi-spacecraft measurements. With the wealth of data that we have today, as well as the affluence of research and analysis performed over the last 40 years, it is dues time to present an alternative paradigm, that better represents those data. In this work, we discuss this new paradigm and the literature leading to it. 

How to cite: Al-Haddad, N. and Lugaz, N.: A New Model to Describe the Magnetic Structure of CMEs, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3172, https://doi.org/10.5194/egusphere-egu2020-3172, 2020.

D2866 |
Manuela Temmer, Lukas Holzknecht, Mateja Dumbovic, Bojan Vrsnak, Nishtha Sachdeva, Stephan Heinemann, Karin Dissauer, Camilla Scolini, Eleanna Asvestari, Astrid Veronig, and Stefan Hofmeister

For better estimating the drag force acting on coronal mass ejections (CMEs) in interplanetary space and ram-pressure at planets, improved knowledge of the evolution of CME density/mass is highly valuable. We investigate a sample of 29 well observed CME-ICME events, for which we determine the de-projected 3D mass (STEREO-A and -B data), and the CME volume using GCS modeling (STEREO, SoHO). Expanding the volume to 1AU distance, we derive the density and compare the results to in-situ proton density measurements separately for the ICME sheath and magnetic structure. A fair agreement between calculated and measured density is derived for the magnetic structure as well for the sheath if taking into account mass pile up of solar wind plasma. We give evidence and observational assessment that during the interplanetary propagation of a CME 1) the magnetic structure has rather constant mass and 2) the sheath region at the front of the driver is formed from piled-up mass that is rather depending on the solar wind density ahead of the CME, than on the CME speed. 

How to cite: Temmer, M., Holzknecht, L., Dumbovic, M., Vrsnak, B., Sachdeva, N., Heinemann, S., Dissauer, K., Scolini, C., Asvestari, E., Veronig, A., and Hofmeister, S.: Relating CME density derived from remote sensing data to CME sheath solar wind plasma pile up as measured in-situ , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3341, https://doi.org/10.5194/egusphere-egu2020-3341, 2020.

D2867 |
Brigitte Schmieder, Stefaan Poedts, and Christine Verbeke

In 2002 (Cycle 23), a weak impact on the magnetosphere of the Earth has been reported for six halo CMEs related to six X-class flares and with velocities higher than 1000 km/s. The registered Dst minima are all between -17 nT and -50 nT.  A study of the Sun-Earth chain of phenomena related to these CMEs reveals that four of them have a source at the limb and two have a source close to the solar disk center (Schmieder et al., 2020). All of CME magnetic clouds had a low z‑component of the magnetic field, oscillating between positive and negative values.

We performed a set of EUHFORIA simulations in an attempt to explain the low observed Dst and the observed magnetic fields. We study the degree of deviation of these halo CMEs from the Sun-Earth axis and as well as their deformation and erosion due to their interaction with the ambient solar wind (resulting in magnetic reconnections) according to the input of parameters and their chance to hit other planets. The inhomogeneous nature of the solar wind and encounters  are also important parameters influencing the impact of CMEs on planetary magnetospheres.


How to cite: Schmieder, B., Poedts, S., and Verbeke, C.: Can we explain the low geo-effectiveness of the fast halo CMEs in 2002 with EUHFORIA?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5543, https://doi.org/10.5194/egusphere-egu2020-5543, 2020.

D2868 |
Martin Reiss, Peter MacNeice, Karin Muglach, Nick Arge, Christian Möstl, Pete Riley, Jürgen Hinterreiter, Rachel Bailey, Andreas Weiss, Mathew Owens, Tanja Amerstorfer, and Ute Amerstorfer

The ambient solar wind flows and fields influence the complex propagation dynamics of coronal mass ejections in the interplanetary medium and play an essential role in shaping Earth's space weather environment. A critical scientific goal in the space weather research and prediction community is to develop, implement and optimize numerical models for specifying the large-scale properties of solar wind conditions at the inner boundary of the heliospheric model domain. Here we present an adaptive prediction system that fuses information from in situ measurements of the solar wind into numerical models to better match the global solar wind model solutions near the Sun with prevailing physical conditions in the vicinity of Earth. In this way, we attempt to advance the predictive capabilities of well-established solar wind models such as the Wang-Sheeley-Arge model. We perform a statistical analysis of the resulting solar wind predictions for the years 2006 to 2015. The proposed prediction scheme improves all the coronal/heliospheric model combinations investigated by approximately 15-20 percent in terms of various comprehensive prediction validation measures. We discuss why this is the case, and conclude that our findings have important implications for future practice in applied space weather research and prediction.

How to cite: Reiss, M., MacNeice, P., Muglach, K., Arge, N., Möstl, C., Riley, P., Hinterreiter, J., Bailey, R., Weiss, A., Owens, M., Amerstorfer, T., and Amerstorfer, U.: An Adaptive Prediction System for Specifying Solar Wind Conditions Near the Sun, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21455, https://doi.org/10.5194/egusphere-egu2020-21455, 2020.

D2869 |
Réka Winslow, Amy Murphy, Nathan Schwadron, Noé Lugaz, Wenyuan Yu, Charles Farrugia, and Jonathan Niehof

Small flux ropes (SFRs) are interplanetary magnetic flux ropes with durations from a few minutes to a few hours. We have built a comprehensive catalog of SFRs at Mercury using magnetometer data from the orbital phase of the MESSENGER mission (2011-2015). In the absence of solar wind plasma measurements, we developed strict identification criteria for SFRs in the magnetometer observations, including conducting force-free field fits for each flux rope. We identified a total of 48 events that met our strict criteria, with events ranging in duration from 2.5 minutes to 4 hours. Using superposed epoch analysis, we obtained the generic SFR magnetic field profile at Mercury. Due to the large variation in Mercury's heliocentric distance (0.31-0.47 AU), we split the data into two distance bins. We found that the average SFR profile is more symmetric "farther from the Sun", in line with the idea that SFRs form closer to the Sun and undergo a relaxation process in the solar wind. Based on this result, as well as the SFR durations and the magnetic field strength fall-off with heliocentric distance, we infer that the SFRs observed at Mercury are expanding as they propagate with the solar wind. We also determined that the SFR occurrence frequency is nearly four times as high at Mercury as for similarly detected events at 1 AU. Most interestingly, we found two SFR populations in our dataset, one likely generated in a quasi-periodic formation process near the heliospheric current sheet, and the other formed away from the current sheet in isolated events.

How to cite: Winslow, R., Murphy, A., Schwadron, N., Lugaz, N., Yu, W., Farrugia, C., and Niehof, J.: A Survey of Interplanetary Small Flux Ropes at Mercury, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5958, https://doi.org/10.5194/egusphere-egu2020-5958, 2020.

D2870 |
Marian Lazar

Recent advances in kinetic modeling reveal essential properties of the suprathermal populations opening perspectives for a realistic interpretation of their implications. Of particular importance are the suprathermal electron strahl (or beaming) populations, guided by the heliospheric magnetic field as kinetic-scale traces of the continuous solar outflows. We outline the main implications of the strahls by connecting their signatures in the velocity distributions with macroscopic properties of the solar wind, and processes conditioning their relaxation via coherent or non-coherent radiative emissions. The electron strahls may also help understanding major changes in the magnetic field topology in the outer corona, as shown by the most recent data from Solar Parker Probe, and during energetic (transient) events like coronal mass ejections, implying or not reconnection, but leading to strong interaction regions and shocks. 

How to cite: Lazar, M.: Suprathermal electron strahls. From small scale modeling to heliospheric implications, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5845, https://doi.org/10.5194/egusphere-egu2020-5845, 2020.

D2871 |
Evangelia Samara, Jasmina Magdalenic, Rui F. Pinto, Veronika Jercic, Camilla Scolini, Luciano Rodriguez, and Stefaan Poedts

The EUropean Heliospheric FORecasting Information Asset (EUHFORIA) is a new 3D magnetohydrodynamic (MHD) space weather prediction tool (Pomoell and Poedts, 2018). EUHFORIA models solar wind and coronal mass ejections (CMEs) all the way from the Sun to 2 AU. It consists of two different domains; the coronal part, which extends from the solar surface to 0.1 AU and the heliospheric part, which covers the spatial domain from 0.1 AU onwards. For the reconstruction of the global solar corona, the empirical Wang-Sheeley-Arge (WSA, Arge, 2003) model is currently used, in combination with the potential field source surface (PFSS) model and the Schatten current sheet (SCS) model, in order to reconstruct the magnetic field up to 0.1 AU and produce the plasma boundary conditions required by the 3D MHD heliospheric part to initiate. In the framework of the ongoing validation of the solar wind modeling with EUHFORIA, we implemented and tested a different coronal model, the so-called MULTI-VP model (Pinto and Rouillard, 2017). First results and comparisons of EUHFORIA modeled output at Earth produced by employing the WSA and MULTI-VP coronal models, will be presented.

How to cite: Samara, E., Magdalenic, J., Pinto, R. F., Jercic, V., Scolini, C., Rodriguez, L., and Poedts, S.: Coupling the MULTI-VP model with EUHFORIA, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-966, https://doi.org/10.5194/egusphere-egu2020-966, 2020.

D2872 |
Michael Lavarra, Rui Pinto, Alexis Rouillard, Athanasios Kouloumvakos, Alessandro Bemporad, Charles Nickolos Arge, Matthieu Alexandre, and Vincent Genot

The quasi-steady solar wind flow is a key component of space weather, being the source of corotating density structures that perturb planetary atmospheres and affect the propagation of impulsive perturbations (such as CME). Fast and slow wind streams develop at different places in the solar atmosphere, reflecting the global distribution of the coronal magnetic field during solar cycle and its consequences for heat and mass transport across the corona. I will present recent advances on global solar wind simulations that provides robust and fully physics-based predictions of the structure and physical parameters of the solar wind based on a multi-1D approach (MULTI-VP, ISAM). Such advances relate to the driving the models with time-dependant magnetogram data, to the inclusion of transient heating phenomena, and to switching from a fluid to a multi-species description of the solar wind. The model was also driven by daily synchronic magnetograms (ADAPT) for a full solar rotation and the simulation results were compared to UVCS plane-of-sky data.The simulations produce a large range of synthetic observables (e.g multi-spacecraft in-situ measurements, white-light and EUV imagery) meant to be compared to data from current and future missions (e.g Solar Orbiter and Parker Solar Probe), and to establish physiccal connections between remote observation of the solar surface and corona and the interplanetary medium.

How to cite: Lavarra, M., Pinto, R., Rouillard, A., Kouloumvakos, A., Bemporad, A., Arge, C. N., Alexandre, M., and Genot, V.: Modeling and forecasting the background solar wind with data-driven physics-based models, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17669, https://doi.org/10.5194/egusphere-egu2020-17669, 2020.

D2873 |
Jorge Amaya, Romain Dupuis, and Giovanni Lapenta

During the past decades different methods of classification of the solar wind have been proposed. These include simple models separating the “fast” from “slow” flows (Arya and Freeman, 1991, Yordanova et al., 2009, among others), complex empirical methods grouping its properties in multiple categories associated to its origin in the solar atmosphere (Xu et Borovsky, 2015), and more recently probabilistic classifications based on Gaussian processes (Camporeale et al., 2017).

Solar wind classification serves four main purposes: 1) statistical analysis of different wind types, 2) interpretation of observations in the magnetosphere, 3) diagnostics of physical processes in the Sun, and 4) identification of solar cycle effects on the Earth’s plasma environment. In this work, instead of using empirical methods, we use the machine learning technique known as Self-Organizing Maps (SOM) to automatically classify the solar wind at 1AU, without human intervention, using observations gathered by the ACE mission.

The ACE spacecraft has been continuously recording solar wind data for the past 22 years. We use hourly averaged solar wind parameters from the ACE Science Center in CalTech for this study. Each entry in this database can be considered as a single point in a multi-dimensional (ND) space. SOM techniques transform all the points in this space into a single 2D space with a small number of L x L nodes. The nodes are the 2D representation of the cloud of points in the ND space, grouping together around each node, points with similar properties. The nodes in this 2D map are interrelated, maintaining a structural topology that is useful for their interpretation. Each one of the nodes in the SOM map can viewed as one of the possible L x L classes. We go one step further, automatically grouping together nodes in the map that are close in the ND space, reducing the total number of classes to only a few. We compare the results obtained using SOM with the methods introduced above, showing the similarities and differences. We show that the SOM technique, which does not rely on human intervention, can be used to properly describe the different types of solar wind conditions observed in a full solar cycle.

How to cite: Amaya, J., Dupuis, R., and Lapenta, G.: Unsupervised classification of the solar wind using Self-Organizing Maps, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15568, https://doi.org/10.5194/egusphere-egu2020-15568, 2020.

D2874 |
Erika Palmerio, Christina Lee, Leila Mays, and Dusan Odstrcil

The evolution of coronal mass ejections (CMEs) as they travel away from the Sun is one of the major issues in heliophysics and space weather. After erupting, CMEs propagate outwards through the background solar wind flow, which in turn may significantly affect CME evolution by means of e.g. acceleration, deflection, and/or rotation. In order to determine to which extent the ambient wind can alter the speed, trajectory, and orientation of a CME, we run a series of 3D magnetohydrodynamics simulations (using the coupled solar–heliospheric WSA–Enlil model) to conduct a multi-vantage point study of the radial and longitudinal evolution of CME structures as they propagate up to Earth’s (1 AU) and Mars’ (1.5 AU) orbits. We explore a broad range of input CME parameters (initial radial speed, angular width) and ambient solar wind conditions (slow versus fast wind) to investigate the different evolutionary behaviours of CMEs and their driven shocks and sheath regions. To study the radial and longitudinal evolution for the modelled CME ejecta and shock events, we examine the resulting magnetic field and plasma time series at different heliocentric distances (0.5 AU, 1 AU, and 1.5 AU) and heliolongitudes (in 30° increments). This work will help establish a set of expected CME behaviours at Earth’s and Mars’ radial distances, which can be used for analysing real CME events.

How to cite: Palmerio, E., Lee, C., Mays, L., and Odstrcil, D.: Modelling the evolution of CMEs and their shocks through different solar wind structures, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11003, https://doi.org/10.5194/egusphere-egu2020-11003, 2020.

D2875 |
David Barnes, Jackie Davies, and Richard Harrison

Understanding the evolution of the solar wind is fundamental to advancing our knowledge of energy and mass transport in the solar system, rendering it crucial to space weather and its prediction. The advent of truly wide-angle heliospheric imaging has revolutionised the study of Coronal Mass Ejections (CMEs) by enabling their direct and continuous observation out to 1 AU and beyond. A catalogue of CMEs has been compiled using data from the Heliospheric Imagers (HIs) on board the two STEREO spacecraft, which began as part of the FP7 HELCATS project. The mission was launched in 2006 and continues to provide data, therefore spanning 13 years, over which more than two-thousand CMEs have been observed using HI. To these CMEs, we apply geometric models that make use of both single-spacecraft and stereoscopic observations in order to determine their kinematic properties. These include CME speed, acceleration, propagation direction and launch time. The resulting kinematic properties and their statistics are discussed in the context of existing CME catalogues produced from coronagraph observations. This is done with emphasis on how the different models we apply influence our results and how these differences evolve over the solar cycle and as the angular separation of the STEREO spacecraft increases throughout the mission.

How to cite: Barnes, D., Davies, J., and Harrison, R.: A Catalogue of Coronal Mass Ejections Observed by the Heliospheric Imagers throughout the STEREO Mission, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16546, https://doi.org/10.5194/egusphere-egu2020-16546, 2020.

D2876 |
Dominique Fontaine, Emiliya Kilpua, Matti Alalathi, Erika Palmerio, Adnane Osmane, Clement Moissard, Emiliya Yoradanova, Lina Z. Hadid, and Miho Janvier

We have analysed magnetic field fluctuations in sheath regions ahead of interplanetary coronal mass ejections (CMEs). CME sheaths are one of the key drivers of space weather disturbances, but their detailed structure and formation are relatively poorly understood. The level of magnetic field fluctuations in sheaths is generally much higher than in the ambient solar wind. We compare fluctuation properties in different parts of a sheath observed at the orbit of Earth using by the Wind spacecraft. Our findings show that in general the transition from the preceding solar wind to the sheath generates new fluctuations that are mostly compressive and which increase intermittency.  Spectral indices are mostly steeper than the -5/3 Kolmogorov index. The standard p-model did not show a good fit (in either the Kraichnan or Kolmogorov form), but the extended p-model was in a very good agreement. This suggests that turbulence may not be fully developed in CME sheaths in general. Our study also reveals that turbulent properties can vary considerably between different sheaths and in different subregions of the sheath, and can be significantly modified by the presence of small coherent structures. The findings support the view that sheath formation is a complex process with multiple physical mechanisms playing a role in generating the turbulence. 

How to cite: Fontaine, D., Kilpua, E., Alalathi, M., Palmerio, E., Osmane, A., Moissard, C., Yoradanova, E., Hadid, L. Z., and Janvier, M.: Turbulent properties of CME-driven sheath regions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18165, https://doi.org/10.5194/egusphere-egu2020-18165, 2020.

D2877 |
Evangelos Paouris, Angelos Vourlidas, Athanasios Papaioannou, and Anastasios Anastasiadis

Images of Coronal Mass Ejections (CMEs) are primarily acquired by space-based coronagraphs. Such images capture the outward flow of density structures from the Sun by observing Thompson-scattered sunlight from the free electrons entrained in these structures. Because the emission is optically thin, CMEs images are projections of their real 3D structure on the field of view (FOV) of the coronagraph. As a result, the CME characteristics (e.g. linear speed, angular width) calculated from these images, suffer from projection effects and their reliability needs to be quantified. In this work we apply a geometrical method for the de-projection of the linear CME speeds of 4009 CMEs from the CDAW catalog, associated with solar flares (3225 C-class, 736 M-class and 48 X-class solar flares). Our aim is to provide a robust quantification of the reliability of the CME properties from L1 (SOHO/LASCO) single viewpoint measurements.

In addition, we compare the intensity and location of solar flares with the CME kinematic characteristics. In particular, 482 M-class solar flares associated with CMEs with an angular width 30°< w < 120°, show a dependence of the mean CME linear speed with the longitude of the parent solar flare, indicating that projection effects of CMEs should be reduced near the solar limb. However, such deprojections tend to overcorrect the CME speed for sources near the solar meridian. They result in speeds of the order of 5000-7000 km/s, which seem physically unreasonable. By considering the 3D extent of the CMEs, we provide a novel geometrical correction of the deprojected CME linear speed. The resulting speeds range from a few 100 km/s up to almost 2600 km/s, a much more physically acceptable correction. This study has important implications for Space Weather applications since the reliable estimation of the CME linear speed has a direct effect on the time of arrival of CMEs at Earth and the quantification of the expected peak flux of solar radiation storms.

Acknowledgement: This work was funded from the State Scholarships Foundation of Greece (I.K.Y.), in the framework of: "Funding Post-doctoral Researchers" of the b.p.: "Human Resources Development, Education and Lifelong Learning" from ESPA (2014-2020).


How to cite: Paouris, E., Vourlidas, A., Papaioannou, A., and Anastasiadis, A.: How Reliable are CME speeds derived from single viewpoint observations?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-625, https://doi.org/10.5194/egusphere-egu2020-625, 2020.

D2878 |
Johan von Forstner, Jingnan Guo, Robert F. Wimmer-Schweingruber, Mateja Dumbović, Miho Janvier, Pascal Démoulin, Astrid Veronig, Manuela Temmer, Athanasios Papaioannou, Sergio Dasso, Donald M. Hassler, and Cary J. Zeitlin

Interplanetary coronal mass ejections (ICMEs), large clouds of plasma and magnetic field regularly expelled from the Sun, are one of the main drivers of space weather effects in the solar system. While the prediction of their arrival time at Earth and other locations in the heliosphere is still a complex task, it is also necessary to further understand the time evolution of their geometric and magnetic structure, which is even more challenging considering the limited number of available observation points.

Forbush decreases (FDs), short-term drops in the flux of galactic cosmic rays (GCR), can be caused by the shielding from strong and/or turbulent magnetic structures in the solar wind, such as ICMEs and their associated shock/sheath regions. In the past, FD observations have often been used to determine the arrival times of ICMEs at different locations in the solar system, especially where sufficient solar wind plasma and magnetic field measurements are not (or not always) available. One of these locations is Mars, where the Radiation Assessment Detector (RAD) onboard the Mars Science Laboratory (MSL) mission's Curiosity rover has been continuously measuring GCRs and FDs on the surface for more than 7 years.

In this work, we investigate whether FD data can be used to derive additional information about the ICME properties than just the arrival time by performing a statistical study based on catalogs of FDs observed at Earth or Mars. In particular, we find that the linear correlation between the FD amplitude and the maximum steepness, which was already seen at Earth by previous authors (Belov et al., 2008, Abunin et al., 2012), is likewise present at Mars, but with a different proprtionality factor.

By consulting physics-based analytical models of FDs, we find that this quantity is not expected to be influenced by the different energy ranges of GCR particles observed by the instruments at Earth and Mars. Instead, we suggest that the difference in FD characteristics at the two planets is caused by the radial enlargement of the ICMEs, and particularly their sheath regions, as they propagate from Earth (1 AU) to Mars (~ 1.5 AU). This broadening factor derived from our analysis extends observations for the evolution closer to the Sun by Janvier et al. (2019, JGR Space Physics) to larger heliocentric distances and is consistent with these results.

How to cite: von Forstner, J., Guo, J., Wimmer-Schweingruber, R. F., Dumbović, M., Janvier, M., Démoulin, P., Veronig, A., Temmer, M., Papaioannou, A., Dasso, S., Hassler, D. M., and Zeitlin, C. J.: Using Forbush decreases at Earth and Mars to measure the radial evolution of ICMEs, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7838, https://doi.org/10.5194/egusphere-egu2020-7838, 2020.

D2879 |
Christine Verbeke, Marilena Mierla, M. Leila Mays, Christina Kay, Mateja Dumbovic, Manuela Temmer, Erika Palmerio, Evangelos Paouris, Hebe Cremades, Pete Riley, Camilla Scolini, and Juergen Hinterreiter

Coronal Mass Ejections (CMEs) are large-scale eruptions of plasma and magnetic fields from the Sun. They are considered to be the main drivers of strong space weather events at Earth. Multiple models have been developed over the past decades to be able to predict the propagation of CMEs and their arrival time at Earth. Such models require input from observations, which can be used to fit the CME to an appropriate structure.

When determining input parameters for CME propagation models, it is common procedure to derive kinematic parameters from remote-sensing data. The resulting parameters can be used as inputs for the CME propagation models to obtain an arrival prediction time of the CME f.e. at Earth. However, when fitting the CME structure to obtain the needed parameters for simulations, different geometric structures and also different parts of the CME structure can be fitted. These aspects, together with the fact that 3D reconstructions strongly depend on the subjectivity and judgement of the scientist performing them, may lead to uncertainties in the fitted parameters. Up to now, no large study has tried to map these uncertainties and to evaluate how they affect the modelling of CMEs.  

Fitting a large set of CMEs within a selected period of time, we aim to investigate the uncertainties in the CME fittings in detail. Each event is fitted multiple times by different scientists. We discuss statistics on uncertainties of the fittings. We also present some first results of the impact of these uncertainties on CME propagation modelling.

Acknowledgements: This work has been partly supported by the International Space Science Institute (ISSI) in the framework of International Team 480 entitled: Understanding Our Capabilities In Observing And Modelling Coronal Mass Ejections'.

How to cite: Verbeke, C., Mierla, M., Mays, M. L., Kay, C., Dumbovic, M., Temmer, M., Palmerio, E., Paouris, E., Cremades, H., Riley, P., Scolini, C., and Hinterreiter, J.: Understanding our capabilities in observing and modelling Coronal Mass Ejections, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20456, https://doi.org/10.5194/egusphere-egu2020-20456, 2020.

D2880 |
Noé Lugaz, Tarik Salman, Réka Winslow, Nada Al-Haddad, Charles Farrugia, Bin Zhuang, and Antoinette Galvin

The radial expansion of magnetic ejecta (ME) has been investigated through the analysis of remote observations, the variation of their properties with radial distance and from local in situ plasma measurements showing a decreasing speed profile, as first discussed almost 40 years ago. However, little is known on how local measurements compare to global measurements of expansion and what causes the different expansion properties of different CMEs. In order to correctly forecast CME properties at Earth from measurements below 0.9 AU CME expansion must be considered, and first, understood.  Here, we take advantage of 42 CMEs being measured by two spacecraft in radial conjunction to determine how the magnetic field decrease with distance, as a measure of their global expansion. As all these CMEs are also measured near 1 AU by STEREO or Wind, we are able to determine their local expansion from the speed decrease. We find that these two measures have little relation with each other, even when looking only at the events with the closest conjunctions (in term of angular separation). We also determine the relation between measures of the CME expansion and the CME properties. Lastly, we also determine the evolution of the ME radial, azimuthal and north-south magnetic field with distance, which allow us to compare their evolution with the expectations from force-free field configurations.

How to cite: Lugaz, N., Salman, T., Winslow, R., Al-Haddad, N., Farrugia, C., Zhuang, B., and Galvin, A.: CME Expansion as Revealed by Joint Measurements by STEREO, Wind, MESSENGER and Venus Express , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6272, https://doi.org/10.5194/egusphere-egu2020-6272, 2020.

D2881 |
Jürgen Hinterreiter, Tanja Amerstorfer, Martin A. Reiss, Manuela Temmer, Christian Möstl, Maike Bauer, Ute V. Amerstorfer, Rachel L. Bailey, and Andreas J. Weiss

Forecasting the arrival time and speed of CMEs is of high importance. However, uncertainties in the forecasts are high. We present the results of post-event prediction of CME arrivals using ELEvoHI (ELlipse Evolution model based on Heliospheric Imager observations) ensemble modeling. The model uses time-elongation profiles provided by HI (Heliospheric Imager) onboard STEREO (Solar TErrestrial RElations Observatory) and assumes an elliptical shape of the CME front. The drag force exerted by the ambient solar wind is an essential factor influencing the dynamic evolution of CMEs in the heliosphere. To account for this effect, ELEvoHI utilizes the modeled ambient solar wind provided by the Wang-Sheeley-Arge model. We carefully select 12 CMEs between February 2010 and July 2012, which show clear signatures in STEREO-A and STEREO-B HI images, have a corresponding in-situ signature, and propagate close to the ecliptic plane. As input to ELEvoHI, we make use of STEREO-A and STEREO-B time-elongation profiles for each CME and compare the predicted arrival times and speeds based on both vantage points with each other. We present our model results and discuss possible reasons for the differences in the arrival times of up to 15 hours.

How to cite: Hinterreiter, J., Amerstorfer, T., Reiss, M. A., Temmer, M., Möstl, C., Bauer, M., Amerstorfer, U. V., Bailey, R. L., and Weiss, A. J.: Prediction of CME arrivals; differences based on stereoscopic heliospheric imager data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7829, https://doi.org/10.5194/egusphere-egu2020-7829, 2020.