Exploring solar-terrestrial interactions via multiple imaging observers

How does solar wind energy flow through the Earth’s magnetosphere, how is it converted and distributed? is the question we want to address. We need to understand how geomagnetic storms and substorms start and grow, not just as a matter of scientific curiosity, but to address a clear and pressing practical problem: space weather, which can influence the performance and reliability of our technological systems, in space and on the ground, and can endanger human life and health. Much knowledge has already been acquired over the past decades, particularly by making use of multiple spacecraft measuring conditions in situ, but the infant stage of space weather forecasting demonstrates that we still have a vast amount of learning to do. A novel global approach is now being taken by a number of space imaging missions which are under development and the first tantalising results of their exploration will be available in the next decade. In this White Paper, submitted to ESA in response to the Voyage 2050 Call, we propose the next step in the quest for a complete understanding of how the Sun controls the Earth’s plasma environment: a tomographic imaging approach comprising two spacecraft in highly inclined polar orbits, enabling global imaging of magnetopause and cusps in soft X-rays, of auroral regions in FUV, of plasmasphere and ring current in EUV and ENA (Energetic Neutral Atoms), alongside in situ measurements. Such a mission, encompassing the variety of physical processes determining the conditions of geospace, will be crucial on the way to achieving scientific closure on the question of solar-terrestrial interactions.

Space weather: the solar perspective

The Sun, as an active star, is the driver of energetic phenomena that structure interplanetary space and affect planetary atmospheres. The effects of Space Weather on Earth and the solar system is of increasing importance as human spaceflight is preparing for lunar and Mars missions. This review is focusing on the solar perspective of the Space Weather relevant phenomena, coronal mass ejections (CMEs), flares, solar energetic particles (SEPs), and solar wind stream interaction regions (SIR). With the advent of the STEREO mission (launched in 2006), literally, new perspectives were provided that enabled for the first time to study coronal structures and the evolution of activity phenomena in three dimensions. New imaging capabilities, covering the entire Sun-Earth distance range, allowed to seamlessly connect CMEs and their interplanetary counterparts measured in-situ (so called ICMEs). This vastly increased our knowledge and understanding of the dynamics of interplanetary space due to solar activity and fostered the development of Space Weather forecasting models. Moreover, we are facing challenging times gathering new data from two extraordinary missions, NASA’s Parker Solar Probe (launched in 2018) and ESA’s Solar Orbiter (launched in 2020), that will in the near future provide more detailed insight into the solar wind evolution and image CMEs from view points never approached before. The current review builds upon the Living Reviews article by Schwenn from 2006, updating on the Space Weather relevant CME-flare-SEP phenomena from the solar perspective, as observed from multiple viewpoints and their concomitant solar surface signatures.

NMDB database and global survey method

The method of a global survey developed in the 1970s allows using a world-wide network of neutron monitor stations as a single multidirectional device. Wherein, receiving characteristics of each device, which reflects their geometries and geographical positions, are taken into account. Such an approach makes it possible to define the first two angular moments of the distribution function of cosmic rays in the interplanetary space at each hour of observation. With the creation in 2008/2009 and subsequent development of an international database of neutron monitors NMDB, for the first time it appeared an opportunity to use the global survey method in real-time mode. Such a situation creates a unique possibility to use the results not only for scienti- fic researches but also for space weather forecasting. To use the data of the world-wide network of neutron monitors it is necessary to carry preliminary preparations. Thereby, in the current work, the main attention is attracted to a solution to some practical questions that arise when using the NMDB in real-time.

Improving the Medium-Term Forecasting of Space Weather: A Big Picture Review From a Solar Observer's Perspective

We have improved considerably our scientific understanding of the key solar drivers of Space Weather, i.e., Coronal Mass Ejections, flares, in the last 20+ years thanks to a plethora of space missions and modeling advances. Yet, a major breakthrough in assessing the geo-effectiveness of a given CME and associated phenomena still escapes us, holding back actionable medium-term (up to 7 days) forecasting of Space Weather. Why is that? I adopt a two-pronged approach to search for answers. First, I assess the last 20+ years of research on solar drivers by identifying lessons-learned and paradigm shifts in our view of solar activity, always in relation to Space Weather concerns. Then, I review the state of key observation-based quantities used in forecasting to isolate the choke points and research gaps that limit medium-term forecasting performance. Finally, I outline a path forward along three vectors—breakthrough capabilities, geo-effective potential, and actionable forecast—with the strongest potential to improve space weather forecasting horizon and robustness.

Comparative study of halo CME arrival predictions

<p>Halo coronal mass ejections (CMEs) are one of the most effective drivers of intense geomagnetic storms. Despite the recent advances in space weather forecasting, the accurate arrival prediction of halo CMEs remains a challenge.  This is because in general CMEs interact with the background solar wind during their propagation in the interplanetary space. In addition, in the case of halo CMEs, the accurate estimation of their kinematics is difficult due to projection effects in the plane-of-sky.</p><p>In this study, we are revisiting the arrival of twelve geoeffective Earth-directed fast halo CMEs using an empirical and a numerical approaches. For this purpose we refine the input to the Drag-based Model (DBM) and to the EUropean Heliospheric Forecasting Information Asset (EUHFORIA), which are recently available for users from the ESA Space Situational Awareness Portal (http://swe.ssa.esa.int).</p><p>The DBM model has been tested using different values for the input drag parameter.  On average, the predicted arrival times are confined in the range of ± 10 h. The closest arrival to the observed one has been achieved with a drag value higher than the recommended for fast CMEs. Setting a higher drag also helped to obtain a closer to the observed CME arrival speed prediction. These results suggest that the exerted solar wind drag was higher than expected. Further, we are searching for clues about the CME propagation by performing EUHFORIA runs using the same CME kinematics. Preliminary results show that both models perform poorly for CMEs that have possibly undergone CME-CME interaction, underlying again the importance of taking into account the state of the interplanetary space in the CME forecast.</p>

NASA Space Weather Science Application Strategy and Activities

<p>The NASA Heliophysics Division Space Weather Science Application (SWxSA) program has as its strategic mission to establish a preeminent space weather capability that supports human and robotic space exploration and meets national, international, and societal needs. This is done by advancing measurement and analysis techniques and expanding knowledge and understanding that improves space weather forecasts and nowcasts. Ultimately, the SWxSA program enables space weather forecasting capability that the Agency and Nation and international community require, in partnership with NASA’s Artemis Program and other Federal agencies, and international partners. This includes the development and launch of missions/instruments that advance our knowledge of space weather and improve its prediction, and the transitioning of technology, tools, models, data, and knowledge from research to operational environments. This presentation will provide an update on NASA’s SWxSA space weather strategy and activities.</p>

Investigating the drag-based model parameters through statistical methods

<p>Due to their simplicity and relatively short computational time, empirical models for Solar Wind Transients, based on a restricted number of assumptions and on the values of a small set of parameters, play an important role in Space Weather forecasting. For this reason, an optimal choice of values for the model parameters is of critical importance in this approach. In this work, we compiled a list of CME events by merging and cross-referencing several databases and made use of such experimental data to evaluate statistical distributions for the model parameters of a chosen forecasting model for ICME arrivals, namely the Drag-Based model. Our results lead to several considerations and refinements to be implemented in the future in this and other forecasting models.</p>

Influence of the CME orientation on the ICME propagation

<p>Beyond certain distance the ICME propagation becomes mostly governed by the interaction of the ICME and the ambient solar wind. 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 inclination of the CME flux rope axis i.e. tilt, influences the propagation of the ICME itself. In order to study the relation between the tilt parameter and the ICME propagation we investigated isolated Earth-impacting CME-ICME evets in the time period from 2006. to 2014. We determined the CME tilt in the “near-Sun” environment from the 3D reconstruction of the CME, obtained by the Graduated Cylindrical Shell model using coronagraphic images provided by the STEREO and SOHO missions. We determined the tilt of the ICME in the “near-Earth” environment using in-situ data. We constrained our study to CME-ICME events that show no evidence of rotation while propagating, i.e. have a similar tilt in the “near-Sun” and “near-Earth” environment. We present preliminary results of our study and discuss their implications for space-weather forecasting using the drag-based(ensemble) [DB(E)M] model of heliospheric propagation.</p>

Quality assessment for objective inter-comparison of coronal models

<p>With the increasing amount of space weather forecasting simulation codes being developed, assessing their performance becomes crucial. Especially the errors resulting from coronal magnetic field models are a critical factor, because these will get propagated further by various solar wind models. We present a first result for a benchmarking system that allows a rather easy-to-implement  assessment of the performance quality of any coronal magnetic field model. This will allow for a standardized comparison between different models. The benchmarking system is based on stepwise visual and semi-automatized comparisons between model output and EUV on-disk and coronograph white-light data. We are using various viewpoints and instrumental data provided by STEREO, SOHO and SDO. <br>In our work we exemplarily apply this scheme to the coronal model currently implemented in EUHFORIA, an adaption of the Wang-Sheeley-Arge (WSA) model, with varying input parameters. Furthermore, with this system we also show its possible usage for the derivation of an ideal parameter set. </p>

Development of space environment customized risk estimation for satellites (SECURES)

Plasma variations in the geospace environment driven by solar wind–magnetosphere interactions are one of the major causes of satellite anomaly. To mitigate the effect of satellite anomaly, the risk of space weather disturbances predicted by space weather forecasting needs to be known in advance. However, the risk of satellite anomaly owing to space weather disturbances is not the same for all satellites, because the risk depends not only on the space environment itself but also on the design and materials of individual satellites. From the viewpoint of satellite operators, it is difficult to apply a general alert level of the space environment to the risk of individual satellites. To provide tailored space weather information, we have developed SECURES (Space Environment Customized Risk Estimation for Satellites) by combining models of the space environment and those of spacecraft charging. In SECURES, we focus on the risk of spacecraft charging (surface/internal) for geosynchronous satellites. For the risk estimation of surface charging, we have combined the global magnetosphere magnetohydrodynamics (MHD) model with the satellite surface charging models. For the risk estimation of internal charging, we have combined the radiation belt models with the satellite internal charging models. We have developed prototype products for both types of charging/electrostatic discharge (ESD). The development of SECURES and our achievements are introduced in this paper.