This team of investigators will use three-dimensional magnetohyrodynamic simulations to study the impact of prior solar eruptions and plasma interaction processes on the ultimate properties of coronal mass ejections (CMEs) reaching Earth's orbit. The team will assess how earlier CMEs precondition the heliosphere and solar wind, as well as how prior CME interactions deflect, rotate, compress, and accelerate subsequent CMEs. The team will identify the causes of enhanced geo-effectiveness in complex CME events at Earth and the extent to which these causes can be forecasted from remote-sensing observations.
The team will conduct self-consistent simulations of selected CME events using existing and improved models of CME evolution, the interplanetary magnetic field, and the solar wind, and they will then compare their model output to spacecraft observations. The investigators argue that these direct comparisons will result in better constraints on their numerical models, as well as in new tools to better understand these complex measurements.
The team is a collaborative effort among the University of Hawaii (the lead institution), the University of New Hampshire, and the Naval Research Laboratory. The team members will broadly disseminate their research results to the space weather community by organizing and participating in workshops and conferences, as well as through their journal publications and the enhancement of existing community models at the Community Coordinated Modeling Center at NASA Goddard Space Flight Center. The invesitgators at the University of Hawaii and the University of New Hampshire will integrate local undergraduates in this research. The investigators pledge to recruit under-represented minorities into this effort wherever possible. The lead investigator also plans to take advantage of the Hawaii Center for Advancing Systemic Heliophysics Education for engaging in public outreach, while exploiting the colorful graphics and movies derived from these research simulations.
Project Outcomes Science Massive eruptions from the Sun, called coronal mass ejections (CMEs), tend to be very frequent near the peak phase of the 11-year-long solar activity cycle. One expects then to see individual CMEs ''colliding'' and interacting with each other. Two questions arise. The first is about the physical nature of these CME interactions, which may lead to the (total or partial) merging of two or more CMEs. The second question concerns the effects interacting CMEs elicit at Earth. It is known that isolated CMEs result in large disturbances of the Earth's magnetosphere which may lead to deleterious effects on our technological infrastructure (aka space weather), particularly when a southward component of above-average strength and of long duration is present. Total or partial mergers CME complicate this picture because they produce geomagnetic disturbances over and above those of isolated CMEs. This is in large measure due to the compression of fields and plasmas when the interplanetary shock that was being driven by the trailing CME passes through the leading CME. This latter aspect was reviewed in a paper supported by this grant. In our work we devoted plenty of attention to the former aspect, i.e. the physics of CME interactions. In a number of papers we analyzed a very active interval during early August 2010 when multiple CMEs were observed at various locations between the Sun and Earth. This circumstance allowed us to use these multiple-point observations to study the physics involved when CMEs interact, and how the propagation of the participating CMEs is affected. For example, are the CMEs deflected? This is an important issue if for nothing else because if they are going to impact the terrestrial environment at all, they have to be directed towards Earth. We presented clear cases of deflection by combining remote, imaging data with in-situ observations. A very extreme event resulted when two CMEs, launched in close succession on July 23, 2012, interacted with each other and were subsequently observed by the STEREO-A spacecraft situated on the farside of the Sun. The event was analyzed with multiple-point remote-sensing and in-situ observations. It was found that the interaction resulted in a change in the propagation direction toward a head-on impact with STEREO-A. An extremely high magnetic ?eld strength resulted from the interaction and was observed by STEREO-A. A major feature was the very fast transit time from Sun to Earth (~19 hrs), implying an exceptionally modest deceleration en route. Together, these effects caused a unprecedented solar storm which, had it hit the Earth, would have produced a geomagnetic storm of record strength. These results provide new insights as to how an extreme space weather event can arise from a combination of solar eruptions. The very fast Sun-to-STEREO-A transit time was shown to be due to a pre-conditioning of the upstream solar wind by an earlier solar eruption. This pre-conditioning strongly reduced the aerodynamic drag force, in agreement with other studies, In our work we also postulated a new type of CME merger resulting from the interaction of two CMEs with different orientations. When observed later at 1 AU, the merger was associated with a smooth rotation of the magnetic ?eld vector over an extended duration and did not show clear signs of interaction. We determined the characteristics of such events based on a numerical simulation and identified and analyzed a potential case in the long-duration CME measured in-situ on 19--22 March, 2001. Such events, which may result in intense, long-duration geomagnetic storms, may sometimes be misidenti?ed as isolated CMEs. Public Outreach The public outreach aspect of the proposal are the following. The results obtained were widely disseminated to the scientific community. The project resulted in thirteen publications, eleven of which were in peer-reviewed journals. Two of these publications were review articles. Results from this work was presented at: (i) the Fall AGU 2012, 2013 Meetings; (ii) the SHINE 2012 and 2013 Workshops in Wailea Maui, Hawaii, and in Telluride, Colorado, respectively, and (iii) the Solar Wind 13 Conference at Big Island, Hawai . Some of this work was reported by Wenyuan Yu, who is a graduate student of the PI and N. Lugaz at the University of New Hampshire. Two publications appeared in the Proceedings of the Solar Wind 13 Conference. The PIs C. J. Farrugia and N. Lugaz organized the session "What exactly is a Coronal Mass Ejection?" at the SHINE 2013 Meeting in Buford, Ga.
