Interaction of COronal HOles and Solar Storms


ICOHOSS logohrzz logo

Acronym: ICOHOSS
Duration: 01.03.2021. - 28.02.2025.
Total value: 1.217.865,00 HRK
Financed trough: Croatian Science Foundation

Project leader: Mateja Dumbović

The research in the scope of ICOHOSS project is expected to have significant impact on the understanding of the propagation and evolution of CMEs, which is one of the fundamental problems of the Heliospheric Physics. The current models and theories mostly regard simplified structures, therefore, extensive analysis of the complex structures will bring new knowledge to expand and deepen the theoretical approaches. With the proposed research, we will not only improve our knowledge of the solar storms but also improve our current knowledge from the perspective of forecasting space weather in order to mitigate damages related to complex and, hence, hazardous space weather events.

Coronal mass ejections (CMEs), popularly known as “Solar storms”, are the most violent eruptive phenomena in the solar system and most prominent drivers of the space weather. The modern paradigm is that these are eruptions of the magnetic plasma structures with field lines helicoidally winding around the central axis, so-called flux ropes, caused by magnetic instabilities which trigger their eruption. CMEs are typically propagating radially outward, where their kinematics in the interplanetary space is governed by the magnetohydrodynamical (MHD) drag. Modelling CME propagation based on MHD drag has resulted in a very successful analytical drag-based model for heliospheric propagation of CMEs (DBM) and its ensemble version (DBEM). A number of studies revealed that CME propagation can substantially deviate from its initial, radial direction due to the non-uniform restoring force of the magnetic background. The deflections typically occur close to the Sun due to vicinity of the “open-field” regions of coronal holes or helmet streamers. Coronal holes (CH) are low plasma density regions in the solar corona, observed as dark regions in EUV image data and are associated with open magnetic fields and high-speed solar wind. The interaction between the fast-solar wind from CHs and the intervening slower solar wind leads to the creation of so-called stream interaction regions (SIRs), which persist for several solar rotations corotating with the Sun and are then called corotating interaction regions (CIRs).

As DBM and other propagation models use input parameters starting in the outer corona (15Rs and beyond), deflections are typically not included. The numerical simulations provide excellent means to study complex events such as interactions of CMEs with coronal holes, however their results are not always easy to interpret. Systematic parameter studies for less complex events are usually done using analytical physics-based models as these are straightforward to interpret and computationally cheap with performances comparable to numerical model results. As CMEs propagate through the solar corona and interplanetary space, they pile-up plasma and may drive shock waves ahead, where both the magnetic structure and the disturbed interplanetary plasma and magnetic field are usually referred to as interplanetary coronal mass ejection (ICME), consisting of the shock/sheath region and the magnetic structure. In interplanetary space, they are typically observed in situ, using plasma, magnetic field and/or particle measurements. The evolution of CMEs also involves their expansion. The most common assumption is that they expand self-similarly, i.e. in a way that the plasma element at a later time is a scaled copy of it at some previous time. The evolution of the CME can deviate significantly from the uniform self-similar expansion due to magnetic reconnection. Magnetic reconnection can lead to the reduction in the magnetic flux when it e.g. occurs at the interface between CMEs and coronal holes (interchange reconnection), as well as a complex interaction where a CME is “squeezed” between two magnetic structures can inhibit its expansion. It is therefore clear that the interaction of the CME with a coronal hole and its corresponding magnetic structure can change not only its propagational, but also its evolutionary properties on route to Earth.

Dr Mateja Dumbovic (project leader)
Dr Bojan Vrsnak
Dr Manuela Temmer
Dr Astrid Veronig

Science questions:
1) What types of in situ signatures are expected from CME-CH interactions, and what kind of interaction are they related to?
2) Do CME-CH interactions occur at all radial distances? What governs that distance of interaction, and how does it influence the effects of the interaction?
3) Does CME-CH interaction change the inner magnetic structure of the CME, and how? Does this change/reflect on the geo- and GCR-effectiveness of the CME?

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