LWS TR&T Focus Teams:
Magnetic Flux Ropes From the Sun to the Heliosphere
Target Description: Magnetic flux ropes are widely believed to play a central role in space weather. Essentially all models for the magnetic field that emerges from below the photosphere to form active regions assume a flux rope structure. Observations of coronal cavities, prominences and active region sigmoids suggest a flux rope structure for the preeruption field, and coronagraph observations invariably show a flux rope for the eruption itself. Furthermore, many models for the preeruption coronal magnetic field of CMEs/eruptive flares invoke a twisted flux rope topology, and all CME models predict a highly twisted flux rope for the eruption, irrespective of the preeruption structure. Ground truth is provided by in situ measurements of the field in the heliosphere. These generally show a twisted flux rope. Hence, flux ropes are a unifying theme across Heliophysics, and understanding the mechanisms of their formation, evolution, and propagation is critical to predicting space weather.
Despite their central importance to space weather, many basic questions on flux ropes remain. For example, where, when, and how flux ropes are formed on the Sun remains highly controversial. Some observations and models support emergence of fully or partially formed flux ropes from the convection zone, while others support local formation in the corona due to magnetic reconnection preceding or during eruptions. We also do not understood how a flux rope, once formed, evolves and eventually erupts. Finally, the posteruption transport and evolution of flux ropes through the heliosphere remain unclear. Even though all current eruption and propagation models predict a flux rope at 1 AU, in situ measurements frequently appear to show a nonrope structure for ICMEs. We are also far from understanding how the observed fields at the Sun determine the IMF at Earth, which is critical to space weather prediction.
It is timely to undertake investigations that unify the observation of flux ropes at the Sun by SDO and Hinode, as well as propagation in the heliosphere by LASCO and STEREO, and their in situ measurement by ACE, Wind, and STEREO. In addition, a growing network of ground-based instrumentation, including interplanetary scintillation arrays, muon detectors, and low-frequency radio telescopes, has been deployed that has the potential to detect the propagation of heliospheric structures as they travel through interplanetary space. As flux-rope related activity increases over the current solar cycle, we now have new observational, numerical, and theoretical capabilities with the potential to make great progress. For example, SDO and Hinode have provided unprecedented high-resolution (spatial and temporal) observations of coronal cavities, prominences/filaments, and sigmoids and early development of CMEs in active regions. SDO/HMI and Hinode/SOT also provide vector magnetic field observations that are critical to determining the magnetic roots of flux ropes in the photosphere.
Such observations, in combination with those from STEREO and ACE, can now monitor flux ropes continuously from the Sun to the heliosphere. Meanwhile, 3D MHD models covering a wide domain ranging from the convection zone to the corona and heliosphere can now simulate flux ropes that can be directly compared with new observations. These numerical efforts are being complemented by parallel theoretical/analytical modeling of relevant elementary processes, such as those leading to prominence formation in flux ropes.
Goals and Measures of Success: The overall objective of this Focused Science Team is to advance our observation and understanding of the "life cycle" of a magnetic flux rope, from its birth in the Sun, through its evolution and growth phase in the corona, to its eruption and transport through the heliosphere. Measures of success will, in all cases, be sought to reconcile observations/measurements and predictions with model-based simulations and/or theoretical investigations, as well as the elimination of theoretical ideas demonstrably not supported by observations. The primary goals are fourfold:
• Identify the formation mechanisms of flux ropes in the solar atmosphere
Types of Solicited Investigations: This FST seeks broad interdisciplinary studies that tie together the heliospheric and solar observations. Possible studies include:
• Observational studies of flux rope formation and evolution, such as vector field data from SDO or from the ground and high-resolution coronal imaging/spectroscopy from SDO, Hinode, and STEREO