The magnetic environment of Earth is strongly influenced by the Sun and its activity, and it is nowadays recognized to be a highly interlinked system whose variability is known as space weather. The ability to forecast its evolution relies on our understanding of the physical processes that take place on the Sun, such as flares and coronal mass ejections (CMEs). In recent years, magnetic helicity has become an attractive, seemingly viable, and promising candidate for the general description and interpretation of many solar events relevant to space weather. In particular, the conservation properties of helicity under typical solar conditions justifies its use as a tracer during different phases of the life of twisted, tangled magnetic structures, from their formation below the photosphere, to their stability properties in the coronal atmosphere, to their propagation in interplanetary space as ICME. Such a powerful description requires a deep understanding of the properties of magnetic helicity, and accurate methods for its estimation. In spite of the first applications to solar observations already appearing in the literature, no systematic effort has been placed so far in order to assess the reliability of methods for the estimations of magnetic helicity.
The goal of the proposed working group is to redefine the state of the art of existing methods for the estimation of magnetic helicity, based both on photospheric injection, inferred photospheric magnetic connectivity, and volume computations. The comparison between different methods will firstly exploit few numerical test cases that are used in the literature for modeling solar events. This first part of the project is aimed at assessing the accuracy of different methods in a controlled environment. Secondly, we will apply the methods to actual observations, using models of the coronal atmosphere and active regions where necessary (eg., obtained using nonlinear force-free extrapolation). Such a comparison of methods for the estimations of magnetic helicity has never been thoroughly performed yet. By supporting this project, ISSI would therefore provide an unique opportunity for the proposed group of international scientists, who are experts in helicity estimations, to test the practical significance of this physical quantity for space weather predictions.
To this aim, we propose to set up an international team consisting of eight (8) experts representative of the state-of-the-art techniques of magnetic helicity estimations in the solar atmosphere. In a series of three meetings, we plan to compare different methods within a coherent framework using model and observational test cases, and to provide the solar community with thorough and accurate reference works on helicity estimations in solar observations.
Created, 1 Nov. 2014 by G. Valori