Magnetic Helicity from the Sun to Earth

Monitoring, understanding, and successful prediction of the conditions in the interplanetary near- Earth environment (our space weather) are becoming essential, given the reliance of humanity on satellite-based services. Especially Earth-directed coronal mass ejections (CMEs), magnetized clouds of coronal plasma ejected from the outermost layer of the solar atmosphere, the corona, severely impact space weather. For a better understanding, the combined analysis of disturbances registered in our near-Earth environment, their interplanetary evolution, as well as their solar source region is required. A single quantity provides a well-defined physical link: magnetic helicity. Its magnitude indicates the degree of complexity while its sign is unambiguously related to the geometrical sense of the underlying magnetic field. Being quasi-conserved, it can be used to trace magnetic complexity consistently in different spatial regimes: in the CMEs near-surface solar source region (in the form of photospheric helicity flux), in the active-region solar atmosphere (in the form of the instantaneous coronal helicity budget), as well as in interplanetary space (in the form of the magnetic helicity of the ICME modeled on the basis of in-situ measurements). The estimation of the magnetic helicity requires knowledge of the magnetic field vector. Direct measurements are well-established and routinely performed at photospheric levels where the Solar Dynamics Observatory represents an unique data source. The coronal magnetic field can be approximated by data-constrained nonlinear force-free modeling techniques which require the measured photospheric data as an input. The magnetic field vector in our near-Earth environment is provided in the form of time series of localized in-situ measurements at the location of the operating spacecraft (e.g., Advanced Composition Explorer and WIND, and since recently and operating closer to the Sun, Parker Solar Probe and Solar Orbiter). The simulation of the ICMEs interplanetary propagation provides predicted arrival times at different targets in the solar system, and thus allows an unambiguous identification of the in-situ signatures of an associated magnetic cloud (MC), based on which its helicity budget can be estimated. Here, we propose a research project going beyond the state of the art with the main aim to provide a more coherent picture of the physical properties of solar eruptions in interplanetary space. We will do so by systematically relating associated measures of the magnetic helicity in different spatial regimes: the helicity flux in the solar source region, the helicity budget of the corona above, the helicity of the near-Sun CME, and that of the MC in interplanetary space. The unprecedented near-Sun in-situ data from Parker Solar Probe and Solar Orbiter will improve our knowledge especially on the near-Sun properties of ICMEs, which are largely unknown to date.