NSF Award
1358270
Solar magnetism is what powers the solar wind and coronal mass ejections (CME) and it is the ultimate source of space weather. Forecasting space weather and the onset and acceleration of CMEs is a critical goal of solar and space physics. For modern society it is crucial to respond to geo-effective CMEs that can damage satellites or ground-based technology. Reliable forecast of geo-effective events requires knowledge of the coronal magnetic field within a few solar radii where its structure and variability affects space weather by modifying solar wind conditions and CME propagation. Unfortunately, measurements of the coronal magnetic field are inherently very difficult to make and, therefore, constitute a weak link in our understanding of many physical mechanisms at work in the heliosphere. This project introduces and explores a new technique for measuring both the strength and direction of the magnetic field in the solar corona. If successfully demonstrated, this will pave the way to synoptic (whole sun) measurements of the coronal fields with the upcoming NSF Major Research Equipment and Facilities Construction project, the Daniel K. Inouye Solar Telescope (DKIST, formerly the Advanced Technology Solar Telescope, ATST), which is scheduled to begin operation soon after the completion of this project. <br/><br/>The project will promote hands-on Science Technology Engineering and Match (STEM) education through the NSF funded Akamai Workforce Initiative (AWI) for which the investigators on this project have served as mentors, participants and organizers. Three STEM AWI students will be involved in summer projects with hands-on experience in remote sensing technology. In addition, the project will fully enable one graduate student and partially enable a second student to complete their PhDs in solar and heliospheric physics. Furthermore, the new magnetometry technique that is developed under this grant will be integrated into the community coronal study tool FORWARD developed at the High Altitude Observatory of NSF's National Center for Atmospheric Research in Boulder, Colorado.<br/><br/>The project concerns the development, implementation, and demonstration of a new technique for measuring coronal magnetic fields. It employs simultaneously linear spectropolarimetry of (i) the unsaturated Hanle effect in permitted lines, such as He I 1083 nm line being adsorbed from inter-planetary or comet matter in the hot corona and (ii) the saturated Hanle effect in the bright forbidden [Fe XIII] 1074.7 nm and [Si X] 1430 nm lines. The technique does not depend on the Zeeman effect in these lines. Observing these lines (quasi-) simultaneously can provide unambiguous measurements of the full magnetic vector in the corona. The goals of this project are to implement this new approach, determine specific requirements for observations and sensitivity limits, obtain a catalog of line polarization measurements, and infer vector images of magnetic fields in the solar corona. In addition to the He I line other permitted lines of neutral atomic and molecular species sublimating from Sun-grazing comets near their perihelion will be investigated. Observations will be carried out with the Scatter-Free Observatory for Limb Active Regions and Coronae (SOLARC), an IR imaging spectropolarimeter located on the summit of Haleakala, Maui. Furthermore, potential and nonlinear force-free field extrapolations as well as MHD-based magnetic field models will be computed and compared with magnetic vector maps inferred from observations.
