Chromospheric flare ribbons are one of the most direct observational link to the magnetic reconnection region and can provide unique information on the 3D magnetic geometry of the energy release…

This federal contract award is a grant to the Smithsonian Astrophysical Observatory (SAO), a division of the Smithsonian Institution. The $233,283.51 grant from the National Aeronautics and Space Administration (NASA) will support research on solar flares and magnetic reconnection using data from the Solar Dynamics Observatory (SDO) and other NASA missions.

The research aims to better understand the 3D magnetic topology and energy release processes in solar flares by studying the motions, morphologies, and evolutions of chromospheric flare ribbons. The project will combine observations from SDO, IRIS, and Hinode/XRT with magnetohydrodynamic modeling to quantify reconnection parameters and investigate the role of quasi-separatrix layers. This work is expected to provide new insights into the origins of solar activity and fundamental astrophysical processes of magnetic reconnection. The grant was awarded in June 2018 and is scheduled for completion in May 2023.

Chromospheric flare ribbons are one of the most direct observational link to the magnetic reconnection region and can provide unique information on the 3D magnetic geometry of the energy release site and channels in solar flares. Flare ribbons appear in different configurations, which tell US about the 3D magnetic topology of the flaring region. Some archetypal examples include circular ribbon flares with or without a remote ribbon that are interpreted as occurring in a fan-spine magnetic topology involving a null point; or two-ribbon flares associated with the failed or successful eruption of a magnetic flux rope as in the standard flare picture. Intriguingly, there can be combinations of these two configurations when in some circular-ribbon flares an active filament is embedded under a fan dome. The solar dynamics observatory (SDO) has revealed details in the evolution of solar flares that have never been seen before. In particular, the multi-wavelength, high-cadence, and full-sun coverage allows the detailed observation of many ribbons with the possibility to describe their apparent motions, morphologies, and evolutions. The 12S cadence of AIA allows the determination of the ribbon apparent motion velocities and their changes in time and space and HMI provides precise measurements of the magnetic field. Using these two measurements a number of reconnection parameters can be determined, such as the local and global reconnected flux as a function of time and space over the duration of the flare, and employing the 2D flare approximation also the electric field at the reconnection site and the poynting flux. The goodness of the 2D approximation can be tested if the same experiment is done using an idealized MHD simulation of an erupting flux rope, where we do have the full 3D information. Using the HMI magnetograms and AIA and hinode/XRT observations we will use the flux rope insertion method to build non-linear force-free field and unstable magnetofrictional models of the erupting configurations. Then, utilizing a new unprecedentedly fast code for finding the locations of topological features starting from the 3D magnetic field, we will compute in a 3D volume the squashing factor, q, which describes the strength of the quasi-separatrix layers, the qsls. IT has been shown that parts of the volume where q is high are the preferred sites for the build-up of current sheets and hence reconnection, such as at a hyperbolic flux tube (HFT) under an erupting flux rope. With the current capabilities the computation of the q-factor is so fast that IT is conceivable that in the future IT can be used to predict solar activity. In addition, we plan to utilize spectral observations from iris and EIS to reveal the heat flow into and from the flare ribbons, as well as determine the amount of non-thermal energy at their locations. We plan to answer the following science questions: 1. How good is the 2D approximation in determining the reconnection parameters in two-ribbon flares? 2. Does reconnection proceed faster and is more efficient in high-q regions? Is there a correlation between the reconnection parameters derived from the ribbon motions as well as the velocity of the evaporation flows and non-thermal widths derived from iris and EIS spectral observations and the order of magnitude of the q-factor at the these ribbon locations and at their 3D extensions up to the HFT above? From a preliminary event survey, we have compiled a list of 20 flares and more such events are expected as SDO and iris continue observing. This makes IT an opportune moment to quantitatively address the above questions by detailed case-by-case as well as comparative studies. By answering these questions, we will explore the origins of the sun s activity and characterize fundamental processes in astrophysics, i.e. reconnection.