On the interaction between solar photospheric flow and magnetic field

Abstract

The interaction between plasma flow and magnetic field transports energy and magnetic helicity through the solar photosphere. It plays a fundamental role in heating the corona and powering eruptions. In active regions, the rising, twisted magnetic flux tubes expand and unwind; the resulting net Lorentz force drives systematic photospheric flows that injects significant magnetic energy and helicity into the corona. In the quiet-Sun region, these interactions will introduce undulations in the magnetic field lines, resulting in the concentration, cancellation, and reconnection of the magnetic fields. Studying the photospheric flows and their interaction with the magnetic fields are of fundamental importance to understanding the dynamics of the lower atmosphere, and its role in transporting energy and helicity that power solar eruptions.An overarching goal of this dissertation is to accurately infer the flow fields from a time sequence of photospheric spectropolarimetric data, which is essential to quantifying the energy and helicity transport in both active regions and quiet Sun. The first part focuses on studying the flow field in active regions. Specifically, I investigate the apparently supersonic Doppler flows in the core of active region 12673 with a new flow tracking method and SDO/HMI and Hinode/SP observations. I show that the flows are parallel to the magnetic fields, and the large Doppler velocity is just a projection effect. In the second part, in preparation for quiet-Sun studies with the 4-m Daniel K. Inouye Solar Telescope (DKIST), I explore the capability of its high-resolution observation in quantifying the energy transport with the realistic magnetohydrodynamic simulation and forward modeling. I find that existing method can capture the majority of unsigned energy flux, but the net flux remains poorly estimated. In the third part, using active region 12673 as an example, I investigate the reasons for significant discrepancies between several widely used methods that estimate energy and helicity flux. I demonstrate that the curl-free part of the electric field, which is not well-constrained by observation and is treated in ad hoc fashion, is the main cause for the differences. The interaction between the flow field and the magnetic field in the solar photosphere is key to understanding the dynamics in the solar atmosphere. My work demonstrates the capability of new methods and observations in characterizing complex flow fields in both active regions and quiet Sun, though many challenges persist. The future multi-line, high spatial-, spectral-, and temporal-resolution observation as well as the observations from different vantage points will provide more constraints and expand our capabilities.