3D Structure of Microwave Sources from Solar Rotation Stereoscopy vs Magnetic Extrapolations

TL;DR

This study combines rotation stereoscopy and radio imaging to determine the 3D structure of solar radio sources and compares the results with magnetic extrapolations, revealing that gyroresonance emission originates from higher coronal heights.

Contribution

It adapts a stereoscopy algorithm for single- and two-dimensional data and applies it to multi-frequency solar radio observations to estimate coronal source heights and magnetic field profiles.

Findings

Gyroresonance emission occurs above the third gyrolayer height.

Estimated source heights are consistently higher than magnetic extrapolation predictions.

Results have implications for coronal magnetography and plasma physics.

Abstract

We use rotation stereoscopy to estimate the height of a steady-state solar feature relative to the photosphere, based on its apparent motion in the image plane recorded over several days of observation. The stereoscopy algorithm is adapted to work with either one- or two-dimensional data (i.e. from images or from observations that record the projected position of the source along an arbitrary axis). The accuracy of the algorithm is tested on simulated data, and then the algorithm is used to estimate the coronal radio source heights associated with the active region NOAA 10956, based on multifrequency imaging data over 7 days from the Siberian Solar Radio Telescope near 5.7 GHz, the Nobeyama Radio Heliograph at 17 GHz, as well as one-dimensional scans at multiple frequencies spanning the 5.98--15.95 GHz frequency range from the RATAN-600 instrument. The gyroresonance emission mechanism, which is sensitive to the coronal magnetic field strength, is applied to convert the estimated radio source heights at various frequencies, h(f), to information about magnetic field vs. height B(h), and the results are compared to a magnetic field extrapolation derived from photospheric magnetic field observations obtained by Hinode and MDI. We found that the gyroresonant emission comes from the heights exceeding location of the third gyrolayer irrespectively on the magnetic extrapolation method; implications of this finding for the coronal magnetography and coronal plasma physics are discussed.