Determination of the Height-Temperature Profile Above a Solar Active Region from Multi-Frequency Radio Observations

TL;DR

This paper introduces an iterative method to reconstruct the height-temperature profile of the solar atmosphere above sunspots using multi-frequency microwave observations, assuming gyroresonance emission and magnetic field extrapolation.

Contribution

It presents a novel iterative reconstruction technique combining magnetic field extrapolation and regularized linear solving for solar atmospheric profiling.

Findings

Temperature profiles match contemporary active region models.

Reproduces observed spectra with a few percent accuracy.

Method is validated on synthetic and real data.

Abstract

An iterative method is presented for reconstructing the height-temperature profile of the solar atmosphere above a sunspot using multi-frequency spectro-polarimetric microwave observations. It is assumed that the emission is formed predominantly under gyroresonance conditions at harmonics of the electron gyrofrequency, and that the contribution at each frequency is associated with a layer of optical depth of order unity. The frequency-height correspondence is determined from extrapolation of the photospheric magnetic field into the corona. The reconstruction of the profile is reduced to solving an overdetermined system of linear equations with regularization, ensuring noise stability and physical smoothness of the solution. The method is tested on synthetic data for a dipole sunspot model and applied to observations of active region NOAA 11312 obtained with the RATAN-600 radio telescope. The derived temperature profiles are consistent with contemporary models of active regions and reproduce the observed spectra in the 3-18~GHz range with an accuracy of a few percent.