Journal of Astrobiology & Outreach

Abstract

Estimating the Coronal and Chromospheric Magnetic Fields of Solar Active Regions as Observed with the Nobeyama Radioheliograph Compared with the Extrapolated Linear Force-free Field

A Mouner, Abdelrazek MK Shaltout, MM Beheary, KAK Gadallah and KA Edris

Adopting the thermal bremsstrahlung or so-called free-free emission process, the coronal and chromospheric magnetic fields are derived from the polarization and spectral observations with the Nobeyama Radioheliograph (NoRH) at 17 GHz. The solar active regions (ARs) located near the disk center observed on January 8, 2015 (NOAA 12257) and December 4, 2016 (NOAA 12615) are used for the estimate of the chromospheric and coronal magnetic fields with the microwave radio observations. We compare solar radio maps of active regions for both intensity and circularly polarized component with the photospheric magnetograms from observations with the Helioseismic & Magnetic Imager (HMI) and the chromosphere-corona transition region images obtained with the Atmospheric Imaging Assembly (AIA), on board the Solar Dynamic Observatory (SDO). From our analysis, we find a different structure in the radio intensity maps between two active regions owing to possibly the differential rotation of the Sun, where the AR 12257 clearly shows a widespread structure of radio intensity, but in the case of AR 12615 which exhibits a narrow structure in the total intensity map. We notice from the comparison between radio maps of both ARs that the circular polarization degree in the AR 12257 is about 2%, but the AR 12615 has a higher existent value by 3%. Radio observations provide us for direct measurements of magnetic fields in the chromospheric and coronal layers. We estimate the coronal magnetic fields using the AIA observations by adopting magnetic loops in the corona over some patches with weak photospheric magnetic fields. However, the coronal magnetic field derived from the SDO/AIA data was 90-240 G. We also study the coronal magnetic fields based on the structure of the extrapolated field, where the result of the magnetic fields was in the range 35 – 145 G, showing that the difference in the coronal magnetic fields between both results is attributed to the assumption of the force-free approximation.