Strongest coronal magnetic fields in solar cycles 23-24: probing, statistics, and implications

TL;DR

This study analyzes over two decades of high-frequency microwave observations to identify and statistically characterize the strongest coronal magnetic fields during solar cycles 23-24, revealing their rarity but regular appearance and association with solar activity.

Contribution

It provides the first comprehensive statistical analysis of strong coronal magnetic fields using high-frequency microwave data over two solar cycles, challenging previous expectations of maximum field strength.

Findings

Active regions with strong magnetic fields are rare (<1%)

Strong magnetic fields are regularly observed on the Sun

These regions are linked to significant solar activity

Abstract

Strong coronal magnetic field, when present, manifests itself as bright microwave sources at high frequencies produced by gyroresonant (GR) emission mechanism in thermal coronal plasma. The highest frequency at which this emission is observed is proportional to the absolute value of the strongest coronal magnetic field on the line of sight. Although no coronal magnetic field larger than roughly 2,000 G was expected, recently the field at least twice larger has been reported. Here, we report a search for and statistical study of such strong coronal magnetic fields using high-frequency GR emission. A historic record of spatially resolved microwave observations at high frequencies, 17 and 34 GHz, is available from Nobeyama RadioHeliograph for more than 20 years (1995-2018). Here we employ this data set to identify sources of bright GR emission at 34 GHz and perform a statistical analysis of the identified GR cases to quantify the strongest coronal magnetic fields during two solar cycles. We found that although active regions with the strong magnetic field are relatively rare (less than 1% of all active regions), they appear regularly on the Sun. These active regions are associated with prominent manifestations of solar activity.