Microwave Polar Brightening and Its Connection to Polar Coronal Holes

Polar brightening (PB) observed at microwave frequencies serves as an important probe to study the thermal and magnetic properties in the Sun’s polar regions. Building on earlier studies that linked microwave PB to polar faculae, small-scale loops, and the polar coronal holes (PCHs), we present a comprehensive analysis of the long-term behaviour of 17 GHz microwave PB and its relation to polar magnetic field and the evolution of PCH. Using daily Nobeyama Radioheliograph observations spanning 1992–2018, we quantify microwave PB peak temperature variations and compare them with the temporal evolution of PCH area extracted from Solar Dynamics Observatory/Atmospheric Imaging Assembly–based Spatial Possibilistic Clustering Algorithm coronal hole catalogs during the period 2010–2018. We also examine the correspondence between microwave PB and the polar magnetic field to assess the nature of their association. Our results show a strong correlation between microwave PB peak temperature and PCH area, as well as with the polar magnetic-field strength. In addition, we found that regions of enhanced microwave emission are frequently associated with small-scale loop structures, consistent with coronal bright points, which are often associated with the eruption of jets. Overall, this study aims to investigate the impact of PCHs, polar magnetic fields, and small-scale polar activity on PB observed at 17 GHz and its long-term evolution.