Indian-Led Study Ties Solar Microwave Polar Brightening to Polar Magnetic Field Strength

Key facts

• A 2026 Indian-led study linked solar microwave polar brightening more closely with the strength of polar magnetic fields than with the area of polar coronal holes.
• Coronal holes are low-density regions of the solar corona with predominantly open magnetic field lines extending into interplanetary space; they appear dark in extreme-ultraviolet and X-ray images and generate high-speed solar wind.
• Polar brightening is enhanced microwave radio emission from the Sun's polar regions, not ordinary visible-light brightness.
• Large-scale polar magnetic fields shape coronal holes, while small closed magnetic loops produce compact coronal bright points within them.
• A coronal bright point is a small, transient bright feature associated with magnetic loops, often found inside coronal holes.
• 17 GHz microwave observations are used for solar mapping, and solar radio emission is produced by energetic electrons and thermal plasma processes.
• The solar magnetic cycle lasts approximately 11 years, and polar magnetic fields reverse near solar maximum.
• NASA's Solar Dynamics Observatory (SDO), launched in 2010, provides continuous solar observations including extreme-ultraviolet imaging.
• The Nobeyama Radioheliograph is a Japanese solar radio observatory operating at microwave frequencies, and the Wilcox Solar Observatory is a ground-based facility measuring the Sun's large-scale magnetic field.