Coronal hole

When observed in extreme ultraviolet, coronal holes appear as relatively dark patches in the Sun's corona. Here, there is a large coronal hole in the northern hemisphere.

Coronal holes are regions of the Sun's corona that emit low levels of ultraviolet and X-ray radiation compared to their surroundings. They are composed of relatively cool and tenuous plasma permeated by magnetic fields that are open to interplanetary space.[1] Compared to the corona's usual closed magnetic field that arches between regions of opposite magnetic polarity, the open magnetic field of a coronal hole allows solar wind to escape into space at a much quicker rate. This results in decreased temperature and density of the plasma at the site of a coronal hole, as well as an increased speed in the average solar wind measured in interplanetary space.[2]

Streams of fast solar wind originating from coronal holes can interact with slow solar wind streams to produce co-rotating interaction regions. These regions can interact with Earth's magnetosphere to produce geomagnetic storms of minor to moderate intensity. During solar minima, CIRs are the main cause of geomagnetic storms.

  1. ^ Freedman, Roger A., and William J. Kaufmann III. "Our Star, the Sun." Universe. 8th ed. New York: W.H. Freeman, 2008. 419–420. Print.
  2. ^ Kennewell, John; McDonald, Andrew. "What is a Coronal Hole?". Australian Government Bureau of Meteorology. Archived from the original on 11 August 2015.