A high-speed stream from a coronal hole is expected to lead to G2 (Moderate) geomagnetic storming on December 4 (UTC Day) and G1 (Minor) storming on December 5, 2023, according to an alert from the NOAA Space Weather Prediction Center (SWPC).
Coronal holes are unique features of the Sun, often appearing as dark regions in solar corona images.
These regions are cooler and less dense than their surroundings, attributed to their open, unipolar magnetic fields.
The magnetic field structure of coronal holes allows the solar wind, a stream of charged particles from the Sun, to flow more freely into space.
This results in a fast solar wind stream, known as a high-speed stream.
Coronal holes can develop at any time and place on the Sun but are more common during solar minimum. They can persist for several solar rotations, lasting approximately 27 days.
These features are most common and stable at the solar north and south poles, expanding to lower latitudes. They serve as sources for high-speed solar wind streams.
As the high-speed stream interacts with the slower solar wind, a compression region forms called a co-rotating interaction region (CIR). This precedes the coronal hole high-speed stream (CH HSS).
Impacts of Coronal Holes on Auroras
The CIR can increase particle density and interplanetary magnetic field (IMF) strength. As the CH HSS approaches Earth, solar wind speed and temperature rise while particle density decreases.
After CIR passage and transitioning into the CH HSS flow, IMF strength typically weakens.
Coronal holes near the solar equator are most likely to affect Earth, causing geomagnetic storms of G1-G2 levels (Minor to Moderate) on the NOAA Space Weather Scale.
Stronger storming may occur in the presence of larger coronal holes with extended solar wind impacts.
Forecasters keep a careful eye on coronal holes because they may trigger geomagnetic activity. They contribute substantially to the formation of auroras on Earth.
High-speed solar winds from coronal holes may interact with Earth’s magnetosphere to cause geomagnetic storms, which can excite gases in the atmosphere and produce the aurora borealis, or shimmering lights..
The intensity and frequency of auroras depend on the strength of the solar wind and geomagnetic storms induced by coronal holes.
These features enhance the likelihood and intensity of auroras, making them a crucial factor in understanding and predicting these natural phenomena on Earth.
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