Butterfly-Shaped Coronal Hole on the Sun Sparks Geomagnetic Storm Watch
A massive, butterfly-shaped coronal hole has been detected in the sun's atmosphere, releasing a high-speed stream of solar wind towards Earth. This event could trigger a moderate geomagnetic storm between September 13 and 14, potentially leading to visible auroras.
The Butterfly Coronal Hole and Solar Wind
The coronal hole, spanning approximately 500,000 kilometers (310,000 miles), was observed by NASA's Solar Dynamics Observatory. Coronal holes are regions where the sun's magnetic field lines open up, allowing solar wind – charged particles – to escape into space. The absence of hot plasma makes these regions appear dark in telescope images.
This particular formation is notable for its distinct butterfly shape and significant size, making it a subject of interest for space weather scientists. The expelled solar wind is currently traveling towards Earth and is expected to arrive around September 14.
Geomagnetic Storm Potential and Aurora Visibility
Space weather forecasters are predicting potential geomagnetic storm conditions. The U.K. Met Office anticipates active to G1 (minor) geomagnetic storm conditions, with a chance of reaching G2 (moderate) levels. NOAA's Space Weather Prediction Center offers a slightly more conservative estimate, predicting peaks of G1 conditions. Geomagnetic storms are classified on a scale from G1 (minor) to G5 (extreme).
If a G2 storm develops, auroras could be visible at mid- to high-latitudes in the Northern Hemisphere, including regions like Canada, Alaska, Scandinavia, and northern parts of the U.K. In the Southern Hemisphere, auroras might be seen over Antarctica, with a slight possibility of visibility from Tasmania and southern New Zealand.
The Russell-McPherron Effect and Equinox Season
The timing of this solar event is particularly significant due to the Russell-McPherron effect. This phenomenon describes the increased connectivity between the sun's and Earth's magnetic fields around the time of the equinoxes. During these periods, Earth's orientation makes it easier for solar wind to interact with our planet's magnetic field.
Christopher Russell and Robert McPherron, geophysicists, first described this effect in 1973. Geomagnetic storms are statistically twice as likely to occur during equinox months compared to solstice months. The upcoming autumnal equinox on September 22 further enhances the potential for auroras, even from relatively modest solar wind streams.
The interaction of solar wind with Earth's magnetic field energizes gases in the upper atmosphere, causing them to emit light – the vibrant displays we see as auroras. The intensity of the solar wind directly impacts the dynamism and extent of these auroral displays.
