Auroras to be visible as solar flare erupts

High-latitude sky watchers should remain alert for auroras as a magnetic filament erupted around 4 pm UT (11 am EST) on September 4, hurling a bright coronal mass ejection off the sun's northwestern limb. The coronal mass ejection is not expected to hit Earth, but auroras are possible in the nights ahead.

A solar wind stream flowing from a coronal hole is heading Earth’s way, which is expected to arrive on September 5 or 6. With the approach of northern autumn, Arctic nights are getting dark enough again to see the Northern Lights. People in Alaska, Canada and Scandinavia should keep an eye on the night sky.

The National Oceanic and Atmospheric Administration (NOAA) forecasters estimate a 50 percent chance of high-latitude geomagnetic activity when the solar wind hits. The forecasters estimate a 40 percent chance of geomagnetic activity during the next 24 hours as the solar wind continues to buffet Earth's magnetic field.

Recent scientific research has shown that the phenomenon of magnetic reconnection is responsible for coronal mass ejection (CME) and solar flares.

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Magnetic reconnection is the name given to the rearrangement of magnetic lines of force when two oppositely directed magnetic fields are brought together. This rearrangement is accompanied with a sudden release of energy stored in the original oppositely directed fields.

On the sun, magnetic reconnection may happen on solar arcades, a series of closely occurring loops of magnetic lines of force. These lines of force quickly reconnect into a low arcade of loops, leaving a helix of magnetic field unconnected to the rest of the arcade.

The sudden release of energy in this reconnection causes the solar flare. The unconnected magnetic helical field and the material that it contains may violently expand outwards forming a CME.

When the ejection is directed towards the Earth and reaches it as an interplanetary CME, the shock wave of the traveling mass of Solar Energetic Particles causes a geomagnetic storm that may disrupt the Earth's magnetosphere, compressing it on the day side and extending the night-side magnetic tail.

When the magnetosphere reconnects on the night-side, it releases power on the order of terawatt scale, which is directed back toward the Earth's upper atmosphere. This process can cause particularly strong auroras in large regions around Earth's magnetic poles.

NOAA space weather prediction center issued a 3-day solar-geophysical forecast on September 5 at 10:00 pm UTC, when solar activity is expected to be very low for the next three days with a chance for C-class events and a slight chance for M-class events

The geomagnetic field is expected to range from quiet-to-active conditions on September 6 and 7. Conditions are expected to return to quiet conditions on September 8.