A series of enormous holes in the sun's corona have been causing disturbances in the Earth's magnetic field, and their effects are likely to continue for the next several weeks.
Space weather forecasters are calling for active levels of geomagnetic activity for the next week. They predict that this moderate level of disturbance will likely continue into mid-November as the coronal holes remain on the sun's surface for several rotations, essentially taking turns shooting charged-particle radiation toward the Earth.
"It seems that every coronal hole we have detected in the past two months has caused some geomagnetic effects (effects on Earth's magnetic field), from unsettled conditions to major storming," said Bill Murtagh, a space weather forecaster at the Space Environment Center in Boulder, Colo.
Forecasters classify magnetic disturbances into six levels. Rising in intensity from the weakest to the most severe, they are: quiet; unsettled; active; minor (geomagnetic) storming; major storming and severe storming.
The corona is the outermost layer of the sun. This layer of plasma -- and the magnetic field that keeps it attached to the solar sphere -- blocks a lot of radiation that emanates from the deeper layers of the sun.
When a hole develops, that radiation escapes, sending charged particles streaming into space at speeds up to 1.5 million mph. When such a hole faces Earth, the charged particles stream Earthward, affecting our planet's magnetic field when they arrive.
High levels of this radiation can cause brilliant shows of the aurora borealis at high latitudes, but it can also be quite troublesome -- disrupting satellite electrical and communications systems and causing electrical surges at power-generating stations.
Although such dramatic effects have not been reported in recent months, the serial coronal-hole activity is somewhat unusual, Murtagh said.
Images at the right show a large coronal hole in the upper left of the solar disk. It is the black patch shaped somewhat like Africa. During the coming week that spot will rotate to face Earth, with its effects hitting Earth from Oct. 23 to 26, Murtagh said.
"On the last rotation that gave us about three to four days of disturbed conditions, and it did give us some minor storming," he said. The sun rotates over a period of 28 days.
Several days ago, the sun's rotation carried another coronal hole to the far side of the sun. It followed shortly behind a previous one on the carousel of the sun's surface. All these holes have caused disturbances on Earth, and will probably continue to do so during future rotations, Murtagh said.
The affects will not likely severely interfere with satellites or power grid systems, though.
Conditions in the active to minor-storm range can cause weak power fluctuations power grids, have minor impacts on satellites and cause auroras that are visible at latitudes as low as 60 degrees. Minor storming can begin to affect migratory animals.
The Space Environment Center is operated by the National Oceanic and Atmospheric Administration to monitor the effects of solar activity and provides early warnings when solar weather may adversely affect Earth.
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