This is an aurora resulting from the Aug. 3 geomagnetic storm. Facing North from Silkeborg, Denmark, Jesper Grønne photographed this beautiful scene using a Canon 5D II camera. Credit: Jesper Grønne.

It’s hard to imagine the magnetic battle that’s ensuing above my head right now, especially during this hot and calm Southern Californian day. But over the last few hours, orbiting space weather observatories and ground-based magnetometers have detected the moment a coronal mass ejection (CME) — fired from the sun on Sunday — slammed into the Earth’s magnetosphere.

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It started slowly enough, when one of the Geostationary Operational Environmental Satellites (GOES) detected an increase in the density of protons in the near-Earth environment. Then a sudden fluctuation in the magnetic field was reported, signifying the onset of a geomagnetic storm.

By measuring the number of protons and the intensity of the magnetic field fluctuations, space weather scientists are able to deduce that the CME launched from the sun early on Sunday morning arrived at the Earth on schedule.

Further measurements by instruments that can detect geomagnetic fluctuations on the ground — i.e. when the magnetic field of the Earth (the magnetosphere) interacts with the solar magnetic field wrapped around the “bubble” of gas from the CME — have also deduced that a geomagnetic storm is underway.

Left: Proton flux measurements made by the GOES 13 satellite detect an increase in solar particles near Earth (the red line) starting at approximately 15:00 UT (10 am EST), Aug. 3. Right: Both GOES 11 and GOES 13 detect a rapid fluctuation in the magnetic field surrounding Earth at approximately 18:00 UT (1 pm EST). Credit: NOAA/Space Weather Prediction Center

Where there’s a geomagnetic storm, a light display is sure to follow.

Known as the Auroral Borealis (the “Northern Lights,” focused around high latitudes in the Northern Hemisphere) and the Aurora Australis (“Southern Lights,” around high latitudes in the Southern Hemisphere), these spectacular light displays are caused when energetic particles from the sun (mainly protons) stream into our magnetosphere.

BIG PIC: See the sunspot, as photographed by a photographer located in South Africa, responsible for today’s geomagnetic turmoil.

If the conditions are right — and in today’s case, the conditions seem to be ideal — these protons will collide with Earth’s atmospheric gases, generating light.

At the time of writing, aurorae have been spotted over Denmark, Norway and Germany.

Due to the magnetic configuration of our magnetosphere, the field lines enter the Earth’s crust around the poles. These descending field lines funnel the solar protons from the CME into a “crown” surrounding the North and South Poles. This crown is known as the “auroral oval.”

The current oval (at 01:41 UT, Aug. 4 or 8:41 pm EST, Aug. 3) — as observed by the NOAA’s Polar Operational Environmental Satellites (POES) project — can be seen above.

There is an obvious intensity of auroral activity (shaded red) over Scandinavia, Northern Europe and North America.

Another very strong indicator that suggests a geomagnetic storm is underway is the “Kp index.” This measurement is derived by measuring how much the horizontal component of the Earth’s magnetic field varies over a 3-hour period. Depending on the intensity of fluctuations, the Kp index is assigned values between 0 to 9. If the value hits 5, this means a geomagnetic storm is occuring and auroral displays can be expected.

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Currently, this geomagnetic storm has been rated “6″ on the Kp scale (a value estimated by a magnetometer in Boulder, Colo.), so it is considered to be a “moderate” G2 geomagnetic storm.

It is unlikely that the arrival of this CME will cause damage to satellites or any sensitive electronics on the ground, but it is incredibly exciting to know we have the ability to track a CME ejected from the sun and accurately predict when it might strike Earth.

As we become more and more dependent on satellite technology and vast national power grids, the ability to forecast space weather will become paramount because bigger and more destructive CMEs will be blasted in the direction of Earth in the future.

But for now, if you are located at high latitudes, take a look outside tonight, you might be in for an auroral treat.

Data source: NOAA

Credits: Jesper Grønne (top), NOAA