Apparently the sun is observing the summer solstice by ramping up its activity and setting the stage for a potentially stunning aurora show here on Earth on Monday and Tuesday night.

Three coronal mass ejections over the past few days have erupted and have made their way to Earth to cause a G4 (severe) geomagnetic storm on Monday afternoon. G4 storms are the second-highest on the five-point severity scale. Effects here on Earth include potential voltage control issues in power systems, high- and low-frequency radio issues, and orientation adjustments may be required for satellites.

The last time a G4-severe storm occurred was on St. Patrick’s Day, when a beautiful, green aurora was seen far south as Tennessee, Oklahoma and even New Mexico.

The NASA satellite in charge of monitoring solar activity headed our way, the Advanced Composition Explorer, first detected the incoming coronal mass ejection (CME) as it blew at 2 p.m. The ever-vigilant solar satellite sits 1 million miles upstream between Earth and the sun.

[St. Patrick’s Day geomagnetic storm spurs green aurora]

On Monday afternoon, the solar wind was very fast and contained a southward-oriented magnetic field. A fast solar wind with this characteristic tends to produce the largest geomagnetic storms — and most intense auroras — on Earth.

In addition, there is an S3 (strong) solar radiation storm occurring, filling the polar caps with charged particles. High-latitude flights may make the decision to use a more southerly route to avoid the storm.

In tandem, these two space weather storms — the geomagnetic storm and the solar radiation storm — will drive the auroras to lower latitudes over the next few days.

The good news is that there’s a high chance of an auroral show to mark the start of our summer. With just a sliver of a moon tonight, the skies will be dark in the early morning hours. However, yesterday was the longest day of the year, so the lower 48 will have to wait until it gets truly dark. Also, the higher north you go, the longer the daylight lasts! For example, the sun doesn’t set in Fairbanks, Alaska, until 12:47 a.m.

Here in the District, sunset is slated for 8:37 p.m., but you may have to wait until 10 p.m. for it to be dark enough to see the aurora, if clouds cooperate. We could see enough clearing overnight to catch a glimpse, especially if you’re using a long exposure on your camera.

If you’re planning on trying to see the northern lights, you’ll want to track the K-Index — the larger the K-Index, the farther south the aurora is dipping. Usually in the Mid-Atlantic we want to see a K-Index of at least an 8. A K-Index of 7 might be good enough for Pennsylvania and New Jersey to see the aurora, but anything south of Virginia will need a K-Index of 9.

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