Monday, June 11, 2012

Solar-Earth DefCon Levels, Part 1

As I told you last week, NOAA has a scale of geomagnetic activity that ranges from G0 to G5, where G0 is quiescent, and G5 is the worst geomagnetic storm around. Now, we've already talked a little bit about what geomagnetic storms do...

No, we didn't, you say?

Ah, but we did. Back when I told you about all the effects that Coronal Mass Ejections can have. (Solar, Space, and Geomagnetic Weather, Part 4.) Because those sorts of things are what cause the geomagnetic storms.

But probably the best way I can tell you about the effects is simply to quote from NOAA's scale itself (which can be found here:

As I mentioned last week, a G0 is the normal, quiescent geomagnetic field. This holds until the Kp index reaches 5, and then we begin minor geomagnetic storming, with the scale hitting G1. According to NOAA, “Power systems: weak power grid fluctuations can occur. Spacecraft operations: minor impact on satellite operations possible. Other systems: migratory animals are affected at this and higher levels; aurora is commonly visible at high latitudes (northern Michigan and Maine).” These are fairly frequent, with on average close to 2000 per 11-year solar cycle.

At Kp=6, G2 is considered a moderate storm. “Power systems: high-latitude power systems may experience voltage alarms, long-duration storms may cause transformer damage. Spacecraft operations: corrective actions to orientation may be required by ground control; possible changes in drag affect orbit predictions. Other systems: HF radio propagation can fade at higher latitudes, and aurora has been seen as low as New York and Idaho (typically 55° geomagnetic lat.).” These are a little less frequent than G1, but still occur at a rate of about 600 every solar cycle.

When Kp=7, G3 is a strong geomagnetic storm. “Power systems: voltage corrections may be required, false alarms triggered on some protection devices. Spacecraft operations: surface charging [static electricity buildup; this can lead to arcing]may occur on satellite components, drag may increase on low-Earth-orbit satellites, and corrections may be needed for orientation problems. Other systems: intermittent satellite navigation and low-frequency radio navigation problems may occur, HF radio may be intermittent, and aurora has been seen as low as Illinois and Oregon (typically 50° geomagnetic lat.).” These are less frequent still, with on average 200 per solar cycle. Also, as the geomagnetic storms increase in strength, their likelihood of occurrence tends to concentrate around solar maximum, though this is not a hard and fast rule.

At Kp=8, G4 is a severe geomagnetic storm. “Power systems: possible widespread voltage control problems and some protective systems will mistakenly trip out key assets from the grid. Spacecraft operations: may experience surface charging and tracking problems, corrections may be needed for orientation problems. Other systems: induced pipeline currents affect preventive measures, HF radio propagation sporadic, satellite navigation degraded for hours, low-frequency radio navigation disrupted, and aurora has been seen as low as Alabama and northern California (typically 45° geomagnetic lat.). These are rarer still, with only about 100 seen per solar cycle.

And then there's the big boys. Kp=9 means a G5 extreme geomagnetic storm. “Power systems: widespread voltage control problems and protective system problems can occur, some grid systems may experience complete collapse or blackouts. Transformers may experience damage. Spacecraft operations: may experience extensive surface charging, problems with orientation, uplink/downlink and tracking satellites. Other systems: pipeline currents can reach hundreds of amps, HF (high frequency) radio propagation may be impossible in many areas for one to two days, satellite navigation may be degraded for days, low-frequency radio navigation can be out for hours, and aurora has been seen as low as Florida and southern Texas (typically 40° geomagnetic lat.).” These are the rarest of all, but still occur on average 4 per solar cycle.

-Stephanie Osborn