The Sun in Time Slide Show, Page 6

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Slide Show page 6 for
The Sun in Time

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The Sun affects the Earth in many familiar ways: we wear sunglasses and sunscreen to protect us from harmful radiation, we feel the warmth of the Sun which helps plants grow and heats the atmosphere which creates our cycles of weather. But out in space, the Sun affects the Earth in many not-so-familiar ways. Particles from the Sun stream through interplanetary space, causing the Earth's magnetic field to shake about. The resultant changes in the Earth's magnetic field cause enourmous currents to be induced on the ground, which in turn affects electric power plants.

The picture to the left is one phase of a 1200 MVA bank of three transformers which was knocked out by a solar particle storm in 1989. The unit can cost up to $10 million dollars and replacement can take up to one year. Inside the large blue boxes are copper coils of wire (below left). As a result of the extra induced current, the coils essentially melted and buckled (below right).

Here is an example of the internal damage to the transformer due to Geomagnetic Induced Current (GIC) which resulted from a Coronal Mass Ejection (CME).

This image shows heating related damage to the current carrying windings of the transformer.To provide cooling for normal operations, the coils are immersed in an oil-bath. As you can see, an oil-bath does not cool well enough to protect against the GIC.

For more details about the power outage of March, 1989, select this page:

http://www.mpelectric.com/storms/index.htm#gic failures

So the way to prepare for solar induced magnetic storms, is to more fully understand the magnetic field of the Sun. Since the visible manifestation of the solar magnetic field is sunspots, we start there.

The dark spots in this image to the right are sunspots. Sunspots are dark because they are cooler (about 1-2000 K cooler) than the surrounding photsphere; the non-spotted photosphere has a temperature of about 6000 K. The coolest (darkest) part of a sunspot, called the umbra, is where the magnetic field is strongest. The less dark region surrounding the umbra is called the penumbra.

Note also that in the photosphere outside the sunspots, the solar surface appears granular; this is called granulation and is caused by convection.

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