Magnetic Storms

ECE120 Space Physics.

The direction of the IMF is highly variable and the intensity of plasma flowing from the sun fluctuates greatly. The radial field is known to reverse direction 2 to 4 times during a solar rotation (27 earth days). Flare activity and solar cycles of varying intensity occuring on the sun can cause large changes in plasma intensity reaching the earth. The earths magnetosphere is pushed and pulled by the constantly changing solar wind. The magnetopause boundary can move from 12 earth radii in quiet solar activity down to half this distance during intense solar eruptions.

The changing field line direction of the IMF is believed to cause "magnetic reconnection" to occur when the IMF field line is opposite to that of the earths magnetic field.

In 1961 James Dungey in England proposed that when the field lines were in opposite directions a neutral point occurred that allowed IMF field lines to join with field lines of the earth.

Figure 11
Figure 11.

The Dungey process of "magnetic reconnection" is expected to increase the flow of solar energy into the magnetosphere. It has been observed during southward slants of the IMF that there was increased magnetic storm activity in the earths magnetosphere. However direct evidence of reconnection is hard to obtain and some researchers believe it does not occur at all.

The earths magnetosphere is never stable and periods of increased activity in the earths magnetotail have been labeled "magnetospheric substorms". The most visible signs of magnetic substorms is increased auroral activity in the polar regions at night. The activity may build up for half an hour then decay slowly away. During "sub storms" the magnetic field is drawn into the tail and the tail lobes expand storing additional energy. It is believed the lobes store energy that power the sub storms.

Geomagnetic storms result from large changes in IMF intensity and direction. These storms usually follow intense solar flare activity. The auroral activity becomes extremely active and is seen more toward the middle latitudes. These intense magnetic storms can cause current surges in power lines causing flickering lights and electrical equipment damage. There is also an increase in radio, telephone and television interference.



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