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Observations & Reports
VLF Report Archive
Flare Classifications
Interpreting SID's
Combined VLF and Magnetometer Programme
Magnetometer Observations

Possible observation program integrating the VLF receiver and Magnetometer

Variations in geomagnetic activity are caused by variations in the pressure of the Solar Wind or the impact of Coronal Mass Ejections (CMEs). There is also some disturbance due to the so-called high-speed flow from coronal holes. The latter is a relatively broad event like the water shaken off a wet dog. The disturbances due to the CME in contrast is like the impact of a ball of fast moving plasma. Many CMEs are associated with the eruption of solar flares which we attempt to detect with our VLF receivers. These take approximately 9 minutes to reach the earth so are virtually instantaneous. Assuming a CME is ejected at the same instant, this ball of plasma travels much more slowly, and the time to reach the earth and provoke a magnetic storm is usually around 56 hours. This time delay depends upon the ejection speed, and tends to be related to the intensity of the flare event producing it. It seems that it might be an interesting experiment to try to relate the arrival time of a CME and the onset of a Magnetic Storm, with the time of of the associated flare emission. The delay can allow the speed of the plasma ball to be calculated, and an attempt to correlate this with the flare intensity. CMEs emitted with very energetic flares (X-Class) can take as little as 32 hours to reach Earth. This does have some impact on public awareness as recent "scare" stories in the press, and on TV, about the the consequences of gigantic solar eruptions have all stated that there is no warning. Even the august Scientific American make the mistake of repeating this as fact.

Alan Melia

If you would like to contribute observations to this study please contact Paul Hyde at radiogroup@britastro.org

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