Auroral displays are very rare during the days of solar minimum. And if there is an aurora anyway, it is so weak in most cases that one can only detect it using digital cameras. In September 2006 there has been one of these rare occasions.
The cause of the September 23/24 event was a big coronal hole in the middle of the solar disc. For such regions, open magnetic field lines reach out into space, producing gust of a highspeed solar wind stream. Just bevor such a stream reaches earth, one can observe a phase of high particle density in the solar wind. This time the density was exceptionally high, reaching more than 40 protons/cm3 (peak values of more than 80p/cm3) for many hours. Due to the hard pressure of the solar wind on the earth magnetosphere, a weak geomagnetic storm (Kp=5) developed.
This was enough activity to enable a detection of weak aurora by a Mintron camera at 21:05 UTC in Elmshorn. The magnetometers in Wingst and Niemegk registered a 100nT deviation of the horizontal component of the earth magnetic field at that time.
Sometime later that night (00:39-00:55 UTC) I was able to detect the upper red fringes of the auroral oval near Witzhave, using my digital camera Olympus Camedia 5060WZ. As was the case before, the magnetometers in Wingst und Niemegk registered another 60nT deviation in the H-component.
The northern lights on the evening of January 21 could be observed in multiple
substorms. I was able to observe the first and strongest one:
1st substorm: 21:05 - 21:06 UTC
2nd substorm: 00:39 - 00:55 UTC
Here are my pictures, all taken in Witzhave near Hamburg (53.56°North, 10.33°East).
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