Astronomical Society of Edinburgh
Journal 43

Where has the Aurora gone?

Mid latitude observers had been commenting that geomagnetic and auroral activities have been very low in December, January and February in spite of proximity to the peak of the sunspot cycle. An inspection of British records kept since January 1976 confirms that there are, on average, low levels of auroral and geomagnetic activity in December and January with peaks of activity generally in the spring and autumn periods. The summer observing period in UK is affected by twilight conditions but a secondary average low level auroral period appears in North Dakota observations, where skies are darker in summer. There is also a similar effect in the global geomagnetic activity.

In contrast, the record of shock waves in the solar wind impacting the Earth's magnetic field does not show any marked average seasonal variation.

Because the Sun's rotational axis lies at an angle of 7.25 degrees to the perpendicular of the ecliptic the Earth tends to face the effects of activity on the Sun's southern hemisphere in springtime and the northern hemisphere in autumn. At midwinter and midsummer the Earth faces the Sun's equatorial regions which are less active and contain the magnetically neutral zone. These effects may account for the long term average variations in geomagnetic and mid-latitude activity.

Ron Livesey

P.S. Faint auroral arcs were seen March 19/20 and 20/21.
A major aurora was seen on the night of Mar 31/Apr 1. Magnetometers were active all over the country, and the auroral light was first seen by Dave as it started to get dark at 2000. There were several coronal peaks with long red blue and green rays to the zenith, but it wasn't particularly bright and had long quiet intervals between bursts of activity which included pulsations and flaming. (Editor)