Watheroo Magnetic Observatory, July to September, 1941

Abstract

(Latitude 30° 19′.1 S., longitude 115° 52′.6 or 7h 43m.5 E. of Gr.)July 4–7—This disturbance of unusual severity began at 03h 42m GMT, July 4, with sudden small movements followed by irregular, but relatively small, fluctuations in the traces. These conditions lasted until 04h 59m, July 5, when sudden impulses were recorded in all three elements and the traces immediately became violently disturbed,, remaining so until 16h. During this period H decreased to a value of 530 gammas below normal. The greatest sudden change in the interval was between 14h 07m and 14h 33m when H increased 285 gammas. Between 14h 23m and 14h 33m westerly declination decreased by 63′, which was practically the total range in declination during the whole disturbance. Z increased to such values between 08h and 15h that they were beyond the limits of registrations for the greater portion of the time. Although the violence of the disturbance had abated by 16h, July 5, and H had gradually regained its normal value, the traces continued to be moderately disturbed as follows: 20h to 22h on July 5; 13h to 16h on July 6; 00h to 05h on July 7. The disturbance ceased at 21h, July 7. Ranges: D, 65′2; H, 563 gammas; Z, greater than 215 gammas (probably more than 500 gammas). A brilliant display of the Aurora Australis was visible at the Observatory during the evening of July 5. At 10h 30m GMT, or 18h 30m 120° MT (E. of Gr.), an hour after sunset, a bright glow was seen on the southern horizon; it gradually became more pronounced and by 11h 50m had developed into an arch spreading from south‐southeast to south‐southwest and about 35° above the horizon at its highest part. At 12h 10m the arch was at its brightest and was tinged with red. at its eastern and western extremities. Brilliance then diminished slightly and by 12h 30m had almost disappeared, although the general glow still persisted. Between 14h and 14h 30m the glow, still visible, was varied by the appearance of luminous vertical shafts changing rapidly in range, intensity, and position. This display continued until after 14h 40m after which time only the glow was observed and this gradually faded. The whole display would have been even more imposing but for the presence of the Moon which was nearing the full.