Major Effects Of Bomb Test In N.Z.

Press, Volume CI, Issue 29871, 11 July 1962, Page 12

Major Effects Of Bomb Test In N.Z.

New Zealand possibly had brighter auroras and greater magnetic disturbances on Monday evening after the American highaltitude bomb test than any other place outside the immediate danger area. Scientists who spent many weeks setting up stations all over the South Pacific to record effects, expected to be minor if not negligible in New Zealand, found the most impressive records in their own home laboratories.

None of the scientists spoken to was prepared to commit himself to any explanation of why such unexpectedly large disturbances were recorded in New Zealand. Men who walked out to a north-facing cape on Campbell Island, 5000 miles from the bomb, on the off-chance of seeing a slight glimmer in the northern sky. were rewarded with the sight of a bright • orange-red glow Down in the Antarctic, scientists at McMurdo station and Scott Base had. no thought whatever that any:hing could be seen from so far away and did not look outside, fixing their attention on their instruments. Those that gave direct readings showed nothing abnormal. At Hallett station, the only sign of anything unusual was the sudden eclipse of radio station WWV, the United States time-check station, at 9 p.m.. the time the bomb was detonated. "Moderate to Severe" At the magnetic observatory at Amberley, the disturbance in the earth's magnetic field was classed as between moderate and severe—magnitude seven on the “K index," which runs from nought to nine, said the superintendent of the Magnetic Survey, Department of Scientific and Industrial Research (Mr A. L. Cullington). Messages he had received from Mr G. J. Keys, observer in charge of the survey’s observatory at Apia. Western Samoa, indicated that the disturbance there was very much less than that at Amberley, although the motion of the trace at Apia was too rapid during the most disturbed phase for a reliable calculation of the index At both Amberley and Apia, a complex disturbance lasting about 10 minutes was followed by a relatively smooth return to normal over about another 40 minutes. One of the magnetographs at Amberley had been specially modified so that it ran at 12 times the normal rate for the duration of the disturbance At the survey's earthcurrent recording station at Lincoln, the effects were so great that the pen-recorder was off the scale during the most disturbed periods. Mr R. N. De Witt, of the University of Alaska, who operates a magnetic station at Papakaio. near Oamaru, also found that his earthcurrent recorder went off the scale. This was not unusual in an auroral zone, but was probably rare in the magnetic latitude of Oamaru. he said. He intended to use a lesssensitive arrangement for the . next bomb -test. to try to I record the peak disturbances. I The magnetometer at his station showed "a fair jump” at the time of the explosion. | although he had not yet i finished calculating the [change in magnetic field . which this indicated. Mr De Witt also noticed small magnetic fluctuations about an hour after the main disturbance. He did not know whether these were connected with the bomb. Fluctuations at 10.15 p.m.

were recorded on the direct--1 reading instrument at Scott ! Base. No effect was noticeI able at the time the bomb , was detonated The more sensitive instruments at the Antarctic stations are all photographic-recording, and up to last evening none of the records had been developed. „ lonospheric Effects The superintendent of the Geophysical Observatory iMr J. W. Beagley) said there were two ionospheric*effects observed at Christchurch almost immediately after the detonation of the bomb The first was the presence of a dense cloud of electronat a height of 100 miles, recorded for six minutes. The second was a moderate degree pt ionospheric absorption lasting for about 10 minutes. Until midnight, the ionosphere remained dsturbed, with electron dens.ties appreciably higher than normal. A telephone report from Mr I. G. Fisher a’ Campbell Island indicated similar activity there. These effects were much more dramatic than had been expected, and differed m kind from those recorded during the 1958 high-altitude tests. Monday's disturbance had many features in common with a normal ionospheric storm.