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Forbush Decrease

30 December 2014

A sudden decrease in cosmic rays bombarding the Earth's atmosphere has coincided, accidentally or otherwise, with a week or so of very cold weather. On December 21st ground based neuton monitors detected a sudden decrease in cosmic radiation – http://spaceweather.com December 29th – and this was due to three CMEs thrown out by the Sun, over the previous 48 hours, sweeping away, broom like, many of the cosmic rays normally in the vicinity of the Earth. The CMEs did not engage with the Earth or its atmosphere – they swept on by (sweeping up the cosmic rays in the process). It was, in other words, three near misses in two days and these events are known as 'Forbush Decreases', a feature of the atmosphere currently being investigated by students in the US in what is known as the 'Earth to Sky calculus' experiment. This involved launching a pair of radiation sensors into the stratosphere carried aloft by a helium balloon. The latest ballon reached 117,900 feet in the air – before exploding. At that point the sensors parachuted back to the surface of the Earth. They were programmed to land in open country, the Death Valley National Park. They used sniffer dogs to locate them in what is essentially a desert environment rather than a woodland or one with a lot of vegetation. The instrument also took images that recorded a profile of ionising radiation from the surface to the stratosphere.

Comet Lovejoy has also brightened significantly, according to http://spaceweather.com December 30th, over the Christmas period. It can now be seen, vaguely, as a naked eye object near the bottom of the constellation of Orion. It is a mixture of green (ionised carbon monoxide) and blue (the ion tail) and will probably continue to brighten in the first weeks of January.

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