1184th General Meeting

"Long-term changes in solar activity – including the current Grand Minimum"

Ken McCracken, Jellore Technologies and Senior Research Associate, University of Maryland

Wednesday 1 September 2010 at 7 pm
Conference Room 1, Darlington Centre, University of Sydney

The sunspot record since Galileo's time, and the cosmogenic nuclides 10Be (in ice cores) and 14C (in tree rings) show that the degree of activity of the Sun has varied greatly over time. The solar activity, manifested by the occurrence of sunspots, solar flares, and coronal mass ejections may be quite high, as it has been since 1946; and was during Roman times, or very small as during the Maunder Minimum (1645-1715); the Dalton Minimum (1810-20) or the Gleissberg Minimum of 1900-10. In the first part of the lecture, the speaker will discuss his recent studies with Swiss colleagues of the last 10,000 years of 10Be data from the Arctic and Antarctic that shows that the Sun has exhibited a number of persistent periodicities in solar activity, the most important being of duration 2300yr, 210yr, ~85yr, and the well known 11/22 year solar cycle. He will also outline the last 30 years of satellite data that show that the solar irradiance varies by ~0.1% over the 11 year solar cycle.

Against that background, he will then describe the substantial reduction in solar activity that commenced in 2006. Since then, the sunspot behaviour has been similar to that during the Dalton minimum (1810-20). The interplanetary magnetic fields have been lower than at any time during the space age, and the cosmic radiation intensities are well above those at any time during the past 60 years. The solar irradiance has decreased well below that observed in the previous 30 years. The evidence indicates that the magnetic properties of the Sun are now very different from those at any time in the "Space Age". Based on the 10,000 year 10Be record, he will speculate that the Sun will remain relatively inactive (and cool) for the next 20 years, and it will then resume a steadily increasing state of activity until it reaches a peak of the Hallstatt (2300 year) cycle ~200 years in the future.

Ken McCracken has had a long and varied life as a scientist, technologist, and contrarian. Starting his research career in Tasmania and New Guinea in the 1950s, he was then deeply involved in the early days of the US space program for seven years while at the Massachusetts Institute of Technology and the University of Texas. He designed and built scientific instruments that were flown on seven spacecraft that went to the orbits of Mars and Venus in the 1960s to provide the information needed to protect the US astronauts from being killed, or losing their virility, en route to the Moon. Following a professorship at the University of Adelaide, CSIRO appointed him to inaugurate a new research laboratory to improve geophysical exploration for minerals in the harsh Australian environment. Moving to the Southern Highlands in 1989, he operated a consultancy providing scientific advice to the mining industry. Over the past decade he and his Swiss, US, and Australian colleagues have used results from ice cores from Greenland and Antarctica to understand how the Sun has waxed and waned in activity over the past 10,000 years, and how this has paralleled the twenty two little ice ages, and many warming periods in the Earth's climate over the past 10,000 years. With his wife Gillian, he owns and operates the 850 acre beef breeding property "Jellore" in High Range.

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