Fewer rain storms across southern Australia

Fewer rain storms across southern Australia
The frequency of storms over southern Australia is forecast to continue to fall. (CSIRO)

(PhysOrg.com) -- Decreasing autumn and winter rainfall over southern Australia has been attributed to a 50-year decrease in the average intensity of storms in the region – a trend which is forecast to continue for another 50 years.

In an address today to the International Union of Geodesy and Geophysics conference in Melbourne, CSIRO climate scientist, Dr Jorgen Frederiksen, said these changes are due to reductions in the strength of the mid-latitude jet stream and changes in atmospheric temperatures. The jet stream comprises fast moving westerly winds in the upper atmosphere.   "The drop in winter and autumn observed across southern Australia is due to a large downturn in the intensity of storm formations over at least the last three decades compared with the previous three decades, and these effects have become more pronounced with time," Dr Frederiksen said.

"Our recent work on climate model projections suggests a continuation of these trends over the next 50 years."

Dr Frederiksen's address was based on recent CSIRO and Bureau of Meteorology research that has just been published in the International Journal of Climate Change: Impacts and Responses.

The research, based on observations and climate modelling, centres on the changes in southern Australian winter rainfall linked to atmospheric circulation changes that are directly associated with storm formation, and particularly rain bearing lows and frontal systems crossing southern Australia.

The most important circulation feature associated with winter storm formation is the strength of the sub-tropical jet stream. For example, winter storms give south-west Western Australia much of its rain. Between the 20-year periods 1949 to 1968 and 1975 to 1994 south-west WA rainfall reduced by 20 per cent. In south-east Australia, there were reductions of 10 per cent.

"Our research has identified the historic relationship between the reduction in the intensity of storms, the southward shift in storm tracks, changing atmospheric temperatures and reductions in mid-latitude vertical wind shear affecting rainfall." Vertical wind shear is the change in the westerly winds with height.

"We expect a continuation of these trends as atmospheric temperatures rise based on projections from climate models forced by increasing carbon dioxide concentrations.

"Trends during the 21st Century are likely to be similar to those observed during the second half of the 20th Century, when we saw substantial declines in seasonal rainfall across parts of southern Australia.

"Indeed, reductions in projected southern Australian rainfall during the 21st Century, particularly over south-west WA, may be as much as, or larger than, those seen in recent decades," Dr Frederiksen said.

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Citation: Fewer rain storms across southern Australia (2011, July 4) retrieved 22 August 2019 from https://phys.org/news/2011-07-storms-southern-australia.html
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Jul 04, 2011
Until Al Gore and the UN's IPCC order the release of all experimental data at the base of their dire predictions of "An Inconvenient Truth", I request a moratorium on additional dire climate forecasts by those receiving government research funds.

Do we face "An Inconvenient Truth" or "A Convenient Untruth" for politicians?

That is the question.

With kind regards,
Oliver K. Manuel
Former NASA Principal
Investigator for Apollo

Jul 04, 2011
From the Declaration of Independence, adopted in Congress 235 years ago, on July 4th, 1776:

"We hold these truths to be self-evident, that all men are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty and the pursuit of Happiness."

"That to secure these rights, Governments are instituted among Men, deriving their just powers from the consent of the governed,"

"That whenever any Form of Government becomes destructive of these ends, it is the Right of the People to alter or to abolish it, and to institute new Government, laying its foundation on such principles and organizing its powers in such form, as to them shall seem most likely to effect their Safety and Happiness."


The next 235 years will be better yet, if we can convince politicians and world leaders that they are far less powerful than the forces of Nature !

With best wishes,
Oliver Manuel

Jul 04, 2011
you tell'em omatumr-bot
feel better now

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