Thursday, February 5, 2009

Indian Ocean affects Australian drought

The Climate Change Research Centre at the University of New South Wales has been doing some interesting research. They have found a correlation between three of Australia's largest droughts (1895-1902, 1937-1945, and the present one, since 1995) and oceanic conditions - in the Indian ocean!

Say what? Shouldn't that be the Pacific and El Nino?

Apparently not.

In a paper to be published in Geophysical Research Letters, the team have linked the last three major droughts in Australia with the Indian Ocean Dipole (IOD).

Basically, the dipole consists of a cooler body of water in the central Indian Ocean, and a warmer body of water to the north east. This is a negative IOD (-IOD).

Under these conditions, warm, moist air forms along Indonesia, and is channeled from there, across western Australia and then across southern Australia. This happens because the warm moist air formed over Indonesia is influenced by the weather patterns that run west to east across southern Australia, and the moist air is dragged diagonally across the continent.

This is good, because it brings rain to western and southern Australia

However, when things are reversed, with a warm body of water in the central Indian Ocean, and a cool body of water to the north east (a positive IOD), warm, moist air does not form.

This is bad because it results in drought to western and southern Australia.

So -IOD good, +IOD bad.

The team has found that throughout the period 1995 to present, no -IODs have formed, and similarly -IODs were rare in previous times of extended drought.

What about El Nino? Well, we are actually in an El Nina at the moment, and there have been several in the last 12 years.

So it looks like there is a better fit with IOD than with El Nino/El Nina.


  1. Yeah,

    Couldn't get the little symbol to work

  2. All this hype over the Indian Ocean Dipole must not obscure the problem with this theory. This being that +IOD conditions should produce drought over central and southeastern areas of Western Australia. Yet, since the drought began in Victoria, central and southeastern Western Australia have had four of their six wettest years since 1895 and no year with rainfall generally below the average of the 100 years before 1997. Overall, rainfall over these districts has been 40 percent higher than before 1997.

    It is hard for me to believe these increases are not tightly linked to the drying of southeastern Australia. Since paleoclimatology shows winter-rainfall-type climates exist only during ice ages, one cannot doubt that the drying of southern Australia is entirely anthropogenic.

    The Southern Annular Mode (SAM) or Antarctic Oscillation determines how far the rain-bearing cold fronts penetrate into southern Australia. A more positive SAM means that the midlatitude westerlies weaken and the polar westerlies strengthen, which serves to dry out southern Australia. Because it weakens the dry westerlies and encourages moister east-to-northeasterly wind flow, however, a positive SAM increases rainfall over central and eastern Western Australia. Although no trend in the SAM was observed from 1979 to 2005, I am suspicious that already either:
    - the SAM has become more positive than ever recorded before 2005 and is going to stay that way or;
    - that at present concentrations of carbon dioxide the SAM will become more positive than ever recorded before 2005 and remain so permanently

    I am really worried that the CSIRO and Bureau of Meteorology are ignoring the OSuthern Ocean as a possible source for the drying of southeastern Australia. Ever since the problem was first noted circa 1999 I have always though the drying must be caused solely by changes in the Southern Ocean, but our scientists are perilously ignoring that possibility.


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