I’ve looked at clouds (and global weather) from both sides now

It's Christmas time and you're flying an intercontinental jet from Sydney to London at a common altitude of 10 km (30,000 feet). Things are pretty quiet across Australia, and you can see a few clouds well below the plane. But wait, now you're approaching Indonesia, and things are getting turbulent as you head into some high convective clouds. After all, it is monsoon season between November and March. Someone warns you that you're also going to meet these same clouds and turbulence at the opposite monsoonal season over Thailand, and the Indian sub-continent. But what's causing these high convective clouds?

It's the Warm Pool—the Indo-Pacific Warm Pool. It covers a huge area of the tropical oceans; its extent is larger that the entire USA. (It simply looks rather small on global maps because areas in the higher latitudes appear larger due to map projections we frequently use.)

The Warm Pool area is characterized by sea-surface temperatures that are at least 28°C or more. Due to the high sea-surface temperatures and the vast array of islands in the Indonesian region, the Warm Pool is also characterized by the formation of deep-convective clouds. These clouds travel up to 10 to 15 km in altitude and carry a vast amount of moisture and foster a vast amount of heat exchange between the ocean, land, and the atmosphere. As a consequence of high rainfall, the oceans in the region have low salinities near the surface.

Meteorologists have now found that there is a very close link in the Western Pacific Ocean between sea-surface temperatures and the formation of high convective clouds. The range of temperatures peaks around 29.5 °C, but if sea-surface temperatures go below 26°C or above 30.5°C, the convective clouds disappear altogether. This phenomenon has been observed at times with severe consequences for the region. One being the associated drought in some of the highlands of Papua New Guinea [=PNG] during the major ENSO event of 1997-98 which was associated also with nocturnal frosts as there were no cloud cover during the nights. Famine occurred as a direct result of unusually high sea-surface temperatures offshore PNG.

Patrick De Deckker, a geologist at the Australian National University has discovered that in the past, sea-level changes did change the ratio of land to sea in the Warm Pool area and these changes had significant effects on the formation of deep-convective clouds. De Deckker, who has a Ph.D. in Zoology, will present his findings, "The Role of Tropical Oceans in Climate Forcing: Evidence from the Indo-Pacific Warm Pool During the Quaternary" at the Earth Systems Processes conference on Wednesday, June 27, in Edinburgh, Scotland. The Geological Society of America and the Geological Society of London will co-convene the June 24-28 meeting.

"These sea-level changes were common and cyclic during the last two million years," De Deckker explained, "with even sea level having been some 125 meters below present-day level some 20,000 years ago, a time when there were already inhabitants on many islands of Indonesia." A slight change of sea-surface temperature in the region also could have had a dramatic effect on precipitation, the resultant salinity of the ocean at the surface and vegetation in the region. As a consequence of atmospheric and oceanic changes in the Warm Pool region in the past, large-scale atmospheric re-organization would have occurred –as compared to today, with consequences for the broad-scale atmospheric cells which are linked with the Walker Circulation and the Southern Oscillation and El Nino phenomena.

"I will argue, for example, that during the period some 20,000 years ago when large ice caps existed in North America (4 km of ice over parts of Canada) and a large portion of northern Europe (including much of the UK), the Warm Pool region was much drier, and monsoons did not exist there. Much of the Pacific was locked into a permanent 'El Nino' system," he said. "The Warm Pool is a key player in global climate and should not be ignored."

CONTACT INFORMATION

During the Earth System Processes meeting, June 25-28, contact the GSA/GSL Newsroom at the Edinburgh International Conference Centre for assistance and to arrange for interviews: 44-131-519-4134

Ted Nield, GSL Science and Communications Officer
Ann Cairns, GSA Director of Communications

The abstract for this presentation is available at:
http://gsa.confex.com/gsa/2001ESP/finalprogram/abstract_8243.htm

Post-meeting contact information:

Lawrence Tanner
Dept. of Geography and Geosciences
Bloomsburg University
Bloomsburg, PA 17815 USA
[email protected]

Ted Nield
Geological Society of London
44-20-7434-9944
[email protected]

To view other Earth System Processes press releases, see
http://www.geosociety.org/pubntrst/media.htm