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Ocean temperature patterns in tropics and subtropics will change rainfall patterns | A team of scientists has found that that ocean temperature patterns in the tropics and subtropics
will change in ways that will lead to significant changes in rainfall patterns.
The research was carried out by a team of scientists headed by meteorologist Shang-Ping
Xie at the University of Hawaii at Manoa's International Pacific Research Center
Scientists have mostly assumed that the surfaces of Earth's oceans will warm rather
evenly in the tropics. This assumption has led to "wetter-gets-wetter" and "drier-gets-drier"
regional rainfall projections. Xie's team has gathered evidence that, although
ocean surface temperatures can be expected to increase mostly everywhere by the
middle of the century, the increase may differ by up to 1.5 degree Celsius depending
upon the region. "Compared to the mean projected rise of 1degree C, such differences
are fairly large and can have a pronounced impact on tropical and subtropical
climate by altering atmospheric heating patterns and therefore rainfall," explained
Xie. "Our results broadly indicate that regions of peak sea surface temperature
will get wetter, and those relatively cool will get drier," he said. Two patterns
stand out. First, the maximum temperature rise in the Pacific is along a broad
band at the equator. Already today the equatorial Pacific sets the rhythm of a
global climate oscillation as shown by the world-wide impact of El Nino. This
broad band of peak temperature on the equator changes the atmospheric heating
in the models. By anchoring a rainband similar to that during an El Nino, it influences
climate around the world through atmospheric teleconnections. A second ocean warming
pattern with major impact on rainfall noted by Xie and his colleagues occurs in
the Indian Ocean and would affect the lives of billions of people. Overlayed on
Indian Ocean warming for part of the year is what scientists call the Indian Ocean
Dipole that occasionally occurs today once every decade or so. Thus, the models
show that warming in the western Indian Ocean is amplified, reaching 1.5 degree
C, while the eastern Indian Ocean it is dampened to around 0.5 degree C. "Should
this pattern come about, it can be expected to dramatically shift rainfall over
eastern Africa, India , and Southeast Asia . Droughts could then beset Indonesia
and Australia , whereas regions of India and regions of Africa bordering the Arabian
Sea could get more rain than today," said Xie. |
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