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Warming in central Pacific Ocean
may offer better cyclone predictor
Find suggests shifts in activity are more reliable than El Niño
By Sid Perkins
Warmer than normal sea-surface temperatures in the central Pacific lead to
stronger, more frequent tropical storms
and hurricanes in the North Atlantic, a
new analysis suggests. Unlike the more
familiar El Niño, or warming in the equatorial region of the eastern and central
Pacific, patterns in central Pacific warming alone are more predictable and may
offer forecasters a more accurate method
of anticipating hurricane activity during
the upcoming year.
The sea-surface warming characteristic of El Niño typically stretches along the
equator from the coast of South America
to the international date line, with the
largest temperature anomalies in the
eastern Pacific. During El Niño episodes,
the number of tropical storms and hurricanes — both called cyclones — is lower
than average across the North Atlantic,
says Peter J. Webster of Georgia Institute
of Technology in Atlanta. But when the
equatorial sea-surface warming is concentrated mostly around the international date line, hurricane activity is much
higher than normal, Webster and his colleagues report in the July 3 Science.
“This is a pattern that we [scientists]
hadn’t really recognized before,” comments Chris Landsea of the National Oceanic and Atmospheric Administration’s
hurricane research division in Miami.
Webster and his colleagues analyzed
patterns in North Atlantic cyclone
activity from 1950 through 2006 during August, September and October,
the height of hurricane season. As many
previous studies had noted, the number
and strength of tropical cyclones were
markedly lower in El Niño years than
during La Niña episodes, when sea-surface temperatures in the eastern and
central Pacific are substantially cooler
than normal. Unlike previous research,
says Webster, the new study reveals that
when sea-surface warming is confined
to the central Pacific, hurricane activity
is higher, particularly in the Caribbean,
the Gulf of Mexico and along the eastern
coast of the United States.
Models suggest that high-altitude wind
shear over the North Atlantic is stronger
than normal during El Niño events, disrupting the formation and strengthening
of tropical storms there, Webster notes.
During La Niña years, wind shear is low,
and storms more readily form and gain
strength. When sea-surface warming
is confined to the central Pacific, wind
shear in the North Atlantic region is
about average but not large enough to
totally disrupt cyclone formation.
Identifying the new central Pacific
warming pattern is important because
the transition between El Niño warming and La Niña cooling isn’t always predictable, says Webster. Sometimes, just
when it looks like a shift will occur from
warm to cool, for example, temperatures
will swing back to warm again, thwarting
forecasters’ attempts to predict cyclone
activity for the upcoming season. But
shifts in central Pacific warming seem
to follow a more predictable path, the
new analysis suggests.
Erosion, on the down low
S. BONNEVILLE ET AL./GEOLOG Y
Scientists have for the ;rst time observed how the tiny fungi that live
on plant roots physically erode rocks and set the stage for chemical
breakdown. Steeve Bonneville of the University of Leeds in England
and his colleagues set up a lab test to study the effects of the fungi
Paxillus involutus on biotite, a potassium-rich mineral found in granite
and other rock types. In the test, reported in the July Geology, the
researchers planted a pine seedling with fungi-covered roots in a
dry nutrient-poor soil free of other microorganisms (right). A ;ake of
biotite (arrow) near the tree’s roots provided nourishment and was
the only source of potassium in the soil, Bonneville says. After three
months, the team analyzed the ;ake in areas where fungi ;laments,
known as hyphae, had attached. Microscopy revealed that mineral
layers beneath the attachments were wedged apart by at least
14 degrees. Material near the attachment had lost as much as
70 percent of its potassium. These changes allowed iron-bearing
compounds in the rocks to react with oxygen from the air, encouraging further erosion, the team reports. — Sid Perkins
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