Friday, December 5, 2014
Hurricanes self-feed, sucking up El Nino heat from the deep ocean
It has long been asserted that El Nino events, warming the
tropical Pacific as they do, promote hurricanes—but it may not occur as we’ve
previously assumed.
(Image: Hurricane tracks shown in black in the eastern and
central Pacific. Credit: Jin/SOEST.)
University of Hawai`i researchers have identified a two or
three-season delay that explains a lot about hurricane behavior. The El Nino
hot water sinks, moves in the ocean, and then surges back to the surface to
fuel tropical cyclones.
And that’s important information in terms of predicting
hurricane frequency and ferocity.
Fei-Fei Jin and Julien Boucharel, both of the UH Mānoa
School of Ocean and Earth Science and Technology (SOEST), published their study in the journal Nature.
The researchers looked into the phenomenon in which El Nino
is strongest in winter, but hurricane frequency picks up in the following summer
and fall. At that time, most of the heated water from the El Nino is stored
deep in the ocean of the eastern North Pacific.
But it may be that the activity of a young hurricane can
suck that warm water to the surface, in essence finding the heat needed to
fuel itself and supercharge the hurricane’s strength.
“We did not connect the discharged heat of El Niño to the
fueling of hurricanes until recently, when we noticed another line of active
research in the tropical cyclone community that clearly demonstrated that a
strong hurricane is able to get its energy not only from the warm surface
water, but also by causing warm, deep water – up to 100 meters deep – to upwell
to the surface,” Jin said. He was quoted in a University of Hawai`i press release.
Boucharel said that extra heat provides a lot of destructive
energy.
“The Northeastern Pacific is a region normally without
abundant subsurface heat. El Niño’s heat discharged into this region provides
conditions to generate abnormal amount of intense hurricanes that may threaten
Mexico, the southwest of the U.S. and the Hawaiian islands,” he said.
The authors wrote in the Nature paper: “we show that El
Niño—the warm phase of an ENSO cycle—effectively discharges heat into the
eastern North Pacific basin two to three seasons after its wintertime peak,
leading to intensified TCs.”
They continue: “As a result of the time involved in ocean
transport, El Niño’s equatorial subsurface ‘heat reservoir’, built up in boreal
winter, appears in the eastern North Pacific several months later during peak (tropical cylone) season (boreal summer and autumn).
"By means of this delayed ocean transport
mechanism, ENSO provides an additional heat supply favourable for the formation
of strong hurricanes.”
© Jan TenBruggencate 2014
Posted by Jan T at 10:16 AM
Labels: Climate Change, Energy, Marine Issues, Oceanography, Weather, Wind
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