Thursday, May 24, 2007

Woods Hole Geologists Compile Longest Hurricane Record

Terra Daily: The frequency of intense hurricanes in the Atlantic Ocean appears to be closely connected to long-term trends in the El Nino/Southern Oscillation (ENSO) and the West African monsoon, according to new research from the Woods Hole Oceanographic Institution (WHOI). Geologists Jeff Donnelly and Jonathan Woodruff made that discovery while assembling the longest-ever record of hurricane strikes in the Atlantic basin.

Donnelly and Woodruff began reconstructing the history of land-falling hurricanes in the Caribbean in 2003 by gathering sediment-core samples from Laguna Playa Grande on Vieques (Puerto Rico), an island extremely vulnerable to hurricane strikes. They examined the cores for evidence of storm surges-distinctive layers of coarse-grained sands and bits of shell interspersed between the organic-rich silt usually found in lagoon sediments-and pieced together a 5,000-year chronology of land-falling hurricanes in the region.

In examining the record, they found large and dramatic fluctuations in hurricane activity, with long stretches of frequent strikes punctuated by lulls that lasted many centuries. The team then compared their new hurricane record with existing paleoclimate data on El Nino, the West African monsoon, and other global and regional climate influences. They found the number of intense hurricanes (category 3, 4, and 5 on the Saffir-Simpson scale) typically increased when El Nino was relatively weak and the West African monsoon was strong.

"The processes that govern the formation, intensity, and track of Atlantic hurricanes are still poorly understood," said Donnelly, an associate scientist in the WHOI Department of Geology and Geophysics. "Based on this work, we now think that there may be some sort of basin-wide 'on-off switch' for intense hurricanes."

No comments: