Originally posted on sciy.org by Ron Anastasia on Fri 10 Aug 2007 08:48 AM PDT
Scientists examine African dust link to hurricanes
By Jim Loney
MIAMI (Reuters) - Storm scientists are taking a closer look at whether giant dust clouds from the Sahara could join the El Nino phenomenon as a leading indicator of the ferocity of Atlantic hurricane seasons.
El Nino, a warming of eastern Pacific waters, has become a dominant storm indicator because it can flatten an Atlantic hurricane season by increasing the wind shear that can rip apart cyclones.
The jury is still out on the effects of the Saharan dust storms that can span the Atlantic, but scientists are intrigued by preliminary research showing a direct correlation between the sandy plumes and tropical cyclones.
"What we've seen is, more dust, fewer hurricanes," said William Lau, chief of the Laboratory for Atmospheres at NASA's Goddard Space Flight Center in Maryland.
The busy and damaging hurricane seasons of 2004 and 2005, which rattled global energy and insurance markets, have heightened interest in storm forecasting and in research on factors that make tropical cyclones spin up into monster storms or wither and die at sea.
Four powerful hurricanes hit Florida in 2004 and the record-setting 2005 season produced Hurricane Katrina, which became the costliest natural disaster in U.S. history when it crushed the U.S. Gulf coast and swamped New Orleans, causing $80 billion in damage and killing 1,500 people.
Studies so far indicate that dust clouds from Africa, which can grow as big as the continental United States and reach all the way to the Caribbean and Central America, tend to cool the Atlantic by reflecting sunlight.
Hurricanes are fueled by warm water, so cooler seas could mean fewer or less intense storms.
The hot, dry masses of dust may also interfere with already-formed hurricanes. Researchers say such a cloud can increase wind shear and inject dry air into a cyclone if the two come into direct contact."The air is incredibly dry, and we know dry air is not good for the development of hurricanes," said Jason Dunion, a meteorologist at the National Oceanic and Atmospheric Administration's Hurricane Research Division in Miami.
DUSTY SUMMER
The giant masses of Saharan dust that originate in West Africa generally peak over the Atlantic in May, June, July and early August and retreat just before the height of the hurricane season from around mid-August to mid-October.
"These last couple months have been the dustiest summer since 1999, about five times as dusty as last year. Right now ocean temperatures are cooler than average," said Amato Evan, a climate researcher at the University of Wisconsin. "There's a big difference compared to the last two years."
There have been three named storms so far this year, and none grew to hurricane strength.
Last year Evan and other researchers studied 25 years of data and found a direct correlation between years that had more dust and fewer hurricanes.
But scientists have yet to answer key questions. For example, most of the weather systems that emerge from the African coast don't develop into cyclones.
"Why does only one in 10 of those turn into a tropical storm?" said Dunion. "Dust is probably one of the reasons for that."
Can African dust be used reliably to forecast hurricanes?
Researchers say not yet. NOAA, the agency that oversees the National
Hurricane Center, does not use dust data in its forecasts.
"That area of research is too new," Dunion said.
African dust storms are now tracked by satellite. And in 2005 and 2006, NOAA sent hurricane hunter aircraft to investigate the dust clouds.
Lau said much more study is needed, but African dust eventually could become a key element of hurricane forecasting.
"We know El Nino is No. 1. Maybe African dust could become a close No. 2," he said.
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