It is hurricane season again in the tropical Atlantic Ocean, and residents of the Caribbean and the U.S. and Mexican coastal areas are on guard. Many of the tropical storms that batter these regions originate off West Africa's coast. U.S. government and university scientists are starting a study of how they intensify so they can improve forecasts to avoid the death and devastation hurricanes cause.
The U.S. agency responsible for ocean and atmosphere matters, NOAA, says thunderstorms off West Africa account for 60 percent of all hurricanes in the tropical Atlantic and 85 percent of the biggest ones.
One such weather disturbance gave rise to Hurricane Katrina, which devastated New Orleans and a large swath of the U.S. Gulf Coast a year ago.
But that does not mean that most of these so-called African atmospheric waves intensify to hurricanes. There are 60 to 70 of these distrubances each year, but only about half a dozen begin spinning enough to grow into tropical cyclones.
Scientists like Jeffrey Halverson of the University of Maryland want to know why more do not.
"About 10 percent of these waves change their character from being long traveling lines of thunderstorms. They begin acquiring some rotation. That's the big mystery, why so very few of those waves actually start picking up some spin. We don't really know where that spin comes from. That's part of the big question we're out to answer as they come off Africa."
The hurricane research director at NOAA, Jason Dunion, says two factors seem to suppress cyclone development, cold sea surface temperatures off West Africa and dry air and dust blowing from the Sahara Desert. But Dunion says if a storm survives to reach warmer waters and it begins spinning, it can merge with other such vortices into a larger one, a prerequisite for a twisting, churning hurricane.
"How do those come together? There certainly are some things we know, but there are a lot of mysteries out there. Some of it is because we just haven't observed it all that much," he said.
That will change with the research mission Dunion's agency is jointly undertaking through August with the U.S. space agency NASA and academics like Halverson. From their base on the Cape Verde islands off West Africa, they will take moisture, temperature, wind speed and other readings about storms from several U.S. satellites, an aircraft that flies through storms, weather balloons, and ground stations.
Dunion says the ability to track the path of emerging hurricanes has improved greatly in recent years, but the science of monitoring their growth and intensity is lagging far behind.
Jeff Halverson says this is a vital need.
"Better understanding the physics that generate these storms will extend the time of skillful forecasts, and thus save lives and property," he said.
The U.S. hurricane researchers will share data with European and African scientists who are working to understand the influence of the West African monsoon on regional and global weather.