It’s not just what’s in the water. What’s blowing in the wind, shifts in atmospheric circulation, play a major hand in shaping hurricanes.
That’s what scientists at Woods Hole Oceanographic Institute say in a study which put together a 5,000-year history of hurricanes that struck the Puerto Rican island of Vieques.
Geologists Jeff Donnelly and Jonathan Woodruff looked at sleepy Laguna Playa Grande, which escapes the notice of all but the strongest storms. When a hurricane strikes, storm surges push stuff from the beach into the lagoon. Donnelly and Woodruff took core samples of the lagoon sediment, and storm surges over thousands of years showed up in the geologic record as bands of clumpier sand and shell fragments layered in with the fine silt of the lagoon mud.
They then compared the frequency of hurricanes with other climate records. And what they found were more and stronger hurricanes in times of La Nina and when West African monsoon were strong.
“The processes that govern the formation, intensity, and track of Atlantic hurricanes are still poorly understood,” said Donnelly. He added that, “based on this work, we now think that there may be some sort of basin-wide ‘on-off switch’ for intense hurricanes.”
La Nina is characterized by cool ocean temperatures in the tropical Pacific, the opposite phase of the climate pattern known as El Nino, which is associated with a warmer tropical Pacific. La Nina’s coolness causes jet streams over the Caribbean to shift north. It’s these jet streams which typically interfere with the formation of hurricanes that might hit the Atlantic coast.
In today’s New York Times article by Andrew Revkin on the La Nina-hurricane link, it was emphasized that warmer waters from climate change might not be the only factor in increasing the frequency and intensity of hurricanes. What’s more, NASA research meteorologist Scott Braun told Earth & Sky (in this podcast) that there’s still much uncertainty on the matter, mainly from the unreliability of historical records based on human reporting.
Looking ahead this year, NOAA predicts an above average hurricane season for 2007, which typically picks up in July and August.
Yet another story that shows us, very clearly, that we’re all living on a single Planet Earth.