Thursday, January 29, 2009

Hurricanes' climate footprint felt for months

Michael Reilly at MSNBC: Just as a changing climate shapes the strength and frequency of hurricanes, the storms may have a huge effect on climate, leaving "footprints" in the atmosphere and ocean. …[T]he full interplay between hurricanes and climate remains an enigma.

Robert Hart of Florida State University analyzed two decades of climate data from the tropics, and found that each storm leaves a wake of anomalously cool water and warm air behind it that can persist anywhere from one to two months, depending on the storm's strength.

Scientists have known for years that hurricanes cause cool ocean waters to well up, but Hart was surprised at how long the atmosphere retained a "memory" of each storm. That got him thinking: if one storm can have such a lasting impact, what does a whole season of storms do to Earth's climate? Would there be a difference in effect between an active hurricane season and a quiet one?

Hart performed a series of calculations and came up with a striking preliminary answer: hurricane seasons that spawned more storms (like 2005, for example) led to quieter winters in the northern hemisphere, and quiet hurricane seasons led to winters with lots of storm activity.

The reason, Hart speculates, is that hurricanes bring large amounts of heat out of the tropics and toward the poles. When a season has more storms, more heat is deposited closer to the poles and the tropics are cooled off more, so that when winter sets in there is less temperature difference between the poles and tropics….

Hurricane Wilma, 2005

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