Hurricanes form over warm waters. The evaporation of the warm ocean waters condenses to form clouds and precipitation releasing latent heat energy that helps to maintain the storm.
A general rule of thumb is that hurricanes will not form unless the water temperature is at least 80 degrees. Photographs of hurricanes over the ocean clearly show that hurricanes churn water at the surface, mixing it with cooler waters below.
Measurements also show that hurricanes can push heat deep below the sea surface. The mixing of heat into the ocean by hurricanes occurs by the strong winds and also by underwater waves produced by the storm. Ocean measurements before and after hurricanes show that these waves transport heat to depths where the heat is stored far below the surface. The depth is such that the heat cannot by quickly released into the atmosphere. In fact, the deep ocean currents can transport that heat thousands of miles away from the storm.
One recent study found that a hurricane traveling across the western Pacific Ocean could supply warm water to the coast of Ecuador years later. The heat transported deep in the ocean by the storm doesn’t resurface in the vicinity of the hurricane.
The impacts of hurricanes on climate will depend on the depth to which the storms deposits the heat. Mixing of cooler waters below the ocean surface by the hurricane winds cools the sea surface temperature. The heat transported deep in the ocean from hurricanes may reside there for decades without returning to the surface. Hurricanes can help to slow down global warming by transporting heat deep in the ocean where it is stored.
Steve Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on WHA radio (970 AM) at 11:45 a.m. the last Monday of each month. Send them your questions at stevea@ssec.wisc.edu or jemarti1@wisc.edu.
