Climate Fact: Hurricanes and Heat Distribution
In the Atlantic, the frequency of hurricane formation and the strength of the storms that form during a given year are controlled by things like Atlantic sea surface temperatures, temperature differences between the eastern and western tropical Pacific (i.e. the El Niño-Southern Oscillation) and even things like dust storm frequency in the Sahara Desert. On the other hand, the momentum that hurricanes have can actually change the properties of Earth’s thermohaline circulation (THC) and changes in the THC cause changes in atmospheric circulation, affecting weather across the globe. The mixing between the surface and subsurface layers that hurricanes cause in the waters over which they move results in an increase in surface layer evaporation. This causes an increase in salinity and density at the surface, which leads to a strengthening of the overturning that occurs around Greenland (where the warm northward moving current “overturns” and becomes a cold, deep water current – a critical component of Earth’s THC). This strengthening of the overturning increases the strength of poleward heat transport as well. On the other hand, the heavy rains land-falling hurricanes cause result in an increase in runoff and freshwater discharge into the ocean. This phenomenon causes a freshening of the surface layer, leading to a weakening of the overturning. Whether there will be a strengthening or a weakening of the overturning circulation after hurricane season is likely dependent on which is larger: the area of the ocean where freshening dominates or the area of the ocean where evaporation dominates.
Seasons: Summer, Fall
Source: Hu, A and Meehl, GA. “Effect of the Atlantic hurricanes on the oceanic meridional overturning circulation and heat transport.” Geophysical Research Letters 36 (2009): L03702.
