Fog in the Gulf of Maine

July 8th, 2008 |

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Fog that formed in the Gulf of Maine on Tuesday July 8th developed when relatively moist air moved from the continent over the cooler ocean waters and was cooled from beneath by conduction to the dewpoint. In other words, Advection Fog.

An obvious question arises from the loop: Why does the fog persist over the ocean east of Nantucket and along the coast of Maine even as it clears out in the central part of the Gulf of Maine? The answer is shown in the color-shaded image of SST (available from the Applied Physics Lab at Johns Hopkins University) below. Warmer waters over the central Gulf of Maine will promote the faster erosion of ocean fog because of enhanced vertical mixing because of lower stability. Ocean fog that moves over land — as over southwestern Nova Scotia — also dissipates as heating over land promotes vertical mixing. Dryer air aloft mixed towards the surface reduces the boundary layer relative humidity and the fog evaporates. The dryer air just above the surface is readily apparent in Skew-T plots from Yarmouth, Nova Scotia and from Gray, Maine.

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