18 July 2011
My fellow AGU blogger John Freeland (over at Terra Central) spotted this gorgeous pic of the lake breeze around Lake Erie and sent it my way. I love images like this because they illustrate an atmospheric circulation that many people are familiar with, especially those who live near the coast, or around the Great Lakes. It was one of the first pieces of atmospheric science I understood well (as a student) and having lived on the coast of Florida for several years, I enjoyed the benefits of the cooling sea breeze in summer.
A sea-breeze and a lake-breeze are the same thing, and form by temperature differences translating into pressure differences in the atmosphere. They are called thermally induced circulations for that very reason.
The basics are these: the land heats up very quickly in the summer sun, but the water of Lake Erie changes little on a diurnal basis. So, by afternoon you have very warm air over the land around the lake and cool air over the lake itself. The warm air expands and the pressure drops, allowing the cooler and denser air over the lake to rush landward.
The bigger the temperature difference between the water and land, the stronger the circulation. It is indeed a circulation, with a return flow aloft going from land back to sea. At night, when the land becomes cooler than the water, a land-breeze develops and blows from the land to the sea/lake.
The sea-breeze front marks the area where the wind from the lake meets the warm air over land and this convergence causes rising motion in the atmosphere. Forecasters in Florida know that the afternoon summer storms will form on the sea-breeze and in areas where the coast bends the right way, you can get sea breezes converging and this forms plenty of thunderstorms with lightning. One place where this happens is Merritt Island, home to the Kennedy Space Center!
The folks at COMET (Cooperative Online Meteorological Education and Training) have a great module on sea-breezes for you amateur meteorologists or just those interested in how the atmosphere works. COMET is mainly designed for meteorologists and students of atmospheric science, but you are free to download their modules (registration required but free), and they are excellent. As an AMS Certified Broadcast meteorologist, I’m required to complete continuing education requirements, and these COMET modules count toward them.
PS: You likely already knew that the land heats quicker than the water, but have you ever asked yourself why this is so??