marine meteorology

Related Overviews

Robert Fitzroy (1805—1865) hydrographer and meteorologist

Matthew Fontaine Maury (1806—1873) American oceanographer

Coriolis force

remote sensing

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Was founded by the American naval officer Lieutenant Matthew Fontaine Maury, when he convened an international meeting in Brussels in 1853 to establish standards for the reporting of weather at sea and around coastlines. One result was the setting up of the International Meteorological Organization, which has now become the World Meteorological Organization. Thanks to Maury's efforts in standardization, and recent major advances in observational methods—especially through remote sensing, the development of theoretical understanding, and increasingly powerful computers—today we benefit from high standards in weather forecasting. For example, ‘sea winds’ is an orbiting microwave radar device that is used to predict big storms. It measures wind, rain, and even ice on the world's oceans, and data from it is supplemented by readings from ocean radio transmitting buoys. It is particularly useful for surfers looking for outsize waves.

Our weather is generated by the disparity in the amounts of radiant energy received from the sun at polar and tropical latitudes. In the tropics, as the warmed air rises, it is replaced by air coming from the poles. At the poles the cold air is continually sinking. This generates a basic pattern of convection, in which winds in the lower atmosphere blow towards the equator, while those in the upper atmosphere blow towards the poles. Once the air begins to move latitudinally, Coriolis force comes into play and rotates its direction. So the basic pattern of airflow is broken up globally into a series of circulation cells.

Weather is latitudinally zoned. Near the equator are the doldrums, the trade winds blow between the latitudes of 10° and 20°, and then around 30° are the horse latitudes, which are high-pressure zones. At temperate latitudes cyclonic and anticyclonic pressure systems generate more variable weather patterns. At 60° is a zone of low-pressure systems, and finally over the poles high pressure dominates. The contrast in the high and low pressure systems between these high latitude regions fluctuates, and leads to decadal cycles in climate. In the North Atlantic this cycle is known as the North Atlantic Oscillation. In the tropics there are also significant variations in the geographical location of features like the Intertropical Convergence Zone (ITCZ), which irregularly generates El Niño events.

The water cycle plays a central role in determining weather patterns. The evaporation of water vapour from the ocean's surface cools the sea surface temperature. In the atmosphere, water vapour is the third most abundant gas, although only about 0.001% of all the water on earth is in the atmosphere at any one time. The warmer the air the more water vapour it can contain. Conversely, if air is cooled some of the water condenses into cloud and mist. When the air rises, the atmospheric pressure it is subjected to falls, so it expands and cools, and clouds are formed. Where there are coastal hills and mountains, onshore winds are forced up by the topography so a line of clouds forms along the coast. In the days of sail, clouds on the horizon were a useful indication of the proximity of land. Clouds affect the heat balance of the ocean, as they insulate the surface of the ocean surface from much of the sun's radiant heat. Winds accelerate the rate at which heat is exchanged across the ocean's surface; the fiercer the wind the faster heat is exchanged. Convection resulting from rapid heat exchange in the tropics can generate tropical storms.


Subjects: Maritime History.

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