Buys Ballot's law

Buys Ballot's law

In meteorology, Buys Ballot's law may be expressed as follows: In the Northern Hemisphere, stand with your back to the wind; the low pressure area will be on your left. This is because wind travels counterclockwise around low pressure zones in the Northern Hemisphere. It is approximately true in the higher latitudes of the Northern Hemisphere, and is reversed in the Southern Hemisphere, but the angle between the pressure gradient force and wind is not a right angle in low latitudes. See Coriolis effect#Flow around a low-pressure area.

This rule, which was first deduced by the American meteorologists J.H. Coffin and William Ferrel, is a direct consequence of Ferrel's law. The law takes its name from C. H. D. Buys Ballot, a Dutch meteorologist, who published it in the Comptes Rendus, November 1857. While William Ferrel theorized this first in 1856, Buys-Ballot was the first to provide an empirical validation.

Buys Ballots law first appeared in early versions (prior to 1900) of Bowditchs' American Practical Navigator other publications written to assist in passage planning and the safe conduct of ships at sea and is still included today both in Bowditch and in Sailing Directions (see following reference) as an item of practical reference and information. The law outlines general rules of conduct for masters of both sail and steam vessels, to assist them in steering the vessels away from the center and right front (in the Northern Hemisphere and left front in the Southern Hemisphere) quadrants of hurricanes or any other rotating disturbance at sea.

Note that prior to radio, satellite observation and the ability to transmit timely weather information over long distances, the only method a ships master had at his disposal to forecast the weather was observation of meterological conditions (visible cloud formations, wind direction and atmospheric pressure) at his location.

As early as the 1500 s extensive weather observations were included as part of a ships log. These observations as well as other log information, were turned over to national hydrographic institutes in various nations, most notably Germany and England and later the US. The information from many ships about individual voyages was compiled ashore and later became what today is still published by England, a 3 volume set complete with charts titled "Sailing Directions for the World" . Additionally the US Defense Mapping Agency publishes a 47 volume set "Sailing Directions " serves much the same purpose. The information is the distillate of empirical observations of thousands of ships masters over thousands of voyages spanning several hundred years. Included are Buys Ballots Law techniques for avoiding the worst part of any rotating storm system at sea using only locally observable phenomena i.e. cloud formations, wind speed and barometric pressure tendencies over a number of hours. These observations and application of the principles of Buys Ballots Law help to establish the probability of the existence of a storm and the best course to steer to try avoid the worst of it--with the best chance of survival.

From a slightly less esoteric standpoint the underlying principles of Buys Ballots Law state that for anyone ashore in the Northern Hemisphere and in the path of a hurricane, the most dangerous place to be is in the right front quadrant of the storm. There, the observed wind speed of the storm is the sum of the speed of wind in the storm circulation plus the velocity of the storms forward movement. Buys Ballots Law calls this the Dangerous Quadrant. Likewise in the left front quadrant of the storm the observed wind is the DIFFERENCE between the storms wind velocity and its forward speed. This is called somewhat euphemistically the Safe Quadrant due to the lower observed wind speeds.

To look at it another way in the Northern Hemisphere if you are to the right of where a hurricane or tropical storm makes landfall that is considered the dangerous quadrant. If you are to the left of the point of landfall that is the safe quadrant.

In the dangerous quadrant an observer will experience higher wind speeds and generally a much higher storm surge due to the wind direction (onshore).

In the Safe quadrant, the observer will experience somewhat lower wind speeds and the possibility of lower than normal water levels due to the direction of the wind being offshore.

These are very general rules that are subject to many other factors i.e. shapes of the coastline, and topography in any location. Although the principles here to a very limited extent apply to a coastal observer during the approach and passage of a storm in any location, Buys Ballots Law was primarily formulated from empirical data to assist ships at sea.

External links

*M. Buys-Ballot, "Note sur le rapport de l'intensité et de la direction du vent avec les écarts simultanés du baromètre", [ "Académie des sciences (France). Comptes rendus hebdomadaires"] , TOME XLV, JUILLET - DÉCEMBRE (1857) pp. 765–768.

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Look at other dictionaries:

  • Buys-Ballot's law — /buys beuh lots /, Meteorol. the law stating that if one stands with one s back to the wind, in the Northern Hemisphere the atmospheric pressure will be lower on one s left and in the Southern Hemisphere it will be lower on one s right:… …   Universalium

  • Buys-Ballot's law — /buys beuh lots /, Meteorol. the law stating that if one stands with one s back to the wind, in the Northern Hemisphere the atmospheric pressure will be lower on one s left and in the Southern Hemisphere it will be lower on one s right:… …   Useful english dictionary

  • Buys Ballot's law — ▪ atmospheric science       the relation of wind direction with the horizontal pressure distribution named for the Dutch meteorologist C.H.D. Buys Ballot (Buys Ballot, Christophorus), who first stated it in 1857. He derived the law empirically,… …   Universalium

  • Buys Ballot’s Law — The law states that if an observer stands with his back to the wind, then the lower pressure will be on his left in the Northern Hemisphere, and on the right in the Southern Hemisphere. The law is named after Christoph Hendrik Diedrik Buys Ballot …   Aviation dictionary

  • Buys Ballot's Law — /bis bəˈlɒts lɔ/ (say bees buh lots law), /bɔɪs/ (say boys) noun the principle that in the Northern Hemisphere atmospheric pressure is higher on the left when facing into the wind; in the Southern Hemisphere it is higher on the right. {named… …   Australian English dictionary

  • buys ballot's law — ˈbīsbəˈläts , ˈbȯis noun Usage: usually capitalized both Bs Etymology: after C.H.D. Buys Ballot died 1890 Dutch meteorologist : a law in meteorology: when the observer has his back to the wind the lower barometric pressure is to his left in the… …   Useful english dictionary

  • Buys Ballot’s law — if someone in Northern Hemisphere stands with back to wind, atmospheric pressure will be lower to his left hand than to his right, and the reverse in Southern Hemisphere …   Eponyms, nicknames, and geographical games

  • Buys Ballot, Christophorus — ▪ Dutch meteorologist born October 10, 1817, Kloetinge, Neth. died February 3, 1890, Utrecht       Dutch meteorologist particularly remembered for his observation in 1857 that the wind tends to blow at right angles to the atmospheric pressure… …   Universalium

  • BUYS BALLOT, Christophorus Henricus Diederlcus — (1817–1890)    Chemist and physicist. After studying mathematics and physics at Utrecht University, Buys Ballot became a lecturer in geology and mineralogy. In 1847, he was appointed professor of mathematics at the same university, and in 1867,… …   Historical Dictionary of the Netherlands

  • Buys Ballot , Christoph Hendrik Diederik — (1817–1890) Dutch meteorologist Buys Ballot was the son of a minister from Kloetinge in the Netherlands. He was educated at the University of Utrecht, obtaining his PhD in 1844, and became professor of mathematics in 1847 and professor of physics …   Scientists

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