Buys Ballot's law

Buys Ballot's law relates wind direction to nearby pressure: with your back to the wind, lower pressure lies to the left in the Northern Hemisphere and to the right in the Southern Hemisphere.

Coriolis effect: The apparent deflection of moving objects caused by observing motion in a rotating reference frame. Earth’s rotation deflects winds and helps set the pressure-relative direction the law describes.
Wind: The movement of air relative to Earth’s surface, driven chiefly by pressure differences. The law uses the wind’s direction as its starting observation.
Christophorus Buys Ballot: A Dutch meteorologist and chemist who formulated a practical relation between wind direction and atmospheric pressure. His name is attached to the empirical rule.
Weather map: A map displaying observed or forecast atmospheric conditions over a region. The law helps interpret mapped winds alongside pressure patterns.
Gradient wind: A curved-flow wind in which pressure-gradient, Coriolis, and centrifugal forces balance. It describes curved winds around pressure systems more fully than the simplest geostrophic balance.
Pressure gradient force: The force per unit mass that accelerates air from higher pressure toward lower pressure. It drives air toward low pressure, while rotation bends that motion into the pattern behind the law.
Atmospheric pressure: The force per unit area exerted by the weight and motion of air. The law identifies the direction of lower pressure relative to the wind.
Buys Ballot's law experiment: A nineteenth-century comparison of wind observations with pressure measurements across the Netherlands. The observations established the relation that became known as the law.
Surface weather analysis: The interpretation of near-surface observations to identify fronts, pressure systems, and weather features. The rule supports a quick check of where a low lies relative to surface wind.
Cyclostrophic wind: A curved wind in which pressure-gradient and centrifugal forces dominate, with Coriolis effects small. It applies to small, intense vortices where the usual hemisphere-based circulation rule can fail.

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C. H. D. Buys BallotBroader topic: This is the meteorological rule most closely associated with Buys Ballot.