lowpressure

Low pressure refers to a region where atmospheric pressure is lower than surrounding areas. In meteorology, a low-pressure center is associated with rising air, cloud formation, and often precipitation. Lows develop when air near the surface converges or when air aloft cools and becomes unstable, causing vertical motion that reduces surface pressure. In the Northern Hemisphere, winds rotate counterclockwise around a low, while in the Southern Hemisphere they rotate clockwise; the exact motion is controlled by the Coriolis effect and the pressure gradient force.

Low-pressure systems come in several forms, including tropical cyclones, extratropical or mid-latitude cyclones, and mesoscale lows. Tropical lows form over warm oceans and can intensify into storms; extratropical lows typically form along frontal zones and fronts. The weather associated with low pressure often includes clouds, rain, and gusty winds, though showers can occur with narrow or weak lows, and some lows bring clear spells.

Measurement of surface pressure is done in hectopascals (hPa) or millibars. Standard sea level pressure is about 1013 hPa; lows are typically below this value, with stronger systems reaching around 970–990 hPa or lower at their centers.

Other uses: in engineering and physics, "low pressure" can describe environments with pressures below atmospheric, as in vacuum systems or sealed vessels. In fluid dynamics, low-pressure regions can form on the upper surface of a wing or around moving bodies, where faster flow lowers pressure and creates lift.

Related concepts include high pressure, cyclones, troughs, and isobars.