Air pressure and wind — Earth science, 14–17 years
Uneven heating makes air pressure differ from place to place. Air moves from higher pressure towards lower pressure, and Earth’s rotation changes the path of that movement.
Air pushed by differences
Air pressure is the push made by the weight of air above a surface. When pressure is higher in one area than another, air is pushed sideways towards the lower-pressure area. We feel that moving air as wind, although friction and Earth’s rotation alter its speed and direction.
Why winds form
A weather map needs more than the idea that warm air rises. The real problem is explaining why air then travels across large distances and why winds curve instead of moving in perfectly straight lines. Pressure differences provide the push; rotation and friction help explain the observed pattern.
Reading a pressure map
Suppose two nearby places have pressures of 1020 and 1000 hectopascals, and the lines between them are close together. Air is pushed from the 1020 side towards the 1000 side. Close lines mean a large change over a short distance, so the pressure-gradient force is strong and winds are likely faster.
Wind does not always blow straight
A natural mistake is to draw wind as a straight arrow directly from high pressure to low pressure. That is a sensible first picture because pressure supplies the push. Near Earth’s surface, friction slows the air, and the rotating planet deflects its path, so real wind crosses or curves around pressure lines.
Forecasts and flight
Meteorologists use pressure measurements and maps to estimate wind, storms and approaching weather systems. Pilots also account for wind because it changes travel time, fuel use and an aircraft’s path. A pressure map supports a forecast, but observations and models are still needed.
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