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The thermal wind is the difference in the geostrophic wind between two levels in the atmosphere. It exists only in an atmosphere with horizontal temperature gradients. [5] The ageostrophic wind component is the difference between actual and geostrophic wind, which is responsible for air "filling up" cyclones over time. [6]
It is also referred as the geostrophic wind. [2] Pressure differences depend, in turn, on the average temperature in the air column. As the sun does not heat the Earth evenly, there is a temperature difference between the poles and the equator, creating air masses with more or less homogeneous temperature with latitude.
The rising air creates a low pressure zone near the equator. As the air moves poleward, it cools, becomes denser, and descends at about the 30th parallel, creating a high-pressure area. The descended air then travels toward the equator along the surface, replacing the air that rose from the equatorial zone, closing the loop of the Hadley cell. [3]
A similar phenomenon to a weather front is the dry line, which is the boundary between air masses with significant moisture differences instead of temperature. When the westerlies increase on the north side of surface highs, areas of lowered pressure will form downwind of north–south oriented mountain chains, leading to the formation of a lee ...
The wind speeds are greatest where temperature differences between air masses are greatest, and often exceed 92 km/h (50 kn; 57 mph). [24] Speeds of 400 km/h (220 kn; 250 mph) have been measured. [29] The jet stream moves from west to east bringing changes of weather. [30]
This rising air over the land lowers the sea level pressure by about 0.2%. The cooler air above the sea, now with higher sea level pressure, flows towards the land into the lower pressure, creating a cooler breeze near the coast. The strength of the sea breeze is directly proportional to the temperature difference between the land mass and the sea.
There are also links to be found between wind speed and wind direction, notably with the pressure gradient and terrain conditions. The Pressure gradient describes the difference in air pressure between two points in the atmosphere or on the surface of the Earth. It is vital to wind speed, because the greater the difference in pressure, the ...
Wind gradient is also a hazard for aircraft making steep turns near the ground. It is a particular problem for gliders which have a relatively long wingspan, which exposes them to a greater wind speed difference for a given bank angle. The different airspeed experienced by each wing tip can result in an aerodynamic stall on one wing, causing a ...