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Concept
Pressure system
Résumé
A pressure system is a peak or lull in the sea level pressure distribution. The surface pressure at sea level varies minimally, with the lowest value measured and the highest recorded . High- and low-pressure systems evolve due to interactions of temperature differentials in the atmosphere, temperature differences between the atmosphere and water within oceans and lakes, the influence of upper-level disturbances, as well as the amount of solar heating or radiationized cooling an area receives. Pressure systems cause weather to be experienced locally. Low-pressure systems are associated with clouds and precipitation that minimize temperature changes throughout the day, whereas high-pressure systems normally associate with dry weather and mostly clear skies with larger diurnal temperature changes due to greater radiation at night and greater sunshine during the day. Pressure systems are analyzed by those in the field of meteorology within surface weather maps.
Low-pressure area and Cyclone
A low-pressure area is a region where the atmospheric pressure at sea level is below that of surrounding locations. Low-pressure systems form under areas of wind divergence that occur in the upper levels of the troposphere. The formation process of a low-pressure area is known as cyclogenesis. Within the field of atmospheric dynamics, areas of wind divergence aloft occur in two areas:
On the east side of upper troughs, which form half of a Rossby wave within the Westerlies (a trough with large wavelength, which extends through the troposphere).
Ahead of embedded shortwave troughs, which have smaller wavelengths.
Diverging winds aloft ahead of these troughs cause atmospheric lift within the troposphere below, which lowers surface pressures as upward motion partially counteracts the force of gravity.
Thermal lows form due to localized heating caused by greater sunshine over deserts and other land masses. Since localized areas of warm air are less dense than their surroundings, this warmer air rises, which lowers atmospheric pressure near that portion of the Earth's surface.
Source officielle
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