Anticyclone

An atmospheric disturbance in which a loosely defined center of high barometric pressure generates circular winds that flow outward, away from the center, and with diminishing degrees of intensity. Commonly referred to as a high, an anticyclone (as its name indicates) is the opposite of a cyclone, or a well-defined center of low pressure in which the winds roar inward. In an anticyclone, warm, sinking air does not allow sea-level moisture to rise high enough into the troposphere for rain clouds to form. For this reason, anticyclonic weather tends to be fair, with few clouds and warm temperatures, while cyclonic systems frequently produce the torrential precipitation and high winds associated with mature hurricanes and typhoons.

Although meteorologists are not completely certain how anticyclones are formed, it is known that as isolated pockets of high pressure air expand, they begin to spin in a clockwise direction in the Northern Hemisphere and in a counter clockwise direction in the Southern Hemisphere. When combined with the relentless expansion of the high pressure air, this circular motion allows an anticyclone to fling its temperate influence over wide expanses of land and sea. This characteristic makes the anticyclone a much more powerful (though less intense) system than the smaller, more concentrated cyclone. Indeed, the intensity and track of cyclonic storm systems are often determined by the size and proximity of highlevel anticyclones. The Bermuda High, for instance, has a tendency to draw North Atlantic hurricanes westward along its southern flank and then up, over, and back toward the east again. Smaller, more localized anticyclones can serve to both vent a hurricane’s critical outflow layer smoothly and distribute cool, dry air to the storm’s outermost fringes. In both scenarios, the anticyclone aids in the hurricane’s immediate intensification by either creating a space for the rapidly rising winds within the eye to ascend to or by returning spent air to the storm’s edges,

where it sinks to sea level, becomes laden with evaporation, and is once again drawn into the developing cyclone.