<P> A simple rule is that for high - pressure areas, where generally air flows from the center outward, the coriolis force given by the earth's rotation to the air circulation is in the opposite direction of earth's apparent rotation if viewed from above the hemisphere's pole . So, both the earth and winds around a low - pressure area rotate counter-clockwise in the northern hemisphere, and clockwise in the southern . The opposite to these two cases occurs in the case of a high . These results derive from the Coriolis effect; that article explains in detail the physics, and provides an animation of a model to aid understanding . </P> <P> High - pressure systems form due to downward motion through the troposphere, the atmospheric layer where weather occurs . Preferred areas within a synoptic flow pattern in higher levels of the troposphere are beneath the western side of troughs . </P> <P> On weather maps, these areas show converging winds (isotachs), also known as convergence, near or above the level of non-divergence, which is near the 500 hPa pressure surface about midway up through the troposphere, and about half the atmospheric pressure at the surface . </P> <P> High - pressure systems are alternatively referred to as anticyclones . On English - language weather maps, high - pressure centers are identified by the letter H in English, within the isobar with the highest pressure value . On constant pressure upper level charts, it is located within the highest height line contour . </P>

Which of the following is not a characteristic of a high-pressure system