Low-pressure area
A clockwise spinning low pressure area or cyclone off southern Australia. The center of the spiral-shaped cloud system is also the center of a low, and usually is where the pressure is lowest. This low-pressure system over Iceland spins counter-clockwise due to balance between the Coriolis force and the pressure gradient force. "Weather system" redirects here. For a general discussion on pressure areas, see Pressure system. For the opposite effect, see High-pressure area. A low-pressure area , low , depression or cyclone is a region on the topographic map where the atmospheric pressure is lower than 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 meteorology, atmospheric divergence aloft occurs in two areas. The first area is on the east side of upper troughs, which form half of ...