"Gradient winds or general winds are named because of the gradient that exists between a high and low pressure system. A high pressure system is a large invisible mountain of air in the atmosphere. A low pressure system is like a sinkhole. Around a low pressure system the air flows in a counterclockwise manner into the area of low pressure. Around a high pressure system the air flows in a clockwise manner. These highs and lows are caused by the differential heating of the earth's surface."