Arctic oscillation is a measure of the differences in air pressure between air within the Arctic Circle and air that is between the circle and about 55°N longitude. The arctic oscillation can be either positive (air pressure is lower over the arctic region) or negative (the air pressure is higher). In the case of the former, winds become stronger across mid-latitude regions, Eurasia becomes warmer, and drier conditions prevail in the American West and the Mediterranean. Also, storms move farther north into Alaska and northern Europe. When the arctic oscillation is negative, the opposite is mainly true, and the American West Coast and the Mediterranean experience wet weather, while Eurasia cools.