The determination of air movement or wind, is a vector that is specified by speed and direction. Meteorological convention indicates wind direction as the direction from which the wind blows (for example, a southeast wind blows toward the northwest). Conventional anemometers are devices that measure wind speed, while wind vanes indicate direction. Other devices, such as sonic anemometers and Doppler wind profilers, measure the unit wind speed in each of various directions to then determine the total wind speed and direction. On average, the wind blows horizontally over flat terrain; however, gusts, thermals, cloud outflows, and many other conditions have significant short-term vertical wind motions. Whereas research wind instruments typically measure both horizontal and vertical air movement, operational and personal wind sensors typically measure only the horizontal component.