EFFECT OF A SUDDEN CHANGE IN TERRAIN HEIGHT ON THE THREE-DIMENSIONAL LOW-LEVEL AIR FLOW, AS ESTIMATED FROM TETROON FLIGHTS

Abstract

Tetroon flights across the northern California coast indicate the influence of a laterally extensive and fairly abrupt 100-m change in terrain height near the shoreline on the three-dimensional low-level air flow. Beneath the wind speed maximum at a height of 300 m, the wind speed is stronger over the land than over the sea, resulting in nearly equal horizontal mass transport between this height and the earth's surface. Across the 4-km interval bracketing the shoreline, the wind backs by 11° and 4° at heights of 200 and 400 m, respectively. The maximum upward velocity, of magnitude 6 cm sec?l, occurs 250 m above the sudden change in terrain height near the shoreline, with the compensating downward motion commencing 3 km inland. Over the hills inland from the coast, the magnitude of the tetroon height variation is closely related to the magnitude of the height variations of the underlying terrain, with tetroon oscillations in the vertical generally preceding the variations in terrain height by a distance exceeding the height of the tetroon above the ground.