Abstract
When it is fine and surface pressure gradient is weak, a small-scale Cyclonic vortex is often formed under the mountain breeze regime in the planetary boundary layer of the Kanto plains. This wind system is quite different from what will be deduced from the theory of land-sea breeze. The horizontal dimension of the vortex is about 100km and it extends to 1km in height. Vorticity of the vortex is as large as 3•10-4 sec-1. Convergence in the lowest layer and divergence above it bring an upward flow in the vortex. The circulation in the vertical cross section may well be regarded as a secondary circulation which pumps the air in the Ekman layer up into the free atmosphere.
