Abstract
Theoretical considerations on the Ekman pumping actions in the planetary boundary layer are made for small scale cyclonic vortex with the horizontal dimension of about 100km. These are applied to the nocturnal small-scale cyclonic vortex which is formed in the Ekman layer of the Kanto plains.
It is analytically shown that a secondary circulation is superposed on a primary one. An upward and a radial motion maximum of the secondary circulation are estimated 2.5cm s-1 and 1.5m sec-1 respectively. Although surface friction will cause a decrease in angular momentum of the circulation in the friction layer, the relative distribution of angular momentum shows an increase in the lowest layer and a decrease above the Ekman layer. This will be a result of the work done by the cross-isobaric flows due to the secondary circulation, and will be an indication of the action of Ekman pumping.
