A Numerical Experiment on the Nocturnal Low Level Jet Over the Kanto Plain

Abstract

The nocturnal low level jet, which appears over the southeastern part of the Kanto Plain, is simulated using a three-dimensional numerical model of the local winds. The results agree well with observations of the horizontal and vertical distribuitons of the jet. The diurnal variation of the jet generally agrees with the observation. However, the amplitude of the diurnal variation is a little smaller and the maximum wind velocity appears a few hours earlier than the observation.
From some additional numerical experiments, e.g., without the thermal effect of the ground, it is found that the primary factor of the low level jet formation is the mechanical effect of the mountains in central Japan upon the large scale wind. The thermal effect of the mountains enhances the low level jet and produces a diurnal variation. The turbulent stress is also important to the diurnal variation of the jet, but the inertia oscillation, which is generated by the large scale wind and the diurnal variation of the stress, is unlikely to be a primary factor of the jet formation.