Dynamics of the Jet Stream

抄録

In discussing the structure of typhoon before, the author pointed out the existence of a maximum of wind velocity, that is, a sort of jet stream, just at the outer side of the tropopause funnel which forms the eye of typhoon.. The jet stream associated with the general circulation of the atmosphere seems essentially to be the same as that with the typhoon. Therefore the author tried to explain the phenomenon, adopting the following four assumptions: (A) stationary, (B) uniform in one direction, (C) frictionless, (D) autobarotropic, and deriving integrals from the initial equations of motion including inertia terms, in the same way as in the previous paper. The integrals represent respectively the law of conservation of (angular) momentum, vorticity and energy.
From the law of co n servation of energy can be derived an equation which determines the form of the surface of discontinuity. The surface inclines the steeper, the smaller the temperature difference and the larger the wind velocity difference between the both sides of the surface. In the neighbourhood of the surface, however, develops a mixing layer at the same time owing to the discontinuity of wind velocity. The thickness of the layer becomes the larger, the smaller the temperature difference and the larger the wind velocity defference, that is, the steeper the surface inclines, the larger the mixing, l ayer becom es in thickness.
From the law of conservation of vorticity it results that there must exist convective motions in the meridional sect ion of the atmosphere. Now, air particles displacing northward get extremely stronger in west wind velocity as they, approach the axis of the earth, as momentum is conserved along a streamline in an air mass. The strong wind thus developed draws down the surface of discontinuity lying above it a nd draws up that lying beneath. It follows thus that air particles can not proceed on their way over some extent northward, owing to the barrier which they form themselves. In, this way, th e meridional circulation of the troposphere presents necessarily a cellular strU. cture, and the air in lower latitudes can not arrive directly at the pole. Oil the other hand, the effect of fri ction is the most intense and, the, mixing layer becomes the largest at the northern end of the cell thus formed. The exchange of a ir between lower and higher latitudes is carried out only through friction. Thus the jet stream is developed the northern part of each cell, that is, at the northern end of the southern side of the mixing layer.
The structure of the jet stream thus derived is, shown in the figures. These figures, which are derived theoretically, coincide very well with those analysed hitherto by many investigators.