The Characteristic Feature of Medium-scale Disturbances in the Atmosphere (I)

Abstract

The stability of medium scale disturbances is discussed in connection with the Rossby and Richardson numbers. In case where the Richardson number is of the order of magnitude unity, we may find the unstable disturbances whose wave lengths are about 1,000km-2,000km in middle latitudes.Numerical experiments are also performed in order to simulate the rapid cyclogenesis of medium scale disturbances, which is frequently observed in the lower atmosphere near the southern part of the jet stream over Japan throughout all seasons except summer.

Non-Geostrophic and Non-Hydrostatic Stability of a Baroclinic Fluid

“…As seen in the left side of the figure, the most preferred scale of the Eady's mode changes to larger scale with the decrease of Ri. The sense of the change of the maximum growth rate and the preferred scale with the change of the static stability at a constant vertical shear agrees with the results of geostrophic models of Eady (1949) and Gambo (1970a). The structure of the unstable wave at a small Ri differes little from that obtained at a large Ri.…”

“…The maximum growth rate increases with the decrease of Ri. Gambo (1970a) also showed the same results as the criterion of Eady (1949) after appropriate scale considerations.…”

“…A growth rate peak at an intermediate value of * and small * suggested by Gambo (1970b) was not obtained in the range of parameters so far examined.…”

“…(4-2) are easily obtained. (imaginary part of c) at *=m*/2(m=*1, *2*), but as Gambo (1970b) noted, the linear theory may lose its validity in the neighbourhood of infinite growth rates. Also, the adaptation of (4-8) is limited to small k because of the geostrophic assumption.…”

“…Recently Gambo (1970b) studied a baroclinic stability property at a small Rossby number and suggested a possibility of growth rate maximum at a moderate l and a small k when Ri is less than 1.…”