The instability of medium-scale disturbances in a moist atmosphere is discussed comparing with the characteristics of medium-scale disturbances in a dry atmosphere. In case of a dry atmosphere, the prefered mode of medium-scale disturbances is expected when the Richardson number Ri is of the order of unity. In case of a moist atmosphere, we assume the condensation processes due to the large-scale upward motion of the conventional baroclinic wave and also due to the (sub-grid scale) convective motion. In this paper, the released latent heat of convective motion is treated in a way of the so-called CISK mechanism. The parameter λ which represents the ratio of the vertical p-velocity due to the frictional convergence in the planetary boundary layer to that of the conventional baroclinic wave is introduced. The instability of medium-scale disturbances is discussed analytically in cases where λ_??_1 and λ_??_1. It is shown that the unstable disturbance where λ_??_1 corresponds to the modified conventional baroclinic unstable wave. However, the unstable disturbance where λ_??_1 shows the different characteristics in a sense that there is no steering-level and the trough axis tilts eastward in the westerlies. The role of the Rossby number in the meridional direction, Ry on the growth rate is also discussed when Ri∼0(1) and λ_??_1.
This is a second part of a paper on the structure of a westward propagating monsoon depression. In this study, we examine the dynamical structure of the disturbance. We note that the meridional variation of potential vorticity showed an inflection point in its profile. This implies that the disturbance is imbedded in a region where the necessary condition for the existence of the combined barotropic-baroclinic instability is satisfied. In order to examine this question one step beyond the necessary condition, we carried out a quasi-geostrophic baroclinic prediction experiment. The energy exchanges of this experiment confirmed that the eddy kinetic energy over a domain, enclosing the disturbance, did increase by the combined barotropic-baroclinic processes. The westward propagation speed of the monsoon depression was examined in a number of simple numerical prediction experiments. The barotropic non-divergent model and quasi-geostrophic model were found inadequate to account for the westward phase speed. A multi-level primitive equation model was used to carry out a 48 hour forecast. The model physics includes features such as air-sea interaction, parameterization of cumulus convection, large scale condensation, heat balance of the earth's surface and smoothed orography. A somewhat reasonable 48 hour real data forecast was carried out in this study. The forecasted fields include the motion, thermal mass and moisture variables. A discussion of the calculated versus the observed rainfall rates and associated heating function is presented. Finally, we present the energetics of the monsoon depression based on the primitive equation prediction and those based on observa-tions. The primary result here is that the disturbance is primarily driven by cumulus convection.
Periodic variations of divergence and vertical motion and the daily march of the atmospheric moisture budget are evaluated based on special upper-air and surface observation programs conducted over the Western Tropical Pacific in April-July 1956 and 1958. Daily variations of divergence and vertical motion are in their timing broadly consistent with the tidal pressure and wind oscillations. For the daily average, estimates of large-scale atmospheric water vapor flux convergence, precipitation, and evaporation are 6.5, 10.0, and 2.8 mm H2O day-1, respectively. The vector departure from the daily mean of the vertically integrated moisture flux shows a periodic clockwise turning in the course of the day, which is linked with the mechanism of the tidal pressure and wind variation. Budget terms with the largest daily range are, in order, change in precipitable water, water vapor flux convergence, and precipitation rate.
The habit and the growth feature of small ice crystals formed in a free fall state in high- and low-pressure helium and argon gases at the temperatures of -7 and -15°C were studied experimentally. It is found that the habit and the growth feature of small ice crystals in the range of about 20 to 50μm depend not only on the temperature and the degree of supersaturation but also on the kind and the pressure of the carrier gas and the size of crystals when small ice crystals were formed at water saturation. It is found that the dependence of the habit of small ice crystals on temperature is more emphasized under a high pressure but has a tendency to vanish under a low pressure. In high-pressure gas, ice crystal shapes which have never been observed in the earth's atmospheres are found. Such ice crystals may form in the atmospheres of Jupiter and Saturn where pressures are higher than that of the earth.
To clarify the structure of the atmospheric boundary layer, airborne measurements were carried out above the Kanto Plain in the vicinity of Tokyo, in March and August, 1972. We analised characteristics of the atmospheric boundary layer, using the rate of turbulent energy dissipation ε, which can be calculated from the isotropic region of the power spectrum, where an airplane can be regarded as a fixed platform. We define Hε, which is the height where ε decreases rapidly, as a thickness of the atmospheric boundary layer. Hε in many cases coinsides with the base height of inversion layer Hi during daylight measurements. Hε from sunrise to about 1500 hrs can be described as a function of the root of an integral quantity of insolation, which shows Hε is strongly correlated with the heat flux from the ground. We clarified relations between vertical temperature profiles and characteristics of turbulance. In the atmospheric boundary layer up to Hε or Hi, temperature profiles show nearly neutral stratification, even when a free convection is predominant. However profiles of ε show the difference between a free convection case (AA (strong), A (moderate)), and a forced convection case (B). In case AA and A, ε is nearly constant up to Hε (averaging ε∼z-(1/3-5); z, height) and it is independent of wind velocity U. On the other hand in case B, ε decreases with height linealy, and proportional to U3. R.M.S, of vertical turbulence σω is proportional to ε1/3 in both case AA (including A) and case B. The profiles of the eddy coefficient Kz obtained by Hanna's equation show that in case AA and A, Kz is almost constant up to Hε, in case B, Kz has its peak at some level.