Response of a stably stratified Boussinesq fluid to differential heating with periodic time variation is investigated with linearized vorticity and thermodynamic equations. By introducing a suitable scaling, it is shown that the flow structures are controlled by a single non-dimensional parameter defined as Ω=ω*/N2/3(υ/l2)1/3 where ω* is the frequency of the thermal forcing, N is the buoyancy frequency, υ is the diffusion coefficient for heat and momentum and l is the horizontal scale of the heating (cooling) area. Internal gravity waves, conduction waves (propagating temperature perturbations governed by the equation of thermal conduction) and a steady heat island convection are regarded as basic physical phenomena contained in disturbances. When Ω is smaller than 1.3, the flow structures are not sensitive to Ω. They are essentially the same as that of the steady heat island convection. When Ω is greater than 1.3, horizontal and vertical scales of the disturbance are mainly controlled by the internal gravity waves and the conduction waves, respectively. SinceΩ is near 1.3 in the atmosphere, importance of the three basic physical phenomena is expected to be same in the sea- and land-breeze circulation observed in the atmosphere. By comparing these results with those of a numerical experiment and observational data at Osaka-city, non-linear effects near the sea-breeze front are discussed.
The formation of the mean zonal wind in the lower thermosphere is discussed from a viewpoint of induction and transmission of zonal mean momentum by tidal waves. As a preliminary discussion, in Section 3, the momentum of the mean zonal wind averaged meridionally along isobaric surface is shown theoretically to be equal to the tidal wave momentum E/C as is in the case for other atmospheric waves. The momentum of the meridionally averaged Eulerian mean zonal wind is not equal to the wave momentum. In Section 4, numerical integration with a simplified atmospheric model is performed as an initial value problem to show that the results are consistent with those in. Section 3, and that in case of the first mode of the semidiurnal tide, the direction of the mean zonal wind averaged meridionally is opposite to that of the wave momentum if the vertical wave length is longer than 4πH (scale height) as suggested by Nakamura (1976). In Section 5, the similar numerical integration is performed with somewhat realistic atmospheric model including ion drag and molecular viscosity and conductivity to discuss how much zonal winds are induced by tidal waves in the lower thermosphere. It is shown that the first mode of the solar semidiurnal tide excited in lower layers (zonal component of tidal wind is 10m/sec in amplitude at about 100km height over the equator) induces easterly winds in the lower thermosphere with a maximum speed of a few m/sec at about 150km height over the equator. Based on the above result and a rough order estimation, it is suggested that tidal waves excited in lower layers, especially, the first mode of the solar diurnal tide and the second symmetric mode of the semidiurnal tide, may induce easterlies with a maximum speed of an order of -100m/sec at a height of about 110km over the equator.
A suitable way of distributing variables over the vertical grid points is studied from the standpoint of proper simulation of vertical wave propagations as well as eliminating any computational modes in a discrete model. Based on the above considerations, a vertical differencing scheme is derived by use of Arakawa's conserving scheme. Some arbitrary factors in that scheme are eliminated by requiring a proper simulation of internal waves and accurate hydrostatic relations.
A simple method has been developed to incorporate the wing contributions made by distant lines lying outside the interval concerned into the random band model for the transmittance calculation. Solutions have been obtained for four types of intensity-distribution function. The functional form of the transmittance obtained in this work for each intensity-distribution function is much simpler than that obtained by Wyatt et al. (1962) for the quasi-random band model. It has also been shown that the usual version of the quasi-random band model can be improved by using the same technique. Improvements are achieved in accuracy and, especially, in computation time. One of the models developed here has been applied to the transmittance calculations on the H2O rotational band. The results are in excellent agreement with the “exact”lineby-line calculation.
Radiative budgets of the troposphere are highly dependent on cloud conditions present. Thus, estimates of quantities for these budgets taken from climatological studies are not applicable to specific cases of cyclone development and/or strong air mass modification. A radiative scheme, using cloud information obtained from the operational Three Dimensional Nephanalysis (3DNEPH) Model of the U.S. Air Force Global Weather Central, has been developed to study radiative transfer during different synoptic conditions during the Air-Mass Transformation Experiment (AMTEX). Comparisons of calculated downward irradiance components with measured values indicate that the model provides acceptable results when the cloud data, which are spatial averages, are representative of the location where the model is applied. Effect of clouds on tropospheric radiation budgets, and time and spatial variations of atmospheric radiation budget components over the AMTEX region are discussed.
This paper describes the results of snow drift measurements made on a slope near Mizuho Camp where katabatic winds prevail. A handy collector, that is, a chest with ten drawers, was devised, to measure the amount of drifting snow under severe conditions in. Antarctica. Called a drawer-type collector, it has a collection efficiency of about 0.23 and measures mass fluxes at ten levels up to 1 m above the snow surface at one time. A maximum total drift transport was obtained at each place by integrating the measured and extrapolated mass fluxes from the lowest level to the height of 10m, as given by the following empirical formula: log Qmax=0.2U1-0.12 where Qmax (gm-1 s-1) is the maximum total drift transport across a unit width of 1 m per unit time, and U1 (ms-1) is the wind speed at a 1-m height above the snow surface. Using the distribution of wind speed and the relative frequencies of occurrence of drifting and blowing snow at Mizuho Camp (70°42.6'S, 44°18.9'E, 2, 230m above mean sea level) and its vicinity, the actual amount of snow transported across a cross-slope line of 1km in width was obtained, which was about 1×109kg km-1 a-1.
Because of interest in the relationship between vertical wind velocity skewness and the stability, considerable data of skewness observed by many workers are accumulated and an empirical formula about the relationship mentioned above is derived. It appears to be in considerable agreement with observed data.