Vertical Velocity Perturbations Research Articles

On the efficiencies of atmospheric processes

Parameters for calculating the efficiencies of atmospheric transport of zonal momentum and sensible heat are introduced. Numerical values for these efficiencies for the standing and transient eddies of January 1970 are presented. From these data it is seen that standing eddies have equal efficiency in transporting sensible heat and west-momentum horizontally, whereas transient eddies transport zonal momentum more efficiently than sensible heat in the meridional direction. The efficiencies for the vertical transport of sensible heat and zonal momentum are shown to be equal to the efficiencies for the horizontal transport of these parameters, if atmospheric eddies are represented by amplifying quasi-geostrophic baroclinic waves, the phase differences between the meridional and vertical velocity perturbations of which are assumed to be negligible. DOI: 10.1111/j.2153-3490.1975.tb01687.x

Waves and Turbulence in the Stratosphere

Detailed stratospheric wind and temperature data were gathered by aircraft over the mountains of southern Colorado on 1 March 1970. In a unique operation, two instrumented RB-57F aircraft flew a total of twelve upwind and downwind legs at altitudes of 13 to 20km,.with an average separation of 600 m. The observational data show that the stratosphere was disturbed by sporadically-turbulent gravity waves of length 20–30 km, which were apparently generated directly or indirectly by the mountainous terrain. Wave amplitudes and turbulence frequency showed a general increase with height up to about 17 km, where they reached a maximum. The maximum amplitude layer was also characterized by a minimum in the mean wind speed. The horizontal and vertical velocity and temperature variances and covariances were evaluated and found to be generally consistent with predictions of linear gravity wave theory. The spectra of horizontal kinetic and potential energy were also calculated and appear to follow a −3 law over about a decade in wavenumber space. The covariance of the horizontal and vertical velocity perturbations is everywhere negative, with a mean downward momentum flux of about ∼2 dyn cm−2. The correlation spectra show that most of this momentum flux is contributed by the long waves.

Mesoscale Cellular Convection

A linear stability model for mesoscale cellular convection in the atmosphere is developed. The model includes a forcing term which is a parameterization of the net heating due to small-scale cumulus convection. A sub-cloud and cloud layer are defined, with the forcing term having non-zero values only in the cloud layer. Positive static stability is assumed in both layers so that the only source of buoyant energy is the forcing term. The parameterization of latent heating due to cumulus convection is accomplished by assuming that the heating is proportional to the cloud-environment temperature difference and the vertical flux of moisture by the perturbation vertical velocity. Normal mode horizontal dependence and exponential time dependence is assumed for the vertical velocity, and the forcing term is defined as proportional to the vertical velocity at the interface between the two layers. The solutions in the two layers are matched across the interface and the particular solution associated with the forcing term is expressed in terms of the arbitrary constants contained in the homogeneous solutions. This yields a homogeneous solution matrix which is solved. Solutions are found for a wide range of values of atmospheric static stability, system depth, mean temperature and relative humidity, as well as varying degrees of anisotropy of the eddy mixing coefficients. The observed flattening of atmospheric cells, with diameter-to-depth ratios an order of magnitude greater than predicted by the stability analysis of classical Rayleigh convection, is duplicated by the model. Anisotropy of the eddy mixing coefficients is not a requirement for flattened cells in the model. The choice of boundary conditions is also of minor importance in producing cell flattening. Growth rates and preferred cell diameters are most sensitive to the relative humidity and static stability of the atmosphere. These two parameters represent, respectively, the source and sink of buoyant energy in the model. Positive static stability is responsible for cell flattening because it suppresses very strongly the relatively large vertical velocities associated with smaller cells.

非均質流体中をつたわる分散波の特性を計算するプログラム

A computer program was made by which we can calculate sound wave dispersion characteristics in vertically heterogeneous liquid media. By this program, group velocity U is calculated without numerical differentiations. An example given by Pekeris is worked out in detail. Phase and group velocities thus obtained are shown in Table 1. Corresponding vertical particle velocity and pressure perturbation are shown in Fig. 1 and 2.