Showing papers by "Geophysical Fluid Dynamics Laboratory published in 1977"

One-Way Nested Grid Models: The Interface Conditions and the Numerical Accuracy

Abstract: Tests of several interface conditions in a one-way nested grid model were undertaken, where the ratio of grid size for the coarse mesh in the large domain and the fine mesh in the small domain was 4:1. The interface values for all parameters are specified by the solutions of the larger domain model, although they are modified in some cases. Scheme A includes a “boundary adjustment” and the consideration of mountain effect for the surface pressure along the interface. Scheme B uses, in addition to Scheme A, a “radiation condition” at the outward propagation boundaries. Scheme C uses viscous damping along five rows adjacent to the border lines in addition to Scheme A. The solutions for the fine-mesh models obtained by these schemes are compared quantitatively with the solution of a control model. The results show how quickly the effect at the interface propagates into the interior. The proper treatment of the mountain effect on the surface pressure along the interface, and the boundary adjustment a...

Global Analysis of Oceanographic Data

Abstract: A project to objectively analyze a large quantity of oceanographic data for the world ocean is described. Preliminary results are encouraging within the limits of data available. Results are being used in a variety of ways but at present primarily for studies of the ocean's role in the global heat balance. A brief discussion of the data used, the method of analysis, and some preliminary results is presented.

Towards a theory of irregular variations in the length of the day and core-mantle coupling

Abstract: Determinations of fluctuations in the length of the day reveal changes due to the transfer of angular momentum between the Earth’s ‘solid’ mantle and the overlying atmosphere on time scales upwards of a few weeks, as well as the slower but more pronounced ‘decade variations’ due largely (according to current ideas) to angular momentum transfer between the mantle and the Earth’s liquid core. Improvements in techniques for monitoring the Earth’s rotation, such as those afforded by recent advances in methods of ranging to artificial satellites and the Moon and of very long baseline interferometry, should therefore lead to results of interest to meteorologists concerned with planetary-scale motions in the atmosphere and to geophysicists con­cerned with the magnetohydrodynamics of the core and the origin of the main geo­magnetic field. The consideration of the stresses at the Earth’s surface and at the core­mantle interface that bring about angular momentum exchange between the solid and fluid parts of the Earth raises a number of basic hydrodynamical questions requiring further experimental and theoretical research. In the case of the core, quantitative difficulties encountered by the suggestion that the stresses are electromagnetic in origin led to the idea of topographic coupling associated with hypothetical undulations of the core-mantle interface.

The Circulation Associated with a Cold Front. Part II: Moist Case

Abstract: The effect of moisture upon the dynamics of mature idealized cold front systems is investigated using a two-dimensional numerical model. Lifting produced by the initial cross-stream frontal circulation studied by Orlanski and Ross (1977) is shown to saturate the warm moist air above the nose of the front when initial humidity levels are sufficiently high. If the atmosphere is convectively unstable, this saturated air will develop into deep convection with the convection-induced circulation overwhelming the initial frontal circulation. The initial development of convection is also shown to produce a gravity wave exhibiting similar scales to those of the convective zone. This wave propagates into the warm air at a much faster speed than the moving front-cloud system. Comparisons are made of the intensity of convection for different initial humidity and temperature conditions and when a low-level capping inversion is present. Also a comparison is made of cloud development caused by a combination of ...

Space-Time Spectral Analysis of Mid-Latitude Disturbances Appearing in a GFDL General Circulation Model.

Abstract: A space-time spectral analysis is applied to the Northern Hemisphere winter of an 11-layer GFDL general circulation model with seasonal variation. A statistical study is made of the stationary and transient ultra-long waves and transient long waves with respect to their wave characteristics, three-dimensional structure and energetics. The stratospheric stationary waves attain their maximum amplitude in geopotential at the latitudes of the stratospheric jet in agreement with observations and theories, although their amplitude is too large. The tropospheric stationary waves corresponding to the Siberian high and the Aleutian low are characterized by large eddy available potential energy which is mainly converted from zonal available potential energy. On the other hand, the tropospheric stationary wave corresponding to the local intensification of the subtropical jet is characterized by large eddy kinetic energy which is supplied by the energy flux from the region of large eddy energy conversion occ...

The stability of small amplitude Rossby waves in a channel

Abstract: The breakdown of Rossby waves in a bounded system is studied for the case in which the wave amplitude is small. In a very long, laterally bounded, channel all waves are unstable via second-order resonant interactions except those of wavenumber π/L in the cross-channel direction (where L is the channel width), which are stable if their longitudinal wavenumber is greater than 0·681π/L. These waves are, however, unstable to weaker side-band interactions, so that all waves with non-zero longitudinal wavenumber are unstable. The transition from sideband to triad instability occurs where the group velocity of the basic wave is equal to the velocity of long waves.

Forced plume characteristics

Abstract: This paper describes an investigation of turbulent forced plumes generated by the steady release of mass, momentum and buoyancy from a finite source in a uniform environment. The entrainment coefficient assumption has been made; however a variable coefficient has been used so that the characteristics of the transition from jet to plume behaviour can be presented more clearly. A modified Boussinesq approximation has been made which corrects for the effect of density variations in the mass and momentum fluxes. The treatment reveals that the characteristics of forced plumes can best be discussed by reference to the Froude number. For all cases of forced plumes (except a pure jet) the Froude number approaches a particular constant value as the height increases. DOI: 10.1111/j.2153-3490.1977.tb00758.x

A Study of Turbulence Parameterization in a Cloud Model

Abstract: A diagnostic second-order turbulence parameterization has been incorporated into a shallow anelastic three-dimensional numerical cloud model. The turbulence closure scheme for the subgrid-scale motions includes the effects of buoyancy, condensation and liquid water drag. This model has been used to study trade wind cumuli which are roughly 1200 m thick. The simulated cloud has many features in common with observed clouds (Malkus, 1954); however, the observed clouds are made up of several thermal elements instead of one as in the numerical simulation, and they persist over a much longer time period. When comparing the present model with another using deformation eddy viscosity, the following results are obtained: 1) The deformation model has a larger smoothing effect on the horizontally averaged potential temperature and water vapor mixing ratio. 2) Early in the cloud's development, the subgrid-scale kinetic energy is larger than the computed-scale kinetic energy. At the mature stage, the subgrid-...

Momentum and Energy Exchanges due to Orographically Scattered Gravity Waves

Abstract: The scattering of two-dimensional, hydrostatic, Boussinesq, internal gravity waves by orographic features is considered, with special attention paid to energy and momentum fluxes. A general integral equation for the streamfunction is derived from which a special Fourier representation is shown to hold in a well-defined region of the atmosphere. This leads to simple expressions for the energy and momentum fluxes and to a useful form for the energy conservation law. Scattering efficiency functions are defined. When the topography satisfies certain conditions, analytic approximations can be used to determine the scattering; it is found that the reflected momentum flux is larger than the incident flux. The manner in which viscosity affects this result is discussed. In the special case that the maximum topographic slope is less than that of the incident wave fronts, a simple integral equation is derived and used to calculate numerically the scattering from several different orographies. In every case,...