Showing papers by "Geophysical Fluid Dynamics Laboratory published in 1978"

Cosmical magnetic fields

Abstract: Magnetic Field Generation in Electrically-Conducting Fluids. By H. K. Moffatt. Pp. 343. (Cambridge University Press: Cambridge and London, 1978.) £15.50.

Planetary Circulations: 1. Barotropic Representation of Jovian and Terrestrial Turbulence

Abstract: We seek the formative processes of the planetary circulations of Jupiter and Saturn. The study concentrates on examining whether processes known to control the terrestrial circulation, namely, two-dimensional turbulence and baroclinic instability, can produce Jovian circulations under Jovian conditions. The first numerical model involves a spherical barotropic vorticity equation subjected to a stochastic representation of baroclinic processes. The resulting solutions suggest that a strong affinity exists between the Jovian and terrestrial circulations. This leads to a reevaluation of terrestrial circulation theory from the broader perspective of parameter space. The solutions in the Jovian regime support the hypothesis that a variation of the Rhines effect—an interaction of the two-dimensional turbulence cascade and Rossby wave propagation—creates the pseudoaxisymmetry and scale Lβ=π(2U/β)½ of the bands (U is the rms zonal velocity, and β the northward gradient of the Coriolis force). The anisotr...

A Numerical Simulation of the Landfall of Tropical Cyclones.

Abstract: A GFDL tropical cyclone model was applied to simulate storm landfall. The numerical model is a three-dimensional, primitive equation model and has 11 vertical levels with four in the planetary boundary layer. The horizontal grid spacing is variable with finest resolution being 20 km near the center. This model was used successfully in the past to investigate the development of tropical cyclones over the ocean. In the present experiments, a simple situation is assumed where a mature tropical cyclone drifts onto flat land. In such a case, the landfall can he simulated by changing the position of the coastline in the computational domain rather than by moving the storm. As the coastline moves with a specified speed, the surface boundary conditions are altered at the shore from those for the ocean to those for the land by increasing the surface roughness length and also by suppressing the evaporation. Despite the simplicity and idealization of the experiments, the cyclone's filing rates are quite rea...

The annual variation in the global heat balance of the Earth

Abstract: An annual variation with a range of 31 W/sq m is found in the global net radiation balance of the earth. The net radiation flux values measured from satellites and the changes in total heat content computed from independent sets of atmospheric and oceanic data show annual variations which are consistent with each other in both phase and magnitude. The net energy gain and loss by the planet within a year is stored and released within the system primarily by the oceans.

How to locate the electrically conducting fluid core of a planet from external magnetic observations

Abstract: A NEW method is proposed here for locating the electrically conducting fluid core of a planet from external magnetic observations. When tested with the aid of geomagnetic data, the method gives for the radius of the Earth's liquid metallic core a value which differs insignificantly from the accepted value (based on seismic data). These findings have important implications for future investigations of the magnetic fields and internal structure and dynamics of the Earth, Jupiter, and other magnetic planets.

Adequacy of the Rawinsonde Network for Global Circulation Studies Tested through Numerical Model Output

Abstract: Numerical output from a GFDL global climate model was used to determine whether the present distribution of rawinsonde stations is adequate to deduce the atmospheric structure and its variability in space and time over the globe. Spatial data gaps were found to cause typical rms wind errors averaged over a hemisphere of 2 to 3 m s−1, increasing for the zonal wind component to 5 or 6 m s−1 at jet stream levels. In temperature the spatial data gaps led to rms errors on the order of 0.5 to 1°C in the free atmosphere, in geopotential height between 20 and 30 gpm in, the upper troposphere, and in specific humidity between 1 and 2 g kg−1 near the surface and about 0.3 g kg−1 at 500 mb. Errors due to instrumental deficiencies, unrepresentativeness of the local soudings, deficiencies in the analysis technique and gaps in the time series were found to he less important than those due to the, spatial gaps, even in the Northern Hemisphere. In the Northern Hemisphere, the rawinsonde network was found to be g...

Boundary Conditions for Limited-Area Forecasts

Abstract: The smoothness of solutions of the barotropic and baroclinic filtered and primitive equations in limited areas, subject to inflow boundary conditions, is in doubt due to the necessary occurrence of points on the boundaries where the flow is tangential. The problem is described in detail for the barotropic filtered equations; it is the classical situation of Cauchy data being specified for a hyperbolic equation on a boundary curve which is locally characteristic. A necessary set of conditions is developed for the data which must be satisfied if a smooth solution is to be ensured. The set is far too complex to allow their satisfaction in practice. Only the objectionable practice of introducing very high viscosity near the boundaries provides a simple way out of the problem. A more reasonable and not too complicated alternative is suggested.

The Generation of Equatorial Transient Planetary Waves: Control Experiments with a GFDL General Circulation Model

Abstract: In order to study the generation of transient planetary waves in the tropics, the effects of topography, midlatitude disturbances and condensational heat are eliminated one by one from a GFDL general circulation model during the period June and July. The time development and three-dimensional propagation of waves are examined by a space-time spectral analysis using the maximum entropy method. It is found that the characteristic scale and period of Kelvin and mixed Rossby-gravity waves do not depend on land-sea contrast or the zonal variation of sea surface temperature. Even if midlatitude disturbances are eliminated, both these waves appear in the stratosphere due to the effect of latent heat release in the troposphere. In contrast to Kelvin waves, however, mixed Rossby-gravity waves can be significantly intensified by westward moving midiatitude disturbances which are found to propagate intermittently toward the equator.

A physical explanation of the static core paradox

Abstract: Summary. The introduction of Rdyleigh friction and Newtonian cooling into the dynamical problem of determining the excitation of the normal modes of oscillation of an earth model with a fluid core by a transient earthquake source is shown to provide a fully satisfactory resolution and a clear physical explanation of the difficulties and paradoxes which have arisen in previous treatments of the corresponding static deformation problem. The source of the previous difficulties is that the dissipation-free limit is associated with an essential singularity in the static response, unless the stratification in the core is neutral. This singularity, in turn, exists because the eigenfrequency spectrum of any earth model with a non-neutrally stratified core has an accumulation point at zero frequency.

A Scheme of Dynamic Initialization of the Boundary Layer in a Primitive Equation Model

Abstract: A scheme of dynamic initialization of a primitive equation model is proposed with an emphasis on the dynamic adjustment in the boundary layer. The pre-initialintion analysis is important since the restorative method is used in the subsequent dynamic initialization. The first phase of dynamic initialization is designed to establish a reasonable boundary layer structure. For this purpose, a time integration of the primitive equations is performed under a strong constraint such that all meteorological fields except momentum in the boundary layer are frozen. Use of an implicit form for the vertical diffusion term is recommended. The second phase is formulated to reduce the high-frequency noise in the final initialized field. Cyclic integration with a selective damping scheme is carried out under a restorative constraint. The proposed scheme is applied to a case of simple zonal flow and the evolution of the boundary layer flow is shown. The scheme is also tested for a cam of mature tropical cyclone. S...

Initialization with the data assimilation method

Abstract: The initial conditions generated by a data assimilation technique with a general circulation model were evaluated. Two types of dynamic initialization, i.e., “the forward adjustment” and “the forward-backward adjustment”, were tested using the real data produced by the NMC objective analysis. The degree of balance in the initial condition was examined in terms of the smoothness in the development of the rate of precipitation, angular momentum, and kinetic energy during the starting period of the prediction. The quality of the initialization was, however, appraised by the performance of the subsequent prediction. For the forward adjustment, various types of schemes of data insertion were studied with regard to the amount of shock produced and the degree of faithfulness of the injected data. In dealing with forward-backward processes, one difficult problem is how to design a reversible algorithm. An approximate method is presented for maintaining the reversibility in a system which includes kinetic energy dissipation, radiation, and the moist heating. In addition, the question is discussed as to which physical processes of the model must be included for the forward-backward initialization. It is found that the dynamic initialization using the forward-backward data assimilation produces predictions that are, in some ways, better than those from the static or conventional initialization. However, for the forward data assimilation the predictions are consistently worse than those from the static initialization. DOI: 10.1111/j.2153-3490.1978.tb00816.x