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At least 253 records · Page 14

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NASA NTRS1981

Parameterization of subgridscale mixing based on quasi-geostrophic turbulence theory

A parameterization of subgridscale mixing based on quasi-geostrophic turbulence theory is presented. In this parameterization, not only the horizontal diffusion coefficients for momentum and heat, but also the vertical diffusion coefficients for momentum and heat are uniquely determined. A form of the mixing is derived which simulates the subgridscale mixing process in the inertial subrange of enstrophy cascade.

Tokioka, T.↗

NASA NTRS1982

Parameterization of IR cooling in a middle atmosphere dynamics model. I - Effects on the zonally averaged circulation

A computationally efficient two-stream parameterization of IR cooling is developed for a middle atmosphere dynamics model. The parameterization combines the monochromatic feature of an emissivity formulation with the computational simplicity of a single spatial integral to evaluate the monochromatic transfer equation. Calculations show strong radiative control of the mesopause region and the need for substantial deceleration of the mean zonal winds. Calculated temperatures show good agreement in the summer hemisphere where planetary wave activity is negligible, but in the polar night of the winter hemisphere they are about 30 K too cold, which suggests planetary wave heating must make up the deficit. With observed ozone densities, globally averaged radiative equilibrium temperatures in the 65-75 km region are too cold and an additional heat source about 1 K/day is required.

Apruzese, J. P.↗

NASA NTRS1982

A parameterized model for global insolation under partially cloudy skies

A simple and efficient parameterization of insolation under partially cloudy skies is discussed and compared with a set of exact radiative transfer results for clear skies, an empirical equation and observations. The parameterization is physically based and requires, as input variables, the ozone path length, precipitable water, Angstrom turbidity, surface air pressure and albedo, fractional cloud-cover and cloud thickness. Multiple reflection between the surface and the overlying atmosphere, and clouds are considered. The albedo of the earth-atmosphere system is also formulated and compared with a set of exact radiative transfer results. As compared to the exact radiative transfer results, the errors in the insolations are generally less than 1 percent, and in the albedo of the earth-atmosphere system less than 10 percent. The errors in the calculated insolations using climatological data are 2-3 percent when compared with many years averaged observations at Maudheim (Antarctica) and at Rockville (U.S.A.). A parametric equation for calculating directly the daily total insolation is also given.

Choudhury, B.↗

NASA NTRS1983

A parameterization of the absorption in the 15 micron CO2 spectral region with application to climate sensitivity studies

A technique for quantifying the absorption that takes place in the 15 micron CO2 band in the atmosphere is developed as a function of the scaled CO2 content. A spectrally averaged transmission function is defined and a scaling approximation for the absorption coefficient is calculated, as is the width of the absorption band. An assessment is made of the accuracies of the parameterized atmospheric transmittance and cooling rate. The resulting radiation parameterization is applied in a climate sensitivity study. The model is concluded useful in examining atmospheres with a variable CO2 content, with the highest accuracies being available in the troposphere and the lower stratosphere. CO2 doubling the earth's atmosphere is projected to cause a 20 percent warming in the surface temperatures and a 30 percent warming for the tripling of the CO2 content, provided the spectral range for CO2 absorption is extended from 580-760 to 540-800/cm.

Chou, M.-D.↗

NASA NTRS1984

Lidar observations of mixed layer dynamics - Tests of parameterized entrainment models of mixed layer growth rate

Ground based lidar measurements of the atmospheric mixed layer depth, the entrainment zone depth and the wind speed and wind direction were used to test various parameterized entrainment models of mixed layer growth rate. Six case studies under clear air convective conditions over flat terrain in central Illinois are presented. It is shown that surface heating alone accounts for a major portion of the rise of the mixed layer on all days. A new set of entrainment model constants was determined which optimized height predictions for the dataset. Under convective conditions, the shape of the mixed layer height prediction curves closely resembled the observed shapes. Under conditions when significant wind shear was present, the shape of the height prediction curve departed from the data suggesting deficiencies in the parameterization of shear production. Development of small cumulus clouds on top of the layer is shown to affect mixed layer depths in the afternoon growth phase.

Boers, R.↗

NASA NTRS1983

A parameterization for downward longwave radiation from satellite meteorological data

An accurate and efficient parameterization is developed which computes clear-atmosphere downward longwave flux in terms of the water vapor burden and water-vapor-weighted average temperature of the surface-700 mb region. The parameterization is based on detailed radiative transfer calculations performed for a wide meteorological data base, consisting of 180 atmospheric models generated from climatological data and 106 radiosonde-measured models. The standard error of the computed fluxes was found to be about 4 percent of the mean value. It is also pointed out that strong heating or cooling of the surface, as shown by many TOVS data sets, caused larger errors in the computed fluxes.

Gupta, S. K.↗

NASA NTRS1985

Tracer transport by planetary waves - A comparison of explicit and parameterized models

A two-dimensional stratospheric tracer transport parameterization is developed using the theory of small-amplitude generalized Lagrangian means and tested by two experiments. The first tests the parameterization for mean climatological winter conditions without wave transience; the second tests it in the presence of transience and critical layers, when nonacceleration conditions are strongly violated. Tracer transport by Eulerian velocity, the residual velocity, and the nondivergent mean meridional Lagrangian velocity are compared.

Hess, P. G.↗

NASA NTRS1985

A parameterization technique for nonlinear spectral models

An objective parameterization technique is developed for general nonlinear hydrodynamical systems. The typical structure of hydrodynamical systems, regardless of their complexity, is one in which the rates of change of the dependent variables depend on homogeneous quadratic and linear forms, as well as on inhomogeneous forcing terms. As a prototype of the generic problem containing this typical structure, the parameterization technique is applied to various three component subsets of a five component nonlinear spectral model of forced, dissipative quasi-geostrophic flow in a channel. The results obtained lead to specification of the necessary data coverage requirements for applying the technique in general.

Gelaro, R.↗

NASA NTRS1985

Advances in parameterization of cumulus convection in numerical models

Observational studies over the last decade have revealed new sources of difficulty in the already complex problem of parameterization of precipitating cumulus convection in large scale numerical weather prediction models. The structure of mesoscale updrafts and downdrafts and the difficulties they present for cumulus parameterization is reviewed. An approach is proposed which follows Kuo (1974) but includes cumulus and mesoscale downdrafts in the vertical distributions of heating and moistening. The development of a realistic life cycle behavior in the numerical prediction of a mesoscale convective complex will be shown.

Molinari, J.↗

NASA NTRS1985

A radiative parameterization of stratocumulus cloud fields

A parameterization scheme is presented which allows the calculation of radiative reflected fluxes from a stratocumulus cloud field. The scheme is based upon plane-parallel calculations, such as delta-Eddington, and a simple procedure is outlined by which the plane-parallel fluxes may be transformed to those of the broken cloud case. This parameterization scheme has been tested for optical thicknesses ranging from tau = 3 to 49, solar zenith angles ranging from theta sub 0 = 0 to 72.5 deg, and all values of cloud cover. Plane-parallel calculations become increasingly more accurate as optical depth decreases. This suggests that calculations including broken cloudiness effects such as shadowing are probably unnecessary in thin cirrus or aerosol layers over water.

Welch, R. M.↗

NASA NTRS1986

A parameterization technique for nonlinear spectral models

Gelaro, R.↗

NASA NTRS1986

Parameterized materials and dynamic response characterizations in unidirectional composites

The values of phase velocities of ultrasonic waves in transversely isotropic media are presented in terms of the fiber volume fraction of a unidirectional fiberglass epoxy composite with constant matrix properties and the ratio between extensional moduli in the longitudinal and transverse directions of the composite when the properties of the fibers are changed, at a constant fiber volume fraction. The model of a homogeneous transversely isotropic medium is adopted to describe the relations between elastic properties and velocities. The displacements due to an oscillatory point source in an infinite medium are used as one measure of comparison of the behavior of the unidirectional composite according to the variations of the parameters, as described above. Values of phase velocities, elastic moduli, Poisson's ratios and displacements due to a point source can be read from the parameterized plots for a known fiber volume fraction or a known ratio between extensional moduli of the composite. Alternatively fiber volume fraction and the ratio between extensional moduli can be inferred from the plots when the values of the phase velocities are known; for example from experimental measurements. Therefore, such parameterized curves may be useful in nondestructive mechanical property and material degradation characterizations.

Williams, J. H., Jr.↗

NASA NTRS1985

A new scheme for the parameterization of the turbulent planetary boundary layer in the GLAS fourth order GCM

Methods being used to increase the horizontal and vertical resolution and to implement more sophisticated parameterization schemes for general circulation models (GCM) run on newer, more powerful computers are described. Attention is focused on the NASA-Goddard Laboratory for Atmospherics fourth order GCM. A new planetary boundary layer (PBL) model has been developed which features explicit resolution of two or more layers. Numerical models are presented for parameterizing the turbulent vertical heat, momentum and moisture fluxes at the earth's surface and between the layers in the PBL model. An extended Monin-Obhukov similarity scheme is applied to express the relationships between the lowest levels of the GCM and the surface fluxes. On-line weather prediction experiments are to be run to test the effects of the higher resolution thereby obtained for dynamic atmospheric processes.

Helfand, H. M.↗

NASA NTRS1985

A new convective parameterization scheme for global models

A convective adjustment scheme is presented for parameterization of the vertical temperature and moisture structure for large-scale numerical weather models. The temperature and moisture structure is adjusted toward observed quasi-equilibrium structures to maintain a realistic vertical temperature and moisture structure in grid-scale global models during convection. Two reference thermodynamic structures are modeled analytically to account for shallow and deep convection. The thermodynamic structure obtained is permitted to change as a function of large-scale advective terms, radiation and surface fluxes. The reference profiles are applied when an energy integral provides a description of the shallow or deep convective processes occurring. Comparisons with GATE, BOMEX and ATEX data and a 10 day forecast for weather over the tropical ocean illustrate the climate and precipitation forecast accuracy improvements available with the adjustment scheme relative to standard parameterization schemes.

Miller, M. J.↗

NASA NTRS1986

A method for coupling a parameterization of the planetary boundary layer with a hydrologic model

Deardorff's parameterization of the planetary boundary layer is adapted to drive a hydrologic model. The method converts the atmospheric conditions measured at the anemometer height at one site to the mean values in the planetary boundary layer; it then uses the planetary boundary layer parameterization and the hydrologic variables to calculate the fluxes of momentum, heat and moisture at the atmosphere-land interface for a different site. A simplified hydrologic model is used for a simulation study of soil moisture and ground temperature on three different land surface covers. The results indicate that this method can be used to drive a spatially distributed hydrologic model by using observed data available at a meteorological station located on or nearby the site.

Lin, J. D.↗

NASA NTRS1987

The role of convective parameterization in the simulation of a Gulf Coast precipitation system

Three simulations were performed with the Limited Area Mesoscale Prediction System (LAMPS) model in order to examine the role of convective parameterization in the simulation of the Gulf Coast precipitation system of March 6-7, 1982. The first simulation neglected moist processes, the second used the representation for moist physics of Orlanksi and Ross (1984) and Rosenthal (1978, 1979), and the third simulation incorporated the LAMPS sequential plume cumulus cloud model as convective parameterization for the model. The effects of various representations of moist physics on the evolution of the model's precipitation, kinematic and diabatic heating, and mass and wind fields are investigated. It is determined that the representation of moist thermodynamics in the meso-alpha-scale model influences the manner in which the model describes the mesoscale structures.

Kalb, Michael W.↗

NASA NTRS1987

Parameterization of radiative flux profiles within layer clouds

This paper presents simple formulations for the vertical structure of solar and infrared radiative fluxes within a layer cloud overlying a partially reflective surface. The parameterized profile shapes are analytic, with governing parameters derived from bulk radiative properties and more physically based radiative transfer models. The bulk cloud, subcloud layer, and surface radiative properties are assumed to be known. The parameterizations are based on exponential functions of height, with decay scales related to cloud liquid water content. Although the results presented here are based on very simple assumptions about the cloud structure in the vertical, the method used is applicable to more general cases as well as to various other analytic and/or numerical radiative transfer calculations.

Hanson, Howard P.↗

NASA NTRS1987

Development of a two-dimensional zonally averaged statistical-dynamical model. II - The role of eddy momentum fluxes in the general circulation and their parameterization

The role of eddy momentum fluxes in the general circulation was investigated using a two-dimensional zonally averaged statistical-dynamical model described by Yao and Stone (1987), which is almost two orders of magnitude faster than the three-dimensional climate model of Hansen et al. (1983). Results show that the vertical structure of the meridional eddy flux has relatively little impact on the general circulation, presumably because the vertical structure is strongly constrained by the thermal wind relation and surface friction. On the other hand, it was found that, in order to simulate accurately the general circulation and its response to climate changes, parameterization of the vertically integrated meridional eddy flux of angular momentum is necessary. A new parameterization of this eddy momentum transport was carried out, which is intended to represent the transport due to large-scale transient eddies arising from baroclinic instability.

Stone, Peter H.↗