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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Equatorial waves in the NCAR stratospheric general circulation model

Equatorially trapped wave modes are very important in the tropical stratospheric momentum balance. Kelvin waves and mixed Rossby-gravity waves are believed to be responsible for the quasi-biennial oscillation of the zonal winds in the equatorial lower stratosphere. Both Kelvin and mixed Rossby-gravity waves have been identified in observations and in numerical models. Kelvin and mixed Rossby-gravity waves are identified in a general circulation model extending from the surface into the mesosphere and looks at the effect on the waves of lowering the top of the model.

Boville, B. A.↗
NASA NTRS1985

The zonally averaged transport characteristics of the atmosphere as determined by a general circulation model

Two dimensional modeling has become an established technique for the simulation of the global structure of trace constituents. Such models are simpler to formulate and cheaper to operate than three dimensional general circulation models, while avoiding some of the gross simplifications of one dimensional models. Nevertheless, the parameterization of eddy fluxes required in a 2-D model is not a trivial problem. This fact has apparently led some to interpret the shortcomings of existing 2-D models as indicating that the parameterization procedure is wrong in principle. There are grounds to believe that these shortcomings result primarily from incorrect implementations of the predictions of eddy transport theory and that a properly based parameterization may provide a good basis for atmospheric modeling. The existence of these GCM-derived coefficients affords an unprecedented opportunity to test the validity of the flux-gradient parameterization. To this end, a zonally averaged (2-D) model was developed, using these coefficients in the transport parameterization. Results from this model for a number of contrived tracer experiments were compared with the parent GCM. The generally good agreement substantially validates the flus-gradient parameterization, and thus the basic principle of 2-D modeling.

Plumb, R. A.↗
NASA NTRS1994

Regional climates in the GISS general circulation model: Surface air temperature

One of the more viable research techniques into global climate change for the purpose of understanding the consequent environmental impacts is based on the use of general circulation models (GCMs). However, GCMs are currently unable to reliably predict the regional climate change resulting from global warming, and it is at the regional scale that predictions are required for understanding human and environmental responses. Regional climates in the extratropics are in large part governed by the synoptic-scale circulation and the feasibility of using this interscale relationship is explored to provide a way of moving to grid cell and sub-grid cell scales in the model. The relationships between the daily circulation systems and surface air temperature for points across the continental United States are first developed in a quantitative form using a multivariate index based on principal components analysis (PCA) of the surface circulation. These relationships are then validated by predicting daily temperature using observed circulation and comparing the predicted values with the observed temperatures. The relationships predict surface temperature accurately over the major portion of the country in winter, and for half the country in summer. These relationships are then applied to the surface synoptic circulation of the Goddard Institute for Space Studies (GISS) GCM control run, and a set of surface grid cell temperatures are generated. These temperatures, based on the larger-scale validated circulation, may now be used with greater confidence at the regional scale. The generated temperatures are compared to those of the model and show that the model has regional errors of up to 10 C in individual grid cells.

Hewitson, Bruce↗
NASA NTRS1988

Derivation of revised formulae for eddy viscous forces used in the ocean general circulation model

Presented is a re-derivation of the eddy viscous dissipation tensor commonly used in present oceanographic general circulation models. When isotropy is imposed, the currently-used form of the tensor fails to return to the laplacian operator. In this paper, the source of this error is identified in a consistent derivation of the tensor in both rectangular and earth spherical coordinates, and the correct form of the eddy viscous tensor is presented.

Chou, Ru Ling↗
NASA NTRS1989

Land surface hydrology parameterization for atmospheric general circulation models including subgrid scale spatial variability

Parameterizations are developed for the representation of subgrid hydrologic processes in atmospheric general circulation models. Reasonable a priori probability density functions of the spatial variability of soil moisture and of precipitation are introduced. These are used in conjunction with the deterministic equations describing basic soil moisture physics to derive expressions for the hydrologic processes that include subgrid scale variation in parameters. The major model sensitivities to soil type and to climatic forcing are explored.

Entekhabi, D.↗
NASA NTRS1990

The sensitivity of latent heat flux to the air humidity approximations used in ocean circulation models

In deriving the surface latent heat flux with the bulk formula for the thermal forcing of some ocean circulation models, two approximations are commonly made to bypass the use of atmospheric humidity in the formula. The first assumes a constant relative humidity, and the second supposes that the sea-air humidity difference varies linearly with the saturation humidity at sea surface temperature. Using climatological fields derived from the Marine Deck and long time series from ocean weather stations, the errors introduced by these two assumptions are examined. It is shown that the errors reach above 100 W/sq m over western boundary currents and 50 W/sq m over the tropical ocean. The two approximations also introduce erroneous seasonal and spatial variabilities with magnitudes over 50 percent of the observed variabilities.

Liu, W. Timothy↗
NASA NTRS1993

The implementation and validation of improved land-surface hydrology in an atmospheric general circulation model

New land-surface hydrologic parameterizations are implemented into the NASA Goddard Institute for Space Studies (GISS) General Circulation Model (GCM). These parameterizations are: 1) runoff and evapotranspiration functions that include the effects of subgrid-scale spatial variability and use physically based equations of hydrologic flux at the soil surface and 2) a realistic soil moisture diffusion scheme for the movement of water and root sink in the soil column. A one-dimensional climate model with a complete hydrologic cycle is used to screen the basic sensitivities of the hydrological parameterizations before implementation into the full three-dimensional GCM. Results of the final simulation with the GISS GCM and the new land-surface hydrology indicate that the runoff rate, especially in the tropics, is significantly improved. As a result, the remaining components of the heat and moisture balance show similar improvements when compared to observations. The validation of model results is carried from the large global (ocean and land-surface) scale to the zonal, continental, and finally the regional river basin scales.

Johnson, Kevin D.↗
NASA NTRS2004

ENSO Bred Vectors in Coupled Ocean-Atmosphere General Circulation Models

The breeding method has been implemented in the NASA Seasonal-to-Interannual Prediction Project (NSIPP) Coupled General Circulation Model (CGCM) with the goal of improving operational seasonal to interannual climate predictions through ensemble forecasting and data assimilation. The coupled instability as cap'tured by the breeding method is the first attempt to isolate the evolving ENSO instability and its corresponding global atmospheric response in a fully coupled ocean-atmosphere GCM. Our results show that the growth rate of the coupled bred vectors (BV) peaks at about 3 months before a background ENSO event. The dominant growing BV modes are reminiscent of the background ENSO anomalies and show a strong tropical response with wind/SST/thermocline interrelated in a manner similar to the background ENSO mode. They exhibit larger amplitudes in the eastern tropical Pacific, reflecting the natural dynamical sensitivity associated with the presence of the shallow thermocline. Moreover, the extratropical perturbations associated with these coupled BV modes reveal the variations related to the atmospheric teleconnection patterns associated with background ENSO variability, e.g. over the North Pacific and North America. A similar experiment was carried out with the NCEP/CFS03 CGCM. Comparisons between bred vectors from the NSIPP CGCM and NCEP/CFS03 CGCM demonstrate the robustness of the results. Our results strongly suggest that the breeding method can serve as a natural filter to identify the slowly varying, coupled instabilities in a coupled GCM, which can be used to construct ensemble perturbations for ensemble forecasts and to estimate the coupled background error covariance for coupled data assimilation.

Yang, S. C.↗
NASA NTRS1977

A three-D circulation model study of the radiative-dynamic coupling within the stratosphere

The role of radiative transfer processes in the general circulation of the stratosphere was studied by comparing the thermal and dynamical structure of the stratosphere as simulated by two controlled numerical experiments performed with the aid of a spectral 3-dimensional quasi-geostrophic circulation model. In the first experiment, a detailed radiative transfer model is employed to treat the longwave radiative transfer in the stratosphere. In the second experiment, longwave radiative transfer is accounted for by employing the Newtonian cooling approximation. It is found that the exchange of longwave radiation between the troposphere and lower stratosphere has a net heating effect on the lower stratosphere. It is shown that this heating effect contributes partly to the maintenance of the warm high-latitude belt in the lower stratosphere during winter and spring seasons. The strong temperature dependence of the Newtonian cooling coefficient plays an important role in determining the zonal temperatures and has a significant influence on the transmissivity of stratosphere to propagating planetary scale waves.

Ramanathan, V.↗
NASA NTRS1983

Rotating-fluid experiments with an atmospheric general circulation model

In order to determine features of rotating fluid flow that are dependent on the geometry, rotating annulus-type experiments are carried out with a numerical model in spherical coordinates. Rather than constructing and testing a model expressly for this purpose, it is found expedient to modify an existing general circulation model of the atmosphere by removing the model physics and replacing the lower boundary with a uniform surface. A regime diagram derived from these model experiments is presented; its major features are interpreted and contrasted with the major features of rotating annulus regime diagrams. Within the wave regime, a narrow region is found where one or two zonal wave numbers are dominant. The results reveal no upper symmetric regime; wave activity at low rotation rates is thought to be maintained by barotropic rather than baroclinic processes.

Geisler, J. E.↗
NASA NTRS1995

Comparison of cloud fields from atmospheric general circulation model, in situ and satellite measurements

This paper focuses on the comparison of cloud amounts derived from an atmospheric general circulation model (AGCM), Satellite-observed clouds, and Ground-based cloud observations. Unlike Earth Radiation Budget Experiment (ERBE)-type comparisons it does not mix potential errors in the cloud amount with those in the radiation code embedded in the model. Long term cloud climatologies were used to compare global cloud amounts and regional seasonal cycles. The AGCM successfully reproduced the signatures of the warm pool and North Pacific seasonal cycle cloudiness but failed in the low stratus region off the coast of South America, a known problem for AGCMs. The data sets also reproduced the anomaly signature associated with El Nino in the warm pool region, but the model amounts were lower. Global results had a similar success rate, with the model generally producing lower total cloud compared to the satellite and in situ measurements. To compare cloud vertical distributions the cloud height may need to be validated using the corresponding radiation fields. Unfortunately there were also some large discrepancies between the two observed cloud data sets. While tremendously improved over the last decade the character of the observed cloud data sets, must be substantially enhanced before they will be useful in validating AGCMs by any but the crudest levels of comparison.

Haskins, Robert D.↗
NASA NTRS1999

Physically-Derived Dynamical Cores in Atmospheric General Circulation Models

The algorithm chosen to represent the advection in atmospheric models is often used as the primary attribute to classify the model. Meteorological models are generally classified as spectral or grid point, with the term grid point implying discretization using finite differences. These traditional approaches have a number of shortcomings that render them non-physical. That is, they provide approximate solutions to the conservation equations that do not obey the fundamental laws of physics. The most commonly discussed shortcomings are overshoots and undershoots which manifest themselves most overtly in the constituent continuity equation. For this reason many climate models have special algorithms to model water vapor advection. This talk focuses on the development of an atmospheric general circulation model which uses a consistent physically-based advection algorithm in all aspects of the model formulation. The shallow-water model is generalized to three dimensions and combined with the physics parameterizations of NCAR's Community Climate Model. The scientific motivation for the development is to increase the integrity of the underlying fluid dynamics so that the physics terms can be more effectively isolated, examined, and improved. The expected benefits of the new model are discussed and results from the initial integrations will be presented.

Rood, Richard B.↗
NASA NTRS1999

Physically-Derived Dynamical Cores in Atmospheric General Circulation Models

The algorithm chosen to represent the advection in atmospheric models is often used as the primary attribute to classify the model. Meteorological models are generally classified as spectral or grid point, with the term grid point implying discretization using finite differences. These traditional approaches have a number of shortcomings that render them non-physical. That is, they provide approximate solutions to the conservation equations that do not obey the fundamental laws of physics. The most commonly discussed shortcomings are overshoots and undershoots which manifest themselves most overtly in the constituent continuity equation. For this reason many climate models have special algorithms to model water vapor advection. This talk focuses on the development of an atmospheric general circulation model which uses a consistent physically-based advection algorithm in all aspects of the model formulation. The shallow-water model of Lin and Rood (QJRMS, 1997) is generalized to three dimensions and combined with the physics parameterizations of NCAR's Community Climate Model. The scientific motivation for the development is to increase the integrity of the underlying fluid dynamics so that the physics terms can be more effectively isolated, examined, and improved. The expected benefits of the new model are discussed and results from the initial integrations will be presented.

Rood, Richard B.↗
NASA NTRS2002

A Comparison of the Lower Stratospheric Age-Spectra Derived from a General Circulation Model and Two Data Assimilation Systems

We use kinematic and diabatic back trajectory calculations, driven by winds from a general circulation model (GCM) and two different data assimilation systems (DAS), to compute the age spectrum at three latitudes in the lower stratosphere. The age-spectra are compared to chemical transport model (CTM) calculations, and the mean ages from all of these studies are compared to observations. The age spectra computed using the GCM winds show a reasonably isolated tropics in good agreement with observations; however, the age spectra determined from the DAS differ from the GCM spectra. For the DAS diabatic trajectory calculations there is too much exchange between the tropics and mid-latitudes. The age spectrum is thus too broad and the tropical mean age is too old as a result of mixing older mid latitude air with tropical air. Likewise the mid latitude mean age is too young due to the in mixing of tropical air. The DAS kinematic trajectory calculations show excessive vertical dispersion of parcels in addition to excessive exchange between the tropics and mid latitudes. Because air is moved rapidly to the troposphere from the vertical dispersion, the age spectrum is shifted toward the young side. The excessive vertical and meridional dispersion compensate in the kinematic case giving a reasonable tropical mean age. The CTM calculation of the age spectrum using the DAS winds shows the same vertical and meridional dispersive characteristics of the kinematic trajectory calculation. These results suggest that the current DAS products will not give realistic trace gas distributions for long integrations; they also help explain why the extra tropical mean ages determined in a number of previous DAS driven CTM s are too young compared with observations. Finally, we note trajectory-generated age spectra . show significant age anomalies correlated with the seasonal cycles. These anomalies can be linked to year-to-year variations in the tropical heating rate. The anomalies are suppressed in the CTM spectra suggesting that the CTM transport scheme is too diffusive.

Schoeberl, Mark R.↗
NASA NTRS2004

Age and Pathway Diagnostics for a Stratospheric General Circulation Model

Using a variety of age diagnostic experiments we examine the stratospheric age spectrum of the Goddard Finite Volume Generd Circulation Model. Pulse tracer release age-of-air computations are compared to forward and backward trajectory computations. These comparisons show good agreement, and the age-of-air also compares well with observed long lived tracers. Pathway diagnostics show how air arrives in the lowermost stratosphere and the age structure of that region. Using tracers with different lifetimes we can estimate the age spectrum - this technique should be useful in diagnosing transport from various trace gas observations.

Schoeberl, Mark R.↗