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At least 127 records · Page 7
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NASA NTRS1982

Planetary-scale waves in the Venus atmosphere

Observed wave-like cloud features on Venus, which at times form a Y-like structure which encircles the planet, were modelled numerically. Linearized primitive equations for a shallow, hydrostatic atmosphere are defined, along with upper boundary layer conditions for the 4-6 day periods detected in the atmospheric response to forcing. The basic state of the Venus atmosphere was considered to display variations in static stability and the mean zonal wind as a function of altitude. Forcing was introduced over a wide range of frequencies in order to produce the target oscillation modes. Combination of a midlatitude Rossby wave and an equatorial Kelvin wave was found to yield the observed Y-shape, which could be preserved with nonlinear coupling.

Covey, C.↗
NASA NTRS1982

Numerical simulation of the development of mean monsoon circulation in July

Eight different experiments are carried out, ranging from 8 to 20 days, with a primitive equation model consisting of five atmospheric layers and one oceanic layer. The purpose is to investigate the relative importance of radiative heating and deep cumulus condensation, orography, and initial conditions for the development of the mean monsoon circulation from June to July in the 0-180 deg E, 25 deg S - 55 deg N region. Two alternative initial states are used, one based on the observed monthly mean June pressure distribution, the other on the mean June zonal average pressure distribution. Whereas large-scale condensation and actual land and sea distributions are included in every experiment, deep cumulus cone condensation and radiative heating are always taken together. It is found that the means sea level pressure distribution and low-level flow pattern produced by these simulations are in the main determined by the diabatic heating distribution and are influenced somewhat by orography; they are, however, almost independent of the initial state. The low pressure systems are found to develop faster when diurnal variation of solar radiation is allowed for; this is thought to be due mainly to the more vigorous cumulus activity during the day.

Kuo, H. L.↗
NASA NTRS1983

Numerical studies of major and minor stratospheric warmings caused by orographic forcing

A primitive equation spectral model using spherical harmonics is formulated to study dynamic interactions between the troposphere and stratosphere in association with sudden stratospheric warmings. Using sigma coordinates for five tropospheric layers and log-pressure coordinates for 26 stratospheric and mesospheric layers, separate model equations for each system are combined to form single matrix governing equations. The gradual introduction of large scale topography to balanced initial states representative of observed mean winter conditions in the Northern Hemisphere is used for the generation of planetary waves during 40-day time integrations. Results of these integrations indicate that stratospheric warmings can be simulated by this orographic forcing and that mean momentum flux divergence due to zonal mean motion appears to be an essential mechanism of these simulated sudden warmings. It was found that the strength of the polar night jet can be a determining factor whether a warming becomes 'major' or 'minor'.

Koermer, J. P.↗
NASA NTRS1984

Climate sensitivity with a seasonal cycle energy balance model

The sensitivity of climate which may have a local maximum as the ice cap passes through a midlatitude region where the atmosphere's transport efficiency varies strongly with latitude is examined. This behavior, found in a two level primitive equations climate model forced with annual mean insolation, was reproduced in an energy balance model (EBM) by making the diffusion coefficient a function of latitude. The two level seasonally varying EBM was applied and the global mean surface temperature vs. solar constant for this model are shown and two regions of enhanced sensitivity appear. The snowcover distributions around the year for three cases are shown.

Suarez, M. J.↗
NASA NTRS1984

Horizontal energy propagation in a baroclinic atmosphere with meridional and zonal structure

A baroclinic model was developed. The model is linear, steady state, baroclinic (2 level) and based on the primitive equations. The unique features of the model are: (1) The basic state u and T fields are functions of wavelength, theta, and rho, (2) A mean meridional circulation v, w, which may be a function of wavelength, theta, and rho, and p may be included, (3) Dissipation may be a function of theta, wavelength, rho, p (e.g., differ over land and sea). Because the basic state is a function of longitude, the equations are not separable in wavelength and the usual semi-spectral solution procedure is not applicable. The model solutions can be found in a straight forward (brute force) way by discretizing the model equations directly on a wavelength, theta, rho, p grid. There are six dependent (perturbation) variables: u, v, and geopotential at levels 1 and 2. The thermal forcing is prescribed at the intermediate vertical level. The linearized equations may be written.

Youngblut, C.↗
NASA NTRS1984

The impact of satellite temperature soundings on the forecasts of a small national meteorological service

The impact of introducing satellite temperature sounding data on a numerical weather prediction model of a national weather service is evaluated. A dry five level, primitive equation model which covers most of the Northern Hemisphere, is used for these experiments. Series of parallel forecast runs out to 48 hours are made with three different sets of initial conditions: (1) NOSAT runs, only conventional surface and upper air observations are used; (2) SAT runs, satellite soundings are added to the conventional data over oceanic regions and North Africa; and (3) ALLSAT runs, the conventional upper air observations are replaced by satellite soundings over the entire model domain. The impact on the forecasts is evaluated by three verification methods: the RMS errors in sea level pressure forecasts, systematic errors in sea level pressure forecasts, and errors in subjective forecasts of significant weather elements for a selected portion of the model domain. For the relatively short range of the present forecasts, the major beneficial impacts on the sea level pressure forecasts are found precisely in those areas where the satellite sounding are inserted and where conventional upper air observations are sparse. The RMS and systematic errors are reduced in these regions. The subjective forecasts of significant weather elements are improved with the use of the satellite data. It is found that the ALLSAT forecasts are of a quality comparable to the SAR forecasts.

Wolfson, N.↗
NASA NTRS1984

Sampling strategies and four-dimensional assimilation of altimetric data for ocean monitoring and prediction

Numerical experiments using simulated altimeter data were conducted in order to examine the assimilation of altimeter-derived sea surface heights into numerical ocean circulation models. A reduced-gravity, primitive equation circulation model of the Gulf of Mexico was utilized; the Gulf of Mexico was chosen because of its amenability to modeling and the ability of low vertical-mode models to reproduce the observed dynamical features of the Gulf circulation. The simulated data were obtained by flying an imaginary altimeter over the model ocean and sampling the model sea surface just as real altimeter would observe the true ocean. The data were used to initialize the numerical model and the subsequent forecast was compared to the true numerical solution. Results indicate that for a stationary, circular eddy, approximately three to four tracks (either ascending or descending) across the eddy are sufficient to ensure adequate spatial resolution.

Kindle, J. C.↗
NASA NTRS1983

A nested-grid limited-area model for short term weather forecasting

The present investigation is concerned with a mesoscale atmospheric simulation system (MASS), incorporating the sigma-coordinate primitive equations. The present version of this model (MASS 3.0) has 14 vertical layers, with the upper boundary at 100 mb. There are 128 x 96 grid points in each layer. The earlier version of this model (MASS 2.0) has been described by Kaplan et al. (1982). The current investigation provides a summary of major revisions to that version and a description of the parameterization schemes which are presently included in the model. The planetary boundary layer (PBL) is considered, taking into account aspects of generalized similarity theory and free convection, the surface energy budget, the surface moisture budget, and prognostic equations for the depth h of the PBL. A cloud model is discussed, giving attention to stable precipitation, and cumulus convection.

Wong, V. C.↗
NASA NTRS1983

A numerical investigation of the President's Day storm of February 18-19, 1979

The reported investigation is based on the use of a three-dimensional, primitive equation model. The President's Day storm, formed in the Gulf of Mexico as a massive anticyclone, affected the northern states with record-breaking cold temperatures. Attention is given to the physical processes relevant to storm formation, the forecast model, a description of experiments and model forecasts, and model results. An attempt is made to determine the important dynamic processes at work during the evolution of the storm. The jet streak interactions which occurred in the cyclogenetic environment, the effects of cold air damming, and the formation of a strong mesoscale coastal front are found to be of particular interest.

Nappi, A. J.↗
NASA NTRS1984

Massively Parallel Processor

The feasibility of using the Massively Parallel Processor (MPP) and possible future machines with parallel architecture for weather prediction and climate simulation was studied. A shallow water model and a two-level primitive equations model were implemented.

Suarez, M. J.↗
NASA NTRS1984

A Study of the Adequacy of Quasi-geostrophic Dynamics for Modeling the Effect of Frontal Cyclones on the Larger Scale Flow

The major objectives of this study are to test the validity of quasi-geostrophic (QG) dynamics, compared to primitive equation (PE) dynamics for modeling the effect of cyclone waves on the larger scale flow, and to study the formation of frontal cyclones and the dynamics of occluded frontogenesis. In order to extend the realism of the initial conditions over those used in earlier work of this nature and in order to include strong surface frontal zones in the initial conditions, a horizontal resolution on the order of 100 km between gridpoints is needed. In order to allow for integrations of up to two weeks simulated time and to keep the logistics and cost of the runs feasible, the horizontal domain of the models must be reduced. Based on work concerning polar lows, the tropospheric static stability was reduced and was also allowed to vary in different tropospheric layers. Previous work used a 'standard atmosphere' temperature lapse rate. Stratospheric stability remains unchanged. The use of one of these 'reduced stability' cases, with no surface frontal zone present resulted in the discovery of normal mode perturbations.

Mudrick, S.↗
NASA NTRS1985

Response of Winter Forecasts Made with the GLA Fourth Order GCM to Changes in the Horizontal Grid Resolution

The GLA Fourth Order General Circulation Model was modified in 1984 to allow it to be run at a finer horizontal grid resolution. Previously the standard model versions integrated the primitive equations on a 4 degree latitude by 5 degree longitude grid. Forecasts made at this resolution are compared to others which were made using the finer 2 degree latitude by 2 1/2 degree longitude grid resolution. Three winter cases are included with initial conditions from 15 December 1978, 5 January 1979 and 21 January 1979. The 21 January 1979 initial conditions were taken from a GLAS analysis (experiment 2728) which incorporated the GLAS temperature retrievals. The other two cases used European Center Analysis for initial conditions. The forecasts were all verified against European Center Analysis.

Pfaendtner, J.↗
NASA NTRS1985

A study of the adequacy of quasi-geostrophic dynamics for modeling the effect of frontal cyclones on the larger scale flow

The validity of quasi-geostrophic (QG) dynamics were tested on compared to primitive equation (PE) dynamics, for modeling the effect of cyclone waves on the larger scale flow. The formation of frontal cyclones and the dynamics of occluded frontogenesis were studied. Surface friction runs with the PE model and the wavelength of maximum instability is described. Also fine resolution PE simulation of a polar low is described.

Mudrick, S.↗
NASA NTRS1984

Baroclinic instability in the Venus atmosphere

A three-dimensional, spherical, primitive equation eigenvalue model is used to investigate the baroclinic stability properties of the wind and temperature fields in the Venus atmosphere as measured by Pioneer Venus. It is found that baroclinic instability occurs in the region of the middle cloud deck. The most unstable modes have growth times less than eight days and are vertically confined to the region near the middle cloud layer. The most unstable baroclinic mode at zonal wavenumber 2 has characteristics similar to those observed for the high latitude rotating dipole thermal feature. Certain planetary scale baroclinic modes can penetrate to relatively high altitudes under the right circumstances, and may therefore explain some of the wave features observed between 60 and 90 km. For example, thermal oscillations with periods between four and seven days occurring at middle latitudes have characteristics which appear to be consistent with computed properties of planetary scale baroclinic modes.

Young, R. E.↗
NASA NTRS1984

The response of a nonlinear, time-dependent, baroclinic model of the atmosphere to tropical thermal forcing

A multi-level, sigma coordinate, primitive equation atmospheric model has been utilized to study both the tropical and extratropical response to an isolated region of steady thermal forcing in the tropics. The nonlinear response during the first 28 days of the simulation is described. The response can be generally characterized by two distinct components. The first component is a quasi-stationary disturbance which extends eastward and poleward away from the source region along a 'great circle' path. The structure of this disturbance is essentially barotropic away from the source region. The second component is a growing baroclinic wave propagating zonally at mid-latitudes. Significantly, this disturbance is apparently the result of baroclinic instability induced by the quasi-stationary wavetrain. The discussion is predominantly heuristic in form and relies heavily on graphical presentation and quasi-geostrophic theory to interpret the response and individual components of the thermodynamic energy and momentum equations.

Grose, W. L.↗
NASA NTRS1984

Thermal tides in the atmosphere of Venus - Comparison of model results with observations

A linearized primitive equation model adapted to Venusian conditions was used to study thermal tidal anomalies in the Venus atmosphere exposed by Venus Orbiter IR sensors. The model received as input the IR data, mean zonal wind and solar input as functions of height and latitude, and the global mean static stability and Newtonian cooling and Rayleigh friction in relation to altitude. Basic state and forcing functions were defined for Venus, and the model generated brightness temperatures which could be compared with the IR data. The good correlations obtained suggest that the model accurately accounts for the low variation of phase with altitude and stronger semidiurnal oscillation features than diurnal oscillations. The model is concluded as a useful tool for assessing the role of thermal tides in maintaining Venus super rotation.

Pechmann, J. B.↗
NASA NTRS1983

Influence of radiative heating and cumulus convection on development of mean monsoon circulation in July

Numerical simulations of July mean monsoon circulation in the tropics are described. The model used in the simulations was based on a series of primitive equations for the combined effects of variations of solar radiation, radiative diurnal warming, and large-scale and deep cumulus condensation, and the kinematic effects of topography. The initial states of the model were derived from the observed mean distributions of pressure and humidity. Analysis of the numerical results showed that the large-scale features of the mean July monsoon circulation in the tropics are created mainly by differential diabatic heating under the influence of the specific topography. The time necessary to establish the large scale features was only about 5 days when the diurnal variation of solar radiation was taken into account. Graphic illustrations of the simulated mean July flow conditions are provided.

Kuo, H. L.↗
NASA NTRS1985

The causation and sensitivity of the northern winter planetary waves

High-resolution calculations of the wintertime stationary atmospheric response to planetary scale topographic and thermal forcings have been made using a numerical model that solves the spherical primitive equations linearized about observed zonal wind and temperature fields. The model equations are presented and their numerical implementation is discussed. The model inputs and parameters are presented and the model's response to relativistic forcing is analyzed. In middle latitudes the response to topographic forcing strongly dominates the response to thermal forcing. In the midlatitude troposphere, the topographic response is insensitive to changes in the zonal wind. In the stratosphere, both the variance and mean are dominated by the topographic response. In general, the sensitivity of the planetary waves to changes in the zonal wind is found to be much smaller than other recent calculations have indicated.

Jacqmin, D.↗