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At least 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Large-amplitude, short-scale stationary Rossby waves in the Southern Hemisphere - Observations and mechanistic experiments to determine their origin

Further observational evidence of the existence of large-amplitude stationary waves in the Southern Hemisphere during January 1979 is presented. Possible forcing mechanisms for the stationary waves are discussed, and two control experimental forecasts are presented: 15-day integrations with the GLAS Fourth Order GCM, starting from January 5 and Febuary 4, 1979. These forecasts are compared with the GLAS analyses for the same periods, discussing the extent to which the observed January waves are reproduced in the forecast. Several mechanistic experiments are reported in which the Andean orography, tropical heating, regional heating, and initial westerly flow are artificially modified. The effects of these changes on the stationary waves are discussed.

Kalnay, E.↗
NASA NTRS1985

Response of the GLA fourth order model to changes in horizontal resolution and terrain heights

The effects the selection of the orographic data for the boundary conditions has on results of simulations with the NASA-Goddard Laboratory for Atmospherics fourth order GCM were examined. Two different lower boundary conditions were compared in generating preliminary weather forecasts: mean areally averaged heights, and an enhanced significant height orography for rugged terrain. The latter condition was developed to emphasize the effects the tallest peaks in a given region have on the atmospheric flow by considering only the highest 1/3 of the 1 deg x 1 deg values in the averaging process. Simulations were carried out for five 10 day forecasts with a 4 deg lat x 5 deg long resolution and six with a horizontal grid resolution of 2 deg lat by 2.5 deg long, three with each boundary condition. The rms errors of the sea level pressure and the 500 mb geopotential heights were calculated. The mean errors decreased after the second or third day with the enhanced significant height orography.

Pfaendtner, J.↗
NASA NTRS1985

Analysis/forecast experiments with a multivariate statistical analysis scheme using FGGE data

A three-dimensional, multivariate, statistical analysis method, optimal interpolation (OI) is described for modeling meteorological data from widely dispersed sites. The model was developed to analyze FGGE data at the NASA-Goddard Laboratory of Atmospherics. The model features a multivariate surface analysis over the oceans, including maintenance of the Ekman balance and a geographically dependent correlation function. Preliminary comparisons are made between the OI model and similar schemes employed at the European Center for Medium Range Weather Forecasts and the National Meteorological Center. The OI scheme is used to provide input to a GCM, and model error correlations are calculated for forecasts of 500 mb vertical water mixing ratios and the wind profiles. Comparisons are made between the predictions and measured data. The model is shown to be as accurate as a successive corrections model out to 4.5 days.

Baker, W. E.↗
NASA NTRS1986

Cloud radiative forcing in a general circulation model

Preliminary results are reported from a simulation carried out with the UCLA/Goddard GCM to investigate cloud radiative forcing phenomena. Of particular interest was cloud feedback, i.e., the changes in forcing brought about by climate change. Early results indicate that clouds cool the tropical oceans and land surface and warm the tropical atmosphere.

Randall, D. A.↗
NASA NTRS1986

The structure and propagation of intraseasonal oscillations appearing in a GFDL general circulation model

The 12-year output of a 15-wavenumber GCM experiment is analyzed, with the objective of describing the spatial and temporal behavior of dominant intraseasonal variations. The parameters analyzed include five-day averages of wind, geopotential height, sea level pressure, and precipitation. It is demonstrated that the spatial structure, propagation characteristics, and seasonal dependence of the model features are consistent with observations reported in the literature. The model findings are interpreted in terms of the current theoretical understanding of tropical and extratropical motions.

Lau, Ngar-Cheung↗
NASA NTRS1986

Constraints on resolving meso-alpha and meso-beta phenomena using a space-based Doppler lidar wind profiler

Lidar shot management and wind computation algorithms are used to determine the constraints on resolving mesoscale (alpha and beta) wind fields. Examples of simulated Doppler lidar performance in resolving wind gradient features are presented using currently proposed scan and signal processing parameters, and GCM model outputs are used as input wind fields. Results indicate that with the present constraints on lidar lifetime, scan rates, and orbit altitudes, the limits of mesoscale wind feature resolution are close to wavelengths of 100 km.

Emmitt, G. D.↗
NASA NTRS1987

Development of a two-dimensional zonally averaged statistical-dynamical model. I - The parameterization of moist convection and its role in the general circulation

The moist convection parameterization used in the GISS 3-D GCM is adapted for use in a two-dimensional (2-D) zonally averaged statistical-dynamical model. Experiments with different versions of the parameterization show that its impact on the general circulation in the 2-D model does not parallel its impact in the 3-D model unless the effect of zonal variations is parameterized in the moist convection calculations. A parameterization of the variations in moist static energy is introduced in which the temperature variations are calculated from baroclinic stability theory, and the relative humidity is assumed to be constant. Inclusion of the zonal variations of moist static energy in the 2-D moist convection parameterization allows just a fraction of a latitude circle to be unstable and enhances the amount of deep convection. This leads to a 2-D simulation of the general circulation very similar to that in the 3-D model. The experiments show that the general circulation is sensitive to the parameterized amount of deep convection in the subsident branch of the Hadley cell. The more there is, the weaker are the Hadley cell circulations and the westerly jets. The experiments also confirm the effects of momentum mixing associated with moist convection found by earlier investigators and, in addition, show that the momentum mixing weakens the Ferrel cell. An experiment in which the moist convection was removed while the hydrological cycle was retained and the eddy forcing was held fixed shows that moist convection by itself stabilizes the tropics, reduces the Hadley circulation, and reduces the maximum speeds in the westerly jets.

Yao, Mao-Sung↗
NASA NTRS1987

Components of the ice age circulation

The effects of ice age boundary conditions on atmospheric dynamics and regional climate patterns are investigated using four GCM simulations. Particular consideration is given to sea surface temperature-sea ice distribution, the appearance of land ice, and the increased elevation of land ice. It is observed that the ice-age sea surface temperature stabilizes the atmosphere over the oceans, increases the frequency of storm tracking through central North America, and amplifies transient eddy energy without increasing baroclinic generation. It is detected that low-elevation ice generates low pressure over eastern North America and southern Europe in winter, while increasing cloud cover and cooling the land in summer. Elevation of the ice sheets cools the land in winter, further intensifies storms off northeastern North America, induces subsidence warming downstream of the European ice sheets in summer, and increases the transient and stationary eddy energy through increased baroclinicity.

Rind, D.↗
NASA NTRS1987

FIRE - The First ISCCP Regional Experiment

The First International Satellite Cloud Climatology Project Regional Experiment (FIRE) designed to study the roles of clouds, in particular marine stratocumulus and cirrus-cloud systems, in the global climate is discussed. The objectives of FIRE are: (1) to develop a cloud-classification scheme; (2) to validate and improve satellite cloud-retrieval techniques; (3) to improve cloud radiation models; (4) to collect cloud space/time statistics; (5) to improve cloud dynamics models; and (6) to validate and improve GCM cloud parameterizations. The methods used to acquire extended time data and intensive field observations are described. The extended time and intensive field data collected during the FIRE are to be archived in the NASA Pilot Climate Data System at Goddard Space Flight Center.

Cox, Stephen K.↗
NASA NTRS1987

Numerical experiments related to the summer 1980 U.S. heat wave

The NASA Goddard Laboratory for Atmospheres fourth-order GCM was used in a series of medium-range numerical forecast experiments in order to improve understanding of the severe summer 1980 heat wave over the U.S. The results show that the derived soil moisture anomalies in the summer of 1980 contributed positively to the model's simulation of the heat wave maintenance, and suggest that once a region of reduced soil moisture is established, it tends to persist and maintain warmer and drier conditions. The lower soil moisture values resulted in reduced evaporation, higher ground temperatures, increased sensible heat flux from ground to air, higher surface air temperature, lower sea-level pressure, and higher 500-mb height. The effects of North Pacific sea-surface-temperature anomalies were mostly opposite to those of the soil-moisture anomalies: enhanced northerly flow of cooler drier air, increased evaporation, lower ground and air temperature, higher sea level pressure, and lower 500 mb heights over the Great Plains.

Wolfson, N.↗
NASA NTRS1988

Simulation studies of the influence of sea-surface temperature anomalies on the Sahelian circulation and rainfall

An investigation was conducted to find out if sea surface temperature (SST) - African rainfall relationships could be simulated in a global climate model (GCM). If indeed that were possible, researchers generated useful diagnostics that can enable them to understand the physical mechanisms which lead to rainfall fluctuations over Africa in response to sea surface temperature anomalies over global ocean.

Sud, Y. C.↗
NASA NTRS1987

A computer model of global thermospheric winds and temperatures

Output data from the NCAR Thermospheric GCM and a vector-spherical-harmonic (VSH) representation of the wind field are used in constructing a computer model of time-dependent global horizontal vector neutral wind and temperature fields at altitude 130-300 km. The formulation of the VSH model is explained in detail, and some typical results obtained with a preliminary version (applicable to December solstice at solar maximum) are presented graphically. Good agreement with DE-2 satellite measurements is demonstrated.

Killeen, T. L.↗
NASA NTRS1987

The effect of increased horizontal resolution on GLA Fourth Order model forecasts

A benchmark series of ten-day weather forecasts has been run with the GLA Fourth Order GCM with both a 4 deg latitude by 5 deg longitude resolution and a 2 deg latitude by 2.5 deg longitude resolution. Ensemble statistics of forecast skill and maps of systematic error fields have been generated for both resolutions. The enhanced resolution added 24 hours of useful predictive skill to the sea level pressure forecasts and 6 hours to the 500 mb height forecasts, but 5 to 6 days into the forecasts the advantage of the finer resolution was lost. The systematic error fields showed that by 8 days the 'climate drift' of the 2 x 2.5 deg forecasts had become pronounced and had caused the loss of predictive skill relative to the 4 x 5 deg forecasts. Additional results indicate that a gravity wave drag parameterization scheme might alleviate the climate drift problem.

Helfand, H. M.↗
NASA NTRS1988

Nonlinear instability of a forced baroclinic Rossby wave

The nonlinear instability of forced baroclinic Rossby waves to finite-amplitude perturbations was investigated using a simple two-layer quasi-geostrophic weakly nonlinear model and a low-order spectral model, developed for this purpose. The results were applied to a study of the interaction of planetary-scale stationary eddies with synoptic-scale transient eddies. A comparison of the energetics of the weakly nonlinear solution with that seen in observational analysis and in GCM experiments indicate three basic properties of the interaction between the two types of eddies: (1) eddy available potential energy is transferred from the planetary-scale stationary eddies to the synoptic-scale transient eddies, (2) eddy kinetic energy is transferred in the opposite direction, and (3) the eddy available potential energy transfer dominates the transfer of eddy kinetic energy. It is concluded that the simple weakly nonlinear model used in these studies does indeed capture much of the fundamental behavior of wave-wave interactions seen in the atmosphere.

Feldstein, Steven B.↗
NASA NTRS1988

Temperature dependence of cirrus extinction - Implications for climate feedback

The sensitivities of changes in cirrus optical properties to the changes in global temperature were investigated using data obtained in previous extensive lidar and radiometer observations of cirrus clouds. It is demonstrated how the temperature dependence of cirrus optical properties can be used in climate sensitivity calculations to yield predictions of feedback effects at various cirrus temperatures and how these properties can be parameterized simply for use in the GCM or climate models.

Platt, C. Martin R.↗
NASA NTRS1989

Nonmigrating tides

Recently an interesting advancement in the study of nonmigrating tides has occurred. There have been two distinct approaches in works on this subject. One is based on mechanistic models as considering nonuniform global distribution of water vapor or heating only on land, solving a set of linear equations. It is found that insolation absorption of the nonuniformly distributed water vapor produces only weak nonmigrating tides in the lower thermosphere; the planetary boundary layer heating on land can explain the enhanced tides on land and those with short vertical wavelengths in the stratosphere. The other approach is novel and uses simulation on the general circulation model (GCM). This realistic model can reproduce tides globally and in many details. The enhancement of two nonmigrating modes as eastward traveling modes with a wave number 3 and westward traveling modes with a wave number 5 is in surprisingly good agreement with observation at sea level, at 700 mb and even at 300 mb.

Kato, S.↗
NASA NTRS1988

Evaporation over land surfaces - First results from HAPEX-MOBILHY Special Observing Period

Preliminary results are presented from the May 7-July 15, 1986 Special Observing Period (SOP) of the HAPEX-MOBILHY program, which examines the hydrological budget and evaporation flux at the scale of a 10,000 sq km GCM grid square to determine soil moisture, surface-energy budgets, and surface hydrology. The SOP used two highly instrumented remote sensing aircraft to obtain detailed measurements of atmospheric fluxes and surface properties. It is noted that the measurements are reliable at spatially local and short time scales, as well as on the monthly time scale. The data base obtained may be used in parametrization schemes against which land-surface water budgets can be tested.

Andre, Jean-Claude↗
NASA NTRS1988

Global precipitation derived from HIRS2/MSU soundings

Atmospheric and surface soundings for the FGGE obtained by the analysis of HIRS2/MSU sounding data (Susskind et al., 1987) were used, along with a modified version of the radiation code used in the Goddard Laboratory for Atmospheres fourth-order GCM, to compute fields of total outgoing longwave radiation (OLR) for the FGGE year. A reasonable agreement was obtained between the computed OLR values and OLR radiation derived from measurements. Coefficients relating the global difference fields for each month of the FGGE year to precipitation derived from rain-gauge measurements for the FGGE year were derived. The results of this study demonstrate that precipitation is derivable from space on a global scale.

Wu, Man-Li C.↗