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Kalnay, E.

Publications and source records attributed to Kalnay, E..

At least 19 records
All sourcesNASA NTRSDOE OSTI
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 NTRS1988

A study of the dynamics of the Intertropical Convergence Zone (ITCZ) in a symmetric atmosphere-ocean model

A numerical model of the circulation of a coupled axisymmetric atmosphere-ocean system was constructed to investigate the physical factors governing the location and intensity of the Intertropical Convergence Zone (ITCZ) over oceans and over land. The results of several numerical integrations are presented to illustrate the interaction of the individual atmospheric and oceanic circulations. It is shown that the ITCA cannot be located at the equator because the atmosphere-ocean system is unstable for lateral displacements of the ITCA from an equilibrium position at the equator.

Charney, J. G.↗
NASA NTRS1987

The effect of a gravity wave drag parameterization scheme on GLA fourth order GCM forecasts

Ten-day forecast experiments have been performed to determined whether the introduction of a simple orographic gravity wave drag scheme into a fourth-order GCM would reduce the climate drift of the fine resolution model and improve the model's medium range predictive skill. Error reduction due to the gravity waves is found in stratospheric predictions, where the improvement is confined mainly to the zonal mean component. Improvements are noted in the Northern Hemisphere climatology, where low level westerlies are weakened and shifted poleward, and in the Southern Hemisphere, where the roaring forties and fifties are better simulated.

Helfand, H. M.↗
NASA NTRS1986

Global analysis of ocean surface wind and wind stress using a general circulation model and Seasat scatterometer winds

Instantaneous and 15-day time-averaged fields of surface wind, wind stress, curl of the wind stress, and wind divergence are presented. These fields are derived from the Goddard Laboratory for Atmospheres four-dimensional analysis/forecast cycle, for the period September 6-30, 1978, using conventional data, satellite temperature soundings, cloud-track winds, and subjectively dealiased Seasat scatterometer winds.

Kalnay, E.↗
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 NTRS1986

Global surface wind and flux fields from model assimilation of Seasat data

Procedures for dealiasing Seasat data and developing global surface wind and latent and sensible heat flux fields are discussed. Seasat data from September 20, 1978 was dealiased using the Goddard Laboratory for Atmospheres (GLA) analysis/forecast system. The wind data obtained with the objective GLA forecast model are compared to the data subjectively dealiased by Peteherych et al. (1984) and Hoffman (1982, 1984). The GLA procedure is also verified using simulated Seasat data. The areas of high and low heat fluxes and cyclonic and anticyclonic wind stresses detected in the generated fields are analyzed and compared to climatological fields. It is observed that there is good correlation between the time-averaged analyses of wind stress obtained subjectively and objectively, and the monthly mean wind stress and latent fluxes agree with climatological fields and atmospheric and oceanic features.

Atlas, R.↗
NASA NTRS1986

The relative importance of mass and wind data in the FGGE observing system

The use of mass and wind data in numerical weather prediction is examined. The applicability of the mass and wind data on the skill of numerical weather prediction is evaluated by real data assimilation experiments using the the NASA/Goddard Laboratory for Atmospheres analysis/forecast system of Baker (1983) and Kalnay et al. (1983). It is observed that the wind observations are important for small scales and in the tropics and that the wind observations are more accurate than mass observations.

Kalnay, E.↗
NASA NTRS1985

Objective analysis and assimilation techniques used for the production of FGGE 3b analyses

A system of seven tables, which cover analysis archiving, observation types, quality control, data assimilation cycles, assimilating models, initialization, and analysis techniques was adopted. The set of prepared tables allows side-by-side comparison of the characteristics of the six data assimilation systems (European Center for Medium Range Weather Forecasts, Geophysical Fluid Dynamics Laboratory, Goddard Laboratory for Atmospheric Science, National Meteorological Center, Florida State University, and Naval Environmental Prediction Research Facility) used to produce FGGE IIIb analyses.

Daley, R. W.↗
NASA NTRS1985

Remote sensing of atmospheric and surface parameters from HIRS2/MSU on TIROS-N

At the Goddard Laboratory for Atmospheric Sciences (GLAS) a physically based satellite temperature sounding retrieval system was developed, involving the simultaneous analysis of sounding data, for determining atmospheric and surface conditions that are consistent with the observed radiances. In addition to determining accurate atmospheric temperature profiles even in the presence of clouds, the system provides global estimates of day and night sea or land surface temperatures, snow and ice cover, cloud amounts, cloudtop heights and temperatures, and albedo. The characteristics of the atmospheric and surface parameters derived from the GLAS Physical Retrieval System are reviewed, results for the FGGE year are presented and, whenever possible, compared with other measurements of the same fields. Some of the model-derived diagnostic fields available from the GLAS Analysis/Forecast System are also discussed. These fields may lead to more accurate determination of the source terms of the atmospheric heat and moisture budgets.

Susskind, J.↗
NASA NTRS1985

Analysis of ocean surface wind fields using SEASAT-A scatterometer data

In addition to the SEASAT forecast impact studies previously conducted with the GLA model, a study was also made of the global analyses of surface wind stress, wind stress curl, and surface sensible and latent heat fluxes, which are generated as a by-product of the assimilation process. Both instantaneous analyses of these quantities and 15-day averages of each of these fields were found to be in good qualitative agreement with published fields.

Kalnay, E.↗
NASA NTRS1985

Forecast Impact Simulation Studies

A series of simulation experiments is being conducted as a cooperative effort between the European Center for Medium Range Weather Forecasts (ECMWF), the National Meteorological Center (NMC) and the Goddard Laboratory for Atmospheres (GLA), to provide a quantitative assessment of the potential impact of proposed observing systems on large scale numerical weather prediction. For these studies an advanced analysis/forecast simulation system was developed which provides for a more realistic assessment of the impact of proposed observing systems than was possible in earlier studies. This system consists of four elements: (1) An atmospheric model integration to provide a complete record of the true state of the atmosphere (called nature); (2) a conventional data assimilation cycle that is used as the control experiment; (3) a satellite data assimilation that differs from the control in also including fabricated satellite data incorporated in the forecast-analysis cycle; and (4) forecasts produced from both control and satellite initial conditions. Comparison of these forecasts with nature provides an assessment of the impact of satellite data.

Atlas, R.↗
NASA NTRS1985

High-Latitude Filtering in a Global Grid-Point Model Using Model Normal Modes

The aim of high-latitude filtering in the vicinity of the poles is to avoid the excessively short time steps imposed on an explicit time-differencing scheme by linear stability due to fast moving inertia-gravity waves near the poles. The model normal mode expansion toward the problem of high-latitude filtering in a global shallow water model using the same philosophy as that used by Daley for the problem for large timesteps in P.E. models with explicit time integration schemes was applied.

Takacs, L. L.↗
NASA NTRS1985

Error Growth in Operational 10-day Forecasts

The rate of growth of forecast errors has been estimated previously, using as data base 100 consecutive 10-day operational forecasts from the European Center for Medium Range Forecasting (ECMWF). The growth of the difference between two model forecasts verifying the same day was parameterized. This parameterization of error growth was extended by including the effect of model deficiencies as well as their scale dependence. In this way the forecaster are able to fit real forecast error growth and determine the scale dependence of the derived parameters (rate of error growth, external error source due to model errors, and saturation levels). This work is a necessary step in the application of the Lagged Average Forecasting (LAF) technique to the ECMWF 10-day forecasts. It is found that for both the analyses and the forecasts, there is an approximate equipartition of energy between all the zonal wavenumbers m corresponding to the same total wavenumber n.

Kalnay, E.↗
NASA NTRS1985

Mechanistic Experiments to Determine the Origin of Southern Hemisphere Stationary Waves

Large amplitude stationary Rossby waves were discovered with zonal wavenumbers of approx. 7 between 20 S and 40 S over and in the lee of South America. These waves, present during January 1979, disappeared in February, 1979. It was concluded that the waves were not orographically forced because they corresponded to a ridge in the lee of the Andes, and were not forced by observed sea surface temperature anomalies because of their space and time phase relationship. Two 15 day forecast experiments were performed with the GLAS Fourth Order General Circulation Model, and initial conditions corresponding to 5 January and 4 February, 1979. These forecasts reproduce reasonably well the presence of the January wave and their absence in February. Several mechanistic experiments to determine the origin of the waves were also performed. A No Andes forecast shows that the waves do indeed exist independently of orographic forcing. Several experiments modifying the coefficient of latent heat lead to the conclusion that tropical heating is important in the maintenance of the waves.

Kalnay, E.↗
NASA NTRS1985

On Fofonoff's Mode

The classical barotropic ocean model of Veronis (1966) is reexamined to verify the possible existence of Fofonoff's (1954) steady free inertial mode by considering the balance where J is the Jacobian, eta is the streamfunction of the horizontal velocity, and R is a parameter of nonlinearity. A linear functional relationship between the potential vorticity and the streamfunction and inertial boundary layers along the ocean basin was suggested by Fofonoff. However, the numerical integration showed that the system is barotropically unstable. The typical instantaneous field is given. The statistical equilibrium state eta is also given. Although it resembles Fofonoff's solution, it is maintained by the Reynolds stress field induced by the eddies in addition to the wind stress and dissipation. The plot of eta versus R delta sq +y is given. It is shown that the Fofonoff's linear relation between the potential vorticity and the streamfunction does not hold uniformly over the entire basin. The above results show that the Fofonoff's solution can not be realized physically.

Merkine, L. O.↗
NASA NTRS1985

Simulation studies of the impact of future observing systems on weather prediction

The features and preliminary results from a simulation system being implemented to develop realistic estimates of the impacts future data acquisition systems will have on large-scale numerical weather simulation are described. The new instruments may include advanced passive IR and microwave satellite sensors, as well as active scatterometer and lidar sounders. A main goal of the impact study is to identify those sensor systems which will provide the most benefit. The realism of the study is being enhanced by assimilating as much real-world data as possible and generating global weather maps for comparison with maps generated on the bases on the projected new, higher resolution data. Early results have indicated a preference for higher resolution wind data than for temperature data for making 1-5 day forecasts. The prime instrument candidate for collecting the data is lidar, provided the sensor resolution design goals are met.

Atlas, R.↗
NASA NTRS1985

Error growth in operational ECMWF forecasts

A parameterization scheme used at the European Centre for Medium Range Forecasting to model the average growth of the difference between forecasts on consecutive days was extended by including the effect of error growth on forecast model deficiencies. Error was defined as the difference between the forecast and analysis fields during the verification time. Systematic and random errors were considered separately in calculating the error variance for a 10 day operational forecast. A good fit was obtained with measured forecast errors and a satisfactory trend was achieved in the difference between forecasts. Fitting six parameters to forecast errors and differences that were performed separately for each wavenumber revealed that the error growth rate grew with wavenumber. The saturation error decreased with the total wavenumber and the limit of predictability, i.e., when error variance reaches 95 percent of saturation, decreased monotonically with the total wavenumber.

Kalnay, E.↗