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  • 1
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    Persistence and predictability in a perfect model (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A realistic two-level GCM is used to examine the relationship between predictability and persistence. Predictability is measured by the average divergence of ensembles of solutions starting from perturbed initial conditions, and persistence is defined in terms of the autocorrelation function based on a single long-term model integration. The average skill of the dynamical forecasts is compared with the skill of simple persistence-based statistical forecasts. For initial errors comparable in magnitude to present-day analysis errors, the statistical forecast loses all skill after about one week, reflecting the lifetime of the lowest frequency fluctuations in the model. Large ensemble mean dynamical forecasts would be expected to remain skillful for about 3 wk. The disparity between the skill of the statistical and dynamical forecasts is greater for the higher frequency modes, which have little memory beyond 1 d, yet remain predictable for about 2 wk. The results are analyzed in terms of two characteristic time scales.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of the Atmospheric Sciences (ISSN 0022-4928); 49; 256-269
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  • 2
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    Low-frequency intraseasonal tropical-extratropical interactions (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Using seven years (1981-1987) of ECMWF initialized analyses, the low-frequency (20-70 day) intraseasonal variability during Northern Hemisphere winter is examined, with emphasis on the zonal wind variability in the Pacific sector and on its relationship to the tropical convection and the middle-altitude wave propagation. Particular consideration is given to changes in the propagation characteristics associated with variations in the subtropical jet and the implications for low-frequency variability in middle latitudes. Also investigated is the relationship between the Pacific sector u-wind fluctuations and tropical convection anomalies.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of the Atmospheric Sciences (ISSN 0022-4928); 48; 629-650
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  • 3
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    Recent secular changes in the wintertime circulation of the Southern Hemisphere (1988)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: Some preliminary evidence is given that suggests that substantial differences exist between the Southern Hemisphere wintertime circulation during 1980 through 1982 and 1984 through 1986. Results suggest that the middle and high latitude secular changes are primarily a winter phenomena and appear to be characterized by a phase locking of naturally occurring modes of variation. The amplitude of the changes (on the order of 5 to 10 m/s) appears to fall within the natural variability of the zonal wind fluctuations. On the other hand, the low latitude variations appear to be tied to changes in forcing associated with El Nino and anti-El Nino events. The mechanisms responsible for the splitting of the jet at high latitudes and possible links with the low latitude zonal wind fluctuations are currently under investigation.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: National Weather Service, Proceedings of the Twelfth Annual Climate Diagnostics Workshop; p 179-188
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  • 4
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    A reduced version of the NMC DERF 2 data set (1989)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The National Meterological Center (NMC) Dynamical Extended Range Forecast (DERF 2) data represents a major computational effort to better ascertain the potential for extended range forecasts and to develop a strategy for performing operational extended range forecasts using dynamical models. A major stumbling block for using this data has been the sheer volume of data that must be processed to perform even simple calculations. The product of the data reduction described is a manageable data set that fits comfortably on five magnetic tapes or on one compact disc. The document outlines the data reduction process of the second phase of DERF data. It contains the description of the fields and the resolution of both the original and final fields. In order to assist the users of this data set, maps of selected fields, using both the original truncation at rhomboidal 30 and the truncation of the final data at triangular 20, are displayed.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: NASA-TM-100727 , REPT-89B00097 , NAS 1.15:100727
    Format: application/pdf
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  • 5
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    A graphics package for meteorological data, version 1.5 (1989)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A plotting package has been developed to simplify the task of plotting meteorological data. The calling sequences and examples of high level yet flexible routines which allow contouring, vectors and shading of cylindrical, polar, orthographic and Mollweide (egg) projections are given. Routines are also included for contouring pressure-latitude and pressure-longitude fields with linear or log scales in pressure (interpolation to fixed grid interval is done automatically). Also included is a fairly general line plotting routine. The present version (1.5) produces plots on WMS laser printers and uses graphics primitives from WOLFPLOT.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: NASA-TM-100742 , REPT-89B00216 , NAS 1.15:100742
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  • 6
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    An intercomparison of intraseasonal variability in general circulation models and observations (1990)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Low frequency oscillations appearing in three GCM seasonal cycle integrations are compared with the analyses of the European Center for Medium Range Weather Forecasting (ECMWF). All three models have the same resolution: 4 deg latitude by 5 deg longitude, with 9 levels. The dominant phase speeds and the differential vertical structure of the heating profiles in the GCMs are in general agreement with current theory involving the positive feedback between latent heating and moist static stability. All three GCMs fail to capture the detailed evolution in the different stages of the development and decay of the oscillation. The results suggest that an improvement in the boundary layer moisture processes may be crucial for a better simulation of the oscillation.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: NASA-TM-100764 , REPT-90E02836 , NAS 1.15:100764
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  • 7
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    Dynamical predictability in a simple general circulation model - Average error growth (1989)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Average predictability and error growth in a simple realistic two-level general circulation model (GCM) were investigated using a series of Monte Carlo experiments for fixed external forcing (perpetual winter in the Northern Hemisphere). It was found that, for realistic initial errors, the dependence of the limit of dynamic predictability on total wavenumber was similar to that found for the ECMWF model for the 1980/1981 winter conditions, with the lowest wavenumbers showing significant skill for forecast ranges of more than 1 month. On the other hand, for very small amplitude errors distributed according to the climate spectrum, the total error growth was superexponential, reaching a maximum growth rate (2-day doubling time) in about 1 week. A simple empirical model of error variance, which involved two broad wavenumber bands and incorporating a 3/2 power saturation term, was found to provide an excellent fit to the GCM error growth behavior.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of the Atmospheric Sciences (ISSN 0022-4928); 46; 353-370
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  • 8
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    GCM simulations of intraseasonal variability in the Pacific/North American region (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: General circulation model (GCM) simulations of low-frequency variability with time scales of 20 to 70 days are analyzed for the Pacific sector during boreal winter. The GCM's leading mode in the upper-tropospheric zonal wind is associated with fluctuations of the East Asian jet; this mode resembles, in both structure and amplitude, the Pacific/North American (PNA) pattern found in the observations on these time scales. In both the model and observations, the PNA anomaly is characterized by: (1) a linear balance in the upper-tropospheric vorticity budget with no significant Rossby wave source in the tropics, (2) a barotropic conversion of kinetic energy from the time mean Pacific jet, and (3) a north/south displacement of the Pacific storm track. In the GCM, the latter is associated with synoptic eddy heat flux and latent heat anomalies that appear to contribute to a strong lower-tropospheric source of wave activity over the North Pacific. This is in contrast to the observations, which show only a weak source of wave activity in this region.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of the Atmospheric Sciences (ISSN 0022-4928); 50; 13; p. 1991-2007.
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  • 9
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    Regional earth-atmosphere energy balance estimates based on assimilations with a GCM (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The Oort and Vonder Haar (1976) column-budget technique is presently used to evaluate the physical consistency and accuracy of regional earth-atmosphere energy balance estimates for (1) atmospheric budget terms, (2) net radiation at the top of the atmosphere, and (3) time tendency and flux divergence of energy, for Special Observing Periods of the FGGE year. It is found that, during winter, the midlatitude oceans supply large quantities of energy to the overlying atmosphere, which then transports the energy to the continental heat-sinks; the energy flows in the opposite direction during summer.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Climate (ISSN 0894-8755); 3; 15-31
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  • 10
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    Dynamically stratified Monte Carlo forecasting (1992)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: A new method for performing Monte Carlo forecasts is introduced. The method, called dynamic stratification, selects initial perturbations based on a stratification of the error distribution. A simple implementation is presented in which the error distribution used for the stratification is estimated from a linear model derived from a large ensemble of 12-h forecasts with the full dynamic model. The stratification thus obtained is used to choose a small subsample of initial states with which to perform the dynamical Monte Carlo forecasts. Several test cases are studied using a simple two-level general circulation model with uncertain initial conditions. It is found that the method provides substantial reductions in the sampling error of the forecast mean and variance when compared to the more traditional approach of choosing the initial perturbations at random. The degree of improvement, however, is sensitive to the nature of the initial error distribution and to the base state. In practice the method may be viable only if the computational burden involved in obtaining an adequate estimate of the error distribution is shared with the data-assimilation procedure.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Monthly Weather Review (ISSN 0027-0644); 120; 6, Ju; 1077-108
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