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  • 1
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    Research on diabatic initialization (1990)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The objective of this research project is to contribute to improvement in the synoptic analyses in the tropics for numerical weather prediction and climate research. In addition to a prediction model, four dimensional data assimilation systems have two principal components. One is objective analysis and the other is initialization. Various methods of objective analysis are designed primarily to analyze the mass and rotational wind fields. Methods of initialization are developed to obtain the irrotational wind and its associated vertical velocity field which are balanced with the mass field and free from meteorological noise. There are essentially three approaches to the problem of initialization: quasi-geostrophic theory, bounded derivative method and nonlinear normal mode method. In the midlatitudes, these approaches generally produce satisfactory results even without diabatic effects for large-scale motions. In the tropics, the situation is quite different from that in the midlatitudes. Because of a small magnitude of the Coriolis parameter and a weak horizontal temperature gradient in the tropics, any method of initialization must incorporate diabatic effects. In fact, it can be said that understanding the problem of diabatic initialization is the key to improving the analysis and weather forecasting in the tropics.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: NASA, Marshall Space Flight Center, NASA(MSFC FY90 Global Scale Atmospheric Processes Research Program Review; p 13-17
    Format: application/pdf
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  • 2
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    Preliminary evaluation of diabatic heating distribution from FGGE level 3b analysis data (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A method is presented for calculating the global distribution of diabatic heating rate. Preliminary results of global heating rate evaluated from the European center for Medium Range Weather Forecasts Level IIIb analysis data is also presented.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: NAS-NRC Proceedings of the First National Workshop on the Global Weather Experiments, Vol. 2, Pt. 1; p 317-329
    Format: text
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  • 3
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    Numerical studies of major and minor stratospheric warmings caused by orographic forcing (1983)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: 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'.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of the Atmospheric Sciences (ISSN 0022-4928); 40; June 198
    Format: text
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  • 4
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    Numerical simulation of stratospheric sudden warmings with a primitive equation spectral model (1980)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A 26-level primitive equation spherical harmonic spectral model allowing for wave-wave and wave-zonal flow interactions is presented for the study of stratospheric sudden warmings. The warmings are simulated by the forcing of a single planetary wave at the tropopause. Four numerical experiments were performed. Nonlinear wave-wave interactions appear to play an important role in the evolution of the flow and temperature fields in the middle to upper stratosphere. In the case involving both wave-wave and wave-zonal flow interactions, this was manifested by the split in the initial polar vortex into a quasi-wave number 2 pattern. In the cases at 60 deg N, easterlies develop first in the upper mesosphere and descend gradually. About the same time or a little later, easterlies also develop in the mid-stratosphere. The linear cases exhibit warmings which are more shallow and more intense at 30 km than the nonlinear cases.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of the Atmospheric Sciences; 37; Dec. 198
    Format: text
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  • 5
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    Impact of cumulus initialization on the spinup of precipitation forecasts in the tropics (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: To ameliorate the precipitation spinup problem, i.e., the prediction model's inability to produce realistic precipitation rates at the beginning of the forecast period, the impact of a tropical initialization procedure on precipitation forecasts is examined. Attention is focused on the examination of the time behavior of precipitation rates and the closely associated variables of horizontal divergence and moisture during the first 42 time steps corresponding to 10.5 h. It is determined that the originally analyzed tropical divergence fields have realistic geographical distributions but there intensities seem to be too low by a factor of two.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Monthly Weather Review (ISSN 0027-0644); 120; 7 Ju
    Format: text
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  • 6
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    Estimates of tropical analysis differences in daily values produced by two operational centers (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: To assess the uncertainty of daily synoptic analyses for the atmospheric state, the intercomparison of three First GARP Global Experiment level IIIb datasets is performed. Daily values of divergence, vorticity, temperature, static stability, vertical motion, mixing ratio, and diagnosed diabatic heating rate are compared for the period of 26 January-11 February 1979. The spatial variance and mean, temporal mean and variance, 2D wavenumber power spectrum, anomaly correlation, and normalized square difference are employed for comparison.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Monthly Weather Review (ISSN 0027-0644); 120; 279-302
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  • 7
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    On the normal modes of Laplace's tidal equations for zonal wavenumber zero (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The characteristic differences between two different rotational modes of Laplace's tidal equations for wavenumber m = 0, called the K- and the S-modes, are compared in their energy ratio and structures. It is shown that the K-mode representation captures most of the observed zonal energy with a few terms, whereas the S-mode representation requires many terms. For small vertical scale components, the K-mode series converges faster than the S-mode series. Attention is also given to the differences between the energy spectra projected upon the K- and S-modes and the merits of each set as expansion functions for the zonal atmospheric motions.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Tellus, Series A - Dynamic Meteorology and Oceanography (ISSN 0280-6495); 44A; 18-32
    Format: text
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  • 8
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    Use of satellite radiometric imagery data for improvement in the analysis of divergent wind in the tropics (1988)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: A scheme is proposed to incorporate satellite radiometric imagery data into the specification of initial conditions for the National Meteorological Center (NMC) operational global prediction model in order to improve the analysis of the divergent wind field in the tropics. The basic assumptions are that outgoing longwave radiation (OLR) data can provide 1) the division between convective (upward motion) and clear sky (downward motion) areas, and 2) the height of convection cells. The intensity of ascending motion in the convective areas is estimated based on OLR data. The intensity of descending motion is evaluated from the thermodynamic energy balance between radiative cooling and adiabatic warming, since the local time change of temperature is small in the tropics. Once the vertical motion field is determined, the horizontal divergence field can be calculated from the mass continuity equation. Then a divergent wind field is determined. The total wind is the sum of the new divergent wind and the rotational part, which is assumed to be unchanged. The proposed scheme is tested using the NMC analysis dataset of 21 January 1985 with satisfactory results.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Monthly Weather Review (ISSN 0027-0644); 116; 866-883
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  • 9
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    Investigation of biogeophysical feedback on the African climate using a two-dimensional model (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: A numerical scheme is specifically designed to develop a time-dependent climate model to ensure the conservation of mass, momentum, energy, and water vapor, in order to study the biogeophysical feedback for the climate of Africa. A vegetation layer is incorporated in the present two-dimensional climate model. Using the coupled climate-vegetation model, two tests were performed involving the removal and expansion of the Sahara Desert. Results show that variations in the surface conditions produce a significant feedback to the climate system. It is noted that the simulation responses to the temperature and zonal wind in the case of an expanded desert agree with the climatological data for African dry years. Perturbed simulations have also been performed by changing the albedo only, without allowing the variation in the vegetation layer. It is shown that the variation in latent heat release is significant and is related to changes in the vegetation cover. As a result, precipitation and cloud cover are reduced.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Climate (ISSN 0894-8755); 3; 337-352
    Format: text
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