Editorial Type:
Article
Article Type:
Research Article

The Second–Generation Global Forecast System at the Central Weather Bureau in Taiwan

Chi–Sann Liou Central Weather Bureau, Taipei, Taiwan

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Jen–Her Chen Central Weather Bureau, Taipei, Taiwan

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Chuen–Teyr Terng Central Weather Bureau, Taipei, Taiwan

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Feng–Ju Wang Central Weather Bureau, Taipei, Taiwan

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Chin–Tzu Fong Central Weather Bureau, Taipei, Taiwan

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Thomas E. Rosmond Central Weather Bureau, Taipei, Taiwan

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Hong–Chi Kuo Central Weather Bureau, Taipei, Taiwan

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Chih–Hui Shiao Central Weather Bureau, Taipei, Taiwan

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Ming–Dean Cheng Central Weather Bureau, Taipei, Taiwan

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Print Publication:
01 Sep 1997
DOI:
https://doi.org/10.1175/1520-0434(1997)012<0653:TSGGFS>2.0.CO;2
Page(s):
653–663
Restricted access

Abstract

The global forecast system (GFS), which started its operation in 1988 at the Central Weather Bureau in Taiwan, has been upgraded to incorporate better numerical methods and more complete parameterization schemes. The second-generation GFS uses multivariate optimum interpolation analysis and incremental nonlinear normal-mode initialization to initialize the forecast model. The forecast model is a global primitive equation model with a resolution of 18 sigma levels in the vertical and 79 waves of triangular truncation in the horizontal. The forecast model includes a 1.5-order eddy mixing parameterization, a gravity wave drag parameterization, a shallow convection parameterization, a relaxed version of Arakawa–Schubert cumulus parameterization, grid-scale condensation calculation, and longwave and shortwave radiative transfer calculations with consideration of fractional clouds. The performance of the second-generation GFS is significantly better than the first-generation GFS. For two 3-month periods in winter 1995/96 and summer 1996, the second-generation GFS provided forecasters with 5-day forecasts where the averaged 500-mb height anomaly correlation coefficients for the Northern Hemisphere were greater than 0.6.

Observational data available to the GFS are much less than those at other numerical weather prediction centers, especially in the Tropics and Southern Hemisphere. The GRID messages of 5° resolution, ECMWF 24-h forecast 500-mb height and 850- and 200-mb wind fields available once a day on the Global Telecommunications System are used as supplemental observations to increase the data coverage for the GFS data assimilation. The supplemental data improve the GFS performance both in the analysis and forecast.

On leave from Naval Research Laboratory, Monterey, California.

On leave from Department of Atmospheric Sciences, National Taiwan University, Taipei, Taiwan.

Corresponding author address: Dr. Chi-Sann Liou, Naval Research Laboratory, 7 Grace Hopper Avenue, Monterey, CA 93943-5502.

liou@nrlmry.navy.mil

Abstract

The global forecast system (GFS), which started its operation in 1988 at the Central Weather Bureau in Taiwan, has been upgraded to incorporate better numerical methods and more complete parameterization schemes. The second-generation GFS uses multivariate optimum interpolation analysis and incremental nonlinear normal-mode initialization to initialize the forecast model. The forecast model is a global primitive equation model with a resolution of 18 sigma levels in the vertical and 79 waves of triangular truncation in the horizontal. The forecast model includes a 1.5-order eddy mixing parameterization, a gravity wave drag parameterization, a shallow convection parameterization, a relaxed version of Arakawa–Schubert cumulus parameterization, grid-scale condensation calculation, and longwave and shortwave radiative transfer calculations with consideration of fractional clouds. The performance of the second-generation GFS is significantly better than the first-generation GFS. For two 3-month periods in winter 1995/96 and summer 1996, the second-generation GFS provided forecasters with 5-day forecasts where the averaged 500-mb height anomaly correlation coefficients for the Northern Hemisphere were greater than 0.6.

Observational data available to the GFS are much less than those at other numerical weather prediction centers, especially in the Tropics and Southern Hemisphere. The GRID messages of 5° resolution, ECMWF 24-h forecast 500-mb height and 850- and 200-mb wind fields available once a day on the Global Telecommunications System are used as supplemental observations to increase the data coverage for the GFS data assimilation. The supplemental data improve the GFS performance both in the analysis and forecast.

On leave from Naval Research Laboratory, Monterey, California.

On leave from Department of Atmospheric Sciences, National Taiwan University, Taipei, Taiwan.

Corresponding author address: Dr. Chi-Sann Liou, Naval Research Laboratory, 7 Grace Hopper Avenue, Monterey, CA 93943-5502.

liou@nrlmry.navy.mil

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