East Asia and Western Pacific METEOROLOGY AND CLIMATE

449
THE OPERATIONAL GLOBAL FORECAST SYSTEM AT CENTRAL WEATHER BUREAU
Chuen-Teyr Terng
Computer Center, Central Weather Bureau,
Taipei, China
ABSTRACT
Because of the limitations of subjective weather forecasting and
the advantages of numerical weather forecasting (NWP), the Central
Weather Bureau (CWB) has begun a five-year project to establish a NWP
system. Due to the fact that Taiwan is situated at the boundary of a
large continent (the Euro-Asia continent) and a large ocean (the
Pacific), and also the fact that Taiwan is located in the sub-tropical
region, being affected by different weather systems in winter and in
summer, four different NWP models are required. The four models are :
Global (for 5 to 7-day forecast and 4-D data assimilation), Regional
(for 2-day forecast and weather patterns of the Asian area), Mesoscale
(for 1 day forecast and weather patterns around Taiwan), and Typhoon
Track (tracking typhoon movements around Taiwan). Besides these
models, there is a control system, which automatically monitors the
entire system, and a data-acquisition system.
A super computer (CDC-205) and a computer for the front end (CDC-
840) were installed in CWB in December 1986. Beginning in July 1987,
the global model underwent testing and it was declarea operational in
July 1988. The global model composes of three parts : analysis,
initialization and forecasting. The objective analysis portion uses
FIB and Barnes's schemes for the analyses of sea-level surface
pressure and upper air mass and wind field.. The initialization scheme
uses variational method. The UCLA general circulation model forms the
basis of the forecasting part.
The procedure of the global model is as follows : The global
observations are transmitted to CWB through GWDI and JWA's satellite
network. The data are then decoded and error-checked by CWB's frontend
computer. The data are then transmitted to the super-computer for
sea-level surface pressure analysis, upper air mass field and wind
field analyses, and initialization, all on isobaric coordinates. The
data are next interpolated to sigma-coordinates. Forecasting
computations are performed as the next step. The forecast results are
interpolated back to isobaric coordinates and drawn as weather charts
for use by the forecasters.
With the advancement of numerical methods, the enlargement of
computer memory and the arrival of faster computers, NWP is facing
rapid improvements. In view of this, CWB is planning its 2nd
generation of NWP system. This includes the introduction of optimal
initialization, normal model initializationj spectral forecasting
model and more advanced physical parameterization. We hope that in the
near future, our forecasting capabilities can be compared with those
of the most advanced operational centers of the world.