OPERATIONAL EXPERIMENTS AND ITS PERFORMANCE ANALYSIS OF
THE TROPICAL CYCLONE NUMERICAL MODEL (GRAPES_TCM)
1
1
2
2
Huang Wei Duan Yihong Xue Jishan Chen Dehui
1 Shanghai Typhoon Institute CMA, Shanghai 200030
2 Chinese Academy of Meteorological Science , Beijing 100081
Abstract
Based on the Global and Regional Assimilation PrEdiction System (GRAPES) developed
by CMA, an operational forecast system for tropical cyclones (TCs) over the West
Pacific Ocean (GRAPES -TCM) is established by Shanghai Typhoon Institute. The
horizontal resolution is set to 0.5°×0.5° and the forecast domain is 0°－50°
N, 90°-170°E. The initial fields data are taken from the NCEP/NCAR reanalysis data
including height, temperature, wind and humidity at a horizontal resolution of 1°
×1° and 17 levels in the vertical. A vortex relocation technique, which has a
positive effect on the TC track forecast, is used. Using the GRAPES-TCM system, a
series of 48 h hindcast experiments of TCs in 2002, 2003 and 48 h quasi
operational forecast experiments in 2004 are performed to evaluate the performance
of the system. The results of TC track experiments show that the GRAPES -TCM has
a satisfactory performance on TC track forecast, with an average 24 h distance error
over 2002-2004 of about 150 km, and a 48 h error of 250km. In comparison with Beijing
and Japan numerical forecasts, the quasi operational forecast results of 2004 by
the GRAPES_TCM is better than Beijing model forecast but worse than Japan model
forecast. The GRAPES_TCM has the ability to forecast northwestward and turning
tracks with an average 24 h and 48 h distance error of 157.1 km and 262.8 km for
northwestward tracks, and of 142.1 km and 242.4 km for turning tracks, respectively.
The case experiments for typhoon Rananim (0414) and Aere (0418) show that the
GRAPES_TCM has good performance on the prediction of landfall site of TCs, and it
forecasts the accurately landfall site for typhoon Rananim and a site of only one
grid point deviation for typhoon Aere. The tracks for stronger TCs are easier to
be forecasted in comparison with those of weaker TCs. The average 24 h and 48h
forecast distance errors of typhoon track by the GRAPES -TCM are only 111 km and
about 210 km, and the corresponding forecast errors for strong tropical cyclones
are 166.6
and 242.6 km, respectively. For tropical storm and even weaker
tropical cyclone, the average 24 h and 48 h forecast distance errors are 177 km
and 300 km, respectively. The average 24 h and 48 h forecast distance errors of abrupt
turning or speed catastrophe tropical cyclone are close to 280 km and about 300 km,
respectively, which are much larger than those of the total average. Some experiments
with a 0.25°×0.25° grid resolution are also performed to examine the effect of
resolution on the track forecast of TC. The experiment results with the higher
resolution show that increase in the resolution of the model does improve the
performance of track forecast after 30 h although there is little difference before
24h between forecast results by the higher and lower resolution models. The mean
48h forecast distance error of TCs in 2004 by the higher resolution GRAPES_TCM is
less than 200 km which is about 50 km less than that by the lower resolution system.
Key words: GRAPES, Track-forecast, Tropical cyclone.