East Asia and Western Pacific METEOROLOGY AND CLIMATE

457
RMS errors for RO is relatively small, 2.0°C and 0.8°C for
the 24 hours and 12 hours respectively. Trend-wise, the afternoon peak
for the Hong Kong area is well predicted but not the sharp drop in
temperatures after 22 hours local time. The forecast values for GZ and
Macau are not so acceptable, both have RMS errors above 2.5°C. The
trend for Macau is however very close to the actual (the bias is large
but the std. dev. is only 0.3°C). The large discrepancies are due to
an inaccurate initial temperature field near the Macau area as attested
by the 3°C lower initial temperature. As for Guangzhou, the deviations
are likely to be the result of wrongly assumed solar condition
because Guangzhou was actually overcast for the day.
The results of the control run for RO and Macau are obviously
less accurate in comparison with the full simulation results.
However, to the contrary, results for GZ compares better with observation
which supports the finding in the last paragraph.
The VFM model outputs are plotted in Fig. 3a for comparison.
It has greater error values for the first 12 hours but decreases
towards the end of the period. The trend prediction is less successful.
To test the case further, another run was made using the
12-UTC upper air data of the same day as the initial data. Only the
results for RO are plotted here on Fig. 4 . The forecast results again
compares favourably with observations especially for the first 12
hours. Both the minimum and the maximum temperatures
degree of accuracy.
are within one
Fl«, 4.
(R.0.1:
Further Validation of Temperature Forecast at (A) the Royal Observatory Hong Kong
FIG. 4
CASE .3— P.O.