dc.description.abstract | In this analysis, we assess the accuracy of temperature forecasts for lead times of 0 to 7 days, issued daily by the Central Weather Bureau (CWB) for Taipei city during 2002-2005. The main purpose of this study is to understand the ability of weather forecasts for metropolis. Furthermore, we also collected weather predictions of other services in foreign countries for comparison, such as CNN, JWA, WMO and WN etc. The detail of skill score of temperature forecasts each month and the distribution of forecast errors were calculated. Besides, in order to find out if there is any correlation between the source of airstream and the ability of temperature forecasts for further evaluation of the existence of systematic errors in each season, we used a three-dimensional airstream IMS-Lagrangian model to analyze the origin of airstream’s trajectory and its distribution pattern in different cases of forecasts.
The result shows that the skill score of 1day forecasts of CWB are better than persistence at most, which means the 1day forecasts have skill. Comparison of skill score of each season shows that the skill score during winter time is the highest. During summer time the skill score is the lowest, especially in June. We also find that the skill score of maximum temperature forecasts is better for less lead times and the skill score of minimum temperature forecasts is better for longer lead times. The skill of forecasts of CWB is the best when comparing with other countries. Since the mean absolute forecast errors increase with lead time, therefore the range of the distributions of forecast errors are narrower for the early forecast days and broader for the later forecast days. The forecast errors were affected by the consistence of airstream’s origin.
After analyzing the trajectory distributions of higher and lower temperature air parcels, we discover that the origin and characteristic of air parcels are closely related to each other. If air parcels actually came from the colder region in the northwest of Mainland China, but forecasts may consider that its origin is from a warmer region instead, then the temperature will be overestimated; if air parcels actually came from east, southeast or south warmer air, but forecasts may consider that its origin is from the northwest colder region instead, then the temperature will be underestimated. And when the air parcels are rather stationary in the vicinity of Taiwan, or brought along by a southbound large scale weather system from the northwest, the characteristics of which can be easily to know well so the forecasts will be more accurate. | en_US |