An Ensemble Ocean Wave Forecast System and Preliminary Experiment

Sun Minghua

Vol.22, NO.6, 2011

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Sun Minghua. An ensemble ocean wave forecast system and preliminary experiment. J Appl Meteor Sci, 2011, 22(6): 673-680.

Citation:

Sun Minghua. An ensemble ocean wave forecast system and preliminary experiment. J Appl Meteor Sci, 2011, 22(6): 673-680.

Sun Minghua. An ensemble ocean wave forecast system and preliminary experiment. J Appl Meteor Sci, 2011, 22(6): 673-680.

Citation:

Sun Minghua. An ensemble ocean wave forecast system and preliminary experiment. J Appl Meteor Sci, 2011, 22(6): 673-680.

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An Ensemble Ocean Wave Forecast System and Preliminary Experiment

Sun Minghua^,

National Meteorological Center, Beijing 100081

Received Date: 2011-03-09
Rev Recd Date: 2011-08-03
Publish Date: 2011-12-31

Abstract

Abstract

The basic methods of ensemble wave prediction at home and abroad and an ensemble wave numerical forecast system are introduced. The system is established by running the operational wave model WAVEWATCH Ⅲ using wind data from the 15 members' ensemble weather forecast system, which is based on the T213L31 model and operational running in China National Meteorological Center. The ensemble model calculates 15 members wave field, including one control forecast and 14 perturbation members forecast. The model computes the waves over all the oceans up to 10 days at 12:00 with 1° by 1° resolution. Based on hot initialization, the model uses the 12 h wave hindcast as its initial field. Through the information extraction and processing from the 15 member's wave fields, the system produces the ensemble wave products such as ensemble mean and spread, spaghetti charts and probability charts. Forecast experiment for the period from 1 Sep to 31 Oct in 2007 is done using the system and buoys data in the Pacific and Atlantic at the same period. The main verifying indexes are bias and root mean square error. For the mean monthly bias of 10 m wind speed and significant wave height, the performance of the ensemble mean is better than the control forecast, however both of them have a relatively low system deviation and one cause is that the spin up time of the system may not be long enough. For the monthly root mean square error, the ensemble mean of 10 m wind speed is lower than the control forecast by 3—12 percentage for the different forecast periods, meanwhile the ensemble mean of significant wave height is lower than the control forecast by 3—17 percentage with consistent variation trend. Comparing 15 ensemble members' forecast to the Buoy_46006 data, it shows that the ensemble members can follow the changes of the observation well and cover the variation range of the observation other than the deterministic forecast. In summary, the verification results show that the ensemble technique can provide a successful method of extending the standard deterministic forecasts to the probabilistic domain and the prediction skill of the ensemble mean is better than that of one single deterministic forecast. The ensemble method could provide additional information that could not be gleaned from a purely deterministic approach and has a good prospect of application in the field of wave forecast.
- ensemble prediction;
- wave numerical forecast;
- WAVEWTCH Ⅲ;
- probability

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References(21)

Figures and Tables

Fig. 1 The products of the ensemble wave forecast system

(a) the 120-hour forecast of ensemble mean (solid line, unit: m) and spread (shaded) of significant wave height at 12:00 17 September 2007, (b) the 24-hour forecast of spaghetti chart of 10 m wind speed of 11.3 m·s^-1 at 12:00 18 September 2007, (c) the 72-hour forecast of probability chart of mean wave period larger than 11 s at 12:00 17 September 2007

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图 2 2007年9月10 m风速和有效浪高不同时效预报误差变化曲线

(a) 风速平均误差，(b) 有效浪高平均误差，(c) 风速均方根误差, (d) 有效浪高均方根误差

Fig. 2 The verification curves of 10 m wind speed and significant wave height in September 2007 (a) wind speed bias, (b) significant wave height bias, (c) root mean square error of wind speed, (d) root mean square error of significant wave height

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图 3 2007年10月10 m风速和有效浪高不同时效预报误差变化曲线

(a) 风速平均误差, (b) 有效浪高平均误差, (c) 风速均方根误差, (d) 有效浪高均方根误差

Fig. 3 The verification curves of 10 m wind and significant wave height in October 2007 (a) wind speed bias, (b) significant wave height bias, (c) root mean square error of wind speed, (d) root mean square error of significant wave height

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Fig. 4 Ensemble of 15 members vs observation data at Buoy_46006 forecast at 12:00 15 Oct 2007 (a)10 m wind speed, (b) significant wave height

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Table 1 Outline of the ensemble wave forecast models

参数	参考值
分辨率	1°× 1°
预报时效/h	240
输出间隔/h	6
天气模式	全球集合天气预报系统扰动预报成员
最小水深/m	25
总体积分步长/s	3600
波浪谱的方向分辨率	15°(24个方向)
频率分辨率	0.0418 Hz~0.4114 Hz, 间距为1.1 Hz, 25个频带

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Table 2 The list of pruducts of spaghetti charts

要素	间隔
有效浪高/m	1，2，4，6，8，10
风速/(m·s^-1)	5.5，8.0，10.8，17.2，24.5，32.7
平均浪周期/s	5，7，9，11，13，15

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