Zhang Bo, Zhao Bin. A spatial verification method for integrating wind speed and direction. J Appl Meteor Sci, 2019, 30(2): 154-163. DOI:  10.11898/1001-7313.20190203.
Citation: Zhang Bo, Zhao Bin. A spatial verification method for integrating wind speed and direction. J Appl Meteor Sci, 2019, 30(2): 154-163. DOI:  10.11898/1001-7313.20190203.

A Spatial Verification Method for Integrating Wind Speed and Direction

DOI: 10.11898/1001-7313.20190203
  • Received Date: 2018-10-22
  • Rev Recd Date: 2018-12-27
  • Publish Date: 2019-03-31
  • In traditional statistical analyses, the vector wind field is always verified by wind speed and wind direction separately. However, assessment results of wind speed are often contrary to those of wind direction, which then makes it difficult to obtain a uniform conclusion. To solve this problem, a novel selection scheme of wind speed thresholds is defined based on the probability distribution of wind speed, which is not affected by geographical and seasonal factors and it can keep universality in different complex environments. A vector wind classification is established based on integrating wind speed classes and wind directions. Using the spatial verification technique of fraction skill score (FSS), a vector wind verification method is developed by integrating wind speed and wind direction together. Based on hourly forecast products with different resolution (10 km and 3 km) simulated by GRAPES_Meso model from 1 April 2018 to 30 April 2018, assessment results show that the randomness of the wind direction forecast will decrease with the increasing of wind speed, which indicates it's difficult to predict the wind direction of weak wind speed successfully. By the comprehensive analysis of the vector wind field, it is found that the high-resolution (GRAPES_3 km) forecasting performance has a maximum score advantage of 0.24 on the 170 km spatial scale than the lower one (GRAPES_10 km). Scores in adjacent region are highly consistent, and it does not change the evolution of the score with the time series. And therefore, a comprehensive score can be calculated and used to assess the modelling performance by averaging skill scores in each spatial scale. In this way, deficiencies of artificial definitions of spatial scale can be avoided, which guarantee the spatial verification score of vector wind better practical application value. Simultaneously, different vector wind field classification methods have an impact on evaluation results. By sensitivity analysis, the higher wind classification method can make the score more stable with moderate wind classification one, and the magnitude of comprehensive scores are basically equivalent. The lower wind classification method has a relatively low overall score due to its single classification score weight, and it leads to the weak consistency with results of higher classification method. Therefore, under conditions of computing ability, choosing an encrypted wind direction classification to obtain a vector wind classification method will help to obtain a more stable verification result and improve the convergence and stability of the comprehensive evaluation.
  • Fig. 1  The definition of 17-class basic wind speed and direction

    Fig. 2  GRAPES_3 km 12-hour wind direction forecast change with observed wind speed initialed on 16 Apr 2018

    Fig. 3  Root mean square errors of wind speed and wind direction for 24-hour forecast from 1 Apr to 30 Apr in 2018

    Fig. 4  Hourly Fw for 36-hour forecast averaged from 1 Apr to 30 Apr in 2018 with GRAPES_10 km(a) and GRAPES_3 km(b)(the black line denotes Fw =0.5)

    Fig. 5  Fw of 24-hour forecast from 1 Apr to 30 Apr in 2018 with 170 km spatial scale

    Fig. 6  Fw for 24-hour forecast from 1 Apr to 30 Apr in 2018 with different spatial scales of 50 km(a), 90 km(b), 130 km(c), 330 km(d)

    Fig. 7  Fc for 24-hour forecast from 1 Apr to 30 Apr in 2018

    Fig. 8  Sample percentage of observation and forecasts in each basic wind class for 24-hour forecast initialed on 6 Apr 2018

    Fig. 9  The definition of 9-class(a) and 33-class(b) basic wind speed and direction

    Fig. 10  Hourly Fw for 36-hour forecast averaged from 1 Apr to 30 Apr 2018(the black line denotes Fw=0.5)

    Fig. 11  Daily Fc for 24-hour forecast from 1 Apr to 30 Apr in 2018

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    • Received : 2018-10-22
    • Accepted : 2018-12-27
    • Published : 2019-03-31

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