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台湾海峡区域格点分析风场极大值订正技术研究

Research on Correction Techniques for the Maximum Wind Speeds of the Gridded Analysis Data in the Taiwan Strait Region

  • 摘要: 中国气象局陆面数据同化系统(CLDAS)和高分辨率CLDAS(HRCLDAS)实况格点分析资料弥补了海面风观测稀疏的不足,然而其风速极大值与实际存在偏差,例如在狭管效应显著的台湾海峡区域普遍存在低估现象,其中CLDAS低估更严重,不能满足气象服务需求。因此本文提出一种基于地面站点观测风速二次融合的格点风场极大值订正技术,即采用反距离权重法将站点风速极大值观测周围一定影响半径区域内的站点风速观测插值到区域内的风场格点上,并综合考虑区域内风场误差和空间平滑程度以确定最优影响半径。利用2021-2023年CLDAS和HRCLDAS数据开展台湾海峡区域分区域(闽东、闽中及闽南渔场)风场极大值订正试验,结果表明:风场极大值订正技术能有效改进CLDAS和HRCLDAS对台湾海峡区域格点风速极大值低估情况,且HRCLDAS改进效果更优。HRCLDAS相较CLDAS出现小值最优影响半径频率增加。极值订正后,CLDAS和HRCLDAS逐小时平均绝对误差(MAE)降低率大多达到70-85%和90-95%;不同月份MAE降低率均超过60%,其中10月至次年1月订正效果最优,MAE降低率分别超过85%和90%;订正后误差空间分布与海岸线平行,自西向东减少,位于福建沿海及台湾海峡区域浮标站点区域MAE极值订正后降低至1m s-1以下。2305号台风“杜苏芮”和2023年1月23-25日典型冷空气大风过程的评估结果进一步表明,风场极大值订正技术对不同类别的大风过程均有效。

     

    Abstract: The China Meteorological Administration Land Surface Data Assimilation System (CLDAS) and the High Resolution CLDAS (HRCLDAS) provide gridded analysis datasets that compensate for the sparsity of in situ wind observations over sea. However, bias exists between their maximum wind speed estimates and observations, particularly in the Taiwan Strait region where the venturi effect is pronounced, leading to underestimations of maximum wind speeds. Notably, CLDAS exhibits a more severe underestimation, which may not satisfy the meteorological service requirements. To address the issue, this paper proposes a maximum wind speed correcting method based on the doubled fusion of wind speed in situ observations from automatic weather stations and buoy stations. It employs the inverse distance weighting (IDW) algorithm to interpolate the wind speed observations of stations to the grid points within the region centered by the location of the maximum speed, which optimal influence radius is determined by considering both wind field errors and spatial smoothness. By using this method, an experiment was conducted to correct the maximum wind speeds of the CLDAS and HRCLDAS in different sub - regions (Mindong, Minzhong and Minnan Fishing Grounds) of the Taiwan Strait region during 2021-2023. The results indicate that the correction method can effectively mitigates the underestimations of maximum wind speeds of gridded analysis data in the Taiwan Strait region for both CLDAS and HRCLDAS, with HRCLDAS showing a more significant improvement. Compared with CLDAS, the frequency of the optimal influence radius for small values increases in HRCLDAS. After correction, the hourly mean absolute errors (MAEs) for the CLDAS and HRCLDAS are mostly decreased by 70-85% and 90-95%. The reduction rates of MAEs exceed 60% in different months, especially exceeding 85% and 90% for CLDAS and HRCLDAS from October to January, respectively. Additionally, the spatial distribution of MAEs is parallel to the coastline, decreasing from west to east, with MAEs near the buoys along the Fujian coast reduced to below 1 m s-1 after correction. Furthermore, it is demonstrated that the correcting method is effective for different kinds of strong wind caused by Typhoon Doksuri (2023) and a typical cold tide occurred from January 23rd to 25th, 2023.

     

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