超强台风“利奇马”(1909)近海路径预报误差的关键影响机制*

Mechanism influencing forecast errors of the nearshore track of super typhoon Lekima (1909)

  • 摘要: 尽管台风路径和强度的数值预报已取得显著进展,但依然难以满足业务预报的需求。资料和方法利用高分辨率中尺度数值预报模式WRF,通过不同的模式初值、起报时间和微物理参数化方案的8组组合试验,揭示模式初值对台风“利奇马”(1909)路径预报的敏感性,并将最大和最小路径误差的模拟结果作为代表性试验,构建了改进模式初值的敏感性试验,目的以此进一步研究不同模式初值导致台风路径预报差异的影响机制。结果与结论结果表明:西北太平洋副热带高压(简称“副高”)强度和范围的准确预报对台风路径的预报质量起着重要作用,初始场中副高偏强将导致模式预报的副高偏强,致使台风沿副高西移、北上受阻且移速偏慢,从而导致路径预报误差显著。其次,台风移动路径与不同阶段台风内核结构的预报误差密切相关,而大尺度环流形势背景下的垂直风切变可能是导致这一误差的重要原因。此外,副高范围和强度偏大,台风中心附近水平风速非对称分布为对流触发提供有利条件,进一步使得台风强度增大,是模拟台风移速偏慢的重要原因。

     

    Abstract: Although significant progress has been made in numerical forecasting of typhoon tracks and intensity, meeting the needs of operational forecasting remains challenging. Based on the high-resolution Weather Research and Forecasting (WRF) model, eight sets of combination experiments are conducted with different model initial conditions, initialization times, and microphysical parameterization schemes. The results indicate that model initial conditions exhibit the highest sensitivity in forecasting the track of typhoon Lekima (1909). Representative experiments are selected based on track errors, and sensitivity experiment is conducted to further explore the mechanisms responsible for significant differences in typhoon track forecasts arising from different model initial conditions. The results indicate that the accurate forecasting of the strength and extent of the Western North Pacific subtropical high (SH) plays a crucial role in determining the quality of typhoon track predictions. An overestimation of the SH in the initial field leads to the stronger predicted SH, results in westward movement of the typhoon being blocked along the SH and its northward progression slowed. This leads to significant errors in track forecasting of typhoon. Additionally, the forecast errors in the typhoon’s inner core structure at different stages are related to the predicted typhoon track. The vertical wind shear in the large-scale circulation field may be a significant factor contributing to this error. Moreover, an overestimation of the SH’s extent and intensity leads to deeper asymmetric distribution of horizontal wind speeds near the typhoon, which contributes to the occurrence and development of deep convection. This is an important reason for the slower moving speed of the typhoon.

     

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