不同年代际背景下青藏高原积雪异常对西北太平洋台风活动的影响

As one of the most significant land forcing factors on the Tibetan Plateau (TP), snow cover plays an important role in the genesis and development of typhoon in the western north Pacific (WNP) by its thermal forcing. However, how the variation of the snow cover in the winter and spring on the TP modulates the typhoon activity in the WNP has not been studied comprehensively. Based on observed and multi-sensor remote sensing data products, this project aims to explore the remote influence of Tibetan Plateau snow cover on typhoon activity in the WNP under various decadal backgrounds via the East Asian summer monsoon system. In particular, the project will analyze the spatial characteristics and temporal variability of the WNP typhoon activity as well as key area of snow cover for the frequency of landfall typhoon in China associated with abnormal TP snow cover. The response of typhoon activity and the related environmental factors to abnormal TP snow cover is also investigated by numerical experiments. Finally, we will propose the processes and possible mechanisms of the TP snow cover modulate the typhoon activity in the WNP by theoretical analysis, data diagnoses, and numerical experiments. The studies of these problems are not only favorable for understanding the climate effect of snow cover and typhoon activity but also provide theoretical basis for improving the forecast skill of typhoon activity in the WNP.

作为青藏高原地表过程中最重要的因子之一，冬春积雪通过热力强迫影响台风生成和发展的背景场，但当前针对高原冬春积雪异常对台风活动的影响还缺乏系统的研究。本项目以东亚夏季风系统作为纽带，从多源积雪资料的诊断分析入手，考察不同年代际背景下青藏高原冬春积雪和西北太平洋台风活动的“隔季相关”关系，分析高原积雪异常对应台风活动的变化特征，揭示登陆中国台风频数对应的积雪关键区域及其年代际变化特征。在此基础上，利用区域气候模式，模拟台风活动及有关大尺度环境因子对青藏高原积雪异常的响应特征。最后，综合理论分析、资料诊断和数值试验的结果，揭示不同年代际背景下高原积雪异常对台风活动的影响及其机理。这些问题的研究不仅有助于我们深入认识高原积雪的气候效应和台风活动的气候特征，而且可以为提高西北太平洋台风活动气候预测水平提供科学依据。

本项目系统研究了不同年代际背景下青藏高原冬季积雪与西北太平洋台风活动的关系及其物理过程。首先诊断得到青藏高原冬季积雪密度的典型主分量模态及其对应时间序列，考察其与台风生成频数/位置、强度、生成/移动密度函数、持续时间以及环流指数等之间的时滞相关关系，同时探讨不同年代际背景下台风活动的异常特征。进一步，利用区域气候模式RegCM3模拟不同年代际背景下高原冬季积雪异常引起的台风活动及有关环流背景场的变化特征。通过研究发现，与气候态相比，第1多雪期对应台风在东侧生成偏多，台风生成之后途经广阔的海域使得强台风频数、ACE、MSW以及台风持续时间显著偏多；同时对应副热带高压在台风北方东退或断裂，台风在高压的西缘或裂口处转向北行，当绕到高压西北边缘，在西南风影响下，促进台风东北转向。高原冬季积雪偏少时，夏季整个西北太平洋均不利于台风形成和发展，尤其是在西北太平洋东南海域。第2多雪期，副高西伸并加强，其南侧的异常东风引导台风向西行进；同时，环境场有利于西北太平洋西南海域台风生成，对应东北转向路径偏少，台风尤其是弱台风频数偏少。该研究有助于更加深入的了解高原积雪的年代际变化特征及其对台风活动的影响机制，提高气候模式对西北太平洋台风活动的预测能力。