潜热通量异常对西北太平洋热带气旋活动影响的机理研究

使用1958—2001年的中国气象局台风年鉴资料和欧洲中心再分析资料,初步揭示了潜热通量异常对西北太平洋(含南海)热带气旋活动的可能影响机理。统计分析发现,西北太平洋(含南海)热带气旋年频数与北太平洋副热带(简称关键区)的潜热通量在过去40余年中均表现为显著的减弱趋势。诊断分析表明,关键区的潜热通量通过低层信风向西的水汽输送—整个西北太平洋热带气旋活动区水汽低层辐合上升而凝结—潜热释放这一链条改变西北太平洋(含南海)大气环境场条件(包括中层湿度场、高低层涡度场和高低层散度场),进而调制热带气旋活动。使用SAMIL模式进行关键区内潜热通量加倍和减半的敏感性试验,进一步证实了关键区潜热通量异常对西北太平洋热带气旋活动调制作用的可能机理,而对南海热带气旋活动影响较小。由此可推断,在过去40余年中,北太平洋副热带中部区潜热通量的减弱趋势可能是造成西北太平洋(含南海)热带气旋频数下降的主要原因之一。

Mechanism for the role of latent heat flux variation on the activities of tropical cyclones in the western North Pacific

By using tropical cyclone data from China Meteorological Administration (CMA) and the ERA reanalysis data for the period of 1958—2001, a possible mechanism for the role of latent heat flux variation on the activities of TCs in the western North Pacific(WNP, including South China Sea) has been proposed. There exist significant decreasing trends in both the frequency of TCs in WNP(including SCS) and the latent heat flux in the key region-central subtropical North Pacific. Diagnostics suggest that latent heat flux in the key region may through a chain of latent heat flux-westward water vapor transportation at lower troposphere-water vapor converging, ascending and then condensing over the WNP(including SCS)-releasing latent heat-changing the atmospheric environment (including relative humidity in the middle troposphere, vorticity in the upper and lower troposphere, divergence in the upper and lower troposphere)-ultimately control the activities of WNP(including SCS) TCs. Modeling study by using SAMIL model further confirms the diagnostics results above and reveals that the activities of WNP TCs are very sensitive to the ocean-atmospheric interaction in the key region, while the activities of SCS TCs are less sensitive. It can be concluded at least tentatively that during the past more than 40 years the decreasing trend in the latent heat flux in the central subtropical North Pacific is one of the main reasons that cause the decreasing trend in the frequency of TCs in WNP(including SCS).