2006年7—9月西北太平洋热带气旋季节活动的数值模拟

利用NCEP（National Centers for Environmental Prediction）提供的1°×1°的FNL（final）资料和中尺度WRF（Weather Research and Forecasting）模式,研究了热带气旋（tropical cyclone,简记TC）动力季节预报的可能性,通过在27km的粗网格中运用张弛逼近（Nudging）技术,对2006年7-9月西北太平洋TC活动进行了92d的连续数值积分。与观测结果比较表明,WRF模式不仅较好地模拟了MJO（Madden-Julian oscillation）和准双周振荡的活动情况,而且模拟的TC频数、移动路径和强度都与实际观测结果比较接近。在嵌套的9km网格中,不仅模拟出眼墙、暖心等TC结构的主要特征和TC的西行盛行路径及登陆活动情况,而且所模拟的生成过程包括早期研究中提出的TC生成过程中的两次快速发展的过程。模拟的TC初始涡旋主要出现在季风槽中,伴随准双周振荡活动,它的第一次发展在初始涡旋中心形成强烈的对流区;经过一段时间的减弱后,在有利的大尺度形势下,涡旋中心湿水汽层迅速增厚,导致气旋的第二次强烈发展。

Simulated seasonal activity of tropical cyclones over the western North Pacific during July-September 2006

To detect the dynamic prediction feasibility of tropical cyclone seasonal activities,a 92-d numerical integration of the WRF（Weather Research and Forecasting） mesoscale model is conducted with the National Centers of Environmental Prediction（NCEP） 1°×1° final（FNL） data as the initial and boundary conditions to simulate the tropical cyclone activity in the northern West Pacific basin during July-September 2006.In order to obtain relatively realistic large-scale circulation in the regional model,the nudging technique is used in the coarse domain with 27 km spacing.Compared with the NCEP reanalysis,the model can reasonably reproduce the Madden-Julian oscillation（MJO） and quasi-biweekly oscillation（QBWO）.The simulated tropical cyclone activity（including frequency,track and intensity） is fairly comparable to the observation.In the 9 km domain,together with the well-simulated tropical cyclone structure such as the eyewall and warm-core,the simulation well captures the westward prevailing tracks and landfall processes.Further analysis suggests that the model can also simulate the tropical cyclogenesis including a two-step development of the convection,as suggested in previous studies.The initial vortex appears around the monsoon trough,accompanied with cyclonic phase of the QBWO.In the first development process,the initial vortex evolves into an extremely convective core.After a short time decline,associated with the favorable large-scale circulation,the extremely convective area is compassed by the high humidity air,which causes the second development process.