赣江流域TRMM遥感降水对地面站点观测的可替代性

多卫星遥感降水产品为无/缺资料地区的水文过程模拟提供了新的数据来源。结合地面高密度雨量站网,在中国典型暴雨区赣江流域定量评估两种TRMM降水产品(3B42V7和3B42RTV7)的精度,并通过耦合分布式水文模型CREST,探讨了水文模拟中TRMM卫星降水产品对地面观测降水的可替代性。研究表明:3B42和3B42RT与地面观测流域平均月降水相关系数达到0.9以上,偏差在5%以内,日尺度上相关性略差,偏差略有增加。同时设计2种水文模拟对比试验:情景I为静态参数,使用地面雨量站降水率定模型参数,采用卫星降雨验证模型;情景II为动态参数,采用卫星数据重新率定模型参数,再利用卫星降雨验证模型。对比结果表明:情景II中完全使用TRMM降水后模型效果明显改善,证明TRMM卫星数据在赣江流域具有替代地面站点观测的潜力,但需要重新根据卫星降雨率定模型。     

一次持续大暴雨过程新一代天气雷达回波特征分析

为探讨西北地区东部的持续大暴雨过程成因及预警指标,利用2010年7月22~23日500~700hPa大气环流背景及天气影响系统和西峰新一代多普勒天气雷达回波资料分析,结果得到:500hPa西太平洋副热带高压外围河套地区环境场的演变高压外围低涡发展及维持,是这次持续性大暴雨过程的大气环流背景和影响天气系统,700hPa强盛的水汽场输送场与汇聚作用为这次持续性大暴雨过程提供了充沛的水汽条件,随着500hPa河套地区低涡-切变辐合系统的准静止维持造成这次持续性大暴雨过程;大暴雨前1.5~9.7km垂直方向上,存在明显的东南风场与西南风场的切变,风向随高度顺转,对应持续的暖平流;天气雷达强度回波反射率因子≥40dBz,暴雨期间维持少变;径向速度回波的水平辐合和气旋性涡旋运动与河套低涡切变天气系统对应一致;垂直液态水含量≥35kg.m2的雨团范围大、持续时间长;云顶回波高度维持在8km以上,对监测预警持续大暴雨天气具有一定指示意义。     

Impacts of the Lowest Model Level Height on Tropical Cyclone Intensity and Structure简

Variable thicknesses in the lowest half-ηmodel level （LML） are often used in atmospheric models to compute surface diagnostic fields such as surface latent and sensible heat fluxes.The effects of the LML on simulated tropical cyclone （TC）evolution were investigated in this study using the Weather Research and Forecasting （WRF） model.The results demonstrated notable influences of the LML on TC evolution when the LML was placed below 12 m.The TC intensification rate decreased progressively with a lowering of the LML,but its ultimate intensity change was relatively small.The maximum 10-m winds showed different behavior to minimum sea level pressure and azimuthally-averaged tangential winds,and thus the windpressure relationship was changed accordingly by varying the LML.The TC circulation was more contracted in association with a higher LML.Surface latent heat fluxes were enhanced greatly by elevating the LML,wherein the wind speed at the LML played a dominant role.The changes in the wind speed at the LML were dependent not only on their profile differences,but also the different heights they were taken from.Due to the enhanced surface heat fluxes,more intense latent heat release occurred in the eyewall,which boosted the storm＇s intensification.A higher LML tended to produce a stronger storm,and therefore the surface friction was reinforced,which in turn induced stronger boundary layer inflow together with increased diabatic heating.     

Can Adaptive Observations Improve Tropical Cyclone Intensity Forecasts?简

In order to investigate whether adaptive observations can improve tropical cyclone （TC） intensity forecasts,observing system simulation experiments （OSSEs） were conducted for 20 TC cases originating in the western North Pacific during the 2010 season according to the conditional nonlinear optimal perturbation （CNOP） sensitivity,using the fifth version of the PSU/NCAR mesoscale model （MM5） and its 3DVAR assimilation system.A new intensity index was defined as the sum of the number of grid points within an allocated square centered at the corresponding forecast TC central position,that satisfy constraints associated with the Sea Level Pressure （SLP）,near-surface horizontal wind speed,and accumulated convective precipitation.The higher the index value is,the more intense the TC is.The impacts of the CNOP sensitivity on the intensity forecast were then estimated.The OSSE results showed that for 15 of the 20 cases there were improvements,with reductions of forecast errors in the range of 0.12％-8.59％,which were much less than in track forecasts.The indication,therefore,is that the CNOP sensitivity has a generally positive effect on TC intensity forecasts,but only to a certain degree.We conclude that factors such as the use of a coupled model,or better initialization of the TC vortex,are more important for an accurate TC intensity forecast.     

2009—2013年中国西南地区连续干旱的成因分析

提2009年以来,中国西南地区连续4年秋、冬、春季出现严重干旱,持续时间长、影响范围大、干旱程度重,给旱区农林业生产和人民生活带来严重影响,造成巨大的经济损失。本文利用多种资料从大尺度大气环流、水汽输送、太平洋及印度洋海温、平流层极涡等方面分析了此次连续干旱的原因。结果表明：南支槽强度偏弱、孟加拉湾水汽输送偏少以及弱极涡背景下,异常波活动造成的 AO 负异常引起的冷空气路径偏东是这4年持续干旱的共同特点。热带海表温度的异常变化对西南地区干旱的影响也不容忽视,主要表现在对孟加拉湾和南海水汽输送的阻碍上。La Nina 事件中,热带印度洋冬、春季海表温度的异常变化对干旱影响更为突出。冬、春季平流层和对流层的动力耦合作用结果使得 AO 位相发生变化,其中异常负位相的强度及持续时间对这4年西南地区秋、冬、春连旱的影响显著。     

登陆广东北上路径热带气旋强降水的分布特征

利用1981-2018年中国气象局上海台风研究所热带气旋最佳路径资料和国家基本气象站逐日降水资料,对登陆广东北上路径热带气旋活动及强降水特征进行统计分析.结果表明北上热带气旋从登陆时到登陆后48 h是陆地强降水产生的集中时段,登陆时24 h是陆地大暴雨最集中的时段.强降水从沿海向内陆逐渐减少,一般登陆后热带气旋持续时间...     

Tides and Wind-Driven Circulation in the Tropical and Southern Atlantic Ocean:The BRAZCOAST System

The Brazilian coast is characterized by dif- ferent tidal regimes and distinct meteorological influ- ences. The northern part has larger tidal amplitudes and is permanently affected by trade winds and tropical distur- bances; the southern portion has smaller tidal amplitudes and is frequently influenced by extratropical cyclone ac- tivity. Besides these aspects, many features regarding current structure and behavior are also present, such as the equatorial system of currents, the subtropical gyre and the corresponding western boundary currents, and the Bra- zil-Malvinas confluence region. Within this context, ef- forts were made to develop the BRAZCOAST system, capable of describing the processes that determine the oceanic circulation from large to coastal scales. A cus- tomized version of the Princeton Ocean Model （POM） was implemented in a basin-scale domain covering the whole of the tropical and southern Atlantic Ocean, with 0.5° spatial resolution, as well as three nested grids with （1/12）° resolution covering the different parts of the Bra- zilian shelf, in a one-way procedure. POM was modified to include tidal potential generator terms and a par- tially-clamped boundary condition for tidal elevations. The coarse grid captured large-scale features, while the nested grids detailed local circulations affected by bathymetry and coastal restrictions. An interesting aspect at the coarse grid level was the relevance of the Weddell Sea to the location of the tidal amphidromic systems.     

一个区域海-气耦合模式的建立:模式验证及其对热带气旋“云娜”的模拟

本文以区域热带气旋模式(GRAPES-TCM)为基础,引入海洋环流模式(Estuarine,Coastal and Ocean Model(semi-implicit),ECOM-si)和Ocean Atmosphere Sea Ice Soil 3(OASIS3)耦合器,建立了一个区域海-气耦合模式。利用该模式对0414号热带气旋"云娜"进行了数值模拟,验证了模式的性能。结果表明,耦合模式模拟的"云娜"强度相比单独的大气模式更接近观测,单独大气模式模拟的近地面风场偏强,而耦合模式模拟的近地面风场的强度和非对称结构均与观测更为接近。数值实验中,"云娜"热带气旋过境引起的海表面温度的下降与实况接近,海表面温度下降引起的海-气热通量相比控制实验的结果明显下降,分析资料表明这一下降是合理的。海洋模式的引入导致了热带气旋"云娜"结构的变化,这种变化不但反应在径向风的减弱(强度下降),还反应在对流强度和最强对流发生位置的变化,并最终引起了热带气旋降水结构的改变。     

论IPCC-AR4模式对影响西北太平洋热带气旋的大气动力环境场的气候特征模拟性能

评估了23个IPCC-AR4模式在低纬地区1948—1999年7—9月大尺度环流场的模拟性能,重点关注西北太平洋区域的西太副高、季风槽以及台风活动海域的垂直风切变。结果显示,绝大多数模式的7—9月低纬地区500hPa平均高度场、850hPa风场空间分布与NCEP都具有很高的相似性,但大多模式500hPa高度场存在系统性偏低,而850hPa风场偏强。所有模式模拟的西北太平洋副高脊线与NCEP都有一致的西南-东北走向,但有些模式的脊线位置偏离NCEP的较远。有4个模式没有模拟出类似于NCEP的季风槽线。综合模式对夏季热带环流场、西北太平洋副热带高压、季风槽以及西北太平洋热带气旋活动关键区域垂直风切变气候特征的模拟性能,按性能优劣,排在前10的模式依次是mpi_echam5、cccma_t63、gfdl_cm2_1、cnrm_cm3、cccma_t47、ukmo_hadgem1、ingv_echam4、ncar_ccsm3_0、csiro_mk3_5、mri_cgcm2_3_2a;排在后6位的模式是inmcm3_0、iap_fgoals1_0_g、ipsl_cm4、miroc3_2_medres、giss_eh、giss_er。     

利用TMI反演的水汽凝结物对热带气旋潜热结构分布的探索研究

本文利用热带测雨卫星TRMM（Tropical Rainfall Measuring Mission）微波成像仪TMI（TRMM Microwave Imager）2A12 水汽凝结物（Hydrometeor）反演资料,对西北太平洋地区从1998～2009 年的236 个热带气旋个例的1776 个“快照”（snapshot）的水汽凝结物的结构特征进行了分析,并探讨了水汽凝结物的时空变化与热带气旋强度演变联系。研究结果表明:（1）TMI 2A12 水汽凝结物资料显示出了热带气旋内部的细致结构及变化特征,水汽凝结物的峰值集中于数十公里到一百多公里的热带气旋眼壁及云墙区;在热带气旋发展过程中,随着热带气旋强度的增强,水汽凝结物增多且往其中心靠拢,从发展阶段到成熟阶段,水汽凝结物的大值中心基本上集中在距离热带气旋中心约50 km 区域,而且强度越强的热带气旋,水汽凝结物的大值中心与热带气旋中心的距离越近;在热带气旋消亡的过程中,水汽凝结物不断减弱且往外围扩散,逐渐扩展到远离中心的区域;（2）热带气旋强度与水汽凝结物的分布关系密切,热带气旋强度变化与热带气旋中心附近200 km 范围内的水汽凝结物含量存在显著的正相关,而200 km 以外的外围水汽凝结物含量存在负相关;（3）热带气旋强度变化与水汽凝结物的变化存在时间差,水汽凝结物的变化超前于热带气旋强度的变化,在热带气旋迅速发展之前数小时,热带气旋中心0～50 km 环状区域的水汽凝结物含量就已经提前增加了,在热带气旋减弱前数小时到十数小时,即使热带气旋还处于它强度的鼎盛时期,其中心0～50 km 环状区域的水汽凝结物含量就已经提前显著减少了,这种水汽凝结物的变化超前于热带气旋强度的变化的现象,可能是热带气旋强度预报的潜在线索。