基于TIGGE资料的西太平洋热带气旋多模式集成预报方法比较

基于TIGGE资料中CMA、ECMWF、JMA和NCEP四中心2010、2011和2012年3年的资料,采用集合平均（EMN）、加权集合平均（WEMN）、消除偏差集合平均（BREM）和加权消除偏差集合平均（即超级集合,SUP）四种方法,对西太平洋地区热带气旋路径与中心气压进行时效为24、48、72、96和120 h的多模式集成预报,评估了不同单中心预报结果,并分析了不同多模式集成预报方法的特点,对比了不同多模式集成方法的效果。结果表明,对于热带气旋路径和中心气压预报,各中心预报技巧不同,其中3年的CMA预报效果均较差,2010、2011年的ECMWF预报和2012年的NCEP预报效果最优;总体上几种多模式集成方法在120 h预报时效内均优于单模式预报,其中EMN作为一种最简单的集成预报方法,具有一定的局限性,而WEMN由于给不同单模式预报赋予了权重,因此相对于EMN能够得到更好的多模式集成预报结果;BREM方案由于消除了模式预报中的系统性偏差,因此集成预报效果也优于EMN;由于去除了模式预报偏差,同时给不同模式赋予了权重,SUP方案得到的集成预报效果最优。     

天津地区城市热岛环流与海风环流相互作用的研究

利用中尺度数值模式（TJ WRF）模拟资料及天津加密自动气象站资料等,选取几个典型天气过程（城区附近局地强雷暴天气过程、受海风影响明显的无天气过程）个例,分析研究天津城市热岛环流与海风环流的空间结构特征及相互作用;重点对城市热岛环流与海风环流相互作用触发局地强雷暴的机制进行分析。结果表明：城市热岛环流的伸展高度基本在800 hPa 附近、空间范围约为20 km、环流内有弱的辐合上升;海风环流的伸展高度在800~750 hPa、空间范围40~60 km,海风环流前沿海风锋的伸展高度为950~900 hPa,垂直上升速度平均为0.2 m·s-1 ,略强于城市热岛环流。海风环流对城市热岛环流有明显消弱作用,城市热岛环流对海风环流有一定的阻挡作用,其阻挡的程度与城市热岛环流强度有关。随海风环流向内陆推进,海风环流与城市热岛环流相遇出现叠加,叠加后的辐合上升运动明显加强,最大上升速度可达0.6 m·s-1,并在不稳定天气形势条件下能触发局地强雷暴天气的出现。     

“2012.4.11”两个强降雹超级单体特征分析

利用常规气象资料、自动站资料、新一代天气雷达和风廓线雷达等资料,对一次强对流天气过程中两个强风暴单体的形势背景、强对流发生条件、强风暴单体演变及结构特征、风暴异同点进行了详细分析。结果表明：（1）本次强对流过程是发生在强的垂直风切变条件下;高层冷平流降温减湿、低层暖平流增温增湿的对流不稳定层结,高CAPE值为强对流发生发展提供了必要的能量条件;上干下湿的水汽分布有利于冰雹、雷暴大风的产生;适宜的0℃、－20℃层高度使此次过程地面以降雹为主;地面倒槽低压、辐合线及低层锋区的南压是这次强对流天气的触发因子。（2）两个强降雹单体雷达回波共同特征是降大雹前均出现了三体散射长钉回波,弱回波区,回波强度强,VIL密度均大于4 kg·m－3,成熟阶段均右偏高空风约30°。（3）长生命史超级单体风暴Ⅱ的中气旋维持2个多小时,它保证了一支强上升气流支撑空中大冰雹的增长,维持了雷暴的持续发展,使其生命史长达近6 h,同时也存在前侧、后侧入流缺口,反映了上升气流与下沉气流共存的风暴动力特征,其高层辐散更强,移动路径东略偏南且移向稳定,平均右偏高空风约28°,移速均匀为14 m·s－1;超级单体风暴Ⅰ的中气旋维持时间仅十几分钟,且处于弱中气旋的下限,其高层辐散和上升气流更弱,风暴生命史更短,移动路径东略偏北,除成熟阶段外右偏高空风10°～20°。这些差异与产生风暴的环境条件如垂直风切变、垂直涡度等存在差异有密切关系。     

Sensitivity of the warm core of tropical cyclones to solar radiation

To investigate the impacts of solar radiation on tropical cyclone (TC) warm-core structure (i.e., the magnitude and height), a pair of idealized simulations are conducted by specifying different strengths of solar shortwave radiation. It is found that the TC warm core is highly sensitive to the shortwave radiative effect. For the nighttime storm, a tendency for a more intense warm core is found, with an elevated height compared to its daytime counterpart. As pointed out by previous studies, the radiative cooling during nighttime destabilizes the local and large-scale environment and thus promotes deep moist convection, which enhances the TC's intensity. Due to the different inertial stabilities, the diabatic heating in the eyewall will force different secondary circulations. For a strong TC with a deeper vertical structure, this promotes a thin upper-level inflow layer. This inflow carries the lower stratospheric air with high potential temperature and descends adiabatically in the eye, resulting in significant upper-level warming. The Sawyer-Eliassen diagnosis further confirms that the height of the maximum temperature anomaly is likely attributable to the balance among the forced secondary circulations.     

Development mechanisms of an explosive cyclone over East Sea on 3–4 April 2012

The development mechanisms of the explosive cyclone that occurred during 3–4 April 2012 over East Sea (Sea of Japan) are examined through numerical simulation and sensitivity experiments using the Weather and Research Forecasting (WRF) model. The characteristics of this explosive cyclone are different from typical cyclonic features observed in this region, including its intensity, deepening rate, and formation time. Numerical simulation, reanalysis data, upper and surface weather charts, and satellite data indicate that the strong baroclinic instability and temperature advection associated with upper-level cut-off low and the interaction of potential vorticity (PV) anomalies between the lower- and upper-level are essential to explosive cyclogenesis.The sensitivity experiments of the explosive cyclone show that latent heat release (LHR) is an important factor in explosive cyclogenesis. The intensification, extent, and movement speed of the cyclone are amplified by LHR as well as the formation of an upper-level cut-off low. The role of LHR is primary important in the generation and evolution of the cyclone. Especially, the LHR contributes to roughly 50% of decrease in sea level pressure (SLP) and 50% of the central cyclone’s low-level PV generation in initial stage. During a 48-h simulation, the contributions of the LHR, surface heat flux, and their interaction on the decrease of SLP of the cyclone are found to be 40.6, −8.2, and 10.5%, respectively. These results reveal that the explosive cyclone has larger deepening rates than OJ cyclones, and develops with a large amount of LHR near the cyclone center.     

干湿交替下水分及氯离子在混凝土中传输的细观数值模拟

氯离子侵蚀已成为影响海洋及近海环境中混凝土结构耐久性的主要因素。考虑材料组成的非匀质特性,将混凝土看作由粗骨料、硬化水泥砂浆及二者界面过渡区组成的三相复合材料的细观层次方法,是开展物质传输过程研究的新途径。建立非饱和混凝土中氯离子传输的一维非线性对流扩散方程,并利用伽略金加权余数法给出了该方程的有限元形式,采用适用于物质传输的细观格构网络模型开展了水分及氯离子在非饱和混凝土中传输过程及分布规律研究,分析了干湿循环周期和循环机制对水分及氯离子传输性能的影响规律。数值计算结果表明,干湿交替下,相同的干燥时间,非饱和混凝土内水分及氯离子的侵入深度主要取决于湿润时间,而干燥时间和循环周期数则影响混凝土表层氯离子含量,并在混凝土表层10 mm处有浓度集中现象。     

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.     

云南哀牢山东侧一次突发性暴雨过程诊断分析

利用加密自动站资料、NCEP每6 h再分析资料和FY-2C红外TBB等资料,对2012年6月15日发生在哀牢山东侧突发性暴雨进行诊断分析。结果表明:700hPa切变线移到哀牢山后受滇缅脊和地形阻挡形成与山脉同向的切变线.地面冷锋移到哀山东侧后形成静止锋,受不断南下冷空气补充.形成冷空气下沉,暖湿气流上升,出现强烈的上升运动。切变线附近辐合云带内形成的中尺度对流云团在高空西北气流引导下产生的"列车效应"导致了突发性暴雨发生。来自东海和孟加拉湾水汽在切变线附近交汇,受切变线两侧风向辐合产生强烈的水汽辐合,并在哀牢山附近形成深厚的水汽辐合层,是本次突发性暴雨天气的主要水汽特征。逐小时地面自动站海平面气压场和对流有效位能在哀牢山沿线突发性暴雨发生前有明显变化,强降水主要发生在地面中尺度暖低压附近和对流有效位能高值区,此分析对此类短时强降水预报和预警具有一定指示意义。