冷空气入侵对0509号台风“麦莎”变性的作用

利用地面和高空的实况观测资料、NCEP／NCAR再分析资料以及FY-2C卫星云图资料,并通过中尺度Barnes滤波和物理量诊断分析,对台风“麦莎”变性过程进行研究。采用非静力平衡的中尺度模式MM5（V3．7）对“麦莎”北上变性,影响京津地区降水的全过程进行了60h模拟。结果表明：“麦莎”登陆北上过程中,西北侧冷空气先随着“麦莎”环流由北向南旋转,尔后冷空气又从台风低压中心的偏南侧向北侵入,逐步侵入“麦莎”暖心结构;在垂直方向上,对流层中高层不断有系统性的冷空气倾斜向下补充,冷空气从对流层低层侵入台风环流,最终使“麦莎”变性。在接近华北地区时,“麦莎”云系发生分裂,偏西侧云系的出现和发展与低层850hPa流场上中尺度辐合线的产生密切相关,其中冷空气的作用显著。     

台风麦莎渤海转向的可预报性研究

利用MM5模式研究了2005年第9号台风麦莎在渤海向东北转向路径的可预报性.试验用不同的积云参数化方案、不同的预报时效分别从确定性和集合预报角度对麦莎在渤海向东北方向的转向过程做了模拟.结果表明,麦莎在渤海的转向可预报时效为48小时左右.不同的积云参数化方案对台风麦莎路径的48小时预报结果显示台风均转向东北,预示麦莎 基本不会直接影响北京.60和72小时的预报结果显示,Kuo和Betts-Miller积云参数化方案的台风模拟路径与实况比较接近,而Grell和KeinFritch积云参数化方案的台风模拟路径却偏向了实际台风位置的西北,台风有可能直接影响北京.研究表明,对于台风麦莎而言,时效超过两天的转向预报可信度较低,Kuo和Betts-Miller积云参数化方案的预报准确性较高.     

雷达径向风速同化对台风麦莎模拟的影响

本文应用WRF-3DVAR系统同化多普勒雷达径向风速资料,并利用WRF模式对台风麦莎（2005年8月6日00时至7日00时）进行数值模拟,以此检验多普勒雷达径向风速资料在改进模式初始场及提高台风路径和降水预报准确度等方面的应用效果及意义,探讨不同同化时间间隔对同化效果的影响。通过对比同化试验和控制试验发现：雷达径向风速资料能通过调整初始风场结构,改进对台风结构的模拟,从而提高模式对台风麦莎的路径、强度和降水的模拟能力;雷达资料信号在进入模式后有一定的时效性,在一定程度上缩小同化时间间隔有助于提高同化效果。     

The Impact of Horizontal Resolution on the CNOP and on Its Identified Sensitive Areas for Tropical Cyclone Predictions

In this study,the impacts of horizontal resolution on the conditional nonlinear optimal perturbation (CNOP) and on its identified sensitive areas were investigated for tropical cyclone predictions.Three resolutions,30 km,60 km,and 120 km,were studied for three tropical cyclones,TC Mindulle (2004),TC Meari (2004),and TC Matsa (2005).Results show that CNOP may present different structures with different resolutions,and the major parts of CNOP become increasingly localized with increased horizontal resolution.CNOP produces spiral and baroclinic structures,which partially account for its rapid amplification.The differences in CNOP structures result in different sensitive areas,but there are common areas for the CNOP-identified sensitive areas at various resolutions,and the size of the common areas is different from case to case.Generally,the forecasts benefit more from the reduction of the initial errors in the sensitive areas identified using higher resolutions than those using lower resolutions.However,the largest improvement of the forecast can be obtained at the resolution that is not the highest for some cases.In addition,the sensitive areas identified at lower resolutions are also helpful for improving the forecast with a finer resolution,but the sensitive areas identified at the same resolution as the forecast would be the most beneficial.     

台风风神海上石油平台预报服务探讨

总结了在对台风风神数值预报失效,预报路径偏东的情况下,预报人员抓住天气形势的细微变化对路径及时修正,并紧密结合用户需求,以“全程跟进,及时沟通,急用户之所急”的高度责任心和服务态度,使海上石油平台1500人安全撤离,避免了人员伤亡和重大经济损失的服务过程。经研究发现：(1)“风神”偏西侧的强对流发展、地面负变压中心、中层正涡度中心、高层正散度中心的存在,以及云图北侧带状黑体区的形成均有利于“风神”西折;(2)在500hPa图上,“风神”前期西南部有一低压环流中心,后期东北侧高压坝形成,造成“风神”两次北翘。     

Impacts of Initial Conditions on Cloud-Resolving Model Simulations

Impacts of initial conditions on cloud-resolving model simulations are investigated using a series of sensitivity experiments. Five experiments with perturbed initial temperature, moisture, and cloud conditions are conducted and compared to the control experiment. The model is forced by the large-scale vertical velocity and zonal wind observed and derived from NCEP/Global Data Assimilation System （GDAS）. The results indicate that model predictions of rainfall are much more sensitive to the initial conditions than those of temperature and moisture. Further analyses of the surface rainfall equation and the moisture and cloud hydrometeor budgets reveal that the calculations of vapor condensation and deposition rates in the model account for the large sensitivities in rainfall simulations.     

The Impacts of Initial Perturbations on the Computational Stability of Nonlinear Evolution Equations

The impacts of initial perturbations on the computational stability of nonlinear evolution equations for non-conservative difference schemes and non-periodic boundary conditions are studied through theoretical analysis and numerical experiments for the case of onedimensional equations.The sensitivity of the difference scheme to initial values is further analyzed.The results show that the computational stability primarily depends on the form of the initial values if the difference scheme and boundary conditions are determined.Thus,the computational stability is sensitive to the initial perturbations.     

初始扰动对一次华南暴雨预报的影响的研究

本文选取了2006年华南前汛期的一次暴雨过程, 采用AREMv2.3中尺度数值模式进行数值模拟, 分别在模式初始场的物理量场 (温度场、 风场、 湿度场) 上加扰动, 分析不同物理量场上的扰动对降水预报的影响, 以及物理量预报误差和扰动能量的增长情况。同时, 通过本个例讨论误差增长与湿对流的关系, 扰动振幅对误差增长的影响和华南区域的中尺度降水的可预报性问题。数值试验结果表明: 初始时刻不同物理量场加实际振幅的正态分布的随机扰动时, 对降水的影响是不同的。对于24小时降水预报, 温度场对降水的影响最大。误差的增长与湿对流不稳定有着密切的关系。小尺度小振幅误差增长很快, 而且是非线性增长。这意味着短期的较小尺度降水的可预报性很小。与大振幅扰动相比, 小振幅扰动造成的误差较小。但是小振幅扰动的迅速发展, 很快就会对降水预报造成较大的影响。因此, 只能有限地提高预报质量, 而且由于扰动非线性增长很快, 在预报时间的提前上, 不会有太大的改善。     

启动对流的初始扰动对热带飑线模拟的影响

在中尺度数值模拟及数值预报中,正确的对流启动是模拟或预报是否取得成功的关键。作者针对一次热带海洋飑线过程,利用一个风暴尺度云分辨数值模式进行数值模拟,采用不同的初始扰动触发与启动对流发展,重点讨论这些不同启动对流的初始扰动对飑线演变、生命史及其成熟结构等模拟的影响。结果表明,初始扰动的结构、形态分布及其与环境场的不同配置对具有深对流的飑线生命史存在重要影响,而对飑线的成熟结构影响较小。     

我国台风灾害年景预评估方法初探

本文以热带气旋年潜在影响力指数(yearly tropical cyclone potential tmpact index,YTCPI)为纽带,初步探讨了我国台风灾害年景预评估方法,预评估检验结果显示,1991 2008年,除1996、1997和2004年预估年景偏轻外,其他年份均与实际年景相一致;2009—2013年独立样本预估结果显示,只有2009年没有预估正确;总体上可以看出借助YTCPI指数来预评估台风灾害年景是可行的。     

台风北冕 (0809) 数值预报敏感初始误差研究

基于WRF四维变分伴随模式建立数值预报敏感初始误差计算流程并对台风北冕 (0809) 进行了分析。结果表明:基于线性化近似的伴随敏感分析方法对台风系统在24 h内适用。构造敏感初始误差的参考系数存在一个合理的取值范围,参考系数取为0.08效果最好。在初始场中去除敏感初始误差能够有效减少预报误差,改善台风路径预报效果,依据24 h预报误差计算出的敏感初始误差订正对24 h后台风数值预报效果也有明显影响。另外,敏感初始误差分布在台风中心附近,伴随台风系统环流且各物理量分布形态相似。对流层下层和中上层的敏感初始误差均对数值预报效果有所影响,对流层中上层的作用略大于对流层下层。敏感初始误差中各物理量对数值预报改善的贡献各不相同,相对而言,风场的贡献最大。     

Impacts of a Large-scale Adaptive Blending Scheme for CMA-MESO on Regional Forecasts-A Case Study of Typhoon Haima

Large-scale atmospheric information plays an important role in the regional model for the forecasts of weather such as tropical cyclone (TC). However, it is difficult to be fully represented in regional models due to domain size and a lack of observation data, particularly at sea used in regional data assimilation. Blending analysis has been developed and implemented in regional models to reintroduce large-scale information from global model to regional analysis. Research of the impact of this large-scale blending scheme for the Global / Regional Assimilation and PrEdiction System (CMA-MESO) regional model on TC forecasting is limited and this study attempts to further progress by examining the adaptivity of the blending scheme using the two-dimensional Discrete Cosine Transform (2D-DCT) filter on the model forecast of Typhoon Haima over Shenzhen, China in 2016 and considering various cut-off wavelengths. Results showed that the error of the 24-hour typhoon track forecast can be reduced to less than 25 km by applying the scale-dependent blending scheme, indicating that the blending analysis is effectively able to minimise the large-scale bias for the initial fields. The improvement of the wind forecast is more evident for u-wind component according to the reduced root mean square errors (RMSEs) by comparing the experiments with and without blending analysis. Furthermore, the higher equitable threat score (ETS) provided implications that the precipitation prediction skills were increased in the 24h forecast by improving the representation of the large-scale feature in the CMA-MESO analysis. Furthermore, significant differences of the track error forecast were found by applying the blending analysis with different cut-off wavelengths from 400 km to 1200 km and the track error can be reduced less than by 10 km with 400 km cut-off wavelength in the first 6h forecast. It highlighted that the blending scheme with dynamic cut-off wavelengths adapted to the development of different TC systems is necessary in order to optimally introduce and ingest the large-scale information from global model to the regional model for improving the TC forecast. In this paper, the methods and data applied in this study will be firstly introduced, before discussion of the results regarding the performance of the blending analysis and its impacts on the wind and precipitation forecast correspondingly, followed by the discussion of the effects of different blending scheme on TC forecasts and the conclusion section.     

Impacts of Multigrid NLS-4DVar-based Doppler Radar Observation Assimilation on Numerical Simulations of Landfalling Typhoon Haikui (2012)

We applied the multigrid nonlinear least-squares four-dimensional variational assimilation(MG-NLS4DVar) method in data assimilation and prediction experiments for Typhoon Haikui(2012) using the Weather Research and Forecasting(WRF) model. Observation data included radial velocity(V_r) and reflectivity(Z) data from a single Doppler radar, quality controlled prior to assimilation. Typhoon prediction results were evaluated and compared between the NLS-4DVar and MG-NLS4DVar methods. Compar...     

FY-2G地表温度反演产品改变模式初值对一次台风暴雨模拟的影响

为探讨地表温度初始场在台风暴雨模拟中的重要性,以2015年第13号台风"苏迪罗"为例,分别用FY-2G卫星反演的陆表温度、海表温度产品替换NCEP资料初始场,进行数值模拟试验。对模拟结果进行分量级降水TS评分和预报正确率检验,并对比分析了各试验方案2 m温度场、感热通量和潜热通量场、900 h Pa流场和850 h Pa垂直速度场间的差异。结果表明:使用FY-2G卫星反演的陆、海表温度产品作模式初始场均能不同程度地改善降水模拟效果,但改善程度随时间降低,24 h后其改善作用已较小;陆表温度试验对小雨和中雨量级的预报质量均有提高,而海表温度试验仅提高了小雨量级的预报质量。进一步分析表明,陆表温度试验主要通过改善陆表温度初始场影响感热通量和潜热通量的分布,进而减小台风东北部低层温度正异常,使该区域气旋性环流减弱、垂直速度减小,有效抑制了虚假对流出现,最终达到改善降水预报质量的效果;海表温度试验原理与陆表温度试验类似,但对降水预报质量改善不明显,仅在广东南部沿海地区降水模拟效果较好。     

Assimilation of FY-3D MWTS-Ⅱ Radiance with 3D Precipitation Detection and the Impacts on Typhoon Forecasts

Precipitation detection is an essential step in radiance assimilation because the uncertainties in precipitation would affect the radiative transfer calculation and observation errors. The traditional precipitation detection method for microwave only detects clouds and precipitation horizontally, without considering the three-dimensional distribution of clouds.Extending precipitation detection from 2D to 3D is expected to bring more useful information to the data assimilation without using the a...