TAMDAR Observation Assimilation in WRF 3D-Var and Its Impact on Hurricane Ike (2008) Forecast

This study evaluates the impact of atmospheric observations from the Tropospheric Airborne Meteorological Data Reporting (TAMDAR) observing system on numerical weather prediction of hurricane Ike (2008) using three-dimensional data assimilation system for the Weather Research and Forecast (WRF) model (WRF 3D-Var). The TAMDAR data assimilation capability is added to WRF 3D-Var by incorporating the TAMDAR observation operator and corresponding observation processing procedure. Two 6-h cycling data assimilation and forecast experiments are conducted. Track and intensity forecasts are verified against the best track data from the National Hurricane Center. The results show that, on average, assimilating TAMDAR observations has a positive impact on the forecasts of hurricane Ike. The TAMDAR data assimilation reduces the track errors by about 30 km for 72-h forecasts. Improvements in intensity forecasts are also seen after four 6-h data assimilation cycles. Diagnostics show that assimilation of TAMDAR data improves subtropical ridge and steering flow in regions along Ike’s track, resulting in better forecasts.     

风垂直切变对飓风波尼（1998）结构与强度的影响

利用大西洋飓风波尼(1998)的MM5模拟资料(格点距4 km),对在风的垂直切变影响下,波尼的结构和强度变化进行了分析.在风的垂直切变影响下,波尼的垂直速度和降水场表现出了明显的1波非对称结构,这种结构与风的垂直切变的强度呈正比;逆切变一侧9-12 km高度上通风作用强烈,在破坏波尼暖心的同时,也导致了边界层中低相当位温对波尼核心的入侵,与低层通风路径相比,中层通风对波尼的破坏作用更甚,鉴于在分析时间段内,波尼所经海域平均海温变化不大,可以认为风的垂直切变主导了波尼强度变化;对波尼强度突变现象的分析发现,强度突变源于通风破坏作用的积累,当边界层中低相当位温侵入热带气旋中心的程度超过某一阈值时,气旋强度会突然减弱;其结果显示风的垂直切变造成的动力和热力效应对热带气旋强度的影响都十分重要,而后者更为直接.     

The Impact Cooling of the Storm-Induced SST on Hurricane Intensity

The effects of storm-induced sea surface temperature （SST） cooling on hurricane intensity are investigated using a 5-day cloud-resolving simulation of Hurricane Bonnie （1998）. Two sensitivity simulations are performed in which the storm-induced cooling is either ignored or shifted close to the modeled storm track. Results show marked sensitivity of the model-simulated storm intensity to the magnitude and relative position with respect to the hurricane track. It is shown that incorporation of the storm-induced cooling, with an average value of 1.3℃, causes a 25-hPa weakening of the hurricane, which is about 20 hPa per 1℃ change in SST. Shifting the SST cooling close to the storm track generates the weakest storm, accounting for about 47% reduction in the storm intensity. It is found that the storm intensity changes are well correlated with the air-sea temperature difference. The results have important implications for the use of coupled hurricane-ocean models for numerical prediction of tropical cyclones.     

飓风Bonnie发生发展过程中的强度结构变化和惯性稳定度分析

利用MM5高分辨率数值模式模拟飓风Bonnie(1998)的资料,根据风垂直切变随时间的变化,将飓风Bonnie的发生、发展划分为3个阶段;在不同阶段中,通过分析飓风结构和强度的变化,研究其惯性稳定度的演变。结果表明,Bonnie在发生发展过程中具有很强的非对称性,并出现眼墙替换过程。在飓风结构发展中,较高的惯性稳定度发展与风暴的内核尺度发展一致;高惯性稳定度区提供抗径向运动,主要出现在主眼墙附近和内部区域,高惯性稳定度区的建立致使Rossby变形半径减小,风垂直切变影响减小,使得潜热释放集中于该区,有利于飓风加强,这是飓风内核发展的一个重要因素。     

The Impact of the Storm-Induced SST Cooling on Hurricane Intensity

The effects of storm-induced sea surface temperature (SST) cooling on hurricane intensity are investigated using a 5-day cloud-resolving simulation of Hurricane Bonnie (1998). Two sensitivity simulations are performed in which the storm-induced cooling is either ignored or shifted close to the modeled storm track. Results show marked sensitivity of the model-simulated storm intensity to the magnitude and relative position with respect to the hurricane track. It is shown that incorporation of the storm-induced cooling, with an average value of 1.3℃, causes a 25-hPa weakening of the hurricane, which is about 20 hPa per 1℃ change in SST. Shifting the SST cooling close to the storm track generates the weakest storm, accounting for about 47% reduction in the storm intensity. It is found that the storm intensity changes are well correlated with the air-sea temperature difference. The results have important implications for the use of coupled hurricane-ocean models for numerical prediction of tropical cyclones.     

Numerical Simulation of the Rapid Intensification of Hurricane Katrina(2005):Sensitivity to Boundary Layer Parameterization Schemes

Accurate forecasting of the intensity changes of hurricanes is an important yet challenging problem in numerical weather prediction. The rapid intensification of Hurricane Katrina(2005) before its landfall in the southern US is studied with the Advanced Research version of the WRF(Weather Research and Forecasting) model. The sensitivity of numerical simulations to two popular planetary boundary layer(PBL) schemes, the Mellor–Yamada–Janjic(MYJ) and the Yonsei University(YSU) schemes, is investigated. It is found that, compared with the YSU simulation, the simulation with the MYJ scheme produces better track and intensity evolution, better vortex structure, and more accurate landfall time and location. Large discrepancies(e.g.,over 10 hPa in simulated minimum sea level pressure) are found between the two simulations during the rapid intensification period. Further diagnosis indicates that stronger surface fluxes and vertical mixing in the PBL from the simulation with the MYJ scheme lead to enhanced air–sea interaction, which helps generate more realistic simulations of the rapid intensification process. Overall, the results from this study suggest that improved representation of surface fluxes and vertical mixing in the PBL is essential for accurate prediction of hurricane intensity changes.     

谱模式中截断方式对月长期天气预报影响的数值研究

以１９９２－０４－０１Ｔ１２（ＧＭＴ）北京国家气象中心的客观分析资料为初始场,通过对比分析ＣＣＭ１（Ｒ１５Ｌ７）模式的月数值预报结果,研究了谱模式在不同截断方式下,水平分辨率及网格结构分地月长期烽值预报的影响。结果表明：虽然以上两模式具有相同的垂直结构,以及相近的高斯网格格点数和计算量,但由于Ｒ１５Ｌ７较Ｔ２１Ｌ７有更为合理的水平分辨率分布,具有由高纬长方形（长轴为南北向）经中纬正方形到低纬长方形     

数值模式垂直分辨率对台风大涡模拟的影响

随着计算能力的提升,台风数值模拟大量采用了大涡尺度模拟,其水平分辨率已达到数10 m的量级,而垂直分辨率提升不大,其问题是数值模式的垂直分辨率对台风大涡模拟的影响如何?因此,本文利用WRF(Weather Research and Forecasting)模式开展理想台风模拟,在不同的模式垂直层次(42,69和90层)...     

An Overview of Nowcasting Development, Applications, and Services in the Hong Kong Observatory

The Hong Kong Observatory （HKO） has been developing a suite of nowcasting systems to support op- erations of the forecasting center and to provide a variety of nowcasting services for the general public and specialized users. The core system is named the Short-range Warnings of Intense Rainstorm of Localized Systems （SWIRLS）, which is a radar-based nowcasting system mainly for the automatic tracking of the movement of radar echoes and the short-range Quantitative Precipitation Forecast （QPF）. The differential, integral （or variational）, and object-oriented tracking algorithms were developed and integrated into the nowcasting suite. In order to predict severe weather associated with intense thunderstorms, such as high gust, hail, and lightning, SWIRLS was enhanced to SWIRLS-II by introduction of a number of physical models, especially the icing physics as well as the thermodynamics of the atmosphere. SWIRLS-Ⅱ was further enhanced with non-hydrostatic, high resolution numerical models for extending the forecast range up to 6h ahead. Meanwhile, SWIRLS was also modified for providing nowcasting services for aviation community and specialized users. To take into account the rapid development of lightning events, ensemble nowcasting techniques such as time-lagged and weighted average ensemble approaches were also adopted in the nowcasting system. Apart from operational uses in Hong Kong, SWIRLS/SWIRLS-Ⅱ was also exported to other places to participate in several international events such as the WMO/WWRP Forecast Demon- stration Project （FDP） during the Beijing 2008 Olympics Games and the Shanghai Expo 2010. Meanwhile, SWIRLS has also been transferred to various regional meteorological organizations for establishing their nowcasting infrastructure. This paper summarizes the history and the technologies of SWIRLS/SWIRLS-Ⅱ and its variants and the associated nowcasting applications and services provided by the HKO since the mid 1990s.     

热带高分辨率模式(TRAMS-V3.0)技术方案及其系统预报性能

在原模式版本TRAMS-V2.0的基础上,通过对三维静力参考大气、拉格朗日矢量投影、云降水物理和辐射等技术方案进行改进,并且针对高分辨率模式易产生强垂直运动和小尺度扰动等问题,引入水平扩散、垂直运动耗散等技术方案,同时优化模式动力物理过程各功能块的调用方式和一些技术参数,最终形成适合热带高分辨率的模式版本TRAMS-V3.0。批量测试表明,新版模式TRAMS-V3.0的预报性能明显优于TRAMS-V2.0,新版模式不仅对形势场和地面要素的预报误差较小,而且各量级降水预报的准确率也比较高,如48小时2 m温度预报RMS由原来的2.4℃降低为1.8℃,晴雨48小时预报准确率由原来的0.736提高到0.810等。基于TRAMS-V3.0建立的预报系统,实时业务应用中展现了系统在晴雨、暴雨、地面要素等方面预报的优势。并针对暴雨空漏报等问题进行了初步的分析,提出下一步技术改进的设想。     

Track of Super Typhoon Haiyan Predicted by a Typhoon Model for the South China Sea

Super Typhoon Haiyan was the most notable typhoon in 2013. In this study, results from the operational prediction of Haiyan by a tropical regional typhoon model for the South China Sea are analyzed. It is shown that the model has successfully reproduced Haiyan’s rapid passage through the Philippines and its northward deflection after its second landfall in Vietnam. However, the predicted intensity of Haiyan is weaker than the observed. An analysis of higher-resolution model simulations indicates that the storm is characterized by an upper-level warm core during its mature stage and a deep layer of easterly flow. Sensitivity experiments are conducted to study the impact of certain physical processes such as the interaction between stratus and cumulus clouds on the improvement of the typhoon intensity forecast. It is found that appropriate boundary layer and cumulus convective parameterizations, and orographic gravity-wave parameterization, as well as improved initial conditions and increased horizontal grid resolution, all help to improve the intensity forecast of Haiyan.     

站点选择对城市热岛效应的影响分析

根据城郊站间距离等对辽宁56个气象站进行筛选,采用城郊温差法对选站和未选站时郊区站点数量有变化的大连、丹东、锦州和铁岭4个城市的月和年热岛特征进行分析。结果表明：对于年热岛特征而言,1980-2011年,大连、丹东、锦州和铁岭4个城市选站和未选站时热岛强度大小明显不同,但其变化趋势基本一致。4城市相比,选站和未选站时后均表现为铁岭年热岛强度最大,多年平均值分别为1.53 ℃和1.85 ℃,其变化范围分别为1.17-1.80 ℃和1.55-2.15 ℃,变化幅度分别为0.63 ℃和0.60 ℃。1980-2011年,铁岭热岛强度等级发生变化的年份最多,占25 %。总体来讲,选站对年热岛特征影响不是很大。对于月热岛特征而言,大连选站和未选站时热岛强度变化较大,但其他3个城市选站选站和未选站时变化不大,尤其是锦州选站和未选站时变化基本一致。4城市均有冬半年热岛效应明显,夏半年热岛效应不明显的特征。1980-2011年,各月平均热岛强度等级在选站和未选站时变化均较大,最大为丹东10月和11月,等级变化的年份占90.6 %,总体而言,选站对月热岛强度特征影响较大。     

WRF模式分辨率对新疆异常降雨天气要素模拟的影响

利用新一代中尺度气候数值模式WRF对中国西北干旱典型地区——新疆2000年10月的异常降雨事件进行模拟,主要研究了不同水平分辨率、垂直分辨率以及不同积云参数化过程对气温、降雨和土壤温度模拟的影响。结果表明：不同分辨率的模拟基本上均模拟出了地面气温的分布特征,且随着水平分辨率的提高,模式模拟能力显著提高,对地面气温值、分布范围的模拟渐趋合理,同时模式对于地形引起的温度分布变化的模拟更加趋近实际。水平分辨率、垂直分辨率的提高同样改善了模式对降水的模拟能力,分辨率的提高不仅改进了模式对降雨分布区模拟的精度,也增强了对于地形引起的降雨变异的模拟能力。在土壤温度模拟上,不同分辨率的试验均能模拟出土壤温度的分布特征,较高水平分辨率有利于描述土壤温度分布细节,但更容易出现“数值点风暴”现象。     

雷达资料和数值模式产品融合技术研究

以雷达外推为基础,配合中尺度数值模式产品作为环境场,提出两种新的雷达资料和数值模式融合技术:动态权重融合法和趋势演变叠加法。且在动态权重融合法中提出用正弦权重、双曲正切权重以及实时滚动权重三种方法计算权重。使用上海及周边地区2009年6月21日的一次对流过程进行个例分析及误差检验,结果表明:利用这两种方法进行融合后的预报结果与雷达外推和数值模式预报结果相比均有所改进,特别是动态权重融合法中的正弦权重和双曲正切权重对于预报结果的改进尤为明显,融合后的结果更接近实况,表明动态权重融合法和趋势演变叠加法这两种方法是有效可行的,对短时临近预报技术研究有较高的参考价值。     

国家气象中心台风数值模式的改进及其应用试验

在国家气象中心台风数值模式中进行了扩大预报区域,两次嵌入人造台风模型和模式网格初始移动3个方案试验。试验结果表明：3个方案对台风路径预报效果都有所改进。该文还介绍了应用国家气象中心台风数值模式进行台风中心强度预报的进展。     

下投式探空资料对Debby飓风路径预报影响的数值试验

在飓风路径的数值预报中，对于初始场的要求很高，然而，由于初始资料的缺乏，经常导致路径预报的误差较大，尤其是当飓风处于远离陆地的海上时，这种误差更大，通过利用UM模式在Debby飓风活动期间，对下投式探空仪所获取探空资料，采用不同使用方案的三个时次共计10次数值试验的结论分析，给出一些有意义的 结论，即非实时资料对实时资料的有效补充，能够提高飓风路径预报精度，而在众多气象要素场中，风场和湿度场对飓风路径预报的影响更大。     

中尺度自忆模式在强降水预报中的应用

根据大气自忆性原理提出的回溯时间积分格式应用于中尺度格点模式MM5,构建了中尺度自忆模式SMM5并做了短期强降水预报的实验.结果表明,SMM5模式与MM5模式相比,由于使用了多个时刻的场资料,预报精度有了明显的提高, SMM5预报的最大雨区的中心位置与降水量也比MM5更接近实际观测场.     

基于小时分辨率的降水过程辨识方法研究

强降水极易造成暴雨灾害,尤其是突发性强的短时强降水,动态监测、影响评估和风险预估是灾害防御的重要手段。但目前气象服务业务中,强降水的定量评估和风险预估还是以天为单位,现代气象服务精细化的需求迫切要将时间分辨率提升至小时尺度。本文利用1951—2018年国家气象观测站小时降水观测资料,从小时尺度界定站点、大区域、小区域降水过程的辨识方法。基于改进的降水过程综合强度评估方法,在概率密度分布的基础上,重新划分了极端、特强、强、较强、中等五个等级的降水过程综合强度指数。检验论证显示,基于小时分辨率降水过程的自动提取和评估方法合理,具有可操作性,能够对过程性降水、短时降水过程动态评估和预评估,可实时支撑气象服务业务,提升气象防灾减灾能力,也为后续开展短时强降水影响评估和风险预估建立基础。     

用数值预报释用方法做近海及登陆热带气旋强度预报

这是一个对GFS数值预报产品进行解释应用的方法.将支持向量机(SVM)回归方法应用于近海和登陆热带气旋(TC)的强度预报.从其本身强度,影响范围内气象因子情况,地形因子等三个方面,设计相关因子,建立预报模式,用来预报12、24、36、48、60和72 h的TC强度.总体上模式强度预报结果与中央气象台的预报结果相近,优于气候持续法的预报;趋势预报优势明显,可高出7～12个百分点.表明可以成为台风强度预报的另一个工具,投入业务应用.     

用T63及日本数值预报产品制作汛期降水预报

该文利用Ｔ６３Ｌ１６和日本数值预报产品，采用相关分析方法提取典型因子场，再由典型因子场选点求取平均场及极值场，用逐步回归法制作黄河三角洲地区汛期降水预报，试用效果较好。