WRF模式中微物理和积云对流参数化方案对台风“莫拉克”模拟敏感性分析

基于WRF模式,研究了不同微物理和积云对流参数化方案对0908号台风"莫拉克"的路径移动、强度变化和降水过程模拟的敏感性。结果显示,积云对流参数化方案对台风"莫拉克"的路径和强度模拟起主导作用,采用Kain-Fritsch积云对流方案模拟的72 h平均路径误差较小;降水量的模拟主要取决于微物理参数化方案,而降水分布的好坏更依赖于积云对流参数化方案,而采用Thompson微物理和Grell-Devenyi积云对流方案的试验导致累积降水极值的偏干误差较大。积云对流方案对环境场和潜热释放模拟存在差异,导致路径和强度、温度廓线和垂直运动的模拟结果不同,而微物理方案对不同相态降水粒子的垂直分布结构模拟存在差异,从而导致降水模拟的差别。此外,由不同试验构造的集合平均能减少单个成员模拟路径和降水的不确定性,特别在强降水方面能减小空报数和漏报数,提高TS评分,改善模拟效果。     

不同降水方案对"03.7"一次暴雨过程模拟的影响

观测和数值模拟研究已经表明,潜热释放对中国东部夏季梅雨锋系统及其锋面降水的维持和发展发挥着非常重要的作用.然而,目前对于梅雨锋降水模拟中各种降水方案的相互协调和系统评估方面的工作仍不多见,为了增进对梅雨锋暴雨模拟中降水过程的认识,作者针对2003年7月4～5日一次梅雨锋暴雨过程,构造了四组试验,利用MM5模式考察了两种分辨率(36 km、12 km),各种隐/显式方案搭配下,对所生成的雨带、雨量和降水类型的配置进行了仔细的研究,得到了一些有意义的结论,为今后更好地使用模式、利用数值模式来认识中尺度降水过程中的气象问题打下基础.主要结论包括:模拟总降水的水平分布和强度,以及显式降水和隐式降水的划分对积云参数化方案的选择非常敏感.但对特定积云参数化方案而言,降水的模拟对36 km、12 km水平分辨率不敏感(除Betts-Miller方案外);在中尺度网格分辨率10～50 km范围内,不同积云参数化方案对梅雨锋降水分布和降水量模拟的影响比不同显式方案带来的变化大得多.     

WRF模式对青藏高原南坡夏季降水的模拟分析

利用中尺度数值模式WRF研究积云对流参数化方案、网格嵌套技术和模式分辨率对陡峭的青藏高原南坡夏季降水模拟的影响。对2006年7月青藏高原南坡地区降水的模拟分析表明:降水对积云对流参数化方案的选择很敏感,不同方案模拟的结果差异显著,采用Grell-Devenyi质量通量方案时的模拟效果优于其他方案。在此基础上,通过5种试验方案比较发现,使用积云对流参数化方案、提高模式分辨率和应用网格嵌套技术能改善降水强度和空间分布的模拟,组合使用时模拟的降水与观测资料更接近。它们均能改进风场,使得水汽的输送和辐合过程的模拟更加准确;还能影响大气的垂直加热状态,导致不同的对流发生,使垂直速度的分布趋于合理。未使用积云对流参数化方案时,大气湿度偏小,而模式分辨率和网格嵌套技术对大气湿度的影响不大。      

积云参数化对0613号台风“珊珊”数值模拟的影响研究

使用W RF的ARW动力核心模拟台风"珊珊",以研究各种积云参数化方案对于台风路径,强度和降水分布等的影响。研究表明,环境场对积云参数化的选取不敏感,积云参数化对台风的强度和路径模拟有明显的影响,KF方案模拟的台风强度较强,增强过程明显,后期移速偏快。KF和BM J对降水的模拟较好,GD方案不够理想。     

不同云降水方案对一次登陆台风的降水模拟

利用美国最新发展的新一代中尺度数值预报模式(WRF),研究了不同云降水方案对一次登陆台风的降水模拟问题,结果表明,在网格距适当小的情况下,同时采用积云对流参数化方案和云微物理方案(Kessler方案)时,其降水预报优于只使用积云对流参数化方案时的预报;在台风降水模拟的初期,Kain-Fritsch方案比Betts-Miller方案产生降水更快,更接近实况降水;在台风登陆后随时间的延长,对流降水重要性逐步下降,网格尺度降水逐渐增强。     

公里尺度分辨率WRF模拟梅雨暴雨对积云对流参数化的敏感性试验研究

本文利用中尺度模式WRF V4.0.2(Weather Research and Forecasting Model,Version 4.0.2)对浙江省两次梅雨锋暴雨过程进行数值模拟,分别选用WSM6和Thompson云微物理方案、YSU和MYJ边界层方案、以及11种对流参数化方案进行试验,探究不同积云对流参数化方案对梅雨锋暴雨的1 km高分辨率预报的影响,结果表明：（1）在对各试验的降水预报评估过程中,使用传统点对点方法和邻域法都能客观表现出各试验的预报水平,而邻域检验法能更客观地评估模式对小范围强降水的预报水平。（2）三类积云对流方案（包括：无积云对流方案、传统积云对流方案和尺度自适应积云对流方案）都能较好地模拟出小雨降水的发生情况,但随着降水强度增强至暴雨、大暴雨量级时,尺度自适应的积云对流方案对降水的预报结果有明显改善。（3）在不同微物理和边界层组合方案下,尺度自适应积云对流方案的模拟结果差异更显著,而传统积云对流方案的模拟结果的效果差异不明显。（4）在1～10 km的“灰色区域”范围内,当网格分辨率逐渐提高到1 km时,尺度自适应积云对流方案较传统积云对流方案对模式的预报结...     

WRF模式物理过程参数化方案对酒泉地区暴雨模拟的影响

利用区域气候站逐时降水实况资料和NCEP l°×l°的6 h全球再分析格点资料,运用WRFV3.2模式,采用不同积云对流和微物理参数化方案组合对2012年6月4 5日发生在酒泉地区的暴雨过程开展了敏感性试验。从降水量和降水落区等方面对各方案组合的模拟效果进行对比分析发现:选择不同的方案组合,可以不同程度地模拟这次暴雨过程的落区范围和降水量,微物理方案的选择对模拟结果的影响较积云对流方案更敏感。18 km水平分辨率下,BMJ-WSM5方案组合模拟效果最优。通过对垂直速度、涡度、散度和雨水混合比等物理量的诊断分析,可以更好地理解不同积云对流和微物理参数化方案对暴雨预报的影响。     

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.     

积云参数化和微物理方案不同组合应用对台风路径模拟效果的影响

利用美国国家环境预测中心(National Centers for Environmental Prediction,NCEP)和国家大气研究中心(NCAR)联合研发的天气研究和预报模式(Weather Research and Forecasting Model,WRF),研究了不同积云对流参数化方案和微物理过程方案对0514号台风"彩蝶"路径的影响.结果表明,积云对流参数化方案对台风路径影响较大,KF方案比BM方案能更好地模拟出台风路径;使用KF方案时,选择微物理方案比不选微物理方案对于台风路径有更好的模拟结果,其中,Ferrier、WSM6和Lin非常接近于实况;KF方案较好地模拟出副热带高压(简称副高)的西伸和东退的变化以及台风环流的风场分布和强度.     

MM5模式中不同对流参数化方案的数值模拟

MM5模式中有多种积云参数化方案可供选择,不同参数化方案及分辨率对降水预报有很大影响。本文利用4种积云参数化方案(GR,KF,BM,AK)对辽东半岛一次大暴雨过程进行试验,结果表明,不同的参数化方案,对强降水落点及强度的模拟,结果差别较大。模拟较好的是GR方案,最差的是AK方案;4种积云对流参数化方案模拟的海平面气压场差别较大,其中GR方案模拟出造成2005年第5号台风暴雨的高低压系统和中尺度气旋;粗网格采用一定的积云对流参数化后,可在一定程度再现一些中尺度特征;4种方案由于闭合假设不同,模拟的云物理特征存在很大差别,这种差别对各种天气要素的准确预报会产生一定的影响。     

不同微物理方案对台风“利奇马”雨带模拟的影响分析

云微物理过程是影响台风降水数值模拟的关键过程。利用华东中尺度模式系统,选取Thompson与CLR两种微物理参数化方案对台风“利奇马”进行数值模拟,对比观测、卫星资料,评估两个微物理参数化方案对台风模拟的影响,结果表明：相比于Thompson方案,CLR方案对台风“利奇马”的模拟在登陆后的路径、强度、降水明显更接近观测;Thompson方案在距离台风中心约100 km形成较强的螺旋雨带,而CLR方案在距离台风中心150 km左右的位置形成了较弱的螺旋雨带。进一步的分析表明,CLR方案模拟出的外围雨带距离台风中心的距离更远,是由于CLR方案中冰、霰等冰相态水凝物下落速度更小,更有可能被推送到距离台风中心更远的位置,从而形成不同的雨带分布。     

A MODIFIED CUMULUS PARAMETERIZATION SCHEME AND ITS APPLICATION IN THE SIMULATIONS OF THE HEAVY PRECIPITATION CASES

According to the characteristics of organized cumulus convective precipitation in China, a cumulus parameterization scheme suitable for describing the organized convective precipitation in East Asia is presented and modified. The Kain–Fristch scheme is chosen as the scheme to be modified based on analyses and comparisons of simulated precipitation in East Asia by several commonly-used mesoscale parameterization schemes. A key dynamic parameter to dynamically control the cumulus parameterization is then proposed to improve the Kain–Fristch scheme. Numerical simulations of a typhoon case and a Mei-yu front rainfall case are carried out with the improved scheme, and the results show that the improved version performs better than the original in simulating the track and intensity of the typhoons, as well as the distribution of Mei-yu front precipitation.     

南海夏季风爆发的数值模拟

利用高分辨率的区域气候模式 (RegCM_NCC) 对南海夏季风爆发进行模拟研究。研究表明:该模式对积云对流参数化方案的选择十分敏感, 其中以Kuo积云参数化方案为最好, 可以比较成功地模拟出南海夏季风的爆发时间、爆发前后高、低层风场的剧烈变化以及季风与季风雨带的向北推进。然而该方案对于雨量和副热带高压位置的模拟, 与观测相比尚存在一定的偏差, 主要表现为副热带高压位置模拟偏北、偏东; 南海地区的降水量模拟偏少、降水范围偏小。此外, 采用4种参数化方案 (Kuo, Grell, MFS, Betts-Miller) 集成的结果在某种程度上要优于单个方案的结果, 这种改善主要体现在对南海地区季风爆发后降水的模拟上。     

Implementation of a new cumulus parameterization scheme based on an explicit time-dependent tilting cloud model in ARPS model

A one-dimensional Explicit Time-dependent Tilting cloud Model (ETTM) that separates updraft and downdraft columns and takes into account the effect of cloud tilting on precipitation is introduced and incorporated into the Advanced Regional Prediction System (ARPS). Results of the stand-alone ETTM are compared with that of cloud resolving simulations using the ARPS mesoscale model. Inter-comparison is performed by qualitative examination of simulated parameters such as vertical distribution of fluxes of mass, heat, and moisture. Although there is a great degree of similarity between the vertical profiles, ETTM systematically underestimates magnitudes of all fluxes. Sensitivity tests carried with ETTM show that the effect of varying cloud radius and tilting angle is considerable on the simulated cloud behavior. Increasing the cloud radius, results in a corresponding increase in fluxes of mass, heat, and moisture, while increasing the cloud tilt angle has the opposite effect. Since ETTM showed promise as a suitable sub-grid cumulus parameterization scheme; it was incorporated into ARPS as an additional cumulus parameterization scheme (CPS) to be available for the wider community. Results of simulations using ETTM and other CPSs already available in ARPS were compared for 2, 4 and 10 km grid spacings to assess its utility. Simulation results of the 2 km grid showed that at this resolution, the simulated time series of updraft velocities using the new scheme (ETTM) compared well with the results of other schemes in the ARPS model. The simulations with horizontal resolution of 4 km that was compared with the convection resolving reference run (No-CPS-2KM) showed almost consistent results for all schemes except for one using KF scheme. The results of the simulation with the ETTM scheme and other schemes in the model with resolution of 10 km showed that at this resolution, there is not significant difference between the uses of these schemes.     

WRF模式物理参数化方案对一次局地大暴雨预报的影响研究

基于WRF(Weather Research and Forecasting)模式及其3Dvar(3-Dimentional Variational)资料同化系统,采用36、12、4 km嵌套网格进行快速更新循环同化和不同的微物理及积云对流参数化方案对比试验,对2011年5月8日鲁中一次局地大暴雨过程进行了研究。结果表明,快速更新循环同化地面观测资料是影响模式降水落区预报准确性的关键因素,不同的微物理和积云对流参数化方案主要影响降水强度预报。采用不同的微物理参数化方案和积云对流参数化方案进行降水预报对比试验表明,LIN方案和WSM6(WRF Single-Moment 6-class)微物理参数化方案对降水预报均较好,LIN方案降水预报较WSM6方案略强。4 km网格预报使用K-F (Kain-Fritsch)积云对流参数化方案或不使用积云对流参数化方案,预报的降水均较好。4 km网格使用旧的K-F积云对流参数化方案,预报的近地层大气风场偏弱,导致大气动力抬升作用偏弱,从而造成模式降水预报偏弱。     

Impact of Horizontal Resolution and Cumulus Parameterization Scheme on the Simulation of Heavy Rainfall Events over the Korean Peninsula

In this paper, we present the results from high-resolution numerical simulations of three heavy rainfall events over the Korean Peninsula. The numerical results show that the prediction accuracy for heavy rainfall events improved as horizontal resolution increased. The fine-grid precipitation fields were much closer to the real precipitation fields in the case of large synoptic forcing over the Korean Peninsula. In the case of large convective available potential energy and weak synoptic forcing, it seems that even when using a high resolution, the models still showed poor performance in reproducing the observed high precipitation amounts. However, activation of the cumulus parameterization scheme in the intermediate resolution of 9 km, even at a grid spacing of 3 km, had a positive impact on the simulation of the heavy rainfall event.     

Spatial patterns and trends of daily rainfall regime in Peninsular Malaysia during the southwest and northeast monsoons: 1975–2004

Model precipitation can be produced implicitly through convective parameterization schemes or explicitly through cloud microphysics schemes. These two precipitation production schemes control the spatial and temporal distribution of precipitation and consequently can yield distinct vertical profiles of heating and moistening in the atmosphere. The partition between implicit and explicit precipitation can be different as the model changes resolutions. Within the range of mesoscale resolutions (about 20 km) and cumulus scale, hybrid solutions are suggested, in which cumulus convection parameterization is acting together with the explicit form of representation. In this work, it is proposed that, as resolution increases, the convective scheme should convert less condensed water into precipitation. Part of the condensed water is made available to the cloud microphysics scheme and another part evaporates. At grid sizes smaller than 3 km, the convective scheme is still active in removing convective instability, but precipitation is produced by cloud microphysics. The Eta model version using KF cumulus parameterization was applied in this study. To evaluate the quantitative precipitation forecast, the Eta model with the KF scheme was used to simulate precipitation associated with the South Atlantic Convergence Zone (SACZ) and Cold Front (CF) events. Integrations with increasing horizontal resolutions were carried out for up to 5 days for the SACZ cases and up to 2 days for the CF cases. The precipitation partition showed that most of precipitation was generated by the implicit scheme. As the grid size decreased, the implicit precipitation increased and the explicit decreased. However, as model horizontal resolution increases, it is expected that precipitation be represented more explicitly. In the KF scheme, the fraction of liquid water or ice, generated by the scheme, which is converted into rain or snow is controlled by a parameter S ₁. An additional parameter was introduced into KF scheme and the parameter acts to evaporate a fraction of liquid water or ice left in the model grid by S ₁ and return moisture to the resolved scale. An F parameter was introduced to combine the effects of S ₁ and S ₂ parameters. The F parameter gives a measure of the conversion of cloud liquid water or ice to convective precipitation. A function dependent on the horizontal resolution was introduced into the KF scheme to influence the implicit and explicit precipitation partition. The explicit precipitation increased with model resolution. This function reduced the positive precipitation bias at all thresholds and for the studied weather systems. With increased horizontal resolution, the maximum precipitation area was better positioned and the total precipitation became closer to observations. Skill scores for all events at different forecast ranges showed precipitation forecast improvement with the inclusion of the function F.     

Improvements in WRF simulation skills of southeastern United States summer rainfall: physical parameterization and horizontal resolution

Realistic regional climate simulations are important in understanding the mechanisms of summer rainfall in the southeastern United States (SE US) and in making seasonal predictions. In this study, skills of SE US summer rainfall simulation at a 15-km resolution are evaluated using the weather research and forecasting (WRF) model driven by climate forecast system reanalysis data. Influences of parameterization schemes and model resolution on the rainfall are investigated. It is shown that the WRF simulations for SE US summer rainfall are most sensitive to cumulus schemes, moderately sensitive to planetary boundary layer schemes, and less sensitive to microphysics schemes. Among five WRF cumulus schemes analyzed in this study, the Zhang–McFarlane scheme outperforms the other four. Further analysis suggests that the superior performance of the Zhang–McFarlane scheme is attributable primarily to its capability of representing rainfall-triggering processes over the SE US, especially the positive relationship between convective available potential energy and rainfall. In addition, simulated rainfall using the Zhang–McFarlane scheme at the 15-km resolution is compared with that at a 3-km convection-permitting resolution without cumulus scheme to test whether the increased horizontal resolution can further improve the SE US rainfall simulation. Results indicate that the simulations at the 3-km resolution do not show obvious advantages over those at the 15-km resolution with the Zhang–McFarlane scheme. In conclusion, our study suggests that in order to obtain a satisfactory simulation of SE US summer rainfall, choosing a cumulus scheme that can realistically represent the convective rainfall triggering mechanism may be more effective than solely increasing model resolution.