ECMWF 数值预报模式简介ppt课件

1、,ECMWF 数值预报模式简介,1,气象预报的四个方面问题,当前的天气或气候信息完备的综合观测系统完善的观测系统；资料信息识别；资料的综合处理（同化） 天气或气候的演变规律从资料得到新认识从资料得到新认识；反映大气运动数学物理规律的微分方程组。 外力和强迫的变化地形和边界强迫；太阳常数；引力等 从已知预报未来的手段完备的数值模 式；承载数值模式计算、显示和通讯平台 驾驭观测、资料分析和数值模式发展和应 用的人才队伍,2,大气圈,水圈,冰晶圈 /冰冻圈,生物圈,岩石圈,人类圈,3,纷繁多样数值预报产品-什么会有差别？,4,分辨率不同 模式的表述的物理过程有差异 计算方案、网格、变量分布等 再分析

2、资料分析的初值能代表大气实况吗？,5,Orography and Resolutions,GSM T213 (60km),RSM(20km),MSM(10km),Orographic effects are better captured by higher resolution models. The surface parameters such as Tsurf might be predicted more realistically by those models.,6,ECMWF 致力于2016-2025 数值预报发展战略： 利用集合预报方法提前2周预报高影响天气事件 提前4周，无

3、缝隙地预报大尺度系统形势和系统移动 提前1年预测全球范围的异常状况,7,研究和更丰富的知识 基于集合预报的分析和预报技术 如何实现目标： Observations High resolution ensemble Earth-system Scalability Funding People （引自 Erland Klln，“Earth system modelling for seamless prediction” ECMWF Annual Seminar 2016）,8,Future Earth System model and assimilation developmentsErla

4、nd Klln, ECMWF,9,10,Ocean model (NEMO),Wave model (ECWAM),Atmosphericmodel (IFS),Air density,Gustiness,Neutral wind,Roughness,Currents,Sea surface temperature,All configurations,Ensemble FC,Solar and non solar fluxes, E-P,Towards a fully coupled system (currently only operational in EPS),ORCA1_Z42,T

5、Co1279/TCo639,14km/28km,9km/18km,Ensemble systems only: - Medium range forecast - Monthly forecast - Seasonal forecast,Every IFS time step,Every coupling time step (1 or 3 hours),Single executable,11,Ocean model (NEMO),Wave model (ECWAM),Atmosphericmodel (IFS),Air density,Gustiness,Neutral wind,Roug

6、hness,Turbulent energy,Stokes drift,Currents,Sea surface temperature,All configurations,Stress,Ensemble FC,Solar and non solar fluxes, E-P,Towards a coupled system,ORCA1_Z42,TCo1279/TCo639,14km/28km,9km/18km,Single executable,Operational from day 0 since 2013,12,Ocean model (NEMO),Ice concentration,

7、Wave model (ECWAM),Atmosphericmodel (IFS),Air density,Gustiness,Neutral wind,Roughness,Turbulent energy,Stokes drift,Currents,Ice model (LIM),Sea surface temperature,Ice concentration,All configurations,Stress,Ensemble FC,future operational,Solar and non solar fluxes, E-P,Towards a coupled system,OR

8、CA0.25_Z75,Adding active sea ice model,Implementation: End 2016.,Single executable,13,Calling sequence of the single executable,Simplified flow chart of the coupled model, here two time steps are shown. In reality, IFS/WAM coupling every IFS time step, but Call to NEMO every hour (or 3 hours) with a

9、veraged accumulated fluxes.,14,Impact of Resolution on tropical cyclone forecast,For instance Typhoon Haiyan: forecasts from 4th, 5th and 6th November 2013, 0 UTC all from operational analysis.,Black: estimated from observations Red: old operational Ensemble resolution (32 km) Blue: old operational

10、HRES configuration (16 km) Green: experimental: new HRES configuration (10km),Typhoon Haiyan at peak intensity on November 7, 2013,15,Impact of Coupling on tropical cyclone forecast,For instance Typhoon Neoguri: forecasts from 6 July 2014, 0 UTC,Black: estimated from observations Green: old operatio

11、nal HRES configuration (uncoupled) (16km) Red: experimental: 16km coupled to NEMO (ORCA025_Z75) Blue: 16km coupled to NEMO + new physics,min MSLP (hPa),900,950,Neoguri affecting Okinawa on July 8, 2014,16,Climate reanalyses for the coupled earth model,ECMWF coupled Earth model for medium-range weath

12、er forecasting,New coupled assimilation system (CERA) for the coupled Earth model: atmospheric and ocean observations assimilated simultaneously ocean observations can impact atmospheric estimate and conversely CERA-20C reanalysis in production (1900-2010),Karl and Trenberth 2003,Coupled assimilatio

13、n system (CERA),EDA variational approach with a 24-hour window that assimilates simultaneously atmospheric and ocean observations,coupled model computes observation misfits in each outer iteration,atmospheric and ocean increments are computed in parallel to correct the initial state,SST computed in

14、NEMO and constrained by relaxation,analysis dynamically consistent with respect to the coupled model,Conclusions:,ECMWF has a coupled atmosphere-wave-ocean circulation forecasting system, currently operational in the Ensemble Prediction System. Work is ongoing on using a higher resolution ocean comp

15、onents (ORCA025z75) planned for end of 2016 in the Ensemble forecasts and later in the High resolution system. There is a clear benefit in coupling the different models, but it creates new challenges in determining what physical parameters need to be exchanged. Furthermore, model parameterisations m

16、ight need revisiting.,19,EC模式动力框架,垂直采用坐标，U=ucos ；V=vcos,20,21,22,对比球坐标系中的基本方程组,曲率项,23,重力不是指向地心，等位势面也不是球面。,24,非静力学模式 静力学模式,静力学平衡：运动的垂直尺度远小于水平尺度的情况下成立,模式的分类,25,基于连续方程的模式分类,非静力学模式根据模式中是否包含声波，分为： 滞（非）弹性（anelastic)模式 假定大气不可压，滤掉声波 弹性(elastic)模式 大气可压、由散度预报气压的变化，但声波 需要特殊的处理,26,根据连续方程的近似程度， 滞弹性和弹性模式又可进 行不同的分

17、类：,滞弹性模式,不可压缩模式,滞弹性模式,弹性模式,准可压模式,完全可压模式,27,数值计算方案,大气运动方程组是一套复杂的非线性方程组，目前，还没有理论解存在，只能借助数值方法求解。 数值方法有很多，目前气象上用的主要用的是差分方法、谱方法、有限元法等。 差分方法：就是在离散的网格点上，以差商代替微商，求解微分方程的方法。,28,关于有限差分与谱方法的图例,有限差分,谱方法,29,30,| | | n-1 n n+1,从物理上考虑，差分的精度还与采样点密即网格，与要素在采样区的变化分布有关。即采样数据是否能有代表性。,中央差,精确值,采样值,混淆误差,31,离散网格所能表示的最短波长 上表中当L/ x =2时，即两倍格距波，R=0，误差100%，因此，离散网柜完全不能表示两倍格距以下的短波。如格距为100km，则你只能预报出200km以上的天气系统。,1.5倍格距波,3倍格距波,最短的波，2倍格距波,1.5倍格距波被当成3倍格距的波 混淆误差会把小于2倍格距的波歪曲为2倍格距以上的波。 因此混淆误差主要集中在24倍格距间。 预报员会在什么情况下遇到“混淆误差”？,32,拉格朗日和半拉格朗日方法,拉格朗日和半拉格朗日方法是从另外一个角度来求取平流方程的解。 有解析解： 不失一般性，考虑 情况下平流方程的解。,可以证明下述