Assimilation of GPM Microwave Imager Radiance for Track Prediction of Typhoon Cases with the WRF Hybrid En3DVAR System

The impact of assimilating radiance data from the advanced satellite sensor GMI(GPM microwave imager) for typhoon analyses and forecasts was investigated using both a three-dimensional variational(3DVAR) and a hybrid ensemble-3DVAR method. The interface of assimilating the radiance for the sensor GMI was established in the Weather Research and Forecasting(WRF) model. The GMI radiance data are assimilated for Typhoon Matmo(2014), Typhoon Chan-hom(2015), Typhoon Meranti(2016), and Typhoon Mangkhut(2018) in the Pacific before their landing. The results show that after assimilating the GMI radiance data under clear sky condition with the 3DVAR method, the wind,temperature, and humidity fields are effectively adjusted, leading to improved forecast skills of the typhoon track with GMI radiance assimilation. The hybrid DA method is able to further adjust the location of the typhoon systematically. The improvement of the track forecast is even more obvious for later forecast periods. In addition, water vapor and hydrometeors are enhanced to some extent, especially with the hybrid method.     

GRAPES混合同化方法在青藏高原区域的初步试验

针对青藏高原地区气象观测站点稀少和模式同化分析质量较低的问题,将GRAPES区域集合变分(En-3DVAR)混合同化系统应用于青藏高原地区,进行了单点理想试验和真实观测资料同化分析预报试验,分析评估青藏高原混合同化分析增量及预报误差的水平垂直结构特征及其合理性,并与中国东部平原地区进行比对。单点理想试验表明,En-3DVAR混合同化系统中背景误差协方差具备流依赖属性。真实资料混合同化试验结果表明,基于集合预报估计的分析增量具有流依赖的特征,特别是在高原地区和槽脊系统附近;青藏高原地区分析场的绝对误差总体低于3DVAR系统,其平均绝对误差在中层和高层低于平原地区,说明在青藏高原地区的改进效果略优于平原地区。需要关注的是,青藏高原地区En-3DVAR混合同化分析增量总体大于3DVAR,特别是近地面层u风分量分析增量明显偏大,这可能与青藏高原复杂地形有关。     

Impact of Assimilating Radiances with the WRFDA ETKF/3DVAR Hybrid System on Prediction of Two Typhoons in 2012

The impacts of AMSU-A and IASI (Infrared Atmospheric Sounding Interferometer) radiances assimila-tion on the prediction of typhoons Vicente and Saola (2012) are studied by using the ensemble transform ...     

面向WRF/Chem模式MOSAIC气溶胶方案的资料同化实现

CMA-CUACE-Haze化学天气模式是中国研发的气溶胶过程模拟和评估工具,但目前还没有配套的大气化学天气耦合同化分析系统。文中在CMA-MESO三维变分分析的基础上建立了区域化学天气耦合同化系统,该系统把变量之间不相关的PM_2.5 和PM_2.5-10作为控制变量,采用模型化的背景误差协方差,初步实现气溶胶观测PM_2.5和PM₁₀的同化分析。通过单站气溶胶观测的理想同化试验验证耦合同化系统设计的合理性,并针对2016年12月的重污染天气过程进行GTS传输的常规观测与气溶胶PM_2.5和PM₁₀观测资料同化与预报试验。试验结果表明,大气化学天气耦合同化系统可对气溶胶观测和天气变量观测同时进行极小化分析,大气化学变量和天气变量分析场互不影响;气溶胶观测资料的同化合理修正了大气化学背景场,PM_2.5和PM₁₀变量分析场更接近观测;气溶胶观测资料同化对污染物预报的影响可持续72 h。搭建的区域化学天气耦合同化系统能为CMA-CUACE-Haze化学天气模式提供更准确的化学初始场。     

台风“鲇鱼”(1013)路径突变过程的成因分析

利用NCEP提供的GFS(Global Forecast System)再分析资料,对2010年西北太平洋最强台风“鲇鱼”(1013)路径突变的成因开展诊断分析,研究其影响系统、引导气流的演变特征等,并运用CPS(Cyclone Phase Space)方法对其生命史中的热力结构演变过程进行定量描述,重点分析路径突变前后各因子的变化。结果表明,“鲇鱼”移入南海后,冷空气南侵导致其热力结构发生变化,台风环流右侧较暖,此时引导气流微弱,“趋暖”运动占主导,首先引起路径向右偏转,随后引导气流转为西南气流并逐渐增强,在二者共同作用下,“鲇鱼”路径持续右转,逐渐向东北方向移动,完成路径突变。     

A validation of the multivariate and minimum residual method for cloud retrieval using radiance from multiple satellites

The Multivariate and Minimum Residual(MMR) cloud detection and retrieval algorithm, previously developed and tested on simulated observations and Advanced Infrared Sounder radiance, was explored and validated using various radiances from multiple sensors. For validation, the cloud retrievals were compared to independent cloud products from Cloud Sat, MODIS(Moderate Resolution Imaging Spectroradiometer), and GOES(Geostationary Operational Environmental Satellites). We found good spatial agreement within a single instrument, although the cloud fraction on each pixel was estimated independently. The retrieved cloud properties showed good agreement using radiances from multiple satellites, especially for the vertically integrated cloud mask. The accuracy of the MMR scheme in detecting mid-level clouds was found to be higher than for higher and lower clouds. The accuracy in retrieving cloud top pressures and cloud profiles increased with more channels from observations. For observations with fewer channels, the MMR solution was an "overly smoothed" estimation of the true vertical profile, starting from a uniform clear guess. Additionally, the retrieval algorithm showed some meaningful skill in simulating the cloudy radiance as a linear observation operator, discriminating between numerical weather prediction(NWP) error and cloud effects. The retrieval scheme was also found to be robust when different radiative transfer models were used. The potential application of the MMR algorithm in NWP with multiple radiances is also discussed.     

地形对台风Megi(2010)过岛阶段路径偏折影响的数值研究

采用谱逼近方法减小大尺度环境场模拟偏差,通过地形敏感性试验,研究吕宋岛山脉地形高度对台风Megi(2010)过岛阶段路径偏折的影响。模拟试验表明,谱逼近700 hPa高度层以上天气尺度风场分量的数值试验不仅能够反映大尺度环流对台风路径的引导作用,同时保留了中低层环流对地形影响的响应,较为准确地反映了Megi靠近和登陆吕宋岛过程中的持续南压过程,以及离开吕宋岛后的突然北折过程。在此模拟基础上,通过对地形高度敏感性试验结果诊断和影响区域空气质点进行后向轨迹分析,表明在台风向山脉靠近过程中,台风外围和内核环流均受地形影响,迎风坡存在明显气流辐合,有利于台风流场与南北向山脉之间出现北风急流和轨迹汇聚带,从而产生狭管效应,造成台风移动路径南折;而台风过山后,不仅受到地形次生低压涡旋的吸引,其东侧同样出现以南风急流和轨迹汇聚为特征的狭管效应,有利于台风路径向北偏折。     

Assimilation and Simulation of Typhoon Rusa （2002） Using the WRF System

Using the recently developed Weather Research and Forecasting (WRF) 3DVAR and the WRF model, numerical experiments are conducted for the initialization and simulation of typhoon Rusa (2002).The observational data used in the WRF 3DVAR are conventional Global Telecommunications System (GTS) data and Korean Automatic Weather Station (AWS) surface observations. The Background Error Statistics (BES) via the National Meteorological Center (NMC) method has two different resolutions, that is, a 210-km horizontal grid space from the NCEP global model and a 10-km horizontal resolution from Korean operational forecasts. To improve the performance of the WRF simulation initialized from the WRF 3DVAR analyses, the scale-lengths used in the horizontal background error covariances via recursive filter are tuned in terms of the WRF 3DVAR control variables, streamfunction, velocity potential, unbalanced pressure and specific humidity. The experiments with respect to different background error statistics and different observational data indicate that the subsequent 24-h the WRF model forecasts of typhoon Rusa‘s track and precipitation are significantly impacted upon the initial fields. Assimilation of the AWS data with the tuned background error statistics obtains improved predictions of the typhoon track and its precipitation.     

WRF模式中同化地基微波辐射计对降水的影响

地基微波辐射计观测已经用于数值预报中,并对预报效果产生不同的影响。目前,中国约有上百台地基微波辐射计,但是观测数据用到数值预报系统的很有限。本文尝试将两台地基微波辐射计数据同化到WRF数值预报模式,并针对北京一次暴雨过程,进行同化试验,结合地面雨量计测量结果进行比对。试验结果比较表明:同化地基微波辐射计能较明显影响降水初期的降水强度和分布,与雨量计分布更为接近;随着暴雨系统发展,同化两台地基微波辐射计对大面积强降水系统的影响甚微。     

基于WRF-3DVAR同化多源融合数据对近海风模拟的改进试验

本文利用WRF模式及其3DVAR同化系统,以2008年4月20日00时—23日00时的江苏近海10 m风场为研究个例,对Quik SCAT、Wind SAT、多源测风融合数据进行同化试验,通过比较WRF-3DVAR同化系统对模拟风场初始场和预报场的改进,检验了同化不同类型资料后WRF模式对研究区域内单点及区域近地层风速的预报效果。结果表明:同化试验对初始场有改进,且对预报场的改进较FNL资料明显;不同资料对风场模拟的影响不同,同化星星、星地多源融合资料效果最佳,Quik SCAT次之,Wind SAT最差。此外,在模式分辨率一定的情况下,提高观测资料的分辨率并不一定能够改善模拟效果,资料的稀疏分辨率存在最佳选择。     

Evolution of the Mid-tropospheric Vortex during the Formation of Super Typhoon Megi(2010)

As a follow-up of a previously published article on the contribution of tropical waves, this study explores the evolution of the mid-tropospheric mesoscale cyclonic vortex(MV) during the formation of Typhoon Megi(2010) with a successful cloud-resolving simulation. It is found that the formation and intensification of the MV were related to the deep convection and subsequent stratiform precipitation, while the weakening of the MV was related to the shallow convection. Both the upward transport of...     

Analyses and forecasts of a tornadic supercell outbreak using a 3DVAR system ensemble

As part of NOAA’s "Warn-On-Forecast" initiative, a convective-scale data assimilation and prediction system was developed using the WRF-ARW model and ARPS 3DVAR data assimilation technique. The system was then evaluated using retrospective short-range ensemble analyses and probabilistic forecasts of the tornadic supercell outbreak event that occurred on 24 May 2011 in Oklahoma, USA. A 36-member multi-physics ensemble system provided the initial and boundary conditions for a 3-km convective-scale ensemble system. Radial velocity and reflectivity observations from four WSR-88 Ds were assimilated into the ensemble using the ARPS 3DVAR technique. Five data assimilation and forecast experiments were conducted to evaluate the sensitivity of the system to data assimilation frequencies, in-cloud temperature adjustment schemes, and fixed- and mixed-microphysics ensembles. The results indicated that the experiment with 5-min assimilation frequency quickly built up the storm and produced a more accurate analysis compared with the 10-min assimilation frequency experiment. The predicted vertical vorticity from the moist-adiabatic in-cloud temperature adjustment scheme was larger in magnitude than that from the latent heat scheme. Cycled data assimilation yielded good forecasts, where the ensemble probability of high vertical vorticity matched reasonably well with the observed tornado damage path. Overall, the results of the study suggest that the 3DVAR analysis and forecast system can provide reasonable forecasts of tornadic supercell storms.     

雷达反射率资料的三维变分同化研究

应用天气研究和预报模式(WRF)三维变分系统中一种新的雷达反射率资料间接同化方法来进行反射率资料的三维变分同化研究,评估雷达反射率资料对夏季短时定量降水预报的作用.该方法不直接同化雷达反射率资料,而是同化由反射率资料反演出的雨水和估计的水汽.以2009年夏季北京地区发生的4次强降水过程为例,考察了北京市气象局业务运行的快速更新循环同化预报系统对京津冀地区雷达网的雷达反射率资料的同化性能以及雷达反射率资料和径向风资料同时同化的效果.数值试验结果表明:(1)同化反演雨水或水汽都能改善降水预报,但同化反演水汽对降水预报效果的改善起了更重要的作用;(2)同化反射率资料能极大地提高短时降水预报的效果,其稳定的正面效果可以延伸到6h的预报时效,而同化径向风资料不能得到稳定的正效果;(3)同化雷达资料时,应用快速更新循环同化预报系统是提高短时定量降水预报的一个有效途径.     

Assimilating surface observations in a four-dimensional variational Doppler radar data assimilation system to improve the analysis and forecast of a squall line case

This paper examines how assimilating surface observations can improve the analysis and forecast ability of a fourdimensional Variational Doppler Radar Analysis System(VDRAS).Observed surface temperature and winds are assimilated together with radar radial velocity and reflectivity into a convection-permitting model using the VDRAS four-dimensional variational(4DVAR) data assimilation system.A squall-line case observed during a field campaign is selected to investigate the performance of the technique.A single observation experiment shows that assimilating surface observations can influence the analyzed fields in both the horizontal and vertical directions.The surface-based cold pool,divergence and gust front of the squall line are all strengthened through the assimilation of the single surface observation.Three experiments—assimilating radar data only,assimilating radar data with surface data blended in a mesoscale background,and assimilating both radar and surface observations with a 4DVAR cost function—are conducted to examine the impact of the surface data assimilation.Independent surface and wind profiler observations are used for verification.The result shows that the analysis and forecast are improved when surface observations are assimilated in addition to radar observations.It is also shown that the additional surface data can help improve the analysis and forecast at low levels.Surface and low-level features of the squall line—including the surface warm inflow,cold pool,gust front,and low-level wind—are much closer to the observations after assimilating the surface data in VDRAS.     

不同资料大气扰动分量对2010年台风鲇鱼强度变化的描述

基于模式分析和再分析资料绘制的天气图是诊断和预报极端天气事件的常用方法。近年来的研究表明,这些资料中的气象变量分解为瞬变气候和扰动两个分量后,其中的扰动分量不但能够很好地指示地面上发生的暴雨落区、热浪与低温的位置,也能指示极端天气事件的异常强度。本文以近年来研究者们广为关注的2010年台风鲇鱼为例,首先分析四家气象机构对台风强度估计的不一致性,并比较不同分析与再分析资料中大气变量对台风强度的描述;然后描述欧洲再分析资料分解的高度扰动和温度扰动之间存在的静力平衡关系,得到大气扰动分量可以直接指示台风强度随时间的相对变化。本文研究指出,各家发布的路径资料以及再分析资料对台风的定强都有差异,但大气变量分解后的扰动分量对台风强度变化有一定指示意义,可为诊断和预报提供参考。     

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...     

雷达资料同化对2015年台风彩虹数值模拟改进

基于WRF中尺度模式,采用集合卡尔曼滤波方法同化中国岸基多普勒天气雷达径向速度资料,对2015年登陆台风彩虹（1522）进行数值试验。从台风强度、路径、结构等方面验证了同化效果,并对不同区域雷达观测资料的同化敏感性进行讨论。试验结果表明:在同化窗内同化分析场台风位置误差相比未同化平均减小15 km,最多时刻减小38 km,同化资料时次越多,确定性预报路径误差越小。同化雷达资料后较好地反映出台风彩虹（1522）近海加强过程,台风中心最低气压同化分析和预报误差相比未同化最大减小超过25 hPa,台风眼的尺度、眼墙处对流非对称结构相比未同化与观测更加接近。试验还表明:台风内核100 km范围内的雷达观测对同化效果影响最大,仅同化这部分资料（约占总量的20%）各方面效果与同化全部资料相近,而仅同化100 km以外资料效果明显不及同化所有资料。仅同化台风内核雷达观测资料可以在不影响同化效果的前提下,使集合同化计算机时减小为原来的1/3,该策略可为台风实际业务预报提供一定参考。     

位涡倾向分布与台风Megi(2010)移动的关系及其影响因子

结合数值试验结果对台风Megi(2010)不同半径内的位涡倾向(potential vorticity tendency,PVT)质心位置变化与台风移动的关系进行了探讨,并对PVT方程中不同因子影响PVT质心位置的作用范围进行了研究。结果表明,较小台风半径内的正PVT质心位置变化与台风移动具有较好对应关系,可指示"Megi"转向,较大台风半径内的PVT分布变化虽不直接指示"Megi"转向,但可反映对应区域内大气动力、热力状况发生了有利于"Megi"转向的调整。PVT质心移动受位涡水平平流项的影响较大,受垂直平流项和非绝热加热项的影响相对较小,PVT方程中与台风内部对流活动有关的垂直平流项和非绝热加热项可对"Megi"中心附近PVT分布产生影响,而与台风水平环流有关的水平平流项除可对较小台风半径内PVT分布造成影响外,还可将台风位涡向外输送,是导致不同半径内PVT质心位置差异的主要原因。     

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.