区域GPS气象网站点合理布设的几点依据

区域GPS气象网反演的可降水量资料（GPS／PWV）对提高灾害性天气的监测和预报能力，改进数值天气预报精度已显示出广阔的应用前景，我国许多省市相继计划建设区域的GPS气象网。在区域GPS气象网中如何科学合理地布设GPS站就成了大家关注的问题。结合长江三角洲地区GPS气象网的情况，从长江三角洲地区的水汽通道，PWV分布的气候统计、GPS反演PWV资料的有效半径和在数值天气预报中资料同化的最大影响半径等4个方面，讨论了区域GPS网站点的分布和间距的几点依据：重点沿区域的水汽通道和强对流天气主要路径上布站，经向（南北向）的站点密度应大于纬向密度，站点的最大间距小于60km才能使反演的PwV的有效代表性和对数值预报的影响覆盖整个区域。 距     

GPS观测资料应用于中尺度数值预报模式的初步研究

利用建立在长江三角洲地区GPS观测网中 11个站点的可降水量资料 ,对 2 0 0 2年 6月 2 3～ 2 4日影响长江三角洲地区的降水过程进行了MM5模式初始湿度场调整和Nudging同化试验。试验表明 :利用GPS测量的可降水量对模式初始湿度场进行调整能明显增强模式初始场描述水汽分布的能力 ,从而有效地控制模式积分初期对可降水量预报的误差 ,并对模式 6h累积降水量预报有较明显的改善作用。利用Nudging技术同化GPS可降水量资料对MM5预报效果改善较小 ,并且Nudging系数的增加对预报效果的影响不大。总体上 ,利用GPS可降水量资料调整模式初始湿度场对模式 6h累积降水预报效果的改善明显好于连续Nudging同化。试验还表明 :GPS资料对模式初始湿度场调整改善模式对累积降水量的预报主要是通过改善网格降水预报来实现的 ,而Nudging同化主要是通过改善次网格降水而提高模式降水预报能力的。     

GPS可降水量资料应用于MM5模式的变分同化试验

利用建立在长江三角洲地区GPS观测网中13个站点的资料对2002年6月27~28日影响长江三角洲地区的降水过程进行了MM5背景误差调节和可降水量资料的三维变分同化试验。试验结果表明:背景误差对三维变分同化的效果起着关键作用,模式变量(u,v,T,p和q)误差的水平尺度与NMC方法的平均时间长度有直接的关系。利用NMC方法重新构建的背景误差更接近实际的背景误差。三维变分技术能有效地同化GPS可降水量资料。GPS可降水量资料的同化使用不仅能调整模式初始湿度场,而且也能相应地调整模式初始气压场、温度场和风场。GPS可降水量资料的同化有利于减小模式初始场对可降水量的分析误差,并且有利于减小模式积分初期(3~6 h)可降水量的预报误差。与没有进行GPS可降水量同化相比,通过GPS可降水量资料的三维变分同化,使MM5模式6 h和24 h累计降水能力得到提高,改善了MM5模式降水预报性能。总体上,GPS可降水量资料的变分同化有利于模式降水预报能力的提高。     

“00.7”北京特大暴雨模拟中气象资料同化作用的评估

针对2000年7月4～5日北京地区的一次特大暴雨过程(24 h降水量达240 mm),文中利用MM5/WRF三维变分系统和MM5非静力模式,对此次特大暴雨过程中的各种气象监测资料(地基GPS大气柱水汽含量、常规探空、高空测风、地面常规观测和地面自动气象站)的同化作用通过观测系统数值试验进行了评估.结果表明与传统的客观分析方案相比较,MM5/WRF三维变分同化系统可直接引入非常规地基GPS大气柱水汽含量监测资料,提供更好的大气初始分析场.在三维变分同化方案下,各种大气监测资料均对改进此次特大暴雨模拟有不同程度的贡献,其中,常规探空和高空测风监测资料对改进预报结果的影响最大,地面常规观测和地面自动气象站观测资料作用次之,地基GPS大气柱水汽含量资料在与其他大气监测资料相互优势互补后,可很好地改善模式大气的分析质量,通过三维变分同化技术在区域数值天气预报模式初始场中引入地基GPS大气水汽监测网资料,使此次强降水个例的6 h和24 h测站降水预报的TS评分值在1,5,10和20 mm预报检验阈值下分别提高了1%～8%.研究结果对利用三维变分数值系统,评估气象监测网资料在改进高影响天气事件预报中的作用有借鉴意义.     

同化GPS可降水量资料在安徽地区暴雨预报中的应用

利用2014年5月10日08时和5月24日08时的中国GPS(Global Positioning System)可降水量资料、地面气象观测资料及探空资料,基于WRF(Weather Research Forecast)模式及其三维变分同化系统对安徽地区2014年5月10日区域性暴雨过程和5月24日局地性暴雨过程进行了同化研究。结果表明:同化GPS水汽资料能较好地改善WRF模式的湿度场,对风场的调整较小;同化探空资料和地面常规气象观测资料可以同时调整湿度场与风场,但对湿度场的改善效果明显不如同化GPS水汽资料。仅同化GPS可降水资料,可以改进暴雨落区和强度的WRF模式模拟预报效果;而同化探空资料和地面常规气象观测资料对暴雨落区与强度预报的改进效果低于仅同化GPS水汽资料;同时同化地面常规气象观测资料、探空资料和GPS可降水资料对暴雨强度与落区的预报效果改进明显,与实况更接近,暴雨预报的TS评分更高,空报率更低。     

GPS/PWV资料同化在强降水过程中的定量作用评估

基于WRF模式及其三维变分同化系统,分别采用江苏GPS观测网的大气可降水量资料及区域内探空和地面气象站资料,对2011年8月25日江苏苏南地区的一次区域性暴雨和2008年苏皖地区的一次局地特大暴雨过程进行了同化试验,用以比较分析GPS/PWV、探空和地面观测资料同化对强降水预报的定量作用。结果表明:探空和地面资料的同化通过对模式动力和热力场的影响,在强降水中心附近形成了强烈的辐合上升运动和热力不稳定条件,直接改进了强降水中心分布结构和强度特征,对数值模拟的成功与否起着决定性作用。而GPS/PWV在探空和地面资料同化的基础上,将使水汽条件得到增强且更有组织性,无论对降水中心强度还是位置都具有较为显著的改进作用。     

2002年台风Ramasun影响华东沿海期间可降水量的GPS观测和分析

介绍了2002年建成的长江三角洲地区GPS(全球定位系统)网对台风Ramasun影响华东沿海地区时可降水量的探测,指出GPS探测的可降水量(PWV)与加密探空资料所计算的可降水量具有高度的一致性.通过对多站GPS资料时间序列的分析,揭示了在台风影响过程中PWV 的三个阶段的变化特征: 在台风降水产生前PWV 都有一个急升的过程,PWV的急升时间长短、升幅、量值大小反映了水汽累积情况,它与台风过程降水总量、每小时降水量大小有较好的对应关系;PWV 急升达到峰值后进入高值波动阶段,一般在达到峰值后7～10小时开始出现明显的降水, 在这一阶段中PWV 时间序列的波动和空间分布特征与台风降水的短时变化和螺旋雨带演变有较好的对应关系;PWV 的急降则反映台风降水即将结束.     

ATOVS辐射率资料的直接变分同化试验研究

文中采用增量三维变分 ( 3D Var)同化方法 ,对先进的微波探测装置 (AMSU A)探测的辐射亮温资料与常规探空资料在MM5中尺度数值预报模式中的直接同化和预报进行对比试验研究。结果表明 ,同化AMSU A辐射亮温资料对中高层温度分析场的影响最明显 ,对MM5模式的温度和水汽混合比预报有总体上的正效应 ,但对降水预报的改善作用不大     

不同观测资料在西南地区数值预报中的应用

利用3.4版WRF同化与预报系统开展自动站、探空、GPS大气可降水量和云迹风资料的同化对比试验,了解现有业务中已同化观测资料在新版系统中的应用效果,确定资料同化优选方案,为西南区域中心数值预报业务改进提供参考。试验表明:(1)自动站资料测站多、分布不均,对初猜场低层要素调整作用大,会减小温度、相对湿度误差;探空资料站点少、垂直信息丰富,对初猜场各层误差减小均有贡献;云迹风资料垂直分布不均,集中在对流层中高层,因此对初猜场的最大调整集中在中高层,会减小位势高度误差;GPS测站少,被剔除的比例高,对初猜场调整作用很小;(2)单独同化试验发现探空、云迹风资料有助于该地区降水预报改进,而自动站和GPS资料对降水预报有负作用;(3)同时同化探空、云迹风资料有利于西南地区降水预报准确率提高,尤其对大降水中心预报。     

湖北地基GPS大气可降水量变化特征分析及应用

利用探空资料、地基GPS/MET水汽监测资料,对恩施、宜昌、武汉三站地基GPS反演大气可降水量(GPS Precipitable Water Vapor,GPS/PWV)与探空进行了对比,表明GPS/PWV与探空RS/PWV具有良好的一致性。湖北省17站3 a GPS/PWV资料分析表明,GPS/PWV具有明显的月变化及日变化特征,分布具有从南往北逐渐递减,从西至东逐渐增加的特点。强降水个例分析表明GPS/PWV峰值略早于降水以及雷达回波峰值出现时间,高时空分辨率的GPS/PWV配合雷达对天气形势的分析以及降水的判断有一定的指导作用。     

Intercomparison of the performance of MM5/WRF with and without satellite data assimilation in short-range forecast applications over the Indian region

The present study is conducted to verify the short-range forecasts from mesoscale model version5 (MM5)/weather research and forecasting (WRF) model over the Indian region and to examine the impact of assimilation of quick scatterometer (QSCAT) near surface winds, spectral sensor microwave imager (SSM/I) wind speed and total precipitable water (TPW) on the forecasts by these models using their three-dimensional variational (3D-Var) data assimilation scheme for a 1-month period during July 2006. The control (without satellite data assimilation) as well as 3D-Var sensitivity experiments (with assimilating satellite data) using MM5/WRF were made for 48 h starting daily at 0000 UTC July 2006. The control run is analyzed for the intercomparison of MM5/WRF short-range forecasts and is also used as a baseline for assessing the MM5/WRF 3D-Var satellite data sensitivity experiments. As compared to the observation, the MM5 (WRF) control simulations strengthened (weakened) the cross equatorial flow over southern Arabian sea near peninsular India. The forecasts from MM5 and WRF showed a warm and moist bias at lower and upper levels with a cold bias at the middle level, which shows that the convective schemes of these models may be too active during the simulation. The forecast errors in predicted wind, temperature and humidity at different levels are lesser in WRF as compared to MM5, except the temperature prediction at lower level. The rainfall pattern and prediction skill from day 1 and day 2 forecasts by WRF is superior to MM5. The spatial distribution of forecast impact for wind, temperature, and humidity from 1-month assimilation experiments during July 2006 demonstrated that on average, for 24 and 48-h forecasts, the satellite data improved the MM5/WRF initial condition, so that model errors in predicted meteorological fields got reduced. Among the experiments, MM5/WRF wind speed prediction is most benefited from QSCAT surface wind and SSM/I TPW assimilation while temperature and humidity prediction is mostly improved due to latter. The largest improvement in MM5/WRF rainfall prediction is due to the assimilation of SSM/I TPW. The assimilation of SSM/I wind speed alone in MM5/WRF degraded the humidity and rainfall prediction. In summary the assimilation of satellite data showed similar impact on MM5/WRF prediction; largest improvement due to SSM/I TPW and degradation due to SSM/I wind speed.     

青藏高原东缘GPS水汽资料对暴雨模拟的影响分析

选取2009年6月30日发生在云南南部和湖南北部的强降水过程,利用WRF模式和建立在青藏高原东缘地区18个地基GPS站点观测的可降水量资料（GPS/PWV）进行同化试验.试验表明：选取全部18个站和云南省8个站GPS/PWV资料进行同化,发现下游地区的强降水区湖南北部降水强度发生较大变化.选取100.E附近的6个站GPS/PWV资料进行同化,发现下游地区的强降水区湖南北部降水强度变化不大.利用全部站点GPS/PWV资料,模式初始场大部分地区湿度增加,对应下游降水中心强度增加,少部分地区湿度减少,对应降水区域南移.GPS/PWV资料同化对模式初始场湿度场和高度场影响较大,而对温度和风场影响较小.     

LAPS同化GPS/PWV资料在暴雨预报中的应用研究

利用LAPS(Local Analysis and Prediction System)系统同化GPS(Global Positioning System)/PWV(Precipitable Water Vapor)资料,分析GPS/PWV资料对LAPS输出场的影响,并结合WRF模式,将LAPS输出场作为其初始场进行降水预报,进一步考察GPS/PWV资料对降水预报的作用。选取2009年6月28日湖北地区的一次强降水过程,设计三种方案进行试验。结果表明:同化GPS/PWV资料后对LAPS湿度场有显著的改善,而对高度场及风场的作用则不明显;GPS/PWV资料对区域平均可降水量的影响比雷达资料大一个量级;与此同时,利用多种评分方法对6 h累计降水做了检验,分析结果表明同化GPS/PWV资料能够有效地改进WRF模式的初始场,增加丰富的中小尺度信息,并对随后的确定性预报产生正影响。     

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.     

Numerical Assessing Experiments on the Individual Component Impact of the Meteorological Observation Network on the ＂July 2000＂ Torrential Rain in Beijing

In an effort to assess the impact of the individual component of meteorological observations (ground-based GPS precipitable water vapor,automatic and conventional meteorological observations) on the torrential rain event in 4-5 July 2000 in Beijing (with the 24-h accumulated precipitation reaching 240 mm),24-h observation system experiments are conducted numerically by using the MM5/WRF 3DVAR system and the nonhydrostatic MM5 model.Results indicate that,because the non-conventional GPS observations are directly assimilated into the initial analyses by 3DVAR system,better initial fields and 24-h simulation for the severe precipitation event are achieved than those under the MM5/Litter_R objective analysis scheme. Further analysis also shows that the individual component of meteorological observation network plays their special positive role in the improvement of initial field analysis and forecasting skills.3DVAR scheme with or without radiosonde and pilot observation has the most significant influence on numerical simulation,and automatic and conventional surface meteorological observations rank second.After acquiring the supplement information from the other meteorological observations,the ground-based GPS precipitable water vapor data can more obviously reflect initial field assimilation and precipitation forecast.By incorporating the ground- based GPS precipitable water vapor data into the 3DVAR analyses at the initial time,the threat scores (TS) with thresholds of 1,5,10,and 20 mm are increased by 1%-8% for 6- and 24-h accumulated precipitation observations,respectively.This work gives one helpful example that assesses the impact of individual component of the existing meteorological observation network on the high influence weather event using 3DVAR numerical system.     

Operational convective-scale data assimilation over Iran: A comparison between WRF and HARMONIE-AROME

The impact of applying three-dimensional variational data assimilation (3D-Var DA) on convective-scale forecasts is investigated by using two mesoscale models, the Weather Research and Forecasting model (WRF-ARW) and the Hirlam and Aladin Research Model On Non-hydrostatic-forecast Inside Europe (HARMONIE-AROME). One month (1 to 30 December 2013) of numerical experiments were conducted with these two models at 2.5 km horizontal resolution, in order to partly resolve convective phenomena, on the same domain over a mountainous area in Iran and neighboring areas. Furthermore, in order to estimate the domain specific background error statistics (BES) in convective scales, two months (1 November to 30 December 2017) of numerical experiments were carried out with both models by downscaling operational ECMWF forecasts. For setting the numerical experiments in an operational scenario, ECMWF operational forecast data were used as initial and lateral boundary conditions (ICs/LBCs). In order to examine the impact of data assimilation, the 3D-Var method in cycling mode was adopted and the forecasts were verified every 6 hours up to 36 hours for selected meteorological variables. In addition, 24 h accumulated precipitation forecasts were verified separately. Generally, the WRF and HARMONIE-AROME exhibit similar verification statistics for the selected forecast variables. The impact of DA on the numerical forecast shows some evidence of improvement in both models, and this effect decreases severely at longer lead times. Results from verifying the 24 h convective-scale precipitation forecasts from both models with and without DA suggest the superiority of the WRF model in forecasting more accurately the occurred precipitation over the simulation domain, even for the downscaling run.     

GPS/PWV资料在梅雨锋暴雨个例中的同化试验

基于WRF(Weather Research and Forecasting Model,天气预报模式)及其三维变分同化系统3DVAR,利用江苏省GPS/PWV(PWV:Precipitable Water Vapor,GPS反演得到可降水量)资料,并将其与探空资料比对订正,针对2011年6月18日梅雨锋暴雨进行3 h循环同化模拟。在降水参数化方案敏感性试验与单点同化试验基础上,设计多组试验对6 h降水量进行TS(Threat Score)评估。结果表明:(1)同化订正GPS/PWV资料对降水预报能力显著提高,特别是大雨、暴雨量级以上的预报能力;(2)降水量的RMSE(Root Mean Squared Error,均方根误差)相比控制试验均减小,CC(Correlation Coefficient,相关系数)均增大,最显著试验RMSE从19.1 mm下降到12.6 mm,CC从0.45上升到0.74;(3)NMC方法统计的背景误差协方差条件下中雨至暴雨量级TS评分均有一定程度提高,默认的背景误差协方差在大雨以上量级TS评分大幅提高。     

Moisture Analysis of a Squall Line Case Based on Precipitable Water Vapor Data from a Ground-Based GPS Network in the Yangtze River Delta

A squall line swept eastward across the area of the Yangtze River Delta and produced gusty winds and heavy rain from the afternoon to the evening of 24 August 2002. In this papers the roles of moisture in the genesis and development of the squall line were studied. Based on the precipitable water vapor （PWV） data from a ground-based GPS network over the Yangtze River Delta in China, plus data from a Pennsylvania State University/National Atmospheric Center （PSU/NCAR） mesoscale model （MM5） simulation, initialized by three-dimensional variational （3D-VAR） assimilation of the PWV data, some interesting features are revealed. During the 12 hours prior to the squall line arriving in the Shanghai area, a significant increase in PWV indicates a favorable moist environment for a squall line to develop. The vertical profile of the moisture illustrates that it mainly increased in the middle levels of the troposphere, and not at the surface. Temporal variation in PWV is a better precursor for squall line development than other surface meteorological parameters. The characteristics of the horizontal distribution of PWV not only indicated a favorable moist environment, but also evolved a cyclonic wind field for a squall line genesis and development. The ＂＋2 mm＂ contours of the three-hourly PWV variation can be used successfully to predict the location of the squall line two hours later.