利用NOAA/AMSU资料和GRAPES同化系统对陆面比辐射率计算的改进研究

地表比辐射率计算的不确定性,直接影响到卫星资料在数值预报中同化应用的效果。本文采用美国NOAA/NESDIS的Weng等[1,2]提出的复杂陆面比辐射率模式,同时用NOAA卫星AMSU-ACh1或Ch2反演的地表比辐射率来调整该模式所需的地表参数,从而在缺少详细地表参数的情况下,改进AMSU-A Ch3和Ch15的地表比辐射率计算精度。在积雪地表情况下,用NOAA卫星AMSU-A资料直接反演各通道的比辐射率,在GRAPES同化系统中的应用表明,结果有明显的改进。     

数值预报产品资料预处理软件的设计及应用

运用Visual BASIC6．0和Borland Delphi7．0混合编程,设计了一套NWP资料预处理软件。该软件可用于对国家气象中心T213、HLAFS以及ECMWF数值分析预报产品进行实时处理加工,建立了NWP实时资料库和历史资料库。对该应用软件的开发环境、设计思路、主要功能、技术特点和实际应用等做了简单介绍。     

卫星探测的辐射率资料在数值天气预报中的直接应用

最近,在卫星探测资料和数值分析技术的研究中探索出在数值天气预报(NWP)系统中利用卫星资料的新途径。如果这些资料更直接地、而不是经由独立的温度和湿度反演廓线在NWP场中同化的话,预期可以从中获得更大的效益。本文概述英国气象局有关这一新方法背后的理论及实现这些思想的某些方面。     

微波辐射率仪和地物微波辐射率

根据微波辐射传输的特性,研制了微波辐射率仪,它可以隔离外界的干扰,用以研究不同因子对于地物微波辐射率的作用。微波辐射率仪由微波辐射计、辐射室和样品箱三部分组成。本文介绍了它的测量原理;在实验中对于微波辐射率仪的可靠性、稳定性及其精度进行了检验,结果证明其性能是好的,可在地物微波辐射率测量中使用。在实验中,进行了8.5mm和3.2cm波段地物(水、土壤)微波辐射率的测量,并分析其结果。     

AMSR2辐射率资料同化对台风“山神”分析和预报的影响研究

在WRFDA-3DVar（Weather Research and Forecasting model's 3-dimensional variational data assimilation）的框架下,添加了新的探测器AMSR2（Advanced Microwave Scanning Radiometer 2）微波辐射率资料的同化模块,实现了AMSR2辐射率资料在中小尺度同化系统中的有效使用。台风"山神"（Son-Tinh）直接同化AMSR2资料的个例试验结果表明,AMSR2资料可以很好的探测出台风的形态,并且与没有同化该资料的控制试验相比,同化AMSR2辐射率资料可以有效提高模式分析场的质量,进一步提高了台风中心气压,最大风速和台风路径的预报。     

台风试验陆地加密观测在数值天气预报中的作用

采用国家气象中心（NMC）有限区同化预报系统（HLAFS）和华北区域分析预报系统（NCAFS）的基本方案,选择“八五”期间台风试验期进行陆地测站特殊加密观测的两个台风个例作数值天气预报（NWP）试验,探讨这些资料在NWP中的作用。试验结果表明:陆地测站加密地面观测资料,对NMC的NWP系统的预报,尤其在较高分辨率情况下,具有较明显的改进作用。     

单部多普勒天气雷达风场反演及其在数值预报中的应用试验

针对1998年7月5日下午到夜间北京地区出现的一次强降雨过程, 采用“局部VAD法”, 对中国气象科学研究院多普勒雷达测得的1998年7月5日12:00UTC的径向风反演成水平风, 并将反演风应用到数值天气预报 (NWP) 同化系统中, 进行了同化预报试验。结果表明, 反演的雷达风基本符合事实, 将其应用到NWP中, 有助于分析和预报时空尺度较小的中尺度系统。     

IBM 4381-P03型双CPU计算机实现NWP模型的并行计算

本文介绍数值天气预报（NWP）问题，用IBM4381—P03型计算机的两个CPU，实现气象物理模型x-y方向“分解-联合”的自稳定差分格式的并行计算的初步情况:（1）4381-3型的CPU可按通常理解的分开任务方式实现并行计算；（2）MVS大型操作系统控制VS FORTRAN库中的MTF（Multitasking Facility）实行分开任务-并行处理-等待同步，从而实现NWP模型的并行运算，这在我国气象问题计算中还是第一次，今后卫星数据处理的新方案可用4381-3双CPU并行处理，老方案也可逐步变成并行计算；（3）并行加速达到1.3—1.5，尚未达到IBM公司的1.8加速水平，还有潜力可挖。     

反演寿县TMI微波频率的地表比辐射率

利用一个微波辐射传输模式，晴天下的大气探测廓线，地面的部分观测资料以及卫星观测的亮温，计算了淮河流域能量和水循环实验(HUBEx)中，寿县地区的热带降雨观测卫星微波成像仪(TRMM／TMI)微波频率的地表比辐射率。通过比较所计算的微波地表比辐射率随地表状况的改变，发现地表微波比辐射率随地表状况的变化存在敏感性，并且其变化是合理的。本中，地表肤温设定等于地表空气温度，并且仅计算了寿县的地表比辐射率，在HUBEx区域上的地表比辐射率的计算需要更多的观测资料。     

利用分裂窗算法反演陆地表面温度的研究进展

本文以LST反演的分裂窗算法作了回顾和比较，LST反演的分裂窗算法最一般的形式是Ts=T4 A(T4-T5) B,其中Ts是陆地表面温度，T4和T5分别是AVHRR分裂窗通道4和5的亮温度，A和B是由大气、观测角及地表辐射率所决定的系数，不同的算法其系数的确定有很大的不同，地表比辐射率的确定是LST反演中的主要难点，目前也有多种方法来确定地表比辐射率值，最后本文还指出了目前在LST反演中存在的局限性。     

气象卫星资料同化的科学问题与前景

从数值天气预报资料同化的角度,分析了气象卫星观测与常规气象观测的不同特点形成了卫星资料同化的特殊科学问题.由于各类星载遥感仪器所观测到的是一定波长的电磁辐射,不能像传统的直接观测资料一样被预报模式直接应用.又由于卫星观测对象是整个大气层,而不是特定高度的大气,因此确定卫星观测影响的高度和它的潜在垂直分辨率成为一个关键问题.卫星观测还可能存在着系统性的偏差,这与直接观测的误差互相独立也有很大区别.资料同化通常建立在模式预报(即背景信息)与观测量的比较的基础上,为了实现同化,需要将模式的基本大气变量转换成星载仪器所获得的特定波长的电磁波特征量,或者将观测到的电磁辐射特征量反算成大气的特征量.前者需要引入复杂的观测算子,后者则将复杂的反演过程交给了前处理阶段.这就形成了直接与间接同化卫星资料的两种不同策略,策略的选择取决于同化系统处理复杂观测资料的能力,对同化效果有决定性的影响.逐个分析了目前用于数值预报的5种卫星观测资料,即星载大气垂直探测器资料、大气运动矢量资料、散射仪海面风资料、卫星观测的云与降水信息资料与GPS掩星观测资料的同化的进展与有待解决的主要问题,概述了中国近年在大气垂直探测器等卫星资料同化中的研究进展及其业务应用的效果,并提出了今后需要予以特别关注的研究方向.     

On the assimilation of satellite sounder data in cloudy skies in numerical weather prediction models

Satellite measurements are an important source of global observations in support of numerical weather prediction (NWP). The assimilation of satellite radiances under clear skies has greatly improved NWP forecast scores. However, the application of radiances in cloudy skies remains a significant challenge. In order to better assimilate radiances in cloudy skies, it is very important to detect any clear field-of-view (FOV) accurately and assimilate cloudy radiances appropriately. Research progress on both clear FOV detection methodologies and cloudy radiance assimilation techniques are reviewed in this paper. Overview on approaches being implemented in the operational centers and studied by the satellite data assimilation research community is presented. Challenges and future directions for satellite sounder radiance assimilation in cloudy skies in NWP models are also discussed.     

区域极轨卫星ATOVS辐射偏差订正方法研究

近年来,卫星辐射资料在数值天气预报(NWP)系统中的直接同化研究取得了长足进展。为了利用TIROS业务垂直探测器(ATOVS)的辐射资料,必须对卫星观测辐射值的系统性偏差进行订正。在ECMWF原全球TOVS辐射偏差订正方案基础上,结合ATOVS资料特征和中国的实际情况,建立了适用于区域NOAA-15/16/17极轨气象卫星ATOVS辐射资料的偏差订正方案。该方案偏差订正分两步进行:首先进行扫描偏差订正,然后进行气团偏差订正。扫描偏差是临边测量相对于星下点测量的系统偏差,统计显示该种偏差具有一定的纬度依赖性,所以订正时按每10度的纬度带分别进行订正。气团偏差订正主要就是根据当时的天气条件进行订正,而天气条件一般用预报因子来定量表示。文中从中国国家气象中心T213背景场导出预报因子:(1)1000—300 hPa的厚度,(2)200—50 hPa的厚度,(3)模式地表温度,(4)总可降水量。模式预报因子的使用从观念上将对观测值的订正变为对计算前向辐射值的订正问题。试验结果表明,订正结果显著。     

Quality Assessment and Forecast Sensitivity of Global Remote Sensing Observations

The satellite-derived wind from cloud and moisture features of geostationary satellites is an important data source for numerical weather prediction(NWP) models. These datasets and global positioning system radio occultation(GPSRO)satellite radiances are assimilated in the four-dimensional variational atmospheric data assimilation system of the UKMO Unified Model in India. This study focuses on the importance of these data in the NWP system and their impact on short-term24-h forecasts. The quality of the wind observations is compared to the short-range forecast from the model background. The observation increments(observation minus background) are computed as the satellite-derived wind minus the model forecast with a 6-h lead time. The results show the model background has a large easterly wind component compared to satellite observations. The importance of each observation in the analysis is studied using an adjoint-based forecast sensitivity to observation method. The results show that at least around 50% of all types of satellite observations are beneficial. In terms of individual contribution, METEOSAT-7 shows a higher percentage of impact(nearly 50%), as compared to GEOS, MTSAT-2and METEOSAT-10, all of which have a less than 25% impact. In addition, the impact of GPSRO, infrared atmospheric sounding interferometer(IASI) and atmospheric infrared sounder(AIRS) data is calculated. The GPSRO observations have beneficial impacts up to 50 km. Over the Southern Hemisphere, the high spectral radiances from IASI and AIRS show a greater impact than over the Northern Hemisphere. The results in this study can be used for further improvements in the use of new and existing satellite observations.     

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.     

Exploration of the remote sounding of infrared cooling rates due to water vapor

Summary We explore the feasibility of deriving atmospheric infrared cooling rates by direct inversion of radiances observed by satellites from space. In order to convert radiances to fluxes and achieve vertical profiling at the same time, we show that it is necessary to combine radiances from narrow channels with radiances averaged over spectral bands. We demonstrate that the vertical integral of the cooling rate in the spectral band, convolved with a kernel function associated with the narrow channel, can be related to a weighted sum of the channel and band radiances. The band radiance must be evaluated at a specific zenith angle, which is a result of use of the mean value theorem. With known kernel functions, the combined radiances may be inverted to obtain the cooling rate profile. These results are derived from use of a random model for the transmittance in its strong-and weak-line limits. The results are similar in the two limits leading us to conclude that there are expressions that are approximately valid over the entire range of transmittance. We show by numerical methods that this conclusion is correct and apply the retrieval technique successfully to get the cooling rate profile in the rotational band of water vapor.With 3 Figures     

A PRELIMINARY STUDY ON THE 3DVAR ASSIMILATION OF THE AMSU-A DATA IN SPACE-TIME MULTISCALE ANALYSIS SYSTEM

Assimilating satellite radiances into Numerical Weather Prediction (NWP) models has become an important approach to increase the accuracy of numerical weather forecasting. In this study, the assimilation technique scheme was employed in NOAA’s STMAS (Space-Time Multiscale Analysis System) to assimilate AMSU-A radiances data. Channel selection sensitivity experiments were conducted on assimilated satellite data in the first place. Then, real case analysis of AMSU-A data assimilation was performed. The analysis results showed that, following assimilating of AMSU-A channels 5–11 in STMAS, the objective function quickly converged, and the channel vertical response was consistent with the AMSU-A weighting function distribution, which suggests that the channels can be used in the assimilation of satellite data in STMAS. With the case of the Typhoon Morakot in Taiwan Island in August 2009 as an example, experiments on assimilated and unassimilated AMSU-A radiances data were designed to analyze the impact of the assimilation of satellite data on STMAS. The results demonstrated that assimilation of AMSU-A data provided more accurate prediction of the precipitation region and intensity, and especially, it improved the 0–6h precipitation forecast significantly.     

大气遥感辐射传输模式的一种有效的Jacobian算法

介绍并验证了一种快速、精确地计算Jacobian的解析方法(辐射传输方程的线性化,简称LR方法),将其结果与NAST-I真正的线性模式及数值方法(差分方法)的Jacobian值进行比较。结果表明,这种解析算法不仅快速、精确,而且独立于辐射传输方程,在有效Jacobian计算中只需要输入大气透过率,可适用于任何垂直探测器权重函数的计算。     

风云三号卫星微波湿度计的扫描角偏差订正

首先统计分析了FY-3A卫星MWHS(Micro Wave Humidity Sounder,微波湿度计)2010年1月整月和8月28日—9月6日Level-1b全球观测亮度温度T_O和背景场(NCEP GFS 6 h预报场)用辐射传输模式(美国通用辐射传输模式CRTM 2.0版本)模拟的亮度温度T_B随扫描角的分布特征,发现通道3和4的观测随仪器扫描角有抖动、不连续现象。同时沿着仪器扫描线在星下点两测存在观测不对称现象,而且权重函数峰值越接近地面的通道该不对称现象越明显。在统计观测增量T_O-T_B随扫描角和纬度变化的基础上,定量给出了不同纬度带内(每隔5个纬度)MWHS通道3、4和5的扫描角偏差订正系数,该系数可直接提供给各种资料同化系统同化FY-3A MWHS资料时使用。     

用不确定度指数实时评价模式预报场业务性能

引入不确定度概念,结合“马赛克化”方法,定义不确定度指数和不稳定度指数,开发了实时业务系统,对ECMWF、JMA和T213的数值预报场进行了实时的性能评价;通过一段时间的资料统计,对3个模式的总体性能进行了对比。结果显示,该方法可为实时评价数值预报产品的性能提供一种客观依据,为预报员在日常预报工作中对数值预报模式性能的了解和科学选用数值预报产品提供科学定量的参考。