Resolving SSM/I-ship radar rainfall discrepancies from AIP-3

The third algorithm intercomparison project （AIP-3） involved rain estimates from more than 50 satellite rainfall algorithms and ground radar measurements within the Intensive Flux Array （IFA） over the equatorial western Pacific warm pool region during the Tropical Ocean Global Atmosphere coupled Ocean-Atmosphere Response Experiment （TOGA COARE）. Early results indicated that there was a sys- tematic bias between rainrates from satellite passive microwave and ground radar measurements. The mean rainrate from radar measurements is about 50% underestimated compared to that from passive microwave-based retrieval algorithms. This paper is designed to analyze rain patterns from the Florida State University rain retrieval algorithm and radar measurements to understand physically the rain discrep- ancies. Results show that there is a clear range-dependent bias associated with the radar measurements. However, this range-dependent systematical bias is almost eliminated with the corrected radar rainrates. Results suggest that the effects from radar attenuation correction, calibration and beam filling are the major sources of rain discrepancies. This study demonstrates that rain retrievals based on satellite mea- surements from passive microwave radiometers such as the Special Sensor of Microwave Imager （SSM/I） are reliable, while rain estimates from ground radar measurements are correctable.     

Physical retrievals of over-ocean rain rate from multichannel microwave imagery. Part II: Algorithm implementation

Summary A new physical inversion-based algorithm for retrieving rain rate over the ocean with the Special Sensor Microwave Imager (SSM/I) is described. In a departure from other rain rate retrieval algorithms, the satellite observables inverted in the present algorithm are not the raw brightness temperatures but rather normalized polarizations for 19.35, 37.0, and 85.5 GHz, plus an 85.5 GHz scattering index which is sensitive primarily to ice particles aloft. The normalized polarizations are interpreted as footprint-averages of theoretically derived analytic functions of the column optical depth associated primarily with liquid water. The effective vertical depth of the rain layer is specified as a function of the SSM/I estimated column water vapor.The retrieval algorithm performs an iterative search for a high resolution (12.5 km) rain field which is simultaneously consistent with the 19.35 and 37.0 GHz normalized polarizations. The first-guess rain rate field is supplied by the 85.5 GHz scattering index. At gridpoints for which the rain column optical depth exceeds the dynamic range of the attenuation-based indices, the first-guess field is left essentially unmodified; elsewhere, the required consistency with the 19 and 37 GHz indices usually results in significant modification of the scattering-based rain rate estimates.The algorithm as described here is a prototype implementation which was developed with reference only to idealized theoretical models; empirical improvements to the numerical scheme and the model coefficients will be made in the future as results from the first Precipitation [algorithm] Intercomparison Project 1 (PIP-1) and the second phase of the GPCP (Global Precipitation Climatology Project) algorithm Intercomparison Project (AIP/2) are analyzed, as well as data from individual validation efforts. Although the algorithm is physically based and uses all SSM/I channels, it is computationally much less demanding than cloud/radiative transfer model-based inversion algorithms published else-where.With 9 Figures     

Research on the Application of the Radiative Transfer Model Based on Deep Neural Network in One-dimensional Variational Algorithm

As a typical physical retrieval algorithm for retrieving atmospheric parameters, one-dimensional variational(1 DVAR) algorithm is widely used in various climate and meteorological communities and enjoys an important position in the field of microwave remote sensing. Among algorithm parameters affecting the performance of the 1 DVAR algorithm, the accuracy of the microwave radiative transfer model for calculating the simulated brightness temperature is the fundamental constraint on the retrieval ...     

多层四流球谐函数算法的构建及在大气辐射传输模式中的应用

为了在不大幅度增加计算成本的情况下提高大气辐射传输计算的精度,利用单层四流球谐函数结合多层二流累加法,构造了可用于多层大气的四流球谐函数算法。为了比较与其他辐射传输算法的差异,引入48流离散纵坐标算法作为比较标准,Eddington 近似、四流离散纵坐标算法作为比较对象。在真实大气廓线条件下,计算了晴空和有云大气顶向上辐射通量、地表向下辐射通量以及加热率廓线。得出以下结论：在晴空情况下,与作为标准的48流离散纵坐标法相比,Eddington 近似、四流离散纵坐标法和新构造的四流球谐函数方法加热率绝对误差都小于0?3 K／d;向上、向下辐射通量的相对误差分别小于1％和0?6％。这表明在晴空情况下,3种算法对加热率的计算精度差别不大;对辐射通量的计算精度,两种四流近似算法比传统的 Eddington 近似更为精确。在有云情况下,与48流离散纵坐标法相比,四流球谐函数和四流离散纵坐标法计算的云顶加热率相对误差小于1％,而 Eddington 近似计算的云顶加热率相对误差大于5％。结果表明：新构造的四流球谐函数算法可用于大气辐射传输模式,在不大幅度增加计算成本的同时,提高了晴空大气的整体辐射计算精度和有云大气辐射加热率的计算精度。     

云对地基微波辐射计反演湿度廓线的影响

利用中国气象局大气探测试验基地的L波段探空数据和微波辐射计观测数据,采用MonoRTM辐射传输模型作为正演亮温模型,BP (back propagation) 神经网络作为反演工具,在由亮温反演大气湿度廓线的过程中,添加与样本匹配的云底高度和云厚度信息,建立新的反演模型,使新反演模型得到的反演湿度廓线和未添加云信息的反演湿度廓线分别与探空数据进行对比,获取两种反演方法各高度层的均方根误差,分析云信息对反演大气湿度廓线的影响。对比结果表明:未添加云信息时,测试样本的反演湿度廓线与探空廓线的相关系数平均值为0.685,而添加云信息后,相关系数平均值为0.805。相比未添加云信息的反演廓线,添加云信息之后多数高度层的均方根误差均有不同程度减小,而在有云以上高度层表现尤为明显。     

Tabulation of Mie properties for an effective microwave radiative model

Summary In microwave radiative transfer model simulations of atmospheric convective systems, the Mie calculations usually consume the majority of the computer time necessary for the calculations (70 to 90% for frequencies ranging from 6 to 300 GHz). For a large array of atmospheric profiles, the repeated Mie scattering calculations make the radiative transfer modeling not only expensive, but often impossible. A set of Mie tables, therefore, is developed to replace the actual Mie calculations in the microwave radiation model.The tables are divided into categories of liquid water (cloud water and rain), ice, snow, graupel and hail. The tables are free from restriction on variation of size distribution, particle density and mixing phases. Results from this study show that by using the Mie tables, the total CPU time is reduced by at least one order of magnitude, depending on the frequency. Compared to using full Mie calculation in the radiative model, the bias and root-mean-square (rms) deviation from the Mie tables are less than 1.2 K for any atmosphere with precipitation rates up to 125 mm hr^–1 at any frequency and any viewing angle.The Mie tables are particularly useful in simulating the microwave radiation field over a mesoscale meteorological system. Such a study would not be satisfactory using a Mie parameterization scheme, because one would have to trade off the accuracy and flexibility for modeling efficiency.With 7 FiguresThis research was done under contract at the Goddard Space Flight Center, Greenbelt, Maryland.     

On the Tropical Rainfall Measuring Mission (TRMM)

Summary The importance of quantitative knowledge of tropical rainfall, its associated latent heating and variability is summarized in the context of climate change. Since the tropics are mainly covered with oceans, with some deserts and jungles, the monthly precipitation is not known within a factor of two. Hence the only way to measure it adequately for climate and general circulation models is from space. The paper describes the Tropical Rainfall Measuring Mission (TRMM). This joint Japan-U.S. cooperative Earth Probe satellite will be launched from Japan in 1997 for a three-year mission. The scientific basis of the instrument and orbit selection is explained. The precipitation instrument complement comprises the first rain radar to be flown in space (PR), and a multi-channel passive microwave sensor (TMI) improved relative to the SSM/I¹ by an additional channel at 10 GHz. The third rain instrument is a five-channel VIS/IR (VIRS) sensor. Progress in construction of instruments, observatory, data system, and the ground validation program is summarized. A report is also given concerning development of the algorithms by which rainfall and its associated latent heat release will be calculated from the several instruments, separately and in combination, and how the scientists will interact with the data system to obtain the 32 rain data products necessary to fulfill the science requirements.With 9 FiguresSSM/I stands for Special Sensor Microwave Imager.     

Remote sensing of cloud liquid water

Summary A method is presented to infer cloud liquid water path (LWP in kg/m²) over the ocean from passive microwave measurements of SSM/I. The algorithm to retrieve LWP is based on simulated satellite observations. They are calculated with a radiative transfer model applied to about 3000 radiosonde ascents over the Atlantic Ocean. Since radiosonde observations do not contain direct information about cloud water and ice, these parameters are parameterized based on relative humidity and temperature using modified adiabatic liquid water density profiles. A multiple linear regression is applied to the simulated radiances and the calculated LWP to derive the algorithm. The retrieval accuracy based on the regression analysis including instrumental noise is 0.03 kg/m². Validation of the LWP-algorithm was pursued through a comparison with measurements of a ground-based 33 GHzmicrowave radiometer on board of R.V. Poseidon during the International Cirrus Experiment 1989 at the North Sea (ICE'89). The LWP values agree within the range of uncertainty caused by the different sampling characteristics of the observing systems. The retrieval accuracy for clear-sky cases determined using colocated METEOSAT data over the North Sea is 0.037 kg/m² and confirms the accuracy estimated from regression analysis for the low liquid water cases.The algorithm was used to derive maps of monthly mean LWP over the Atlantic Ocean. As an example the Octobers of the 5 years 1987–1991 were selected to demonstrate the interannual variability of LWP. The results were compared with the cloud water content produced by the climate model ECHAM-T2 from the Max-Planck-Institut Hamburg.Observations during ICE'89 were used to check the accuracy of the applied radiative transfer model. Brightness temperatures were calculated from radiosonde ascents launched during the overpass of DMSP-F8 in cloud-free situations. The channel-dependent differences range from about –2 to 3 K.The possibility to identify different cloud types using microwave and infrared observations was examined. The main conclusion is that simultaneous microwave and infrared measurements enable the separation of dense cirrus and cirrus with underlying water clouds. A classification of clouds with respect to their top heights and LWP was carried out using a combination of SSM/I derived LWP and simultaneously recorded Meteosat IR-data during ICE'89.With 11 Figures     

基于径向基神经网络的地基微波辐射计反演算法研究

利用兰州大学半干旱气候与环境观测站(SACOL站)2009—2010年的地基微波辐射计亮温资料和榆中站探空资料,建立了应用于地基微波辐射计温度、相对湿度和水汽密度反演的径向基神经网络,并将反演结果与地基微波辐射计自带反演产品进行了对比,探究了径向基神经网络在地基微波辐射计气象要素反演算法本地化的应用效果。结果表明:径向基神经网络反演的温度、相对湿度和水汽密度的均方根误差最大值分别为2.72 K、22.32%和0.73 g·m^-3,在所有高度层上径向基神经网络的反演结果均优于微波辐射计,反演产品对2—10 km、1—7 km、0—3 km的大气温度、相对湿度和水汽密度廓线的反演均有明显改善,径向基神经网络能够应用于地基微波辐射计气象要素的反演算法的本地化。     

基于系留气艇平台的红外辐射传输算法实验验证

中国科学院大气物理研究所中层大气和全球环境探测重点实验室 (LAGEO) 建立了以系留气艇为平台的综合探测系统。通过气艇在大气边界层上升、下降过程获得不同高度的气象参数和同时的辐射参数。以气象参数为输入,应用辐射传输模式 (MODTRAN4.0) 获得模式辐射输出,将其与实测辐射值作对比,验证MODTRAN4.0模式的准确性,为有关目标识别与遥感提供基础。2006年8月在中国科学院大气物理研究所香河综合观测站利用系留气艇平台进行了验证实验,并对热红外波段的模式对比结果进行分析。结果表明:所建实验系统具备进行模式验证的能力,在热红外波段,MODTRAN4.0模式输出结果与实测辐射亮度之间的相对误差的均方差在边界层大气条件下小于3%。     

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。     

Impact of Different Aerosols on the Evolution of the Atmospheric Boundary Layer

The present work analyzes the effect of aerosols on the evolution of the atmospheric boundary layer (ABL) over Shangdianzi in Beijing.A one-dimensional ABL model and a radiative transfer scheme are incorporated to develop the structure of the ABL.The diurnal variation of the atmospheric radiative budget,atmospheric heating rate,sensible and latent heat fluxes,surface and the 2 m air temperatures as well as the ABL height,and its perturbations due to the aerosols with different single-scattering albedo (SSA) are studied by comparing the aerosol-laden atmosphere to the clean atmosphere.The results show that the absorbing aerosols cause less reduction in surface evaporation relative to that by scatting aerosols,and both surface temperature and 2 m temperature decrease from the clean atmosphere to the aerosol-laden atmosphere.The greater the aerosol absorption,the more stable the surface layer.After 12:00 am,the 2 m temperature increases for strong absorption aerosols.In the meantime,there is a slight decrease in the 2 m temperature for purely scattering aerosols due to radiative cooling.The purely scattering aerosols decrease the ABL temperature and enhance the capping inversion,further reducing the ABL height.     

RETRIEVING ATMOSPHERIC SOUNDING PROFILES AROUND TYPHOON YUNNA USING INFRARED HYPERSPECTRAL MEASUREMENTS AIRS

In this study,we derived atmospheric profiles of temperature,moisture,and ozone,along with surface emissivity,skin temperature,and surface pressure,from infrared-sounder radiances under clear sky (cloudless) condition.Clouds were detected objectively using the Atmospheric Infrared Sounder under a relatively low spatial resolution and cloud-mask information from the Moderate Resolution Imaging Spectroradiometer under a high horizontal resolution;this detection was conducted using space matching.Newton’s nonlinear physical iterative solution technique is applied to the radiative transfer equation (RTE) to retrieve temperature profiles,relative humidity profiles,and surface variables simultaneously.This technique is carried out by using the results of an eigenvector regression retrieval as the background profile and using corresponding iterative forms for the weighting functions of temperature and water-vapor mixing ratio.The iterative forms are obtained by applying the variational principle to the RTE.We also compared the retrievals obtained with different types of observations.The results show that the retrieved atmospheric sounding profile has great superiority over other observations by accuracy and resolution.Retrieved profiles can be used to improve the initial conditions of numerical models and used in areas where conventional observations are sparse,such as plateaus,deserts,and seas.     

Rain rate estimation from a synergetic use of SSM/I, AVHRR and meso-scale numerical model data

Summary In this paper a retrieval technique for estimating rainfall rates is introduced. The novel feature of this technique is the combination of two satellite radiometers — the Special Sensor Microwave/Imager (SSM/I) and the Advanced Very High-Resolution Radiometer (AVHRR) — with mesoscale weather prediction model data. This offers an adjustment of the model atmospheres to reality which is necessary for calculating brightness temperatures that can be compared with microwave satellite measurements.In sensitivity studies it was found that the estimation of precipitation is determined to a high degree by the particle size distribution of rain and snow, especially by the size distribution of solid hydrometeors. These studies also reveal the influence of the knowledge of the correct cloud coverage inside a SSM/I pixel and the importance of using a realistic temperature profile instead of using standard atmospheres.The retrieval technique is based on radiative transfer calculations using the model of Kummerow et al. (1989). The algorithm consists of two parts: First Guess (FG) brightness temperatures for the SSM/I frequencies are generated as a function of the cloud top height and the cloud coverage, derived from AVHRR data and predictions from a meso-scale model. The rainfall rate of different types of clouds containing raindrops, ice particles and coexisting ice and water hydrometeors is then calculated as a function of the cloud top height. As an example, a strong convective rain event over the western part of Europe and over the Alps is taken to evaluate the performance of this technique. Good agreement with radar data from the German Weather Service was achieved. Compared to statistical rainfall algorithms, the current algorithm shows a better performance of detecting rainfall areas.With 12 Figures     

Statistics of shallow convection on Mars based on large-eddy simulations. Part 1: shearless conditions

Results of large-eddy simulations of shallow, quasi-steady, shear-less convection in the Martian boundary layer are presented and discussed. In the considered three cases, turbulence is forced by the radiative flux divergence, prescribed as given functions of height, and the strength of the surface heat flux. It is constrained by the temperature inversion at the boundary-layer top. The resulting convective boundary layer exhibits horizontal cellular structures. The presence of radiative heating causes dimensionless statistics of turbulence to depend on the parameter F, defined in terms of the integrated radiative and turbulent heating rates in the boundary layer.     

基于一维变分算法的地基微波辐射计遥感大气温湿廓线研究

为研究地基微波辐射计遥感温、湿度廓线的一维变分算法的反演能力,用北京地区2010—2011年00和12时(世界时)的多通道地基微波辐射计亮温资料进行试验。首先,利用同时次的地面观测资料、红外亮温(由地基微波辐射计自带红外传感器测得)及探空观测数据,给出提取无云样本的方案,得到432个无云样本;再以辐射传输模式计算得到的模拟亮温为参考,对无云条件下的观测亮温进行质量控制;然后利用探空数据进行模拟试验,结果发现,一维变分算法对3 km以下的温度廓线有较大调整。使反演结果更加接近探空,而对湿度廓线在0—10 km都有不同程度的优化;最后利用一维变分算法对地基微波辐射计观测亮温进行大气温湿廓线反演,将结果与探空对比可以看出,温度廓线的均方根误差小于2.9 K,绝对湿度的均方根误差小于0.47 g/m~3;进一步与地基微波辐射计自带神经网络的反演结果比较表明,一维变分的反演结果更接近实际大气。     

The impact of doubled CO2 on the energetics and hydrologic processes of mid-latitude transient eddies

The Northern Hemisphere winter (DJF) stationary eddy response of a general circulation model (GCM) to a doubling of atmospheric CO₂ is simulated with a linear steady state model as a response to anomalies in diabatic heating (latent, sensible and radiative), mountain and transient eddy effects. For this analysis the doubled CO₂ experiment performed by Wilson and Mitchell (1987) is used. The linear simulations of the control and perturbation climate capture most of the important features of the GCMs stationary eddies. The simulation of the anomalous stationary eddy pattern in the Northern Hemisphere captures only some of the important features of the GCMs anomalies. The climate anomalies in the Southern Hemisphere are poorly simulated. In the Northern Hemisphere the climate anomalies are dominated by the effect of transient eddies and mountains. In low latitudes also the contribution of latent heating is important. The contributions of sensible and radiative heating are small.     

El Nio与La Nia期间大气加热场的特征及其对大气环流的影响

本文采用欧洲中心７层网格点逐月平均全球资料和同期美国ＫＷＢＣ的太平洋海温资料分析了１９８２年１月～１９８３年１２月ＥｌＮｉｎｏ期间和１９８８年１月￣１９８９年１２月ＬａＮｉｎａ期间大气加热场的特征。结果表明，海表温度异常时，海面向上输送的感热、潜热通量变化并不大，有时甚至出现和海温距平变化相反的趋势，而另一方面，各辐射量和凝结加热量变化却很重要。进一步本文又分别以多年平均的１２月、ＥｌＮｉｎｏ及ＬａＮｉｎａ强盛时的１９８２年１２月和１９８８年１２月的实测海温和实测大气资料为初值作了数值模拟，模拟的大气状况与真实大气状况一致。根据资料分析和数值模拟的结果，本文认为作大尺度中长期天气预报及研究海气相互作用时应充分考虑辐射收支和凝结加热量的变化。     

A polarized microwave radiative transfer model for passive remote sensing

The objective of the present work is to develop a general purpose, polarized, microwave radiative transfer forward model, including calculation of interaction parameters for fast, simultaneous and accurate generation of radiances, for use in a wide variety of atmospheric retrieval applications. This complete polarized model includes the generation of atmospheric profiles, calculation of the interaction parameters and the solution of the vector radiative transfer equations. In the present work, the doubling and adding method is used to calculate radiances. Mie theory is used for spherical particles to evaluate the polarized scattering matrix. Two types of sea surface models applicable for specular and diffuse surfaces respectively are implemented. The model has been validated against standard benchmark cases and experimental data available in literature. While the model is itself generic, parametric studies are performed to study the influence of the vertical structure of the atmosphere, for two polarizations and a set of frequencies to be used on the microwave imager aboard the proposed Indo-French climate research satellite MEGHA-TROPIQUES.     

华南前汛期一次大暴雨过程的扰动位涡反演与数值研究

利用NCEP 1°×1° 6h再分析资料、位涡反演和数值试验方法,分离与不同物理过程有关的扰动位涡进行反演诊断．在此基础上移除模式初始场中包含的与不同物理过程有关的扰动位涡反演的平衡场进行敏感性试验．对2006年5月21—22日一次热带扰动系统北上在广东珠江三角洲地区引发的大暴雨天气过程进行了探讨。结果发现：对流层中低层与潜热释放有关的正扰动位涡是影响热带扰动形成、维持及发展的主要因子之一;与潜热释放无关的扰动位涡对副热带高压的形成和维持有重要作用,影响热带扰动系统的移动路径;边界层内的扰动位涡有利于南海热带洋面北上气旋性扰动的发生、发展与维持;中高层扰动位涡对气旋性扰动系统的直接影响很小;下边界扰动位温不利于气旋性扰动系统的形成、维持与发展。数值敏感性试验表明,初始场中包含的与不同物理过程有关的扰动位涡在暴雨数值模拟中有重要作用,它们不同程度地影响热带扰动的强度、活动路径的模拟．并影响暴雨强度和落区;与非绝热物理过程有关的扰动位涡很大程度上影响暴雨强度,而与非绝热物理过程无关的扰动位涡很大程度上决定暴雨落区。