飑线型降水云微波辐射特性的数值研究

本文将三维云的微物理模式的输出作为三维辐射传输模式的输入，对降水云的微波上行辐射率同地球物理参数间的关系进行了初步研究。在侧边界条件不对称的情况下，如果不考虑实际存在的云间相互辐射作用而模拟降水云的上行辐射率时，模拟出的亮温在低频段将低估卫星上测到的亮温值；在高频段则依降水云上层含冰量的大小而异，即在降水云上层含冰量小的区域，将低估星上测到的亮温，且低估的幅度较低频通道的大，而在降水云上层含冰量大的区域，可能高估星上测到的亮温，但高估的幅度较小。     

STUDIES OF THE VERTICAL STRUCTURE MODEL AND THE MICROWAVE ATTENUATION OF CLOUDS AND PRECIPITATION OVER TROPICAL OCEAN AREA*

Using radiosonde data and other related observations in the TOGA-COARE IOP(from November 1,1992 to February 28,1993),the microwave attenuation of non-precipitating clouds is investigated based on microwave radiative transfer model(MRTM) at the specific frequencies of 6.8,10.65,13.9,19.35,22.235,37.0,85.5 and 90.0 GHz.Besides,utilizing the data of the airborne radar and radiometer at 13.8 GHz in the IOP(Intensive Observation Period),vertical structure models for different types of precipitating clouds are obtained,and also the microwave attenuation of precipitating cloud is studied.Some statistical characteristics of 13.8 GHz microwave path integrated attenuation for stratiform and convective precipitating clouds are presented.The results given here are valuable for the spaceborne microwave remote sensing of precipitation,and the cloud and precipitation attenuation corrections in the spaceborne microwave remote sensing of earth surface over tropical ocean area.     

STUDIES OF THE VERTICAL STRUCTURE MODEL AND THE MICROWAVE ATTENUATION OF CLOUDS AND PRECIPITATION OVER TROPICAL OCEAN AREA

Using radiosonde data and other related observations in the TOGA-COARE IOP(fromNovember 1,1992 to February 28,1993),the microwave attenuation of non-precipitating clouds isinvestigated based on microwave radiative transfer model(MRTM)at the specific frequencies of6.8,10.65,13.9,19.35,22.235,37.0,85.5 and 90.0 GHz.Besides,utilizing the data of theairborne radar and radiometer at 13.8 GHz in the IOP(Intensive Observation Period),verticalstructure models for different types of precipitating clouds are obtained,and also the microwaveattenuation of precipitating cloud is studied.Some statistical characteristics of 13.8 GHzmicrowave path integrated attenuation for stratiform and convective precipitating clouds arepresented.The results given here are valuable for the spaceborne microwave remote sensing ofprecipitation,and the cloud and precipitation attenuation corrections in the spaceborne microwaveremote sensing of earth surface over tropical ocean area.     

不同侧边界条件下水平有限降水云的微波辐射模式研究

从空间微波遥感降水定量分布的目标出发，本文研究在非对称侧边界条件下水平有限降水云的微波辐射率的计算公式。由普适性三维辐射传输方程出发，推导出非对称横向边界条件下的微波辐射率解析表达式。用热带降水云典型参数所作初步数值试验表明，相对于对称侧边界条件非对称侧边界条件对于上行（卫星所测）辐射率具有不可忽略的作用，且这种作用对于不同的微波频率具有不同的强度，甚至有符号的差别。云的不均匀尺度越小，这种作用越强。由于热带降水大多具有高度非均匀对流云带状或云团结构，本文所发展的模式将对微波遥感这类降雨定量分布发挥重要作     

用云和辐射传输模式研究对流性降水云微物理及辐射特性

利用中国气象科学研究院的三维对流云模式模拟了 1 998年发生在我国武汉地区的特大暴雨过程中的对流云。在模拟云的成熟阶段 ,模拟结果和地面最大降水量实况及热带测雨卫星TRMM (TropicalRainfallMeasureMission)的降水雷达PR(Pre cipitationRadar)的零度层高度和降水粒子达到的高度较接近。将该云物理模式的输出结果输入到Liu的三维辐射模式的输入场 ,模拟了以TRMM的微波成像仪TMI(TRMMMicrowaveImager)的扫描角为入射角 ,频率为 85 5GHz和 37 0GHz的星载微波辐射仪接受到的亮温 ,模拟的结果表明云中各微物理量的分布对上行微波辐射的影响较大。     

The effect of cirrus clouds on microwave limb radiances

This study presents and analyses the first simulations of microwave limb radiances with clouds. They are computed using the 1D unpolarized version of the Atmospheric Radiative Transfer System (ARTS). The study is meant to set a theoretical foundation for using microwave limb measurements for cloud monitoring. Information about clouds is required for the validation of climate models.Limb spectra are generated for the frequency bands of the Millimeter wave Acquisitions for Stratosphere/Troposphere Exchange Research (MASTER) instrument. For these simulations, the radiative transfer equation is solved using the Discrete Ordinate ITerative (DOIT) method, which is briefly described. Single scattering properties for the cloud particles are calculated using the T-matrix method.The impact of various cloud parameters is investigated. Simulated brightness temperatures most strongly depend on particle size, ice mass content and cloud altitude. The impact of particle shape is much smaller, but still significant. Increasing the ice mass content has a similar effect as increasing the particle size; this complicates the prediction of the impact of clouds on microwave radiances without exact knowledge of these cloud parameters.     

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.     

Subpixel fractional cloud cover and inhomogeneity effects on microwave beam-filling error

Using synthetic geometrical clouds and radiative microwave model, we examine the possibility to correct the estimations of liquid water path (LWP) or rain rate with cloud cover measurement. This information may be gotten by co-localized measurements of microwave and infrared/visible measurements on new satellites (TRMM, ADEOS 2, …). In a first step, the effects of fractional cloud cover on microwave brightness temperatures (TB) are investigated in three typical cases of nonprecipitating and precipitating (stratiform and convective) clouds. The beam-filling error (BFE) on brightness temperatures may be analyzed with the known spatial variability using 1D or 3D radiative transfer model. Relationships between BFE and subpixel cloud fraction (CF) are discussed according to the cloud type. We tested several parameters that characterize the horizontal cloud inhomogeneity within a radiometer field of view. BFE was found very sensitive to cloud type and inhomogeneity and is maximum for raining cloud with open spatial structure. In order to account for the uncertainty introduced by the spatial distribution, dependence of BFE on textural-based parameters is also discussed using homogeneity, entropy and an indicator of CF horizontal gradient.     

对流性降水云辐射特性研究

结合MM5模式和三维微波辐射传输模式,对2002年7月22～23日发生在湖北宜昌附近一次中尺度强降水过程中的强降水中心的对流性降水云的微波辐射特性进行了模拟,模拟结果表明：MM5模式可以较好地模拟此次降水过程;云中各微物理量的含量和分布对上行微波辐射亮温有重要影响;就物理方法而言,选用适当的云廓线,是利用微波信息反演降水的关键。     

Retrieval of Liquid Water Path Inside Nonprecipitating Clouds Using TMI Measurements

Quantitative estimates of liquid water path （LWP） in clouds using satellite measurements are critical to understanding of cloud properties and the assessment of global climate change. In this paper, the relationship between microwave brightness temperature （TB） and LWP in the nonprecipitating clouds is studied by using satellite microwave measurements from the TRMM Microwave Imager （TMI） onboard the Tropical Rainfall Measuring Mission （TRMM）, together with a radiative transfer model for microwave radiance calculations. Radiative transfer modeling shows that the sensitivity is higher at both 37.0- and 85.5-GHz horizontal polarization channels for the LWP retrievals. Also, the differences between the retrieved values responding to TBs of various channels and the theoretical values are displayed by the model. Based upon above simulations, with taking into account the factor of resolution and retrieval bias for a single,channel, a nonprecipitating cloud LWP in the summer subtropical marine environment retrieval algorithm is formulated by the combination of the two TMI horizontal polarization channels, 37.0 and 85.5 GHz. Moreover,by using TMI measurements （1Bll）, this algorithm is applied to retrieving respectively LWPs for clear sky, nonprecipitating clouds, and typhoon precipitating clouds. In the clear sky case, the LWP cl~anges from -1 to 1 g m-2, and its mean value is about 10^-5 g m^-2. It indicates that, using this combination retrieval algorithm, there are no obvious systemic deviations when the LWP is low enough. The LWP values varying from 0 to 1000 g m^-2 in nonprecipitating clouds are reasonable, and its distribution pattern is very similar to the detected results in the visible channel of Visible and Infrared Scanner （VIRS） on the TRMM. In typhoon precipitating clouds, there is much more proportion of high LWP in the mature phase than the early stage. When surface rainfall rate is lower than 5 mm h^-1, the LWP increases with increasing rainfall rate.     

南海中尺度大气海浪耦合模式及其对该区一次强台风过程的模拟研究

利用中尺度大气模式MM5(V3)和第3代海浪模式WWATCH建立考虑大气-海浪相互作用的风浪耦合模式.在耦合模式中引入考虑波浪影响的海表粗糙度参数化方案,大气模式分量提供海面10 m风场驱动海浪模式分量运行,并利用海浪模式分量反馈的波龄参数计算海表粗糙度.利用耦合模式模拟南海的一次台风过程,通过3组对比试验,检验耦合模式对台风过程的模拟效果并研究大气-海浪相互作用对台风过程的影响.结果表明:耦合模式能够较好地模拟南海的台风过程,与非耦合大气模式相比,其模拟的台风强度略有增强,路径变化不大;耦合模式对台风过程中海表热通量及降水影响显著,在台风充分发展过程中,耦合模式模拟的海表热通量增强,台风螺旋雨带上尤其是台风路径的右侧,耦合模式模拟的降水强于非耦合模式;耦合模式较好地模拟了台风过程海浪场的分布和演变,与非耦合模式相比,其模拟的海浪场增强,与实际更为接近;考虑了海表粗糙度对波浪的依赖关系后,海浪场同时影响海表的动力过程和热力过程,从本次个例看,在台风发展初期,海浪对海表动力作用影响显著,其反馈作用使台风系统减弱,但在台风充分发展后,耦合系统中海表热通量增加,热力作用显著增强,海浪的反馈作用有利于台风系统的发展和维持.     

A STUDY OF MICROWAVE RADIATION TRANSFER CHARACTERISTICS IN STRATIFIED PRECIPITATION CLOUDS BY COMBINING STRATIFIED CLOUD MODEL WITH MICROWAVE RADIATION TRANSFER MODEL

In this paper,the effect of precipitation particles on microwave radiation transfer characteristics in stratified clouds over the ocean is studied by combining stratified cloud model with microwave radiation transfer model.By comparing the calculated results with the true data,it is found that precipitation particle distribution and water shell around ice phase particle strongly affect the upwelling radiation.Therefore,the precipitation particle distribution and water shellaround ice phase particle must be considered when a calculating scheme is designed for retrieving precipitation in stratified clouds by the use of microwave radiation transfer model.     

基于亮温通道变率的FY-3C微波湿度计陆地云检测新方法

云检测是卫星资料同化的重要前处理步骤,无论是晴空资料同化还是有云资料同化,都需要准确地区分有云和晴空资料。由于陆地地表发射率的多变性和微波能穿透部分云类的特点,微波湿度计资料在陆地上空的云检测研究一直是难点。利用快速辐射传输模式（CRTM）分析了不同云类条件下FY-3C微波湿度计（MWHS-Ⅱ）各通道亮温的通道间变率特征,根据MWHS-Ⅱ亮温通道间变率随云高以及云中液态水含量的增大而减小的特点,提出了一个基于亮温通道变率的MWHS-Ⅱ陆地资料云检测方法。与已有的云产品比较结果表明:新的云检测算法能有效地剔除大部分受云影响的资料,剔除后的晴空资料观测和模拟偏差更好地符合高斯分布。新方法对过冷水云、冰云、重叠云的检测能力较强,正确检测率可以达到80%,对卷云以及高度较低的水云的检测能力相对较弱。新方法能有效利用MWHS-Ⅱ观测资料自身完成云检测,在MWHS-Ⅱ资料同化中有很好的应用前景。      

对流性降水云微波辐射特性

结合MM5模式和三维微波辐射传输模式, 对2003年7月9日宜昌地区一次典型的中尺度降水中心的对流性降水云微波辐射特性进行研究。结果表明:MM5模式模拟的降水量和落区与实况一致,模拟的水凝物廓线也与TMI反演值接近,85.5 GHz通道辐射亮温与TMI实测情况相近。85.5 GHz通道亮温与地面雨强相关性很弱, 受云中云冰和雪花的散射降温作用显著, 由于其他粒子的综合作用以及斜角观测造成的位置偏移, 霰粒子对该通道亮温散射作用不明显。19.35 GHz通道亮温随雨强增加先升温后降温; 与霰粒子含量表现出明显的负相关关系。37.0 GHz通道亮温随雨强的增加而降温, 雨强大于20 mm/h后达到饱和, 主要受雨水降温作用影响。倾斜观测比天顶垂直观测产生更低的亮温低值中心, 且频率越高, 低值中心的偏移越严重。     

Cloud Base Height and Effective Cloud Emissivity Retrieval with Ground-Based Infrared Interferometer

Based on ground-based Atmospheric Emitted Radiance Interferometer (AERI) observations in Shouxian, Anhui province, China, the authors retrieve the cloud base height (CBH) and effective cloud emissivity by using the minimum root-mean-square difference method. This method was originally developed for satellite remote sensing. The high-temporal-resolution retrieval results can depict the trivial variations of the zenith clouds continu-ously. The retrieval results are evaluated by comparing them with observations by the cloud radar. The comparison shows that the retrieval bias is smaller for the middle and low cloud, especially for the opaque cloud. When two layers of clouds exist, the retrieval results reflect the weighting radiative contribution of the multi-layer cloud. The retrieval accuracy is affected by uncertainties of the AERI radiances and sounding profiles, in which the role of uncertainty in the temperature profile is dominant.     

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...     

Development and initial assessment of a new land index for microwave humidity sounder cloud detection

This paper describes a new quality control (QC) scheme for microwave humidity sounder (MHS) data assimilation. It consists of a cloud detection step and an O–B (i.e., differences of brightness temperatures between observations and model simulations) check. Over ocean, cloud detection can be carried out based on two MHS window channels and two Advanced Microwave Sounding Unit-A (AMSU-A) window channels, which can be used for obtaining cloud ice water path (IWP) and liquid water path (LWP), respectively. Over land, cloud detection of microwave data becomes much more challenging due to a much larger emission contribution from land surface than that from cloud. The current MHS cloud detection over land employs an O–B based method, which could fail to identify cloudy radiances when there is mismatch between actual clouds and model clouds. In this study, a new MHS observation based index is developed for identifying MHS cloudy radiances over land. The new land index for cloud detection exploits the large variability of brightness temperature observations among MHS channels over different clouds. It is shown that those MHS cloudy radiances that were otherwise missed by the current O–B based QC method can be successfully identified by the new land index. An O–B check can then be employed to the remaining data after cloud detection to remove additional outliers with model simulations deviated greatly from observations. It is shown that MHS channel correlations are significantly reduced by the newly proposed QC scheme.     

气候模式中云的垂直重叠及其辐射传输问题研究进展

概述了全球气候模式中云的垂直重叠的处理方法及其辐射物理过程的最新研究进展。从云垂直重叠模型的构造、模型在气候模式中的实现方式,得到与观测一致的云重叠结构所采用的数据和方法、重叠云的辐射传输等方面,给出了针对这一国际研究难点问题的最新研究进展。关于气候模式中云的垂直重叠问题的研究至今已取得了许多成果,表现在:重叠模型上有了更为科学的描述形式(如指数衰减重叠);重叠云的辐射传输也有了更快速的处理方法(如蒙特卡洛独立柱近似)并被广泛应用;连续的三维云遥感观测(如CloudSat/CALIPSO)和云分辨尺度的三维云模式的发展为在气候模式中精确描述云的垂直结构提供了丰富的观测资料和模式数据。但是,气候模式中现有的云重叠结构处理及其辐射传输方法还远不够完善,仍然存在很多没有解决的问题需要在未来进行探索。     

Cloud mapping from the earth's surface using infrared radiance contrasts*

Abstract

Radiance criteria for distinguishing low, middle, and high clouds in the 9.5–11.5 μm band of the infrared are developed and used to produce local cloud maps. The performance of this radiance contrast method for mapping clouds from the earth's surface is evaluated with a view to using the technique for objective observation of cloud amount and distribution in the sky hemisphere.

Discrimination radiance formulas are developed using a multilayer, wavenumber‐specific infrared radiative transfer model including cloud parameters measured by other workers and atmospheric conditions measured by radiosonde. The clear sky radiance (N₀) is the dominant independent variable in the discrimination formulas. The variation of N₀ with time (primarily due to changes in atmospheric water vapour content) and zenith angle are found to be important in distinguishing cirriform clouds from clear sky and other clouds.

The local cloud maps are produced by applying the discrimination radiances (in voltage form) to the output from a narrow‐view infrared radiometer pointed at a sky‐scanning mirror. It is necessary to assume that the radiance from a cloud observed at the surface decreases unambiguously with an increase in cloud base height. Cloud maps for five days in July 1978 indicate the mapping technique shows promise under a wide range of sky conditions. Cloud motions rapidly degrade the maps’ quality over time‐scales that are much less than the current manual cloud sampling period of 1 h.