Climatological characteristics of summer precipitation over East Asia measured by TRMM PR: A review

Precipitation is an important indicator of climate change and a critical process in the hydrological cycle, on both the global and regional scales. Methods of precipitation observation and associated analyses are of strategic importance in global climate change research. As the first space-based radar, the Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) has been in operation for almost 17 years and has acquired a huge amount of cloud and precipitation data that provide a distinctive view to help expose the nature of cloud and precipitation in the tropics and subtropics. In this paper we review recent advances in summer East Asian precipitation climatology studies based on long-term TRMM PR measurements in the following three aspects: (1) the three-dimensional structure of precipitation, (2) the diurnal variation of precipitation, and (3) the recent precipitation trend. Additionally, some important prospects regarding satellite remote sensing of precipitation and its application in the near future are discussed.     

SIMULATION AND ANALYSIS ON OBSERVATIONAL ERRORS OF CLOUD INTENSITY AND STRUCTURE WITH TRMM PR AND GROUND-BASED RADAR*

In order to explain theoretically the observational biases of reflectivity and structure of precipitation systems by TRMM Precipitation Radar (TRMM PR) and ground-based radar,the effects of wavelengths,incident direction of radar waves and radar beam width on the reflectivity observation are simulated.The results show that the error due to the different wavelength and incident direction of radar wave is within 2.0 dB,TRMM PR can observe a larger reflectivity than ground-based radar in echo center.TRMM PR smoothes the cloud structure,overestimates and underestimates reflectivity by 3-5 dB in strong and week echo areas,respectively.Beam width and long distance from TRMM PR to target cause it to overestimate the large echo area and area integrated rainfall amount,and to underestimate the averaged refleetivity.The theoretical results above can only explain part of observational facts,meaning that the comparison of observation results between TRMM PR and ground-based radar is complicated,the attenuation of radar wave within precipitation area is the main factor to affect the observed result.     

利用TRMM卫星资料对人工增雨云系模式云微观场预报能力的检验

文中利用TRMM卫星测雨雷达探测反演的云水、雨水、云冰和降冰4种云参数产品及实况降水资料,对比检验该人工增雨云系业务模式对云微观场和地面降水场的预报能力.结果表明,人工增雨云系模式系统对降水的预报能力要略优于现行业务运行的GRAPES模式;人工增雨云系模式系统能较好地预报云系系统云物理微观量的垂直结构特征,模式预报的微观场与卫星监测吻合较好;在播撒窗区的水平分布上,模式预报的各水凝物分布形势和强中心位置与卫星监测一致,其大小也接近监测值;人工增雨云系模式能较好地预报云的微观场和天气形势场,可作为云系人工增雨条件决策的重要参考依据.     

星载降水测量雷达降水产品研究进展

利用星载技术获得的降水信息与其他常规观测手段得到的信息相比,具有更广的空间覆盖性。星载产品的研究对降水微观信息的认识、数值预报的改进和水文农业的发展都有十分重要的意义。本文对美国宇航局NASA和日本宇航局JAXA联合开发的气象卫星降水产品,即第1部TRMM(Tropical Rainfall Measuring Mission)卫星的降水雷达(PR))和GPM(Global Precipitation Measurement)卫星的双频降水雷达(DPR)的降水产品,从评估验证、统计分析和个例分析的角度分类阐述了目前对TRMM和GPM降水产品的相关研究工作,最后提出了目前星载降水产品存在的一些问题、星载仪器的局限性以及对未来星载降水产品发展的展望。     

Tropical Precipitation Estimated by GPCP and TRMM PR Observations

In this study, tropical monthly mean precipitation estimated by the latest Global Precipitation Climatology Project （GPCP） version 2 dataset and Tropical Rainfall Measurement Mission Precipitation Radar （TRMM PR） are compared in temporal and spatial scales in order to comprehend tropical rainfall climatologically. Reasons for the rainfall differences derived from both datasets are discussed. Results show that GPCP and TRMM PR datasets present similar distribution patterns over the Tropics but with some differences in amplitude and location. Generally, the average difference over the ocean of about 0.5 mm d^-1 is larger than that of about 0.1 mm d^-1 over land. Results also show that GPCP tends to underestimate the monthly precipitation over the land region with sparse rain gauges in contrast to regions with a higher density of rain gauge stations. A Probability Distribution Function （PDF） analysis indicates that the GPCP rain rate at its maximum PDF is generally consistent with the TRMM PR rain rate as the latter is less than 8 mm d^-1. When the TRMM PR rain rate is greater than 8 mm d^-1, the GPCP rain rate at its maximum PDF is less by at least 1 mm d^-1 compared to TRMM PR estimates. Results also show an absolute bias of less than 1 mm d^-1 between the two datasets when the rain rate is less than 10 mm d^-1. A large relative bias of the two datasets occurs at weak and heavy rain rates.     

Analysis of the Relationship between the Cloud Water Path and Precipitation Intensity of Mature Typhoons in the Northwest Pacific Ocean

The relationship between precipitation intensity and cloud water in typhoon systems remains unclear.This study combined time-and space-synchronized precipitation and spectral data obtained by the Precipitation Radar(PR)as well as the Visible and Infrared Scanner(VIRS)onboard the TRMM satellite,to overcome the limitations of precipitation properties and cloud parameters not being synchronized in previous studies.A merged dataset of near-surface rain rate(RR)and corresponding cloud water path(CWP)was established and used to analyze the potential correlation between cloud microphysical properties and precipitation,to deepen our understanding of the evolution of cloud to rain.In addition,25 collocated satellite overpasses of mature typhoon cases in the Northwest Pacific Ocean from 1998 to 2012 were obtained,and the relationships between the CWP and RR of 144515 pixels were analyzed in detail.The results show that the CWP and RR of mature typhoon systems with different precipitation types,precipitation cloud phases,and vertical depths of precipitation can be fitted by a notable sigmoid function,which may be useful for estimating CWP and parameterizing precipitation in models.Furthermore,the relationship was applied and tested with an independent sample to show that RR is a significant indicator of CWP.     

一次高原涡和西南涡作用下强降水的回波结构和演变分析

2009年7月30—31日,青藏高原东侧背风坡发生了一次持续性强降水过程。在高原涡和西南涡相继出现并相互作用的天气环境中,四川盆地内生成了3个中尺度对流系统。使用新一代天气雷达组网的反射率因子,美国环境预报中心(NCEP)再分析资料,以及热带测雨卫星搭载的测雨雷达(TRMM PR)反射率因子,可以得到这次暴雨的发展演变及其三维结构特征。通过与TRMM PR探测资料的对比验证,地基组网雷达的结果与其非常一致,基本能反映出对流系统的演变全貌,而在高原和山区地基雷达缺测的区域,测雨雷达探测资料可以做为补充。分析表明,降水落区的低层正涡度和水汽辐合上升与高层负涡度和水汽辐散相配合,是触发暴雨的有利条件。第1个降水系统位于高原涡东南侧,随着高原涡的移动衰亡移出盆地并最终消散,降水系统和高原涡在时间上有滞后相关,二者移动速度的突变较为一致;第2和第3个降水系统在西南涡出现的时段强烈发展,在局地停留维持并打通成为一条沿山脉走向的贯穿整个盆地的混合降水回波带,在西南涡发展至成熟阶段给四川盆地南部带来最大小时降水,降水系统和西南涡的相关无论在强度还是移速上都非常显著。在复杂的地形条件下,青藏高原和四川盆地相接处,降水云团的0℃层高度并未随地表发生明显变化,但降水云团进入盆地后,低于0℃层高度的降水粒子融化变为液相,使得云团从对流型降水变为分层结构的层云降水。     

台风麦莎与赤道穿透对流云团的初步比较分析

利用TRMM卫星的测雨雷达、微波成像仪、可见光和红外扫描仪资料详细分析比较了麦莎台风和位于南海南部的赤道穿透对流云团(EPCC)的云高以及降水结构特征.首先,对热带地区对流层到平流层的过渡带(TTL)以及进入TTL的穿透对流云团进行了阐述和定义.然后,分析对比了赤道穿透对流云团和台风麦莎不同生命史阶段的云高、降水结构特征,分析对比结果表明:(1)在强降水区:麦莎台风和EPCC的云顶上部均出现了冰粒子散射现象,但EPCC的散射强度强,微波亮温值均低于180 K,并且其雷达云高和红外云顶亮温云高相差较大、云顶亮温曲线平缓.(2)EPCC的深对流数量四分比、穿透对流数量百分比、尤其是穿透对流数量占深对流数量比,都比麦莎台风各阶段的高;在麦莎台风和EPCC(10-20 km)云体中大部分云高集中在10-12 km,但EPCC(10-20 km)的云高谱相对具有连续性、相对较宽.(3)麦莎台风以层云降水为主,对总降水量的贡献中也是从云降水贡献大,但是EPCC中却是对流性降水的贡献大,且EPCC对流降水与层云降水的像素数量比值和降水量比值也比麦莎台风的3个时次都高.(4)EPCC的降水廓线深度无论是从云降水还是对流降水都比麦莎台风深,层云廓线深度达11 km,对流廓线深度达18 km.另外,从EPCC的穿透对流数量百分比比麦莎台风多,层云、对流降水廓线比麦莎台风深这几方面,一定程度上说明了EPCC的局部垂直对流强度比麦莎台风强.     

TRMM卫星测雨雷达及其应用研究综述

热带降水测量卫星测雨雷达（TRMM－PR）是第一部星载测雨雷达。卫星于1997年11月28日成功发射，其测雨雷达经过在轨测试定标之后，已向地面发回大量的雷达观测信息。本文主要根据1999年7月如开的第29届雷达气象国际会议的文集和作者所看到的其它文献资料，简要介绍该卫星、星载测雨雷达及其测信息处理和应用的一些研究成果。     

热带测雨卫星的星载雷达和地基雷达探测云回波强度及结构误差的模拟分析

为了揭示热带测雨卫星上的测雨雷达热带测雨卫星的星载雷达与X波段多普勒雷达在探测云的反射率因子的大小和结构方面的差异 ,用散射模式和数值模拟的方法讨论了这两种雷达的波长、雷达波入射方向、波瓣宽度等参量对反射率因子的大小和结构的影响 ,并利用所得结果讨论了两种雷达实际观测的差异。结果表明 :雷达波长和入射方向的不同引起的两种雷达测量的反射率因子的差异在 2 .0dBz以内 ,TRMMPR可在强回波中心探测到更大的反射率因子 ,并在很大程度上平滑了回波的结构 ,在强回波和弱回波区分别低估和高估 3～ 5dBz,造成了观测的云的面积增大、平均回波强度减小、面积积分降水量增大。这些理论结果还不能完全揭示两种雷达实际观测结果的差异 ,看来星载雷达和地基雷达探测结果的对比问题很复杂 ,其中雷达波的衰减问题是必须考虑的。     

Estimation of Indian summer monsoon rainfall using Kalpana-1 VHRR data and its validation using rain gauge and GPCP data

In the present study, an attempt has been made to estimate and validate the daily and monthly rainfall during the Indian summer monsoon seasons of 2008 and 2009 using INSAT (Indian National Satellite System) Multispectral Rainfall Algorithm (IMSRA) technique utilizing Kalpana-1 very high resolution radiometer (VHRR) measurements. In contrary to infrared (IR), microwave (MW) rain rates are based on measurements that sense precipitation in clouds and do not rely merely on cloud top temperature. Geostationary satellites provide broad coverage and frequent refresh measurements but microwave measurements are accurate but sparse. IMSRA technique is the combination of the infrared and microwave measurements which make use of the best features of both IR- and MW-based rainfall estimates. The development of this algorithm included two major steps: (a) classification of rain-bearing clouds using proper cloud classification scheme utilizing Kalpana-1 IR and water vapor (WV) brightness temperatures (Tb) and (b) collocation of Kalpana-1 IR brightness temperature with Tropical Rainfall Measuring Mission (TRMM)-Precipitation Radar (PR) surface rain rate and establishment of a regression relation between them. In this paper, the capability of IMSRA as an operational algorithm has been tested for the two monsoon seasons 2008 and 2009. For this, IMSRA has been used to estimate daily and monthly rainfall and has been intercompared on daily and monthly scales with TRMM Multisatellite Precipitation Analysis (TMPA)-3B42 V6 product and Global Precipitation Climatology Project (GPCP) rain product during these two monsoon years. The daily and monthly IMSRA rainfall has also been validated against ground-based observations from Automatic Weather Station (AWS) Rain Gauge and Buoy data. The algorithm proved to be in good correlation with AWS data over land up to 0.70 for daily rain estimates except orographic regions like North-East and South-West India and 0.72 for monthly rain estimates. The validation with Buoys gives the reasonable correlation of 0.49 for daily rain estimates and 0.66 for monthly rain estimates over Tropical Indian Ocean.     

9914号台风降水云系雨强的三维结构初探

利用TRMM卫星的测雨雷达资料，研究了9914号台风降水云系在3个不同时次雨强的水平和垂直结构。结果表明：3个时次层状云降水在像素数量上及对总降水量的贡献上均比对流性降水大；3个时次层状云降水和对流性降水的平均雨强均随台风强度加强有较大的增幅；对流性降水与层状云降水的雨强的垂直廓线有明显的差别，但两类降水廓线本身在3个时次差别不大。对流性降水廓线按斜率不同大致分为3段，雨强均随高度减小，5～6km高度段减速最快。层状云降水廓线大致分为4段，在4．5km高度附近出现明显的亮带结构。     

The Structure and Rainfall Features of Tropical Cyclone Rammasun （2002）

Tropical Rainfall Measuring Mission (TRMM) data [TRMM Microwave Imager/Precipitation Radar/Visible and Infrared Scanner (TMI/PR/VIRS)] and a numerical model are used to investigate the structure and rainfall features of Tropical Cyclone (TC) Rammasun (2002). Based on the analysisof TRMM data, which are diagnosed together with NCEP/AVN [Aviation (global model)] analysis data,some typical features of TC structure and rainfall are preliminary discovered. Since the limitations of TRMM data are considered for their time resolution and coverage, the world observed by TRMM at several moments cannot be taken as the representation of the whole period of the TC lifecycle, therefore the picture should be reproduced by a numerical model of high quality. To better understand the structure and rainfall features of TC Rammasun, a numerical simulation is carried out with mesoscale model MM5 in which the validations have been made with the data of TRMM and NCEP/AVN analysis.     

我国云量及其与降水关系的研究进展综述

云是大气垂直运动和湿状况的综合体现,云量的变化从另一个侧面反映了气候变化。气候模式中云参数的任何变化,都可能对全球气候产生重大影响。本文主要总结了近几十年有关我国云量的时空变化及其与降水关系的研究成果,同时也指出了目前多种云资料的优缺点。此外提出应充分利用现有的资料来研究云量最多、云层最厚的西南地区云的特征及其变化。      

Variations of Precipitation Structure and Microwave Tbs During the Evolution of a Hailstorm from TRMM Observations

In this paper, a hailstorm occurring on 9 May 1999 in Huanghuai region was studied by using the combined data from the precipitation radar (PR), microwave image (TMI), and visible infrared scanner (VIRS) on the Tropical Rainfall Measuring Mission (TRMM) satellite. According to the 3-orbit observations of 5-h duration from the TRMM satellite, the variation characteristics of the precipitation structures as well as cloud top temperature and microwave signals of the precipitating cloud were comprehensively analyzed during the evolution of hailstorm. The results show that the precipitation is obviously converted from early hail cloud with strong convection into the later storm cloud with weak convection. For hail cloud, there exists some strong convective cells, and the heavy solid precipitation is shown at the middle-top levels so that the contribution of rainfall amount above the freezing-layer to the column precipitation amount is rather larger than that within the melting-layer. However, for storm cloud, the convective cells are surrounded by the large area of stratiform precipitation, and the precipitation thickness gradually decreases, and the rainfall above the freezing-layer obviously reduces and the contribution of rainfall amount within the melting-layer rapidly increases. Therefore, the larger ratio of rainfall amount above the freezing layer to column precipitation amount is, the more convective the cloud is; reversely, the larger proportion of rainfall below the melting layer is, the more stable the stratiform cloud is. The different changing trends of microwave signals at different precipitation stages show that it is better to consider the structures and stages of precipitating cloud to choose the optimal microwave channels to retrieve surface rainfall.     

青藏高原地面Doppler雷达与TRMM星载雷达测云比较

利用 1998年青藏高原地面Doppler雷达资料和TRMMPR资料进行对比分析 ,分别从不同角度出发 ,分析了Doppler雷达和TRMMPR所测云区在回波结构和回波强度等方面的相同和差异之处 ,以及产生误差的必然和可能的原因     

Three-dimensional Fusion of Spaceborne and Ground Radar Reflectivity Data Using a Neural Network–Based Approach

The spaceborne precipitation radar onboard the Tropical Rainfall Measuring Mission satellite(TRMM PR) can provide good measurement of the vertical structure of reflectivity, while ground radar(GR) has a relatively high horizontal resolution and greater sensitivity. Fusion of TRMM PR and GR reflectivity data may maximize the advantages from both instruments.In this paper, TRMM PR and GR reflectivity data are fused using a neural network(NN)–based approach. The main steps included are: quality control of TRMM PR and GR reflectivity data; spatiotemporal matchup; GR calibration bias correction;conversion of TRMM PR data from Ku to S band; fusion of TRMM PR and GR reflectivity data with an NN method;interpolation of reflectivity data that are below PR's sensitivity; blind areas compensation with a distance weighting–based merging approach; combination of three types of data: data with the NN method, data below PR's sensitivity and data within compensated blind areas. During the NN fusion step, the TRMM PR data are taken as targets of the training NNs, and gridded GR data after horizontal downsampling at different heights are used as the input. The trained NNs are then used to obtain 3D high-resolution reflectivity from the original GR gridded data. After 3 D fusion of the TRMM PR and GR reflectivity data, a more complete and finer-scale 3D radar reflectivity dataset incorporating characteristics from both the TRMM PR and GR observations can be obtained. The fused reflectivity data are evaluated based on a convective precipitation event through comparison with the high resolution TRMM PR and GR data with an interpolation algorithm.     

河南省非降水云中液态水的卫星微波反演试验研究

云中液态水分布对全球气候和局地天气变化有重要影响, 是判别人工影响天气作业潜力区的重要依据。利用TRMM卫星微波成像仪 (TMI) 85.5 GHz通道垂直极化亮温资料与NCEP再分析资料, 结合VDISORT模式采用逐步逼近方法反演了河南地区地表比辐射率; 再利用TRMM/TMI 85.5 GHz通道垂直极化亮温资料、TRMM/VIRS红外辐射资料及NCEP再分析资料, 结合VDISORT模式采用迭代的方法反演了河南地区云中液态水的垂直积分总含量。与红外卫星云图、TRMM卫星2A12产品及NCEP资料对比分析表明:该研究提出的反演陆地上空非降水云中液态水方法是可行的, 且对云中液态水垂直积分总含量水平分布的反演结果较对比产品结果更好。     

利用星载测雨雷达探测结果对夏季中国南方对流和层云降水气候特征的分析

本文利用热带测雨卫星(TRMM)上搭载的测雨雷达(PR)十年的探测结果, 对夏季中国南方对流降水和层云降水的气候特征进行了分析。研究结果表明:夏季中国南方层云降水频次较对流降水频次高出两倍以上, 而对流降水强度至少是层云降水强度的4倍; 就整个中国南方而言, 这两种类型的降水对总降水量贡献相当。日变化分析表明夏季中国南方大部分地区的对流降水主要出现在午后, 层云降水出现时间并不集中, 但这两类降水的频次日变化均显示了明显的地域性特征; 对降水廓线日变化的分析结果表明, 对流降水和层云降水廓线的日变化主要表现在“雨顶”高度的日变化, 即对流降水云的厚度有明显的日变化变化特征, 不同地区的降水廓线存在明显的差异。降水率剖面分析结果显示了对流降水的“雨顶” 高度日变化较层云降水剧烈, 降水率的日变化则相反, 且层云降水率的地域性特征更强。     

The Challenges of Modeling Climate Variability and Change in West Africa

This paper overviews observations and examines modeling issues associated with the mean state, climate variability and climate change in West Africa. The Tropical Rain Measuring Mission (TRMM) satellite allows for the first time estimates of Unconditional, Convective and Stratiform rain rates in West Africa. The 1998 estimated TRMM rates are compared to long-term observed rain rates and a merged rain data set (CMAP) during 1998. Further, the TRMM estimates are compared to the simulated rain rates from the Community Climate Model Version 3.6. The TRMM Precipitation Radar rain estimates are generally lower than either the long-term observations or the CMAP rates during 1998. Moreover, the TRMM rain estimates show a significant fraction of the total rain (convective + stratiform) is characterized as stratiform rain (30–40%). The CCM3 simulates primarily convective rain and negligible amounts of non-convective rain for West Africa. Furthermore, the TRMM high-resolution rain patterns strongly imply that rain in West Africa occurs on mesoscales in association with mesoscale convective systems (squall lines, mesoscale convective complexes and non-squall tropical clusters). We demonstrate this by briefly examining two mesoscale convective systems during May 1998 with METEOSAT data. Regional climate models may offer the best solution to understanding climate change in West Africa because of their ability to capture mesoscale systems and better their representation of orographic features. Adequate boundary conditions from Global Climate Models are still necessary for regional climate model simulations to successfully reproduce mean climate conditions and provide understanding with respect to future climate change. Observations in West Africa should be maintained or increased for monitoring climate variability and possibility of climate change in West Africa, proper initialization of numerical weather prediction models and the validation of climate models.