中国近20 a卫星遥感土壤湿度的季节变化及其验证

分析了欧洲空间局最近基于多颗卫星微波资料研发的ECV土壤湿度产品的季节性干湿变化,并与国家气象局提供的站点资料做了对比验证。研究发现:主动与被动遥感土壤湿度的干湿季节变化在中国东部季风区有显著的不一致性。在中国东部季风区,被动遥感土壤湿度的干湿季变化和站点观测一致,均表现出夏季是干季、冬季是湿季的特征;而主动遥感的数据则存在较大的空间差异,华北地区与被动遥感数据较为一致,华南地区则呈现夏季为湿季、冬季为干季的反位相特征。两者的不一致性说明,针对欧洲空间局开发ECV土壤湿度产品的过程,融合主动遥感和被动遥感资料,研制长序列土壤湿度产品的思路在中国东部季风区不可行。     

四川盆地及周边地区TRMM 3B42数据精度检验

多源信息融合的流域水文模拟及预报技术,是目前水文预报发展的一个重要方向。以易发生长江流域特大洪水的四川盆地及周边地区为研究区域,从单个站点及子流域降水量相关性、降雨空间分布和相对误差等方面对TRMM卫星3B42产品探测精度进行了检验分析。结果表明:研究区TRMM 3B42数据与地面观测数据在日、月尺度上具有较高的相关性(R >0.5),3 h尺度相关性较差(R<0.5),且3 h和日尺度在降水量峰值拟合上存在较为明显的数值偏差和时间上的提前或延迟;不同时间尺度下两组数据的空间分布特征总体具有较好的一致性;两组数据2008—2010年降水量序列均值相对偏差在±10%的概率密度百分数为32.26%。总体上研究区TRMM 3B42数据呈现高估(四川盆地大部分区域),局部出现低估(四川盆东南及地周边地区);研究区3 h尺度TRMM 3B42数据探测精度明显低于日尺度,高程变化对TRMM 3B42数据的探测精度具有一定影响。因此,针对该区域TRMM 3B42数据3 h和日尺度数据序列精度相对较差的问题,应用该卫星数据进行3 h尺度流域水文模拟及预报研究时,就需要对该区域卫星数据和地面观测数据进行融合,充分发挥两种数据的优势。     

5月南亚高压与云南地区夏季降水的关系

应用1961—2012年NCEP/NCAR月平均再分析资料和云南124个测站逐月降水资料,分析了5月南亚高压与云南夏季降水的关系,发现高压脊线位置与降水有显著的相关。利用滤波处理和合成分析方法,分析了5月南亚高压脊线位置变化及其异常与云南夏季降水异常的联系。结果表明:5月南亚高压脊线位置偏北(南)时,夏季云南降水偏多(少);5月南亚高压脊线位置和云南夏季降水都存在显著的年代际变化,去除年代际变化影响之后两者之间的年际变化相关较为显著。5月南亚高压脊线位置偏北年,夏季南亚高压强度偏弱、范围偏小,500 hPa上西太平洋副高东移南压、强度减弱。低层700 hPa上副高西伸加强、云南上空出现明显的风场辐合,反之亦然。5月脊线位置偏北年,夏季南海和西太平洋向云南输送水汽,而脊线偏南年没有明显的水汽来源。     

中国地面气象要素格点融合业务产品检验

对2018年5 km分辨率中国地面气象要素2m温度、10 m风速和24 h累积降水格点融合产品进行非独立和独立检验.非独立检验结果表明:(1)相比于站点观测,2m温度格点融合产品整体偏暖,各月平均均方根误差在1 ℃左右,35 ℃以上高温和-20 ℃以下低温天气时均方根误差分别在1 ℃和2 ℃以上.(2)10m风速格点融...     

基于贝叶斯融合方法的高分辨率地面-卫星-雷达三源降水融合试验

为了探讨一种适用于区域性的地面、雷达、卫星等多源降水资料融合的方法,一种曾用于高分辨雷达、卫星土壤湿度产品反演的贝叶斯融合(Bayesian Merging)方法被尝试应用于江淮地区1 h-0.05°×0.05°经纬度高分辨率的雷达估测降水、卫星反演降水与地面站点观测降水3种资料的融合。在应用该方法时,通过2009年8月样本统计分别估计卫星和雷达反演降水的误差关系,通过曲线拟合建立误差方程,并以卫星资料作为背景场,但在融合时将雷达估测降水作为新的观测信息与地面观测降水同时引入。融合试验检验结果表明:贝叶斯融合方法能够有效实现雷达、地面、卫星3种不同来源资料的融合,该方法生成的多源融合产品的精度均优于任何单一来源的降水产品。     

非静力中尺度高分辨率模式模拟中的垂直坐标影响研究

近几年来,随着高性能计算机技术的高速发展,甚高分辨率的中尺度数值预报模式业务应用已成为可能,与之相关的一系列模式技术的新问题也随之提了出来,垂直坐标系的影响就是其中之一。文中借助于美国新一代数值预报模式WRF(WeatherReseachandForecast),比较了非静力中尺度模式高分辨率模拟应用的垂直坐标影响问题。研究表明,当选用几何高度(z)和气压(p)来构造地形追随坐标时,低层两坐标引起的误差基本一样,中高层高度地形追随坐标引起的误差小于气压地形追随坐标;而且分辨率越高差异愈大。高分辨率模拟结果也表明,这种差异趋势是存在的;此外,本文对天气过程的预报要素场进行了相关的分析。     

Evaluation of TMPA satellite-based research and real-time rainfall estimates during six tropical-related heavy rainfall events over Louisiana, USA

This study focuses on the evaluation of 3-hourly 0.25° × 0.25° satellite-based rainfall estimates produced by the Tropical Rainfall Measuring Mission (TRMM) Multi-satellite Precipitation Analysis (TMPA). The evaluation is performed during six heavy rainfall events that were generated by tropical storms passing over Louisiana, United States. Two surface-based rainfall datasets from gauge and radar observations are used as a ground reference for evaluating the real-time (RT) version of the TMPA product and the post-real-time bias adjusted research version. The evaluation analysis is performed at the native temporal and spatial scales of the TMPA products, 3-hourly and 0.25° × 0.25°. Several graphical and statistical techniques are applied to characterize the deviation of the TMPA estimates from the reference datasets. Both versions of the TMPA products track reasonably well the temporal evolution and fluctuations of surface rainfall during the analyzed storms with moderate to high correlation values of 0.5–0.8. The TMPA estimates reported reasonable levels of rainfall detection especially when light rainfall rates are excluded. On a storm scale, the TMPA products are characterized by varying degrees of bias which was mostly within ± 25% and ± 50% for the research and RT products, respectively. Analysis of the error distribution indicated that, on average, the TMPA products tend to overestimate small rain rates and underestimate large rain rates. Compared to the real-time estimates, the research product shows significant improvement in the overall and conditional bias, and in the correlation coefficients, with slight deterioration in the probability of detecting rainfall occurrences. A fair agreement in terms of reproducing the tail of the distribution of rain rates (i.e., probability of surface rainfall exceeding certain thresholds) was observed especially for the RT estimates. Despite the apparent differences with surface rainfall estimates, the results reported in this study highlight the TMPA potential as a valuable resource of high-resolution rainfall information over many areas in the world that lack capabilities for monitoring landfalling tropical storms.     

Land surface sensitivity of monsoon depressions formed over Bay of Bengal using improved high-resolution land state

Monsoon depressions (MDs) constitute a large fraction of the total rainfall during the Indian summer monsoon season. In this study, the impact of high-resolution land state is addressed by assessing the evolution of inland moving depressions formed over the Bay of Bengal using a mesoscale modeling system. Improved land state is generated using High Resolution Land Data Assimilation System employing Noah-MP land-surface model. Verification of soil moisture using Soil Moisture and Ocean Salinity (SMOS) and soil temperature using tower observations demonstrate promising results. Incorporating high-resolution land state yielded least root mean squared errors with higher correlation coefficient in the surface and mid tropospheric parameters. Rainfall forecasts reveal that simulations are spatially and quantitatively in accordance with observations and provide better skill scores. The improved land surface characteristics have brought about the realistic evolution of surface, mid-tropospheric parameters, vorticity and moist static energy that facilitates the accurate MDs dynamics in the model. Composite moisture budget analysis reveals that the surface evaporation is negligible compared to moisture flux convergence of water vapor, which supplies moisture into the MDs over land. The temporal relationship between rainfall and moisture convergence show high correlation, suggesting a realistic representation of land state help restructure the moisture inflow into the system through rainfall-moisture convergence feedback.     

中国东部夏季分区降水对海温异常响应特征的研究

用刘征宇最新发展的广义平衡反馈方法结合经验正交分析和旋转经验正交分析法,研究中国东部6个分区夏季降水异常对各海盆海温异常(SSTA)模态的响应特征,探讨了东北区降水异常对SSTA的响应机制。结果表明:各分区降水异常对SSTA的响应特征有明显差异。东北区降水异常对热带太平洋SSTA的回应显著,当SSTA表现为类似El Niño模时,该区夏季降水增加;江淮区降水异常同时受到中纬度以及热带SSTA的强迫,对热带太平洋SSTA的类似La Niña Modoki模、北大西洋SSTA三极型模等回应显著;西南地区的降水异常主要与中纬度SSTA有密切关联。对流层高度场对热带太平洋SSTA类似El Niño模的直接回应在热带太平洋上空为显著正异常。通过东亚—太平洋型遥相关波列使东北地区上空高度场出现负异常,并在其西侧形成负异常中心,对流层低层为气旋性环流异常。这一环流回应与东北地区夏季降水偏多时的环流特征相近。     

Application of LPW and SAI SAFNWC/MSG satellite products in pre-convective environments

The Spinning Enhanced Visible and Infrared Imagery (SEVIRI) instrument, on board the Meteosat Second Generation (MSG), is a radiometer with eight infrared (IR) spectral bands. Seven of these channels are used to retrieve Layer Precipitable Water (LPW) and Stability Analysis Imagery (SAI). Both products are the PGE07 and the PGE08 of SAFNWC (Satellite Application Facility on support to Nowcasting and Very Short-Range Forecasting). The authors at Instituto Nacional de Meteorología (INM) have developed the LPW and SAI algorithms, in the SAFNWC framework. Both products are retrieved using statistical retrieval based on neural networks. The main advantage of these algorithms versus physical retrieval algorithms is the independence from the Numerical Weather Prediction (NWP) models. The LPW provides information on the water vapor contained in a vertical column of unit cross-section area in three layers in the troposphere (low, middle and high) and in the total layer in cloud free areas. The SAI provides estimations of the atmospheric instability in cloud free areas, in particular the Lifted Index (LI).The stability and precipitable water obtained with both products are routinely generated every 15 min at a satellite horizontal resolution of 3 km in NADIR. A significant advantage of these MSG products, compared to traditional measurements such as radiosondes, is their ability to measure high resolution temporal and spatial variations of atmospheric stability and moisture in pre-convective environments. The main disadvantage is that they do not have the vertical resolution of radiosonde. The MSG moisture and stability time trend fields are especially useful during the period preceding the outbreak of convection due to the high resolution. Once the outbreak of convection occurs, the products calculated in the clear air pixels surrounding the convective system will allow to foresee the evolution of the convection.     

用TRMM资料研究1998年长江流域暴雨

热带测雨卫星ＴＲＭＭ资料于１９９８年６月起向公众用户开放。本文使用了１９９８年７月２０日世界时２１：４０分的ＴＲＭＭ资料对长江流域暴雨作了初步研究。ＴＲＭＭ导出的降水产品亦与雨量计，地面雷达观测以及数值模拟结果进行了比较。由此得出，ＴＲＭＭ资料非常适合于暴雨监测研究。此外，它们还有其他广泛得用途。     

近30 a江苏夏季降水日变化的气候学特征

基于1980—2013年江苏省61站小时降水资料,分析了江苏省夏季降水日变化的特点及小时极端降水、不同级别雨日的日变化特征。结果表明,江苏省夏季降水日变化具有显著的双峰分布特征,然而江苏省北部和南部降水的主峰时段并不一致。从降水频次、累积降水量来看,江苏省北部降水以清晨至早上时段为主峰、午后至傍晚时段为次峰,南部降水与之相反。长持续性降水占夏季降水的2/3左右,且江苏北部占比多于南部,均为清晨至早上的单峰分布;短持续性降水占夏季降水的1/3,在江苏北部呈现出以午后至傍晚为主峰,清晨至早上为次峰的双峰分布,而在江苏南部呈现出以午后至傍晚的单峰分布特点。小时极端降水,阈值分布南低北高,虽然频次较少,但占夏季降水的40%左右。小时极端降水日变化的双峰分布和夏季总体降水分布类似,但主峰大都出现在午后至傍晚。不同级别雨日的日变化分布各有不同,但全省各区无显著差异。累积降水量贡献主要来自于暴雨和大雨。暴雨无论是从降水频次、累积降水量还是降水强度都呈现清晨至早上的单峰分布。     

辽宁土地利用动态遥感监测分析

介绍了在RS与GIS支持下,以Landsat TM和ETM及SPOT数据为主要信息源,采用栅格数据与矢量数据、多源与多时相数据、遥感数据与生态环境基础图件相结合和内业处理与外业调查相结合的技术路线,应用遥感信息提取技术和遥感影像处理及DOM制作方法,得出近15 a辽宁土地面积变化及趋势。结果表明:近年辽宁耕地、水域和工矿等用地面积逐年上升;湿地、草地和未利用土地面积逐年下降。     

基于西南地区台站降雨资料空间插值方法的比较

以西南地区1996～2000年93个气象台站观测的月均降雨量为基础,对各月降雨量进行空间自相关性,变异特征等空间分析后,采用反距离加权法(IDW)和以不同变异函数模型(指数模型、球面模型、高斯模型)为基础的普通克里金(O-Kriging)两种方法进行空间插值,通过交叉验证结果对两种方法进行分析比对。结果表明:(1)西南地区月均降雨量存在明显的空间集聚现象,并具有显著的空间自相关性和变异特征,可对该研究区域降雨量进行空间插值研究。(2)在O-Kriging插值时,变异函数选用指数模型的效果最好,球面模型次之,高斯模型最差。(3)两种方法对月均降雨量及其极大值和极小值插值时,O-Kriging的插值误差均小于IDW,插值误差整体上与降雨量呈正相关关系。在剔除各月降雨量极大值较为集中的两个站点后进行插值,插值结果的误差均明显降低。(4)对研究区域整体来说,O-Kriging的插值效果优于IDW,但就单个站点来看,结果并非如此。在降雨量的空间插值中,由于研究区域和时间尺度的不同,并不存在绝对的最优方法,应根据实际应用效果选择最适方法。     

不同类型大尺度环流背景下强对流天气的短时临近预报预警研究

利用乌鲁木齐多普勒天气雷达、风廓线雷达、GPS/MET水汽探测仪以及FY—2E/G卫星、区域加密自动气象站资料和GFS/NCEP 0.5°×0.5°逐6 h再分析资料,对2015年6月9日18:30—20:00出现在乌鲁木齐的短时强降水过程进行分析,重点分析了强降水过程的环境场和中小尺度特征。结果表明：该短时强降水过程有4个降水集中时段,每个时段约为10~15 min。降水发生在高压脊前低槽后部的西北气流控制之下,700 hPa β中尺度西北急流上γ尺度对流单体是短时强降水直接影响系统。该降水过程水汽来自于乌鲁木齐周围并在2~3 h内快速集中。对流不稳定潜势从午后14 h开始发展,到降水开始仅4.5 h。沿西北低空急流出现多个γ中尺度对流单体以“列车效应”形式依次影响乌鲁木齐造成短时强降水,对流单体组合反射率最强达45~50 dBz,生命史仅15~20 min。降水发生在局地新生中尺度对流云团西南侧云顶亮温TBB梯度最大处,TBB最低达-44 ℃,对流云团生命史2~3 h。

     

夏季亚洲-太平洋遥相关季节演变与大气环流和降水

利用1981-2007年逐日大气再分析资料和降水资料以及统计分析方法,研究了夏季(5-9月)亚洲与太平洋区域的大气遥相关,并分析了其季节演变与夏季亚洲-太平洋大气环流和亚洲季风区降水的联系.结果表明:在5-9月逐日对流层上层扰动温度场上,亚洲与北太平洋中纬度存在着类似于亚洲太平洋涛动的遥相关现象,即在季节尺度上,当亚洲大陆中纬度对流层上层偏暖时,北太平洋中纬度对流层上层偏冷,反之亦然;亚洲与太平洋对流层上层温度的反位相变化特征也出现在对流层中下层和平流层低层.亚洲-太平洋涛动指数不仅可以指示夏季亚洲与太平洋中纬度纬向热力差异的变化特征,也可以较好地指示亚洲与热带印度洋经向热力差异的变化特征.亚洲-太平洋涛动指数最大值常出现在7月中旬到8月初,并且从1981年到2007年该最大值出现时间有偏早趋势.当夏季亚洲太平洋涛动指数偏高(低)时,亚洲大陆上空的南亚高压和其下方的亚洲大陆低压系统偏强(弱),太平洋副热带高压偏强(弱)并偏北(南),亚洲-非洲上空的热带东风急流和低层的西南风偏强(弱),从印度到中国华南的广大地区、中国华北以及东北亚等地降水偏多(少).     

Operational Implementation of the ATOVS Processing Procedure in KMA and Its Validation

The Korea Meteorological Administration (KMA) has processed the data from the advanced TOVS(ATOVS) onboard NOAA-16 satellite since May 2001. The operational production utilizes the AAPP(ATOVS and AVHRR Processing Package) of EUMETSAT and IAPP (International ATOVS ProcessingPackage) of the University of Wisconsin. For the initial guess profiles, the predicted fields (usually 6 to 12hour forecasted fields) from the global aviation model of NOAA/NCEP are used. The average number ofprofiles retrieved from the ATOVS data is about 1,300 for each morning and afternoon orbit at about 18 and06 UTC, respectively. The retrieved temperature and dew point temperatures are provided to forecastersin real time and used for initialization of prediction models. With the advanced microwave sensor (AMSU;Advanced Microwave Sounding Unit), accuracy of the ATOVS products is expected to be better than thatof the TOVS products, especially in cloudy conditions. Indeed, the preliminary results from a validationstudy with the collocated radiosonde data during a 8-month period, from May to December 2001, for theEast Asia region show an improved accuracy of the ATOVS products for cloudy skies versus the TOVS,especially for higher altitudes. The RMS (Root Mean Square) difference between the ATOVS productsand radiosonde data is about 1.3℃ for both clear and cloudy conditions, except for near the ground and athigher altitudes, at around 200 hPa. There is no significant temporal variation of the error statistics at allpressure levels. In case of the water vapor mixing ratio, the largest difference is shown at lower altitudes,while the accuracy is much better for the clear sky cases than the cloudy sky cases. The bias and RMSEat lower altitudes is about 0.557 g kg-1 and 2.5 g kg-1 and decrease significantly with increasing altitude.     

2008年T213与德国降水数值预报产品对比检验分析

为了解各种数值预报的误差特点,更好地在预报过程中选择数值预报产品作为参考依据,将中国国家气象中心的T213降水预报和德国降水预报分别进行晴雨预报检验,对2008年5—8月期间东北地区降水资料进行对比分析。结果表明：两种模式24—120h预报正确率为60%—70%左右,随着预报时效的增加,正确率呈下降趋势,德国降水预报的正确率高于T213,两种预报漏报率均明显小于空报率,T213漏报率较低,为5%左右,德国降水预报空报率较低,为20%左右。对2008年4—6月出现东北冷涡过程的两种模式降水预报进行对比分析,发现德国降水预报正确率明显高于T213预报,对冷涡降水预报有一定的指示意义。     

Quantitative estimation of skin soil moisture with the Special Sensor Microwave/Imager

A physically based retrieval scheme is described toinfer near surface moisture content of bare soilpatches from time series of the Special SensorMicrowave/Imager (SSM/I) Polarisation DifferenceTemperature (PDT) at 19.35 GHz. The PDT is modelled asa function of soil moisture using Fresnel's relationsfor specular reflection at the air-soil boundary,together with a dielectric mixing model for themoisture-dependent soil dielectric constant. Theproblem of the specification of parameters describingatmospheric and soil roughness effects is avoided byconsidering temporal variations of the PDT. Theretrieval method is applied to the FIFE site for atwo-week period in summer, during which heavy rainfalloccurred on a dry upper soil. Although differences insensing depths made a rigorous validation impossible,remotely sensed soil moisture showed a high degree ofconsistency with ground measurements. An erroranalysis shows that the method is capable of providingan accuracy of approximately 20% of moisture contentat field capacity. Finally, it is demonstrated thatthe method is relatively insensitive to soil texturalcharacteristics when moisture content is scaled withfield capacity.     

西伯利亚高压对亚洲大陆的气候影响分析

西伯利亚高压是冬季影响亚洲大陆地区的重要环流因子 ,本文用冬季 (1～ 3月 ) 70°～ 12 0°E ,40°～ 6 0°N区域平均海平面气压值代表其强度 ,分析其变化特征。结果表明 ,从 192 2年到 1970年代中期 ,西伯利亚高压略有增强趋势 ,但并不显著。但近 2 0多年来的显著减弱非常突出。用NCAR资料计算的线性趋势是 - 1.78hPa/ 10a(1976— 2 0 0 0年 ) ,用CRU气压资料计算的趋势是 - 2 .15hPa/ 10a(1976— 1995年 )。西伯利亚高压对中高纬亚洲大陆平均 (30°～ 140°E ,30°～ 70°N)温度和降水都有显著影响 ,与两个要素的相关系数分别达到 - 0 .5 8和 - 0 .44。如果同时考虑其他的影响因子 (如北极涛动、欧亚遥相关型等 ) ,72 %的温度变化及 2 6 %的降水变化能得到解释。其中北极涛动对亚洲大陆的温度贡献最高达到 30 % ,西伯利亚高压的贡献为 2 4%。而区域平均降水变化的 9.8%与西伯利亚高压有关