Applicability of TRMM Precipitation Product in Qinba Mountainous Area of Shaanxi Province

The applicability of Tropical Rainfall Measuring Mission (TRMM3B42V7) precipitation data in the region was evaluated using the measured daily precipitation data in 16 hydrological stations in Shaanxi Province from 1998 to 2014. The evaluation process with several statistical error metrics was applied to daily, monthly, and annual timescale. The results show that the satellite and gauge stations show good consistency for monthly and annual timescale, but rather worse accuracy of daily timescale. All timescales produced the overestimated result of average precipitation measurement. The spatially statistical distribution shows a slight correlation between the observation and satellite estimation, especially at the higher elevation area such as Taibai. The TRMM precipitation value is closer to the gauge station precipitation value at a place with lower elevation, whether the timescale is daily, monthly or annual. At the same time, the smaller timescale leads to closer relations between elevation and metrics. The research results are important value of the research study of meteorological process in the Qinba mountain area.

Research on the Summer Drought in Chongqing Using MODIS-EVI Time Series Data

MODIS-EVI time series data from 2000 to 2009 in Chongqing were selected for this study.By the use of best index slope extraction （BISE） method for cloud elimination,analysis on the change vector of EVI time series data were conducted to investigate the EVI response on drought; then,four typical regions were selected to study the relationship between precipitation,temperature and EVI when the sever drought occurred in 2006; finally,based on the time series of vegetation condition index （VCI） and precipitation abnormity percentage,the temporal and spatial distributions of drought were studied.The results showed that,the EVI value of the summer in 2006 was significantly lower than the average EVI at the corresponding period of the other years in Chongqing.In addition,summer drought occurred mainly during the hot and dry weather.Except the southeast area,most of the other regions in Chongqing were all under severe drought.

Relationship between Atmospheric Heat Source over the Tibetan Plateau and Precipitation in the Sichuan–Chongqing Region during Summer

NCEP-NCAR reanalysis data and a 47-yr daily precipitation dataset from a network of 42 rain gauges are used to analyze the atmospheric heat source （〈Q1〉） anomaly over the Tibetan Plateau （TP） and its influence on the summer precipitation anomaly in the Sichuan-Chongqing region. Results show that the vertical advection of 〈Ql〉 over the central TP is a major factor affecting summer precipitation in the Sichuan-Chongqing region. When the vertical ad- vection of〈Q1〉 over the central TP is strengthened, the South Asian high shifts further than normal to the south and east, the western Pacific subtropical high shifts further than normal to the south and west, and the Indian low weak- ens. This benefits the transport of warm moist air from the low latitude oceans to the Sichuan-Chongqing region. Correspondingly, in the high latitudes, two ridges and one trough form, which lead to cool air moving southward. These two air masses converge over the Sicbuan -chongqing region, leading to significant precipitation. In contrast, when the vertical advection of 〈Q1〉 over the central TP is weakened, the South Asian high moves to the north and west, the subtropical high moves eastward and northward, and the Indian low strengthens. This circulation pattern is unfavorable for warm air advection from the south to the Sichuan-Chongqing region, and the cool air further north cannot move southward because of the presence of two troughs and one ridge at high latitude. Thus, ascent over the Sichuan-Chongqing region is weakened, resulting in less precipitation.

Seasonal Characteristics of Precipitation in 1998 over East Asia as Derived from TRMM PR

Precipitation radar data derived from the Tropical Rainfall Measuring Mission (TRMM) satellite are used to study precipitation characteristics in 1998 over East Asia (10?38癗, 100C-145癊), especially over mid-latitude land (continental land) and ocean (East China Sea and South China Sea). Results are compared with precipitations in the tropics. Yearly statistics show dominant stratiform rain events over East Asia (about 83.7% by area fraction) contributing to 50% of the total precipitation. Deep convective rains contribute 48% to the total precipitation with a 13.7% area fraction. The statistics also show the unimportance of warm convective rain in East Asia, contributing 1.5% to the total precipitation with a 2.7% area fraction. On a seasonal scale, the results indicate that the rainfall ratio of stratiform rain to deep convective rain is proportional to their rainfall pixel ratio. Seasonal precipitation patterns compare well between Global Precipitation Climatology Project rainfall and TRMM PR measurements except in summer. Studies indicate a clear opposite shift of rainfall amount and events between deep convective and stratiform rains in the meridional in East Asia, which corresponds to the alternative activities of summer monsoon and winter monsoon in the region. The vertical structures of precipitation also exhibit strong seasonal variability in precipitation Contoured Rainrate by Altitude Diagrams (CRADs) and mean profiles in the mid-latitudes of East Asia. However, these structures in the South China Sea are of a tropical type except in winter. The analysis of CRADs reveals a wide range of surface rainfall rates for most deep convective rains, especially in the continental land, and light rain rate for most stratiform rains in East Asia, regardless of over land or ocean.

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.

Characterizing Spatial Patterns of Precipitation Based on Corrected TRMM_3B_(43) Data over the Mid Tianshan Mountains of China

The poor distribution of meteorological stations results in a limited understanding of the precipitation pattern in the Tianshan Mountains. The spatial patterns of precipitation over the mid Tianshan Mountains were characterized based on the TRMM 3B43 monthly precipitation data. By comparing satellite estimates with observed data, it shows that TRMM 3B43 data underestimate the precipitation in mountain region. Regression models were developed to improve the TRMM 3B43 data, using geographic location and topographic variables extracted from DEM using GIS technology. The explained variance in observed precipitation was improved from 64% (from TRMM 3B43 products alone) to over 82% and the bias reduced by over 30% when location and topographic variables were added. We recalculated all the TRMM 3B43 monthly precipitation grids for the period 1998 to 2009 using the best regression models, and then studied the variation patterns of precipitation over the mid Tianshan Mountains. The results are well explained by a general understanding of the patterns of precipitation and orographic effects. This indicated that the Tianshan Mountains strongly influences the amount and distribution of precipitation in the region. This is highlighted by the confinement of the precipitation maxima to the windward (northern slope). And complex vertical changes in the provenance and distribution of precipitation, like that a negative increasing rate of precipitation in the vertical direction exists in the north but does not in south. The results have also revealed large gradients and different patterns in seasonal precipitation that are not simply related to elevation, the distribution of precipitation may also be affected by other seasonal factors such as the sources of moist air, wind direction and temperature.

Spatial and temporal distribution of precipitation based on corrected TRMM data around the Hexi Corridor,China

Accurate rainfall distribution is difficult to acquire based on limited meteorological stations, especially in remote areas like high mountains and deserts. The Hexi Corridor and its adjacent regions （including the Qilian Mountains and the Alxa Plateau） are typical districts where there are only 30 available rain gauges. Tropical Rainfall Measuring Mission （TRMM） data provide a possible solution. After precision analysis of monthly 0.25 degree resolution TRMM 3B43 data from 1998 to 2012, we find that the correlations between TRMM 3B43 estimates and rain gauge precipitation are significant overall and in each station around the Hexi Corridor; however, the biases of annual precipitation differ in different stations and are seriously overestimated in most of the sites. Thus, Inverse Distance Weighting （IDW） interpolation method was used to rectify TRMM data based on the difference between TRMM 3B43 estimates and rain gauge observations. The results show that rectified TRMM data present more details than rain gauges in remote areas where there are few stations, alt- hough they show high coherence of distribution. Precipitation decreases from southeast to northwest on an annual and seasonal scale. There are three rainfall centers （〉500 mm） including Menyuan, Qilian and Toson Lake, and two low rain- fall centers （〈50 mm） including Dunhuang and Ejin Banner. Meanwhile, precipitation in most of the study area presents an increasing trend; especially in northern Qilian Mountains （〉5 mm/a）, Badain Jaran Desert （〉2 mm/a）, Toson Lake （〉20 mm/a） and Qingtu Lake （〉20 ram/a） which shows a significant increasing trend, while precipitation in Hala Lake （〈-2 mm/a） and Tengger Desert （〈-3 mm/a） demonstrates a decreasing trend.

Spatio-temporal Distribution of Drought in the Belt and Road Area During 1998–2015 Based on TRMM Precipitation Data

Drought is a worldwide natural disaster that has long affected agricultural production as well as social and economic activities. Frequent droughts have been observed in the Belt and Road area, in which much of the agricultural land is concentrated in fragile ecological environment. Based on the Tropical Rainfall Measuring Mission Satellite（TRMM） 3 B43 precipitation data, we used the Precipitation Abnormity Percentage drought model to study the monthly spatio-temporal distribution of drought in south region of N50° of the Belt and Road area. It was observed that drought during winter was mainly distributed in Northeast Asia, Southeast Asia, and South Asia, while it was mainly distributed in Central Asia and West Asia during summer. The occurrence of historical droughts indicates an obvious seasonal cycle. The regional variations in drought were analyzed using the Breaks for Additive Season and Trend tool（BFAST） in six sub-regions according to the spatial distribution of six economic corridors in the Belt and Road area. The average drought conditions over the 18 years show a slight decreasing trend in Northeast Asia, West Asia, North Africa, South Asia, Central and Eastern Europe, and a slight increasing trend in Central Asia. However, it was a fluctuating pattern of first increasing and then decreasing in Southeast Asia. The results indicate that the total drought area in the Belt and Road region showed a general decreasing trend at a rate of 40,260 km^2 per year from 1998 to 2015.

Observed Diurnal Cycle of Summer Precipitation over South Asia and East Asia Based on CMORPH and TRMM Satellite Data

The characteristics of the summer precipitation diurnal cycle over South Asia and East Asia during 2001–13 are investigated based on the high spatiotemporal resolution estimates of the CPC(Climate Prediction Center) Morphing(CMORPH) technique. The results show that summer precipitation over South Asia and East Asia possesses a remarkable diurnal cycle, with obvious regional differences. Over the coastal areas, plateau, and high mountains, summer precipitation peaks in the late afternoon; while over low altitude areas, such as valleys, basins, and inshore seas, it peaks during midnight to early morning. In addition to these general features consistent with previous studies, the high resolution CMORPH technique can depict finer regional details, such as the less coherent phase pattern over a few regions. Besides, through comparative analysis of the diurnal cycle strength and precipitation fields, the authors find that for humid areas the summer precipitation diurnal cycle is especially significant over Southeast China, the Sichuan Basin, Hainan Province, Taiwan Province, the Philippines, and Indonesia. And it is relatively weak over the south of Northeast China, central East China, Yunnan Province, the central Indian Peninsula, and most oceanic areas. Comparisons between two satellite datasets—those of the CMORPH and Tropical Rainfall Measuring Mission(TRMM) 3B42 products—are also presented. For summer precipitation and the main diurnal cycle features, the results from both products agree over most regions, except a few areas, e.g., the Tibetan Plateau.

Morphological Characteristics of Precipitation Areas over the Tibetan Plateau Measured by TRMM PR

The multidimensional morphological characteristics(including scale, horizontal shape and 3 D morphology) of precipitation areas over the Tibetan Plateau in summer were studied using 15 years(1998–2012) of observational data from the precipitation radar onboard the Tropical Rainfall Measuring Mission satellite. As the scale of the precipitation area increased from 20 to 150 km, the near-surface rain rate(RRav) of the precipitation area increased by up to 78%(from ~1.12 to ~2 mm h~(-1)). Linear precipitation areas had the lowest median RRav(~1 mm h~(-1) over the eastern Tibetan Plateau),whereas square-shaped precipitation areas had the highest median RRav(~1.58 mm h~(-1) over the eastern Tibetan Plateau).The 3D morphology was defined as the ratio of the average vertical scale to the average horizontal scale, where a large value corresponds to thin and tall, and a small value corresponds to plump and short. Thin-and-tall precipitation areas and plump-and-short precipitation areas had a greater median RRav, whereas the precipitation areas with a moderate 3D morphology had the lowest median RRav. The vertical structure of the precipitation-area reflectivity was sensitive to both size and 3D morphology, but was not sensitive to the horizontal shape. The relationship between RRav and the morphological characteristics was most significant over the southern slopes of the Tanggula Mountains and the Tibetan Plateau east of 100°E. The morphological characteristics of precipitation areas are therefore closely related to the intensity of precipitation and could potentially be used to forecast precipitation and verify numerical models.

How do GPM and TRMM precipitation products perform in alpine regions?A case study in northwestern China's Qilian Mountains

Satellite technologies provide valuable areal precipitation datasets in alpine mountains.However,coarse resolution still limits the use of satellite precipitation datasets in hydrological and meteorological research.We evaluated different time scales and precipitation magnitudes of Tropical Rainfall Measurement Mission 3B43 V7(TRMM)and Global Precipitation Measurement(GPM)products for alpine regions using ground precipitation datasets from January 2015 to June 2019 obtained from 25 national meteorological stations and 11 sets of T-200B weighing precipitation gauges in the Qilian Mountains.The results indicated that GPM outperformed TRMM at all temporal scales at an elevation<3500 m with a higher probability of detection(POD),false alarm ratio(FAR),and frequency bias index(FBI)and performed best at 3000 m;TRMM performed better than GPM at an elevation>3500 m,with the best performance at 4000 m.GPM and TRMM had the best estimation accuracy in areas with monthly precipitation of 30 mm and 40 mm,respectively.Both TRMM and GPM products underestimated mid to large daily precipitation and overestimated light daily precipitation averaging<2 mm/d.This research not only emphasizes the superiority of GPM/TRMM in different regions but also indicates the limitations of precipitation algorithms.

Diurnal Variations of Precipitation over the Steep Slopes of the Himalayas Observed by TRMM PR and VIRS

This study investigates diurnal variations of precipitation during May–August, 1998–2012, over the steep slopes of the Himalayas and adjacent regions(flat Gangetic Plains–FGP, foothills of the Himalayas–FHH, the steep slope of the southern Himalayas–SSSH, and the Himalayas-Tibetan Plateau tableland–HTPT). Diurnal variations are analyzed at the pixel level utilizing collocated TRMM precipitation radar and visible infrared data. The results indicate that rain parameters(including rain frequency, rain rate, and storm top altitude) are predominantly characterized by afternoon maxima and morning minima at HTPT and FGP, whereas, maximum rain parameters at FHH typically occur in the early morning. Rain parameters at SSSH are characterized by double peaks;one in the afternoon and one at midnight. Over HTPT and FGP,convective activity is strongest in the afternoon with the thickest crystallization layer. Over FHH, the vertical structure of precipitation develops most vigorously in the early morning when the most intense collision and growth of precipitation particles occurs. Over SSSH, moist convection is stronger in the afternoon and at midnight with strong mixing of ice and water particles. The results of harmonic analysis show that rain bands move southward from lower elevation of SSSH to FHH with apparent southward propagation of the harmonic phase from midnight to early morning. Moreover, the strongest diurnal harmonic is located at HTPT, having a diurnal harmonic percentage variance of up to 90%. Large-scale atmospheric circulation patterns exhibit obvious diurnal variability and correspond well to the distribution of precipitation.

Evaluation of Precipitation Datasets from TRMM Satellite and Down-scaled Reanalysis Products with Bias-correction in Middle Qilian Mountain,China

Accurate estimates of precipitation are fundamental for hydrometeorological and ecohydrological studies,but are more difficult in high mountainous areas because of the high elevation and complex terrain.This study compares and evaluates two kinds of precipitation datasets,the reanalysis product downscaled by the Weather Research and Forecasting(WRF)output,and the satellite product,the Tropical Rainfall Measuring Mission(TRMM)Multisatellite Precipitation Analysis(TMPA)product,as well as their bias-corrected datasets in the Middle Qilian Mountain in Northwest China.Results show that the WRF output with finer resolution perfonns well in both estimating precipitation and hydrological simulation,while the TMPA product is unreliable in high mountainous areas.Moreover,bias-corrected WRF output also performs better than bias-corrected TMPA product.Combined with the previous studies,atmospheric reanalysis datasets are more suitable than the satellite products in high mountainous areas.Climate is more important than altitude for the\falseAlarms'events of the TRMM product.Designed to focus on the tropical areas,the TMPA product mistakes certain meteorological situations for precipitation in subhumid and semiarid areas,thus causing significant"falseAlarms"events and leading to significant overestimations and unreliable performance.Simple linear bias correction method,only removing systematical errors,can significantly improves the accuracy of both the WRF output and the TMPA product in arid high mountainous areas with data scarcity.Evaluated by hydrological simulations,the bias-corrected WRF output is more reliable than the gauge dataset.Thus,data merging of the WRF output and gauge observations would provide more reliable precipitation estimations in arid high mountainous areas.

ANALYSIS OF TROPICAL CYCLONE PRECIPITATION FOR DIFFERENT INTENSITY CLASS IN NORTHWEST PACIFIC WITH TRMM DATA

Combined with TRMM products and Tropical Cyclone(TC) best track data in Northwest Pacific from 1 January 2003 to 31 December 2009,a total of 118 TCs,including 336 instantaneous TC precipitation observations are established as the TRMM TC database,and the database is stratified into four intensity classes according to the standard of TC intensity adopted by China Meteorological Administration(CMA):Severe Tropical Storm(STS),Typhoon(TY),Severe Typhoon(STY) and Super Typhoon(SuperT Y).For each TC snapshot,the mean rainfall distribution is computed using 10-km annuli from the TC center to a 300-km radius,then the axisymmetric component of TC rainfall is represented by the radial distribution of the azimuthal mean rain rate;the mean rain rates,rain types occurrence and contribution proportion are computed for each TC intensity class;and the mean quadrantal distribution of rain rates along TCs motion is analyzed.The result shows that:(1) TCs mean rain rates increase with their intensity classes,and their radial distributions show single-peak characteristic gradually,and furthermore,the characteristics of rain rates occurrence and contribution proportion change from dual-peak to single-peak distribution,with the peak rain rate at about 5.0mm/h;(2) Stratiform rain dominate the rain type in the analysis zone,while convective rain mainly occurred in the eye-wall region;(3) The values of mean rain rate in each quadrant along TCs motion are close to each other,relatively,the value in the right-rear quadrant is the smallest one.

滦河流域TRMM卫星降水数据适用性研究

利用滦河流域8个雨量站点2003—2019年实测降水资料,对TRMM卫星降水数据在滦河流域的适用性进行了评估。结果表明,TRMM降水量与实测降水量具有一致的年内分布规律和时空分布特征。在年、季、月时间尺度上,TRMM降水量具有较高的精度,普遍高于实测值,7月存在低估现象;夏秋季降水精度较高,冬季略差;7—10月精度较高,12月—次年2月精度较差。空间上,TRMM降水量精度随着海拔的降低而增加,在流域中上游TRMM降水量高估,沿海地区略微低估,乐亭站、秦皇岛站存在低估现象。

Assessing the Applicability of Multi-Source Precipitation Products over the Chinese Mainland and Its Seven Regions

Satellite-based and reanalysis precipitation products provide valuable information for various applications.However,their performance varies widely across regions due to different data sources and production processes.This paper evaluated the daily performance of four precipitation products(MSWEP,ERA5,PERSIANN,and TRMM)for seven regions of the Chinese mainland,using observations from 2462 ground stations across the country as a benchmark.We used four statistical and four classification indicators to describe their spatial and temporal accuracy,and capability to detect precipitation events while analyzing their applicability.The results show that according to the precipitation char-acteristics and accuracy of different types of precipitation products over the Chinese mainland,MSWEP was the most suitable product over the Chinese mainland,having the lowest root mean square error and mean absolute error,along with the highest coefficient of determination.It was followed by TRMM and ERA5,whereas PERSIANN lagged behind in terms of performance.In terms of different regions,MSWEP still performed well,especially in North China and East China.The accuracy of the four precipitation products was relatively low in the summer months,and they all overestimated in the northwest region.In other months,MSWEP and TRMM were better than PERSIANN and ERA5.The four precipitation products had good detection performance over the Chinese mainland,with probability of detection above 0.5.However,with the increase of precipitation threshold,the detection capability of the four products decreased,and MSWEP and ERA5 had good detection capability for moderate rain.TRMM’s detection capability for heavy rain and rainstorms was better than that of the other three products,and PERSIANN’s detection capability for moderate rain,heavy rain and rainstorms was relatively poor,with a large deviation.

Comprehensive applicability evaluation of four precipitation products at multiple spatiotemporal scales in Northwest China

Precipitation plays a crucial role in the water cycle of Northwest China.Obtaining accurate precipitation data is crucial for regional water resource management,hydrological forecasting,flood control and drought relief.Currently,the applicability of multi-source precipitation products for long time series in Northwest China has not been thoroughly evaluated.In this study,precipitation data from 183 meteorological stations in Northwest China from 1979 to 2020 were selected to assess the regional applicability of four precipitation products(the fifth generation of European Centre for Medium-Range Weather Forecasts(ECMWF)atmospheric reanalysis of the global climate(ERA5),Global Precipitation Climatology Centre(GPCC),Climatic Research Unit gridded Time Series Version 4.07(CRU TS v4.07,hereafter CRU),and Tropical Rainfall Measuring Mission(TRMM))based on the following statistical indicators:correlation coefficient,root mean square error(RMSE),relative bias(RB),mean absolute error(MAE),probability of detection(POD),false alarm ratio(FAR),and equitable threat score(ETS).The results showed that precipitation in Northwest China was generally high in the east and low in the west,and exhibited an increasing trend from 1979 to 2020.Compared with the station observations,ERA5 showed a larger spatial distribution difference than the other products.The overall overestimation of multi-year average precipitation was approximately 200.00 mm and the degree of overestimation increased with increasing precipitation intensity.The multi-year average precipitation of GPCC and CRU was relatively close to that of station observations.The trend of annual precipitation of TRMM was overestimated in high-altitude regions and the eastern part of Lanzhou with more precipitation.At the monthly scale,GPCC performed well but underestimated precipitation in the Tarim Basin(RB=-4.11%),while ERA5 and TRMM exhibited poor accuracy in high-altitude regions.ERA5 had a large bias(RB≥120.00%)in winter months and a strong dispersion(RMSE≥35.00 mm)in summer months.TRMM showed a relatively low correlation with station observations in winter months(correlation coefficients≤0.70).The capture performance analysis showed that ERA5,GPCC,and TRMM had lower POD and ETS values and higher FAR values in Northwest China as the precipitation intensity increased.ERA5 showed a high capture performance for small precipitation events and a slower decreasing trend of POD as the precipitation intensity increased.GPCC had the lowest FAR values.TRMM was statistically ineffective for predicting the occurrence of daily precipitation events.The findings provide a reference for data users to select appropriate datasets in Northwest China and for data developers to develop new precipitation products in the future.

TRMM测雨雷达和微波成像仪对两个中尺度特大暴雨降水结构的观测分析研究

文中利用TRMM卫星的测雨雷达和微波成像仪探测结果,研究了1998年7月20日21时(世界时)和1999年6月9日21时发生在武汉地区附近和皖南地区的两个中尺度强降水系统的水平结构和垂直结构,以及TMI微波亮温对降水强弱和分布的响应。研究结果表明:这两个中尺度强降水系统中对流降水所占面积比层云降水面积小,但对流降水具有很强的降水率,它对总降水量的贡献超过了层云降水。降水水平结构表明,两个中尺度强降水系统由多个强雨团或雨带组成,它们均属于对流性降水;降水垂直结构分析表明,强对流降水的雨顶高度可达15km,强对流降水主体中存在垂直方向和水平方向非均匀降水率分布区,层云降水有清晰的亮度带,层云降水的上方存在多层云系结构。降水廓线分布表明:对流降水廓线与层云降水廓线有明显的区别,并且降水廓线清晰地反映了降水微物理过程的垂直分布。整个中尺度强降水系统中对流降水与层云降水的区别还反映在标准化的总降水率随高度的分布。微波信号分析表明:TMI85 GHz极化修正亮温,19.4与37.0,19.4与85.5,37.0与85.5 GHz的垂直极化亮温差均能较好地指示陆面附近的降水分布。

基于TRMM数据的青藏高原降水的空间和季节分布特征

庞大的青藏高原不仅影响其周围的气候,也影响整个亚洲甚或全球的气候,而且本身还形成了独特的高原气候。但高原上气象观测站点极为稀少,降水资料奇缺,难以完整、深刻地认识高原降水的时空分布格局。选用热带降雨测量计划卫星（Tropical Rainfall Measuring Mission,TRMM）3B43月尺度降水率数据,并根据114个气象站点数据与TRMM数据的差额和克里格球形插值模型对原数据进行了修正,克服了原数据低值高估、高值低估的问题,并以此分析了青藏高原1998~2011年的多年平均降水的空间格局与季节分布特征。研究结果证实了青藏高原降水的空间格局呈现自东南向西北递减、自南向北逐渐减少的基本分布规律,包括喜马拉雅山北坡雨影区、高原西北部＂寒旱核心＂的存在;还发现了一些新的规律,包括阿里喀喇昆仑山少雨区、高原腹地相对湿润区、横断山脉中心相对干旱区等。高原降水的季节分配不均匀,其中,西、北部春（3~5月）、秋（9~11月）和冬（12~2月）的降水占全年降水比例均为20%~30%,夏季（6~8月）降水稍多,比例为30%~40%;东南部降水主要集中在夏季,比例高达40%~60%,春、秋降水比例为20%~30%,冬季降水比例低于10%。

TRMM降水数据在复杂山地的精度评估——以重庆市为例

在地形复杂的重庆地区,利用研究区内34个气象站点实测数据,分别从年、季、月3个尺度,对2000—2011年间TRMM 3B43降水数据精度进行了验证,并分析了高程和坡度对月尺度验证结果的影响,同时利用主成分分析法比较了高程与坡度对TRMM 3B43降水数据的影响程度。研究表明:(1)年尺度上,TRMM 3B43年降水数据普遍高于气象站点的实测结果(平均偏高5.86%),渝西、渝南的结果比渝东北的准确。季尺度上,秋季拟合效果高于其它3个季节。月尺度上,相关系数R=0.85,两者之间存在显著相关性。(2)逐站点验证,研究区TRMM 3B43月降水数据具有较高精度(相关系数均大于0.80)。(3)随着海拔的升高,相关系数呈"增加—减少—增加"的变化趋势,绝对偏差呈减小趋势;随着坡度的升高,绝对偏差呈"增加—减少—增加"的变化趋势,绝对偏差呈线性增加的趋势。(4)利用主成分分析方法得出,高程对数据精度的影响大于坡度。