青藏高原地区地表及行星反射率

文章讨论了利用ISCCP卫星观测资料确定青藏高原地区地表反射率的方法,在无积雪地区和季节,地表反射率可以ISCCP可见光反射率为基础,在模式计算过程中,假定紫外反射率以及红外与可见光反射率的比值分别为常数。敏感性试验表明,由这两个假设所产生的误差并不显著。在有积雪地区或季节,地表平均反射率可直接由ISCCP可见光反射率表示。试验结果与地面实际观测作了比较,除沙漠区外,两者比较一致。文中还计算了高原晴天行星反射率。经与ERBE卫星观测比较,发现从5月至9月高原周围沙漠区气溶胶对辐射平衡有较显著的影响。而在其     

青藏高原不同季节地表温度变化特征分析

基于欧洲中尺度气象预报中心(ECMWF)提供的ERA-Interim地表温度,利用经验正交函数(EOF)等方法,分析了青藏高原四季地表温度的时空变化特征.结果发现:青藏高原春、夏、冬季地表温度变化以整体型为主,并且大部地区地表温度呈现升高的趋势;秋季地表温度略有下降趋势,并且以东部和西部地表温度的反向型异常变化最为显著.此外还发现,青藏高原不同季节地表温度的异常变化具有一定的联系,其中整体型变化可以持续3个季节.     

青藏高原气温变化的研究进展

青藏高原(简称高原,下文同)是全球气候系统的重要组成部分,其气候因子、动力及热力作用对全球气候系统的变化有着深刻的影响。本文就近代高原地表气温不同年代际的变化、空间分布及其与我国其它区域同期气温变化的关系等方面的研究进展进行回顾和总结。经过研究分析表明,高原的气温变化呈明显的年代际特征。近百年来高原的气温可分2个冷期2个暖期,其间有3次突变,即1920年代以前偏冷,1920～1950年代气温回升,1950～1980年代气温下降,1980年代至今气温持续偏高。各次气温突变时间中高原均提前于我国其它地区,且全国有北方提前于南方,高纬提前于低纬的现象;高原上大多数区域日最低气温增温幅度是日最高温度的增温幅度的1～3倍,日较差变小,4季中冬季增温最为明显;由于地域辽阔,地形复杂,就高原本身主体而言,各区域的温度变化也存在差异。已有的研究成果表明,高原主体的气温变化最先出现在高原东南部和海拔较高的区域。     

青藏高原表面过程对夏季青藏高压的影响--数值试验

利用IAP/LASGGOALS气候模式设计了两组敏感性试验,分别考察青藏高原表面感热输送和表面摩擦拖曳对夏季青藏高压的影响.结果表明,表面感热输送显著增强了高原近地层气柱中正涡度的制造和气旋性环流,同时增强了高原上空气柱高层的负涡度制造和反气旋性环流.另一方面,高原表面摩擦拖曳虽然使得低层的辐合略有增加,但施加给整层气柱以反气旋性涡度.因而高原表面的感热输送和表面摩擦拖曳对夏季青藏高压都有增强的作用.表面摩擦拖曳对上空环流的影响随着高度升高而减弱,而表面感热输送引起的高层负涡度的增加与低层正涡度的增加在数值上相当甚至更大.     

青藏高原地区TRMM PR地面降雨率的修正

为掌握并改进青藏高原地区TRMM卫星降水雷达 (precipitation radar,PR) 地面降雨率准确度,统计分析了2005—2007年TRMM PR 2A25资料和逐小时地面雨量计,结果表明:青藏高原地区TRMM PR地面降雨率在层云降水时平均偏低35%,在对流云降水时平均偏高42%。Z-R关系的适用性是PR产生偏差的原因之一,研究将TRMM PR层云降水模型中20℃层Z-R关系的初始系数A和b分别修正为0.0288和0.6752,对流云降水模型中20℃层的初始系数A和b分别修正为0.0406和0.5809,得到两类降水模型0℃层与20℃层之间不同高度Z-R关系的更新系数。检验结果表明,修正降水模型后能够提高青藏高原地面降雨率测量的准确度。     

青藏高原感热与黄土高原春季降水异常关系研究

利用1961～2000年黄土高原56站的春季降水、气温资料,用SVD方法分析了其与青藏高原感热场的关系。结果表明,降水量与青藏高原感热场的前两模态代表了两场间的主要耦合特征;上年冬季和秋季青藏高原感热场的异常通过影响大气环流,能够导致次年黄土高原春季降水异常;青藏高原感热对黄土高原西部和南部、北部的部分地区影响较显著,而对陕西北部、山西中部影响不明显。前期高原感热场SVD第一、二模态的变化,可以作为黄土高原春季降水异常的预测信号。     

三种再分析气温降水资料在青藏高原的适用性评价

基于青藏高原61个区域级气象站的气温降水地面观测数据,对CMFD(中国区域高分辨率地区驱动数据集)、CRA(全球大气和陆面再分析资料)以及MERRA-2(大气再分析资料)数据集的日、月、季节以及年气温、降水数据进行精度对比分析,评估3套数据的准确性以及在青藏高原的适用性,结果表明：(1)3套年平均气温资料70%的R_MSE<4℃,其中CMFD拟合精度最高,2/3的站点R_MSE<2℃;CMFD和CRA对年降水的拟合精度较高,MERRA-2低估了高原中部的年降水量。(2)CMFD对季节平均气温整体拟合结果最好,尤其是气温较高的夏季和秋季;CRA在降水较为集中的夏季和秋季拟合结果最接近观测值,而在降水较少的春季和冬季CMFD拟合结果最好。(3)CMFD对月平均气温拟合结果整体上最接近观测值;月降水拟合结果与季节降水结果相似,CMFD对降水偏少月份拟合结果较好,CRA在降水偏多月份最接近观测值。(4)对61个区域站进行日尺度平均气温和降水数据精度评估,发现CMFD和CRA拟合效果最好,CMFD拟合趋势一致性好。     

青藏高原六套陆面蒸散发产品的评估

Uncertainties in the evapotranspiration (ET) products used in the Tibetan Plateau (TP) region were determined based on the data from satellite remote sensing and observations having different spatial and temporal resolutions, limiting their utility for hydrometeorological and climate assessment. Six ET (PML, EB-ET_V2, GLEAM, GLDAS, ERA5_Land, and MOD16) products were evaluated based on eddy observations, and the differences between the products were compared. Moreover, the uncertainties in ET products in the TP region were analyzed. The results of the analysis are as follows: (1) A good correlation and consistency exist in the mean state and seasonal cycle between the observed and ET values of the corresponding pixel. Moreover, GLEAM product exhibits a high degree of agreement with the observed values and has applicability, and MOD16 product exhibits poor performance at most sites. (2) In terms of seasonal changes, ERA5_Land product values are highly consistent with the observed changes during spring, GLEAM product values are nearly consistent with the observed changes during summer and winter, and EB-ET_V2 product values are highly consistent with observed values during autumn. (3) Spatially, GLEAM product has higher correlation (the correlation coefficient R＞ 0.88) and consistency (index of agreement IOA＞ 0.89) compared to those of EB-ET_V2 product and GLDAS product. Substantial differences exist in the temporal and spatial distribution of various products during different seasons, especially during spring. Compared with other products, MOD16 product is underestimated in summer and overestimated in winter in most regions. (4) The annual average ET for each product except for MOD16 product is considerably different. The annual average ET values of the remaining five products over multiple years arranged in descending order are as follows: ERA5_Land product (401.46 mm a−1)＞ PML product (334.37 mm a−1)＞GLEAM product (298.46 mm a−1)＞EB-ET_V2 product (271.39 mm a−1)＞GLDAS product (249.67 mm a−1). The total annual evaporation in the TP region is 330.59 mm a−1. The assessment results provide a detailed understanding of the quality and dynamics of ET products in the TP region, which can serve as reference data for regional water management and water resource assessment in the TP region. © 2023 Science Press. All rights reserved.     

三种再分析地表温度资料在青藏高原区域的适用性分析

利用气象台站观测地表温度,比较和分析了ERA-Interim、NCEP/NCAR和NCEP/DOE再分析地表温度资料在青藏高原的适用性.结果表明:三种再分析资料都揭示了青藏高原地表温度的基本特征,并较好地描述了高原地表温度的季节变化和年际变化特征;但三种再分析资料都比观测地表温度明显偏低,且对地表温度的长期变化趋势估计不足.比较而言,ERA-1nterim再分析地表温度产品在青藏高原的适用性最好,与观测地表温度的相关最显著,且能较好地反映高原地表温度的异常变化强度,可作为研究高原地表温度年际变化的代用资料;而NCEP/NCAR和NCEP/DOE 再分析地表温度产品在青藏高原的适用性不佳,其适用时段和适用区域需要进一步考察.     

卫星遥感藏北高原非均匀陆表地表特征参数和植被参数

卫星遥感在研究青藏高原北部地区(藏北高原地区)非均匀陆表地表特征参数和植被参数时有其独到的作用.作者提出了基于NOAA-14 AVHRR资料推算藏北高原地区地表特征参数和植被参数的方案,并把其用于全球能量水循环之亚洲季风青藏高原试验(GAME/Tibet)试验区.同时利用3个景的NOAA-14 AVHRR资料进行了分析研究,得到了一些有关藏北地区非均匀地表的区域地表特征参数(地表反射率、地表温度)和植被参数(INDV、植被覆盖度和叶面指数ILA).     

A Study on Parameterization of Surface Albedo over Grassland Surface in the Northern Tibetan Plateau

The relationship of surface albedo with the solar altitude angle and soil moisture is analyzed based on two-year (January 2002 to December 2003) observational data from the AWS (Automatic Weather Station) at MS3478 in the northern Tibetan Plateau during the experimental period of CEOP/CAMP-Tibet (Coordinated Enhanced Observing Period Asia-Australia Monsoon Project on the Tibetan Plateau). As a double-variable (solar altitude angle and soil moisture) function, surface albedo varies inconspicuously with any single factor. By using the method of approximately separating the double-variable function into two, one-factor functions (product and addition), the relationship of albedo with these two factors presents much better. The product and additional empirical formulae of albedo are then preliminarily fitted based on long-term experimental data. By comparison with observed values, it is found that the parameterization formulae fitted by using observational data are mostly reliable and their correlation coefficients are both over 0.6. The empirical formulae of albedo though, for the northern Tibetan Plateau, need to be tested by much more representative observational data with the help of numerical models and the retrieval of remote sensing data. It is practical until it is changed into effective parameterization formulae representing a grid scale in models.     

青藏高原改则地区近地层湍流特征

分析了第二次青藏高原气象科学试验（TIPEX）1998年6～7月加强期在改则取得的湍流资料,讨论了近地层湍流宏观统计量、温度、湿度结构参数以及通量整体输送系数等变化规律,结果表明在不稳定层结下,湍流宏观统计量等随稳定度的变化满足过去在平原地区得到的相似关系。     

Unprecedented recent warming rate and temperature variability over the east Tibetan Plateau inferred from Alpine treeline dendrochronology

Climate Dynamics - Despite instrumental records showing recent large temperature rises on the Tibetan Plateau (TP), only a few tree-ring temperature reconstructions do capture this warming trend....     

地表反照率与高原夏季风爆发关系分析

利用2000～2016年MODIS地表反照率和ECMWF/ERA-Interim再分析资料,选取有代表性的高原季风指数DPMI,统计分析了青藏高原地表反照率与高原季风之间的联系,结果表明:1)11月高原地表反照率大小与次年高原夏季风爆发存在密切关系:11月高原地表反照率偏低(高),次年4月高原夏季风爆发偏早(晚),强度偏强(弱)。2)可能的影响机制为:当前期11月高原地表反照率偏低时,后期高原主体对大气的感热加热信号更强,从而引起4月高原上空近地面层上升运动明显加强,这有利于热量向高空传输,导致对流层加热作用加强,高原上空对流层温度偏高,使得高原季风环流系统加强,最终导致高原季风季节变化相应提前;反之亦然。     

Estimation of Land Surface Temperature over the Tibetan Plateau Using AVHRR and MODIS Data

Estimation of large-scale land surface temperature from satellite images is of great importance for the study of climate change. This is especially true for the most challenging areas, such as the Tibetan Plateau (TP). In this paper, two split window algorithms (SWAs), one for the NOAA’s Advanced Very High Resolu-tion Radiometer (AVHRR), and the other for the Moderate Resolution Imaging Spectroradiometer (MODIS), were applied to retrieve land surface temperature (LST) over the TP simultaneously. AVHRR and M...     

近50 a青藏高原地面气温序列的重建

利用NCEP／NCAR500hPa高空再分析资料插补得到青藏高原1950—2000年50个海拔在3000m以上台站500hPa完整可靠的月平均温度序列。基于青藏高原地面气温和其上空500hPa温度有着密切关系，设计了这50个台站地面月平均温度序列的回归方案，用回归估计值将近50a各台站的现有月平均气温记录进行补齐、延长，得到重建的高原台站完整连续的地面月平均气温资料，并对回归效果进行独立样本实验。重建的青藏高原地面气温资料能够真实地反应高原实际气温的变化特征。     

Understanding the Surface Temperature Cold Bias in CMIP5 AGCMs over the Tibetan Plateau

The temperature biases of 28 CMIP5 AGCMs are evaluated over the Tibetan Plateau(TP) for the period 1979–2005. The results demonstrate that the majority of CMIP5 models underestimate annual and seasonal mean surface 2-m air temperatures(T_(as)) over the TP. In addition, the ensemble of the 28 AGCMs and half of the individual models underestimate annual mean skin temperatures(T_s) over the TP. The cold biases are larger in T_(as) than in T_s, and are larger over the western TP. By decomposing the T_s bias using the surface energy budget equation, we investigate the contributions to the cold surface temperature bias on the TP from various factors, including the surface albedo-induced bias, surface cloud radiative forcing, clear-sky shortwave radiation, clear-sky downward longwave radiation, surface sensible heat flux, latent heat flux,and heat storage. The results show a suite of physically interlinked processes contributing to the cold surface temperature bias.Strong negative surface albedo-induced bias associated with excessive snow cover and the surface heat fluxes are highly anticorrelated, and the cancelling out of these two terms leads to a relatively weak contribution to the cold bias. Smaller surface turbulent fluxes lead to colder lower-tropospheric temperature and lower water vapor content, which in turn cause negative clear-sky downward longwave radiation and cold bias. The results suggest that improvements in the parameterization of the area of snow cover, as well as the boundary layer, and hence surface turbulent fluxes, may help to reduce the cold bias over the TP in the models.     

Variations of the Surface Wettability Index over the Tibetan Plateau During 1971-2005

Based on 1971-2005 monthly mean maximum/minimum temperature,wind speed,relative humidity,sunshine duration,and precipitation data at 25 stations over the Tibetan Plateau,a study of the largest potential evapotranspiration(LPE)is performed by using the Penman-Monteith model.The surface wettability index(SWI)is calculated and examined,together with its space distribution,interannual and seasonal variations,as well as associated causes.The results suggest that the annual area rainfall exhibits a pronounced increasing trend at 15.0 mm per decade; the annual LPE shows a different-degree decrease at-4.6-71.6 mm/10 yr.In the southwestern Ngari prefecture and Nyalam county,the annual SWI displays insignificant decline trends compared to increasing trends in other areas of Tibet(0.02-0.09 per decade).For Tibet,on average,the SWI experiences a noticeable rise at 0.04/10 yr,particularly in 1981-2005.On a seasonal basis,the SWI shows increasing trends,especially in summer.In the 1970s-1980s,the interannual variation is characterized mainly by lower temperature and lower humidity.From the 1990s,air temperature keeps on rising,leading to an appreciable increase in SWI,displayed as a type of warm and humid climate.The salient increases(decrease)of precipitation and relative humidity(mean temperature daily range)are the principal causes of the greatly enhanced SWI in the region.The pronounced decrease in mean wind and sunshine duration also plays an active role.     

青藏高原东南部昌都地区近地层湍流输送的观测研究

利用我国1998年第2次青藏高原气象科学试验 (TIPEX) 昌都的湍流观测资料, 初步分析了三维风速、温度和湿度湍流谱、归一化方差与稳定度的关系、湍流通量和整体输送系数.结果表明, 白天标准化的湍流谱大多数满足2/3次方定律.风速方差与稳定度的关系在不稳定条件下基本服从1/3次方定律, 但水平风速方差比垂直速度方差与稳定度的关系离散.中性层结下的A、B值比平原地区大, 与起伏地形的值接近, C值与平原地区和起伏地区的差异不大.温度和湿度方差与不稳定层结的关系基本满足1/3次方定律, 而在稳定层结下的关系均无明显规律.湍流通量在干湿期转换中有突变现象, 干期的动量和热量通量均大于湿期, 热源强度以感热为主, 占80%.湿期热源强度明显增大, 其中以潜热为主, 占热源强度的60%.整体输送系数与稳定度的关系明显, 拟合得到的中性层结条件下的CDN和CHN分别为4.40×10-3和4.70×10-3, 其结果大于高原中、西部的同期观测值.