Global Water Vapor Content Decreases from 2003 to 2012： An Analysis Based on MODIS Data

Water vapor in the earth′s upper atmosphere plays a crucial role in the radiative balance, hydrological process, and climate change. Based on the latest moderate-resolution imaging spectroradiometer(MODIS) data, this study probes the spatio-temporal variations of global water vapor content in the past decade. It is found that overall the global water vapor content declined from 2003 to 2012(slope b = –0.0149, R = 0.893, P = 0.0005). The decreasing trend over the ocean surface(b = –0.0170, R = 0.908, P = 0.0003) is more explicit than that over terrestrial surface(b = –0.0100, R = 0.782, P = 0.0070), more significant over the Northern Hemisphere(b = –0.0175, R = 0.923, P = 0.0001) than that over the Southern Hemisphere(b = –0.0123, R = 0.826, P = 0.0030). In addition, the analytical results indicate that water vapor content are decreasing obviously between latitude of 36°N and 36°S(b = 0.0224, R = 0.892, P = 0.0005), especially between latitude of 0°N and 36°N(b = 0.0263, R = 0.931, P = 0.0001), while the water vapor concentrations are increasing slightly in the Arctic regions(b = 0.0028, R = 0.612, P = 0.0590). The decreasing and spatial variation of water vapor content regulates the effects of carbon dioxide which is the main reason of the trend in global surface temperatures becoming nearly flat since the late 1990 s. The spatio-temporal variations of water vapor content also affect the growth and spatial distribution of global vegetation which also regulates the global surface temperature change, and the climate change is mainly caused by the earth's orbit position in the solar and galaxy system. A big data model based on gravitational-magmatic change with the solar or the galactic system is proposed to be built for analyzing how the earth's orbit position in the solar and galaxy system affects spatio-temporal variations of global water vapor content, vegetation and temperature at large spatio-temporal scale. This comprehensive examination of water vapor changes promises a holistic understanding of the global climate change and potential underlying mechanisms.

REMOTE SENSING OF WATER VAPOR CONTENT USING GROUND-BASED GPS DATA

Spatial and temporal resolution of water vapor content is useful in improving the accuracy of short_term weather prediction.Dense and continuously tracking regional GPS arrays will play an important role in remote sensing atmospheric water vapor content.In this study,a piecewise linear solution method was proposed to estimate the precipitable water vapor (PWV) content from ground_based GPS observations in Hong Kong.To evaluate the solution accuracy of the water vapor content sensed by GPS,the upper air sounding data (radiosonde) that are collected locally was used to calculate the precipitable water vapor during the same period.One_month results of PWV from both ground_based GPS sensing technique and radiosonde method are in agreement within 1～2 mm.This encouraging result will motivate the GPS meteorology application based on the establishment of a dense GPS array in Hong Kong.

Spatial and Temporal Variability of Water Vapor Content during 1961-2011 in Tianshan Mountains,China

Based on the climate factors data and surface vapor pressure(SVP) data of 44 weather stations in Tianshan Mountains during the years 1961-2011, this paper establishes a water vapor content(WVC) estimation model according to the relationship between monthly WVC of radiosonde and corresponding SVP and analyzes the spatial and temporal variability of WVC and their causes. The results show that the WVC is linearly and negatively related to the elevation and longitude(Vertical zonality and Longitude zonality), while it was not linearly related to the latitude. The westerly wind, geographical situation and sea level elevation composed complex surface conditions to influence the spatial distribution of WVC in the Tianshan Mountains. The Mann-Kendall(M-K) statistical test shows a significant increasing trend in the mean annual WVC in Tianshan Mountains during 1961-2011(P < 0.001), with a rate of 0.23 mm/decade, and indicates an abrupt turning point in 1985(P < 0.001). Correlation analysis shows that the WVC are significantly correlated to the temperature, especially during the winter, but the summer WVC are significantly correlated to the precipitation. In addition, the North Atlantic Oscillation Index(NAOI)and the Arctic Oscillation Index(AOI) are significantly correlated to the winter WVC in the Tianshan Mountains. As a new Microwave radiometric profilers(MWRPs) instrument, the MP-3000 A provides continuous, real-time and high temporal resolution atmospheric profiles up to 10 km. In order to monitor water vapor and atmosphere profiles in Tianshan Mountains, an MP-3000 A was established in Urumqi(43.8°N, 87.58°N) in May 2008. The results indicated that the MP-3000 A was applicable to this area, and the evolutionary process of water vapor and the WVC peak values of MP-3000 A were a strong signal for rainstorm and flood forecasts for Urumqi and the Tianshan Mountains.

An Improved 6S Code for Atmospheric Correction Based on Water Vapor Content

Water vapor content in the atmosphere is very significant for atmospheric correction of optical remote sensing data. Nowadays, the common atmospheric correction models use a single value of the average water vapor content of the study area to perform atmospheric correction. As the distribution of water vapor content varies greatly with time and space, it is obviously inaccurate to represent the total water vapor conditions of the whole area by just reading the average water vapor content. In this study, we altered the 6S sources so that it could read the water vapor content image which was retrieved from MODIS 1 km data. Atmospheric correction was implemented for the band 1 of MODIS 500 m data pixel-by-pixel using the improved 6S model. In comparison with the traditional 6S model, this improved 6S model is more reasonable in atmospheric correction, for it considers the spatial distribution of the water vapor content retrieved from MODIS data in the near infrared to define the atmospheric conditions for simulating the atmospheric radiative transfer. The results corrected by the improved 6S model showed more reasonable in pixel spatial distribution and closer histogram with the original image than those by traditional 6S model.

WATER VAPOR CONTENT AND MEAN TRANSFER IN THE ATMOSPHERE OVER NORTHWEST CHINA

The interannual and intermonthly climatic features of the water vapor content(hereafter WVC)and its mean transfer in the atmosphere over Northwest China(hereafter NWC)are calculated and analyzed by using the NCEP/NCAR global reanalysis grid data(2.5°×2.5°Lat/Lon) for 40 years(1958—1997).The results show that the WVC in the total air column over NWC in four seasons of the year is mainly concentrated on eastern and western NWC respectively.On the average,the WVC over eastern NWC decreases obviously during recent forty years except for winter.while it decreases over western NWC in the whole year.But the WVC over NWC has been increasing since late 1980s in summer.The water vapor comes from the southwestern warm and wet air current along the Yarlung Zangbo River Valley and the Bay of Bengal.and from mid- western Tibetan Plateau and also from the Qinling Mountains at southern Shaanxi Province.The yearly water vapor divergence appears over the middle of NWC to northern Xinjiang and southeastern Shaanxi Province.The yearly water vapor convergence appears over the Tarim Basin and the Tibetan Plateau as well as western Sichuan and southern Gansu.

A Comparative Study of Cloud Liquid Water Content from Radiosonde Data at a Tropical Location

In this paper, some features of cloud liquid water content with respect to rain and water vapor are presented. Cloud liquid water density profile is obtained from radiosonde observation with Salonen's model and Karsten's model at Kolkata, a tropical location in the Indian region. Cloud liquid water contents (LWC) are obtained from these profiles which show a prominent seasonal variation. The monsoon months exhibit much higher values of LWC than in other months. However Salonen's model yields higher LWC values than that obtained with Karsten's model. The variation of daily total rainfall with LWC shows a positive relationship indicating the role of LWC in controlling the rainfall. Also the variation pattern of LWC with integrated water vapor (IWV) content of the atmosphere indicates that a threshold value of water vapor is required for cloud to form and once cloud is formed LWC increases with IWV.

中昆仑山北坡水汽含量的计算及其特征分析

干旱区水汽变化影响区域水资源系统的结构和演变,基于2020年1月—2022年12月中昆仑山北坡地区4个地基GPS遥感大气可降水量资料(GPS-PWV)、2个探空站观测资料和108个地面气象观测站逐时水汽压资料,利用一元线性拟合方法建立了适用于中昆仑山北坡地区的大气水汽含量(W-PWV)和地面水汽压计算模型(W-e)并对计算结果进行评估,分析了中昆仑山北坡地区东段、中段、西段W-PWV的时空分布特征及降水开始时刻与W-PWV峰值的关系。结果表明:(1)W-PWV年平均高值区位于研究区西段,中段次之,东段沙漠南缘W-PWV最低。海拔高度大于1500 m测站W-PWV随高度升高逐渐减少。夏季地面气象观测站平均W-PWV是春、秋季的2倍左右;(2)研究区W-PWV月变化具有单峰型特征,其中海拔高度1300~1500 m测站的W-PWV在7月和8月达到峰值,其余测站的W-PWV在8月达到峰值,海拔低于2000m和高于2000m测站W-PWV分别在夜间和白天维持较高值;(3)水汽含量模型计算的测站W-PWV与降水开始时刻有较好的对应关系,降水前各站W-PWV均存在不同程度跃变过程,降水过程前1~2h内W-PWV峰值达到测站W-PWV月平均值的1.5倍以上。

基于GNSS/MET的宁夏大气水汽分布及其与降水关系研究

为科学合理开发宁夏空中水资源,提升人工增雨作业效率和水平,摸清宁夏空中水资源时空变化特征及水汽变化与降水的关系,利用2014年1月—2020年12月宁夏23个全球导航卫星系统大气探测(GNSS/MET)站、地面自动气象站及银川市和平凉市探空站气象资料,采用统计诊断和对比分析方法,检验评估了GNSS/MET资料在宁夏不同地区的适用性,分析了宁夏大气水汽含量的时空变化特征及其与降水的关系,建立了宁夏大气水汽含量人工增雨作业指标,并对不同降水强度下的降水转化率进行了初步分析。结果表明:(1)GNSS/MET资料和探空观测数据反演得出的大气水汽含量间的相关系数为0.80~0.92,两者之间的相关性随天气过程中降水量的增大呈减小趋势,GNSS/MET资料反演的大气水汽含量在宁夏具有较好的代表性和适用性。(2)受东亚夏季风年变化影响,宁夏整层大气水汽含量夏季的最大,秋春季的次之,冬季的最小;8月大气水汽含量最大,12月大气水汽含量最小。受季风边缘区位置年际波动、六盘山和贺兰山地形抬升作用影响,宁夏大气水汽含量月均值呈现出南部和北部地区的波动较大、中部地区的波动较小的显著特征。(3)宁夏1—12月适宜人工增雨作业的大气水汽含量指标分别为4.9~7.0 mm、7.6~10.0 mm、12.7~17.8 mm、16.6~19.1 mm、22.4~25.7 mm、28.0~32.7 mm、36.2~42.0 mm、34.9~44.0 mm、27.5~32.5 mm、19.2~21.0 mm、10.4~14.5 mm、5.0~8.8 mm。(4)受到纬度、六盘山地形及西南季风等影响,六盘山西侧及宁夏最东侧的盐池大气水汽降水转化率较高;与腾格里沙漠、毛乌素沙地等相邻的宁夏中部的西部地区和北部的东部地区可能受到沙尘等影响,大气水汽降水转化率低。

水蒸汽增湿重塑非饱和黄土地基现场应用参数研究

天然状态下,非饱和黄土地基中土体含水率较低,导致强夯法处理黄土地基时夯实效果较差,无法满足地基承载特性,因此,如何对黄土地基进行增湿成为研究的重点。为了研究非饱和黄土在水蒸汽作用下的增湿效果,以重塑非饱和黄土为研究对象,开展水蒸汽增湿模型试验,分析了不同水蒸汽压力梯度、花管开孔数量及开孔间距条件下,水蒸汽扩散速率、温度及气体运移随时间的变化规律。结果表明:水蒸汽增湿是含水率梯度、压力梯度和温度梯度三者耦合且相互影响的动态变化过程,其中,温度梯度是影响水蒸汽运移的主要因素。水蒸汽通入土体后,体积含水率、气压和温度在各个测点处随通气时间的推移,均呈现快速上升−逐渐稳定的两个阶段。试验中,增大水蒸汽压力,增湿程度和增湿范围变化明显;增加开孔数量,土体增湿的均匀程度提高;减小开孔间距,土体增湿程度变化不大。研究成果可为水蒸汽增湿非饱和黄土地基相关工程提供一定的经验。

金沙江流域石鼓断面上游水汽含量与降水量特征

在流域尺度上研究水文循环过程中的水汽含量和降水量,为流域综合治理和水资源开发利用提供依据。基于ASTER GDEM V2地形数据、ERA-Interim逐月再分析资料及降水资料,研究金沙江流域石鼓断面上游上空水汽含量和降水量的时空分布特征,并讨论两者的相关性。研究表明:研究区上空水汽含量由南向北、由东向西呈递减趋势,西南部呈斜倒“U”型,东南部呈正“U”型;多年平均降水量自西北向东南逐渐增加;年平均水汽含量和降水量呈现上升趋势,四季水汽含量和降水量从大到小均依次为“夏、秋、春、冬”,多年平均月水汽含量和降水量为单峰型分布;年平均水汽含量同降水量之间为弱相关关系,各季节相关性差异显著,逐月相关性更具有指导意义。

内蒙古中部干旱半干旱区水汽和液态水特征研究

基于多通道微波辐射计数据与呼和浩特站逐小时降水数据分析2017、2018年4—9月内蒙古中部干旱和半干旱区35个降水日积分水汽含量、积分液态水含量月变化特征,进一步分析层状云稳定性降水和积状云对流性降水中液态水含量、水汽含量的垂直分布特征和积分液态水含量、积分水汽含量的相位特征。结果表明,降水日积分水汽含量和积分液态水含量具有明显的季节变化特征,两者均在夏季和初秋较大。降水发生前积分水汽含量与积分液态水含量有明显跃增,这种变化在对流性降水中更明显,且超过80%的样本显示积分水汽含量与积分液态水含量存在反相位变化。对流性降水水汽含量主要分布在0~6 km高度,且随高度递减,而液态水含量随高度先增加后减小;稳定性降水水汽含量和液态水含量的垂直分布与对流性降水一致,但两者均小于对流性降水。基于积分水汽含量与积分液态水含量的降水发生判断条件对指导当地人工增雨作业、缓解旱情有实际应用价值。

基于电阻率法的非饱和路基水汽迁移试验研究

非饱和土路基中水分的迁移不仅以液态形式发生,同时也会以气态形式发生,水汽的耦合迁移作用会在路基长期运营过程中对路基的长期稳定性及服役性能造成严重影响。因此,开展了针对典型非饱和土路基的电阻率测试及水汽迁移试验,研究了初始含水率和初始压实度对电阻率的影响,揭示了水汽迁移过程中非饱和土路基的电阻率变化规律,建立了电阻率-含水率模型。研究结果表明:随着含水率、压实度的增加,黏性土的电阻率均减小,呈指数特征,且电阻率对含水率这一影响因素更为敏感。随着迁移时间增加,土体顶部电阻率越来越小,土体底部电阻率越来越大。不同初始含水率试验,初始含水率增大,顶部土壤电阻率衰减率先增大后减小。不同压实度试验,压实度越大,土体顶部电阻率降低程度越小。电阻率-含水率模型计算结果与试验数据较吻合,模型拟合程度良好。

不同水热老化条件对Cu-SSZ-13分子筛催化剂理化特性的影响

使用催化剂小样老化装置对Cu-SSZ-13催化剂样品进行不同条件的水热老化处理,利用X射线衍射(X-ray diffraction,XRD)、N2吸脱附、X射线光电子能谱(X-ray photoelectron spectroscopy,XPS)等表征测试评价了水热老化处理中温度和水含量对于催化剂的晶体结构、气体吸附特性等理化的影响。结果表明,随水热老化温度的升高,由于表面分子筛结构出现坍塌,造成菱沸石(CHA)特征峰峰强降低,比表面积、孔容减小,总的NH3脱附量降低,表面Cu^(2+)比例增加。在5%水蒸气体积分数下,水热老化会在一定程度上破坏分子筛结构的完整性,造成比表面积的减小和CuO比例的升高;在10%及更高水蒸气体积分数下水热处理后,比表面积劣化减弱,表面Cu^(2+)比例增加。

基于Landsat8 TIRS数据的海表温度反演算法对比

海表温度(Sea Surface Temperature,SST)是研究气候变化的重要参数,具有重要研究意义。为了选出适用于近海海域的最优温度反演算法,本文基于Landsat8卫星遥感数据,以北部湾海域为研究区,对比分析了包括辐射方程传输法(Radiative Transfer Model,RTM)、单窗算法(Mono-window model,MW)、单通道算法(Single-channel model,SC)、线性劈窗算法(Linear Split-window Algorithm,SW_(1))和非线性劈窗算法(Non-linear Split-window Algorithm,SW_(2))在内的海表温度反演算法的反演精度并进行了敏感性分析。同时本文利用劈窗协方差-方差比值法(Split Window Covariance-variance Ratio,SWCVR)来反演大气水汽含量数据,减少了温度反演过程中对外部数据的依赖,研究结果表明:基于Landsat8 TIRS(Thermal Infrared Sensor)数据的SWCVR法进行大气水汽含量反演的效果较好,误差约在0.5 g/cm2;与实测海温数据相比SW_(2)与SC算法精度较高,误差约为0.6 K;RTM与SW_(1)算法次之,误差约为1.6 K与1.9 K;MW算法精度较低,误差约为2.5 K;与AVHRR(Advanced Very High Resolution Radiometer)SST产品进行相比两种劈窗算法的精度较高,误差约为1 K和1.3 K,SC算法精度较劈窗算法略低,误差约为1.4 K左右,RTM与MW算法精度较低,误差约为2 K与3 K;SW_(2)算法对参数的敏感性最低,其次是SC算法、SW_(1)算法与MW算法,RTM算法的敏感性最高。

不同含量的固体颗粒对喷嘴内空化流动特殊演化影响的研究

本文研究了不同含量的固体颗粒对喷嘴内空化流动特殊演化的影响。固体颗粒含量从1%变至6%,平均粒径从0.0015 mm增加至0.070 mm。修正适用于清水介质空化流动的Schnerr-Sauer空化模型用于含固体颗粒空化流动的数值模拟。结果表明:含固体颗粒空化流动的含汽量高于清水介质空化流动下的。不同含量的固体颗粒促进空化流动的演化。随着固体颗粒含量的增加,平均粒径的促进范围逐渐变小。研究含固体颗粒空化流动的流动参数与作用于固体颗粒上的力用于揭示机理。最大滑移速度与最小滑移速度的绝对值均高于清水介质空化流动下的。最大与最小湍动能均高于清水介质空化流动下的。含固体颗粒空化流动的混合动能高于清水介质空化流动下的。它们是降低压力促进空化流动发展的主导影响因素。计算所得的萨夫曼升力的量级是10^(−2),对空化流动的影响相对较弱,是次要影响因素。这些因素共同作用,促进喷嘴内含固体颗粒空化流动的特殊发展。

中国北方水汽与云和降水的关系

利用中国35°N以北地区1961年1月1日-2001年12月31日58个探空站逐日高空观测资料以及地面观测的逐日总云量、低云量、降水量资料,分析了42a来中国北方各区水汽质量分数的变化特征,水汽质量分数与总云量、低云量以及降水量的年际变化特征,逐区讨论了水汽质量分数与总云量、低云量和降水量的相关关系.结果表明:中国北方地区42a水汽质量分数有微弱的增加;水汽质量分数与云量、降水量呈明显的正相关.水汽质量分数与云量、降水量的相关中,平均水汽质量分数与低云量、降水量的正相关最显著;云量与降水量的相关中,低云量与降水量的相关最显著.这三种相关的季节变化特征均为春季最显著,秋、夏季次之,冬季最弱.沙区的各相关系数均低于非沙区的,说明荒漠化对空中水资源也有一定的影响,尤其是在沙尘暴多发的春季,这一影响就更显著了.

利用多源遥感数据反演城市地表温度

目前利用单通道热红外遥感数据反演地表温度的方法有大气校正法、单窗算法和普适性单通道算法,使用这3种算法反演地表温度时的一个关键问题就是需要获取大气参数。目前大气参数的获取主要根据近地表(地表2m左右的高度)的大气水分含量或湿度和平均气温的观测值来估计,这种方法只能获得个别点上的数据,而无法获取面上像元尺度的大气参数。本文利用多源遥感数据的优势,首先利用MODIS近红外数据,在像元尺度上获取温度反演中所需大气参数——大气水分含量,再利用同时相的Landsat ETM+影像,采用Jim啨nez-Mu oz和Sobrino的普适性单通道算法反演地表温度。研究结果表明,多源遥感数据的综合应用是城市地表温度反演的有效途径与方法,可获得较合理的地表温度反演结果。

SF_6气体水分管理标准的探讨及密度与湿度监测的研究

该文对国内外SF6气体水分控制标准进行了认真的分析,提出采用气体实时相对湿度(RH%)来保证SF6电气设备的安全可靠运行。为了在温度变化很大的情况下使离线监测的数据具备可比较性,修正到20℃时的绝对水气压不失为一个比较好的控制参数。针对目前因为水分受温度影响造成的监测难点,指出采用在线监测方法对SF6气体进行监测具有很大的优势。并用实验室数据曲线验证了对气体在线监测的可行性。

天山山区空中水汽含量及与气候因子的关系

利用建立的天山山区水汽含量与地面水汽压的经验关系式,计算天山山区及周边44站1961~2009年的水汽含量值,分析水汽含量的时空分布及其与气候变化因子的关系。结果表明：天山北麓的河谷平原地带是水汽含量高值区,中天山和东天山是低值区。水汽含量在近50 a内呈增加趋势,夏、秋季增加明显。水汽含量是影响天山山区降水量的最主要的因素之一,水汽对全球变暖和气候变化可能有负反馈作用,而冬季NAO和AO与水汽相关性最显著。这些研究对于揭示区域水分循环过程和全球变暖背景下的区域响应有重要意义。

地基微波辐射计探测在黄河上游人工增雨中的应用

利用2003、2004年夏秋季在青海省河南县的地基双频段微波辐射计连续观测资料，在实施系统探测实验以进行辐射亮温值（TB（23．87），TB（31．65））与大气汽态总水汽含量（Q）和云中积分液态水含量（L）值反演处理的基础上，分析了黄河上游河曲地区的云水特征，并进行了降水预测及人工增雨作业指标的探讨。结果表明：在黄河上游河曲地区，7—9月纯晴天无云天气条件下，L值基本为0，表明了统计回归反演的显著性。多云条件下Q值和L值分别在3．76～4．75g·cm^-2、227．34～859．42g·m^-2的范围内。可降水云天气，Q值在5．23～8．65g·cm^-2间，L值在421．18～1016．37g·m^-2的范围内；积雨云个例分析表明，在降雨开始前近5小时的降雨酝酿期内，Q及L的增加有明显的波动，但在对流云出现并发展时，Q和L总是急剧上升，在降雨前达到一峰值；由河南站和西安站的Q、L值比较差异可以看出，Q、L值受水汽输送、地形等因素的影响，黄河上游河曲地区的人工增雨潜力有显著的优势；所计算出的降水预测阈值。可作为该地区人工增雨作业指标的参考。