Decadal trends in precipitable water vapor over the Indus River Basin using ERA5 reanalysis data

Precipitable Water Vapor(PWV)constitutes a pivotal parameter within the domains of atmospheric science,and remote sensing due to its profound influence on Earth’s climate dynamics and weather patterns.It exerts a significant impact on atmospheric stability absorption and emission of radiation,thus engendering alterations in the Earth’s radiative equilibrium.As such,precise quantification of PWV holds the potential to enhance weather prognostication and fortify preparedness against severe meteorological phenomena.This study aimed to elucidate the spatial and temporal changes in seasonal and annual PWV across the Indus River Basin and its sub-basins using ERA5 reanalysis datasets.The present study used ERA5 PWV(entire atmospheric column),air temperature at 2 m(t2m)and 500 hPa(T_500hPa),evapotranspiration,and total cloud cover data from 1960 to 2021.Theil Sen slope estimator and Mann-Kendall test were used for trend analysis.Correlation and multiple regression methods were used to understand the association of PWV with other factors.The findings have unveiled the highest increase in mean PWV during the monsoon(0.40 mm/decade),followed by premonsoon(0.37 mm/decade),post-monsoon(0.27 mm/decade),and winter(0.19 mm/decade)throughout the study period.Additionally,the mean PWV exhibited the most pronounced positive trend in the sub-basin Lower Indus(LI),followed by Panjnad(P),Kabul(K),and Upper Indus(UI)across all seasons,except winter.Annual PWV has also risen in the Indus basin and its sub-basins over the last six decades.PWV exhibits a consistent upward trend up to an elevation of 3500 m within the basin which is most pronounced during the monsoon season,followed by the pre-monsoon.The escalating PWV within the basin is reasonably ascribed to increasing air temperatures,augmented evapotranspiration,and heightened cloud cover.These findings hold potential utility for pertinent authorities engaged in water resource management and planning.

The diurnal transport of atmospheric water vapor during major dust storms on Mars based on the Mars Climate Database,version 5.3

In recent studies of the Martian atmosphere,strong diurnal variation in the dust was discovered in the southern hemisphere during major dust storms,which provides strong evidence that the commonly recognized meridional transport process is driven by thermal tides.This process,when coupled with deep convection,could be an important part of the short-term atmospheric dynamics of water escape.However,the potential of this process to alter the horizontal distribution of moist air has not been systematically investigated.In this work,we conducted pre-research on the horizontal transport of water vapor associated with the migrating diurnal tide(DW1)at 50 Pa in the upper troposphere during major dust storms based on the Mars Climate Database(MCD)5.3,a state-of-the-art database for Martian atmospheric research that has been validated as simulating the relevant short-period atmospheric dynamics well.We found westward-propagating diurnal patterns in the global water vapor front during nearly all the major dust storms from Martian years(MYs)24 to 32.Statistical and correlation analyses showed that the diurnal transport of water vapor during global and A-season regional dust storms is dominated by the DW1.The effect of the tidal transport of water vapor varies with the types of dust storms in different seasons.During regional dust storms,the tidal transport induces only limited diurnal motion of the water vapor.However,the horizontal tidal wind tends to increase the abundance of daytime water vapor at mid-to low latitudes during the MY 28 southern summer global dust storm while decreasing it during the MY 25 southern spring global dust storm.The tidal transport process during these two global dust storms can induce opposite effects on water escape.

RESEARCH ON THE LOCAL CORRECTION MODEL OF ATMOSPHERIC DRY DELAY IN GPS REMOTE SENSING WATER VAPOR

The precision of atmospheric dry delay model is closely correlated with the accuracy of GPS water vapor in the process of GPS (Global Position System) remote sensing. Radiosonde data (from 1996 to 2001) at Qingyuan are used to calculate the exact values of the atmospheric dry delay. Base on these calculations and the surface meteorological parameters, the local year and month correction models of dry delay at the zenith angle of 0° are established by statistical methods. The analysis result shows that the local model works better and is slight more sensitive to altitude angle than universal models and that it is not necessary to build models for each month due to the slight difference between year model and month model. Furthermore, when the altitude angle is less than 75°, the difference between curve path and straight path increases rapidly with altitude angle’s decrease.

Correlation between Atmospheric Water Vapor and Diurnal Temperature Range over China

Diurnal temperature range(DTR) is an important measure in studies of climate change and variability. The changes of DTR in different regions are affected by many different factors. In this study, the degree of correlation between the DTR and atmospheric precipitable water(PW) over China is explored using newly homogenized surface weather and sounding observations. The results show that PW changes broadly reflect the geographic patterns of DTR long-term trends over most of China during the period 1970–2012, with significant anticorrelations of trend patterns between the DTR and PW, especially over those regions with higher magnitude DTR trends. PW can largely explain about 40% or more(r2 ≥0.40) of the DTR changes, with a d(PW)/d(DTR) slope of-2% to-10% K-1 over most of northwestern and southeastern China, despite certain seasonal dependencies. For China as whole, the significant anticorrelations between the DTR and PW anomalies range from-0.42 to-0.75, with a d(PW)/d(DTR) slope of-6% to-11% K-1. This implies that long-term DTR changes are likely to be associated with opposite PW changes, approximately following the Clausius-Clapeyron equation. Furthermore, the relationship is more significant in the warm season than in the cold season. Thus, it is possible that PW can be considered as one potential factor when exploring long-term DTR changes over China. It should be noted that the present study has a largely statistical focus and that the underlying physical processes should therefore be examined in future work.

A comparative study on the spectral characteristics of nanosecond pulsed discharges in atmospheric He and a He+2.3%H_(2)O mixture

Nanosecond pulsed discharges at atmospheric pressure in a pin-to-pin electrode configuration are well reproducible in time and space, which is beneficial to the fundamentals and applications of low-temperature plasmas. In this experiment, the discharges in helium(He) and He with 2.3%water vapor(H_(2)O) are driven by a series of 10 ns overvoltage pulses(~13 k V). Special attention is paid to the spectral characteristics obtained in the center of discharges by time-resolved optical emission spectroscopy. It is found that in helium, the emission of atomic and molecular helium during the afterglow is more intense than that in the active discharge, while in the He^(+)2.3%H_(2)O mixture, helium emission is only observed during the discharge pulse and the molecular helium emission disappears. In addition, the emissions of OH(A-X) and Hα present similar behavior that increases sharply during the falling edge of the voltage pulse as the electrons cool down rapidly. The gas temperature is set to remain low at 540 K by fitting the OH(A-X) band. A comparative study on the emission of radiative species(He, He_(2), OH and H)is performed between these two discharge cases to derive their main production mechanisms. In both cases, the dominant primary ion is He^(+) at the onset of discharges, but their He^(+) charge transfer processes are quite different. Based on these experimental data and a qualitative discussion on the discharge kinetics, with regard to the present discharge conditions, it is shown that the electron-assisted three-body recombination processes appear to be the significant sources of radiative OH and H species in high-density plasmas.

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.

ARTICLE Analyzing Potential Water Harvesting from Atmosphere in Near Coastal Area

Water is a basic need.However there are many near coastal regions which have very limited access to fresh water.The water in area close to coastal is mainly affected by ocean,indirectly by weather/climate conditions and directly from seawater intrusion.While abundant fresh water is actually available in the atmosphere in the form of moisture.Recent technology,such as Atmospheric Water Generator(AWG),is a possible solution to gain water from our atmosphere.However,comprehensive study is need­ed to understand the potential water harvesting in our atmosphere.Here,we examine the water availability in the atmosphere based on several parameters like temperature and humidity.The data are collected from observation using WS1040 Automatic Weather Station in a year of 2020 with a half-hour interval.Then,we calculate the availability of water con­tent during each season,especially in dry conditions.We also simulate the water harvesting to fulfil daily basic need of fresh water.The atmospheric parameters have shown a monsoonal pattern.Water content decrease in atmosphere during the dry season but the water deficit occurs after the dry season.Although water harvesting able to supply daily freshwater need,it is not recommended to be a single source as it requires massive water storage and high-efficient AWG.

GPS Water Vapor and Its Comparison with Radiosonde and ERA-Interim Data in Algeria

Remote sensing of atmospheric water vapor using global positioning system（GPS） data has become an effective tool in meteorology,weather forecasting and climate research. This paper presents the estimation of precipitable water（PW）from GPS observations and meteorological data in Algeria,over three stations located at Algiers,Bechar and Tamanrasset.The objective of this study is to analyze the sensitivity of the GPS PW estimates for the three sites to the weighted mean temperature（T;）,obtained separately from two types of T;–T;regression [one general,and one developed specifically for Algeria（T;stands for surface temperature）],and calculated directly from ERA-Interim data. The results show that the differences in T;are of the order of 18 K,producing differences of 2.01 mm in the final evaluation of PW. A good agreement is found between GPS-PW and PW calculated from radiosondes,with a small mean difference with Vaisala radiosondes.A comparison between GPS and ERA-Interim shows a large difference（4 mm） in the highlands region. This difference is possibly due to the topography. These first results are encouraging,in particular for meteorological applications in this region,with good hope to extend our dataset analysis to a more complete,nationwide coverage over Algeria.

Empirical model for mean temperature and assessment of precipitable water vapor derived from GPS

The estimation of Precipitable Water Vapor （PWV） derived from Global Positioning System （GPS） data at the IGS site WUHN is assessed by comparing with PWV obtained from radiosonde data （No.57494） in Wuhan. The applicability of Saastamoinen （SAAS）, Hopfield and Black models used for estimating Zenith Hydrostatic Delay （ZHD） and Zenith Wet Delay （ZWD） and different models is verified in the estimation of GPS-derived PWV for the applied area. The experimental results demonstrated that ： 1 ） the precision of PWV estimated from Black model used for calculating ZHD （ ZHDs ） is lower than that of SAAS （ ZHDsAAs ） model and Hopfield model （ZHDn） with the RMS of 4. 16 ram; 2） the RMS of PWV estimated from SAAS model used for calculating ZWD （SAAS） is 3.78 ram; 3 ） the well-known Bevis model gives similar accuracy compared with the site-specific models for Tm in terms of surface temperature （ Ts ） and surface pressure （Ps）, which can reach the accuracy inside 1 mm in the GPS-derived PWV estimates.

A New Way to Study Water-Vapor Absorption Coefficient

In the visible spectrum, the atmospheric attenuations to sunlight mainly include aerosol scattering, atmospheric molecule Rayleigh scattering and ozone absorption, while in the near-infrared spectrum (from 650 nm to 1 000 nm), we must take water-vapor absorption into account. Based on the atmospheric correction theory, using spectrum irradiance data measured by Instantaneous Ground spectrometer, ozone content measured by Microtops Ⅱozone monitor, water-vapor content and aerosol optical thickness measured by sun photometer, we give a new way to study water-vapor absorption to sunlight, and the result shows that the main peak values of water-vapor absorption coefficients are 0.025 cm-1, 0.073 cm-1, 0.124 cm-1, 0.090 cm-1, 0.141 cm-1 and 0.417 cm-1, which respectively lie at 692 nm, 725 nm, 761 nm, 818 nm, 912 nm and 937 nm.

塔里木盆地及其周边地区大气可降水量分布及其与降水关系的研究

利用2018年7月至2022年6月塔里木盆地及其周边地区17部地基GPS水汽探测仪遥感的大气可降水量(PWV)资料、 14个地面气象站逐时和逐日降水资料,分析了塔里木盆地西部(区域A)和东部(区域B)PWV分布特征及其与降水关系。结果表明:(1)研究区年平均PWV高值区主要集中于盆地北部和盆地西南部平原地区,海拔超过1300 m站点的PWV年平均值与海拔成反比,低于1300 m的低海拔地区PWV年平均值在10~12 mm。夏季测站PWV平均值是春、秋季节的2倍。(2)区域A和区域B PWV月变化呈单峰型分布,分别在8月和7月达到峰值。区域A有、无降水日PWV均在23:00(北京时,下同)达到日峰值。区域B有、无降水日PWV日峰值出现时间相差5 h,分别出现在11:00和17:00。(3)区域A和区域B多数测站ΔPWV(PWV与PWV月平均值差值)峰值分别在降水开始前0~1 h和降水开始时刻前后1 h出现。春季区域B降水前PWV跃变程度较区域A更剧烈,夏季各区域σPWV(PWV与PWV月平均值倍数)提前降水开始时刻1 h、 5~6 h达到1~1.8倍的天气过程较其余时次偏多。秋季和冬季区域BσPWV分别集中在1.4~2.0倍和1.6~2.4倍。(4)海拔高于1400 m测站的5-6月、 7-8月PWV值达到10~20 mm和15~25 mm,对应降水结束时刻。海拔低于1400 m测站5-8月降水结束时刻PWV值逐渐由15~25 mm增至25~35 mm。

云贵地区顾及高度改正的大气加权平均温度模型

针对云贵地区地形起伏特点,分析T_(m)与高程、Ts的关系,利用2016—2018年的ERA5数据,建立两种顾及高度改正的T_(m)模型——YGTrop-T_(m)和YGMete-T_(m)。以2019年ERA5和探空数据为参考值,结合Bevis公式、GPT2w和CTrop模型,对新模型精度进行评估。结果表明,以ERA5数据为参考值,YGTrop-T_(m)和YGMete-T_(m)模型的年均RMS分别为2.72和2.16 K,相较于Bevis公式、GPT2w-5和GPT2w-1模型,YGTrop-T_(m)模型RMS减少了20%、28%、9%,与CTrop模型相当,而YGMete-T_(m)模型RMS相较于Bevis公式、GPT2w-5、GPT2w-1和CTrop模型减少了36%、43%、28%和20%;以探空数据为参考值,YGTrop-T_(m)模型年均RMS与Bevis公式和CTrop模型相当,分别为2.88、2.93和2.80 K,而YGMete-T_(m)模型的年均RMS最小,为2.45 K,相较于Bevis公式、GPT2w-5、GPT2w-1和CTrop模型,减少了16%、21%、20%和12%。此外,将YGTrop-T_(m)和YGMete-T_(m)模型用于GNSS水汽计算,对应的水汽理论RMS误差分别为0.25和0.21 mm,相对误差分别为1.01%和0.86%。

塔什库尔干河流域河谷大气降水同位素特征与水汽输送路径

利用塔什库尔干河流域河谷2018年9月—2020年5月的降水事件的大气降水同位素数据,以及流域河谷代表性气象站点温度、降水、相对湿度等气象资料,分析降水中δ^(18)O、δ^(2)H和氘盈余(d-excess)变化特征,探讨影响因素,并基于拉格朗日后向轨迹模型(HYSPLIT)追踪解析流域河谷大气降水的水汽输送路径。结果表明:(1)降水δ^(2)H、δ^(18)O值总体上呈现夏季富集、冬季贫化的季节变化特征,且具有显著的温度效应(1.33‰·℃^(-1)),但未见显著雨量效应;(2)局地大气降水线方程为δ^(2)H=7.63δ^(18)O-3.55,呈现出显著的干旱气候特征;(3)HYSPLIT模拟结果表明研究流域降水水汽主要受西风环流和局地水汽再循环影响,其中夏半年局地水汽蒸发占比54.09%,冬半年西方路径中较长距离输送占比45.53%。8月源自印度洋的水汽可绕过青藏高原到达研究区域。成果可为塔什库尔干河流域水资源管理和气候应对提供参考依据。

六盘山地区大气水汽的时空差异与驱动因子分析

为有效开发六盘山地区空中云水资源,提高人工增雨的科学性,需掌握该区域大气水汽的时空分布特征及其原因。利用1989—2018年六盘山地区国家基本站降水观测资料和同期欧洲中期天气预报中心(European Centre for Medium-Range Weather Forecasts,ECMWF)第五代大气再分析资料(ERA5),分析该区域大气可降水量、比湿、相对湿度、水汽通量等大气水汽要素的时空变化,并从水汽输送、地形作用、浮力频率的影响等方面分析六盘山不同地区水汽条件及降水差异的原因。结果表明:一年中绝大多数时间六盘山山顶及东坡大气水汽条件均优于西坡,大值区主要集中在六盘山系主峰附近,并具有明显的季节变化特征。六盘山东坡,受地形抬升作用引起500 hPa辐散、700 hPa辐合的动力场,在夏季最明显,冬季最弱;浮力频率冬季最高,夏季最低;东坡更高的浮力频率及更陡峭的地形,使重力波效应更为明显,具备更有利的垂直上升扩散条件及更大的降水潜力。

反应温度及压力对三塘湖盆地褐煤热解产物分布影响

煤在气化通道中气化反应效率是影响煤炭地下气化气体组分与热值的关键问题。为揭示反应温度和压力对三塘湖盆地褐煤在水蒸气中气化行为和产物分布特征影响,基于固定床热解炉对三塘湖盆地西山窑组褐煤进行不同反应温度和压力热解试验。结果表明:随反应温度升高(300~900℃),气体质量分数由3.84%增至24.29%,水和焦油质量分数先增后减;高温下反应温度升高,加剧二次反应,H_(2)和CH_(4)体积显著增加,900℃体积最大分别为100.89、106.09 mL/g,污染物总质量减少,900℃质量分数相对小,17.72 mg/g。增加反应压力(1.5~3.0 MPa),利于提高半焦转化率和增加气体质量分数。高温下反应压力增加,加剧二次反应,利于反应加氢气化和甲烷化发生,导致CH_(4)体积显著增加,700℃CH_(4)体积最多增加26.89 mL/g,但在700℃会促进自由基加氢饱和反应,污染物总质量增加。建议在实际生产中,通过控制注汽移动速度适当增加反应温度并提高反应压力,且控制气化反应区的温度远离700℃,利于H_(2)和CH_(4)生成,以提高煤炭地下气化工艺高效清洁开发。研究成果可为三塘湖盆地西山窑组褐煤煤炭地下气化工艺提供指导。

基于多系统的GNSS三维水汽层析质量评价方法

本文基于提出的水汽层析廓线评价指标(tomographic profic fit score,TPFS),首次对GPS、北斗卫星导航系统(BeiDou Navigation Satellite System,BDS)、GLONASS和Galileo 4个系统的水汽层析结果进行了精度评估.结果表明:各GNSS水汽层析解算结果差异较小,最大均方根误差(root-mean-square error,RMSE)差距在11%之内,其中BDS水汽层析表现最好,GLONASS水汽层析表现最差.相较于GPS、GLONASS、Galileo,BDS在低层区域(2406 m以下)具有更好的层析解算优势.尤其在底层,BDS与GPS、GLONASS、Galileo的RMSE相比分别改进了3.2%、16.2%、5.2%.此外,在层析水汽廓线TPFS对比中,BDS平均TPFS最小;在暴雨天气下BDS水汽廓线TPFS最低,相较于GPS、GLONASS、Galileo改进了25.2%、31.5%、32.8%.

长白山麓夏秋季气态和液态水分布特征

利用2019—2020年6—10月中国气象局吉林云物理野外科学试验基地MWP967KV型多通道微波辐射计、地面雨量计及L波段探空雷达资料,分析了长白山麓夏秋季大气中气态和液态水分布及其在降水前的演变特征。结果表明:微波辐射计反演数据与探空雷达数据具有较好的相关性,但反演值整体偏大。大气可降水量(PWV)和液态水路径(LWP)呈一峰一谷日变化特征,峰值出现在夜间而谷值出现在白天,有降水时峰值出现在01:00—03:00,谷值出现在11:00前后。受长白山地形和森林植被影响,PWV和LWP月平均最大值分别出现在8月和9月。PWV在降水前和降水中分布频率均呈现先升后降趋势,而降水前LWP在0.00~0.42 mm内频率占比最高;降水强度越强,PWV及LWP频率分布越集中,PWV大于45 mm、LWP大于4.20 mm出现强降水的可能性较大。降水开始前1 h内LWP和PWV均出现跃增,LWP跃增幅度更明显,该特征可作为降水临近预报、人工增雨作业条件分析的参考指标。

湖南省地基北斗卫星导航系统大气可降水量反演及降水分析

水汽是影响天气变化的重要因子,灾害天气的发生往往伴随着水汽含量、空间分布的急剧变化。针对目前关于地基北斗卫星导航系统(BDS)反演大气可降水量(PWV)研究相对较少现状,进一步验证BDS PWV的反演精度和PWV与实际降水的关系,利用湖南探空站和邻近的连续运行基准站(CORS)数据,构建湖南本地化大气加权平均温度(Tm)模型,基于此模型进行水汽反演,分析BDS水汽探测的精度,与实际降水结合探究PWV与降水之间的响应关系。结果显示:与探空数据相比,CORS测站解算的BDS PWV均具有较强的相关性,均方根误差(RMSE)和平均绝对误差(MAE)均在4 mm以内,符合水汽监测的要求;PWV与实际降水之间存在明显的联系,降水前6~12 h水汽快速聚集为降水发生提供充足的条件,PWV为60 mm可以作为降水预报的阈值。因此,利用BDS对水汽的持续监测在降水、水旱灾害监测预报中可以发挥重要作用。

基于普适型GNSS的数据质量评估与水汽反演研究

为确保普适型全球卫星导航系统(GNSS)接收机所在监测站的合理布设及数据处理结果的可靠性,需对普适型GNSS观测数据质量进行评估。为此,本文以安置在西安市不同环境下的普适型GNSS接收机实测数据为例,分别利用TEQC、ANUBIS和RINGO软件对观测数据质量进行了可视化对比分析;基于预处理后的普适型GNSS数据获取了大气可降水量(PWV)信息,并结合西安强降雨事件分析GNSS-PWV与降雨量的相关变化和内在联系。研究结果表明:普适型GNSS接收机所采集的观测数据质量较好,且北斗数据在遮挡环境下具有较好的抗干扰性。此外,利用普适型GNSS观测数据反演的PWV具有较好的精度,PWV在强降雨发生前会出现快速抬升的现象,在降雨期呈现随降雨量的增加而抬升,后随降雨量的减少而下降的趋势,PWV与强降雨事件具有较强的内在联系。

增强物理交联提升聚乙烯醇耐湿耐热性能

利用玉米淀粉(CS)和桃胶(PG)协同改性聚乙烯醇(PVA)法,制备了PVA/CS/PG复合膜,考察了PVA分子量、不同CS添加量以及PG添加量(在相同CS添加量条件下)对PVA/CS/PG复合膜耐湿、耐热性能的影响。结果表明:CS与PG的羟基与PVA发生了氢键相互作用,PVA/CS/PG复合膜的晶粒尺寸减小,交联密度增加。同时,随着CS和PG含量的增加,复合膜的网格尺寸逐渐减小,热稳定性能提升。水蒸气透过测试表明,当w(CS)=2%和w(PG)=2%时,PG/CS/PVA复合膜含水率较未处理原膜提升了11.5%,水蒸气透过率下降了43%。