Observed changes in relative humidity and dew point temperature in coastal regions of Iran

The analysis of trends in hydroclimatic parameters and assessment of their statistical significance have recently received a great concern to clarify whether or not there is an obvious climate change. In the current study, parametric linear regression and nonparametric Mann?CKendall tests were applied for detecting annual and seasonal trends in the relative humidity (RH) and dew point temperature (T _dew) time series at ten coastal weather stations in Iran during 1966?C2005. The serial structure of the data was considered, and the significant serial correlations were eliminated using the trend-free pre-whitening method. The results showed that annual RH increased by 1.03 and 0.28?%/decade at the northern and southern coastal regions of the country, respectively, while annual T _dew increased by 0.29 and 0.15°C per decade at the northern and southern regions, respectively. The significant trends were frequent in the T _dew series, but they were observed only at 2 out of the 50 RH series. The results showed that the difference between the results of the parametric and nonparametric tests was small, although the parametric test detected larger significant trends in the RH and T _dew time series. Furthermore, the differences between the results of the trend tests were not related to the normality of the statistical distribution.     

黑龙江省土壤湿度及其对气温和降水的敏感性分析

气温和降水量变化是影响土壤湿度变化的主要原因,研究土壤湿度对气温和降水的敏感性对区域农业生产、生态环境治理和经济可持续发展有重要意义。采用1984-2007年黑龙江省73个气象观测站的气温、降水数据和13个土壤湿度观测站土壤观测数据,利用EOF、相关分析等数理分析方法,对黑龙江省土壤湿度与气温、降水量之间的关系进行了研究。结果表明：1984-2007年黑龙江省土壤湿度变化在不同区域存在差异：除三江平原中西部地区外,大部分农区土壤湿度变化趋势一致,20世纪90年代中期以前基本偏湿,而90年代中期以后则为偏干,2001年偏干严重。土壤湿度对气候变化响应的敏感性也不同,松嫩平原（西南部除外）是土壤湿度对气温和降水变化敏感区域;松嫩平原西南部对气温敏感;伊春南部地区-哈尔滨东部-三江平原西部为降水敏感区;逊克、伊春北部、牡丹江和三江平原东部土壤湿度对气温和降水均不敏感。     

中国东部地区冬季和夏季地面湿度空间分布特征的对比分析

利用中国东部地区315个台站1963~2012年月平均地面观测资料,揭示了东部地区冬季和夏季地面比湿(SH)和相对湿度(RH)多年平均值及其变率的空间分布特征,并分析和比较了地理因素(经度、纬度和海拔高度)对其空间分布的影响。结果表明:1)在冬季,SH(0.4~7 g kg-1)以秦岭-淮河线为界,呈现出"北低南高"的分布特征;RH(41%~82%)则呈现出"南北高、中间低"的分布特征;一般冬季地面湿度相对较低的地区其变化幅度相对较大。2)在夏季,SH(7~20 g kg-1)整体上明显大于冬季,RH(44%~89%)则与冬季差异不大,均呈现由东南部沿海向西北内陆递减的分布特征;同样夏季地面湿度较低的地区通常其变化幅度也相对较大。3)东部地区冬季地面湿度空间分布受地理因素影响,其中纬度是最主要的影响因素,经度次之,海拔高度对其整体分布影响不明显,且地理因素对冬季SH的回归效果明显好于对冬季RH的回归效果。4)东部地区夏季地面湿度空间分布受地理因素影响较冬季显著,纬度同样是影响夏季地面湿度最主要的因素,但海拔高度对夏季SH、经度对夏季RH的影响程度较冬季增大,且地理因素对夏季SH的回归效果同样好于对RH的回归效果。     

1966—2015年天山南北坡空气湿度差异及其影响因素

利用天山地区近50年(1966—2015年)逐日气象资料,采用Mann-Kendall趋势检验法研究了天山南北坡相对湿度(RH)的时空变化特征,分析了天山南北坡RH对平均气温、降水量、平均风速、参考蒸散量、日照时数的敏感性,并探讨了引起RH变化的主导因素。结果表明：(1)整个天山地区RH变化有略微上升的趋势但不显著,北坡RH总体呈下降趋势,南坡RH总体呈上升趋势。(2) RH空间分布呈自北向南递减趋势,南北坡全年及春季以下降趋势为主,而夏、秋、冬三季均以上升趋势为主,且南坡变化趋势的显著性高于北坡。(3) RH对风速、气温、日照时数及参考蒸散量均为负敏感,对降水量为正敏感。北坡RH对各气象因子的敏感程度依次为日照时数>参考蒸散量>风速>气温>降水量,南坡敏感程度依次为日照时数>风速>参考蒸散量>气温>降水量。空间分布上,仅降水量敏感系数高值区位于北坡伊犁河谷,其余要素敏感系数高值区均位于南坡。(4)参考蒸散量是影响天山地区RH变化的主导因子,整个天山地区参考蒸散发贡献率较高,日照时数贡献率高值区集中于北坡伊犁河谷,风速、降水量、气温贡献率高值区均集中于南坡克孜勒苏地区。     

贵州省冬季人体舒适度对温湿环境的响应

在贵州冬季相对湿度大、风速小的气候背景下,综合考虑气温和相对湿度对人体舒适度的影响,计算并讨论了9个市州代表站人体舒适度指数IHC及其对温湿环境的响应,发现贵州省冬季低温、高湿对IHC指数具有负贡献,其中气温的高低对IHC指数影响尤为明显,并且在平均相对湿度越高的环境下,IHC指数对平均气温的变化就具有越高的敏感性,因此在贵州省西部和北部地区冬季由于平均气温较低、加之平均相对湿度较大,人体舒适感降低尤为明显。从回归方程出发,讨论贵州省冬季△IHC对△T=1σ或△RH=1σ变化的响应,发现平均气温是影响IHC指数变化的主要指标,而相对湿度作为辅助指标对IHC指数有着增大或减小的调节作用。通过分析IHC指数的稳定持续性,发现其能有效客观的表征出贵州省低温的持续性特征,并且能反映出在平均相对湿度较高的环境下,人体感觉的不舒适持续日数增加,即加大了人体的不舒适感。     

基于能见度数据分析的气溶胶吸湿增长特征研究

基于相对湿度、能见度等气象数据,分析气溶胶吸湿增长特性,有助于了解气溶胶对大气环境和区域气候的影响。利用南京地区2016年1—12月、2017年2—12月、2018年1—8月和12月相对湿度和能见度等数据,通过非线性拟合研究气溶胶吸湿增长因子(f(RH))与相对湿度(RH)之间的关系。结果表明,吸湿增长因子在RH值较低(<80%)时,增长率较小;当RH值较高(>80%)时,增长率迅速增大。吸湿增长因子随着月RH值变化而表现出较大差异。此外,当南京地区盛行西风时,高能见度出现的时次较多。f(RH)与PM_2.5/PM₁₀成正比,PM_2.5/PM₁₀值越高,对应的气溶胶光学吸湿增长因子往往会越高。     

Simulations of the effects of soil temperature and humidity disturbances on regional climate of China

Summary ?This simulation study was applied by a regional climate model (RegCM2) and forced by reasonable soil temperature and humidity disturbances, in order to examine the disastrous weather and climate-produced such disturbances that were performed in a series of experiments of different climatic zones, seasons and space/time scales, to recognize the persistence and to understand the mechanisms of their respective climatic responses under the current climatic background of China. The simulation results showed that, in regions of East Asian monsoon climate, the soil humidity disturbance (SHD) has greater impact on posterior climate responses than the temperature disturbance has. The SHD forcing exerts noticeable influence on rainfall generally. Although the centers of changed precipitation generally do not coincide with those of the disturbances, the centers are located mostly in downwind areas of the SHD core and in areas of prevailing updraft, even some places far away; with neighboring dry/moist SHD zones, a bigger rainfall increase tends to show up in the dry region instead of in the wet one. The simulation suggested that the SHD lasts for a rather long time, whose length is controlled by the presence of a positive feedback between the precipitation, the synchronous circulation patterns, the latitude and season, and the intensity of the SHD forcing. This study has found that the humidity disturbance (especially from rainfall) is in good correspondence to posterior temperature that the previous SHD enhancement leads to the subsequent temperature drop in the surface and near-surface layer, while the centers of lowered temperature can remain more than three months. Received April 3, 2001; Revised December 19, 2001     

SEAS5模式对新疆月尺度气温和降水的预测性能评估

检验评估气候模式，有利于发挥这一客观预测方法在新疆气候预测业务中的应用效果，提高新疆气候预测能力。基于欧洲中期天气预报中心第五代季节预测系统SEAS5模式的历史回报数据和新疆98个气象站的气温、降水观测资料，利用距平符号一致率Pc、趋势异常综合评分Ps、距平相关系数ACC、时间相关系数TCC等方法，综合评估了SEAS5模式对新疆1993—2019年月尺度气温和降水的预测性能。结果表明：SEAS5模式对新疆月气温、降水的总体预测性能较好，对降水趋势和量级有一定的预测能力。模式的预测性能存在明显的月际差异和空间差异。模式对新疆4—9月气温和4月、6—8月降水的预测性能较好。气温预测评分中，4月Pc最高（61.3分），7月Ps最高（74.4分），6月ACC最高（0.17）。降水预测评分中，4月Pc最高（58.7分），7月Ps最高（72.1分），4月ACC最高（0.16）。空间分布上，模式对1月、3月、6月和12月南疆的气温预测性能普遍高于北疆，对7月和9月南疆西部的预测性能低于其他地区。模式对南疆的降水预测性能普遍高于北疆。     

温湿统计平衡约束关系对GRAPES全球湿度分析的作用

为改进GRAPES全球三维变分同化系统(GRAPES-3DVar)的湿度分析,借鉴Hólm等(2002)的思想,在背景误差协方差结构中引入湿度与温度的统计平衡约束关系。通过扣除湿度变化中与温度有关的平衡部分获取非平衡拟相对湿度,并引入非线性对称变换对其做标准化处理,将处理后的变量作为新的湿度控制变量。统计结果表明,温湿统计平衡约束主要出现在中高纬度对流层中层相对湿度大于80%的区域,与大尺度抬升凝结加热有关;新的湿度控制变量能满足无偏、高斯分布特征。单点理想观测试验结果表明,新的湿度分析具备了流依赖特征,并能有效地抑制负水汽与超饱和水汽的出现。同化循环与预报试验结果表明,新方案给出的湿度分析的偏差和均方根误差均有所减小。而针对降水预报的检验结果表明,引入新方案后的0.1-10 mm降水预报,在ETS评分没有显著降低的情况下,BIAS评分更靠近1,降水空报有所减缓。然而60-84 h的25 mm以上的降水漏报现象更为明显,表明湿度同化分析方案还有改进空间。通过引入温湿统计平衡约束关系,完善了GRAPES-3DVar分析框架,为全球湿度分析的持续改进奠定了坚实基础。      

土壤湿度年际变化对中国区域极端气候事件模拟的影响研究Ⅱ.敏感性试验分析

利用NCARCAM3.1大气环流模式,设计了有、无土壤湿度年际异常的两组数值试验,探讨了土壤湿度年际异常对极端气候事件模拟的可能影响。结果表明,模式模拟的极端气候事件对土壤湿度异常十分敏感,土壤湿度异常对极端气候指标的多年平均空间分布、年际变率以及年际变化均具有重要影响。当不考虑土壤湿度的年际异常时:(1)模拟的暖夜日数、暖昼日数和热浪持续指数的发生频次在全国范围内均明显减少,而霜冻日数则明显增加。极端降水指标的响应表现出明显的空间差异,极端降水频次在江淮流域明显减小,而极端降水强度则表现为东北减弱、长江流域增强;中雨日数和持续湿期在我国大部分地区减少。(2)极端气温指标的年际变率在我国大部分地区呈减小趋势;而极端降水事件的变化则较为复杂,极端降水频次和极端降水强度的年际变率在长江以南有所增强,而北方地区则有所减弱。中雨日数和持续湿期的年际变率在我国呈现出较为一致的减少趋势。(3)模式对暖夜日数、霜冻日数的年际变化的模拟能力明显下降,并对4个极端降水指标的年际变化的模拟能力在全国多数区域均有不同程度的下降。     

Temporal evolution of surface humidity in Spain: recent trends and possible physical mechanisms

We analyzed the evolution of surface relative humidity (RH) and specific humidity (q) in Spain, based on complete records available from the State Meteorological Agency of Spain. The surface RH records used span the period 1920–2011, but because of spatial and temporal constraints in the dataset we used a subset of the data, covering the period 1961–2011. The subset contained 50 monthly series of RH, which were created through a process of quality control, reconstruction and homogenization. The data shows that there was a large decrease in RH over mainland Spain from 1961 to 2011, which was greatest in spring and summer. In contrast, there was no overall change in the specific humidity in this period, except in spring, when an increase was observed. The decrease in RH affected the entire country, but the changes in specific humidity were less homogeneous. For specific humidity there was a general increase in the northern and eastern parts of Spain, whereas negative trends dominated in the central and southern areas, mainly during the summer months. The results suggest that an increase in the water holding capacity of the atmosphere as a consequence of warming during recent decades has not been accompanied by an increase in the surface water vapor content, probably because the supply of water vapor from the main terrestrial and oceanic areas has been constrained. We discuss the implications of these findings for evapotranspiration processes, precipitation and water management in Spain.     

Spatio-temporal variability of seasonal rainfall in western equatorial Africa

This study reveals homogeneous sub-regions over the poorly studied area of western equatorial Africa (10S?C7N and 7E?C30E). Monthly totals of 141 stations covering the period 1955?C1984 are used. The stations are grouped based on the similarity of their interannual rainfall variability. In addition to annual totals, four different seasons are examined separately for regionalization, an approach that has lacked in previous studies. The four 3-month seasons are defined as follows: January?CFebruary?CMarch (JFM), April?CMay?CJune (AMJ), July?CAugust?CSeptember (JAS), and October?CNovember?CDecember (OND). Two different algorithms are applied and compared: the rotated principal component analysis (RPCA) in conjunction with Ward's method, and the RPCA in conjunction with k-means method. The principal components that explain about 65% of total variance are retained and then varimax rotated. The corresponding scores are utilized as input for cluster analysis. Using Ward's method, five sub-regions are recognized for AMJ, JAS and OND and 4 sub-regions for JFM and annual data. The regions are geographically well distributed over the area and consist of roughly the same number of stations. The F-test is used to evaluate the homogeneity of each sub-region. The results show that all sub-regions are strongly homogeneous. Assuming the same number of clusters, the k-means method provides comparable spatial patterns with those of Ward's method. However, there are some differences, which are more evident in JAS and OND. Like Ward's method, the values of F-ratio for the k-means algorithm also confirm the homogeneity of all seasons/sub-regions. The interannual variability of rainfall for each season/sub-region is also provided and compared.     

土壤湿度年际变化对中国区域极端气候事件模拟的影响研究 I. 基于CAM3.1的模式评估

利用NCAR大气模式CAM3.1对中国区域近40年的极端气候事件进行了模拟试验;在此基础上, 利用1961～2000年中国区域452站的逐日最高、最低气温和降水资料, 从气候平均、年际变化和长期变化趋势等方面全面评估了该模式对中国极端气候事件的模拟能力。结果表明:(1)模式对中国区域极端气候指数气候平均态的大尺度空间分布特征具有一定的模拟能力;模式对极端降水指标空间分布的模拟能力较好, 而对极端气温指标的模拟较差;模式对极端气候指标的模拟存在系统性的偏差, 模拟的极端降水的系统性偏差要远大于对极端温度的模拟。(2)模式对极端气温指数的年际变化特征具有较强的模拟能力, 而对极端降水指数的年际变化基本没有模拟能力;模式模拟的各极端降水指标的年际变幅与观测存在较大的偏差。(3)模式较好地模拟出了暖夜和暖昼指数在中国大部分区域的增加趋势, 但变幅较实测偏小;模式对热浪持续指数长期趋势的模拟则相对略差。模式对极端气温指标长期趋势的模拟能力总体优于对极端降水指标的模拟。模式对极端降水频次和中雨日数长期趋势的模拟尚可, 但对持续湿期长期趋势的空间分布模拟较差。研究结果可为该模式用于极端气候的模拟研究提供一定参考。     

Modulation of interannual variability of tropical cyclone activity over Southeast Indian Ocean by negative IOD phase

Tropical cyclones (TCs) over Southeast Indian Ocean (SEIO) have the notable interannual variability caused by ENSO and Indian Ocean Dipole (IOD). In the September–November of El Niño and October–November of positive IOD (PIOD), SEIO TCs is far less than its climatology. However, it is hard to separately understand El Niño and PIOD's impact on SEIO TCs due to their similar occurrence time and time scale. Unlike El Niño and PIOD, SEIO TCs is remarkably more than its climatology only in September–November of negative IOD (NIOD) instead of La Niña. Consequently, it is concluded NIOD mainly affects SEIO TCs’ increase. Diagnose results suggest the relative humidity (RH) contributes mostly to the TCs’ increase, vertical wind shear provides the secondary positive contribution, vorticity term also makes a weak positive contribution and PI term's contribution even may be negligible. The study still uncovers the process of RH change: NIOD reaches its peak period and changes atmosphere circulation to make a positive low-level vorticity anomaly over SEIO. Vorticity anomaly strengthens upward motion. The vertical velocity anomaly and climatogical specific humidity (SH) work together to make vertical advection play a dominant role in SH variation. SH's change mainly reflects in RH variation. Eventually, all of these associates with NIOD lead to more SEIO TCs in September–November and the significance of difference is above 99%.     

Estimation methods for monthly humidity from dynamical downscaling data for quantitative assessments of climate change impacts

Methods are proposed to estimate the monthly relative humidity and wet bulb temperature based on observations from a dynamical downscaling coupled general circulation model with a regional climate model (RCM) for a quantitative assessment of climate change impacts. The water vapor pressure estimation model developed was a regression model with a monthly saturated water vapor pressure that used minimum air temperature as a variable. The monthly minimum air temperature correction model for RCM bias was developed by stepwise multiple regression analysis using the difference in monthly minimum air temperatures between observations and RCM output as a dependent variable and geographic factors as independent variables. The wet bulb temperature was estimated using the estimated water vapor pressure, air temperature, and atmospheric pressure at ground level both corrected for RCM bias. Root mean square errors of the data decreased considerably in August.     

L波段与59-701探空系统相对湿度对比分析

通过统计全国探空系统早期换型时获取的59个高空站L波段雷达-GTS1型电子探空仪系统相对于59-701探空系统在1000 hPa到200 hPa之间各规定等压面相对湿度的差值,分析探空系统换型对于相对湿度一致性的影响。结果表明:GTS1型探空仪测得的相对湿度明显比59型探空仪低,且差值随高度增加而增大,近地层二者相对湿度差值低于5%,200 hPa高度二者差值达到20%以上;冬季两套探空系统相对湿度的差值明显大于夏季,且差值随高度分布情况不尽相同。分析表明:相对湿度差值的变化除了与探空仪施放过程中外界温度变化相关,还与湿度变化趋势和变化幅度密切相关,湿度传感器存在湿滞回线和滞后现象。分析还发现,太原无线电一厂与上海长望气象科技有限公司制造的59型探空仪的性能差异不明显,且GTS1型探空仪与59型探空仪的两种湿度传感器在白天受太阳辐射的残余影响差异也不明显。     

Water Vapor Variability in the Tropical Western Pacific from 20-year Radiosonde Data

The 20-year (1976-1995) daily radiosonde data at 17 stations in the tropical western Pacific was ana lyzed. The analysis shows that the atmosphere is more humid in a warmer climate on seasonal, inter-annual and long-term (20-year) time scales, implying a positive water vapor feedback. The vertical structure of the long-term trends in relative humidity (RH) is distinct from that on short-term (seasonal and inter-annual) time scales, suggesting that observed water vapor changes on short time scales could not be considered as a surrogate of long-term climate change. The increasing trend of RH (3%-5%/decade) in the upper troposphere is stronger than that in the lower troposphere (1%-2% / decade). Such vertical structure would amplify positive water vapor feedback in comparison to the common assumption of constant RH changes vertically. The empirical orthogonal function (EOF) analysis of vertical structure of RH variations shows distinct features of the vertical structure of the first three EOFs. The first three EOFs are optimal for repre sentation of water vapor profiles and provide some hints on physical mechanisms responsible for observed humidity variability. Vaisala radiosondes were used at nine stations, and VIZ radiosondes used at other eight stations. The Vaisala data are corrected for temperature-dependence error using the correction scheme developed by NCAR / ATD and Vaisala. The comparison of Vaisala and VIZ data shows that the VIZ-measured RHs after October 1993 have a moist bias of ～ 10% at RHs ＜ 20%. During 1976-1995, several changes in cluding both instruments and reporting practice have been made at Vaisala stations and introduce errors to long-term RH variations.     

京津冀及周边地区冬季能见度与PM2.5浓度和环境湿度的多元回归分析

2013年至今,中国冬季与雾霾相伴的低能见度事件频发,京津冀及周边地区尤为严重。PM_2.5浓度与环境湿度是导致低能见度的最关键影响因素。为了深入研究PM_2.5浓度与环境湿度对大气能见度的影响,利用2017年1月京津冀及周边地区MICAPS气象数据与PM_2.5观测数据,运用天气学诊断分析方法讨论了不同相对湿度下PM_2.5浓度、环境湿度对冬季能见度变化的相对贡献,按照地理环境与污染程度差异将京津冀及周边地区划分为北京-天津地区与河北-山东地区,建立了PM_2.5浓度与环境湿度（由露点温度、温度代表）对能见度的多元回归方程,并对2015、2016、2018、2019年冬季能见度进行了回算检验。结果显示:相对湿度低于70%、PM_2.5浓度低于75 μg/m3时,北京-天津地区与河北-山东地区能见度多高于10 km,PM_2.5浓度升高是此时能见度迅速降低的主导因素;相对湿度从70%上升至85%和PM_2.5浓度从75 μg/m3升高200 μg/m3的共同作用导致了能见度降低到10 km至5 km;能见度进一步从5 km下降至2 km则更多依赖于相对湿度进一步从85%升高至95%,PM_2.5浓度与此时能见度相关减弱;能见度降低至2 km甚至更低主要是由于水汽近饱和状态下（相对湿度95%以上）的雾滴消光引起,与PM_2.5浓度的变化关系不大。与不分组直接拟合相比,以相对湿度85%为界线,分别拟合能见度能够很大程度优化多元回归模型,相对湿度高于85%时能见度拟合值的均方根误差从9.2和5.2 km下降至0.5和0.7 km,5 km以下拟合能见度的误差大幅度减小。按相对湿度85%将数据分组所得的拟合方程对2015、2016、2018、2019年1月能见度估算结果较好,观测值与拟合值相关系数均高于0.91,为雾-霾数值预报系统提供了新的能见度参数化算法。      

Use of Surface Observations to Estimate Upper Air Humidity for the Objective Analysis of Relative Humidity over Indian Region

In the present study objective analyses of relative humidity (RH) at surface and at the levels of 850,700 and 500 hPa have been made using Gandin’s (1963) optimum interpolation scheme. As the horizontal resolution of the radiosonde stations is rather inadequate for upper air humidity analysis, a scheme has been developed, following Rasmussen (1982) to estimate the upper air RH from the surface observations like surface RH, present weather and cloud cover. The relative humidities at the levels 850, 700 and 500 hPa were related to the surface observations through three separate regression relations. The RH values at 850, 700 and 500 hPa levels were estimated from the surface RH, cloud coverage and present weather using the above regression relations and subsequently the objective analyses at 00 GMT for the period from 4 July to 8 July 1979, were made using these estimated data along with the observed radiosonde data. Objective analyses were also made for the same period using only the radiosonde data for comparison to study the impact of those estimated data. Root mean square errors were computed for all the five days by interpolating RH at the observing stations from the objectively analysed field and comparing them with the actually observed RH to examine how best the analyses (with and without estimated data) fitted the observations. Lastly they were compared with satellite cloud pictures. This study shows that the estimated upper air RH values have positive impact on the analysis of upper air RH and could be used over radiosonde date sparse region and even over oceanic regions.     

大气气溶胶散射吸湿增长特性研究进展

大气气溶胶的散射吸湿增长特性反映了相对湿度对气溶胶散射能力的影响。研究气溶胶散射吸湿增长对于评估气溶胶辐射强迫、了解气溶胶对大气能见度的影响具有重要意义。文中对气溶胶散射吸湿增长特性的研究意义、监测方法、中外研究进展、参数化拟合和模型模拟等方面进行了系统回顾和总结,并对未来发展方向做出展望。中国在该领域开展的研究数量偏少,广泛开展气溶胶散射吸湿增长特性研究十分必要。