The effect of temperature‐humidity similarity on Bowen ratios,dimensionless standard deviations,and mass transfer coefficients over a lake

Similarity between heat and water vapor turbulent transport in the Atmospheric Surface Layer has been the basis of many engineering models to calculate surface fluxes, including the widely applied Bowen ratio equation, for a long time. Modernly, it is best understood within the context of Monin‐Obkhov Similarity Theory (MOST). In this work we study similarity between temperature and humidity, the Bowen ratio, and turbulent mass and heat transfer coefficients over a tropical lake in Brazil (Furnas Lake). The analysis was partly based on the concept of ‘Surface flux numbers’ recently proposed to diagnose scalar similarity, and considered wind directions and flux footprints. A period of 50 days of 30‐min. micrometeorological runs was used. Several cases of dissimilar temperature‐humidity behavior were found in the data. Both footprint extent and an aggregate temperature‐humidity Surface flux number turned out to be insufficient to diagnose these situations, but separate flux numbers for each scalar were able to diagnose their individual conformity to MOST. Overall, temperature displayed consistently larger relative variances and fluxes in comparison with humidity. The results highlight the need of careful analysis when measurements are made at sites close to land, when flux footprints may extend over there, indicating the possibility of advection effects. Copyright © 2016 John Wiley & Sons, Ltd.     

Analysis of long-term variations of fog and haze in China in recent 50 years and their relations with atmospheric humidity

Our analysis of fog and haze observations from the surface weather stations in China in recent 50 years(from 1961 to 2011)shows that the number of fog days has experienced two-stage variations,with an increasing trend before 1980 and a decreasing trend after 1990.Especially,an obvious decreasing trend after 1990 can be clearly seen,which is consistent with the decreasing trend of the surface relative humidity.However,the number of haze days has demonstrated an increasing trend.As such,the role of reduction of atmospheric relative humidity in the transition process from fog into haze has been further investigated.It is estimated that the mean relative humidity of haze days is about 69%,lower than previously estimated,which implies that it is more difficult for the haze particles to transform into fog drops.This is possibly one of the major environmental factors leading to the reduction of number of fog days.The threshold of the relative humidity for transition from fog into haze is about82%,also lower than previously estimated.Thus,the reduction of the surface relative humidity in China mainly due to the increase of the surface temperature and the saturation specific humidity may exert an obvious impact on the environmental conditions for the formations of fog and haze.In addition,our investigation of the relationship between haze and visibility reveals that with the increase of haze days,the visibility has declined markedly.Since 1961,the mean visibility has dropped from 4–10to 2–4 km,about a half of the previous horizontal distance of visibility.     

Experimental characterization of the impact of temperature and humidity on the breakdown of soil water repellency in sandy soils and composts

Soil water repellency is a widespread phenomenon with the capacity to alter hydrological and geomorphological processes. Water repellency decays with time, and the consequences are only of concern during the timescale at which the water repellency persists. This study aimed to characterize the influence of temperature and humidity on the breakdown of water repellency. Apparent contact angle measurements were carried out on samples consisting of sand treated with stearic acid as well as naturally repellent dune sands and composts. Temperature and humidity were controlled using a cooled incubator and a purpose designed enclosed box in which humidity could be raised or lowered. Results showed the contact angle of the stearic‐acid‐treated sands decayed with time and that there was a significant increase with stearic acid concentration. For all samples, the decay in apparent contact angle could be described with a continuous breakdown model. The stearic‐acid‐treated sands showed a significant increase in contact angle with relative humidity at a temperature of 10 and 20 °C. These differences diminished with increasing temperature. Similar results were seen for the dune sands and composts. Despite the influence of temperature and humidity on contact angles, there was no significant change in the rate at which the contact angle decayed in any sample. Absolute humidity was found to provide a more relevant indicator than relative humidity when assessing the influence of humidity on repellency over a range of temperatures. The contact angle initially increased with absolute humidity before plateauing owing to the confounding effect of temperature. Copyright © 2014 John Wiley & Sons, Ltd.     

Relation of the atmospheric potential gradient with meteorological elements-cross power spectral analysis

Summary Simultaneous measurements of the atmospheric electric potential gradient, relative humidity, temperature, pressure and wind speed were made for seven months and the diurnal variations, power spectra, coherence spectra, cross-spectral phase spectra, contribution to variance and the time of maximum of diurnal, semi-diurnal, terdiurnal and quartodiurnal components were calculated. The rate of decrease of relative humidity together with the rate of increase of temperature appeared to influence the potential gradient. The terdiurnal component of the potential gradient was much larger than the semi-diurnal component during summer and seemed to be governed by the terdiurnal component of the rate of change of relative humidity and temperature.     

Nowcasting with INCA During SNOW-V10

A Central-European nowcasting system which has been developed for use in mountainous terrain is tested in the Whistler/Vancouver area as part of the SNOW-V10 experiment. The integrated nowcasting through comprehensive analysis system provides hourly updated gridded forecasts of temperature, humidity, and wind, as well as precipitation forecasts which are updated every 15 min. It is based on numerical weather prediction (NWP) output and real-time surface weather station and radar data. Verification of temperature, relative humidity, and wind against surface stations shows that forecast errors are significantly reduced in the nowcasting range compared to those of the driving NWP model. The main contribution to the improvement comes from the implicit bias correction due to use of the latest observations. Relative humidity shows the longest lasting effect, with >50 % reduction of mean absolute error up to +4 h. For temperature and wind speed this percentage is reached after +2 and +3 h, respectively. Two cases of precipitation nowcasting are discussed and verified qualitatively.     

Visibility and Incidence of Respiratory Diseases During the 1998 Haze Episode in Brunei Darussalam

— Air pollution episodes as a result of forest fires in Brunei Darussalam and neighbouring regions have reached hazardous levels in recent years. Such episodes are generally associated with poor visibility and air quality conditions. In the present study, data on PM₁₀ (particulate matter of size less than 10 microns) and CO in Brunei Darussalam have been considered to study the incidence of respiratory diseases whereas data on relative humidity (RH) in addition to PM₁₀ have been used to explain the visibility with a particular emphasis on haze episode during 1998.¶Initial exploratory analysis indicates significant correlation of visibility with PM₁₀ and RH. An attempt has been made to explain visibility on the basis of PM₁₀ and RH using multiple linear regression analysis. The regression model shows that PM₁₀ and RH are two significant factors affecting the visibility at a given site. Further, canonical correlation, a multivariate method of analysis, has been used to explain the incidence of respiratory diseases as a function of air quality during the haze period. The results indicate that PM₁₀ and CO levels during the haze period have a significant bearing on the incidence of respiratory diseases (Asthma, Acute Respiratory Infections and Influenza (ARII)).     

Are peatlands cool humid islands in a landscape?

This study proposed that due to their high standing water tables that peatlands would be cold humid islands within their landscape, and especially so relative to farmland on mineral soils. To test this hypothesis, we measured air temperature and humidity at 17 locations along a 7.8 km transect across the UK's largest lowland raised bog from February 2018 to January 2019. Air temperature and humidity were measured hourly for 1 year and supported with spot albedo measurements. The study represented a factorial experiment with respect to sites of measurement, the type of land use (peat vs. arable land) and time of sampling over both the seasonal and diurnal cycles. We show that: (a) That although mean annual temperature was not significantly different between arable and peatlands, the arable land showed a decreased amplitude to its seasonal cycle – this is the reverse of the expected pattern. (b) The albedo of the peatland was significantly lower than that of arable land showing that vegetated peatland still absorbed more solar radiation. (c) The specific humidity was lower on the peatland than on the surrounding arable land. The study showed that while shrubby vegetation exists over a peatland then energy budgets are more likely to be dominated by the lower aerodynamic resistance and lower albedo of the vegetated peatland relative to arable land. Thus, shrub-dominated peatlands will not be a cold humid island in their landscape.     

Analysis of meteorological drought variability in Niger and its connection with climate indices

Based on a three-month-scale standardized precipitation index (SPI-3) computed from the available rainfall data of 13 stations of Niger, meteorological drought trends, periodicities and the relationships with 10 oceanic–atmospheric variables were analysed using the Mann-Kendall test, continuous wavelet transform and cross-wavelet analysis, respectively. The results revealed a significant (p < 5%) increase in drought at five of the 13 stations. A common dominant drought periodicity of 2 years was found at all of the stations, whereas significant periodicities varied from 2 to 32 years at six stations. Among the considered climate indices, South Atlantic sea-surface temperature, Southern Oscillation Index, sea-level pressure, geopotential height and relative humidity from the Atlantic basin oscillated in anti-phase relative to the SPI-3 at an inter-annual to decadal time scale from 1960 to 1990. In this period, relative humidity from the Mediterranean basin and zonal wind oscillated in phase with the drought index.     

Dependence of evaporation on meteorological variables at different time-scales and intercomparison of estimation methods

This paper consists of two parts. In the first part, the significance of five major factors, including solar radiation, vapour pressure deficit, relative humidity, wind speed and air temperature, that control evaporation were evaluated comparatively at different time-scales using the data from Changines station in Switzerland. The comparative evaluation was made at hourly, daily, 10-day and monthly time-scales. It was found that the role of controlling variables in evaporation varied with the time-scale. The vapour pressure deficit was best correlated with pan evaporation at all time-scales, while the wind speed was least correlated with pan evaporation, especially when the time period was longer than a day. In the second part, four equations for calculating evaporation, including temperature-based methods, humidity-based methods, mass transfer methods and radiation-based methods, were compared with pan evaporation. Of these four equations, the Penman equation, representing the mass transfer method, resulted in monthly evaporation values that agreed most closely with pan evaporation values. The Romanenko equation, representing the humidity method, also compared reasonably well with pan evaporation. The Turc equation, representing the radiation method, and the Thornthwaite equation, representing the temperature method, were found to underestimate evaporation significantly, especially for cold months. © 1998 John Wiley & Sons, Ltd.     

Laboratory simulation of rock weathering by salt crystallization and hydration processes in hot,arid environments

The results of a series of experiments are reported in this paper which were designed to differentiate between the forces of crystal growth and hydration in salt weathering, using a single salt-hydrate system (sodium sulphate), five contrasting rock types, and several diurnal temperature-relative humidity cycles which permitted or inhibited these processes and simulated ground surface climates in hot, arid environments. It was shown that hydration of sodium sulphate is an effective mechanism of rock disintegration but that it is significantly less destructive than crystal growth pressure. Crystallization of thenardite (Na₂SO₄) is, in turn, more effective in rock weathering than the crystal growth of mirabilite (Na₂SO₄.10H₂O). In general, rates of disintegration were most rapid where the diurnal temperature range was extreme and relative humidity lowest.     

Hydrological responses to climate shifts for a minimally disturbed mountainous watershed in northwestern China

Much attention has been focused on investigating the effects of precipitation and temperature changes on runoff; however, the influence of wind speed, relative humidity and total solar radiation on hydrological components needs to be studied further. Hydrological responses to climate variations in a minimally disturbed mountainous watershed in the period 1971–2012 are identified and evaluated by statistical analysis and hydrological simulation. The results indicate that the impact of climate component changes on the hydrological process cannot be discounted. The temperature and relative humidity exhibit significant upward trends, while the wind speed exhibits a clear downward trend. The potential and actual evapotranspiration dramatically increased, but the observed pan evaporation substantially decreased. The surface water, soil water, baseflow and water yield are positively correlated with precipitation and relative humidity but negatively correlated with the temperature, wind speed and solar radiation.     

基于流体动力学的探空仪GTS1湿度测量误差修正研究

准确的湿度垂直廓线对短期数值天气预报和中长期气候研究分析均具有重要参考价值,但太阳辐射与高空云雨等因素导致探空湿度测量精度较低.针对探空仪GTS1白天进行湿度测量时存在明显偏干误差的现象,本文建立了GTS1湿度测量结构模型,采用计算流体动力学方法重点研究了太阳辐射对GTS1湿度测量的影响,同时探讨了其防雨/防辐射罩的防雨效果.结合改进的太阳辐射计算模型,利用Fluent模拟分析了防雨/防辐射罩云雨滴轨迹和内部温度场分布,数值仿真结果表明:在垂直气流下防雨/防辐射罩基本保护湿度传感器免受高空云雨的影响,对太阳辐射也起到一定防护作用.但太阳辐射对GTS1湿度测量的偏干影响仍较显著,海拔30km左右相对误差甚至高达70%.通过与RS92及GTS1探空湿度测量中的太阳辐射偏干误差相对比,发现基于流体动力学数值计算的湿度相对误差随海拔高度的变化趋势与之基本吻合.本文也给出了理论计算与实验测量存在一定差异的原因,进而以南京探空站2014年不同季节的温度、气压、气球的上升速度等探空数据为计算参数,获取了太阳辐射误差与海拔及环境温度的关系,并对四组探空湿度廓线进行太阳辐射误差修正,提升了GTS1探空仪高空湿度测量的精度.本文研究结果为探空湿度测量太阳辐射偏干误差的有效修正提供了一定的参考.     

Statistical characteristics of detectable inhomogeneities in observed meteorological time series

Statistical characteristics of detectable inhomogeneities [IHs] in more than 600 observed meteorological time series have been investigated using 16 objective homogenisation methods. Forty and 100 year long series of monthly or annual characteristics of surface air temperature, precipitation total and relative air humidity from the Czech Republic and Hungary were examined. The area of the part of the Czech observing network used here is smaller, and the density of sites is larger, than in the Hungarian network, resulting in higher spatial correlations among data in the Czech dataset relative to the Hungarian dataset. Time series with low number of gaps were supplied with interpolated data. Before homogenisation relative time series were created, using weighted averages of time series from the same geographical region as reference series. For ease of comparison, the magnitudes of the detected IHs are normalised with the standard deviation of the noise in the relative time series. Results show that observed meteorological time series usually contain large number of small IHs, and that the magnitude distribution of IHs from different data segments are surprisingly similar. Effects of different spatial coherences on the results are discussed.     

肝癌DSA下两组导管的图像质量与造影参数相关性研究

目的:针对两种不同类型造影导管（美国COOK公司RH导管及日本TERUMO公司RH导管）,造影参数的选择探讨原发性肝癌的图像质量。方法:选取广州中医药第一附属医院2018年6月至2019年1月行肝动脉化疗栓塞术患者共40例,男23例,女17例,年龄最大75岁,最小30岁,平均56.3岁,均为原发性肝癌,其中20例采用美国COOK公司RH导管,20例采用日本TERUMO公司RH导管。在同一参数设置、机器设备以及图像后处理软件下,分析两组患者腹腔干动脉及肠系膜上动脉实际造影压力,以及对图像质量评判。结果:在40例患者的340幅造影图像中,图像质量良好36例（COOK组16例,TERUMO组20例）;图像质量欠佳4例,均来自COOK组。所得数据以SPSS25.0软件处理分析并作t检验,在腹腔干动脉造影,COOK组实际压力平均值为107.6psi,TERUMO组为93.1psi,差异有统计学意义（P<0.05）;在肠系膜上动脉造影,COOK组实际压力平均值为101.4psi,TERUMO组为88.9psi,差异有统计学意义（P<0.05）。结论:选择造影参数时应根据不同的造影导管选择合适的压力。若使用TERUMO RH导管,选择较小的压力即可得到良好的图像质量。      

Quantifying the impact of climate variables on reference evapotranspiration in Pearl River Basin,China

ABSTRACT

The impact of climate variables on monthly reference evapotranspiration (ET_o) is a critical issue in water resources management and irrigation planning. The spatio-temporal contribution of climate variables to ET_o in the Pearl River Basin (PRB), China, from 1960 to 2016 were calculated based on sensitivity and relative change of each climatic variable. The results show that annual ET_o total decreased by 1.64% and diminished in magnitude from the southeast to the northwest. Sunshine duration, wind speed and relative humidity decreased by 15.5%, 7.4%, and 4.0%, respectively, while average temperature increased by 4.25%. The ET_o showed a positive sensitivity to all variables except relative humidity, which showed a negative sensitivity. Sunshine duration had the highest contribution of ?4.26%, and the overall decrease in ET_o was mainly caused by the declines in sunshine duration and wind speed, which offset the positive impact of rises in average temperature and reduction in relative humidity.     

Calculation of humidity during evaporation from soil

The relative humidity at the surface of a soil is calculated as a function of time from a realistic, exactly solvable model for unsaturated fluid flow.When the evaporation rate is constant, as in the atmosphere-controlled phase, the surface relative humidity suddenly drops at a particular time, even though the humidity–time function is differentiable. This sudden transition still occurs, but is smoother, when more realistic radiation-type boundary conditions are introduced and when the soil-water diffusivity approaches zero continuously at zero water content. In these cases, solutions are obtained by a numerical method of lines which has been validated against the analytically solvable model. A gradual decrease in surface water content is not inconsistent with a sharp, step-like decrease in relative humidity. This is due to the universal exponential Gibbs–Boltzmann relationship between relative humidity and soil-water potential.     

德都台地磁观测与温度影响关系的分析

选用德都台2011—2012年的地磁基线值数据,来分析绝对观测数据、相对记录数据和温度数据对基线值的影响。通常基线值的主要影响因素除温度外,还与人为观测误差、湿度和记录墩的稳定性有关。首先保证绝对观测固定为同一人员,确保人为观测误差忽略不计,再排除湿度与记录墩的不稳定性,最后利用回归分析计算方法,得到基线值数据与温度数据的回归方程,并对该方程进行显著性检验,表明地磁基线值与温度之间存在良好的线性关系,再以此回归方程来判断我台地磁数据的好坏,为更好的改进我台地磁观测数据质量提供依据。     

A Study on the Impact of Observation Assimilation on the Numerical Simulation of Tropical Cyclones JAL and THANE Using 3DVAR

In this work, the impact of assimilation of conventional and satellite remote sensing observations (Oceansat-2 winds, MODIS temperature/humidity profiles) is studied on the simulation of two tropical cyclones in the Bay of Bengal region of the Indian Ocean using a three-dimensional variational data assimilation (3DVAR) technique. The Weather Research and Forecasting (WRF)-Advanced Research WRF (ARW) mesoscale model is used to simulate the severe cyclone JAL: 5–8 November 2010 and the very severe cyclone THANE: 27–30 December 2011 with a double nested domain configuration and with a horizontal resolution of 27 × 9 km. Five numerical experiments are conducted for each cyclone. In the control run (CTL) the National Centers for Environmental Prediction global forecast system analysis and forecasts available at 50 km resolution were used for the initial and boundary conditions. In the second (VARAWS), third (VARSCAT), fourth (VARMODIS) and fifth (VARALL) experiments, the conventional surface observations, Oceansat-2 ocean surface wind vectors, temperature and humidity profiles of MODIS, and all observations were respectively used for assimilation. Results indicate meager impact with surface observations, and relatively higher impact with scatterometer wind data in the case of the JAL cyclone, and with MODIS temperature and humidity profiles in the case of THANE for the simulation of intensity and track parameters. These relative impacts are related to the area coverage of scatterometer winds and MODIS profiles in the respective storms, and are confirmed by the overall better results obtained with assimilation of all observations in both the cases. The improvements in track prediction are mainly contributed by the assimilation of scatterometer wind vector data, which reduced errors in the initial position and size of the cyclone vortices. The errors are reduced by 25, 21, 38 % in vector track position, and by 57, 36, 39 % in intensity, at 24, 48, 72 h predictions, respectively, for the two cases using assimilation of all observations. Simulated rainfall estimates indicate that while the assimilation of scatterometer wind data improves the location of the rainfall, the assimilation of MODIS profiles produces a realistic pattern and amount of rainfall, close to the observational estimates.     

鄱阳湖夏季水面蒸发与蒸发皿蒸发的比较

水面蒸发是湖泊水量平衡要素的重要组成部分.基于传统蒸发皿观测蒸发不能代表实际水面蒸发,而实际水面蒸发特征仍不清楚.本研究基于涡度相关系统观测的鄱阳湖水体实际水面蒸发过程,在小时和日尺度分析了水面蒸发的变化规律及其主要影响因子,并与蒸发皿蒸发进行比较.研究表明,实际水面蒸发日变化波动剧烈,变化范围在0~0.4 mm/h之间.水面蒸发的日变化特征主要受风速的影响.鄱阳湖8月份日水面蒸发量与蒸发皿蒸发量在总体趋势上具有很好的一致性.8月份平均日水面蒸发速率(5.90 mm/d)比蒸发皿蒸发速率(5.65 mm/d)高4.6%.水面日蒸发量与蒸发皿蒸发量的比值在8月上、中、下旬平均值分别为1.24、1.00、0.92,呈现下降的趋势.鄱阳湖夏季水面日蒸发量与风速和相对湿度相关性显著,而蒸发皿蒸发与净辐射、气温、饱和水汽压差和相对湿度均呈显著相关.这是由于蒸发皿水体容积小,与湖泊相比其水体热存储能力小,因此更容易受到环境因子的影响.     

Spatio-temporal variation and abrupt changes for major climate variables in the Taihu Basin, China

Long-term trend and abrupt changes of major climate variables in the Taihu Basin were investigated based on the mean, maximum and minimum air temperature, diurnal temperature range (DTR), precipitation, relative humidity and sunshine duration at six meteorological stations from 1954 to 2006. Results showed that the long-term trend for annual precipitation was not statistically significant during the past 53?years, but a wetter tendency was detected and the increasing centre for annual precipitation was located in the southeast of the study area. Mean air temperature has increased by 1.43°C, similar trends were also identified for maximum and minimum air temperature, which have increased by 1.06 and 1.54°C, respectively, while DTR exhibited a slight decreasing trend with a rate of about ?0.09°C/(10?year). The annual mean relative humidity and sunshine duration exhibited a decreasing trend, with Kendall slope values of ?0.99%/10?year and ?7.797?h/10?year, respectively. Examination of long-range dependence showed that all climate variables exhibited strong persistence at annual scale except minimum air temperature. Detection of abrupt changes using nonparametric Mann–Kendall and Pettitt methods showed different results. Abrupt changes occurred in the 1980s and 2000s for annual precipitation using the nonparametric Mann–Kendall method, while no abrupt changes were detected using the Pettitt method. Abrupt changes of temperature and relative humidity took place in the early 1990s using the nonparametric Mann–Kendall method, which occurred in the late and mid 1980s using the Pettitt method, while abrupt changes of sunshine duration and DTR detected by two methods occurred in the similar period. The result will be helpful for local flood control and drought relief in urban planning and construction under future global climate change.