The characteristics of rain electricity in Nigeria. I — Magnitudes and variations

The characteristics of rain and point charges based on routine measurements extending over four rainy seasons are presented. An average rain current density of (1.0±0.1)×10^–10 A m^–2 and charge per unit volume of rain water of (0.43±0.02)×10^–4 C m^–3 for the locality are obtained, which are compared with data obtained elsewhere by other workers. The point-discharge current measurements lead to a revised estimate of (0.86±0.08)×10^–9 A m^–2 for the average point discharge current below storm clouds.     

Characteristics of climate change in the “significant impact zone” affected by aerosols over eastern China in warm seasons

Through analysis of the distribution pattern and changing characteristics of atmospheric aerosols over the East Asia region during warm seasons in recent 20 a and beyond as well as their possible interac- tive relationship with a variety of meteorological elements, it is found that the high-value zone of aerosol optical depth derived from the Total Ozone Mapping Spectrometer (TOMS), its significant negative correlation zones in terms of sunshine duration (SD) and surface air temperature (SAT) and its significant positive correlation zones with low-level cloud amount (LCC) are co-located in the South China region during warm periods. Based on this finding, the region is referred to as a "significant impact zone" (SI zone) affected by aerosols. Then, a comparative analysis is made on variation differ- ences of observed SAT, SD and LCC, etc. in different regions. It is also found that the LCC is increased and the SD is decreased within the "SI zone" over eastern China during the warm season. These characteristics are more evident than those beyond the zone, while the warming trend within the zone is evidently weaker than that outside it. Studies show that since recent 20 a, under the influence of aerosols, the LCC tend to increase substantially with a clear decrease of SD and an unnoticeable warming trend within the "SI zone". Comparing with the climate change beyond the zone, the difference is significant. Therefore, the effects of atmospheric aerosols on climate is possibly one of the contri- butions to the difference of climate change existed between the southern and northern parts of the Eastern China during a warm season.     

Surfactants in the sea-surface microlayer and their contribution to atmospheric aerosols around coastal areas of the Malaysian peninsula

A study was done to determine the concentrations of surfactants on the sea-surface microlayer and in atmospheric aerosols in several coastal areas around the Malaysian peninsula. The concentrations of surfactants from the sea-surface microlayer (collected using rotation drum) and from aerosols (collected using HVS) were analyzed as methylene blue active substances and disulphine blue active substances through the colorimetric method using a UV-vis spectrophotometer. The results of this study showed that the average concentrations of surfactants in the sea-surface microlayer ranged between undetected and 0.36 ± 0.34 μmol L⁻¹ for MBAS and between 0.11 ± 0.02 and 0.21 ± 0.13 μmol L⁻¹ for DBAS. The contribution of surfactants from the sea-surface microlayer to the composition of surfactants in atmospheric aerosols appears to be very minimal and more dominant in fine mode aerosols.     

The role of organic material in atmospheric aerosols

An estimated budget of organic substances in the atmosphere is compiled to whow the importance of organics in the aerosol. The distribution of organic compounds in background aerosols is estimated and it will be shown that the Aitken particles probably consist of roughly one quarter of organic substances. This is important for the dynamics of the aerosol and calculations are presented to estimate the aerosol production distribution for gas-to-particle conversion processes.     

Variations of thermodynamical parameters in the atmospheric boundary layer over the Deccan plateau region,India

The thermodynamical structure of the atmospheric boundary layer over the Deccan plateau region has been studied with aerological data for 1980 and 1981.The temperatures in the sub-cloud layer were lower on active monsoon days than dose on weak monsoon days. An opposite trend was noticed in the layer above the 900 mbar level. The moisture content on active monsoon days was higher than that on weak monsoon days. The profile of relative humidity above the 850 mbar level showed large deviations between the active and weak monsoon conditions. On active monsoon days the values of dry static stability were higher than those on weak monsoon days. An opposite trend was noticed in the case of moist static stability. On active monsoon days the magnitudes of thev components of wind were small compared with those of theu components, and the latter showed a gradual decrease with height.     

Black carbon aerosols and their radiative properties in the Pearl River Delta region

The climatic and environmental effects of atmospheric aerosols are a hot topic in global science community, and radiative properties of the aerosols are one of the important parameters in assessing climatic change. Here we studied the black carbon concentration and absorption coefficient measured with aethalometers, scattering coefficient measured with nephelometers, and single scattering albedo derived at an atmospheric composition watch station in Guangzhou from 2004 to 2007. Our main results are as follows. The data of black carbon concentration and absorption coefficients measured with instruments cannot be directly used until they are measured in parallel with internationally accepted instruments for comparison, calibration, and reduction. After evaluation of the data, the result shows that the monthly mean of BC concentration varies 3.1–14.8 μg·m⁻³ and the concentration decreases by about 1 μg·m⁻³ in average over the four years; It is higher in the dry season with a multi-year mean of 8.9 μg/m³ and lower in the rainy season with a multi-year mean of 8.0 μg·m⁻³; The extreme maximum of monthly mean concentration occurred in December 2004 and extreme minimum in July 2007, and a 4-year mean is 8.4 μg·m⁻³. It is also shown that monthly mean scattering coefficient derived varies 129 −565 Mm⁻¹, monthly mean absorption coefficient 32–139 Mm⁻¹, and monthly mean single scattering albedo 0.71–0.91, with annual mean values of 0.80, 0.82, 0.79 and 0.84 for 2004, 2005, 2006 and 2007, respectively. Three instruments were used to take simultaneous measurements of BC in PM₁₀, PM_2.5, and PM₁ and the results showed that PM_2.5 took up about 90% of PM₁₀ and PM₁ accounted for about 68% of PM_2.5, and BC aerosols are mainly present in fine particulates. The variability of BC concentrations is quite consistent between the Nancun station (141 m above sea level) and the Panyu station (13 m above sea level), which are 8 km apart from each other. The concentration in higher altitude station (Panyu) is consistently lower than the lower altitude station (Nancun), and the difference of annual mean is about 4 μg·m⁻³. Supported by Natural Science Foundation of China (Grant Nos. U0733004, 40375002, 40418008, 40775011), National High Technology R & D Program of China (Grant Nos. 2006AA06A306 and 2006AA06A308) and National Basic Research Program of China (Grant No. 2005CB422207)     

基于GPS和大气传输模型的InSAR大气改正方法研究

利用GPS数据改正InSAR大气影响中,GPS站网的低空间密度是限制改正精度的一个主要因素.文中引入大气传输模型（ATM）来考虑大气状态在时间上的演化,并兼顾了风向的估计,把GPS-ZWD（GPS湿延迟）时间序列观测值转换为空间上分布比较稠密的GPS-ZWD网络,然后利用该稠密网络在空间上内插产生水汽延迟图,来更好地模拟InSAR影像获取时刻的水汽场,提高大气改正精度.实验结果表明,在研究地区有限的数据条件下（即只有6个GPS点的情况下）,GPS+ATM算法在重现大气信号能力方面比单纯的使用影像获取时刻的GPS-ZWD数据要强,并且其对长波的大气误差去除更明显;用来做实验的三幅差分干涉图中,GPS+ATM算法对两幅以长波信号为主的干涉图中的大气影响分别降低了21.7%和22.6%,比仅使用SAR过境时刻GPS-ZWD数据时的结果分别改进了4.5%和8.7%.而对以短波信号为主的干涉图没有明显提高.     

梅雨期江淮地区极端高温事件的非均匀性特征及其与环流系统的配置

本文基于集中度和集中期的定义方法,利用1960~2007年的48年江淮地区站点的日平均温度资料和累积频率的阈值统计方法,分析梅雨期江淮地区极端高温事件的非均匀分布特征.结果表明,集中度和集中期的方法能够定量地表征梅雨期江淮地区极端高温事件的非均匀分布特征.集中期的异常型为全场一致和南北异常型,集中度的异常分布主要为南北异常和东西异常.进一步比较集中度和集中期异常与同期环流系统的配置关系得知,当集中期南北异常变化时,在高纬度的北太平洋区域出现一对正负的异常模态,且随高度增加而增强,为相当正压结构.海温的异常集中在北太平洋的北美沿岸的显著负异常中心.当集中度为东西异常时,主要环流异常型为约在160°W左右出现 + - + - 的200 hPa纬向西风异常波列形式从低纬度到高纬度地区传播以及与ENSO的显著负相关.     

Impact of wind on the spatial distribution of rain over micro‐scale topography: numerical modelling and experimental verification

The wind‐driven‐rain effect refers to the redistribution of rainfall over micro‐scale topography due to the existence of local perturbed wind‐flow patterns. Rainfall measurements reported in the literature point to the fact that the wind‐driven‐rain distribution can show large variations over micro‐scale topography. These variations should be taken into account in hillslope hydrology, in runoff and erosion studies and in the design of rainfall monitoring networks. In practice, measurements are often not suitable for determining the wind‐driven‐rain distribution. Therefore, a few researchers have employed numerical modelling. In order to provide confidence in using numerical models, experimental verification for a range of different topographic features is imperative. The objective of this study is to investigate the adequacy of a two‐dimensional Computational Fluid Dynamics (CFD) model to predict the wind‐driven‐rain distribution over small‐scale topography. The numerical model is applied to a number of topographic features, including a succession of cliffs, a small isolated hill, a small valley and a field with ridges and furrows. The numerical results are compared with the corresponding measurement results reported in the literature. It is shown that two‐dimensional numerical modelling can provide a good indication of the wind‐driven‐rain distribution over each type of micro‐scale topography that is considered in this study. It is concluded that more detailed verification procedures are currently inhibited due to the lack of available and detailed spatial and temporal rainfall data from field measurements. Copyright © 2005 John Wiley & Sons, Ltd.     

Effects of soil compaction,rain exposure and their interaction on soil carbon dioxide emission

Soils release more carbon, primarily as carbon dioxide (CO₂), per annum than current global anthropogenic emissions. Soils emit CO₂ through mineralization and decomposition of organic matter and respiration of roots and soil organisms. Given this, the evaluation of the effects of abiotic factors on microbial activity is of major importance when considering the mitigation of greenhouse gases emissions. Previous studies demonstrate that soil CO₂ emission is significantly affected by temperature and soil water content. A limited number of studies have illustrated the importance of bulk density and soil surface characteristics as a result of exposure to rain on CO₂ emission, however, none examine their relative importance. Therefore, this study investigated the effects of soil compaction and exposure of the soil surface to rainfall and their interaction on CO₂ release. We conducted a factorial laboratory experiment with three soil types after sieving (clay, silt and sand soil), three different bulk densities (1·1 g cm^–3, 1·3 g cm^–3, 1·5 g cm^–3) and three different exposures to rainfall (no rain, 30 minutes and 90 minutes of rainfall). The results demonstrated CO₂ release varied significantly with bulk density, exposure to rain and time. The relationship between rain exposure and CO₂ is positive: CO₂ emission was 53% and 42% greater for the 90 minutes and 30 minutes rainfall exposure, respectively, compared to those not exposed to rain. Bulk density exhibited a negative relationship with CO₂ emission: soil compacted to a bulk density of 1·1 g cm^–3 emitted 32% more CO₂ than soil compacted to 1·5 g cm^–3. Furthermore we found that the magnitude of CO₂ effluxes depended on the interaction of these two abiotic factors. Given these results, understanding the influence of soil compaction and raindrop impact on CO₂ emission could lead to modified soil management practices which promote carbon sequestration. Copyright © 2012 John Wiley & Sons, Ltd.     

The role of dynamics in total ozone deviations from their long-term mean over the Northern Hemisphere

Total ozone anomalies (deviation from the long-term mean) are created by anomalous circulation patterns. The dynamically produced ozone anomalies can be estimated from known circulation parameters in the layer between the tropopause and the middle stratosphere by means of statistics. Satellite observations of ozone anomalies can be compared with those expected from dynamics. Residual negative anomalies may be due to chemical ozone destruction. The statistics are derived from a 14 year data set of TOMS (Total Ozone Mapping Spectrometer January 1979-Dec. 1992) and corresponding 300 hPa geopotential (for the tropopause height) together with 30 hPa temperature (for stratospheric waves) at 60°N. The correlation coefficient for the linear multiple regression between total ozone (dependent variable) and the dynamical parameters (independent variables) is 0.88 for the zonal deviations in the winter of the Northern Hemisphere. Zonal means are also significantly dependent on circulation parameters, besides showing the known negative trend function of total ozone observed by TOMS. The significant linear trend for 60°N is 3 DU/year in the winter months taking into account the dependence on the dynamics between the tropopause region and the mid-stratosphere. The highest correlation coefficient for the monthly mean total ozone anomalies is reached in November with 0.94.     

一次切断低压诱发的暖区深对流与异常副热带锋及其平流层-对流层交换

采用Cloudsat/CPR云雷达,FY2C/TBB亮温,Aura/MLS大气成分等卫星遥感资料,结合ECMWF气象分析资料和HYSPLIT4轨迹模式,研究了2009年6月一次东亚切断低压的暖区深对流和异常副热带锋面的结构和演变.分析表明,由于低压切断前的旧槽背景,在低涡的近成熟期,内部冷、暖锋降水偏弱,边沿的高空副热带锋面异常发展到对流层底部,低空西南暖湿水汽在副热带锋前聚集,形成千公里长的暖区深对流降水带.随着该锋面的快速东移,副热带锋区进入原暖区雨带,锋区热力间接次级环流的强上升支,加强了锋下冷侧（原暖湿区）的深对流,但该锋面阻挡了来自暖侧的水汽补充,降水结束.该异常副热带锋区还发生了强烈的平流层-对流层相互交换,在高空急流出口区的下方,平流层1.5PVU等位涡线向下入侵可达5.5 km（约500 hPa）处,锋下向上的深对流注入可达10 km,在入侵-注入混合区,臭氧和水汽的散点图上出现了二者浓度双高和双低的特殊气团.     

机载激光雷达对青岛及周边海域的气溶胶探测

工作波长为532 nm的机载大气环境探测激光雷达AEDAL（Atmospheric Environment Detecting Airborne Lidar）装载在CMS_3807飞机上,于2005年11月7～11日期间在青岛地区及周边海域上空进行了飞行探测.此次实验的目的有两个：验证我国用于大气环境探测的激光雷达技术已经具备从地基向空基乃至天基发展的条件;获得青岛地区及周边海域边界层结构及大气气溶胶时空分布变化的特点.激光雷达的高时空分辨率为获取飞行路径上的边界层结构及气溶胶时空分布提供了可能.为了研究下垫面对边界层及气溶胶时空分布的影响,预定的飞行路径上包含了丰富的地形变化,有城市、丘陵、海区等.通过给出11月8日及11日的探测结果,不仅得到了不同地区边界层结构及气溶胶的时空分布特点,还可以看到冷锋、地形、地面气象场等因素对它们的影响.     

Thermal structure of hot events and their possible role in maintaining the warm isothermal layer in the Western Pacific warm pool

Ocean Dynamics - The short-lived events of high SST are called hot events (HEs) and can only be generated under the conditions of large daily heat gain due to strong solar radiation and weak wind....     

Differences in the concentrations of atmospheric trace gases in and above the tropical boundary layer

Weekly air samples were collected at Cape Kumakahi (0 km) and at nearby Mauna Loa Observatory (3.4 km) which is above the boundary layer. EC/GC and GC/FID techniques were used to measure CH₃I, CHCl₃, CO and CH₄, which are largely natural in origin, and C₂Cl₄, CCl₄, CH₃, CCl₃, CCl₃F (F-11), CCl₂F₂ (F-12), CHClF₂ (F-22) and C₂F₃Cl₃ (F-113), which are due to anthropogenic activities. It was found that all these gases are significantly (0.05) more abundant in the boundary layer than above it.     

三维分层流动过双山脉地形激发的大气船舶重力波动力学理论和数值试验

利用我们建立的三维分层线性理论计算模式和中尺度数值模式ARPS, 分别研究了三维分层流动过双山脉地形产生的三维线性和非线性山脉重力波和大气船舶的结构特征及其形成机制.线性理论计算结果表明三维三层流动过双山脉地形时,两个山脉各自强迫出一个发散模态的山脉背风波,在第二个山脉背风面,三维三层流动过双山脉地形可以强迫出两个发散模态的拦截背风波,大大加强了对大气环流的拖曳作用.非线性数值模拟结果表明,流动过山所产生的非线性山脉重力波和大气船舶完全不同于三维分层线性理论计算模式所产生的山脉重力波和大气船舶的结构和特征,由于分层流体之间的非线性相互作用,三维三层流动过双山脉地形时,可在第二个山脉背风面激发4个发散模态的拦截背风波. 三维三层流动过双山脉地形所强迫的山脉重力波和大气船舶,具有同三维三层流动过孤立山脉所产生的山脉重力波和大气船舶完全不同的结构和特征,三维流动过双山脉地形对两个山脉之间的距离表现出极大的敏感性.对于相距较远的两个山脉,流动过双山脉所强迫的山脉重力波表现为4个发散模态的拦截背风波,波动的能量相对于相距较近的两个山脉能传播到更高的高度.     

Variations of widespread extreme cold and warm days in winter over China and their possible causes

The two leading modes of winter surface air temperature(SAT) over China during 1961–2017 are a spatially consistent pattern and a north-south dipole pattern. Based on the two leading modes, the characteristics of the extreme cold and warm days in the two patterns, defined by the standard deviation larger than 1.28 or smaller than-1.28 in the time series of the two leading modes, are analyzed. With the increase of winter SAT during 1961–2017, the number of spatially consistent extreme cold days decreased and their occurrence was restricted to late December to early January, whereas the number of spatially consistent extreme warm days increased significantly in January and February. Global warming is associated with an increase in the spatially consistent extreme warm days and a decrease in spatially consistent extreme cold days, but has little relation to the sum of extreme cold and warm days of either the spatially consistent or north-south dipole pattern. The Siberian High(SH) is the main factor controlling the sum of spatially consistent extreme warm and cold days. The strong(weak) SH before(after) the1990 s corresponds to an increase(decrease) in the sum of the spatially consistent extreme warm and cold days. The occurrences of extreme south-cold-north-warm and extreme south-warm-north-cold days are related to the north-south difference of the SH.When the center of the SH is in mid-high latitudes, the extreme south-warm-north-cold(south-cold-north-warm) days occur more(less) often. During the winters of 1961–2017, the total number of extreme cold and warm days of the north-south dipole pattern changes negligibly. The North Atlantic meridional overturning circulation(AMOC) may be the main factor affecting the sum of the extreme cold and warm days of the two types of SAT pattern in China.     

Hydrological impact and potential flooding of convective rain cells in a semi-arid environment

Abstract

t Spatio-temporal storm properties have a large impact on catchment hydrological response. The sensitivity of simulated flash floods to convective rain-cell characteristics is examined for an extreme storm event over a 94 km² semi-arid catchment in southern Israel. High space–time resolution weather radar data were used to derive and model convective rain cells that then served as input into a hydrological model. Based on alterations of location, direction and speed of a major rain cell, identified as the flooding cell for this case, the impacts on catchment rainfall and generated flood were examined. Global sensitivity analysis was applied to identify the most important factors affecting the flash flood peak discharge at the catchment outlet. We found that the flood peak discharge could be increased three-fold by relatively small changes in rain-cell characteristics. We assessed that the maximum flash flood magnitude that this single rain cell can produce is 175 m³/s, and, taking into account the rest of the rain cells, the flash flood peak discharge can reach 260 m³/s.

Editor Z.W. Kundzewicz; Guest editor R.J. Moore

Citation Morin, E. and Yakir, H., 2013. Hydrological impact and potential flooding of convective rain cells in a semi-arid environment. Hydrological Sciences Journal, 59 (7), 1275–1284. http://dx.doi.org/10.1080/02626667.2013.841315     

The role of sodium bicarbonate in the nucleation of noctilucent clouds

It is proposed that a component of meteoric smoke, sodium bicarbonate (NaHCO₃), provides particularly effective condensation nuclei for noctilucent clouds. This assertion is based on three conditions being met. The first is that NaHCO₃ is present at sufficient concentration (10⁴ cm^–3) in the upper mesosphere between 80 and 90 km. It is demonstrated that there is strong evidence for this based on recent laboratory measurements coupled with atmospheric modelling. The second condition is that the thermodynamics of NaHCO₃(H₂O)_n cluster formation allow spontaneous nucleation to occur under mesospheric conditions at temperatures below 140 K. The Gibbs free energy changes for forming clusters with n = 1 and 2 were computed from quantum calculations using hybrid density functional/Hartree-Fock (B3LYP) theory and a large basis set with added polarization and diffuse functions. The results were then extrapolated to higher n using an established dependence of the free energy on cluster size and the free energy for the sublimation of H₂O to bulk ice. A 1-dimensional model of sodium chemistry was then employed to show that spontaneous nucleation to form ice particles (n > 100) should occur between 84 and 89 km in the high-latitude summer mesosphere. The third condition is that other metallic components of meteoric smoke are less effective condensation nuclei, so that the total number of potential nuclei is small relative to the amount of available H₂O. Quantum calculations indicate that this is probably the case for major constituents such as Fe(OH)₂, FeO₃ and MgCO₃.