Modifications in aerosol physical,optical and radiative properties during heavy aerosol events over Dushanbe,Central Asia

The location of Central Asia,almost at the center of the global dust belt region,makes it susceptible for dust events.The studies on atmospheric impact of dust over the region are very limited despite the large area occupied by the region and its proximity to the mountain regions(Tianshan,Hindu Kush-Karakoram-Himalayas,and Tibetan Plateau).In this study,we analyse and explain the modification in aerosols'phys-ical,optical and radiative properties during various levels of aerosol loading observed over Central Asia utilizing the data collected during 2010-2018 at the AERONET station in Dushanbe,Tajikistan.Aerosol epi-sodes were classified as strong anthropogenic,strong dust and extreme dust.The mean aerosol optical depth(AOD)during these three types of events was observed a factor of～3,3.5 and 6.6,respectively,higher than the mean AOD for the period 2010-2018.The corresponding mean fine-mode fraction was 0.94,0.20 and 0.16,respectively,clearly indicating the dominance of fine-mode anthropogenic aerosol during the first type of events,whereas coarse-mode dust aerosol dominated during the other two types of events.This was corroborated by the relationships among various aerosol parameters(AOD vs.AE,and EAE vs.AAE,SSA and RRI).The mean aerosol radiative forcing(ARF)at the top of the atmosphere(ARFTOA),the bottom of the atmosphere(ARFBOA),and in the atmosphere(ARFATM)were-35±7,-73±16,and 38±17 Wm-2 during strong anthropogenic events,-48±12,-85±24,and 37±15 Wm-2 during strong dust event,and-68±19,-117±38,and 49±21 Wm-2 during extreme dust events.Increase in aerosol loading enhanced the aerosol-induced atmospheric heating rate to 0.5-1.6 K day-1(strong anthropogenic events),0.4-1.9 K day-1(strong dust events)and 0.8-2.7 K day 1(extreme dust events).The source regions of air masses to Dushanbe during the onset of such events are also identified.Our study con-tributes to the understanding of dust and anthropogenic aerosols,in particular the extreme events and their disproportionally high radiative impacts over Central Asia.     

艾比湖区域地表水水化学特征干湿季变化及其控制因素

对2014年艾比湖区域的地表水进行观测和取样,综合运用多元统计、Piper阴阳离子三角图、Gibbs图等方法,对艾比湖区域干湿季地表水化学特征及控制因素进行了分析.结果表明：在湿季5月,Na⁺和Cl^-是占绝对优势的离子,分别占阳离子和阴离子总量的70.34%和52.97%,其次是Mg²⁺和SO₄^2-;在干季10月,Na⁺和Cl^-是占绝对优势的离子,分别占阳离子和阴离子总量的70.57%和66.48%,其次是Mg²⁺和SO₄^2-.进而判断出在湿季,艾比湖区域地表水水化学类型为以碳酸盐岩石和蒸发岩来源为主的HCO₃^--Ca²⁺-Na⁺型;而在干季,艾比湖区域地表水水化学类型为以碳酸盐岩石和蒸发岩来源为主的HCO₃^--Ca²⁺型.此外,探讨了离子控制的因素.就自然因素而言,在干湿季,艾比湖区域地表水化学离子组成受岩石风化作用和蒸发结晶作用的共同影响,大气降水的输入作用十分微弱.就人为因素而言,根据相关研究,干湿季人为活动中的主要因素是人口和地区生产总值,说明该区域受到人为活动的影响.本研究为我国干旱地区对于河水水化学变化、水质特征、水质保护都具有重要的意义.     

末次冰盛期和全新世中期东亚地区水汽输送的模拟研究

利用国际古气候模拟比较计划最新第3阶段中9个气候模式针对末次冰盛期、13个气候模式针对全新世中期的数值试验数据,集中研究了这两个时期东亚地区的水汽输送变化。结果表明,相对于工业革命前期,末次冰盛期东亚地区冬季异常水汽输送主要来自跨赤道气流和西北太平洋,东亚大陆沿岸及其临近海域为主要的水汽异常辐合区,对应冬季净降水量增加,异常辐散区主要位于热带海洋和西北太平洋,净降水量减少;夏季,东亚地区异常水汽输送通量以辐散为主,大部分地区净降水量减少,对应东亚夏季风减弱。全新世中期东亚地区冬季水汽输送变化较弱,东南部及临近海域和赤道中太平洋为异常辐散区,不利于冬季净降水;夏季异常水汽输送分别来自热带中西太平洋广阔洋面和西北太平洋异常反气旋式环流西南侧,东亚大陆大部分地区为水汽异常辐合区,夏季净降水量增加,对应东亚夏季风增强。两个时期外强迫驱动下的经向温度梯度、海陆热力对比和大气含水量变化是上述冬、夏季东亚水汽输送异常的主因。

     

龙羊峡水库水温结构演变及其对下游河道水温影响

多年调节水库由于年际运行过程的差异引起水库水温结构变化,探明其规律及对下游河道水温响应具有重要意义。以黄河龙羊峡水库为研究对象,利用水库蓄水后的1988～2008年运行过程及水温观测资料,分析了水库运行方式与水温结构变化关系,探讨了水库不同运用过程对下游河道水温的影响。研究结果表明:龙羊峡水库水温结构演变及其对下游河道水温影响程度与水库运用过程密切相关。12～3月,水温结构为弱分层或等温分布,较高水位的蓄热增温效应明显,下游河道水温与水库水位变化具有同相位关系;5～10月,水温结构为分层分布,水位是决定分层形态变化最主要因素,下游河道水温与水库水位变化具有反相位关系,同时,水位与河道水温在不同的出入库水量条件下,呈现不同的线性相关关系。11月和4月,水温结构近乎为等温状态,也是水温结构变化的转折点。研究成果为分析大型水库在不同运行条件下水温结构及下游河道水温提供一定的参考依据。     

Study of total column atmospheric aerosol optical depth,ozone and precipitable water content over Bay of Bengal during BOBMEX-99

The spatial and temporal variations in aerosols and precursor gases over oceanic regions have special importance in the estimation of radiative forcing parameters and thereby in the refinement of general circulation models. Extensive observations of the columnar aerosol optical depth (AOD), total column ozone (TCO) and precipitable water content (PWC) have been carried out using the on-line, multi-band solar radiometers onboard ORV Sagar Kanya (Cruise # SK 147B) over Bay of Bengal during 11th–28th August 1999. Aerosol optical and physical properties (optical depth and angstrom parameter) have been estimated at six wavelengths covering from UV to NIR (380–1020 nm) while TCO and PWC have been determined using the UV band around 300 nm and NIR band around 940 nm, respectively. Added, concurrent meteorological and satellite observations during this field phase of BOBMEX-99 have been utilized to investigate spectral-temporal variations of AOD, TCO and PWC in marine environment. The results indicate lower AODs (around 0.4 at characteristic wavelength of 500 nm) and size distributions with abundance of coarse-mode particles as compared to those aerosols of typical land origin. An interesting result that is found in the present study is the significant reduction in AOD at all wavelengths from initial to later part of observation period due to cloud-scavenging and rain-washout effects as well as signature of coastal aerosol loading. The clear-sky daytime diurnal variation of TCO shows gradual increase during post-sunrise hours, broad maximum during afternoon hours and gradual decrease during pre-sunset hours, which is considered to be due to photochemical reactions. The diurnal variation curve of PWC showed maximum (~ 4 cm) during morning hours and gradual decrease (~ 3.5 cm) towards evening hours, which are found to be greater as compared to typical values over land. Another interesting feature observed is that although the PWC values are very high, there was no proportionate or appreciable enhancement in AOD—a feature that can be utilized to infer composition of aerosols over the study region.     

Spatial and temporal variability of surface water and groundwater before and after the remediation of a Portuguese uranium mine area

The old Senhora das Fontes uranium mine, in central Portugal, consists of quartz veins which penetrated along fracture shear zones at the contact between graphite schist and orthogneiss. The mine was exploited underground until a depth of 90 m and was closed down in 1971. The ores from this mine and two others were treated in the mine area by the heap-leach process which ended in 1982. Seven dumps containing a total of about 33,800 m³ of material and partially covered by natural vegetation were left in the mine area. A remediation process took place from May 2010 to January 2011. The material deposited in dumps was relocated and covered with erosion resisting covers. Surface water and groundwater were collected in the wet season just before the remediation, in the following season at the beginning of the remediation and also after the remediation in the following dry season. Before, at the beginning and after the remediation, surface water and groundwater have an acid-to-alkaline pH, which decreased with the remediation, whereas Eh increased. In general, before the remediation, uranium concentration was up to 83 μg/L in surface water and up to 116 μg/L in groundwater, whereas at the beginning of the remediation it increases up to 183 μg/L and 272 μg/L in the former and the latter, respectively, due to the remobilization of mine dumps and pyrite and chalcopyrite exposures, responsible for the pH decrease. In general, after the remediation, the U concentration decreased significantly in surface water and groundwater at the north part of the mine area, but increased in both, particularly in the latter up to 774 μg/L in the south and southwest parts of this area, attributed to the remobilization of sulphides that caused mobilization of metals and arsenic which migrated to the groundwater flow. Uranium is adsorbed in clay minerals, but also in goethite as indicated by the geochemical modelling. After the remediation, the saturation indices of oxyhydroxides decrease as pH decreases. The remediation also caused decrease in Cd, Co, Cr, Ni, Pb, Zn, Cu, As, Sr and Mn concentrations of surface water and groundwater, particularly in the north part of the mine area, which is supported by the speciation modelling that shows the decrease of most dissolved bivalent species. However, in general, after the remediation, Th, Cd, Al, Li, Pb, Sr and As concentrations increased in groundwater and surface water at south and southwest of the mine area. Before and after the remediation, surface water and groundwater are contaminated in U, Cd, Cr, Al, Mn, Ni, Pb, Cu and As. Remediation caused only some improvement at north of the mine area, because at south and southwest part, after the remediation, the groundwater is more contaminated than before the remediation.