Late Pleistocene–Holocene environmental change in eastern Turkey: multi‐proxy palaeoecological data of vegetation and lake‐catchment changes          下载免费PDF全文

Demet Bİltekİn  Kürşad Kadİr Erİş  Memet Namık Çağatay  Sena Akçer Ön  Dİcle Bal Akkoca 《第四纪科学杂志》2018,33(5):575-585

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Retention of mercury in sediments of the Baltic Sea near Oulu,Finland     

Kimmo Tolonen  Erkki Alasaarela  Anita Liehu 《Journal of Paleolimnology》1988,1(2):133-140

Several cores were compared to elucidate the grade of mercury retention in sediments of the Baltic Sea near Oulu, Finland. The known history of the mercury discharge to waste water from a chlor-alkali plant, the primary pollution source, was compared to that in the sedimentary record. One core was dated by lead-210 and varve counts. During the past thirty years, the rate of sedimentation was up to 10 mm per year corresponding to a dry matter accumulation rate of about 3 kg m^–2a^–1. Under these conditions, most of the mercury reaching the sediment was retained. Correspondingly, the mercury levels in fish were considerably lower, with a delay of some five years.The present mercury content of the upper layers is some 1/4 or 1/5 that of the late 1970's, but it is still some twentyfold compared to levels at the beginning of the century. The extent to which the present mercury level in the sediment represents the various phases of industrial emission remains unsolved due to the origin of mercury in this sea area from several other sources and due to difficulties in exact core correlations from different years.  相似文献   

Spectroscopic diagnostics for N III ion     

B. N. Dwivedi  Anita Mohan  A. K. Gupta 《Astrophysics and Space Science》1996,243(1):163-163

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Line diagnostics for Ne V and Mg V solar ions     

B. N. Dwivedi  Anita Mohan 《Solar physics》1995,158(2):237-248

Spectroscopic diagnostics for the Nev and Mgv solar ions have been investigated. The theoretical forbidden line ratios from these ions are presented for estimating the Ne/Mg variation in different solar structures. Calculations for density and temperature line diagnostics of these ions are given for the several spectral line ratios and their applications are discussed with the help of available solar observations in space. Future observations from the CDS and the SUMER experiments aboard the SOHO satellite are also discussed.  相似文献   

Trend removal in spatially correlated datasets     

Anita Singh  Ashok K. Singh 《Mathematical Geology》1996,28(1):111-132

Typically, datasets originated from mining exploration sites, industrially polluted and hazardous waste sites are correlated spatially over the region under investigation. Ordinary kriging (OK) is a well-established geostatistical tool used for predicting variables, such as precious metal contents, biomass, species counts, and environmental pollutants at unsampled spatial locations based on data collected from the neighboring sampled locations at these sites. One of the assumptions required to perform OK is that the mean of the characteristic of concern is constant for the entire region under consideration (e.g., there is no spatial trend present in the contaminant distribution across the site). This assumption may be violated by dalasets obtained from environmental applications. The occurrence of spatial trend in a dataset collected from a polluted site is an indication of the presence of two or more statistical populations (strata) with significantly different mean concentrations. Use of OK in these situations can result in inaccurate kriging estimates with higher SDs which, in turn, can lead to incorrect decisions regarding all subsequent environmental monitoring and remediation activities. A univariate and a multivariate approach have been described to identify spatial trend that may be present at the site. The trend then is removed by subtracting the respective means from the corresponding populations. The results of OK before and after trend removal are being compared. Using a real dataset, it is shown that standard deviations (SDs) of the kriging estimates obtained after trend removal are uniformly smaller than the corresponding SDs of the estimates obtained without the trend removal.  相似文献   

An analysis of surges triggered by a small flare     

Ágnes Kovács  L. Dezső 《Solar physics》1990,129(2):313-324

On 22 October, 1980, near the solar central meridian in the western vicinity of a large spot group, a subflare of the two-ribbon type was observed. Three surges were associated with this flare. Their starting points were situated close to the principal flare patches on both sides of a short filament that was visible for only a few hours. True flow velocities and decelerations along the arch-shaped surge trajectories have been determined for two of the surges. The highest velocities were found at the onset of the surges.The event was studied from a series of H on- and off-band flltergrams taken with the Debrecen coronagraph of 53 cm aperture.  相似文献   

用检测极端降水过程的EID方法确定梅雨雨期   总被引：1，自引：1，他引：0  

袁典  陆尔  赵玮 《气象科学》2018,38(1):37-45

梅雨期是江淮流域夏季降水最为集中的时段。先前研究提出的从时域上寻找极端降水过程的EID方法,可用来确定梅雨雨期的开始和结束及梅雨的强度。该方法含有一个介于0~1之间的可调参数a,通过对其设定不同的值,可确定出一年中不同时间尺度的降水最为集中的时段(雨期)。以南京的梅雨为例,通过试验将参数a取值为0.10,用EID方法获得了气候态的梅雨雨期,它于6月19日开始,7月12日结束,这大体与传统认定的梅雨期相符。对于逐年梅雨雨期的确定,情况稍有复杂。在用同样的方法确定出各年的强降水时段后,在62 a里去掉了12个异常的年份,包括雨期太长和太短、及太早和太晚的年份。然后对其余50个梅雨较为典型的年份进行平均。结果显示,平均的入梅日期为6月24日,平均的出梅日期为7月14日,平均雨期为20 a,这也大体与传统认定的结果相符。  相似文献   

在用降水逐日监测干旱的方法中引入蒸发     

李路遥  陆尔  赵玮 《气象科学》2018,38(3):385-391

降水是旱涝最重要的影响因子。在加权平均降水量WAP方法中,当目前没有降水,且前期降水的影响衰减掉以后,WAP便接近于0了,然而此时土壤可能还是较湿润的;若在随后的日子里仍没有降水,WAP则继续保持接近于0的值,但土壤会变的越来越干。为了区分出在WAP同样都为接近于0的状态下土壤湿度(反映在蒸发上)的差异,本文将WAP指数作了进一步的发展,即在所建立的模型中,将蒸发量E显式地表达出来。也就是,涝(旱)状态的变化不仅受降水量P所强迫,而是受P-E所强迫。新方法的基本原理和模型是与WAP方法相仿的,这个显式地考虑了蒸发的新指数WAPE,其值有正有负,接近于正态分布,因而不需再作正态化处理。结果表明,WAPE指数对旱涝的逐日监测有很好的效果。  相似文献   

长江中下游6—7月降水的降尺度模型          下载免费PDF全文

宋进波  陆尔  屠菊青  丁滢  刘思源 《大气科学学报》2018,41(1):85-92

基于偏相关的强迫因子选取方法,以长江中下游6—7月降水为例,进行了降水变率的归因分析,并建立了相应的统计降尺度模型。结果表明,影响长江中下游6—7月降水的强迫因子主要有两个:西太平洋850 h Pa的位势高度(W_(PH8))和黑潮延伸区的海表温度(K_(SST))。W_(PH8)反映的是西太平洋副热带高压对长江中下游降水的影响;K_(SST)反映了黑潮延伸区的变率。基于这两个因子的线性降尺度模型能较好地拟合长江中下游6—7月的降水,在独立检验和模式检验阶段,模型体现出了可靠性,因而可用于长江中下游降水的季节预测。  相似文献   

Asymmetries during the maximum phase of solar cycle 22     

Anita Joshi 《Solar physics》1995,157(1-2):315-324

This paper presents the results of studies of the asymmetries (N-S and E-W) for different manifestations of solar activity events (sunspot groups, H flares and active prominences/filaments) during the maximum-phase (1989–1991) of solar cycle 22. During the period considered, the results obtained show the existence of a real N-S asymmetry, whereas the E-W asymmetry may exist only for H flares. There is no definite relationship between the asymmetries and the occurrence of events; however, around low activity sometimes we find enhanced asymmetry, and low asymmetry around high activity. Our study suggests a good agreement with similar studies made by others.  相似文献