2009年1月强爆发性增温期间突发E(Es)层的响应

平流层爆发性增温(SSW)期间,低层大气温度场和风场等的剧烈变化会直接影响潮汐和风剪切作用.此举可能会导致电离层Es的相应变化.本文以2009年1月事件为例,分析了SSW期间Es层的响应.首先,在排除太阳活动和地磁活动对Es层影响的前提下,分析了昆明站附近MLT区域行星波和潮汐波的波动特性,发现此期间存在显著的2日行星波,并伴有日潮汐减弱和半日潮汐增强等波动现象;随后,分析相应时间段内Es层的变化特性发现,重庆和昆明站附近Es层强度明显减弱,且其高度显著抬升.这一现象与低层大气的波动变化具有同步性.最后,通过模拟经典风剪切理论下Es层金属离子的汇聚过程和运动轨迹,再现了SSW期间Es层与低层大气波动的耦合演化过程.该分析结果为研究低层-中层-高层大气的耦合过程提供了一种新的思路.     

Relative effects of multi-decadal climatic variability and changes in the mean and variability of climate due to global warming: future streamflows in Britain

Climate change impact assessments conventionally assess just the implications of a change in mean climate due to global warming. This paper compares such effects of such changes with those due to natural multi-decadal variability, and also explores the effects of changing the year-to-year variability in climate as well as the mean. It estimates changes in mean monthly flows and a measure of low flow (the flow exceeded 95% of the time) in six catchments in Britain, using the UKCIP98 climate change scenarios and a calibrated hydrological model. Human-induced climate change has a different seasonal effect on flows than natural multi-decadal variability (an increase in winter and decrease in summer), and by the 2050s the climate change signal is apparent in winter and, in lowland Britain, in summer. Superimposing natural multi-decadal variability onto the human-induced climate change increases substantially the range in possible future streamflows (in some instances counteracting the climate change signal), with important implications for the development of adaptation strategies. Increased year-to-year variability in climate leads to slight increases in mean monthly flows (relative to changes due just to changes in mean climate), and slightly greater decreases in low flows. The greatest effect on low flows occurs in upland catchments.     

长江中下游典型湖泊营养盐历史变化模拟

湖泊营养盐变化在自然条件下受到气候水文因素控制,同时受到湖泊生态系统生物群落作用和反馈.作为动力机制探讨,本文试图基于水文和生态动力学方法,分别构建气候-流域水文作用于湖泊营养盐的外源模式和湖泊生物群落作用于湖泊营养盐的內源模式.针对长江中下游典型湖泊,经过控制实验和率定,发现营养盐模拟与观测数据在时间序列上达到90%百分位的正相关,因此用来模拟1640 1840 A.D.期间的营养盐演变历史.研究表明:(1)模拟的湖泊营养盐变化与沉积钻孔揭示的历史营养盐变化基本一致,沉积记录与模式模拟的7个湖泊的营养盐变化均显著相关;(2)气候因素是湖泊营养盐历史演变的主控因子,来自于湖泊生物群落的反馈作用贡献约占40%;(3)在温度和降水因子的驱动下,湖泊营养盐历史变化主要受降水控制,在极端干旱时期,60%的营养盐变化同步响应于降水变化.同时,面积在400 km2以下的湖泊营养盐对气候变化的响应比2000 km2以上的大湖更为敏感.研究结果对长江中下游湖泊营养状态的长期变化机理认识和趋势控制提供科学依据.     

中国平均降水和极端降水对气候变暖的响应:CMIP5模式模拟评估和预估

基于24个CMIP5全球耦合模式模拟结果,分析了中国区域年平均降水和ETCCDI强降水量(R95p)、极端强降水量(R99p)对增暖的响应.定量分析结果显示,CMIP5集合模拟的当代中国区域平均降水对增温的响应较观测偏弱,而极端降水的响应则偏强.对各子区域气温与平均降水、极端降水的关系均有一定的模拟能力,并且极端降水的模拟好于平均降水.RCP4.5和RCP8.5情景下,随着气温的升高,中国区域平均降水和极端降水均呈现一致增加的趋势,中国区域平均气温每升高1 ℃,平均降水增加的百分率分别为3.5%和2.4%,R95p增加百分率为11.9%和11.0%,R99p更加敏感,分别增加21.6%和22.4%.就各分区来看,当代的区域性差异较大,未来则普遍增强,并且区域性差异减小,在持续增暖背景下,中国及各分区极端降水对增暖的响应比平均降水更强,并且越强的极端降水敏感性越大.未来北方地区平均降水对增暖的响应比南方地区的要大,青藏高原和西南地区的R95p和R99p增加最显著,表明未来这些区域发生暴雨和洪涝的风险将增大.     

Statistical models for the estimation of net phosphorus sedimentation in lakes

The empirical adequacy of four phosphorus mass-balance models is evaluated with respect to how the prediction error variance of the corresponding net sedimentation parameters is propagated in the steadystate equations. Using the criterion of minimum propagation error variance (PEV), different groups of lakes can be distinguished for which different empirical equations are used to predict net phosphorus sedimentation. The classification reduced prediction error significantly and also reflected different patterns of sedimentation. Application of this criterion to time-series of individual lakes shows that it is possible to determine a priori whether net annual sedimentation will be better correlated to the annual loading or to the lake content. The correlations depended also on the load/lake content ratio, suggesting that net sedimentation is best viewed as the sum of the partial sedimentation of the load and of the partial sedimentation of the lake content. On average, 25% of the load and 18% of the lake content are sedimented annually. Viewing net phosphorus sedimentation as a function of both the load and the lake content can also explain and predict the well-known cross-sectional correlation between phosphorus retention and water residence time.     

Shelf-basin exchange in the Laptev Sea in the warming climate: a model study

GCM-based forecast simulations predict continuously increasing seasonality of the sea ice cover and an almost ice-free, summer-time, Arctic Ocean within several decades from the present. In this study we use a primitive equation ocean model: NEMO, coupled with the sea ice model LIM2, to test the hypothesis that under such an increased range in seasonal ice cover the intensity of shelf-basin water exchange will significantly increase. We use the simulated results for the Laptev Sea from a global model run 1958–2007 and compare results for two years with anomalously high and low summer sea ice extents: 1986–1987 and 2006–2007. The shelf–basin fluxes of volume, heat and salt during specific seasons are evaluated and attributed to plausible driving processes, with particular attention to dense water cascading. Analyses of the model temperature distribution at the depth of the intermediate maximum, associated with Atlantic Water, have shown a marked increase of the amount of the local origin cold water in late winter 2007 in the region, where dense water typically appears as a result of its formation on the shelf and subsequent downslope leakage. Calculation of the shelf-basin exchange during March-May in both years confirmed a substantial increase (a factor of two) of fluxes in “ice-free” 2007 compared to the “icy” 1987. According to several past model studies, dense water production on Arctic shelves in winter driven by ice freezing and brine rejection is not likely to cease in a warmer climate, but rather to increase. There is also observational evidence that cascading in the seasonally ice covered seas (e.g. the Barents Sea) is much more efficient than it is in the permanently ice covered Arctic Ocean, which supports these model results.     

Climate change and agricultural pollution effects on the trophic status of a Mediterranean lake

Trichonis Lake is the largest natural freshwater body in Greece with a surface area of 97 km². It receives pollutants from numerous anthropogenic activities, especially from intensive agricultural practices, urban sewages, stock grazing land and small industries. In this study, hydrologic and chemical parameters are assessed during two periods (1990–1991) and (2001–2002) to evaluate the effects of the climatic changes on phosphorous trends and consequently on the trophic status of Trichonis Lake. Even though large quantities of fertilizers are applied in the lake's catchment, phosphorus loads are still in the permissible level as estimated according to Vollenweider's relationship based on total phosphorus concentration. Due to relatively higher rainfall precipitation during the last years, an increased amount of the phosphorus entering into the lake system is flushed out, thus keeping the trophic status of the lake in oligotrophic levels. In contrast, lower rainfall rates during the first period (1990–1991) have led to the decrease in phosphorus flush out and its detainment into the lake water and sediment resulting to mesotrophic conditions. As the trophic status of the lake is mainly hydrologically dependent and thus unpredictable, effective management plans targeting the elimination of nutrient pollution loadings are necessary.     

滨江平原的形成模式是江—湖、洲—陆转化——以长江武汉段武昌北部为例

长江武汉城区段呈SSW-NNE向从城市中心流过.两岸滨江平原是武汉城市的黄金地段.分布于汉阳和武昌沿岸的滨江平原,平面形状似弓形分布于晚更新世岗地与长江之间.研究发现,其形成经历了江-洲-湖-陆的转变过程,是长江中的沙洲并岸的产物.本文以武昌北滨江平原为例,对其形成过程进行了解析.长江武汉蛇山-青山段在明代江面十分开阔...     

全球气候变化模拟结果数据的远程抽取及其可视化

本文针对气候模式在超大规模数值模拟中产生的Tb至Pb量级的四维体数据的可视化和分析诊断方法, 提出了基于Server-Client方式的远程数据抽取和并行可视化解决方案。 针对气候模拟数据中的海洋模式和大气模式数值模拟结果数据的抽取和可视化数值试验分析, 验证了解决方案的可行性和抽取算法的高效性、 可靠性和灵活性。 本文提出的远程数据抽取方法对于帮助气候模式领域中的专家快速抽取、 快速可视化和实现实时交互式模拟结果的诊断分析具有重要的应用价值。     

Climate warming and its impact on natural regional boundaries in China in the 1980s

The global climate warming accelerated in the 1980s has become a focus in the world. Based on the month by month and year by year temperature data from 160 representative stations throughout the country during 1951-1999, this paper analyses annual and four seasons' temperature variations of China since the 1980s. It was found out that the non-equalibrium response with relative great regional and seasonal differences is represented in the country's climate warming. In regional changes a trend of "warm in the north and cold in the south" occurs whereas in seasonal changes, the characters of "warm in winter and cool in summer" present. Significant verification of the temperature variations conducted in terms of mathematical statistics reveals that a confidence level of over 95% has been basically reached in areas north of the Yangtze River. Meanwhile, according to data of diurnal mean temperature steadily passing through accumulated temperature ≥10℃ from 335 stations since 1951 or since the founding of the stations in the early 1950s to 1999, comparative analysis of the data of the last 19 years with that of the first 30 years was conducted and the accumulated temperature ≥10℃ and the variation range of the persistent number of days ≥10℃ were obtained. It was concluded that a general northward shift of central subtropics, north subtropics, warm temperate zone, mesothermal zone and frigid temperate zone of eastern China was observed. The northward shift of north subtropics and warm temperate zone was obvious but changes of south subtropics and marginal tropics were insignificant. In western China, in addition to southwestern Yunnan, the Qinghai-Tibet Plateau and western Inner Mongolia where the temperature zones of each either shifted northward or trended to move upward, not much changes were found in other areas or they shifted southward slightly and declined.     

River water and nutrient discharges in the Northern Adriatic Sea: Current importance and long term changes

Runoff and nutrient transport by rivers were analysed in the Northern Adriatic continental shelf, in order to evaluate their interannual and multidecal variability, as well as their current contribution to determine freshwater and nutrient budgets in this marine region. During the years 2004-2007, the runoff in the basin (34.1-64.6 km³ yr⁻¹) was highly imbalanced, being 84% of freshwater discharged along the western coast, because of the contributions of Po, Adige and Brenta rivers. In the northern and eastern sections of the coast, freshwater discharge by rivers was less important (10 and 6%, respectively), but not negligible in determining the oceanographic properties at sub-regional scales. The oscillations of the transport of biogenic elements (124-262×10³ t N yr⁻¹ for TN, 72-136×10³ t N yr⁻¹ for DIN, 4.5-11.1×10³t P yr⁻¹ for TP, 2.2-3.5×10³ t P yr⁻¹ for PO₄ and 104-196×10³ t Si yr⁻¹ for SiO₂) were strictly dependant to the differences in the annual runoff. A strong excess of N load in comparison to P load characterised all rivers, both in inorganic nutrient (DIN/PO4=37-418) and total (TN/TP=48-208) pools, particularly in the northern and eastern areas of the basin.The annual runoff showed significant oscillations for Po on multidecadal time scale, whereas a general decrease (−33%) was observed for the other N Adriatic rivers as the recent discharges were compared to those before the 1980s. During the dry years 2005-2007, a strong reduction of river water flows and nutrient loads was experienced by the N Adriatic ecosystem with respect to years characterised by medium-high regimes. An increased frequency of similar drought periods, due to ongoing climate changes or to a larger human usage of continental waters, would be easily able to significantly change the biogeochemistry of this basin.     

The reproductive phenology of Isoetes lacustris L.: Results of field studies in Scandinavian lakes

The phenologic change of the leaf rosette structure of Isoetes lacustris L. was studied in 26 lakes of temperate, boreal, or subarctic Scandinavia between 59° and 70° n.l. The investigations were carried out during six defined seasons: late winter, spring, early summer, late summer, autumn, and early winter. From 640 plants, gained with the aid of SCUBA, six leaf types were distinguished: immature megasporophylls, mature megasporophylls, immature microsporophylls, mature microsporophylls, and sporophylls that had released their spores and leaves with undeveloped sporangia. Mean numbers per rosette of each leaf type were established in each study lake and study season, resulting in a common pattern embracing all lakes studied.

Megasporophylls are developed throughout the year, whenever the water temperature is about 10 °C. Their share was always more than 30%, excepting winter. Microsporophylls are produced preferentially in spring/early summer when the days are longest; they amount to more than 50% of the rosette leaves during this period, but only to some 10% in the remaining seasons. The spores mature and are released between late summer and early winter. It is concluded that not all spores mature in the year of their birth, and those that do not mature are released in the early summer of the following year, as well as the old empty leaves become detached.     

气候变化对沅江流域径流影响研究

温室气体排放量增加造成气候变化,对全球资源环境产生重要影响.本文在水量平衡基础上,建立考虑气象要素和地形变化的月水文模型,利用实测径流资料对模型在时空尺度上进行验证.利用全球气候模型(GCMs)预测的未来气候变化情形,对处于湿润区的沅江流域径流过程进行预测.分析结果表明,该区域径流过程对降雨和气温变化十分敏感.根据英国Hadcm2模型对本世纪中叶气候变化预测结果,沅江流域未来年降雨量减少0.43%气温升高1.55℃,丰水期降雨增加,而枯水期将有较大幅度减少.年径流量相应减少6.8%,丰水期径流量增大11%,枯水期径流减少47%,不利于防洪和水资源开发利用.     

The issue of global warming and changes in the runoff of Russian rivers

Maps of a series of characteristics were calculated and constructed for RF territory, including mean values of changes in runoff depths (evaluated by the main climate models of the Intergovernmental Panel on Climate Change) due to greenhouse effect estimated for 2040–2070; root-mean-square deviations from these values; relative errors of the estimates; mean values of changes in the runoff depth for different scenarios of greenhouse gas emissions; absolute and relative deviations of these values from their means for scenarios and integration of models. Chronological forecasts of possible changes in the mean runoff values for the rivers of Volga, Northern Dvina, Pechora, Ob, Yenisei, Lena, Yana, Indigirka, Kolyma, and Amur up to 2100 are calculated, and the root-mean-square errors of these characteristics are evaluated for the maximum number of uncertainties in the forecast. The greenhouse effect is shown to be less significant, other factors being the same, for rivers with small drainage basins and rivers with small modulus of flow.     

Hydraulic and salinity regime of two affected sites in the Yizre'el valley,Israel

Causes of recent salinization of numerous plots in the Yizre'el Valley of Israel were examined through a detailed field study of two severely affected sites. in particular, the theory of artesian influence on salt build-up in the upper cultivated soil layer was investigated. Two piezometer nests and 12 wells were installed to study the subsurface hydraulic regime. Water samples and soil extracts were taken to characterize the chemical composition down to 10m. No significant head differences were measured at the lower site, while at the upper site 96 per cent of the head that existed at the deep (7.5 m) artesian layer was dissipated within the overlying thick clay layer. Slight head differences were noted in the shallow layers. the deep-lying, coarse-textured aquifer differs markedly from the upper confining layers and constitutes an independent water body that has little relevance to surface processes. Chemical and hydrological analyses indicate that applied low-quality irrigation waters May, be the primary cause of downward-moving salinity and alkalinity which, in turn, affect soil permeability and site productivity.     

Metacommunity dynamics of Ostracoda in temporary lakes: Overall strong niche effects except at the onset of the flooding period

Metacommunity research usually focuses on the structure of species assemblages and their influencing factors, chiefly environment and space. However, the temporal dynamics of metacommunities and their structuring processes are rarely investigated. Here, we analyze the temporal variations in a metacommunity of ostracods from temporary shallow lakes of the Iberian Peninsula. Our aims were to determine the variability of the ostracod assemblages throughout a hydrological cycle by means of partial triadic analysis (PTA), and to analyze the response of these communities to both environmental and spatial variables. The metacommunity was moderately stable through the study period, with larger variability between sites than between months. However, the metacommunity structure at the beginning of the hydroperiod was notably different from the rest of months. Species sorting was the predominant mechanism structuring the metacommunity through monthly samples, establishing a conspicuous separation between species that inhabit saline lakes and those preferring freshwater bodies. Spatial processes were negligible. Our results show the strength of a temporal approach in the study of metacommunities, against a single snapshot, stressing differences at the onset and the end of hydroperiod in temporary water bodies, but still surpassed by species sorting effects under a steep environmental gradient.     

气候变化对湖库水环境的潜在影响研究进展

本文着重归纳气候变化对湖库热力特性、冰期、溶解氧、营养盐、浮游植物和水生植物等方面的影响规律,探讨气候变化对湖库水环境潜在影响的区域差异,讨论现有研究方法的优缺点和发展前景.研究表明,气候变暖对湖库物理过程的影响最为显著;热带草原气候和温带海洋性气候对于气候变暖和降雨变化的响应较其他气候类型突出;气候变化对湖库水环境的影响效果具有两面性.通过分析各气候类型中气候变暖对磷水平的潜在影响差异表明,亚热带季风气候的湖库更可能受气候变暖的影响趋于富营养状态.在今后研究中,建议深入开展各气候类型中区域性气候变化对湖库水环境影响的实例研究.     

气候变化对长江流域汉江和赣江径流的影响

近几年来,国家气候中心己经建立了中国主要四大流域气候对水资源影响评估的模式框架.本文拟进一步证明其中之一的两参数分布式月水量平衡水文模式对长江之上汉江和赣江两子流域径流的模拟能力,结果表明该水文模式对目前气候条件下径流模拟效果较好,运行稳定,可用于实时业务运行.在此基础上,利用ECHAM4和HadCM2两GCM(General Circulation Model)未来气候情景模拟结果及目前实测气候情况,对汉江和赣江两子流域的径流对未来气候变化的敏感性进行评估.经检验,两GCM对未来气候,特别是降水情景模拟存在一定差异,因此,造成径流对气候变化的响应不同,这充分反映了全球模式模拟结果不确定性在气候变化影响研究中的重要性.     

Rapid expansion of glacial lakes caused by climate and glacier retreat in the Central Himalayas

Glacial lake outburst floods are among the most serious natural hazards in the Himalayas. Such floods are of high scientific and political importance because they exert trans‐boundary impacts on bordering countries. The preparation of an updated inventory of glacial lakes and the analysis of their evolution are an important first step in assessment of hazards from glacial lake outbursts. Here, we report the spatiotemporal developments of the glacial lakes in the Poiqu River basin, a trans‐boundary basin in the Central Himalayas, from 1976 to 2010 based on multi‐temporal Landsat images. Studied glacial lakes are classified as glacier‐fed lakes and non‐glacier‐fed lakes according to their hydrologic connection to glacial watersheds. A total of 119 glacial lakes larger than 0.01 km² with an overall surface area of 20.22 km² (±10.8%) were mapped in 2010, with glacier‐fed lakes being predominant in both number (69, 58.0%) and area (16.22 km², 80.2%). We found that lakes connected to glacial watersheds (glacier‐fed lakes) significantly expanded (122.1%) from 1976 to 2010, whereas lakes not connected to glacial watersheds (non‐glacier‐fed lakes) remained stable (+2.8%) during the same period. This contrast can be attributed to the impact of glaciers. Retreating glaciers not only supply meltwater to lakes but also leave space for them to expand. Compared with other regions of the Hindu Kush Himalayas (HKH), the lake area per glacier area in the Poiqu River basin was the highest. This observation might be attributed to the different climate regimes and glacier status along the HKH. The results presented in this study confirm the significant role of glacier retreat on the evolution of glacial lakes. Copyright © 2014 John Wiley & Sons, Ltd.