A Nonlinear Representation of Model Uncertainty in a Convective-Scale Ensemble Prediction System

How to accurately address model uncertainties with consideration of the rapid nonlinear error growth characteristics in a convection-allowing system is a crucial issue for performing convection-scale ensemble forecasts. In this study, a new nonlinear model perturbation technique for convective-scale ensemble forecasts is developed to consider a nonlinear representation of model errors in the Global and Regional Assimilation and Prediction Enhanced System(GRAPES)Convection-Allowing Ensemble Predi...     

珠穆朗玛峰地区雪冰中重金属浓度与季节变化

对2005 年9 月采自珠穆朗玛峰北坡海拔6523 m 的东绒布冰川积累区一批雪坑样品中重金属Ba, Co, Cu, Zn 和Pb 的浓度利用电感耦合等离子体质谱仪进行了测试, 重金属浓度范围分别为(pg/ml); Ba2~227、Co2.8~15.7、Cu 10~120、Zn29~4948、Pb14~142。并利用气体稳 定同位素质谱仪MAT-252 对样品稳定氧同位素比率(δ¹⁸O) 进行了测试, 雪坑样品对应的时间为2004 年夏到2005 年秋, δ¹⁸O和重金属元素的浓度都存在着季节变化特征。在夏季风期间δ¹⁸O 值和重金属元素的浓度都很低,而在非夏季风期间δ¹⁸O值和重金属元素浓度升高,反映了不同的水汽来源对重金属浓度季节变化的影响及其环境意义。Co, Cu, Pb, Zn 的地壳富集系数(EF_c) 分别为: 3.6、27、33、180, 表明该地区Pb, Cu, Zn 已经受到了人类活动的污染, 其中Zn 受到的污染最大。     

西安高陵人工林土壤干层与含水量季节变化研究

通过野外调查和室内测定,利用烘干称重法对高陵地区丰水年前后不同人工林下0~6 m土壤含水量及土壤水分的季节变化进行研究。结果表明,2002年高陵田家村中国梧桐林和杨树林下160~400 cm范围内均已发育了土壤干层。经过2003年丰水年充沛的降水补给,2004年高陵团庄槐树林、杏树林0~6 m土层均未出现土壤干层,说明水分在丰水年得到很好恢复。丰水年后梨、杏、槐三种人工林160~400、410~600 cm层位土壤含水量均显示春季最高,夏季次之,秋季降到最低或略微上升。     

辽宁省霾天气季节变化特征及其主导因子分析

利用辽宁省51个地面气象观测站的能见度、均一化相对湿度和天气现象资料,采用最优距离法和固定比例法对能见度资料进行一致性处理,重建了1961—2020年的辽宁省逐日霾资料,并利用该资料对辽宁省年和四季霾日时空变化特征和主导因子进行分析。结果表明,1961—2020年辽宁省平均年霾日呈显著增加趋势[2.1 d·(10 a)^-1],但2015年以来霾日显著减少;空间上,年和四季霾日呈现一致的分布特征,均存在1个高值中心(沈阳)和2个副高值中心(北票和锦州),年平均霾日分别为139、52、46 d,辽东和辽西山区为霾日低发区,年平均霾日在20 d以内。风向和风速是霾日形成的重要气象因子,西南偏南风增加带来的暖湿气流对春季、夏季和秋季霾日的形成贡献较大,北风的减少则对冬季霾日的形成贡献较大。霾发生时辽宁省春季、夏季和秋季发生西南偏南风的频率分别由11.4%、12.1%和8.0%增加至15.8%、19.8%和13.5%,冬季则表现为北风发生频率的减少和静风发生频率的增加;霾发生时四季风速均较平均状况偏小,说明小风有利于霾的形成。辽宁省霾长期演变受到污染物排放、风力因子和环境政...     

Paleoclimate studies and natural-resource management in the Murray-Darling Basin I: past,present and future climates

This paper provides an incisive review of paleoclimate science and its relevance to natural-resource management within the Murray-Darling Basin (MDB). The drought of 1997–2010 focussed scientific, public and media attention on intrinsic climate variability and the confounding effect of human activity, especially in terms of water-resource management. Many policy and research reviews make statements about future planning with little consideration of climate change and without useful actionable knowledge. In order to understand future climate changes, modellers need, and demand, better paleoclimate data to constrain their model projections. Here, we present an insight into a number of existing long-term paleoclimate studies relevant to the MDB. Past records of climate, in response to orbital forcing (glacial–interglacial cycles) are found within, and immediately outside, the MDB. High-resolution temperature records, spanning the last 10⁵ years, exist from floodplains and cave speleothems, as well as evidence from lakes and their associated lunettes. More recently, historical climate records show major changes in relation to El Niño–Southern Oscillation cycles and decadal shifts in rainfall regimes. A considerable body of research currently exists on the past climates of southeastern Australia but, this has not been collated and validated over large spatial scales. It is clear that a number of knowledge gaps still exist, and there is a pressing need for the establishment of new paleoclimatic research within the MDB catchment and within adjacent, sensitive catchments if past climate science is to fulfil its potential to provide policy-relevant information to natural-resource management into the future.     

Hydrodynamic and isotopic investigations for evaluating the mechanisms and amount of groundwater seepage through a rockslide dam

This study addresses the influence of landslide dams on surface water drainage and groundwater flow. In the study area of Scanno Lake and Sagittario River (Central Italy), a limestone rockslide‐avalanche formed a lake, which has an outlet that is occasionally active, showing infiltration into the rockslide dam. Several springs are present at the lake's base and are partly fed by seepage through the rockslide debris. Piezometric surveys, discharge measurements, pumping tests and chemical analyses are tools used to build a conceptual model of the groundwater flow and to evaluate the flow through the rockslide debris. Seasonal water isotopic signatures validate the assumed model, showing a mixing of infiltration recharge and groundwater seepage throughout the rockslide debris. Various recharge areas have been found for springs, pointing out those directly fed by the rockslide debris aquifer. Hypotheses about seasonal groundwater mixing between the regional carbonate aquifer and the rockslide debris aquifer are supported by isotope results. Seasonal changes in groundwater table level due to recharge and surface losses from seasonal outlet have been correlated with isotopic groundwater composition from the rockslide debris aquifer and the downstream springs; this relationship highlights the role of the rockslide dam body on the hydrodynamics of the studied area. Relationships between surface waters and groundwater in the area have been completely understood on the basis of water isotopic fingerprinting, finally obtaining a complete evaluation of groundwater renewable resources and its regimen. Copyright © 2010 John Wiley & Sons, Ltd.     

Can Eddy Forcing be Responsible for the Spatial Structure of the Northern Hemisphere Annular Mode?

In order to study the origin of the spatial structure of the Northern Hemisphere Annular Mode (NAM),a linear stochastic model is constructed empirically from the output of a GCM run.Optimal stochastic forcing in terms of the maximum variance contribution,which may be potentially related to the maintenance of the NAM,is investigated.Theoretical analysis on the dominant non-modal response to the stochastic forcing shows that this dominance is jointly decided by the properties of forcing and the non-modal grow...     

Developing a large‐scale water‐balance approach to seasonal forecasting: application to the 2012 drought in Britain

Seasonal hydrological forecasts, or outlooks, can potentially provide water managers with estimates of river flows and water resources for a lead time of several months ahead. An experimental modelling tool for national hydrological outlooks has been developed which combines a hydrological model estimate of sub‐surface water storage across Britain with a range of seasonal rainfall forecasts to provide estimates of area‐wide hydrological conditions up to a few months ahead. The link is made between a deficit in sub‐surface water storage and a requirement for additional rainfall over subsequent months to enable sub‐surface water storage and river flow to return to mean monthly values. The new scheme is assessed over a recent period which includes the termination of the drought that affected much of Britain in the first few months of 2012. An illustration is provided of its use to obtain return‐period estimates of the ‘rainfall required’ to ease drought conditions; these are well in excess of 200 years for several regions of the country, for termination within a month of 1 April 2012, and still exceed 40 years for termination within three months. National maps of sub‐surface water storage anomaly show for the first time the current spatial variability of drought severity. They can also be used to provide an indication of how a drought situation might develop in the next few months given a range of possible future rainfall scenarios. © 2013 CEH/Crown and John Wiley & Sons, Ltd.     

西北地区太阳辐射量变化的研究

根据西北地区１５个日射甲种站观测的近３０年来到达地面的太阳辐射量观测资料，经方差分析表明：太阳散射辐射量有２／５的地区在增加，２／５的地区在减少，还有１／５的地区太阳散射、直接辐射量在时间变化上差异都不明显；太阳直接辐射量有４／５的地区在显著减减少；太阳总辐射量几乎各地都在减少，这种减少趋势大致从１９７８年开始，并且用太阳辐射倾向率的形式概括出３种太阳辐射量季节变化类型。     

MODULATION OF ATMOSPHERIC THERMAL AND MECHANICAL FORCINGS AND NUMERICAL MODELING OF MEAN MERIDIONAL CIRCULATION

Upon investigating the relative locations of internal and external forcing and the resultant mean meridional circulation,it was found that thermal forcing and mechanical forcing for the formation of atmospheric mean meridional circulation are modulated by a certain ratio.This ratio is determined by the inherent baroclinity,static stability and absolute vorticity of the atmosphere.By employing a parameterization scheme for radiative heating and condensation heating,together with the analysisdata of the European Center for Medium-range Weather Forecasts,the mean meridional circulation for January wassimulated numerically.It was found that latent heat release in the tropics may result in the formation of double-layeredHadley circulation,so do the eddy momentum transfer processes.On the other hand,mean meridional circulations in extra-tropics are mainly determined by external momentum forcing and atmospheric properties of eddy momentum andheat transfer.