Towards a comprehensive approach to parameter estimation in land surface parameterization schemes

In climate models, the land–atmosphere interactions are described numerically by land surface parameterization (LSP) schemes. The continuing improvement in realism in these schemes comes at the expense of the need to specify a large number of parameters that are either directly measured or estimated. Also, an emerging problem is whether the relationships used in LSPs are universal and globally applicable. One plausible approach to evaluate this is to first minimize uncertainty in model parameters by calibration. In this paper, we conduct a comprehensive analysis of some model diagnostics using a slightly modified version of the Simple Biosphere 3 model for a variety of biomes located mainly in the Amazon. First, the degree of influence of each individual parameter in simulating surface fluxes is identified. Next, we estimate parameters using a multi‐operator genetic algorithm applied in a multi‐objective context and evaluate simulations of energy and carbon fluxes against observations. Compared with the default parameter sets, these parameter estimates improve the partitioning of energy fluxes in forest and cropland sites and provide better simulations of daytime increases in assimilation of net carbon during the dry season at forest sites. Finally, a detailed assessment of the parameter estimation problem was performed by accounting for the decomposition of the mean squared error to the total model uncertainty. Analysis of the total prediction uncertainty reveals that the parameter adjustments significantly improve reproduction of the mean and variability of the flux time series at all sites and generally remove seasonality of the errors but do not improve dynamical properties. Our results demonstrate that error decomposition provides a meaningful and intuitive way to understand differences in model performance. To make further advancements in the knowledge of these models, we encourage the LSP community to adopt similar approaches in the future. Copyright © 2012 John Wiley & Sons, Ltd.     

A physically constrained wavelet-aided statistical model for multi-decadal groundwater dynamics predictions

A physically constrained wavelet-aided statistical model (PCWASM) is presented to analyse and predict monthly groundwater dynamics on multi-decadal or longer time scales. The approach retains the simplicity of regression modelling but is constrained by temporal scales of processes responsible for groundwater level variation, including aquifer recharge and pumping. The methodology integrates statistical correlations enhanced with wavelet analysis into established principles of groundwater hydraulics including convolution, superposition and the Cooper–Jacob solution. The systematic approach includes (1) identification of hydrologic trends and correlations using cross-correlation and multi-time scale wavelet analyses; (2) integrating temperature-based evapotranspiration and groundwater pumping stresses and (3) assessing model prediction performances using fixed-block k-fold cross-validation and split calibration-validation methods. The approach is applied at three hydrogeologicaly distinct sites in North Florida in the United States using over 40 years of monthly groundwater levels. The systematic approach identifies two patterns of cross-correlations between groundwater levels and historical rainfall, indicating low-frequency variabilities are critical for long-term predictions. The models performed well for predicting monthly groundwater levels from 7 to 22 years with less than 2.1 ft (0.7 m) errors. Further evaluation by the moving-block bootstrap regression indicates the PCWASM can be a reliable tool for long-term groundwater level predictions. This study provides a parsimonious approach to predict multi-decadal groundwater dynamics with the ability to discern impacts of pumping and climate change on aquifer levels. The PCWASM is computationally efficient and can be implemented using publicly available datasets. Thus, it should provide a versatile tool for managers and researchers for predicting multi-decadal monthly groundwater levels under changing climatic and pumping impacts over a long time period.     

Estimation of Nash's IUH parameters using stochastic search algorithms

In rainfall–runoff studies, it is often necessary to change the duration of a given unit hydrograph. Nash's Instantaneous Unit Hydrograph (IUH) is an ideal method that eliminates the hydrograph duration. This paper presents the results of the application of search algorithms, namely a genetic algorithm and hill climbing, to develop the IUH that minimizes the error between the observed and generated hydrographs. Also the performance of these methods has been compared with that of the classical method used for estimation of IUH, namely the method of moments. The genetic algorithm is a popular search procedure for function optimization that applies the mechanics of natural genetics and natural selection to explore a given search space. Hill climbing is an optimization technique that belongs to the family of local search and algorithms can be used to solve problems that have many solutions, with some solutions better than others. The results obtained from both the genetic algorithm and hill climbing algorithm for estimation of Nash's IUH parameters were compared with the results obtained by the method of moments for storms from two river basins that are located in different climatic regions. It was found that both the genetic algorithm and hill climbing provided improved and consistent results. Copyright © 2008 John Wiley & Sons, Ltd.     

矿物热电系数及其在地质找矿中的应用

作者的研究表明,在非本征激发区,矿物热电系数随着活化温度的增高而增大;在本征激发区,随活化温度的增高而减小。矿物晶体中所含杂质的种类和含量多少决定矿物的导电类型。矿物热电系数可广泛应用于地质找矿和矿床评价中,以黄铁矿为例,在同一水平面上的含金矿脉,矿脉中黄铁矿热电系数正值高时,其矿石含金量也高。应用黄铁矿热电系数的正高值、混合型和负值可确定矿体和矿体的剥蚀深度。     

辽宁省中晚元古代—中生代页岩的化学元素丰度及其演化特征

作者利用全省不同地质时代和不同地质构造单元内的页岩41种元素的分析数据,计算出辽宁省全域内的页岩元素丰度休系。同时探讨了元素从中、晚元古代至中生代的演化规律,指出Ca、Cd、Sb、As、Na、Mn、P、Sr的元素丰度随时间序列的演化不断增长,B、F、K、Rb、W、Mg则显示出降低的趋势。某些元素比值从老至新表现出明显的规律性变化,如Sr/Ba、Ca/Mg值的演化具有阶段性,K/Na、Th/U值的演化具有方向性,Al/Ti值的演化则具有周期性。     

鄂尔多斯盆地及其周边的新构造运动

本区新构造运动十分活跃,表现出多次波动性,周边山系呈不均衡抬升,盆地则呈不均衡沉降,因此使盆地呈现不对称的簸箕状,盆地中的水系结构也呈现不对称性。区内构造变形主要有褶皱、断裂、新隆起、新坳陷、拱曲和掀斜等,并产生现代地震、地热和火山活动。不均衡掀斜是导致上述现象的根本原因。     

洛川黄土地层渗透性与孔隙性的关系

本文用逐步回归分析方法对洛川黄土孔隙性诸要素进行了变量筛选,选出了影响渗透系数的孔隙要素,并建立了随机数学模型,定量解决了影响渗透系数的孔隙多少和孔隙形状问题,初步确定出了洛川黄土地层透水性与孔隙性的关系。     

SOFTWARE REVIEWS

ATLAS*GIS , Version 1.0. ATLAS*MapMaker , Version 4.0. FIVFIV-SINSIN , Release 9.0. Geo-EAS , Version 1.2.1. Evan Englund Sim City , Version 1.0 Statistix , Version 3.1.     

用线性规划法求解瞬变电磁场反射系数

讨论了在水平层状介质中的反射系数的物理意义 ,推出时间域含有以反射系数序列为未知项的欠定方程组 ,提出用线性规划法求解瞬变电磁场反射系数序列 ,并给出求解思路和程序框图。对两个理论模型进行了处理 ,计算出了其反射系数。算例分析结果表明 ,算法可靠 ,程序可行。这一方法可用于瞬变电磁成像数值计算中。