不同陆面方案对降水模拟的影响

基于区域气候模式RegCM4.0(Regional Climate Model 4.0),分别选取BATS(Biosphere Atmosphere Transfer Scheme)和CLM(Community Land Model)陆面方案,对2001-2005年中国的气候状况进行模拟,并将模拟结果与CRU(Climatic Research Unit)及GPCP(Global Precipitation Climatology Project)降水资料进行对比,研究不同陆面方案对降水模拟的影响。结果表明:在两种陆面方案下,区域气候模式均较合理地模拟出了中国降水的空间分布、时间变化;模拟降水对陆面方案敏感,RegCM_BATS总体上表现为正偏差,在东北区域的模拟偏差较大;RegCM_CLM表现为负偏差,在长江以南区域的模拟偏差较大;模拟结果的偏差在夏季较大,冬季较小;两模式模拟结果间的差异在空间上由东南向西北减少;两模式均较准确地模拟了不同强度降水出现频率的分布形势,总体上RegCM_CLM模拟低强度降水偏多;高强度降水偏少,而RegCM_BATS模拟低强度降水偏少,高强度降水偏多;不同陆面方案对地表蒸发量以及地表潜热通量模拟的差异是导致模拟降水差异的主要原因,夏季地表蒸发对降水的影响较冬季更强;水汽平流输送对两模式模拟降水差异的影响较小。     

破碎岩体浅埋大跨公路隧道开挖方案对比研究

三车道高速公路隧道通常跨度较大、高跨比较小属于大跨扁平隧道。这种结构型式对围岩稳定和结构受力均产生不利影响,因此施工中有必要通过开挖方案比选确定合理的开挖方法。江苏省宁波-常州高速公路茅山东隧道为上下行分离式双向6车道浅埋大跨扁平隧道。对于破碎的Ⅳ级围岩,针对设计阶段拟采用CRD法和实际施工采用下断面左右分部台阶法的开挖方案在设计支护条件下的三维数值模拟,从理论上分析了下断面左右分部台阶法是可行的。与实际施工过程的监控量测结果进行对比分析,进一步证实了实际开挖方案的合理性。研究成果可以为同类工程的设计与施工提供理论参考。     

A temporally second-order accurate Godunov-type scheme for solving the extended Boussinesq equations

A numerical scheme for solving the class of extended Boussinesq equations is presented. Unlike previous schemes, where the governing equations are integrated through time using a fourth-order method, a second-order Godunov-type scheme is used thus saving storage and computational resources. The spatial derivatives are discretised using a combination of finite-volume and finite-difference methods. A fourth-order MUSCL reconstruction technique is used to compute the values at the cell interfaces for use in the local Riemann problems, whilst the bed source and dispersion terms are discretised using centred finite-differences of up to fourth-order accuracy. Numerical results show that the class of extended Boussinesq equations can be accurately solved without the need for a fourth-order time discretisation, thus improving the computational speed of Boussinesq-type numerical models. The numerical scheme has been applied to model a number of standard test cases for the extended Boussinesq equations and comparisons made to physical wave flume experiments.     

求解非稳定对流占优水质模型的非标准Galerkin有限元法

在求解非稳定地下水溶质运移模型时,若对流项占优,则模型表现出双曲方程的特性。针对这种特性,采用非标准Galerkin有限元方法进行求解是解决这类问题的有效途径。分别采用Wavelet-Galer-kin有限元方法、迎风有限元方法和特征有限元方法对强对流溶质运移模型进行了求解,并将其结果与标准Galerkin有限元和解析解进行对比。结果表明:标准Galerkin有限元方法会产生强烈的数值振荡;Wavelet-Galerkin有限元方法的时空定位效果好;迎风有限元方法能够有效降低数值振荡现象,但迎风因子对解的影响较大,而且会带来时间延迟;特征有限元方法能够提高解的精度,故可以认为特征有限元方法是求解强对流地下水溶质运移模型的首选方法。     

A LAYERED NUMERICAL MODEL FOR SIMULATING THE GENERATION AND PROPAGATION OF INTERNAL TIDES OVER CONTINENTAL SLOPE I. MODEL DESIGN

A layered three-dimensional nonlinear numerical model was constructed to simulate the generation and propagation of internal tides over the continental slope. The simulation was split into external mode computation (EMC) and internal mode computation (IMC) to minimize the computational load. IMC was carried out once after EMC was implemented N times. As to EMC, a semi-implicit numerical scheme was applied in such a way that the pressure gradient terms and the velocity divergence terms were discretized semi-implicitly, but the other terms were discretized explicitly. Eulerian-Lagrangian explicit discretization was applied to the convective terms simultaneously. As a result, the stability of EMC did not depend on the wave celerity and time step was not limited by the CFL condition. More than that, use of the conjugate gradient accelerated Jacobi method further improved the computational efficiency of the model.     

Preissmann隐式格式在分汊和环状河道中的应用

环状河道在平原地区水系中非常常见,分汊河道也较常见,对这两种河道基于Preissmann格式的水流计算提出了可行的方法。对圣维南方程组进行离散后,用追赶法对各河道进行演算,由水量平衡原理对各结点进行计算,就可求得河道各断面的水流情况。用长江下游江阴至青龙港及杨林段河道的实例进行计算,取得了较为理想的效果。     

21层大气环流模式IAP AGCM-III的设计及气候数值模拟I.动力框架

设计了IAP (InstituteofAtmosphericPhysics,ChineseAcademyofSciences)AGCM III,对其动力框架作说明和检验 ,时间积分采用改进的非线性迭代法。用Rossby Haurwitz波对框架进行了波型检验、能量检验和波速检验。结果表明 ,非线性迭代 3次的时间积分方案具有较好的稳定性 ,能够有效地抑制短波 ,同时对长波的歪曲较小 ,且时间积分步长可放得较大 ;该框架能够较长时间地保持Rossby Haurwitz 4波波型 ,在积分过程中能够较高精度地保持总有效能量守恒 ;模式计算的Rossby Haurwitz波速为每天西传 1 5个经度 ,这与理伦值很接近。     

双参数云物理方案中谱形参数作用分析和数值模拟试验

云物理参数化方案中,各种粒子通常采用Г谱分布函数n(D)=N0Dαexp(-λD)。双参数方案中谱参数截距N0和斜率λ通过预报给出,谱形参数α设为固定值。为了讨论谱形参数的作用,理论上分析了谱形参数取值对沉降过程和微物理源汇项的影响。利用MM5模式中增加的双参数显式云物理方案模拟了西北地区一次层状云降水过程,模拟针对雨滴谱的谱形参数rα不同取值分别做了试验。模拟结果基本符合理论分析,谱形参数rα变化时模拟出的地面降水和云的宏微观特征有差异。     

陆面过程模式研究简评

主要总结了陆面过程模式的发展状况, 对一些国际间合作进行的计划、试验成果以及我国在这方面的研究情况加以介绍和评述, 最后给出陆面模拟研究中存在的难点、问题及可能的解决途径.     

Investigation of Uncertainties of Establishment Schemes in Dynamic Global Vegetation Models简

In Dynamic Global Vegetation Models （DGVMs）, the establishment of woody vegetation refers to flowering, fertiliza- tion, seed production, germination, and the growth of tree seedlings. It determines not only the population densities but also other important ecosystem structural variables. In current DGVMs, establishments of woody plant functional types （PFTs） are assumed to be either the same in the same grid cell, or largely stochastic. We investigated the uncertainties in the competition of establishment among coexisting woody PFTs from three aspects： the dependence of PFT establishments on vegetation states; background establishment; and relative establishment potentials of different PFTs. Sensitivity experi- ments showed that the dependence of establishment rate on the fractional coverage of a PFT favored the dominant PFT by increasing its share in establishment. While a small background establishment rate had little impact on equilibrium states of the ecosystem, it did change the timescale required for the establishment of alien species in pre-existing forest due to their disadvantage in seed competition during the early stage of invasion. Meanwhile, establishment purely fiom background （the scheme commonly used in current DGVMs） led to inconsistent behavior in response to the change in PFT specification （e.g., number of PFTs and their specification）. Furthermore, the results also indicated that trade-off between irtdividual growth and reproduction/colonization has significant influences on the competition of establishment. Hence, further development of es- tablishment parameterization in DGVMs is essential in reducing the uncertainties in simulations of both ecosystem structures and successions.