A SIMPLE PROGNOSTIC CLOSURE ASSUMPTION TO DEEP CONVECTIVE PARAMETERIZATION:I

In this work,the problem of dependency of the predicted rainfall upon the grid-size in mesoscale numerical weatherprediction models is addressed.We argue that this problem is due to (i) the violation of the quasi-equilibrium assump-tion,which is underlying most existing convective parameterization schemes,and states that the convective activity maybe considered in instantaneous equilibrium with the larger-scale forcing;and (ii) the violation of the hydrostatic approx-imation,made in most mesoscale models,which would induce too large-scale circulation in occurrence of strong con-vection.On the contrary,meso-β and meso-α scale models,i.e.models with horizontal grid size ranging from 10 to 100km,have a capacity to resolve motions with characteristic scales close to the ones of the convective motions.Wehypothesize that a possible way to eliminate this problem is (i) to take a prognostic approach to the parameterization ofdeep convection,whereby the quantities that describe the activity of convection are no longer diagnosed from the instan-taneous value of the large-scale forcing,but predicted by time-dependent equations,that integrate the large-scale forc-ing over time;(ii)to introduce a mesoscale parameter which varies systematically with the grid size of the numericalmodel in order to damp large-scale circulation usually too induced when the grid size becomes smaller (from 100 km to10 kin).We propose an implementation of this idea in the frame of one existing scheme,already tested and used for along time at the French Weather Service.The results of the test through one-dimensional experiments with the Phase Ⅲof GATE data are reported in this paper;and the ones on its implementation in the three-dimensional model with theOSCAR data will be reported in a companion paper.     

新疆北天山西段构造应力场分析

利用地表构造形迹、地震震源机制解、现代水系展布的优势方向以及激光全息光弹模拟等综合分析方法,研究了北天山西段(东经82°～86°)地壳构造应力场的基本特征。指出,该区构造应力场的主压应力方向为近南北向。通过激光全息光弹实验获得模型的等差线及等和线条纹图,从而求解各点的主张应力σ_1主压应力σ_2和最大剪应力τ_max的相对值并绘制相应的等值线图,结果发现:实验区σ_1值普遍偏低,σ_2值明显偏大,说明本区处于整体受压状态。τ_max值的分布较均匀,仅在一些断裂的交汇部位和端点剪应力值较高。分析结果认为:萨尔萨拉西南、独山子——安集海断裂西端、乌苏林场西南、阿尔夏特一带、婆罗科努达坂东南都是围压很高的剪应力集中区。这些地区易积累大量的应变能而产生突发式剪切破裂和粘滑引起强烈地震,是在地震预报中值得注意的地震危险地段。     

Phase transformations in the earth's mantle and subducting slabs: Implications for their compositions, seismic velocity and density structures and dynamics

Abstract Phase transformations in model mantle compositions and those in subducting slabs have been reviewed to a depth of 800 km on the basis of recent high-pressure experimental data. Seismic velocity and density profiles in these compositions have also been calculated using these and other mineral physics data. The nature of the seismic velocity and density profiles calculated for a pyrolite composition was found to generally agree with those determined by seismic observations (e.g. PREM). The locations of the seismic discontinuities at 400 and 670 km correspond almost exactly to the depths where the transformations of the olivine component to denser phases take place. Moreover, the steep gradients in the seismic velocity/density profiles observed between these depths are qualitatively consistent with those expected from the successive transformations in the complementary pyroxene-garnet component in the pyrolite composition. Further, the calculated seismic velocity and density values agree well with those observed in the upper mantle and mantle transition region within the uncertainties attached to these calculations and observations. Pyrolite or peridotite compositions are thus most likely to represent the composition of the mantle above 670 km depth, although some degrees of chemical heterogeneity may exist in the transition region. The observed sharp discontinuous increases of seismic velocities and density at this depth may be attributed either to the phase transformation to a perovskite-bearing assemblage in pyrolite or to chemical composition changes. Density profiles in subducted slabs have been calculated along adequate geotherms assuming that the slabs are composed of the former oceanic crust underlain by a thicker harzburgitic layer. It is shown that the former oceanic crust is substantially less dense than the surrounding pyrolite mantle at depths below 670 km, while it is denser than pyrolite in the upper mantle and the transition region. The subducted former oceanic crust may be trapped in this region, forming a geochemically enriched layer at the upper mantle-lower mantle boundary. Thick and cool slabs may penetrate into the lower mantle, but the chemically derived buoyancy may result in strong deformation and formation of megalith structures around the 670 km seismic discontinuity. These structures are consistent with those detected by recent seismic tomography studies for subduction zones.     

A SIMPLE PROGNOSTIC CLOSURE ASSUMPTION TO DEEP CONVECTIVE PARAMETERIZATION:Ⅱ

A series of 3D predictions,dealing with the development of a heavy storm observed during the OSCAR experiment,were carried out by utilizing the PERIDOT model,and introducing alternatively the cumulus parameterization scheme of Bougeault (1985) and the prognostic one (Chen,1989;Chen and Bougeault,1993),with three different grid sizes:160 km,80 km,40 km.The feasibility of the new prognostic scheme and its improvement on the problem of dependency of the predicted rainfall upon the grid size of the numerical model were verified by comparison of the rainfall observed and those predicted.The results demonstrate that,in general,the predicted rainfall increases when the grid size decreases for both diagnostic and prognostic schemes.However,with the new prognostic scheme,the numerical model is capable,on the one hand,for the larger grid sizes,to increase the rainfall,which is under-estimated with the scheme of Bougeault (1985);on the another hand,for the smaller grid sizes,to reduce the rainfall,which is usually over-estimated.In other word,there is an obvious improvement on the problem under study.     

观测点的变形过程曲线“三点法”修匀通用计算公式

本文推导了“三点法”修匀通用计算公式．采用该公式便于计算机编程自动处理，计算结果精度比图解法精度高．     

1991年江淮暴雨期间环流异常的动力延伸预报试验

介绍了利用Ｔ４２Ｌ９模式对１９９１年夏季江淮流域暴雨期间旬和月平均环流异常的动力延伸预报（ＤＥＲＦ）试验和利用ＯＳＵ－ＡＧＣＭ进行青藏高原热力异常敏感性试验的结果，指出Ｔ４２Ｌ９模式对造成暴雨的环流异常有一定的预报能力，并证实高原的热力异常是引起江淮暴雨的一个重要因子。     

不同暴雨系统中潜热反馈作用的对比研究

选择两种类型的暴雨个例用数值试验研究了不同条件下潜热反馈作用的大小，结果发现对于不同的暴雨系统，潜热作用差别很大，“６２６”（１９８６年６月２６日）京津冀暴雨中它使雨量增加约一倍，而“７５８”（１９７５年８月７日）河南暴雨却增加约四倍。此外，潜热反馈对高低空急流强度、位置，以及对上升运动大小的影响程度，也都是在“７５８”暴雨过程中较大。数值试验证明了造成这种差别的重要原因是高空急流强度和风速铅直切     

贵州丹寨汞矿方解石的微观特征及其与构造成矿关系初探

鉴于方解石是研究低温碳酸盐型汞矿床构造应力作用的良好对象,作者对贵州丹寨汞矿床中24件方解石样品进行构造形变及构造成矿模拟试验,经光学显微镜及透射电子显微镜对比观察指出:多种应力作用叠加及微观构造形变的先后生成关系,可视为多期次构造动力作用的结果;汞矿的成矿作用和构造作用的相关和同步性,说明构造作用既可提供成矿的空间,又是促进成矿的动力。     

工程地质测试技术与方法

本文分别论述了室内试验,原位测试,资料整理及数值分析方法、地基加固4个方面所取得的进展,并指出存在问题及努力的方向     

Selective dissolution of late cretaceous and earliest tertiary calcareous nannofossils: Experimental evidence

The effects of carbonate dissolution on the taxonomic composition of ancient nannofossil assemblages were investigated by deploying them on a deep mooring at depths of 1039 m–5500 m for 117 days in the Sargasso Sea. The relative proportions of only a few taxa change significantly with increasing dissolution: Cruciplacolithus primus is by far the most susceptible and Micula staurophora by far the most resistant species. The average dissolution indices calculated for the deployed assemblages closely follow the gradients of other dissolution indicators in the North Atlantic.