ON THE SYMMETRIC DEVELOPMENT OF MESOSCALE DISTURBANCES

The effects of baroclinic basic flow on a paralleled mesoscale disturbance development are investigated.By using the WKB method,two-dimensional perturbation equations with the anelastic approximation areanalyzed.The result indicates that the symmetric development of a mesoscale disturbance is due to the in-homogeneous thermal wind deviations and unstationality of the basic field.     

Hydrodynamics of Lake Lugano

The hydrodynamic processes in the Lake of Lugano (Lago di Lugano) have been the object of three major measuring campaigns. The first during summer 1979 in the North Basin, the second in the autumn of 1984 in the South Basin and the last in 1989 again in the North Basin. It is expected that analysis of the collected data in conjunction with theoretical concepts will yield conclusive findings on the driving forces and hydrodynamics of the lake. Numerical models have been applied to the lake and the results have been compared to the measurements. Some models calculate the periods and distributions of amplitude, as well as surface velocities and internal seiches. Other models calculate wind-induced water circulation. Evidence is given to the peculiarities of the North Basin and the difficulties related with the depth-width ratio and with its deep chemical stratification.     

Current structure and volume transport of the Soya Warm Current in summer

ADCP, CTD and XBT observations were conducted to investigate the current structure and temperature, salinity and density distributions in the Soya Warm Current (SWC) in August, 1998 and July, 2000. The ADCP observations clearly revealed the SWC along the Hokkaido coast, with a width of 30–35 km and an axis of maximum speed of 1.0 to 1.3 ms⁻¹, located at 20–25 km from the coast. The current speed gradually increased from the coast to a maximum and steeply decreased in the offshore direction. The SWC consisted of both barotropic and baroclinic components, and the existence of the baroclinic component was confirmed by both the density front near the current axis and vertical shear of the alongshore current. The baroclinic component strengthened the barotropic component in the upper layer near the axis of the SWC. The volume transport of the SWC was 1.2–1.3 SV in August, 1998 and about 1.5 SV and July, 2000, respectively. Of the total transport, 13 to 15% was taken up by the baroclinic component. A weak southeastward current was found off the SWC. It had barotropic characteristics, and is surmised to be a part of the East Sakhalin Current.     

Meso-scale available gravitational potential in the world oceans

The pitfalls of applying the commonly used definition of available gravitational potential energy （AGPE） to the world oceans are re-examined. It is proposed that such definition should apply to the meso-scale problems in the oceans, not the global scale. Based on WOA98 climatological data, the meso-scale AGPE in the world oceans is estimated. Unlike previous results by Oort et al. , the meso-scale AGPE is large wherever there is a strong horizontal density gradient. The distribution of meso-scale AGPE reveals the close connection between the baroclinic instability and the release of gravitational potential energy stored within the scale of Rossby deformation radius.     

Instability of planetary waves in a high vertical resolution model

Abstract

A high vertical resolution model is used to examine the instability of a baroclinic zonal flow and a finite amplitude topographically forced wave. Two families of unstable modes are found, consisting of zonally propagating most unstable modes, and stationary unstable modes. The former have time scale and spatial structure similar to baroclinic synoptic disturbances, but are localized in space due to interaction with the zonally asymmetric forcing. These modes transport heat efficiently in both the zonal and meridional directions. The second family of stationary unstable modes has characteristics of modes of low frequency variability of the atmosphere. They have time scales of 10 days and longer, and are of planetary scale with an equivalent barotropic vertical structure. The horizontal structure resembles blocking flows. They are maintained by available potential energy of the basic wave, and have large zonal heat fluxes. The results for both families of modes are interpreted in terms of an interaction between forcing and baroclinic instability to create favoured regions for eddy development. Applications to baroclinic planetary waves are also considered.     

Failure and size effect for notched and unnotched concrete beams

Modelling failure in geomaterials, concrete or other quasi‐brittle materials and proper accounting for size effect, geometry and boundary effects are still pending issues. Regularised failure models are capable of describing size effect on specimens with a specific geometry, but extrapolations to other geometries are rare, mostly because experimental data presenting size effect for different geometries and for the same material are lacking. Three‐point bending fracture tests of geometrically similar notched and unnotched specimens are presented. The experimental results are compared with numerical simulations performed with an integral‐type non‐local model. Comparisons illustrate the shortcomings of this classical formulation, which fails to describe size effect over the investigated range of geometries and sizes. Finally, experimental results are also compared with the universal size effect law. Copyright © 2013 John Wiley & Sons, Ltd.     

斜压涡度的变化与台风暴雨的关系研究

台风暴雨作为台风引起的最主要灾害之一,一直被人们关注。台风常被认为是对称结构,但从实际状况来看台风的非对称性非常明显,所以有必要研究斜压性涡度在台风中的表现。在高分辨率数值模拟的基础上,通过引入斜压涡度的概念,分析和总结了斜压涡度在2009年台风“莫拉克”暴雨过程中的表现。通过模拟与分析得到如下的结果:斜压涡度和MPV对比,可以看出在登陆前和登陆后,明显低层斜压涡度有更强的异常信号,围绕台风内核呈现正负正的位相特点;从沿着台风中心时间剖面可以看出,登陆前斜压涡度低层多为负正负的位相,并且随着时间的推移,斜压涡度有从大气的高层向台风的移动中心传递的趋势,即在台风即将到达时原先的正涡度被替换为负涡度,所以对其移动有一定指示意义;在台风“莫拉克”过台湾岛时,其斜压涡度表现为负涡度消失,在山地附近有正涡度生成,完成过岛,台风中心被替换;斜压涡度的异常值主要位于大气的低层时,一般会产生较强的降水。      

ADS 80数码航摄系统应用及精度探讨

以项目部分区域为实例,通过项目工作流程及分阶段作业细节、进度状况、精度指标等的统计,阐述了使用ADS 80数码航摄系统,用少量像控点就可进行加密和测图,大大减少了外业控制测量工作及成本,成果满足大比例地形图精度要求,并能快速提高生产进度,缩短成图周期。     

对流层上层斜压波包活动与2003年江淮流域梅雨的关系

利用NCEP/NCAR再分析和中国740站逐日降水资料, 研究了2003年淮河流域梅雨期间对流层上层斜压波动的传播情况。结果发现, 斜压波组织成波包向下游传播且具有明显的下游频散效应。波动起源于巴尔喀什湖西北侧, 沿着西北－东南向的路径向东南传播, 传至江淮流域大约需要3天。斜压波包所带来的扰动能量为江淮流域暴雨的发生发展提供了必要的能量积聚。通过与1998和1997年这两个梅雨年份的比较, 发现1998年异常强梅雨年的斜压波包的活动特征与2003年的相似, 但在梅雨降水非常偏少的1997年, 未发现有明显的斜压波包向下游的传播。     

广西大暴雨期间西南低涡涡动动能收支分析

Based on the 6-hour-interval reanalysis data with 1°× 1°resolution from the National Center for Environmental Prediction/the National Center for Atmospheric Research （NCEP/NCAR）, the eddy kinetic energy （EKE） budget of a southwest vortex （SWV） that caused heavy rainfall in Guangxi over South China （from 1200 UTC 11 to 0000 UTC 13 June） is calculated. The results are as follows： （a） The SWV is a kind of subtropical vortex, with characteristics of both an extratropical vortex and a tropical vortex. （b） In the case examined, large-scale circulation and other perturbation fields contributed to the formation and development of the SWV. （c） When the SWV moved from weak large-scale circulation EKE areas to strong ones, the EKE of the SWV increased, and vice versa. （d） Sub-grid processes and frictional dissipation were the main sinks of the SWV EKE, which contributed to the decay of the SWV. （e） The residual term （RES） and the Total （composite effect of all right hand side （rhs） terms except the RES in the EKE equation） varied almost in the same tendency, which kept the EKE varying in a moderate way. （f） The EKE between 550 hPa and 850 hPa increased most intensively, corresponding to the vertical stretching of the SWV.