Residual fields from extinct dynamos

Abstract

The paper explores some of the many facets of the problem of the generation of magnetic fields in convective zones of declining vigor and/or thickness. The ultimate goal of such work is the explanation of the magnetic fields observed in A-stars. The present inquiry is restricted to kinematical dynamos, to show some of the many possibilities, depending on the assumed conditions of decline of the convection. The examples serve to illustrate in what quantitative detail it will be necessary to describe the convection in order to extract any firm conclusions concerning specific stars.

The first illustrative example treats the basic problem of diffusion from a layer of declining thickness. The second adds a buoyant rise to the field in the layer. The third treats plane dynamo waves in a region with declining eddy diffusivity, dynamo coefficient, and large-scale shear. The dynamo number may increase or decrease with declining convection, with an increase expected if the large-scale shear does not decline as rapidly as the eddy diffusivity. It is shown that one of the components of the field may increase without bound even in the case that the dynamo number declines to zero.     

A Case Study of the Initiation of Parallel Convective Lines Back-Building from the South Side of a Mei-yu Front over Complex Terrain

Parallel back-building convective lines are often observed extending to the southwest of some mesoscale convective systems(MCSs)embedded in the mei-yu front in China.The convective lines with echo training behavior can quickly develop into a stronger convective group of echoes,resulting in locally heavy rainfall within the mei-yu front rainband.The initiation mechanism of the back-building convective lines is still unclear and is studied based on high-resolution numerical simulation of a case that occurred during 27?28 June 2013.In the present case,the new convection along the convective lines was found to be forced by nonuniform interaction between the cold outflow associated with the mei-yu front MCSs and the warm southerly airflow on the south side of the mei-yu front,which both are modified by local terrain.The mei-yu front MCSs evolved from the western to the eastern side of a basin surrounded by several mesoscale mountains and induced cold outflow centered over the eastern part of the basin.The strong southwest airflow ahead of the mei-yu front passed the Nanling Mountains and impacted the cold outflow within the basin.The nonuniform interaction led to the first stage of parallel convective line formation,in which the low mountains along the boundary of the two airflows enhanced the heterogeneity of their interaction.Subsequently,the convective group quickly developed from the first stage convective lines resulted in apparent precipitation cooling that enhanced the cold outflow and made the cold outflow a sharp southward windshift.The enhanced cold outflow pushed the warm southerly airflow southward and impacted the mountains on the southeast side of the basin,where the roughly parallel mountain valleys or gaps play a controlling role in a second stage formation of parallel convective lines.     

两次昆明准静止锋的对比分析

利用EAR5再分析气象数据,分析了两次昆明准静止锋天气过程的高低空环流形势、锋面结构、锋面位置、以及相关要素场等基本特征及其异同。结果表明：中高纬度地区阻塞形势的存在是昆明准静止锋形成的背景环流。当冷暖气团均强且势均力敌时,更有利于锋面的维持;冷空气较强时,锋面会向西移动,越过云贵高原地形的阻挡;反之,锋面则会向东移动。当锋面维持在高原地形东侧时,冷空气被地形阻挡时,锋面的移动缓慢,此时锋区最为明显。当锋面维持在地形东侧时,风场的最大水平切变、温度的最大水平梯度和相当位温的密集区,描述的锋面位置几乎相同。两次过程寒潮爆发时冷空气均只能维持到700hPa附近,且水平风场也均为600hPa以下的低空切变,说明昆明准静止锋为浅薄系统。昆明准静止锋与一般冷锋锋后不同,两次个例昆明准静止锋锋后低空为湿区,而锋前水汽是否充足则要看南支槽所处的位置。     

鄂尔多斯盆地林镇地区延长组长2沉积微相与油气分布

鄂尔多斯盆地林镇地区处于伊陕斜坡西南部,在长2沉积期研究区内发育辫状河三角洲前缘亚相沉积,沉积微相主要为水下分流河道、水下分流河道间、河口坝和远砂坝,物源主要来自北东和南西两个方向.林镇地区长2油藏的分布与沉积相关系密切,油藏主要分布于水下分流河道末端和河口坝的混合区,以及水下分流河道的侧缘,另外在远砂坝区也有少量油藏分布.区内长2期的辫状河三角洲前缘亚相沉积环境控制了长2储集层岩性的横向变化,同时区内长2地层普遍发育低幅度鼻状构造隆起,因此在构造圈闭条件和岩性圈闭条件共同作用下形成构造—岩性复合油藏.     

双TC和梅雨锋共同作用下的一次暴雨过程分析

通过NCEP再分析资料计算各种物理量和应用卫星云图、雷达资料,并用WRF中尺模式做数值模拟,从动力过程、水汽输送过程、中小尺度系统等3个方面对TC和梅雨锋共同作用在浙北产生的一次暴雨过程进行分析。结论如下:(1)动力过程特点:300 hPa急流出口区辐散,中层3支气流汇合形成变形场锋生,产生强烈上升运动。低层TC外围的东南气流输入暖平流和湿位涡,使海上台风倒槽向北传播发展,最终形成气旋。TC高层流出气流对梅雨锋南侧垂直环流的维持有利;(2)水汽主要由两个TC外围的环流输送;(3)卫星云图和雷达回波显示有不同的降水云团合并且有加强的过程。用WRF中尺模式做数值模拟显示:700 hPa中小尺度的切变线或辐合区与强降水回波相对应。过程主要特点是中低层两个TC外围的气流与西风带气流在华东地区汇合,形成变形场锋生,产生强烈的辐合上升。在不同的气流汇合后产生了强急流输送水汽,加强垂直环流和中小尺度的辐合,是强降水产生的主要原因。西南季风经过台风绕流后在合适的环境场下仍有可能到达华东地区,这时往往与中纬度西风带汇合,在这种情况下会加强梅雨降水。     

山东半岛冷流暴雪雷达回波特征

利用烟台多普勒雷达资料,结合天气形势,对2005年12月3-7日和2008年12月3-6日山东半岛北部的冷流暴雪过程进行了分析研究。结果表明：东北冷涡造成强冷空气频繁,在对流层低层山东半岛存在强冷平流,海面温度和低层大气温度的较大温差造成了低层大气不稳定;渤海和黄海北部海区为降水提供了丰富的水汽;冷流暴雪产生在对流层低...     

Weathering mechanisms and their effects on landsliding in pelitic schist

Physical, chemical, and mineralogical analyses of undisturbed drill cores of pelitic schist from a landslide area in Japan clarified the mechanisms of chemical weathering of pelitic schist. Oxidizing surface water percolates downward and reaches an oxidation front, where chlorite is altered to Al‐vermiculite, graphite and pyrite are oxidized and depleted, and goethite precipitates. Oxidation of pyrite also occurs just below the oxidation front, probably by ferric iron. Pyrite oxidation yields sulphuric acid, which penetrates further downward, interacting with and weakening the rocks. In addition to this chemical weakening, stress release and shearing along schistosities form an incipient shear zone, which propagates to a sliding zone that forms the rupture surface of a landslide. Once a sliding zone has developed, it inhibits downward groundwater flow across it because of its low permeability, slowing the downward propagation of the weathering zone until this filtration barrier is broken by landslide movement. Copyright © 2010 John Wiley & Sons, Ltd.     

Sediment transport in the Yellow Sea and East China Sea

Eight survey cruises in different seasons have been conducted in the Yellow Sea (YS) and East China Sea (ECS) during the period from 2000 to 2008. Suspended sediment concentration (SSC) and hydrological data were collected during each cruise. Data analysis showed that total suspended sediment mass was approximately 0.18 × 10⁹ tons in the surveyed area during spring and autumn seasons. Highly turbid waters were found in the shallow waters between the Subei coast, the Changjiang estuary and the Zhejiang coast with seasonal variations.     

Q矢量的改进与完善

在完全考虑非绝热加热项潜热作用的前提下，从原始方程出发，推导出改进后的湿Q矢量(以下记为Q^M)的表达式以及用其散度作强迫项的ω方程，并结合一次梅雨锋暴雨天气过程将改进前、后的湿Q矢量诊断能力进行比较，结果发现：(1)改进后的湿Q矢量对同时刻的地面降水的反映能力较原湿Q矢量(Q^*)有显著的提高。(2)在整个梅雨锋暴雨过程中，600hPa高度上的改进后的湿Q矢量散度辐合场的辐合强度及其辐合中心的位置对同时刻的地面实际降水的强度及雨区位置都有非常好的指示作用。     

青藏高原东侧一次区域性暴雨天气过程分析

根据河套锢囚锋与山西暴雪的统计关系，分析研究了有利于锢囚锋形成的500hPa平均高度场、850hPa平均温度场、地面合成平均图以及暴雪落区的概念模型，旨在提高我们对冬春季节强降雪的预报能力。