Diagnosis of a Moist Thermodynamic Advection Parameter in Heavy-Rainfall Events

A moist thermodynamic advection parameter, defined as an absolute value of the dot product of hori- zontal gradients of three-dimensional potential temperature advection and general potential temperature, is introduced to diagnose frontal heavy rainfall events in the north of China. It is shown that the parameter is closely related to observed 6-h accumulative surface rainfall and simulated cloud hydrometeors. Since the parameter is capable of describing the typical vertical structural characteristics of dynamic, thermodynamic and water vapor fields above a strong precipitation region near the front surface, it may serve as a physical tracker to detect precipitable weather systems near to a front. A tendency equation of the parameter was derived in Cartesian coordinates and calculated with the simulation output data of a heavy rainfall event. Results revealed that the advection of the parameter by the three-dimensional velocity vector, the covariance of potential temperature advection by local change of the velocity vector and general potential temperature, and the interaction between potential temperature advection and the source or sink of general potential temperature, accounted for local change in the parameter. This indicated that the parameter was determined by a combination of dynamic processes and cloud microphysical processes.     

移出与未移出高原的高原切变线背景环流对比分析

利用NCEP再分析资料,采用对比分析方法,对2000-2004年汛期（5～9月）青藏高原（下称高原）上高原切变线活动过程进行了普查和分类,并对移出与未移出高原的高原切变线的生成日,移出高原的高原切变线的移出日与未移出高原的高原切变线的强盛日的背景环流特征场进行了对比分析。结果表明,500hPa层上,两槽一脊的背景环流形...     

广州市11月强冷空气特征概述及典型个例分析

强冷空气过程是广州市11月的高影响天气类型之一.通过分析广州地区5个站1961～2009年11月的日平均气温、日最高气温、日最低气温及日雨量等数据,以及NCEP 2°×2°再分析资料.并根据广东省气象局的灾害性天气标准,发现1961～ 2009年影响广州的强冷空气过程共有8次,没有寒潮过程出现.从24h的降温幅度看,1...     

Decadal variability and scales of the sea surface structure in the northern Ionian

The variability and scales of the sea surface structure of the northern Ionian Sea from January 1993 to December 2007 were studied by means of altimeter remotely-sensed weekly Sea Level Anomaly (SLA) objective maps. Variability in the sea surface structure was addressed by means of empirical orthogonal function (EOF) analysis and, assuming an exponential correlation model, scales of the SLA field were quantified as e-folding distances of the SLA autocorrelation function. The variability in the sea surface structure, described by the first three EOFs, which cumulatively explain 60.3% of the data set variance, is characterized by a large-scale structure with variability on a time scale of ∼10-13 years and, on shorter scales, an eddy system with variability on an annual scale. The variability in the large-scale structure describes an overturning of the SLA field, which took place in 1997, and determines a reversal of the geostrophic upper-layer circulation. As the large-scale circulation transition takes place, time-dependent spectral analysis of EOF coefficients shows a redistribution of the spectral energy from inter-annual to semi-annual and monthly components. Spatial scales display variability on an annual and inter-annual time scale. On the annual time scale, variability in spatial scales is characterized by longer values in summer-fall and shorter in winter-spring. Inter-annual variability in spatial scales is demonstrated by a remarkable drop in the values during fall in the period 1998-2000. We propose an explanation of the variability in horizontal scales in terms of the redistribution of water masses and related modifications of the vertical structure of the water column associated with different regimes of the basin-scale circulation.     

影响春季热带太平洋地区海温变化的动力热力作用分析

厄尔尼诺—南方涛动（ENSO）春季预报障碍是ENSO预测的一个难点问题,弄清影响春季热带太平洋地区海表温度（SST）变化的动力和热力作用对于理解ENSO关键区SST的异常变化及ENSO春季预报障碍成因非常重要。本文利用BCC-CSM2-MR数值模式,模拟产生一套1986～2017年间相互协调的逐月海表风应力、感热、潜热、长波和短波净辐射能量、海洋流场等观测代用数据。利用这些数据对影响海温变化的动力和热力作用及其相对重要性进行了诊断分析,结果表明:（1）与其他季节相比,春季Ni?o3.4区海洋表层温度（后文中用T_S表示）呈现出独特的先增暖后趋冷的不对称季节性转换特征,这一变化主要是由于影响T_S的大气风应力、海流以及能量净通量在春季均表现出明显的季节性转换过程。进一步的分析表明,热力作用对局地海温的季节性变化影响最为重要,水平平流输送以反向作用为主,其中经向平流输送起到了反向作用,不利于该区域T_S的季节性转变,纬向平流输送仅在春季转为弱的正贡献,浅层垂直平流输送对春季T_S变化的影响很小。（2）动力热力作用与T_S异常的变化倾向相关关系也表明,春季Ni?o3.4区热力作用与T_S异常变化呈现显著的正相关,纬向海流异常的输送项也表现为正相关,而经向海流输送项展现出由负相关向正相关转化的特征。（3）对Ni?o3.4区T_S变化的方差贡献分析结果表明,春季热力作用对T_S的异常变化的贡献达50%以上,相关系数超0.7,其次是纬向、经向平流项贡献,各占10%～20%左右,但两者作用相反,其他项贡献较小。     

2011年1月九江地区暴雪过程的流场特征及强回波成因分析

利用九江、南昌多普勒天气雷达资料和常规气象观测资料及0.5°×0.5°的NCEP再分析资料,对2011年1月19-20日九江地区的暴雪天气过程进行了分析.结果表明:南支槽前强盛的西南暖湿气流沿低层东北冷回流在长江流域形成的冷垫爬升是暴雪产生的动力机制;高低空急流的耦合作用形成次级环流,700 hPa以上正涡度平流和低层暖平流表明天气尺度上升运动较强;700 hPa等θ se线密集,表明锋区稳定维持.低层暖平流,中下层风速加强,急流中心降低,预示降雪回波将发展;低层暖平流结构转为冷平流漉场结构,预示降雪减弱.分析表明,本次过程没有强雷暴影响,回波异常增强不是由大水滴和霰雹等固态水凝物粒子造成,雪花下降经过0℃以上的暖层时表面融化,使雪花外裹了一薄层水膜,产生类似于大水滴的等同效果,从而出现了雷达图上反射率因子异常增强的现象;同时,中下层强的上升运动和凝结潜热释放的反馈机制可导致局部较强的反射率因子而产生强降雪.     

Investigations on the influence of pore‐space geometry on concentration patterns and transportation properties of dissolved oxygen in a bioactive sandy sediment by a lattice Boltzmann automaton model

A lattice Boltzmann automaton (LBA) is used as a modelling approach to investigate the influence of pore‐space geometry on intrinsic processes and component distributions in recent tidal sediments. The simulations are performed on real pore‐space structures obtained from scanning electron photomicrographs, which document the mesoscopic geometry of bioactive sandy surface sediments. The discrete transport–reaction model for dissolved oxygen shows that in advective controlled systems oxygen concentration properties can be clearly related to the pore‐space geometry. Variability of measured high‐resolution concentration gradients can therefore can be attributed to the structural heterogeneity of pore‐space geometry. Copyright © 2001 John Wiley & Sons, Ltd.     

2011年12月3-7日山东省连续大雾分析

利用2011年12月1-7日的常规探测资料和NCEP再分析资料,采取诊断分析的方法,分析了山东省大范围连续性大雾产生的天气背景、温湿条件和大气层结等特征。结果表明：此次连续大雾发生在稳定的大气层结下,高空中纬度环流平直,地面气压场上表现为从东西伯利亚到华南一个庞大的变性高压区（山东处于高压的中部）,天气形势稳定;在高分辨率可见光云图上,大雾图像顶部较光滑、边缘较清晰,在红外云图上特征不明显;近地面层是弱的东到东北风（风力在2 m·s^-1以下）,既有利于海洋上暖湿气流的平流输送,也为较冷的下垫面的建立创造了条件;大气边界层湍流活跃,湍流动力垂直输送明显;大雾初期低空有明显的逆温层,天气状况较好,辐射降温明显,大雾性质以辐射雾为主,中后期是暖湿空气平流到温度较低的下垫面上时冷却而形成,以平流雾为主。