A sensitivity of squall-line intensity to environmental static stability under various shear and moisture conditions

Squall lines develop in various climate regions having diverse environmental profiles of wind shear, moisture, and temperature. In order to explore the sensitivity of squall lines to these environmental profiles, we have performed an extensive set of numerical simulations under various shear and moisture conditions in midlatitude-continental and tropical–oceanic temperature environments. From the results of the sensitivity simulations and the analyses of the environmental parameters, it is found that the static stability in a convectively unstable layer is of primary importance in determining the strength of squall lines. Under temperature environments having the same static stability, convective available potential energy (CAPE) and precipitable water content (PWC) well describe the squall-line intensity. Vertical shear also plays an important role in determining the squall-line structure as well as the intensity through the interaction with surface cold pool. The combination of the static stability in a convectively unstable layer, CAPE, and PWC should be examined in diagnosing the intensity of squall lines that develop with an optimal shear for their environment.     

梅雨锋云系的结构特征及其成因分析

利用逐时卫星遥感观测资料和地面测站的降水资料，分析了江淮流域2003年6月22～26日暴雨过程中梅雨锋云系的演变、结构特征和形成原因。结果表明，梅雨锋云系为一条TBB的低值带，稳定少动，其上分布着中尺度对流系统（MCS），而中尺度对流系统是由不同尺度、不同强度．的对流单体（包括中β和中γ尺度对流单体）组成的，从而使得梅雨锋云系产生不均匀的降水分布（包括时间上和空间上）。在该暴雨过程中，梅雨锋云系充分体现了中尺度对流系统中所包括的3类组织结构形式。梅雨锋云系与中高纬度云系或热带辐合带云系之间的相互作用与暴雨过程关系密切，梅雨锋云系的维持和发展与强大的黄淮气旋云系直接相关，它是江淮流域上空冷暖气流交汇的结果。     

三维地闪监测数据分析与校验

选取福建省2015年三维系统地闪资料,采用同期雷电定位系统(ADTD)资料对其时空分布特征进行分析,利用雷电流峰值记录仪数据对2套系统地闪探测效率和定位误差校验,同时结合IEEE工作组和电力行业推荐的概率公式对三维系统地闪雷电流分布特征进行分析。结果表明:(1)2套系统监测到全省地闪密度空间分布趋势比较一致,在三明西南部地区及福州西部零星地区,三维系统地闪密度更低。(2)2套系统地闪频次年变化和日变化均呈单峰变化特征,但年变化中的10—12月,以及日变化中的09:00—12:00,三维系统监测到地闪频次更少。(3)三维系统地闪回击探测效率为40%,平均定位误差为2.75km。(4)在0~50kA区间,相比于负极性地闪,三维系统正极性地闪雷电流幅值分布更加集中,在26~84kA区间三维地闪雷电流幅值相比于IEEE推荐值和规程推荐值偏大。     

水成相沉积物细颗粒石英光释光综合生长曲线的建立与应用

选择中国不同地区的冲洪积相等水成相沉积物样品,根据其简单多片再生法(SMAR)测量数据建立了细颗粒石英光释光信号的综合生长曲线(Standardised growth curves,SGC)。对未知年龄的水成相沉积物细颗粒石英样品,通过测量其天然光释光信号和试验剂量响应信号,并利用上述SGC方程可计算出其等效剂量值。将此值与简单多片再生法(SMAR)测量结果相比较,统计得出对于天然等效剂量为12~65Gy的样品,其误差可达19%;对于天然剂量>65Gy的样品,其误差更大;对于等效剂量<12Gy的样品,最大误差也达25%。实验表明,应用这个SGC估计未知年龄样品的等效剂量值范围,再对样品采用简单多片再生法(或单片再生法)进一步测量,可大大节省测量时间     

RC框架结构直接基于位移的抗震优化设计方法

探讨了静力弹塑性分析验证过程中遇到的几种情况及其产生原因,指出建筑结构设计方案在基于位移的抗震设计中的重要性。从框架结构的侧移模式出发,导出结构一定性能水平的目标顶点位移,建立结构目标顶点位移与等效位移的关系式,根据位移反应谱,由等效位移推出框架结构在各性能水平的目标周期。然后,由pushover曲线确定结构刚度退化机理,导出结构各性能水平相应的自振周期比例关系,根据结构各性能水平自振周期与目标周期的关系确定结构最优设计方案。通过例题加以验证,说明了此设计方法的可行性。     

高精度温度采集系统设计

针对高精度温度采集的需求,设计了一个以低功耗单片机MSP430F149作为核心处理器,以PT100铂电阻为传感器的温度采集系统。为了提高系统的复用性,采用精密电阻法,从硬件设计上消除了恒流源电流漂移以及A/D转换电路参考电压精度对温度测量数据的影响。重点描述了系统设计方案,详细说明了恒流源选择的原则、电流偏差的消除以及AD7792转换器的操作步骤。实验结果表明,温度测量精度优于0.1 ℃。对比试验表明,系统稳定性良好,已应用于业务产品中。     

The mesoscale convection life cycle: Building block or prototype for large-scale tropical waves?

A cumulonimbus cloud may ascend and spawn its anvil cloud, precipitation, and downdrafts within an hour or so. This paper inquires why a similar progression of events (life cycle) is observed for tropical weather fluctuations with time scales of hours, days, and even weeks. Regressions using point data illustrate the characteristic unit of rain production: the mesoscale convective system (MCS), covering tens of kilometers and lasting several hours, with embedded convective rain cells. Meanwhile, averages over larger spatial areas indicate a self-similar progression from shallow to deep convection to stratiform anvils on many time scales.Synthetic data exercises indicate that simple superpositions of fixed-structure MCS life cycles (the Building Block hypothesis) cannot explain why longer period life cycles are similar. Rather, it appears that an MCS may be a small analogue or prototype of larger scale waves. Multiscale structure is hypothesized to occur via a Stretched Building Block conceptual model, in which the widths (durations) of zones of shallow, deep, and stratiform anvil clouds in MCSs are modulated by larger scale waves.Temperature (T) and humidity (q) data are examined and fed into an entraining plume model, in an attempt to elucidate their relative roles in these large-scale convection zone variations. T profile variations, with wavelengths shorter than troposphere depth, appear important for high-frequency ( 2–5-day period) convectively coupled waves, as density directly links convection (via buoyancy) and large-scale wave dynamics (via restoring force). Still, the associated q anomalies are several times greater than adiabatic, suggesting a strong amplification by shallow convective feedbacks. For lower frequency (intraseasonal) variability, q anomalies are considerably larger compared to T, and may be dominant.     

2009年7月17日唐山地区强降水成因分析

利用常规天气资料和NCEP/NCAR再分析资料,对2009年7月17日唐山地区暴雨天气过程进行分析。结果表明：强降水是暖湿空气向北输送与低层冷空气交汇引起的。降水前期,唐山地区中低层水汽强辐合为强降水准备了条件。冷空气从底层侵入,抬升暖湿气流,低层暖锋锋生使对流不稳定性增大,上升运动加强,降水量增大。强降水区存在低层辐合、高层辐散和斜升运动机制。850hPa湿位涡正压项MPV1＞0区域能较好地反映出冷空气活动特征,强降水出现在MPV1零线附近偏冷空气一侧。     

台风移动规律的研究 Ⅱ.小地形与边界层的动力作用

从支配台风中心移动的基本方程出发，着重分析了小地形（地形高度与台风系统的的垂直厚度相双为小量）的抬升作用和边界层的摩擦作用对台风移动影响的定性特征。结果表明，较高地势对台风有“吸收”作用；边界层摩擦辐合引起的艾克曼抽吸有利于台风产生沿局地流场引导速度方向的加速度。     

The Role of β-effect and a Uniform Current on Tropical Cyclone Intensity

A limited-area primitive equation model is used to study the role of the β-effect and a uniform current on tropical cyclone (TC) intensity.It is found that TC intensity is reduced in a non-quiescent environment compared with the case of no uniform current.On an f-plane,the rate of intensification of a tropical cyclone is larger than that of the uniform flow.A TC on a β-plane intensifies slower than one on an f-plane.The main physical characteristic that distinguishes the experiments is the asymmetric thermodynamic (including convective) and dynamic structures present when either a uniform flow or β-effect is introduced.But a fairly symmetric TC structure is simulated on an f-plane.The magnitude of the warm core and the associated subsidence are found to be responsible for such simulated intensity changes.On an f-plane,the convection tends to be symmetric,which results in strong upper-level convergence near the center and hence strong forced subsidence and a very warm core.On the other hand,horizontal advection of temperature cancels part of the adiabatic heating and results in less warming of the core,and hence the TC is not as intense.This advective process is due to the tilt of the vortex as a result of the β-effect.A similar situation occurs in the presence of a uniform flow.Thus,the asymmetric horizontal advection of temperature plays an important role in the temperature distribution.Dynamically,the asymmetric angular momentum (AM) flux is very small on an f-plane throughout the troposphere.However,the total AM exports at the upper levels for a TC either on aβ-plane or with a uniform flow environment are larger because of an increase of the asymmetric as well as symmetric AM export on the plane at radii ＞450 km,and hence there is a lesser intensification.