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1.
FengXia Guo GanYi Lu Xin Wu HaoLiang Wang ZuPei Liu Min Bao YaWen Li 《中国科学:地球科学(英文版)》2016,59(7):1401-1413
The purpose of this study was to understand the reasons why frequent positive cloud-to-ground (+CG) flashes occur in severe thunderstorms. A three-dimensional dynamics-electrification coupled model was used to simulate a severe thunderstorm to permit analysis of the conditions that might easily cause +CG flashes. The results showed that strong updrafts play an important role in the occurrence of intracloud flashes. However, frequent +CG flashes require not only strong updrafts but also strong downdrafts in the lower cloud region, conditions that correspond to the later phase of the mature stage and the period of the heaviest solid precipitation of a thunderstorm. During this stage, strong updrafts elevated each charge area in the updraft region to a higher level, which resulted in an inverted tripole charge structure. A wide mid-level region of strong positive charge caused largely by positively charged graupel, presented in the middle of the updraft region because of a non-inductive ice-ice collisional charging mechanism. The charge structure in the downdraft region was consistently more complex and revealed several vertically stacked charge regions, alternating in polarity. Much of the graupel/hail outside the updrafts was lowered to cloud-base by strong downdrafts. In this area, the graupel/hail was charged negatively because of the transportation of negatively charged graupel/hail from higher regions of negative charge in the updrafts, and via the inductive charging mechanism of collisions between graupel/hail and cloud droplets at the bottom of the cloud. Consequently, a large region of negative charge formed near the ground. This meant that +CG flashes were initiated more easily in the lower inverted dipole, i.e., the middle region of positive charge and lower region of negative charge. Frequent +CG flashes began almost synchronously with dramatic increases in the storm updrafts, hail volume, and total flash rate. Therefore, the occurrence of +CG flashes appears a good indicator of storm intensification and it could have some use as a predictor of severe weather in the form of hail. 相似文献
2.
FengXia Guo Yang Li ZhaoChu Huang ManFei Wang FanHui Zeng ChunHao Lian YiJun Mu 《中国科学:地球科学(英文版)》2017,60(12):2204-2213
Based on the Weather Research Forecasting (WRF) model that features charging and discharging parameterization, relationships between tornado, hail and lightning were investigated for a tornado-producing (EF4 intensity) supercell thunderstorm over Yancheng City in Jiangsu Province, China, on 23 June 2016. Based on a sounding at 0800, there was a low lifting condensation level, substantial convective available potential energy (CAPE), and strong vertical wind shear near Yancheng City, which promote supercell development. At 1400, observations revealed that hail production and a dramatic increase of positive cloud-to-ground flash rates occurred simultaneously, maximizing five minutes later. The tornado occurred 30 min after the hail production. The time of minimum positive cloud-to-ground flash rates was 15 min later. The simulation indicated that the tornadic supercell moved eastward and that positive cloud-to-ground flash rates increased dramatically at 1400, the same as observed, but their maximum was 5 min later than observed. The simulated updraft volume peaked at 1425 and the simulated downdraft volume maximized 5 min later, when the mesocyclone formed. Simulated reflectivities showed no hook echo and horizontal winds for different height at mid-low levels had a different cyclonic shear at 1430, favorable to mesocyclone formation. Based on the simulated results, the region of positively charged graupel ascended resulting from the region of high liquid water content was lifted by the strong updraft, forming a mid-level strong positive charge region. A lower negative charge region formed by the inductive charging mechanism of collisions between graupel and droplets at the bottom of the cloud, conducive to positive cloud-to-ground flashes. 相似文献
3.
本研究利用加入起电、放电参数化方案的数值模式（Weather Research and Forecasting Model（Version 3.7.1）,WRF3.7.1_ELEC）,通过设计五组不同非感应起电及感应起电参数化方案敏感性试验,对发生在青藏高原东北部青海大通地区的一次雷暴过程进行模拟研究,对比分析了不同非感应起电机制及感应起电机制对雷暴云电荷结构的影响.结果表明：在雷暴云发展旺盛阶段,Saunders（S91）、Riming Rate（RR）、和Saunders和Peck（SP98）三种非感应起电方案模拟的雷暴云最低层均为负电荷区,而混合方案（Brooks and SP98,BSP）模拟的雷暴云最低层为正电荷区,主电荷区自下而上为"+-+-"排列的四层电荷结构.与甚高频辐射源定位法推算的结果对比,BSP方案模拟的本次高原雷暴云电荷结构更接近实际情况;几种不同非感应起电方案模拟的主电荷区外围与主电荷区电荷结构不同,说明在雷暴发展的不同阶段雷暴云的电荷结构是不同的;几种非感应起电方案模拟的电荷结构不尽相同,主要是由于霰、冰和雪粒子在不同高度所带电荷的极性及电量的大小不同,霰粒子的电荷密度对低层的影响较大,冰粒子和雪粒子的电荷密度对中上层的影响较大;加入感应起电机制后,雷暴云电荷结构分布几乎没有变化,但能使雷暴云发展旺盛阶段低层和中层的正负电荷区电荷密度有所加强. 相似文献
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A 3-D convective cloud model with compressible non-hydrostatic dynamics and the spectral bin microphysics of a 2-D slab-symmetric
model has been used to simulate an observed supercell storm occurring on 29 June, 2000 near Bird City, Kansas, USA. The main
objective of this paper is to study the evolution of particles in this convective storm with bin spectral microphysics scheme.
Graupels form and grow through two mechanisms, deposition and riming, with the riming process dominant on top of the inflow
and in the upper portion of main updraft. Over the outflow and during the developing and mature stages of the storm, graupel
particles mainly grow through deposition with dominant unimodal spectra. Most fall out after growing up. Reducing initial
relative humidity disturbance (increasing initial potential temperature disturbance) has negative impact on the formation
and growth of graupels over the inflow (outflow). This study shows that large graupel and hail could be suppressed by altering
the deposition and coalescence process over the inflow and main updraft. At different locations of the convective cells and
with different initial humidity and potential temperature disturbance, the graupel formation and growth mechanisms are different,
so as to the feasible hail suppression locations and methods.
Supported by National Natural Science Foundation of China (Grant Nos. 40537034, 40805057), and Foundation of Key Laboratory
of Meteorological Disaster of Ministry of Education in Nanjing University of Information Science & Technology (Grant No. KLME060202) 相似文献
6.
本文在已有的三维雷暴云起、放电模式中加入了一种经典的气溶胶活化参数化方案,结合一次长春雷暴个例,进行了雷暴云起放电数值模拟试验.研究显示气溶胶浓度改变对雷暴云微物理、起电及放电过程都有重要影响.结果表明:(1)污染型雷暴云中气溶胶浓度增加时,云滴数目增多,上升风速加强;云中冰晶与霰粒子数浓度增加但尺度减小;(2)相对于清洁型雷暴云,污染型雷暴云非感应起电过程弱,感应起电过程强,起电持续时间长;(3)污染型雷暴云中首次放电时间延迟,闪电持续发生的时间长,总闪电频次增加,正地闪频次增加明显. 相似文献
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Recondensed meteoric material, so-called meteoric smoke, has long been considered the main candidate for condensation nuclei for mesospheric ice formation. Recently however, model studies have shown that meteoric smoke particles are transported away from the polar region, where ice phenomena such as noctilucent clouds occur, before they can grow large enough to serve as ice condensation nuclei. In the accompanying paper it is argued that charging of the meteoric smoke particles may solve this dilemma by significantly altering the efficiency of the particles as condensation nuclei. In the present paper, the feasibility of this idea is investigated more quantitatively, by analysing the time scales of processes such as charging, recombination, and particle growth. Despite large uncertainties, especially in the charging efficiency of the smallest smoke particles, we show that reasonable assumptions yield number densities of charged condensation nuclei that are consistent with what is expected for mesospheric ice phenomena. 相似文献
9.
High resolution 3-cm weather radar was used to observe the three dimensional structure of a weak echo region of a severe convective storm in northern Minnesota, U.S.A. Observations show that a seemingly steady-state updraft in the lower portion of the storm broke into an unsteady structure in the upper levels. This is interpreted as indicating that precipitation loading gradually decelerated the upper reaches of the updraft, resulting in periodic breakout of a new updraft core on the inflow side. This periodic behavior of the updraft may be related to hailstreaks and what has been termed the multi-celled storm. 相似文献
10.
Kenneth C. Young 《Pure and Applied Geophysics》1975,113(1):1005-1017
A numerical model of ice phase growth in an ascending parcel is used to delineate seeding requirements under the competing embryo and glaciation hypotheses. The strong updraft core is found to remain virtually all liquid until homogeneous freezing occurs, AgI or dry ice seeding having negligible effects with achievable seeding rates. This suggests that the glaciation hypothesis is untenable. Natural hail embryo formation is noted to be limited to updrafts less than 3 to 4 m sec?1 at cloud base. AgI seeding of such updraft regions at rates currently used is found to produce concentrations of hail embryos sufficient to enhance competition in multi-cell hailstorms, although super-cell storms may require significantly greater seeding rates. 相似文献
11.
A one-dimensional, time-dependent numerical cloud model is used to analyze the factors in the dynamic and thermodynamic equations which lead to a steady-state or nonsteady-state solution for the cloud vertical motion, buoyancy, precipitation, and cloud water fields. ‘Bulk water’ microphysical techniques are used for the cloud, rain, and hail variables. An atmospheric sounding from a severe storm situation is used as initial and environmental conditions, yielding model updrafts of 40 m sec?1 maximum and more than 10 m sec?1 over the entire cloud region. ‘Early conversion’ of the cloud water to rain leads to loading of lower portions of the updraft by rain, the formation of appreciable amounts of hail by freezing of the supercooled rain, and subsequent loading of the middle and upper portions of the updraft so that the updraft erodes throughout the cloud depth and the cloud dissipates, yielding a vigorous rain shower. A delay in the conversion of the cloud water to rain results in a steady-state solution, no rain or hail falling through the updraft. A two-dimensional cloud simulation of this same case shows rain and hail in the upper cloud regions recycled in the two-dimensional flow into the updraft near cloud base and a breakdown of the updraft with resultant rainout (negligible hail reaching the ground). The breakdown of the updraft has profound effects on the temperature field within the cloud, causing the lapse rate to deviate from the steady-state condition and approach the initial environmental conditions. The results emphasize the fact that the local change in temperature (and other dependent variables as well) is not independent of the vertical velocity, in general. This has implications for the interpretation of measurements made within clouds. 相似文献
12.
利用闪电放电辐射源三维时空分布测量,分析了山东低海拔地区一次多单体雷暴过程的电荷结构演变以及与回波强度的关系.结果表明对流云区电荷结构是典型的上正下负电偶极结构,且随着雷暴发展正负电荷层强度增大,高度抬升.负电荷区处在40 dBz以上的强回波区域中,正电荷层处在约40 dBz区域中.层状云区也有类似结构,只是强度弱,高度低.观测到的四层电荷结构是出现在对流区消散阶段,此时,由于云体不同部位的不同消散程度,电荷结构发生断裂,云体前部正负电荷区下沉,云体中部正负电荷区高度变化不大,但负电荷区域变薄,呈现出四层电荷结构.从本例结果说明,雷暴优势起电机制通常能形成电偶极或三极性结构,多极结构可能不是起电形成.本文还分析了一次负地闪传输过程,和宏观电荷结构很好吻合,说明利用三维定位系统观测,可以较好地描述雷暴宏观电荷结构. 相似文献
13.
Edwin Kessler 《Pure and Applied Geophysics》1975,113(1):971-981
Condensed water in a vertical column is related through continuity equations to the updraft speed, column depth, height of the condensation level, and strength of microphysical processes. When the ratio of updraft to characteristic particle fall speed is small, as in stratiform rain, the mass of precipitation in the steady state is proportional to the product of that ratio, column depth, and condensation function. When the ratio is only slightly above unity, two water content regimes are defined by continuity equations. The regime of large water content, an extension of the case described above, occurs when the condensation level is low and when there is rapid conversion of cloud to precipitation. Another regime characterized by a water mass about one-third as large (or less), and absence of precipitation at the ground beneath the updraft column, appears if the condensation level is high enough or cloud conversion slow enough. When the ratio is large, the total water content is usually much smaller than when updrafts and fall speeds are similar, and declines slowly toward a limiting value with increasing ratio. As updrafts intensify, precipitation is more limited near the top of the column, with increasing depth and amount of cloud beneath. In the limit of very fast updraft and weak cloud conversion process, the condensate profile is simply the profile of cloud in air risen from the condensation level without conversion of cloud to precipitation. These findings contrast substantially with those presented by Sulakvelidze,et al., who proposed that the water mass associated with strong updrafts increases with the square of the updraft speed. The difference in results is traced to its origins in different model assumptions. 相似文献
14.
This paper proposes a new model for thunderstorm electric field generation which directly utilizes the dynamic turbulent motion to separate the charges. Postulating a microphysical charge separation mechanism, such as is commonly accepted in most other theories, and which places a negative charge on the larger particles with a positive charge on the smaller ones, it is described how evaporation and cooling at the tops of small cumuli will release the positive charges as ions. These ions migrate to the surrounding cloud as the cooled parcel, with negatively charged particles in it, sinks down through the cloud. Since the sinking parcel contains mostly ice, it will be more buoyant than its surroundings when it reaches rising regions of water cloud, and hence should come to rest near the –10°C level. Thus the cloud will acquire an accumulation of negative charge at about this level before substantial hydrometeors begin falling out of it. 相似文献
15.
Klaus D. Beheng 《Pure and Applied Geophysics》1980,119(4):820-830
Riming growth of ice particles is simulated by numerically solving the stochastic collection equations, simultaneously considering coagulation of water droplets. By introducing a special criterion which defines the habit of a riming particle, the influence of this habit on the growth of several kinds of ice particles assumed to be formed during riming was investigated.It was found that (i) hexagonal rimed ice plates are growing more efficiently than lump graupel or rimed columns, (ii) the use of different collection kernels for the lump graupel evolution leads to widely differing results and that (iii) the time dependent decrease of liquid water substance and the size of the resulting ice particles were more strongly influenced by the initial ice crystal concentration than by the initial ice crystal size and the habit of the ice particles. By decreasing the number density of ice crystals gradually a critical ice crystal concentration was found at which the present liquid water was not completely consumed by the riming process even after 1800 s model time, causing large drops of radii >100 m to be formed in appreciable concentrations. 相似文献
16.
2007年3月3-5日和2013年11月24-25日,受江淮气旋北上影响,我国北方大部地区遭遇罕见暴风雪天气,2次暴雪过程有很多相似之处.利用常规观测、CloudSat卫星云廓线雷达的探测资料和NECP/NCAR再分析资料,分析了这2次暴雪过程江淮气旋云系结构和微物理特征.结果表明：（1）北上江淮气旋的冷锋云系较窄,以深厚对流云为主,回波核心在2~7 km,其结构在气旋发展的不同阶段变化不大;（2）逗点头云系范围宽广,在气旋的不同发展阶段,结构和强度有显著差异.气旋初始锋面波动和锋面断裂阶段,逗点头云系有两个降水区：北部为由多个单体组成的大范围层状云区,强回波从地表向上伸展,上空有高空对流泡,建立了播撒云-供水云机制,有利于下部冰晶粒子长大;南部有对流云柱发展.逗点头西部的冷输送带云系主要集中在6 km以下,强度弱,冰粒子含量少;（3）气旋暖锋后弯阶段,干侵入加强,冷锋后部的无云区或少云区范围扩大,逗点头云系南北范围收缩、变窄,云系的高度、强度和含水量减弱,冷锋云系也减弱;（4）气旋冷锋云系和逗点头南部的对流云柱以降雨为主,位于高纬度陆地上的逗点头云系以降雪为主,当逗点头云系处于海上有对流不稳定发展,以降雨为主.冷锋云系北部和逗点头云系南部均有由层积云或高积云组成的低云,以毛毛雨为主.冷锋云系和逗点头云系北部100-200 km的范围为随高度和距离逐渐变薄的高层云,无降水对应. 相似文献
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The cloud-microphysical cause of torrential rainfall amplification associated with Bilis (0604) 总被引：1，自引：0，他引：1
After its landfall in China’s mainland in 2006, Typhoon Bilis brought about torrential rainfall amplification at the edge of Guangdong, Jiangxi, and Hunan provinces, causing severe disasters. From a cloud-microphysical perspective, we discuss the differences of cloud-microphysical processes before and during the precipitation amplification and possible causes of the rainfall amplification by using high-resolution simulation data. The results show that the cloud-microphysical characteristics during the above two periods are significantly different. With the distinct increase in the rainfall intensity, the cloud hydrometeor contents increase markedly, especially those of the ice-phase hydrometeors including ice, snow and graupel, contributing more to the surface rainfall. The clouds develop highly and vigorously. Comparisons of conversion rates of the cloud hydrometeors between the above two periods show that the distinct increases in the cloud water content caused by the distinct enhancement of the water vapor condensation rate contribute to the surface rainfall mainly in two ways. First, the rain water content increases significantly by accretion of cloud water by rain water, which thus contributes to the surface rainfall. Second, the accretion of cloud water by snow increases significantly the content of snow, which is then converted to graupel by accretion of snow by graupel. And then the graupel melts into rain water, which subsequently contributes to the surface rainfall amplification. In summary, a flow chart is given to clarify the cloud-microphysical cause of the torrential rainfall amplification associated with Bilis. 相似文献
19.
Exposed to space plasma and solar radiation, electrostatic potential may build up in the lunar regolith, leading to a wealth of dust phenomena, including levitation, oscillation, and transport over the surface. Based on plasma sheath theory, the global near-surface plasma environment is modeled, and the dynamics of charged dust are investigated. Results show that sub-micron sized dust particles can be levitated by the electric field over the surface, forming a dust belt that changes in position and thickness depending on the solar zenith angle. On the dayside of the Moon, stably levitated particles are about ten times smaller, and collect in a thinner belt closer to the surface than do those on the nightside. Although the size and charge of stably levitated dust particles are dependent on ambient plasma conditions, initial charge and velocity, which are closely related to the dynamics of dust particles including charging, oscillation, and damping, will determine whether, or not, a particle can attain stable levitation. Horizontal electrostatic dust transport near to the terminator region may lead to net deposition of dust from the dark into the sunlit hemisphere. Finally, because of different charging processes that result due to rotation of the Moon, before precipitation, dust particles in the dusk terminator region may be transported much longer distances and oscillate to much higher altitude than these in the dawn terminator. 相似文献
20.
Between 1966 and 1973, National Severe Storms Laboratory mesonetwork soundings were taken near thunderstorms and squall lines. Thirty-four of these soundings sampled updrafts at various levels. Because of instrumental noise and atmospheric fine structure, many of the individual soundings were hard to interpret. However, significant results were obtained from the data as a whole and from the four fastest updraft cases. Typically, the updrafts were associated with moderate thunderstorms that formed in baroclinic regions with maritime tropical air near the surface overlaid by drier air aloft. The immediate environments were potentially, conditionally, and latently unstable but were stable with respect to parcel displacement from the lifted condensation level. The updrafts were generally located in regions of strong radar reflectivity gradient at 0° antenna tilt. The updraft soundings often showed pseudo-adiabatic lapse rates immediately above the updraft condensation level. Statistical analysis of the data confirms that updrafts are warm core at mid- and upper levels and that they are relatively cool at low levels (below 700 mb). Important effects of perturbation pressure gradient forces are emphasized. We also find that local updraft speed is positively correlated at the 95% confidence level with local potential wet-bulb temperature between 0.9 and 9.3 km MSL. The average vertical velocity is a maximum at a relatively low height (4.8 km MSL); this agrees with other experiments that involve tracking objects released below cloud base. However, flight train icing and other extraneous factors may be influencing this result. The average horizontal winds in the updraft and environment agree with recent conceptual Great Plains thunderstorm models. 相似文献