Climatology of tropical cyclone tornadoes in China from 2006 to 2018

We surveyed the occurrence of tropical cyclone(TC) tornadoes in China from 2006 to 2018. There were 64 cataloged TC tornadoes, with an average of five per year. About one-third of the landfalling TCs in China were tornadic. Consistent with previous studies, TC tornadoes preferentially formed in the afternoon shortly before and within about 36 h after landfall of the TCs. These tornadoes mainly occurred in coastal areas with relatively flat terrains. The maximum number of TC tornadoes occurred in Jiangsu and Guangdong provinces. Most of the TC tornadoes were spawned within 500 km of the TC center. Two notable characteristics were found:(1) TC tornadoes in China mainly occurred in the northeast quadrant(Earth-relative coordinates) rather than the right-front quadrant(TC motion-relative coordinates) of the parent TC circulation;and(2) most tornadoes were produced by TCs with a relatively weak intensity(tropical depressions/storms), in contrast with the United States where most tornadoes are associated with stronger TCs. Further analyses showed that TC tornadoes in China tend to be spawned in an environment with large low-level storm relative helicity and large convective available potential energy taking entrainment effects into account. TC tornadoes were particularly active in 2018, with 24 reported tornadoes accounting for 37.5% of the total surveyed samples. The first recorded tornado outbreak in the modern history of China occurred in the envelope of TC Yagi(2018), in which 11 tornadoes were reported in association with significant midlevel intrusions of dry air and the interaction of Yagi with an approaching midlatitude midlevel trough.     

Numerical simulation on the evolution of cloud particles in 3-D convective cloud

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)     

A multifractal model of crack coalescence in rocks

Geometric characteristics of fractal sets of cracks are investigated from the standpoint of their coalescence. A 1D computer model, in which a realistic character of forms of crack sets is achieved through the inducing of sets with the use of the multiplicative cascade procedure, is considered. The investigation is aimed at the determination of conditions of coalescence of cracks organized as a superposition of fractal subsets of a unified set of cracks. The process of crack coalescence is investigated for three different values of the coalescence criterion. The geometric characteristics of the sets of cracks that are necessary for the transition of the crack coalescence process into an avalanche-like stage are estimated.     

雷暴电活动对冰雹增长影响的数值模拟研究

利用三维强风暴动力-电耦合模式,数值模拟了风暴演变过程 中电活动对冰雹增长及地面降雹的影响. 结果指出,带电冰雹与云内强电场作用使地面降雹 量增加约50[HTK]髎[HTSS],雹块直径增大0.7mm,降雹时间滞后约3min. 文中还讨论了强电 场通过对水成物降落速度的调制来影响冰雹微观增长过程,即主要是影响碰并过程和冰雹融 化过程. 电活动使冰雹源、汇总量都减少,但汇总量减少更多,总体效果使冰雹总量增加, 数目减少,冰雹长得更大,更易降落到地面.     

Structures of Mesocirculations Producing Tornadoes Associated with Tropical Cyclone Frances (1998)

Radar structures of one mesocyclone and one mesocirculation (the term mesocirculation refers to a class of rotating updrafts, which may or may not be as spatially and temporally large as a typical mesocyclone) that developed a total of four tornadoes in association with Tropical Cyclone (TC) Frances 1998 are presented. One tornado developed within an inner rainband near the time of landfall while three of the other tornadoes developed within an outer rainband nearly 24 hours after the landfall. Radar reflectivities of the tornadic circulations averaged upwards of 40 dBZ while Doppler radar wind components directed toward the radar averaged 11 m s−1. It is realized that although TC Frances was a minimal hurricane it spawned several tornadoes (four of which were studied) causing damage exceeding $2 million. These tornadoes were not all located close to the TC center, serving as a caution to forecasters and emergency personnel that the immediate landfalling area is not the only place to watch.While it is difficult to accurately predict the TC tornado location and time of occurrence, the degree of low-level baroclinicity seems to play an important role in tornadogenesis. Another significant finding is that the tornadoes were produced on the inward side of an inner rainband, as well as the inward side of an outer rainband. Consistent with climatology, the forward right quadrant of the TC developed the four tornadoes studied here.The lead author, Professor G. V. Rao died 31 July 2004 at the age of 70. He fell victime to the waves while swimming in Mazatlan, Mexico. This is the last paper he publilshed as lead author.     

Lightning Applications in Weather and Climate Research

Thunderstorms, and lightning in particular, are a major natural hazard to the public, aviation, power companies, and wildfire managers. Lightning causes great damage and death every year but also tells us about the inner working of storms. Since lightning can be monitored from great distances from the storms themselves, lightning may allow us to provide early warnings for severe weather phenomena such as hail storms, flash floods, tornadoes, and even hurricanes. Lightning itself may impact the climate of the Earth by producing nitrogen oxides (NOx), a precursor of tropospheric ozone, which is a powerful greenhouse gas. Thunderstorms themselves influence the climate system by the redistribution of heat, moisture, and momentum in the atmosphere. What about future changes in lightning and thunderstorm activity? Many studies show that higher surface temperatures produce more lightning, but future changes will depend on what happens to the vertical temperature profile in the troposphere, as well as changes in water balance, and even aerosol loading of the atmosphere. Finally, lightning itself may provide a useful tool for tracking climate change in the future, due to the nonlinear link between lightning, temperature, upper tropospheric water vapor, and cloud cover.     

一次冰雹过程的惯性重力波观测及数值模拟

使用高灵敏度的电容式微压波传感器对1998年4月11日16时发生在贵州省普定县的一次降冰雹过程的重力波进行观测,利用WRF（Weather Research and Forecast）中尺度模式对这一过程进行数值模拟,使用Morlet小波方法对模拟结果进行分析,得出这一过程中惯性重力波的分布和变化规律,并分析急流、地形及切变线对惯性重力波的影响.观测发现：在降冰雹前,每隔1~4小时出现一次短周期重力波阵性增强的现象.数值模拟结果显示：在低空降冰雹前几个小时有强的短周期重力波出现,其中周期较长的出现早、存在时间长,周期较短的出现晚、存在时间短;强的低空急流和风速垂直切变触发对流或湍流的发生和加强,对流或湍流又激发了80~200 min的短周期重力波;短周期重力波更容易向垂直方向传播,而长周期重力波倾向于水平方向传播.长周期重力波在降冰雹后周期有明显变短现象,随高度越加明显.由地形形成的重力波在最高山峰上空振幅最大.     

Bubble coalescence in basalt flows: comparison of a numerical model with natural examples

Gas accumulation in magma may be aided by coalescence of bubbles because large coalesced bubbles rise faster than small bubbles. The observed size distribution of gas bubbles (vesicles) in lava flows supports the concept of post-eruptive coalescence. A numerical model predicts the effects of rise and coalescence consistent with observed features. The model uses given values for flow thickness, viscosity, volume percentage of gas bubbles, and an initial size distribution of bubbles together with a gravitational collection kernel to numerically integrate the stochastic collection equation and thereby compute a new size spectrum of bubbles after each time increment of conductive cooling of the flow. Bubbles rise and coalesce within a fluid interior sandwiched between fronts of solidification that advance inward with time from top and bottom. Bubbles that are overtaken by the solidification fronts cease to migrate. The model predicts the formation of upper and lower vesicle-rich zones separated by a vesicle-poor interior. The upper zone is broader, more vesicular, and has larger bubbles than the lower zone. Basaltic lava flows in northern California exhibit the predicted zonation of vesicularity and size distribution of vesicles as determined by an impregnation technique. In particular, the size distribution at the tops and bottoms of flows is essentially the same as the initial distribution, reflecting the rapid initial solidification at the bases and tops of the flows. Many large vesicles are present in the upper vesicular zones, consistent with expected formation as a result of bubble coalescence during solidification of the lava flows. Both the rocks and model show a bimodal or trimodal size distribution for the upper vesicular zone. This polymodality is explained by preferential coalescence of larger bubbles with subequal sizes. Vesicularity and vesicle size distribution are sensitive to atmospheric pressure because bubbles expand as they decompress during rise through the flow. The ratio of vesicularity in the upper to that in the lower part of a flow therefore depends not only on bubble rise and coalescence, but also on flow thickness and atmospheric pressure. Application of simple theory to the natural basalts suggests solidification of the basalts at 1.0±0.2 atm, consistent with the present atmospheric pressure. Paleobathymetry and paleoaltimetry are possible in view of the sensitivity of vesicle size distributions to atmospheric pressure. Thus, vesicular lava flows can be used to crudely estimate ancient elevations and/or sea level air pressure.     

Structure and physical characteristics of pumice from the climactic eruption of Mount Mazama (Crater Lake), Oregon

The vesicularity, permeability, and structure of pumice clasts provide insight into conditions of vesiculation and fragmentation during Plinian fall and pyroclastic flow-producing phases of the ~7,700 cal. year B.P. climactic eruption of Mount Mazama (Crater Lake), Oregon. We show that bulk properties (vesicularity and permeability) can be correlated with internal textures and that the clast structure can be related to inferred changes in eruption conditions. The vesicularity of all pumice clasts is 75-88%, with >90% interconnected pore volume. However, pumice clasts from the Plinian fall deposits exhibit a wider vesicularity range and higher volume percentage of interconnected vesicles than do clasts from pyroclastic-flow deposits. Pumice permeabilities also differ between the two clast types, with pumice from the fall deposit having higher minimum permeabilities (~5᎒^-13 m²) and a narrower permeability range (5-50᎒^-13 m²) than clasts from pyroclastic-flow deposits (0.2-330᎒^-13 m²). The observed permeability can be modeled to estimate average vesicle aperture radii of 1-5 µm for the fall deposit clasts and 0.25-1 µm for clasts from the pyroclastic flows. High vesicle number densities (~10⁹ cm^-3) in all clasts suggest that bubble nucleation occurred rapidly and at high supersaturations. Post-nucleation modifications to bubble populations include both bubble growth and coalescence. A single stage of bubble nucleation and growth can account for 35-60% of the vesicle population in clasts from the fall deposits, and 65-80% in pumice from pyroclastic flows. Large vesicles form a separate population which defines a power law distribution with fractal dimension D=3.3 (range 3.0-3.5). The large D value, coupled with textural evidence, suggests that the large vesicles formed primarily by coalescence. When viewed together, the bulk properties (vesicularity, permeability) and textural characteristics of all clasts indicate rapid bubble nucleation followed by bubble growth, coalescence and permeability development. This sequence of events is best explained by nucleation in response to a downward-propagating decompression wave, followed by rapid bubble growth and coalescence prior to magma disruption by fragmentation. The heterogeneity of vesicle sizes and shapes, and the absence of differential expansion across individual clasts, suggest that post-fragmentation expansion played a limited role in the development of pumice structure. The higher vesicle number densities and lower permeabilities of pyroclastic-flow clasts indicate limited coalescence and suggest that fragmentation occurred shortly after decompression. Either increased eruption velocities or increased depth of fragmentation accompanying caldera collapse could explain compression of the pre-fragmentation vesiculation interval.     

The dynamics and thermodynamics of precipitation loading

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.     

Experimental constraints on degassing and permeability in volcanic conduit flow

This study assesses the effect of decompression rate on two processes that directly influence the behavior of volcanic eruptions: degassing and permeability in magmas. We studied the degassing of magma with experiments on hydrated natural rhyolitic glass at high pressure and temperature. From the data collected, we defined and characterized one degassing regime in equilibrium and two regimes in disequilibrium. Equilibrium bubble growth occurs when the decompression rate is slower than 0.1 MPa s^–1, while higher rates cause porosity to deviate rapidly from equilibrium, defining the first disequilibrium regime of degassing. If the deviation is large enough, a critical threshold of super-saturation is reached and bubble growth accelerates, defining the second disequilibrium regime. We studied permeability and bubble coalescence in magma with experiments using the same rhyolitic melt in open degassing conditions. Under these open conditions, we observed that bubbles start to coalesce at ~43 vol% porosity, regardless of decompression rate. Coalescence profoundly affects bubble texture and size distributions, and induces the melt to become permeable. We determined coalescence to occur on a time scale (~180 s) independent of decompression rate. We parameterized and incorporated our experimental results into a 1D conduit flow model to explore the implications of our findings on eruptive behavior of rhyolitic melts with low crystal contents stored in the upper crust. Compared to previous models that assume equilibrium degassing of the melt during ascent, the introduction of disequilibrium degassing reduces the deviation from lithostatic pressure by ~25%, the acceleration at high porosities (>50 vol%) by a factor 5, and the associated decompression rate by an order of magnitude. The integration of the time scale of coalescence to the model shows that the transition between explosive and effusive eruptive regimes is sensitive to small variations of the initial magma ascent speed, and that flow conditions near fragmentation may significantly be affected by bubble coalescence and gas escape.Editorial responsibility: D. Dingwell     

Spatial and Temporal Variations in Indian Summer Monsoon Rainfall and Temperature: An Analysis Based on RegCM3 Simulations

Regional climate models are important tools to examine the spatial and temporal characteristics of rainfall and temperature at high resolutions. Such information has potential applications in sectors like agriculture and health. In this study, the Regional Climate Model Version 3 (RegCM3) has been integrated in the ensemble mode at 55 km resolution over India for the summer monsoon season during the years 1982–2009. Emphasis has been given on the validation of the model simulation at the regional level. In Central India, both rainfall and temperature show the best correlations with respective observed values. The model gives rise to large wet biases over Northwest and Peninsular India. RegCM3 slightly underestimates the summer monsoon precipitation over the Central and Northeast India. Nevertheless, over these regions, RegCM3 simulated rainfall is closer to the observations when compared to the other regions where rainfall is overestimated. The position of the monsoon trough simulated by the model lies to the north of its original observed position. This is similar to the usual monsoon break conditions leading to less rainfall over Central India. RegCM3 simulated surface maximum temperature shows a large negative bias over the country while the surface minimum temperature is close to the observation. Nevertheless, there is a strong correlation between the all India weighted average surface temperature simulated by RegCM3 and IMD observed values. While examining the extreme weather conditions in Central India, it is found that RegCM3 simulated frequencies of occurrence of very wet days, extremely wet days, warm days and warm nights more often as compared to those in IMD observed values. However, these are systematic biases. The model biases in the frequencies of distribution of rainfall extremes explain the wet and dry biases in different regions in the country. Overall, the inter-annual characteristics of both the rainfall and temperature extremes simulated by RegCM3 in Central India are well in phase with those found in the observed data.     

中国东部层积云发展过程中云微物理特征的演变

基于2007—2010年的CloudSat卫星观测数据,以云层液态水路径为指标将层积云的发展过程划分为五个阶段,对比研究了中国东部降水与非降水层积云发展过程中云微物理特征和云微物理机制的演变,并分析了其海陆差异.研究表明:非降水层积云中,云滴增长主要通过凝结过程完成,但云滴的凝结增长有限,难以形成降水,在非降水层积云发展的旺盛阶段,云层中上部云滴发生较弱的碰并过程.降水层积云中云滴碰并增长活跃,当云层液态水路径小于500 g·m~(-2)时,云滴在从云顶下落至云底的过程中持续碰并,并在云底附近出现云水向雨水的转化;当降水层积云液态水路径超过500 g·m~(-2)时,云滴碰并增长主要发生在云层上部,在云层中部,云液态水含量、液态粒子数浓度和液态粒子有效半径达到最大,云水向雨水的转化最为活跃.层积云微物理特征的海陆差异主要是由海陆上空气溶胶浓度和云中上升气流强度不同导致的.在非降水层积云中下部,陆地丰富的气溶胶为云滴凝结增长提供了充足的云凝结核,因而云微物理量的量值在陆地上空更大,而在云层中上部,云滴凝结增长达到极限,海洋充足的水汽输送使云微物理量的量值在海洋上空更大.当降水层积云液态水路径大于500 g·m~(-2)时,陆地层积云中更强的上升气流使大量云滴在云层中上部累积滞留,云滴碰并增长活跃,云层中上部云微物理量的量值在陆地上空更大.     

Occurrence conditions of positive cloud-to-ground flashes in severe thunderstorms

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.     

Experimental evaluation of the coalescence efficiencies of colliding water drops

The coalescence of water drops of sizes comparable to rain drops (200–2500 m diameter) was investigated. The method used provided a good separation between collision and coalescence effects. The result suggests a dependence of the coalescence efficiency on both the size of the large drop and the ratio of the radii of the interacting drops (p-ratio). The coalescence was observed to rapidly decrease due to bouncing and partial coalescence as the angle of impact increased from head-on to grazing angle. However, some bouncing was observed at very low impact angles.The results of the coalescence efficiency were fitted with an empirical equation for use in numerical models of cloud growth and precipitation development.On sabbatical leave (1976–77) from the Department of Geophysics and Planetary Sciences, Tel Aviv University, Ramat Aviv, Israel.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

The Relation Between Humidity and Liquid Water Content in Fog: An Experimental Approach

Microphysical measurements of orographic fog were performed above a montane cloud forest in northeastern Taiwan (Chilan mountain site). The measured parameters include droplet size distribution (DSD), absolute humidity (AH), relative humidity (RH), air temperature, wind speed and direction, visibility, and solar short wave radiation. The scope of this work was to study the short term variations of DSD, temperature, and RH, with a temporal resolution of 3?Hz. The results show that orographic fog is randomly composed of various air volumes that are intrinsically rather homogeneous, but exhibit clear differences between each other with respect to their size, RH, LWC, and DSD. Three general types of air volumes have been identified via the recorded DSD. A statistical analysis of the characteristics of these volumes yielded large variabilities in persistence, RH, and LWC. Further, the data revealed an inverse relation between RH and LWC. In principle, this finding can be explained by the condensational growth theory for droplets containing soluble or insoluble material. Droplets with greater diameters can exist at lower ambient RH than smaller ones. However, condensational growth alone is not capable to explain the large observed differences in DSD and RH because the respective growth speeds are too slow to explain the observed phenomena. Other mechanisms play key roles as well. Possible processes leading to the large observed differences in RH and DSD include turbulence induced collision and coalescence, and heterogeneous mixing. More analyses including fog droplet chemistry and dynamic microphysical modeling are required to further study these processes. To our knowledge, this is the first experimental field observation of the anti-correlation between RH and LWC in fog.     

Growth of the ice phase in strong cumulonimbus updrafts

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.     

Impact of human activities on stream flow in the Biliu River basin,China

The obvious decline in stream flow to the Biliu River reservoir over the period 1990–2005 has raised increasing concerns. Climate change and human activities, which mainly include land use changes, hydraulic constructions and artificial water consumption, are considered to be the most likely reasons for the decline in stream flow. This study centres on a detailed analysis of the runoff response to changes in human activities. Using a distributed hydrological model, (Soil and Water Assessment Tool), we simulated runoffs under different human activity and climate scenarios to understand how each scenario impacts stream flow. The results show that artificial water consumption correlates with the precipitation (wet, normal and dry) of the year in question and is responsible for most of the decrease in runoff during each period and for each different wetness year. A Fuzzy Inference Model is also used to find the relationship between the precipitation and artificial water consumption for different years, as well as to make inferences regarding the future average impact on runoff. Land use changes in the past have increased the runoff by only a small amount, while another middle reservoir (Yunshi) has been responsible for a decrease in runoff since operation began in 2001. We generalized the characteristics of the human activities to predict future runoff using climate change scenarios. The future annual flow will increase by approximately 10% from 2011 to 2030 under normal human activities and future climate change scenarios, as indicated by climate scenarios with a particularly wet year in the next 20 years. This study could serve as a framework to analyse and predict the potential impacts of changes both in the climate and human activities on runoff, which can be used to inform the decision making on the river basin planning and management. Copyright © 2012 John Wiley & Sons, Ltd.     

Study of hydrological processes by the combination of environmental tracing and hill slope measurements: application on the Haute‐Mentue catchment

The objective of this research is to improve the comprehension of the hydrological behaviour of natural catchments. The main originality of this work is to associate different types of measurement in order to obtain a better vision of hydrological processes responsible for streamflow generation. First, the hydrological behaviour is studied at the catchment scale by the application of environmental tracing. A three‐component mixing model based on the silica and calcium concentrations of water allows one to distinguish the contributions of direct precipitation, soil water and groundwater during flood generation. Despite the different hydrological responses observed between the four subcatchments studied, a common behaviour is apparent. Soil contribution increases with a rise in the basin humidity. The subsurface water dominates the generation of major floods, which occur in wet conditions. In order to discover the processes responsible for the important soil water contributions, a large‐scale time‐domain reflectometry experiment (64 probes) was conducted. On the whole, this experiment indicates that the water flow in soil is spatially quite heterogeneous and depends on local properties. Macropore flows were clearly identified during a rainfall simulator experiment. Preferential flows may be responsible for the important contribution of soil water and the heterogeneity of the soil moisture. In order to test this hypothesis, a dye‐tracing experiment was done. This new investigation confirms that an important part of soil water reaches the stream by preferential flows. So as to synthesize all these observations, a conceptual model is proposed. This model respects both the hydrochemical responses highlighted by the environmental tracing experiment and the observations done at the local scale. This conceptual model suggests that the important contribution of soil water is due to the extent of the hydrographic network and the role of preferential flows. Copyright © 2005 John Wiley & Sons, Ltd.     

8.12桦南清晨局地突发短时冰雹过程分析

本文对2010年8月12日清晨桦南县发生的局地突发短时冰雹天气进行了天气成因分析,表明冷锋前强烈上升气流为冰雹云形成提供了动力条件,锋前新生对流云团发展形成冰雹云。利用雷达基本数据产品揭示了冰雹云形成发展、成熟和消散全过程的主要回波特征,并应用雷达产品对冰雹的识别及与人工识别进行对比,其产品比人工提前10分钟识别冰雹,具有很高的临近冰雹预警应用性能。