闪电放电特征和雷暴电荷结构研究

文章综述了近10年来对闪电物理过程和雷暴电荷结构等方面的主要研究进展。利用自行研制的高时间分辨率新型闪电探测和定位技术,获得中国不同地区的闪电特征及放电参数,组织首次青藏高原综合闪电观测实验,揭示高原雷暴及其闪电活动的特殊性,并利用数值模式探讨其成因;将原子结构理论应用于闪电光谱研究,并进行闪电光谱的实验观测和理论研究,获得可见光频段的闪电光谱记录;完善空中人工引发闪电技术,解决近距离严酷电磁环境条件下闪电的光、电信号测量技术,寻找闪电双向先导传输的光学和甚高频辐射证据,并利用人工引发闪电技术对防雷设施进行试验研究;另外,在闪电与天气、气候关系的研究方面也进行了初步探讨。     

青藏高原雷暴天气层结特征分析

青藏高原那曲地区夏季雷暴活动相当频繁,这种雷暴主要是受地形的影响,在地形的热力和动力作用下形成雷暴,但强度不大,最大反射率一般不超过4 0 dBz,相对云顶高度可伸展到1 0.0~13.0 km,强弱雷暴差别不大。雷暴持续时间大约为30 min左右,主要发生在13:00~19:00(北京时,下同)之间,峰值出现在16:00左右。此外,在晚上也有弱对流,最大反射率约为20 dBz。高原雷暴天气层结具有与平原雷暴完全不同的特征,一般为整层弱不稳定,高度可以伸展到100 hPa,整层不稳定能量不大,强雷暴CAPE值平均为782 J.kg-1,弱雷暴约为406 J.kg-1,分布较均匀,不出现能量特别大的不稳定层次。近地层相对湿度有“逆湿”现象,厚度约1~2 km,平均为60%~80%(雨季后)。无论是强雷暴天气还是弱雷暴天气都具有上述相似层结。这种层结可触发对流,发展高度很高,但强度不大,能量较小。这种特殊层结揭示了高原雷暴的特殊结构。雷暴的闪电频数可以表征雷暴发展强度,通常可以建立闪电频数与雷暴单一参量(云顶高度)之间的统计关系式,从而可以利用测量闪电频数来预报雷暴的强弱,但上述关系对于高原雷暴并不适用,必须建立闪电频数与多参量之间的综合关系。     

On the generation of charge layers in MCS stratiform regions

We suggest a quantitative one-dimensional model treating the formation of charge layers near the 0 °C isotherm in stratiform regions of mesoscale convective systems. A number of factors principal for the field generation have been taken into account: both non-inductive and inductive melting charging, light ions, a complicated profile of the vertical air velocity near the 0 °С isotherm, the boundary conditions proper for the horizontally extended systems in the global electric circuit. Non-inductive collisional charging near the 0 °C isotherm was not considered. It was found that both non-inductive and inductive melting mechanisms can contribute; the inductive melting charging of ice aggregates was found more preferable, while the contribution of non-inductive mechanisms might be significant depending on particular conditions. The role of light ions in the formation of the positive charge layer near the 0 °C isotherm may be important. If the advection from the convective region ensures charge inflow to the upper charged layers, the melting charging mechanisms are able to explain an observable electric field structure in the whole stratiform region. It is important that the mutual position of the zero point on the vertical air velocity profile and the point of maximum melting-charge-transfer determines the fine structure of the electric field in the vicinity of the 0 °C isotherm.     

CAPE values and hailstorms on northwestern Spain

A study has been carried out in León (in the northwest of the Iberian Peninsula) on atmospheric convection during summer periods, by analyzing the values of the Convective Available Potential Energy (CAPE) around 07:00 UTC. The project analyzed the data provided by a network of voluntary observers, a hailpad network, and a meteorological station on a sample of 224 days. The CAPE values found were not high: they never reached 2000 J/kg, not even on hail days, i.e. on days with high convective activity. These values are much lower than the ones measured in convective situations in tropical regions, but they are within the usual values found in Europe. The same happens with the wet bulb potential temperature measured in León. The frequency distribution of the CAPE values shows a clear prevalence of very low or zero values. The group of days with the lowest CAPE value is that which included days with no storm. The mean value increases on storm days, and it is even higher for the days with recorded hailfalls. All these differences are significantly marked. Nevertheless, the differences across the years are not significant enough to be able to speak of an influence of the climatic change on the CAPE. The correlation of the CAPE with some of the variables previously used for hail forecasts was analyzed, and the correlation found was higher for the lifted index. The possible use of the CAPE as a thunderstorm and hailstorm forecasting method was considered. The results were encouraging, especially for hail forecasting, although the CAPE should not be used as the only variable, but combined with other parameters. Moreover, the relationships between the CAPE and the wet bulb potential temperature and between the CAPE and the physical parameters of the hailstones were also analyzed. A relationship was observed with the parameters of the hailstone size distribution. Nonetheless, these results are provisional, and they should be confirmed by analyzing a more representative sample. With a more detailed analysis of these and other relationships, the present forecast model used by the Laboratory for Atmospheric Physics at the University of León is expected to be greatly improved by including the CAPE in this model.     

青海地区一次雷暴的地闪活动及云内的电场探空观测

2016年夏季在青海大通地区获得一次局地雷暴云内的电场探空资料,结合雷达、地闪定位资料,详细分析了该雷暴的地闪活动特征及云内的电荷结构.结果显示,该雷暴过程的负地闪在时间上呈间歇性发生,在空间分布上表现为不连续,且所有的正地闪都发生于雷暴的成熟阶段.在雷暴成熟阶段与消散阶段过渡期获得云内的垂直电场廓线表明,雷暴内的电荷结构在探空阶段呈四极性,最下部为处于暖云区内负电荷区,往上依次改变极性.最上部的正电荷区由于数据丢失无法判断其上边界外,其余3个电荷区的海拔高度分别为：5.5~5.7 km（3.4~2.3℃）、5.7~6.2 km（2.3~-0.4℃）和6.2~6.6 km（-0.9~-1.7℃）,对应的电荷密度为-1.81 nC·m^-3、2.47 nC·m^-3和-1.76 nC·m^-3.其中,下部正电荷区的强度最大,其次为上部的负电荷区.通过分析电荷区分布与正地闪活动的关系,认为暖云区内负电荷区的形成有利于诱发下部正电荷区的对地放电.

     

青藏高原雷暴的闪电特征及其成因探讨

通过对2003—2004年夏季青藏高原那曲地区30次雷暴过程的地面电场及闪电电场变化的分析,发现高原雷暴具有三极性电荷结构特征,其中73%(22次)的雷暴过程在其成熟阶段地面电场呈正极性,表明在雷暴云下部存在较常规雷暴范围广、电荷量大的正电荷区(LPCC),其余27%(8次)的雷暴同样具有三极性电荷结构特征,但LPCC相对要小得多。高原雷暴平均闪电频数一般只有1 fl.min-1,相对其它地区要小几十倍。对雷暴云闪电特征的进一步分析发现,具有较大LPCC的雷暴按照闪电特征可分为以云闪(IC)、负地闪(-CG)和正地闪( CG)为主的三类雷暴。结合气象参量分析发现IC型雷暴对应较高的地气温差和地表温度,相对湿度较小,而 CG型雷暴发生在傍晚,因此对应的地气温差偏小。     

积云动力和电过程二维模式研究 Ⅰ．理论和模式

提出了一个模拟积云动力和电力发展的二维时变轴对称模式。考虑了１０种主要微物理过程，它们包括凝结（凝华）、蒸发、自动转换、粒子间的碰撞以及冰晶核化，次生冰晶等。在起电过程中除了考虑常规的扩散和电导起电外，重点引入了感应和非感应起电，以及次生冰晶起电的作用。作者认为后三个过程是形成积云电结构的主要物理因子。     

A modelling study of the effect of cloud saturation and particle growth rates on charge transfer in thunderstorm electrification

Numerical studies have been made of the importance of cloud saturation to the sign of charge transfer during graupel/ice crystal interactions in thunderstorms. Previous laboratory studies led to the idea that the diffusional growth rates of the interacting ice surfaces may influence the sign of the charge transferred during brief collisional contact. The ice crystals grow by vapour diffusion in a supersaturated environment while the graupel surface grows by diffusion under low accretion rate conditions, but will sublimate when heated sufficiently by riming. The graupel surface is also influenced, even under net sublimation conditions, by the vapour released to it from droplets freezing on its surface. In a cloud, the diffusional growth rates are also affected by ventilation when the supercooled droplets and their local environment flow past the riming surface.The diffusional growth rates of ice crystals and riming graupel particles are calculated for various cloud saturation ratios, then the sign of electric charge transferred during crystal/graupel collisions is determined according to the concept of the relative vapour diffusional growth rates, according to Baker et al., 1987 [Baker, B., Baker, M.B., Jayaratne, E.J., Latham, J., Saunders, C.P.R., 1987. The influence of diffusional growth rates on the charge transfer accompanying rebounding collisions between ice crystals and soft hailstones. Quart. J. Roy. Met. Soc. 113, 1193–1215]. It is found necessary, in order to account for the observation of positive charging of riming graupel at high accretion rates, to modify the assumptions of Baker et al. in order to increase the flux of vapour to the graupel surface. The variable growth parameters available may be adjusted to represent the environmental saturation conditions in various laboratory experiments, including the mixing of clouds from regions having different growth conditions, and are used to determine charge sign sensitivity to cloud saturation ratio, temperature and accretion as measured by the cloud effective liquid water content.     

一次中尺度温度和湿度锋区对冰雹回波系统的影响

为了更好地监测预警冰雹和雷暴大风等强天气,使用常规天气图、TBB云图、自动气象站、雷达拼图、雷达PUP产品等资料,对2021年5月10日江西雷暴回波群冰雹天气过程,采用中尺度气象学和雷达气象学等方法进行分析,结果表明：雷暴回波群中超级单体产生大冰雹并伴随雷暴大风天气,没有出现短时强降水;超单往往造成较大冰雹,强单出现较小冰雹;樟树、丰城的对流云系发展成为中尺度对流系统MCS。湿度锋区达到≥40%/100 km和温度锋区达到≥10℃/100 km时,就能够触发产生对流运动而形成新的对流回波;当原有对流回波移到锋区附近时,回波会快速发展加强,强回波面积迅速扩大。风暴跟踪信息STI能较好地指示超级单体和强单体回波的移动方向和移动速度,多条STI指向一致时可信度更高。超单CR在65 dBZ以上,强回波面积较大,VIL在60 kg/m2,V0.5有正负速度对,RCS有冰雹回波特殊结构特征;VCS有正负速度切变;强单CR在60～65 dBZ之间,强回波面积较小,VIL在45～50 kg/m2之间,V0.5不一定有速度切变,RCS冰雹回波特殊结构特征不明显,VCS表现在负值区中出现大值区。     

大理机场雷暴特征及潜势预报分析

利用大理机场5年天气观测资料和FNL 1.0X1.0数据,对大理机场雷暴特征及潜势预报进行分析,结果发现：大理机场全年各月都有可能出现雷暴天气,雷暴天气主要出现在6~9月,每年7月和8月雷暴天气出现最为频繁;雷暴天气持续时间0~1小时的次数最多,持续时间1~2小时的雷暴也比较常见,持续时间4~6小时的次数较少,没有出现持续时间6小时以上的雷暴;雷暴可以出现在大理机场的任何方向,出现在东边的次数最多,出现在天顶的次数最少;雷暴初期平均在1月31日,雷暴终期平均在11月14日,雷暴的初期和终期年际差别较大。选取对流有效位能、500hPa相对湿度、0度层高度、近地表四层等压面的抬升指数和可降水量作为预报因子建立大理机场雷暴预报方程,预报方程是显著的,有较好的雷暴潜势预报能力。