一次伴有雷暴大风的飑线天气过程分析及数值模拟研究

利用NCEP/NCAR(1°×1°)的逐6 h再分析资料、WRF中尺度预报模式,对2014年7月30—31日发生在江淮地区的一次强飑线天气过程进天气学分析和数值模拟研究。研究结果表明,此次飑线过程是在高空槽后有强冷空气输送、中层阶梯槽引导干冷空气南下并叠加在低层暖湿气流之上的有利背景条件下产生的,低空切变线是此次飑线过程的重要触发机制。在飑线成熟阶段,气流下沉速度极大值区在高(低)层与霰(雨水)混合比极大值区有很好的对应关系,水凝物粒子下落时对周围空气的拖曳作用是下沉气流形成的关键。雨水蒸发率影响飑线维持期间地面冷池的强度和分布,雨水蒸发率越大,地面冷池强度越强、范围越广;雨水蒸发率越小,地面冷池越弱,甚至消失。雨水蒸发率与地面风速也有很好的正相关性,增大雨水蒸发率可使地面风速增大,使模拟的地面最大风速更接近实况。     

Simulation of location-specific severe thunderstorm events using high resolution land data assimilation

In this study, the impact of different land initial conditions on the simulation of thunderstorms and monsoon depressions is investigated using the Weather Research and Forecasting (WRF) model. A control run (CNTL) and a simulation with an improved land state (soil moisture and temperature) using the High Resolution Land Data Assimilation System (HRLDAS, experiment name: EHRLDAS) are compared for three different rainfall cases in order to examine the robustness of the assimilation system. The study comprises two thunderstorm cases (one in the pre-monsoon and one during the monsoon) and one monsoon depression case that occurred during the Interaction of Convective Organisation, Atmosphere, Surface and Sea (INCOMPASS) field campaign of the 2016 Indian monsoon. EHRLDAS is shown to yield improvements in the representation of location-specific rainfall, particularly over land. Further, it is found that surface fluxes as well as convective indices are better captured for the pre-monsoon thunderstorm case in EHRLDAS. By analysing components of the vorticity tendency equation, it is found that the vertical advection term is the major contributor towards the positive vorticity tendency in EHRLDAS compared to CNTL, hence improving localised convection and consequently facilitating rainfall. Significant improvements in the simulation of the pre-monsoon thunderstorm are noted, as seen using Automatic Weather Station (AWS) validation, whereas improvements in the monsoon depression are minimal. Further, it is found that vertical advection (moisture flux convergence) is the major driver modulating the convective circulation in localised thunderstorm (monsoon depression) cases and these dynamics are better represented by EHRLDAS compared to CNTL. These findings underline the importance of accurate and high resolution land-state conditions in model initial conditions for forecasting severe weather systems, particularly the simulation of localised thunderstorms over India.     

Calibration of particle detectors for secondary cosmic rays using gamma-ray beams from thunderclouds

After observation of hundreds of Thunderstorm Ground Enhancements (TGEs) we measure energy spectra of particles originated in clouds and directed towards Earth. We use these “beams” for calibration of cosmic ray detectors located beneath the clouds at an altitude of 3200 m at Mount Aragats in Armenia. The calibrations of particle detectors with fluxes of TGE gamma rays are in good agreement with simulation results and allow estimation of the energy thresholds and efficiencies of numerous particle detectors used for studying galactic and solar cosmic rays.     

A comparison of the midlevel kinematic characteristics of a pair of supercell thunderstorms observed by airborne Doppler radar

The midlevel kinematic characteristics of two supercell thunderstorms observed during the Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX), one tornadic and the other nontornadic, are compared using airborne pseudo-dual-Doppler wind retrievals. The most significant difference between the two cases was that a midlevel rear-inflow jet was observed in the nontornadic supercell (12 May 1995), whereas such rear-to-front, storm-relative flow was absent at midlevels in the tornadic supercell (16 May 1995). The midlevel jet in the nontornadic supercell was located on the north flank of a prominent region of anticyclonic vertical vorticity. Some speculations are provided pertaining to the possible importance of the midlevel kinematic differences between the two storms.     

闪电宽带电场三维定位及其回波特征

利用自制闪电宽带电场三维定位系统, 分析了山东地区一次雷暴过程闪电三维时空结构。结果表明, 在云内击穿放电整个时间序列中, 辐射源空间分布（对应强电场区分布）呈现明显的三极性分层电荷结构, 并分布在3个高度层次： 6~8 km为上部正电荷区, 4~6 km为中部负电荷, 2.5~4 km为下部次正电荷区。云内放电首先出现在中部负电荷区, 然后产生向上发展的负流光进入上部正电荷区传输, 形成向上发展的云闪; 随着雷暴发展, 产生向下发展的负流光进入下部次正电荷区, 形成向下发展的云闪, 且能维持到雷暴发展后期。结合雷达回波分析表明, 雷达回波的强度影响着闪电活动, 强回波区的增加会使得强电场区域增加, 但是强电场区域并不与最强回波区域对应, 除下部正电荷区的底部会有部分辐射源出现在回波强度为40~50 dBz的区域中以外, 大多数的辐射源出现在25~35 dBz的中等回波区范围内, 强回波区域中通常较少出现击穿放电。     

Lifetime of the thunderstorm electric energy in the global atmospheric circuit and thunderstorm energy characteristics

The lifetime of electric energy in the atmosphere is introduced and investigated as is the total electric energy of the atmosphere related to the total mean rate of electric energy dissipation. This lifetime, as determined from general estimations and convenient analytical expressions, turns out to be very small – from about 10 to about 100 s, depending on the assumptions on the control parameters of principal sources in the global electric circuit. In particular the energy lifetime is less than the relaxation time of the “global condenser” and field relaxation time near the ground surface. It is explained by the high dissipative rate of the electric energy in the atmosphere, taking into account that the regions mainly contributing to the total energy and its dissipative rate are connected to the altitudes of active parts of electrified (thunderstorm) clouds in the atmosphere with exponentially increasing conductivity.     

北京首都国际机场暖切初雷天气的特征分析

针对近两年北京首都国际机场的两次暖切初雷进行研究,总结预报经验,探讨预报的可行性,结果表明:1)两次暖切初雷中,500 h Pa高度层均有浅槽存在,且500 h Pa高度层的正涡度区到达本场附近的时间与雷雨发生时间一致,同时低层有较强的辐合抬升;2)从雷达图像来看,两次雷雨发生时,本场附近均存在明显的速度辐合,雷雨回波为局地生成;3)相当黑体温度(Black Body Temperature,TBB)越低,对流越旺盛,所以TBB等值线图可以用来推断对流的发展趋势;4)在雷雨发生时段,基于风云2号气象卫星的雷暴云指数值介于0~0.5之间,雷暴云指数的变化趋势可以较准确表征雷雨发生的时间。     

我国南方雷暴的气候特征研究

本文根据我国南方62个气象观测着1971-995年月雷暴日数资料，应用EOF和小波统计分析方法，研究了雷暴的气候特征，包括它们的空间分布类型、季节变化特征和年际变化规律，所得结论，为进一步探讨大范围雷暴与大气环流的联系打下了基础。     

Geomorphic effects of a 10-year storm on a small drainage Basin in the Texas Panhandle

Bedded Permian salt in the Palo Duro Basin of the Texas Panhandle is being considered for isolation of nuclear waste. Studies underway to evaluate the geomorphic processes affecting any waste repository that may be sited in the region include studies of the geomorphic events associated with individual storms. On 26 May, 1978, thunderstorms occurred near Canyon, Texas, which received 130mm of rain, and on a small instrumented watershed at Buffalo Lake, 16 km to the southwest, which received 71 mm of rain. Rainfall at Buffalo Lake was concentrated in a period of 3 hours, representing a return period of approximately 10 years and a maximum 30-minute intensity of 64 mm/hour. Erosion-pin fields, topographic surveys, and stakes for headcut monitoring had been established 2 to 3 months before the storm in a 640-m long tributary canyon to Tierra Blanca Creek downstream of Buffalo Lake. Canyon slopes of moderately to slightly calichified sands and gravels of the Ogallala Formation are capped by well-indurated caliche on the canyon rim. Erosion-pin fields showed average net erosion of 2·4 cm (0° to 9° slope) to 2·7 cm (10° to 19° slope) and a single-pin maximum value of 6·2 cm in the 20° to 29° slope class. Headcuts 1 to 2 m deep in alluvial-colluvial material on the floor of the canyon migrated as much as 12 m upstream. Canyon floor deposition occurred as a series of elongate bars, 16m long and longer, located at the mouth of tributary gullies, downstream from scours, and at slope breaks. Grain sizes ranged from boulders up to 70cm in intermediate axis deposited in the upper canyon to fine to very fine sand deposited as a sheet up to 25cm thick beyond the mouth of the canyon at Tierra Blanca Creek. In an adjacent canyon a sequence of irregular beds of caliche gravel, mixed sand and gravel, and fine sand up to 3 m thick is exposed. Comparison of this sequence with deposits resulting from the 26 May, 1978, storm suggests that the coarse fraction of the alluvial sequence is deposited by repetitive major storm events. Cobble and boulder units 30 to 70cm thick can evidently be deposited in a few hours. Under the continental climate of the Texas Panhandle, erosion, deposition, and stream incision are taking place primarily in discrete steps related to episodes of intense rainfall.     

Electric charge separation in severe storms

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.