北部湾中小尺度灾害性强对流天气系统的次声电磁波预警系统的研制与机理探讨

THE USE OF VLF AND IF-SOUND SOUNDING SYSTEM FOR DEVELOPING AND DISCUSSING MESOSCALE CATASTROPHIC STRONG CONVECTION WEATHER(THUNDER STORMS) NOWCASTING AND WARNING SYSTEM OVER NORTHERN BAY OF SOUTH CHINA SEA

自行研制了次声阵与单台雷暴次声电磁波报警仪 ,它针对雷暴系统在夹卷过程中的电荷积累与释放和气流电磁特性与声学特性 ,利用其辐射电磁波和次声波作为源地与强度的信息指标 ,三年来对大于 1 7m s(阵性 )以上雷暴大风系统与过程无一漏报。1 997年对 7次灾害性雷雨大风 ,全部提前 3～ 6h报出 ,减少了 7千万元以上的损失。分析发现 ,雷暴系统孕育期间前兆次声信息 ,这与过去所得到的国内外雷暴成熟期的次声信息在频响特性上不同。本文还对其次声发生的机理、夹卷过程、湍流进行了初步探讨。

The warning system to be composed of infra sound sounding net and single thunder warning station by use of VLF and IF sound emitted from lightning was developed in 1995. After that, during three years(1995～1997) the system ran on in the 4～6 months every year and forecast 21 strong thunder storms. The convection 17 m/s gale had been happened in Northern Bay of South China Sea since the IF sound signal appeared 3～6 hours in advance. From April to June 1997, the seven catastrophic convection thunderstorms had been forecasted by the authors and had been protected by NHOC before it appeared 40 minutes ago. The nowcast decreased the loss about seventy million RMB predicted. In the strong convection weather system, the strong turbulence exists in the beginning, a lot of the vapor phase changes and water drops increase and grow up with the turbulence in the unstable cloud, and the charge accumulate or release go on, the drops grow up with collision and electric attraction again and again, turbulent and entrainment motion might be caused selforganization and positive feedback. Consequently the turbulent motion would evolute to some single direction motion(prosconvection) and then emit the IF sound if the conditions exist for very strong extra unstability and more moisture exchange. By the time the turbulent motions develop to the convection that can emit another long period IF sound. The results show that the pros 1～2 seconds period IF sound wave of the turbulence is different from 5～100 seconds period of IF sound waves of the convection, besides, the waves pattern don't show dispersion and always appear in half amplitude form. The mechanism has been discussed.