"See" Thunder etc.

With thunder， there's always lots to hear. Now there's also something to see. For the first time， scientists have precisely mapped the loud clap radiating from a lightning strike. This picture of thunder's origins could reveal the energies involved in powering some of nature's flashiest light shows.

Lightning strikes when an electric current flows from a negatively charged cloud to the ground. This rapidly heats and expands the surrounding air， creating sonic shock waves. We hear this as thunder.

Scientists have a basic understanding of the origins of thunder. Still， experts have lacked a detailed picture of the physics powering the loud cracks and low rumbles.

Maher Dayeh works at the Southwest Research Institute in San Antonio， Texas. As a heliophysicist， he studies the sun and its effects on the solar system， including Earth. He and his colleagues also study lightning — by making their own. These experts trigger the bolts by firing a small rocket into an electrically charged cloud. Trailing behind the rocket is a long， Kevlar-coated copper wire. The lightning travels along that wire to the ground.

For their new experiment， the scientists used 15 sensitive microphones laid out 95 meters （312 feet） from the strike zone. The team then precisely recorded the incoming sound waves. Those from higher elevations took longer to reach the microphones.

That allowed the scientists to map the acoustic （sound） signature of the lightning strike. That map revealed the strike with "surprising detail".

How loud a thunderclap sounds will depend on the peak electric current flowing through the lightning， the researchers found. Explains Dayeh， this discovery could one day allow scientists to use thunder to sound out the amount of energy powering a lightning strike.

用眼睛“看”雷聲

雷聲轟鳴，不絕于耳。但現在雷聲也可用“眼”觀。科學家初次用圖精確地繪制出雷擊所發出的巨大霹靂聲。該雷聲起源圖能夠揭示自然界最耀眼的閃光背后的驅動力量。

當電流從帶負電荷的云團流向地面的時候，雷擊就發生了。雷擊使周圍空氣溫度迅速升高并膨脹，產生沖擊聲波，沖擊聲波就是我們聽到的雷聲。

科學家們已經基本理解了雷聲的起源。但他們還是缺乏一張能夠詳細描寫產生這種巨大霹靂聲和低沉轟鳴聲的物理學動因的圖。

Maher Dayeh就職于美國得克薩斯州圣安東尼奧市的西南研究所。作為一名太陽物理學家，他從事研究太陽以及太陽對太陽系的影響，包括對地球的影響。他和同事們也研究閃電，他們通過自己創造的閃電來一探閃電的究竟。這些專家將一枚小型火箭發射到負電荷云團來觸發雷電，火箭的尾部系著一根長長的、用凱夫拉爾纖維進行過表面處理的銅線。閃電通過那根銅線傳導到地面。

在一項新的實驗中，科學家將15個高靈敏度的擴音器安置在離雷擊區95米（312英尺）以外的地方。然后他們精確地記錄了傳導進來的聲波。聲波傳導到擴音器的時間隨著聲波源高度的增加而增加。

這樣，科學家就能繪制出雷擊的聲波標記圖。這張圖揭示的雷擊的精細程度令人驚訝。

這些研究者發現，霹靂的響亮程度取決于穿越閃電的峰值電流。Dayeh解釋道，這一發現有朝一日能夠使科學家運用雷鳴來搞清楚驅動雷擊所需能量的大小?！?br>