《那些古怪又讓人憂心的問題》第133期:雨滴(1)
RAINDROP
Q. What if a rainstorm dropped all of its water in a single giant drop?
Q．如果一場暴雨中所有的水分都匯聚成一顆巨大的水珠並從天上掉下來會發生什麼？——Michael McNeill
——邁克爾•麥克尼爾
A. IT'S MIDSUMMER IN KANSAS. The air is hot and heavy. Two old-timers sit on the porch in rocking chairs.
A．堪薩斯的某個盛夏，空氣燥熱而潮溼。門廊裏兩位老人坐在搖椅裏。On the horizon to the southwest, ominous-looking clouds begin to appear. The towers build as they draw closer, the tops spreading out into an anvil shape.
在西南邊的天際，一股不祥的雲涌現出來，並在逐漸接近的過程中形成雲柱，頂部向外擴散形成鐵氈樣形狀。They hear the tinkling of wind chimes as a gentle breeze picks up. The sky begins to darken.
老人們聽到了微風吹過風鈴時發出的丁零聲。天色漸漸暗了下來。Moisture
溼氣Air holds water. If you walled off a column of air, from the ground up to the top of the atmosphere, and then cooled the column of air down, the moisture it contained would condense out as rain. If you collected the rain in the bottom of the column, it would fill it to a depth of anywhere between zero and a few dozen centimeters. That depth is what we call the air's total precipitable water (TPW).
空氣中攜帶着水分。如果你從地面開始向上豎起一道牆直至大氣層頂端，使包圍在其中的空氣柱降溫，其中所含的水分就會凝結成雨。如果你在底部收集這些雨水，就會發現雨水的深度在零到幾十釐米之間。這個深度就是我們所說的空氣的總可降水量（TPW）。Normally, the TPW is 1 or 2 centimeters.
通常來說，總可降水量爲1～2釐米。Satellites measure this water vapor content for every point on the globe, producing some truly beautiful maps.
衛星會測量地球上每一點的水蒸氣含量，並得到一些非常漂亮的地圖。We'll imagine our storm measures 100 kilometers on each side and has a high TPW content of 6 centimeters. This means the water in our rainstorm would have a volume of:
不妨假設一個暴雨雲團長寬各100千米，具有較高的總可降水量——6釐米。這意味着整個雲團中含水：That water would weigh 600 million tons (which happens to be about the current weight of our species). Normally, a portion of this water would fall, scattered, as rain-at most, 6 centimeters of it.
這些水的質量有6億噸（恰好差不多是人類的總重量）。一般情況下，其中一部分水會分散地落下來形成雨，降水量最多也是6釐米。In this storm, all that water instead condenses into one giant drop, a sphere of water over a kilometer in diameter. We'll assume it forms a couple of kilometers above the surface, since that's where most rain condenses.
而在這個雲團中，所有的水都凝結成了一大滴水，一個直徑超過1千米的水球。假設這個水球離地若干千米，絕大多數雨都在這裏冷凝形成。The drop begins to fall.
然後巨大的水滴開始下落。
