2023届高考英语三轮复习冲刺押题外刊阅读理解训练 (16)

2023届高考英语三轮复习·冲刺押题 外刊阅读理解训练16 ——改编自How much does a cloud weigh? 【文章】 Have you ever wondered how much a cloud weighs? Clouds may look light and fluffy, but they are much heavier than air. Clouds are formed from air and tiny water droplets when water condenses around a "seed" particle such as nitric acid or vapors released by trees. There are a few ways that the weight of a cloud can be measured. One method involves weighing the water vapor within the cloud, which requires understanding the dimensions of the cloud along with how densely packed its droplets are. Margaret LeMone, an atmospheric scientist at the National Center for Atmospheric Research in Colorado, estimated the water weight of an average cumulus cloud. She measured the size of its shadow and estimated the height, since cumulus clouds tend to be roughly the same height as they are wide. Based on prior research, LeMone calculated the density of water droplets to be around 1/2 gram per cubic meter and arrived at an estimate of 550 tons of water for the cloud she was studying. That's equivalent to about 100 elephants! Despite their weight, clouds don't fall down because the droplets within them are minute and don't fall very quickly. They're approximately one million times smaller than raindrops, and high-altitude wind currents keep them afloat longer. Additionally, heat convection helps keep these droplets airborne, as warm air is more buoyant than the cold air located beneath it. Eventually, clouds will release their contents in the form of rain. The droplets cool and conglomerate until they become heavy enough to plummet back to Earth. However, each raindrop is still only around 0.08 inches (2 millimeters) in diameter, which distributes the weight and prevents several hundred pounds of water from crashing onto someone's head all at once. In conclusion, clouds may appear gentle and feathery, but they're actually quite heavy due to the numerous water droplets that comprise them. Thanks to various wind c