This is why an observer on the ground watching a thunderstorm approach can often feel a gust of cool air before the storm passes overhead. When such air hits the ground, it usually moves outward ahead of the storm at a higher speed than the storm itself. If the descending air originated at a height of 10,000 metres (33,000 feet), for example, it might reach the ground with a horizontal velocity much higher than the wind at the ground. Not only is the sinking air more dense than its surroundings, but it carries a horizontal momentum that is different from the surrounding air. Thunderstorm downdrafts originate at altitudes where the air temperature is cooler than at ground level, and they are kept cool even as they sink to warmer levels by the evaporation of water and melting of ice particles. Weather under thunderstorms Downdrafts and gust fronts A large, multicell storm can easily be 10 to 100 times more energetic. In a typical case, this energy is about 10 7 kilowatt-hours, roughly equivalent of a 20-kiloton nuclear explosion (though it is released over a broader area and in a longer span of time). A rough estimate of the total energy in a thunderstorm can be made from the total quantity of water that is precipitated by the cloud. The release of latent heat energy in an updraft is converted, at least in part, to the kinetic energy of the air motions. When water drops freeze in the upper parts of the cloud, another 80 calories per gram are released. For every gram of water that is condensed, about 600 calories of heat are released to the atmosphere. The energy that drives thunderstorms comes primarily from the latent heat that is released when water vapour condenses to form cloud drops. In large, multicell storms, the new cells tend to form to the right of the steering winds in the Northern Hemisphere and to the left in the Southern Hemisphere. When winds are light, an individual cell may move very little, less than two kilometres, during its lifetime however, in a larger storm, new cells triggered by the outflow from downdrafts can give the appearance of rapid motion. Most storms continually evolve and have new cells developing while old ones dissipate. In extreme circumstances, a supercell storm may move 65 to 80 km (about 40 to 50 miles) per hour. The speed of isolated storms is typically about 20 km (12 miles) per hour, but some storms move much faster. The motion of a thunderstorm across the land is determined primarily by the interactions of its updrafts and downdrafts with steering winds in the middle layers of the atmosphere in which the storm develops. SpaceNext50 Britannica presents SpaceNext50, From the race to the Moon to space stewardship, we explore a wide range of subjects that feed our curiosity about space!.Learn about the major environmental problems facing our planet and what can be done about them! Saving Earth Britannica Presents Earth’s To-Do List for the 21st Century.Britannica Beyond We’ve created a new place where questions are at the center of learning.100 Women Britannica celebrates the centennial of the Nineteenth Amendment, highlighting suffragists and history-making politicians.COVID-19 Portal While this global health crisis continues to evolve, it can be useful to look to past pandemics to better understand how to respond today.Student Portal Britannica is the ultimate student resource for key school subjects like history, government, literature, and more.Demystified Videos In Demystified, Britannica has all the answers to your burning questions.This Time in History In these videos, find out what happened this month (or any month!) in history.#WTFact Videos In #WTFact Britannica shares some of the most bizarre facts we can find.Britannica Classics Check out these retro videos from Encyclopedia Britannica’s archives.Britannica Explains In these videos, Britannica explains a variety of topics and answers frequently asked questions.
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