The flag cloud, the weather vane on Mount Everest


Flag cloud is a kind of topographic cloud that appears at the top of isolated mountain at high altitude. It is named “flag cloud” because its cloud body is tilted to the side of the mountain and looks like a flag, blowing in the wind.Flag cloud is a kind of topographic cloud that appears at the top of isolated mountain at high altitude. It is named “flag cloud” because its cloud body is tilted to the side of the mountain and looks like a flag, blowing in the wind.How are flag clouds created?When water vapor in the atmosphere gets cold, it liquefies into water droplets or condenses into ice crystals. Clouds are formed when countless water droplets or ice crystals gather together.Therefore, the first element to form a flag cloud is sufficient water.On the north slope of Mt. Qomolangma, the underlying surface varies greatly at different elevations, such as gravel surface above 7000 m, and snow and ice surface between 5500 and 7000 m.After sunrise, as the surface temperature of the mountain slopes gradually rises, the surface temperature of the mountain slopes above 7000 meters is greater than the temperature of the free atmosphere at the same altitude.According to the principles of isotherms and isobars, upward winds prevail above 7,000 meters on the north slope, carrying water vapor from sublimation of ice and snow at lower altitudes to the top of The mountain.When strong winds blow over prominent peaks, this moist air cools and condenses into droplets or ice crystals, providing the necessary conditions for flag clouds to form.What do flag clouds have to do with weather?When a flag cloud appears on Mount Qomolangma, it means that there is a strong wind on the top of the mountain. The direction of the flag cloud is determined by the direction of the upper wind, and the direction of the flag cloud extension is the downwind direction. Therefore, the direction and thickness of the flag cloud can be used as the basis for judging the weather and wind direction when climbing.Strong westerly winds blow over the Qinghai-Tibet Plateau all the year round, so the direction of the flag cloud generally points east. If the flag cloud points north, it indicates that heavy snow is coming.If the flag clouds curl up like cooking smoke, the weather will be bad.Do mountain cap clouds belong to flag clouds?Both cap clouds and flag clouds hang around mountaintops, but the way they form is quite different.A cap cloud is a type of cloud formed when a steady stream of air rises over a mountain and cools as it goes over. It looks like a cap resting on the mountain.If you do reach the summit, don’t forget to look up and admire the unique view above the summit — the flag cloud.This article is carried out by Wang Heyi, a teacher of the second branch school affiliated to Renmin University of China.Declaration: The copyright of this article belongs to the original author, if there is a source error or infringement of your legitimate rights and interests, you can contact us through the mailbox, we will promptly deal with.Email address: jpbl@jp.jiupainews.com

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