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Radiation burst ?
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» DanielVan - Coldest temperature before sunrise Can anyone give an explanation to why the ambient - temperature drops; just before sunrise.I have experienced this on many a winter morning under clear African skies. One would think that the earth had enough time to lose all it's heat during the night ; but why this sudden chill just before sunrise ? -- posted by DanielVan » weather_doctor - Re: Coldest temperature before sunrise In response to Coldest temperature before sunrise posted by DanielVan:Hi Daniel, The earth loses its heat constantly, day and night, just like we do through thermal (infrared) radiation. I wrote in more detail on this topic in "Laying Some Groundwork: Balancing Radiation".. (Note that this answer assumes a clear sky and day with no frontal or other changes in the weather due to traveling weather systems and air masses.) During most daylight hours, and this depends greatly on latitude being less as you move poleward during winter, the sun's radiation is able to generate more heat at the ground than the earth loses, so we warm during the day, until an hour or so before sunset. But during those last light hours, the net radiation balance shifts from gain to loss. Now at night, the balance shifts to a loss of heat from the earth, though clouds and the atmosphere send some back and make the net loss small. This radiation loss continues all night, and even for some hours after dawn because the sun is so low in the sky. Its early rays are spread over a large area and thus solar heating is low. It takes an hour or so for the balance to again turn to a gain of heat. During these early "sunlight" hours, the earth is still cooling, losing heat faster than gaining it, and the the temperature continues to drop as you experienced. -- posted by weather_doctor
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