Warm air rising is responsible for a variety of weather-related phenomena, including wind currents, air pressure changes, precipitation and extreme weather events, such as supercells, hurricanes and tornadoes. Knowing the basics of weather-related events can help to predict oncoming storms and changes in weather conditions.
Why Hot Air Rises
As air becomes heated near the surface of the Earth, air molecules expand, thus making the air less dense than the cooler air layers on top of it. When the heated air's density reaches a certain point of expansion, it becomes significantly lighter than denser colder air and changes places with the cooler air layer on top of it, creating a convection current.
Wind is caused by multiple layers of hot air rising and colder air falling around the Earth. As hot air rises, the loss of atmospheric pressure causes the hot air's temperature to lower. Decreasing the pressure causes the hot air to further expand as it cools, providing more force, via the air molecules, for the creation of wind currents.
Thunderstorms are formed as warm moist air rises and collects moisture in the atmosphere through condensation, in addition to the strong updrafts of warm air and downdrafts of cold air along the squall line of a cold front. Supercell thunderstorms have strong updrafts and downdrafts as an unstable body of warm air is forced to rise by the dense air of the approaching cold front. As the moist, hot air rises and cools, water vapor condenses and forms clouds. As it begins to rain, latent heat energy is released from warm air near the surface of the Earth as cold downdrafts accompany the rain as it falls.
Larger supercells occasionally give birth to tornadoes, especially during warmer parts of the year. As supercell clouds grow more than 40,000 feet, large columns of warm, moist air rise quickly. If conditions are right, winds at two or more different altitudes will begin to blow at varying speeds, creating a wind shear, which leads to a horizontal column of spinning air. Depending on the conditions, this horizontal wind shear can get caught in an updraft, which will decrease the girth of the column and increase the speed of the rotational spin, causing a funnel cloud.
- History for Kids: Hot Air Rises
- Science Kids at Home: Hot Air
- University Cooperation for Atmospheric Research: Web Weather for Kids: How in the World are Thunderstorms Formed?
- University Cooperation for Atmospheric Research: Web Weather for Kids: How in the World are Tornadoes Formed?
- University of Wisconsin: How a Tornado Forms
- Newton: Ask A Scientist: Hot Air Rising
- WAFB: Weather from Rising Warm Air
- Pacific Island Travel: Nature Gallery (Earth - Climate)