What is convection?
Heat can be transported by radiation, conduction or convection. Low temperature bodies like the earth’s surface and the atmosphere emit infrared radiation. Infrared radiation is ineffective in transmitting heat upward in the atmosphere because infrared radiation is absorbed by the atmosphere, mainly by water vapor and carbon dioxide. Conduction is the primary heat transport process in solids. In a gas heated from the bottom the contribution of conduction is negligible compared to the contribution of convection. Heat convection is heat transport resulting from change of position of warm and cold fluid masses. In the troposphere heat is transported upward by convection by the upflow of warmed air and the downflow of cooled air.
• How does convection happen in our atmosphere? • How do clouds form? • What makes the sky clear or without clouds? Objectives Concepts: • Convection is the organized motion or movement of large groups of molecules based on their relative densities or temperatures. For example, convection is the upward motion of a warm fluid spreading through a cooler one. • Weather is the state of the atmosphere and conditions such as dry or wet, cold or hot, stormy or calm, cloudy or clear. In plain terms, we can say that weather happens when wet air goes up in the atmosphere. Principles: • Weather activity happens when wet air goes up into the atmosphere and cooler air comes down from the atmosphere. • One cause of rising air in our atmosphere is from the process called convection. • Warm air rises above cold air by convection. • Clouds form when water vapor condenses and molecules cling to each other. • While convection is happening and warm moist air is going upwards, there is also the sinking of
“Convection” has several, related meanings in weather….but it always involves rising air. It usually refers to “moist convection”, where the excess water vapor in rising air parcels condenses to form a cloud. The heat released through this condensation can help to sustain the convection by warming the air further and making it rise still higher, which causes more water vapor to condense, so the process feeds on itself. Convection can also be dry, as occurs on a sunny day over the desert. The sun warms the ground, and convective air currents help to remove the excess heat from the surface. Dry convection also occurs during the day even when clouds are forming…you just can’t see it.
