Energy in the Atmosphere

Energy in the Atmosphere.

How Solar Radiation Heats Earth’s Surface and Atmosphere Energy from the sun travels to Earth and heats the surface. Different parts of the surface receive different amounts of solar energy. Generally, the equator receives the most energy because the sun’s rays strike the surface most directly at the equator. 

The amount of solar radiation received at higher latitudes depends on the season. The seasons are caused by the direction Earth’s axis of rotation is pointing relative to the sun. The axis is always tilted 23.5 degrees relative to Earth’ plane of orbit around the sun, but the north and south poles may tilt toward or away from the sun. When it is summer in the Northern Hemisphere, the north pole tilts toward the sun. As a result, the sun’s rays strike the Northern Hemisphere more directly at this time of year. Light from the sun is more concentrated where the rays are more direct, so the Northern Hemisphere is heated more during the summer than at other times of year. The opposite is true when it is winter in the Northern Hemisphere.

The north pole tilts away from the sun, so the sun’s

rays strike the Northern Hemisphere less directly. Sunlight is less concentrated where the rays are less direct. As a result, Northern Hemisphere is heated less in the winter than at other times of year. The Southern Hemisphere has seasons for the same reasons, but the seasons are reversed relative to the Northern Hemisphere. Much of the heat that Earth’s surface receives by radiation from the sun is radiated back into the atmosphere where it heats the troposphere. Radiation is the transfer of energy between two objects by electromagnetic waves. Heat from Earth’s surface also travels to the troposphere by conduction. In conduction, heat is transferred between two objects that are in direct contact. Molecules of the warmer object vibrate rapidly and collide with nearby molecules,

transferring their energy.

The Southern Hemisphere has seasons for the same reasons, but the seasons are reversed relative to the Northern Hemisphere. Much of the heat that Earth’s surface receives by radiation from the sun is radiated back into the atmosphere where it heats the troposphere. Radiation is the transfer of energy between two objects by electromagnetic waves. Heat from Earth’s surface also travels to the troposphere by conduction. In conduction, heat is transferred between two objects that are in direct contact. Molecules of the warmer object vibrate rapidly and collide with nearby molecules,

transferring their energy.

In the atmosphere, conduction is more effective at lower altitudes where air density is higher and gas molecules are closer together. Heat is transferred throughout the troposphere by convection. Convection occurs when molecules of a substance—in this case, gases in the atmosphere—move in currents because of differences in density. Air near the surface warms

because of heat transferred from the surface. The warm air is low in density, so it rises. The rising warm air cools, becomes denser, and sinks to the surface again. These air movements form convection currents that mix air throughout the troposphere.