|HEAT DISTRIBUTION IN THE TROPOSPHERE
METEOROLOGIST JEFF HABY
Energy is distributed by radiation, conduction and convection. Radiation is the movement of energy
in waves/particles at or near the speed of light. All objects emit radiation and the amount and
wavelength of emitted radiation depends on temperature. Conduction is the movement of energy
by direct contact. The classic example of this is a pan warming that is on the range. Convection is
the movement of heat by the mixing that takes places in a fluid. A fluid is a gas or liquid. Convection
does not take place to a significant degree in solids since the molecules are not free to move like
with gas or liquids.
All three processes are important to energy transfer in the troposphere. The primary warming of the
earth's surface is from the sun's radiation. Right at the surface all three distribution
mechanisms take place. The sun warms the ground by radiation. The ground warms the air adjacent to the
surface through conduction. Wind mixes the warmer air at the surface with cooler air aloft through
convection. Certain gases can absorb radiation and warm. The classic examples of the gases that
do this are ozone, carbon dioxide and water vapor. Ozone is good at absorbing UV radiation and warming.
Carbon dioxide and water vapor (greenhouse gases) are good at absorbing infrared radiation and
warming. At night, clouds will keep the temperatures warmer than than otherwise would be due
to the absorption and thus "trapping" of infrared radiation emitted from the surface. Conduction is
a significant process immediately at the earth's surface but is not really significant above the surface
since the atmosphere is composed of fluids. The temperature of the earth's surface will have a significant
influence on the surface air temperature due to the conduction process. The bulk of heat energy
transferred in the troposphere is done by convection. Convection does not only mean thunderstorm
clouds but means any mixing of air. Air is always on the move (rising, sinking and advecting). The
air mixes as it moves into the surrounding air. The winds in the troposphere and the thermals rising
from the earth's surface are constantly mixing the air.
Next time you are outside look for the processes of radiation, conduction and convection that
are occurring in the troposphere.