Temperature Variations Temperature Variation with Altitude Temperature Variations with Topography Heat Transfer Radiation Conduction 4-4 Conduction is the transfer of heat energy from one substance  to another or within a substance. As with electricity,  some materials are good conductors while others are poor  conductors. Poor conductors are considered to be insulators.  Air is one of the poorest conductors of heat in comparison  to silver, one of the best conductors. Silver will pass 20,000  times more heat than an equal mass of air across a similar  temperature difference during a fixed period of time.  Conduction in the atmosphere is considered to be a significant  Prevailing wind is also a factor in temperature control. In  an area where prevailing winds are from large water bodies,  temperature changes are rather small. Most islands enjoy  fairly constant temperatures. On the other hand, temperature  Abrupt temperature differences develop along lake and ocean  shores. These variations generate pressure differences and  local air flows or winds, which may become a consideration  in the balloon pilot’s study of the air mass. These topographical influences are both diurnal and seasonal.  For example, the difference between a daily maximum and  minimum may be 10° or less over water, near a shore line,  or over a swamp or marsh, while a difference of 50° or more  is common over rocky or sandy deserts. Radiation is the transfer of heat by electromagnetic waves.  No medium of transfer is required between the radiator  and the body being irradiated (receiving the radiation).  Heat waves, a form of this electromagnetic energy, may be  reflected. In meteorology, the principal reflectors are the  Earth’s surface, water vapor in the air, and particulate matter  in the atmosphere. Temperature variations are also induced by water and terrain.  Water absorbs and radiates heat energy with less temperature  change than does land. Large, deep water bodies tend to  minimize temperature changes, while large land masses  induce major temperature changes. Wet soil, such as that  found in swamps and marshes, is almost as effective as  water in suppressing temperature changes. Thick vegetation  tends to control temperature changes since it contains some  water and also insulates against heat transfer between the  ground and the atmosphere. Arid, barren surfaces generate  the greatest temperature changes. The heat source for this planet is the sun; energy from the sun  is transferred through space and the Earth’s atmosphere to  the Earth’s surface. As this energy warms the Earth’s surface  and atmosphere, some of it is or becomes heat energy. Heat  is transferred into the atmosphere in three ways: radiation,  conduction, and convection. The amount of solar radiation (insolation) received by any  region varies with the time of day, with seasons, and with  latitude. These differences in insolation create temperature  variations. Temperatures also vary with differences in  topographical surface and with altitude. These temperature  variations create forces that drive the atmosphere in its  motion. Simply stated, heat and, therefore, temperature  differences cause weather.  Temperature normally decreases with increasing altitude  throughout the troposphere. This decrease of temperature  with altitude is defined as lapse rate. The standard lapse rate  seldom exists. In fact, temperature sometimes increases with  height. An increase in temperature with altitude is defined  as an inversion.  changes are more pronounced where prevailing wind is from  dry, barren regions. An inversion often develops near the ground on clear, cool  nights when wind is light. The ground radiates and cools  much faster than the overlying air. Air in contact with the  ground becomes cold, while the temperature a few hundred  feet above changes very little. Thus, temperature increases  with height. Inversions may also occur at any altitude when  conditions are favorable. For example, a current of warm  air aloft overrunning cold air near the surface produces an  inversion aloft.  Low level inversions, which are usually of most interest to  the balloon pilot, generally dissipate as the air mixes with  insolation.  Diurnal variation is the change in temperature from day  to night brought about by the daily rotation of the Earth.  The Earth receives heat during the day by insolation, but  continually loses heat by terrestrial radiation. Warming  and cooling depend on an imbalance of insolation and  terrestrial radiation. During the day, insolation exceeds  terrestrial radiation and the surface becomes warmer. At  night, insolation ceases, but terrestrial radiation continues  and cools the surface. Cooling continues after sunrise until  insolation again exceeds terrestrial radiation. Minimum  temperature usually occurs after sunrise, sometimes as much  as one hour after. The continued cooling after sunrise is one  reason that fog sometimes forms shortly after the sun is  above the horizon.