In the troposhere temperature tends to decrease as height increases. In the theoretical International Standard Atmosphere the temperature decrease or ‘lapse rate’ is defined as 1.98oC per 1000 feet gain in altitude. Like most things theoretical this doesn’t always happen in practice. Almost always at some level in the troposhere the temperature will increase with height with the result that there is a warm layer of air above a cooler layer. This condition is known as a temperature inversion.
There are several mechanisms by which temperature inversions are formed. Radiation inversions, Frontal inversions and Subsidence inversions are the most common.
The temperature changes found within a piece of the atmosphere that includes an inversion layer affect a balloon when climbing or descending through the inversion layer. As the balloon begins to penetrate the bottom of the inversion it will encounter cooler more dense air. As there is now a greater difference in temperature inside the balloon compared to outside the balloon, more lift will be generated which will cause the descent rate to reduce.
When climbing towards an inversion from below the top of the balloon will encounter the warmer air mass and create less lift because there is now less difference between the temperature inside the balloon when compared to outside the balloon. As a result of the reduction in lift the balloon’s ascent rate will reduce.
When descending through an inversion layer from above the balloon will encounter cooler air below the inversion and create more lift because there is now a greater difference between the temperature inside the balloon when compared to outside the balloon. As a result of the increase in lift the balloon’s descent rate will reduce.
There can also be winshear and false lift associated with temperature inversions.
Comprehensive information about temperature inversions can be found on our temperature inversions page. Bob Tait’s book ‘CPL Meteorology’ has further information about temperature inversions commencing at around page 3.8.
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Technical data content credited to Mr Steve Griffin