a) Explain the term temperature inversion.
b) Examine the causes and weather conditions associated with temperature inversions.
Cameroon GCE June 2001
Temperature is a temporary situation during which temperature instead of decreasing with an increase height, rather increases with an increasing height at lower Troposphere near the ground. It is a reverse situation of the Environmental lapse rate or Normal lapse rate. Therefore when temperature increases with height there is temperature inversion. There is an increase of temperature with height in two layers namely: The Stratosphere and the Thermosphere. Two types of temperature inversions can be recognized namely, Ground or surface (lower level) temperature inversion and above the ground (upper level) temperature inversion.
Lower level or ground temperature inversion occurs as a result of rapid loss of heat from the ground due to radiation at night, as such after the loss, cold air will be found close to the ground surface. Lower level inversion can best occur during longer nights, clear skies, dry air, calm air and snow covered surfaces. Low level temperature inversions usually occur under anti-cyclonic conditions when there is a rapid loss of heat from the ground due to radiation at night.
Lower level or ground temperature inversion with rapid loss of heat through radiation during longer nights.
Upper level temperature
They occur during fronts or depressions. This is when different air masses with contrasting characteristic meet. that point of convergence is called a front. The two air masses could be light warmer air mass meeting with a denser cold air mass. The light air mass rises while the cold one sinks to the lower surface, though not touching the ground. Cold air therefore lies below warm air at the lower heights thus temperature inversion.
CAUSES OF TEMPERATURE INVERSIONS
Many reasons ca be accounted for the abnormal tendency o temperature increasing with an increasing height at the troposphere.
Longer nights: During longer nights more intense cooling by terrestrial radiation occurs. This is a result of the chilling of the air layers in contact with the ground, which is rapidly losing its heat by terrestrial radiation. The rapidly cooling ground surface at nights causes the air layers in contact with it to be chilled or lose its heat by conduction. Consequently, the air layers further up not affected by cold ground, remains at a temperature higher than that of the chilled air layer below in contact with the ground. Thus with increasing height the temperature rises, the normal lapse rated is reserved.
Clear skies: Skies with few or no clouds and low humidity permits rapid escape of heat back to the atmosphere, this is because of the absence of clouds with enough moisture or water vapour in the air to trap heat and prevent it from escaping. For instance, the heavy cloud cover of the equatorial regions explains why the day temperatures rarely exceed 30°C and why the night's temperatures are not much lower. In desert with clear skies and no clouds, dry air, high daily temperatures are witnessed of about 38°C and much lower night temperatures of °C or even below.
Fairly stable air with little mixing, such that it remains on the cold ground surface long enough to be chilled. Under such conditions, the air can condense and give rise to fogs, mist and even frost, when the sun begins to shine, the inversion soon disappears. Temperature inversion has many effects on weather conditions. It is associated with stable atmospheric conditions characterized by:
i) Subsiding air masses which warms adiabatically
ii) Reverse lapse rate
iii) Calm weather/ High pressure
iv) Very low temperatures
v) Foggy weather
vi) Smog / pollution flume
vii) Reduced reversibility