When temperature inversion occurs, cold air underlies warmer air at higher altitudes.
Normally, temperature decreases with an increase in elevation. It is called the normal lapse rate.
At times, the situation is reversed and the normal lapse rate is inverted. It is called Inversion of temperature.
Inversion is usually of short duration but quite common nonetheless. A long winter night with clear skies and still air is an ideal situation for inversion.
The heat of the day is radiated off during the night, and by early morning hours, the earth is cooler than the air above.
Over polar areas, a temperature inversion is normal throughout the year. Surface inversion promotes stability in the lower layers of the atmosphere.
Smoke and dust particles get collected beneath the inversion layer and spread horizontally to fill the lower strata of the atmosphere.
Dense fogs in the mornings are common occurrences, especially during winter season. This inversion commonly lasts for few hours until the sun comes up and beings to warm the earth.
The inversion takes place in hills and mountains due to air drainage. Cold air at the hills and mountains, produced during night, flows under the influence of gravity.
Being heavy and dense, the cold air acts almost like water and moves down the slope to pile up deeply in pockets and valley bottoms with warm air above.
This is called air drainage. It protects plants from frost damages.
Causes of Temperature Inversions
Normally, air temperature decreases at a rate of 3.5°F for every 1000 feet (or roughly 6.4°C for every kilometer) you climb into the atmosphere.
When this normal cycle is present, it is considered an unstable air mass and air constantly flows between the warm and cool areas.
As such the air is better able to mix and spread around pollutants.During an inversion episode, temperatures increase with increasing altitude. The warm inversion layer then acts as a cap and stops atmospheric mixing.
This is why inversion layers are called stable air masses.
Temperature inversions are a result of other weather conditions in an area.
They occur most often when a warm, less dense air mass moves over a dense, cold air mass.
This can happen for example, when the air near the ground rapidly loses its heat on a clear night. In this situation, the ground becomes cooled quickly while the air above it retains the heat the ground was holding during the day.
Additionally, temperature inversions occur in some coastal areas because upwelling of cold water can decrease surface air temperature and the cold air mass stays under warmer ones.
Topography can also play a role in creating a temperature inversion since it can sometimes cause cold air to flow from mountain peaks down into valleys.
This cold air then pushes under the warmer air rising from the valley, creating the inversion.
In addition, inversions can also form in areas with significant snow cover because the snow at ground level is cold and its white color reflects almost all heat coming in.
Thus, the air above the snow is often warmer because it holds the reflected energy