Thermal Inversion over Po Valley, Italy

March 22, 2023

Michela_Inversione termica nebbia e smog su Milano

Photographer: Michela Meda  
Summary Author: Michela Meda  

Thermal inversions aren’t uncommon on the plains of northern Italy. Shown above is a look at the Po Valley and the city of Milan taken from the Sacred Mount of Varese (altitude of 2,897 ft or 883 m) in northern Italy. Note the brownish layer of air in the distance, just above the surface. During nights when skies are clear and absent any ventilation, the ground loses heat by radiation to space, and as a result the lowest atmospheric layer is cooled by the Earth’s surface. So, the layer of air slightly above the surface becomes warmer than the surface layer – a classic thermal inversion. Cooling is all the more intense the longer and colder the night, thus thermal inversion layers are more noticeable (the inversion layer is thicker) in autumn and winter. 

In order for thermal inversions to occur, the atmosphere must be stable, so there’s little vertical air mixing. Thus, moisture and pollutants tend to stagnate in the near-surface layer, resulting in formation of fog along with a deterioration of air quality.  Photo taken on December 27, 2022.


Po Valley, Italy Coordinates: 45.854608, 8.794576

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Thermal Inversion and Fog