Radiation inversion, also known as surface temperature inversion, is a condition where the air temperature increases with altitude near the ground, the opposite of the normal temperature gradient.
This phenomenon primarily develops when the Earth's surface cools rapidly through radiation, most commonly occurring on clear, calm nights. Here's a breakdown of how it happens:
- Clear Skies: Clear skies allow for unimpeded radiative heat loss from the ground. Clouds act as a blanket, trapping heat, so their absence is crucial.
- Calm Winds: Calm or light winds prevent the mixing of air layers. Strong winds would disrupt the temperature gradient by mixing the cooler surface air with the warmer air aloft.
- Long Nights: Longer nights, especially during winter, provide more time for the ground to cool.
- Cool Surface Contact: The air in direct contact with the cold ground becomes cooler than the air above it. This is because the ground is losing heat more rapidly than the air can warm it.
- Temperature Gradient Reversal: As the ground continues to cool, the air immediately above it also cools, creating a layer of air that is colder than the air at higher altitudes. This reverses the normal temperature gradient, resulting in a temperature inversion.
Key Characteristics of Radiation Inversions:
- Surface-Based: The inversion layer is located near the surface of the Earth.
- Temporary: Radiation inversions are usually temporary, often dissipating after sunrise as the sun warms the ground and mixes the air.
- Common Occurrence: They are a frequent occurrence, particularly in valleys and areas with little wind.
- Impact on Pollution: Radiation inversions can trap pollutants near the ground, leading to poor air quality. The stable air prevents vertical mixing, concentrating pollutants in the lower atmosphere.
Conditions Favoring Radiation Inversions:
| Condition | Explanation |
|---|---|
| Clear Skies | Allows for maximum radiative cooling of the ground. |
| Calm Winds | Prevents mixing of air layers, maintaining the temperature gradient. |
| Long Nights | Provides more time for the ground to cool. |
| Dry Air | Dry air emits radiation more readily than moist air, enhancing the cooling process. |
| Snow Cover | Snow reflects solar radiation and enhances radiative cooling. |
| Topography | Valleys and basins are prone to radiation inversions as cold air drains down the slopes and settles at the bottom. |
In summary, radiation inversion is a temperature inversion that forms near the ground due to radiative cooling, primarily occurring on clear, calm nights and leading to a stable atmospheric layer.
