Lämpötilakääntäminen

Lämpötilakääntäminen, also known as temperature inversion, is an atmospheric phenomenon where a layer of warmer air is trapped above a layer of colder air near the Earth's surface. Normally, air temperature decreases with altitude, but during an inversion, this pattern is reversed. This can occur under various conditions, often associated with stable atmospheric conditions.

One common cause is radiational cooling. On clear, calm nights, the Earth's surface loses heat through radiation, cooling the air directly above it. If this cooling is significant, the air near the ground can become colder than the air higher up, creating an inversion. Another type is subsidence inversion, which forms when a large mass of air sinks and compresses, warming as it descends. This descending warm air can then sit above cooler surface air. Advection inversions occur when a warm air mass moves horizontally over a colder surface, such as a cold ocean current or snow-covered land.

Lämpötilakääntäminen has several notable effects. It can trap pollutants, such as smog and particulate matter, near the ground, leading to poor air quality. This is because the stable stratification prevents vertical mixing of the air. In colder climates, inversions can exacerbate cold temperatures at the surface, especially during winter. Conversely, in mountainous regions, inversions can lead to higher temperatures at higher elevations compared to valleys. The phenomenon typically breaks down when the sun rises and warms the surface, or when wind mixes the air layers.