Something that always got my attention is how the temperature always drops when you go higher up in the mountain. This is called the “lapse rate”. I always repeated like a parrot that temperature drops 1° C when the altitude increases by 100 m. And how come this sometimes is not true with the inversion phenomenon?
It is not always the case, that temperature decreases by 1° C when the altitude increases by 100 meters but is not that off the reality. Looking online to get my info well, this is what I’ve found.
As altitude increases, the temperature decreases due to – in part, air pressure and the water-vapour content.
Pressure is Lower at Altitude. Lapse Rate in the Temperature with Altitude and the Inversion Phenomenon.
With every 100 meters of increase in altitude, the temperature drops by an average of 0.65°C. But when the air is very dry, as when there is high pressure, the air can cool 1°C every 100 meters of altitude. What makes this possible is the air pressure, the heat radiation and the water vapour content in the air.
With higher pressure there will always be more temperature. As in the lowlands or on the beach the pressure is higher (pressure is higher at sea level), the temperatures are usually higher there, that when going up the mountain. The higher you go, the more the pressure sinks, therefore the temperature also drops down.
Another thing that affects the temperature is the way in which the atmosphere is heated. The atmosphere is warmed mostly by the Earth’s surface. The short-solar radiation wave incoming towards the Earth’s surface warms the Earth’s surface and in turn, it emits a long-wave thermal radiation to the atmosphere above.
At altitude there is less water vapour content. Lapse Rate in the Temperature with Altitude and the Inversion Phenomenon.
When the atmosphere has more water vapour it can absorb more heat radiation. When a layer of the atmosphere is warmed, it becomes itself a heat radiator, reemitting the heat. Most of the heat from the atmosphere is radiated back to the Earth’s surface. This is called long-wave atmospheric counter-radiation. Counter-radiation also takes place at night. This process with incoming short-wave radiation and long-wave atmospheric counter-radiation constitutes the natural greenhouse effect.
The content of water vapour in the atmosphere depends on the air pressure, and, as there is less pressure at altitude, the atmosphere loses its ability to absorb thermal radiation and radiate it back to Earth. Therefore, with more altitude, the atmosphere is more permeable to the heat, and it dissipates in space.
Rising warm air turns cool when going upwards. Lapse Rate in the Temperature with Altitude and the Inversion Phenomenon.
When the warm air rises, it expands with altitude due to the decrease in pressure. This expansion requires energy, which is drawn from the heat that the air carries with itself. This means that the air then turns cooler and cooler as it goes up.
What does it all mean for a common mountain lover? Lapse Rate in the Temperature with Altitude and the Inversion Phenomenon.
Basically, even if you are in the valley and temperatures are high, or if you are at the base of the resort and it is warm, you cannot count it being warm when going up the mountain. Weather can feel even colder if you see some white wind on the top of the mountains. Just dress up warm!
What is temperature inversion? Lapse Rate in the Temperature with Altitude and the Inversion Phenomenon.
Temperature inversion is when temperature increases with height. Generally, as I wrote above, temperature drops with altitude. But sometimes, a small layer can form where the temperature increases with height. This layer is called an inversion.
Usually this happens when there is high pressure, where the air high up sinks towards the ground. As it falls, it dries out and warms up. This warm layer of air could act as a lid that traps the cooler air near the surface. This happens sometimes when there is fog and mist in winter that traps the cooler air down the lower ground, whereas when you start going up the mountain, it gets warmer. Usually you must pass the ‘cloud’ stuck on the mountain, and you get up to sunny skies and beautiful weather.
I love this effect. In Argentina, we call it the “efecto plafón”, and I remember seeing it a lot in Las Leñas. You kind of ski on top of a sea of clouds!
When I lived in Crested Butte, I remember that Gunnison, (down valley and at 2,348 m or 7,703 ft) tended to be colder than Crested Butte (at 2,708 m or 8885 ft.), and it was many times in the news as having -20°F!
This is kind of common during the clear days in winter, where the cold air sinks down the Gunnison Valley, settling in Gunnison.
More info:
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