Why is it colder in the mountains than in the valley?
If you want to escape the summer heat in the valley, you should climb as high as possible to the mountain peaks. How are increases in altitude and decreases in temperature related, and by how many degrees does temperature decrease with altitude?
The entire atmosphere weighs on the air near the ground and generates an average pressure of 1013 hPa (hectopascals), which roughly corresponds to the pressure at a depth of 10 meters. As the altitude increases, the amount of air above decreases and with it the pressure with which the air is compressed. So when an air parcel rises, it expands and does work. The work done is lost to the air in the form of heat – it cools down.
How much a gas cools down as it expands also depends on its heat capacity, a physical quantity that describes how much the temperature changes when a certain amount of energy is added or removed. With air, which consists mainly of nitrogen (78 percent) and oxygen (21 percent), there is a cooling of almost exactly one degree Celsius for every 100 meters increase in altitude. At this value, no other energy is added to or removed from the air in the form of heat, which is referred to as adiabatic.
However, this only applies if you don’t get caught in clouds on the way. In this case, the physics get a little complicated. The air always contains invisible water vapour. The warmer the air, the more water vapor it can contain. If the air cools with increasing altitude, it can happen that the water vapor it contains condenses and clouds form. The water vapor gives off a lot of energy to its surroundings, since the water molecules in the liquid state have significantly less kinetic energy than when they are whizzing through the area in gaseous form.
The excess kinetic energy of the now liquid water molecules is released into the surrounding air and heats it up. Overall, however, the cooling of the rising air due to its expansion predominates. Now it cools down in the clouds by only about 0.5 to 0.9 degrees when you gain 100 meters in height. On Monday, a maximum temperature of 25.9 degrees was measured in Garmisch at an altitude of 719 meters, on the Zugspitze at 2962 meters it was only 11.2 degrees. This corresponds to an average decrease of 0.66 degrees Celsius for every 100 meters increase in altitude.