Cold in a balloon?

Many people think it gets cold in a hot air balloon. Think again! It is actually quite comfortable in a balloon, and even warmer than you might expect. In fact, the burner acts like a central heating system directly above your head. We therefore recommend wearing a cap or other head covering during your flight, especially if you are tall.

Some scientific facts can help you better understand this phenomenon:

The troposphere extends from 0 to 11 km in altitude, with temperatures decreasing linearly by 6.5°C per kilometre. At the tropopause, the temperature reaches approximately −56.5°C. Hot air balloons generally fly at an altitude of around 450 metres, where the temperature does not change significantly up to 700 metres.

• Air pressure decreases with altitude. It represents the weight of the column of air above you. The higher you go, the less air there is above you, so the pressure is lower.
• A gas cools down when its pressure decreases. This is particularly true for a carbon dioxide fire extinguisher: when the valve is opened, the gas, initially stored under pressure at room temperature, expands and can even solidify, producing dry ice.

To understand why the atmosphere cools with altitude, we need to consider air as a dynamic system. Air in contact with the ground heats up, expands, becomes less dense and rises (thanks to Archimedes' principle). As it rises, it cools because the pressure decreases. This model applies to the lower atmosphere, where this circulation generally occurs.

At certain altitudes, the opposite phenomenon can occur: when the cold ground cools the air in contact with it, a layer of cold air can form and become trapped beneath a layer of warmer air. This creates a temperature inversion, which traps pollutants and can lead to smog.

At sufficiently high altitudes, cooling eventually stops, and the outer reaches of the atmosphere can reach temperatures of around 400°C at an altitude of approximately 200 km, due to heating from the sun.