1. Altitude and Thinning Atmosphere:
* Less Air: As you ascend a mountain, the air becomes thinner. There are fewer air molecules to absorb and hold heat from the sun.
* Lower Pressure: Lower air pressure at higher altitudes also means the air molecules are spread further apart, making it less effective at trapping heat.
2. Adiabatic Cooling:
* Air Expansion: When air rises, it expands. As the air expands, it cools down. This is because the molecules have more space to move and collide less frequently, transferring less heat.
* Dry Adiabatic Lapse Rate: Dry air cools at a rate of approximately 5.5°F (3°C) per 1000 feet (300 meters) of altitude.
3. Reduced Sunlight Absorption:
* Angle of Incidence: The sun's rays hit the Earth at a steeper angle at higher altitudes. This means the same amount of solar energy is spread over a larger area, resulting in less heat absorption.
* Cloud Cover: Mountains often have more cloud cover than lower altitudes, which can block sunlight and further reduce heating.
4. Other Factors:
* Snow and Ice: Snow and ice at high altitudes are very reflective and reflect much of the incoming solar radiation back into space, preventing warming.
* Wind: Mountainous areas often experience stronger winds, which can also contribute to cooling.
In summary: The combination of thinner air, lower pressure, adiabatic cooling, reduced sunlight absorption, and other factors like snow and ice contribute to the lower temperatures experienced at higher altitudes.
