Question

Explain the effect of altitude/elevation on air temperature. Why is air at higher altitude/elevation lower in temperature? Why does it feel cooler standing in shadows at higher elevation than at lower elevation?

Short answer

Air temperature decreases with altitude because of decreasing atmospheric pressure, which reduces the air's ability to hold onto heat. When standing in shadows at higher altitudes, the temperature feels cooler because fewer molecules can hold heat and sunlight, a significant source of heat, is absent.

Step-by-step solution

Understanding the effect of altitude on temperature

First, one must understand the effect of altitude on temperature. Altitude or elevation refers to the height of a point above mean sea level. In the troposphere, which is the part of the atmosphere where weather occurs, the temperature generally decreases with increasing altitude. This temperature decrease, or temperature lapse, happens because as we go higher in the atmosphere, there are fewer air molecules and the pressure decreases. These molecules are what absorb and hold heat, so with fewer molecules to hold heat, the temperature is lower.

Understanding the effect of atmospheric pressure

Atmospheric pressure, which is the force exerted by the weight of the air above, decreases as one goes higher in altitude. With less air above an elevated location, there is less pressure, so the air is less dense. The rate at which temperature decreases with height is known as the lapse rate. The lower atmospheric pressure at higher elevations affect the ability of the air to hold onto heat, leading to lower temperatures.

Explaining the cooler feeling in shadows at high elevation

When standing in the sun, the direct sunlight can make a person feel warmer, but the actual air temperature does not change significantly. However, when standing in the shadow, particularly at high elevation where there are fewer molecules to hold heat, the temperature can feel significantly cooler than in the sunlight at the same altitude or at lower altitudes.

Key concepts

Temperature Lapse Rate

The temperature lapse rate is a crucial concept to understand when studying how altitude affects air temperature. It describes the rate at which the air temperature decreases as altitude increases. This happens mainly in the troposphere, which is the layer of the atmosphere closest to Earth's surface.
In the troposphere, as we climb higher, the air becomes thinner. This thinning of air is due to a decrease in the number of air molecules available to absorb heat. Consequently, the temperature drops.
The standard average lapse rate is approximately 6.5 degrees Celsius per 1000 meters (or about 3.6 degrees Fahrenheit per 1000 feet) ascent. But, keep in mind that the actual lapse rate can vary due to weather conditions and altitude-specific factors such as moisture content.

Atmospheric Pressure

Atmospheric pressure plays a significant role in temperature variations associated with altitude. It is the force exerted by the weight of the air above a particular point on Earth.
As altitude increases, there is less air pressing down, resulting in lower atmospheric pressure. This reduction in pressure causes the air to expand and become less dense, leading to a decrease in the temperature observed at higher altitudes.
The interplay between lower pressure and temperature is crucial. As air rises, it expands due to the lower pressure and cools down, which contributes to the temperature lapse rate previously mentioned. Understanding how atmospheric pressure decreases with altitude gives insight into why it becomes cooler the higher we go.

Troposphere

The troposphere is the lowest layer of Earth's atmosphere and is where all weather phenomena occur. It extends from Earth's surface to about 8 to 15 kilometers (5 to 9 miles) high, depending on the geographic location.
Within the troposphere, the air is constantly moving and mixing, which impacts weather patterns. The temperature in this layer decreases with elevation due to the temperature lapse rate and the lower density of air molecules capable of absorbing heat.
This part of the atmosphere is crucial for life on Earth as it contains the most oxygen and supports cloud formation and precipitation. All these factors make the troposphere a critical component when discussing weather and temperature patterns at various altitudes.

Heat Absorption by Air Molecules

Heat absorption by air molecules is essential in determining air temperature. Air molecules absorb heat energy from the sun and the Earth's surface, which warms the air.
At higher altitudes, there are fewer air molecules due to lower atmospheric pressure, meaning there is less material to absorb heat, contributing to cooler temperatures in elevated areas.
In addition to air composition, factors like humidity affect heat absorption. Water vapor in the air holds heat more effectively than dry air. Therefore, altitude aside, areas with higher humidity might hold heat differently than drier regions. Understanding how air molecules interact with heat is vital for grasping why certain altitudes feel cooler even when in direct sunlight.