Question

Explain why it will be cooler if you climb to a higher elevation in a desert.

Short answer

Higher elevation leads to cooler temperatures due to adiabatic cooling and the lapse rate.

Step-by-step solution

Understanding Temperature Variation

In a desert climate, temperatures generally decrease as you move to higher elevations. This occurs due to changes in atmospheric conditions like air pressure and density, which affect temperature.

Concept of Adiabatic Cooling

When air rises, it expands due to lower air pressure at higher altitudes. As it expands, it cools down because it does work against atmospheric pressure, leading to cooler temperatures at higher elevations.

Lapse Rate

The rate at which air temperature falls with an increase in altitude is known as the lapse rate. In dry conditions, which is typical in deserts, the dry adiabatic lapse rate causes a temperature decrease of approximately 9.8°C for every 1000 meters (or about 5.4°F per 1000 feet) gained in altitude.

Applying the Concept to Elevation Changes

If you climb a mountain or a high plateau in the desert, the temperature will drop at the rate given by the lapse rate. This is why it is generally cooler at higher elevations, even in a desert.

Key concepts

Lapse Rate

The lapse rate is a crucial concept to grasp when understanding why temperatures change with elevation. It is defined as the rate at which atmospheric temperature decreases with an increase in altitude. This concept is particularly relevant in desert environments, where the air is generally dry. The dry adiabatic lapse rate in such areas is about 9.8°C per 1,000 meters (or 5.4°F per 1,000 feet) of elevation gain. This means that as you climb higher in a desert landscape, the temperature will decrease predictably according to this rate. This consistent decrease allows us to estimate how much cooler it will get as we ascend. Remember, the lapse rate is not influenced by the actual starting temperature; it is a measure of the rate of temperature change.

Atmospheric Pressure

Atmospheric pressure plays a significant role in the cooling process as you climb higher elevations in a desert. It is the weight of the air above us pressing down. At higher elevations, there is less air above, which results in lower atmospheric pressure.
As air rises, it encounters less pressure and begins to expand. This expansion causes the air to cool, a process known as adiabatic cooling. The decrease in pressure with altitude accelerates the rate of expansion and thus the rate of cooling. Therefore, even though deserts are known for their heat, at higher elevations, the drop in atmospheric pressure has a cooling effect.

Desert Climate

Desert climates are characterized by extreme temperatures, usually hot during the day and cooler at night. The arid conditions with low moisture content in the air mean that deserts experience what's called a dry adiabatic lapse rate. Because there is little moisture to moderate temperatures, the lapse rate in deserts is purely driven by changes in air pressure and not by the release of latent heat through condensation.
Deserts have little vegetation to absorb or radiate heat, which causes rapid temperature changes with elevation. This is why you can feel such a noticeable difference in temperature as you climb at higher altitudes in a desert.

Temperature Variation

Temperature variation in a desert climate can be stark due to the clear skies and lack of moisture in the air. During the day, the sun’s rays heat the ground directly. However, at night or at higher altitudes, the temperatures can plunge significantly because clear skies allow heat to escape into the atmosphere.
The concept of temperature variation is crucial in understanding why it is cooler at higher elevations. With an increase in altitude, there is less atmospheric pressure, resulting in a cooler environment. The varying temperatures at different elevations create unique conditions that are part of the desert climate's dynamics.

• High daytime temperatures due to direct sunlight.
• Rapid nighttime cooling and cooling at higher elevations.
• Minimal cloud cover to trap heat.

Understanding these variations helps explain how altitude affects temperature changes in desert regions.