Question

Why are many deserts concentrated along zones at 30 " latitude in both the Northern Hemisphere and the Southern Hemisphere?

Short answer

Deserts form at 30° latitude due to dry descending air and high-pressure systems from the Hadley Cell.

Step-by-step solution

Understand the Earth's Atmospheric Circulation

The Earth has a system of atmospheric circulation that helps distribute heat around the planet. One of the key components of this system is the Hadley Cell, which extends from the equator to about 30° latitude in both hemispheres.

Examine the Role of the Hadley Cell

In the Hadley Cell, warm air rises near the equator where solar heating is intense. As the air rises, it cools and loses moisture through precipitation. This dry air then moves poleward and descends around 30° latitude.

Analyze the Impact of Descending Air

When the dry air descends around 30° latitude, it warms as it sinks. This warming effect inhibits cloud formation and precipitation, creating favorable conditions for desert environments.

Recognize the Pressure Systems

The descending air results in high-pressure zones at these latitudes. High-pressure systems are typically associated with stable, dry conditions, reinforcing the formation of deserts.

Conclude the Geographic Pattern

The combination of descending dry air and high-pressure systems at around 30° latitude in both hemispheres leads to the concentration of many of the world's largest deserts, such as the Sahara, the Arabian Desert, and the Atacama.

Key concepts

Hadley Cell

The Hadley Cell is a crucial part of the Earth's atmospheric circulation system. It represents a pattern of moving air that stretches from the equator to roughly 30° latitude north and south. This cell begins at the equator, where solar energy is most intense, causing air to heat up. As the air warms, it rises due to its lower density. Rising air loses moisture through precipitation, leading to the formation of rainforests along the equator.

As the air continues to move away from the equator towards the poles, it cools and becomes drier. Eventually, this air descends around 30° latitude as it becomes denser. This process of rising and descending air within the Hadley Cell plays a significant role in creating deserts around this latitude.

Atmospheric Circulation

Atmospheric circulation is a large-scale movement of air that helps distribute thermal energy across the surface of the Earth. The movement of air follows specific patterns due to the rotation of the Earth and the uneven distribution of solar energy. At a global scale, this circulation is divided into three main cells per hemisphere: the Hadley Cell, the Ferrel Cell, and the Polar Cell.

These air circulations are driven by differences in air pressure and temperature between the equator and the poles. Warm air rises by the equator and moves toward higher latitudes. Then, it cools down and sinks back towards the Earth's surface as it transfers heat. The returning cooler air forms a loop, or cell, that is crucial for maintaining Earth's climate zones.

• The Hadley Cell, in particular, contributes to the formation of the equatorial rainforests and subtropical deserts.
• The Ferrel and Polar cells function differently but also contribute to our understanding of the weather systems around the globe.

High-Pressure Zones

High-pressure zones are areas where the atmospheric pressure is higher than the surrounding areas. In these regions, air is descending, leading to the compression of air molecules, which heats the air. This process inhibits cloud formation and limits precipitation, resulting in dry weather conditions.

In the context of desert formation, high-pressure zones occur around 30° latitude north and south, primarily due to the descending limbs of the Hadley Cell. As the dry air sinks, it creates a stable atmosphere that's not favorable for clouds or precipitation. This is why areas under these high-pressure zones tend to be some of the driest places on Earth, such as the Sahara and the Arabian Desert.

• These zones are characterized by clear skies.
• They have limited weather disturbances.
• They are generally associated with low humidity and high temperatures.

Latitude Effect

The effect of latitude on climate and the formation of deserts is an intriguing aspect of our planet. Latitude refers to the distance of a place from the equator and has a direct impact on climate patterns due to varying angles of solar radiation.

Close to the equator, there's intense solar radiation leading to warm climates. As we move towards 30° latitude, the angle of sunlight decreases, causing different climatic conditions. Here, the impact of the Hadley Cell and high-pressure zones leads to the creation of dry desert areas. These latitudes are often termed as the "horse latitudes" due to their historical significance and weather patterns.

Moreover, latitude determines the path of atmospheric cells, such as the Hadley Cell, affecting where deserts form. Essentially, regions at approximately 30° latitude receive less rainfall because the descending air prevents cloud formation, ensuring these areas remain arid. This is why many of the world's large deserts are situated along these latitudes.