Question

Describe the various changes in climate that Occur with changing latitude, including an explanation of why deserts are more likely to be found at around \(30^{\circ}\) latitude than at other latitudes.

Short answer

Deserts often occur at 30° latitude due to dry, descending air from Hadley cells, causing arid conditions.

Step-by-step solution

Understanding Latitude and Climate

Latitude measures how far north or south a location is from the equator, with the equator at 0° latitude and the poles at 90° north and south. As you move from the equator toward the poles, the climate changes due to differences in sun exposure, temperature, and precipitation patterns.

Climate Zones by Latitude

The Earth can be divided into different climate zones based on latitude. The major zones are tropical, temperate, and polar. The tropical zone is near the equator and is typically warm and humid. The temperate zones, found between the tropics and the polar regions, experience more seasonal variation in temperature and precipitation. The polar zones are cold year-round with little precipitation.

The Role of the Hadley Cell

Hadley cells are large-scale atmospheric circulations that occur between the equator and about 30° latitude in both hemispheres. Warm, moist air rises at the equator, causing heavy rainfall. As it rises and moves toward the subtropics, the air cools and descends around 30° latitude, where it becomes dry, explaining the presence of many of the world's deserts.

Why Deserts Form at 30° Latitude

The descending air in the subtropical high-pressure zones (around 30° latitude) results in clear skies and little precipitation, creating arid desert conditions. Notable examples include the Sahara Desert in Africa and the Mojave Desert in North America, both located around 30° latitude.

Key concepts

Climate Zones

Climate zones are areas of the Earth that have similar climatic characteristics. These zones are primarily defined by latitude, which measures how far a location is from the equator. The three primary climate zones are tropical, temperate, and polar.
Tropical zones are located near the equator and are known for their warm temperatures and high humidity. These regions often experience heavy rainfall and are home to rainforests.
Temperate zones are situated between the tropics and the polar regions. These areas typically have four distinct seasons, with moderate temperature and precipitation changes throughout the year.
Polar zones are found near the poles and are characterized by their cold temperatures and dry conditions. Despite having low precipitation, these zones are often covered in snow and ice.

Hadley Cells

Hadley cells are critical systems in atmospheric circulation that help explain the distribution of climate zones. They are named after George Hadley, who proposed this model in the 18th century. Hadley cells operate between the equator and about 30° latitude both north and south.
The process begins with warm, moist air rising at the equator due to direct solar heating. As this air ascends, it cools down and releases moisture in the form of rain, contributing to the humid tropical climate.
Once the air rises, it moves toward higher latitudes. The cooling and the decrease in pressure cause the air to sink around 30° latitude. As it descends, the air warms up and loses its moisture, resulting in dry conditions. This explains why many of the world’s deserts are located at this latitude.

Desert Formation

Desert formation is closely tied to the behavior of Hadley cells and atmospheric dynamics. Deserts are regions that receive very little precipitation, typically less than 250 millimeters per year, making them arid environments.
Most deserts around the world are found near 30° latitude in both hemispheres. This is primarily due to the descending branches of the Hadley circulation. As air descends in these regions, it leads to high pressure at the surface, causing dry conditions.
Deserts like the Sahara, Arabian, and Kalahari are all located within these subtropical latitudes. Similarly, the Sonoran and Mojave Deserts in North America fall within this zone, underscoring the pattern of desert formation along the 30° latitude line.

Subtropical High-Pressure Zones

Subtropical high-pressure zones are regions of high atmospheric pressure situated around 30° latitude, both in the northern and southern hemispheres. These zones are an integral part of global climate dynamics.
In these areas, air that has risen from the equatorial region cools, sinks, and compresses as it moves towards the surface. This compression also warms the air, drying it significantly and leading to clear, cloudless skies.
The presence of high pressure inhibits the formation of clouds, which translates to little to no precipitation. As a result, these high-pressure zones are often associated with arid climates, which promote desert formation at these latitudes. These zones are crucial in explaining why deserts such as the Sahara and the deserts in Australia are so dry.