Most Of The World's Deserts Are Located At Latitudes Where

Most of the World's Deserts are Located at Latitudes Where... High-Pressure Systems Reign

The world's driest regions, its deserts, aren't randomly scattered across the globe. A significant majority are found within specific latitude bands, a pattern directly linked to global atmospheric circulation and the resulting distribution of precipitation. Understanding this connection is crucial to comprehending the formation and characteristics of deserts. This article delves into the atmospheric science behind desert formation, exploring why most of the world's deserts are located at latitudes where high-pressure systems dominate.

The Role of Atmospheric Circulation: The Engine of Desert Formation

The Earth's climate system is a complex interplay of various factors, but atmospheric circulation plays a pivotal role in determining precipitation patterns. The sun's uneven heating of the Earth's surface drives large-scale atmospheric circulation patterns, creating distinct climate zones. These patterns, driven by convection and the Coriolis effect (the deflection of moving objects due to the Earth's rotation), are responsible for the distribution of rain and the creation of deserts.

Hadley Cells: The Primary Driver

The most influential circulation cells for desert formation are the Hadley cells. These are large-scale convection cells that rise at the equator, where solar radiation is most intense. As warm, moist air rises, it cools and condenses, leading to heavy rainfall in equatorial regions, creating lush rainforests.

However, as this air reaches the upper atmosphere, it moves towards the poles. As it travels, it gradually cools and sinks around 30 degrees north and south latitude. This descending air is dry, because much of its moisture has already been precipitated out near the equator. The sinking air compresses and warms adiabatically (without heat exchange with the surroundings), further inhibiting cloud formation and rainfall. This is the primary reason why many of the world's deserts are located around these latitudes, often referred to as the subtropical high-pressure belts.

Subtropical Highs: Zones of Desiccation

The descending air in the subtropical highs creates areas of high atmospheric pressure. This high pressure inhibits the upward movement of air, suppressing cloud formation and precipitation. The absence of clouds means that solar radiation reaches the surface unimpeded, leading to high temperatures. The combination of low precipitation and high temperatures is the defining characteristic of a desert climate.

Key characteristics of subtropical highs and their influence on desert formation:

• Descending air: This prevents the formation of clouds and precipitation.
• High pressure: The high pressure suppresses upward air movement, hindering the development of rain-bearing clouds.
• Adiabatic warming: As the air sinks, it compresses and warms, reducing the relative humidity and suppressing cloud formation.
• High temperatures: The lack of cloud cover allows for intense solar radiation, leading to high surface temperatures.
• Dry air: The descending air is characterized by low moisture content, further contributing to arid conditions.

Geographic Examples: Deserts in the Subtropical High-Pressure Belts

The theory of subtropical high-pressure systems driving desert formation is supported by the geographic distribution of major deserts worldwide. Consider these examples:

• Sahara Desert (North Africa): Situated largely within the 30°N latitude band, the Sahara is a prime example of a desert formed under a subtropical high-pressure system. The descending air from the Hadley cell creates a vast area of aridity.
• Arabian Desert (Middle East): Located similarly to the Sahara, the Arabian Desert experiences similar atmospheric conditions, resulting in extremely low precipitation and a hyper-arid climate.
• Australian Desert (Australia): The interior of Australia, largely situated between 20°S and 30°S, experiences extremely low rainfall due to the influence of the subtropical high-pressure belt in the Southern Hemisphere.
• Atacama Desert (South America): While influenced by other factors like the cold Humboldt Current, the Atacama's extremely arid conditions are partially attributed to the prevailing subtropical high-pressure system.
• Sonoran Desert (North America): While influenced by other factors like rain shadows, its location partly within the 30°N latitude band contributes to its aridity.

Other Factors Contributing to Desert Formation

While subtropical high-pressure systems are a primary driver of desert formation, it's important to recognize that other factors can contribute to the aridity of a region:

Rain Shadows: Mountains Blocking Moisture

Mountain ranges can create significant rainfall gradients. As moist air is forced to rise over a mountain range, it cools and condenses, resulting in precipitation on the windward side. By the time the air reaches the leeward side, much of its moisture has been lost, resulting in a dry "rain shadow" region. Many deserts are partially formed within rain shadows, enhancing the effect of subtropical highs.

Cold Ocean Currents: Coastal Deserts

Cold ocean currents, like the Humboldt Current off the coast of South America, cool the air above them. This reduces the air's capacity to hold moisture, leading to less precipitation and contributing to the aridity of coastal deserts. The combination of a cold current and the subtropical high further exacerbates the arid conditions in these areas.

Continentality: Distance from the Ocean

Regions located far from large bodies of water are less likely to receive precipitation. The vast continental interiors of North America, Asia, and Africa are more susceptible to arid conditions due to their distance from moisture sources. This factor often works in conjunction with the effects of subtropical high-pressure systems and rain shadows.

Climate Change and Deserts: A Shifting Landscape

Climate change is expected to significantly impact global precipitation patterns, potentially leading to changes in the extent and severity of deserts. Changes in atmospheric circulation patterns, altered temperature gradients, and modifications to ocean currents could all contribute to shifts in the location and size of desert regions. Increased temperatures may also lead to more intense evaporation, exacerbating aridity in existing desert areas. Predicting these changes with accuracy requires advanced climate models and continuous monitoring of atmospheric and oceanic systems.

Conclusion: A Complex Interplay of Forces

The location of most of the world's deserts is not a matter of chance, but a direct consequence of the Earth's atmospheric circulation. The subtropical high-pressure belts, driven by Hadley cells, create regions of descending, dry air, inhibiting cloud formation and precipitation. While other factors like rain shadows, cold ocean currents, and continentality also play important roles, the influence of the subtropical highs remains a dominant factor in determining the global distribution of deserts. Understanding these atmospheric processes is crucial for comprehending the complex interactions that shape our planet's climate and the delicate balance of its ecosystems. Furthermore, appreciating the scientific underpinnings of desert formation is essential for tackling the challenges posed by desertification and climate change in these vulnerable environments. Continued research and monitoring are critical for adapting to and mitigating the impacts of these global changes.