Why are most of the arid and semi-arid environments world found between 20 degrees north 40 latitudes south latitudes?

The distribution of arid and semi-arid environments around the world is the influence of several geographical and atmospheric factors, but the concentration between the 20 degrees north and 40 degrees south latitudes is primarily associated with the global atmospheric circulation patterns.

1. Hadley Cell Circulation: The Earth's atmosphere circulates in large, convective cells called Hadley Cells. These cells are characterized by rising air at the equator, poleward air movement at higher altitudes, descending air at around 30 degrees latitude (subtropical regions), and return airflow toward the equator near the surface.

2. Subtropical Deserts: As air descends in subtropical regions, it warms through compression and loses moisture, leading to the formation of high-pressure weather systems known as subtropical highs or subtropical ridges. These regions experience clear skies and little precipitation. This sinking air creates stable atmospheric conditions that suppress cloud development and result in arid and desert conditions.

3. Rain Shadow Effects: The rain shadow effect occurs on the leeward side of mountain ranges, where prevailing winds have already released most of their moisture on the windward side. Descending air on the leeward side further warms and dries, resulting in lower precipitation. This effect contributes to the aridity in regions located on the rain shadow side of major mountain ranges.

4. Horse Latitudes: The subtropical latitudes between the 20 and 40 degrees parallels are often referred to as "horse latitudes." This term is historically associated with the days of sailing ships, where sailing vessels frequently encountered calm winds and currents in these latitudes, sometimes causing long delays or even stranding ships.

5. Global Wind Patterns: The large-scale atmospheric circulation patterns, including the Trade winds, Westerlies, and Polar front jet streams, interact and reinforce aridity in certain regions. For instance, the descending air masses from the Hadley Cells in the subtropics contribute to the formation of trade winds, further enhancing the dryness of these regions.

6. Influence of Ocean Currents: In some cases, aridity can also be influenced by cold ocean currents. For example, the Humbolt Current along the west coast of South America generates cold coastal waters that cool the overlying air, reducing evaporation and leading to arid conditions in coastal regions.

It's important to note that, while the majority of arid and semi-arid the world are found between 20 degrees north and 40 degrees south latitudes, there are several exceptions due to local geographical and climatic factors. Polar and high mountain regions can also experience arid conditions due to the influence of rain shadows, cold temperatures, and continental air masses.