Atmospheric pressure is the force exerted on the Earth’s surface by the weight of the air column above it. This weight is not distributed uniformly across the globe, leading to variations that drive all weather systems. A pressure belt is a band of either high or low atmospheric pressure that encircles the Earth horizontally along specific latitudes. These belts are fundamental to the planet’s climate, acting as the primary engines that determine the direction of global winds and the distribution of rainfall.
The Physics Behind Pressure Belts
The formation of these planetary pressure systems is governed by two distinct physical forces: thermal factors and dynamic factors. Thermal influences relate directly to how the sun heats the Earth’s surface. When air is intensely heated, such as near the equator, it expands, becomes less dense, and rises, creating a low-pressure zone. Conversely, in extremely cold regions like the poles, the air cools, contracts, and sinks toward the ground, establishing a high-pressure zone.
Dynamic factors are caused primarily by the Earth’s rotation. As large masses of air move away from the equator in the upper atmosphere, the Coriolis force deflects this air, causing it to accumulate at specific latitudes. This accumulation forces the air to descend toward the surface, dynamically forming a high-pressure belt. Dynamic low-pressure zones are created where converging air masses force air upward, such as at the boundary between warm and cold air streams.
Identifying the Major Global Belts
The interplay between thermal and dynamic forces creates a system of seven distinct pressure belts that alternate across the globe. At the equator, the Equatorial Low pressure belt extends roughly between 5° North and 5° South latitude. This zone is thermally induced and characterized by consistently rising air. Moving poleward, the Subtropical Highs are found around 30° North and South latitude, representing two separate belts of dynamic high pressure. Here, dry, sinking air creates clear skies and is responsible for the location of most of the world’s major hot deserts.
Further toward the poles, the Subpolar Lows are centered near 60° North and 60° South latitude, forming two belts of dynamic low pressure. This is where warmer air masses from the subtropics meet frigid air masses from the poles, forcing the air to rise and resulting in unsettled, stormy weather. Finally, the Polar Highs cap the system at the North and South Poles, close to 90° latitude. These two thermally induced high-pressure belts are characterized by extremely cold, dense air that sinks, creating persistent high pressure and very dry conditions.
How Pressure Belts Drive Global Weather
The alternating high- and low-pressure belts are the driving force behind the global atmospheric circulation cells, which dictate long-term climate patterns. Air naturally moves from areas of high pressure to areas of low pressure, a motion known as the pressure gradient force, which generates the Earth’s steady wind systems. The Subtropical Highs, for example, feed air into the Equatorial Low, creating the dependable Trade Winds.
These pressure gradients define the boundaries of the three major circulation cells in each hemisphere: the Hadley, Ferrel, and Polar cells. The Hadley cell, centered in the tropics, is driven by the rising air at the Equatorial Low and the sinking air at the Subtropical High. The type of weather associated with each belt is determined by the vertical motion of the air. In the low-pressure zones, rising air cools, leading to condensation, cloud formation, and frequent precipitation.
Conversely, the high-pressure zones are dominated by sinking air, which warms as it descends, suppressing cloud formation and preventing precipitation. This results in the clear skies and arid conditions typical of the Subtropical Highs. The pressure belts systematically organize the planet’s climate, linking the movement of the atmosphere to the distribution of rainfall, temperature, and wind.