Introduction
Earth’s atmosphere has different pressure belts that influence global winds, ocean currents, and climate regions. These belts develop because of uneven heating from the sun and the Earth’s rotation, known as the Coriolis effect. Understanding these belts are important for predicting weather, monsoons, and desert formation.
The 7 Major Pressure Belts
1. The Equatorial Low Pressure Belt (Doldrums)
2. The Subtropical High Pressure Belt in N and S hemisphere
3. The Subpolar Low Pressure Belt N and S hemisphere
4. The Polar High Pressure Belt N and S hemisphere
1. Equatorial Low-Pressure Belt (Doldrums)
- Location: 0°- 5° N/S (near the Equator)
- Characteristics:
- Intense solar heating → warm air rises → low pressure.
- Frequent thunderstorms and heavy rainfall (e.g., Amazon Rainforest).
- Weak winds, nicknamed "doldrums" by sailors due to stagnant air.
Located around the equator, this low-pressure zone is characterised by warm temperatures and rising air. The air here is typically moist, and since the air rises, it leads to frequent thunderstorms and cloudy conditions.
The equatorial zone is called the Doldrums because of its calm, windless conditions, resulting from the rising of warm air, creating a low-pressure system with little horizontal wind movement. It is also marked by frequent thunderstorms and heavy rainfall.
2. Subtropical High-Pressure Belts (Horse Latitudes)
- Location: 30°-35° N/S (e.g., Sahara, Australian Outback)
- Characteristics:
- Descending cool air creates high pressure → clear skies, minimal rain.
- Home to most hot deserts (Sahara, Kalahari).
- Named after ships abandoning horses here due to lack of wind.
Found around 30° north and south of the equator, the subtropical high-pressure zones are caused by the cool air descending from the upper atmosphere. This zone is associated with dry, clear weather, which is why many of the world’s major deserts (like the Sahara and the Arabian Desert) are located in this belt.
3. Subpolar Low-Pressure Belts
- Location: 60°-65° N/S (e.g., Alaska, Patagonia)
- Characteristics:
- Warm tropical air collides with cold polar air → low pressure → cyclones.
- High precipitation (e.g., Pacific Northwest rainforests).
This belt is found around 60° latitude in both the Northern and Southern Hemispheres. It is a low-pressure area where warm air from the tropics rises and meets colder air from the poles. This clash causes unstable weather and is where regions like the North Atlantic and North Pacific are located. These areas often experience stormy conditions.
4. Polar High-Pressure Belts
- Location: 85°-90° N/S (Poles)
- Characteristics:
- Cold, dense air sinks → high pressure → extremely dry (polar deserts).
- Source of polar easterly winds.
At the poles, cold air sinks, creating high-pressure systems. The polar high-pressure belt is dominated by extremely cold, dense air, leading to clear, calm, but frigid conditions. This zone influences the polar climates and helps regulate the global air circulation.
What Are Atmospheric Cells?
Atmospheric cells refer to large-scale convection currents that form due to the differential heating of the Earth's surface. These cells are integral in understanding how air moves through the atmosphere and how pressure zones develop.
Each hemisphere of the Earth has three main wind circulation cell. These cell work with pressure areas to create the global wind patterns we see around the world.
1.Hadley Cell:
The Hadley cell occurs between the equator and 30° latitude. In this cell, warm air rises at the equator, creating a low-pressure zone. As the air cools, it moves toward the poles at high altitudes, then descends around 30° latitude, creating the subtropical high-pressure belt.This cell causes the trade winds to blow. In the Northern Hemisphere, these winds come from the northeast. In the Southern Hemisphere that blow from the southeast. Trade Winds: Blow from subtropical highs to equatorial lows (easterlies).
2.Ferrel Cell:
Between 30° and 60° latitude lies the Ferrel cell. Here, warm air from the tropics moves towards the poles at the surface, while cold air from the poles moves toward the equator at higher altitudes. This cell is responsible for the prevailing westerlies, winds that blow from west to east in the middle latitudes. This cell important for the climate of temperate zones, including much of Europe and North America. Westerlies: Dominate mid-latitudes (30°–60°), driving weather in Europe/N. America.
3.Polar Cell:
The Polar cell is found between 60° latitude and the poles. Cold air sinks at the poles and moves toward the equator at the surface. As it warms up, the air rises around 60° latitude, creating the subpolar low-pressure belt. This circulation is much weaker compared to the other cells but still contributes to the overall atmospheric dynamics, particularly influencing polar regions.
Polar Vortex: Forms due to polar highs, causing Arctic cold waves.
How Do These Systems Influence Weather and Climate?
The global pressure belts and atmospheric cells work together to create Earth's weather patterns. For example:
- The Trade Winds: The movement of air in the Hadley cell creates the trade winds, which blow from east to west near the equator. These winds are important for ocean currents and tropical weather systems.
- Storms and Precipitation: The rising air in the low-pressure belts often leads to cloud formation and precipitation, while the descending air in the high-pressure belts leads to dry conditions. The interaction of these zones contributes to the formation of storms, including tropical cyclones and mid-latitude storms.
- Desert Formation: The subtropical high-pressure belts are associated with the world's major deserts because of the dry, descending air that inhibits rainfall
Summary
The global pressure belts and atmospheric cells are shaped Earth’s climate and weather systems. The pressure belts determine the movement of air and moisture, influencing wind patterns and the formation of weather systems. Atmospheric cells help transfer heat and regulate temperature across the planet. By understanding how these systems work, we can better explain why different parts of the world have different weather and climates.
