Pressure Belts: Classification and Significance

What are Pressure Belts? What are the factors controlling the Pressure belts? What are the different types of Pressure Belts? To answer these questions, read further.

Pressure belts are those areas on the surface of the earth where the same pressure is distributed differently based on latitude. These are developed due to High or Low-Pressure cells. These high- or low-pressure cells produce high- or low-pressure belts.

The atmosphere is a multi-layered gas envelope over the earth’s surface, suspended over the surface due to its gravitational attraction.

The mechanical mixture of the atmosphere includes both constant and variable gases, although all the constant gases become variable above 80 km height.

Different types of air pressure on the earth’s surface can be observed in various regions of the world due to a natural occurrence called pressure belts.

Factors Controlling Pressure Systems

High and low-pressure systems are produced by pressure differences that are primarily caused by thermal and dynamic processes, respectively.

Thermal Aspects:

• Heat causes air to expand, which reduces its density. As a result, low pressure is created.
• On the contrary, cooling results in contraction. As a result, the density rises and the pressure rises.
• Examples of thermal lows and highs are the formation of equatorial lows and polar highs, respectively.

Dynamic Elements:

• In addition to temperature changes, the dynamic elements resulting from pressure gradient forces and earth rotation can be used to explain how pressure belts form Coriolis force.

Classification

Based on the mass-energy exchange mechanism between the earth and the atmosphere and within the atmosphere several sequential pressure belts can be classified from the equator toward the pole.

There are seven pressure belts on the surface of the world. There are the two Subtropical highs, the two Subpolar lows, the two Polar highs, and the Equatorial Low.

Equatorial low-pressure belt

It is a thermally induced pressure belt created by almost vertical solar insolation throughout the year. It is found near the equator between 5 degrees north and south latitude.

• High range of insolation heating and extreme thermal conditions. Air parcels over the surface of the earth remain relatively warmer and up well from the surface in the form of convection currents to create low-pressure conditions over the surface.
• Since insulation heating and convection remained persistent and permanent phenomena over the equator, a vacuum type of atmospheric condition developed over the surface, called Doldrums.

Significance:

• Contributes to the development of the Intertropical Convergence Zone (ITCZ), where trade winds converge and result in significant rainfall.
• Plays a crucial role in the Earth’s heat redistribution by initiating the Hadley cell circulation.

Subtropical high-pressure belt

It is a dynamically induced pressure belt developed over subtropical latitudes by regular subsidence of air masses originating from the equator. It is found around 30 degrees north and south latitudes.

• Subtropical latitudes are referred to symbolically as horse latitudes. It is because subsiding air parcels apply tremendous pressure over the earth’s surface and wind drifts away from the surface to fill the low-pressure vacuum of the equator and sub-polar latitude.
• Consequently, a vacuum type of atmospheric conditions develops over the surface where the horizontal movement of air parcels remains very low.

Significance:

• Leads to the formation of subtropical deserts, such as the Sahara in Africa and the Sonoran in North America.
• Influences the trade winds that blow towards the equator.

Subpolar low-pressure belt

It is developed between 55 to 65 degrees northern and Southern hemispheres by several dynamic and thermal components. Relative low-pressure condition is acknowledged over the polar surface since they lie between two prominent high-pressure zones of sub-trophic and polar origin.

• Atmospheric conditions over subpolar latitude remain comparatively high to the Polar surface. Consequently, warm and comparatively like their forces of subpolar origin apply less pressure over the surface, creating a low-pressure condition
• Cold and dense air masses initially meeting from polar high-pressure belts and advancing towards subpolar low-pressure vacuum also cover more surface area and the net pressure applied by them shall subsequently decrease.

The surface of some polar latitude always remains a converging zone of two contrasting air masses. Air masses originating from polar and subtropical high-pressure belts are distinct in their physical properties and implications.

• When these contrasting air masses converge with each other a transition zone or boundary known as a front develops between the distinct air masses and the boundary ultimately transforms into a zone of turbulence between the contrasting air masses.
• Along the boundary of the front always a warm air mass up well or take up lifted from the surface chased by the high-pressure condition of a cold air parcel originating from a higher latitude.
• As a result, both warm and cold air parcels get up and lifted from the surface and the next pressure applied by themselves subsequently be low.

Significance:

• Contributes to the development of the polar front, a zone of weather systems and storms.
• Influences the westerlies, the prevailing winds in the mid-latitudes.

Polar high-pressure belt

It is again a thermally induced Pressure Belt characterized by almost incline and solar insolation, less insulation and heating, and subsidence of cold and denser air parcels.

• This pressure belt system is an abstract representation. The Pressure belt placement is not fixed.
• As they move between the Tropics of Cancer and Capricorn, they move northward in July and southward in January, following the shifting positions of the sun’s direct rays. The belt of maximum temperature usually referred to as the thermal equator also moves north and south of the equator.
• There is a shift in pressure belts to the north and south of their yearly average location along with the thermal equator’s movement northward in summer and southward in winter.

Intertropical Convergence Zone (ITCZ)

A region near the equator where the trade winds converge.

• Associated with low pressure and rising warm, moist air.
• Experiences intense convection and thunderstorm activity.

Significance:

• Plays a crucial role in the global water cycle and tropical weather patterns.
• Affects the distribution of rainfall and the development of monsoons.

Overall Significance of Pressure Belts

• Global Wind Patterns: Pressure belts influence the development of global wind patterns, including trade winds, westerlies, and polar easterlies.
• Climate Zones: Pressure belts contribute to the establishment of major climate zones, such as tropical, subtropical, and polar climates.
• Weather Systems: The interaction of pressure belts leads to the formation of weather systems, including cyclones, anticyclones, and monsoons.
• Ocean Circulation: Atmospheric circulation driven by pressure belts influences ocean currents, playing a role in the distribution of heat around the globe.

Understanding pressure belts is fundamental to comprehending the Earth’s atmospheric circulation and the resulting weather and climate patterns. The movement of air masses between these belts contributes to the dynamic and interconnected nature of the Earth’s atmospheric system.

Article written by Chetna Yadav.