Pressure and Winds – UGC NET Geography – Detailed Notes

Pressure

The weather is determined by atmospheric pressure. Cloudiness, wind, and precipitation are common when a low-pressure system moves into a region. Fair and quiet weather is frequently associated with high-pressure systems. When air pressure rises, the temperature must rise as well. When the air pressure drops, the temperature drops as well. It also explains why air becomes colder at greater altitudes due to decreased pressure. 

Primary Elements of Weather And Climate

• Weather is nothing more than the various elements that make it up, as well as how they interact with one another to produce various atmospheric conditions and weather events.
• All-weather is driven by eight basic elements/factors.

The primary elements include:

1. Temperature
2. Air (Atmospheric) Pressure
3. Wind
4. Precipitation
5. Humidity
6. Visibility
7. Clouds
8. Duration of Sunshine

Pressure As An Element

• An important aspect of weather is air pressure, which is especially important when it comes to establishing or changing atmospheric conditions.
• It’s also one of the most important factors in precise weather forecasting.
• The pressure formed by the weight of air in the Earth’s atmosphere is known as air pressure. It’s also known as barometric pressure, named after the device that measures air pressure.
• Air has weight, even if it isn’t apparent, because it isn’t empty.
• It’s filled with nitrogen, oxygen, argon, carbon dioxide, and a few more gases in microscopic particles.
• Due to the gravitational force of the Earth, the weight of the particles in the air causes pressure.
• Because there is more air above the air near the ground, air pressure is higher.

Distribution of Atmospheric Pressure

The worldwide horizontal distribution of pressure refers to the distribution of atmospheric (air) pressure across the latitudes. The most distinguishing aspect is its zonal character, which is referred to as pressure belts. Throughout the year, the Equatorial region receives a lot of heat. The air in the Equator rises because warm air is light, resulting in low pressure. High pressure is created/formed at the poles due to the cold, heavy air.

Isobars depict the distribution of atmospheric pressure on a map. An isobar is a hypothetical line constructed between two points with equal atmospheric pressure at sea level.

1. Vertical Variation of Pressure
2. Horizontal Variation of Pressure

Vertical Distribution of Pressure

• Vertical pressure distribution refers to the columnar distribution of air pressure.
• Although air pressure lowers as the altitude rises, it does not necessarily do so at the same rate.
• The lowest sections of the atmosphere, near the mean sea level, contain dense components.

Vertical Distribution of Atmospheric Pressure

Horizontal Distribution of Pressure

• On the surface of the planet, pressure gradients are tiny, yet even a slight change in pressure has a big impact on wind speed and direction.
• Isobars are used to study the horizontal distribution of atmospheric pressure.
• One or more isobars surround the low-pressure system, with the lowest pressure in the center.
• High pressure is similarly encased by one or more isobars, with the highest pressure at the center.
• We study the isobars of January and July because they are the wettest months of the year for a huge area of the globe.

World Pressure Belts

• Pressure belts are areas on Earth that are dominated by either high or low-pressure cells. On the surface of the Earth, the high and low-pressure belts alternate. The atmospheric pressure fluctuates indirectly with temperature in general.
• There are seven pressure bands on the earth’s surface.
• The Equatorial Low, two Subtropical Highs, two Subpolar Lows, and two Polar Highs comprise the four.
• The others, with the exception of the Equatorial low, form matching pairs in the Northern and Southern Hemispheres.
• Over the world, there is a pattern of alternate high and low-pressure belts.
• This is related to the earth’s spherical form, which causes uneven heating in different places of the globe.
• Throughout the year, the Equatorial region receives a lot of heat.
• The air in the Equator rises because warm air is light, resulting in low pressure.
• High pressure is created/formed at the poles due to the cold, heavy air. It’s also because of the earth’s rotation.
• The rotation of the globe drives the bulk of the air towards the Equator in the Subpolar zone about latitudes 60° to 65° North and South of the Equator, creating a low-pressure belt in this region.

Pressure Belts of the Earth

Equatorial Low-Pressure Belts

• From 0 to 5 degrees north and south of the Equator, this low-pressure belt exists.
• There is a lot of heat here because of the sun’s vertical rays.
• As a result of the convection current, the air expands and rises, causing low pressure to occur here.
• Because it is a zone of complete quiet with no breeze, this low-pressure belt is also known as the doldrums.

Subtropical High-Pressure Belts

• The location where the ascending equatorial air currents drop is located around 30° North and South of the Equator.
• As a result, this is a high-pressure zone.
• The Horse latitude is another name for it.
• Winds are continually blowing from high to low pressure.
• As a result, trade winds blow from the subtropical zone towards the Equator.

Circum Polar Low-Pressure Belts

• Circum Polar Low-Pressure Belts are belts that run between 60° and 70° in each hemisphere.
• The descending air in the Subtropical zone is split into two portions.
• One part of the wind is directed toward the Equatorial Low-Pressure Belt.
• The remaining half of the wind is directed towards the Circumpolar Low-Pressure Belt.
• The rise of warm Subtropical air above frigid polar air moving from the poles defines this zone.
• The winds that encircle the Polar area blow towards the Equator due to the earth’s rotation.
• The Circumpolar Low-Pressure Belt is a low-pressure belt created by centrifugal forces occurring in this region.
• During the winter, this area is known for its strong storms.

Polar High-Pressure Areas

• Temperatures are always exceptionally low between 70° and 90° North and South at the North and South Poles.
• High pressures from above the Poles due to the chilly descending air.
• The Polar Highs are these areas of high pressure in the Arctic.
• Permanent IceCaps describe these locations.