Atmospheric circulation
Introduction
Atmospheric circulation is the large-scale movement of air, and the means (together with the smaller ocean circulation) by which thermal energy is distributed on the surface of the Earth. The large-scale structure of the atmospheric circulation varies from year to year, but the basic structure remains fairly constant because it is determined by the Earth's rotation rate and the difference in solar radiation between the equator and poles.
Driving Factors of Atmospheric Circulation
The driving factors of atmospheric circulation are primarily the rotation of the Earth (Coriolis effect) and the heat from the Sun. The rotation of the Earth causes the air to be deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. This is known as the Coriolis Effect. The heat from the Sun warms the Earth's surface, causing the air above it to rise and create areas of low pressure. This causes air from surrounding areas of high pressure to move towards the low pressure area, creating wind.
Global Circulation Models
Global circulation models, also known as general circulation models or GCMs, are mathematical models used to simulate the atmosphere, ocean, and climate system. These models are used for weather forecasting, understanding the climate, and projecting climate change. The models take into account the laws of physics, chemistry, and fluid dynamics to simulate the circulation of the atmosphere.
Atmospheric Circulation Cells
There are three main cells of atmospheric circulation: the Hadley cell, the Ferrel cell, and the Polar cell. The Hadley Cell is the circulation of air in the tropics and is characterized by warm, moist air rising near the equator. The Ferrel cell is found at mid-latitudes and is characterized by air sinking at around 30 degrees latitude and rising at around 60 degrees latitude. The Polar Cell is found at the poles and is characterized by cold, dry air sinking at the poles and rising at around 60 degrees latitude.
Trade Winds
Trade winds are the prevailing pattern of easterly surface winds found in the tropics, within the lower portion of the Earth's atmosphere, in the lower section of the troposphere near the Earth's equator. The trade winds blow predominantly from the northeast in the Northern Hemisphere and from the southeast in the Southern Hemisphere.
Westerlies
The Westerlies, anti-trades, or Prevailing Westerlies, are prevailing winds from the west toward the east in the middle latitudes between 30 and 60 degrees latitude. They originate from the high-pressure areas in the horse latitudes and trend towards the poles and steer extratropical cyclones in this general manner.
Jet Streams
Jet streams are fast flowing, narrow, meandering air currents in the atmospheres of some planets, including Earth. On Earth, the main jet streams are located near the altitude of the tropopause and are westerly winds (flowing west to east). Their paths typically have a meandering shape. Jet streams may start, stop, split into two or more parts, combine into one stream, or flow in various directions including opposite to the direction of the remainder of the jet.
Monsoons
A monsoon is a seasonal change in the direction of the prevailing, or strongest, winds of a region. Monsoons cause wet and dry seasons throughout much of the tropics. Monsoons are most often associated with the Indian Ocean.