Geography- G3- Contemporary themes- Theme 3- Section A

  • Created by: Lozza8
  • Created on: 06-02-16 15:15

1.1 How does global atmospheric circulation give

Key terms and definition on atmospheric circulation and climate zones:

  • Trade wind belts - In the tropics, on both sides of the equator, lies a wide region where winds blow from east to west (easterlies) with a slight equatorward tilt. This region is names the trade wind belt, because of the steadiness of the air flow here. These winds made for reliable travel westward
  • Intertropical Convergence Zone (ITCZ) - Trade winds from the Northern and Southern Hemispheres converge into a narrow belt close to the equator. The convergence of the trade winds results in rising motion of the colliding air masses. This region is knows as the doldrums, where the weather is generally cloudy and periods of light winds are frequently interrupted by hard rain, making for a troubled and uncertain sea voyage
  • Midlatitude westerlies - North and south of the trade wind belt lie regions where winds tend to blow from west to east (westerlies), and are therefore referred to as the westerly wind belts. They are highly variable and unsteady, especially so during winter. In these regions during wintertime, midlatitude storms and their frontal systems travel from west to east bringing frequent changes in weather
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1.1 How does global atmospheric circulation give

  • Subtropics - lie between the trade wind regions. Regions of divergence and subsidence, where sunny weather with little clouds and no rain prevails. During days of sailing these latitudes were referred to as the horse latitudes because winding up in these latitudes meant serious delays in the voyage
  • Polar easterlies - Poleward from the westerly wind beld, winds with a generally easterly component prevail. The air here is cold, dry and stable, especially during winter, and is accompanies by subsidemce from above
  • Polar front - convergence zone between polar easterlies and midlatitude westerlies. Seperates between the cold (and dry) polar air, and the relatively warm (and more humid) midlatitude air. The polar front can be thought of as the average expression of the transient frontal systems that move along with midlatitude cyclones
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Atmospheric movement

  • Solar energy (insolation) powers the atmospheric system and the energy circulations within it. The amount of solar energy (heat budget) received varies with latitude
  • The tropics have an energy surplus as they gain more from insolation than is lost by radiation. The higher temperate and polar latitudes have an energy deficiency, losing more by radiation than is gained by insolation
  • This imbalance in energy distribution sets up a transfer of heat energy from the tropics to higher latitudes
  • As temperature increases air heats, expands, becomes less dense and rises, creating an area of low pressure below. Conversely, a drop in temperature produces an area of high pressure.
  • Air circulates in a convectional fashion, but this brings consequences for the atmosphere. These include the rate at which air can rise or fall, the ability of air to expand or contract, and that air will continually circulate.
  • Because we view movement from a platform, an apparent deflection of moving objects due to the Eath's rotation occurs. This is called the Coriolis Effect.
  • In mid-latitudes pressure gradient and Coriolis Effect are in balance. This leads to a geostrophic wind blowing not from high to low pressure areas, but between the two.
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1.1 How does global atmospheric circulation give

  • Global air movements - there is a close relationship between major winds and the world's pressure systems. Windbelts also contain the world's major weather systems, including hurricanes in the tropics and anticyclones and depressions in the midlatitudes (tornadoes at a smaller scale)
  • Midlatitude movements - found between the polar and tropical circulations is an area of complex upper air movements. The combination of the powerful Ferrel westerlies (so-called circumpolar vortex) and the jet streams in the midlatitudes, affect surface winds and pressure systems. These surface winds and weather belts are bound up in a series of waves known as Rossby waves. The link between Rossby waves, jet streams and weather systems in the low and high pressure circulation is called the Index cycle
  • Influence of the oceans on atmospheric movement - the oceans proide water for the hydrological cycle, the oceans absorb and redistribute energy, e.g. the Gulf Stream and North Atlantic Drift benefit Western Europe by releasing heat and providing a milder climate than it may otherwise be. Warm oceans and their currents can therefore affect local and distant locations
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A hierarchy of atmospheric motion

The extent to which atmospheric motion influences local weather and climate depends on winds at a variety of scales and their interaction in a hierarchy of patterns. These systems include...

  • Rossby waves and the ITCZ (planetary scale)
  • Monsoons, hurricanes, depressions, and anticyclones (synoptic or macro scale)
  • Land and sea breezes, mountain and valley winds, and thunderstorms (meso-scale)
  • Smoke plumes and urban turbulence (small or micro scale)

Atmospheric circulation: planetary scale and the tricellular model

  • The global transfer of energy is the basis of global atmospheric circulations, which give rise to the low and high pressure belts and the planetary wind systems associated with the Earth's three major convection cells: the Hadley, Ferrel and Polar cells.
  • These make up the tricellular model that controls atmospheric movements and the redistribution of heat energy
  • The meeting of the trade winds in the equatorial regions forms the Intertropical Convergence Zone (ITCZ). The trade winds, which pick up latent heat as they cross warm, tropical oceans, are forced to rise by violent convection currents...
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A hierarchy of atmospheric motion (x2)

  • The unstable, warm, moist air is rapidly cooled adiabatically to produce the towering cululonimbus clouds, frequent afternoon thunderstorms and low pressure characteristic of the equatorial climate
  • It is these strong upward currents that form the 'powerhouse of the general global circulation' and which turn latent heat first into sensible heat and later into potential energy
  • At ground-level, the ITCZ experiences very gentle, variable winds, known as the doldrums
  • As rising air coold to the temperature of the surrounding environmental air, uplift ceases and it begins to move away from the equator.
  • Further cooling, increasing density, and diversion by the Coriolis force causes the air to slow down and subside, forming the descending limb of the Hadley Cell
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1.2 Why do seasonal and periodic variations of cli

Seasonal variations

The reasons for seasonal variations in climate are:

  • The seasonal movement of the ITCZ, and pressure and wind belts associated with the movement of the sun's overhead position during the year
  • The effects of the warm and cool ocean currents
  • Temperature differences between continental landmasses and neighbouring ocean waters

Two different climatic types:

  • Tropical - marked seasonal changes in savanna and monsoon climates (Lagos-tropical wet climate, and Kano-tropical dry climate)
  • Temperate - pronounced seasonal changes found in the continental interior and east-coast margin
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1.3 What are the world's major climates

The main climatic types in tropical regions

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