Unit 2 topic 2

• Latitude


  Lines that run east-west around the Earth, parallel to the equator
• Equator


  0 degrees latitude, the hottest part of the Earth
• The Equator is the hottest part of the Earth


  The Sun's rays are more concentrated there due to the shape of the Earth
• The poles are colder


  The Sun's rays are less concentrated there due to the shape of the Earth
• Heat from the Equator


  Goes to the poles as the Earth balances out the heat
• Diffusion


  The movement of something (in this case heat) from a high concentration to a low concentration
• Global atmospheric circulation


  Air is heated at the Equator, rises, spreads out, cools, and sinks at the poles
• Hadley cells


  • Stretch from the Equator to 30°N and 30°S
  • Warm trade winds blow towards the Equator
  • Air rises at the Equator, sinks at 30°N and 30°S
• Latitudinal variations in the ITCZ


  Occur due to the movement of the overhead Sun
• Asia induces the monsoon


  Causes winds to blow outwards from high pressure in winter but pulls the southern trades into low pressure in the summer
• In winter, surface temperatures in Asia


  Can be as low as -20°C, while the surrounding oceans have temperatures of 20°C
• In summer, the land in Asia


  Heats up quickly and may reach 40°C, while the sea remains cooler at about 27°C
• This temperature difference


  Initiates a land-sea breeze blowing from the cooler sea (high pressure) in summer to the warmer land (low pressure), whereas in winter, air flows out of the cold land mass (high pressure) to warm water (low pressure)
• Ferrel cells


  • Stretch from 30°N and 30°S to 60°N and 60°S
  • Air on the surface is pulled towards the Poles
  • Warm south-westerly winds in the northern hemisphere and northwesterly winds in the southern hemisphere
• Polar cells


  • Stretch from 60°N and 60°S to the north and south poles
  • Air sinks over the poles, causing high pressure
  • Air then flows towards the low pressure in the mid-latitudes
• The Earth's rotation


  Distorts winds on the ground, causing them to curve as they move from high pressure to low pressure areas
• Major wind systems


  • Trade winds
  • Mid-latitude westerlies
  • Polar easterlies
• Atmospheric circulation in the Northern Hemisphere


  Air is heated at the Equator, rises, diverges, sinks at the tropics, and moves over the surface either back to the Equator or towards the poles
• At the Equator, rainfall is high and constant all year, with hot and humid conditions
• At the tropics, rainfall is low, with dry air sinking and hot and dry (arid) conditions
• In the UK, the warm air from the south meets the cold air from the poles, resulting in unstable conditions with clouds and rain
• At the poles, precipitation is very low, with sinking air and high pressure
• The line labelled A in the map is the Intertropical Convergence Zone (ITCZ)
• South of the Equator, the surface winds blow from the southeast (trade winds)
• Low pressure


  Air rising
• Hot and humid conditions


  Tropical rainforests are found here
• Rainfall is low


  Dry air is sinking (cannot condense)
• High pressure


  Results in hot and dry (arid) conditions
• UK


  55o (just below 60o line)
• When hot and cold air meets


  We get unstable conditions
• The warm air is forced to rise


  Forming clouds and rain
• Precipitation is very low


  Air is sinking
• High pressure


  The air is cold so that it can hold less water vapour
• The line labelled A shown in the map is the Inter Tropical Convergence zone
• Pattern of surface winds south of the Equator


  1. West-to-east winds in high southern latitudes

  2. Winds radiating out of high-pressure zones

  3. Winds blowing towards the Equator (south-east trade winds)
• In the northern hemisphere, there are low-pressure systems in the landmass and general high-pressure systems in the oceans
• In the southern hemisphere, the distribution is somewhat different because of the relative lack of land masses
• Rossby Waves


  Large-scale fast "rivers of air" formed by westerly winds, which follow a ridge and trough-like pattern
• Rossby Waves


  • They are affected by significant topographic barriers such as The Rockies and the Andes
  • The shape of Rossby waves varies over a six-week cycle from a low zonal index to a high zonal index
• Jet Streams


  • Strong and regular winds which blow in the upper atmosphere about 10km above the surface as part of the Rossby waves
  • They blow at around 100-300 km per hour
  • There are two streams in each hemisphere: the polar jet between 30-50o and the subtropical jet between 20-20o