energy budgets

• Incoming UV radiation from the Sun goes into different places:

  • 18% reflected by clouds back to space
  • 5% scattered by atmosphere to space
  • 23% absorbed by the atmosphere (including clouds)
  • 48% absorbed by surface and sub-surface
  • 6% reflected by the Earth's surface (water, snow and ice)
• Some absorbed energy is transferred into the soil by conduction. Conductivity is influenced by colour and moisture. Wet dark rock is a better thermal conductor than dry light sand.
• Heat leaves the surface of the earth by:

  • 12% long wave radiation
  • 5% sensible heat transfer
  • 25% latent heat transfer
• Sensible heat transfer occurs due to convection. Air is warmed by the surface and expands, so it rises because it is less dense than air above it. Cool air sinks then warms at the surface, so the process repeats.
• Latent heat transfer occurs when water evaporates, which uses heat. The heat energy is stored in the water vapour. Condensation then releases heat, which is the latent heat of condensation.
• Long wave radiation is absorbed by greenhouse gases. Clouds absorb the radiation and re-radiate it back to the Earth. Heat loss is greatest in dry air through radiation windows.
• Dark oceans have a low albedo whereas white ice caps have a high albedo. As ice caps melt, there is ocean that replaces it, causing an increase in absorption This raises global temperatures, making more ice melt. The process repeats, causing the ice-albedo loop.
• The albedo of oceans vary depending on the time of day and angle of the sun. Albedo is low at midday, but high in evenings.
• With a clear sky at night, long wave radiation escapes through radiation windows, as heat absorbed by the surface during the day returns to space by conduction. Sensible heat transfer also causes heat loss. However, latent heat transfer is reversed, as dew formed by condensation on cold surfaces releases heat.
• With a cloudy sky at night, long wave radiation is absorbed by the clouds, then reradiated in all directions. Sensible heat transfer also causes heat loss. Latent heat transfer can work in either direction depending on the temperatures.
• Latitudinal contrasts in isolation:

  • sun rays arriving at the equator have a shorter distance to go through the atmosphere so there is less scattering, and a smaller area of land is reached, so the land has an excess
  • sun rays at the poles have a longer distance to go through the atmosphere so there is more scattering, and a larger area of land is reached, so the land has a deficit
• Due to the Earth's tilt, different parts of the planet are perpendicular to the sun at different times of year.
• Areas with rainforests are cooler than areas of desert due to a higher cloud coverage, so more radiation is reflected back into space, even though they have the same latitude.
• Oceans absorb energy, but the energy is moved around by currents, so the ocean warms up very slowly. Land masses heat up quickly because the energy is absorbed by the land, then emitted again. This is due to a high specific heat capacity of water. The oceans maintain their heat for longer when going from summer to winter.
• variations in mean temperatures:

  • lag between highest/coldest temperatures and insulation by 2 months, so in summer, there is cold ocean and warm land
  • land is often hotter than oceans at the same latitude as it in summer, but cooler than oceans in winter
  • deserts have highest temperatures, but rainforests have lower temperatures, due to cloud coverage
  • mountains have thinner atmospheres so heat isn't held well, and snow has a high albedo
  • ocean currents either cool or warm neighbouring land
• ITCZ - inter tropical convergence zone
• STJS - sub tropical jet stream
• PFJS - polar front jet stream
• The tri-cellular model is made up of 3 cells. Hadley cell is driven by heat created by direct insolation near the equator. Polar cell is driven by intense cold at the poles. These two cells are thermally direct. Ferrel cell is driven by the movement of the Hadley cell and Polar cell, so it is thermally indirect.
• continentality - places far from the coastline experience extreme weather e.g. Moscow is very cold in winter, and hot in summer.
• Ocean currents:

  1. water at the surface is warmed due to high specific heat capacity, and low albedo, at the equator
  2. warm water moves away from the equator, and slowly evaporates, so there is a higher salt content, making the water more dense
  3. as warm water moves North, it cools becoming more dense, and it becomes more salty and more dense
  4. water at surface is more dense than water below, so it sinks
  5. cold, salty water moves to replace the warm water at the equator
• El niño occurs when the winds change so hot water stays in the middle of the ocean, so hot air rises. This causes warm, dry weather to the West with fires and droughts, and warm, wet weather to the East with floods and storms.
• Normal conditions without El Niño are that wind pushes warm water on the surface towards the west, where the hot air rises causing warm weather. To the east, cold water comes up to replace the hot water, causing cold dry weather.
• Tropical storms form over the tropics, over areas of warm ocean. Water evaporates from the ocean's surface, creating a storm cell. The storm cell then tracks north west in the northern hemisphere. This moves heat from the tropics to the mid-latitudes, changing global temperatures.
• Temperature inversion is a reversal of the normal atmospheric conditions meaning that cooler air at the surface is over lain by warmer air above. This means that temperature increases with height. This is a problem in valleys, especially in cities, because the cold air does not rise, so air pollution is stuck in the bottom, as it can not rise either. This can cause respiratory illnesses.
• Radiation / nocturnal inversion is when the earth's surface cools at night due to heat being lost via radiation, so the air next to it cools due to conduction. This requires calm conditions to stop the air from mixing with air above.
• Coriolis effect - the rotation of the earth causes an apparent deflection of wind direction