2.2 The global energy budget Flashcards
What is the latitudinal radiation pattern? (excess and deficits)
Excess: positive radiation budget in the tropics, occurs as insolation is so concentrated
Deficit: negative radiation budget at higher latitudes. Insolation has a larger amount of atmosphere to pass through, there is more chance of reflection back to space, and rays are less concentrated.
How is the global energy budget balanced?
- sensible heat transfers (horizontal heat transfers) take place, where heat is moved horizontally away from hot tropical areas towards the cold polar areas
- either by winds (80%) or movement of ocean currents (20%) moving heat away from tropics
- warm currents flow to poles and cold currents towards equatore
What are the pressure belts/variations?
- air moves from high to low pressure
- low pressure systems bring poor weather
- low pressure in equatorial regions, as warm air rises and leaves the surface.
- ## Higher pressures seen in polar regions, where cool air descends onto the surface and becomes compressed and less humid, so often fair weather/limited precipitation
What are the wind belts?
- driven by rotation of earth and incoming energy from the sun
- heated air in equatorial areas and this rises and then travels towards poles before descending in sub-tropical areas
- three major global wind belts are polar easterlies, westerlies, and trade winds.
- polar easterlies flow from the north and south poles towards 60 degrees north and south, respectively. They are very cold and dry winds.
- westerlies are found between 30 and 60 degrees north and south of the Equator. They flow poleward and are dry as well.
- trade winds (also known as the tropical easterlies) flow from 30 degrees north and south towards the Equator. These winds are associated with high precipitation at the Equator.
What is the ocean conveyor belt?
- cold, salty water sinks from polar regions and moves towards equator, where warm water gives its heat away to the surface winds.
- More evaporation in North Atlantic, which leaves saltier water behind – denser so sinks and cools.
- Water is transported to Pacific, dilutes, less dense so rises.
What are the seasonal variations in temperature due to latitude?
- between the tropics, the angle of Sun is high, so greater intensity of insolation is received, and hence more heating.
- Where there is more atmosphere to pass through, a greater proportion of insolation is lost/scattered/reflected by atmosphere.
- Also, the longer the sun shines, the more insolation is received (so depending on time of year the northern/southern hemisphere receive more daylight)
What are the seasonal variations in temperature due to land/sea distribution?
Land:
- lower reflectivity, so more absorption of radiation (apart from ice)
- heat confined to near surface as most surfaces poor conductors
- low specific heat capacity, so a set amount of energy raised land temp by more
- less water, so *8less energy wasted to evaporation**
Sea:
- higher reflectivity; so less absorption of radiation
- sun’s rays penetrate deep, convection currents distribute heat to great depths
- high specific heat capacity, so set amount of energy raises temp by less
- large amounts of energy used for evaporation
- in winter, land loses heat much more rapidly than sea so oceans act as heat reservoirs and areas close to sea have much smaller annual range of temps
What are the seasonal variations in temperature due to ocean currents?
- surface currents caused by prevailing winds.
- heat is transferred from tropics to higher latitudes
- in NHemisphere, ocean currents circulate clockwise and in SHemisphere anticlockwise
- due to coriolis effect
- ocean current moving towards equator carry cooler water south, currents moving away carry warmer water north
How does altitude cause temperature variations?
- air temperature decreases with altitude, as air is thinner, contains less moisture and is therefore less able to absorb longwave radiation.
What are jet streams?
- narrow bands of strong, high-altitude winds within upper troposphere and lower stratosphere
- flow from west to east and form where major air masses meet
- Rossby waves are the large-scale meanders that form within these jet streams
- waves can allow pressure systems to move further north/south
What is the global circulation model?
3 Cell Model:
Hadley Cell: adjacent to ITCZ, where insolation is most intense. Doldrums created (permanent low-pressure belt) due to constant rising of air, trade winds are drawn in. Air subsides around 30°N/S and is deflected right/left depending on hemisphere.
Ferrel Cell: not thermally induced, but a result of adjacent cells – creating a ‘cog-like’ system. Air is forced to rise at the polar front, and forced to sink at the high-pressure zone, where it meets the Hadley cell.
Polar Cell: cold polar air sinks, creating high pressure. As the air moves towards the equator, it spreads out, pressure reduces, and it rises. Low pressure zone created at 50-60°N/S
What are the seasonal variation in global wind belts?
- Winds are created by differences in atmospheric pressure.
- Atmospheric
pressure is affected by heating from the sun. - affected by overhead position of the Earth in relation to the sun. Most heating Especially between 30 and 45 degrees north and south of equator, and smaller at low latitudes. - Winds blow from the sub-tropical high pressure areas to the equatorial low
pressure areas (doldrums). North east to south west in the northern
hemisphere and reversed in the southern hemisphere. - In higher latitudes,
winds blow from the sub-tropical high pressure areas to the sub-polar low
pressure areas; south west to north east in the northern hemisphere and
north west to south east in the southern hemisphere. - These pressure
systems move north and south according to the relative position of the sun.
