ATMOSPHERIC CIRCULATION MODELS
This page last updated July 2008 and now ARCHIVED.
Atmospheric Circulation:
Models: Unicellular model derived by Hadley: one 'cell': warm air rising at the equator and sinking at the poles.
Reviewed and updated by Ferrel: based on the idea that there would be more than one 'cell' as the rising heat would not have enough energy to make it all the way to the Poles - also modified by the CORIOLIS effect which would divert the winds as they moved N and S (to the right in the Northern Hemisphere...)
HEAT BUDGET graph
Define WIND:
LABELS: get a large (A2 or A1) piece of paper and draw a hemisphere taking up the bottom 40% and the central 70% so that there is space for the labels, which can be enlarged as necessary. These could also be added as labels to a similar diagram on a PowerPoint presentation.
Thanks to colleague Mr. Nunnerley for these resources. Print off, cut out and hand out in a different order (it's a bit too easy if you don't...)
| Trade winds meet in the equator creating the Inter-Tropical convergence zone (ITCZ) |
| The trade winds are forced to rise because of the heat that they have gained from the warm tropical oceans |
| This air is rapidly cooled, often producing towering cumulonimbus clouds (NB: these strong upward currents form the 'powerhouse of global circulation') |
| As the air cools, it ceases to rise and it begins to move away from the equator |
| Increased density as a result of the air cooling, together with the Coriolis force, causes the air to sink (causing a high pressure area as it pushes downwards on the earth's surface) |
| Subsiding air causes the descending limb of the 'Hadley Cell' - usually found at about 30° N of the equator |
| Area of high pressure |
| Area of low pressure |
| Mirror image of the Northern Hemisphere occurs in Southern Hemisphere |
| On reaching the earth' surface the cell is completed |
| Some of the air returns to the equator as the NE trade winds |
| Remaining air is diverted pole-wards, forming the warm SW winds |
| Warm air of the South Westerlies meets the cold air at the Polar Front (about 60°N) |
| Warm air rises above cold air creating the rising limbs of the Polar and Ferrel Cells |
| Polar Front Jet Stream occurs aloft at this point (PFJS) |
| Resulting unstable conditions produce cyclonic rainfall associated with mid-latitude depressions |
| Some of this rising air returns to tropics, while some travels towards to the poles |
| Stable area of high pressure |
Use BLUE and RED to represent the changes in the air temperature as the cells form.
Lead on from this to a discussion of: ROSSBY WAVES, JET STREAMS and CONVEYOR MODEL as it relates to mid-latitude depressions.
Mr. Nunnerley may provide his POWERPOINT presentation soon as well.
Could also bring in Buys-Ballot's Law at this stage too.
Also mention DOLDRUMS and HORSE LATITUDES.