2.1.1 Global Atmospheric Circulation (2025)

What is insolation?

Incoming short wave solar radiation energy from the sun

What is long wave radiation?

Long wave terrestial radiation refers to energy absorbed by the earth and re-radiated back to space

What is the dominant factor determining temperature?

Latitude: - difference in beam spreading --> tropics: sun is directly overhead, insolation is most concentrated --> less beam spreading + amt of radiation per unit area is highest whereas with increasing latitude, solar radiation reaches the surface at a lower angle & spreading out + solar radiation pua is lower - insolation has more atmosphere to pass through near poles due to low angle of approach - albdeo (surface's reflectivity) is higher in polar regions since snow and ie are reflective

What are the 3 main forces that affect air movement?

1) Pressure Gradient Force 2) Coriolis effect 3) Friction

What is pressure gradient force?

Basic force affecting atmospheric movement and the greater the difference the greater the wind speed Affects direction and magnitude Magnitude is determined by spacing of isobars Direction of force is from areas of higher pressure to areas of lower pressure + right angle to isobar

Why are there differences in air pressure in different areas?

Unequal heating of earth's land-sea surface Specific heat capacity of water is 5 times as great as land --> water cools down and heats up slower than land Variations in the amount of solar radiation received due to variations in sun angle with latitude generate the much larger atmospheric circulation

What is the Coriolis effect?

Apparent deflection due to rotation of Earth Greatest at the poles (Earth's surface is right angle to axis of rotation) and gets progressively less towards the equator (reaches 0) Deflection is always at right angle to direction of wind Affects DIRECTION, not speed Affected BY speed --> stronger the wind, greater the deflecting force

What is friction?

Friction does not affect winds aloft, only surface Friction reduces wind speed --> reduces Coriolis effect at the surface Wind speed aloft is very high due to absence of friction

Briefly, what is the Tri-Cellular Model?

William Ferrel Hadley, Ferrel, Polar cells Composed of surface winds, vertical uplift, upper level winds and subsidence

Where can Hadley Cells be found?

The circulation in the zones between the equator and roughly 30ºN and S is the Hadley Cell

When is the Hadley cell circulation strongest?

In the winter season, when the temperature gradients are strongest, since cell is produced thermally

Explain the formation of the Hadley cell

1) Near the equator, warm rair rises and condenses, releasing latent heat. During the formation of cumulus towers, latent heat is believed to provide the energy to drive the Hadley cell 2) As upper flow in the cell moves poleward, it acquires increasing west-to-east motion. This westerly component is so strong that the air circles the Earth a couple of time sbefore reaching itsultimate destination in the subtropics. 3) Upon reaching the subtropical high the air that has moved poleward at the upper atmosphere begins to subside. This is because as air moves away from the storym equatorial region, radiation cooling increases the density of air aloft resulting in subsidence. This subsiding air is relatively dry, for it has released its moisture near the equator. 4) The effect of adiabatic compression and adiabatic heating during descent further reduces the relative humidity of the air. Consequently, this dry subsidence zone is the site of the world's subtropical deserts 5) From the center of the subtropical highs, the surface flow then splits into a poleward branch and an equatorward branch where the equatorward flow is deflected by the Coriolis effect to form reliable trade winds. 6) In the northern hemisphere, the trade winds blow from the northeast. In the southern hemisphere, the trades are from the southeast. 7) The trade winds from both hemispheres meet or converge near the equator in a region that has a low pressure known as the equatorial trough or the Intertropical Convergence Zone (ITCZ).

Draw the diagram for the Hadley Cell

How do the trade winds blow in the northern and southern hemisphere?

Northen: Blow from NE Southern: Blow from SE

What is the Intertropical Convergence Zone?

Region where trade winds from both hemispheres meet or converge near the equator The position of the ITCZ is not fixed --> when overhead sun moves from northern hemisphere in June to southern in Dec, trough will move to north and south of the equator Over the oceans, ITCZ is fairly static and shift in position is minimal as seasonal temp changes are small

Where are winds generally weak and variable?

1) Near the intertropical convergence zone 2) Subtropical high pressure belt where there is descending air