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Chapter 4 Atmospheric Circulation. Earth Regions near the equator receive light at 90 o High latitudes receive light at low angles.

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Presentation on theme: "Chapter 4 Atmospheric Circulation. Earth Regions near the equator receive light at 90 o High latitudes receive light at low angles."— Presentation transcript:

1 Chapter 4 Atmospheric Circulation

2 Earth Regions near the equator receive light at 90 o High latitudes receive light at low angles

3 Earth Regions near the equator receive light at 90 o High latitudes receive light at low angles Light energy is more concentrated near the equator. In other words, there is a greater flux per unit area (W/m 2 )

4 Solar energy is concentrated near the equator Image: Netherlands Center for Climate Research

5 Energy Latitude absorbed solar energy

6 Energy Latitude absorbed solar energy Emitted IR energy

7 Energy Latitude absorbed solar energy Emitted IR energy More energy is absorbed near the equator than emitted And more energy is emitted near the poles than is absorbed.

8 Energy Latitude net radiation surplus

9 Energy Latitude net radiation surplus net radiation deficit Excess energy at the equator is transferred towards the poles by convection cells

10 Solar energy received is greatest near the equator. Energy is moved from the equator to the poles.

11 Solar energy received is greatest near the equator. Energy is moved from the equator to the poles. Energy is transferred by wind and ocean currents

12 Air near the equator is warmed, and rises solar radiation

13 The rising air creates a circulation cell, called a Hadley Cell solar radiation L H H Rising air  low pressure Sinking air  high pressure

14 Warm air rises Rising air is replaced Hadley Circulation Cell

15 Warm air rises Air cools, sinks Rising air is replaced Hadley Circulation Cell

16 Warm air rises Air cools, sinks Rising air is replaced Hadley Circulation Cell LOW HIGH

17 The Earth would have two large Hadley cells, if it did not rotate. --This is exactly what we think occurs on Venus (which rotates very slowly)! Rotation of the Earth leads to the Coriolis Effect This causes winds (and all moving objects) to be deflected: to the right in the Northern Hemisphere to the left in the Southern Hemisphere

18 The Coriolis Effect Based on conservation of angular momentum We experience linear momentum when we are in a car that is traveling fast and then stops suddenly.

19 Planet Earth rotates once per day. Objects near the poles travel slower than those near the equator.

20 Angular Momentum L = mvr r m v Angular momentum is conserved unless some force (a torque) is applied

21 Objects near the poles have less angular momentum than those near the equator. When objects move poleward, their angular momentum causes them to go faster than the surrounding air. Conversely, they slow as they move towards the equator.

22 When objects move north or south, their angular momentum causes them to appear to go slower or faster. This is why traveling objects (or air parcels) deflect to the right in the northern hemisphere and to the left in the southern hemisphere.

23 Example of Coriolis effect: hurricanes L Hurricanes are low pressure centers Air moves from high pressure towards low pressure HH isobar (line of constant pressure)

24 Hurricanes : Northern hemisphere L As the air moves in, it is deflected towards the right in the NH Resulting circulation is counter-clockwise HH

25 The Coriolis effect causes winds to deflect as they travel within circulation cells This breaks up the two large Hadley cells into six smaller cells.

26 In the tropics, surface air is moving equatorward. It is deflected to the right in the NH (left in the SH), giving rise to easterly flow (the trade winds) Easterlies

27 At midlatitudes, surface air is moving poleward. It is deflected to the right in the NH (left in the SH), giving rise to westerly flow (the prevailing westerlies) Westerlies

28 Credit: NASA

29 Warm air rises Air cools, sinks Rising air is replaced Hadley Circulation Cell LOW HIGH

30 Warm air rises Air cools, sinks Rising air is replaced LOW HIGH Rising air cools; the air’s capacity to hold water drops. Rain! No rain in regions where air is descending

31 : orbit-net.nesdis.noaa.gov/arad/ gpcp/maps/frontmap.gif

32 Intertropical Convergence Zone (ITCZ)

33

34 Caution: Zonal weather pattern is not completely true The pattern is disrupted by land-sea contrasts

35 Land heats and cools rapidly Water heats and cools slowly

36 Warm air rises Onshore wind DAY Sea Breezes

37 Warm air rises Onshore wind DAY Offshore wind NIGHT

38 Tibetian Plateau--Monsoon Circulation


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