1. The Atmospheric Circulation System
Cumulonimbus “Thunderhead” Storm Cloud with Anvil Flatiiron Top
Lots of vertical convection and mixing
Usually Vapour, liquid droplets and ice crystals coexist in this mixed dynamic system
Geos 110 Lectures: Earth System Science
Chapter 4: Kump et al 3rd ed.
Dr. Tark Hamilton, Camosun College

2. Overall the Earth’s Climate is in Balance
In Balance Kind-of:
But you have to average over night and day
It helps to average for many seasons or years
And we need to overlook trivialities like burning all of Earth’s fossil Carbon from the past ~350 Ma in < 3 centuries!
However:
Region to region there are hot and cold spots, wet and dry places, rain forests and deserts, mountains and plains, seas and glaciers, tropics and polar climes & a whole lot of weather!

3. The Ideal Gas Law: Relationships of Pressure, Temperature, Volume & Moles
P V = n R T; P=Pressure, T=Temperature, n=moles of gas particles (with mass), R=ideal gas constant
Special Case 1 – Boyle’s Law: T=constant)
Pinitial Vinitial = Pfinal Vfinal
PV has units of work e.g. F/d2 x d3 = F x d
At constant E, a P increases V decreases
Special Case 2 – Charles’ Law: P=constant)
Vinitial / Tinitial = Vfinal / Tfinal

4. There are Big Latitudinal Differences
Fig 4.1
The Tropics have Energy Surplus
The Poles run a Deficit
Temperate zones have transitory seasonal swings

5. There are Big Latitudinal Differences IR emission doesn’t match
There are Big Latitudinal Differences IR emission doesn’t match? How does heat move?
Fig 4.2
The Tropics have a Net Radiation Surplus (Sin>Eout)
The Poles run a Net Radiation Deficit (Sin<Eout)
Temperate zones have transitory seasonal swings

6. There has to be a Global Circulation System
Fig 4.3
Ferrel Cell
Ferrel Cell
IR conversion to Latent Heat (LiquidVapor)
Convection driven by density and pressure differences between different air masses

7. Convergent versus Divergent Winds at Earth’s Surface
Rising light warm air of the Tropic Lows is replaced laterally by denser air flowing in from higher latitudes & converges towards the ~Equator
This position changes seasonally by ~5° of Latitude
Descending cold dense air from the Horse Latitude Temperate Highs hits the Earths surface and gently diverges
This position is fixed by the stable Tropopause
The troposphere is well mixed by convection and is heated from below.
The overlying stratosphere is warmer, heated from above and puts a lid on this mixing 7

8. Weather & Climate Vary Across the Globe
Fig 4.4
Wind & Ocean Currents Redistribute Solar Heating
Solid Earth processes buffer CO2 levels by weathering rocks over few hundred Ka to Ma
Eddies on all spatial & temporal scales prevent the heat redistribution from being complete or even.
Very long term ~100’s of Ma heat redistribution in the core and mantle affect the shapes and positions of continents and ocean basins via solid state convection and plate dynamics.

9. Eastern Pacific & Central America w/ ITCZ Intertropical Convergence Zone
Fig 4.5
NOAA Satellite Image
Cloud Band marks ITCZ at top of Troposphere
The Troposphere, heated from below convects

10. Convective Towers Cumulonimbus drive Hadley Cells of ITCZ
Fig 4.5
Cloud Band marks ITCZ at top of Troposphere
Solar Evaporation & Latent Heat from Condensation make the heat pump that drives the Convection

11. Horizontal & Vertical Air Movements result from Temperature & Pressure differences driving Buoyancy
Buoyancy is due to density contrasts, Δmass/volume
Fast molecules, more collisions more F/A = Pressure
Temperature increase  Pressure increase
Pressure increase  Volume increase, buoyancy
Air columns heated from below expand and rise
Other denser air moves in laterally to replace it
Cooling upper Troposphere cools air shrinks & sinks

12. Mid-latitude Convective Mixing
Fig 4.6
This calls for steep lateral temperature gradients and abrupt storm fronts with all kinds of wind and weather blowing through, especially at the polar front zone ~ 60°N & S.
Cold fronts descend from higher latitudes
Replacing/passing beneath tropical warm fronts
This rapid mixing of air masses is an ever changing recipe for weather

13. N-S Meridional Mixing of Troposphere
Fig 4.7
Tropics to Horse Latitudes - Hadley Cells
Mid-Latitudes – Ferrel Cells
High Latitude - Polar Front 13

14. Hadley Cells Individual atmospheric cells
Between the Equator and 30-35° N
Over the ocean in Atlantic and Pacific
Driven by heat from below absorbed by ocean
The rocky planet rotates faster than the atmosphere
Hadley Cells are broken up by continents

15. The Horse Latitudes
The Dead Horse Shanty
Oh, poor old man your horse will die And we say so, and we know so Oh, poor old man your horse will die Oh, poor old man
We'll hoist him up to the main yardarm We'll hoist him up to the main yardarm
Say, I old man your horse will die Say, I old man your horse will die
We'll drop him down to the depths of the sea We'll drop him down to the bottom of the sea
We'll sing him down with a long, long roll Where the sharks'll have his body and the devil have have his soul
Spanish ships bound for the New World became becalmed w. Hi Pressure, no wind and Horses died
English “Dead Horse Shanty”, working off advance

16. Idealized Tropospheric Circulation
Rising moist air cools and engenders rain or snow, especially Tropical Lows
Descending cold dry air dessicates underlying landscapes making deserts & drylands, especially under Polar Highs.
This idealized image would work best on an all water covered world or at least one with longitudinal oceans!
If you are a convecting fluid or a fish, land kind of gets in the way!
ITCZ & Polar Front Storm Belts – Hi Precipitation
Horse Latitude & Polar Deserts 16

17. A Simple Pressure Model for Winds
Fig 4.8
Winds blow out of descending High Pressure limbs ~30-35° N&S between Hadley & Ferrel Cells
Winds blow towards rising Low Pressure limbs on equatorial edge of Hadley Cells at ITCZ & also PCZ 17

18. Coriolis Rotational Effects on a Sphere
0 m/s
Fig 4.9a
N-S motions are deflected in apparent curved paths due to the rotating reference frame.
E-W motions are subjected to centrifugal force due to the velocity of rotation and momentum mv
4.64 m/s
Since the Earth revolves once a day….
Bantu’s and Guajiran’s move a lot faster and further
Than Innu or Lapplanders! 18

19. Apparent Wind Deflection to the Right N in N. Hem
Apparent Wind Deflection to the Right N in N.Hem. (rotating reference frame)
Fig 4.9b
The curved paths are relative to fixed points on the ground which revolves.
This is the same right wise rotation for S flowing air in the northern hemisphere
This is the opposite way, leftwards deflection for S flowing air in the Southern hemisphere
While the Earth revolves from AA’ & BB’
The N flowing Air moves from P1  X,
This is really in a straight line viewed from Space 19

20. Coriolis (Centrifugal) Force acts on East or West moving Winds (increasing w/Latitude)
Fig 4.10
This Coriolis effect increases towards higher latitude due to decreasing rotational velocity!
It is at its maximum at the poles and zero at the equator.
This is like the NW Trade Winds in the Northern Hemisphere or the opposite,
The SE Trade Winds in the Southern Hemisphere
A Vector with 2 components in a plane defined by the spin axis and the location on the Earth’s surface
1 Component is vertical, 1 horizontal-tangent away
In N Hem. E moving wind deflects Right to South 20

21. A More Realistic Model for Surface Winds: Pressure Differences, Buoyancy & Coriolis Effects
Fig 4.11
Big Seasonal Changes
Tropic of Cancer 23.5°N
~1 Season
Tropic of Capricorn 23.5°S
Winds are names by where they blow from rather than where they blow to.
This works for Sailors and Meteorologists as they really need to pay attention to where the weather is coming from.
In detail the divergence zones are weak and wind speed and direction vary considerably on a day to day basis.
Big Seasonal Changes
The same divergence & convergence zones are shown
Coriolis force effects are shown
Permanent Peri-equatorial Trades & Winter Polar Easteries 21

22. High Pressure Systems tend to be Localized
Descending limbs of Hadley-Ferrel Cells in Mid latitudes tends to be fixed
Trade Winds blow from the Equator-ward side of these Sub-Tropical Highs
Temporary passing fronts of High or Low pressure form near the edge of the Polar Front affecting these
~1000 km wide Low Pressure systems form from T° gradients and convective winds in upper troposphere
Inwards directed wind deflects to right in Northern hemisphere (Cyclonic Flow)
Outwards directed flow from Highs creates Anticyclones

23. Tropical Cyclones: Hurricanes & Monsoons
Box Fig 4.1
Centripetal acceleration is experienced by objects rotating at constant tangential speed.
The acceleration is inwards along the radius vector of rotation at ω2 r.
This and the pressure gradient and the coriolis force all interact to determine cyclone wind speed and rotational velocity.
The Circle is an Isobar = line of constant pressure
High Pressure winds deflect to the right
Hurricane flow is set by P gradient & Centripetal Acceleration*
Cyclonic storm rotate counterclockwise in North hemisphere
Cyclonic storms from at 26-27°C & > 5° Latitude from the Equator 23

24. Causes of Tropical Cyclones
Box Fig 4.1
Low Vertical Wind Shear or the storms tear apart as they build
Maximal humidity in lower Troposphere, builds latent heating
Steep vertical thermal gradient, promotes upwards buoyant convection
Initial atmospheric disturbance from ordinary Trade wind flow: old frontal boundaries, easterly waves (off Africa or S. Pacific), usually late summer & fall when ITCZ is furthest from equator
Centripetal acceleration is experienced by objects rotating at constant tangential speed.
The acceleration is inwards along the radius vector of rotation at ω2 r.
This and the pressure gradient and the coriolis force all interact to determine cyclone wind speed and rotational velocity. 24

25. Extratropical Cyclones
Box Fig 4.1
From outside the tropics > 23.5° N or S latitude
Flow of Warm air from Equator hits cold air from High Latitudes
These air masses do not mix well so
Warmer less dense humid air rises above a cold front
Lots of Mid-latitude rain or snow
Lots of daily weather variations due to transient fronts
While polar easterlies are stable all winter, in summer this flow breaks down and the storms can migrate to the Arctic. 25

26. Flow of Troposphere
Fig 4.7
Surface Flow is dominated by latitudinal belts  Upper Level Flow is Dominantly Polewards! 26

27. Upper Level Tropospheric Flow
Fig 4.12a
The troposphere is warmer and thicker in the tropics
&
Colder and thinner at the Poles 27

28. Tropospheric Pressure Surfaces
Fig 4.12b
Tropics more expanded & < vertical pressure gradient
Poles are more compressed w/ > vertical pressure gradients

29. Mid-latitude Upper Level Jet Streams
 Flow 
Fig 4.12c
At any elevation there is Hi P towards the Equator
Flow naturally moves from High to Low Pressure
These control the paths of Low Pressure Storms 29

30. Geostrophic Wind
Fig 4.13
There are also curved Geostrophic currents from storm set up across broad shallow continental shelves.
Pressure Gradient decreases upwards (less mass)
Coriolis Force decreases downwards, net Geostrophic Right/Left flow
Centrifugal & Centripetal Forces contribute around Lows/Highs
(Similar curved flow occurs across mid latitude continental shelves) 30

31. Friction acts near surface at High Pressure
Fig 4.20
Fig 4.13
There are also curved Geostrophic currents from storm set up across broad shallow continental shelves.
Slows and deflects wind < 90° from coriolis
Causes winds to spiral in cyclonic storms 31

32. Height of the 300 mb Geopotential Surface in January (Winter N. Hem.)
Fig 4.14
As per the previous 3 figures, this show the Polar Low
& Equatorial High 32

33. Seasonal Variation in Insolation
Fig 4.15
Perhelion
Aphelion
Obliquity (tilt) affects vertical incidence & heating
More than Eccentricity (elliptical orbit)
At Spring-Fall equinoxes Sun is Overhead 33

34. The Analemma & Equation of Time
The maximum noon shadow And Elevation of the Sun trace out the Figure of 8 or Analemma over the year.
More heat at top and less at bottom

35. Seasonal Migration of Atmospheric Circulation Patterns
The circulation is weaker on the Summer hemisphere because of less thermal gradient
Fig 4.16
The ITCZ shifts to the summer hemisphere side of the Equator and the weaker circulation cells shift Polewards
Discreet Subtropical Highs mark descending Hadley Cells 35

36. Diurnal Wind Changes on Arid Coasts Strong Onshore breeze by day Weak Offshore breeze by night
Ships sail in by day and out by night 36

37. Coastlands heat by day creating Low Pressure
Fig 4.17a
Water has 3-4X the heat capacity of dry land. 1cal/g°C
Counterintuitively, this makes the land heat 3-4 times faster than the sea!
Land, especially dark or forested land heats quickly but transfers this heat up by evaporation and convection. This sets up small thermal lows, ideal for birds along the coast.
Oceans with lower albedo heat better at the same latitude. They are also more transparent than rock or dirt so they absorb heat below the surface too, but thy also transfer this heat both ways by convection in the top of the sea and convection of overlying air. Especially large flat layers like shallow bays have high Renyolds’ numbers favouring turbulent mixing downwards. This and the larger thermal mass of the ocean makes for very small temperature changes.
Great for sailboarding!
Coastlands heat by day creating Low Pressure
This “sets-up” Onshore Adiabat winds
As denser High Pressure Cool Air flows in to replace 37

38. Land cools faster than sea, less water & thermal mass
Fig 4.17b
As the weak daytime lows on shore collapse by rapid cooling, the air falls bringing high pressure down especially along arid coastlines.
The Ocean cools relatively little so it now gets to play the low as weak breezes flow out to sea.
Land cools faster than sea, less water & thermal mass
Cool high pressure air falls on land & flows to the Bay 38

39. Continentality: Land Heats & Cools Faster than the Ocean: Winter in North
Fig 4.18a
Greenland & Siberia hit -48°C
While Australia, Madagascar & Brazil pass +24°C
The Thermal Equator shifts to about 10°South
This deflection of the isotherms at sea makes the Northern Continents colder and the Southern continents warmer.
This is because in the North the cold of the seas is felt preferentially further south (arctic fronts), weather from the Gulf of Alaska.
By contrast the tropic equatorial air bends further south across the southern lands warming them and giving them summer.
The interior of Antarctica warms to a balmy -30°C!
January
Isotherms deflect Southwards in Northern Hemisphere
& in the Southern Hemisphere too! 39

40. Continentality: Land Heats & Cools Faster than Ocean: Summer up North
Greenland & Siberia hit a “balmy” +12°C
While Australia, Johannesburg & Brazil dip to a “frigid” +12°C
Much smaller climate variation in the southern hemisphere, zonal air flow over southern oceans.
The Thermal Equator shifts to about 10°North
This deflection of the isotherms at sea makes the Northern Continents warmer and the Southern continents colder.
This is because in the North the warmth of the tropic seas is felt further north inland. Mild summer southerly breezes.
By contrast the cold southern seas from the Antarctic convergence zone lend cold air on land. cooling the southern lands and giving them winter.
The interior of Antarctica chills like a step mother’s breath to -66°C!
Polar and Continental is seemingly a real recipe for an ice age no matter what the sun and earth are doing.
Fig 4.18b
July
Isotherms deflect Northwards in Northern Hemisphere
& in the Southern Hemisphere too! 40

41. Annual Temperature Difference Between Summer and Winter
Fig 4.18c
Bumpy 
Flat 
The Tropics and Southern Oceans Experience little ΔT While the Southern Continents get a little more Northern Continents & Oceans Get more Δ T 41

42. Average Sea Level Pressure January
Fig 4.19a
Pressure in mbar, 1 atm = bar
2 Belts of Highs +/-30° from Equator & ITCZ
Lows at 60-70°South 42

43. Average Sea Level Pressure July
Fig 4.19b
Northern Belts of Highs +40° from Equator & ITCZ
Southern Belts of Highs -25° from Equator & ITCZ
Lows still at 60-70°South & Cape Stiff Blows! 43

44. Wind Field @ 00Z Aug 1, 1999 Radar Satellite Data
ITCZ ~ 10°N of equator
Where NE & SW trade winds converge
Left curves to south & right to north
Subtropical highs as spirals
Fig 4.20
Which way does the wind blow at the equator?
So which way should you sail around the world? 44

45. Reversing Monsoon Flow
Summer High over Tibetan Plateau but Winter Low 45

46. Fig 4.21a 46

47. Fig 4.21b 47

48. Fig 4.22 48

49. Fig 4.23 49

50. Fig 4.24 50

51. Fig 4.24 51

52. Fig 4.24b 52

53. Fig 4.25 53

54. Fig 4.26 54

55. Fig 4.26a 55

56. Fig 4.26b 56

57. Fig 4.27 57

58. 58

59. 59

60. 60

61. 61

62. 62