1. ESS 111 – Climate & Global Change
Lecture 1
Structure of the Atmosphere
Global Wind Belts

2. Where is the atmosphere?
Everywhere!
Completely surrounds Earth
Held to Earth by gravitational attraction

3. What makes up the atmosphere?

4. Water Vapor Location of this in the atmosphere is highly variable
Significantly influences climate & weather
How?

5. Atmospheric Thickness
No defined top to the atmosphere
The atmosphere is very shallow—and is less than 2% of the Earth’s thickness
Over 90% of
atmosphere in
the lowest 16km
& is where nearly
all weather occurs

6. Temperature Basics
Temperature – measure of average kinetic energy (motion) of individual molecules in matter
Three temperature scales (units): Kelvin (K), Celsius (C), Fahrenheit (F)
All scales are relative
degrees F = 9⁄5 degrees C + 32
degrees K = degrees C

7. Temperature Layers Due to Solar winds, Cosmic rays
Due to ozone absorption of sunlight
Temperature decreases with height in the Troposphere
Due to surface heating (Longwave, Latent heat, Sensible heat)

8. Density & Pressure

9. Density & Pressure
Lower layers of atmosphere are compressed by air above it
This compression increases pressure & density of the lower layers of the atmosphere

10. What is atmospheric pressure?
Weight of the overlying air
Taller the column of air above an object, the greater the air pressure exerted on that object

11. Standard Atmospheric Pressuremb
hPa
29.92 inches of Hg

12. The Layers of the Atmosphere
Thermosphere

13. Troposphere Lowest region of the atmosphere
Contains ½ of the Earth’s atmosphere
density
density

14. Troposphere

15. Depth of tropopause
Between the Troposphere & Stratosphere is the tropopause
Height is variable – Thermal expansion & contraction

16. How do we determine where the tropopause is located?

18. Stratosphere Temperature increases with an increase in altitude
What is this called?

19. Why is there a temperature inversion in the stratosphere?
Temp Inversion – temperature warms with height instead of cooling w/ height
Ozone
Gas that absorbs ultraviolet (UV) solar energy
Increases the temperature of the air surrounds ozone

20. Mesosphere Temperature decreases with an increase in altitude
Where meteors burn up while entering the Earth’s atmosphere

21. Thermosphere
First exposed to the Sun's radiation and so is first heated by the Sun
Air is so thin that a small increase in energy can cause a large increase in temperature

22. Vertical Structure of the Atmosphere

23. Space shuttle Endeavour straddles mesosphere & stratosphere

24. Planetary Winds
Well-defined pressure patterns exist across the Earth that induce the global wind patterns on the planet

25. Idealized Single-Cell Convection Model for a Planet
Features of the
circulation pattern:
horse latitude
trade winds
doldrums
prevailing westerlies
polar easterlies
polar front

26. The Three-Cell Model Polar cell -- northeasterly winds at surface
Ferrel cell -- southwesterly winds at surface
Subtropical high -- Air subsides (dry climate)
Hadley cell -- tropical convection cell
Intertropical convergence zone (ITCZ) -- surface low pressure with clouds and rain

27. Observed Distribution of Pressure and Winds
(a) An imaginary uniform Earth with idealized zonal (continuous) pressure belts
(b) Actual planetary winds belts on Earth taking into account continents and ocean currents

28. Idealized Pressure Belts
Equatorial Low- warm air rising creates cell of low pressure.
Intertropical Convergence Zone (ITCZ)- referred to as the
convergence zone because this region is where the trade winds
converge. Ascending air leads to cloud formation which makes this
region clearly visible on satellite imagery.
Subtropical Highs- These zones are caused primarily by Coriolis
deflection which restricts upper-level winds from moving poleward.
Subsiding air and divergent winds at the surface cause warm, cloud-
free weather (many large desert areas are located along this
latitudinal belt). Subtropical Highs tend to persist throughout the
year, with the center of the high migrating, and are regarded as
semi-permanent pressure systems.

29. Idealized Pressure Belts (cont.)
Subpolar Low – located around 50 to 60  latitude. Associated
with the polar front. The belt of low pressure is formed by the
interaction (convergence) of the polar easterlies and the westerlies
Polar Highs – located over the poles! The process which produces
the polar highs is different than the process which produces the
subtropical highs. Surface cooling is the principle reason the
polar high.

30. The ITCZ is a band of clouds across the tropics

31. The three-celled model vs. reality:
Hadley cells are close approximations of real world equatorial winds
Ferrel and polar cells do not approximate the real world winds very well at all
Model is unrepresentative of westerly flow aloft
Continents and topographic irregularities cause significant variations in real world wind patterns compared to the model

32. Northern hemisphere semi-permanent cells
Semi-Permanent Pressure Cells are large areas of higher or lower atmospheric pressure than the surface average
They may be thermally induced (rising warm air or subsiding cold air) or they may be caused dynamically by converging or diverging wind patterns)
They fluctuate seasonally
Northern hemisphere semi-permanent cells
The Aleutian, Icelandic, and Tibetan lows
Siberian, Hawaiian, and Bermuda-Azores highs
ITCZ (low)

33. Vertical structure and mechanisms
Polar Cell (thermal):
Driven by heating at 50 degree latitude and cooling at the poles
Ferrel Cell (dynamical): Dynamical response to Hadley and polar cells
Hadley Cell (thermal): Heating in tropics  forms surface low and upper level high  air converges equatorward at surface, rises, and diverges poleward aloft  descends in the subtropics

34. Average atmospheric air pressure and wind patterns in January

35. Average atmospheric air pressure and wind patterns in July