ESS 111 Climate & Global Change. Week 1 Weather vs Climate Structure of the Atmosphere Global Wind Belts

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1 ESS 111 Climate & Global Change Week 1 Weather vs Climate Structure of the Atmosphere Global Wind Belts

2 Weather is the state of the atmosphere at a given place and time. For example, right now, the temperature in Huntsville, AL is 90 F with Partly Sunny skies.

3 Climate is the average condition of the atmosphere (such as temperature or precipitation) over a long period of time. For example, the average annual temperature over the past 30 years for Huntsville is 62 F. The average annual precipitation is 54 inches. Climate is the average of weather conditions in a place.

4 Just as the weather differs from day to day, the climate differs from place to place. Seattle, WA Houston, TX Phoenix, AZ Barrow, AK Cool Warm Hot Cold Moist Moist Dry Dry

5 Two important elements of weather and climate are: precipitation and temperature Precipitation includes all forms of moisture falling to the surface of the earth. (Examples: rain, sleet, snow, hail) Temperature is how warm or cool the air is outside. * For this class, mean temperature/precipitation is the same as average temperature/precipitation. Mean=Average

6 Climograph A graph that indicates average temperature and precipitation for an area. These graphs can answer the following types of questions: How much rain is there in a particular location? When is it dry? Is it wet when it s cool? What vegetation can grow there?

7 How to Read a Climograph The numbers on the left show you the amount of precipitation. Make sure you check to see if the precipitation is measured in millimeters or inches. Look at the title to see what location s climate is being described by the graph. The numbers on the right show you the temperature. Make sure you check to see if the temperature is measured in degrees Fahrenheit of Celsius. The letters at the bottom show you the months of the year.

8 In case you re not great at interpreting Celsius temperatures 30 is hot 20 is nice 10 is cold 0 is ice **Remember: This is for Celsius, not Fahrenheit!

9 How to Read a Climograph The bar graph measures the average precipitation for each month. The numbers that measure it are on the left side of the graph. The line graph shows you the average temperature for each month. The numbers that measure it are on the right side of the graph.

10 One factor that effects the temperature of a place is the amount of sunlight it receives. Notice how the temperature line on the climograph is almost level? This location is near the equator. It receives the same amount of sunlight all year which results in an almost straight temperature line. Tropical Wet and Dry Location

11 The second location is further from the equator. The curved temperature line shows that the amount of sunlight this location receives varies with the seasons. Humid Subtropical Location

12 Study the two climographs below. Can you pick out the one that depicts a tropical climate? How do you know? Is it a tropical wet or a tropical wet and dry climate? How do you know? Climate A Climate B

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

14 What makes up the atmosphere?

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

16 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

17 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

18 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)

19 Density & Pressure

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

21 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

22 Standard Atmospheric Pressure mb hpa inches of Hg

23 The Layers of the Atmosphere Thermosphere

24 Troposphere Lowest region of the atmosphere Contains ½ of the Earth s atmosphere density

25 Troposphere

26 Depth of tropopause Between the Troposphere & Stratosphere is the tropopause Height is variable Thermal expansion & contraction

27 How do we determine where the tropopause is located?

28

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

30 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

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

32 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

33 Vertical Structure of the Atmosphere

34 Space shuttle Endeavour straddles mesosphere & stratosphere

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

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

37 Ferrel cell -- southwesterly winds at surface The Three-Cell Model Polar cell -- northeasterly 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

38 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

39 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, cloudfree 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.

40 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.

41 The ITCZ is a band of clouds across the tropics ITCZ

42 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

43 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)

44 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 à forms surface low and upper level high à air converges equatorward at surface, rises, and diverges poleward aloft à descends in the subtropics

45 Average atmospheric air pressure and wind patterns in January

46 Average atmospheric air pressure and wind patterns in July