ESS 111 – Climate & Global Change

Week 1 Weather vs Climate

Structure of the Atmosphere Global Wind Belts

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.

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.

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

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

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?

How to Read a Climograph

The letters at the bottom show you the months of the year.

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 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.

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!

How to Read a Climograph

The line graph shows you the

average temperature for

each month. The numbers

that measure it are on the right

side of the graph.

The bar graph measures the average precipitation for each month. The numbers that measure it are on the left side of the graph.

Tropical Wet and Dry Location

• 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.

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

Climate A Climate B

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?

Where is the atmosphere?

 Everywhere!   Completely surrounds Earth   Held to Earth by gravitational attraction

What makes up the atmosphere?

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

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

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 + 273.15

Temperature Layers

Due to surface heating (Longwave, Latent heat, Sensible heat)

Due to ozone absorption of sunlight

Due to Solar winds, Cosmic rays

Temperature decreases with height in the Troposphere

Density & Pressure

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

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

Standard Atmospheric Pressure  1013.25 mb  1013.25 hPa  29.92 inches of Hg

The Layers of the Atmosphere

Thermosphere

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

Troposphere

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

How do we determine where the tropopause is located?

Stratosphere

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

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

Mesosphere

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

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

Vertical Structure of the Atmosphere

Space shuttle Endeavour straddles mesosphere & stratosphere

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

 Idealized Single-Cell Convection Model for a Planet

Features of the circulation pattern:

• horse latitude • trade winds • doldrums • prevailing westerlies • polar easterlies • polar front

The Three-Cell Model

Intertropical convergence zone (ITCZ) -- surface low pressure with clouds and rain

Subtropical high -- Air subsides (dry climate)

Hadley cell -- tropical convection cell

Ferrel cell -- southwesterly winds at surface

Polar cell -- northeasterly winds at surface

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

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.

Idealized Pressure Belts

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.

The ITCZ is a band of clouds across the tropics

ITCZ

  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

 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)

Vertical structure and mechanisms

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

Ferrel Cell (dynamical): Dynamical response to Hadley and polar cells

Polar Cell (thermal): Driven by heating at 50 degree latitude and cooling at the poles

Average atmospheric air pressure and wind patterns in January

Average atmospheric air pressure and wind patterns in July