LESSON 3!

Albedo,Air and Water Currents

Today:

• Hand in Albedo Investigations• In the News (10 mins)• Discussion on Albedo• Review Radiation• Intro to Conduction and Convection

Next Class: Convection Lab!

Albedo

• “Reflectiveness” of a surface• Measured on a scale from 0 – 1,

Where α = 0 has no albedo, and α = 1 is pure reflection (high albedo)• Surfaces with a high albedo reflect more incoming solar radiation and

therefore absorb less thermal energy• Snow, glaciers, and ice have high albedos

AT HOME ALBEDO INVESTIGATION! REVIEW FINDINGS + DISCUSS/EXPLAIN

Buildings, etc

Ashphalt, RockSnow , Ice, Clouds

Shiny vs Matte

Forest / Vegetation

Oceans

What is a Negative Feedback Loop?

What is a Positive Feedback Loop?

Changes in sea ice in the last few decades ←

How does this figure →relate to feedback loops?

Question #1

Which of the following statements about albedo and its effect on global climate is true?A. As the snow and polar icecaps grow, a decrease in albedo will result

and more solar energy will be reflected from the ice.B. As the snow and the polar icecaps melt, a decrease in albedo will

result from the oceans reflecting more solar energy.C. As snow and polar icecaps melt, a decrease in albedo will result in

the oceans absorbing more solar energy.D. As the snow and polar icecaps grow, an increase in albedo will result

in the ice absorbing more radiation.E. As the snow and polar icecaps melt, there will be no effect on

albedo.

Energy Transfer Within the Climate System

The atmosphere and hydrosphere are the two essential parts of the climate system. Why?

• They are both able to absorb and store thermal energy, so they act as heat sinks.

• Through (Conduction) and Convection, this energy is transferred from regions that receive a lot of solar radiation to regions that receive less solar radiation.

• In Earth’s energy transfer system, heat is always being transferred from hotter objects to colder objects

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Recall Earth’s Energy Budget

3 Mechanisms of Heat Transfer in the Atmosphere

1. Radiation: the transfer of heat energy by electromagnetic waves. Think of feeling the sun on your face on a cold winter’s day (warm!). Sunlight warms your face without warming the air around it. We then emit infrared radiation which can be absorbed by the atmosphere.

2. Conduction: Conduction is the transfer of heat from one molecule to another within a substance. Air is an extremely poor conductor of heat. Therefore, conduction is only important in the atmosphere within the first several millimeters closest to the surface.

So how does the air transfer energy from one region to another?

3. Convection! Convection is the transfer of heat through the movement of a fluid, such as water or air stimulated by uneven heating of the earth. Temperature gradients create convection currents.

Radiation•Radiation is a method of heat transfer that does not require any medium.

•It can take place in a vacuum.

•In radiation, energy is transmitted in the form of waves.

Conduction!

Conduction• Conduction is the process by which heat is transmitted

through a medium from one particle to another.• It is due to temperature differences.• Heat is conducted from a high temperature region to a

lower temperature region.

Think of holding a match close to a candleDoes the match get hot enough to burst into flame?

Is air good conductor or insulator?

No! This shows that air is a very poor conductor – it is a very good insulator.

All gases are poor conductors.

Conduction & Climate• Air is a really poor conductor of heat

• Conduction happens close to the Earth’s surface (land and water)(Think of the hot pavement on a summer evening – doesn’t heat the air)

• Important in climate because: Hot air rises ↑ (helps fuel convection currents)

Because air is such a poor energy conductor, large vertical temperature gradients can exist near the ground, particularly on clear and windless days. Onsuch days, the land surface may experience a great deal of heating, as direct solar radiation is absorbed and converted to infrared radiation (heat energy). However, a series of thermometers mounted at different heights above the ground would reveal that air temperature falls off rapidly with height due to thepoor conductivity of air.(www.ucar.edu/learn/1_1_2_6t.htm)

Convection!

Convection

Hold your hand over and under the flame of a match.

What do you notice?

Why?

Hot air expands, becomes less dense and then rises.

Heat is convected upwards ↑

Convection in Liquids

ConvectionThe circulation of thermal energy in fluids (gases & liquids)

Cold air/water sinks = more dense

Warm air/water rises = less dense Creating a current

Eg. Water: Pot of water being heated

Eg. Air: Sea breeze

Eg. Think of a sea breeze:Sea breezes occur during the day time:

Sun-heated land heats the air, which then rises. Land heats faster than water (poor conductor) thus creating a temperature gradient

= Warm air rises, cold air from water takes its place = sea breeze

What do you think happens

during a land breeze?

(at night)

Convection Currents

• When the suns rays reaches the equator with greatest intensity, the air at the equator heats up and becomes less dense.

• The colder air moves the dense air above it, forcing the worm air up in the atmosphere, this creates a area of low pressure below it.

• When the warm air is high in the atmosphere, it spreads out towards the poles and cools down. And the cooler air sinks back to the earths surface, creating an area of high pressure

• These cold and warm air creates a circular current called a convection current.

Heat Transfer as it Affects Climate

Air Currents

Ocean Currents

Ocean Currents

What drives ocean currents?• Driven by DIFFERENCES IN DENSITY, caused by

salinity and temperature the more saline the denser the colder the denser

Changes in density based on Temperature & Salinity = Thermohaline Circulation

• Get animations for ocean currents and for air currents

• The great lakes are also known for the strong moderating effect they have on the climate of the areas that surrounded these lakes. These huge water masses keep summer and winter temperature moderate, they also provide a lot of moisture.

Regional Climate

Homework!

• Read & Answer “Check Your Learning” questions:

Text 8.3, 8.4, 8.6, 8.8

• Develop some enthusiasm for our lab next class on Convection Currents!

• The ocean and atmosphere are connected. • They work together to move heat and fresh water across the

globe. • Wind-driven and ocean-current circulations move warm

water toward the poles and colder water toward the equator. • The ocean can store much more heat than the land surfaces

on the Earth. The majority of the thermal energy at the Earth’s surface is stored in the ocean.

• Thus, the absorption and movement of energy on the Earth is related to the ocean-atmosphere system.

How do ocean currents effect the heat transfer of the atmosphere?