GEOGRAPHY 204

PHYSICAL GEOGRAPHY

Spring, 1999

 

LECTURE NOTES

Go back to Lecture 5
LECTURE 6 -- EARTH'S ENERGY BALANCE, TEMPERATURE, LAPSE RATES

Electromagnetic Spectrum (see p. 35)

Direct Radiation from Sun --

Solar Constant -- 1.95 calories per sq cm per minute at top of atmos

INCOMING SOLAR RADIATION -- INSOLATION

Some is

· Scattered

· Absorbed

· Reflected from Surface

Albedo -- percent of insolation Reflected from different surfaces

Earth's Albedo is 30 -- that is, 30% of insolation is reflected

 

SOLAR RADIATION IN THE ATMOSPHERE

Energy in the Universe is constantly being transformed from one form to another -- (heat energy produced as part of every transformation -- entropy)

E.G. from solar energy to heat energy or

kinetic energy (motion) or

chemical energy (photosynthesis) or

potential energy (energy of position)

TEMPERATURE -- Average Kinetic energy of molecules

HEAT -- Total kinetic energy of molecules

Thermometer measures Average Kinetic energy of a body

Energy can be transferred from one body to another by three ways:

Conduction, Convection, Radiation

Conduction -- energy transfer between two bodies in contact -- molecular energy transfer, high to low

E.G. touch a hot pan -- burn your hand

Convection -- the transfer of energy through movement of matter, generally from high energy (temperature) to low

E.G. boiling oatmeal, bubbles up from bottom

Conduction and convection involve contact of materials

Radiation -- (not just solar) energy travel between bodies through space, doesn't involve contact of materials

E.G. radiant energy heater -- red-hot -- doesn't heat the air between heater and your legs to same extent

Your text says "only important means of energy transfer" (p. 24) I disagree

Need conduction and convection to transfer energy from tropics to poles, (circulation)

other types of energy transfer also essential to life

Nature of Radiation -- Discussed last time -- see lecture 5

EARTH'S ENERGY BALANCE

Incoming Solar Radiation (Shortwave) needs to balance Outgoing Earth Radiation (Longwave) in order to have an equilibrium in global temperature

Review Overheads -- Incoming Shortwave; Outgoing Longwave

Incoming Shortwave
Out of 100 units, (these numbers are approximate)

approx. 44 units pass through the atmosphere

and of those 44, 26 reach the surface as direct radiation

of the 26, 4 units are reflected from the surface to space

the remainder of the 44 (18) are absorbed by gases in the atmosphere

38 units pass through clouds,

and of those 16 diffuse to the surface

the remainder (22) are absorbed by clouds

18 units are scattered,

and of those 12 are scattered to the surface and 6 are scattered to space

This results in a total of 30 units of SW reflected or scattered back to space

20 units absorbed by clouds and atmosphere

and 50 units received at the surface, for a total of 100 units of SW

Outgoing Longwave

The 70 units of SW that are absorbed by the atmosphere and earth are transformed into Longwave (LW), which is then emitted by the earth as heat (infrared)

6 units of LW are emitted directly to space

109 units are emitted from the surface to the atmosphere,

some of this LW is reradiated by the atmosphere back to the surface (~95 units)

some of this energy absorbed by the atmosphere, plus some of the SW absorbed and changed to LW, is radiated out to space (38 units)

some of the surface heat (7 units) is conducted and convected as Sensible Heat

some is stored as Latent Heat (23 units) during evaporation or melting of water

some of the LW is absorbed by clouds (gases and water droplets), and of that 26 units is emitted by clouds to space

Summary:

50 units of SW received at the surface, 20 units of SW absorbed by the atmosphere. These 70 units are transformed into LW.

Some of the LW is lost to space by radiation directly from the surface to space, a large portion heats the lower atmosphere, some is absorbed and reradiated by clouds and atmosphere, and some goes to heating the surface or evaporating water. A net of 20 units is absorbed and reradiated in the atmosphere, and a net of 70 units is longwave returned to space. Add that 70 units of LW to the 30 units of SW (earth's albedo), and you have an equal amount of LW leaving as SW entering earth's system.

 

Temperature, how it varies from place to place

See maps in text -- p 93. Mean January and July temperatures worldwide, in degrees C.

What are reasons for this distribution?

 

Lapse Rates, Adiabatic Lapse Rates

TERMS:

Define Adiabatic

The process by which a parcel of air changes temperature due to expansion or compression,

without any exchange of energy with the air outside the parcel

As an air parcel rises, it cools at a specific rate, independent of the surrounding air, depending on the amount of water vapor in the air parcel

The change in temperature of a dry parcel of air with change in volume is fixed

At about 10oC per 1000 m, or 5.5oF per 1000 feet

This works in both directions:

A rising parcel of dry air cools at a rate of 10oC per 1000 meters.

That same parcel of air will warm at the same rate when it descends

In general, there is some moisture in every air parcel

If the initial temperature of the air parcel is WARMER than the temperature at which condensation occurs, that is, when the Relative Humidity is below 100%

Then the air parcel will cool at the DRY ADIABATIC LAPSE RATE

When it cools to the temperature at which the Relative Humidity reaches 100%, then

Condensation will commence, and LATENT HEAT WILL BE RELEASED

When Latent Heat is released, the RATE OF COOLING IS SLOWED as the parcel continues to rise

THIS SLOWER RATE OF COOLING IS THE SATURATED OR WET ADIABATIC LAPSE RATE

The WET Adiabatic Lapse Rate varies with the Temperature of the Air Parcel, since

Temperature Controls the Rate of Condensation or Vaporization

The WET Adiabatic Lapse Rate Varies between about

4oC per 1000 m for VERY WARM Saturated Air, to

9oC per 1000 m for VERY COLD Saturated Air (almost dry, since very cold air holds much less moisture)

The Standard WET Adiabatic Lapse Rate is 6oC per 1000 m

Go To Lecture 7

 

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