DAILY INSOLATION OVER THE YEAR AT VARIOUS LATITUDES (NORTH

HEMISPHERE)

SOLAR DECLINATION (δ): the latitude at which the Sun is directly overhead at solar noon (estimated from the analemma)

-the left axis tells you your declination

-as you follow the analemma, you’ll notice that long dashes indicate the beginning/end of a month

-small dashes indicate a labeled date (e.g. Dec 15)

-once you find the date of interest, look to the left axis for δ

• What would happen if the Earth had no tilt?

• What would happen in Newark if the Earth was tilted 40°?

ELECTROMAGNETIC RADIATION:

• It’s a kind of energy• All objects emit electromagnetic radiation•It’s a collection of waves traveling away from the surface of the objects

Short waves (warmer temperatures)

Long waves (cooler temperatures)

TEMPERATURE

Less energy

More energy

SOLAR AND EARTH RADIATION

In general, the higher the temperature of an object the greater the amount of total energy emitted by that object (Stefan-Boltzman Law)

Earth Temp: 6000 K (5727 C)

Sun Temp: 288 K (15 C)

σ = 5.67 X 10-8 Wm-2K-4

4TE

Solar radiation wavelength range 0.2 – 2.0 micrometers

Shortwave radiation

Tsun= 5798 K ≈ 6000 K

Terrestrial radiation wavelength range 4 – 25 micrometers

Longwave radiation

Tearth = 288 K ≈ 255 K

SOLAR CONSTANT

The amount of solar radiation striking the top of earth’s atmosphere, which is constant (theoretically):

1372 W/m2

SOLAR RADIATION (short wave radiation, SWR)

•As solar radiation passes through the atmosphere, is affected by absoption and reflection

•Absorption: Molecules and particles in the atmosphereintercept and absorb radiation (oxygen and ozone)

•Reflection: Solar radiation passing through the Atmosphere can be reflected

Albedo: An important property of a surface. It measures how much solar energy will be reflected:A surface with high albedo (snow, ice) reflects most of the solar radiationA surface with low albedo (black pavement) absorbs most of incoming solar radiation

INCOMING LWR

Albedo: reflectivity of the surface to the solar radiation

ESTIMATION OF ALBEDO

LONG WAVE RADIATION (LWR)

•The solar energy is absorbed by the atmosphere, land or ocean and raises the temperature

•The atmosphere, land and ocean also emit energy in the form of long wave radiation

INCOMING LWR

Incoming LWR: Counterradiation

The Earth’s surface emits energy to the atmosphere that is absorbed by the atmosphere and radiated back down to Earth’s surface

R = INPUT – OUTPUTR = ( SWR + LWR) – ( SWR + LWR)

INCOMING LWR

NET RADIATION (RADIATION BUDGET)

It is the difference between total upward and downward radiation fluxes and is a measure of the energy available at the ground surface.

WHY IS NET RADIATION IMPORTANT?

Net radiation is the energy available at the earth’s surface to drive climate and life processes (evaporation, air temperature, photosynthesis)