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°?

SOLAR AND EARTH RADIATION 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) More energy TEMPERATURE Long waves (cooler temperatures) Less energy

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

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 7

SOLAR RADIATION (short wave radiation, SWR) INCOMING LWR As solar radiation passes through the atmosphere, is affected by absoption and reflection Absorption: Molecules and particles in the atmosphere intercept 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 radiation A surface with low albedo (black pavement) absorbs most of incoming solar radiation 8

Albedo: reflectivity of the surface to the solar radiation ESTIMATION OF ALBEDO Albedo: reflectivity of the surface to the solar radiation

LONG WAVE RADIATION (LWR) INCOMING 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 10

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

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. R = INPUT – OUTPUT R = ( SWR + LWR) – ( SWR + LWR) INCOMING LWR

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)