Topic 5A INSOLATION

WORDS TO KNOW Radiation Insolation Intensity Altitude Zenith Latitude Tropic of Cancer Tropic of Capricorn Solstice Equinox Duration

RADIATION from the SUN is the principal energy source for Earth’s surface processes  INSOLATION: SOLAR RADIATION reaching Earth’s surface

INTENSITY OF INSOLATION INTENSITY OF INSOLATION: The RATE at which SOLAR RADIATION strikes an area of Earth’s surface MAXIMUM Intensity of Insolation is VISIBLE LIGHT

The Sun’s ALTITUDE, also called the ANGLE of Insolation, determines the INTENSITY of Insolation at any location   The GREATER the ANGLE of Insolation, the GREATER the INTENSITY MAXIMUM Intensity of Insolation occurs when the SUN is in the ZENITH (ALTITUDE = 90°)

Factors affecting the ANGLE of Insolation: 1)1) Earth’s SPHERICAL Shape: The SUN can be in the ZENITH at only ONE POINT on Earth’s surface at any given time 2) LATITUDE: The SUN passes through the ZENITH at NOON at only ONE LATITUDE on any given date

3) SEASON: MAXIMUM ANGLE of Insolation occurs on the first day of SUMMER at any location, MINIMUM on the first day of WINTER 4) TIME of DAY: ANGLE of Insolation is GREATEST at SOLAR NOON, ZERO during the NIGHT Factors affecting the ANGLE of Insolation:

Maximum ANGLE of Insolation  1) PLACE: Greatest Possible ANGLE is 90° Only between the two TROPICS TROPIC of CANCER on the SUMMER SOLSTICE (JUNE) TROPIC of CAPRICORN on the WINTER SOLSTICE (DEC) The EQUATOR on the EQUINOXES (MAR and SEPT)

Maximum ANGLE of Insolation  2) YEAR: Greatest on JUNE 21 for the NORTHERN Hemisphere 3) DAY: At LOCAL SOLAR NOON

WORDS TO KNOW Radiation Insolation Intensity Altitude Zenith Latitude Tropic of Cancer Tropic of Capricorn Solstice Equinox Duration

DURATION OF INSOLATION: Number of hours of DAYLIGHT  GREATER Duration means more ENERGY is received from the SUN But ANGLE of Insolation is much more important than DURATION DURATION OF INSOLATION

In the NORTHERN Hemisphere: Maximum DURATION of Insolation  1) On the SUMMER SOLSTICE (JUNE 21) 2) Maximum possible At the POLES (24 Hours) [ On or above the Arctic or Antarctic Circles (66½° North or South ) ]

Summer Solstice 12 hours 15½ hours 24 hours

In the NORTHERN Hemisphere: Minimum DURATION of Insolation  1) On the WINTER SOLSTICE (DECEMBER 21) 2) Minimum possible At the POLES (0 Hours) [ On or above the Arctic or Antarctic Circles (66½° North or South ) ]

Winter Solstice 12 hours 8½ hours 0 hours

DIFFERENCE in DURATION of Insolation  1) Maximum possible At the POLES (since DURATION changes from 0 to 24 Hours during the year) 2) Minimum At the EQUATOR(0 Hours DIFFERENCE, since there are TWELVE Hours of Daylight all YEAR)

So in the NORTHERN Hemisphere, ANGLE, INTENSITY, and DURATION of Insolation are all GREATEST on JUNE 21, and Maximum ENERGY is received from the SUN on that date

WORDS TO KNOW Radiative Balance Reradiation Surplus Deficit Equilibrium Solar Noon Ice Age

RADIATIVE BALANCE Earth’s surface TEMPERATURES depend upon the BALANCE between Energy received as INSOLATION and Energy lost by RERADIATION from Earth’s SURFACE, so  Highest and Lowest TEMPERATURES do not come at the same time as Maximum and Minimum INSOLATION

If INSOLATION is greater than RERADIATION, an Energy SURPLUS exists, and TEMPERATURES RISE If INSOLATION is less than RERADIATION, an Energy DEFICIT exists, and TEMPERATURES FALL

MAXIMUM and MINIMUM TEMPERATURES occur at shifts between SURPLUS and DEFICIT, when INSOLATION and RERADIATION are EQUAL  RADIATIVE BALANCE (EQUILIBRIUM): Energy gained EQUALS Energy lost

Feb 1 Aug 1 ANNUAL TEMPERATURE CYCLE

During the YEAR  Highest and Lowest TEMPERATURES occur about SIX WEEKS after Maximum and Minimum INSOLATION, at the time when RADIATIVE BALANCE is reached

Insolation Ground Radiation Solar Noon Surplus Deficit Maximum Temperature (Radiative Balance) Minimum Temperature (Radiative Balance) DAILY TEMPERATURE CYCLE

Solar Noon Insolation Ground Radiation Surplus Deficit Minimum Maximum Just after SunriseMidafternoon DAILY TEMPERATURE CYCLE

During the DAY  Maximum INSOLATION is at SOLAR NOON, but Highest TEMPERATURES occur at MID–AFTERNOON, when RADIATIVE BALANCE is reached Lowest TEMPERATURES are just after SUNRISE, again when RADIATIVE BALANCE is reached

Average TEMPERATURES remain CONSTANT when Earth is in RADIATIVE BALANCE over a long period of time When Earth is not in RADIATIVE BALANCE over a long time period, if INSOLATION is less than RERADIATION, Average TEMPERATURES drop,

and an ICE AGE results

WORDS TO KNOW Atmosphere Absorbed Reflected Aerosols Ozone Stratosphere Concentration

INSOLATION and the ATMOSPHERE SOLAR RADIATION reaching the ATMOSPHERE is affected in one of three ways (Different WAVELENGTHS are affected differently) 

1) ABSORBED by the ATMOSPHERE: About 1/5 of the total, including X–RAYS, absorbed in the upper ATMOSPHERE, and most ULTRAVIOLET, absorbed by a layer of OZONE (a form of OXYGEN) in the STRATOSPHERE

OO OXYGEN OO OZONE O

OO O O O O O O OOOOOO OO OO

OZONE absorbs ULTRAVIOLET in the upper Stratosphere Gamma Rays and X-Rays (short ) are absorbed as they energize molecules in the Thermosphere Heat is radiated from Earth’s surface into the Troposphere Lowest Temperature in the Atmosphere

2) REFLECTED (and SCATTERED) back into Space: About 1/3 of the total, 1/4 by CLOUDS, the rest from the SURFACE, or from AEROSOLS (Tiny SOLID particles such as dust and pollutants) As AEROSOLS increase, INSOLATION reaching the surface DECREASES, and TEMPERATURES DECREASE

3) ABSORBED by Earth’s SURFACE: Almost 1/2 of the total, which is then RERADIATED by the SURFACE as INFRARED (HEAT) RADIATION

19% absorbed by the atmosphere 25% scattered and reflected by clouds 47% absorbed by Earth’s surface and reradiated as Infrared 5% reflected by Earth’s surface 4% scattered by aerosols and gas molecules

WORDS TO KNOW Greenhouse Effect Evaporation Potential Heat Energy Inlet Outlet Continental United States

INFRARED heat RERADIATED from Earth’s SURFACE is ABSORBED by two key GASES in the Lower ATMOSPHERE: CARBON DIOXIDE and WATER VAPOR  These GASES let LIGHT pass through, while ABSORBING and holding RERADIATED HEAT near the SURFACE, a process called the GREENHOUSE EFFECT

Earth’s Nighttime TEMPERATURES remain relatively WARM because of the GREENHOUSE EFFECT, making LIFE possible on Earth

ULTRAVIOLET is absorbed in the upper Stratosphere by OZONE Gamma Rays and X-Rays (short ) are absorbed as they energize molecules in the Thermosphere LIGHT is absorbed at Earth’s surface and Reradiated as INFRARED Heat

AEROSOLS scatter Insolation back into Space, DECREASING Earth’s Surface Temperatures INFRARED HEAT is held near Earth’s Surface by CARBON DIOXIDE, METHANE, and WATER VAPOR INCREASING Earth’s Surface Temperatures GREENHOUSE EFFECT

HEAT is transferred from Earth’s SURFACE to the ATMOSPHERE by: 1) RERADIATION of INSOLATION as INFRARED heat 2) EVAPORATION of WATER  The resulting WATER VAPOR transports POTENTIAL HEAT ENERGY over long distances The HEAT is eventually released by CONDENSATION