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Variation of Insolation. Insolation can vary by changes in its intensity and duration . Variation in Intensity and Angle of Insolation. When insolation strikes the Earth at 90° (perpendicular to the Earth surface), it has maximum intensity . - PowerPoint PPT Presentation
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Variation in Intensity and Angle of Insolation
Intensity of Insolation = The rate at which solar energy is received by a given area
per unit of time.
Insolation is measured in joules/m/s.
90°
When insolation strikes the Earth at 90°
(perpendicular to the Earth surface), it has maximum intensity.
There are several factors that can affect
the intensity of insolation receives by a certain area on Earth’s
surface.
Factors that Affect the Intensity of Insolation
Earth’s Shape
Earth is a sphere. Due to its shape, only one area of the planet can receive maximum intensity of insolation (Sun’s rays = 90°).
All other areas of Earth’s surface would receive less direct insolation.
Sun’s Rays 90°
Factors that Affect the Intensity of Insolation
Earth’s Atmosphere When the Sun is directly overhead, the intensity of insolation is greatest.
The Sun’s radiation passes through a smaller area of the
atmosphere.
When the Sun is on the horizon (dusk/dawn), the intensity of
insolation is smallest.
The Sun’s radiation passes through a greater area of the atmosphere.
The radiation has a stronger chance of being reflected, absorbed or scattered in the atmosphere.
Factors that Affect the Intensity of Insolation
Latitude During the Summer Solstice
(June 21st), the maximum intensity of insolation
(90°) strikes the Tropic of
Cancer – 23 ½ ° N
90°
Factors that Affect the Intensity of Insolation
Latitude During the Winter Solstice
(December 21st), the maximum intensity of insolation
(90°) strikes the Tropic of
Capricorn– 23 ½ ° S
90°
Factors that Affect the Intensity of Insolation
LatitudeDuring the Fall
and Spring Equinox (Sept. 23rd and March
21st ), the maximum intensity of insolation
(90°) strikes the Equator 0°
90°
Factors that Affect the Intensity of Insolation
Seasonal Change Due to the Earth’s tilted axis (23 ½ °) and the its revolution
around the Sun, the maximum
intensity of insolation will vary between 23 ½ ° N to 23
½ °S throughout the year.
Factors that Affect the Intensity of Insolation
Time of Day
Maximum insolation will occur for an area when
solar noon is reached.
Solar Noon
Factors that Affect the Duration of Insolation
Duration of Insolation = The length of time
insolation is received within a day.
Latitude and Seasonal Change
Factors that Affect the Duration of InsolationLatitude and Seasonal Change During the summer solstice, NY state receives
more direct insolation because the Sun is higher in the sky. Likewise, the apparent path the Sun takes from sunrise to sunset is greater.
Sun rises North of East and sets North of West
Summer Solstice = 15 hrs. of daylightApparent Pathways of of the Sun from NY State
During the winter solstice, NY state receives less direct insolation because the Sun is lower in the sky. Likewise, the apparent path the Sun takes from sunrise to sunset is small.
Sun rises South of East and sets South of West
Winter Solstice = 9 hrs. of daylight
During the equinoxes, NY state receives more insolation when compared to the winter solstice, but less when compared to the summer solstice. Likewise, the apparent path the Sun takes from sunrise to sunset is greater when compared to the winter solstice, but less when compared to the summer solstice.
Sun rises dueEast and sets dueWest
Equinoxes = 12 hrs. of daylight
Relationship of Surface Temperature to Insolation
The temperature of the Earth’s surface at a given location will change throughout the day ….as well as
throughout the year.
A rise in temperature will occur when the intensity and/or duration of insolation received is greater
than the energy lost by the earth’s surface radiation.
Yearly Maximum and Minimum Temperatures
In Westhampton Beach, the maximum intensity and duration of insolation is on June 21st – the Summer Solstice. Yet, the maximum
temperature here is not felt until late July or early August.
Why???
Westhampton Beach, NYJune 2181°F
Westhampton Beach, NYAugust 393°F
It takes time for the change in balance between energy received from the sun (insolation) and energy lost from the Earth (surface radiation) to occur.
After the summer solstice, the Earth continues to heat up due to a general increase in insolation. It isn’t until a month later when the balance between incoming insolation and terrestrial radiation is the same.
The result? An increase in surface temperature!
Yearly Maximum and Minimum Temperatures
The same process occurs for when Westhampton Beach receives its minimum temperatures.
Westhampton Beach, NYDec. 2137°F
Westhampton Beach, NYFebruary 320°F
It takes time for the change in balance between energy received from the sun (insolation) and energy lost from the Earth (surface radiation) to occur.
After the winter solstice, the Earth continues to lose heat due to a general decrease in insolation. It isn’t until a month later when the balance between incoming insolation and terrestrial radiation is the same.
The result? An decrease in surface temperature!
Times of Daily Maximum and Minimum Temperatures
In Westhampton Beach, the maximum intensity of insolation would be at solar noon – when the Sun is highest in the sky. Yet the
maximum temperature of the day would not be at solar noon, but later in the afternoon.
Again, there is a need for a balance to be reached between insolation and terrestrial radiation. It takes time for the Earth’s surface to “heat up” after solar noon and for the surface temperature to reflect this.