topic 6: insolatio n and the seasons. solar radiation and insolation insolation – incoming solar...

TOPIC 6:

INSOLATION AND THE SEASONS

Solar Radiation and Insolation

• Insolation – Incoming solar radiation

• Components of Insolation (by EM type)→Infrared – 48% →Visible Light – 44%→Ultraviolet – 7%

Effects of Earth’s Atmosphere on Insolation

• Absorption of EM→UV rays are absorbed by the ozone layer.

However, there is a hole in the ozone which allows UV to hit Earth and can cause cancer.

→Infrared radiation absorbed by carbon dioxide, water vapor and methane These are called greenhouse gasses

Effects of Earth’s Atmosphere on Insolation

• Reflection and Scattering→Conditions that cause HIGH REFLECTION

of insolation Clouds = lots of visible and IR reflected Aerosols – small suspended particles

in the atmosphere (dust, ice, water, ash) –Lots of aerosols cause lots of

scattering of insolation Low transparency of atmosphere

Balance of Energy from Insolation

→ Half of the insolation hitting Earth’s atmosphere will reach Earth’s surface (land or water) Transmitted through atmosphere

→ The Earth will re-radiate energy at longer wavelengths of EM usually in the form of heat (IR) Earth is cooler than the sun

Balance of Energy from Insolation

→The amount of heat absorbed, over time, will EQUAL amount of heat radiated so that Earth’s surface temperature will tend to balance Dynamic equilibrium

Factors Affecting Absorption and Reflection

of Insolation• Angle of Incidence – the angle at

which the sun’s energy hits the surface of the earth→Angle varies with latitude, time of

day and season→The higher the angle of incidence the

more energy is absorbed


of Insolation• Characteristics of Earth’s Surface

→More energy is absorbed if Earth’s surface is dark and rough


of Insolation• Change of State (of water) and

Transpiration→In general, when water is changing

phase solid liquid gas energy is absorbed

→If energy needs to be absorbed to change phase it isn’t available to raise temperature of Earth’s surface

Heating Land and Water• Land heats faster over time than

water because land has a lower specific heat

• Insolation can penetrate deeper into water.

• Heating water is done by convection so water layers mix.

Greenhouse Effect• Works on the idea that re-radiated

energy is at a longer wavelength than incoming insolation→Greenhouse gasses (CO2, H2O, CH4)

allow short wave EM in, but absorb longer wave EM that is re-radiated by Earth

• The Greenhouse Effect keeps Earth’s temperature warm enough to support life

Greenhouse Effect

• Global Warming - an increase in the Earth’s average temperature→Due to an increase in CO2 and methane

which traps re-radiated waves and raises Earth’s surface temperature

→Causes include burning of fossil fuels and deforestation

Variation of Insolation

• Insolation varies 2 ways→Intensity→Duration

Intensity of Insolation

• Intensity of insolation - amount of solar energy received by an area over a certain amount of time→Intensity of insolation received by an

area depends on the angle of incidence

Angle of Incidence

→Intensity of insolation is the greatest when the sun’s rays hit the surface of the earth at 90o

Angle of Incidence

→At angles less than 90o the insolation gets spread out over a larger area The same amount of energy is

spread out over a bigger area, so each part of that area receives less energy

Angle of Incidence

Angle of Incidence

→As the angle of incidence increases, the intensity of insolation increases

Angle of Incidence

Inte

nsity

of

Inso

latio

n


→The sun’s rays are parallel to each other as they approach Earth If the earth was flat, all insolation

would reach earth perpendicular to the surface (90o)

Since the earth is round the angle at which insolation hits the earth’s surface varies

Angle of Incidence

→As the latitude increases, the angle of incidence decreases

Latitude

Ang

le o

f In

cide

nce

Angle of Incidence

→As the latitude increases, the intensity of insolation decreases

Latitude

Inte

nsity

of

Inso

latio

n

Angle of Incidence• Only one location on earth receives

the sun’s energy at 90o at a given time→The location varies throughout the

yearDate Location

March 21

June 21

September 23

December 21


• The angle of incidence varies for a given location throughout the year→Angle is the highest on the day that

the sun is highest in the sky Most intense insolation = summer

solstice= June 21 for New York→Angle is lowest on the day that the

sun is the lowest in the sky Least intense insolation = winter

solstice = Dec. 21 for New York


June 21Summer Solstice in NYS

Dec 21Winter Solstice in NYS

Dec 21Winter Solstice in NYS


• The angle of incidence varies for a given location during the day→Angle is the highest a solar noon

Most intense insolation

Duration of Insolation• Duration of insolation - the length

of time between sunrise and sunset

• Duration of insolation varies for a given location throughout the year→Longest day = longest duration of

insolation June 21 in New York

→Shortest day = shortest duration of insolation December 21 in New York

Duration of Insolation

Sun’s path in summer in NYS

June 21

Sun’s path in winter in NYS

Dec 21

Duration of Insolation• Duration of insolation is usually

different at different locations on Earth→June 21 is the longest day in the

Northern Hemisphere, shortest day in the Southern Hemisphere

Duration of Insolation• Duration of insolation is 12 hours

all over the earth on the equinoxes March 21, September 23

Duration of Insolation

Insolation and Surface Temperatures

• The intensity of insolation and the duration of insolation together determine the surface temperatures for an area→The more intense the insolation, the

more energy an area receives, the higher the temperature

→The longer insolation is received at an area, the more energy absorbed, the higher the temperature


• The Earth heats up when it absorbs more energy than it radiates

• When the energy gained by an area is GREATER than the energy it radiates, its temperatures will rise

• When the energy gained by an area is LESS than the energy it radiates, its temperatures will fall

Minimums and Maximums of Temperature

• The highest temperatures of the year for an area tend to occur later than the time of maximum insolation


Yearly• Highest surface temperature in

NYS: Late July – Early August→Day of maximum duration and

intensity of insolation occurs on June 21

→Why the delay? Earth is still receiving more energy than it is losing Heat surplus


Yearly• Lowest surface temperature in

NYS: Late January – Early February→Day of minimum duration and

intensity of insolation occurs on Dec 21

→Why the delay? Earth is still receiving less energy than it is radiating Heat deficit


Daily• Solar noon is the time when the

sun is the highest in the sky for the day

• Mid-afternoon (~3pm) tends to be the time period for the highest temperatures for the day→Even though the sun is getting lower

in the sky, the earth is still receiving more energy than it is radiating (heat surplus)


• When would you expect the lowest temperatures for the day to occur? Explain.

Heat Budget and Climate Change

Heat budget

• Heat budget - the result of the balance between heat absorbed and heat lost→The temperature of an object

• For Earth - the balance between the energy gained from the sun and lost through radiation from Earth to space→Earth’s average temperature

Climate Change

• If there is a change in the heat budget - or average temperatures of the earth - global climate change can occur

• In the past the climate of the earth has changed dramatically due to changes in the Earth heat budget

Examples of Climate Change

• Ice Ages/Long Warm Periods→Ice Ages – Large glaciers covered large

parts of Earth’s surface during cold periods Most recent ice age - 10,500 years ago

→During cold periods the average sea-level is lower and coastlines are further out than their present location Much of the water is in the glaciers

→During warm periods coastlines flood and sea levels rise


• El Niño/La Niña→El Niño occurs when a shift in wind

patterns across the Pacific push warm waters toward the west coast of South America Causes major changes in weather

patterns all over the world–Can cause droughts, flooding,

tornadoes El Niño events usually occur every 5-10

years


• El Niño/La Niña→La Niña occurs when very cold waters

occur off the coast of South America Also cause changes in global weather

patterns


• Global Warming→The average temperature of the earth is

rising

Causes of Heat Budget Shifts

Solar Energy Changes• Sunspots are dark areas on the sun’s

surface• When there are a lot of sunspots, the

sun emits more electromagnetic energy = more insolation

Causes of Heat Budget ShiftsChanges in Shape of Earth’s Orbit and Tilt• There are changes that occur in the

eccentricity of Earth’s orbit and the tilt of Earth’s axis

May cause cooler summers and warmer winters

Possible cause of ice ages


• Changes in Earth’s Axis→Earth rotates on an axis tilted at 23 1/2

degrees→Since earth is not a perfect sphere, it

“bobbles” like a top North pole not always pointed at the

same place Called precession


• Changes in Earth’s Axis


• Changes in Earth’s Tilt→Earth’s tilt on its axis changes through

time Varies between 22o and 24o

Currently at 23½o

→When the tilt is greater summers are warmer, winters are colder

Causes of Heat Budget Shifts• Volcanic Eruptions

→Volcanic eruptions cause temperature of Earth to cool

→When volcanoes erupt they throw ash that can stay in the atmosphere for months or years Called aerosols = low transparency

→Aerosols reflect insolation back into space and prevent it from reaching the earth’s surface Less energy = cooler temperatures


Human Causes• Desertification

→Over use of land in areas with deserts causes grasslands to turn into desert areas Deserts heat faster than grasslands =

higher temperatures


Human Causes• Deforestation – Trees removed from

areas →More insolation reaching Earth’s surface→Less transpiration

Less water in atmosphere = less precipitation


Human Causes• Urbanization – Areas changed from

rural areas to cities→More paved surfaces = more absorption

of insolation→Increase in greenhouse gases

Carbon dioxide

Seasons

• The mid-latitudes experience seasons→Winter, Spring, Summer, Fall

• Seasons are distinguished by changes in temperature, moisture, weather conditions and vegetation

• Regions near the equator have little seasonal changes

Seasons

Direct Causes of the Seasons• Cyclic variations in:

→Intensity of insolation Angle of Incidence

→Duration of insolation

• Seasons follow the North-South path of the direct rays of the sun

Seasons

Indirect Causes of the Seasons• Tilt of Earth’s Axis• Revolution of Earth Around Sun

Seasons

topic 6: insolatio n and the seasons. solar radiation and insolation insolation – incoming solar...

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