1. TOPIC 6: INSOLATION AND THE SEASONS

2. Solar Radiation and Insolation
Insolation – Incoming solar radiation
Components of Insolation (by EM type)
Infrared – 48%
Visible Light – 44%
Ultraviolet – 7%

3. 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

4. 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

5. 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

6. 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

7. 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

8. Factors Affecting Absorption and Reflection of Insolation
Characteristics of Earth’s Surface
More energy is absorbed if Earth’s surface is dark and rough

9. Factors Affecting Absorption and Reflection 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

10. 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.

11. 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

12. 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

13. Variation of Insolation
Insolation varies 2 ways
Intensity
Duration

14. 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

15. Angle of Incidence
Intensity of insolation is the greatest when the sun’s rays hit the surface of the earth at 90o

16. 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

17. Angle of Incidence

18. Intensity of Insolation
Angle of Incidence
As the angle of incidence increases, the intensity of insolation increases
Angle of Incidence
Intensity of Insolation

19. Intensity of Insolation
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

22. Angle of Incidence
As the latitude increases, the angle of incidence decreases
Latitude
Angle of Incidence

23. Intensity of Insolation
Angle of Incidence
As the latitude increases, the intensity of insolation decreases
Latitude
Intensity of Insolation

24. Intensity of Insolation

25. Angle of Incidence
Only one location on earth receives the sun’s energy at 90o at a given time
The location varies throughout the year
Date
Location
March 21
June 21
September 23
December 21

26. Intensity of Insolation
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

27. Intensity of Insolation
June 21
Dec 21
Dec 21
Summer Solstice in NYS
Winter Solstice in NYS
Winter Solstice in NYS

28. Intensity of Insolation
The angle of incidence varies for a given location during the day
Angle is the highest a solar noon
Most intense insolation

29. Intensity of Insolation

30. 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

31. Duration of Insolation
Sun’s path in summer in NYS
June 21
Sun’s path in winter in NYS
Dec 21

32. 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

33. Duration of Insolation
Duration of insolation is 12 hours all over the earth on the equinoxes
March 21, September 23

34. Duration of Insolation

35. 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

36. Insolation and Surface Temperatures

37. Insolation and Surface Temperatures
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

38. Minimums and Maximums of Temperature
The highest temperatures of the year for an area tend to occur later than the time of maximum insolation

39. Minimums and Maximums of Temperature
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

40. Minimums and Maximums of Temperature
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

41. Minimums and Maximums of Temperature

42. Minimums and Maximums of Temperature
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)

43. Minimums and Maximums of Temperature
When would you expect the lowest temperatures for the day to occur? Explain.

44. Minimums and Maximums of Temperature

45. Heat Budget and Climate Change

46. 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

47. 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

48. 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

49. Examples of Climate Change
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

50. Examples of Climate Change
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

51. Examples of Climate Change
Global Warming
The average temperature of the earth is rising

52. 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

53. Causes of Heat Budget Shifts
Changes 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

54. Causes of Heat Budget Shifts
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

55. Causes of Heat Budget Shifts
Changes in Earth’s Axis

56. Causes of Heat Budget Shifts
Changes in Earth’s Axis

57. Causes of Heat Budget Shifts
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

58. 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

59. Causes of Heat Budget Shifts
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

60. Causes of Heat Budget Shifts
Human Causes
Deforestation – Trees removed from areas
More insolation reaching Earth’s surface
Less transpiration
Less water in atmosphere = less precipitation

61. Causes of Heat Budget Shifts
Human Causes
Urbanization – Areas changed from rural areas to cities
More paved surfaces = more absorption of insolation
Increase in greenhouse gases
Carbon dioxide

62. 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

63. 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

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

65. Seasons