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

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

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

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

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

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

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

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

Intensity of Insolation

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

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

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

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

Intensity of 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

Insolation and Surface Temperatures

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

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

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

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

Minimums and Maximums of Temperature

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)

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

Minimums and Maximums of Temperature

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

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

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

Examples of Climate Change 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 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

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

Causes of Heat Budget Shifts Changes in Earth’s Axis

Causes of Heat Budget Shifts Changes in Earth’s Axis

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

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

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

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

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

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