INSOLATION AND THE SEASONS

Topic 6 inReview Book

Energy from the sun drives:

global wind patterns ocean currents the water cycle

Without solar energy:

Earth would be a frozen wasteland

All the water and gases in the atmosphere would only be found in the solid phase.

Earth and the moon would be completely dark.

The rate at which energy is radiated is called the

intensity of radiation In general, the higher the

temperature, the shorter the wavelength at which maximum intensity occurs.

The sun’s maximum intensity of radiation occurs in the

visible wavelength

INSOLATION

is the portion of the sun’s electromagnetic energy that is received by the earth.

Insolation stands for:IncomingSolarRadiation

Intensity of Insolation

is the relative strength of the sun’s radiation that reaches a specific area of Earth in a specific amount of time

Effects of the atmosphere

The atmosphere is mostly transparent to visible light.

Consequently this is the wavelength most received by the surface of the Earth.

Most of the ultraviolet radiation from the sun is absorbed in the ozone layer

This layer is located 20 to 50 km above Earth’s surface

Concentrations vary seasonally with the smallest concentrations occurring in the spring.

The ozone layer is being depleted (decreased) due to the chemical reaction between ozone (O3) molecules and chlorofluorocarbons (CFCs)

This reaction creates “ozone holes” that tend to be found near the poles

The depletion of the ozone layer results in greater amounts of ultraviolet radiation reaching the surface of the earth.

UV radiation is very harmful – causing skin cancer in humans and tissue mutations in plants and animals

Water vapor, carbon dioxide (CO2) and methane (CH4)

absorb incoming and radiated infrared radiation.

Increases in these gases result in an increase in atmospheric temperature – “global warming”

These gases act like the glass walls of a greenhouse…

Visible wavelengths are absorbed by the earth’s surface and reradiated as infrared wavelengths

which are absorbed by the water vapor, CO2 and CH4 in the atmosphere

preventing the natural cooling of the earth’s surface

CO2

Ozonelayer

Particulates in the atmosphere (called aerosols)such as dust, bacteria, salts, volcanic ash, air pollutants, pollen etc.can reflect or scatter insolationdecreasing temperatures

FACTORS THAT INFLUENCE INTENSITY OF INSOLATION

The shape of the earth:The curvature of the earth

causes the angle of insolation to vary

Latitude:influences angle of insolation.As latitude increasesangle of insolation decreaseswhich decreases the intensity

of insolation

Seasons:determine which areas receive

the most direct rays of insolation and for what duration

In the northern hemisphere, summer months have the greatest intensity and duration of insolation

Time of day:determines the angle of

insolation.Solar noon has the highest

angle of insolation, therefore, the highest intensity

TEMPERATURE AND INSOLATION

As intensity of insolation increasesthe amount of energy received by the area increasesincreasing the amount of energy absorbedincreasing the temperature

High altitude sun:

High intensity of insolation More energy is absorbed Resulting in high temperatures Highest altitudes occur at solar

noon and during the summer

Low altitude sun:

Low intensity of insolation Low temperatures (ineffective

heating) Occurs in the morning, evening

and during the winter months

TEMPERATURE LAGS

Air temperature depends on the relationship between the amount of insolation received and the amount radiated by the earth

The cooler the surface, the less energy is radiated

High temperatures lag behind times of high intensity due to the fact that the surface must be warmed by the sun to radiate the energy and heat the atmosphere.

Highest intensity:solar noon and June

Highest temperatures:after noon and July/August

Radiative Balance

occurs when the amount of heat energy being lost through radiation is equal to the amount of heat energy gained by insolation

Temperatures increase when the amount of heat energy gained by insolation is greater than the amount lost through radiation

The earth takes in more heat energy than it gives off

Temperatures decrease when the amount of heat energy gained by insolation is less than the amount lost through radiation

The earth gives off more than it takes in.

ATMOSPHERIC TEMPERATURE

The radiation of infrared energy from the surface of the earth heats the atmosphere.

When the surface of the earth is warmer than the air above it, the heat energy is transferred to the air and circulated through the atmosphere by convection currents.

HEATING OF EARTH’S SURFACES

Land surfaces aredark and rough and have a low specific heat

This means that they readily absorb and radiate heat energy and change temperature rapidly

Water surfaces are transparent and reflective and

have a high specific heat This means that they reflect

more energy than they absorb and heat up and cool down slowly

LAND SURFACES HEAT UP AND COOL DOWN FASTER THAN WATER SURFACES!!!

CLIMATE CHANGE

Long-term changes in the radiative balance of the earth can result in climate changes.

ICE AGES ANDINTERGLACIAL WARM PERIODS

Ice ages occur when the earth radiates more energy than it receives.

When this occurs, glaciers advance through mid-latitudes

The last ice age began ~ 1.6 million years ago and lasted until 10 thousand years ago.

We are now believed to be in an interglacial warming period – the time between ice ages when the earth receives more energy than it radiates

EL NIN ̃O AND LA NIÑA

El Nino is an unusual warm period caused by the change in the ocean currents of the eastern Pacific Ocean…these currents are normally cool currents and when replaced by warm currents result in warmer temperatures

La Nina is a similar event, but the cool current is made exceptionally cold resulting in much lower temperatures.

GLOBAL WARMING AND HEAT WAVES

World wide temperatures have increased from the early 1980s. Scientists are unsure as to whether this is a natural warming trend or if it is an anthropogenic (man-made) problem.

A heat wave is an extended period of exceptionally warm temperatures that can result in health issues such as hyperthermia.

Prevention steps include:limit outdoor exercisedrink plenty of waterstay in shaded areas when outdoorsstay in air conditioned locations

CAUSES OF TEMPERATURE SHIFTS

Changes in the output of the sunTimes of increased sunspot

activity are linked to times of increased temperature due to the increase in electromagnetic energy released by the sun during increased sunspot activity

Changes in Earth’s orbit and tiltOver thousands of years, the

tilt of the earth changes by a few degrees which influences the intensity of insolation at each latitude

Also over thousands of years, the eccentricity of Earth’s orbit changes by a minor amount which would change the distance between the earth and the sun.

VOLCANIC ERUPTIONS

Volcanic eruptions disperse ash, dust and sulfur compounds into the atmosphere.These are distributed over vast

areas through the atmosphere remaining there for extended periods of time

These particles decrease the transparency of the atmosphere decreasing insolation and globally decreasing temperatures

ANTHROPOGENIC CAUSES

Humans have an impact on climate…Deforestation and

desertification cause climates to be hotter and drier

Deforestation is the cutting down of forests.

Forests absorb more insolation – when cut down, more insolation is received by the earth.

Less trees = less transpiration = less moisture in the atmosphere = less precipitation

Desertification is the expansion of desert regions due to the destruction of grasslands.

This can occur due to overgrazing of livestock

Less plants = less transpiration = less precipitation

Deserts heat up faster than grasslands = higher temperatures

URBANIZATION

The development of land reduces plants…

industries, transportation and energy needs produce “greenhouse gases”…

all of which increases temperatures