Solar Energy to Earth and the Seasons

Finish Numerical Modeling

Electromagnetic Spectrum  

Radiation Laws

Greenhouse Effect

Seasonality

Solar Elevation at Noon

For Wednesday: Read Ch. 4 (pp. 101-116)

2015 Peru Summer Study Abroad: Andean Societies and Environments

July 6 to July 26, 2015GHY 1011: Global Climate Change (4 hrs)

GHY 3140: Andean Mountain Geography (3 hrs) This 20-day intensive program introduces students to Andean Mountain Geography and Climate and Tropical Glaciers through direct field experience and research activities, readings, discussions, and meetings with guest speakers. Field excursions to Machu Picchu and other locations in the Sacred Valley and an 8-day trek in the Cordillera Vilcanota (with strenuous ascents to over 17,000 ft) will provide an outstanding setting for the study of Andean human-environment interactions and the impacts of climate variability and change on tropical glaciers, ecosystems, and human populations.

Program Leaders: Dr. Baker Perry, Mrs. Patience Perry, and Dr. Anton Seimon

Interested? Contact Dr. Perry (perrylb@appstate.edu) to apply or for more information.

Numerical Weather Prediction

We will keep a close eye on the numerical forecast models, including the Global Forecast System (GFS) model run by the National Centers for Environmental Prediction (NCEP):• http://mag.ncep.noaa.gov/• Specifically, we will look at the 850 mb temperature

(equivalent to ~4750 ft asl or the top of Rich Mountain), mean sea level pressure, and quantitative precipitation forecast (850temp_mslp_precip).

© AMS 4

Modeling Earth’s Climate System

Short-Term Climate Forecasting• NCEP’s Climate Prediction Center• 30-day (monthly), 90-day (seasonal), and multi-seasonal

climate outlooks prepared• Outlooks issued two weeks to 12.5 months in advance for

the coterminous U.S., Hawaii, and other Pacific islands

Climate Prediction Center

http://www.cpc.ncep.noaa.gov/products/forecasts/

© AMS 6

Modeling Earth’s Climate System

Long-Term Climate Forecasting• Global Climate Model (GCM): simulates Earth’s climate

system Numerical models Boundary conditions can be changed to determine how

Earth adjusts to new conditions

The Electromagnetic Spectrum

Figure 2.6

Wavelength and Frequency

Figure 2.5

The relationship between the wavelength, , and frequency, , of electromagnetic radiation is based on the following formula, where c is the speed of light:

The relationship between the wavelength, , and frequency, , of electromagnetic radiation is based on the following formula, where c is the speed of light:

Wave Model of Electromagnetic EnergyWave Model of Electromagnetic Energy

vc

Note that frequency, (nu), is inversely proportional to wavelength, (lambda).The longer the wavelength, the lower the frequency, and vice-versa.

Note that frequency, (nu), is inversely proportional to wavelength, (lambda).The longer the wavelength, the lower the frequency, and vice-versa.

The total emitted radiation (Ml) from a blackbody is proportional to the fourth power of its absolute temperature. This is known as the Stefan-Boltzmann law and is expressed as:

where s is the Stefan-Boltzmann constant, 5.6697 x 10 -8 W m-2 K -4. Thus, the amount of energy emitted by an object such as the Sun or the Earth is a function of its temperature.

The total emitted radiation (Ml) from a blackbody is proportional to the fourth power of its absolute temperature. This is known as the Stefan-Boltzmann law and is expressed as:

where s is the Stefan-Boltzmann constant, 5.6697 x 10 -8 W m-2 K -4. Thus, the amount of energy emitted by an object such as the Sun or the Earth is a function of its temperature.

Stefan Boltzmann LawStefan Boltzmann Law

4TM

Wien’s Displacement LawWien’s Displacement Law

In addition to computing the total amount of energy exiting a theoretical blackbody such as the Sun, we can determine its dominant wavelength (lmax) based on Wien's displacement law:

where k is a constant equaling 2898 mm K, and T is the absolute temperature in kelvin. Therefore, as the Sun approximates a 6000 K blackbody, its dominant wavelength (lmax ) is 0.48 mm:

In addition to computing the total amount of energy exiting a theoretical blackbody such as the Sun, we can determine its dominant wavelength (lmax) based on Wien's displacement law:

where k is a constant equaling 2898 mm K, and T is the absolute temperature in kelvin. Therefore, as the Sun approximates a 6000 K blackbody, its dominant wavelength (lmax ) is 0.48 mm:

T

kmax

K

Kmm

6000

2898483.0

Solar vs. Terrestrial RadiationSolar Radiation (Insolation): Short-wave, high intensity, mostly in the visible portion of the EM spectrum.

Source is the Sun.

Terrestrial Radiation: Long-wave, lower intensity.

Source is the Earth and Atmosphere (or Earth-Atmosphere System)

Solar and Terrestrial Energy

Figure 2.7

Group ExerciseWhat is the Greenhouse Effect and why is it important?

© AMS 15

Outgoing Infrared Radiation

Greenhouse Effect Heating of Earth’s surface and lower

atmosphere caused by strong absorption and emission of infrared radiation (IR) by certain atmospheric gases• known as greenhouse gases

Similarity in radiational properties between atmospheric gases and the glass or plastic glazing of a greenhouse is the origin of the term greenhouse effect

© AMS 16

Outgoing Infrared Radiation

Greenhouse Effect Responsible for considerable warming of

Earth’s surface and lower atmosphere Earth would be too cold without it to support

most forms of plant and animal life

© AMS 17

Outgoing Infrared Radiation

Greenhouse Gases Water Vapor is the principal greenhouse gas

• Clear-sky contribution of 60% Other contributing gases:

• carbon dioxide (26%)• ozone (8%)• methane plus nitrous oxide (6%)

© AMS 18

Outgoing Infrared Radiation

Greenhouse Gases Atmospheric window: range of

wavelengths over which little or no radiation is absorbed• Visible atmospheric window extends

from about 0.3 to 0.7 micrometers• Infrared atmospheric window from

about 8 to 13 micrometers

© AMS 19

Outgoing Infrared Radiation

Greenhouse Gases Water vapor strongly absorbs outgoing IR and

emits IR back towards Earth’s surface• Does not instigate warming or cooling trends in

climate• Role in climate change is to amplify rather than to

trigger temperature trends Clouds affect climate in two ways:

• Warm Earth’s surface by absorbing and emitting IR• Cool Earth’s surface by reflecting solar radiation

Figure 2.9

SeasonalityWhy is seasonality important?

SeasonalityTwo important seasonal changes

Sun’s altitude – angle above horizon or Solar Elevation at Noon (SEN)

Day length

Reasons for Seasons Revolution

Earth revolves around the Sun

Voyage takes one year

Earth’s speed is 107,280 kmph (66,660 mph)

RotationEarth rotates on its axis once every 24 hours

Rotational velocity at equator is 1674 kmph (1041 mph)

Revolution and Rotation

Figure 2.13

Annual March of the SeasonsWinter solstice – December 21 or 22

Subsolar point Tropic of Capricorn

Spring equinox – March 20 or 21Subsolar point Equator

Summer solstice – June 20 or 21Subsolar point Tropic of Cancer

Fall equinox – September 22 or 23Subsolar point Equator

Annual March of the Seasons

Figure 2.15

11:30 P.M. in the Antarctic

Figure 2.16

Insolation at Top of Atmosphere

Figure 2.10

Solar Elevation at Noon

Figure 2.18

Solar Elevation at Noon (SEN)

SEN is the angle of the noon sun above the horizon SEN = 90˚ - ArcDistance ArcDistance = number of degrees of latitude between location

of interest and sun’s noontime vertical rays If the latitude of location of interest and sun are in opposite

hemispheres, add to get ArcDistance If they are in the same hemisphere, subtract from the larger of

the two values

SEN Example

What is the SEN on June 21 for Boone (36 N)

SEN = 90 – ArcDistance Where are the sun’s noontime

vertical rays? ArcDistance = 36 – 23.5 ArcDistance = 12.5 SEN = 90 – 12.5 SEN = 77.5˚

Analemma