Announcements Class survey results in just a minute. Turn on your clickers and get ready to use them!

Announcements

Class survey results in just a minute.

Turn on your clickers and get ready to use them!

And the big winner in the survey is…

GLOBAL WARMING!

Class survey results: winners!

Global warming or climate change (47)What will the effects be? Can we prevent or fix it?Is there truth behind it?Isn’t there global cooling??

Hurricanes (33)

Severe weather and tornadoes (26)

Ozone hole and air pollution (20)

Monsoons (17)

Class survey results: some also rans

Wind

Alternative energy

Mid-latitude cyclones and fronts

Winter weather

Optical phenomena

Climatology

Extraterrestrial weather

Weather forecasting

Meteorological instruments

Clouds

Class survey results: Other insightful or humorous ones…

How accurate are the movies and documentaries—like the Day After Tomorrow?

Will we need a calculator for this class?

Are unicorns really responsible for why the sky is blue?

If the atmosphere was completely depleted, would everything burst into flames?

How does chaos theory relate to weather?

Summary of Lecture 4

Defined a new quantity, energy: product of a force over a distance which it is applied.

Temperature is the measure of the average kinetic energy of a given substance, or internal energy. Defined °F, °C, and K scales and their conversions.

Assuming pressure remains constant, an increase in temperature means the volume of air expands and its density decreases

Heat is energy in the process of being transferred. Conduction: heat transfer molecule by moleculeConvection: mass movement of a fluid or gas

Latent heat is energy associated with phase changes from one state of matter to another.

NATS 101Section 4: Lecture 5

Radiation

Clicker Instructions

1. Turn on clicker

2. Make sure you’ve entered in your student ID number

3. Join the class: NATS101s4

4. When a question comes up, enter the answer on your key pad.

5. You will have a certain number of seconds to enter an answer, as indicated on the presentation

6. When you successfully send your answer, you will see a “received” message on the device.

7. Can change your answer as long as time has not run out.

1st Clicker Question: Let’s test it out!

I HAVE MY CLICKER DEVICE, AND I AM ALIVE AND BREATHING!

TRUE OR FALSE

Participation Scoring + Attendance

WARNING: IF YOU DON’T ENTER ANY ANSWER THEN YOU WILL BE RECORDED AS ABSENT, SO ALWAYS ENTER SOMETHING.

SEE SYLLABUS POLICY FOR ADMINSTRATIVE DROP POLICY.

Always get one point for entering an answer, whether right or wrong

An additional point if you get the right answer

2nd Clicker Question: Let’s see what we remember from last time

The SI Units for energy (Joules) are:

A.kg m s-1

B.kg m s-2

C.kg m2 s-2

D.kg m2 s-3

3rd Clicker Question

When water vapor condenses:

A. Energy is released to the surrounding environment

B. Energy is taken from the surrounding environment

C.The energy of the surrounding environment doesn’t change

What causes your hand to feel warm when you place it near the pot?

NOT conduction, because air is a very poor conductor of heat.

NOT convection, because there is no movement of air along the sides of the pot.

Therefore, there must be an mechanism of heat transfer which DOES NOT require the presence of molecules.

Radiation: Third mode of heat transfer

Radiation: Energy propagated by electromagnetic waves, which travel at the speed of light (~3.0 x 108 m s-1) in a vacuum. The electromagnetic waves are caused by acceleration of charges within atoms and molecules.

All matter that has a temperature above absolute zero emits some kind of radiation.

Radiation and photons

Radiation can be thought of as a photon, or discrete packet of electromagnetic radiation. The energy of the photon corresponds to the type of radiation.

Longer wavelengths low energy

Shorter wavelengths high energy

When we think of “radiation” what comes to mind?

Probably something dangerous!

McCoy: “Are you out of your Vulcan mind? No human can withstand the radiation in there!”

Spock: “As you are so fond of noting doctor, I’m not human.”

--Star Trek II, The Wrath of Khan

High energy radiation is hazardous to life because it can affect the DNA in our cells!

Well, Dr. McCoy had a good point!High energy radiation certainly can be dangerous!

GAMM

A RAYS

GAMM

A RAYS

X-RAYS

X-RAYS

UV RAYS

UV RAYS

Much of the technology of our present age has developed because of our understanding of the nature of radiation during the past century!

RADIO WAVES

RADIO WAVES

MICROWAVES

MICROWAVES

VISIBLE LIGHT

VISIBLE LIGHTINFRARED

INFRARED

Note that for electromagnetic waves:

c = fλSpeed of light = frequency X wavelength

c = speed of light

f = frequency (s-1 or Hertz)

λ = wavelength (m)

HIG

H E

NER

GY

THE

“REA

LLY

BA

D”

KIN

D O

F R

AD

IATI

ON

KIND O

F,RADIA

TION

YOU ENCOUTER

EVERY D

AY

Visible Spectrum through a Prism

0.7 µm 0.4 µm

Longer wavelength

Shorterwavelength

Visible part of the spectrum:

0.7 to 0.4 µm

1 µm = 10-6 m

Rainbow: Nature’s Prism

Rainbows occur as a result of sunlight being reflected within raindrops.

Each wavelength of the visible spectrum is reflected at a slightly different angle.

(Wikipedia figure)

Radiation and Human Senses

Nature has equipped us to sense the electromagnetic spectrum through our sense of sight and touch. The bands at which we sense the spectrum, as we’ll see, correspond to dominant type of radiation respectively emitted by the sun and the Earth.

Human eyes detect radiation in the visible part of the spectrum: (0.4 – 0.7 µm).

Typically, this radiation is reflected off objects, not generated by them, unless you’re looking directly at the sun or light bulb—which I strongly advise against!

The Human Eye: Sensor of the Visible Spectrum

Our touch is designed to sense the infrared part of the spectrum (around 5 – 15 µm) and gives us our sense of “hot” and “cold.”

It is thus the infrared radiation emitted from the boiling pot which causes your hand to feel hot.

The Human Skin: Sensor of the Infrared Spectrum

What if we could “see” in infrared?

Hot areas appear in red and orange

Cold areas appear in blue and purple.

Areas in between relatively hot and cold appear green.

This is what a house on a cold winter day might look like…

Who were the first ones to figure out all this radiation business?

Some really smart German physicists way back when…

Not Einstein—but pretty close to it!

Planck Function

The intensity of radiation as it relates to the frequency (or wavelength) and temperature of a body was first described by Max Planck in 1900

1

122

3

kThfec

hfTfI ,

Variables

I(f,T) = Intensity of radiation

f = frequency

T = Temperature

Constants

h = Planck’s constant

k = Boltzmann’s constant

e = natural logarithm

c = speed of light

Max Planck

Wavelength

Rad

iati

on

In

ten

sity

Planck Function Characteristics

Peak radiation intensity is inversely related to the wavelength and temperature.

Figure fromWikipedia

Greater intensity with smaller wavelength, higher temperature

PEAK RADIATION

(λmax)

Wien’s Displacement Law

Gives an expression for the wavelength at which peak radiation emission occurs

TK μm 2897

max

Reflects the characteristics of the Planck curve we just observed:

The wavelength of maximum radiation emission is inversely proportional to an object’s temperature.

Wilhelm Wien

Total Radiant Energy per unit area: Stefan-Boltzmann Law

The total radiant energy per unit area (E) is obtained by integration (or computation of the area under the curve) the Planck function (I) over all wavelengths over a half sphere.

4TE

dfddTfIE

))(sin(cos,

0

2

0

2

0

Solution:

σ = Stefan-Bolzmann constant

σ = 5.67 X 10-8 W m-2 K-4

JosefStefan

Ludwig Boltzmann

Prof. Castro, THAT’S TOO HARD! Pleasegive us another way we can think about it!

Total Radiant Energy per unit area: Stefan-Boltzmann Law

Wavelength

Rad

iatio

n In

tens

ity

AREA

JosefStefan

Ludwig Boltzmann

Main point I want you to remember…

The total radiant energy is proportional to the AREA UNDER the Planck function curve.

More area more radiant energy!

4TE

Total Radiant Energy per unit area: Stefan-Boltzmann Law

Relatively SMALL changes in temperature cause LARGE changes in the total radiant energy

Double temperature 16 (or 24) X more energy!

Danke und Auf Wiedersehen to those smart German physicists!

Sehr gut!

Now we want to understand just how this all applies to the atmosphere

Plain English, please…

NOTE: More shaded area underneath the curve 1. Shorter the wavelength of maximum intensity (λmax) 2. Greater the total radiant energy

PEAK RADIATION

(λmax)

Solar and Terrestrial Radiation

The Planck curves based on the emission temperatures of the Sun and Earth define the range of solar and terrestrial radiation.

By application of Wein’s law, we can obtain λmax. This is shown in the textbook.

SOLARλmax = 0.5 µm

TERRESTRIALλmax = 10 µm

How much more radiant energy per unit area does the sun emit compared to the Earth?

Answer: About 160,000 times more!

How can we use the concepts we’ve discussed so far to determine that answer?

Total radiant energy per unit area: Sun vs. Earth

4SunSun TE

438 108510675 K .)K m W .( 4-2- SunE

-2m W . 710416 SunE

Sun: T = 5800 K

428 1088210675 K .)K m W .( 4-2- EarthE

-2m W 390EarthE

00016010641 5 ,. Earth

Sun

E

E

4EarthEarth TE

Earth: T = 288 K

Keep in mind that we’re talking about the total radiant energy

PER UNIT AREA.

Accounting for the area of the Earth and the Sun, the Sun emits almost 2 billion times the amount

of energy as the Earth!

Not all stars are created equal in the universe!

OUR SUN IS HERE

Source: Faulkes Telescope Educational Guidehttp://www.le.ac.uk/ph/faulkes/web/stars/r_st_evolution.html

Summary of Three Modes of Heat Transfer

CONDUCTION CONVECTION RADIATION

Molecule to molecule within a

substance

Mass movement of a fluid or gas

Electromagnetic waves

Summary of Lecture 5

The three modes of heat transfer are conduction, convection, and radiation. Radiation is energy propagated by electromagnetic waves and is emitted by all objects so long as they have a temperature.

The type of radiation an object emits is dependent on its temperature. The smaller the wavelength of radiation, the greater the energy and the higher the temperature. The entire range of radiation types is given by the EM spectrum.

The total radiant energy emitted by an object is described by the Stefan-Boltzmann law.

The wavelength of maximum radiation emission is described by Wien’s law.

Solar radiation, or shortwave radiation, is that which comes from the sun and is most intense in the visible part of the spectrum.

Terrestrial radiation, or longwave radiation, is that which comes from the Earth and is most intense in the infrared part of the spectrum.

Reading Assignment and Review Questions

Ahrens, Chapter 2, pp. 40-51 (8th ed.)

pp. 40-52 (9th ed.)

Chapter 2 Questions

Questions for Review: 4c,7,8,9,10

Questions for Thought: 6

Problems and Exercises: 2,3