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 molecule Convection: mass movement of a fluid or gas Latent heat is energy associated with phase changes from one state of matter to another.

NATS 101 Section 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.

1 st 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

2 nd 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 m 2 s -2 D.kg m 2 s -3

3 rd 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 10 8 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! GAMMA RAYS X-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 MICROWAVES VISIBLE LIGHT INFRARED

Note that for electromagnetic waves: c = fλ Speed of light = frequency X wavelength c = speed of light f = frequency (s -1 or Hertz) λ = wavelength (m) HIGH ENERGY THE “REALLY BAD” KIND OF RADIATION KIND OF,RADIATION YOU ENCOUTER EVERY DAY

Visible Spectrum through a Prism 0.7 µm0.4 µm Longer wavelength Shorter wavelength Visible part of the spectrum: 0.7 to 0.4 µm 1 µm = 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 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 Radiation Intensity Planck Function Characteristics Peak radiation intensity is inversely related to the wavelength and temperature. Figure from Wikipedia Greater intensity with smaller wavelength, higher temperature PEAK RADIATION ( λ max )

Wien’s Displacement Law Gives an expression for the wavelength at which peak radiation emission occurs 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. Solution: σ = Stefan-Bolzmann constant σ = 5.67 X W m -2 K -4 Josef Stefan Ludwig Boltzmann Prof. Castro, THAT’S TOO HARD! Please give us another way we can think about it!

Total Radiant Energy per unit area: Stefan-Boltzmann Law Wavelength Radiation Intensity AREA Josef Stefan 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!

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 2 4 ) 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 (λ max ) 2. Greater the total radiant energy PEAK RADIATION ( λ max )

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 λ max. This is shown in the textbook. SOLAR λ max = 0.5 µm TERRESTRIAL λ max = 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 Sun: T = 5800 K 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 Guide

Summary of Three Modes of Heat Transfer CONDUCTIONCONVECTION 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 (8 th ed.) pp (9 th ed.) Chapter 2 Questions Questions for Review: 4c,7,8,9,10 Questions for Thought: 6 Problems and Exercises: 2,3