Tuesday Aug. 21, 2012
click here to download today's notes  in a more printer friendly format

Welcome to ATMO 170A1 - Introduction to Weather and Climate.  I had a hard time deciding on some music for the 1st day of class but finally settled on "Intro" from a group called The XX.   I played a long version in class though you might want to check out the following short version which comes with a nice video.  For the last couple of years I have been filling the few minutes before class with some kind of music, often local talent.  Music won't ordinarily take up any actual class time.  Hopefully you'll like at least some of the selections.  Comments and ideas from students are welcome.

I also like to stick up an occasional picture of the day as often as I can at the start of each day's lecture notes.  Here are some photos from the surface of Mars sent back recently by the rover Curiosity.

Today was the first day of class.  We first briefly discussed the Course Information handout.  Please read through that information carefully on your own and let me know if you have any questions.

A textbook is not required for this class.  If you want to get a more complete picture of the subject than we will have time to do in class, you might want to purchase one of the textbooks that are being used in the other NATS 101 sections.  Or if you'd like to borrow one of the copies of introductory level textbooks that I have in my office, just let me know.  Otherwise you should be able to do perfectly well in the class by reading the online notes and any other suggested online sources. 

A set of photocopied ClassNotes (available in the ASUA Bookstore in the Student Union) is required.  You should try to purchase a copy as soon as you can because we will probably be using the first page in class later on Friday.  If you know someone with photocopied ClassNotes from the Fall 2011 or Spring 2012 class they should work fine this semester also. 

This class does appear, sort of, on D2L.  You'll find a link on D2L to the class homepage.  I will be using D2L mainly just to give you a way of keeping track of your class grade.

Writing is an important part of this class and is described in more detail on the Writing Requirements handout.  Please read through the information on the writing requirements handout and let me know if you have any questions. 

The first half of your writing grade is an experiment report.  You only need to do one of the experiments, so think about which of the experiments listed on the handout you would like to do.  I'll bring a signup sheet to class on Wednesday and will probably bring some materials Experiment #1 materials on Friday.

The so-called One Side of One Page (1S1P) reports make up the second part of your writing grade.  Topics will appear periodically on the class webpage during the semester.  As you write reports you will earn points (the exact number of points will depend on the topic).  Your objective should be to earn 45 1S1P pts, the maximum number allowed.

Your grade in this class will depend on your quiz scores, how much extra credit you earn (from optional take home and in class assignments), your writing grade, and (perhaps) your score on the final exam.  A sample grade report from the S;pring 2012 class is shown below (the numbers are class averages)


The quiz grades are shown in Part 1.  At Point 2 you can see the average student scored 33 out of 40 on the experiment report and earned 34 1S1P pts (45 points are possible).  This resulted in a writing percentage grade of 83.8%.  The average student earned 1.4 extra credit points (3.35 pts were possible). 

Point 4a shows the average of the 4 quizzes and the writing grade with the extra credit points added  in.  If this is 90.0% or above you don't have to take the final.  If that doesn't happen you will have to take the final exam but the average will be recomputed with the lowest quiz score dropped.  That is shown at Point 4b. 

If you do well on the final exam it will count 40% of your overall grade.  If you don't do so well on the final it only counts 20%.  In this example the final exam score (72.1%) was lower than the semester average (80.7%) so the final only counted 20%.  The overall score ended up 79.0.  This would mean the student got a C in the class.  Note that if the student had earned just a little more extra credit and a few more 1S1P pts they would probably have earned a B. 


We did cover a little course material in class today just so you can get an idea of how that will work.   If we were using a book we'd start in Chapter 1 and here's some of what we would be looking at first in this course.

We had enough time today to look at the first question, the composition of the atmosphere.  Here are a few questions to get you thinking about the air around you.

Can you see air?

This is a little more detailed answer to this question than was given in class.  Air is normally clear, transparent, and invisible (that would be true of the air in the classroom).  Sometimes the air looks foggy, hazy or smoggy.  In these cases you are seeing the effects of small water droplets or ice crystals (fog) or small particles of dust or smoke (haze and smog).  The particles themselves may be too small to be seen with the naked eye but are visible because they scatter (redirect) light.  Scattering is a pretty important concept and we will learn more about it in a week or so.

The atmosphere isn't actually clear.  When sunlight shines through the atmosphere the sky appears blue.  This is a little more complicated form of scattering of sunlight by air molecules.  We'll come back to this later as well.

Can you smell air?

I don't think you can smell or taste air (air containing nitrogen, oxygen, water vapor, argon and carbon dioxide) though, as a student pointed out, this might just be because we are so used to it.  Some pollutants do have a smell.  And I suspect our sense is sensitive enough for us to detect certain air pollutants even when their concentration is very small (probably a good thing because many of them are poisonous).  There are also lots of other odors you can sometimes smell (freshly cut grass, hamburgers on an outdoor grill, etc) but I don't consider these normal constituents of the atmosphere.

Someone in the other section of the class mentioned natural gas (methane) used in hot water heaters, some stoves, and furnaces.  Because methane is odorless, a chemical (mercaptan) is added so that you can smell it and know when there is a leak before it builds up a concentration that could cause an explosion. 

Can you feel air


It is harder to answer this question.  We're always in contact with air.  Maybe we've grown so accustomed to it we aren't aware of how it feels.  We can certainly feel whether the air is hot or cold, but that have more to do with energy exchange between us and our surroundings.  And we can feel wind. 

We will see that here in the classroom air pressure is pressing on every square inch of our bodies with 12 or 13 pounds of force.  If that were to change suddenly I'm pretty sure we'd feel it and it would probably really hurt.

What are the 5 most abundant gases in air?

Let's start with the most abundant gas in the atmosphere.  A lot of people seemed to know this is nitrogen.  I poured some liquid nitrogen into a styrofoam cup.  Here's a photo I took back in my office.


You can see the liquid, it's clear, it looks like water.  We'll use liquid nitrogen in several class demonstration this semester.  Once the liquid nitrogen evaporates and turns into a gas it is invisible.

Nitrogen was discovered in 1772 by Daniel Rutherford (a Scottish botanist).  Atmospheric nitrogen is relatively unreactive and is sometimes used to replace air in packaged foods to preserve freshness. 

Oxygen is the second most abundant gas in the atmosphere.  Oxygen is the most abundant element (by mass) in the earth's crust, in ocean water, and in the human body.  





from: http://www.webelements.com/oxygen/
The webelements site credits Prof. James Marshall's Walking Tour of the Elements.
 from: http://en.wikipedia.org/wiki/Oxygen
Wikipedia credits Dr. Warwick Hillier of Australia National University


A couple of photographs of liquid oxygen are shown above.  It has a (very faint) blue color (I was pretty disappointed when I saw the pictures for the first time because I had imagined the liquid oxygen might be a deep vivid blue).

 When heated (such as in an automobile engine) the oxygen and nitrogen in air react to form compounds such as nitric oxide (NO), nitrogen dioxide (NO2), and nitrous oxide (N2O).  Together as a group these are called oxides of nitrogen; the first two are air pollutants, the last is a greenhouse gas. 

Here are the 5 most abundant gases in the earth's atmosphere.



Water vapor and argon are the 3rd and 4th most abundant gases in the atmosphere.  A 2% water vapor concentration is listed above but it can vary from near 0% to as high as 3% or 4%.  Water vapor is, in many locations, the 3rd most abundant gas in air.  In Tucson most of the year, the air is dry enough that argon is in 3rd position and water vapor is 4th.

Water vapor, a gas, is invisible.  Clouds are visible because they are made up of small drops of liquid water or ice crystals.  We can see clouds even though the individual water droplets are too small to be seen because they scatter light.  Water is the only compound that exists naturally in solid, liquid, and gaseous phases in the atmosphere.

Argon is an unreactive noble gas (helium, neon, krypton, xenon, and radon are also inert gases). 

Here's a little more explanation (from Wikipedia) of why noble gases are so unreactive.  Don't worry about all these additional details.  The noble gases have full valence electron shells.  Valence electrons are the outermost electrons of an atom and are normally the only electrons that participate in chemical bonding.   Atoms with full valence electron shells are extremely stable and therefore do not tend to form chemical bonds and have little tendency to gain or lose electrons.




Noble gases are often used used in neon signs; argon produces a blue color.  The colors produced by Argon (Ar), Helium (He), Kryton (Kr), Neon (Ne) and Xenon (Xe), which are also noble gases, are shown above (source of the images).  This picture wasn't shown in class.

Water plays an important role in the formation of clouds, storms, and weather.  Meteorologists are very interested in knowing and keeping track of how much water vapor is in the air at a particular place and time.  One of the variables they use is the dew point temperature.  The value of the dew point gives you an idea of how much water vapor is actually in the air.  The higher the dew point value, the more water vapor the higher the water vapor concentration.


The chart below gives a rough equivalence between dew point temperature and percentage concentration of water vapor in the air.


Air temperature will always be equal to or warmer than the dew point temperature.  Experiencing 80o dew points would be very unpleasant (and possibly life threatening because your body might not be able to cool itself).  Click here to see current dew point temperatures across the U.S.  And here's an interesting link concerning unusually high, even record setting dew point temperatures. 

Don't worry about remembering all these numbers.  Just remember that the higher the dew point temperature the more water vapor is in the air and vice versa. 

Here's a chart showing actual dew point temperatures across the US.


This is about as far as we got in class on Tuesday.  Here's a little more information to finish off this topic.  We'll go over this again at the start of class on Thursday.

In addition to giving you an idea of how much water vapor is in the air, the dew point has another job.

We can use the styrofoam cup of liquid nitrogen to see this in action.


First of all you can see liquid nitrogen (it's a clear not purple as shown in the figure).  Once the liquid evaporates and turns into nitrogen gas it is invisible.

Water vapor (water in gaseous form) is also invisible.  When moisture in the air comes into contact with the cold liquid nitrogen in the cup, the water vapor condenses and forms a visible cloud of very small water droplets (liquid water) and ice crystals (solid water).

The white cloud comes from moisture in the air.  It's no different from the clouds you see forming in the sky outdoors.  The cloud is not made of nitrogen gas.  It isn't made up of water vapor (a gas) either.  The cloud only becomes visible when small droplets of liquid water or small ice crystals (solid water) form.

Here's a summary:

Liquid nitrogen evaporates and turns into invisible nitrogen gas.  Nitrogen is the most abundant gas in the atmosphere.  Invisible water vapor (a gas) in the air is cooled to its dew point temperature and condenses to form a visible cloud composed of water droplets and ice crystals.



Here's the chart I showed in class just in case you're interested.  It is way more detailed than you'll need to worry about in this class.

Composition of dry atmosphere, by volume
ppmv: parts per million by volume (note: volume fraction is equal to mole fraction for ideal gas only, see volume (thermodynamics))
Gas Volume
Nitrogen (N2) 780,840 ppmv (78.084%)
Oxygen (O2) 209,460 ppmv (20.946%)
Argon (Ar) 9,340 ppmv (0.9340%)
Carbon dioxide (CO2) 394.45 ppmv (0.039445%)
Neon (Ne) 18.18 ppmv (0.001818%)
Helium (He) 5.24 ppmv (0.000524%)
Methane (CH4) 1.79 ppmv (0.000179%)
Krypton (Kr) 1.14 ppmv (0.000114%)
Hydrogen (H2) 0.55 ppmv (0.000055%)
Nitrous oxide (N2O) 0.325 ppmv (0.0000325%)
Carbon monoxide (CO) 0.1 ppmv (0.00001%)
Xenron (Xe) 0.09 ppmv (9×10−6%) (0.000009%)
Ozone (O3) 0.0 to 0.07 ppmv (0 to 7×10−6%)
Nitrogen dioxide (NO2) 0.02 ppmv (2×10−6%) (0.000002%)
Iodine (I2) 0.01 ppmv (1×10−6%) (0.000001%)
Ammonia (NH3) trace
Not included in above dry atmosphere:
Water vapor (H2O) ~0.40% over full atmosphere, typically 1%-4% at surface

this table above is from a Wikipedia article about the earth's atmosphere