Tue., Aug. 25 notes

Tuesday Aug. 25, 2009
click here to download today's notes in a more printer friendly format

A couple of songs from Leftover Salmon (their Ask the Fish CD) were played before the start of class today. Here's the Wikipedia entry on them. You can listen to "The Jokester" on YouTube, but I wasn't able to find the second song, "Stay Away Monday".

For about the last year I have been filling the few minutes before class with some kind of music, often local talent. Music won't take up any actual class time. Hopefully you'll enjoy at least some of the selections. Comments and ideas from students are welcome. If you know anything about the UA Steel Drum Band, particularly if they have a CD with lots of steel drum music, please let me know.

Today was the first day of class. We first briefly discussed the Course Information handout. You should be aware that there are a couple of topics (a daily weather discussion/forecast and climate change) that won't receive as much emphasis in this class as they might in the two other sections of Introduction to Weather and Climate (largely due to the interests and background of the instructor). Climate change in particular might be covered in more depth in the other two sections (MWF 9-9:50 in ILC 120 and TR 2:00-3:15 pm in ILC 120). Don't get the idea I'm encouraging you to change sections, I'm not. The other two sections are large (230 students per section) and may well be full at this point anyways.

I teach another section of this class. It meets Mon., Wed., and Fri at 2 pm in AME 202. If for some reason you know that you are not going to be able to take one of the quizzes in this class (always on Thursdays) you take the quiz with the other section (their quizzes are on Wednesday). You should let me know ahead of time if this happens.

A textbook is not required for this class. A couple of texts were listed on the Course Information handout for people who want to get a more complete coverage of the subject than we will be able to do in class (we would only cover perhaps 25% to 30% of the text). Otherwise you should be able to do perfectly well in the class by reading the online notes and other suggested online sources.

A set of photocopied ClassNotes (available in the Student Union Bookstore) is requred, you should try to purchase a copy right away as we will probably be using some of them in class on Thursday. If you know someone with photocopied ClassNotes from the Fall 2008 or Spring 2009 class they should work fine for this semester also. You will not find this section of NATS 101 on D2L.

Examples of quizzes and a final exam (both with answers) from a previous section of the course can be downloaded here.

Next we looked at the Writing Requirements handout. You should be thinking about which of the 4 experiments (or book or scientific paper reports) you would like to do so that you can sign up in class on Thursday. There aren't enough materials for everyone to do the same experiment, the class will be split up into 4 roughly equal groups. Distribution of the materials for the first experiment will probably begin in class on Thursday.

Your grade in this class will depend on your quiz scores, how much extra credit you earn (from optional homework assignments), your writing grade, and (perhaps) your score on the final exam. A sample grade report from the Fall 2008 MWF Nats 101 class is shown below.

Don't worry about all the details at this point. Note that this student earned Cs on all the quizzes but ended up with a B in the class largely because of the high (98.8%) writing grade and because of the extra credit (EC) points. Be sure to do the writing assignments and try to do most of the optional extra credit assignments.

We're not using a book in this class, though I might try to get the NATS 101 students to write one sometime. A text would probably start by describing the atmosphere. What is the atmosphere made of, how do air temperature, air density, air pressure change with altitude? That kind of thing. That's what we'll do in this class (we'll also throw in a little material on air pollutants). Today we just had enough time to start to look at the composition of the atmosphere.

I suspect that quite a few people knew the answer to the following question.

The answer is nitrogen. I poured some liquid nitrogen into a styrofoam cup. You can see liquid nitrogen, it is clear and looks like water (though you certainly wouldn't want to drink it, it is very cold: -320 F ). The liquid nitrogen was evaporating and turning into nitrogen gas. Nitrogen gas is invisible as are most of the other gases in the atmosphere. 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. We'll use liquid nitrogen in several class demonstration this semester.

This next question was also pretty easy.

The answer is oxygen. Oxygen is the most abundant element (by mass) in the earth's crust, in ocean water, and in the human body. Here's a photograph of liquid oxygen. It has a (very faint) blue color (I was a little disappointed when I saw the picture 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. More about those in class on Thursday.

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. The concentration of water vapor 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. 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). Noble gases are often used in "neon signs."

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.

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 higher the water vapor concentration, and vice versa.

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 80^o dew points would be very unpleasant (and possibly life threatening). Click here to see current dew point temperatures across the U.S.

The second job of the dew point temperature is

We could use the cup of liquid nitrogen to show this.

The cloud came from moisture in the air. The cloud was not made of nitrogen gas (which is invisible). Note also that a certain amount of "artistic" license was used in the figure above; liquid nitrogen is not blue and water clouds are not green.

Here's what I call a hidden optional assignment. You can earn extra credit points (usually tenths of a point per assignment) by doing optional assignments. You'll be able to earn 0.1 or 0.2 pts on this assignment. The assignments are optional, you don't have to do them.
This assignment will be due at the beginning of class on Thu. Aug. 27. Just bring your work down to the front of the classroom and stick it in my box. What I'm really trying to do with an assignment like this is to see if anyone is reading the online notes.

The remaining material was not covered in class. We'll review some of this quickly in class on Thursday.

The earth's original atmosphere, which was composed mostly of hydrogen (H) and helium (He), was very different from the atmosphere that we have today. This original atmosphere either escaped (the earth was hot and the gases were moving around with enough speed that they could overcome the pull of the earth's gravity) or was swept into space (by the solar wind).

Our present atmosphere is though to have come from volcanic eruptions.

Volcanoes emit a lot of water vapor and carbon dioxide. As the earth began to cool the water vapor condensed and began to create oceans. Carbon dioxide dissolved in the oceans and was slowly turned into rock. Smaller amounts of nitrogen (N2) are emitted by volcanoes. Nitrogen is relatively inert and remained in the air. Nitrogen concentration built up over time.

Volcanoes didn't add any of the oxygen that is the atmosphere. Where did that come from?

The oxygen is thought to have first come from photodissociation of water vapor and carbon dioxide by ultraviolet light (the high energy UV light is able to split the H₂0 and CO₂ molecules into pieces). The O and OH react to form O₂ and H.

Once molecular oxygen (O₂) begins to accumulate in the air it can react with atomic oxygen (O) to form ozone (O₃). The ozone then begins to absorb ultraviolet light and life forms can safely move from the oceans (which would absorb UV light in the absence of ozone) onto land. Eventually plants and photosynthesis would become the main source of atmospheric oxygen.

Note that combustion (and respiration) is really just the opposite of photosynthesis. We burn fossil fuels to generate energy. Water vapor and carbon dioxide are by products.

In class on Thursday we will see that blue-green algae (cyanobacteria) in the ocean began to produce oxygen by photosynthesis even before plants were able to move from the oceans onto land.