Wed., Jan. 13 notes

Wednesday Jan. 13, 2010
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A couple of songs from Mumbo Gumbo ("Gimme Noise" and "Little Birds") were played before the start of class today. For about the last year or two 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 like at least some of the selections. Comments and ideas from students are welcome.

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 three other sections of Introduction to Weather and Climate (largely due to the interests and background of the instructor). Don't get the idea I'm encouraging you to change sections, I'm not.

I also teach Section 5 of this class. It meets Tue. and Thu. morning at 8:00 in ILC 140. If you ever miss a Wednesday quiz in this class, you can make it up on Thursday in the T Th section (please try to let me know ahead of time).

A textbook is not required for this class. If you want to get a more complete picture of the subject than we will be able to cover in class, you might want to purchase one of the textbooks that are being used in the other NATS 101 sections (I've also have several copies of introductory level textbooks that you would be welcome to borrow for the duration of the semester). 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 Wednesday If you know someone with photocopied ClassNotes from the Spring or Fall 2009 classes they should work fine this semester also. You will not find either of my two sections 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 Friday. There aren't enough materials for everyone to do the same experiment. Distribution of the materials for the first experiment will probably begin in class on Wednesday next week.

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 2009 MWF Nats 101 class is shown below.

Don't worry about all the details at this point. Note that this (fictitious) student earned a D+ and three Cs on the quizzes but ended up with a B in the class largely because of the high (99.4%) 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. The quiz scores shown above were the actual average grades from last semester's class .

An optional, anonymous survey was conducted during today's class. Here are the first two questions

I'll answer Questions 1a and 1b in class on Friday. No one answered the complete question correctly. The closest answer was in "France" at some kind of a "cooking" school. Most people answered "No" to Question 1c. Many people seemed to think I might have been at Traffic or Defensive Driving School (good answer but wrong).

Several people had heard or were concerned that the quizzes are difficult and that the average grade on the quizzes last fall was a C. We'll discuss this further before and after the Practice Quiz on Feb. 3. I'll give you some ideas for how to prepare for the quizzes. And if you do find you aren't doing as well as you would like on the quizzes come see me early in the semester.

If we were using a textbook it would probably begin with an introductory chapter that described 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). Here are some questions about air that were on the anonymous survey.

These questions aren't as easy to answer as you might originally think. You might think of air as being clear, transparent, and invisible (that would be true of the air in the classroom). But sometimes the air looks foggy or hazy. In these two cases you are seeing the effects of small water droplets (fog) or small particles of some sort (haze). The particles themselves may be too small to be seen with the naked eye but are visible because they scatter (redirect) light. We will learn more about the scattering of light in a week or two. The sky itself is blue. This is a little more complicated form of scattering of sunlight by air molecules.

I don't think you can smell or taste air unless air pollutants are present. I suspect we can smell certain air pollutants even when the concentration is very small.

It is hard to answer 3c because we are always in contact with air. We will see that 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 hurt. Air can feel hot or cold.

The answer to Question 3d 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 or something like that). 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.

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. Here's a photograph of liquid oxygen. It has a (very faint) blue color (I was pretty 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 Wednesday.

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 often 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.

This is about as far as we actually go in class. Some addtional material has been added below. We'll review this quickly on next Wednesday. Here is the last of the survey questions.

1S1P stands for "one side of one page." They are a required part of this class. If you don't do them your grade will suffer. You only need to do one experiment.

The following material wasn't covered in class. We'll review most of this quickly in class on Friday.

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 80^o 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.

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.

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.

Here's a comment from the anonymous survey

It is sometimes easier and clearer to show or explain a reaction in formulas instead of words. I wouldn't expect you to remember the chemical formulas in the example above. You might just remember that the earth's original oxygen came from oxygen in water and carbon dioxide. It's probably also good to remember that ultraviolet light is capable of breaking molecules apart.

Once molecular oxygen (O₂) begins to accumulate in the air it can react with atomic oxygen (O) to form ozone (O₃). This is an example of two formulas that you should probably be able to remember.

Once formed, 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 Wednesday 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.