Wednesday Jan. 16, 2008

The first day of class.  We first briefly discussed the Course Information handout.  Note the various options you have for purchasing a copy of the course textbook.  You should try to purchase a copy of the photocopied Classnotes (in the bookstore) right away as we will probably be using some of them in class on Friday.

 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.  Distribution of the materials for the first experiment could begin as early as Friday this week.
Your grade in this class will depend on your quiz scores, how much extra credit you earn, your writing grade, and (perhaps) your score on the final exam.  A sample grade report from the Spring 2007 MWF Nats 101 class was shown.

Doe_J
quiz1 -36 (160 pts possible) 77.5%
quiz2 -46 (155 pts possible) 70.3%
quiz3 -48 (165 pts possible) 73.1%
quiz4 -35 (160 pts possible) 78.1%
2.6 EC points (3.3 pts possible)
writing scores: 33.0 (expt/book report) + 45.0 (1S1P pts)
writing grade: 97.5%
average (no quiz scores dropped): 79.3% + 2.6 = 81.9%
average (lowest quiz score dropped): 81.6% + 2.6 = 84.2
you DO need to take the final exam
-24.8 pts missed on the final exam = 75.3%
3Q&W>F overall average is 82.4

Don't worry about all the details at this point.  Note that this student earned C grades on all the quizzes and the final exam but ended up with a B in the class.  This is due largely to the high writing grade and the extra credit points.

We'll begin this new semester in Chapter 1 of the text.  Before opening the book and beginning the first reading assignment, try to imagine what you would put in the first chapter of a meteorology and climatology textbook.


Student answers to the question above included:  whether you could breath the air, temperature of the outside air, nature of the planet's surface, gravity, and pressure.  Many of these are covered in Chapter 1 of the text.

Today we were concerned with the composition of the earth's atmosphere, in particular the 5 most abundant gases in the earth's atmosphere.

Some of the most abundant gas, in liquid form, was poured into a styrofoam cup.


The liquid was nitrogen (you can fill in the blank above with the word nitrogen).  You can see liquid nitrogen, it is clear (not blue as shown above) and looks like water.  Once it has evaporated and turned 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.   Here's a photograph of liquid oxygen.  It really does have a blue (light blue) color.

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

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, 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.

The variable concentration of water vapor means it is sometimes more abundant, sometimes less abundant than argon which has a concentration of about 1%.  Argon is an unreactive noble gas (helium, neon, krypton, xenon, and radon are also inert gases).  Noble bases are often used in "neon signs."

Here's the complete list that we came up with 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; it has two "jobs."

Its first job is to provide a measure of the amount of water vapor in the air. The dew point is just a number.  When the value is low the air doesn't contain much moisture.  The higher the dew point value, the more water vapor there is in the air.

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




We are in the summer thunderstorm season in Tucson and dew points have been in the 60s.  Many people use an evaporative cooler to cool their homes in the summer.  Evaporative coolers don't work very well when dew points are as high as they are now.

Click here to see current dew point temperatures across the U.S.  Note that a large part of the SE US currently has dew points in the 70s.

The second job of the dew point temperature is illustrated below.  When you cool moist air to its dew point, the relative humidity becomes 100% and a cloud forms.


The following material wasn't covered in class. 
Our present atmosphere is very different from the earth's original atmosphere. 

The earth's first atmosphere was composed mainly of hydrogen and helium.  These light-weight gases escaped into space and were lost.  The next atmosphere was built up of gases emitted during volcanic eruptions, mostly water vapor, carbon dioxide, and nitrogen.  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.  Much of the nitrogen remained in the atmosphere.

volcanoes didn't add oxygen to the atmosphere.

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

Once O2 begins to accumulate in the air it can react with 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.