Tue., Dec. 10 notes

Here are the key details to remember about our original atmosphere and the origins & composition of our present day atmosphere. The 0 to 3 or 4% concentration of water vapor in the atmosphere wasn't mentioned in class.

Topic 2

The comment about clouds and precipitation cleaning the air was added after class.

Topic 3

It is the chlorine in CFCs that reacts with and destroys stratospheric ozone. It is worth emphasizing that destruction of stratospheric ozone by CFCs (thinning of the ozone layer) is not the cause of climate change and global warming. The small additional amount of UV light arriving at the ground will not cause global warming. That UV light could cause skin cancer and cataracts, that sort of thing, but not global warming.

Topic 4

I picked the best parts of several figures to produce this one. Note the word bar that appears in millibars, barometer, and isobars.

Topic 5

You don't need to memorize the two ideal gas law equations, I write them on the board during the exam. You should remember what the variables in the two equations stand for (k and R are constants).

Volumes of air in the atmosphere can freely expand or shrink. Heating air in the atmosphere will cause it to expand and the air density will decrease. A volume of cold air will shrink and its density will increase. The changes in volume, density, and temperature all occur in a way that keeps the pressure of the air inside the volume constant and equal to (in balance with) the air outside the volume.

This is about where we stopped in class today. We'll start up at this point on Wednesday next week.

A volume of air that has the same density as the air around it won't rise or sink, it will hover. The downward force of gravity is canceled by an upward pressure difference force.

Here's a statement of Archimedes principle:

An object immersed in a fluid experiences
an upward buoyant force equal to the
weight of the fluid displaced by the object.

Topic 6

Station model notation

Dew points in Tucson fall between 25 F and 45 F most of the year, those are normal or average values. They rise into the 50s and 60s during the summer thunderstorm season (these would be relatively high values for Tucson. I won't expect you to decode the pressure information plotted on a map, though you should be able to determine which of the two possibilities is more reasonable. Meteorologists usually specify the direction the wind is coming from.

Surface weather map features


The labels on the contours are reasonable sea level pressure values. These are pressure contours, isobars. The fact that the values decrease as you move in toward the center means this is a center of low pressure.	Surface winds blow across the isobars always toward low pressure. That's another way of figuring out this is a center of low pressure. The term cyclone refers to winds spinning around a center of low pressure. Is this a Northern or Southern hemisphere chart?

Upper level charts

Upper level charts usually have more of a wavy pattern rather than the bulls-eye pattern of circular high and low pressure centers found on surface weather maps.

You should be able to identify the ridge (n-shape) and trough (u-shape) features. Warmer than average air produces ridges, troughs are associated with colder than average air. Upper level winds blow parallel to the contours and from west to east.

Topic 7

You should be able to identify cold fronts (at left above) and warm fronts (right), determine where the cold and warm air would be found, and show their direction of motion.


In these crossectional views of cold and warm fronts you should be able to determine whether the cold air is advancing or retreating (bunched up shape vs a ramp like shape). Which ever air mass is rising is the lower density warmer air mass. Both warm and cold fronts cause air to rise.