Wednesday Sept. 26, 2012
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After listening to an initial song, "Gitanos Californeros" from Fishtank Ensemble, a decision was made to not play a second song ("Tchavo" from the same group).

The Experiment #1 reports have all been graded and were returned in class today.  You now have two weeks to revise your report if you want to (you don't have to).  You only need to change sections were you want to earn additional credit.  Please return the original report with your revised report.  The revised reports are due on or before Wed., Oct. 10.

A second Optional Assignment on Upper Level Charts is now available.  If you make an honest effort to answer all the questions and have the assignment done before coming to class you can earn extra credit.  If you answer at least 85% of the questions correctly you'll earn extra credit and a "Green Card."  The assignment is due next Wednesday, Oct. 3.

Up to this point we've been learning about surface weather maps.  Maps showing conditions at various altitudes above the ground are also drawn.  Upper level conditions can affect the development and movement of surface features (and vice versa).  We covered some of the basic concepts at the start of the period today.  Some additional supplementary information is available online.  This supplementary reading provides all the background information you'll need to be able to answers the questions on the new optional assignment mentioned above.l

Here we'll mostly just learn 3 basic facts about upper level charts.  First the overall appearance is somewhat different from a surface weather map.  The pattern on a surface map can be complex and you generally find circular (more or less) centers of high and low pressure (see the bottom portion of the figure below).  You can also find closed high and low pressure centers at upper levels, but mostly you find a relatively simple wavy pattern like is shown on the upper portion of the figure below (sort of a 3-dimensional view).  You'll find this basic picture on p. 41 in the ClassNotes.

A simple upper level chart pattern is sketched below (a map view).  There are two basic features: wavy lines that dip southward and have a "u-shape" and lines that bend northward and have an "n-shape".

The u-shaped portion of the pattern is called a trough.  The n-shaped portion is called a ridge.

Troughs are produced by large volumes of cool or cold air (the cold air is found between the ground and the upper level that the map depicts).  The western half of the country in the map above would probably be experiencing colder than average temperatures.  Large volumes of warm or hot air produce ridges.  You can find out why this is true by reading "Upper level charts pt. 2".

The winds on upper level charts blow parallel to the contour lines generally from west to east.  This is a little different from surface winds which blow across the isobars toward low pressure.  An example of surface winds is shown below.

That's it for this first section.  Really all you need to be able to do is
1. identify troughs and ridges,
2. remember that troughs are associated with cold air & ridges with warm air, and
3. remember that upper level winds blow parallel to the contour lines from west to east.

Here's the earlier picture again overlaying surface and upper-level maps.

On the surface map above you see centers of HIGH and LOW pressure.  The surface low pressure center, together with the cold and warm fronts, is a middle latitude storm.

Note how the counterclockwise winds spinning around the LOW move warm air northward (behind the warm front on the eastern side of the LOW) and cold air southward (behind the cold front on the western side of the LOW).  Clockwise winds spinning around the HIGH also move warm and cold air.  The surface winds are shown with thin brown arrows on the surface map.

Note the ridge and trough features on the upper level chart.  We learned that warm air is found below an upper level ridge.  Now you can begin to see where this warm air comes from.  Warm air is found west of the HIGH and to the east of the LOW.   This is where the two ridges on the upper level chart are also found.  You expect to find cold air below an upper level trough.  This cold air is being moved into the middle of the US by the northerly winds that are found between the HIGH and the LOW. 

Note the yellow X marked on the upper level chart directly above the surface LOW.  This is a good location for a surface LOW to form, develop, and strengthen (strengthening means the pressure in the surface low will get even lower than it is now.  This is also called "deepening").  The reason for this is that the yellow X is a location where there is often upper level divergence.  Similary the pink X is where you often find upper level convergence.  This could cause the pressure in the center of the surface high pressure to get even higher.  You can read more about this in Upper level charts pt. 3.
  The upper level winds could also cause the surface storm to weaken (the low pressure would get higher).

The following picture  wasn't shown in class on Wednesday.

One of the things we have learned about surface LOW pressure is that the converging surface winds create rising air motions.  The figure above gives you an idea of what can happen to this rising air (it has to go somewhere).  Note the two arrows of air coming into the point "DIV" and three arrows of air leaving (more air going out than coming in), this is upper level divergence).  The rising air can, in effect, supply the extra arrow's worth of air.

Three arrows of air come into the point marked "CONV" on the upper level chart and two leave (more air coming in than going out = upper level convergence).  What happens to the extra arrow?  It sinks, it is the source of the sinking air found above surface high pressure.

OK we're done with weather maps for the time being.  Though if interesting weather appears imminent I'll try to mention it in class (earlier in the week  it looked like the remnants of Hurricane Miriam might bring some rainy weather to Tucson this weekend, but that no longer seems to be the case).

If we were using a textbook in this class we'd be moving into Chapter 2!  During the next couple of weeks we will be concerned with energy, temperature, heat, energy transport, and energy balance between the earth, atmosphere, and space.

It is easy to lose sight of the main concepts because there are so many details.  Most of the following figures are found on pps 43&44 in the photocopied ClassNotes.

Types of energy
We will learn the names of several different types or forms of energy.

Kinetic energy is energy of motion. Some examples (both large and microscopic scale) are mentioned and sketched above.  This is a relatively easy to visualize and understand form of energy.

Latent heat energy is an underappreciated and rather confusing type of energy. The word latent refers to energy that is hidden in water and water vapor.  The hidden energy emerges when water vapor condenses or water freezes (the energy had been added earlier when ice was melted or water was evaporated).  The fact that the energy is hidden is part of what makes it confusing.

Radiant energy is a very important form of energy that was for some reason left off the original list in the ClassNotes.  Sunlight is an example of radiant energy that we can see and feel (you feel warm when you stand in sunlight).  There are many types of radiant energy that are invisible (such as the infrared light that people emit - something I didn't mention in class).  Electromagnetic radiation is another name for radiant energy.

Energy transport
Four energy transport processes are listed below.


By far the most important process is at the bottom of the list above.  Energy transport in the form of electromagnetic radiation (sunlight is a common form of electromagnetic radiation) is the only process that can transport energy through empty space.  Electromagnetic radiation travels both to the earth (from the sun) and away from the earth back into space.  Electromagnetic radiation is also responsible for about 80% of the energy transported between the ground and atmosphere.

You might be surprised to learn that latent heat is the second most important transport process.

Rising parcels of warm air and sinking parcels of cold air are examples of free convection.  Because of convection you feel colder or a cold windy day than on a cold calm day (the wind chill effect).  Ocean currents are also an example of convection.  Ocean currents transport energy from the warm tropics to colder polar regions.

Convection is a 3rd way of causing rising air motions in the atmosphere (convergence into centers of low pressure and fronts are other 2 ways we've encountered so far) 

Conduction is the least important energy transport at least in the atmosphere.  Air is such a poor conductor of energy that it is generally considered to be an insulator.

Energy balance and the atmospheric greenhouse effect
The next picture (the figure in the ClassNotes has been split into three parts for improved clarity) shows energy being transported from the sun to the earth in the form of electromagnetic radiation.

We are aware of this energy because we can see it (sunlight also contains invisible forms of light) and feel it.  With all of this energy arriving at and being absorbed by the earth, what keeps the earth from getting hotter and hotter?  If you park your car in the sun it will heat up.  But there is a limit to how hot it will get.  Why is that? 

It might be helpful when talking about energy balance to think of a bank account.  If you periodically deposit money into your account why doesn't the balance just grow without limit.  The answer is that you also take money out of the account and spend it.  The same is true of energy and the earth.  The earth absorbs incoming sunlight energy but also emits energy back into space (the orange and pink arrows in the figure below).  Energy is being emitted by both the surface of the earth and the atmosphere.

Energy is emitted in the form of infrared light is an invisible form of energy (it is weak enough that we don't usually feel it either).  A balance between incoming and outgoing energy is achieved and the earth's annual average temperature remains constant.

We will also look closely at energy transport between the earth's surface and the atmosphere (see the figure below). This is where latent heat energy transport, convection and conduction operate (they can't transport energy beyond the atmosphere and into outer space).

That is also where the atmospheric greenhouse functions.  That will be a important goal - to better understand how the atmospheric greenhouse effect works.

The greenhouse effect is getting a lot of "bad press".  If the earth's atmosphere didn't contain greenhouse gases and if there weren't a greenhouse effect, the global annual average surface temperature would be about 0 F (scratch out -4 F and put 0 F, it's easier to remember).  Greenhouse gases raise this average to about 60 F and make the earth a much more habitable place.  That is the beneficial side of the greenhouse effect.

The detrimental side is that atmospheric greenhouse gas concentrations are increasing (no real debate about that).  This might enhance or strengthen the greenhouse effect and cause the earth to warm (some debate here particularly about how much  warmer there might be).  While that doesn't necessarily sound bad it could have many unpleasant side effects (lots of debate and uncertainty about this also).  That's a subject we'll explore briefly later in the semester.

That's about all we had time for.  Though on Friday I want to do an experiment in class.  Actually I want a couple of groups of students (two groups of two students would be ideal) to do the experiment.  You'll be able to write a report about the experiment and use the data you collect to satisfy the Experiment Report part of the Writing Requirements.  I.e. you won't have to worry about checking out materials and doing Expt. #1, #2, or #3. 

Someone has already volunteered.  So I'll need three more people on Friday.