Thursday Feb. 7, 2008

Assignment #1 1S1P reports were collected at the start of class.  You can turn in up to two reports next Thursday (Feb. 14). 

Be sure to return your Experiment #1 materials this week, your report is due next Tuesday.  The first Optional Assignment is also due next Tuesday.
We'll finish up learning about how weather data is plotted on surface weather maps using the station model notation.  We didn't have time to learn about decoding the pressure data.

Meteorologists hope to map out small horizontal pressure changes on surface weather maps (that produce wind and storms).  Pressure changes much more quickly when moving in a vertical direction.  The pressure measurements are all corrected to sea level altitude to remove the effects of altitude.  If this were not done large differences in pressure at different cities at different altitudes would completely hide the smaller horizontal changes. 

In the example above, a station pressure value of 927.3 mb was measured in Tucson.  Since Tucson is about 750 meters above sea level, a 75 mb correction is added to the station pressure (1 mb for every 10 meters of altitude).  The sea level pressure estimate for Tucson is 927.3 + 75 = 1002.3 mb.

To save room, the leading 9 or 10 on the sea level pressure value and the decimal point are removed before plotting the data on the map.  For example the 10 and the . in 1002.3 mb would be removed; 023 would be plotted on the weather map (to the upper right of the center circle).  Some additional examples are shown above.

When reading pressure values off a map you must remember to add a 9 or 10 and a decimal point.  For example
138 could be either 913.8 or 1013.8 mb. You pick the value that falls between 950.0 mb and 1050.0 mb (so 1013.8 mb would be the correct value, 913.8 mb would be too low).
Another important piece of information that is included on a surface weather map is the time the observations were collected.  Time on a surface map is converted to a universally agreed upon time zone called Universal Time (or Greenwich Mean Time, or Zulu time).  That is the time at 0 degrees longitude.  There is a 7 hour time zone difference between Tucson (Mountain Standard Time year round) and Universal Time.  You must add 7 hours to the time in Tucson to obtain Universal Time. 

Here are some examples:

8 am MST:
add the 7 hour time zone correction --->  8:00 + 7:00 = 15:00 UT (3:00 pm in Greenwich)

2 pm MST:
first convert 2 pm to the 24 hour clock format 2:00 +12:00 = 14:00 MST
then add the 7 hour time zone correction ---> 14:00 + 7:00 = 21:00 UT (9 pm in Greenwich)

18Z:
subtract the 7 hour time zone correction ---> 18:00 - 7:00 = 11:00 am MST

02Z
if we subtract the 7 hour time zone correction we will get a negative number.  We will add 24:00 to 02:00 UT then subtract 7 hours
02:00 + 24:00 = 26:00
26:00 - 7:00 = 19:00 MST on the previous day
2 hours past midnight in Greenwich is 7 pm the previous day in Tucson


A few pieces of historical information (highlighted below) on pps. 31-32 in the photocopied Classnotes were mentioned before a short video was shown in class.

Click here to see a description of an experiment that Galileo conducted to show that air had weight.

The stratosphere was discovered in the earlier 1900s by Leon Philippe Teisserence de Bort.

Capt. Hawthorne C. Grey was mentioned at the beginning of the 10 minute video shown in class (from a PBS program called "The Adventurers").  Note especially the amount of clothing worn by Grey in an early flight to stay warm at the top of the troposphere.

Auguste Piccard and Paul Kipfer's trip into the stratosphere was the main subject of the video segment shown in class.  They nearly ran out of oxygen too before descending in their balloon.  Note the involvement of the Soviets and Americans in later attempts at high altitude balloon records.  Auguste Piccard would even wife to the stratosphere on one of his flights.  World War II put an end to this Age of Stratospheric Exploration.
The remainder of the class was devoted to the Practice Quiz.