Factoid...We often speak of pressure in terms of atmospheres. One atmosphere is equal to the weight of the earth's atmosphere at sea level, about 14.7 pounds per square inch. If you are at sea level, each square inch of your surface is subjected to a force of 14.7 pounds.
In water, the pressure increases about one atmosphere (14.7 pounds per square inch) for every 33 feet (10 meters) of water depth. At the deepest part of all the earth's oceans, Marianas Trench's (east of the Philippine Islands) depth is about 35,800 feet (7 miles/11 km). The pressure of nearly 7 miles of water overhead is about 1080 atmospheres or 16,000 pound per square inch.
Normal sea-level pressure = 14.7 lbs/in2 = 1013.2 mb = 760 torr = 29.92 in Hg
1) Intro. to the Atmosphere and Air Pressure...Click here.
2) The surface weather maps, etc
3) Why the surface weather map is so useful
4) Storm Prediction Center's Virtual Surface Map
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If necessary...go to Lab #1 tutorials to review contouring.
There are many lines on weather maps. Lines of equal temperature are "isotherms", lines of equal air pressure are called "isobars", lines of equal height are called "isoheights" to name a few. Regardless of the type of line...the general name is called "isopleths"....lines of equal concentration....and there are some rules to drawing them. After completeing this lab, you should be able to:
- Draw lines of equal concentration.
- Locate regions of relatively high and low values of air pressure.
- Locate areas of greatest change (ie gradient).
To complete this lab, analyze the data fields as instructed, sign and turn in by next lab.
Rules for drawing lines of equal pressure-Isobars:
- Always draw isobars so that values greater than the value being drawn
are consistently on one side of the isopleth and lower values are on the other side.
- When positioning isobars, assume a steady change between neighboring stations.
Ex. an isobar of 1001 mb would be drawn between 1000 and 1004 about one-quarter
the way from 1000.
- Adjacent isobars tend to look alike. Ex.
Isobars and will generally parallel the curves of its neighbors because horizontal changes in air
pressure from place to place are usually gradual.
- Continue drawing an isobar until it reaches the boundary of the plotted data
or "closes" to form a loop by making its way to its starting point.
- Isobars NEVER stop or end within a data field, and they never fork, touch or
cross one another.
- Isobars cannot be skipped if their values fall within the range of values reported
on the map. Isopleths must always appear in sequence; for example, there must always be
a 1000 mb isopleth between the 996 mb isopleth and 1004 mb isobar.
- Start with pencils....then Smooth!
- Always label all isopleths.
Complete the following Tutorials:
5)Analyze the example surface weather map in intervals of 4 mb's starting at 992, 996, 1000, 1004, 1008, etc....
Locate the highest pressure regions and place the letter "H" for the high pressure centers.
Locate the lowest pressure regions and place the letter "L" for the low pressure centers.
Also....circle AND SHADE in the area of greatest winds.
Analyze these Maps: Today's Pressure,
Temperature
Precip map (Contour 0.01, 0.25, 0.50, & 1.00 inches).
HISTORY here...
Yesterday's surface weather map.
Yesterday's surface frontal analysis weather map.
Yesterday's surface temperature weather map.
Yesterday's precip map (Contour 0.01, 0.25, 0.50, & 1.00 inches).
Lab #2A...due next Tuesday
