1. Atmospheric Composition and Contour Weather Maps
Val Bennington
AOS 101
September, 2008

2. Station Map Review

3. Atmospheric Composition
How does temp change as we go up in the atmosphere?
Why?
What makes up the atmosphere? Where do these species reside?

4. Temperature in Atmosphere

5. What’s in the Atmosphere?
Nitrogen (78%)
Oxygen (21%)
Argon (1%)
Water vapor (0-4%)
CO2 (380 ppm)
Ozone (O3) – (4 ppb)
Methane (CH4) – (1.7 ppm)
CFCs

6. Questions Where is the ozone layer?
Why does temp go up in the stratosphere?
What level are we usually talking about when we talk about weather?
Where is most of the water vapor?
Why is it hard to breathe at high altitudes if it is still 21% oxygen??

7. Contour Maps

8. What Do They Tell Us?

9. Why Contour?
Contour maps organize all the available data so we can make sense of it
We have all that station map data!!!! Let’s use it. Let’s be able to forecast from it!
Once contoured, you can determine wind direction, high and low pressure systems, locations of possible precipitation, fronts, regions of strong winds and changing temperatures --- ALL FROM A MAP!

10. BEFORE

11. AFTER

12. What They Tell Us Regions of High and Low Pressure Fronts Temperature
Wind Direction and Speed
How your weather is going to change!

13. How to Think about Contouring
Like topographic map
Lines of constant height in this picture
Walk along one of these lines -- stay at exactly the same altitude the ENTIRE time

14. What Else Do We Contour?
Isopleth is a line on a map that connects all the points of a given variable with the SAME SPECIFIED VALUE
Isobar - line of constant pressure
Isotherm - line of constant temperature
Isotach - line of constant wind speed
Isodrosotherm - a line of constant dewpoint
Isohyet - a line of constant precipitation accumulation
Isoneph - a line of constant cloudiness
Isohaline - a line of constant salinity (saltiness in the ocean)
Isoheight - a line of constant height

15. Isobars in Blue (lines of constant pressure)
Can you spot Hurricane Ike???

16. Which Way Do the Winds Go?
Geostrophy

17. Notes about Isobars
Closeness of lines tells us how strong pressure gradient force (PGF) is
Very close lines = great pressure difference over small distance
----> large PGF!
**Think of topographic map
** Steep terrain where lines close together
** Here: large PGF when lines close together = Big Force

18. Isotachs (wdsp) and Isoheights

19. Isotherms

20. Contouring Rules Contours never cross each other
A contour line has values higher than the line value on one side and values lower on the other side of it
Isotherm of 10°F has temps below 10°F on one side and temps above 10°F on the other
Contours are only drawn where there is data!
Evenly spaced increments are always used (say every 5 degrees and every 4 mb for pressure)
Easiest to find a high or low value first and work from there

21. Examples  Temperature observations
Where do we draw the 15°F isotherm????

22. Examples Temperature observations
Where do we draw the 15°F isotherm????

23. Examples Temperature observations
Where should we draw the 75ºF and 80ºF isotherms?
Where should we draw the 75F and 80F isotherms?

24. Examples Temperature observations
Where should we draw the 75ºF and 80ºF isotherms?
Where should we draw the 75F and 80F isotherms?

25. New Times
In the olden days, all weather maps and contour maps were done by hand!
Now, computers draw contour maps and determine wind direction and speed - as well as many other things
Contouring is very tedious - so you will only be asked to do simple contouring