Atmospheric Composition and Contour Weather Maps

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Atmospheric Composition andContour Weather Maps

• Val Bennington
• AOS 101
• September, 2008

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Station Map Review
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Atmospheric Composition

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

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Temperature in Atmosphere
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Whats 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

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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??

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Contour Maps
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What Do They Tell Us?
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Why Contour?

• Contour maps organize all the available data so
  we can make sense of it
• We have all that station map data!!!! Lets use
  it. Lets 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!

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BEFORE
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AFTER
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What They Tell Us

• Regions of High and Low Pressure
• Fronts
• Temperature
• Wind Direction and Speed
• How your weather is going to change!

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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

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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

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Isobars in Blue (lines of constant pressure)
Can you spot Hurricane Ike???
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Which Way Do the Winds Go?
Geostrophy
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Notes about Isobars

• Closeness of lines tells us how strong pressure
  gradient force (PGF) is
• Very close lines great pressure difference over
  small distance
• ----gt large PGF!
• Think of topographic map
• Steep terrain where lines close together
• Here large PGF when lines close together
  Big Force

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Isotachs (wdsp) and Isoheights
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Isotherms
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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 10F has temps below 10F on one side
  and temps above 10F 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

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Examples

• Temperature observations
• Where do we draw the 15F isotherm????

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Examples

• Temperature observations
• Where do we draw the 15F isotherm????

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Examples

• Temperature observations
• Where should we draw the 75ºF and 80ºF isotherms?
• Where should we draw the 75F and 80F isotherms?

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Examples

• Temperature observations
• Where should we draw the 75ºF and 80ºF isotherms?
• Where should we draw the 75F and 80F isotherms?

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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