Lecture 5 1007 METR 1111

1
Lecture 5 (10/07)METR 1111

• Isolining and
• Upper Air Maps

2
What are isolines?

• Isolines (also called isopleths)- lines that
  connect equal values of a variable
• In meteorology, we frequently use
• - isobars (pressure)
• - isotherms (temperature)
• - isotachs (wind speed)

3
Isolines

• Isolines make it easy to see different values on
  a map
• Allow us to interpolate values at a point
• Can pick out different features like fronts,
  jetstreams, drylines, pressure fields, etc.
• How can I draw an isoline?

4
Drawing Isolines

• When drawing isolines/isopleths, keep in mind
• Lines cannot cross.
• They must close themselves off or start and end
  at the edge of the map
• You must have greater values on one side and
  smaller values on the other

5
Upper Air

• Upper air can refer to anything not on the
  surface
• Rawinsonde (weather balloons) launched twice a
  day from stations across country world at 0 and
  12 Z
• Measures temperature, pressure, humidity, and
  wind speed and direction

6
Upper Air Maps

• UAM have many stations readings at a certain
  constant pressure level
• Ex On an 850mb map, all stations are at a
  pressure of 850mb.
• Most common upper level maps 850mb, 700mb,
  500mb, 250mb, 200mb.

7
Temperature

• Temperature is in upper left corner
• Measured in Celsius

8
Dew Point/Dew Point Depression

• Dew point or dew point depression is in lower
  left corner
• Measured in Celsius
• Dew point depression difference between the
  temperature and dew point
• Can look for map label or use intuition
• If you see a dew point greater than a
  temperature, dew point depression is plotted
  (here dew pt -2 C)

9
Geopotential Height

• Upper right corner geopotential height
• Geopotential height -- the height above sea level
  that the instrument is at when it reads the
  specified pressure level.
• Often truncate last number or two but measured in
  meters
• Need to decode geopotential height.

10
To try clear up confusion in class

• The following pattern appears between isobars and
  lines of constant geopotential height
• If we draw lines of constant height on a constant
  pressure surface it will look like lines of
  constant pressure (isobars) drawn at a given
  height (as long as data at about the same
  elevation above the earth is used)
• Thus, an area of low heights means you have an
  area of low pressure
• An area of high heights means you have an area of
  high pressure

11
What does it all mean?

• Heres an example if youre interested
• Compare this pattern of constant height lines on
  a constant pressure surface http//weather.unisys
  .com/upper_air/previous/ua_250-1.html
• With this pattern of constant pressure lines on a
  constant height surface http//weather.unisys.com
  /upper_air/previous/ua_36000ft-2.html
• The height contours from the first should
  approximately line up with the isobars from the
  second (except that they use fewer lines on one).
  
• To see this best, look in regions where the lines
  are closest together (greatest pressure gradient)
  and compare between the two maps
• A viewing tip Click on the first url to display
  it on your web browser and then cut and paste the
  second url into the box and hit returnthen hit
  the forward and back button to switch between the
  two

12
Decoding Geopotential Heights

• Not all map-makers use the same truncation rules
• These are the most common
• 850 mb add 1000m 5331,533m
• 500 mb multiply by 10 5915,910m
• 250 mb multiply by 10 09810,980m
• add 10,000m

13
Wind Barb

• Wind symbols are the same as with surface plots
• Remember a triangle means 50 knots
• Ex 1 triangle, 3 long flags and 1short flag add
  up to 5030585 kts
• This wind is 90 (Easterly) at 50 kts

14
Announcements

• Pick up graded hmwks quizzes after you turn in
  your quiz
• Read Ch 6 (Floods Droughts)
• Complete homework 5 for next time (available on
  web)