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Meteo 3: Chapter 1
Tools and basic terms we use to
describe the weather
Read Chapter 1
 Atmosphere: The envelope of air surrounding the
– Includes gases, clouds and particles
– Relatively thin
 Meteorology: The study of the physics, chemistry,
and dynamics of the atmosphere
 Weather: The state of the atmosphere
 Climate: describes prevailing weather conditions
in a location in terms of averages/extremes over
long periods
Atmospheric Gases
Table 1.1 Grenci/Nese
 Permanent Gasesconstant concentration
 1) Nitrogen- 78.08%
 2) Oxygen- 20.95%
 3) Argon- 0.93%
 4) Neon- 0.0018%
 Variable Gasesvariable concentration
 1) Water Vapor- 0-4%
 2) CO2- 0.038%
 3) Methane- .00018%
 4) N2O- 0.00003%
 Need to know when, where, what and how much
we are referring to with respect to the weather!
 Easier to communicate about the weather when
we have standards for these
 Where -> geography, topography,
 What -> e.g. temperature, pressure
 When -> standardized time, timescales
 How much -> statistics, UNITS
Political Map: Know Your States!
Show boundaries made and used by humans
PA Topography
 Physical Maps: Show natural features
– Important b/c earth’s surface influences flow of air
Latitude & Longitude
 Latitude lines run
parallel with equator
 Longitude lines run
pole to pole
Earth divided by Latitudes
 Tropics lie between 23.5ºN (Tropic of Cancer) &
23.5ºS (Tropic of Capricorn)
 From 23.5º-30º in each hemisphere = subtropics
 Polar regions lie poleward of 66.5º
 Mid-latitudes located between polar regions and
A Standardized Time Scale
 8:00 am here is not 8:00 am in Chicago,
Ulaanbaatar or Ouagadougou
 Zulu-Time (Z) or Coordinated Universal Time
(UTC) = time scale all weather observations are
reported in…represents local time on Prime
– Ranges from 0-24 hrs
– Eastern Time Zone is 5 hrs behind UTC, 4 hours behind
during Daylight Savings Time
 E.g. 12Z = 7:00am EST or 8:00 am EDT
The larger a weather phenomenon, the longer it
 Temperature = measure of the avg. kinetic energy of a
substance’s molecules
– kinetic energy (KE) = energy associated with motion
– High KEs correspond to higher temperatures
– 3 Scales to Describe Temperature
– 1) Kelvin- 0 K corresponds to temperature at which
molecular motion ceases, known as absolute zero
– 2) Celsius Scale- used to give temperatures in all
countries but US.…0ºC corresponds to ice’s melting
 ºC = K - 273.15
– 3) 3) Fahrenheit= temperature scale used in US…32ºF
corresponds to ice’s melting point
 ºF = (1.8)ºC +32
 Scientists commonly use SI units => meter (m),
second (s), kilogram (kg), and Kelvin (K) and
scientific notation to represent numbers
(e.g. 4.02 * 104)
 All kinds of tutorials on the web on how to convert
units using ‘dimensional analysis’ or ‘factor label’
 For example:
 And if you don’t learn how…
 Average (Mean)- sum of all observed
values divided by number of observations
 In meteorology, normals (averages)
computed by averaging 30 years of data
– Weather rarely conforms to “normals”
 Range- maximum and minimum values
 Probability of Precipitation (POP)- 70%
chance of rain means a 7 in 10 chance that any
point in the forecast area receives measurable rain
Weather Observations
 In the U.S., surface weather observations taken
automatically at ~1500 locations, mainly near
airports…coordinated by government (FAA & NWS)
 Weather conditions above the surface are measured using
radiosondes- weather-sensing instruments carried aloft by
weather balloons
– Upper-air obs. are made at fewer spots (~100 in North
America) and less frequently (2 times/day) than surface
– Sparse upper-air network limits predictive capabilities
Displaying Weather Data: The Station
 CD from
Grenci/Nese has
cool interactive tool
to make and modify
station models, let’s
take a look
So, what’s the temperature trend here?
Eliminate the extraneous data…
How about contours?
 Isopleths connect points of equal value on
a weather map
– Isotherms = lines of equal temperature
– Isobars = lines of equal pressure
– Isotachs = lines of equal wind speed
 Helps forecasters see patterns in data and
estimate values at places where
observations are not taken
How to Contour
 Java applet from University of Wisconsin
 Isopleths that close in on themselves represent a
maximum or minimum of a quantity
 Usually drawn at equal intervals
 Lines are neat/smooth, don’t cross or fork
 More direction given in Grenci/Nese, p. 18-21 and
in lab
 Gradient- A change in some quantity over a
– Ex. Ski slopes
– The larger the change over a given distance, the larger
the gradient
– Large gradients indicated by tightly packed isopleths
– Meteorologists focus on large gradients of temperature,
pressure, etc. because they indicate areas of changing