Meteorology
12.1 The Causes of Weather
12.2Weather Systems
12.3 Gathering Weather Data
12.4 Weather Analysis

Weather is the study of atmospheric
phenomena.
◦ Greek meaning of meteorology is
 Meteor- high in the sky
◦ Clouds, raindrops, snowflakes, fog, dust, and rainbows
are types of atmospheric meteors.

ology-the study of
The Causes of Weather
Weather
Climate
Description
Atmospheric
phenomena
interacting
Long-term variations
of weather
Short or long term;
measure of variations
Short-term; minutes,
hours, days, weeks,
or months
Long term; 30 year
or more
Weather vs. Climate
A Balance Act
Type of Air Masses
Source of Air
Masses
Weather
Associated with Air
Mass
Continental tropical
Deserts of Southwest
and Mexico
Hot, dry summers
Maritime tropical
Tropical and
subtropical oceans
Hot, humid summers
Continental polar
Interior of Canada
and Alaska
Frigid winters; cool
dry summers
Maritime polar
Cold water of North
Atlantic and North
Pacific
Heavy rains in winter
on West Coast
Arctic
Latitudes over 60 N
Extreme cold
Air Masses
Air Masses
The Coriolis effect is where moving
particles such as air are deflected to the
right in the northern hemisphere and to
the left in the southern hemisphere.
 It combines with the heat imbalance to
create distinct global wind systems

◦ These systems transport colder air to warmer
areas and warmer air to colder areas.
Weather systems
Coriolis effect

Three basic wind systems
◦ Trade winds
 Occur at 30o North and South Latitude
 Also know as the Hadley cell
◦ Air sinks, warms, and moves toward equator in a
westerly direction, it rises again and moves back toward
latitude 30 , where it sinks and starts again.
 Convergence
◦ Occurs when the trade winds from both hemispheres
move together from two different directions and air
converges, is forced upward, and creates an area of low
pressure.
Global Wind Systems
◦ Prevailing Westerlies
 Flows between 30o and 60o north and south
latitude in a circulation pattern opposite that of
the trade winds.
 Responsible for much of the movement of
weather across the United States and Canada
 Move weather in the United States from west to
east across the continent.
◦ Polar Easterlies
 Lies between 60o latitude and the poles
 Characterized by cold weather

El Nino describes episodes of ocean
warming that affect the eastern tropical
Pacific.

La Nina periods occur when the surface
temperatures in the eastern Pacific are
colder than average.
◦ increase in precipitation
◦ Increase in hurricane activity
El Nino vs. La Nina

How would the weather be affected if the
jet stream moved north?
◦ If the jet stream dipped south of the north east
location, then the colder, arctic air would be
dragged down with it.
◦ This would bring colder weather to the north
east.
◦ If the jet stream moved north, the warmer
weather from the southeast would enter the
northeast region.
Jet Streams
Jet Stream
Type of front
Map Symbol
Description of
air movement
Associated
Weather
Cold Front
Cold air
Clouds,
displaces warm showers,
air, forces warm thunderstorms
air up
Warm Front
Warm air
displaces cold
air
Very cloudy,
precipitation
Stationary
Front
Two air masses
meet, neither
advances
Some-what
cloudy, light
precipitation
Occluded Front
Fast moving
cold air wedges
warm air up
where it gets
trapped
between two
cold air masses
precipitation
Fronts
Cold Front

http://www.phschool.com/atschool/phscie
xp/active_art/weather_fronts/

Low Pressure Systems

High Pressure Systems

Characteristics in Common
◦ Winds move counterclockwise in northern
hemisphere
◦ Rising air
◦ Stormy weather
◦ Winds move clockwise in northern hemisphere
◦ Sinking air
◦ Fair weather
◦ Formed by internal forces
◦ Air moves in circular motion
Pressure Systems
Pressure Systems
Instrument
What does it
measure?
How does it work?
Thermometer
Temperature
Mercury or alcohol
expands when
warmed
Barometer
Air Pressure
Changes in pressure
measured by changes
in height of column of
mercury
Anemometer
Wind Speed
Cupped arms that
rotate as wind blows
Hygrometer
Relative Humidity
Wet- and dry-bulb
thermometers
Cellometer
Height and amount of Data collected by
cloud cover
ASOS
Gathering Weather Data

Doppler Effect is the change in wave
frequency that occurs in energy as the
energy moves toward or away from an
observer.
Weather Radar
Scientist can
determine
location of
precipitation
and clouds
using
Radar
Tracks
precipitation
Satellites
Tracks Clouds
Weather Satellite
Infrared imagery detects differences in
thermal energy
 The temperature of a cloud tells
meteorologists about its type and height.

Weather Satellites

Isopleths are lines that connect points of
equal or constant values.
◦ Isotherm
 Represents lines of equal temperature
 Used to identify temperature gradients
◦ Isobar
 Represents lines of equal pressure
 Used to indicate how fast the wind blows
◦ The closer the lines the faster the wind.
Weather Analysis