Download Chapter 12 Meteorology - Belle Vernon Area School District

Chapter 12
Meteorology
Section 12-1
The Causes of Weather
Objectives:
• Compare and contrast weather and climate
• Analyze how imbalances in the heating of the
Earth’s surface create weather
• Describe how and where air masses form
Meteorology is the study of
atmospheric phenomena,
from the ancient Greek
meteor “high in the air”.
The Causes of Weather
Three main categories of “meteors”
• “Hydrometeors”- precipitation
• “Lithometeors” – smoke, dust, and haze
(condensation nuclei)
• “Electrometeors” – thunder and lightning
Weather and Climate
• Atmospheric phenomena interact to affect
the environment and life on Earth
• Weather is defined as the current state of the
atmosphere
• Climate is the average weather over the
course of a 30 year period
A Question of Balance
The Sun heats the surface of the Earth as its
rays hit, some rays hit directly and some hit the
Earth at a low angle.
A Question of Balance
Why then doesn’t the heat continue
to rise at the equator and make it
even warmer than it is?
The air/wind and ocean water
redistribute the heat around the
globe, the equator is the main
entry point.
Air Masses
• An air mass is a large area of air that takes on
the characteristics of the area over which it
forms. The land or water area is called the
source region.
• The characteristics that the air mass can have
are humidity, dryness, hot, or cold.
Classifying Air Masses
•
•
•
•
•
Warm and dry continental tropical (cT)
Warm and humid maritime tropical (mT)
Cold and dry continental polar (cP)
Cold and humid maritime polar (mP)
Arctic (A)
Source Regions
• North America experiences all five types of
air masses and the climate and weather
varies greatly.
Air Mass Modification
• Air masses do not stay in one place for very
long, as they move they transfer heat from
one area to another and they begin to
acquire the characteristics of the source
region that they travel to.
• Table 12-1 pg. 304
Section 12-2
Weather Systems
Objectives:
• Describe how the rotation of Earth affects
the movement of air
• Compare and contrast wind systems
• Identify the various forms of fronts
The Coriolis Effect
• The Earth rotates from East to West as it
spins, this has an effect on the air, the air is
deflected to the right in the northern
hemisphere and to the left in the southern
hemisphere.
• This effect forms very specific and distinct
global wind systems
Coriolis Effect
Global Wind Systems
• There are three basic wind systems in
each hemisphere
–Trade Winds
–Prevailing Westerlies
–Polar Easterlies
Trade Winds
• Wind that occurs from equator to 30 N and
30 S
• Air sinks, warms, and moves toward the
equator in a westerly direction when it
reaches the equator, it rises again and goes
toward 30 N and 30 S again…cycle complete
Prevailing Westerlies
• Winds between 30 and 60 north and south
• The surface winds move toward the poles in
a generally easterly direction (the blow from
west to east, hence the name)
• This wind is responsible for the weather
patterns that move across the United States
and Canada
Polar Easterlies
• Winds that occur from 60 N and 60 S and the
north and south poles
• In both hemispheres the winds are
characterized by cold air
Jet Streams
• Wind, temperature, and pressure are all
related and effect climate and weather
• Differences in temperature and pressure
create wind high up in the atmosphere that
can reach 185 km/h
Jet Stream
Large Scale Weather Systems
Despite the jet streams high altitude, it has a dramatic
effect on weather, it pushes air across the globe
quickly if the air get caught up in the current. It is a hit
and miss situation…
Fronts
• A front is a narrow region separating two air
masses of different densities. The density
differences can be caused by differences in
temperature, pressure, and humidity.
• The interaction between colliding air masses
can bring dramatic changes in weather
Four Types of Fronts
•
•
•
•
Cold Fronts
Warm Fronts
Stationary Fronts
Occluded Fronts
Cold Fronts
• In a cold front, cold dense air pushes warm
air up steeply. As the warm air rises, it begins
to cool and thereby lose its moisture…clouds,
showers, and thunderstorms are associated
with cold fronts
• Solid blue line with blue triangles pointing in
the direction of the fronts motion
Warm Fronts
• A warm front occurs when warm air displaces
cold air near the surface, the air ahead of a
warm front moves slowly and because of less
land friction can gradually push up the cold
air
• Cloudiness and precipitation
• Solid red line with semicircles pointing in the
direction of the front’s motion
Stationary Fronts
• When two similar air masses collide
sometimes neither can advance or overtake
the other this results in a stationary front or a
stall.
• Solid blue line with alternating blue triangles
and red semicircles
Occluded Fronts
• A warm front that gets wedged in between
two cold fronts, the warm air gets pushed
upward and rain is common on both sides of
the cold air boarder
• A purple line with alternating purple triangles
and semicircles pointing in the direction of
motion
Pressure Systems
• Rising air is associated with low pressure and
sinking air is associated with high pressure
• Rising and sinking air combined with the
Coriolis Effect result in rotating high and low
pressure systems
High-Pressure Systems
• In a high pressure system, air is sinking…so
when it finally hits the surface of the Earth it
spreads out pushing everything away.
• This clears the skies
Low-Pressure Systems
• As air rises, it creates space beneath it that is
usually filled in by dense colder air. Lowpressure systems pull air in to the Earth’s
surface as they rise.
• This forms clouds and rain
Section 12-3
Gathering Weather Data and
Analysis
Objectives:
• Describe the technology used to collect
weather data
• Describe problems with long-term forecasts
Surface Weather Data
• Thermometers use mercury or alcohol that
expand when heated are used to measure
temperature
• Barometers use mercury to measure air
pressure
Surface Weather Data
• Anemometer is used to measure wind speed
• Hygrometer measures relative humidity
Upper-Level Data
• While surface data is important, the weather
that we experience is caused by changes that
take place in the upper atmosphere
• Weather Radar including Doppler Radar and
Vipir Radar along with Weather Satellites
Short-Term Forecasts
In the early days of weather forecasting,
meteorologists simply observed what was going on
currently and compared it to the last couple of days
and tried to predict the future based upon that…
Short-Term Forecasts
• The key to unlocking the weather forecast
puzzle is to understand that the atmosphere
acts much like a fluid, so we can apply
concepts like temperature, density and
pressure to understand it.
Digital Forecast
High speed computers can analyze large
amounts of data very quickly and enable
meteorologists to make more dependable
forecasts…the more available data, the better
the forecast.
Long-Term Forecasts
• The further into the future that you try and
predict the weather, the less accurate the
forecasts become.
• Too many variables to predict accurately over
a long period