Earth Science
Section 16.2 Notes
Air Mass
- Large body of air
- Has properties similar to the surface over which it develops
- 6 major air masses affect the U.S.
High and Low Pressure Systems
- Winds blow from areas of high to areas of low pressure
- Earth’s rotation causes winds to swirl in a counter clockwise
direction
Cyclone
- Large, swirling areas of low pressure
- Associated with stormy weather
- Winds blow away from a center of high pressure
Anticyclone – high pressure area with fair weather
Barometer – Measures air pressure
Low Pressure Systems
- Regions of rising air
- Cloudy weather
High Pressure Systems
- Difficult for clouds to form
- Good Weather
Front - Boundary between two air masses of different density,
moisture or temperature
Four Types of Fronts
1) Cold – Cold air advances toward warm air
2) Warm – Lighter, warm air advances toward heavy cold air
3) Occluded – 3 air masses at different temperatures - cool –
warm- cold
4) Stationary – Boundary between air masses stops advancing
Severe Weather
Thunderstorms
- Involve rain, hail and wind
- Occur in warm, moist air masses and along fronts
- Cumulonimbus clouds form when warm air cools and
condenses
- Raindrops form
- Sinking, rain-cooled air and strong updrafts of warm air
cause strong winds
- Hail may form
- Flooding may occur
- Damaging winds
Lightning and Thunder
- Different parts of a cloud become oppositely charged and a
current flows between them
- Lightning can occur within a cloud, between clouds or
between a cloud and the ground
- Thunder results from the rapid heating of air around a
lightning bolt.
- Rapid movement of molecules forms sound waves
Tornado
- Violently rotating column of air in contact with the ground
- Wind at different heights blows in different directions and at
different speeds causing wind shear
- Rotating column parallel to the ground is created
- Updraft tilts the column creating a funnel cloud
- If the funnel cloud touches the surface, it is a tornado
Hurricane
- Most powerful storm
- Large, swirling, low pressure system that forms over the
Atlantic Ocean
- Winds of at least 119 km/h
- Pacific Ocean – typhoon
- Indian Ocean – cyclone
- High winds, tornadoes, heavy rain, high waves(flooding)
cause damage
- Loses energy when it reaches land
Blizzard
- High winds
- Cold Temps
- Low Visibility due to blowing snow for 3 hours or more
Earth Science
Section 16.3 – Weather Forecasts
Meteorologist
- Person who studies weather
- Take weather information to make weather maps
- Use weather maps to make forecasts
The National Weather Service depends on 2 sources of weather
information:
1) Data from upper atmosphere
2) Data from Earth’s surface
Station Model – shows the weather conditions at a specific location
on Earth’s surface
Isotherms – lines on weather maps that connect locations of equal
temperature
Isobar
- Line that connects locations of equal pressure
- Close together – Large pressure difference over a small area –
strong winds
- Far apart – Small difference in pressure – gentle winds