High and Low Pressure High and Low Pressure Weather SystemsWeather Systems

Air (Atmospheric) Pressure Air (Atmospheric) Pressure • Is the force exerted by

air particles

• Air moves from an area of high pressure to an area of low pressure.

• The moving air is called wind.

Air Pressure is always changing Air Pressure is always changing and depends on factors such as:and depends on factors such as:

• Temperature/Time of day - hotter air has higher pressure

• Altitude – higher up = lower pressure

• Humidity – higher = lower pressure

• Migrating weather systems – Highs and Lows

Low Pressure SystemsLow Pressure Systems

• Bring cloudy, rainy or stormy weather.

• Warm air is forced up.

• As it rises, the air spins

• As the air rises, it also cools and water vapor condenses to form clouds.

• Low pressure systems can cause stormy weather and extreme weather events like cyclones, hurricanes and typhoons

Represented on a weather map by:

• isobars with an “ L ” written in the

central most isobar

•arrows traveling clockwise in the Southern Hemisphere or counter-clockwise in the Northern Hemisphere

High Pressure SystemsHigh Pressure Systems• Bring clear blue skies, calm winds, cooler

temperatures and lower chance of precipitation.

• Drier air usually results in a greater range of high and low temperatures

• Cold air falls down

• As it falls, the air spins

• As the air falls, it loses humidity and clear skies are the result

Represented on a weather map by

•isobars with an “H” in the central most isobar

•arrows showing which direction the wind is flowing (clockwise in Northern Hemisphere, counter-clockwise in the Southern Hemisphere).

Highs and Lows on Weather MapsHighs and Lows on Weather Maps

The Coriolis EffectThe Coriolis Effect• Caused by the Earth’s rotation• Results in the curving of moving

objects, including air • It is one thing that causes wind

and the direction of prevailing winds that exist in each major latitude belt

•

Prevailing WindPrevailing Wind

• The direction the wind blows most of the time in a certain location

Jet StreamsJet Streams• Narrow currents of fast moving air flowing

in the upper levels of the atmosphere

• Flow between cold and warm air masses

• Usually move weather systems from place to place – always WEST to EAST

Northern vs. Southern Northern vs. Southern HemisphereHemisphere

The direction that the air spins is opposite

Highs vs. LowsHighs vs. Lows

Highs vs. LowsHighs vs. Lows

Clockwise = Anti- Cyclone Counter-Clockwise = Cyclone

ADD

Highs & Lows on a weather mapHighs & Lows on a weather map

Review VideoReview Video

• http://www.youtube.com/watch?v=aiYyCurh_SU&safe=active

• Fox 9 weather 3:24

Question Page – do as notesQuestion Page – do as notes

Question 1Question 1

• Why do high pressure systems cause clear skies?

• B/c Cool air falls. Cool air does not hold much moisture as warm air, thus preventing the formation of clouds.

Question 2Question 2

• Why do Low pressure systems cause clouds?

• B/c Warm air rises and cools, causing water vapor to condense and form clouds

Question 3Question 3

• Why do high pressure systems cause weather to stay the same for days?

• B/c HP systems are large, usually the size of an entire air mass, therefore they take a longer time to move out of an area.

The Crushing Can - videosThe Crushing Can - videos

• Pop Can Crush• http://www.stevespanglerscience.com/experi

ment/incredible-can-crusher

• 55 gallon Barrel Crush

• http://www.youtube.com/watch?v=JsoE4F2Pb20&safe=active

AssignmentAssignment

• Do the Crushing Can lab pages 41- 42

• Do the Worksheets on pages 44 - 50

Page 44 answersPage 44 answers

• 1. Solar Energy• 2. Clouds• 3. Earth’s Rotation• 4. The Jet Stream• 5. Prevailing Winds• 6. Ocean Currents• 7. Lithosphere• 8. Hydrosphere

Page 45 answersPage 45 answers1. Cold, warm, stationary, occluded

2. Warm – moves slow, gentle, warm air moves towards

colder air, gentle sloped straight boundary line

Cold – moves fast, stormy, cold air moves toward

warmer air, steeply curved boundary line

3. Cold fronts – cold air mass over takes a warm

air mass

4. High – clear sky, nice weather

Low – cloudy, bad weather

5. High – clockwise (NH), falling air, clear, sunny

Low – counterclockwise (NH), rising air, clouds, rain

Page 46 answersPage 46 answers

1. Warm air rises and cools. Water vapor condenses out of the air to form clouds.

2. In A, the warm air is less dense.

3. In B the warm air is forced up by the mtn

4. C

5. A

6. E

7. B

Page 46 continuedPage 46 continued8. (b) Air Mass

9. (a) Condensation

10. (c) Advective

11. (b) Precipitation

12. (a) Coriolis Effect

13. (b) Jet Streams

14. (c) Polar Easterlies

15. True or False. True – Clouds form when air rises and cools. False – different things can make air to rise (fronts, mountains, etc)

Page 47 answers

Answers to Highs, Lows and Answers to Highs, Lows and Fronts Worksheet. P. 48Fronts Worksheet. P. 48

Name Clouds Before Front arrives

Air that Rises

Weather after Front passes

Time to pass

Warm Front Cirrus, Altostratus Warmer Warm, humid, cloudy Long

Cold Front Cumulonimbus Warmer Dry, cold, Clear Short

2. A) H = High Pressure SystemB) Clear, blue sky, sunny, cool, stable, mild wind

1.

3. In terms of fronts – a warm front is arriving,

and hence the formation of cirrus clouds

•The thick grey blanket are altostratus clouds

•By night, it is likely that nimbostratus clouds will have formed and light rain will have begun to occur.

•The light rain will continue into the next day b/c warm fronts pass slowly

Page 49 answersPage 49 answers

1. B 2. C 3. A

4.

a) NE

b) SE

Page 49 question 5Page 49 question 5Page 49 Question 5

Page 50 answersPage 50 answers1. Warm front, Cold Front, Stationary Front

2. High pressure system, cold air

3. SE, Cold front

4. Moving blob of air

5. Cold Front

6. Stationary Front

7. Cold Air Mass

8. Clear due to High Pressure

9. Cold air mass passed over; caused snow