Aim: What are factors of Air Pressure?

Observe what happens…

Why do you think the water rushed out of the bottom opening and poured out slower on top?

• the air above it is pushing down on the molecules below

• more pressure at the bottom

Where would you find the highest pressure in a column of air?

• The atmosphere exerts 14.7 lbs of pressure on us.

• Why don't we feel it?

1. What is air pressure?

• The force of air pushing on an area or surface

2. How does temperature affect air?

• When temperature increases, the volume of air ____________ & density ____________. Pressure will _______________.

• When temperature decreases, the volume of air _____________ & density ___________.

Pressure will ______________.

increases decreases

decreases increases

decrease

increase

L

H

3. Measuring air pressure

a. Instrument used is called a barometer

b. Air pressure is also called barometric pressure

c. 2 kinds of barometers:1) Mercury Barometer-

• 1st invented

• When air pressure increases, it pushes down on the mercury pushing it up the tube

2) Aneroid Barometer- • Means “without liquid”• Has an airtight metal

chamber sensitive to pressure change

• When pressure increases, chamber is pushed inward

• Needle on dial moves

4. Units for barometric pressure

• Measured in inches of mercury or

• *Measured in millibars (mb)

900s to 1,000s

*1in of mercury= 33.87 millibars

5. Isobars: connected points of equal air pressure

They are used to show areas of High and Low pressure.

Isobars

• Same rules apply….– Connect equal values– Calculate gradient– Steep side where lines

are closest together

Draw the isobars

6. What does a rising barometer indicate?

• High pressure- Happy weather

• Clearing or pleasant

• Cooling temp

HOC: High Pressure Outward Clockwise

7. What does a falling barometer indicate?

• Low pressure- Lousy weather

• Storm may be coming

• Warming temp

LICC: Low Pressure Inward Counter Clockwise

High vs. Low Air

High: Anticyclone

Clockwise, outward

More dense

Air sinks

Good weather

Dry air

Lows : Cyclones

Counter clockwise, inward

Less DenseRising airMoist airBad weather

Warm air rises, cool air sinks

Maps show us where the rising and sinking air is…..

8. Air moves from H to L-Creates wind

9. Pressure gradients

• Pressure Gradient - the change in air pressure with distance.

• The windiest areas have the steepest gradients.

• Calculate the gradient between A – B and C – D on the following map

A

BD

C

10. Wind barbs on station models

• Tell us direction and speed.

The wind is blowing from the southeast at 15-20 mph

In the plotted station model the 3 digit number to the upper right of the station circle is the barometric pressure.

It will look like 196 for pressures 1000 millibars and higher: and 992 for pressures below 1000.

So, 196 means 1019.6 mb and 992 means 999.2 mb. Basically, add a 10 in front of anything starting with a 0 or 1, and a 9 for anything starting with a 9.

Convert each station and then draw the isobars.1016, 1012, 1008 and 996, 1004, 1008

Barometric pressure on station models

HL

1004 mb

1000 mb

996 mb

1008 mb

1012 mb

1016 mb

How do these storms form?

It's time for a little bit of science magic...

Aim: What are factors of air pressure?

Do Now: Copy the following in your notes section.

1)As altitude increases, density of air ____________.

2) As altitude increases, air pressure ___________.

3)As temperature increases, air volume ___________.increases

decreases

decreases

1. What is wind?• Wind – the horizontal

movement of air

• ***Wind is created when the uneven heating of Earth’s surfaces creates areas of high and low pressure***.

• Air likes to move from Higher pressure (H) to Lower pressure (L)

2. How is wind named and measured?

A Named by the direction and speed from which it comes. Ex. Westerly wind comes from the West

B. Anemometer – measures wind speed using cups connected to a speedometer

C. Wind vane – points to direction that wind comes from

3. What are local winds?

a. Local winds blow over short distances.

b. Part of the weather report. weather.com

c. Examples: Land breezes, sea breezes• Observe an animation of land and sea breezes.

4. Sea and Land Breezes• During day, warmer air

rises over the sand, cooler air sinks over sea.

• Air moves from water to land = sea breeze

• During night, cooler air sinks over the sand, warmer air rises over sea.

• Air moves from land to sea = land breeze

H HLL

Sea and Land breezes are local winds that affect us near TOBAY or Jones Beach

5. Larger local breezes

• Monsoon – sea or land breezes covering a large area that change directions with the seasons (Southeast Asia)

Monsoons

• Winter: A large land breeze, sinking higher pressure air over land keeps moist air off shore =Good weather

• Summer: A large sea breeze, rising, moist air from over the ocean blows onto land = Bad weather, rain

Please Do Now:

6. Global Winds • Global winds blow over a long distance from a specific direction

• Created by uneven heating of equator and poles – H = poles, cool, sinking– L = equator, warm, rising

• Weather patterns are affected by the prevailing winds in an area.

Name the prevailing winds that affect each area…ESRT pg 14

• Latitude – distance from Equator

• Horse latitudes – areas where air sinks, at 30°N and 30°S

• Doldrums – areas with little wind (at the Equator)

7. Global Convection Currents

• Poles have higher pressure (cold air)

• Equator has lower pressure (warmer air)

• Air sinks from poles Equator creating convection cells

Bands of H and L air are created

The convection currents create a distribution system for earth’s heat

http://www.youtube.com/watch?v=QbvHglFyZbg&playnext=1&list=PL9014F9D947576497

8. Why do the winds curve?a. The Earth’s rotation

curves the global winds.

• Right in the Northern hemisphere

• Left in the Southern hemisphere

a. This is called Coriollis Effect.

• Coriolis Force: an artifact of the earth's rotation

• Observe an animation of the Coriolis effect over Earth's surface.

9. Jet Streams• Jet stream – bands of high speed winds• 200 to 400 kilometers/hour• Up near the Tropopause• Can “stear” weather and pollution patterns

http://www.youtube.com/watch?v=CgMWwx7Cll4

http://www.youtube.com/watch?v=UFC6819LS5w&feature=related

ESRT pg 14.

Question…

• Why do you think there are bands of wet and dry air at the equator, 30o, 60o and 90 o?

Wet air is warmer, lower pressure, and rising, creating clouds and rain

Dry air is cooler, higher pressure, and sinking,

creating more arid regions

10. Wind Chill factor• Wind chill factor – increased cooling, increased

evaporation, make the temperature feel colder. The stronger the wind, the colder you feel!

Summary: What affect do winds have on weather?

a. Moves weather

b. Creates weather patterns (seasonal changes)

c. Increases evaporation (dry things out)

d. Creates a wind chill (colder temperatures)

Video Reviews

Brain Pop Wind

http://www.youtube.com/watch?v=kPueXIHGQrg&feature=related

http://www.youtube.com/watch?v=fYfrWLhZy1A&feature=related