Weather - Winds, air masses, air pressures, fronts
Why Do We Have Weather?
An IntroductionTake good notes! There will be a quiz at the end of this presentation.
WHY DO WE HAVE THE WEATHER ?• Why is there wind? Why does it blow from one direction one day and another the next? • Why is it rainy one day and dry the next? • How come it’s cold in the winter?• How can we have hail in the summer?• What causes snow and freezing rain?
If we were to pick one term to helpexplain why we have weather, what do you think would be a good word?You might pick heat or sun….but another good choice would be Convection
Convection is the transfer of heat, usually in gases or liquids.
After the atmosphere is warmed by radiation (sun) and conduction, the heat is transferred throughout the atmosphere by convection.• Since warmed air has more space between the molecules, it’s less dense and rises• Cooled air is more dense and tends to sink• In general, air near the equator tends to rise and air near the poles tends to sink.
Take a look at this! Notice the band of clouds around the equator ?
Why do you think there is this band of clouds near the equator?
Did you figure it out?• Warm, moist air rises• Cold air can hold less moisture than warm air• Warm air can hold more moisture than cold air• As the moist air rises, it condenses and forms clouds! More on this later
Consequences of Rotation: The Coriolis Effect - Video
The Weather Highways Coriolis Effect • The rotation of the earth creates the Coriolis effect. • The Coriolis effect causes the air and water to be deflected to the right when traveling north of the equator. • This creates global weather highways
The Westerlies• Because of our latitude, most of our weather comes from the west• West-to-east motion of the air masses,• Looking at the weather map, what type of weather might we expect?• What type of weather might we expect in a few days?
Let’s break for a short review:1.Transfer of heat in liquids or gases_____.2. _____ air is dense and tends to sink.3. Cold air holds _____ moisture than warm air.4. The Coriolis effect causes the air and water to be deflected to the _____ North of the equator.
How did you do?1. CONVECTION2. COLD3. LESS4. RIGHT
Cloud in a Bottle Demo• Why does it work? – Water molecules in the air (water vapor) normally don’t stick together – Pumping the bottle (high pressure) forces molecules to stick together (compress) – Releasing the pressure (low pressure) allows the air to expand. – As it expands, it cools. – As the molecules cool and condense, they stick together and form water droplets (clouds)
Any Questions?Important thing to know:• Clouds don’t form in thin air, they need a surface.• Pollen, dust, pollution and other tiny specs in the atmosphere are what water droplets condense onto.
Cloud in a Bottle Questions• What things did we • Decrease in pressure, need to happen to cooler temperature, make the cloud in water vapor to condense a bottle? • The atmosphere has• How do these vapor, cooler variables relate to temperatures and the conditions in varying pressures the atmosphere? • To create evaporation,• Why did I rotate t which makes a water the bottle to help vapor the experiment?
Data Table Pumps Results1 Pump2 Pumps3 Pumps4 Pumps5 Pumps
Turn In• How did the increased pressure (pumping air inside the bottle) affect the visibility of a cloud?• How did the decrease in pressure (releasing the cork) affect the visibility of the cloud?
End of Day Questions1. Explain how clouds are formed. (2-3 sentences)2. What type of weather is associated with a high pressure system? Think about the bottle with pressure and without pressure.3. Explain what you should be doing for your homework.4. What affect does the Coriolis Effect have on weather?5. Explain how the cloud in a bottle works.
Quick Review• How are clouds formed?• What type of weather is associated with a high pressure system?• What type of weather is associated with a low pressure system?• What affect does the Coriolis Effect have on weather?
Now What?• Ok, so we know that the weather moves around on these highways and that warm air rises and cold air sinks.• But why is it sunny one day, and rainy the next?
Weather in the Troposphere • Weather occurs in the troposphere • Airplanes usually fly above the troposphere in the stratosphere. • That’s why they can fly above bad weather.
Let’s take another look at the weather map:• Notice that there are H’s and L’s on the map• There are also blue lines with spikes and red lines with half circles• Let’s take a closer look!
These highs and lows move alongthe jet stream and bring us our weather changes.• Video
Jet Stream• A fast flowing river of air found in the atmosphere at around 12 km above the surface of the Earth.• They form at the boundaries of air masses with large differences in temperature, such as of the polar region and the warmer air to the south.
Jet StreamUsing: Hair Dryer, ping pong ball•The hair dryer shoots a column of air up betweenair that is also in the room.•When I tilt the hair dryer left and right, the pingpong ball stays in the column of air.•Jet streams are columns of air in upperatmosphere.•These weather columns are like currents. Thesecolumns of air move throughout the year.
Fronts and Air Masses • Air mass: a large body of air whose temperature and moisture are fairly similar at a given altitude• Fronts: boundaries separating different air masses • There are four different air masses that affect the United States
The Air Masses - Video• cP( continental polar) : cold, dry stable• cT( continental tropical) : hot, dry, stable air aloft, unstable at the surface• mP( maritime polar) : cool, moist, unstable• mT( maritime tropical) : warm, moist, unstable
This map shows the air mass source regions and there paths
Describe Cold and Warm Fronts• Your group should use printer paper to: – Draw and label a cold front on the front side of your paper. – Draw and label a warm front on the back side of your paper. – Describe in your own words what happens using words like: pushes, pressure, storms, air masses, fronts, clouds, and more – Color and decorate it – Use the computer for extra information if needed (diagrams, pictures, better explanations)
High and Low Pressure DemoYour Group Needs: • Bag Represents:•Straw Cold Air System – High Pressure•Book • Book Represents:•Ziploc bag Warm Air System – Low Pressure • The cold air system pushes the warm air•Place the book over system the Ziploc bag. • The warm air rises above the cold air.•Place the straw insidethe Ziploc bag. • The warm air cools as it rises, which•Blow air into the bag. makes the water vapor (GAS) condense and form clouds (possible precipitation).
Cold Front is Moving In – 5:28• As the warm air was pushed up (low pressure allowed it to rise), the warm air cooled and condensed.• The condensed water vapor (gas) caused clouds, which could not hold as much moisture (water vapor [gas]).• This caused rain and thunderstorms.• What will the weather be like after the cold front passes through?
Stationary Fronts• Surface positions of the front do not move• Often a region of clouds• Neither the cold or the warm front are ‘winning’.
Ready for a little quiz? You’ll need a sheet of paper• Write your answers as we go • Here we go!
1.• What causes a low pressure system to create clouds and sometimes precipitation? L
2.• What type of front can be found close to point D ?
3.• Which of these fronts would you expect to have greater precipitation, but be short lived as the front passes?
4. • Give the name of the air mass that would have the following characteristics: • cool, moist, unstable
5.That important weather word that refers to the transfer of heat
6.In general, air near the equator tends to_____ ( rise or fall ).
7. ________ causes air andwater to be deflected to the right north of the equator.
8.Which of the weather highways usually controls our weather
9.Warm air holds ( more or less ) moisture than cold air?
10.• If there is a big H on the H weather map where you live, would you expect fair or stormy weather?
Answers1. The low pressure allows the warm air to rise. As the warm air rises, it cools. Water vapor cools and condenses into clouds. Cold air can hold less moisture, so eventually it might rain. 8. Westerlies2. Cold front 9. More3. Cold front 10. Fair4. Maritime polar (mP)5. Convection6. Rise7. Coriolis Effect