6 What is an air mass?Because air and moisture move in the atmosphere, weather is constantly changingAir pressure – measured by barometerAn air mass is a large body of air whose temperature and moisture are fairly similar at a given altitude; properties like the part of Earth’s surface over which it formedThere are 5 different air masses that affect the United States
7 How do we classify air masses? Classified via moisture and temperaturecP( continental polar) : cold, dry stablecT( continental tropical) : hot, dry, stable air aloft, unstable at the surfacemP( maritime polar) : cool, moist, unstablemT( maritime tropical) : warm, moist, unstableA (artic):same as cP but colder
9 What is air mass modification? As air masses move from their source region, their temperature and moisture characteristic change with the regions they come in contact with.
10 What is a front?Fronts are boundaries separating different air masses of two different densities caused by temperature, pressure and humidity.clouds, precipitation, and storms occur at frontal boundaries
11 How do warm fronts work? A warm front is warm air displacing cool air Shallow leading edge warm air must “overrun” cold airThese are usually slow movingHot, humid weather to follow
12 How does a warm front look on a weather map? A red-line with solid semi-circles
13 How do cold fronts work? Cold air advances into region of warm air Intensity of precipitation greater, but short livedClearing conditions after front passes. Fair and cool weatherUsually approaches from W or NW
14 How does a cold front look on a weather map? Solid blue line with triangles
15 How does a stationary front form? Surface positions of the front do not moveOften a region of clouds but no precipitation
16 How does a stationary front look on a weather map? When the front starts moving again it returns to either being a cold or warm frontRed semi-circles and blue triangles
17 How do occluded fronts form? Cold front overtakes warm frontInvolves three air masses of different temperaturesOften found close to the low pressure centerStrong winds and precipitation on both sides of the front.
18 How does a occluded front look on a weather map? This occurrence usually results in storms over an areaIn U.S., the colder air usually lies to the westPurple semi circles and triangles.
19 Review questionWhat type of front can be found close to point D ?
20 Review questionWhich of these fronts would you expect to have greater precipitation, but be short lived as the front passes?
21 Review questionGive the name of the air mass that would have the following characteristics:cool, moist, unstable
22 Review questionThat important weather word that refers to the transfer of heat
23 What are pressure systems? Created by air molecules, product of motion, size and number.Since warmed air has more space between the molecules, it’s less dense and risesCooled air is more dense and tends to sinkIn general, air near the equator tends to rise and air near the poles tends to sink
24 Take a look at this Notice the band of clouds around the equator ? This is the ITCZ or inter tropical convergence zone
25 Why do you think there is this band of clouds near the equator?
26 Did you figure it out? Warm, moist air in the tropics rises Cold air can hold less moisture than warm airAs the moist air rises, it condenses and forms clouds!
27 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?
28 Let’s take another look at the weather map Notice that there are H’s and L’s on the mapThere are also blue lines with spikes and red lines with half circles
29 What is air pressure? Air weight that varies over Earth’s surface Warmer air is less dense and exerts less pressureCooler air is more dense and exerts more pressure
30 How does a high pressure system form? When cooler air sinks and is warmed, the air can hold more moistureThis usually means sunny skiesWinds tend to move clockwise around a high in the Northern hemisphere.Anti-cyclonesDiverging and descending winds
31 How do low pressure systems form? When warm air rises and is cooled, the air can not hold as much moistureOften, these areas are associated with precipitation and stormy weatherWinds tend to move counter clockwise around the low in the northern hemisphere.Rising and converging air
32 What to expect on a weather map? If you see a big L in your area you should expect stormy weather and if you see a big H in your area expect clear, sunny skies.
33 What else affects weather? Wind: Movement of air from one temperature or pressure area to anotherDifferent areas of Earth receive different amounts of the Sun’s energyEquator’s warm air, being less dense, is pushed upward by denser, colder airPoles’ cold air, being more dense, sinks and moves along Earth’s surfaceCORIOLIS EFFECT: spinning of the Earth causes moving air to turn to the right in the northern hemisphere and to the left in the southern hemisphere
34 How do global wind patterns affect weather? Wind patterns, caused by convection currents combined with the Coriolis effect, of Earth that affect the world’s weatherNear equator, very little wind and daily rain patterns called the doldrumsSurface winds:Between equator and 30 degrees N and S latitude are steady trade windsBetween 30 and 60 degrees N and S latitude, the westerlies blow in opposite direction from the trade winds. Affect weather in the United States.The polar easterlies blow from northeast to southwest near the north pole and from southeast to northwest near the south pole
35 Global WindsTRADEWINDSEquatorial doldrums (Low P)TRADEWINDS
36 How does the Coriolis effect create weather highways? The rotation of the earth creates the Coriolis effect.The Coriolis effect causes the air and water to be deflected to the right north of the equator.This creates global weather highways
37 What is a jet stream?An irregular, concentrated band of wind occurring at several different locations that supports surface weather conditions.Occur at the boundaries between wind zones.polar jet stream and subtropical jet stream
38 Short Review 7. Warm air holds ( more or less ) moisture than cold air 1.Transfer of heat in liquids or gases_____2. _____ air is dense and tends to sink.3. Band of clouds found around the equator______4. Cold air holds _____ moisture than warm air5. The Coriolis effect causes the air and water to be deflected to the _____ of the equator6. If there is a big H on the weather map where you live, would you expect fair or stormy weather?7. Warm air holds ( more or less ) moisture than cold air8. Which of the weather highways usually controls our weather ?
39 2. COLD 3. ITCZ 4. LESS 5. RIGHT 6. FAIR 7. MORE 8. WESTERLIES 1. CONVECTION2. COLD3. ITCZ4. LESS5. RIGHT6. FAIR7. MORE8. WESTERLIES