aosc 200 lesson 9
DESCRIPTION
AOSC 200 Lesson 9. Clear area in middle of the image is a hot, cloud-free air mass – resulting heat wave caused 200 deaths in the Midwest. Fig. 9.2. Major air masses of the world. Fig. 9.3. AIR MASS. AN AIR MASS IS A BODY OF AIR 1500 KM OR MORE ACROSS AND SEVERAL KM THICK - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/1.jpg)
AOSC 200Lesson 9
![Page 2: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/2.jpg)
Fig. 9.2
Clear area in middle of the image is a hot, cloud-free air mass – resulting heat wave caused 200 deaths in the
Midwest
![Page 3: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/3.jpg)
Fig. 9.3
Major air masses of the world
![Page 4: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/4.jpg)
AIR MASS
• AN AIR MASS IS A BODY OF AIR 1500 KM OR MORE ACROSS AND SEVERAL KM THICK
• AS THE AIR MASS MOVES IT CARRIES ITS TEMPERATURE AND MOISTURE CONDITIONS WITH IT.
• CAN TAKE SEVERAL DAYS FOR AN AIR MASS TO TRAVERSE AN AREA.
• WHERE THE AIR MASS ORIGINATES IS KNOWN AS THE SOURCE REGION
![Page 5: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/5.jpg)
• http://www.youtube.com/watch?v=neWN-lEmnbk
• http://www.youtube.com/watch?v=neWN-lEmnbk
![Page 6: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/6.jpg)
CLASSIFICATION• FOUR BASIC CATEGORIES OF AIR MASSES:
• POLAR - P• ARCTIC - A• TROPICAL - T• EQUATORIAL - E• TWO DESIGNATIONS OF SURFACE IN SOURCE REGION
• MARITIME - m• . CONTINENTAL - c
![Page 7: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/7.jpg)
CLASSIFICATION
• THUS WE GET:
• cA - CONTINENTAL ARCTIC
• cP - CONTINENTAL POLAR
• cT - CONTINENTAL TROPICAL
• mT - MARITIME TROPICAL
• mP - MARITIME POLAR
• mE - MARITIME EQUATORIAL
![Page 8: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/8.jpg)
Fig. 9.4
Major air masses that affect North American weather
![Page 9: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/9.jpg)
CONTINENTAL POLAR (cP) AND CONTINENTAL ARCTIC (cA)
• THESE ARE COLD AND DRY AIR MASSES
• CONTINENTAL POLAR AIR COMES FROM POLEWARD OF THE 50TH PARALLEL.
• CONTINENTAL ARCTIC AIR COMES FROM OVER THE ARCTIC BASIN, AND THE GREENLAND ICE CAP.
• OFTEN CALLED THE SIBERIAN EXPRESS OR ARCTIC CLIPPER
![Page 10: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/10.jpg)
Siberian Express. An extremely cold arctic air mass covers nearly 90% of the United States.
![Page 11: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/11.jpg)
Fig. 9.6
Ice in a Florida orange grove as a result of a continental arctic air mass coming down from Canada.
![Page 12: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/12.jpg)
Fig. 9.8
Temperature at Madison, WI, as a result of a continental arctic
air mass
![Page 13: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/13.jpg)
MARITIME POLAR (mP) AIR MASSES
• FORM OVER OCEANS AT HIGH LATITUDES• COOL TO COLD AND HUMID. TWO IMPORTANT REGIONS FOR THE US ARE THE NORTH PACIFIC AND NORTHWESTERN ATLANTIC.
• DURING THE WINTER, mP FROM THE PACIFIC USUALLY BEGIN AS cP FROM SIBERIA.
• OROGRAPHIC FORCING PRODUCES HEAVY SNOW OVER THE WEST COAST.
• IF WE HAVE STRONG CYCLONIC FLOW OVER LOWER EASTERN US, THEN UPPER PART BRINGS IN ATLANTIC mP - NOR'EASTER
![Page 14: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/14.jpg)
Northeaster.
![Page 15: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/15.jpg)
MARITIME TROPICAL (mT) AIR MASSES
• THOSE AIR MASSES WHICH AFFECT THE US MAINLY ORIGINATE FROM THE GULF OF MEXICO, THE CARIBBEAN SEA, OR THE ADJACENT WESTERN ATLANTIC OCEAN.
• THESE AIR MASSES ARE LARGELY RESPONSIBLE FOR THE HOT AND HUMID WEATHER OF THE SUMMER OVER THE EASTERN AND CENTRAL PARTS OF THE US.
• GIVE US MUCH OF THE WINTERTIME PRECIPITATION OVER THE EASTERN AND CENTRAL STATES, WHEN THE AIR MASS IS FORCED UP OVER COLDER AIR MASSES.
![Page 16: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/16.jpg)
Fig. 9.9
Maritime Tropical air mass
![Page 17: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/17.jpg)
CONTINENTAL TROPICAL (cT) AIR MASSES
• NORTH AMERICA NARROWS AS IT EXTENDS SOUTHWARD.
• SO THERE IS NO EXTENSIVE SOURCE REGION FOR THESE AIR MASSES.
• HOT, DRY AIR.• WHEN cT AND mT INTERACT OVER THE SOUTH-CENTRAL US THE CONTRAST CAN BE SO LARGE THAT METEOROLOGISTS LABEL IT AS A DRYLINE.
• THE DRYLINE PROVIDES A FOCUS FOR THUNDERSTORMS JUST LIKE A COLD FRONT
![Page 18: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/18.jpg)
Box 9.2
Average annual snowfall for the Great Lakes region
![Page 19: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/19.jpg)
http://www.youtube.com/watch?v=o_ioV4MAUnMhttp://www.youtube.com/watch?v=o_ioV4MAUnM
![Page 20: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/20.jpg)
Lake Effect Snowfall• Two distinct patterns.• Firs,t the snowfall increases as one goes northward.
• To be expected as the temperature gets colder as one goes northward.
• Second, regions with localized maximum in snowfall are on the Southerly and Easterly side of the Lakes.
• Why?
![Page 21: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/21.jpg)
Box 9.2
Formation of Lake Effect snowfall
![Page 22: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/22.jpg)
Lake Effect Snowfall
• As the polar air mass moves over the Lakes the lower layers of the air mass are warmed and moistened by the lake.
• This makes the air mass unstable.• The moist warm air rises and forms clouds – snow.
• Effect can be enhanced if the air mass is lifted by hills.
• Lake effect snow is most prevalent in early winter.
![Page 23: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/23.jpg)
• http://www.youtube.com/watch?v=MbfCre7-wCw
![Page 24: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/24.jpg)
FRONTS
• POLAR FRONT THEORY FIRST PUT FORWARD BY BJERKNES AND HIS COLLEAGUES IN. NORWAY, 1914
• FRONTS ARE BOUNDARY SURFACES THAT SEPARATE AIR MASSES.
• IN GENERAL ONE AIR MASS IS WARMER AND OFTEN CONTAINS MORE MOISTURE THAN THE OTHER.
• FRONTS FORM BETWEEN TWO CONTRASTING AIR MASSES.
• IN GENERAL ONE AIR MASS MOVES FASTER THAN THE OTHER.
• THIS PROCESS IS KNOWN AS OVERRUNNING
![Page 25: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/25.jpg)
Fig. 9.14
Weather associated with a cold front
![Page 26: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/26.jpg)
Fig. 9.15
Warm, moist air is forced upward by cold front
![Page 27: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/27.jpg)
COLD FRONT
• COLD AIR MOVING INTO WARM AIR• SHOWN ON WEATHER MAP BY TRIANGLES POINTING INTO THE WARM AIR.
• AVERAGE COLD FRONT MOVES AT 35 KM PER HOUR. WARM FRONT AT 25 KM PER HOUR.
• WARM AIR IS FORCEFULLY MOVED UPWARD. • IF WARM AIR IS MOIST THE LARGE AMOUNTS OF LATENT HEAT IS RELEASED.
• THUNDERSTORMS, HEAVY DOWNPOURS, VIGOROUS WIND GUSTS, TORNADOS
• DARK BAND OF OMINOUS CLOUDS AS FRONT APPROACHES.
![Page 28: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/28.jpg)
Fig. 9.16
Surface weather associated with a warm front
![Page 29: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/29.jpg)
Fig. 9.17
Warm, moist air is slowly raised as it flows over the cold air
![Page 30: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/30.jpg)
WARM FRONT
• WARM AIR MASS MOVING INTO COLD AIR MASS.• SHOWN ON WEATHER MAP BY A LINE WITH SEMICIRCLES EXTENDING INTO THE COOLER AIR
• AS WARM AIR CLIMBS OVER THE RETREATING COLD AIR, IT EXPANDS AND COOLS - CLOUDS - PRECIPITATION
• CIRRUS CLOUDS FOLLOWED BY CIRROSTRATUS AND THEN NIMBOSTRATUS.
• LIGHT TO MODERATE PRECIPITATION OVER A LARGE AREA AND FOR EXTENDED PERIODS.
• IF RAIN EVAPORATES IN COLD AIR MASS THEN HIGH HUMIDITY CAN RESULT - HEAVY FOGS,.
![Page 31: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/31.jpg)
Fig. 9.18
Occluded Fronts
![Page 32: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/32.jpg)
OCCLUDED FRONTS
• OCCLUDED FRONTS• WHEN A COLD FRONT OVERTAKES THE WARM FRONT, FORCING THE WARM AIR UP ABOVE THE TWO COLD AIR MASSES.
• WEATHER IS COMPLEX.• CAN HAVE WARM OCCLUDED FRONTS (COLD FRONT IS WARMER THAN FRONT IT OVERTAKES) - PACIFIC COAST.
• COLD OCCLUDED FRONT IS REVERSE OF ABOVE - EAST OF THE ROCKIES.
![Page 33: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/33.jpg)
Birth of a an Extratropical Cyclone
![Page 34: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/34.jpg)
![Page 35: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/35.jpg)
LIFE CYCLE OF AN EXTRATROPICAL CYCLONE
• THE LEFT HAND SIDE SHOWS HOW BJERKNES DEPICTED THE LIFE CYCLE.
• FORM ALONG THE LINE BETWEEN THE POLAR AIR MASS AND THE MARITIME TROPICAL AIR MASS.
• SHEARING ACTION OF OPPOSING WINDS PRODUCES CYCLONIC MOTION.
• UNDER SUITABLE CONDITIONS FRONTAL SURFACE WILL ASSUME A WAVE SHAPE.
• OPEN WAVE DEVELOPS COLD AND WARM FRONTS• COLD FRONT CATCHES UP WITH WARM FRONT• CYCLONE DISSIPATES
![Page 36: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/36.jpg)
Fig. 10-6a, p. 281
![Page 37: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/37.jpg)
Fig. 10-6b, p. 281
![Page 38: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/38.jpg)
Box 10.1
![Page 39: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/39.jpg)
Box 10.1
![Page 40: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/40.jpg)
Cyclones over the Rockies
• In order for Cyclones formed over the Pacific to each the mid-west they have to go over the Rockies.
• This squeezes the cyclone down, which increases the radius of rotation
• This decreases the rate of rotation (conservation of angular momentum)
• The cyclone appears to weaken.• East of the Rockies the cyclone expands and regains its full rate of rotation
![Page 41: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/41.jpg)
Fig. 10.11
![Page 42: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/42.jpg)
![Page 43: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/43.jpg)
Dish-pan Experiment
![Page 44: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/44.jpg)
Fig. 6.11
Centrifugal Force
![Page 45: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/45.jpg)
Centrifugal Force
![Page 46: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/46.jpg)
Fig. 10-12, p. 290
![Page 47: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/47.jpg)
Formation of Cyclones
• .CLOSE RELATIONSHIP BETWEEN SURFACE DISTURBANCES AND THE FLOW IN THE JET STREAM.
• .FOR A MID-LATITUDE CYCLONE TO FORM:CYCLONIC FLOW MUST BE ESTABLISHED
• .INWARD FLOW OF AIR NEAR SURFACE MUST BE SUPPORTED BY OUTFLOW ALOFT.
• DIVERGENCE AND CONVERGENCE ALOFT• TOTAL SPIN / CYCLONIC HEIGHT = CONSTANT• .VORTICITY - TENDENCY OF AIR TO ROTATE IN A WHIRLPOOL LIKE VORTEX – SPIN AROUND A VERTICAL AXIS
![Page 48: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/48.jpg)
Fig. 10.13
![Page 49: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/49.jpg)
![Page 50: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/50.jpg)
![Page 51: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/51.jpg)
![Page 52: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/52.jpg)
![Page 53: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/53.jpg)
![Page 54: AOSC 200 Lesson 9](https://reader036.vdocument.in/reader036/viewer/2022062322/568148f7550346895db618fa/html5/thumbnails/54.jpg)