1. AOSC 200 Lesson 15

2. Fig. 8-18, p. 223 Computer generated image of Hurricane Mitch – October 26, 1998. Near Honduras Note the distinct ‘eye’ and the large extent of the hurricane

4. Fig. 8-19, p. 224 Damage from hurricane Andrew, August 1992

6. Fig. 8-23, p. 228

8. Fig. 8.29

9. TROPICAL CYLONES THESE INTENSE TROPICAL STORMS ARE KNOWN BY DIFFERENT NAMES IN VARIOUS PARTS OF THE GLOBE: HURRICANES - ATLANTIC TYPHOONS - WESTERN PACIFIC CYCLONES - INDIAN OCEAN MOST FORM BETWEEN THE LATITUDES OF 5 TO 20 DEGREES. LESS THAN 5 DEGREES, THE CORIOLIS FORCE IS TOO SMALL MORE THAN 20 DEGREES, THE TEMPERATURE OF THE OCEAN IS TOO COLD MUST HAVE WIND SPEEDS OF MORE THAN 119 KM PER HOUR AND HAVE A ROTARY CIRCULATION TO BE A HURRICANE/TYPHOON

10. TROPICAL CYCLONE FORMATION HURRICANES DEVELOP MOST OFTEN WHEN OCEAN WATERS HAVE REACHED MAXIMUM TEMPERATURES - 25 C OR HIGHER. INITIAL STAGE IS SOME FORM OF DISTURBANCE - NAMED BY THE WEATHER SERVICE AS TROPICAL DISTURBANCES. ONLY A FEW TROPICAL DISTURBANCES DEVELOP 119 KM PER HOUR WINDS IF WINDS 61 - TROPICAL STORM NAMES GIVEN WHEN STORM REACHES TROPICAL STORM STATUS

11. TROPICAL CYCLONES MATURE TROPICAL CYCLONES AVERAGE ABOUT 600 KM ACROSS BAROMETRIC PRESSURE CAN DROP ACROSS CYCLONE FROM 1010 TO 950 MILLIBARS THIS GENERATES RAPID, INWARD SPIRALING WINDS. AS AIR MOVES CLOSER TO CENTER ITS VELOCITY INCREASES CONSERVATION OF ANGULAR MOMENTUM. IN THE CENTER OF THE EYE THE AIR IS DESCENDING – HENCE IT IS FREE OF CLOUDS.

12. TROPICAL CYCLONES MOIST SURFACE AIR IS TURNED UPWARD AND ASCENDS. AS MOIST AIR MOVES UP IT COOLS AND WATER VAPOR CONDENSES. THIS PROVIDES LATENT HEAT TO INCREASE BUOYANCY OF THE RISING AIR. NEAR THE TOP OF THE HURRICANE THE AIRFLOW IS OUTWARD. AIR MUST BE PULLED AWAY FROM HURRICANE AT THE TOP – REINFORCEMENT FROM ABOVE. THE CENTRAL DOUGHNUT AREA HAS DOWNWARD MOTION, IS CALLED THE EYE OF THE STORM EYE WALL CONTAINS STRONGEST WINDS.

13. Fig. 8-24, p. 229

14. Schematic of a Hurricane

17. TROPICAL CYCLONES TROPICAL CYCLONES DIMINISH WHEN THEY MOVE OVER COLDER OCEAN WATERS MOVE ONTO LAND REACH A LOCATION WHEN LARGE-SCALE FLOW ALOFT IS UNFAVORABLE

19. Fig. 8.27

21. STORM SURGE

23. Fig. 8.35

24. TROPICAL CYCLONE DAMAGE WIND DAMAGE STORM SURGE INLAND FLOODING

25. Fig. 8-39, p. 247

26. 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

27. Fig. 9.3 Major air masses of the world

28. 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

29. 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

30. CLASSIFICATION THUS WE GET: cA - CONTINENTAL ARCTIC cP - CONTINENTAL POLAR cT - CONTINENTAL TROPICAL mT - MARITIME TROPICAL mP - MARITIME POLAR mE - MARITIME EQUATORIAL

31. Fig. 9.4 Major air masses that affect North American weather

32. 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

33. Siberian Express. An extremely cold arctic air mass covers nearly 90% of the United States.

34. Fig. 9.6 Ice in a Florida orange grove as a result of a continental arctic air mass coming down from Canada.

35. Fig. 9.8 Temperature at Madison, WI, as a result of a continental arctic air mass

36. 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

37. Northeaster.

38. 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.

39. Fig. 9.9 Maritime Tropical air mass

40. 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

41. Box 9.2 Average annual snowfall for the Great Lakes region

42. 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?

43. Box 9.2 Formation of Lake Effect snowfall

44. 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.

45. 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

46. Fig. 9.14 Weather associated with a cold front

47. Fig. 9.15 Warm, moist air is forced upward by cold front

48. 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.

49. Fig. 9.16 Surface weather associated with a warm front

50. Fig. 9.17 Warm, moist air is slowly raised as it flows over the cold air

51. 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,.

52. Fig. 9.18 Occluded Fronts

53. 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.