1. AOSC 200 Lesson 8

2. Oceanography The oceans play three important roles in determining weather and climate (1) They are the major source of water vapor needed to form precipitation. This drives the hydrological cycle. This water vapor is also the source of the latent heat that, when released in condensation, is the driving force behind severe weather.

3. Fig. 8-1, p. 210 Energy gains and losses in the oceans

4. Oceanography (2) They exchange heat with the atmosphere. The previous slide showed the net energy gains and losses in the oceans. On average the ocean gains energy in the summer and loses energy in the winter. The oceans cool the atmosphere in the summer and heat the atmosphere during the winter The oceans act like a thermostat.

5. Fig. 8-2, p. 211

6. Oceanography (3) The oceans transport energy poleward. The Pacific basin and the North Atlantic basin have two major currents that transport heat to the Pole. The Gulf Stream The Kuroshio Current These will be discussed later.

7. Fig. 8-3, p. 212

8. Fig. 8-4, p. 213

9. Ocean Temperature Can divide the ocean into three layers Top 100 meters is called the surface zone, or mixed layer Wind driven waves and currents mix this layer – uniform temperature Bottom layer, below about 1000 meters, cold water -1 to 3 ºC Transition zone – Thermocline Sea Surface Temperature (SST)

10. Fig. 8-5, p. 213 Sea Surface Temperature

11. Fig. 8-6, p. 214 Major Ocean Currents

12. Fig. 8-8, p. 215

13. Ocean Currents You may note that the currents actually move to the right of the wind direction Why? Because the Coriolis force also acts on the oceans. At the surface of the ocean the wind exerts a force on the water due to friction between the waves and the wind. As soon as the ocean moves it acquires a Coriolis force so that the resultant motion is to the right of the wind direction in the Northern hemisphere. But this is only true for the top layer of the ocean

14. Ekman Spiral The second layer is dragged along by the top layer by a frictional force. It in turn will also acquire a Coriolis force and the resultant motion of the second layer will be to the right of the first layer. This process continues down through the ocean until the direction of the ocean current at a depth can be at 90 degrees to the direction at the surface Known as the Ekman spiral Currents induced in the deeper parts of the ocean are called Ekman transport.

15. Fig. 8-9, p. 215

17. Upwelling along the California Coast Los Angeles is at about 30 degrees latitude. At most times of the year there is a high pressure system in the Pacific and this can produce Northerly winds along the coast. The resultant Ekman spiral produces a current that flows away from the coast. Water from deep in the ocean is brought up to replace the water transported away. This is know as upwelling. This water is full of nutrients – large population of plankton – bottom of food chain – good fishing.

18. OCEAN CURRENTS MASSIVE PATTERN OF WATER FLOW WINDS BLOW STEADILY OVER THE OCEAN AND FRICTION PUSHES THE OCEAN SURFACE IN THE DIRECTION OF THE WINDS. OCEAN CURRENTS TEND TO FOLLOW THE WIND PATTERNS HOWEVER THE CORIOLIS FORCE WILL MAKE THE OCEAN CURRENT MOVE AT AN ANGLE TO THE WIND DIRECTION EKMAN SPIRAL AND EKMAN TRANSPORT UPWELLING

19. Fig. 8-12, p. 218

20. EL NINO AND LA NINA.EL NINO IS THE PERIODIC WARMING OF THE EQUATORIAL PACIFIC OCEAN BETWEEN SOUTH AMERICA AND THE DATE LINE. USUALLY THE WINDS (TRADE WINDS) ARE NORTH WESTERLY IN THE NORTHERN HEMISPHERE, SOUTH WESTERLY IN THE SOUTHERN HEMISPHERE, WHICH CAUSES THE OCEAN AT THE EQUATOR TO FLOW IN A WESTERLY DIRECTION STRONG UPWELLING ALONG THE PERUVIAN COAST - HIGH NUTRIENT LEVEL - LARGE SCHOOLS OF FISH IN EL NINO THE WINDS WEAKEN OR REVERSE- NO UPWELLING - POOR FISHING LA NINA IS THE COUNTERPOINT OF EL NINO. WINDS INTENSIFY AND THE UPWELLING INCREASES

21. Sea surface map shows the position of the warm water (red) in December 1997 (El Nino) and the cold water (blue) in December 1988 (La Nina)

22. Fig. 8-14, p. 219

23. El Nino and La Nina How does El Nino affect global weather patterns? Western Pacific experiences less rainfall as warm water moves east. This shift in rain patterns moves the subtropical jet stream from its normal path. This change in the path of the sub-tropical Jet allows El Nino to affect the weather and climate of the mid-latitudes as well as the tropics. The commodities markets use the NOAA El Nino forecasts to influence their buying and selling.

24. http://www.youtube.com/watch?v=pOhqzx LrS0ghttp://www.youtube.com/watch?v=pOhqzx LrS0g

25. 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

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

29. Fig. 8-23, p. 228

31. Fig. 8.29

32. 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

33. 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

34. 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.

35. 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.

36. Fig. 8-24, p. 229

37. Schematic of a Hurricane

40. 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

42. Fig. 8.27

44. STORM SURGE

46. Fig. 8.35

47. TROPICAL CYCLONE DAMAGE WIND DAMAGE STORM SURGE INLAND FLOODING