Presentation on theme: "AOSC 200 Lesson 14. Oceanography The oceans plat three important roles in determining weather and climate (1) They are the major source of water vapor."— Presentation transcript:
Oceanography The oceans plat 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.
Fig. 8-1, p. 210 Energy gains and losses in the oceans
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.
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.
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)
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
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.
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 an 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.
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
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 BLOW TOWARDS THE EQUATOR - WHICH CAUSES THE OCEAN TO FLOW IN A WESTERLY DIRECTION (REMEMBER THE CORIOLIS FORCE ACTS IN A WESTERLY DIRECTION IN THE SOUTHERN HEMISPHERE 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
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.