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Oceanic CirculationThe Role of Oceans in Global Climate VariabilityThe Role of Oceans in Hydrological CycleI. How oceans workI. How oceans work (Cont’d)Relative proportions of dissolved salts in seawaterAnnual Mean Ocean Surface TemperatureAnnual Zonal Mean Ocean Surface TemperatureAnnual Mean Ocean Surface SalinityAnnual Zonal Mean Ocean SalinityOcean Meridional Overturning (Global)Ocean Meridional Overturning in AtlanticSlide 13Mixed Layer ProcessesSlide 15Slide 16QuizII. Surface currentsSlide 19B. Global wind patterns cause surface ocean currents because of frictional dragC. Coriolis effectC. Coriolis effect (Cont’d)Slide 23D. Pressure gradientsG. Resultant overall current patternEffects of surface currentsSlide 277. Zones of upwellingIII. Deep CurrentsB. Global Conveyor Belt (Cont’d)Slide 31Slide 32The Role of OceansThe Air-Sea InteractionsA. Inter-tropical Convergence Zone (ITCZ)El Nino: How it WorksKnown for over 400 years ...Occurs during Christmas season ...Food ChainB. El Niño - Southern Oscillation, a.k.a. ENSOEl Niño and SOISlide 42Reading the Index2. Importance of understanding ENSO3. Basics of ENSOSlide 46Oscillation of surface water in the PacificWhat causes ENSO? large-scale internal wavesWhat Causes ENSO?Slide 505. If it’s a tropical phenomenon, why does it affect us in Texas?Slide 52Slide 53Slide 54Slide 55El Nino and TexasSlide 576. What’s good and bad about the effects of ENSO?b. 1997-1998 event and the media’s response7. Measuring El NinoMeasuring El Nino Weather StationsWeather Station: ColoradoMeasuring El Nino BuoysSlide 64Slide 65Slide 66Measuring El Nino SatellitesSatellites: TemperaturesMeasuring El Nino Sea Surface TemperaturesMeasuring El Nino: Coral BleachingSlide 71Oceanic CirculationI. How oceans work II. Surface currents III. Deep CurrentsIV: The Air-Sea Interactions (ENSO)The Role of Oceans in Global Climate VariabilityThe Role of Oceans in Hydrological Cycle 97% of the Earth’s free water86% of the global evaporation78% of global precipitationI. How oceans work1. Area: covers 70% of the Earth’s surface2. Volume: 97% of all the water on the Earth3. Depth: 4 kilometers4. Density: 1034-1035 kg/m3 (Pure water: 1000 kg/m3) over 90% of the ocean. Depends on temperature and salinity. cold water  high densityloss of water by evaporation  increase salinity  high densityprecipitation and river discharge  decrease salinity  low density5. Heat capacity: high6. Temperature: less variable than in the atmosphere7. Freezing point: – 1.9°C, not at 0°C because of salinity8. Surface is not level due to currents, waves, atmospheric pressure differences, and variations in gravity.9. Two main forms of circulation: wind-driven circulation (horizontal, surface waters, fast)thermohaline circulation (vertical, deep waters, slow)I. How oceans work (Cont’d)Relative proportions of dissolved salts in seawaterAnnual Mean Ocean Surface TemperatureAnnual Zonal Mean Ocean Surface TemperatureAnnual Mean Ocean Surface SalinityAnnual Zonal Mean Ocean SalinityOcean Meridional Overturning (Global)Ocean Meridional Overturning in AtlanticI. How oceans work (Cont’d)A. Heated primarily by Sun, largely at the Equator, with global heat transfer by ocean currents  profound effect of oceans on climateB. Two overall layers1. Thin, warm, less dense surface layer well mixed by turbulence generated by wind2. Thick, cold, more dense deep layer that is calm and marked by slow currents3. Thermocline is the boundary between the layersMixed Layer Processes Vigorous mixing processes lead to uniform conditions within the surface mixed layer.Mixed Layer ProcessesI. How oceans work (Cont’d)Quiz1. Which of the following is NOT true about the oceans? A. Approximately 97% of the total water on Earth is located in the oceans B. The oceans cover about 70% of Earth’s surface C. The average depth of the oceans is about 4 km. D. The sea surface is level for all the oceans. E. Because it takes far more energy to change the temperature of water than land or air, water warms up and cools off much more slowly than either. 2. The three largest reservoirs of water at the earth’s surface in decreasing order of volume are: A. oceans, ice caps/glaciers, and ground water B. oceans, ice caps/glaciers, and soils C. oceans, lakes/rivers, and soils D. oceans, atmosphere, and biosphere E. oceans, ground water, and soils 3. What is the primary salt in the ocean? A. methane B. CO2 C. FeO2 D. CaSO4 E. NaCl4. Which of the following increase salinity? A. Evaporation B. Precipitation. C. Formation of sea ice. D. River runoff. E. A and C only.II. Surface currentsII. Surface currentsA. Three primary forces1. Global wind patterns cause surface ocean currents because of frictional drag2. Coriolis effect 3. Pressure gradientsB. Global wind patterns cause surface ocean currents because of frictional drag1. Creation of waves2. Creation of hemisphere-scale gyres3. Decrease in current speed with depthJanuary JulyC. Coriolis effect1. Earth rotation speed is greatest at Equator falling to zero at Poles2. Conservation of angular momentuma. Deflection to the right for component of Equator-to-Pole flow in Northern Hemisphereb. Deflection to the left for component of Equator-to-Pole flow in Southern HemisphereC. Coriolis effect (Cont’d)3. Creation of Ekman Spiral a. To depth of 100 mb. Surface current moves 20-45o from the wind direction (45o in theory)c. Deflection increases with depth, forming a spirald. Net transport of water is 90o from the wind directionC. Coriolis effect (Cont’d)3. Creation of Ekman Spiral a. To depth of 100 mb. Surface current moves 20-45o from the wind direction (45o in theory)c. Deflection increases with depth, forming a spirald. Net transport of water is 90o from the wind directionD. Pressure gradients1. Differences in water height (i.e., piling of water against a continent because of the wind) 2. Density differences because of temperature or salinity 3. Atmospheric pressure differencesE. Geostrophic currents - balance of Coriolis force by pressure gradient F. Land forms barriers to global ocean currentsG. Resultant overall current pattern1. Currents converge toward Equator following Trade Winds and ITCZ2. Westward flow along Equator (i.e., North and South Equatorial Currents)3. Equatorial Currents turn poleward where they encounter land barriers (e.g., Gulf Stream)4. Eastward flow of currents is enhanced by the Westerlies


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UT GEO 387H - Oceanic Circulation

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