SST Observations of large scale ocean processesenvisat.esa.int/Ocean2006/course_material/Thu_AATSR/...SST Observations of large scale ocean processes ESA Training Course: Ocean2006
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SST: Large scale processes 325-29 Sep, HamburgESA Training Course: Ocean2006
Satellite data provide the best means to observe large scale ocean processes
Satellite data provide the best means to Satellite data provide the best means to observe large scale ocean processesobserve large scale ocean processes
Applications to large scale oceanography exploit the unique benefits of satellite data
Global coverage with good spatial detailRepeated coverage over many yearsA consistent view from the same sensorOpportunity to combine data from different sensor types
Special data analysis methods for time series of large scale images
SST: Large scale processes 425-29 Sep, HamburgESA Training Course: Ocean2006
Large scale ocean processes from SpaceLarge scale ocean processes from SpaceLarge scale ocean processes from Space
Climatology of the oceansObserve the whole world ocean at onceIsolate the seasonal cycleIdentify long term fluctuations or trendsLook for characteristic patterns of ocean behaviour
Large scale propagating featuresRossby wavesTropical instability waves
El Niño Detection from multiple data typesPossibility of prediction
SST: Large scale processes 1325-29 Sep, HamburgESA Training Course: Ocean2006
Analysing a 3-dimensional dataset Analysing a 3Analysing a 3--dimensional dataset dimensional dataset The challenge of extracting the information distributed in latitude, longitude and time
Longitude
Tim
eLa
titude
Tim
eLongitude
Hovmüller Diagram
SST: Large scale processes 1425-29 Sep, HamburgESA Training Course: Ocean2006
Applications of space-time section plots Applications of spaceApplications of space--time section plots time section plots To emphasise a process in which a property changes its distribution quite slowly with time
Section across the Arctic to show the ice edge advance / retreat.A North-South (Meridional) section to show the seasonal migration of temperature contours at a particular longitude.Compare response of different variables, and at different longitudes
Any wavelike motionWaves on the Antarctic Circumpolar CurrentRossby WavesTropical Instability Waves
Compare SST, altimetry and wind sections to reveal atmosphere-ocean interactions.
SST: Large scale processes 1525-29 Sep, HamburgESA Training Course: Ocean2006
Rossby waves are revealed in Hovmöller plotsRossby waves are revealed in Hovmöller plotsRossby waves are revealed in Hovmöller plots
SST: Large scale processes 1625-29 Sep, HamburgESA Training Course: Ocean2006
Estimating the speed of Rossby WavesEstimating the speed of Rossby WavesEstimating the speed of Rossby Waves
Proportional to slope of linesMust be measured objectively for consistencyNeeds to be automated for global coverageUse Radon Transform AnalysisCan detect several waves of different speeds if present
(From Cipollini, Cromwell, Quartly and Challenor, 2000)
SST: Large scale processes 2525-29 Sep, HamburgESA Training Course: Ocean2006
Filtered Hovmöller Plots from TMI
TropicalInstability
Waves (TIW)
SST: Large scale processes 2625-29 Sep, HamburgESA Training Course: Ocean2006
El NiñoEl NiñoEl NiñoA change in the ocean-atmosphere pattern over the Pacific ocean – recurs after 3 – 7 yearsClear example of atmosphere-ocean feedback
Interesting scientificallyIt is not in itself an effect of global warming - though it may be affected by it
Has large, global human and economic consequences
1982-3 event had estimated insurance costs in $ billions due to changes in global weather patternsLeads to excessive rainfall or droughts (and drought-related wildfires) in parts of globe with consequent human impactsAffects marine living resources
SST: Large scale processes 2725-29 Sep, HamburgESA Training Course: Ocean2006
The El Niño process (1) Normal tropical Pacific conditions
The El Niño process The El Niño process (1) Normal tropical Pacific conditions(1) Normal tropical Pacific conditions
Westward blowing winds (easterlies) along equator generate a current that results in warmer water at the western side (near Indonesia; so-called “warm pool”)
Temperature gradient east-west of ~6-7˚ (~23˚→ ~29˚)Sea surface higher in west than eastThermocline deeper to west, shallower to east → upwelling in east → supply of nutrients → growth of plankton → fish“warm pool” leads to increased atmospheric convection and precipitation in the west (Note: precipitation and evaporation affect sea surface salinity)
West East
SST: Large scale processes 2825-29 Sep, HamburgESA Training Course: Ocean2006
The El Niño process (2) El Niño conditionsThe El Niño process (2) El Niño conditionsThe El Niño process (2) El Niño conditionsWestward blowing winds weaken along equator allowing warm water to propagate from west to east (equatorial Kelvin wave) → a positive feed back effect
Temperature gradient east-west is almost non-existentSea surface higher in east than westThermocline shallows in west, deepens in east → suppresses upwelling in east → less nutrients → decreased plankton → less fish“warm pool” moves east leading to increased atmospheric convection and precipitation in the mid-tropical Pacific
SST: Large scale processes 2925-29 Sep, HamburgESA Training Course: Ocean2006
The El Niño process (3) La Niña conditionsThe El Niño process (3) La Niña conditionsThe El Niño process (3) La Niña conditions
Westward blowing winds intensify along equator pushing warm water to back to west from eastTemperature gradient east-west re-established, but cool “tongue” extends further into central tropical PacificSea surface now lower across central tropical PacificThermocline deepens in west,shallows in east →increased upwelling in east → more nutrients →increased plankton → more fish“warm pool” moves west leading to increased atmospheric convection and precipitation beyond Indonesia (overshoot)
SST: Large scale processes 3025-29 Sep, HamburgESA Training Course: Ocean2006