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![Page 1: Characterization and causes of variability of sea level and thermocline depth in the tropical South Indian Ocean Laurie Trenary University of Colorado.](https://reader035.fdocuments.us/reader035/viewer/2022062806/56649e6a5503460f94b67013/html5/thumbnails/1.jpg)
Characterization and causes of variability of sea level and thermocline depth in the tropical South
Indian Ocean
Laurie TrenaryUniversity of Colorado
![Page 2: Characterization and causes of variability of sea level and thermocline depth in the tropical South Indian Ocean Laurie Trenary University of Colorado.](https://reader035.fdocuments.us/reader035/viewer/2022062806/56649e6a5503460f94b67013/html5/thumbnails/2.jpg)
Seasonal cycle: winds and thermocline depth
Schott et al. 2009
![Page 3: Characterization and causes of variability of sea level and thermocline depth in the tropical South Indian Ocean Laurie Trenary University of Colorado.](https://reader035.fdocuments.us/reader035/viewer/2022062806/56649e6a5503460f94b67013/html5/thumbnails/3.jpg)
Open Ocean Upwelling and Weather/Climate
Tropical Cyclone1851-2006
NASA-Earth Observatory
Saji et al. 2006
SSTXie et al. 2002
Tropical Cyclones Formation
Strong intraseaonal SST variabilityInteractions with the MJO?
Interannually: Intrinsic part of the IOD with significant climatic consequences
![Page 4: Characterization and causes of variability of sea level and thermocline depth in the tropical South Indian Ocean Laurie Trenary University of Colorado.](https://reader035.fdocuments.us/reader035/viewer/2022062806/56649e6a5503460f94b67013/html5/thumbnails/4.jpg)
What are the possible mechanisms?
Rossby waves?
Local Ekman Pumping?
![Page 5: Characterization and causes of variability of sea level and thermocline depth in the tropical South Indian Ocean Laurie Trenary University of Colorado.](https://reader035.fdocuments.us/reader035/viewer/2022062806/56649e6a5503460f94b67013/html5/thumbnails/5.jpg)
Remote Influence from the Pacific
Wijffels and Meyers (2004)
Interannual:5-10% Energy flux from the Pacific(Clarke 1991; Spall and Pedlosky 2005)
Annual:80% energy flux from the Pacific-- -only 10% is found off shore (Potemra 2001)
![Page 6: Characterization and causes of variability of sea level and thermocline depth in the tropical South Indian Ocean Laurie Trenary University of Colorado.](https://reader035.fdocuments.us/reader035/viewer/2022062806/56649e6a5503460f94b67013/html5/thumbnails/6.jpg)
Present Study What drives sea level/thermocline depth
variability on multiple timescales and what is the relative importance of ?
1. Local: Direct Ekman pumping
2. Regionally Remote: Regionally forced large scale Ekman pumping and Rossby wave propagation
3. Remote: Transmission from the Pacific
![Page 7: Characterization and causes of variability of sea level and thermocline depth in the tropical South Indian Ocean Laurie Trenary University of Colorado.](https://reader035.fdocuments.us/reader035/viewer/2022062806/56649e6a5503460f94b67013/html5/thumbnails/7.jpg)
2. Models and ExperimentsModelsHYbrid Coordinate Ocean Model (HYCOM):
Domain: Indian-Pacific basin 55oS-55oN; 30 °E to 290 °E Resolution: 0.33ox0.33o resolution; 20 vertical layers Forcing: ERA40: 3-day-mean winds, specific humidity, air temperature,
precipitation, net shortwave and longwave radiation (1958-2001)Linear Ocean Model (LOM)
Domain: Indian-Pacific basin 45oS-45oN; 30 °E to 290 °E. Damping is applied in a 5o band extending from the boundaries
Resolution: 0.33ox0.33o resolution; 15 vertical mode Continuously stratified using Levitus temperature and salinity (Levitus and
Boyer 1994; Levitus et al. 1994)
Reanalysis and Observations SODA-POP: D20A Aviso: SSHA INSTANT : ITF Transport and Water Mass Properties
![Page 8: Characterization and causes of variability of sea level and thermocline depth in the tropical South Indian Ocean Laurie Trenary University of Colorado.](https://reader035.fdocuments.us/reader035/viewer/2022062806/56649e6a5503460f94b67013/html5/thumbnails/8.jpg)
2. Methods: Experiment Design
INDOPAC = Pacific +Indian Ocean forcingIND= Indian Ocean forcing
Experiment Design Model bathometry
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3. Results: Model/Data ComparisonStandard Deviation of Seasonal to Interannual SSHA and D20
MODEL OBSERVATIONS
REANALYSIS
SSHA
D20A
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3. Results: Model/Data ComparisonSeasonal to Interannual SSHA and D20A
Good agreement with observations!!!
SSHA
D20A-SSHA highly correlated
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3. Results: Model/Data ComparisonStandard Deviation of Intraseasonal SSHA
MODEL OBSERVATIONS
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3. Results: Model/Data ComparisonObserved and modeled ITF
Decent agreement of ITF transport
Model captures variability of hydrodynamic properties
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Interannual Variability
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SSHA SSHA: INDIAN
D20A
D20A: INDIAN
3. Interannual: Standard Deviation Maps
INDOPAC IND DIFF
LOM:SSHA
var( ) var( ) var( ) *x y x y r x y
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Interpreting our results
2
2
h c h
t f x f
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3. InterannualRegion 1 Region 1
INDOPAC (total) Local Forcing : IND (Indian Ocean)INDOPAC-IND (Pacific forcing) Remote Forcing IO :
fτ
ew
1, curl ,
R R
xx t x t dx
C Ch
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3. InterannualRegion 2
Region 2
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D20A: IO
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3. Interannual: Positive CompositeINDOPAC IND DIFF
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Seasonal Variability
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3. SeasonalRegion 1
Region 2
Region 2
20_
Dw w wtotal local IO Rossby t
wlocal
τf
Region 1
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D20A: IO
3. Seasonal Evolution: Hovmöller INDOPAC IND DIFF
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D20A: PACIFIC+IO D20A: IO D20A: PACIFIC
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Intraseasonal Variability
![Page 25: Characterization and causes of variability of sea level and thermocline depth in the tropical South Indian Ocean Laurie Trenary University of Colorado.](https://reader035.fdocuments.us/reader035/viewer/2022062806/56649e6a5503460f94b67013/html5/thumbnails/25.jpg)
3. Intraseasonal : Standard Deviation Maps
INDOPAC IND DIFF
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Controls of ITF
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![Page 28: Characterization and causes of variability of sea level and thermocline depth in the tropical South Indian Ocean Laurie Trenary University of Colorado.](https://reader035.fdocuments.us/reader035/viewer/2022062806/56649e6a5503460f94b67013/html5/thumbnails/28.jpg)
Conclusions• On seasonal-to-interannual timescales sea level/thermocline depth
variability is driven by winds acting on Indian Ocean
• Interannual– SSHA/D20A is associated with Rossby wave propagation forced by
windstress curl in the eastern IO
– Pacific influence is greatest south of 10oS and transmission strongly modifies ITF
• Seasonal:– SSHA/D20A forcing varies based on location: combination of local Ekman
pumping and Rossby wave propagation
– Indian Ocean determines phase of the ITF, the Pacific damps the transport
• Intraseasonal:– In the ridge region, sea level variability is relatively weak, and it results from
IO wind forcing
– Forcing over the IO is the major cause for intraseasonal variability of the ITF
• Decadal:– Pacific appears to contribute to the subsurface temperature variability of the
SIO
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Thank You!
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Decadal Variability
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3. Long term trend
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3. Subsurface temperature variability
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INDOPAC IND DIFF
INDOPAC IND DIFF
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INDOPAC IND DIFF
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INDOPAC IND DIFF
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3. Pacific Tropical winds
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c = phase speed = frequencyR
Earth = Earth radius
Turning latitude
Earth
c R
c
2tan
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3. Interannual: Negative Composite
D20A: HYCOM-MR D20A: HYCOM-EXP D20A: MR-EXP
Composite events: 73-74;74-75;75-76;80-81;81-82;84-85;92-93;98-99
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Thermocline Ridge of the Indian Ocean
Vialard et al. 2009
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3. Transmission and the ITF