The ocean-atmosphere response to wind-induced thermocline changes in the tropical South Western Indian Ocean

Manola, Iris; Selten, Frank; Ruijter, W. P. M. de; Hazeleger, Wilco

doi:10.1007/s00382-014-2338-7

Cited by 11 publications

(10 citation statements)

References 43 publications

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“…The simulations for 1994 revealed a similar pattern of warming in the upper ocean over the western Indian Ocean, but the magnitude was slightly smaller than the year 1991 (Figure b). Generally, the observed and simulated western Indian Ocean subsurface temperature anomalies that resulted from an AO‐related Rossby wave were consistent with the theoretical baroclinic Rossby wave model and ocean general circulation model simulations [e.g., Zhuang et al , ; Tozuka et al , ; Manola et al , ]. Why the warming in 1994 was smaller than in 1991 is an interesting topic.…”

Section: Numerical Experimentssupporting

confidence: 75%

“…Numerical experiments showed that without the arrival of the downwelling Rossby wave, the western Indian Ocean SSTs cooled significantly [ Tozuka et al , ]. Another simulation study showed that the upwelling Rossby wave generated by wind stress over the Seychelles Dome in November and December resulted in SST cooling during the subsequent spring and early summer over the western Indian Ocean [ Manola et al , ]. It should be pointed out that the SST anomalies decayed rapidly and no longer significant after August, whereas the positive upper ocean heat content anomalies persisted into September and October.…”

Section: Possible Mechanismsmentioning

confidence: 99%

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Interannual modulation of East African early short rains by the winter Arctic Oscillation

et al. 2016

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In the present study, we analyzed the interannual linkage between the boreal winter Arctic Oscillation (AO) and East African early short rains. When the Indian Ocean Dipole and El Niño–Southern Oscillation variance are excluded by linear regression, the boreal winter AO index is significantly correlated with the October East African precipitation over the domain of 5°N–5°S and 35°–45°E for the period 1979–2014, r =+ 0.46. The upper ocean heat content likely acts as a medium that links the AO and East African precipitation. Significant subsurface warming and positive upper ocean heat content anomalies occur over the western Indian Ocean during the autumn following positive AO winters, which enriches the atmospheric moisture, intensifies convection, and enhances precipitation. Oceanic dynamics play a key role in causing this subsurface warming. Winter AO‐related atmospheric circulation creates anomalous wind stress, which forces a downwelling oceanic Rossby wave between 60°–75°E and 5°–10°S, where the thermocline significantly deepens. This Rossby wave propagates westward and accompanies significant subsurface warming along the thermocline. The Rossby wave arrives at the western Indian Ocean in the late summer, significantly warming the region to the west of 55°E at a depth of 60–100 m. This warming remains significant through October. Correspondingly, the upper ocean heat content significantly increases by approximately 2–3 × 108 J m−2 in the region west of 60°E between 5° and 10°S. The role of these oceanic dynamics in linking the winter AO, and anomalous subsurface warming was tested by numerical experiments with an oceanic general circulation model. The experiments were performed with the forcing of AO‐related wind stress anomalies over the Indian Ocean in the winter. The oceanic Rossby wave generated in the central Indian Ocean during boreal winter, the consequent subsurface warming, and the anomalous upper ocean heat content in October over the western Indian Ocean were all adequately reproduced. The winter AO can serve as a precursor of East African short rain anomalies.

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Section: Numerical Experimentssupporting

confidence: 75%

Section: Possible Mechanismsmentioning

confidence: 99%

Interannual modulation of East African early short rains by the winter Arctic Oscillation

et al. 2016

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“…The possibility of using ST-borne observations to identify the thickness of the OML (aka MLD) is thus a very important result that demonstrates the potential of animal-borne observations to both study the properties and variability of tropical oceans and improve research on ocean dynamics and climate change. Such capability is notably key in the SWIO as the strong air-sea interactions prevailing in the SCTR region create thermocline disturbances that can influence the climate system throughout the basin and possibly beyond (Manola et al, 2015).…”

Section: Conclusion Discussion and Perspectivesmentioning

confidence: 99%

Sea Turtles for Ocean Research and Monitoring: Overview and Initial Results of the STORM Project in the Southwest Indian Ocean

et al. 2020

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Surface and sub-surface ocean temperature observations collected by sea turtles (ST) during the first phase (Jan 2019-April 2020) of the Sea Turtle for Ocean Research and Monitoring (STORM) project are compared against in-situ and satellite temperature measurements, and later relied upon to assess the performance of the Glo12 operational ocean model over the west tropical Indian Ocean. The evaluation of temperature profiles collected by STs against collocated ARGO drifter measurements show good agreement at all sample depths (0-250 m). Comparisons against various operational satellite sea surface temperature (SST) products indicate a slight overestimation of ST-borne temperature observations of ∼0.1 • ± • 0.6 • that is nevertheless consistent with expected uncertainties on satellite-derived SST data. Comparisons of ST-borne surface and subsurface temperature observations against Glo12 temperature forecasts demonstrate the good performance of the model surface and subsurface (<50 m) temperature predictions in the West tropical Indian Ocean, with mean bias (resp. RMS) in the range of 0.2 • (resp. 0.5-1.5 • ). At deeper depths (>50 m), the model is, however, shown to significantly underestimate ocean temperatures as already noticed from global evaluation scores performed operationally at the basin scale. The distribution of model errors also shows significant spatial and temporal variability in the first 50 m of the ocean, which will be further investigated in the next phases of the STORM project.

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“…This SCTR region is an important region for air‐sea interaction and is unique in that the variability of the subsurface ocean processes can influence the cyclogenesis [ Hermes and Reason , ]. The strong connection between the depth of the thermocline and Sea Surface Temperature (SST) in the SCTR region, and its proximity to the equator where the atmosphere is already sensitive to variations in SST, suggests that the SCTR is an important region for not only air‐sea interaction but also variations in tropical circulations [ Manola et al ., ]. Variations in the SCTR affect cyclogenesis over the SWTIO because the thermocline is shallowest from December to June (austral summer), a period that overlaps with the cyclone season [ Xie et al ., ; Hermes and Reason , ; Manola et al , ].…”

Section: Introductionmentioning

confidence: 99%

“…The strong connection between the depth of the thermocline and Sea Surface Temperature (SST) in the SCTR region, and its proximity to the equator where the atmosphere is already sensitive to variations in SST, suggests that the SCTR is an important region for not only air‐sea interaction but also variations in tropical circulations [ Manola et al ., ]. Variations in the SCTR affect cyclogenesis over the SWTIO because the thermocline is shallowest from December to June (austral summer), a period that overlaps with the cyclone season [ Xie et al ., ; Hermes and Reason , ; Manola et al , ]. Cyclogenesis over this region is also impacted by atmospheric stability, which in turn is influenced by SST [ Annamalai et al ., ; Hermes and Reason , ].…”

Section: Introductionmentioning

confidence: 99%

Tropical cyclone activity over the Southwest Tropical Indian Ocean

et al. 2016

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The Southwest Tropical Indian Ocean (SWTIO) is a key region for air‐sea interaction. Tropical cyclones (TCs) regularly form over the SWTIO and subsurface ocean variability influences the cyclogenesis of this region. Tropical cyclone days for this region span from November through April, and peak in January and February during austral summer. Past research provides evidence for more tropical cyclone days over the SWTIO during austral summer (December–June) with a deep thermocline ridge than in austral summer with a shallow thermocline ridge. We have analyzed the Argo temperature data and HYbrid Coordinate Ocean Model (HYCOM) outputs while focusing on the austral summer of 2012/2013 (a positive Indian Ocean Dipole (IOD) year and neutral El Niño Southern Oscillation (ENSO) year) when seven named tropical cyclones developed over the SWTIO region. This study reveals that the climatic events like the IOD and ENSO influence the cyclonic activity and number of TC days over the SWTIO. We ascertain that the IOD events have linkages with the Barrier Layer Thickness (BLT) in the SWTIO region through propagating Rossby waves, and further show that the BLT variability influences the cyclonic activity in this region.

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The ocean-atmosphere response to wind-induced thermocline changes in the tropical South Western Indian Ocean

Cited by 11 publications

References 43 publications

Interannual modulation of East African early short rains by the winter Arctic Oscillation

Interannual modulation of East African early short rains by the winter Arctic Oscillation

Sea Turtles for Ocean Research and Monitoring: Overview and Initial Results of the STORM Project in the Southwest Indian Ocean

Tropical cyclone activity over the Southwest Tropical Indian Ocean

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