Evaluation of Thermocline Depth Bias in the Seychelles-Chagos Thermocline Ridge (SCTR) simulated by the CMIP6 models

Evaluation of Thermocline Depth Bias in the Seychelles-Chagos Thermocline Ridge (SCTR) simulated by the CMIP6 models
Mubarrok, Saat; Jang, Chan Joo
KIOST Author(s)
Jang, Chan Joo(장찬주)
Alternative Author(s)
Saat Mubarrok; 장찬주
Publication Year
The Seychelles-Chagos Thermocline Ridge (SCTR) refers to an open ocean upwelling region in the southwestern
Indian Ocean (5oS–10oS, 50oE–80oE), a result of the negative wind stress curl between the southeasterly trade
wind and equatorial westerlies. Considering the increasing need to understand the sea-air interaction that shapes
the variability of the Indian Ocean, the simulation of SCTR is evaluated using outputs from the Coupled Model
Intercomparison Project Phase Sixth (CMIP6) and Phase Fifth (CMIP5) models. Compared with observations,
by calculating the 20°C isotherm depth (D20), 23 of 27 CMIP6 models tend to simulate considerably deeper
thermocline depth – a common bias in CMIP5 models. The thermocline dome, the shallowest D20 in the 5oS–10oS
band, is also located in the eastern part of the Indian Ocean in most of the CMIP6 and CMIP5 models, whereas
the dome from observation is located at the western part around 60oE. These biases are found to be associated
with the easterly wind bias in the equator, which generates markedly weak Ekman pumping velocity. The models
with deeper thermocline depth bias showed a relatively warmer sea surface temperature, probably owing to a
weaker thermocline feedback mechanism. Quantitative analysis showed that the CMIP6 models simulate better
the thermocline depth and dome, compared to the CMIP5 models. This study highlights the problems with the
CMIP6 models for reproducing the SCTR region in the Indian Ocean and might assist the improvement of climate
models in the future.
Bibliographic Citation
PICES-2022 Annual Meeting, 2022
The North Pacific Marine Science Organization (PICES)
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