Seasonal variability of near-surface thermal structure and heat budget of the mixed layer of the tropical Indian Ocean from a new global ocean temperature climatology

Abstract Using results from the Simple Ocean Data Assimilation (SODA), this study assesses the mixed layer heat budget to identify the mechanisms that control the interannual variation of sea surface temperature (SST) off Java and Sumatra. The analysis indicates that during the positive Indian Ocean Dipole (IOD) years, cold SST anomalies are phase locked with the season cycle. They may exceed −3°C near the coast of Sumatra and extend as far westward as 80°E along the equator. The depth of the thermocline has a prominent influence on the generation and maintenance of SST anomalies. In the normal years, cooling by upwelling–entrainment is largely counterbalanced by warming due to horizontal advection. In the cooling episode of IOD events, coastal upwelling–entrainment is enhanced, and as a result of mixed layer shoaling, the barrier layer no longer exists, so that the effect of upwelling–entrainment can easily reach the surface mixed layer. Horizontal advection spreads the cold anomaly to the interior tropical Indian Ocean. Near the coast of Java, the northern branch of an anomalous anticyclonic circulation spreads the cold anomaly to the west near the equator. Both the anomalous advection and the enhanced, wind-driven upwelling generate the cold SST anomaly of the positive IOD. At the end of the cooling episode, the enhanced surface thermal forcing overbalances the cooling effect by upwelling/entrainment, and leads to a warming in SST off Java and Sumatra.

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On the mechanism of the seasonal variability of SST in the tropical Indian Ocean

Advances in Atmospheric Sciences ◽

10.1007/bf02918758 ◽

2005 ◽

Vol 22 (3) ◽

pp. 451-462 ◽

Cited By ~ 2

Author(s):

Hu Ruijin ◽

Liu Qinyu ◽

Meng Xiangfeng ◽

J. Stuart Godfrey

Keyword(s):

Indian Ocean ◽

Seasonal Variability ◽

Tropical Indian Ocean

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Basin-Wide Connections of Upper-Ocean Temperature Variability in the Equatorial Indian Ocean

Journal of Climate ◽

10.1175/jcli-d-20-0419.1 ◽

2021 ◽

pp. 1-50

Author(s):

Ge Song ◽

Bohua Huang ◽

Rongcai Ren ◽

Zeng-Zhen Hu

Keyword(s):

Indian Ocean ◽

Equatorial Indian Ocean ◽

Reanalysis Data ◽

Upper Ocean ◽

Ocean Temperature ◽

Ocean Reanalysis ◽

Near Surface ◽

Surface Warming ◽

Transition Mechanism ◽

Wide Range

AbstractIn this paper, the interannual variability of upper-ocean temperature in the equatorial Indian Ocean (IO) and its basin-wide connections are investigated using 58-year (1958-2015) comprehensive monthly mean ocean reanalysis data. Three leading modes of an empirical orthogonal function (EOF) analysis dominate the variability of upper-ocean temperature in the equatorial IO in a wide range of timescales. A coherent interannual band within the first two EOF modes identifies an oscillation between the zonally tilting thermocline across the equatorial IO in its peak phases and basin-wide displacement of the equatorial thermocline in its transitional phases. Consistent with the recharge oscillation paradigm, this oscillation is inherent of the equatorial IO with a quasi-periodicity around 15 months, in which the wind-induced off-equatorial Rossby waves near 5°S-10°S provide the phase-transition mechanism. This intrinsic IO oscillation provides the biennial component in the observed IOD variations. The third leading mode shows a nonlinear long-term trend of the upper-ocean temperature, including the near-surface warming along the equatorial Indian Ocean, accompanied by cooling trend in the lower thermocline originating further south. Such vertical contrary trends may lead to an enhanced stratification in the equatorial IO.

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