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- Title
Combined Effects of Tidal Mixing in Narrow Straits and the Ekman Transport on the Sea Surface Temperature Cooling in the Southern Indonesian Seas.
- Authors
Nagai, T.; Hibiya, T.
- Abstract
Although the SST cooling events around the Lesser Sunda Islands (LSIs), which contribute to the seasonal variation of SST in the southern Indonesian Seas, are thought to be controlled by tidal mixing, the distribution of tidal mixing was highly idealized in previous studies. This study reinvestigates the mechanisms of such SST cooling events using MITgcm, which incorporates the realistic distribution of tidal mixing. The observed SST variability is well reproduced in the numerical experiment; SST is largely reduced along the northern (or southern) coast of the LSIs during austral summer (or winter). Particle tracking suggests that the narrow tidal straits between the LSIs, where well‐mixed waters are produced by vigorous tidal mixing, play a key role in controlling the SST cooling. During austral summer, the cold SST signal of well‐mixed waters propagates both northward and southward from the narrow straits as baroclinic Kelvin waves. On the northern side of the LSIs, in particular, coastal upwelling caused by the northwest monsoon raises the background thermocline, which affects the propagation of baroclinic Kelvin waves such that the accompanying cold SST signal becomes much enhanced compared with that on the southern side of the LSIs. During austral winter, in contrast, the Ekman transport enhances southward through‐strait flow so that baroclinic Kelvin waves can propagate only southward affecting the SST on the southern side of the LSIs. This demonstrates the importance of the combined effects of tidal mixing in narrow straits and the Ekman transport on the SST cooling in the southern Indonesian Seas. Plain Language Summary: The Indonesian Archipelago has numerous narrow straits where tide‐induced vertical mixing (called "tidal mixing") is significantly enhanced. Understanding how tidal mixing affects the SST in the Indonesian Archipelago is one of the remaining issues toward the accurate prediction of global climate. In the present study, we carry out a series of numerical experiments to find that vigorous tidal mixing produces well‐mixed waters in the narrow tidal straits between Lesser Sunda Islands (LSIs) and the cold SST signal originating from the well‐mixed waters is found only north (or south) of the LSIs during austral summer (or winter), subject to the direction of monsoonal winds. This strongly suggests that mixing hotspots in narrow tidal straits, which are hardly resolved in the existing OGCMs, should be taken into account in future climate models. Key Points: The physical mechanisms for the SST cooling in the southern Indonesian Seas are investigated through a series of numerical experimentsStrong tidal mixing in the narrow straits between the Lesser Sunda Islands creates cold SST signal propagating as baroclinic Kelvin wavesThe Ekman transport associated with monsoonal winds regulates the northward and/or southward propagation of these baroclinic Kelvin waves
- Subjects
LESSER Sunda Islands; OCEAN temperature; EKMAN motion theory; THERMOCLINES (Oceanography); OCEAN waves
- Publication
Journal of Geophysical Research. Oceans, 2020, Vol 125, Issue 11, p1
- ISSN
2169-9275
- Publication type
Article
- DOI
10.1029/2020JC016314