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Experimental Assessments on Impacts of Salinity Anomalies on the Positive Indian Ocean Dipole
Author(s) -
Kido Shoichiro,
Tozuka Tomoki,
Han Weiqing
Publication year - 2019
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1029/2019jc015479
Subject(s) - thermocline , stratification (seeds) , subtropical indian ocean dipole , indian ocean dipole , salinity , forcing (mathematics) , ocean heat content , climatology , ocean general circulation model , geology , ocean dynamics , deep ocean water , mixed layer , ocean current , oceanography , temperature salinity diagrams , ocean surface topography , water mass , thermohaline circulation , sea surface temperature , general circulation model , climate change , seed dormancy , botany , germination , dormancy , biology
Impacts of salinity anomalies associated with the positive Indian Ocean Dipole (pIOD) are assessed through novel sensitivity experiments using a regional ocean model (Regional Ocean Model System) and detailed diagnostics of heat and momentum budget. During the pIOD, density stratification in the eastern equatorial Indian Ocean is enhanced due to anomalous surface freshening and subsurface saltening. This causes momentum inputs from the wind forcing to be more strongly trapped in the surface layer, and zonal and vertical current anomalies to be more confined to the upper layer. As a result, upward transports of cold water from below the thermocline to the surface layer are significantly suppressed, and the cooling in the eastern equatorial Indian Ocean is suppressed by as much as 1.0 °C. The above arguments are further corroborated by a set of sensitivity experiments using a linear continuously stratified ocean model, which can isolate the effect of stratification change caused by salinity anomalies associated with the pIOD in the Regional Ocean Model System simulation. Our results suggest that salinity does play an active role in the evolution of the pIOD, rather than being passively affected by large‐scale anomalous atmospheric and oceanic conditions.