Mechanisms controlling the seasonal mixed-layer temperature and salinity of the Indonesian seas |
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Authors: | Daria Halkides Tong Lee Shinichiro Kida |
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Institution: | (1) University of California at Los Angeles-Joint Institute For Research in Earth System Science and Engineering (JIFRESSE), Los Angeles, CA, USA;(2) Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA;(3) Earth Simulator Center, Japan Agency for Marine-Earth Science and Technology, Yokohama, Japan |
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Abstract: | We examine the seasonal mixed-layer temperature (MLT) and salinity (MLS) budgets in the Banda–Arafura Seas region (120–138°
E, 8–3° S) using an ECCO ocean-state estimation product. MLT in these seas is relatively high during November–May (austral
spring through fall) and relatively low during June–September (austral winter and the period associated with the Asian summer
monsoon). Surface heat flux makes the largest contribution to the seasonal MLT tendency, with significant reinforcement by
subsurface processes, especially turbulent vertical mixing. Temperature declines (the MLT tendency is negative) in May–August
when seasonal insolation is smallest and local winds are strong due to the southeast monsoon, which causes surface heat loss
and cooling by vertical processes. In particular, Ekman suction induced by local wind stress curl raises the thermocline in
the Arafura Sea, bringing cooler subsurface water closer to the base of the mixed layer where it is subsequently incorporated
into the mixed layer through turbulent vertical mixing; this has a cooling effect. The MLT budget also has a small, but non-negligible,
semi-annual component since insolation increases and winds weaken during the spring and fall monsoon transitions near the
equator. This causes warming via solar heating, reduced surface heat loss, and weakened turbulent mixing compared to austral
winter and, to a lesser extent, compared to austral summer. Seasonal MLS is dominated by ocean processes rather than by local
freshwater flux. The contributions by horizontal advection and subsurface processes have comparable magnitudes. The results
suggest that ocean dynamics play a significant part in determining both seasonal MLT and MLS in the region, such that coupled
model studies of the region should use a full ocean model rather than a slab ocean mixed-layer model. |
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