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This study deals with the physical properties and 3D structures of the wave motions with finite wavelengths of O(100-550) km in the tropical western North Pacific and their variation as propagating from the Pacific to the South China Sea (SCS) using conductivity-temperature-depth observations taken in October and November 2005 and concurrent satellite altimeter data. Three wave components with wavelength bands of O(100), O(200), and O(550) km are derived from the isopycnal undulation signals along 21°, 18°, and 15°N using the ensemble empirical mode decomposition analysis. Their maximum amplitudes are over 100 m in the layer of 1000-2000 m. Phase speeds are derived from cruise-observed vertical profiles of zonal-mean geostrophic flow velocity and the Brunt-Väisälä frequency based on linear quasigeostrophic wave theory with background flow and topography. The speeds are also derived from concurrent sea level anomaly data with the objective Radon transform method. They are close to that of the first baroclinic mode of theoretical solutions, implying that the observed wave motions possess the physical properties of Rossby waves (RWs). The vertical structures of the first generalized modes are derived from cruise observations at three sections. It is shown that the RWs continuously propagate from the Pacific to the SCS, and the available potential energy of RWs 1 and 2 intensify 3-4 times in the Luzon Strait and the SCS compared to that in the Pacific. [ABSTRACT FROM AUTHOR]

Sea level variabilities in the southwest Pacific contribute to the variations of equatorial current bifurcation and the Indonesian Throughflow transport. These processes are closely related to the recharge/discharge of equatorial heat content and dynamic distribution of anthropogenic ocean heating over the Indo-Pacific basin, thus being of profound significance for climate variability and change. Here we identify the major features of seasonal and interannual sea level variabilities in this region, confirming the dominance of the first baroclinic mode in the tropics (contributing 60%–80% of the variances) and higher baroclinic modes in the extratropics (40%–60% of the seasonal variance). Seasonally, except in the western Coral Sea where the Ekman pumping is significant, the wind-driven first-mode baroclinic Rossby waves originating to the east of the date line control the sea level variations over most tropical Pacific regions. In the domain where the 1.5-layer reduced gravity model becomes deficient, the surface heat fluxes dominate, explaining ∼40%–80% of sea level variance. For interannual variability, ∼40%–60% of the variance are El Niño–Southern Oscillation (ENSO) related. The wind-driven Rossby and Kelvin waves east of the date line explain ∼40%–78% of the interannual variance in the tropical Pacific. Outside the tropics, small-scale diffusive processes are presumed critical for interannual variability according to a thermodynamic analysis using an eddy-permitting ocean model simulation. Further process and predictive understandings can be achieved with the coupled climate models properly parameterizing the subgrid-scale processes. [ABSTRACT FROM AUTHOR]

This study focuses on the statistical features of dissipation flux coefficient Γ in the upper South China Sea (SCS). Based on the microscale measurements collected at 158 stations in the upper SCS and derived dissipation rates of turbulent kinetic energy and temperature variance ε and χT, via a modified method, we estimate Γ and analyze its spatiotemporal variation in an energetic and a quiescent region. We show that Γ is highly variable, which scatters over three orders of magnitude from 10−2 to 101 in both regions. Ιn the energetic region, Γ is slightly greater than in the quiescent region; their median values are 0.23 and 0.17, respectively. Vertically, Γ presents a clear increasing tendency with depth in both regions, though the increasing rate is greater in the energetic region than in the quiescent region. In the upper SCS, Γ positively depends on the buoyancy Reynolds number Reb and negatively depends on the ratio of the Ozmidov scale to the Thorpe scale ROT and is scaled as Γ ∝ Re ⁡ b 1 / 2 R OT − 4 / 3 , which holds for both regions. The vertical decreasing of ROT is observed, which yields parameterization of ROT = 10−0.002z; this parameterization improves the performance of the Thorpe-scale method by reducing at least 50% of the bias between the observed and parameterized ε. These results shed new light on the spatiotemporal variability and modulating mechanism of Γ in the upper ocean. Significance Statement: The great global ocean conveyor is maintained by vertical mixing. Turbulent kinetic energy released by local internal wave breaking goes into two parts: one part is used to furnish this vertical mixing, and the rest is dissipated into irreversible heat. The ratio of these two parts is termed as the dissipation flux coefficient and is usually treated as a constant. Our measurements suggest that this coefficient is highly spatiotemporally variable. Specific relationships are obtained when scaling this coefficient with other parameters, and mechanisms modulating this coefficient are also explored. This study sheds light on how much turbulent kinetic energy contributes to elevating the potential energy and its associated influences not only in marginal seas but also in open oceans. [ABSTRACT FROM AUTHOR]