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Internal waves play important roles in modulating the temperature variations and heat transfers in stratified oceans. However, due to the deep ocean measuring approach limitations, it is still challengeable to characterize the temperature fluctuations induced by internal waves in the deep oceans below 2,000 m. In this study, a fleet of rapid‐sampling deep profiling floats with an approximately daily sampling rate was deployed in the northeastern South China Sea (SCS), Philippine Basin (PB), Mariana Arc (MA), and Kuroshio Extension (KE). Results show that the internal waves, internal tides or near‐inertial waves, have considerable imprints on local temperature fluctuations. Geographically, the internal wave induced temperature fluctuations are generally larger in the PB and MA, indicative of a strong deep signature of internal tides generated by local energetic tide‐topography interactions or radiation from remote sources. The temperature fluctuations at 4,000 m can reach up to 7 m°C in most regions, which may cover up real signals of temperature change, posing challenges to assess the deep ocean warming rate through currently insufficient deep profiling floats. Besides, the amplitude of isopycnal displacement in the PB and MA is evidently larger than in KE at 4,000 m, which implies enhanced diapycnal diffusivity and mixing in the deep layers of open oceans with rough topography. Plain Language Summary: Internal waves are ubiquitous in the global ocean, and their propagations are accompanied by the rise and falls of isopycnals which induce fluctuations in local temperature. However, in situ observations of high‐frequency temperature fluctuations in the deep ocean are still insufficient. Here we used a fleet of rapid‐sampling deep profiling floats to assess the temperature fluctuations induced by internal waves. We found that the magnitude of internal wave induced deep ocean temperature fluctuations is evidently stronger than the long‐term trend, especially in the Philippine Basin (PB) and Mariana Arc (MA) with rough topography. Therefore, a more cautious approach should be used to assess the deep ocean warming rate in areas with strong internal waves. Key Points: Internal waves are found to have considerable imprints on temperature fluctuations using rapid‐sampling deep profiling floatsThe temperature fluctuations can reach 7 m °C at 4,000 m, posing challenges to assess the real deep ocean warming rateThe internal waves induced temperature fluctuations in the deep ocean are generally larger in the Philippine Basin and Mariana Arc [ABSTRACT FROM AUTHOR]

Spatiotemporal variations in internal solitary wave (ISW) polarity over the continental shelf of the northern South China Sea (SCS) were examined based on mooring-array observations from October 2013 to June 2014. Depression ISWs were observed at the easternmost mooring, where the water depth is 323 m. Then, they evolved into elevation ISWs at the westernmost mooring, with a depth of 149 m. At the central mooring, with a depth of 250 m, the ISWs generally appeared as depression waves in autumn and spring but were elevation waves in winter. Seasonal variations in stratification caused this seasonality in polarity. On the intraseasonal time scales, anticyclonic eddies can modulate ISW polarity at the central mooring by deepening the thermocline depth for periods of approximately 8 days. During some days in autumn and spring, depression ISWs and ISWs in the process of changing polarity from depression to elevation appeared at time intervals of 10–12 h because of the thermocline deepening caused by internal tides. Isotherm anomalies associated with eddies and internal tides have a more significant contribution to determining the polarity of ISWs than do the background currents. The observational results reported here highlight the impact of multiscale processes on the evolution of ISWs. [ABSTRACT FROM AUTHOR]

Both internal solitary waves (ISWs) and mesoscale eddies are ubiquitous in the northern South China Sea (SCS). In this study, the authors examine the impacts of mesoscale eddies on the ISWs transiting the northern SCS deep basin that evolve from the steepening internal tide generated in the Luzon Strait, using in situ data collected from a specifically designed mooring array. From November 2013 to January 2014, an energetic mesoscale eddy pair consisting of one anticyclonic eddy (AE) and one cyclonic eddy (CE) propagated across the mooring array. Observations revealed that the amplitude, propagation direction, and speed of the transbasin ISWs were significantly modulated by the eddy pair. When the moorings were covered by the southern portion of the AE, the ISW amplitudes decreased by as much as 67% because of the thermocline deepening along the wave direction and the energy divergence along the wave front. When the moorings were covered by the northern portions of both eddies, the amplitude of ISWs also decreased but to a relatively smaller degree. ISWs propagated the fastest inside the southern portion of the AE, where both the thermocline deepening and eddy currents enhanced the propagation speed of ISWs. Under the influence of the AE (CE) core, ISWs propagated more northward (southward) than usual. The observational results reported here highlight the importance of resolving mesoscale eddies in circulation-internal wave coupled models to accurately predict kinematic characteristics of ISWs. [ABSTRACT FROM AUTHOR]

A new method of estimating the phase speed and vertical velocity of internal solitary waves (ISW) based on dynamic governing equations using Acoustic Doppler Current Profiler (ADCP) data was developed. This method was applied to a representative ISW case, which was captured in the South China Sea in the 2007 summer experiment. The result shows that this ISW had a phase speed of approximately 2.6 m s. This method provides an excellent alternative in estimating the phase speed of ISWs, especially useful in the absence of vertical stratification needed in solving the Korteweg-de Vries (KdV)-type equation, e.g., long-term mooring observation. Analyses show that the new method is fairly self-consistent, and it can be applied when only a part of the ISW observations is available. The computed vertical velocity of the ISW using the new method has a good agreement with the ADCP observations both in magnitude and pattern. [ABSTRACT FROM AUTHOR]