Journal
JOURNAL OF PHYSICAL OCEANOGRAPHY
Volume 52, Issue 7, Pages 1415-1430Publisher
AMER METEOROLOGICAL SOC
DOI: 10.1175/JPO-D-21-0147.1
Keywords
Abyssal circulation; Ocean circulation; Ocean dynamics; Intraseasonal variability
Categories
Funding
- National Natural Science Foundation of China [92158204, 91958202, 42076019, 41776036, 91858203]
- Open Project Program of State Key Laboratory of Tropical Oceanography [LTOZZ2001]
- Key Special Project for Introduced Talents Team of Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou) [GML2019ZD0304]
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Strong subinertial variability near a seamount in the South China Sea was revealed by mooring observations. The study found that topographic Rossby waves (TRWs) and deep eddies were the main factors causing this variability, explaining a significant portion of the kinetic energy of the deep subinertial currents. The generation of TRWs was induced by mesoscale perturbations in the upper layer, while the interaction between cyclonic-anticyclonic eddy pairs and the seamount topography contributed to the generation of deep eddies.
Strong subinertial variability near a seamount at the Xisha Islands in the South China Sea was revealed by mooring observations from January 2017 to January 2018. The intraseasonal deep flows presented two significant frequency bands, with periods of 9-20 and 30-120 days, corresponding to topographic Rossby waves (TRWs) and deep eddies, respectively. The TRW and deep eddy signals explained approximately 60% of the kinetic energy of the deep subinertial currents. The TRWs at the Ma, Mb, and Mc moorings had 297, 262, and 274 m vertical trapping lengths, and similar to 43, 38, and 55 km wavelengths, respectively. Deep eddies were independent from the upper layer, with the largest temperature anomaly being >0.4 degrees C. The generation of the TRWs was induced by mesoscale perturbations in the upper layer. The interaction between the cyclonic-anticyclonic eddy pair and the seamount topography contributed to the generation of deep eddies. Owing to the potential vorticity conservation, the westward-propagating tilted interface across the eddy pair squeezed the deep-water column, thereby giving rise to negative vorticity west of the seamount. The strong front between the eddy pair induced a northward deep flow, thereby generating a strong horizontal velocity shear because of lateral friction and enhanced negative vorticity. Approximately 4 years of observations further confirmed the high occurrence of TRWs and deep eddies. TRWs and deep eddies might be crucial for deep mixing near rough topographies by transferring mesoscale energy to small scales.
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