Observations of internal waves and their damping process in the East China Sea in late summer 2014

Abstract

A field measurement was carried out to observe generation, propagation and dampingof the internal waves on the continental shelf around 31oN in the East China Sea duringSeptember 16-27, 2014. Two trawl-resistant bottom mount ADCPs (M1, M2) weredeployed along 126.5oE with 10 km apart. CTD castings were also carried out on theADCP sites. The ADCPs were equipped with an additional acoustic Doppler sensor tomeasure precise vertical velocity.We observed intermittent events of internal wave groups propagating from southeastto northwest. Frequencies of internal waves show mixtures between local buoyancyfrequency and lower frequencies. Based upon the assumption of long crest waves, thedamping of the internal wave groups were examined in terms of both total and verticalturbulent kinetic energy (TKE).Over the 10 km distance the dominant frequency internal wave group with periodsaround 500 s is estimated to dissipate its energy by about 30%. The damping processappears to be partly related with the higher-mode evolution at the downward stationM1, compared with the 1st-mode dominancy at the upstream station (M2). Thisdamping process can scatter the internal wave energy into smaller scales (highermodes), and hence can induce cascading of the internal wave spectra to higherfrequencies. Our observations suggest that the damping processes of internal waves onthe continental shelf of the East Ch, M2) weredeployed along 126.5oE with 10 km apart. CTD castings were also carried out on theADCP sites. The ADCPs were equipped with an additional acoustic Doppler sensor tomeasure precise vertical velocity.We observed intermittent events of internal wave groups propagating from southeastto northwest. Frequencies of internal waves show mixtures between local buoyancyfrequency and lower frequencies. Based upon the assumption of long crest waves, thedamping of the internal wave groups were examined in terms of both total and verticalturbulent kinetic energy (TKE).Over the 10 km distance the dominant frequency internal wave group with periodsaround 500 s is estimated to dissipate its energy by about 30%. The damping processappears to be partly related with the higher-mode evolution at the downward stationM1, compared with the 1st-mode dominancy at the upstream station (M2). Thisdamping process can scatter the internal wave energy into smaller scales (highermodes), and hence can induce cascading of the internal wave spectra to higherfrequencies. Our observations suggest that the damping processes of internal waves onthe continental shelf of the East Ch