New method estimating diapycnal eddy diffusivity under background-turbulence dominancy in the East China Sea

Abstract

A field measurement was carried out to observe eddy diffusivity on the continentalshelf around 31oN in the East China Sea during September 16-27, 2014. Twotrawl-resistant bottom mount ADCPs were deployed along 126.5oE with 10 km apart.CTD castings were also carried out on the ADCP sites. The ADCPs were equippedwith an additional acoustic Doppler sensor to measure precise vertical velocity. ADCPdata are newly used to estimate the continuous diapycnal eddy diffusivity, withtraditional TurboMap instrument and Thorpe methods.As reported in 2015, the intermittent events of internal wave groups propagating fromsoutheast to northwest. Frequencies of internal waves show mixtures between localbuoyancy frequency and lower frequencies. We forcus upon the turbulence driven eddydiffusivity under background turbulence dominant environment or local buoyancyfrequency dominancy. Three methods was used for comparison between the methods:The direct measurement by TurboMap was carried along with ADCP measurement onSep.26, 2014. The Thorpe method was utilized to calculate the eddy diffusivity usingthe temperature and salinity profiles. ADCP data with minimum information of CTD datawas also newly introduced.The results of estimating eddy diffusivity coefficients in the thermocline layer arecompared with that of ADCP-induced values, first, with assumption that the turbulentmotion in the thermocline layerCTD castings were also carried out on the ADCP sites. The ADCPs were equippedwith an additional acoustic Doppler sensor to measure precise vertical velocity. ADCPdata are newly used to estimate the continuous diapycnal eddy diffusivity, withtraditional TurboMap instrument and Thorpe methods.As reported in 2015, the intermittent events of internal wave groups propagating fromsoutheast to northwest. Frequencies of internal waves show mixtures between localbuoyancy frequency and lower frequencies. We forcus upon the turbulence driven eddydiffusivity under background turbulence dominant environment or local buoyancyfrequency dominancy. Three methods was used for comparison between the methods:The direct measurement by TurboMap was carried along with ADCP measurement onSep.26, 2014. The Thorpe method was utilized to calculate the eddy diffusivity usingthe temperature and salinity profiles. ADCP data with minimum information of CTD datawas also newly introduced.The results of estimating eddy diffusivity coefficients in the thermocline layer arecompared with that of ADCP-induced values, first, with assumption that the turbulentmotion in the thermocline layer