Estimation of vertical diffusivity due to double difussion and turbulence in the western equatorial Pacific during low turbulence level period

Abstract

Estimation of vertical diffusivity is central conundrum because of the paucity of observation data. This study aims to understand the impacts of double diffusion and turbulence on vertical diffusivity under weak turbulence condition based on 14-day time series observation at 0N, 156E in 2012. Vertical diffusivity in the upper 300 m is estimated with two methods: from CTD-ADCP data using the method in Large et al. (1994) (Method 1) and from TurboMAP micro-scale data using methods in Osborn (1980) and McDougall and Ruddick (1992) (Method 2). Method 1 yields vertical diffusivity of 9.3x10-4 m2 s-1 due to shear, 1.3x10-4 m2 s-1 for heat, and 1.8x10-4 m2 s-1 fpr salt. Vertical diffusivity from <Method 2 is about 100 times smaller: 2.7x10-6 me s-1 from the dissipation rate, and 5.5x10-6 me s-1 for heat and 2.5x10-6 me s-1 for salt based on the directly observed temperature variance.