Intercomparison and validation of the mixed layer depth fields of global ocean syntheses

Abstract

5-7 (14-16) m with the vertical resolution of 25 (50) m when the criterion of potential density exceeding the 10-m value by 0.03 kg m −3 is used for the MLD estimation. Using the larger criterion (0.125 kg m −3 ) generally reduces the underestimations. In addition, positive biases greater than 100 m are found in wintertime subpolar regions when MLD criteria based on temperature are used. Biases of the reanalyses are due to both model errors and errors related to differences between the assimilation methods. The result shows that these errors are partially cancelled out through the ensemble averaging. Moreover, the bias in the ensemble mean field of the reanalyses is smaller than in the observation-only analyses. This is largely attributed to comparably higher resolutions of the reanalyses. The robust reproduction of both the seasonal cycle and interannual Abstract Intercomparison and evaluation of the global ocean surface mixed layer depth (MLD) fields estimated from a suite of major ocean syntheses are conducted. Compared with the reference MLDs calculated from individual profiles, MLDs calculated from monthly mean and gridded profiles show negative biases of 10-20 m in early spring related to the re-stratification process of relatively deep mixed layers. Vertical resolution of profiles also influences the MLD estimation. MLDs are underestimated by approximately This paper is a contribution to the special issue on Ocean estimation from an ensemble of global ocean reanalyses consisting of papers from the Ocean Reanalyses Intercomparsion Project (ORAIP), coordinated by CLIVAR-GSOP and GODAE OceanView. The special issue also contains specific studies using single reanalysis systems.

Multidecadal-scale adjustment of the ocean mixed layer heat budget in the tropics: examining ocean reanalyses

“…1d, e), and produce h distributions that are similar to the reanalyses in the eastern Pacific and Atlantic, but significantly shallower in the central ocean basins. Toyoda et al (2015) show that monthly mean ocean mixed layer depths from de Boyer Montegut et al (2004) are more shallow than individual observed profiles due to rapid restratification in spring and vertical resolution issues. The Naval Research Lab (Kara et al 2003) annual mean mixed layer depth climatology is shown in Fig.…”

Interannual-decadal variability of wintertime mixed layer depths in the North Pacific detected by an ensemble of ocean syntheses

“…Toyoda et al (2015) revealed that this definition results in an MLD field with less errors relative to definitions using other criteria for potential density (0.03 kg m −3 ) or potential temperature (0.2 and 0.5 °C) in terms of both the seasonal cycle and interannual variability since errors due to monthly averaging of profiles and to weak thermal stratification at high latitudes are relatively small with this definition. Moreover, we use only wintertime maximum MLDs, since we consider that such MLDs are thought to be a most important factor for the thermocline layer dynamics via water mass formation and subduction.…”

“…These syntheses/reanalyses are all different in ocean general circulation model, resolution, surface forcing, ML parameterization, assimilated data and assimilation method (see details in Toyoda et al 2015). MLDs are obtained from the monthly mean TS fields on the original grids for the individual datasets and then interpolated onto the common longitude-latitude grids at one-degree intervals.…”

“…As part of this project work, Toyoda et al (2015) have investigated the fidelity in MLD of a suit of global ocean estimates consisting of two model-independent estimates, produced by using only observations, and 17 ocean syntheses, produced using data assimilation approaches that combine ocean models and observations based on the maximum likelihood principle ("reanalyses" hereafter). In addition to the discussion on biases in the MLDs of the individual syntheses, they demonstrated that the skillful MLD reproduction for both the seasonal cycle and interannual variability is possible by using the ensemble mean of the reanalyses.…”

Seasonal dynamics and disturbance of phytoplankton biomass in the wake of Tahiti as observed by Biogeochemical-Argo floats

“…The mixed layer depth (MLD) is estimated according to the difference in potential density (σ) between 10 m and the base of the mixed layer using a threshold of 0.125 kg m -3 (a reference for studies regarding subtropical gyres; e.g. Levitus, 1982;Ohno et al, 2004;Nicholson et al, 2015;Toyoda et al, 2015). 20…”