DOI: 10.26190/5ebe1f389dd87
title: A high-resolution reanalysis of the East Australian Current System assimilating an unprecedented observational data set using 4D-Var data assimilation over a two-year period (2012-2013). Version 2017.

description: For the EAC region, we combine a high-resolution state-of-the-art numerical ocean model with a variety of traditional and newly available observations using an advanced variational data assimilation scheme. The numerical model is configured using the Regional Ocean Modelling System (ROMS 3.4) and takes boundary forcing from the BlueLink ReANalysis (BRAN3). For the data assimilation, we use an Incremental Strong- Constraint 4-Dimensional Variational (IS4D-Var) scheme, which uses the model dynamics to perturb the initial conditions, atmospheric forcing, and boundary conditions, such that the modelled ocean state better fits and is in balance with the observations. In addition to the traditional data streams (satellite derived SSH and SST, Argo profiling floats and XBT lines) we exploit newly available observations collected by Australia's Integrated Marine Observing System (IMOS). These include velocity and hydrographic observations from a deep-water mooring array (the EAC transport array, 27.5S) and several moorings on the continental shelf (27.5S, 30S and 34S), surface radial velocities from a high-frequency (HF) radar array (at Coffs Harbour, 30S), and temperature and salinity observations from ocean gliders.
description: For the assimilation, we use a time-dependent variational scheme (4D-Var) that uses the model physics to compute increments in the initial conditions, boundary and surface forcings such that the difference between the modelled time-evolving flow and the observations is minimised over a time window. The hydrodynamic model configuration, the observations and the data assimilation system as described in detail in Kerry, C., B. Powell, M. Roughan and P. Oke: Development and evaluation of a high-resolution reanalysis of the East Australian Current region using the Regional Ocean Modelling System (ROMS 3.4) and Incremental Strong-Constraint 4-Dimenesional Variational data assimilation (IS4D-Var), Geosci. Model Dev, 9, 3779-3801, doi:10.5194/gmd-9-3779-2016, 2016. Version 2017 had some minor changes compared to the 2016 version described in the above mentioned paper, outlined here. 1.) Improved the upper ocean temperature (warm) bias in the free-running model by scaling the ACCESS air temperature by a factor of 0.95 (as the air temperature was too warm compared to other atmospheric products). 2.) Removed day time SST observations and any night observations when wind speed &lt;2m/s. The percentage of SST observations removed per 5 day cycle is 0.33-54.3% (mean of 20.77%) compared to the 2016 version. 3.) The nominal minimum observation error covariances for the XBT observations were doubled compared to the 2016 version, such that in the 2017 version the variances are twice those applied to Argo to account for greater uncertainty in the XBT observation locations. 4.) The vertical decorrelation length scales for temperature were relaxed to 20m (from 10m in the 2016 version).
description: https://www.geosci-model-dev.net/9/3779/2016/