Abstract
Abstract. Global ocean reanalyses combine in situ and satellite ocean observations with a general circulation ocean model to estimate the time-evolving state of the ocean, and they represent a valuable tool for a variety of applications, ranging from climate monitoring and process studies to downstream applications, initialization of long-range forecasts and regional studies. The purpose of this paper is to document the recent upgrade of C-GLORS (version 5), the latest ocean reanalysis produced at the Centro Euro-Mediterraneo per i Cambiamenti Climatici (CMCC) that covers the meteorological satellite era (1980–present) and it is being updated in delayed time mode. The reanalysis is run at eddy-permitting resolution (1∕4° horizontal resolution and 50 vertical levels) and consists of a three-dimensional variational data assimilation system, a surface nudging and a bias correction scheme. With respect to the previous version (v4), C-GLORSv5 contains a number of improvements. In particular, background- and observation-error covariances have been retuned, allowing a flow-dependent inflation in the globally averaged background-error variance. An additional constraint on the Arctic sea-ice thickness was introduced, leading to a realistic ice volume evolution. Finally, the bias correction scheme and the initialization strategy were retuned. Results document that the new reanalysis outperforms the previous version in many aspects, especially in representing the variability of global heat content and associated steric sea level in the last decade, the top 80 m ocean temperature biases and root mean square errors, and the Atlantic Ocean meridional overturning circulation; slight worsening in the high-latitude salinity and deep ocean temperature emerge though, providing the motivation for further tuning of the reanalysis system. The dataset is available in NetCDF format at doi:10.1594/PANGAEA.857995.
Highlights
Ocean retrospective analyses combine available in situ and satellite observations with an ocean general circulation model (OGCM) forced by atmospheric reanalyses by means of advanced data assimilation techniques, with the aim of estimating the state of the ocean in the past few decades (Balmaseda et al, 2015)
Masina et al (2016) have cross-compared the four global ocean reanalyses produced in the framework of the MyOcean project, showing that C-GLORSv4 is a stateof-the-art reanalysis as it compares very well with other reanalyses and validating datasets, at least for the parameters investigated in the aforementioned comparison
The meridional heat transport (MHT) at 26◦ N appears slightly larger in C-GLORSv5 (1.0 vs. 0.9 PW) compared to C-GLORSv4, closer to the mean value derived from the RAPID-MOCHA heat flux array (1.23 PW, Johns et al, 2011)
Summary
Ocean retrospective analyses (or reanalyses, or ocean syntheses) combine available in situ and satellite observations with an ocean general circulation model (OGCM) forced by atmospheric reanalyses by means of advanced data assimilation techniques, with the aim of estimating the state of the ocean in the past few decades (Balmaseda et al, 2015). Masina et al (2016) have cross-compared the four global ocean reanalyses produced in the framework of the MyOcean project, showing that C-GLORSv4 is a stateof-the-art reanalysis as it compares very well with other reanalyses and validating datasets, at least for the parameters investigated in the aforementioned comparison (i.e. sea surface temperature and salinity, averaged temperature in the layers 0–800 and 0–2000 m, sea-ice concentration, Atlantic meridional overturning circulation at 2◦ N and volume transports in selected transects) Starting from these results, the aim of this paper is to describe and assess the improvements present in the latest version of C-GLORS released (v5) and compare it with its predecessor. Version 5 of C-GLORS will be updated in delayed time mode, typically with an approximate 1-year delay beyond present time due to the dissemination of quality-checked observational data
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