Development of an atmosphere–ocean coupled operational forecast model for the Maritime Continent: Part 1 – Evaluation of ocean forecasts

Abstract. This article describes the development and ocean forecast evaluation of an atmosphere-ocean coupled prediction system for the Maritime Continent (MC) domain, which includes the eastern Indian and western Pacific Oceans. The coupled system comprises regional configurations of the atmospheric model MetUM and ocean model NEMO, at a uniform horizontal resolution of 4.5 km × 4.5 km, coupled using the OASIS3-MCT libraries. The coupled model is run as a pre-operational forecast system from 1 to 31 October 2019. Hindcast simulations performed for the period 1 January 2014 to 30 September 2019, using the stand-alone ocean configuration, provided the initial condition to the coupled ocean model. This paper details the evaluations of ocean-only model hindcast and 6-day coupled ocean forecast simulations. Direct comparison of sea surface temperature (SST) and sea surface height (SSH) with analysis as well as in situ observations are performed for the ocean-only hindcast evaluation. For the evaluation of coupled ocean model, comparisons of ocean forecast for different forecast lead times with SST analysis, and in situ observations of SSH, temperature and salinity have been performed. Overall, the model forecast deviation of SST, SSH, and subsurface temperature and salinity fields relative to observation is within acceptable error limits of operational forecast models. Typical runtimes of the daily forecast simulations are found to be suitable for the operational forecast applications.