Improving the Ocean Temperature in a Coupled Atmosphere-Ocean System using Microwave Imager Observations
| Title | Improving the Ocean Temperature in a Coupled Atmosphere-Ocean System using Microwave Imager Observations
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Report
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| Date Published |
10/2025
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| Series/Collection |
EUMETSAT/ECMWF Fellowship Programme Research Report
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| Document Number |
RR65
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| Author | |
| Abstract | Knowledge of the ocean temperature is vital to the accurate use of satellite radiances in weather forecasting and it helps improve the quality of forecasts for the ocean and atmosphere. Recent work has shown that a sink variable approach can be used in atmospheric data assimilation to extract information about the ocean temperature from satellite-borne instruments measuring in the microwave range. In the present work, we build on these developments to include, for the first time, ocean temperature information from microwave imager radiances in ECMWF’s ocean analysis. This is achieved via the assimilation of radiances in a coupled atmosphere/ocean assimilation system. Demonstrating the use of such information from satellite-borne instruments measuring in the microwave range is not only important for current instruments, but will also enhance the exploitation of upcoming sensors such as the Copernicus Imaging Microwave Radiometer (CIMR) from the European Space Agency (ESA) and the Microwave Imager / Ice Cloud Imager (MWI/ICI) from the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT). At cycle 50r1 of the ECMWF Integrated Forecast System, the coupling between the atmosphere and the ocean has been developed at the level of the outer loop of the atmospheric data assimilation. This allows information to be passed from the atmosphere to the ocean and back again within one data assimilation window. The work presented here uses this method to pass skin temperature estimates derived from microwave imagers (AMSR2 and GMI) to the ocean data assimilation system. The updated ocean state is then passed back to the atmospheric data assimilation system. At the current stage of development the ocean is re-initialised every 24 hours from a separate 8-12 day window ocean analysis, which depends on external ocean temperature retrieval products. The current work demonstrates that the use of these skin temperature estimates improve the fit of the ocean to ARGO float observations, resulting in up to 4% improvements in the Eastern Tropical Pacific. Improvements in the modelled SKT are also recorded indirectly through improvements in the fit of significant wave height observations and infra-red channels sensitive to the surface on-board geostationary satellites. In terms of the forecast, the most significant changes in the mean field and improvements to the forecast verification are apparent in the medium range (2 to 6 days). Statistically significant improvements in the Root Mean Squared Error (RMSE) are seen in the tropics for relative humidity at the surface and in the Southern Hemisphere for temperature, vector winds and geopotential height in the upper atmosphere. In the long run, as the methods used in this work are further developed and more observations become available, it may be possible to cut the dependence on the 8-12 day external ocean analysis and to fully constrain the ocean within the atmospheric 12 hour assimilation window. This scenario would be expected to extract even more benefit from the skin temperature estimates and would negate the need to use external ocean temperature product. |
| URL | https://www.ecmwf.int/en/elibrary/81682-improving-ocean-temperature-coupled-atmosphere-ocean-system-using-microwave |
| DOI | 10.21957/bf0d7466b0 |
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