Reanalysis of the AMOC

The Atlantic Meridional Overturning Circulation (AMOC for short) transports warm and saline Atlantic surface waters northward to high polar latitudes where it is transformed into colder (and also fresher) water, which sinks and returns southward underneath the warm waters. The Gulf stream is the best known surface current that contributes to carrying the warm surface waters to the north. The strength of this exchange flow has been monitored now for 10 years at Latitude 26N (Florida-Africa). Models suggest that low frequency changes in this AMOC flow may (i) be predictable some years ahead, and (ii) lead to changes in North Atlantic weather and climate some years later due to changing the warm water distribution at the ocean surface. To realise the potential of the AMOC monitoring measurements at 26N these observations need to be successfully "assimilated" into the ocean and climate prediction models being currently used at the Met Office and elsewhere. This project will develop novel methods to introduce the AMOC observational data into the latest ocean and climate model environments, in combination with other complementary datasets that are available, e.g. from ocean profiling floats (ARGO), and from satellites measuring sea surface temperatures and sea level. The experiments will be carried out in close collaboration with scientists from the Met Office and the European Centre for Medium Range Weather Forecasts (ECMWF) in order to allow rapid take up of successful innovations.

The project will allow a key climate monitoring dataset, the Trans-Atlantic "Atlantic Meridional Overturning Circulation or AMOC" array at 26N across the N Atlantic ocean, to be used for the first time to directly constrain transports in ocean and climate models that are used operationally in seasonal and longer term climate predictions.

By addressing the upstream causes of variations in the AMOC in the way that the data are assimilated we hope to generate dynamically consistent AMOC circulations which can be realistically persistent within climate models and lead to increased predictability of changes in N Atlantic Sea surface temperatures, as indicated should be possible from climate model simulations.

The results will have an impact on the operational forecasting activities at the Met Office and at the ECMWF where the new assimilation approach for the AMOC should be easily adopted into the operational systems currently in use for initialising climate predictions.

The archiving and publication of the AMOC reanalysis results at BADC will lead to opportunities to use the results of the project for many other studies (as has been demonstrated from previous reanalysis datasets published in this way).