A recently published study supported by CPO’s Climate Variability & Predictability (CVP) and Modeling, Analysis, Predictions and Projections (MAPP) programs tests the physics-based assumptions made in two subtropical North Atlantic observational arrays in order to improve the tools scientists use to evaluate the Atlantic Meridional Overturning Circulation (AMOC). Lead author Gokhan Danabasoglu and a team of researchers from the National Center for Atmospheric Research (NCAR), University of Southampton, and UC San Diego compared model simulations of AMOC characteristics with those available from observational arrays.Their work, published in Geophysical Research Letters, reinforces the need for proper treatment of reference depths and velocities in the calculations that underpin both observational and modeling estimates.
MOVE (Meridional Overturning Variability Experiment) and RAPID are the two longest-recording observational arrays in the subtropical North Atlantic that measure ocean circulation. Notably, RAPID is funded in part by CPO. Measurements made at both these sites are key to understanding how AMOC moves transports—heat, freshwater, and carbon—as well as the climate impacts associated with this transport. These arrays do not measure ocean currents directly, but rely on a set of technically, logistically, and financially simplified measurements combined with fundamental physics-based assumptions to calculate current characteristics.
The authors revisit the underlying assumptions used to generate RAPID and MOVE transports by comparing them to transports simulated in an ocean transport model with the same assumptions built into the models programming, as well as transports simulated with alternative approaches. The areas of agreement and disagreement between the observations and model results pinpoint key physics-based areas of improvement. Strengthening the assumptions underlying observational instruments such as MOVE and RAPID will advance the understanding of circulation in the Atlantic Ocean and allow for better evaluation of future AMOC characteristics.
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Image: RAPID-MOCHA-WBTS array, courtesy of NOAA's Atlantic Oceanographic and Meteorological Laboratory.
This study was also supported by the NOAA Global Ocean Monitoring and Observing (GOMO) Program and by the Department of Energy, Earth and Environmental System Modeling, Regional and Global Model Analysis Program.