AMOC and water-mass transformation in high- and low-resolution models:
Climatology and variability
Abstract
Water-mass transformation in the North Atlantic plays an important role
in the Atlantic Meridional Overturning Circulation (AMOC) and its
variability. Here we analyze subpolar North Atlantic water-mass
transformation in high- and low-resolution versions of the Community
Earth System Model (CESM1) and investigate whether differences in
resolution and climatological water-mass transformation impact
low-frequency AMOC variability. We find that high-resolution simulations
reproduce the water-mass transformation found in a reanalysis-forced
high-resolution ocean simulation more accurately than low-resolution
simulations. We also find that the low-resolution CESM1 simulations,
including one forced with the same atmospheric reanalysis data, have
larger biases in surface heat fluxes, sea-surface temperatures and
salinities compared to the high-resolution simulations. Despite these
major climatological differences, the mechanisms of low-frequency AMOC
variability are similar in the high- and low-resolution versions of
CESM1. The Labrador Sea WMT plays a major role in driving AMOC
variability, and a similar NAO-like sea-level pressure pattern leads
AMOC changes. However, the high-resolution simulation shows a more
pronounced atmospheric response to the AMOC variability. The consistent
role of Labrador Sea WMT in low-frequency AMOC variability across high-
and low-resolution coupled simulations, including a simulation which
accurately reproduces the WMT found in an atmospheric reanalysis-forced
high-resolution ocean simulation, suggests that the mechanisms are
similar in the real world.