The representation of marine surface fluxes is linked to intertropical
convergence zone biases
Abstract
Ocean-atmosphere coupled climate models struggle to produce a single
northern hemisphere intertropical convergence zone (ITCZ), and instead
simulate ITCZ bands in both hemispheres. This “double ITCZ’ bias can
negatively impact representations of large-scale modes of variability,
such as the Madden-Julian oscillation and El Ni\
no–Southern Oscillation. A new method to estimate model fluxes that
would have been obtained with the COARE3.0 bulk flux algorithm indicates
that twelve of fourteen CMIP6 models overestimate surface fluxes in the
ITCZ region, suggesting that biases rooted in model flux algorithms may
contribute to ITCZ biases. This finding is supported by atmosphere-only
simulations of two models where the original flux algorithms are
replaced with the COARE3.0 algorithm. In the experiments, precipitation
root mean square errors in the double ITCZ region were reduced by
26\% and 15\%, respectively. We
interpret these findings through the lenses of global energy constraints
and convection-boundary layer interactions.