An overview of the performance of CMIP6 models in the tropical Atlantic: mean state, variability, and remote impacts
- PDF / 5,786,759 Bytes
- 23 Pages / 595.276 x 790.866 pts Page_size
- 52 Downloads / 193 Views
An overview of the performance of CMIP6 models in the tropical Atlantic: mean state, variability, and remote impacts Ingo Richter1 · Hiroki Tokinaga2 Received: 31 December 2019 / Accepted: 29 July 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract General circulation models of the Coupled Model Intercomparison Project Phase 6 (CMIP6) are examined with respect to their ability to simulate the mean state and variability of the tropical Atlantic and its linkage to the tropical Pacific. While, on average, mean state biases have improved little, relative to the previous intercomparison (CMIP5), there are now a few models with very small biases. In particular the equatorial Atlantic warm SST and westerly wind biases are mostly eliminated in these models. Furthermore, interannual variability in the equatorial and subtropical Atlantic is quite realistic in a number of CMIP6 models, which suggests that they should be useful tools for understanding and predicting variability patterns. The evolution of equatorial Atlantic biases follows the same pattern as in previous model generations, with westerly wind biases during boreal spring preceding warm sea-surface temperature (SST) biases in the east during boreal summer. A substantial portion of the westerly wind bias exists already in atmosphere-only simulations forced with observed SST, suggesting an atmospheric origin. While variability is relatively realistic in many models, SSTs seem less responsive to wind forcing than observed, both on the equator and in the subtropics, possibly due to an excessively deep mixed layer originating in the oceanic component. Thus models with realistic SST amplitude tend to have excessive wind amplitude. The models with the smallest mean state biases all have relatively high resolution but there are also a few low-resolution models that perform similarly well, indicating that resolution is not the only way toward reducing tropical Atlantic biases. The results also show a relatively weak link between mean state biases and the quality of the simulated variability. The linkage to the tropical Pacific shows a wide range of behaviors across models, indicating the need for further model improvement.
1 Introduction The eastern equatorial Atlantic is marked by a pronounced seasonal cycle, with warm sea-surface temperature (SST) during boreal spring (MAM; Fig. 1a) giving way to a cold tongue in boreal summer (JJA; Fig. 1b). During the transition period, the intertropical convergence zone (ITCZ) shifts from a position just on the equator in MAM to a Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00382-020-05409-w) contains supplementary material, which is available to authorized users. * Ingo Richter [email protected] 1
Application Laboratory, Research Institute for ValueAdded-Information, Japan Agency for Marine-Earth Science and Technology, 173‑25 Showa‑machi, Kanazawa‑ku, Yokohama, Kanagawa 236‑0001, Japan
Research Institute for Applied Mechanics, Kyushu Univer
Data Loading...
