Inter-model comparison of subseasonal tropical variability in aquaplanet experiments: Effect of a warm pool

Stephanie Leroux (1, 2) , Gilles P Bellon (3, 1) , Romain Roehrig (1) , Mihaela Caian (4) , Nicholas P Klingaman (5) , Jean-Philippe P Lafore (1) , Ionela P Musat (6) , Catherine P Rio (6) , Sophie Tyteca (1)

1 CNRM - Centre national de recherches météorologiques
2 LGGE - Laboratoire de glaciologie et géophysique de l'environnement
3 University of Auckland [Auckland]
4 SMHI - Swedish Meteorological and Hydrological Institute
5 UOR - University of Reading
6 LMD - Laboratoire de Météorologie Dynamique (UMR 8539)

This study compares the simulation of subseasonal tropical variability by a set of six state-of-the-art AGCMs in two experiments in aquaplanet configuration: a zonally symmetric experiment, and an experiment with a warm pool centered on the equator. In all six models, the presence of the warm pool generates zonal asymmetries in the simulated mean states in the form of a ''Gill-type'' response, made more complex by feedbacks between moisture, convective heating and circulation. Noticeable differences appear from one model to another. Only half the models simulate mean low-level equatorial westerlies over the warm pool area. The presence of the warm pool can also favor the development of large-scale variability consistent with observed Madden-Julian Oscillation (MJO) characteristics, but this happens only in half the models. Our results do not support the idea that the presence of the warm pool and/or of mean low-level equatorial westerlies are sufficient conditions for MJO-like variability to arise in the models. Comparing spectral characteristics of the simulated Convectively Coupled Equatorial Waves (CCEWs) in the aquaplanet experiments and the corresponding coupled atmosphere-ocean (i.e., CMIP) and atmosphere-only (i.e., AMIP) simulations, we also show that there is more consistency for a given model across its configurations, than for a given configuration across the six models. Overall, our results confirm that the simulation of subseasonal variability by given model is significantly influenced by the parameterization of subgrid physical processes (most-likely cloud processes), both directly and through modulation of the mean state.

Domaines: Océan, Atmosphère

Stephanie Leroux, Gilles P Bellon, Romain Roehrig, Mihaela Caian, Nicholas P Klingaman, et al.. Inter-model comparison of subseasonal tropical variability in aquaplanet experiments: Effect of a warm pool. Journal of Advances in Modeling Earth Systems, 2016, 8 (4), pp.1526 - 1551. ⟨10.1002/2016MS000683⟩. ⟨hal-01478432⟩