Robust Evaluation of ENSO in Climate Models: How Many Ensemble Members Are Needed?

Jiwoo Lee (1) , Yann Planton (2) , Peter Gleckler (1) , Kenneth Sperber (1) , Éric Guilyardi (3) , Andrew Wittenberg (4) , Michael J. Mcphaden (5) , Giuliana Pallotta (1)

1 LLNL - Lawrence Livermore National Laboratory
2 PMEL - NOAA Pacific Marine Environmental Laboratory [Newport]
3 VARCLIM - Océan et variabilité du climat
4 GFDL - NOAA Geophysical Fluid Dynamics Laboratory
5 PMEL - NOAA Pacific Marine Environmental Laboratory [Seattle]

Large ensembles of model simulations require considerable resources, and thus defining an appropriate ensemble size for a particular application is an important experimental design criterion. We estimate the ensemble size (N) needed to assess a model’s ability to capture observed El Niño-Southern Oscillation (ENSO) behavior by utilizing the recently developed International CLIVAR ENSO Metrics Package. Using the larger ensembles available from CMIP6 and the US CLIVAR Large Ensemble Working Group, we find that larger ensembles are needed to robustly capture baseline ENSO characteristics (N > 50) and physical processes (N > 50) than the background climatology (N ≥ 12) and remote ENSO teleconnections (N ≥ 6). While these results vary somewhat across metrics and models, our study quantifies how larger ensembles are required to robustly evaluate simulated ENSO behavior, thereby providing some guidance for the design of model ensembles.

Domaines: Géophysique [physics.geo-ph]

Jiwoo Lee, Yann Planton, Peter Gleckler, Kenneth Sperber, Éric Guilyardi, et al.. Robust Evaluation of ENSO in Climate Models: How Many Ensemble Members Are Needed?. Geophysical Research Letters, 2021, 48 (20), ⟨10.1029/2021GL095041⟩. ⟨hal-03403002⟩