Tropical climate variability and ENSO in ACCESS models

Tropical climate variability and ENSO in ACCESS models for CMIP 6 Harun Rashid, Climate Science Centre, CSIRO Oceans and Atmosphere

Models and experiments • Historical simulations: • ACCESS-CM 2 (1850 -1961) • ESM 1. 5 (1850 -1907) • Variables: • Sea surface temperatures (SSTs) • Zonal wind stress (Taux) • Thermocline depth (Z 20) • Stats: Mean, variance, EOFs and spectral analysis

Time mean SST, Taux and Z 20. Cold tongue bias in the western to central Pacific in both models Westerly bias in the central to eastern Pacific Deeper thermocline, with a shallow patch to the south

Temporal standard deviations Max SST variance is confined to the Nino 3 region (east Pacific) for CM 2 Smaller Taux variance in the tropics than in obs Also smaller tropical Z 20 variance

EOFs of Pacific SST anomalies The 1 st EOF has too small (large) area in CM 2 (ESM 1. 5) The observed 2 nd EOF appears as the (weaker) 3 rd EOF in CM 2

EOFs of zonal wind stress anomalies Too little tropical Taux variability The leading EOFs are dominated by subtropical variances, unlike in obs

EOFs of thermocline depth anomalies The leading east-west mode is not pronounced In the models (appears as the 2 nd mode? ) The 1 st EOF in CM 2 looks more like the rechargedischarge mode (2 nd mode in obs)

Wavelet and power spectra

Cross-correlations and coherence SST-Taux coherence occurs at very low frequencies for ESM 1. 5 SST, Taux and Z 20 in CM 2 are strongly coupled at the biennial frequency Max +ve correlations occur at shorter lags for the models