An improved atmospheric component of Zebiak-Cane model for simulating ENSO winds

Abstract

The atmospheric component of the Zebiak–Cane (ZC) coupled model is a simple elegant framework that plays an instrumental role in the investigation of the fundamental coupled dynamics of the tropical ocean–atmosphere interaction and the El Niño/Southern Oscillation (ENSO) phenomenon. We attempt two simple thermal and dynamical modifications to reduce apparently spurious wind activities simulated by this atmospheric model in the eastern tropical Pacific under ENSO sea surface temperature (SST) anomaly forcing. First, motivated by established observational evidences, we manipulate the anomalous convective heating to be dependent on the sum of mean SST and SST anomalies and the low-level convergence. Second, we add an ad hoc parameterization for the effect of convective momentum transport (CMT) into the zonal momentum balance. By adding a background-dependent efficiency factor into convective heating and further adjusting the convective feedback parameter used in the original model, we are able to substantially reduce the wind bias in the tropical Pacific, especially in the eastern tropical Pacific. Meanwhile, with a simple CMT parameterization, it compensates an over reduction in the central Pacific wind due to the first modification. By comparing the simulated wind anomalies in our modified version with that from the original version and with the observation, we find that the equatorial wind response to observation SST anomaly forcing for the period 1982–2010 has been improved in terms of amplitudes and spatial patterns. We also show that these improvements are carried over to ZC coupled model as well when we add these modifications to coupled simulations.