Multi-Model Prediction for Western Pacific Cross-Equatorial Flow

The Western Pacific low-level cross-equatorial flows (CEF) show evident interannual variability in boreal summer. Our results indicate that the CEF is strongly modulated by ENSO, thus is predictable. To understand the physical mechanism of the interannual change of CEF, Matsuno-Gill and Lindzen-Nigam mechanism are introduced and applied. The CEF is decomposed into two pressure gradient contributions, free-atmosphere and boundary layer, and is mainly contributed by the latter one. The intensity of boundary layer pressure gradient is highly coinciding with the distribution of sea surface temperature (SST) gradient on Western Pacific, which is modulated by ENSO, thus indicating that the Lindzen-Nigam mechanism plays a major role on the interannual change of CEF. A model experiment is included to support the explanation. North American Multi-Model Ensemble (NMME) is further adopted to understand the seasonal predictability of CEFs.