Greater Impacts of summer CP ENSO on the Cross-Equatorial Flows over the Maritime Continent Compared with EP ENSO

Based on the reanalysis data and CMIP6 simulations, this study investigates the distinct responses of the cross-equatorial flows (CEF) over the Maritime Continent (MC) under the simultaneous summer condition of two types of ENSO, i.e., central Pacific (CP) and eastern Pacific (EP). Results indicate that CP ENSO tends to exert stronger impacts on CEF. In CP ENSO years, significant lower-level southerly anomalies can be observed across all CEF branches adjacent to MC, accompanying with broader and deeper upper-level northerly anomalies, indicating a well-organized strengthening of both upper- and lower-level CEFs. In contrast, CEF anomalies in EP ENSO years tend to be weaker, with significant meridional wind anomalies confined east of MC. The disparities in the CEF responses can be elucidated from the perspective of convection over MC, a crucial factor in triggering CEF. In CP ENSO years, westward leaning SST anomalies result in a distinct cooling in MC and suppressed convection above, driving pronounced CEF anomalies. Conversely, the absence of such organized SST cooling during EP ENSO results in weaker convective forcing and subdued CEF responses. Furthermore, historical simulations from 48 CMIP6 models are utilized to validate the observational findings. Results show that model simulations can well reproduce the stronger impacts of CP ENSO, with a remarkable inter-model consistency. This research gains a comprehensive understanding on the diversity of relationship between CEF and ENSO types, and has implications for seasonal forecasting of CEF variability.