Projections of the Walker circulation and Asian monsoon rainfall variability related to two types of ENSO in the 21st century
Monday, June 15, 2015
Kang Xu1,2, Chi-Yung Francis Tam1 and Congwen Zhu3, (1)Chinese University of Hong Kong, Earth System Science Programme, Hong Kong, China, (2)South China Sea Institute of Oceanology, Chinese Academy of Sciences, State Key Laboratory of Tropical Oceanography, Guangzhou, China, (3)Chinese Academy of Meteorological Sciences, Institute of Climate Systems, Beijing, China
Abstract:
Future projections of the Walker circulation and Asian Monsoon rainfall variability, in relation to the Eastern-Pacific (EP) and Central-Pacific (CP) types of El Nino-Southern Oscillation (ENSO), have been studied based on historical runs from the Coupled Model Intercomparison Project phase 5 (CMIP5) and model simulations for the 21st century corresponding to the Representative Concentration Pathways (RCP) 4.5 and 8.5. EP- and CP-ENSO events, as well as their coupling with the Walker circulation, were identified based on empirical orthogonal function (EOF) analysis of the tropical Pacific sea surface temperature (SST), and by singular vector decomposition (SVD) between the SST and the sea level pressure (SLP) fields. Results from the historical runs indicate that while the majority of CMIP5 models are able to capture EP-ENSO and its coupling with the Walker circulation, only a half of models can reproduce the anomalous Walker cells associated with CP-ENSO. Based on their performance in capturing the tropical Pacific SST variability and its coupling with the atmospheric circulation, the best models for simulating the two types of ENSO were selected, and their projections for the 21st century climate state were further examined. There is evidence that SST variability associated with CP-ENSO will become stronger in the future climate; on the other hand, there seems to be no significant change in the EP-ENSO-related SST variability. However, the monsoon and Walker circulation rainfall response to both EP- and CP-ENSO was found to be enhanced, in the sense that stronger rainfall variations are expected for either type of ENSO events with their amplitude properly standardized in the 21st century. Implications of our results to the interannual to interdecadal rainfall variability over East Asia will be discussed.
