Decadal shifts of East Asian summer monsoon in a climate model free of explicit GHGs and aerosols

Abstract

The East Asian summer monsoon (EASM) experienced decadal transitions over the past few decades, and the associated "wetter-South-drier-North" shifts in rainfall patterns in China significantly affected the social and economic development in China. Two viewpoints stand out to explain these decadal shifts, regarding the shifts either a result of internal variability of climate system or that of external forcings (e.g. greenhouse gases (GHGs) and anthropogenic aerosols). However, most climate models, for example, the Atmospheric Model Intercomparison Project (AMIP)-type simulations and the Coupled Model Intercomparison Project (CMIP)-type simulations, fail to simulate the variation patterns, leaving the mechanisms responsible for these shifts still open to dispute. In this study, we conducted a successful simulation of these decadal transitions in a coupled model where we applied ocean data assimilation in the model free of explicit aerosols and GHGs forcing. The associated decadal shifts of the three-dimensional spatial structure in the 1990s, including the eastward retreat, the northward shift of the western Pacific subtropical high (WPSH), and the south-cool-north-warm pattern of the upper-level tropospheric temperature, were all well captured. Our simulation supports the argument that the variations of the oceanic fields are the dominant factor responsible for the EASM decadal transitions.

Timescale dependence of the relationship between the East Asian summer monsoon strength and precipitation over eastern China in the last millennium

“…The spatial pattern of summer winds and precipitation anomalies between the MCA and LIA ( Fig. 2d) further indicate that when southerlies over East Asia reinforce, precipitation over almost all of eastern China increases, consistent with the findings of Liu et al (2011a). In addition, the in-phase changes of the EASM strength and precipitation over eastern China are shown in both the MEM and individual PMIP3 models' results ( Fig.…”

“…Numerical simulations offer a useful tool to examine climate change and the associated dynamic mechanisms in the past. Based on the ECHO-G simulation, Liu et al (2011a) indicated that the EASM was strengthened and summer precipitation increased over eastern China during the MCA, which were attributed to the increased total solar irradiation. Man et al (2012) indicated that the EASM became stronger during the MCA, but precipitation increased (decreased) in north (south) China in the Max Planck Institute Earth system model (MPI-ESM) simulations.…”

Can coupled models perform better in the simulation of sub‐seasonal evolution of the western North Pacific subtropical high than atmospheric models in boreal summer?

“…According to previous studies, air–sea interaction is very important to climate simulation in East Asia and western North Pacific region (Wang et al ., ; Zou and Zhou, ; Song and Zhou, ; Lin et al ., ). Thus, besides AMIP‐type simulation, we also examined coupled simulation in 37 CMIP5 models.…”

“…Thus in AMIP‐type experiments, warm (cold) local SST will lead to more (less) local precipitation over tropical areas. However, the atmospheric feedback cannot be ignored in WNPSH region (Zou and Zhou, ; Lin et al ., ). Worth noting is that the process explained here applied only to tropical areas.…”

“…In the WNP regions, the SST and precipitation anomalies are negatively correlated in the observation and positively correlated in AMIP models. Positive correlation means the SST affect atmosphere more than atmosphere affect SST (Wang et al ., ; Lin et al ., ). The best models reveal negative correlation or small positive correlation over some small areas.…”