Changes in Summer Precipitation Modes over Eastern China in Simulated Warm Intervals of the Last Interglacial, Mid-Holocene, and Twenty-First Century

The East Asian summer monsoon (EASM) and associated summer precipitation patterns over eastern China have exhibited interannual and interdecadal variations in recent decades, but whether the precipitation modes vary with climate conditions remains unclear. In this study, we investigate the changes in summer precipitation modes over eastern China and associated mechanisms in simulated past and future warm periods, namely, the last interglacial (LIG), mid-Holocene, and the twenty-first century under the Shared Socioeconomic Pathway (SSP) based on representative concentration pathway 8.5 (SSP5-8.5) scenario, using Coupled Model Intercomparison Project Phase 6 (CMIP6) models. The model evaluation indicates that only one out of nine CMIP6 models, specifically the Community Earth System Model, version 2 (CESM2), can well reproduce the observed summer precipitation modes at the present. The empirical orthogonal function (EOF) analyses of the CESM2 simulations reveal that during the warm peri-ods induced by either orbital parameters or greenhouse gas concentrations, the first leading mode of summer precipitation switches from its present meridional tripolar structure to a dipole pattern, and the second leading mode is generally a meridional tripolar mode that differs from the present dipole pattern. This summer precipitation regime interchange in the warm intervals is associated with the formation of the dipole and tripolar circulation patterns. The large-scale circulation changes responsible for the altered precipitation modes are attributed to the enhanced EASM and relevant southerly winds due to intensified land-sea thermal contrast, although the external forcings and the mag-nitude of EASM enhancement are different in the interglacial and future periods.

Automated summary

In this study, the changes in summer precipitation modes over eastern China and associated mechanisms in past and future warm periods were investigated using CMIP6 models. The results showed that only the CESM2 model could well reproduce the observed summer precipitation modes at present. The CESM2 simulations indicated that the first leading mode of summer precipitation switches from meridional tripolar structure to dipole pattern during warm periods, and the second leading mode is generally a meridional tripolar mode different from the present dipole pattern.