Simulations and assimilations of Asian summer monsoon since LGM

The characteristics of multi-scale Asian summer monsoon (ASM) variability and corresponding dominating mechanisms since the Last Glacial Maximum (LGM) are investigated through model simulations, and also comparisons and assimilations with proxy records. The evolutions of ASM precipitation, oxygen isotope, and circulation are first investigated using the isotope-enabled transient experiment (iTraCE). On orbital and millennial scales, the monsoon variability are dominated mainly by external forcings (e.g., orbital parameter, ice sheet, melting water) through dynamic terms, while shorter scale monsoon variability are dominated mainly by internal variability (e.g., AMOC, AMV, PDV).

Then, high-resolution simulations of ASM precipitation are performed using dynamical downscaling through RegCM. The downscaled results show better consistence with proxy records. Paleoclimate data assimilation is applied to the model simulations to improve the underestimation of isotope and precipitation on orbital scale. Assimilated results show a new mega-tripolar pattern of ASM precipitation variations accompanying a continental‐wide enrichment of δ¹⁸O from the early to late Holocene over the entire ASM continental region. This pattern is dominated by the strengthening of westerly jet and weakening of ASM dominated by the precession. Characteristics of centennial scale ASM weakening events (such as 4.2 ka BP event) are also investigated using the assimilated results.