Oral

IAMAS

M18 - Monsoon systems: variability, processes, predictability, change and extremes

A novel Asian Summer Monsoon Index reconstructed from mixed approach and the multidecadal variability revealed in 1400-1900s

The Asian summer monsoon (ASM) is a distinctive component of the Asian climate system due to orographic forcing. One of the main challenges to study ASM is the extensive domain of the ASM encompassing tropics, subtropics and midlatitudes and thus the complex space and time structures making it difficult to quantify the ASM variability. Despite the challenges, studying the evolution of ASM over hundreds or thousands of years is essential to build a comprehensive understanding on the monsoon behaviors and their associations with the general circulations. Many previous studies used geochemical proxy records from oceanic sedimentary or continental archives to reconstruct paleo-ASM indices by depending mostly on rainfall information retrieved from the records at some sporadic sites. The geochemical methods are valuable but still face inevitable issues in spatial coverage and the limited explanatory power for the overall ASM. In this study, we present a novel approach to reconstruct an ASM index from 1 degree x 1 degree latitude/longitude rainfall data reconstructed from historical Chinese documents in the REACHES (Reconstructed East Asian Climate Historical Encoded Series) database (Wang et al., 2018). First, the current observational Western North Pacific monsoon index (Wang et al. 2008, in Journal of the Climate) approach was used to calculate the wind fields (zonal and meridional winds at 850hPA) from 1950 to 2020 using ERA5 data and rainfall data from NOAA Precipitation Reconstruction over Land to construct the modern ASM index. Then, the ASM rainfall pattern was projected to the gridded REACHES rainfall data from 1368 to 1911CE. Thus, the reconstructed REACHES-ASM index is considered by both temporal and spatial variability. In addition, the linkage of REACHES-ASM index and extreme events such as flood and drought were examined. Therefore, the indication of the dominate large-circulation is able to be investigated through the multidecadal to centennial time scale.