Migration of the Northern Boundary of the East Asian Summer Monsoon Over the Last 21,000 years

Abstract

Monsoons are a crucial component of the atmospheric circulation system, playing a vital role in affecting the human's living environment and social economies worldwide. The East Asian monsoon, an important part of the global monsoon system, consists of tropical and subtropical monsoons (

Northwestward advance of the northern boundary of the East Asian summer monsoon over the 21st century in CMIP6 projections

“…According to the MMM, the linear trends of the 400 mm isohyet are 0.26°−1.21° (uncertainty due to different scenarios), 0.24°−1.26°, and 1.05°−2.29° of latitude, those of the P summer boundary are 0.31°−1.14°, 0.26°−0.83° and 0.61°−1.38° of latitude, and those of the GM metric are 0.17°−1.01°, 0.38°−0.75° and 0.61°−1.29° of latitude in the western, middle, and eastern parts of the boundary during 2015–2099, respectively. There are larger change trends and model spreads in the east for three metrics (Table S4), which is probably due to the regional difference in the precipitation gradient (Wu et al, 2021). The 400 mm isohyet generally exhibits the largest migration trend in the three parts, especially in the east (Figure 4d).…”

“…As the movement magnitudes of the EASM northern boundary are spatially uneven, we divide the boundary into three segments, as in previous studies (Chen et al, 2018; Wu et al, 2021). The fluctuations are mild with a range of 1.37°−2.45° of latitude for the MMM in the western part of the boundary (105° E−110° E), while in the east (115° E−120° E), there are larger fluctuations ranging from 3.50° to 4.70° of latitude under the three scenarios (Figure S4).…”

“…This metric has important climatic, ecological and geographical implications, which separates the sub‐humid from the semi‐arid zones, forest from grassland vegetation, and monsoonal from non‐monsoonal regions. Moreover, this index can reflect the annual range of the total monsoonal precipitation, which is closely associated with the monsoon intensity (Liu et al, 2009; Wang et al, 2012; Wu et al, 2021). Second, the 2 mm day −1 isohyet in May–September (MJJAS) (hereafter P summer ) is utilized to indicate the climatological EASM northern boundary (Chen et al, 2018; Wang et al, 2022).…”

“…Specifically, the simulated ratios of monthly precipitation in 2015–2099 at each grid in each model over the 1981–2010 precipitation climatology are calculated, and then the ratios are multiplied by the observed climatological precipitation during 1981–2010. This correction method has been widely used when calculating indicators that are sensitive to threshold values in previous studies (e.g., Belda et al, 2016; Déqué, 2007; Wu et al, 2021). The statistical significance of the linear trends of the EASM northern boundary migration in 2015–2099 is measured by Student's t test, and the linear trends are multiplied by 85 years for convenience.…”

Evaluation and Projection of Wind Speed in the Arid Region of Northwest China Based on CMIP6

“…The possible reason is that the decreasing surface wind speed in China is related to the weakening trend of the monsoon in East Asia and South Asia [42,43]. Besides, some related studies [44][45][46] predict that the Asian summer monsoon index will increase significantly, and the winter monsoon index will weaken significantly in the future. However, the ARNC is deeply inland and weakly affected by the monsoon, so the variation trends of the surface wind speed in summer and winter are different from those in China.…”