The East Asian summer monsoon (EASM) northern boundary is a critical indicator of EASM variations. Movement of the boundary is modulated by both the EASM and the mid-latitude westerlies. Here, we use the Earth system model EC-Earth to quantify the contribution of orbital forcing and vegetation feedbacks in modulating the movement of EASM northern boundary. The results show that the simulated EASM northern boundary during the mid-Holocene shifts by a maximum of ∼213 km northwestward due to orbital forcing. When the model was coupled with a dynamic vegetation module LPJ-GUESS, the northern boundary shifts further northwestward by a maximum of ∼90 km, indicating the importance of vegetation feedbacks.

During the mid-Holocene, temperature increased in the mid-latitude during the boreal summer due to insolation, leading to increased meridional air temperature differences (MTDs) over the region north of 45°N and to decreased MTDs to the south. The changes in the temperature gradient weakened the East Asian Westly Jet (EAWJ) and displaced it northward, resulting in an earlier transition of the Meiyu stage and a more prolonged Midsummer stage. The northward movement of EAWJ, combined with the enhanced southerly moisture flow from South China, caused more precipitation in North China and eventually to a northwestward shift of the northern boundary of the EASM. The coupled dynamic vegetation module LPJ-GUESS simulated more grassland and less forest over Northeast Asia during the mid-Holocene. The increased surface albedo tended to lower the temperature in the region, and further enhanced the MTDs in mid-latitude East Asia, leading to the further northward movement of the EAWJ and a northwestward shift of the EASM northern boundary. Although the simulated vegetation distribution in several regions may be not accurate, it reflects the substantial contribution of climate-vegetation interaction on modulating the EASM.

东亚夏季风 (EASM) 北部边界是 EASM 变化的关键指标。边界的运动受到东亚夏季风和中纬度西风带的调节。在这里，我们使用地球系统模型 EC-Earth 来量化轨道强迫和植被反馈在调节 EASM 北边界运动中的贡献。结果表明，由于轨道强迫，模拟的 EASM 北边界在全新世中期向西北方向移动了最大约 213 公里。当模型与动态植被模块 LPJ-GUESS 结合时，北部边界进一步向西北移动，最大约 90 公里，表明植被反馈的重要性。

在全新世中期，由于日照，北半球夏季中纬度地区的温度升高，导致 45°N 以北地区的经向气温差 (MTD) 增加，而南面的 MTD 则降低。温度梯度的变化削弱了东亚西急流（EAWJ）并向北移动，导致梅雨期过渡提前，仲夏期延长。EAWJ向北移动，加上来自华南的偏南水汽流动增强，导致华北降水增多，最终导致EASM北部边界向西北移动。耦合动态植被模块 LPJ-GUESS 模拟了中全新世期间东北亚更多的草地和更少的森林。地表反照率增加有利于降低该地区的温度，并进一步增强中纬度东亚地区的MTD，导致EAWJ进一步向北移动，EASM北边界向西北移动。虽然几个地区的模拟植被分布可能不准确，但它反映了气候 - 植被相互作用对调节 EASM 的重要贡献。