The responses of various east Asian summer monsoon northern boundary indicators to monsoon intensity and their applicability

The expansion and contraction of the East Asian summer monsoon (EASM) northern boundary serve as a key indicator of its intensity variations and exert profound influences on the formation and movement of the summer rainbelt in China. Currently, the definition of the EASM northern boundary can be derived from multiple perspectives. However, there are still no unified views for the response of different indicators to variations in monsoon intensity, and their applicability in climate research remains to be further clarified. In this study, we selected three common indicators that reflect the EASM northern boundary: precipitation, water vapor flux divergence, and wind field. A systematic comparison was conducted to evaluate the differences among these three indicators in capturing EASM intensity variations and characterizing the spatiotemporal variation of northern boundary. Furthermore, we assessed the applicability of each indicator from the perspective of precipitation. Results demonstrate that all three indicators can reflect EASM northern boundary intensity variations, with the water vapor flux divergence indicator exhibiting superior performance. Anomalous northward shifts in the precipitation and water vapor flux divergence boundaries are generally associated with enhanced summer precipitation. Conversely, a northward movement of the wind field boundary may be indicative of reduced summer precipitation. Overall, the precipitation northern boundary can indicate the summer precipitation anomalies best. Furthermore, shifts in all three EASM northern boundaries can respond the movements of the summer rainbelt. Notably, anomalous northward displacement of the water vapor flux divergence northern boundary serves as the best indicator of indicating the northward displacement of summer rainbelt.