Precursor Effect of the Tibetan Plateau Heating Anomaly on the Seasonal March of the East Asian Summer Monsoon Precipitation

The East Asian summer monsoon (EASM) has complex drivers and is characterized by an abrupt onset and northward jumps of the main rain band. By analyzing multisource observational data and reanalysis data sets during 1961-2016, we addressed the connection between the preceding diabatic heating of the Tibetan Plateau (TP) and the seasonal march of the EASM. We show that the positive surface sensible heating and condensation heating anomalies over the TP lead the onset, duration, and total precipitation of the rainy season in South China (the first stage of the EASM) by about 2 and 1 month, respectively. A significant positive condensation heating anomaly over the TP can be detected about 1 month before the onset of the rainy season in Southwest China (the second stage of the EASM). By contrast, the relationship between heating of the TP and the onset of the rainy season is relatively weak during the remaining stages of the EASM, including the Meiyu and North China rainy seasons. We suggest that the strong heating of the TP intensifies the low-level southwesterly circulation to the southeast and facilitates the convergence of moisture and ascending motion, leading to an earlier onset of the rainy season. Sensitive experiments with a linear baroclinic model further confirmed the role of heating of the TP in generating circulation conditions favorable for the onset of the rainy season in both South and Southwest China. The TP heating anomaly therefore acts as a precursor of the early stage onset of the EASM.