Seasonal evolution of the intraseasonal variability of China summer precipitation

Seasonal cycle of China summer precipitation has significant impacts on its subseasonal predictability; yet current understanding of seasonal evolution of the intraseasonal variability (ISV) remains limited. Here, we show that the ISV of China summer precipitation features a distinct three-stage evolution during early summer, Meiyu season, and late summer. There are two common leading ISV modes: a uniform mode (UM) over southeastern China and a dipole mode (DM) between coastal southeastern China and mid-lower reaches of the Yangtze River Basin, which occur during all three stages with a dominant period of 8-15 days in the early and late summers and 8-25 days during Meiyu season. These two modes show southward propagation in early summer, but they are independent from each other in the other two stages. In early summer, both UM and DM are only related to mid-latitude wave train, and no preceding signal is found in the tropics due to the weak western North Pacific (WNP) monsoon trough. In contrast, during the Meiyu season and late summer, preceding tropical signals are observed when the WNP monsoon trough becomes strong. In the late summer, the effect of mid-latitude wave train is weak as the westerly jet-induced wave guide is far away from southeastern China. An improved subseasonal prediction system is expected to be benefited from consideration of the seasonal evolution of China summer precipitation ISV.