Chapter 4 - Subseasonal Prediction of the East Asian Summer Monsoon

Abstract

East Asian Meiyu, as a typical precipitation stage in the East Asian summer monsoon (EASM) season activity, is closely related to the tropical Madden and Julian oscillation (MJO) and intraseasonal oscillation (ISO) of the EASM, which is in concert with the timescale of subseasonal forecasting. By taking Meiyu over the Yangtze River–Huaihe basin as an example, this chapter explores subseasonal prediction methods of EASM rainfall by means of a statistical model, an empirical dynamic model, and a dynamic model based on ISO signals including MJO, which can be used for subseasonal prediction. The optimal subset regression model based on the ISO signal of Meiyu itself has an overall good effect on Meiyu precipitation prediction during flood seasons. Prediction experiments by adopting the influence factors of ISO can provide clues for subseasonal forecast of the onset and end of Meiyu in the Yangtzer–Huaihe basin. The tropical MJO signal is superior to ISO at middle–high latitudes in the prediction of the evolution of Meiyu. The empirical wave propagation method exhibits good potential for forecasting ITCZ (Inter-Tropical Convergence Zone) anomalous activity for the next 40 days, which may be a good predictor of the wind-field anomaly evolution in the Meiyu area. Climatological intraseasonal oscillation of Asian summer monsoon is reasonably well captured in the operational monthly forecasting system by the Environment and Climate Change Canada. Forecast skill of 2m air temperature is statistically significant for all lead times up to days 26–32 over East Asian summer region, which is consistent with the forecast skill of 500hPa geopotential height. Significant forecast skill of precipitation, however, is limited to the week of days 5–11.