Multi-Scale Land-Atmosphere Coupling and Its Influence on Subseasonal to Seasonal Drought Prediction over East Asia

The land surface, with a memory longer than the atmosphere in nature, has been recognized as an important source for subseasonal to seasonal (S2S) drought predictability through land-atmosphere coupling (LAC) at multiple time scales, especially when the signal from ocean is absent. However, the LAC was usually quantified climatologically, while its temporal variations and the link with drought predictability received less attention over East Asia. Here we investigate LAC over East Asia from daily to monthly time scales, and consider temporal variability of the coupling based on the joint probability space of surface soil moisture, convective triggering potential, and the low-level humidity. The LAC was classified into four types: atmospherically controlled, transition, dry coupling, and wet coupling. The impact of LAC on S2S drought prediction were further investigated by applying this classification to S2S reforecast datasets, as well as the result from ERA-Interim reanalysis and Climate Forecast System Reanalysis (CFSR). The possible causes for the coupling bias in the reforecasts are being analyzed. This study implicates that daily to subseasonal LAC is a critical source of uncertainty in drought prediction, and it should be carefully diagnosed for understanding the predictability.