Disentangling Impacts of Dynamic and Thermodynamic Components on Late Summer Rainfall Anomalies in East Asia

This study has examined relative contributions of dynamic and thermodynamic components to East Asian summer monsoon (EASM), compared to the others over Asia. We have decomposed of moisture budget into the dynamic and thermodynamic components composing of interannual variability of the EASM. As represented by the moisture budget, the Asian monsoon is mostly caused by changes in winds (dynamic component); interestingly, changes in moisture (thermodynamic component) play an important role in monsoon rainfall anomalies only for East Asia (27.09%). In terms of the dynamic component over East Asia, strong continental heating, resulting in enhanced land-sea contrast, is identified as crucial to a local development of winds toward East Asia, and it ultimately strengthens a meridional wind, which is accompanied by the western North Pacific subtropical high. In addition, the negative winter North Atlantic Oscillation could induce the enhanced moisture advection term of the dynamic component over East Asia through barotropic Rossby wave propagation. The thermodynamic component has a localized effect on net precipitation at mid-latitudes, with an enhanced wave-train pattern with a zonal wavenumber-5, which reinforces the Okhotsk high. These distinct large-scale circulation patterns together create favorable conditions for heavy rainfall over East Asia when the two components are in-phase. Here we have also described that the extreme heavy rainfall is noticeable when the Eurasian blocking occurs. This study is expected to improve the detailed predictability of the EASM by understanding the two components to prevent disaster risks in terms of extreme rainfall.