AOS 271


Thursday, May 23


Jinqiang Chen, Caltech




Math Science 7124

TOPIC: " A New Look into Large-scale Processes Governing the East Asian Summer Monsoon"


"The East Asian summer monsoon (EASM) is an important branch of the larger-scale Asian monsoon and exerts a profound influence on the climate of eastern Asia (the Meiyu-Baiu region, MB) and the northwestern Pacific Ocean. It influences one quarter of the whole world population and its interannual variability can cause floods, droughts, heat waves and other natural hazards. However, even such a large-scale precipitation rainfall band is poorly simulated in most GCMs and its large-scale dynamics, let alone factors controlling its multi-scale variability, remains poorly understood. Here, we use twenty years (1990-2009) of ECMWF ERA Interim reanalysis data to study the energetics of the MB system in the context of the moist static energy (MSE) budget. We find that horizontal advection of atmospheric moist enthalpy, and primarily of dry enthalpy, sustains the front in a region of otherwise negative net energy input into the atmospheric column. The joint spatial pattern of horizontal atmospheric moist enthalpy advection and energy flux into the atmospheric column coincides remarkably well with the region of intense precipitation thus providing a simple but precise framework to locate the EASM rainfall band. A decomposition of the horizontal dry enthalpy advection into transient and stationary eddy fluxes shows that the longitudinal thermal gradient due to zonal asymmetries, meridional eddy velocity and eddy convergence are controlling factors in the local moist enthalpy convergence. Numerical simulations show that the presence of the Tibetan Plateau primarily changes the eddy convergence through meridional eddy velocity with reinforced southerly wind over the MB region and northerly wind to the north of the MB region. We further investigate discrepancies between observed data and CMIP5 model outputs and expose possible factors affecting the representation of the EASM in climate models."