[Seminar on 18 Nov.]Towards understanding the effects of small-scale nonlinear processes on global atmospheric chemistry
Dr. Jintai Lin
14:00, 18 Nov., 2014
Global chemical transport models, a key tool to studying global air pollution and transport, are limited by coarse horizontal resolutions (typically 200-500 km) that cannot capture small-scale nonlinear processes in the atmosphere. These limitations may explain various critical problems in current models including an overestimate (by 10-20%) in tropospheric OH content and an underestimate in CO. Here, we develop the first global-multi-regional two-way coupled system integrating the global GEOS-Chem (at a ~200km resolution) and its three nested models (at ~ 50 km) encompassing Asia, North America and Europe, respectively. We develop a PeKing University CouPLer (PKUCPL) to execute the two-way interaction with small additional computational complexity and costs beyond the global model alone. Under the coupling framework, the nested (regional) models not only obtain lateral boundary conditions from the global model, as done in current regional models, but are also used to adjust global model results in the respective domains. As confirmed by the HIPPO aircraft measurements, our two-way coupled system results in a significant reduction in tropospheric OH (by 4%, greater than the interannual variability of OH at 2.3%) and a large enhancement in CO (by 10%, equivalent to about 25% increase in global CO emissions from all sources). The two-way coupled system also produces much higher CO than ‘one-way’ nesting models, with important implications for regional studies.
Currently, we are developing a global-regional multi-layer (from 200 km to 50 km and to 25 km) two-way coupling system as well as an ultra-fine-resolution global model (at 25 km) to further evaluate the effects of small-scale nonlinear processes on global and regional atmospheric chemistry.