Impact of 3D topography on surface solar radiation  The impact of 3-dimensional interactions between solar radiation and topography, including the difference between sunward and shaded slopes of mountains, shadow cast by nearby terrain, and multiple reflections between surfaces, is totally ignored in all current weather and climate models. I designed a 3D Monte Carlo program to simulate the travel of photons in the atmosphere and their interactions with irregular land surfaces. In addition, I developed a novel and efficient parameterization to estimate the topographic impact on surface solar radiation for application to weather and climate models based on the results of numerous Monte Carlo simulations.

Radiative effect of precipitating snow  When snow is falling in the air, it still can reflect sunlight and absorb infrared. However, most current GCMs do not consider radiative effect of snow because precipitation is assumed to fall to the surface immediately. As a result, GCMs could underestimate/overestimate upward shortwave/longwave radiation at the top of the atmosphere (TOA). We have investigated the impact of this systematic bias on GCM simulations by turning on and off this effect in Community Earth System Model version 1 (CESM1). The result suggests that common biases of Coupled Model Intercomparison Project phase 5 (CMIP5) models is partly attributable to the falling snow radiative effect. We found that the excessive solar heating in the tropics can result in overestimated precipitation and weakened trade winds that further causes biases of sea surface temperature and salinity in the tropical Pacific. In addition, the periodicity and amplitude of the El Niño is also affected. On the other hand, missing of the downward longwave radiation emitted by falling snow could lead to surface cold bias in high-latitude regions. Consequently, the retreat of Arctic sea ice could be underestimated by current CMIP5 models.

Assessing cold bias over the Tibetan Plateau in GCMs  Almost all contemporary GCMs encounter severe cold bias of about 4 K over the Tibetan Plateau in winter. I evaluated the impacts of 3D topography-radiation interaction and falling snow radiative effect on surface energy fluxes. Both mechanisms contribute the deficiency of downward radiation and therefore lead to underestimation of surface temperature. The surface net solar radiation increases at the inland regions and the southern slope of the Himalayas, due to multiple reflection and additional sunlight at the sunward side, respectively. Consequently, the surface temperature can increase by more than 1 K in these regions. The falling snow can emit more downward longwave radiation and warm up the surface.

Development of Taiwan Earth System Model (TaiESM)  For capability and capacity building of climate modeling in Taiwan, we have developed the Taiwan Earth System Model (TaiESM) on the basis of CESM1 from National Center for Atmospheric Research (NCAR). Several locally-designed physical and chemical parameterizations, including deep convection, cloud macrophysics, aerosols, and radiation-topography interaction, are implemented in CESM1. Our goal is to improve climate variability simulations for both spatial and temporal aspects. In addition to development and implementation of my radiation scheme, I am in charge of coordination and programming to integrate all new schemes into TaiESM and arrange series of GCM simulations for the Phase 6 of Couple Model Intercomparison Project (CMIP6).