[세미나] 최현주 박사님

Parameterizations of Subgrid Orographic Drag and Non-Orographic Gravity Wave Drag for Korean Integrated Model (KIM) System

Parameterizations of Subgrid Orographic Drag and Non-Orographic Gravity Wave Drag for Korean Integrated Model (KIM) System

Korea Institute of Atmospheric Prediction Systems (KIAPS) has developed a new global forecast system, the Korean Integrated Model (KIM) system, since 2011 to replace the current operational model at Korea Meteorological Administration (KMA), which has been adopted from the United Kingdom’s Met Office Unified Model. In this talk, the parameterization schemes of subgrid orographic drag and non-orographic gravity wave drag (GWD) for the KIM system are introduced. The mesoscale (the scale range 4 km to the model resolution) orographic drag scheme parameterizes the drag due to gravity wave breaking, low-level wave breaking, and flow blocking. The inclusion of flow-blocking drag increases the orographic drag in the lower troposphere noticeably. The enhanced drag directly weakens the excessive wind speed in the low troposphere and indirectly improves the temperature and mass fields over East Asia during the winter season. In addition, the snowfall overestimation over Korea is improved by the reduced heat fluxes from the surface. Both the low-level wave breaking and flow-blocking drag improve the intensity of a summertime continental high over the northern part of the Korean Peninsula, which is exaggerated with GWD only. This is because the enhanced lower tropospheric drag due to the effects of low-level wave breaking and flow blocking slows down the wind flowing out of the high-pressure system in the lower troposphere. It is found that the decreased lower-level divergence induces a compensating weakening of middle- to upper-level convergence aloft. The effect of drag due to subgrid orography with turbulent scales (the scale range smaller than 4 km), the so-called turbulent orographic form drag, is introduced by revising the surface exchange coefficient for momentum. The inclusion of turbulent orographic

form drag reduces positive wind bias in the near-surface and low atmosphere. The non- orographic GWD scheme parameterizes the effects of convective and frontal gravity waves

with wide phase speed spectra. The convective GWD scheme replaces the existing one that considers only a stationary convective GW, and the frontal GWD scheme is newly introduced. The source-based non-orographic GWD scheme improves the seasonal representation of stratospheric wind, through changes in both the GWD and the resolved wave forcing, which is modulated by the changed large-scale wind due to the GWD. The downward influence, in response to the changed GWD, is also positive in the tropospheric fields, such as subtropical jet and planetary-scale disturbances.