Impacts of subgrid-scale orographic drag on landfalling typhoon precipitation

While the effects of subgrid orographic drag on large-scale circulation have been extensively studied, its influence on typhoon precipitation remains less understood. Using the Weather and Research Forecasting model, this study investigates impacts of subgrid orographic drag components (gravity wave drag (GWD), flow-blocking drag (FBD), and turbulent orographic form drag (TOFD)) on landfalling typhoon precipitation and explores their resolution sensitivity through two representative cases: Super Typhoon Lekima (2019) and Severe Typhoon In-Fa (2021). Results reveal distinct distributions of GWD and TOFD over southeastern coastal China, which significantly modulate precipitation during strong landfalls like Lekima: GWD enhances precipitation in southern land areas affected by the typhoon while suppressing it in northern regions, whereas TOFD exerts precisely opposing effects. This is mainly due to enhanced (weakened) lower-tropospheric wind speed and water vapor transport caused by GWD (TOFD). GWD is highly sensitive to horizontal resolution, exhibiting more pronounced effects on the wind, moisture, and precipitation at coarser resolutions, while TOFD remains relatively invariant to horizontal resolution changes. Resolution of subgrid orography dataset driving these parameterizations is essential for accurately simulating drag distributions and impacts. Finally, typhoon intensity modulates these effects: stronger background circulation exacerbates the precipitation impacts of both GWD and TOFD.