Orographic drag is an essential process for numerical weather predictions in complex terrain regions, which depends on the inflow direction. In this study, we define the orographic asymmetry vector (OAV) for a coarse grid as the normalized vector between the grid's center point and its center of mass, and the orographic asymmetry in a flow direction—which describes the inclination direction and the extent of the subgrid terrain—is calculated as the projection of OAV on this direction. Calculations of the effective orographic length (OL) and the model grid length λ are extended to all flow directions. A new orographic drag scheme, which considers the effect of orographic anisotropy in all directions, is then developed based on the OAV projection and the extended OL and λ for any given direction. Sensitivity tests of the orographic drag under the new scheme are conducted using a 5 m/s vertically uniform wind along different directions for four coarse grid points in typical mountain regions. The new scheme is shown to provide a more continuous transition of the orographic parameters and the resulting stress as a function of flow direction than piecewise transition of schemes with only eight directions. The predicted momentum flux profile of the new scheme is compared with mountain‐wave simulations obtained from the integrated modeling system IAP‐WRF (Institute of Atmospheric Physics‐Weather Research and Forecasting Model) for the Rocky Mountain. The new scheme is shown to predict an overall narrower stress scatter about the reference simulation than the old scheme. Plain Language Summary The orographic drag exerted by the Earth surface on the atmospheric flow is an essential process for numerical weather predictions and depends on the flow direction. Including the effect of the orographic drag in all directions is important for improving weather forecasts and climate prediction. In this study, we refine the derivation method of the subgrid topographic parameters and develop a new orographic drag scheme considering anisotropy in all directions for weather and climate models. It is shown that the new scheme yields a more continuous transition of the orographic parameters and the resulted drag as a function of flow direction than the transition obtained from the standard scheme with only eight directions, and the new scheme exhibits an overall better performance than this old scheme.
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