Orographic gravity‐wave drag over multiple bell‐shaped mountains

Abstract

AbstractMountains exert a drag on the atmospheric flow through breaking gravity waves, known as orographic gravity‐wave drag (OGWD). This article presents a theoretical analysis of the impacts and limitations of missing processes in current parameterization schemes for OGWD and examines the significance of various approximations. We derive OGWD analytically for multiple three‐dimensional bell‐shaped mountains, while previous studies have derived OGWD for a single three‐dimensional elliptic mountain. We take into account the geometric overlap between the mountains, vertical shear of the horizontal wind, nonhydrostatic atmosphere, and Coriolis forces. Our findings show that OGWD depends on the direction of the incoming wind and the degree of overlap between two mountains. OGWD increases with the Richardson and Rossby numbers; however, it decreases with the Froude number. Even when the mountain is isotropic, an associated transverse force is generated if the sheared flow passes over the mountain on the ‐plane. By calculating OGWD analytically from more complex terrain and airflow, this study can contribute to the development of an advanced OGWD parameterization in the numerical models used for climate and weather prediction.