Climatology, long-term variability and trend of resolved gravity wave drag in the stratosphere revealed by ERA5

Internal gravity waves have well-known importance for atmospheric dynamics, transport and coupling between atmospheric layers, and their parameterized forcing affects the circulation in climate models, especially in the stratosphere. The statistical features, spatial distribution, and short- and long-term variability of the parameterized gravity wave drag were studied extensively. Yet, little is known about the gravity wave drag in the real atmosphere. Challenges arise when attempting to constrain gravity wave drag using observational data, leading to the widespread use of wave activity proxies. Moreover, our limited observational capabilities hinder comprehensive assessments of global, long-term changes in stratospheric dynamical quantities. This study presents a quasi-observational analysis of resolved gravity wave drag climatology, variability and trends in the stratosphere. We employ a state-of-the-art methodology for gravity wave drag estimation, applying it to ERA5, the latest-generation atmospheric reanalysis that resolves a substantial portion of the gravity wave spectrum (wavelengths from a few hundred to a few thousand kilometers). The results are provided in the traditional zonal mean perspective, and, for the first time in the literature, we also focus on regional drag estimates over major orographic hotspots, fully taking into account the drag from lateral gravity wave propagation. Overall, our study represents a first step towards validating the climatology and variability of parameterized gravity wave drag in climate models.