Climatology of Mountain Wave Turbulence in the Upper Troposphere and Lower Stratosphere in Recent Decades Using the ERA5 Data

Turbulence in the upper troposphere and lower stratosphere (UTLS) can pose a threat to the safe aircraft operation. Especially, mountain wave turbulence (MWT), which is turbulence generated by breakdown of orographic gravity waves, can cause aircraft accidents in the mountainous regions in the world. Recently, Lee et al. (2023) investigated climatology of clear air turbulence (CAT) in the UTLS using reanalysis data, and Kim et al. (2023) investigated global response of CAT, MWT, and near cloud turbulence (NCT) to climate change using climate model data. For a better understanding of climatology of MWT at flight levels in the world from the state-of-the-art reanalysis data, this study investigates climatology of MWT in the UTLS in recent decades using ECMWF Reanalysis version 5 (ERA5) data and related atmospheric flows near the mountains. From the ERA5 data, several MWT diagnostics were calculated by multiplying mountain wave stress and CAT diagnostics in the mountainous region following the method of Sharman and Pearson (2017) and Kim et al. (2018). When we calculated mountain wave stress, the maximum wind speed projected to the direction perpendicular to the mountain ranges in the lower troposphere was considered. Also, orographic gravity wave drags calculated following Palmer et al. (1986) and parameterized from the ERA5 were compared with the calculated MWT diagnostics. The thresholds of MWT diagnostics indicating strong turbulence were determined based on the probability density functions. Then we analyzed spatiotemporal distributions of strong MWT by calculating the ratio of the number of values exceeding the thresholds to the number of total values in each grid box. Also, long-term trend of strong MWT was investigated with related atmospheric flows near the mountain ranges in the world. More details will be given in the presentation.

Key Words: Mountain wave turbulence, Climatology, ERA5

References:

Lee, J.-H., J.-H. Kim, R. D. Sharman, J. Kim, and S.-W. Son, 2023: Climatology of Clear-Air Turbulence in Upper Troposphere and Lower Stratosphere in the Northern Hemisphere Using ERA5 reanalysis data. J. Geophys. Res. https://doi.org/10.1029/2022JD037679

Kim, S.-H., J.-H. Kim, H.-Y. Chun, and R. D. Sharman, 2023: Global Response of Upper-Level Aviation Turbulence from Various Sources to Climate Change. npj Clim. Atmos. Sci. https://doi.org/10.1038/s41612-023-00421-3

Acknowledgment: This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2019R1I1A2A01060035) and by the Korea Meteorological Administration Research and Development Program under Grant KMI2022-00310.