Climatology of Upper-Level Near-Cloud Aviation Turbulence Revealed in the ERA5 Reanalysis Data

Moist convection is one of the major sources to generate atmospheric turbulence in the upper troposphere and lower stratosphere (UTLS), which affects directly to cruising aircraft. Turbulence associated with convection [near-cloud aviation turbulence (NCT)] can be caused by various generation mechanisms such as shearing and convective instabilities, convectively induced flow deformation, and convective gravity wave (CGW) propagation and its breaking. Recently, Kim et al. showed that moderate-or-greater (MOG)-intensity turbulence generated from various sources including NCT, clear-air turbulence, and mountain wave turbulence is expected to be occurred more frequently due to the changing climate, derived from the long-term climate model data of the high-emission scenario and historical condition. In order to make sure positive long-term trend of NCT at flight levels in the world from the state-of-the-art reanalysis data, this study investigates climatology of upper-level NCT using the European Centre for Medium-range Weather Forecast Reanalysis version 5 (ERA5) data with 0.25° longitude by 0.25° latitude for 43 years (1979-2021). Two indices based on a parameterization scheme of CGW drag (CGWD) of Chun and Baik are calculated for four layers (250, 225, 200, and 175 hPa): CGWD and eddy dissipation rate derived from CGWD (EDR_CGWD). Prior to calculate NCT indices, the convective heating rate, which is required for NCT indices, but is not available as the standard output of ERA5 data, is derived using vertical velocity, relative humidity, air temperature, and air pressure. Also, from a vertical profile of convective heating rate, cloud top and bottom heights are determined. It is found that NCT diagnostics are concentrated in the tropics and the summertime continents. From probability distribution of NCT diagnostics, the 98th percentile is computed and used as a threshold of MOG-intensity turbulence for calculating occurrence frequencies for 43 years. Also, we analyze NCT trends globally during 1979-2021 in ERA5 reanalysis dataset. Detailed results of climatological analysis including occurrence frequency and trend of NCT will be presented in the conference.

Acknowledgement: This work is funded by the Korean Meteorological Administration Research and Development Program under KMI2022-00310 and also supported by the Basic Science Research Program through the National Research Foundation (NRF) funded by the Ministry of Education (grant no. 2022R1I1A1A01071708).