Method for calculating torsional oscillations in Earth's atmosphere from NCEP/NCAR, MERRA-2, ECMWF Era-40, and Era-Interim

In this paper, we describe a method for calculating low-frequency zonal-mean zonal wind variations, which we call torsional oscillations. We compare the torsional oscillations calculated from the NCEP/NCAR reanalysis I, MERRA-2, ECWMF ERA-40, and ERA-Interim projects, using different methods of processing the original data. We estimate the degree of consistency of torsional oscillations, obtained from different reanalysis projects, and discuss the use of torsional oscillations to study circulation processes in the atmosphere.