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The present study investigates dynamical coupling between the equatorial stratospheric Quasi31 biennial oscillation (QBO) and the boreal winter surface climate of the Northern Hemisphere mid and high latitudes using 42 years data (1979–2020). For neutral El Niño Southern Oscillation (ENSO) periods, QBO westerlies (W) at 70 hPa favor high sea level pressure in the polar region, colder conditions and deeper snow over Eurasia and North America, and the opposite effects for QBO easterlies (E). When QBO anomalies arrive in the upper troposphere and lower stratosphere (UTLS), it is observed that planetary wave activity is enhanced in the extratropical UTLS during QBO W and diminished during QBO E. This QBO teleconnection pathway along the UTLS to the high latitude surface is independent of the “stratospheric pathway” (Holton-Tan mechanism). Diagnosis of this pathway can help to improve understanding of internal sub-seasonal to seasonal variations, and long-range forecasting over Eurasia and North America. 

The European Centre for Medium-range Weather Forecasting (ECMWF) Reanalysis v5 (ERA5) data set (1979 – 2020) is used in many climate studies.  The present monthly mean data set of Eliassen-Palm fluxes (EP fluxes) and EP flux divergences, was created from twice-daily gridded values of ERA5 winds and temperature on pressure surfaces and is intended to fill a gap in availability.   It is compatible for use with ERA5 monthly mean data.   The EP flux is a diagnostic tool for assessing wave propagation and wave-mean flow interaction. It is a vector representation for the propagation of synoptic and planetary Rossby wave activity in the meridional plane.  An upward component indicates a poleward heat flux while an equatorward component indicates a poleward momentum flux.   EP flux divergence implies a source of Rossby wave activity, and EP flux convergence implies absorption of Rossby wave activity.  EP flux divergence represents the body force, or net effect of waves on the zonal mean zonal wind, with EP flux convergence causing deceleration of zonal mean westerlies and EP flux divergence causing acceleration. The primary effect of a region of EP flux convergence, however, is to induce poleward motion, with an associated mean meridional circulation and quadrupole of temperature anomalies in the meridional plane. EP fluxes are useful in investigating many planetary and synoptic scale weather phenomena such as the Quasi-Biennial Oscillation (QBO) and Sudden Stratospheric Warmings (SSWs).   The meridional and vertical components of the EP flux are calculated in pressure coordinates using the following initial conditions:  Ground density (rho_0 ):P_0/R_0/T_0 Ground pressure (P_0): 1013hPa Ground temperature (T_0): Temperature at 1000hPa Earth radius (a) = 6378km   Dimensions in the data: Latitude: 90°N-90°S (grid spacing is 0.25°, as in the ERA5 reanalysis)  Pressure: 1 hPa-1000 hPa (levels are the same as in the ERA5 reanalysis)  Time: January 1979 – December 2020; December, January, February (DJF) only; 00z and 12z