“…Unfortunately, representation of the polar vortex in the upper mesosphere is generally not accurate in state-of-the-art global models. In fact, in many models the zonal winds blow in the wrong direction in the polar winter upper mesosphere (Eswaraiah et al, 2016;Harvey et al, 2019;Hindley et al, 2022;Lieberman et al, 2015;Liu, 2016;Marsh et al, 2013;Noble et al, 2022;Rüfenacht et al, 2018;Smith, 2012;Yuan et al, 2008;Griffith et al, 2021;McLandress et al, 2006;McCormack et al, 2017;2021;Pedatella et al, 2014;Schmidt et al, 2006;Stober et al, 2021) compared to observations (e.g., Wilhelm et al, 2019) or meteorological analyses that use data assimilation (Eckermann et al, 2018, Stober et al, 2020. Important impacts of this easterly (westward) wind bias are (1) a reduction in the vertical extent of the MPV (Harvey et al, 2019), (2) an increase in the vertical wind shear, which alters the spectrum of GWs and PWs (e.g., Chandran et al, 2013;France et al, 2015), (3) persistent negative meridional potential vorticity gradients at mid-to-high latitudes, which can generate PWs via baroclinic or barotropic instability (e.g., Charney and Stern, 1962), and (4) a reduction in the amplitude of the migrating wavenumber 2 semidiurnal tide (SW2) in Arctic winter (Zhang et al, 2021).…”