The stratospheric wintertime response to applied extratropical torques and its relationship with the annular mode

Abstract

and the long-term response is less NAM-like and no longer easterly at high latitudes. This is consistent with ray theory and differences in climatological u between the two types of simulations. The response to a tropospheric wave forcing perturbation is also NAM-like. These results suggest that dynamical feedbacks tend to make the long-term NH extratropical stratospheric response to arbitrary external forcings NAM-like, but only if the feedbacks are sufficiently strong. This may explain why the observed polar vortex responses to natural forcings such as the QBO and ENSO are NAMlike. The results imply that wave feedbacks must be understood and accurately modelled in order to understand and predict the influence of GWD and other external forcings on the polar vortex, and that biases in a model's climatology will cause biases in these feedbacks.

Simulating influences of QBO phases and orographic gravity wave forcing on planetary waves in the middle atmosphere

“…Recently, some studies revealed possible compensation of PW drag of the middle atmospheric circulation by parameterized OGWs in general circulation models (McLandress and McFarlane 1993;Cohen et al 2013Cohen et al , 2014Sigmond and Shepherd 2014;Watson and Gray 2015). Our results show that taking account of OGW parameterization can both decrease or increase wave amplitudes, EP-fluxes, and wave drag of the mean flow depending on the considered PW modes.…”

“…Many studies were devoted to the generation of PW modes in the middle atmosphere by horizontally inhomogeneous gravity wave drag (e.g., Holton 1984;McLandress and McFarlane 1993;Watson and Gray 2015). Using the MUAM, Gavrilov et al (2013a, b) simulated the generation of PW modes by inhomogeneous OGW forcing.…”

“…Time and spatial inhomogeneity of the mean wind drag produced by OGWs can be an additional mechanism of PW generation in the middle atmosphere (e.g., Holton 1984;McLandress and McFarlane 1993;Watson and Gray 2015). To study possible OGW drag influences, we decomposed simulated wave drags into herein considered stationary PW modes and travelling NAMs.…”

“…Inhomogeneities of orographic wave sources and conditions of OGW propagation may lead to the generation of additional PW modes, which could have contributed to the results in Figs. 3, 4, and 5 (e.g., Holton 1984;McLandress and McFarlane 1993;Watson and Gray 2015;Gavrilov et al 2013b) curvature of the zonal mean wind for the PW propagation. Eq.…”

Sensitivity of volcanic aerosol dispersion to meteorological conditions: A Pinatubo case study

“…This includes prescribed ozone fields following Cionni et al [2011] and fixed atmospheric concentrations of carbon dioxide (CO 2 ), methane (CH 4 ), and nitrous oxide (N 2 O). Except for the process of methane oxidation, HadGEM2-CCS does not include stratospheric chemistry but does include a well-resolved stratosphere capable of internally generating a realistic QBO Watson and Gray, 2014]. The internal QBO is forced by parameterized orographic and nonorographic gravity wave drag schemes [Martin et al, 2011].…”