Residual Mean Circulation and Temperature Changes during the Evolution of Stratospheric Sudden Warming Revealed in MERRA

Abstract

Abstract.Residual mean circulation and temperature changes during the evolution of major stratospheric sudden warming (SSW) are investigated by composite analyses of 22 SSW events from 1979 to 2012 during the Northern Hemisphere winter (November-March) using four reanalysis data sets (MERRA, ERA-Interim, NCEP-NCAR, and JRA-55). The SSW events are classified as Type-1 or Type-2 based on the relative amplitude of planetary waves with zonal wavenumbers 1 and 2. The residual mean circulation induced by each forcing term in the Transformed Eulerian mean (TEM) momentum equation and 10 the temperature advection associated with the circulation are calculated for both types of SSW, based on the generalized downward control principle using the MERRA data set. When 'Lag = 0' is defined as the day on which the wind reversal occurred at 60° N and 10 hPa, strong poleward and downward motion exists at Lag = -8 and Lag = -1 for Type-1 and at Lag = -3 for Type-2, which is induced primarily by the Eliassen-Palm flux divergence forcing (EPD). The poleward and downward motion is stronger for Type-2 than for Type-1. Gravity wave drag (GWD) produces a smaller contribution to the 15 residual circulation than EPD. During the warming phase (at Lag = -2), strong temperature advection by the EPD induces primarily polar stratospheric warming. On the other hand, during the temperature recovery phase (at Lag = +2), anomalous negative temperature advection and diabatic cooling produce negative temperature tendency anomalies. Structures in the temperature tendency and temperature advection calculated using the MERRA data set are similar to those calculated using the ERA-Interim data set. 20

On the intermittency of orographic gravity wave hotspots and its importance for middle atmosphere dynamics

“…mesosphere (Zülicke et al, 2018). The positive OGWD anomalies reported here are similar as reported in Albers and Birner (2014) and in Song and Chun (2016), i.e. suppressed in the regions of weak winds before the displacement SSWs.…”

Influence of Asian Topography on the Arctic Stratospheric Ozone

“…Equation and Equation reveal that there are four forcing terms in the case of a nonsteady state, $$\nabla \cdot \overrightarrow{F}$$, $$\partial \overline{u}/\partial t$$, $$\overline{\text{GWD}}$$, and $$\overline{X}$$, namely the divergence of the Eliassen‐Palm (E‐P) flux (Equations ), the tendency of zonal mean zonal wind, gravity wave drag, and residual term of the TEM equation, respectively. Among these, only $$\nabla \cdot \overrightarrow{F}$$ and $$\partial \overline{u}/\partial t$$ are significantly important, while the $$\overline{\text{GWD}}$$ and $$\overline{X}$$ are almost negligible, as pointed out by Song and Chun (2016).…”

“…According to the transformed Eulerian mean (TEM) momentum equations (Andrews et al, 1987) ) can be derived (Equations 6 and 7), which is advantageous for quantitatively determining the specific impact of different forcing terms on residual mean velocities (Song & Chun, 2016;Z. Wang et al, 2021)…”

“…According to the transformed Eulerian mean (TEM) momentum equations (Andrews et al., 1987), another description of residual mean circulation ($${\overline{v}}^{\ast }$$, $${\overline{w}}^{\ast }$$) can be derived (Equations and ), which is advantageous for quantitatively determining the specific impact of different forcing terms on residual mean velocities (Song & Chun, 2016; Z. Wang et al., 2021). $$${\overline{v}}^{\ast }=-\frac{1}{{\rho }_{0}\,\mathrm{cos}\,\varphi }\frac{\partial }{\partial z}\left\{-\mathrm{cos}\,\varphi \int \nolimits_{z}^{\infty }{\rho }_{0}\left[\frac{\frac{1}{{\rho }_{0}a\,\mathrm{cos}\,\varphi }\nabla \cdot \overrightarrow{F}-\frac{\partial \overline{u}}{\partial t}+\overline{\text{GWD}}+\overline{X}}{f-\frac{1}{a\,\mathrm{cos}\,\varphi }\frac{\partial }{\partial \varphi }\left(\overline{u}\mathrm{cos}\,\varphi \right)}\right]d{z}^{\prime }\right\}$$$ …”

Propagation of gravity waves and its effects on pseudomomentum flux in a sudden stratospheric warming event

“…The present study explores effects of the 4D (x-z, t) propagation of GWs on distributions of pseudomomentum fluxes, a central quantity in GW-mean-flow interaction, for the 2009 SSW. A ray-tracing model for inertia-gravity waves (IGWs) on a sphere, whose prototype was used by Song et al (2017), is employed to compute trajectories and pseudomomentum fluxes of GWs for specified (time-varying) large-scale flows. Diagnosis of mean flow responses to change in GW pseudomomentum fluxes is not attempted in this study, since slowly varying mean flows are not only modified by GW pseudomomentum but also by the second-order mean pressure fields that can induce mean motions in regions far from localized GW packets (Bühler, 2014).…”