A mechanistic model study of slowly propagating coupled stratosphere‐troposphere variability

Abstract

Abstract. Observational studies reveal the oscillatory nature of coupled stratosphere-troposphere variability, which is characterized by a slowly downward propagating anomalous zonal-mean zonal wind during the winter. The term "slowly" is employed compared to the rapid variation associated with stratospheric sudden warmings. In fact, strong stratospheric warming events are embedded in this slowly propagating variability as is shown in a companion paper [Kodera e! al., this issue]. In the present study, the mechanism producing such variability at all levels of the atmosphere is investigated by developing a simple model that extends from the Earth's surface to 80 km altitude. The model is a quasi-geostrophic channel model similar to that used by Holton and Mass [1976], but it includes two meridional Fourier components and latitudinal variation in the gradient of the Coriolis parameter. By this extension, the present model can incmporate both the subtropical and polar night jet and also treat the horizontal propagation of planetary waves as well as vertical propagation. The results of the simulation reproduce qualitatively well the main observed features: Interaction between the planetary waves and zonal-mean flow produces oscillations in the winter stratosphere, and zonal wind anomalies created in the subtropics of the stratopause propagate downward into the polar region of the troposphere, which provoke changes in the meridional propagation of tropospheric planetary waves. IntroductionIn a companion paper [Kodera et al., this issue] we show that two contrasting types of winter exist in the stratosphere: One is characterized by a persistent strong stratospheric polar night jet, and the other is characterized by a slowly propagating anomalous zonal-mean zonal wind from the stratosphere to the troposphere. The term "slowly" is employed in comparison with the rapid variation associated with stratospheric sudden warmings. In fact, strong stratospheric warming events are embedded in this slowly propagating variability. Although slowly propagating anomalies rarely achieve more than one cycle during a cold season, an approximate periodicity of 3-5 months is suggested. These two different states of the stratospheric circulation may be compared to the vacillating and stationary regimes in a simple mechanistic model by Holton and Mass [ 1976] (hereinafter referred to HM).Another important characteristic of the observed slowly propagating anomalies is that the variation is not limited to the stratosphere. It also propagates into the troposphere, where it is accompanied by changes in the meridional propagation of tropospheric planetary waves. This stratosphere-troposphere coupled mode of variability is, in fact, closely related to that discussed in previous papers in connection with the Arctic Oscillation (

Wave Energy Associated with the Variability of the Stratospheric Polar Vortex

“…Finally, it is worth noting that the observed oscillatory behavior in the correlation curves for s ϭ 1 and m ϭ 1 and 2 closely agrees with the findings by Limpasuvan et al (2004, see their Fig. 10d), and further suggests a stratospheric vacillation cycle (Kodera et al 2000).…”

“…Such studies have naturally generated an increasing interest for a better understanding of the dynamics of the stratosphere-troposphere coupling, and several modeling studies were specifically devoted to the subject (e.g., Kodera and Kuroda 2000;Polvani and Kushner 2002;Song and Robinson 2004).…”

Stratospheric ozone and the morphology of the northern hemisphere planetary waveguide

“…However, changes in the upward flux of planetary wave activity and consequent variations in local wave‐mean flow interaction in the stratosphere can also drive downward propagating zonal‐mean wind anomalies [ Plumb and Semeniuk , ], a “top‐down” effect. Such downward propagating wind anomalies have been shown to be important for stratosphere‐troposphere communication [ Kodera and Kuroda , ; Christiansen , ; Polvani and Waugh , ; Perlwitz and Harnik , ] and NAM variability [e.g., Baldwin and Dunkerton , ; Limpasuvan and Hartmann , ]. The model simulations examined in this paper provide evidence that ZAO affects both the downward propagation of wind anomalies and the phase of the NAM .…”

Advancements in decadal climate predictability: The role of nonoceanic drivers

“…The radiative forcing from these events can be substantial [ Robock , ], with a cooling of the troposphere due to scattering of solar radiation and a warming of the lower stratosphere due to enhanced absorbing of infrared radiation [ Angell , ]. The radiative impact of volcanic aerosols can impact ozone and induce a stronger polar vortex [ Kodera , ; Perlwitz and Graf , ; Kodera and Kuroda , , ; Shindell et al ., ], potentially shifting the tropospheric jet stream and producing a response that generally includes an anomalously positive phase of the AO, more pronounced in the boreal winter but only partially simulated in models [ Stenchikov et al ., ].…”