Sudden Stratospheric Warmings and Anomalous Upward Wave Activity Flux

Abstract

Abrupt breakdowns of the polar winter stratospheric circulation such as sudden stratospheric warmings (SSWs) are a manifestation of strong two-way interactions between upward propagating planetary waves and the mean flow. The importance of sufficient upward wave activity fluxes from the troposphere and the preceding state of the stratospheric circulation in forcing SSWlike events have long been recognized. Past research based on idealized numerical simulations has suggested that the state of the stratosphere may be more important in generating extreme stratospheric events than anomalous upward wave fluxes from the troposphere. Other studies have emphasized the role of tropospheric precursor events. Here reanalysis data are used to define events of extreme stratospheric mean flow deceleration (SSWs being a subset) and events of extreme lower tropospheric upward planetary wave activity flux. While the wave fluxes leading to SSWlike events ultimately originate near the surface, the anomalous upward wave activity fluxes associated with these events primarily occur within the stratosphere. The crucial dynamics for forcing SSW-like events appear to take place in the communication layer just above the tropopause. Anomalous upward wave fluxes from the lower troposphere may play a role for some events, but seem less important for the majority of them.(Citation: Birner, T., and J. R. Albers, 2017: Sudden stratospheric warmings and anomalous upward wave activity flux. SOLA, 13A, 8−12,

Characterizing Stratospheric Polar Vortex Variability With Computer Vision Techniques

“…In describing the onset stage (37 to 23 days prior) to sudden warming events, Limpasuvan et al () noted that the zonal flow is anomalously strong and the vortex anomalously pole centered. Birner and Albers () also noted that the vortex was anomalously strong prior to those sudden stratospheric deceleration events (see their definitions) that were preceded by lower tropospheric wave events (see, e.g., their supporting information Figure S1). The results shown in Figure seem to at least confirm that from the vortex‐centered view of CAVE‐ART, the vortex is anomalously strong prior to many sudden warming events.…”

“…Our vortex strength definition, combined with other CAVE‐ART diagnostics, could be useful for identifying preconditioned states of the vortex prior to weak vortex events, including major and minor sudden warming disturbances. Perhaps more importantly, diagnostics from CAVE‐ART could assist in further understanding the physics through which the stratospheric vortex strengthens and weakens in such extreme ways by helping to reconcile views based on wave mean flow interactions of upward propagating waves (e.g., Limpasuvan et al, , ; Matsuno, ; Nishii et al, ), nonlocal wave effects (e.g., Esler & Matthewman, ; Harnik, ; Matthewman & Esler, ; Plumb, ; Shaw & Perlwitz, ), and internal stratospheric control (e.g., Birner & Albers, ; de la Cámara et al, ; Hitchcock & Haynes, ; Scott & Polvani, , ) with the dynamics in the frame of reference of the vortex itself.…”

“…SSWs are commonly subsetted according to their disturbance to the polar vortex, which includes displacements and splits; in the former case, the vortex ends up displaced far off the pole, while in the latter it splits into two or more offspring vortices (e.g., Charlton and Polvani, , and references therein). While the mechanisms for development of SSWs are still not fully understood (e.g., Birner & Albers, , and references therein), the large disturbances from SSWs have been shown to gradually descend into the troposphere over weeks to months, and they can significantly affect surface weather and climate (e.g., Baldwin & Dunkerton, ; Kuroda, ; Limpasuvan et al, ). The other end of the spectrum includes so‐called vortex intensification events, which have been associated with decreased planetary wave driving and negative poleward heat fluxes (e.g., Dunn‐Sigouin & Shaw, ; Limpasuvan et al, ; Shaw & Perlwitz, ).…”

Evaluation of the Mesospheric Polar Vortices in WACCM

“…Indeed, de la Torre et al () found that while WACCM reproduced the observed frequency of SSWs, they tend to last longer and vortex splits tend to occur earlier in the winter than observed. de la Cámara et al () used WACCM to show that SSW development depends on the stratospheric state, as has been shown using observations (Birner & Albers, ). Zonal asymmetries in WACCM meteorology and phenomenology associated with breaking planetary waves (PWs) at mesospheric altitudes are realistic (e.g., Chandran et al, ; France et al, ; France & Harvey, ; Greer et al, ; Sassi et al, ).…”

The Role of Gravity Wave Drag Optimization in the Splitting of the Antarctic Vortex in the 2002 Sudden Stratospheric Warming

“…However, there are some results that suggest that internal stratospheric dynamics may also play a role during SSWs. Recently, Birner and Albers (2017) showed that only 25% of SSWs were associated to anomalously large tropospheric wave events, while the remaining 75% of SSWs have wave fluxes that are anomalous only in the stratosphere. Recently, Birner and Albers (2017) showed that only 25% of SSWs were associated to anomalously large tropospheric wave events, while the remaining 75% of SSWs have wave fluxes that are anomalous only in the stratosphere.…”