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

Scheffler, Guillermo Federico; Pulido, Manuel; Rodas, Claudio José Francisco

doi:10.1029/2018gl077993

Cited by 11 publications

(10 citation statements)

References 31 publications

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“…GWs exhibit a large spatial and temporal variability, which is closely linked to the synoptic conditions, the propagation conditions and the source of the GWs. Thus, there is a huge variability in the global GW distribution (Ern et al, 2004;Fröhlich et al, 2007;Hoffmann et al, 2013;Schmidt et al, 2016). Most of the regions of enhanced GW activity are connected to (i) orography (Hoffmann et al, 2013), which is quite stable and persistent in space and time, or (ii) deep convection (in the Tropics; Ern and Preusse, 2012) as well as to jet sources (mainly in the midlatitudes; Plougonven and Zhang, 2014), which are spatially and temporally variable.…”

Section: Introductionmentioning

confidence: 99%

Impact of local gravity wave forcing in the lower stratosphere on the polar vortex stability: effect of longitudinal displacement

Samtleben

Kuchař²,

Šácha

et al. 2020

Ann. Geophys.

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Abstract. The effects of gravity wave (GW) breaking hotspots in the lower stratosphere, especially the role of their longitudinal distribution, are evaluated through a sensitivity study by using a simplified middle atmosphere circulation model. For the position of the local GW hotspot, we first selected a fixed latitude range between 37.5 and 62.5∘ N and a longitude range from 112.5 to 168.75∘ E, as well as an altitude range between 18 and 30 km. This confined GW hotspot was then shifted in longitude by 45∘ steps, so that we created eight artificial GW hotspots in total. Strongly dependent on the location of the respective GW hotspot with regard to the phase of the stationary planetary wave of wavenumber 1 (SPW 1) generated in the model, the local GW forcing may interfere constructively or destructively with the modeled SPW 1. GW hotspots, which are located in North America near the Rocky Mountains, lead to an increase in the SPW 1 amplitude and EP flux, while hotspots located near the Caucasus, the Himalayas or the Scandinavian region lead to a decrease in these parameters. Thus, the polar vortex is less (Caucasus and Himalayan hotspots) or more weakened (Rocky Mountains hotspot) by the prevailing SPW activity. Because the local GW forcing generally suppresses wave propagation at midlatitudes, the SPWs 1 propagate into the polar region, where the refractive index turned to positive values for the majority of the artificial GW hotspots. An additional source of SPW 1 may be local instabilities indicated by the reversal in the meridional potential vorticity gradient in the polar region in connection with a positive EP divergence. In most cases, the SPWs 1 are breaking in the polar region and maintain the deceleration and, thus, the weakening of the polar vortex. While the SPWs 1 that form when the GW hotspots are located above North America propagate through the polar region into the middle atmosphere, the SPWs 1 in the remaining GW hotspot simulations were not able to propagate further upwards because of a negative refractive index above the positive refractive index anomaly in the polar region. GW hotspots, which are located near the Himalayas, influence the mesosphere–lower thermosphere region because of possible local instabilities in the lower mesosphere generating additional SPWs 1, which propagate upwards into the mesosphere.

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Section: Introductionmentioning

confidence: 99%

Impact of local gravity wave forcing in the lower stratosphere on the polar vortex stability: effect of longitudinal displacement

Samtleben

Kuchař²,

Šácha

et al. 2020

Ann. Geophys.

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“…Model experiments already showed that changes in GW parameters, e.g. the GW drag or the momentum flux, which modify the polar vortex geometry or even the stability (Samtleben et al, 2019), can lead to different kinds of vortex breakdowns (splitting or displacement) in connection with PW activity (Šácha et al, 2016;Scheffler et al, 2018). As a result, the vortex geometry 2 https://doi.org/10.5194/angeo-2019-120 Preprint.…”

Section: Introductionmentioning

confidence: 99%

“…CC BY 4.0 License. including a weakening or strengthening of the vortex itself strongly depends on the temporal and spatial GW drag distribution (Scheffler et al, 2018;Samtleben et al, 2019). These approaches provide a new basis regarding the evaluation of SSW events, which are strongly affected by GWs as well as by PWs.…”

Section: Introductionmentioning

confidence: 99%

Impact of local gravity wave forcing in the lower stratosphere on the polar vortex stability: Effect of longitudinal displacement

Samtleben¹,

Kuchař²,

Šácha³

et al. 2019

Preprint

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Abstract. The effects of gravity wave (GW) breaking hotspots in the lower stratosphere, especially the role of their longitudinal distribution, are evaluated through a sensitivity study by using a simplified middle atmosphere circulation model. For the position of the local GW hotspot, we first selected a fixed latitude range between 37.5 and 62.5° N and a longitude range from 112.5 to 168.75° E, as well as an altitude range between 18 and 30 km. This confined GW hotspot was then shifted in longitude by 45° steps, so that we created 8 artificial GW hotspots in total. Strongly depending on the location of the respective GW hotspot with regard to the phase of the stationary planetary wave of wavenumber 1 (SPW 1) generated in the model, the local GW forcing may interfere constructively or destructively with the modeled SPW 1. GW hotspots, which are located in North America near the Rocky Mountains lead to an increase of the SPW 1 amplitude and EP flux, while hotspots located near the Caucasus, the Himalayas or the Scandinavian region lead to a decrease of these parameters. Thus, the polar vortex is less (Caucasus and Himalayan hotspots) or more weakened (Rocky Mountains hotspot) by the prevailing SPW activity. Because the local GW forcing generally suppresses wave propagation at midlatitudes, the SPWs 1 are propagating into the polar region, where the refractive index turned to positive values for the majority of the artificial GW hotspots. An additional source of SPW 1 may be local instabilities indicated by the reversal in the meridional potential vorticity gradient in the polar region in connection with a positive EP divergence. In most cases, the SPWs 1 are breaking in the polar region and maintain the deceleration and thus, the weakening of the polar vortex. While the SPWs 1 that form when the GW hotspots are located above North America propagate through the polar region into the middle atmosphere, the SPWs 1 in the remaining GW hotspot simulations were not able to propagate further upwards because of a negative refractive index above the positive refractive index anomaly in the polar region. GW hotspots, which are located near the Himalayas influence the mesosphere/lower thermosphere region because of possible local instabilities in the lower mesosphere generating additional SPWs 1, which propagate upwards into the mesosphere.

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“…Even in the favourable case where a model bias has been convincingly shown to be tied to missing gravity wave drag (McLandress et al ., ), there are several different changes possible to gravity wave parameterizations that will alleviate this bias (Choi and Chun, ; de la Cámara et al ., ; Garcia et al ., ). Stratospheric variability, even in models with relatively fine spatial resolution, remains sensitive to non‐orographic gravity wave parameterizations (Polichtchouk et al ., ; Scheffler et al ., ), making these a key component for tuning.…”

Section: Constraining Gravity Wave Sources In Parameterizationsmentioning

confidence: 99%

How does knowledge of atmospheric gravity waves guide their parameterizations?

Plougonven

Cámara

Hertzog

et al. 2020

Quart J Royal Meteoro Soc

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This note discusses the relation between our knowledge of gravity waves and the parameterization of their effects in global models. Improving these parameterizations represents a major motivation for current research on atmospheric gravity waves. Indeed, as a major portion of the gravity wave spectrum is on the subgrid scale, parameterizations are used to represent their impacts on large-scale flow. Gravity wave parameterizations generally share a common framework, with assumptions on their propagation (columnar only) and their sources (tropospheric only). These assumptions are highly justified to leading order, and parameterizations have been successful in allowing models to reproduce a number of middle-atmospheric features. Once this framework is set up, specifying the sources constitutes a poorly constrained step. In practice, sources are tuned to a large extent in order to improve the modelled atmospheric circulation, a process that includes compensating for model biases. Consequently, significant efforts have been made to better quantify the sources of gravity waves, combining observations, modelling and theory, stimulating ground-breaking progress in our knowledge and understanding of atmospheric gravity waves.As emphasized in this note, however, the transfer to parameterizations is not straightforward: knowledge of the characteristics of lower-stratospheric gravity waves does not directly translate into input parameters for parameterizations.The example of intermittency is used to illustrate the impact of a (minor) shift in the parameterization framework, leading to a redistribution of the resulting forcing in the middle atmosphere. Recent studies have highlighted a number of phenomena which fall outside of the classical framework of parameterizations, notably lateral propagation and secondary generation. This growing body of evidence calls for further investigations to determine which of these phenomena could have systematic and robust implications for the larger-scale flow. To retain appropriate simplicity of the parameterizations, efforts to identify acceptable simplifications should also be undertaken in parallel, in a framework of a model hierarchy. K E Y W O R D Sclimate modelling, gravity waves, middle atmosphere, parameterizations Q J R Meteorol Soc. 2020;146:1529-1543.wileyonlinelibrary.com/journal/qj

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

Cited by 11 publications

References 31 publications

Impact of local gravity wave forcing in the lower stratosphere on the polar vortex stability: effect of longitudinal displacement

Impact of local gravity wave forcing in the lower stratosphere on the polar vortex stability: effect of longitudinal displacement

Impact of local gravity wave forcing in the lower stratosphere on the polar vortex stability: Effect of longitudinal displacement

How does knowledge of atmospheric gravity waves guide their parameterizations?

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