On the origin of the mesospheric quasi-stationary planetary  waves in the unusual Arctic winter 2015/2016

Matthias, Vivien; Ern, Manfred

doi:10.5194/acp-18-4803-2018

Cited by 35 publications

(47 citation statements)

References 34 publications

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“…In some cases, also local instabilities indicated by the reversals in the q y generate new SPWs 1 in the polar region (Charney and Stern, 1962;Garcia, 1991), which cause an additional transfer of momentum and energy. These local instabilities are also observed in the lower mesosphere, so that the SPWs 1 also have a lasting effect on the MLT region see (Smith, 2003;Lieberman et al, 2013;Matthias and Ern, 2018). For those GW hotspots, which are in phase with the modeled SPW 1 and do not create a negative n in the upper polar region, the SPWs 1 propagate through the polar region further upward and influence the polar vortex up to an altitude of 70 km.…”

Section: Discussionmentioning

confidence: 95%

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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Section: Discussionmentioning

confidence: 95%

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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“…These SPWs 1 are breaking around 50 km between 50 and 80 • N and lead to an enhanced negative EP divergence connected with a decreasing zonal mean zonal wind at higher latitudes. In the lower mesosphere between 40 and 70 • N there is a second source of SPW 1 (positive EP divergence) developed as well due to local baroclinic instabilities (reversal of the q y ) (Smith, 2003;Lieberman et al, 2013;Matthias and Ern, 2018). As a consequence, the EP flux and the SPW 1 amplitude are enhanced between 70 and 80 km, right above the positive EP divergence anomaly.…”

Section: Propagation Conditions For Spwsmentioning

confidence: 97%

Effect of latitudinally displaced gravity wave forcing in the lower stratosphere on the polar vortex stability

Samtleben¹,

Jacobi²,

Pišoft³

et al. 2019

Preprint

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Abstract. In order to investigate the impact of a locally confined gravity wave (GW) hotspot, a sensitivity study based on simulations of the middle atmosphere circulation during northern winter was performed with a nonlinear, mechanistic, global circulation model. To this end, for the hotspot region we selected a fixed longitude range in the East Asian region (120° E–170° E) and a latitude range from 22.5° N–52.5° N between 18 km and 30 km, which was then shifted northward in steps of 5°. For the southernmost hotspots, we observe a decreased stationary planetary wave (SPW) 1 activity in the upper stratosphere/lower mesosphere, i.e. less SPWs 1 are propagating upwards. These GW hotspots are leading to a negative refractive index inhibiting SPW propagation at midlatitudes. The decreased SPW 1 activity is connected with an increased zonal mean zonal wind at lower latitudes. This in turn decreases the meridional potential vorticity gradient (qy) from midlatitudes towards the polar region. A reversed qy indicates local baroclinic instability which generates SPWs 1 in the polar region, where we observe a strong positive Eliassen-Palm (EP) divergence. Thus, the EP flux is increasing towards the polar stratosphere (corresponding to enhanced SPW 1 amplitudes) where the SPWs 1 are breaking and the zonal mean zonal wind is decreasing. Thus, the local GW forcing is leading to a displacement of the polar vortex towards lower latitudes. The effect of the local baroclinic instability indicated by the reversed qy also produces SPWs 1 in the lower mesosphere. The effect on the dynamics in the middle atmosphere by GW hotspots which are located northward of 50° N is negligible because the refractive index of the atmosphere is strongly negative in the polar region. Thus, any changes in the SPW activity due to the local GW forcing are quite ineffective.

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“…In a model climatology Chandran et al (2013) found that 68 % of the SSWs with elevated stratopause are split-type events and that the remaining 32 % are displacement events. Matthias et al (2012) compiled a composite of SSW events with an elevated stratopause between 1998 and 2011 using ECMWF data and MF-radar observations revealing the for- mation of an elevated stratopause in the mesospheric wind as strong zonal wind enhancement after the SSW. Later, Limpasuvan et al (2016) made a composite analysis of SSWs with an elevated stratopause using WACCM data and explained the occurrence of an elevated stratopause with strong, waveinduced downwelling in the mesosphere which leads to adiabatic warming.…”

Section: Observations At Ny-ålesundmentioning

confidence: 99%

Small-scale variability of stratospheric ozone during the sudden stratospheric warming 2018/2019 observed at Ny-Ålesund, Svalbard

Schranz¹,

Hagen²,

Stober³

et al. 2020

Atmos. Chem. Phys.

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Abstract. Middle atmospheric ozone, water vapour and zonal and meridional wind profiles have been measured with the two ground-based microwave radiometers GROMOS-C and MIAWARA-C. The instruments have been located at the Arctic research base AWIPEV at Ny-Ålesund, Svalbard (79∘ N, 12∘ E), since September 2015. GROMOS-C measures ozone spectra in the four cardinal directions with an elevation angle of 22∘. This means that the probed air masses at an altitude of 3 hPa (37 km) have a horizontal distance of 92 km to Ny-Ålesund. We retrieve four separate ozone profiles along the lines of sight and calculate daily mean horizontal ozone gradients which allow us to investigate the small-scale spatial variability of ozone above Ny-Ålesund. We present the evolution of the ozone gradients at Ny-Ålesund during winter 2018/2019, when a major sudden stratospheric warming (SSW) took place with the central date at 2 January, and link it to the planetary wave activity. We further analyse the SSW and discuss our ozone and water vapour measurements in a global context. At 3 hPa we find a distinct seasonal variation of the ozone gradients. The strong polar vortex during October and March results in a decreasing ozone volume mixing ratio towards the pole. In November the amplitudes of the planetary waves grow until they break in the end of December and an SSW takes place. From November until February ozone increases towards higher latitudes and the magnitude of the ozone gradients is smaller than in October and March. We attribute this to the planetary wave activity of wave numbers 1 and 2 which enabled meridional transport. The MERRA-2 reanalysis and the SD-WACCM model are able to capture the small-scale ozone variability and its seasonal changes.

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On the origin of the mesospheric quasi-stationary planetary waves in the unusual Arctic winter 2015/2016

Cited by 35 publications

References 34 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

Effect of latitudinally displaced gravity wave forcing in the lower stratosphere on the polar vortex stability

Small-scale variability of stratospheric ozone during the sudden stratospheric warming 2018/2019 observed at Ny-Ålesund, Svalbard

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