A GCM study of the influence of equatorial winds on the timing of sudden stratospheric warmings

Pascoe, Charlotte; Gray, Lesley J.; Scaife, Adam A.

doi:10.1029/2005gl024715

Cited by 56 publications

(63 citation statements)

References 21 publications

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“…The HTE also holds when the QBO is defined by the vertical wind shear between 50 and 70 hPa, but it tends to be weaker for the QBO defined at other levels (Hitchman and Huesmann 2009, hereafter HH09). The HTE has been confirmed by observational studies (e.g., Dunkerton and Baldwin 1991;Naito and Hirota 1997;Lu et al 2008Lu et al , 2014 as well as by both mechanistic (e.g., O'Sullivan and Young 1992; Naito and Yoden 2006;Pascoe et al 2006) and complex general circulation models (e.g., Calvo et al 2009;Marshall and Scaife 2009). However, the mechanism behind the HTE is still under debate (e.g., Naoe and Shibata 2010;Yamashita et al 2011;Garfinkel et al 2012;Lu et al 2014).…”

Section: Introductionmentioning

confidence: 70%

Dynamical Response to the QBO in the Northern Winter Stratosphere: Signatures in Wave Forcing and Eddy Fluxes of Potential Vorticity

White

Mitchell

et al. 2015

Journal of the Atmospheric Sciences

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Wave-mean flow interactions associated with the Holton-Tan effect (HTE), whereby the tropical quasibiennial oscillation (QBO) modulates the Northern Hemisphere wintertime stratospheric polar vortex, are studied using the ERA-Interim dataset. Significant evidence of the HTE in isentropic coordinates is found, with a weaker and warmer polar vortex present when the lower-stratospheric QBO is in its easterly phase (QBOe). For the first time, the authors quantify the QBO modulation of wave propagation, wave-mean flow interaction, and wave decay/growth via a calculation of potential vorticity (PV)-based measures, the zonalmean momentum budget, and up-/downgradient eddy PV fluxes. The effect of the tropospheric subtropical jet on QBO modulation of the wave activity is also investigated. In the subtropical-to-midlatitude lower stratosphere, QBOe is associated with an enhanced upward flux of wave activity, and corresponding wave convergence and wave growth, which leads to a stronger poleward zonal-mean meridional circulation and consequently a warmer polar region. In the middle stratosphere, QBOe is associated with increased poleward wave propagation, leading to enhanced wave convergence and in situ wave growth at high latitudes and contributing to the weaker polar vortex. In agreement with recent studies, the results suggest that the criticalline effect cannot fully account for these wave anomalies associated with the HTE. Instead, it is suggestive of a new, additional mechanism that hinges on the QBO-induced meridional circulation effect on the latitudinal positioning of the subtropical jet. Under QBOe, the QBO-induced meridional circulation causes a poleward shift of the subtropical jet, encouraging more waves to propagate into the stratosphere at midlatitudes.

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Section: Introductionmentioning

confidence: 70%

Dynamical Response to the QBO in the Northern Winter Stratosphere: Signatures in Wave Forcing and Eddy Fluxes of Potential Vorticity

White

Mitchell

et al. 2015

Journal of the Atmospheric Sciences

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“…It is also increasingly apparent that successful modelling of the equatorial semi-annual oscillation and the QBO (e.g. Pascoe et al, 2006) are important for improved characterization of global wind, temperature and PW fields at extratropical latitudes. Such studies would be extremely valuable, as these issues indicate that modelled PW-GW-polar vortex characteristics and wave-interactions are not in fully realistic balance in some models.…”

Section: Summary and Commentsmentioning

confidence: 99%

Winter warmings, tides and planetary waves: comparisions between CMAM (with interactive chemistry) and MFR-MetO observations and data

et al. 2006

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Abstract. Following earlier comparisons using the Canadian Middle Atmosphere Model (CMAM, without interactive chemistry), the dynamical characteristics of the model are assessed with interactive chemistry activated. Timesequences of temperatures and winds at Tromsø (70 • N) show that the model has more frequent and earlier stratospheric winter warmings than typically observed. Wavelets at mesospheric heights (76, 85 km) and from equator to polar regions show that CMAM tides are generally larger, but planetary waves (PW) smaller, than medium frequency (MF) radar-derived values.Tides modelled for eight geographic locations during the four seasons are not strikingly different from the earlier CMAM experiment; although monthly data now allow these detailed seasonal variations (local combinations of migrating and non-migrating components) within the mesosphere (circa 50-80 km) to be demonstrated for the first time. The dominant semi-diurnal tide of middle latitudes is, as in the earlier papers, quite well realized in CMAM. Regarding the diurnal tide, it is shown here and in an earlier study by one of the authors, that the main characteristics of the diurnal tide at low latitudes (where the S (1,1) mode dominates) are well captured by the model. However, in this experiment there are some other unobserved features for the diurnal tide, which are quite similar to those noted in the earlier CMAM experiment: low latitude amplitudes are larger than observed Finally, the seasonal variations of planetary wave (PW) activity available from CMAM and the MFR show quite good agreement, apart from the amplitude differences (smaller in CMAM above 70 km). A major difference for the 16-d PW is that CMAM shows large amplitudes before the winter solstice; and for the 2-d PW, while both CMAM and MFR show summer and winter activity, the observed summer mesopause and winter mesospheric wave activities are stronger and more extended in height.Models such as CMAM, operated without dataassimilation, are now able to provide increasingly realistic climatologies of middle atmosphere tides and PW activity. Differences do exist however, and so discussion of the various factors affecting tidal and PW characteristics in atmospheres, modelled and observed, is provided. Other diagnostics of model-characteristics and of future desirable model experiments are suggested.

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“…Both QBO and SAO have an effect on the tracer transport in the stratosphere (e.g., Huang et al, 2008;Punge et al, 2009;Khosrawi et al, 2013;Shu et al, 2013). Further, the QBO has an effect on the stability of the polar vortex (e.g., Holton and Tan, 1980), and there are indications that both QBO and SAO have an influence on the timing of sudden stratospheric warmings (e.g., Pascoe et al, 2006). It has been found that the QBO has an effect on the weather and climate in the lower atmosphere and even at the surface (e.g., Ebdon, 1975;Boer and Hamilton, 2008;Marshall and Scaife, 2009).…”

Section: Introductionmentioning

confidence: 99%

Driving of the SAO by gravity waves as observed from satellite

Ern¹,

Preusse²,

Riese³

2015

Ann. Geophys.

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Abstract. It is known that atmospheric dynamics in the tropical stratosphere have an influence on higher altitudes and latitudes as well as on surface weather and climate. In the tropics, the dynamics are governed by an interplay of the quasi-biennial oscillation (QBO) and semiannual oscillation (SAO) of the zonal wind. The QBO is dominant in the lower and middle stratosphere, and the SAO in the upper stratosphere/lower mesosphere. For both QBO and SAO the driving by atmospheric waves plays an important role. In particular, the role of gravity waves is still not well understood.In our study we use observations of the High Resolution Dynamics Limb Sounder (HIRDLS) satellite instrument to derive gravity wave momentum fluxes and gravity wave drag in order to investigate the interaction of gravity waves with the SAO. These observations are compared with the ERA-Interim reanalysis. Usually, QBO westward winds are much stronger than QBO eastward winds. Therefore, mainly gravity waves with westward-directed phase speeds are filtered out through critical-level filtering already below the stratopause region. Accordingly, HIRDLS observations show that gravity waves contribute to the SAO momentum budget mainly during eastward wind shear, and not much during westward wind shear. These findings confirm theoretical expectations and are qualitatively in good agreement with ERA-Interim and other modeling studies. In ERAInterim most of the westward SAO driving is due to planetary waves, likely of extratropical origin. Still, we find in both observations and ERA-Interim that sometimes westwardpropagating gravity waves may contribute to the westward driving of the SAO. Four characteristic cases of atmospheric background conditions are identified. The forcings of the SAO in these cases are discussed in detail, supported by gravity wave spectra observed by HIRDLS. In particular, we find that the gravity wave forcing of the SAO cannot be explained by critical-level filtering alone; gravity wave saturation without critical levels being reached is also important.

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A GCM study of the influence of equatorial winds on the timing of sudden stratospheric warmings

Cited by 56 publications

References 21 publications

Dynamical Response to the QBO in the Northern Winter Stratosphere: Signatures in Wave Forcing and Eddy Fluxes of Potential Vorticity

Dynamical Response to the QBO in the Northern Winter Stratosphere: Signatures in Wave Forcing and Eddy Fluxes of Potential Vorticity

Winter warmings, tides and planetary waves: comparisions between CMAM (with interactive chemistry) and MFR-MetO observations and data

Driving of the SAO by gravity waves as observed from satellite

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