Decadal‐scale changes in the effect of the QBO on the northern stratospheric polar vortex

Lu, Hua; Baldwin, Mark P.; Gray, Lesley J.; Jarvis, M. J.

doi:10.1029/2007jd009647

Cited by 87 publications

(154 citation statements)

References 60 publications

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“…1: QBO westerlies are longer lasting than easterlies in the mid-to upper stratosphere, a result contrary to that in observations (Baldwin et al, 2001); the QBO does not descend to 100 hPa and, in particular, the west phase does not reach 50 hPa. The WACCM4 simulations produce differences in the high latitudes as a function of the QBO (not shown) that are similar in magnitude and timing to the observed Holton-Tan variations (e.g., Pascoe et al, 2005;Lu et al, 2008;Naoe and Shibata, 2010;Anstey and Shepherd, 2014). A statistically significant (95 % using two-sided t test) response is seen in the high latitudes in November between 1 and 70 hPa with a magnitude change of ∼ 4 K in WACCM4a.…”

Section: Waccmmentioning

confidence: 86%

Examining the stratospheric response to the solar cycle in a coupled WACCM simulation with an internally generated QBO

et al. 2014

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Abstract. The response of the stratosphere to the combined interaction of the quasi-biennial oscillation (QBO) and the solar cycle in ultraviolet (UV) radiation, and the influence of the solar cycle on the QBO, are investigated using the Whole Atmosphere Community Climate Model (WACCM). Transient simulations were performed beginning in 1850 that included fully interactive ocean and chemistry model components, observed greenhouse gas concentrations, volcanic eruptions, and an internally generated QBO. Over the full length of the simulations we do not find a solar cycle modulation of either the QBO period or amplitude. We also do not find a persistent wintertime UV response in polar stratospheric geopotential heights when stratifying by the QBO phase. Over individual ∼ 40 year periods of the simulation, a statistically significant correlation is sometimes found between the northern polar geopotential heights in February and UV irradiance during the QBO's westerly phase. However, the sign of the correlation varies over the simulation, and is never significant during the QBO's easterly phase. Complementing this is the analysis of four simulations using a QBO prescribed to match observations over the period 1953-2005. Again, no consistent correlation is evident. In contrast, over the same period, meteorological reanalysis shows a strong positive correlation during the QBO westerly phase, although it weakens as the period is extended. The results raise the possibility that the observed polar solar-QBO correlation may have occurred because of the relatively short data record and the presence of additional external forcings rather than a direct solar-QBO interaction.

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Section: Waccmmentioning

confidence: 86%

Examining the stratospheric response to the solar cycle in a coupled WACCM simulation with an internally generated QBO

et al. 2014

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“…Therefore, the solar UV and stratospheric QBO have a key role in affecting the latitude and altitude regions where planetary waves propagate and break and thus modulating the response to geomagnetic forcing. The reason why the strongest QBO modulating effect of the geomagnetic signal was observed in early winter is that the QBO-wave-vortex interaction is at its strongest in early winter rather than late winter [Lu et al, 2008c].…”

Section: Discussionmentioning

confidence: 99%

Geomagnetic activity signatures in wintertime stratosphere wind, temperature, and wave response

et al. 2013

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[1] We analyzed ERA-40 and ERA Interim meteorological re-analysis data for signatures of geomagnetic activity in zonal mean zonal wind, temperature, and Eliassen-Palm flux in the Northern Hemisphere extended winter (November-March). We found that for high geomagnetic activity levels, the stratospheric polar vortex becomes stronger in late winter, with more planetary waves being refracted equatorward. The statistically significant signals first appear in December and continue until March, with poleward propagation of the signals with time, even though some uncertainty remains due to the limited amount of data available ( 50 years). Our results also indicated that the geomagnetic effect on planetary wave propagation has a tendency to take place when the stratosphere background flow is relatively stable or when the polar vortex is stronger and less disturbed in early winter. These conditions typically occur during high solar irradiance cycle conditions or westerly quasi-biennial oscillation conditions. Citation: Seppälä, A., H. Lu, M. A. Clilverd, and C. J. Rodger (2013), Geomagnetic activity signatures in wintertime stratosphere wind, temperature, and wave response,

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“…For La Nina winters during the easterly QBO (EQBO) phase, an anomalous stratospheric temperature increase is observed in early winter, while a nonrobust signal is observed during La Nina winters under westerly QBO (WQBO) condi tions (Garfinkel and Hartmann 2007). Likewise, the occurrence of SSWs can also be modulated by the QBO, as SSW occurrence could be favored during EQBO winters (McIntyre 1982), and delayed to mid-and late winter under WQBO conditions (Lu et al 2008). Therefore, within a short record and by using a low threshold, the interference with the SSWs and QBO signals could lead to an uncertain La Nina response.…”

Section: Introductionmentioning

confidence: 99%

The Stratospheric Pathway of La Niña

2016

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A Northern Hemisphere (NH) polar stratospheric pathway for La Nina events is established during win tertime based on reanalysis data for the 1958-2012 period. A robust polar stratospheric response is observed in the NH during strong La Nina events, characterized by a significantly stronger and cooler polar vortex. Significant wind anomalies reach the surface, and a robust impact on the North Atlantic-European (NAE) region is observed. A dynamical analysis reveals that the stronger polar stratospheric winds during La Nina winters are due to reduced upward planetary wave activity into the stratosphere. This finding is the result of destructive interference between the climatological and the anomalous La Nina tropospheric stationary eddies over the Pacific-North American region.In addition, the lack of a robust stratospheric signature during La Nina winters reported in previous studies is investigated. It is found that this is related to the lower threshold used to detect the events, which signature is consequently more prone to be obscured by the influence of other sources of variability. In particular, the occurrence of stratospheric sudden warmings (SSWs), partly linked to the phase of the quasi-biennial oscil lation, modulates the observed stratospheric signal. In the case of La Nina winters defined by a lower threshold, a robust stratospheric cooling is found only in the absence of SSWs. Therefore, these results highlight the importance of using a relatively restrictive threshold to define La Nina events in order to obtain a robust surface response in the NAE region through the stratosphere.

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Decadal‐scale changes in the effect of the QBO on the northern stratospheric polar vortex

Cited by 87 publications

References 60 publications

Examining the stratospheric response to the solar cycle in a coupled WACCM simulation with an internally generated QBO

Examining the stratospheric response to the solar cycle in a coupled WACCM simulation with an internally generated QBO

Geomagnetic activity signatures in wintertime stratosphere wind, temperature, and wave response

The Stratospheric Pathway of La Niña

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