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

White, Ian; Lu, Hua; Mitchell, N. J.; Phillips, Tony

doi:10.1175/jas-d-14-0358.1

Cited by 49 publications

(75 citation statements)

References 74 publications

(97 reference statements)

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“…13 could be interrupted by other processes. For instance, in the event when the lower-stratospheric QBO is in its easterly phase, the enhanced BPWs in the lower and middle stratosphere would lead to a reduction of the PV gradient along the polar vortex edge (White et al 2015(White et al , 2016. These lower-level QBOinduced BPWs would then inhibit upward wave propagation, shielding the upper stratosphere from BPWs.…”

Section: Conclusion and Discussionmentioning

confidence: 99%

“…In addition, when the waves are resonantly excited, we would also expect the seasonal averages of negative daily u 0 y 0 and/ or y 0 T 0 to be sufficiently larger than their climatology. The momentum and heat fluxes are used instead of the E-P fluxes F (f) and F (z) because they do not involve static stability u z , which was found to introduce relatively large biases in the upper stratosphere during data assimilation (Lu et al 2015).…”

Section: E Diagnostics For Wave Reflection and Resonancementioning

confidence: 99%

“…However, an accurate, process-based quantification remains elusive as a result of a large spread in the solar UV and ozone measurements (Ermolli et al 2013;Hood et al 2015;Ball et al 2016), uncertainties among reanalysis datasets (Dee et al 2011;Lu et al 2015;Mitchell et al 2015a;Martineau et al 2016), and model biases (Mitchell et al 2015b;Dhomse et al 2016).…”

Section: Introductionmentioning

confidence: 99%

“…It is the region where the E-P fluxes and divergence exhibit large discrepancies among different reanalysis products (Lu et al 2015;Martineau et al 2016). It is important to check the robustness of the wave-forcing anomalies shown in Figs.…”

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confidence: 99%

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Stratospheric Response to the 11-Yr Solar Cycle: Breaking Planetary Waves, Internal Reflection, and Resonance

Gray

White

et al. 2017

Journal of Climate

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Breaking planetary waves (BPWs) affect stratospheric dynamics by reshaping the waveguides, causing internal wave reflection, and preconditioning sudden stratospheric warmings. This study examines observed changes in BPWs during the northern winter resulting from enhanced solar forcing and the consequent effect on the seasonal development of the polar vortex. During the period 1979-2014, solar-induced changes in BPWs were first observed in the uppermost stratosphere. High solar forcing was marked by sharpening of the potential vorticity (PV) gradient at 308-458N, enhanced wave absorption at high latitudes, and a reduced PV gradient between these regions. These anomalies instigated an equatorward shift of the upper-stratospheric waveguide and enhanced downward wave reflection at high latitudes. The equatorward refraction of reflected waves from the polar upper stratosphere then led to enhanced wave absorption at 358-458N and 7-20 hPa, indicative of a widening of the midstratospheric surf zone. The stratospheric waveguide was thus constricted at about 458-608N and 5-10 hPa in early boreal winter; reduced upward wave propagation through this region resulted in a stronger upper-stratospheric westerly jet. From January, the regions with enhanced BPWs acted as ''barriers'' for subsequent upward and equatorward wave propagation. As the waves were trapped within the stratosphere, anomalies of zonal wavenumbers 2 and 3 were reflected poleward from the stratospheric surf zone. Resonant excitation of some of these reflected waves resulted in rapid growth of wave disturbances and a more disturbed polar vortex in late winter. These results provide a process-oriented explanation for the observed solar cycle signal. They also highlight the importance of nonlinearity in the processes that drive the stratospheric response to external forcing.

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Section: Conclusion and Discussionmentioning

confidence: 99%

Section: E Diagnostics For Wave Reflection and Resonancementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

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Stratospheric Response to the 11-Yr Solar Cycle: Breaking Planetary Waves, Internal Reflection, and Resonance

Gray

White

et al. 2017

Journal of Climate

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“…Similarly, the direct impact of the QBO on the underlying tropospheric circulation in the tropics and sub-tropics is of interest (Giorgetta et al 1999;Collimore et al 2003;Ho et al 2009;Liess and Geller 2012;Nie and Sobel 2015) and recent studies have shown that the QBO modulates the amplitude of the Madden Julian Oscillation, which may lead to improved predictability of MJO under QBO-E conditions Marshall et al 2016;Son et al 2017;Nishimoto and Yoden 2017). 25 One mechanism for QBO influence at the surface is through the modulation of planetary wave propagation in winter by refraction or horizontal reflection of the waves towards (away from) high latitudes under QBO-E (QBO-W) conditions (Holton and Tan 1980;Garfinkel et al 2012;Watson and Gray 2014;White et al 2015). This influence route (the 'polar route') modulates the strength of the polar vortex, and there have been many studies demonstrating that the polar 30 vortex can subsequently influence the underlying tropospheric circulation and surface temperature / pressure distributions Thompson et al 2002, Mitchell et al 2013.…”

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confidence: 99%

Surface impacts of the Quasi Biennial Oscillation

Gray¹,

Anstey²,

Kawatani³

et al. 2017

Preprint

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Abstract.Teleconnections between the Quasi Biennial Oscillation (QBO) and the Northern Hemisphere zonally-averaged zonal winds, mean sea level pressure (mslp) and tropical precipitation are explored using regression analysis. A novel technique is introduced to separate responses associated with the stratospheric polar vortex from other underlying mechanisms. A previously reported mslp response in January, with a pattern that resembles the positive phase of the North 15Atlantic Oscillation (NAO) under QBO westerly conditions, is confirmed and found to be primarily associated with a QBO modulation of the stratospheric polar vortex. This mid-winter response is relatively insensitive to the exact height of the maximum QBO westerlies and a maximum response occurs with westerlies over a relatively deep range between 10-70hPa.Two additional mslp responses are reported, in early winter (December) and late winter (February / March). In contrast to the January response the early and late winter responses show maximum sensitivity to the QBO winds at ~20 hPa and ~70 20 hPa but are relatively insensitive to the QBO winds in between (~50 hPa). The late winter response is centred over the North Pacific and is associated with QBO influence from the lowermost stratosphere at tropical / subtropical latitudes. The early winter response consists of anomalies over both the North Pacific and Europe, but the mechanism is unclear and requires further investigation. QBO anomalies are found in tropical precipitation amounts and a southward shift of the Intertropical Convergence Zone under westerly QBO conditions is also evident. 25

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Seasonal evolution of the QBO‐induced wave forcing and circulation anomalies in the northern winter stratosphere

White

Mitchell

2016

JGR Atmospheres

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Diagnostics of wave-mean-flow and wave-wave interactions in isentropic coordinates are analyzed regarding the mechanisms that govern the Holton-Tan effect (HTE), whereby the tropical quasi-biennial oscillation (QBO) modulates the northern winter stratospheric polar vortex. We find a clear seasonal evolution of a QBO modulation of Rossby waves and linear and nonlinear wave interactions, along with multiple mechanisms at work. In early winter, when the lower stratospheric QBO is easterly, there is enhanced upward stationary planetary-wave activity in the subtropical to midlatitude lower stratosphere. These upward-propagating waves are first refracted toward the zero-wind line. Approximately 1 month later, poleward-propagating wave anomalies appear at midlatitudes as a result of nonlinear wave interactions. The enhanced upward wave propagation appears to be due to a combination of the QBO influence on the latitudinal location of the zero-wind line and the increased midlatitude baroclinicity associated with the QBO-induced meridional circulation. This is further aided by a gradual poleward shift over the winter of the middle-stratospheric waveguide, refracting waves poleward. The associated wave breaking weakens the polar vortex and drives a stronger meridional circulation throughout the lower to middle stratosphere, contributing to the high-latitude warming. It is additionally found that in late winter, the modified high-latitude waveguide associated with the weaker polar vortex, consequently reduces upward-propagating transient planetary waves at high latitudes while simultaneously enhancing upward-propagating synoptic waves at midlatitudes. This highlights the need to view the HTE and its mechanisms as an evolving phenomenon throughout the winter.

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

Cited by 49 publications

References 74 publications

Stratospheric Response to the 11-Yr Solar Cycle: Breaking Planetary Waves, Internal Reflection, and Resonance

Stratospheric Response to the 11-Yr Solar Cycle: Breaking Planetary Waves, Internal Reflection, and Resonance

Surface impacts of the Quasi Biennial Oscillation

Seasonal evolution of the QBO‐induced wave forcing and circulation anomalies in the northern winter stratosphere

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