scholarly journals The Buffer Zone of the Quasi-Biennial Oscillation

2019 ◽  
Vol 76 (11) ◽  
pp. 3553-3567 ◽  
Author(s):  
Aaron Match ◽  
Stephan Fueglistaler
Keyword(s):  
Angular Momentum ◽  
Momentum Flux ◽  
Buffer Zone ◽  
Far Field ◽  
Flux Divergence ◽  
Momentum Exchange ◽  
Quasi Biennial Oscillation ◽  
Weak Wave ◽  
Vertically Propagating ◽  
Biennial Oscillation

Abstract The quasi-biennial oscillation (QBO) is a descending pattern of winds in the stratosphere that vanishes near the top of the tropical tropopause layer, even though the vertically propagating waves that drive the QBO are thought to originate in the troposphere several kilometers below. The region where there is low QBO power despite sufficient vertically propagating wave activity to drive a QBO is known as the buffer zone. Classical one-dimensional models of the QBO are ill suited to represent buffer zone dynamics because they enforce the attenuation of the QBO via a zero-wind lower boundary condition. The formation of the buffer zone is investigated by analyzing momentum budgets in the reanalyses MERRA-2 and ERA-Interim. The buffer zone must be formed by weak wave-driven acceleration and/or cancellation of the wave-driven acceleration. This paper shows that in MERRA-2 weak wave-driven acceleration is insufficient to form the buffer zone, so cancellation of the wave-driven acceleration must play a role. The cancellation results from damping of angular momentum anomalies, primarily due to horizontal mean and horizontal eddy momentum flux divergence, with secondary contributions from the Coriolis torque and vertical mean momentum flux divergence. The importance of the damping terms highlights the role of the buffer zone as the mediator of angular momentum exchange between the QBO domain and the far field. Some far-field angular momentum anomalies reach the solid Earth, leading to the well-documented lagged correlation between the QBO and the length of day.

Mean-Flow Damping Forms the Buffer Zone of the Quasi-Biennial Oscillation: 1D Theory

2020 ◽  
Vol 77 (6) ◽  
pp. 1955-1967
Author(s):  
Aaron Match ◽  
Stephan Fueglistaler
Keyword(s):  
Lower Boundary ◽  
Buffer Zone ◽  
Critical Levels ◽  
Mean Flow ◽  
Flux Divergence ◽  
Wave Dissipation ◽  
Quasi Biennial Oscillation ◽  
Lower Boundary Condition ◽  
Zone Formation ◽  
Biennial Oscillation

Abstract The quasi-biennial oscillation (QBO) is a descending pattern of alternating easterly and westerly winds in the tropical stratosphere. Upwelling is generally understood to counteract the descent of the QBO. The upwelling hypothesis holds that where upwelling exceeds the intrinsic descent rate of the QBO, the QBO cannot descend and a buffer zone forms. Descent-rate models of the QBO, which represent a highly simplified evolution of a QBO wind contour, support the upwelling hypothesis. Here, we show that the upwelling hypothesis and descent-rate models only correctly describe buffer zone formation in the absence of wave dissipation below critical levels. When there is wave dissipation below critical levels, the 1D QBO response to upwelling can be either to 1) reform below the upwelling, 2) undergo period-lengthening collapse, or 3) expand a preexisting buffer zone. The response depends on the location of the upwelling and the lower boundary condition. Mean-flow damping always forms a buffer zone. A previous study of reanalyses showed that there is mean-flow damping in the buffer zone due to horizontal momentum flux divergence. Therefore, the 1D model implicates lateral terms in buffer zone formation that it cannot self-consistently include.

scholarly journals Mechanisms of Jet Formation on the Giant Planets

2010 ◽  
Vol 67 (11) ◽  
pp. 3652-3672 ◽  
Author(s):  
Junjun Liu ◽  
Tapio Schneider
Keyword(s):  
Angular Momentum ◽  
Rossby Wave ◽  
Momentum Flux ◽  
Wave Generation ◽  
Heat Fluxes ◽  
Giant Planets ◽  
Radiative Heating ◽  
Flux Divergence ◽  
Low Latitude ◽  
Flow Configurations

Abstract The giant planet atmospheres exhibit alternating prograde (eastward) and retrograde (westward) jets of different speeds and widths, with an equatorial jet that is prograde on Jupiter and Saturn and retrograde on Uranus and Neptune. The jets are variously thought to be driven by differential radiative heating of the upper atmosphere or by intrinsic heat fluxes emanating from the deep interior. However, existing models cannot account for the different flow configurations on the giant planets in an energetically consistent manner. Here a three-dimensional general circulation model is used to show that the different flow configurations can be reproduced by mechanisms universal across the giant planets if differences in their radiative heating and intrinsic heat fluxes are taken into account. Whether the equatorial jet is prograde or retrograde depends on whether the deep intrinsic heat fluxes are strong enough that convection penetrates into the upper troposphere and generates strong equatorial Rossby waves there. Prograde equatorial jets result if convective Rossby wave generation is strong and low-latitude angular momentum flux divergence owing to baroclinic eddies generated off the equator is sufficiently weak (Jupiter and Saturn). Retrograde equatorial jets result if either convective Rossby wave generation is weak or absent (Uranus) or low-latitude angular momentum flux divergence owing to baroclinic eddies is sufficiently strong (Neptune). The different speeds and widths of the off-equatorial jets depend, among other factors, on the differential radiative heating of the atmosphere and the altitude of the jets, which are vertically sheared. The simulations have closed energy and angular momentum balances that are consistent with observations of the giant planets. They exhibit temperature structures closely resembling those observed and make predictions about as yet unobserved aspects of flow and temperature structures.

Development of the Extratropical Response to the Stratospheric Quasi-Biennial Oscillation

2021 ◽  
pp. 1-44
Author(s):  
Jian Rao ◽  
Chaim I. Garfinkel ◽  
Ian P. White
Keyword(s):  
Climate Models ◽  
Meridional Circulation ◽  
Polar Vortex ◽  
Late Winter ◽  
Flux Divergence ◽  
Quasi Biennial Oscillation ◽  
Atlantic Sector ◽  
Near Surface ◽  
Surface Response ◽  
Biennial Oscillation

AbstractUsing the Model of an Idealized Moist Atmosphere (MiMA) capable of spontaneously generating a Quasi-Biennial Oscillation (QBO), the gradual establishment of the extratropical response to the QBO is explored. The period and magnitude of the QBO and the magnitude of the polar Holton-Tan (HT) relationship is simulated in a free-running configuration of MiMA, comparable to that in state-of-the-art climate models. In order to isolate mechanisms whereby the QBO influences variability outside of the tropical atmosphere, a series of branch experiments are performed with nudged QBO winds. When easterly QBO winds maximized around 30 hPa are relaxed, an Eliassen-Palm (E-P) flux divergence dipole quickly forms in the extratropical middle stratosphere as a direct response to the tropical meridional circulation, in contrast to the HT mechanism which is associated with wave propagation near the zero wind line. This meridional circulation response to the relaxed QBO winds develops within the first 10 days in seasonally-varying and fixed-seasonal experiments. No detectable changes in upward propagation of waves in the midlatitude lowermost stratosphere are evident for at least 20 days after branching, with the first changes only evident after 20 days in perpetual midwinter and season-varying runs, but after 40 days in perpetual November runs. The polar vortex begins to respond around the 20th day, and subsequently a near-surface response in the Atlantic sector forms in mid-to-late winter runs. These results suggest that the maximum near-surface response observed in mid-to-late winter is not simply due to a random seasonal synchronization of the QBO phase, but also due to the long (short) lag of the surface response to a QBO relaxation in early (mid-to-late) winter.

Anomalous Dynamics of QBO Disruptions Explained by 1D Theory With External Triggering

2020 ◽  
Author(s):  
Aaron Match ◽  
Stephan Fueglistaler
Keyword(s):  
Shear Zone ◽  
Shear Zones ◽  
Flux Divergence ◽  
Quasi Biennial Oscillation ◽  
Zonal Winds ◽  
Momentum Budget ◽  
1D Model ◽  
Triggering Events ◽  
Anomalous Dynamics ◽  
Biennial Oscillation

AbstractThe Quasi-Biennial Oscillation (QBO) is an alternating, descending pattern of zonal winds in the tropical stratosphere with a period averaging 28 months. The QBO was disrupted in 2016, and arguably again in 2020, by the formation of an anomalous easterly shear zone, and unprecedented stagnation and ascent of shear zones aloft. Several mechanisms have been implicated in causing the 2016 disruption, most notably triggering by horizontal eddy momentum flux divergence, but also anomalous upwelling and wave stress. In this paper, the 1D theory of the QBO is used to show how seemingly disparate features of disruptions follow directly from the dynamics of the QBO response to triggering. The perturbed QBO is interpreted using a heuristic version of the 1D model, which establishes that: (1) stagnation of shear zones aloft resulted from wave dissipation in the shear zone formed by the triggering, and (2) ascent of shear zones aloft resulted from climatological upwelling advecting the stagnant shear zones. Obstacles remain in the theory of triggering. In the 1D theory, the phasing of the triggering is key to determining the response, but the dependence on magnitude is less steep. Yet in MERRA-2, there are triggering events only 20% weaker than the 2016 triggering and equal to the 2020 triggering that did not lead to disruptions. Complicating matters further, MERRA-2 has record-large analysis tendencies during the 2016 disruption, reducing confidence in the resolved momentum budget.

scholarly journals Nonstationary Synchronization of Equatorial QBO with SAO in Observations and a Model

2009 ◽  
Vol 66 (6) ◽  
pp. 1654-1664 ◽  
Author(s):  
Le Kuai ◽  
Run-Lie Shia ◽  
Xun Jiang ◽  
Ka-Kit Tung ◽  
Yuk L. Yung
Keyword(s):  
Angular Momentum ◽  
Solar Cycle ◽  
Natural Period ◽  
Quasi Biennial Oscillation ◽  
Integer Multiple ◽  
Weather Forecasts ◽  
Wave Forcing ◽  
Medium Range ◽  
Biennial Oscillation ◽  
Semiannual Oscillation

Abstract It has often been suggested that the period of the quasi-biennial oscillation (QBO) has a tendency to synchronize with the semiannual oscillation (SAO). Apparently the synchronization is better the higher up the observation extends. Using 45 yr of the 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40) data of the equatorial stratosphere up to the stratopause, the authors confirm that this synchronization is not just a tendency but a robust phenomenon in the upper stratosphere. A QBO period starts when a westerly SAO (w-SAO) descends from the stratopause to 7 hPa and initiates the westerly phase of the QBO (w-QBO) below. It ends when another w-SAO, a few SAO periods later, descends again to 7 hPa to initiate the next w-QBO. The fact that it is the westerly but not the easterly SAO (e-SAO) that initiates the QBO is also explained by the general easterly bias of the angular momentum in the equatorial stratosphere so that the e-SAO does not create a zero-wind line, unlike the w-SAO. The currently observed average QBO period of 28 months, which is not an integer multiple of SAO periods, is a result of intermittent jumps of the QBO period from four SAO to five SAO periods. The same behavior is also found in the Two and a Half Dimensional Interactive Isentropic Research (THINAIR) model. It is found that the nonstationary behavior in both the observation and model is caused not by the 11-yr solar-cycle forcing but by the incompatibility of the QBO’s natural period (determined by its wave forcing) and the “quantized” period determined by the SAO. The wave forcing parameter for the QBO period in the current climate probably lies between four SAO and five SAO periods. If the wave forcing for the QBO is tuned so that its natural period is compatible with the SAO period above (e.g., at 24 or 30 months), nonstationary behavior disappears.

Simulated disruptions of the Quasi-Biennial Oscillation

2021 ◽  
Author(s):  
Kevin DallaSanta ◽  
Clara Orbe
Keyword(s):  
Momentum Flux ◽  
Volcanic Eruptions ◽  
Quasi Biennial Oscillation ◽  
Rich Variety ◽  
Surface Weather ◽  
Tropical Ssts ◽  
Model Independent ◽  
Stratospheric Composition ◽  
Observational Record ◽  
Biennial Oscillation

<p>The Quasi-Biennial Oscillation has exhibited remarkable stability over the observational record—until a well-documented 2015/16 disruption and an emerging disruption in 2020/21. The possibility that disruptions are more frequent in a changing climate is important to consider, as the QBO affects predictability, stratospheric composition, and surface weather. However, this possibility is challenging to assess for a variety of reasons. For instance, the 2015/16 disruption has been attributed to anomalous easterly momentum flux from extratropical waves. By comparison, the 2020/21 disruption involves anomalous westerly forcing, less likely to originate from the same mechanism.</p><p>We present a rich variety of QBO disruptions that spontaneously arise in integrations of the high-top NASA GISS Model E2.2. The disruptions loosely fall into several categories, some of which are analogous to the 2015/16 disruption and the 2020 disruption, as well as a previously undocumented possible disruption in 1988. Several factors appear to influence QBO disruptions in the model: natural variability, climate change, tropical SSTs, volcanic eruptions, and model physics/tuning. Although QBO representation is an ongoing challenge for models, the results point to a model-independent framework for assessment of disruptions.</p><p> </p>

scholarly journals Momentum Flux of Convective Gravity Waves Derived from an Offline Gravity Wave Parameterization. Part II: Impacts on the Quasi-Biennial Oscillation

2018 ◽  
Vol 75 (11) ◽  
pp. 3753-3775 ◽  
Author(s):  
Min-Jee Kang ◽  
Hye-Yeong Chun ◽  
Young-Ha Kim ◽  
Peter Preusse ◽  
Manfred Ern
Keyword(s):  
Shear Zone ◽  
Gravity Waves ◽  
Momentum Flux ◽  
Large Scale ◽  
Reanalysis Data ◽  
Equatorial Region ◽  
Small Scale ◽  
Quasi Biennial Oscillation ◽  
Convective Gravity Waves ◽  
Biennial Oscillation

Abstract The characteristics of small-scale convective gravity waves (CGWs; horizontal wavelengths <100 km) and their contributions to the large-scale flow in the stratosphere, including the quasi-biennial oscillation (QBO), are investigated using an offline calculation of a source-dependent, physically based CGW parameterization with global reanalysis data from 1979 to 2010. The CGW momentum flux (CGWMF) and CGW drag (CGWD) are calculated from the cloud top (source level) to the upper stratosphere using a Lindzen-type wave propagation scheme. The 32-yr-mean CGWD exhibits large magnitudes in the tropical upper stratosphere and near the stratospheric polar night jet (~60°). The maximum positive drag is 0.1 (1.5) m s−1 day−1, and the maximum negative drag is −0.9 (−0.7) m s−1 day−1 in January (July) between 3 and 1 hPa. In the tropics, the momentum forcing by CGWs at 30 hPa associated with the QBO in the westerly shear zone is 3.5–6 m s−1 month−1, which is smaller than that by Kelvin waves, while that by CGWs in the easterly shear zone (3.1–6 m s−1 month−1) is greater than that by any other equatorial planetary waves or inertio-gravity waves (inertio-GWs). Composite analyses of the easterly QBO (EQBO) and westerly QBO (WQBO) phases reveal that the zonal CGWMF is concentrated near 10°N and that the negative (positive) CGWD extends latitudinally to ±20° (±10°) at 30 hPa. The strongest (weakest) negative CGWD is in March–May (September–November) during the EQBO, and the strongest (weakest) positive CGWD is in June–August (March–May) during the WQBO. The CGWMF and CGWD are generally stronger during El Niño than during La Niña in the equatorial region.

scholarly journals Impact of the Quasi-Biennial Oscillation on the Northern Winter Stratospheric Polar Vortex in CMIP5/6 Models

2020 ◽  
Vol 33 (11) ◽  
pp. 4787-4813 ◽  
Author(s):  
Jian Rao ◽  
Chaim I. Garfinkel ◽  
Ian P. White
Keyword(s):  
Polar Vortex ◽  
The Arctic ◽  
Early Winter ◽  
Flux Divergence ◽  
Quasi Biennial Oscillation ◽  
Stratospheric Polar Vortex ◽  
Northern Winter ◽  
P Flux ◽  
The Impact ◽  
Biennial Oscillation

AbstractUsing 16 CMIP5/6 models with a spontaneously generated quasi-biennial oscillation (QBO)-like phenomenon, this study investigates the impact of the QBO on the northern winter stratosphere. Eight of the models simulate a QBO with a period similar to that observed (25–31 months), with other models simulating a QBO period of 20–40 months. Regardless of biases in QBO periodicity, the Holton–Tan relationship can be well simulated in CMIP5/6 models with more planetary wave convergence in the polar stratosphere in easterly QBO winters. This wave polar convergence occurs not only due to the Holton–Tan mechanism, but also in the midlatitude upper stratosphere where an Elissen–Palm (E-P) flux divergence dipole (with poleward E-P flux) is simulated in most models. The wave response in the upper stratosphere appears related to changes in the background circulation through a directly excited meridional–vertical circulation cell above the maximum tropical QBO easterly center. The midlatitude upwelling in this anticlockwise cell is split into two branches, and the north branch descends in the Arctic region and warms the stratospheric polar vortex. Most models underestimate the Arctic stratospheric warming in early winter during easterly QBO. Further analysis suggests that this bias is not due to an overly weak response to a given QBO phase, as the models simulate a realistic response if one focuses on similar QBO phases. Rather, the model bias is due to the too-low frequency of strong QBO winds in the lower stratosphere in early winter simulated by the models.

scholarly journals Does the coupling of the semiannual oscillation with the quasi-biennial oscillation provide predictability of Antarctic sudden stratospheric warmings?

2021 ◽  
Vol 21 (17) ◽  
pp. 12835-12853
Author(s):  
Viktoria J. Nordström ◽  
Annika Seppälä
Keyword(s):  
Polar Vortex ◽  
Reanalysis Data ◽  
Early Winter ◽  
Flux Divergence ◽  
Quasi Biennial Oscillation ◽  
Easterly Wind ◽  
Wave Forcing ◽  
A Minor ◽  
Biennial Oscillation ◽  
Semiannual Oscillation

Abstract. During September 2019 a minor sudden stratospheric warming took place over the Southern Hemisphere (SH), bringing disruption to the usually stable winter vortex. The mesospheric winds reversed and temperatures in the stratosphere rose by over 50 K. Whilst sudden stratospheric warmings (SSWs) in the SH are rare, with the only major SSW having occurred in 2002, the Northern Hemisphere experiences about six per decade. Amplification of atmospheric waves during winter is thought to be one of the possible triggers for SSWs, although other mechanisms are also possible. Our understanding, however, remains incomplete, especially with regards to SSW occurrence in the SH. Here, we investigate the effect of two equatorial atmospheric modes, the quasi-biennial oscillation (QBO) at 10 hPa and the semiannual oscillation (SAO) at 1 hPa during the SH winters of 2019 and 2002. Using MERRA-2 reanalysis data we find that the easterly wind patterns resembling the two modes merge at low latitudes in the early winter, forming a zero-wind line that stretches from the lower stratosphere into the mesosphere. This influences the meridional wave guide, resulting in easterly momentum being deposited in the polar atmosphere throughout the polar winter, decelerating the westerly winds in the equatorward side of the polar vortex. As the winter progresses, the momentum deposition and wind anomalies descend further down into the stratosphere. We find similar behaviour in other years with early onset SH vortex weakening events. The magnitude of the SAO and the timing of the upper stratospheric (10 hPa) easterly QBO signal was found to be unique in these years when compared to the years with a similar QBO phase. We were able to identify the SSW and weak vortex years from the early winter location of the zero-wind line at 1 hPa together with Eliassen–Palm flux divergence in the upper stratosphere at 40–50∘ S. We propose that this early winter behaviour resulting in deceleration of the polar winds may precondition the southern atmosphere for a later enhanced wave forcing from the troposphere, resulting in an SSW or vortex weakening event. Thus, the early winter equatorial upper stratosphere–mesosphere, together with the polar upper atmosphere, may provide early clues to an imminent SH SSW.

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