Climatology and Forcing of the Quasi-Biennial Oscillation in the MAECHAM5 Model

Abstract The quasi-biennial oscillation (QBO) in the equatorial zonal wind is an outstanding phenomenon of the atmosphere. The QBO is driven by a broad spectrum of waves excited in the tropical troposphere and modulates transport and mixing of chemical compounds in the whole middle atmosphere. Therefore, the simulation of the QBO in general circulation models and chemistry climate models is an important issue. Here, aspects of the climatology and forcing of a spontaneously occurring QBO in a middle-atmosphere model are evaluated, and its influence on the climate and variability of the tropical middle atmosphere is investigated. Westerly and easterly phases are considered separately, and 40-yr ECMWF Re-Analysis (ERA-40) data are used as a reference where appropriate. It is found that the simulated QBO is realistic in many details. Resolved large-scale waves are particularly important for the westerly phase, while parameterized gravity wave drag is more important for the easterly phase. Advective zonal wind tendencies are important for asymmetries between westerly and easterly phases, as found for the suppression of the easterly phase downward propagation. The simulation of the QBO improves the tropical upwelling and the atmospheric tape recorder compared to a model without a QBO. The semiannual oscillation is simulated realistically only if the QBO is represented. In sensitivity tests, it is found that the simulated QBO is strongly sensitive to changes in the gravity wave sources. The sensitivity to the tested range of horizontal resolutions is small. The stratospheric vertical resolution must be better than 1 km to simulate a realistic QBO.

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Constraints on Wave Drag Parameterization Schemes for Simulating the Quasi-Biennial Oscillation. Part II: Combined Effects of Gravity Waves and Equatorial Planetary Waves

Journal of the Atmospheric Sciences ◽

10.1175/jas3617.1 ◽

2005 ◽

Vol 62 (12) ◽

pp. 4196-4205 ◽

Cited By ~ 8

Author(s):

Lucy J. Campbell ◽

Theodore G. Shepherd

Keyword(s):

Gravity Wave ◽

Gravity Waves ◽

General Circulation ◽

Planetary Wave ◽

General Circulation Models ◽

Wave Drag ◽

Planetary Waves ◽

Small Contribution ◽

Quasi Biennial Oscillation ◽

Biennial Oscillation

Abstract This study examines the effect of combining equatorial planetary wave drag and gravity wave drag in a one-dimensional zonal mean model of the quasi-biennial oscillation (QBO). Several different combinations of planetary wave and gravity wave drag schemes are considered in the investigations, with the aim being to assess which aspects of the different schemes affect the nature of the modeled QBO. Results show that it is possible to generate a realistic-looking QBO with various combinations of drag from the two types of waves, but there are some constraints on the wave input spectra and amplitudes. For example, if the phase speeds of the gravity waves in the input spectrum are large relative to those of the equatorial planetary waves, critical level absorption of the equatorial planetary waves may occur. The resulting mean-wind oscillation, in that case, is driven almost exclusively by the gravity wave drag, with only a small contribution from the planetary waves at low levels. With an appropriate choice of wave input parameters, it is possible to obtain a QBO with a realistic period and to which both types of waves contribute. This is the regime in which the terrestrial QBO appears to reside. There may also be constraints on the initial strength of the wind shear, and these are similar to the constraints that apply when gravity wave drag is used without any planetary wave drag. In recent years, it has been observed that, in order to simulate the QBO accurately, general circulation models require parameterized gravity wave drag, in addition to the drag from resolved planetary-scale waves, and that even if the planetary wave amplitudes are incorrect, the gravity wave drag can be adjusted to compensate. This study provides a basis for knowing that such a compensation is possible.

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Response of the quasi-biennial oscillation to a warming climate in global climate models

10.5194/egusphere-egu2020-18795 ◽

2020 ◽

Author(s):

Jadwiga Richter ◽

Francois Lott ◽

Keyword(s):

Gravity Wave ◽

General Circulation ◽

Climate Models ◽

Global Climate ◽

General Circulation Models ◽

Global Climate Models ◽

Residual Velocity ◽

Quasi Biennial Oscillation ◽

Biennial Oscillation ◽

Wave Momentum

We compare the response of the quasi-biennial oscillation (QBO) to a warming&#160;climate in eleven atmosphere general circulation models that performed time-slice&#160;simulations for present-day, doubled,&#160; and&#160; quadrupled CO2 climates.&#160; No consistency was found among the models for the QBO period response, with the period&#160;decreasing by eight months in some models and lengthening by up to thirteen months in others in the doubled CO2&#160; simulations.&#160; In the&#160;quadruped CO2 simulations&#160; a reduction in QBO period of 14 months was found in some models, whereas in several others the tropical oscillation no longer resembled the present day QBO, although&#160;could still be identified in the deseasonalized zonal mean zonal wind timeseries.&#160; In contrast, all the models projected a decrease in the&#160; QBO&#160;amplitude in a warmer climate with the largest relative decrease&#160; near 60 hPa. In simulations with doubled and quadrupled CO2 the multi-model mean QBO amplitudes decreased by 36\% and 51\%, respectively. Across the&#160; models the differences in the QBO period response were most strongly&#160;related to how the gravity wave momentum flux entering the stratosphere and&#160;tropical vertical residual velocity responded to the increases&#160;in CO2 amounts. Likewise it was found that the robust decrease in QBO amplitudes was&#160;correlated across the models to changes in vertical residual velocity,&#160;parameterized gravity wave momentum fluxes, and to some degree the resolved upward wave flux.&#160; We argue that uncertainty in the representation of the parameterized gravity waves is the most likely cause&#160;of the spread among the eleven models in the QBO's response to climate change.

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Net effect of the QBO in a chemistry climate model

Atmospheric Chemistry and Physics ◽

10.5194/acp-8-6505-2008 ◽

2008 ◽

Vol 8 (21) ◽

pp. 6505-6525 ◽

Cited By ~ 11

Author(s):

H. J. Punge ◽

M. A. Giorgetta

Keyword(s):

General Circulation ◽

Climate Models ◽

Climate Model ◽

Middle Atmosphere ◽

Meridional Circulation ◽

Vortex Formation ◽

General Circulation Models ◽

Quasi Biennial Oscillation ◽

The Mean ◽

The Tropics

Abstract. The quasi-biennial oscillation (QBO) of zonal wind is a prominent mode of variability in the tropical stratosphere. It affects not only the meridional circulation and temperature over a wide latitude range but also the transport and chemistry of trace gases such as ozone. Compared to a QBO less circulation, the long-term climatological means of these quantities are also different. These climatological net effects of the QBO can be studied in general circulation models that extend into the middle atmosphere and have a chemistry and transport component, so-called Chemistry Climate Models (CCMs). In this work we show that the CCM MAECHAM4-CHEM can reproduce the observed QBO variations in temperature and ozone mole fractions when nudged towards observed winds. In particular, it is shown that the QBO signal in transport of nitrogen oxides NOx plays an important role in reproducing the observed ozone QBO, which features a phase reversal slightly below the level of maximum of the ozone mole fraction in the tropics. We then compare two 20-year experiments with the MAECHAM4-CHEM model that differ by including or not including the QBO. The mean wind fields differ between the two model runs, especially during summer and fall seasons in both hemispheres. The differences in the wind field lead to differences in the meridional circulation, by the same mechanism that causes the QBO's secondary meridional circulation, and thereby affect mean temperatures and the mean transport of tracers. In the tropics, the net effect on ozone is mostly due to net differences in upwelling and, higher up, the associated temperature change. We show that a net surplus of up to 15% in NOx in the tropics above 10 hPa in the experiment that includes the QBO does not lead to significantly different volume mixing ratios of ozone. We also note a slight increase in the southern vortex strength as well as earlier vortex formation in northern winter. Polar temperatures differ accordingly. Differences in the strength of the Brewer-Dobson circulation and in further trace gas concentrations are analysed. Our findings underline the importance of a representation of the QBO in CCMs.

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Is Missing Orographic Gravity Wave Drag near 60°S the Cause of the Stratospheric Zonal Wind Biases in Chemistry–Climate Models?

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-11-0159.1 ◽

2012 ◽

Vol 69 (3) ◽

pp. 802-818 ◽

Cited By ~ 97

Author(s):

Charles McLandress ◽

Theodore G. Shepherd ◽

Saroja Polavarapu ◽

Stephen R. Beagley

Keyword(s):

Gravity Wave ◽

Zonal Wind ◽

Climate Models ◽

Middle Atmosphere ◽

Wave Drag ◽

Early Summer ◽

Systematic Bias ◽

Stratospheric Polar Vortex ◽

Column Ozone ◽

The Impact

Abstract Nearly all chemistry–climate models (CCMs) have a systematic bias of a delayed springtime breakdown of the Southern Hemisphere (SH) stratospheric polar vortex, implying insufficient stratospheric wave drag. In this study the Canadian Middle Atmosphere Model (CMAM) and the CMAM Data Assimilation System (CMAM-DAS) are used to investigate the cause of this bias. Zonal wind analysis increments from CMAM-DAS reveal systematic negative values in the stratosphere near 60°S in winter and early spring. These are interpreted as indicating a bias in the model physics, namely, missing gravity wave drag (GWD). The negative analysis increments remain at a nearly constant height during winter and descend as the vortex weakens, much like orographic GWD. This region is also where current orographic GWD parameterizations have a gap in wave drag, which is suggested to be unrealistic because of missing effects in those parameterizations. These findings motivate a pair of free-running CMAM simulations to assess the impact of extra orographic GWD at 60°S. The control simulation exhibits the cold-pole bias and delayed vortex breakdown seen in the CCMs. In the simulation with extra GWD, the cold-pole bias is significantly reduced and the vortex breaks down earlier. Changes in resolved wave drag in the stratosphere also occur in response to the extra GWD, which reduce stratospheric SH polar-cap temperature biases in late spring and early summer. Reducing the dynamical biases, however, results in degraded Antarctic column ozone. This suggests that CCMs that obtain realistic column ozone in the presence of an overly strong and persistent vortex may be doing so through compensating errors.

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Net effect of the QBO in a chemistry climate model

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-8-12115-2008 ◽

2008 ◽

Vol 8 (3) ◽

pp. 12115-12162 ◽

Cited By ~ 1

Author(s):

H. J. Punge ◽

M. A. Giorgetta

Keyword(s):

General Circulation ◽

Climate Models ◽

Climate Model ◽

Middle Atmosphere ◽

Meridional Circulation ◽

Vortex Formation ◽

General Circulation Models ◽

Quasi Biennial Oscillation ◽

The Mean ◽

The Tropics

Abstract. The quasi-biennial oscillation (QBO) of zonal wind is a prominent mode of variability in the tropical stratosphere. It affects not only the meridional circulation and temperature over a wide latitude range but also the transport and chemistry of trace gases such as ozone. Compared to a QBO less circulation, the long-term climatological means of these quantities are also different. These climatological net effects of the QBO can be studied in general circulation models that extend into the middle atmosphere and have a chemistry and transport component, so-called Chemistry Climate Models (CCMs). In this work we show that the CCM MAECHAM4-CHEM can reproduce the observed QBO variations in temperature and ozone mole fractions when nudged towards observed winds. In particular, it is shown that the QBO signal in transport of nitrogen oxides NOx plays an important role in reproducing the observed ozone QBO, which features a phase reversal slightly below the maximum of the ozone mole fraction in the tropics. We then compare two 20-year experiments with the MAECHAM4-CHEM model that differ by including or not including the QBO. The mean wind fields differ between the two model runs, especially during summer and fall on both hemispheres. The differences in the wind field lead to differences in the meridional circulation, by the same mechanism that causes the QBO's secondary meridional circulation, and thereby affecting mean temperatures and the mean transport of tracers. In the tropics, the net effect on ozone is mostly due to net differences in upwelling and, higher up, the associated temperature change. We show that a net surplus of up to 15% in NOx in the tropics above 10 hPa in the experiment that includes the QBO does not lead to significantly different volume mixing ratios of ozone. We also note a slight increase in the southern vortex strength as well as earlier vortex formation in northern winter. Polar temperatures differ accordingly. Differences in the strength of the Brewer-Dobson circulation and in further trace gas concentrations are analysed. Our findings underline the importance of a representation of the QBO in CCMs.

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The Seasonal Cycle of Gravity Wave Drag in the Middle Atmosphere

Journal of Climate ◽

10.1175/2008jcli2006.1 ◽

2008 ◽

Vol 21 (18) ◽

pp. 4664-4679 ◽

Cited By ~ 20

Author(s):

Manuel Pulido ◽

John Thuburn

Keyword(s):

Gravity Wave ◽

Seasonal Cycle ◽

Middle Atmosphere ◽

Three Dimensional ◽

Wave Drag ◽

Smooth Transition ◽

Quasi Biennial Oscillation ◽

Summer Hemisphere ◽

Jet Streaks ◽

Biennial Oscillation

Abstract Using a variational technique, middle atmosphere gravity wave drag (GWD) is estimated from Met Office middle atmosphere analyses for the year 2002. The technique employs an adjoint model of a middle atmosphere dynamical model to minimize a cost function that measures the differences between the model state and observations. The control variables are solely the horizontal components of GWD; therefore, the minimization determines the optimal estimate of the drag. For each month, Met Office analyses are taken as the initial condition for the first day of the month, and also as observations for each successive day. In this way a three-dimensional GWD field is obtained for the entire year with a temporal resolution of 1 day. GWD shows a pronounced seasonal cycle. During solstices, there are deceleration regions of the polar jet centered at about 63° latitude in the winter hemisphere, with a peak of 49 m s−1 day−1 at 0.24 hPa in the Southern Hemisphere; the summer hemisphere also shows a deceleration region but much weaker, with a peak of 24 m s−1 day−1 centered at 45° latitude and 0.6 hPa. During equinoxes GWD is weak and exhibits a smooth transition between the winter and summer situation. The height and latitude of the deceleration center in both winter and summer hemispheres appear to be constant. Important longitudinal dependencies in GWD are found that are related to planetary wave activity; GWD intensifies in the exit region of jet streaks. In the lower tropical stratosphere, the estimated GWD shows a westward GWD descending together with the westward phase of the quasi-biennial oscillation. Above, GWD exhibits a semiannual pattern that is approximately out of phase with the semiannual oscillation in the zonal wind. Furthermore, a descending GWD pattern is found at those heights, similar in magnitude and sign to that in the lower stratosphere.

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Constraints on Wave Drag Parameterization Schemes for Simulating the Quasi-Biennial Oscillation. Part I: Gravity Wave Forcing

Journal of the Atmospheric Sciences ◽

10.1175/jas3616.1 ◽

2005 ◽

Vol 62 (12) ◽

pp. 4178-4195 ◽

Cited By ~ 14

Author(s):

Lucy J. Campbell ◽

Theodore G. Shepherd

Keyword(s):

Gravity Wave ◽

Zonal Wind ◽

Shear Zones ◽

Wave Drag ◽

Planetary Waves ◽

Vertical Diffusion ◽

Quasi Biennial Oscillation ◽

Parameterization Schemes ◽

Downward Propagation ◽

Biennial Oscillation

Abstract Parameterization schemes for the drag due to atmospheric gravity waves are discussed and compared in the context of a simple one-dimensional model of the quasi-biennial oscillation (QBO). A number of fundamental issues are examined in detail, with the goal of providing a better understanding of the mechanism by which gravity wave drag can produce an equatorial zonal wind oscillation. The gravity wave–driven QBOs are compared with those obtained from a parameterization of equatorial planetary waves. In all gravity wave cases, it is seen that the inclusion of vertical diffusion is crucial for the descent of the shear zones and the development of the QBO. An important difference between the schemes for the two types of waves is that in the case of equatorial planetary waves, vertical diffusion is needed only at the lowest levels, while for the gravity wave drag schemes it must be included at all levels. The question of whether there is downward propagation of influence in the simulated QBOs is addressed. In the gravity wave drag schemes, the evolution of the wind at a given level depends on the wind above, as well as on the wind below. This is in contrast to the parameterization for the equatorial planetary waves in which there is downward propagation of phase only. The stability of a zero-wind initial state is examined, and it is determined that a small perturbation to such a state will amplify with time to the extent that a zonal wind oscillation is permitted.

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Explicitly Stochastic Parameterization of Nonorographic Gravity Wave Drag

Journal of the Atmospheric Sciences ◽

10.1175/2011jas3684.1 ◽

2011 ◽

Vol 68 (8) ◽

pp. 1749-1765 ◽

Cited By ~ 37

Author(s):

Stephen D. Eckermann

Keyword(s):

Gravity Wave ◽

General Circulation ◽

Middle Atmosphere ◽

General Circulation Models ◽

Wave Drag ◽

Single Wave ◽

Order Of Magnitude ◽

Simple Conversion ◽

Wave Induced ◽

Stochastic Analog

Abstract A straightforward methodology is presented for converting the deterministic multiwave parameterizations of nonorographic gravity wave drag, currently used in general circulation models (GCMs), to stochastic analogs that use fewer waves (in the example herein, a single wave) within each grid box. Deterministic discretizations of source-level momentum flux spectra using a fixed spectrum of many waves with predefined phase speeds are replaced by sampling these source spectra stochastically using waves with randomly assigned phase speeds. Using simple conversion formulas, it is shown that time-mean wave-induced drag, diffusion, and heating-rate profiles identical to those from the deterministic scheme are produced by the stochastic analog. Furthermore, in these examples the need for bulk intermittency factors of small value is largely obviated through the explicit incorporation of stochastic intermittency into the scheme. When implemented in a GCM, the single-wave stochastic analog of an existing deterministic scheme reproduces almost identical time-mean middle-atmosphere climate and drag as its deterministic antecedent but with an order of magnitude reduction in computational expense. The stochastically parameterized drag is also accompanied by inherent variability about the time-mean profile that forces the smallest space–time scales of the GCM. Studies of mean GCM kinetic energy spectra show that this additional stochastic forcing does not lead to excessive increases in dynamical variability at these smallest GCM scales. The results show that the expensive deterministic schemes currently used in GCMs are easily modified and replaced by cheap stochastic analogs without any obvious deleterious impacts on GCM climate or variability, while offering potential advantages of computational savings, reduction of systematic climate biases, and greater and more realistic ensemble spread.

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Snow–(N)AO Teleconnection and Its Modulation by the Quasi-Biennial Oscillation

Journal of Climate ◽

10.1175/jcli-d-17-0041.1 ◽

2017 ◽

Vol 30 (24) ◽

pp. 10211-10235 ◽

Cited By ~ 12

Author(s):

Y. Peings ◽

H. Douville ◽

J. Colin ◽

D. Saint Martin ◽

Gudrun Magnusdottir

Keyword(s):

General Circulation ◽

Climate Models ◽

Polar Vortex ◽

General Circulation Models ◽

Destructive Interference ◽

Atmospheric Response ◽

Quasi Biennial Oscillation ◽

Atmospheric General Circulation Models ◽

Biennial Oscillation

This study explores the wintertime extratropical atmospheric response to Siberian snow anomalies in fall, using observations and two distinct atmospheric general circulation models. The role of the quasi-biennial oscillation (QBO) in modulating this response is discussed by differentiating easterly and westerly QBO years. The remote influence of Siberian snow anomalies is found to be weak in the models, especially in the stratosphere where the “Holton–Tan” effect of the QBO dominates the simulated snow influence on the polar vortex. At the surface, discrepancies between composite analyses from observations and model results question the causal relationship between snow and the atmospheric circulation, suggesting that the atmosphere might have driven snow anomalies rather than the other way around. When both forcings are combined, the simulations suggest destructive interference between the response to positive snow anomalies and easterly QBO (and vice versa), at odds with the hypothesis that the snow–North Atlantic Oscillation/Arctic Oscillation [(N)AO] teleconnection in recent decades has been promoted by the QBO. Although model limitations in capturing the relationship exist, altogether these results suggest that the snow–(N)AO teleconnection may be a stochastic artifact rather than a genuine atmospheric response to snow-cover variability. This study adds to a growing body of evidence suggesting that climate models do not capture a robust and stationary snow–(N)AO relationship. It also highlights the need for extending observations and/or improving models to progress on this matter.

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Evaluation of the Quasi-Biennial Oscillation in global climate models for the SPARC QBO-initiative

10.5194/egusphere-egu2020-17338 ◽

2020 ◽

Author(s):

Andrew Bushell ◽

Francois Lott ◽

Keyword(s):

General Circulation ◽

Climate Models ◽

Middle Atmosphere ◽

Global Climate ◽

Coupled Model ◽

Global Climate Models ◽

Multimodel Ensemble ◽

Quasi Biennial Oscillation ◽

Modelling Uncertainties ◽

Biennial Oscillation

The Stratosphere-troposphere Processes And their Role in Climate (SPARC) Quasi-Biennial Oscillation initiative (QBOi) seeks to improve confidence in general circulation and earth system model (GCM and ESM) simulations of the QBO, a prominent feature of middle atmosphere tropical variability first identified nearly sixty years ago. Although only five out of 47 models contributing to the Coupled Model Intercomparison Project Phase 5 (CMIP5) had spontaneous QBOs, simulated QBOs are anticipated to be more common among CMIP6 models as more atmospheric GCMs are able to reproduce the phenomenon, both by ensuring adequate vertical resolution in the stratosphere and by parametrizing accelerations due to subgrid nonorographic gravity waves (NOGWs). The complexity of CMIP6 models and their forcing scenarios, however, is an obstacle to using the CMIP6 multimodel ensemble for analysis of modelling uncertainties that are specific to the QBO and its impacts. The QBOi multimodel ensemble represents an alternative approach in which modelling uncertainties related to the QBO are assessed by performing coordinated experiments with atmospheric GCMs that have simplified external forcings and boundary conditions, designed to characterize QBO representation and its response to idealised future climate scenarios.&#160;Results are presented from an analysis of QBOs in thirteen atmospheric GCMs forced with both observed and annually repeating sea surface temperatures (SSTs). Mean QBO periods in most of these models are close to, though shorter than, the period of 28 months observed in ERA-Interim. Amplitudes are within &#177;20% of the observed QBO amplitude at 10hPa, but typically about half of that observed at lower altitudes (50 and 70hPa). For almost all models the oscillation's amplitude profile shows an overall upward shift compared to reanalysis and its meridional extent is too narrow. Asymmetry in the duration of eastward and westward phases is reasonably well captured though not all models replicate the observed slowing as the westward shear descends. Westward phases are generally too weak, and most models have an eastward time mean wind bias throughout the depth of the QBO. Intercycle period variability is realistic and in some models is enhanced in the experiment with observed SSTs compared to the experiment with repeated annual cycle SSTs. Mean periods are also sensitive to this difference between SSTs but only when parametrized NOGW sources are coupled to tropospheric parameters and not prescribed with a fixed value. But, overall, modelled QBOs are very similar whether or not the prescribed SSTs vary interannually. A portrait of the overall ensemble performance is provided by a normalised grading of QBO metrics. To simulate a QBO all but one model used parametrized NOGWs, which provided the majority of the total wave forcing at altitudes above 70hPa in most models. Thus the representation of NOGWs either explicitly or through parametrization is still a major uncertainty underlying QBO simulation in these present-day experiments.&#160;

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