A QBO cookbook: Sensitivity of the Quasi-Biennial Oscillation to resolution, resolved waves, and parameterized gravity waves

2021 ◽  
Author(s):  
Chaim I Garfinkel ◽  
Edwin P Gerber ◽  
Ofer Shamir ◽  
Jian Rao ◽  
Martin Jucker ◽  
...  
Keyword(s):  
Gravity Waves ◽  
Quasi Biennial Oscillation ◽  
Biennial Oscillation

scholarly journals On the Momentum Budget of the Quasi-Biennial Oscillation in the Whole Atmosphere Community Climate Model

2018 ◽  
Vol 76 (1) ◽  
pp. 69-87 ◽  
Author(s):  
Rolando R. Garcia ◽  
Jadwiga H. Richter
Keyword(s):  
Gravity Waves ◽  
Climate Model ◽  
Equatorial Waves ◽  
Quasi Biennial Oscillation ◽  
Community Climate Model ◽  
Westerly Jet ◽  
Momentum Budget ◽  
Zonal Wavenumber ◽  
Biennial Oscillation ◽  
Community Climate

Abstract This study documents the contribution of equatorial waves and mesoscale gravity waves to the momentum budget of the quasi-biennial oscillation (QBO) in a 110-level version of the Whole Atmosphere Community Climate Model. The model has high vertical resolution, 500 m, above the boundary layer and through the lower and middle stratosphere, decreasing gradually to about 1.5 km near the stratopause. Parameterized mesoscale gravity waves and resolved equatorial waves contribute comparable easterly and westerly accelerations near the equator. Westerly acceleration by resolved waves is due mainly to Kelvin waves of zonal wavenumber in the range k = 1–15 and is broadly distributed about the equator. Easterly acceleration near the equator is due mainly to Rossby–gravity (RG) waves with zonal wavenumbers in the range k = 4–12. These RG waves appear to be generated in situ during both the easterly and westerly phases of the QBO, wherever the meridional curvature of the equatorial westerly jet is large enough to produce reversals of the zonal-mean barotropic vorticity gradient, suggesting that they are excited by the instability of the jet. The RG waves produce a characteristic pattern of Eliassen–Palm flux divergence that includes strong easterly acceleration close to the equator and westerly acceleration farther from the equator, suggesting that the role of the RG waves is to redistribute zonal-mean vorticity such as to neutralize the instability of the westerly jet. Insofar as unstable RG waves might be present in the real atmosphere, mixing due to these waves could have important implications for transport in the tropical stratosphere.

scholarly journals Role of equatorial planetary and gravity waves in the 2015–16 quasi-biennial oscillation disruption

2020 ◽  
Author(s):  
Min-Jee Kang ◽  
Hye-Yeong Chun ◽  
Rolando R. Garcia
Keyword(s):  
Gravity Waves ◽  
Rossby Waves ◽  
Wave Mode ◽  
Reanalysis Data ◽  
Small Scale ◽  
Negative Wave ◽  
Quasi Biennial Oscillation ◽  
Rossby Wave Breaking ◽  
Wave Forcing ◽  
Biennial Oscillation

Abstract. In February 2016, the descent of the westerly phase of the quasi-biennial oscillation (QBO) was unprecedentedly disrupted by the development of easterly winds. Previous studies have shown that extratropical Rossby waves propagating into the deep Tropics were the major cause of the 2015–16 QBO disruption. However, a large portion of the negative momentum forcing associated with the disruption still stems from equatorial planetary and small-scale gravity waves, which calls for detailed analyses by separating each wave mode compared with climatological QBO cases. Here, the contributions of resolved equatorial planetary waves [Kelvin, Rossby, mixed-Rossby gravity (MRG), and inertia-gravity (IG) waves] and small-scale convective gravity waves (CGWs) obtained from an offline CGW parameterization to the 2015–16 QBO disruption are investigated using MERRA-2 global reanalysis data from October 2015 to February 2016. In October and November 2015, anomalously strong negative forcing by MRG and IG waves weakened the QBO jet at 0°–5° S near 40 hPa, leading to Rossby wave breaking at the QBO jet core in the southern hemisphere. From December 2015 to January 2016, exceptionally strong Rossby waves propagating horizontally (vertically) continuously decelerated the southern (northern) flank of the jet. In February 2016, when the westward CGW momentum flux at the source level was much stronger than its climatology, CGWs began to exert considerable negative forcing at 40–50 hPa near the equator, in addition to the Rossby waves. The enhancement of the negative wave forcing in the Tropics stems mostly from strong wave activity in the troposphere associated with increased convective activity and the strong westerlies (or weaker easterlies) in the troposphere, except that the MRG wave forcing is more likely associated with increased barotropic instability in the lower stratosphere.

Small-scale gravity waves influence on an idealized quasi-biennial oscillation

2021 ◽  
Author(s):  
Xavier Chartrand ◽  
Louis-Philippe Nadeau ◽  
Antoine Venaille
Keyword(s):  
Gravity Waves ◽  
Wave Spectrum ◽  
Small Scale ◽  
Mean Flow ◽  
Quasi Biennial Oscillation ◽  
Frequency Wave ◽  
Wave Forcing ◽  
Momentum Budget ◽  
Wide Range ◽  
Biennial Oscillation

<p>Recent observations from the ERA5 reanalysis have revealed wave contributions from a wide range of spatial and temporal scales to the momentum budget of the equatorial stratosphere. Although it is generally accepted that the wave forcing at the equator drives the quasi-biennial oscillation (QBO) of equatorial winds, the individual contribution of each type of wave is still poorly understood. Here, we seek to disentangle the role of different wave types in the momentum budget of an idealized stratosphere. Numerical simulations with increasing spatial resolution are used to infer the sensitivity of the wave spectrum and mean flow oscillation to resolved instabilities. At higher resolution, Kelvin-Helmholtz generated small-scale gravity waves are combined to the background low frequency wave forcing and accelerate the period of mean-flow reversals due to an increased momentum transfer from the wave to the mean flow. This mechanism is confirmed using a simplified one-dimensional model for which the wave properties are specified.</p>

A multi-wave model for the Quasi-Biennial Oscillation: Plumb’s model extended

2020 ◽  
Author(s):  
Pierre Léard ◽  
Daniel Lecoanet ◽  
Michael Le Bars
Keyword(s):  
Standard Deviation ◽  
Gravity Waves ◽  
Large Scale ◽  
Internal Gravity Waves ◽  
Quasi Biennial Oscillation ◽  
Periodic Oscillations ◽  
Atmospheric Sciences ◽  
Large Scale Flow ◽  
S Model ◽  
Biennial Oscillation

<p>In the Earth’s stratosphere, equatorial zonal winds reverse from easterlies to westerlies with a period of roughly 28 months. This phenomenon, known as Quasi-Biennial Oscillation (QBO), is driven by internal gravity waves (IGWs) propagating in the stratosphere and interacting with the ambient large-scale flow. Those waves are generated by the turbulent motions of the troposphere. In 1977, an idealised model describing the generation of a reversing large-scale flow by two counter-propagating monochromatic internal gravity waves was developed by Plumb [1]. In 1978, the famous Plumb & McEwan’s experiment [2] validated this model using oscillating membranes to force a standing wave pattern at the boundary of a linearly stratified salty-water layer in a cylindrical shell container.</p><p>Recently, the effects of the wave dissipation and wave energy were studied by Renaud et al. [3] using the Plumb model in order to explain the QBO disruption observed in 2016. It was found that as the Reynolds number increases, bifurcations from periodic to non-periodic regimes are seen for the large-scale flow oscillations.</p><p>Here, we present the results obtained from an extended version of the Plumb’s model, taking into account the stochastic generation of IGWs in Nature. Our new model includes a wide spectrum of waves as forcing for the large-scale flow. A gaussian distribution of energy is used in order to compare monochromatic forcing results (characterised by a gaussian energy spectrum with a small standard deviation) with multi-wave forcing results (large standard deviation). Unexpectedly, we find that in a large parameter domain, gathering the energy of the forcing into one frequency results in non-periodic oscillations for the QBO while spreading the same amount of energy among many frequencies results in periodic oscillations. We also investigate more realistic distribution of energy for the forcing including classical convective spectra, with or without rotation. We find that different forcings result in very similar reversals. This result is quite relevant for Global Circulation Models (GCMs) where internal gravity waves are parameterised in order to drive a realistic QBO. However, our study suggests that driving a QBO with realistic characteristics (amplitude, period) does not involve that the input forcing (i.e. the wave spectrum characteristics) is realistic as well.</p><p><strong>References:</strong></p><p>[1] R. A. Plumb, « The interaction of two internal waves with the mean flow: Implications for the theory of the quasi-biennial oscillation », Journal of the Atmospheric Sciences, 1977.</p><p>[2] R. A. Plumb and A. D. McEwan, « The instability of a forced standing wave in a viscous stratified fluid: a laboratory analogue of the quasi biennial oscillation », Journal of the Atmospheric Sciences, 1978.</p><p>[3] A. Renaud, L.-P. Nadeau, and A. Venaille, « Periodicity Disruption of a Model Quasibiennial Oscillation of Equatorial Winds », Phys. Rev. Lett., vol. 122, n<sup>o</sup> 21, p. 214504, 2019.</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 On the Sensitivity of Convectively Coupled Equatorial Waves to the Quasi-Biennial Oscillation

2019 ◽  
Vol 32 (18) ◽  
pp. 5833-5847 ◽  
Author(s):  
S. Abhik ◽  
Harry H. Hendon ◽  
Matthew C. Wheeler
Keyword(s):  
Gravity Waves ◽  
Austral Summer ◽  
Longwave Radiation ◽  
Kelvin Wave ◽  
Quasi Biennial Oscillation ◽  
Horizontal Structure ◽  
Convectively Coupled Equatorial Waves ◽  
Mechanism Of Impact ◽  
The Impact ◽  
Biennial Oscillation

Abstract The seasonal-mean variance of the Madden–Julian oscillation (MJO) in austral summer has recently been shown to be significantly (p < 5%) enhanced during easterly phases of the quasi-biennial oscillation (QBO). The impact is large, with the mean MJO variance increasing by ~50% compared to the QBO westerly phase. In contrast, we show using observed outgoing longwave radiation that seasonal variations for convectively coupled equatorial Kelvin, Rossby, and mixed Rossby–gravity waves are insensitive to the QBO. This insensitivity extends to all high-frequency (2–30-day period) and the non-MJO component of the intraseasonal (30–120-day period) convective variance. However, convectively coupled Kelvin wave variability shows a modest increase (~13%) that is marginally significant (p = 10%) during easterly phases of the QBO in austral autumn, when Kelvin wave activity is seasonally strongest along the equator. The mechanism of impact on the Kelvin wave appears to be similar to what has previously been argued for the MJO during austral summer. However, the more tilted and shallower vertical structure of the Kelvin waves suggests that they cannot tap into the extra destabilization at the tropopause provided by the easterly phase of the QBO as effectively as the MJO. Lack of impact on the convectively coupled Rossby and mixed Rossby–gravity waves is argued to stem from their horizontal structure that results in weaker divergent anomalies along the equator, where the QBO impact is greatest. Our results further emphasize that the MJO in austral summer is uniquely affected by the QBO.

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

2005 ◽  
Vol 62 (12) ◽  
pp. 4196-4205 ◽  
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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