The role of gravity waves in the quasi-biennial oscillation

1997 ◽  
Vol 102 (D22) ◽  
pp. 26053-26076 ◽  
Author(s):  
Timothy J. Dunkerton
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.

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

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>

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