Importance of gravity wave forcing for springtime southern polar vortex breakdown as revealed by ERA5

2021 ◽  
Author(s):  
Aman Gupta ◽  
Thomas Birner ◽  
Andreas Doernbrack ◽  
Inna Polichtchouk
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Zonal Wind ◽  
Planetary Wave ◽  
Climate Models ◽  
Vortex Breakdown ◽  
Polar Vortex ◽  
Wave Drag ◽  
Planetary Waves ◽  
The Mean

<p>Planetary waves and gravity waves are the key drivers of middle atmospheric circulation and variability. While planetary waves are well resolved in climate models, inaccuracies in representation of gravity waves in climate models persist. Inaccuracies in representation of gravity waves limit our understanding of the planetary wave-gravity wave interactions that can be crucial during the Antarctic polar vortex breakdown. Moreover, "missing" gravity wave drag around 60<sup>o</sup>S in the upper stratosphere is considered to be responsible for the "cold-pole" bias in comprehensive climate models that employ parameterizations to appproximately represent the gravity wave drag.</p><p>We illustrate the strength of the high-resolution ERA-5 reanalysis in resolving a broad spectrum of gravity waves in southern hemisphere midlatitudes and to estimate their contribution to the momentum budget around 60<sup>o</sup>S. We find that most of the resolved mountain waves excited over the Andes and Antarctic peninsula propagate away from their source and deposit momentum around 60<sup>o</sup>S over the Southern Ocean. Further, a composite analysis around 60<sup>o</sup>S during the vortex breakdown period using ERA-5 reveals considerably large fractional contribution of resolved + parameterized GWD towards the vortex deceleration. Upto 30 days prior to the breakdown, a balance between the Coriolis acceleration and the planetary wave deceleration provides a weak net deceleration of the mean winds, following which, they provide a net acceleration of the mean winds. The gravity waves, however, provide a steady deceleration of the mean winds throughout the breakdown period. The resolved drag in ERA-5 accounts for as much as one-fourth of the zonal wind deceleration at 60<sup>o</sup>S and 10 hPa, while the parameterized drag in ERA-5 accounts for more than one-half of the zonal wind deceleration.  The findings establish the crucial role of gravity waves in wintertime stratospheric circulation and opens avenues for further stratospheric gravity wave analysis using ERA-5.</p>

scholarly journals Vortex Preconditioning due to Planetary and Gravity Waves prior to Sudden Stratospheric Warmings

2014 ◽  
Vol 71 (11) ◽  
pp. 4028-4054 ◽  
Author(s):  
John R. Albers ◽  
Thomas Birner
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Planetary Wave ◽  
Surf Zone ◽  
Polar Vortex ◽  
Wave Drag ◽  
Reanalysis Data ◽  
Composite Analysis ◽  
Large Wave ◽  
Wave Forcing

Abstract Reanalysis data are used to evaluate the evolution of polar vortex geometry, planetary wave drag, and gravity wave drag prior to split versus displacement sudden stratospheric warmings (SSWs). A composite analysis that extends upward to the lower mesosphere reveals that split SSWs are characterized by a transition from a wide, funnel-shaped vortex that is anomalously strong to a vortex that is constrained about the pole and has little vertical tilt. In contrast, displacement SSWs are characterized by a wide, funnel-shaped vortex that is anomalously weak throughout the prewarming period. Moreover, during split SSWs, gravity wave drag is enhanced in the polar night jet, while planetary wave drag is enhanced within the extratropical surf zone. During displacement SSWs, gravity wave drag is anomalously weak throughout the extratropical stratosphere. Using the composite analysis as a guide, a case study of the 2009 SSW is conducted in order to evaluate the roles of planetary and gravity waves for preconditioning the polar vortex in terms of two SSW-triggering scenarios: anomalous planetary wave forcing from the troposphere and resonance due to either internal or external Rossby waves. The results support the view that split SSWs are caused by resonance rather than anomalously large wave forcing. Given these findings, it is suggested that vortex preconditioning, which is traditionally defined in terms of vortex geometries that increase poleward wave focusing, may be better described by wave events (planetary and/or gravity) that “tune” the geometry of the vortex toward its resonant excitation points.

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.

Application of the IDEMIX Concept for Internal Gravity Waves in the Atmosphere

2020 ◽  
Vol 77 (10) ◽  
pp. 3601-3618
Author(s):  
B. Quinn ◽  
C. Eden ◽  
D. Olbers
Keyword(s):  
Energy Balance ◽  
Wave Field ◽  
Gravity Wave ◽  
Gravity Waves ◽  
Momentum Flux ◽  
Middle Atmosphere ◽  
Internal Gravity Waves ◽  
Wave Drag ◽  
Mean Flow ◽  
The Mean

AbstractThe model Internal Wave Dissipation, Energy and Mixing (IDEMIX) presents a novel way of parameterizing internal gravity waves in the atmosphere. IDEMIX is based on the spectral energy balance of the wave field and has previously been successfully developed as a model for diapycnal diffusivity, induced by internal gravity wave breaking in oceans. Applied here for the first time to atmospheric gravity waves, integration of the energy balance equation for a continuous wave field of a given spectrum, results in prognostic equations for the energy density of eastward and westward gravity waves. It includes their interaction with the mean flow, allowing for an evolving and local description of momentum flux and gravity wave drag. A saturation mechanism maintains the wave field within convective stability limits, and a closure for critical-layer effects controls how much wave flux propagates from the troposphere into the middle atmosphere. Offline comparisons to a traditional parameterization reveal increases in the wave momentum flux in the middle atmosphere due to the mean-flow interaction, resulting in a greater gravity wave drag at lower altitudes. Preliminary validation against observational data show good agreement with momentum fluxes.

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

2012 ◽  
Vol 69 (3) ◽  
pp. 802-818 ◽  
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.

scholarly journals Influence of Gravity Waves in the Tropical Upwelling: WACCM Simulations

2011 ◽  
Vol 68 (11) ◽  
pp. 2599-2612 ◽  
Author(s):  
Hye-Yeong Chun ◽  
Young-Ha Kim ◽  
Hyun-Joo Choi ◽  
Jung-Yoon Kim
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Zonal Wind ◽  
Annual Cycle ◽  
Climate Model ◽  
Wave Drag ◽  
Flux Divergence ◽  
Relative Contribution ◽  
The Tropics ◽  
Convective Gravity Waves

Abstract The annual cycle of tropical upwelling and contributions by planetary and gravity waves are investigated from climatological simulations using the Whole Atmosphere Community Climate Model (WACCM) including three gravity wave drag (GWD) parameterizations (orographic, nonstationary background, and convective GWD parameterizations). The tropical upwelling is estimated by the residual mean vertical velocity at 100 hPa averaged over 15°S–15°N. This is well matched with an upwelling estimate from the balance of the zonal momentum and the mass continuity. A clear annual cycle of the tropical upwelling is found, with a Northern Hemispheric (NH) wintertime maximum and NH summertime minimum determined primarily by the Eliassen–Palm flux divergence (EPD), along with a secondary contribution from the zonal wind tendency. Gravity waves increase tropical upwelling throughout the year, and of the three sources the contribution by convective gravity wave drag (CGWD) is largest in most months. The relative contribution by all three GWDs to tropical upwelling is not larger than 5%. However, when tropical upwelling is estimated by net upward mass flux between turnaround latitudes where upwelling changes downwelling, annual mean contribution by all three GWDs is up to 19% at 70 hPa by orographic and convective gravity waves with comparable magnitudes. Effects of CGWD on upwelling are investigated by conducting an additional WACCM simulation without CGWD parameterization. It was found that including CGWD parameterization increases tropical upwelling not only directly by adding CGWD forcing, but also indirectly by modulating EPD and zonal wind tendency terms in the tropics.

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

2005 ◽  
Vol 62 (12) ◽  
pp. 4178-4195 ◽  
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.

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

2006 ◽  
Vol 19 (16) ◽  
pp. 3882-3901 ◽  
Author(s):  
M. A. Giorgetta ◽  
E. Manzini ◽  
E. Roeckner ◽  
M. Esch ◽  
L. Bengtsson
Keyword(s):  
Gravity Wave ◽  
Zonal Wind ◽  
General Circulation ◽  
Large Scale ◽  
Climate Models ◽  
Middle Atmosphere ◽  
General Circulation Models ◽  
Wave Drag ◽  
Quasi Biennial Oscillation ◽  
Biennial Oscillation

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.

scholarly journals Satellite observations of middle atmosphere gravity wave activity and dissipation during recent stratospheric warmings

2016 ◽  
Author(s):  
Manfred Ern ◽  
Quang Thai Trinh ◽  
Martin Kaufmann ◽  
Isabell Krisch ◽  
Peter Preusse ◽  
...  
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Middle Atmosphere ◽  
Polar Vortex ◽  
Wave Activity ◽  
Planetary Waves ◽  
Absolute Gravity ◽  
Mountain Waves ◽  
Meridional Shape ◽  
Zonal Average

Abstract. Sudden stratospheric warmings (SSWs) are circulation anomalies in the polar region during winter. They mostly occur in the Northern Hemisphere and affect also surface weather and climate. Both planetary waves and gravity waves contribute to the onset and evolution of SSWs. While the role of planetary waves for SSW evolution has been recognized, the effect of gravity waves is still not fully understood, and has not been comprehensively analyzed based on global observations. In particular, information on the gravity wave driving of the background winds during SSWs is still missing. We investigate the boreal winters 2001/2002 until 2013/2014. Absolute gravity wave momentum fluxes and gravity wave dissipation (potential drag) are estimated from temperature observations of the satellite instruments HIRDLS and SABER. In agreement with previous work, we find that sometimes gravity wave activity is enhanced before the central date of major SSWs, particularly during vortex-split events. Often, SSWs are associated with polar-night jet oscillation (PJO) events. For these events, we find that gravity wave activity is strongly suppressed when winds reverse from eastward to westward (usually after the central date of a major SSW). In addition, gravity wave potential drag at the bottom of the newly forming eastward directed jet is remarkably weak, while considerable potential drag at the top of the jet likely contributes to the downward propagation of both the jet and the new elevated stratopause. During PJO events, we also find some indication for poleward propagation of gravity waves. Another striking finding is that obviously localized gravity wave sources, likely mountain waves and jet-generated gravity waves, play an important role during the evolution of SSWs and potentially contribute to the triggering of SSWs by preconditioning the shape of the polar vortex. The distribution of these hot spots is highly variable and strongly depends on the zonal and meridional shape of the background wind field, indicating that a pure zonal average view sometimes is a too strong simplification for the strongly perturbed conditions during the evolution of SSWs.

On strongly nonlinear gravity waves in a vertically sheared atmosphere

2021 ◽  
Author(s):  
Georg Sebastian Voelker ◽  
Mark Schlutow
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Internal Gravity Wave ◽  
Internal Gravity Waves ◽  
Wave Drag ◽  
Mean Flow ◽  
Flow Strength ◽  
Weakly Nonlinear ◽  
Strongly Nonlinear ◽  
The Mean

<p>Internal gravity waves are a well-known mechanism of energy redistribution in stratified fluids such as the atmosphere. They may propagate from their generation region, typically in the Troposphere, up to high altitudes. During their lifetime internal waves couple to the atmospheric background through various processes. Among the most important interactions are the exertion of wave drag on the horizontal mean-flow, the heat generation upon wave breaking, or the mixing of atmospheric tracers such as aerosols or greenhouse gases.</p><p>Many of the known internal gravity wave properties and interactions are covered by linear or weakly nonlinear theories. However, for the consideration of some of the crucial effects, like a reciprocal wave-mean-flow interaction including the exertion of wave drag on the mean-flow, strongly nonlinear systems are required. That is, there is no assumption on the wave amplitude relative to the mean-flow strength such that they may be of the same order.</p><p>Here, we exploit a strongly nonlinear Boussinesq theory to analyze the stability of a stationary internal gravity wave which is refracted at the vertical edge of a horizontal jet. Thereby we assume that the incident wave is horizontally periodic, non-hydrostatic, and vertically modulated. Performing a linear stability analysis in the vicinity of the jet edge we find necessary and sufficient criteria for instabilities to grow. In particular, the refracted wave becomes unstable if its incident amplitude is large enough and both mean-flow horizontal winds, below and above the edge of the jet, do not exceed particular upper bounds.</p>

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