scholarly journals Diverse dynamical response to orographic gravity wave drag hotspots - a zonal mean perspective

2021 ◽  
Author(s):  
Petr Šácha ◽  
Aleš Kuchař ◽  
Roland Eichinger ◽  
Petr Pišoft ◽  
Christoph Jacobi ◽  
...  
Keyword(s):  
Wave Propagation ◽  
Gravity Waves ◽  
Climate Models ◽  
Rossby Waves ◽  
Middle Atmosphere ◽  
Internal Gravity Waves ◽  
Wave Drag ◽  
Dynamical Response ◽  
Current Generation ◽  
Zonal Winds

<p>In the extratropical atmosphere, Rossby waves (RWs) and internal gravity waves (GWs) propagating from the troposphere mediate a coupling with the middle atmosphere by influencing the dynamics herein. In the current generation chemistry-climate models (CCMs), RW effects are well resolved while GW effects have to be parameterized. Here, we analyze orographic GW (OGW) interaction with resolved dynamics in a comprehensive CCM on the time scale of days. For this, we apply a recently developed method of strong OGW drag event composites for the three strongest northern hemisphere OGW hotspots. We show that locally-strong OGW events considerably alter the properties of resolved wave propagation into the middle atmosphere, which subsequently influences zonal winds and RW transience. Our results demonstrate that the influence of OGWs is critically dependent on the hotspot region, which underlines the OGW-resolved dynamics interaction being a two-way process.</p>

Analysis of interaction between parameterized orographic gravity wave drag and resolved dynamics in CMAM.

2021 ◽  
Author(s):  
Petr Šácha ◽  
Aleš Kuchař ◽  
Christoph Jacobi ◽  
Petr Pišoft ◽  
Roland Eichinger ◽  
...  
Keyword(s):  
Large Scale ◽  
Climate Models ◽  
Rossby Waves ◽  
Middle Atmosphere ◽  
Polar Vortex ◽  
Internal Gravity Waves ◽  
Wave Drag ◽  
Dynamical Analysis ◽  
Future Research ◽  
Stratospheric Polar Vortex

<div class="page" title="Page 1"> <div class="layoutArea"> <div class="column"> <p>In the extratropical atmosphere, Rossby waves (RWs) and internal gravity waves (GWs) propagating from the troposphere mediate a coupling with the middle atmosphere by influencing the dynamics herein. In current generation chemistry-climate models (CCMs), GWs are usually smaller than the model resolution and the majority of their spectrum therefore must be parameterized. From observations, we know that GWs are intermittent and asymmetrically distributed around the globe, which holds to some extent also for the parameterized GW drag (GWD) (in particular for orographic GWD (oGWD)). The GW parameterizations in CCMs are usually tuned to mitigate biases in the zonal mean climatology of particular quantities, but the complex interaction of parameterized GWs with the large- scale circulation and resolved waves in the models remains to date poorly understood.</p> <p>This presentation will combine observational evidence, idealized modeling and dynamical analysis of a CCM output to study both the short-term and long-term model response to the oGWD. Our results demonstrate that the oGW-resolved dynamics interaction is a complex two-way process, with the most prominent oGWD impact being the alteration of propagation of planetary-scale Rossby waves on a time-scale of a few days. The conclusions give a novel perspective on the importance of oGWD for the stratospheric polar vortex and atmospheric transport studies outlining potential foci of future research.</p> </div> </div> </div>

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 Dynamical Control of the Mesosphere by Orographic and Nonorographic Gravity Wave Drag during the Extended Northern Winters of 2006 and 2009

2013 ◽  
Vol 70 (7) ◽  
pp. 2152-2169 ◽  
Author(s):  
Charles McLandress ◽  
John F. Scinocca ◽  
Theodore G. Shepherd ◽  
M. Catherine Reader ◽  
Gloria L. Manney
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Middle Atmosphere ◽  
Wave Drag ◽  
Reanalysis Data ◽  
Zonal Winds ◽  
Mesospheric Temperature ◽  
Mean Circulation ◽  
Dynamical Control ◽  
Good Agreement

Abstract A version of the Canadian Middle Atmosphere Model (CMAM) that is nudged toward reanalysis data up to 1 hPa is used to examine the impacts of parameterized orographic and nonorographic gravity wave drag (OGWD and NGWD) on the zonal-mean circulation of the mesosphere during the extended northern winters of 2006 and 2009 when there were two large stratospheric sudden warmings. The simulations are compared to Aura Microwave Limb Sounder (MLS) observations of mesospheric temperature and carbon monoxide (CO) and derived zonal winds. The control simulation, which uses both OGWD and NGWD, is shown to be in good agreement with MLS. The impacts of OGWD and NGWD are assessed using simulations in which those sources of wave drag are removed. In the absence of OGWD the mesospheric zonal winds in the months preceding the warmings are too strong, causing increased mesospheric NGWD, which drives excessive downwelling, resulting in overly large lower-mesospheric values of CO prior to the warming. NGWD is found to be most important following the warmings when the underlying westerlies are too weak to allow much vertical propagation of the orographic gravity waves to the mesosphere. NGWD is primarily responsible for driving the circulation that results in the descent of CO from the thermosphere following the warmings. Zonal-mean mesospheric winds and temperatures in all simulations are shown to be strongly constrained by (i.e., slaved to) the stratosphere. Finally, it is demonstrated that the responses to OGWD and NGWD are nonadditive because of their dependence and influence on the background winds and temperatures.

A different perspective on how parameterized orographic gravity waves influence atmospheric transport and dynamics in current generation global climate models

2020 ◽  
Author(s):  
Harald Rieder ◽  
Petr Šácha ◽  
Roland Eichinger ◽  
Aleš Kuchař ◽  
Nadja Samtleben ◽  
...  
Keyword(s):  
Gravity Waves ◽  
Large Scale ◽  
Climate Models ◽  
Atmospheric Transport ◽  
Global Climate ◽  
Internal Gravity Waves ◽  
Global Climate Models ◽  
Current Generation ◽  
The Individual ◽  
The Impact

<p>In the atmosphere, internal gravity waves (GWs) are a naturally occurring and ubiquitous, though intermittent phenomenon. In addition, GWs (especially orographic; OGWs) are asymmetrically distributed around the globe. In current generation global climate models (GCMs), GWs are usually smaller than the model grid resolution and the majority of their spectrum therefore must be parameterized. To some extent, the intermittency and asymmetry of a spatial distribution of the resulting OGW drag (OGWD) is present also in GCMs. As the GW parameterization schemes in GCMs are usually tuned to get the zonal mean climatology of particular features right, an important question emerges: what kind of influence do GW parameterizations have on the individual models atmosphere locally? Here we focus on answering this question regarding the impact of spatiotemporally intermittent OGW forcing in the extra-tropical lower stratosphere region (LS). The LS region is characterized by a strong interplay of chemical, physical and dynamical processes. To date, the representation of this dynamically active region in models frequently mismatches observations. Although we can find a climatological maximum of oGWD in the LS, the role of OGW forcing for the transport and composition in this region is poorly understood. We combine observational evidence, idealized modeling and statistical analysis of GCM outputs to study both the short-term and long-term model response to the OGW forcing. The results presented will question the relationship between the advective part of the Brewer- Dobson circulation and the zonally asymmetric GW forcing, and a so-far neglected link between oGWD and large-scale quasi-isentropic stirring will be discussed.</p>

Effects of Nonlinearity on Convectively Forced Internal Gravity Waves: Application to a Gravity Wave Drag Parameterization

2008 ◽  
Vol 65 (2) ◽  
pp. 557-575 ◽  
Author(s):  
Hye-Yeong Chun ◽  
Hyun-Joo Choi ◽  
In-Sun Song
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Momentum Flux ◽  
Lower Thermosphere ◽  
Internal Gravity Waves ◽  
Wave Drag ◽  
Scale Factor ◽  
Wide Range ◽  
Flux Spectrum ◽  
Diabatic Forcing

Abstract In the present study, the authors propose a way to include a nonlinear forcing effect on the momentum flux spectrum of convectively forced internal gravity waves using a nondimensional numerical model (NDM) in a two-dimensional framework. In NDM, the nonlinear forcing is represented by nonlinear advection terms multiplied by the nonlinearity factor (NF) of the thermally induced internal gravity waves for a given specified diabatic forcing. It was found that the magnitudes of the waves and resultant momentum flux above the specified forcing decrease with increasing NF due to cancellation between the two forcing mechanisms. Using the momentum flux spectrum obtained by the NDM simulations with various NFs, a scale factor for the momentum flux, normalized by the momentum flux induced by diabatic forcing alone, is formulated as a function of NF. Inclusion of the nonlinear forcing effect into current convective gravity wave drag (GWD) parameterizations, which consider diabatic forcing alone by multiplying the cloud-top momentum flux spectrum by the scale factor, is proposed. An updated convective GWD parameterization using the scale factor is implemented into the NCAR Whole Atmosphere Community Climate Model (WACCM). The 10-yr simulation results, compared with those by the original convective GWD parameterization considering diabatic forcing alone, showed that the magnitude of the zonal-mean cloud-top momentum flux is reduced for wide range of phase speed spectrum by about 10%, except in the middle latitude storm-track regions where the cloud-top momentum flux is amplified. The zonal drag forcing is determined largely by the wave propagation condition under the reduced magnitude of the cloud-top momentum flux, and its magnitude decreases in many regions, but there are several areas of increasing drag forcing, especially in the tropical upper mesosphere and lower thermosphere.

Observations of internal gravity waves in vicinity of jet streams during SouthTRAC flight on 16 September 2019

2021 ◽  
Author(s):  
Wolfgang Woiwode ◽  
Andreas Dörnbrack ◽  
Felix Friedl-Vallon ◽  
Markus Geldenhuys ◽  
Andreas Giez ◽  
...  
Keyword(s):  
Gravity Waves ◽  
Middle Atmosphere ◽  
Internal Gravity Waves ◽  
Polar Front ◽  
Airborne Lidar ◽  
Jet Streams ◽  
Transport Dynamics ◽  
Research Aircraft ◽  
Forecasting System ◽  
Complex Temperature

<p>The combination of the airborne GLORIA (Gimballed Limb Observer for Radiance Imaging of the Atmosphere) and ALIMA (Airborne LIdar for Middle Atmosphere research) instruments allows for probing of temperature perturbations associated with gravity waves within the range from the troposphere up to the mesosphere. Both instruments were part of the scientific payload of the German HALO (High Altitude and LOng Range Research Aircraft) during the SouthTRAC-GW (Southern hemisphere Transport, Dynamics, and Chemistry - Gravity Waves) mission, aiming at probing gravity waves in the hotspot region around South America and the Antarctic peninsula. For the research flight on 16 September 2019, complex temperature perturbations attributed to internal gravity waves were forecasted well above the Atlantic to the south-west of Buenos Aires, Argentina. The forecasted temperature perturbations were located in a region where the polar front jet stream met with the subtropical jet, with the polar night jet above. We present temperature perturbations observed by GLORIA and ALIMA during the discussed flight and compare the data with ECMWF IFS (European Centre for Medium-Range Weather Forecasts – Integrated Forecasting System) high-resolution deterministic forecasts, aiming at validating the IFS data and identifying sources of the observed wave patterns.</p>

scholarly journals Effects of Horizontal Geometrical Spreading on the Parameterization of Orographic Gravity Wave Drag. Part I: Numerical Transform Solutions

2015 ◽  
Vol 72 (6) ◽  
pp. 2330-2347 ◽  
Author(s):  
Stephen D. Eckermann ◽  
Jun Ma ◽  
Dave Broutman
Keyword(s):  
Gravity Waves ◽  
Wave Breaking ◽  
Climate Models ◽  
Functional Form ◽  
Vertical Displacement ◽  
Wave Drag ◽  
Geometrical Spreading ◽  
Vertical Coordinate ◽  
Sheared Flow ◽  
Weather And Climate

Abstract Numerical transform solutions for hydrostatic gravity waves generated by both uniform and sheared flow over elliptical obstacles are used to quantify effects of horizontal geometrical spreading on amplitude evolution with height. Both vertical displacement and steepness amplitudes are considered because of their close connections to drag parameterizations in weather and climate models. Novel diagnostics quantify the location and value of the largest wavefield amplitudes most likely to break at each altitude. These horizontal locations do not stray far from the obstacle peak even at high altitudes. Resulting vertical profiles of wave amplitude are normalized to remove density and refraction effects, thereby quantifying the horizontal geometrical spreading contribution, currently absent from parameterizations. Horizontal geometrical spreading produces monotonic amplitude decreases with height through wave-action conservation as waves propagate into progressively larger horizontal areas. Accumulated amplitude reductions are appreciable for all but the most quasi-two-dimensional obstacles with long axes orthogonal to the flow, and even these are impacted appreciably if the obstacle is rotated by more than 20°–30°. Profiles are insensitive to the obstacle’s functional form but vary strongly in response to changes in its horizontal aspect ratio. Responses to background winds are captured by a vertical coordinate transformation that remaps profiles to a universal form for a given obstacle. These results show that horizontal geometrical spreading has comparable or larger effects on wave amplitudes as the refraction of vertical wavenumbers and thus is important for accurate parameterizations of wave breaking and drag.

Seasonal modulation of trapped gravity waves and their imprints on trade wind clouds

2020 ◽  
Author(s):  
Claudia Stephan
Keyword(s):  
Gravity Waves ◽  
Large Scale ◽  
Climate Models ◽  
Global Climate ◽  
Wave Theory ◽  
Internal Gravity Waves ◽  
Global Climate Models ◽  
Trade Wind ◽  
Trapped Waves ◽  
Convective Boundary

<p>Idealized simulations have shown decades ago that shallow clouds generate internal gravity waves, which under certain atmospheric background conditions become trapped inside the troposphere and influence the development of clouds. These feedbacks, which occur at horizontal scales of up to several tens of km are neither resolved, nor parameterized in traditional global climate models (GCMs), while the newest generation of GCMs is starting to resolve them. The interactions between the convective boundary layer and trapped waves have almost exclusively been studied in highly idealized frameworks and it remains unclear to what degree this coupling affects the organization of clouds and convection in the real atmosphere. Here, the coupling between clouds and trapped waves is examined in storm-resolving simulations that span the entirety of the tropical Atlantic and are initialized and forced by meteorological analyses. The coupling between clouds and trapped waves is sufficiently strong to be detected in these simulations of full complexity.  Stronger upper-tropospheric westerly winds are associated with a stronger cloud-wave coupling. In the simulations this results in a highly-organized scattered cloud field with cloud spacings of about 19 km, matching the dominant trapped wavelength. Based on the large-scale atmospheric state wave theory can reliably predict the regions and times where cloud-wave feedbacks become relevant to convective organization. Theory, the simulations and satellite imagery imply a seasonal cycle in the trapping of gravity waves. </p>

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.

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