Estimation of Gravity Wave Momentum Flux and Phase Speeds from Quasi-Lagrangian Stratospheric Balloon Flights. Part II: Results from the Vorcore Campaign in Antarctica

2008 ◽  
Vol 65 (10) ◽  
pp. 3056-3070 ◽  
Author(s):  
Albert Hertzog ◽  
Gillian Boccara ◽  
Robert A. Vincent ◽  
François Vial ◽  
Philippe Cocquerez
Keyword(s):  
Gravity Wave ◽  
Momentum Flux ◽  
General Circulation ◽  
General Circulation Models ◽  
Companion Paper ◽  
Wave Drag ◽  
Mountain Waves ◽  
Long Duration ◽  
Momentum Fluxes ◽  
Wave Momentum

The stratospheric gravity wave field in the Southern Hemisphere is investigated by analyzing observations collected by 27 long-duration balloons that flew between September 2005 and February 2006 over Antarctica and the Southern Ocean. The analysis is based on the methods introduced by Boccara et al. in a companion paper. Special attention is given to deriving information useful to gravity wave drag parameterizations employed in atmospheric general circulation models. The balloon dataset is used to map the geographic variability of gravity wave momentum fluxes in the lower stratosphere. This flux distribution is found to be very heterogeneous with the largest time-averaged value (28 mPa) observed above the Antarctic Peninsula. This value exceeds by a factor of ∼10 the overall mean momentum flux measured during the balloon campaign. Zonal momentum fluxes were predominantly westward, whereas meridional momentum fluxes were equally northward and southward. A local enhancement of southward flux is nevertheless observed above Adélie Land and is attributed to waves generated by katabatic winds, for which the signature is otherwise rather small in the balloon observations. When zonal averages are performed, oceanic momentum fluxes are found to be of similar magnitude to continental values (2.5–3 mPa), stressing the importance of nonorographic gravity waves over oceans. Last, gravity wave intermittency is investigated. Mountain waves appear to be significantly more sporadic than waves observed above the ocean.

scholarly journals Vertical resolution dependence of gravity wave momentum flux simulated by an atmospheric general circulation model

2014 ◽  
Vol 7 (6) ◽  
pp. 7559-7573
Author(s):  
S. Watanabe ◽  
K. Sato ◽  
Y. Kawatani ◽  
M. Takahashi
Keyword(s):  
Gravity Wave ◽  
Momentum Flux ◽  
General Circulation ◽  
Circulation Model ◽  
General Circulation Models ◽  
Horizontal Resolution ◽  
Vertical Resolution ◽  
Time Step ◽  
Atmospheric General Circulation ◽  
Wave Momentum

Abstract. The dependence of the gravity wave spectra of energy and momentum flux on the horizontal resolution and time step of atmospheric general circulation models (AGCMs) has been thoroughly investigated in the past. In contrast, much less attention has been given to the dependence of these gravity wave parameters on models' vertical resolutions. The present study demonstrates the dependence of gravity wave momentum flux in the stratosphere and mesosphere on the model's vertical resolution, which is evaluated using an AGCM with a horizontal resolution of about 0.56°. We performed a series of sensitivity test simulations changing only the model's vertical resolution above a height of 8 km, and found that inertial gravity waves with short vertical wavelengths simulated at higher vertical resolutions likely play an important role in determining the gravity wave momentum flux in the stratosphere and mesosphere.

scholarly journals Estimation of Gravity Wave Momentum Flux and Phase Speeds from Quasi-Lagrangian Stratospheric Balloon Flights. Part I: Theory and Simulations

2008 ◽  
Vol 65 (10) ◽  
pp. 3042-3055 ◽  
Author(s):  
Gillian Boccara ◽  
Albert Hertzog ◽  
Robert A. Vincent ◽  
François Vial
Keyword(s):  
Gravity Wave ◽  
Wave Packets ◽  
Phase Speed ◽  
Companion Paper ◽  
Time Frequency ◽  
Long Duration ◽  
Short Period ◽  
Momentum Fluxes ◽  
Stratospheric Balloon ◽  
Wave Momentum

A methodology for estimating gravity wave characteristics from quasi-Lagrangian observations provided by long-duration, superpressure balloon flights in the stratosphere is reviewed. Wavelet analysis techniques are used to detect gravity wave packets in observations of pressure, temperature, and horizontal velocity. An emphasis is put on the estimation of gravity wave momentum fluxes and intrinsic phase speeds, which are generally poorly known on global scales in the atmosphere. The methodology is validated using Monte Carlo simulations of time series that mimic the balloon measurements, including the uncertainties associated with each of the meteorological parameters. While the azimuths of the wave propagation direction are accurately retrieved, the momentum fluxes are generally slightly underestimated, especially when wave packets overlap in the time–frequency domain, or for short-period waves. A proxy is derived to estimate by how much momentum fluxes are reduced by the analysis. Retrievals of intrinsic phase speeds are less accurate, especially for low phase speed waves. A companion paper (Part II) implements the methodology to observations gathered during the Vorcore campaign that took place in Antarctica between September 2005 and February 2006.

scholarly journals Compensation between Resolved and Unresolved Wave Drag in the Stratospheric Final Warmings of the Southern Hemisphere

2015 ◽  
Vol 72 (11) ◽  
pp. 4393-4411 ◽  
Author(s):  
Guillermo Scheffler ◽  
Manuel Pulido
Keyword(s):  
Gravity Wave ◽  
Southern Hemisphere ◽  
Momentum Flux ◽  
General Circulation ◽  
Planetary Wave ◽  
Polar Vortex ◽  
General Circulation Models ◽  
Wave Drag ◽  
Stratospheric Polar Vortex ◽  
Sensitivity Experiments

Abstract The role of planetary wave drag and gravity wave drag in the breakdown of the stratospheric polar vortex and its associated final warming in the Southern Hemisphere is examined using reanalyses from MERRA and a middle-atmosphere dynamical model. The focus of this work is on identifying the causes of the delay in the final breakdown of the stratospheric polar vortex found in current general circulation models. Sensitivity experiments were conducted by changing the launched momentum flux in the gravity wave drag parameterization. Increasing the launched momentum flux produces a delay of the final warming date with respect to the control integration of more than 2 weeks. The sensitivity experiments show significant interactions between planetary waves and unresolved gravity waves. The increase of gravity wave drag in the model is compensated by a strong decrease of Eliassen–Palm flux divergence (i.e., planetary wave drag). This concomitant decrease of planetary wave drag is at least partially responsible for the delay of the final warming in the model. Experiments that change the resolved planetary wave activity entering the stratosphere through artificially changing the bottom boundary flux of the model also show an interaction mechanism. Gravity wave drag responds via critical-level filtering to planetary wave drag perturbations by partially compensating them. Therefore, there is a feedback cycle that leads to a partial compensation between gravity wave and planetary wave drag.

scholarly journals The southern stratospheric gravity wave hot spot: individual waves and their momentum fluxes measured by COSMIC GPS-RO

2015 ◽  
Vol 15 (14) ◽  
pp. 7797-7818 ◽  
Author(s):  
N. P. Hindley ◽  
C. J. Wright ◽  
N. D. Smith ◽  
N. J. Mitchell
Keyword(s):  
Southern Ocean ◽  
Gravity Wave ◽  
General Circulation ◽  
Hot Spot ◽  
Polar Vortex ◽  
General Circulation Models ◽  
Wave Drag ◽  
Southern Andes ◽  
Analysis Technique ◽  
Modelling Studies

Abstract. Nearly all general circulation models significantly fail to reproduce the observed behaviour of the southern wintertime polar vortex. It has been suggested that these biases result from an underestimation of gravity wave drag on the atmosphere at latitudes near 60° S, especially around the "hot spot" of intense gravity wave fluxes above the mountainous Southern Andes and Antarctic peninsula. Here, we use Global Positioning System radio occultation (GPS-RO) data from the COSMIC satellite constellation to determine the properties of gravity waves in the hot spot and beyond. We show considerable southward propagation to latitudes near 60° S of waves apparently generated over the southern Andes. We propose that this propagation may account for much of the wave drag missing from the models. Furthermore, there is a long leeward region of increased gravity wave energy that sweeps eastwards from the mountains over the Southern Ocean. Despite its striking nature, the source of this region has historically proved difficult to determine. Our observations suggest that this region includes both waves generated locally and orographic waves advected downwind from the hot spot. We describe and use a new wavelet-based analysis technique for the quantitative identification of individual waves from COSMIC temperature profiles. This analysis reveals different geographical regimes of wave amplitude and short-timescale variability in the wave field over the Southern Ocean. Finally, we use the increased numbers of closely spaced pairs of profiles from the deployment phase of the COSMIC constellation in 2006 to make estimates of gravity wave horizontal wavelengths. We show that, given sufficient observations, GPS-RO can produce physically reasonable estimates of stratospheric gravity wave momentum flux in the hot spot that are consistent with measurements made by other techniques. We discuss our results in the context of previous satellite and modelling studies and explain how they advance our understanding of the nature and origins of waves in the southern stratosphere.

scholarly journals The Midlatitude Lower-Stratospheric Mountain Wave “Valve Layer”

2016 ◽  
Vol 73 (12) ◽  
pp. 5081-5100 ◽  
Author(s):  
Christopher G. Kruse ◽  
Ronald B. Smith ◽  
Stephen D. Eckermann
Keyword(s):  
New Zealand ◽  
Wind Speed ◽  
Gravity Wave ◽  
Momentum Flux ◽  
Climate Models ◽  
Wave Attenuation ◽  
Wave Drag ◽  
Mountain Wave ◽  
Stratospheric Polar Vortex ◽  
Mountain Waves

Abstract The vertical propagation and attenuation of mountain waves launched by New Zealand terrain during the Deep Propagating Gravity Wave Experiment (DEEPWAVE) field campaign are investigated. New Zealand mountain waves were frequently attenuated in a lower-stratospheric weak wind layer between z = 15 and 25 km. This layer is termed a “valve layer,” as conditions within this layer (primarily minimum wind speed) control mountain wave momentum flux through it, analogous to a valve controlling mass flux through a pipe. This valve layer is a climatological feature in the wintertime midlatitude lower stratosphere above the subtropical jet. Mountain wave dynamics within this valve layer are studied using realistic Weather Research and Forecasting (WRF) Model simulations that were extensively validated against research aircraft, radiosonde, and satellite observations. Locally, wave attenuation is horizontally and vertically inhomogeneous, evidenced by numerous regions with wave-induced low Richardson numbers and potential vorticity generation. WRF-simulated gravity wave drag (GWD) is peaked in the valve layer, and momentum flux transmitted through this layer is well approximated by a cubic function of minimum ambient wind speed within it, consistent with linear saturation theory. Valve-layer GWD within the well-validated WRF simulations was 3–6 times larger than that parameterized within MERRA. Previous research suggests increasing parameterized orographic GWD (performed in MERRA2) decreases the stratospheric polar vortex strength by altering planetary wave propagation and drag. The results reported here suggest carefully increasing orographic GWD is warranted, which may help to ameliorate the common cold-pole problem in chemistry–climate models.

scholarly journals Explicitly Stochastic Parameterization of Nonorographic Gravity Wave Drag

2011 ◽  
Vol 68 (8) ◽  
pp. 1749-1765 ◽  
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.

scholarly journals Sensitivity of Simulated Climate to Conservation of Momentum in Gravity Wave Drag Parameterization

2009 ◽  
Vol 22 (10) ◽  
pp. 2726-2742 ◽  
Author(s):  
Tiffany A. Shaw ◽  
Michael Sigmond ◽  
Theodore G. Shepherd ◽  
John F. Scinocca
Keyword(s):  
Gravity Wave ◽  
Southern Hemisphere ◽  
Momentum Flux ◽  
Middle Atmosphere ◽  
Momentum Conservation ◽  
Wave Drag ◽  
Conservation Of Momentum ◽  
Simulated Climate ◽  
The Impact ◽  
Wave Momentum

Abstract The Canadian Middle Atmosphere Model is used to examine the sensitivity of simulated climate to conservation of momentum in gravity wave drag parameterization. Momentum conservation requires that the parameterized gravity wave momentum flux at the top of the model be zero and corresponds to the physical boundary condition of no momentum flux at the top of the atmosphere. Allowing momentum flux to escape the model domain violates momentum conservation. Here the impact of momentum conservation in two sets of model simulations is investigated. In the first set, the simulation of present-day climate for two model-lid height configurations, 0.001 and 10 hPa, which are identical below 10 hPa, is considered. The impact of momentum conservation on the climate with the model lid at 0.001 hPa is minimal, which is expected because of the small amount of gravity wave momentum flux reaching 0.001 hPa. When the lid is lowered to 10 hPa and momentum is conserved, there is only a modest impact on the climate in the Northern Hemisphere; however, the Southern Hemisphere climate is more adversely affected by the deflection of resolved waves near the model lid. When momentum is not conserved in the 10-hPa model the climate is further degraded in both hemispheres, particularly in winter at high latitudes, and the impact of momentum conservation extends all the way to the surface. In the second set of simulations, the impact of momentum conservation and model-lid height on the modeled response to ozone depletion in the Southern Hemisphere is considered, and it is found that the response can display significant sensitivity to both factors. In particular, both the lower-stratospheric polar temperature and surface responses are significantly altered when the lid is lowered, with the effect being most severe when momentum is not conserved. The implications with regard to the current round of Intergovernmental Panel on Climate Change model projections are discussed.

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 Quantifying the Effect of Horizontal Propagation of Three-Dimensional Mountain Waves on the Wave Momentum Flux Using Gaussian Beam Approximation

2017 ◽  
Vol 74 (6) ◽  
pp. 1783-1798 ◽  
Author(s):  
Xin Xu ◽  
Jinjie Song ◽  
Yuan Wang ◽  
Ming Xue
Keyword(s):  
Gaussian Beam ◽  
Momentum Flux ◽  
General Circulation ◽  
Numerical Models ◽  
Three Dimensional ◽  
Finite Domain ◽  
Mountain Waves ◽  
Regional Prediction ◽  
Beam Approximation ◽  
Wave Momentum

Abstract This work examines the influence of horizontal propagation of three-dimensional (3D) mountain waves on the wave momentum flux (WMF) within finite domains (e.g., the grid cell of general circulation models). Under the Wentzel–Kramers–Brillouin (WKB) approximation, analytical solutions are derived for hydrostatic nonrotating mountain waves using the Gaussian beam approximation (GBA), which incorporates both the wind vertical curvature effect and the height variation of stratification. The GBA solutions are validated against numerical simulations conducted using the Advanced Regional Prediction System (ARPS). In the situation of idealized terrain, wind, and stratification, the WMF obtained from the GBA shows a good agreement with the numerical simulation. The effect of wind curvature in enhancing the WMF is captured, although the WKB-based GBA solution tends to overestimate the WMF, especially at small Richardson numbers of order unity. For realistic terrain and/or atmospheric conditions, there are some biases between the WKB GBA and simulated WMFs, arising from, for example, the missing physics of wave reflection. Nonetheless, the decreasing trend of finite-domain WMF with height, because of the horizontal propagation of 3D mountain waves, can be represented fairly well. Using the GBA, a new scheme is proposed to parameterize the orographic gravity wave drag (OGWD) in numerical models. Comparison with the traditional OGWD parameterization scheme reveals that the GBA-based scheme tends to produce OGWD at higher altitudes, as the horizontal propagation of mountain waves can reduce the wave amplitude and thus inhibit wave breaking.

scholarly journals Propagation Paths and Source Distributions of Resolved Gravity Waves in ECMWF-IFS analysis fields around the Southern Polar Night Jet

2021 ◽  
Author(s):  
Cornelia Strube ◽  
Peter Preusse ◽  
Manfred Ern ◽  
Martin Riese
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
General Circulation ◽  
Lateral Displacement ◽  
General Circulation Models ◽  
Wave Drag ◽  
Wave Activity ◽  
Lateral Shift ◽  
Wave Ray ◽  
Propagation Paths

Abstract. In the southern winter polar stratosphere the distribution of gravity wave momentum flux in many state-of-the-art climate simulations is inconsistent with long-time satellite and superpressure balloon observations around 60° S. Recent studies hint that a lateral shift between prominent gravity wave sources in the tropospheric mid-latitudes and the location where gravity wave activity is present in the stratosphere causes at least parts of the discrepancy. This lateral shift cannot be represented by the column-based gravity wave drag parametrisations used in most general circulation models. However, recent high-resolution analysis and re-analysis products of the ECMWF-IFS show good agreement to observations and allow for a detailed investigation of resolved gravity waves, their sources and propagation paths. In this paper, we identify resolved gravity waves in the ECMWF-IFS analyses for a case of high gravity wave activity in the lower stratosphere using small-volume sinusoidal fits to characterise these gravity waves. The 3D wave vector together with perturbation amplitudes, wave frequency and a fully described background atmosphere are then used to initialise the GROGRAT gravity wave ray-tracer and follow the gravity waves backwards from the stratosphere. Finally, we check for indication of source processes on the path of each ray and thus quantitatively attribute gravity waves to sources that are represented within the model. We find that stratospheric gravity waves are indeed subject to far (> 1000 km) lateral displacement from their sources, taking place already at low altitudes (

Sign in / Sign up

Export Citation Format

Share Document