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 (

scholarly journals Propagation paths and source distributions of resolved gravity waves in ECMWF-IFS analysis fields around the southern polar night jet

2021 ◽  
Vol 21 (24) ◽  
pp. 18641-18668
Author(s):  
Cornelia Strube ◽  
Peter Preusse ◽  
Manfred Ern ◽  
Martin Riese
Keyword(s):  
Southern Ocean ◽  
Gravity Wave ◽  
Gravity Waves ◽  
Lower Stratosphere ◽  
Wave Activity ◽  
Lateral Shift ◽  
Apparent Lack ◽  
Wave Ray ◽  
Propagation Paths ◽  
Wave Momentum

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 part of the discrepancy. This lateral shift cannot be represented by the column-based gravity wave drag parameterisations used in most general circulation models. However, recent high-resolution analysis and re-analysis products of the European Centre for Medium-Range Weather Forecasts Integrated Forecast System (ECMWF-IFS) show good agreement with the 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 Gravity Wave Regional or Global Ray Tracer (GROGRAT) gravity wave ray tracer and follow the gravity waves backwards from the stratosphere. Finally, we check for the 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, which already take place at low altitudes (<20 km). Various source processes can be linked to waves within stratospheric gravity wave (GW) patterns, such as the orography equatorward of 50∘ S and non-orographic sources above the Southern Ocean. These findings may explain why superpressure balloons observe enhanced gravity wave momentum fluxes in the lower stratosphere over the Southern Ocean despite an apparent lack of sources at this latitude. Our results also support the need to improve gravity wave parameterisations to account for meridional propagation.

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.

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 Stratospheric gravity waves at Southern Hemisphere orographic hotspots: 2003–2014 AIRS/Aqua observations

2016 ◽  
Vol 16 (14) ◽  
pp. 9381-9397 ◽  
Author(s):  
Lars Hoffmann ◽  
Alison W. Grimsdell ◽  
M. Joan Alexander
Keyword(s):  
Gravity Wave ◽  
Southern Hemisphere ◽  
Antarctic Peninsula ◽  
Gravity Waves ◽  
General Circulation ◽  
Wave Activity ◽  
Small Scale ◽  
Mountain Wave ◽  
Kerguelen Islands ◽  
The Antarctic

Abstract. Stratospheric gravity waves from small-scale orographic sources are currently not well-represented in general circulation models. This may be a reason why many simulations have difficulty reproducing the dynamical behavior of the Southern Hemisphere polar vortex in a realistic manner. Here we discuss a 12-year record (2003–2014) of stratospheric gravity wave activity at Southern Hemisphere orographic hotspots as observed by the Atmospheric InfraRed Sounder (AIRS) aboard the National Aeronautics and Space Administration's (NASA) Aqua satellite. We introduce a simple and effective approach, referred to as the “two-box method”, to detect gravity wave activity from infrared nadir sounder measurements and to discriminate between gravity waves from orographic and other sources. From austral mid-fall to mid-spring (April–October) the contributions of orographic sources to the observed gravity wave occurrence frequencies were found to be largest for the Andes (90 %), followed by the Antarctic Peninsula (76 %), Kerguelen Islands (73 %), Tasmania (70 %), New Zealand (67 %), Heard Island (60 %), and other hotspots (24–54 %). Mountain wave activity was found to be closely correlated with peak terrain altitudes, and with zonal winds in the lower troposphere and mid-stratosphere. We propose a simple model to predict the occurrence of mountain wave events in the AIRS observations using zonal wind thresholds at 3 and 750 hPa. The model has significant predictive skill for hotspots where gravity wave activity is primarily due to orographic sources. It typically reproduces seasonal variations of the mountain wave occurrence frequencies at the Antarctic Peninsula and Kerguelen Islands from near zero to over 60 % with mean absolute errors of 4–5 percentage points. The prediction model can be used to disentangle upper level wind effects on observed occurrence frequencies from low-level source and other influences. The data and methods presented here can help to identify interesting case studies in the vast amount of AIRS data, which could then be further explored to study the specific characteristics of stratospheric gravity waves from orographic sources and to support model validation.

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 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 Stratospheric gravity waves at southern hemisphere orographic hotspots: 2003–2014 AIRS/Aqua observations

2016 ◽  
Author(s):  
Lars Hoffmann ◽  
Alison W. Grimsdell ◽  
M. Joan Alexander
Keyword(s):  
Gravity Wave ◽  
Southern Hemisphere ◽  
Antarctic Peninsula ◽  
Gravity Waves ◽  
General Circulation ◽  
Wave Activity ◽  
Small Scale ◽  
Mountain Wave ◽  
Kerguelen Islands ◽  
The Antarctic

Abstract. Stratospheric gravity waves from small-scale orographic sources are currently not well-represented in general circulation models. This may be a reason why many simulations have difficulty reproducing the dynamical behaviour of the southern hemisphere polar vortex in a realistic manner. Here we discuss a 12-year record (2003–2014) of stratospheric gravity wave activity at southern hemisphere orographic hotspots as observed by the Atmospheric InfraRed Sounder (AIRS) aboard the National Aeronautics and Space Administration's (NASA's) Aqua satellite. We introduce a simple and effective approach, referred to as the "two-box method", to detect gravity wave activity from infrared nadir sounder measurements and to discriminate between gravity waves from orographic and other sources. From austral mid fall to mid spring (April–October) the contributions of orographic sources to the observed gravity wave occurrence frequencies were found to be largest for the Andes (90 %), followed by the Antarctic Peninsula (76 %), Kerguelen Islands (73 %), Tasmania (70 %), New Zealand (67 %), Heard Island (60 %), and other hotspots (24–54 %). Mountain wave activity was found to be closely correlated with peak terrain altitudes, and with zonal winds in the lower troposphere and mid stratosphere. We propose a simple model to predict the occurrence of mountain wave events in the AIRS observations using zonal wind thresholds at 3 hPa and 750 hPa. The model has significant predictive skill for hotspots where gravity wave activity is primarily due to orographic sources. It typically reproduces seasonal variations of the mountain wave occurrence frequencies at the Antarctic Peninsula and Kerguelen Islands from near zero to over 60 % with mean absolute errors of 4–5 percentage points. The prediction model can be used to disentangle upper level wind effects on observed occurrence frequencies from low level source and other influences. The data and methods presented here can help to identify interesting case studies in the vast amount of AIRS data, which could then be further explored to study the specific characteristics of stratospheric gravity waves from orographic sources and to support model validation.

scholarly journals First tomographic observations of gravity waves by the infrared limb imager GLORIA

2017 ◽  
Vol 17 (24) ◽  
pp. 14937-14953 ◽  
Author(s):  
Isabell Krisch ◽  
Peter Preusse ◽  
Jörn Ungermann ◽  
Andreas Dörnbrack ◽  
Stephen D. Eckermann ◽  
...  
Keyword(s):  
Ray Tracing ◽  
Gravity Wave ◽  
Gravity Waves ◽  
General Circulation ◽  
Wave Packets ◽  
Source Region ◽  
General Circulation Models ◽  
Climate Projections ◽  
Flight Pattern ◽  
The Waves

Abstract. Atmospheric gravity waves are a major cause of uncertainty in atmosphere general circulation models. This uncertainty affects regional climate projections and seasonal weather predictions. Improving the representation of gravity waves in general circulation models is therefore of primary interest. In this regard, measurements providing an accurate 3-D characterization of gravity waves are needed. Using the Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA), the first airborne implementation of a novel infrared limb imaging technique, a gravity wave event over Iceland was observed. An air volume disturbed by this gravity wave was investigated from different angles by encircling the volume with a closed flight pattern. Using a tomographic retrieval approach, the measurements of this air mass at different angles allowed for a 3-D reconstruction of the temperature and trace gas structure. The temperature measurements were used to derive gravity wave amplitudes, 3-D wave vectors, and direction-resolved momentum fluxes. These parameters facilitated the backtracing of the waves to their sources on the southern coast of Iceland. Two wave packets are distinguished, one stemming from the main mountain ridge in the south of Iceland and the other from the smaller mountains in the north. The total area-integrated fluxes of these two wave packets are determined. Forward ray tracing reveals that the waves propagate laterally more than 2000 km away from their source region. A comparison of a 3-D ray-tracing version to solely column-based propagation showed that lateral propagation can help the waves to avoid critical layers and propagate to higher altitudes. Thus, the implementation of oblique gravity wave propagation into general circulation models may improve their predictive skills.

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.

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.

Sign in / Sign up

Export Citation Format

Share Document