scholarly journals Stratospheric mountain waves trailing across Northern Europe

2021 ◽  
Author(s):  
Andreas Dörnbrack
Keyword(s):  
Gravity Waves ◽  
Polar Vortex ◽  
Internal Gravity Waves ◽  
Polar Front ◽  
Wave Drag ◽  
Northern Europe ◽  
Stratospheric Polar Vortex ◽  
Mountain Waves ◽  
Stratospheric Temperature ◽  
Almost All

AbstractPlanetary waves disturbed the hitherto stable Arctic stratospheric polar vortex in the middle of January 2016 in such a way that unique tropospheric and stratospheric flow conditions for vertically and horizontally propagating mountain waves developed. Co-existing strong low-level westerly winds across almost all European mountain ranges plus the almost zonally-aligned polar front jet created these favorable conditions for deeply propagating gravity waves. Furthermore, the northward displacement of the polar night jet resulted in a wide-spread coverage of stratospheric mountainwaves trailing across northern Europe. This paper describes the particular meteorological setting by analyzing the tropospheric and stratospheric flows based on the ERA5 data. The potential of the flow for exciting internal gravity waves from non-orographic sources is evaluated across all altitudes by considering various indices to indicate flow imbalances as δ, Ro, Roζ, Ro┴, and ΔNBE. The analyzed gravity waves are described and characterized. The main finding of this case study is the exceptionally vast extension of the mountain waves trailing to high latitudes originating from the flow across the mountainous sources that are located at about 45°N. The magnitudes of the simulated stratospheric temperature perturbations attain values larger than 10K and are comparable to values as documented by recent case studies of large-amplitude mountain waves over South America. The zonal means of the resolved and parameterized stratospheric wave drag during the mountain wave event peak at − 4.5ms−1 d−1 and − 32.2 ms−1 d−1, respectively.

Stratospheric mountain waves trailing across northern Europe

2021 ◽  
Author(s):  
Andreas Dörnbrack
Keyword(s):  
Gravity Waves ◽  
Polar Vortex ◽  
Internal Gravity Waves ◽  
Polar Front ◽  
Northern Europe ◽  
Polar Night ◽  
Stratospheric Polar Vortex ◽  
Mountain Waves ◽  
Almost All

<table><tbody><tr><td> <p><span>Planetary waves disturbed the hitherto stable Arctic stratospheric polar vortex mid of<br>January 2016 in such a way that unique tropospheric and stratospheric flow conditions<br>for vertically and horizontally propagating mountain waves developed. Co-existing<br>strong low-level westerly winds across almost all European mountain ranges plus the<br>almost zonally-aligned polar front jet created these favorable conditions for deeply<br>propagating gravity waves. Furthermore, the northward displacement of the polar night<br>jet resulted in a wide-spread coverage of stratospheric mountain waves trailling across<br>northern Europe. This paper describes the particular meteorological setting by<br>analyzing the tropospheric and stratospheric flows based on the ERA5 data. The<br>potential of the flow for exciting internal gravity waves from non-orographic sources is<br>evaluated across all altitudes by considering various instability indices as δ , Ro, Ro ζ , Ro<sub>⊥</sub> ,<br>and Δ NBE</span><span>. </span></p> <p><span>The analyzed gravity waves are described and characterized in terms of<br>commonly used parameters. The main finding of this case study is the exceptionally<br>vast extension of the mountain waves trailing to high latitudes originating from the flow<br>across the mountainous sources that are located at about 45 N. As a useful addition to<br>the case study, tracks for potential research flights are proposed that sample the<br>waves by a vertically pointing airborne remote-sensing instrument. Benefits and<br>drawbacks of the different approaches to observe the meridional focussing of the<br>mountain waves into the polar night jet are discussed.</span></p> </td> </tr></tbody></table><p> </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>

scholarly journals Atmospheric Conditions during the Deep Propagating Gravity Wave Experiment (DEEPWAVE)

2017 ◽  
Vol 145 (10) ◽  
pp. 4249-4275 ◽  
Author(s):  
Sonja Gisinger ◽  
Andreas Dörnbrack ◽  
Vivien Matthias ◽  
James D. Doyle ◽  
Stephen D. Eckermann ◽  
...  
Keyword(s):  
New Zealand ◽  
Gravity Wave ◽  
Inversion Layer ◽  
Polar Vortex ◽  
Polar Front ◽  
Atmospheric Conditions ◽  
Mountain Waves ◽  
Wave Experiment ◽  
Stratospheric Wind ◽  
Antarctic Polar Vortex

This paper describes the results of a comprehensive analysis of the atmospheric conditions during the Deep Propagating Gravity Wave Experiment (DEEPWAVE) campaign in austral winter 2014. Different datasets and diagnostics are combined to characterize the background atmosphere from the troposphere to the upper mesosphere. How weather regimes and the atmospheric state compare to climatological conditions is reported upon and how they relate to the airborne and ground-based gravity wave observations is also explored. Key results of this study are the dominance of tropospheric blocking situations and low-level southwesterly flows over New Zealand during June–August 2014. A varying tropopause inversion layer was found to be connected to varying vertical energy fluxes and is, therefore, an important feature with respect to wave reflection. The subtropical jet was frequently diverted south from its climatological position at 30°S and was most often involved in strong forcing events of mountain waves at the Southern Alps. The polar front jet was typically responsible for moderate and weak tropospheric forcing of mountain waves. The stratospheric planetary wave activity amplified in July leading to a displacement of the Antarctic polar vortex. This reduced the stratospheric wind minimum by about 10 m s−1 above New Zealand making breaking of large-amplitude gravity waves more likely. Satellite observations in the upper stratosphere revealed that orographic gravity wave variances for 2014 were largest in May–July (i.e., the period of the DEEPWAVE field phase).

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>

A non-linear investigation of critical levels for internal atmospheric gravity waves

1971 ◽  
Vol 50 (3) ◽  
pp. 545-563 ◽  
Author(s):  
R. J. Breeding
Keyword(s):  
Steady State ◽  
Linear Theory ◽  
Gravity Waves ◽  
Incident Wave ◽  
Critical Level ◽  
Internal Gravity Waves ◽  
Mean Flow ◽  
Non Linear ◽  
Energy And Momentum ◽  
Almost All

The behaviour of internal gravity waves near a critical level is investigated by means of a transient two dimensional finite difference model. All the important non-linear, viscosity and thermal conduction terms are included, but the rotational terms are omitted and the perturbations are assumed to be incompressible. For Richardson numbers greater than 2·0 the interaction of the incident wave and the mean flow is largely as predicted by the linear theory–very little of the incident wave penetrates through the critical level and almost all of the wave's energy and momentum are absorbed by changes in the original wind. However, these changes in the wind are centred above the critical level, so that the change in the wind has only a small effect on the height of the critical level. For Richardson numbers less than 2·0 and greater than 0·25 a significant fraction of the incident wave is reflected, part of which could have been predicted by the linear theory. For these stable Richardson numbers a steady state is apparently reached where the maximum wind change continues to grow slowly, but the minimum Richardson number and wave magnitudes remain constant. This condition represents a balance between the diffusion outward of the added momentum and the rate at which it is absorbed. For Richardson numbers less than 0·25, over-reflexion, predicted from the linear theory, is observed, but because the system is dynamically unstable no over-reflecting steady state is ever reached.

Influence of gravity wave drag parametrisations on the stratospheric circulation of seasonal ICON-NWP experiments

2020 ◽  
Author(s):  
Raphael Köhler ◽  
Dörthe Handorf ◽  
Ralf Jaiser ◽  
Klaus Dethloff ◽  
Günther Zängl ◽  
...  
Keyword(s):  
Gravity Wave ◽  
General Circulation ◽  
Weather Prediction ◽  
Polar Vortex ◽  
Circulation Model ◽  
Seasonal Prediction ◽  
Wave Drag ◽  
Stratospheric Polar Vortex ◽  
Sensitivity Experiments ◽  
Hemisphere Winter

<p>The stratospheric polar vortex is highly variable in winter and thus, models often struggle to capture its variability and strength. Yet, the influence of the stratosphere on the tropospheric circulation becomes highly important in Northern Hemisphere winter and is one of the main potential sources for subseasonal to seasonal prediction skill in mid latitudes. Mid-latitude extreme weather patterns in winter are often preceded by sudden stratospheric warmings (SSWs), which are the strongest manifestation of the coupling between stratosphere and troposphere. Misrepresentation of the SSW-frequency and stratospheric biases in models can therefore also cause biases in the troposphere.</p><p>In this context this work comprises the analysis of four seasonal ensemble experiments with a high-resolution, nonhydrostatic global atmospheric general circulation model in numerical weather prediction mode (ICON-NWP). The main focus thereby lies on the variability and strength of the stratospheric polar vortex. We identified the gravity wave drag parametrisations as one important factor influencing stratospheric dynamics. As the control experiment with default gravity wave drag settings exhibits an overestimated amount of SSWs and a weak stratospheric polar vortex, three sensitivity experiments with adjusted drag parametrisations were generated. Hence, the parametrisations for the non-orographic gravity wave drag and the subgrid‐scale orographic (SSO) drag were chosen with the goal of strengthening the stratospheric polar vortex. Biases to ERA-Interim are reduced with both adjustments, especially in high latitudes. Whereas the positive effect of the reduced non-orographic gravity wave drag is strongest in the mid-stratosphere in winter, the adjusted SSO-scheme primarily affects the troposphere by reducing mean sea level pressure biases in all months. A fourth experiment using both adjustments exhibits improvements in the troposphere and stratosphere. Although the stratospheric polar vortex in winter is strengthened in all sensitivity experiments, it is still simulated too weak compared to ERA-Interim. Further mechanisms causing this weakness are also investigated in this study.</p>

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.

Improvement in Prediction of the Arctic Oscillation with a Realistic Ocean Initial Condition in a CGCM

2015 ◽  
Vol 28 (22) ◽  
pp. 8951-8967 ◽  
Author(s):  
Hae-Jeong Kim ◽  
Joong-Bae Ahn
Keyword(s):  
Arctic Oscillation ◽  
Polar Vortex ◽  
Polar Front ◽  
Forecast Skill ◽  
Sea Surface ◽  
The Arctic ◽  
Initial Condition ◽  
Stratospheric Polar Vortex ◽  
The Arctic Oscillation ◽  
Polar Front Jet

Abstract This study verifies the impact of improved ocean initial conditions on the Arctic Oscillation (AO) forecast skill by assessing the one-month lead predictability of boreal winter AO using the Pusan National University (PNU) coupled general circulation model (CGCM). Hindcast experiments were performed on two versions of the model, one does not use assimilated ocean initial data (V1.0) and one does (V1.1), and the results were comparatively analyzed. The forecast skill of V1.1 was superior to that of V1.0 in terms of the correlation coefficient between the predicted and observed AO indices. In the regression analysis, V1.1 showed more realistic spatial similarities than V1.0 did in predicted sea surface temperature and atmospheric circulation fields. The authors suggest the relative importance of the contribution of the ocean initial condition to the AO forecast skill was because the ocean data assimilation increased the predictability of the AO, to some extent, through the improved interaction between tropical forcing induced by realistic sea surface temperature (SST) and atmospheric circulation. In V1.1, as in the observation, the cold equatorial Pacific SST anomalies generated the weakened tropical convection and Hadley circulation over the Pacific, resulting in a decelerated subtropical jet and accelerated polar front jet in the extratropics. The intensified polar front jet implies a stronger stratospheric polar vortex relevant to the positive AO phase; hence, surface manifestations of the reflected positive AO phase were then induced through the downward propagation of the stratospheric polar vortex. The results suggest that properly assimilated initial ocean conditions might contribute to improve the predictability of global oscillations, such as the AO, through large-scale tropical ocean–atmosphere interaction.

scholarly journals Gravity Waves excited during a Minor Sudden Stratospheric Warming

2018 ◽  
Author(s):  
Andreas Dörnbrack ◽  
Sonja Gisinger ◽  
Natalie Kaifler ◽  
Tanja Portele ◽  
Martina Bramberger ◽  
...  
Keyword(s):  
Gravity Waves ◽  
Polar Vortex ◽  
Internal Gravity Waves ◽  
The Arctic ◽  
Stratospheric Warming ◽  
Sudden Stratospheric Warming ◽  
Coherent Wave ◽  
Propagating Waves ◽  
A Minor ◽  
Inertia Gravity Waves

Abstract. An exceptionally deep upper-air sounding launched from Kiruna airport (67.82° N, 20.337° E) on 30 January 2016 stimulated the current investigation of internal gravity waves excited during a minor sudden stratospheric warming (SSW) in the Arctic winter 2015/16. The analysis of the radiosonde profile revealed large kinetic and potential energies in the upper stratosphere without any simultaneous enhancement of upper tropospheric and lower stratospheric values. Upward propagating inertia-gravity waves in the upper stratosphere and downward propagating modes in the lower stratosphere indicated a region of gravity wave generation in the stratosphere. Two-dimensional wavelet analysis was applied to vertical time series of temperature fluctuations in order to determine the vertical propagation direction of the stratospheric gravity waves in one-hourly high-resolution meteorological analyses and short-term forecasts. The separation of up- and downward propagating waves provided further evidence for a stratospheric source of gravity waves. The scale-dependent decomposition of the flow into a balanced component and inertia-gravity waves showed that coherent wave packets preferentially occurred at the inner edge of the Arctic polar vortex where a sub-vortex formed during the minor SSW.

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