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>

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.

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).

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 Statistical Characterization of Arctic Polar-Night Jet Oscillation Events

2013 ◽  
Vol 26 (6) ◽  
pp. 2096-2116 ◽  
Author(s):  
Peter Hitchcock ◽  
Theodore G. Shepherd ◽  
Gloria L. Manney
Keyword(s):  
Time Scale ◽  
Middle Atmosphere ◽  
Polar Vortex ◽  
Extended Period ◽  
The Arctic ◽  
Polar Night ◽  
Stratospheric Polar Vortex ◽  
Statistical Characterization ◽  
Long Time ◽  
Jet Oscillation

Abstract A novel diagnostic tool is presented, based on polar-cap temperature anomalies, for visualizing daily variability of the Arctic stratospheric polar vortex over multiple decades. This visualization illustrates the ubiquity of extended-time-scale recoveries from stratospheric sudden warmings, termed here polar-night jet oscillation (PJO) events. These are characterized by an anomalously warm polar lower stratosphere that persists for several months. Following the initial warming, a cold anomaly forms in the middle stratosphere, as does an anomalously high stratopause, both of which descend while the lower-stratospheric anomaly persists. These events are characterized in four datasets: Microwave Limb Sounder (MLS) temperature observations; the 40-yr ECMWF Re-Analysis (ERA-40) and Modern Era Retrospective Analysis for Research and Applications (MERRA) reanalyses; and an ensemble of three 150-yr simulations from the Canadian Middle Atmosphere Model. The statistics of PJO events in the model are found to agree very closely with those of the observations and reanalyses. The time scale for the recovery of the polar vortex following sudden warmings correlates strongly with the depth to which the warming initially descends. PJO events occur following roughly half of all major sudden warmings and are associated with an extended period of suppressed wave-activity fluxes entering the polar vortex. They follow vortex splits more frequently than they do vortex displacements. They are also related to weak vortex events as identified by the northern annular mode; in particular, those weak vortex events followed by a PJO event show a stronger tropospheric response. The long time scales, predominantly radiative dynamics, and tropospheric influence of PJO events suggest that they represent an important source of conditional skill in seasonal forecasting.

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.

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.

scholarly journals Synoptic–Dynamic Climatology of the Aleutian High

2018 ◽  
Vol 75 (4) ◽  
pp. 1271-1283 ◽  
Author(s):  
Stephen J. Colucci ◽  
Thomas S. Ehrmann
Keyword(s):  
Wave Breaking ◽  
Geopotential Height ◽  
Polar Vortex ◽  
Heat Fluxes ◽  
Aleutian Islands ◽  
Height Anomaly ◽  
Reanalysis Dataset ◽  
Stratospheric Polar Vortex ◽  
Geometric Moments ◽  
Almost All

Abstract A climatology of the anticyclone that commonly appears over the Aleutian Islands in the wintertime Northern Hemisphere stratosphere is presented. Applying a geometric moments technique to a reanalysis dataset and updating a previously published definition, 68 Aleutian high (AH) events have been identified during 35 winter (October–March) seasons (1979/80–2013/14), or about 2 events per season. The events lasted an average of approximately 33 days. Thirteen of the 68 AH events each temporally and spatially coincided with tropospheric blocking identified with a wave-breaking definition, while 41 of the AH onsets each coincided with a persistently positive geopotential height anomaly in the troposphere. Also, 41 of the 68 AH events each coincided with or were followed by an objectively defined disturbance (split or displacement) to the stratospheric polar vortex. Finally, 47 of these disturbance events were each preceded by an AH onset, such that in almost all winters (33 out of 35), an early season AH was followed by a later-season polar vortex disturbance (PVD). Potential vorticity (PV) inversion revealed that the geopotential height rises associated with composite AH onset were forced primarily by anticyclonic PV increases in the stratosphere, with the troposphere providing a lesser contribution. Poleward eddy heat fluxes in the stratosphere preceded and especially followed composite AH onset, consistent with the findings that composite AH onset was forced primarily by anticyclonic PV increases in the stratosphere and that many AH onsets were each followed by a PVD onset.

scholarly journals Forecasting extreme stratospheric polar vortex events

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
L. J. Gray ◽  
M. J. Brown ◽  
J. Knight ◽  
M. Andrews ◽  
H. Lu ◽  
...  
Keyword(s):  
Lower Stratosphere ◽  
Polar Vortex ◽  
Weather Conditions ◽  
Seasonal Forecast ◽  
Spatial Evolution ◽  
Primary Case ◽  
Quasi Biennial Oscillation ◽  
Stratospheric Polar Vortex ◽  
Biennial Oscillation

Abstract Extreme polar vortex events known as sudden stratospheric warmings can influence surface winter weather conditions, but their timing is difficult to predict. Here, we examine factors that influence their occurrence, with a focus on their timing and vertical extent. We consider the roles of the troposphere and equatorial stratosphere separately, using a split vortex event in January 2009 as the primary case study. This event cannot be reproduced by constraining wind and temperatures in the troposphere alone, even when the equatorial lower stratosphere is in the correct phase of the quasi biennial oscillation. When the flow in the equatorial upper stratosphere is also constrained, the timing and spatial evolution of the vortex event is captured remarkably well. This highlights an influence from this region previously unrecognised by the seasonal forecast community. We suggest that better representation of the flow in this region is likely to improve predictability of extreme polar vortex events and hence their associated impacts at the surface.

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