scholarly journals Satellite observations of middle atmosphere gravity wave activity and dissipation during recent stratospheric warmings

2016 ◽  
Author(s):  
Manfred Ern ◽  
Quang Thai Trinh ◽  
Martin Kaufmann ◽  
Isabell Krisch ◽  
Peter Preusse ◽  
...  
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Middle Atmosphere ◽  
Polar Vortex ◽  
Wave Activity ◽  
Planetary Waves ◽  
Absolute Gravity ◽  
Mountain Waves ◽  
Meridional Shape ◽  
Zonal Average

Abstract. Sudden stratospheric warmings (SSWs) are circulation anomalies in the polar region during winter. They mostly occur in the Northern Hemisphere and affect also surface weather and climate. Both planetary waves and gravity waves contribute to the onset and evolution of SSWs. While the role of planetary waves for SSW evolution has been recognized, the effect of gravity waves is still not fully understood, and has not been comprehensively analyzed based on global observations. In particular, information on the gravity wave driving of the background winds during SSWs is still missing. We investigate the boreal winters 2001/2002 until 2013/2014. Absolute gravity wave momentum fluxes and gravity wave dissipation (potential drag) are estimated from temperature observations of the satellite instruments HIRDLS and SABER. In agreement with previous work, we find that sometimes gravity wave activity is enhanced before the central date of major SSWs, particularly during vortex-split events. Often, SSWs are associated with polar-night jet oscillation (PJO) events. For these events, we find that gravity wave activity is strongly suppressed when winds reverse from eastward to westward (usually after the central date of a major SSW). In addition, gravity wave potential drag at the bottom of the newly forming eastward directed jet is remarkably weak, while considerable potential drag at the top of the jet likely contributes to the downward propagation of both the jet and the new elevated stratopause. During PJO events, we also find some indication for poleward propagation of gravity waves. Another striking finding is that obviously localized gravity wave sources, likely mountain waves and jet-generated gravity waves, play an important role during the evolution of SSWs and potentially contribute to the triggering of SSWs by preconditioning the shape of the polar vortex. The distribution of these hot spots is highly variable and strongly depends on the zonal and meridional shape of the background wind field, indicating that a pure zonal average view sometimes is a too strong simplification for the strongly perturbed conditions during the evolution of SSWs.

scholarly journals Satellite observations of middle atmosphere gravity wave absolute momentum flux and of its vertical gradient during recent stratospheric warmings

2016 ◽  
Vol 16 (15) ◽  
pp. 9983-10019 ◽  
Author(s):  
Manfred Ern ◽  
Quang Thai Trinh ◽  
Martin Kaufmann ◽  
Isabell Krisch ◽  
Peter Preusse ◽  
...  
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Middle Atmosphere ◽  
Polar Vortex ◽  
Vertical Gradient ◽  
Wave Activity ◽  
Planetary Waves ◽  
Absolute Gravity ◽  
Mountain Waves ◽  
Meridional Shape

Abstract. Sudden stratospheric warmings (SSWs) are circulation anomalies in the polar region during winter. They mostly occur in the Northern Hemisphere and affect also surface weather and climate. Both planetary waves and gravity waves contribute to the onset and evolution of SSWs. While the role of planetary waves for SSW evolution has been recognized, the effect of gravity waves is still not fully understood, and has not been comprehensively analyzed based on global observations. In particular, information on the gravity wave driving of the background winds during SSWs is still missing.We investigate the boreal winters from 2001/2002 until 2013/2014. Absolute gravity wave momentum fluxes and gravity wave dissipation (potential drag) are estimated from temperature observations of the satellite instruments HIRDLS and SABER. In agreement with previous work, we find that sometimes gravity wave activity is enhanced before or around the central date of major SSWs, particularly during vortex-split events. Often, SSWs are associated with polar-night jet oscillation (PJO) events. For these events, we find that gravity wave activity is strongly suppressed when the wind has reversed from eastward to westward (usually after the central date of a major SSW). In addition, gravity wave potential drag at the bottom of the newly forming eastward-directed jet is remarkably weak, while considerable potential drag at the top of the jet likely contributes to the downward propagation of both the jet and the new elevated stratopause. During PJO events, we also find some indication for poleward propagation of gravity waves. Another striking finding is that obviously localized gravity wave sources, likely mountain waves and jet-generated gravity waves, play an important role during the evolution of SSWs and potentially contribute to the triggering of SSWs by preconditioning the shape of the polar vortex. The distribution of these hot spots is highly variable and strongly depends on the zonal and meridional shape of the background wind field, indicating that a pure zonal average view sometimes is a too strong simplification for the strongly perturbed conditions during the evolution of SSWs.

scholarly journals Global analysis for periodic variations of gravity wave squared amplitudes and momentum fluxes in the middle atmosphere

2019 ◽  
Author(s):  
Dan Chen ◽  
Cornelia Strube ◽  
Manfred Ern ◽  
Peter Preusse ◽  
Martin Riese
Keyword(s):  
Gravity Wave ◽  
Annual Variation ◽  
Middle Atmosphere ◽  
Global Analysis ◽  
Lower Thermosphere ◽  
Polar Vortex ◽  
Absolute Gravity ◽  
Coupling Mechanism ◽  
Quasi Biennial Oscillation ◽  
Oblique Propagation

Abstract. Atmospheric gravity waves (GWs) are an important coupling mechanism in the middle atmosphere. For instance, they provide a large part of the driving of long-period atmospheric oscillations such as the quasi-biennial oscillation (QBO) and the semiannual oscillation (SAO) and are in turn modulated. They also induce the wind reversal in the mesosphere – lower thermosphere region (MLT) and the residual mean circulation at these altitudes. In this study, the variations of monthly zonal mean gravity wave square temperature amplitudes (GWSTA) and, for a first time, absolute gravity wave momentum flux (GWMF) on different time scales such as the annual, semiannual, terannual and quasi-biennial variations are investigated by spectrally analyzing SABER observations from 2002 to 2015. Latitude-altitude cross sections of spectral amplitudes and phases of GWSTA and absolute GWMF in stratosphere and mesosphere are presented and physically interpreted. It is shown that the time series of GWSTA/GWMF at a certain altitude and latitude results from the complex interplay of GW sources, propagation through and filtering in lower altitudes, oblique propagation superposing GWs from different source locations and, finally, the modulation of the GW spectrum by the winds at a considered altitude and latitude. The strongest component is the annual variation, dominated on the summer hemisphere by subtropical convective sources, and on the winter hemisphere by polar vortex dynamics. At heights of the wind reversal also a 180° phase shift occurs, which is at different altitudes for GWSTA and GWMF. In the intermediate latitudes a semi-annual variation (SAV) is found. Dedicated GW modeling is used to investigate the nature of this SAV, which is a different phenomenon from the tropical SAO also seen in the data. In the tropics a stratospheric and a mesospheric QBO are found, which are, as expected, in anti-phase. Indication for a QBO influence is also found at higher latitudes. In previous studies a terannual variation (TAV) was identified. In the current study we explain its origin. In particular the observed patterns for the shorter periods, SAV and TAV, can only be explained by poleward propagation of GWs from the lower stratosphere subtropics into the mid and high latitude mesosphere. In this way, critical wind filtering in the lowermost stratosphere is avoided and this oblique propagation hence is likely an important factor for MLT dynamics.

Multi-scale mountain waves observed with the ALIMA lidar during SOUTHTRAC-GW above the southern Andes

2021 ◽  
Author(s):  
Natalie Kaifler ◽  
Bernd Kaifler ◽  
Andreas Dörnbrack ◽  
Sonja Gisinger ◽  
Tyler Mixa ◽  
...  
Keyword(s):  
Wave Field ◽  
Gravity Wave ◽  
Gravity Waves ◽  
Momentum Flux ◽  
Middle Atmosphere ◽  
Airborne Lidar ◽  
Horizontal Wind ◽  
Measured Temperature ◽  
Southern Andes ◽  
Mountain Waves

<p>During the SOUTHTRAC-GW (Southern hemisphere Transport, Dynamics and Chemistry – Gravity Waves) field campaign, gravity waves above the Southern Andes mountains, the Drake passage and the Antarctic Peninsula were probed with airborne instruments onboard the HALO research aircraft. The Airborne Lidar for Middle Atmosphere research (ALIMA) detected particularly strong mountain waves in excess of 25 K amplitude in cross-mountain legs above the Southern Andes of research flight ST08 on 12 September 2019. The mountain waves propagated well into the mesosphere up to 65 km altitude with possible generation of smaller-scale secondary waves during wave breaking above 65 km. A superposition of mountain waves with horizontal wavelengths in the range 15-200 km and vertical wavelengths 7-24 km dominated the wave field between 18 and 65 km altitude. Vertical wavelengths predicted by the hydrostatic equation and horizontal wind from the European Center for Medium-Range Weather Forecasts’ Integrated Forecasting System are in good agreement with observed vertical wavelengths. We apply wavelet analysis to the measured temperature field along the flight track in order to identify and separate dominant scales, and estimate their relative contributions to the total gravity wave momentum flux as well as the local and zonal-mean gravity wave drag. Furthermore, we compare our observations to results obtained by Fourier ray analysis of the terrain of the Southern Andes. The Fourier model allows the investigation of the 3d-wave field and trapped waves which are not well sampled by the ALIMA instrument because of the relative alignment between the wave fronts and the flight track. These sampling biases are quantified from virtual flights through the model domain at multiple angles and taken into account in the estimation of the total momentum flux derived from ALIMA observations. The combination of high-resolution observations and model data reveals the significance of this and similar mountain wave events in the Southern Andes region for the atmospheric dynamics at ~60° S.</p>

Importance of gravity wave forcing for springtime southern polar vortex breakdown as revealed by ERA5

2021 ◽  
Author(s):  
Aman Gupta ◽  
Thomas Birner ◽  
Andreas Doernbrack ◽  
Inna Polichtchouk
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Zonal Wind ◽  
Planetary Wave ◽  
Climate Models ◽  
Vortex Breakdown ◽  
Polar Vortex ◽  
Wave Drag ◽  
Planetary Waves ◽  
The Mean

<p>Planetary waves and gravity waves are the key drivers of middle atmospheric circulation and variability. While planetary waves are well resolved in climate models, inaccuracies in representation of gravity waves in climate models persist. Inaccuracies in representation of gravity waves limit our understanding of the planetary wave-gravity wave interactions that can be crucial during the Antarctic polar vortex breakdown. Moreover, "missing" gravity wave drag around 60<sup>o</sup>S in the upper stratosphere is considered to be responsible for the "cold-pole" bias in comprehensive climate models that employ parameterizations to appproximately represent the gravity wave drag.</p><p>We illustrate the strength of the high-resolution ERA-5 reanalysis in resolving a broad spectrum of gravity waves in southern hemisphere midlatitudes and to estimate their contribution to the momentum budget around 60<sup>o</sup>S. We find that most of the resolved mountain waves excited over the Andes and Antarctic peninsula propagate away from their source and deposit momentum around 60<sup>o</sup>S over the Southern Ocean. Further, a composite analysis around 60<sup>o</sup>S during the vortex breakdown period using ERA-5 reveals considerably large fractional contribution of resolved + parameterized GWD towards the vortex deceleration. Upto 30 days prior to the breakdown, a balance between the Coriolis acceleration and the planetary wave deceleration provides a weak net deceleration of the mean winds, following which, they provide a net acceleration of the mean winds. The gravity waves, however, provide a steady deceleration of the mean winds throughout the breakdown period. The resolved drag in ERA-5 accounts for as much as one-fourth of the zonal wind deceleration at 60<sup>o</sup>S and 10 hPa, while the parameterized drag in ERA-5 accounts for more than one-half of the zonal wind deceleration.  The findings establish the crucial role of gravity waves in wintertime stratospheric circulation and opens avenues for further stratospheric gravity wave analysis using ERA-5.</p>

scholarly journals Southern Hemisphere Extratropical Gravity Wave Sources and Intermittency Revealed by a Middle-Atmosphere General Circulation Model

2016 ◽  
Vol 73 (3) ◽  
pp. 1335-1349 ◽  
Author(s):  
Simon P. Alexander ◽  
Kaoru Sato ◽  
Shingo Watanabe ◽  
Yoshio Kawatani ◽  
Damian J. Murphy
Keyword(s):  
Gravity Wave ◽  
Southern Hemisphere ◽  
General Circulation Model ◽  
Gravity Waves ◽  
General Circulation ◽  
Middle Atmosphere ◽  
Circulation Model ◽  
Absolute Gravity ◽  
Atmosphere General Circulation Model ◽  
Time Of Year

Abstract Southern Hemisphere extratropical gravity wave activity is examined using simulations from a free-running middle-atmosphere general circulation model called Kanto that contains no gravity wave parameterizations. The total absolute gravity wave momentum flux (MF) and its intermittency, diagnosed by the Gini coefficient, are examined during January and July. The MF and intermittency results calculated from the Kanto model agree well with results from satellite limb and superpressure balloon observations. The analysis of the Kanto model simulations indicates the following results. Nonorographic gravity waves are generated in Kanto in the frontal regions of extratropical depressions and around tropopause-level jets. Regions with lower (higher) intermittency in the July midstratosphere become more (less) intermittent by the mesosphere as a result of lower-level wave removal. The gravity wave intermittency is low and nearly homogeneous throughout the SH middle atmosphere during January. This indicates that nonorographic waves dominate at this time of year, with sources including continental convection as well as oceanic depressions. Most of the zonal-mean MF at 40°–65°S in January and July is due to gravity waves located above the oceans. The zonal-mean MF at lower latitudes in both months has a larger contribution from the land regions but the fraction above the oceans remains larger.

scholarly journals Gravity Wave Characteristics in the Southern Hemisphere Revealed by a High-Resolution Middle-Atmosphere General Circulation Model

2012 ◽  
Vol 69 (4) ◽  
pp. 1378-1396 ◽  
Author(s):  
Kaoru Sato ◽  
Satoshi Tateno ◽  
Shingo Watanabe ◽  
Yoshio Kawatani
Keyword(s):  
Gravity Wave ◽  
Energy Flux ◽  
Gravity Waves ◽  
Wave Energy ◽  
General Circulation ◽  
Middle Atmosphere ◽  
Polar Vortex ◽  
Circulation Model ◽  
Southern Andes ◽  
Atmosphere General Circulation Model

Abstract Gravity wave characteristics in the middle- to high-latitude Southern Hemisphere are analyzed using simulation data over 3 yr from a high-resolution middle-atmosphere general circulation model without using any gravity wave parameterizations. Gravity waves have large amplitudes in winter and are mainly distributed in the region surrounding the polar vortex in the middle and upper stratosphere, while the gravity wave energy is generally weak in summer. The wave energy distribution in winter is not zonally uniform, but it is large leeward of the southern Andes and Antarctic Peninsula. Linear theory in the three-dimensional framework indicates that orographic gravity waves are advected leeward significantly by the mean wind component perpendicular to the wavenumber vector. Results of ray-tracing and cross-correlation analyses are consistent with this theoretical expectation. The leeward energy propagation extends to several thousand kilometers, which explains part of the gravity wave distribution around the polar vortex in winter. This result indicates that orographic gravity waves can affect the mean winds at horizontal locations that are far distant from the source mountains. Another interesting feature is a significant downward energy flux in winter, which is observed in the lower stratosphere to the south of the southern Andes. The frequency of the downward energy flux is positively correlated with the gravity wave energy over the southern Andes. Partial reflection from a rapid increase in static stability around 10 hPa and/or gravity wave generation through nonlinear processes are possible mechanisms to explain the downward energy flux.

scholarly journals The MaCWAVE program to study gravity wave influences on the polar mesosphere

2006 ◽  
Vol 24 (4) ◽  
pp. 1159-1173 ◽  
Author(s):  
R. A. Goldberg ◽  
D. C. Fritts ◽  
F. J. Schmidlin ◽  
B. P. Williams ◽  
C. L. Croskey ◽  
...  
Keyword(s):  
Gravity Wave ◽  
Large Scale ◽  
Planetary Wave ◽  
Middle Atmosphere ◽  
Lower Thermosphere ◽  
Wave Structure ◽  
Wave Activity ◽  
Small Scale ◽  
Mountain Waves ◽  
The Mean

Abstract. MaCWAVE (Mountain and Convective Waves Ascending VErtically) was a highly coordinated rocket, ground-based, and satellite program designed to address gravity wave forcing of the mesosphere and lower thermosphere (MLT). The MaCWAVE program was conducted at the Norwegian Andøya Rocket Range (ARR, 69.3° N) in July 2002, and continued at the Swedish Rocket Range (Esrange, 67.9° N) during January 2003. Correlative instrumentation included the ALOMAR MF and MST radars and RMR and Na lidars, Esrange MST and meteor radars and RMR lidar, radiosondes, and TIMED (Thermosphere Ionosphere Mesosphere Energetics and Dynamics) satellite measurements of thermal structures. The data have been used to define both the mean fields and the wave field structures and turbulence generation leading to forcing of the large-scale flow. In summer, launch sequences coupled with ground-based measurements at ARR addressed the forcing of the summer mesopause environment by anticipated convective and shear generated gravity waves. These motions were measured with two 12-h rocket sequences, each involving one Terrier-Orion payload accompanied by a mix of MET rockets, all at ARR in Norway. The MET rockets were used to define the temperature and wind structure of the stratosphere and mesosphere. The Terrier-Orions were designed to measure small-scale plasma fluctuations and turbulence that might be induced by wave breaking in the mesosphere. For the summer series, three European MIDAS (Middle Atmosphere Dynamics and Structure) rockets were also launched from ARR in coordination with the MaCWAVE payloads. These were designed to measure plasma and neutral turbulence within the MLT. The summer program exhibited a number of indications of significant departures of the mean wind and temperature structures from ``normal" polar summer conditions, including an unusually warm mesopause and a slowing of the formation of polar mesospheric summer echoes (PMSE) and noctilucent clouds (NLC). This was suggested to be due to enhanced planetary wave activity in the Southern Hemisphere and a surprising degree of inter-hemispheric coupling. The winter program was designed to study the upward propagation and penetration of mountain waves from northern Scandinavia into the MLT at a site favored for such penetration. As the major response was expected to be downstream (east) of Norway, these motions were measured with similar rocket sequences to those used in the summer campaign, but this time at Esrange. However, a major polar stratospheric warming just prior to the rocket launch window induced small or reversed stratospheric zonal winds, which prevented mountain wave penetration into the mesosphere. Instead, mountain waves encountered critical levels at lower altitudes and the observed wave structure in the mesosphere originated from other sources. For example, a large-amplitude semidiurnal tide was observed in the mesosphere on 28 and 29 January, and appears to have contributed to significant instability and small-scale structures at higher altitudes. The resulting energy deposition was found to be competitive with summertime values. Hence, our MaCWAVE measurements as a whole are the first to characterize influences in the MLT region of planetary wave activity and related stratospheric warmings during both winter and summer.

scholarly journals Global analysis for periodic variations in gravity wave squared amplitudes and momentum fluxes in the middle atmosphere

2019 ◽  
Vol 37 (4) ◽  
pp. 487-506 ◽  
Author(s):  
Dan Chen ◽  
Cornelia Strube ◽  
Manfred Ern ◽  
Peter Preusse ◽  
Martin Riese
Keyword(s):  
Gravity Wave ◽  
Cross Sections ◽  
Middle Atmosphere ◽  
Global Analysis ◽  
Lower Thermosphere ◽  
Polar Vortex ◽  
Absolute Gravity ◽  
Coupling Mechanism ◽  
Quasi Biennial Oscillation ◽  
Oblique Propagation

Abstract. Atmospheric gravity waves (GWs) are an important coupling mechanism in the middle atmosphere. For instance, they provide a large part of the driving of long-period atmospheric oscillations such as the Quasi-Biennial Oscillation (QBO) and the semiannual oscillation (SAO) and are in turn modulated. They also induce the wind reversal in the mesosphere–lower thermosphere region (MLT) and the residual mean circulation at these altitudes. In this study, the variations in monthly zonal mean gravity wave square temperature amplitudes (GWSTAs) and, for the first time, absolute gravity wave momentum flux (GWMF) on different timescales such as the annual, semiannual, terannual and quasi-biennial variations are investigated by spectrally analyzing SABER observations from 2002 to 2015. Latitude–altitude cross sections of spectral amplitudes and phases of GWSTA and absolute GWMF in the stratosphere and mesosphere are presented and physically interpreted. It is shown that the time series of GWSTA and GWMF at a certain altitude and latitude results from the complex interplay of GW sources, propagation through and filtering in lower altitudes, oblique propagation superposing GWs from different source locations, and, finally, the modulation of the GW spectrum by the winds at a considered altitude and latitude. The strongest component is the annual variation, dominated in the summer hemisphere by subtropical convective sources and in the winter hemisphere by polar vortex dynamics. At heights of the wind reversal, a 180∘ phase shift also occurs, which is at different altitudes for GWSTA and GWMF. In the intermediate latitudes a semiannual variation (SAV) is found. Dedicated GW modeling is used to investigate the nature of this SAV, which is a different phenomenon from the tropical SAO also seen in the data. In the tropics a stratospheric and a mesospheric QBO are found, which are, as expected, in antiphase. Indication for a QBO influence is also found at higher latitudes. In previous studies a terannual variation (TAV) was identified. In the current study we explain its origin. In particular the observed patterns for the shorter periods, SAV and TAV, can only be explained by poleward propagation of GWs from the lower-stratosphere subtropics into the midlatitude and high-latitude mesosphere. In this way, critical wind filtering in the lowermost stratosphere is avoided and this oblique propagation is hence likely an important factor for MLT dynamics.

Mountain waves penetrating into the mesosphere observed by airborne lidar

2020 ◽  
Author(s):  
Bernd Kaifler ◽  
Andreas Dörnbrack ◽  
Tyler Mixa ◽  
Markus Rapp ◽  
Natalie Kaifler ◽  
...  
Keyword(s):  
Gravity Waves ◽  
Middle Atmosphere ◽  
Polar Vortex ◽  
Airborne Lidar ◽  
Temperature Profiles ◽  
Altitude Range ◽  
Mountain Waves ◽  
Downward Shift ◽  
German Research ◽  
Research Aircraft

<p>We present observations by airborne lidar which were obtained over the southern Andes during the SOUTHTRAC campaign in September 2019. Operated onboard the German research aircraft HALO, the Airborne LIdar for Middle Atmosphere research (ALIMA) acquired high resolution temperature profiles in the altitude range 20-80 km. The data show signatures of mountain waves located at the mountain ridges, but often these signatures also extend several hundred kilometer downstream. While during the first days of the campaign mountain waves were able to penetrate into the mesosphere, observations obtained in the following weeks indicate a downward shift of the breaking zone from the mesosphere to the stratosphere which is consistent with the early breakdown of the polar vortex. Our data also indicate evidence for generation of secondary gravity waves within the breaking zone of the mountain waves.</p>

scholarly journals Seasonal variation of gravity waves in the Equatorial Middle Atmosphere: results from ISRO's Middle Atmospheric Dynamics (MIDAS) program

2006 ◽  
Vol 24 (10) ◽  
pp. 2471-2480 ◽  
Author(s):  
G. Ramkumar ◽  
T. M. Antonita ◽  
Y. Bhavani Kumar ◽  
H. Venkata Kumar ◽  
D. Narayana Rao
Keyword(s):  
Seasonal Variation ◽  
Gravity Wave ◽  
Gravity Waves ◽  
Wind Shear ◽  
Middle Atmosphere ◽  
Wave Activity ◽  
Atmospheric Dynamics ◽  
Horizontal Wind ◽  
Middle Atmospheric Dynamics ◽  
Radar Measurements

Abstract. Altitude profiles of temperature in the stratospheric and mesopheric region from lidar observations at NARL, Gadanki, India, during December 2002–April 2005, as part of ISRO's Middle Atmospheric Dynamics – "MIDAS (2002–2005)" program are used to study the characteristics of gravity waves and their seasonal variation. Month-to-month variation of the gravity wave activity observed during the period of December 2002–April 2005 show maximum wave activity, with primary peaks in May 2003, August 2004 and March 2005 and secondary peaks in February 2003 and November 2004. This month-to-month variation in gravity wave activity is linked to the variation in the strength of the sources, viz. convection and wind shear, down below at the tropospheric region, estimated from MST radar measurements at the same location. Horizontal wind shear is found to be mostly correlated with wave activity than convection, and sometimes both sources are found to contribute towards the wave activity.

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