scholarly journals Observation of Kelvin–Helmholtz instabilities and gravity waves in the summer mesopause above Andenes in Northern Norway

2018 ◽  
Vol 18 (9) ◽  
pp. 6721-6732 ◽  
Author(s):  
Gunter Stober ◽  
Svenja Sommer ◽  
Carsten Schult ◽  
Ralph Latteck ◽  
Jorge L. Chau
Keyword(s):  
Gravity Waves ◽  
Middle Atmosphere ◽  
Phase Speed ◽  
Velocity Measurements ◽  
Wind Variability ◽  
Short Period ◽  
Strong Shear ◽  
Summer Echoes ◽  
Period Wave ◽  
Horizontal Wavelength

Abstract. We present observations obtained with the Middle Atmosphere Alomar Radar System (MAARSY) to investigate short-period wave-like features using polar mesospheric summer echoes (PMSEs) as a tracer for the neutral dynamics. We conducted a multibeam experiment including 67 different beam directions during a 9-day campaign in June 2013. We identified two Kelvin–Helmholtz instability (KHI) events from the signal morphology of PMSE. The MAARSY observations are complemented by collocated meteor radar wind data to determine the mesoscale gravity wave activity and the vertical structure of the wind field above the PMSE. The KHIs occurred in a strong shear flow with Richardson numbers Ri < 0.25. In addition, we observed 15 wave-like events in our MAARSY multibeam observations applying a sophisticated decomposition of the radial velocity measurements using volume velocity processing. We retrieved the horizontal wavelength, intrinsic frequency, propagation direction, and phase speed from the horizontally resolved wind variability for 15 events. These events showed horizontal wavelengths between 20 and 40 km, vertical wavelengths between 5 and 10 km, and rather high intrinsic phase speeds between 45 and 85 m s−1 with intrinsic periods of 5–10 min.

scholarly journals Observation of Kelvin-Helmholtz Instabilities and gravity waves in the summer mesopause above Andenes in Northern Norway

2018 ◽  
Author(s):  
Gunter Stober ◽  
Svenja Sommer ◽  
Carsten Schult ◽  
Ralph Latteck ◽  
Jorge L. Chau
Keyword(s):  
Gravity Waves ◽  
Vertical Structure ◽  
Middle Atmosphere ◽  
Meteor Radar ◽  
Helmholtz Instability ◽  
Beam Experiment ◽  
Short Period ◽  
Strong Shear ◽  
Summer Echoes ◽  
Period Wave

Abstract. We present observations obtained with the Middle Atmosphere Alomar Radar System (MAARSY) to investigate short period wave-like features using polar mesospheric summer echoes (PMSE) as tracer for the neutral dynamics. We conducted a multi-beam experiment including 67 different beam directions during a 9-day campaign in June 2013. We identified two Kelvin Helmholtz Instability (KHI) events from the signal morphology of PMSE. The MAARSY observations are complemented by collocated meteor radar wind data to determine the mesoscale gravity wave activity and the vertical structure of the wind field above the PMSE. The KHIs occurred in a strong shear flow with Richardson numbers Ri 

scholarly journals Gravity wave transmission diagram

2015 ◽  
Vol 33 (12) ◽  
pp. 1479-1484 ◽  
Author(s):  
Y. Tomikawa
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Phase Speed ◽  
Propagation Direction ◽  
Wave Transmission ◽  
Vertical Shear ◽  
Horizontal Wind ◽  
Wave Power ◽  
Power Spectral ◽  
Horizontal Wavelength

Abstract. A new method of obtaining power spectral distribution of gravity waves as a function of ground-based horizontal phase speed and propagation direction from airglow observations has recently been proposed. To explain gravity wave power spectrum anisotropy, a new gravity wave transmission diagram was developed in this study. Gravity wave transmissivity depends on the existence of critical and turning levels for waves that are determined by background horizontal wind distributions. Gravity wave transmission diagrams for different horizontal wavelengths in simple background horizontal winds with constant vertical shear indicate that the effects of the turning level reflection are significant and strongly dependent on the horizontal wavelength.

scholarly journals Influence of tides and gravity waves on layering processes in the polar summer mesopause region

2008 ◽  
Vol 26 (12) ◽  
pp. 4013-4022 ◽  
Author(s):  
P. Hoffmann ◽  
M. Rapp ◽  
J. Fiedler ◽  
R. Latteck
Keyword(s):  
Gravity Waves ◽  
Lower Layer ◽  
Vhf Radar ◽  
Remarkable Feature ◽  
Ice Cloud ◽  
Radar Echoes ◽  
Layer Structures ◽  
Short Period ◽  
Summer Echoes ◽  
Polar Mesosphere Summer Echoes

Abstract. Polar Mesosphere Summer Echoes (PMSE) have been studied at Andenes (69° N, 16° E), Norway, using VHF radar observations since 1994. One remarkable feature of these observations is the fact that {during 50% of the time,} the radar echoes occur in the form of two or more distinct layers. In the case of multiple PMSE layers, statistical analysis shows that the lower layer occurs at a mean height of ~83.4 km, which is almost identical to the mean height of noctilucent clouds (NLC) derived from observation with the ALOMAR Rayleigh/Mie/Raman lidar at the same site. To investigate the layering processes microphysical model simulations under the influence of tidal and gravity waves were performed. In the presence of long period gravity waves, these model investigations predict an enhanced formation of multiple PMSE layer structures, where the lower layer is a consequence of the occurrence of the largest particles at the bottom of the ice cloud. This explains the coincidence of the lowermost PMSE layers and NLC. During periods with enhanced amplitudes of the semidiurnal tide, the observed NLC and PMSE show pronounced tidal structures comparable to the results of corresponding microphysical simulations. At periods with short period gravity waves there is a tendency for a decreasing occurrence of NLC and for variable weak PMSE structures.

Climatological monthly characteristics of middle atmosphere gravity waves (10 min-10 h) during 1979-1993 at Saskatoon

1995 ◽  
Vol 13 (3) ◽  
pp. 285-295 ◽  
Author(s):  
N. M. Gavrilov ◽  
A. H. Manson ◽  
C. E. Meek
Keyword(s):  
Gravity Waves ◽  
Middle Atmosphere ◽  
Radar Data ◽  
Internal Gravity Waves ◽  
Annual Variations ◽  
Long Period ◽  
Short Period ◽  
Annual Component ◽  
Band Pass ◽  
Summer Minimum

Abstract. Saskatoon (52° N, 107°W) medium frequency (MF) radar data from 1979 to 1993 have been analyzed to investigate the climatology of irregular wind components in the height region 60-100 km. This component is usually treated in terms of internal gravity waves (IGW). Three different band-pass filters have been used to separate the intensities of IGWs having periods 0.2-2.5; 1.5-6 and 2-10 h, respectively. Height, seasonal and inter-annual variations of IGW intensities, anisotropy and predominant directions of propagation are investigated. Mean over 14 years' seasonal variation of the intensity of long-period IGWs shows a dominant annual component with winter maximum and summer minimum. Seasonal variations of the intensity of short-period waves have a strong semi-annual component as well, which forms a secondary maximum in summer. Predominant azimuths of long-period IGWs are generally zonal, though they vary with season. For short-period IGWs, the predominant azimuth is closer to the meridional direction. Anisotropy of IGW intensity is larger in summer, winter and at lower altitudes. The IGW intensity shows apparent correlation with both solar and geomagnetic activity. In most cases, this correlation appears to be negative. The variations versus solar activity is larger for longer-period IGW. Possible reasons and consequences of the observed climatological variations of IGW intensity are discussed.

scholarly journals The SAO and Kelvin waves in the EuroGRIPS GCMS and the UK Met. Office analyses

2001 ◽  
Vol 19 (1) ◽  
pp. 99-114 ◽  
Author(s):  
M. Amodei ◽  
S. Pawson ◽  
A. A. Scaife ◽  
U. Langematz ◽  
W. Lahoz ◽  
...  
Keyword(s):  
Gravity Waves ◽  
Climate Models ◽  
Middle Atmosphere ◽  
Phase Speed ◽  
Kelvin Waves ◽  
Planetary Scale ◽  
The United Kingdom ◽  
External Conditions ◽  
Intercomparison Project ◽  
The Uk

Abstract. We compare the tropical oscillations and planetary scale Kelvin waves in four troposphere-stratosphere climate models and the assimilated dataset produced by the United Kingdom Meteorological Office (UKMO). The comparison has been made in the GRIPS framework "GCM-Reality Intercomparison Project for SPARC", where SPARC is Stratospheric Processes and their Role in Climate, a project of the World Climate Research Program. The four models evaluated are European members of GRIPS: the UKMO Unified Model (UM), the model of the Free University in Berlin (FUB–GCM), the ARPEGE-climat model of the French National Centre for Meteorological Research (CNRM), and the Extended UGAMP GCM (EUGCM) of the Centre for Global Atmospheric Modelling (CGAM). The integrations were performed with different, but annually periodic external conditions (e.g., sea-surface temperature, sea ice, and incoming solar radiation). The structure of the tropical winds and the strengths of the Kelvin waves are examined. In the analyses where the SAO (Semi-Annual Oscillation) and the QBO (Quasi-Biennal Oscillation) are reasonably well captured, the amplitude of these analysed Kelvin waves is close to that observed in independent data from UARS (Upper Atmosphere Research Satellite). In agreement with observations, the Kelvin waves generated in the models propagate into the middle atmosphere as wave packets, consistent with a convective forcing origin. In three of the models, slow Kelvin waves propagate too high and their amplitudes are overestimated in the upper stratosphere and in the mesosphere, the exception is the UM which has weaker waves. None of the modelled waves are sufficient to force realistic eastward phases of the QBO or SAO. Although the SAO is represented by all models, only two of them are able to generate westerlies between 10 hPa and 50 hPa. The importance of the role played in the SAO by unresolved gravity waves is emphasized. Although it exhibits some unrealistic features, the EUGCM, which includes a parametrization of gravity waves with a non-zero phase speed, is able to simulate clear easterly to westerly transitions as well as westerlies with down-ward propagation. Thermal damping is also important for the westerly forcing in the stratosphere.Key words. Meteorology and atmospheric dynamics (middle atmosphere dynamics; tropical meterology; waves and tides)

scholarly journals Investigation of horizontal structures at mesospheric altitudes using coherent radar imaging

2013 ◽  
Vol 11 ◽  
pp. 319-325 ◽  
Author(s):  
S. Sommer ◽  
G. Stober ◽  
C. Schult ◽  
M. Zecha ◽  
R. Latteck
Keyword(s):  
High Spatial Resolution ◽  
Middle Atmosphere ◽  
Radar Imaging ◽  
Data Sets ◽  
Good Correspondence ◽  
Scattering Center ◽  
Short Period ◽  
Summer Echoes ◽  
Coherent Radar

Abstract. The Middle Atmosphere Alomar Radar System (MAARSY) in Northern Norway (69.30°N, 16.04°E) was used to perform interferometric observations of Polar Mesosperic Summer Echoes (PMSE) in June 2012. Coherent Radar Imaging (CRI) using Capon's method was applied allowing a high spatial resolution. The algorithm was validated by simulation and trajectories of meteor head echoes. Both data sets show a good correspondence with the algorithm. Using this algorithm, the aspect sensitivity of PMSE was analysed in a case study, making use of the capability of CRI to resolve the pattern within the beam volume. No correction of the beam pattern was made yet. It was found in this case study, that no large variations in the scattering width and the scattering center occured apart from a very short period of time at the upper edge of the PMSE.

scholarly journals Extracting gravity wave parameters during the September 2002 Southern Hemisphere major sudden stratospheric warming using a SANAE imaging riometer

2013 ◽  
Vol 31 (10) ◽  
pp. 1709-1719
Author(s):  
N. Mbatha ◽  
V. Sivakumar ◽  
H. Bencherif ◽  
S. Malinga
Keyword(s):  
Southern Hemisphere ◽  
Gravity Waves ◽  
Middle Atmosphere ◽  
Phase Speed ◽  
Potential Interaction ◽  
Late Winter ◽  
Stratospheric Warming ◽  
Sudden Stratospheric Warming ◽  
Absorption Data ◽  
Average Value

Abstract. Using absorption data measured by imaging riometer for ionospheric studies (IRIS) located at the South Africa National Antarctic Expedition (SANAE), Antarctica (72° S, 3° W), we extracted the parameters of gravity waves (GW) of periods between 40 and 50 min during late winter/spring of the year 2002, a period of the unprecedented major sudden stratospheric warming (SSW) in the Southern Hemisphere middle atmosphere. During this period, an unprecedented substantial increase of temperature by about 25–30 K throughout the stratosphere was observed. During the period of the occurrence of the major stratospheric warming, there was a reduction of both the GW horizontal phase speeds and the horizontal wavelengths at 90 km. The GW phase speeds and horizontal wavelengths were observed to reach minimum values of about 7 m s−1 and 19 km, respectively, while during the quiet period the average value of the phase speed and horizontal wavelength was approximately 23 m s−1 and 62 km, respectively. The observed event is discussed in terms of momentum flux and also a potential interaction of gravity waves, planetary waves and mean circulation.

scholarly journals Momentum and Energy Transport by Gravity Waves in Stochastically Driven Stratified Flows. Part II: Radiation of Gravity Waves from a Gaussian Jet

2008 ◽  
Vol 65 (7) ◽  
pp. 2308-2325 ◽  
Author(s):  
Nikolaos A. Bakas ◽  
Brian F. Farrell
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Energy Transport ◽  
Middle Atmosphere ◽  
Wave Spectrum ◽  
Flux Divergence ◽  
Stochastic Forcing ◽  
Forced Waves ◽  
Horizontal Wavelength ◽  
Wave Momentum

Abstract Interaction between the midlatitude jet and gravity waves is examined, focusing on the nonnormality of the underlying linear dynamics, which plays an essential role in processing the wave activity and selecting structures that dominate wave momentum and energy transport. When the interior of a typical midlatitude jet is stochastically forced, waves with short horizontal wavelength are trapped inside the jet and deposit momentum and energy at jet interior critical levels. Longer waves transport momentum and energy away from the jet, and the resulting momentum flux divergence produces a significant deceleration of the tropospheric and lower-stratospheric jet. This induced drag is found to depend on the shape of the jet and on the horizontal wavelength of the excited waves, reaching a maximum at wavelength λx = 20 km and leading to a deceleration O(1) m s−1 day−1 for a stochastic forcing rate of 0.1 W m−2 distributed over the height of the jet. This deceleration is robust to changes in static stability but is reduced when the stochastic forcing is correlated over too long a time. Implications of gravity wave absorption for middle-atmosphere circulation are discussed, focusing on differences implied for acceleration of the winter and summer midlatitude upper-stratospheric jets. The tropospheric flow is found not only to passively filter transiting waves, but also to amplify portions of the wave spectrum in conjunction with the distributed forcing, leading to enhanced gravity wave momentum and energy fluxes in agreement with observations linking middle-atmosphere enhanced variance with regions of high jet velocities.

scholarly journals Gravity wave exclusion circles in background flows modulated by the semidiurnal tide

1996 ◽  
Vol 14 (5) ◽  
pp. 557-565 ◽  
Author(s):  
L. Zhong ◽  
A. H. Manson ◽  
L. J. Sonmor ◽  
C. E. Meek
Keyword(s):  
Gravity Waves ◽  
Middle Atmosphere ◽  
Phase Speed ◽  
Realistic Model ◽  
Short Paper ◽  
Time Varying ◽  
Semidiurnal Tide ◽  
Directional Filtering ◽  
Propagating Waves ◽  
Stratospheric Wind

Abstract. In this short paper the exclusion circles and vertical phase locities for gravity waves launched from the ground into a time-varying wind are studied using a ray-tracing technique. It is shown that waves with initial observed phase speeds that should place them within the local temporally varying exclusion circle, are often Doppler shifted outside of the circle. This, and the finite lifetime of some critical levels, allow waves to survive the critical layer and reach higher altitudes. Also, for slower phase-speed waves, the temporally varying wind can shift the observed frequency to negative values, so that the observed phase motions will be opposite (i.e. horizontally reversed and vertically upward), even though the energy still propagates upward. This effect can also cause the phase velocity to move inside the local exclusion circle. Due to the directional filtering of wave sources by the stratospheric wind, the percentage of such reverse-propagating waves will change systematically with local time and height in our simplified but realistic model. These results are related to ground-based systems, optical and radar, which sample the wind field and gravity waves in the middle atmosphere.

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