scholarly journals Evidence for tropospheric wind shear excitation of high-phase-speed gravity waves reaching the mesosphere using the ray-tracing technique

2015 ◽  
Vol 15 (5) ◽  
pp. 2709-2721 ◽  
Author(s):  
M. Pramitha ◽  
M. Venkat Ratnam ◽  
A. Taori ◽  
B. V. Krishna Murthy ◽  
D. Pallamraju ◽  
...  
Keyword(s):  
Ray Tracing ◽  
Gravity Waves ◽  
High Frequency ◽  
Phase Speed ◽  
Horizontal Wind ◽  
Climatological Model ◽  
Background Temperature ◽  
The Waves ◽  
High Phase ◽  
Mf Radar

Abstract. Sources and propagation characteristics of high-frequency gravity waves observed in the mesosphere using airglow emissions from Gadanki (13.5° N, 79.2° E) and Hyderabad (17.5° N, 78.5° E) are investigated using reverse ray tracing. Wave amplitudes are also traced back, including both radiative and diffusive damping. The ray tracing is performed using background temperature and wind data obtained from the MSISE-90 and HWM-07 models, respectively. For the Gadanki region, the suitability of these models is tested. Further, a climatological model of the background atmosphere for the Gadanki region has been developed using nearly 30 years of observations available from a variety of ground-based (MST radar, radiosondes, MF radar) and rocket- and satellite-borne measurements. ERA-Interim products are utilized for constructing background parameters corresponding to the meteorological conditions of the observations. With the reverse ray-tracing method, the source locations for nine wave events could be identified to be in the upper troposphere, whereas for five other events the waves terminated in the mesosphere itself. Uncertainty in locating the terminal points of wave events in the horizontal direction is estimated to be within 50–100 km and 150–300 km for Gadanki and Hyderabad wave events, respectively. This uncertainty arises mainly due to non-consideration of the day-to-day variability in the tidal amplitudes. Prevailing conditions at the terminal points for each of the 14 events are provided. As no convection in and around the terminal points is noticed, convection is unlikely to be the source. Interestingly, large (~9 m s−1km−1) vertical shears in the horizontal wind are noticed near the ray terminal points (at 10–12 km altitude) and are thus identified to be the source for generating the observed high-phase-speed, high-frequency gravity waves.

scholarly journals Identification of gravity wave sources using reverse ray tracing over Indian region

2014 ◽  
Vol 14 (13) ◽  
pp. 19587-19623 ◽  
Author(s):  
M. Pramitha ◽  
M. Venkat Ratnam ◽  
A. Taori ◽  
B. V. Krishna Murthy ◽  
D. Pallamraju ◽  
...  
Keyword(s):  
Ray Tracing ◽  
Gravity Waves ◽  
Indian Region ◽  
Vertical Shear ◽  
Horizontal Wind ◽  
Ray Method ◽  
Climatological Model ◽  
Background Temperature ◽  
Atmospheric Inputs ◽  
First Time

Abstract. Reverse ray tracing method is successfully implemented for the first time in the Indian region for identification of the sources and propagation characteristics of the gravity waves observed using airglow emissions from Gadanki (13.5° N, 79.2° E) and Hyderabad (17.5° N, 78.5° E). Wave amplitudes are also traced back for these wave events by including both radiative and diffusive damping. Background temperature and wind data obtained from MSISE-90 and HWM-07 models, respectively, are used for the ray tracing. For Gadanki region suitability of these models is tested. Further, a climatological model of background atmosphere for Gadanki region has been developed using a long-term of nearly 30 years of observations available from a variety of ground-based (MST radar, radiosonde, MF radar), rocket-, and satellite-borne measurements. For considering real-time atmospheric inputs, ERA-Interim products are utilized. By this reverse ray method, the source locations for nine wave events could be identified to be in the upper troposphere, whereas, for five other events the waves seem to have been ducted in the mesosphere itself. Uncertainty in locating the terminal points in the horizontal direction is estimated to be within 50–100 and 150–300 km for Gadanki and Hyderabad wave events, respectively. This uncertainty arises mainly due to non-consideration of the day-to-day variability in tidal amplitudes. As no convection in-and-around the terminal points are noticed, it is unlikely to be the source. Interestingly, large (~9 m s−1 km−1) vertical shear in the horizontal wind is noted near the ray terminal points (at 10–12 km altitude) and is identified to be the source for generating the nine wave events. Conditions prevailing at the terminal points for each of the 14 events are also provided. These events provide leads to a greater understanding of the tropical lower and upper atmospheric coupling through gravity waves.

scholarly journals Investigation of sources of gravity waves observed in the Brazilian equatorial region on 8 April 2005

2020 ◽  
Vol 38 (2) ◽  
pp. 507-516 ◽  
Author(s):  
Oluwakemi Dare-Idowu ◽  
Igo Paulino ◽  
Cosme A. O. B. Figueiredo ◽  
Amauri F. Medeiros ◽  
Ricardo A. Buriti ◽  
...  
Keyword(s):  
Ray Tracing ◽  
Gravity Waves ◽  
Spectral Characteristics ◽  
Phase Speed ◽  
Radar Data ◽  
Equatorial Region ◽  
Horizontal Wind ◽  
Naval Research ◽  
Wind Profiles ◽  
The Waves

Abstract. On 8 April 2005, strong gravity wave (GW) activity (over a period of more than 3 h) was observed in São João do Cariri (7.4∘ S, 36.5∘ W). These waves propagated to the southeast and presented different spectral characteristics (wavelength, period and phase speed). Using hydroxyl (OH) airglow images, the characteristics of the observed GWs were calculated; the wavelengths ranged between 90 and 150 km, the periods ranged from ∼26 to 67 min and the phase speeds ranged from 32 to 71 m s−1. A reverse ray-tracing analysis was performed to search for the possible sources of the waves that were detected. The ray-tracing database was composed of temperature profiles from the Naval Research Laboratory Mass Spectrometer Incoherent Scatter (NRLMSISE-00) model and SABER measurements as well as wind profiles from the Horizontal Wind Model (HWM) and meteor radar data. According to the ray tracing result, the likely source of these observed gravity waves was the Intertropical Convergence Zone, which caused intense convective processes to take place in the northern part of the observatory. Also, the observed preferential propagation direction of the waves to the southeast could be explained using blocking diagrams, i.e. due to the wind filtering process.

scholarly journals Investigation of sources of gravity waves observed in the Brazilian Equatorial region on 08 April 2005

2019 ◽  
Author(s):  
Oluwakemi Dare-Idowu ◽  
Igo Paulino ◽  
Cosme A. O. B. Figueiredo ◽  
Amauri F. Medeiros ◽  
Ricardo A. Buriti ◽  
...  
Keyword(s):  
Ray Tracing ◽  
Gravity Waves ◽  
Spectral Characteristics ◽  
Phase Speed ◽  
Radar Data ◽  
Equatorial Region ◽  
Inter Tropical Convergence Zone ◽  
Wind Profiles ◽  
Ray Path ◽  
The Waves

Abstract. On 08 April 2005, a strong gravity wave activity (more than 3 hours) was observed in São João do Cariri (7.4° S, 36.5° W). These waves propagated to the southeast and presented different spectral characteristics (wavelength, period and phase speed). Using OH airglow images, the parameters of 5 observed gravity waves were calculated; the wavelengths ranged from ~ 90 to 150 km, the periods from ~ 26 to 67 min and the phase speeds from 32 to 71 m/s. A reserve ray-tracing analysis was performed to investigate the likely sources of these waves. The ray-tracing database was composed of temperature profiles from NRLMSISE-00 model and SABER measurements and wind profiles from HWM-14 model and meteor radar data. According to the ray path, the likely source of these gravity waves was the Inter Tropical Convergence Zone with intense convective processes taking place in the northern part of the observatory. Also, the observed preferential propagation direction of the waves to the southeast could be explained using blocking diagrams, i.e., due to the wind filtering process.

scholarly journals Mesospheric gravity waves observed near equatorial and low–middle latitude stations: wave characteristics and reverse ray tracing results

2006 ◽  
Vol 24 (12) ◽  
pp. 3229-3240 ◽  
Author(s):  
C. M. Wrasse ◽  
T. Nakamura ◽  
H. Takahashi ◽  
A. F. Medeiros ◽  
M. J. Taylor ◽  
...  
Keyword(s):  
Ray Tracing ◽  
Gravity Wave ◽  
Gravity Waves ◽  
Source Region ◽  
Phase Speed ◽  
Middle Latitude ◽  
Wave Source ◽  
Middle Latitudes ◽  
Summer Time ◽  
The Waves

Abstract. Gravity wave signatures were extracted from OH airglow observations using all-sky CCD imagers at four different stations: Cachoeira Paulista (CP) (22.7° S, 45° W) and São João do Cariri (7.4° S, 36.5° W), Brazil; Tanjungsari (TJS) (6.9° S, 107.9° E), Indonesia and Shigaraki (34.9° N, 136° E), Japan. The gravity wave parameters are used as an input in a reverse ray tracing model to study the gravity wave vertical propagation trajectory and to estimate the wave source region. Gravity waves observed near the equator showed a shorter period and a larger phase velocity than those waves observed at low-middle latitudes. The waves ray traced down into the troposphere showed the largest horizontal wavelength and phase speed. The ray tracing results also showed that at CP, Cariri and Shigaraki the majority of the ray paths stopped in the mesosphere due to the condition of m2<0, while at TJS most of the waves are traced back into the troposphere. In summer time, most of the back traced waves have their final position stopped in the mesosphere due to m2<0 or critical level interactions (|m|→∞), which suggests the presence of ducting waves and/or waves generated in-situ. In the troposphere, the possible gravity wave sources are related to meteorological front activities and cloud convections at CP, while at Cariri and TJS tropical cloud convections near the equator are the most probable gravity wave sources. The tropospheric jet stream and the orography are thought to be the major responsible sources for the waves observed at Shigaraki.

scholarly journals Frequency variations of gravity waves interacting with a time-varying tide

2013 ◽  
Vol 31 (10) ◽  
pp. 1731-1743 ◽  
Author(s):  
C. M. Huang ◽  
S. D. Zhang ◽  
F. Yi ◽  
K. M. Huang ◽  
Y. H. Zhang ◽  
...  
Keyword(s):  
Gravity Waves ◽  
High Frequency ◽  
Lower Atmosphere ◽  
Horizontal Wind ◽  
Frequency Variation ◽  
Time Varying ◽  
Transient Nature ◽  
Critical Layers ◽  
Favorable Conditions ◽  
Frequency Variations

Abstract. Using a nonlinear, 2-D time-dependent numerical model, we simulate the propagation of gravity waves (GWs) in a time-varying tide. Our simulations show that when a GW packet propagates in a time-varying tidal-wind environment, not only its intrinsic frequency but also its ground-based frequency would change significantly. The tidal horizontal-wind acceleration dominates the GW frequency variation. Positive (negative) accelerations induce frequency increases (decreases) with time. More interestingly, tidal-wind acceleration near the critical layers always causes the GW frequency to increase, which may partially explain the observations that high-frequency GW components are more dominant in the middle and upper atmosphere than in the lower atmosphere. The combination of the increased ground-based frequency of propagating GWs in a time-varying tidal-wind field and the transient nature of the critical layer induced by a time-varying tidal zonal wind creates favorable conditions for GWs to penetrate their originally expected critical layers. Consequently, GWs have an impact on the background atmosphere at much higher altitudes than expected, which indicates that the dynamical effects of tidal–GW interactions are more complicated than usually taken into account by GW parameterizations in global models.

scholarly journals Seasonal and intra-diurnal variability of small-scale gravity waves in OH airglow at two Alpine stations

2019 ◽  
Vol 12 (1) ◽  
pp. 457-469 ◽  
Author(s):  
Patrick Hannawald ◽  
Carsten Schmidt ◽  
René Sedlak ◽  
Sabine Wüst ◽  
Michael Bittner
Keyword(s):  
Gravity Waves ◽  
High Frequency ◽  
Phase Speed ◽  
Propagation Direction ◽  
Field Of View ◽  
Small Scale ◽  
Data Sets ◽  
Data Set ◽  
Diurnal Variability ◽  
Fully Automatic

Abstract. Between December 2013 and August 2017 the instrument FAIM (Fast Airglow IMager) observed the OH airglow emission at two Alpine stations. A year of measurements was performed at Oberpfaffenhofen, Germany (48.09∘ N, 11.28∘ E) and 2 years at Sonnblick, Austria (47.05∘ N, 12.96∘ E). Both stations are part of the network for the detection of mesospheric change (NDMC). The temporal resolution is two frames per second and the field-of-view is 55 km × 60 km and 75 km × 90 km at the OH layer altitude of 87 km with a spatial resolution of 200 and 280 m per pixel, respectively. This resulted in two dense data sets allowing precise derivation of horizontal gravity wave parameters. The analysis is based on a two-dimensional fast Fourier transform with fully automatic peak extraction. By combining the information of consecutive images, time-dependent parameters such as the horizontal phase speed are extracted. The instrument is mainly sensitive to high-frequency small- and medium-scale gravity waves. A clear seasonal dependency concerning the meridional propagation direction is found for these waves in summer in the direction to the summer pole. The zonal direction of propagation is eastwards in summer and westwards in winter. Investigations of the data set revealed an intra-diurnal variability, which may be related to tides. The observed horizontal phase speed and the number of wave events per observation hour are higher in summer than in winter.

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 Short vertical-wavelength inertia-gravity waves generated by a jet–front system at Arctic latitudes – VHF radar, radiosondes and numerical modelling

2014 ◽  
Vol 14 (13) ◽  
pp. 6785-6799 ◽  
Author(s):  
A. Réchou ◽  
S. Kirkwood ◽  
J. Arnault ◽  
P. Dalin
Keyword(s):  
Gravity Waves ◽  
Potential Temperature ◽  
Wrf Model ◽  
Horizontal Wind ◽  
Buoyancy Frequency ◽  
Vertical Wavelength ◽  
Vhf Radar ◽  
The Waves ◽  
Inertia Gravity Waves ◽  
Good Agreement

Abstract. Inertia-gravity waves with very short vertical wavelength (λz≤1000 m) are a very common feature of the lowermost stratosphere as observed by the 52 MHz radar ESRAD (Esrange MST radar) in northern Scandinavia (67.88° N, 21.10° E). The waves are seen most clearly in radar-derived profiles of buoyancy frequency (N). Here, we present a case study of typical waves from 21 February to 22 February 2007. Good agreement between N2 derived from radiosondes and by radar shows the validity of the radar determination of N2. Large-amplitude wave signatures in N2 are clearly observed by the radar and the radiosondes in the lowermost stratosphere, from 9 km to 14–16 km height. Vertical profiles of horizontal wind components and potential temperature from the radiosondes show the same waves. Mesoscale simulations with the Weather Research and Forecasting (WRF) model are carried out to complement the analysis of the waves. Good agreement between the radar and radiosonde measurements and the model (except for the wave amplitude) shows that the model gives realistic results and that the waves are closely associated to the upper-level front in an upper-troposphere jet–front system. Hodographs of the wind fluctuations from the radiosondes and model data show that the waves propagate upward in the lower stratosphere confirming that the origin of the waves is in the troposphere. The observations and modelling all indicate vertical wavelengths of 700 ± 200 m. The radiosonde hodograms indicate horizontal wavelengths between 40 and 110 km and intrinsic periods between 6 and 9 h. The wave amplitudes indicated by the model are however an order of magnitude less than in the observations. Finally, we show that the profiles of N2 measured by the radar can be used to estimate wave amplitudes, horizontal wavelengths, intrinsic periods and momentum fluxes which are consistent with the estimates from the radiosondes.

scholarly journals Seasonal and intra-diurnal variability of small-scale gravity waves in OH airglow at two Alpine stations

2018 ◽  
Author(s):  
Patrick Hannawald ◽  
Carsten Schmidt ◽  
René Sedlak ◽  
Sabine Wüst ◽  
Michael Bittner
Keyword(s):  
Gravity Waves ◽  
High Frequency ◽  
Phase Speed ◽  
Propagation Direction ◽  
Field Of View ◽  
Small Scale ◽  
Data Set ◽  
Diurnal Variability ◽  
Fully Automatic ◽  
One Year

Abstract. Between December 2013 and August 2017 the instrument FAIM (Fast Airglow IMager) observed the OH airglow emission at two Alpine stations. One year of measurements was performed at Oberpfaffenhofen, Germany (48.09° N, 11.28° E) and two years at Sonnblick, Austria (47.05° N, 12.96° E). Both stations are part of the Network for the detection of mesospheric change (NDMC). The temporal resolution is two frames per second and the field of view is 55 km × 60 km and 75 km × 90 km at the OH layer altitude of 87 km with a spatial resolution of 200 m and 280 m per pixel, respectively. This results in two dense datasets allowing precise derivation of horizontal gravity wave parameters. The analysis is based on a two-dimensional Fast Fourier Transform with fully automatic peak extraction. By combining the information of consecutive images time-dependent parameters such as the horizontal phase speed are extracted. The instrument is mainly sensitive to high-frequency small- and medium-scale gravity waves. A clear seasonal dependency concerning the meridional propagation direction is found for these waves in summer in direction to the summer pole. The zonal direction of propagation is eastwards in summer and westwards in winter. Investigations of the data set revealed an intra-diurnal variability, which may be related to tides. The observed horizontal phase speed and the number of wave events per observation hour are higher in summer than in winter.

scholarly journals Propagation of gravity waves and its effects on pseudomomentum flux in a sudden stratospheric warming event

2020 ◽  
Vol 20 (12) ◽  
pp. 7617-7644
Author(s):  
In-Sun Song ◽  
Changsup Lee ◽  
Hye-Yeong Chun ◽  
Jeong-Han Kim ◽  
Geonhwa Jee ◽  
...  
Keyword(s):  
Ray Tracing ◽  
Gravity Waves ◽  
Lower Thermosphere ◽  
Upper Atmosphere ◽  
Lower Atmosphere ◽  
Wave Number ◽  
Horizontal Wind ◽  
Stratospheric Warming ◽  
Sudden Stratospheric Warming ◽  
Curvature Effects

Abstract. Effects of realistic propagation of gravity waves (GWs) on distribution of GW pseudomomentum fluxes are explored using a global ray-tracing model for the 2009 sudden stratospheric warming (SSW) event. Four-dimensional (4D; x–z and t) and two-dimensional (2D; z and t) results are compared for various parameterized pseudomomentum fluxes. In ray-tracing equations, refraction due to horizontal wind shear and curvature effects are found important and comparable to one another in magnitude. In the 4D, westward pseudomomentum fluxes are enhanced in the upper troposphere and northern stratosphere due to refraction and curvature effects around fluctuating jet flows. In the northern polar upper mesosphere and lower thermosphere, eastward pseudomomentum fluxes are increased in the 4D. GWs are found to propagate more to the upper atmosphere in the 4D, since horizontal propagation and change in wave numbers due to refraction and curvature effects can make it more possible that GWs elude critical level filtering and saturation in the lower atmosphere. GW focusing effects occur around jet cores, and ray-tube effects appear where the polar stratospheric jets vary substantially in space and time. Enhancement of the structure of zonal wave number 2 in pseudomomentum fluxes in the middle stratosphere begins from the early stage of the SSW evolution. An increase in pseudomomentum fluxes in the upper atmosphere is present even after the onset in the 4D. Significantly enhanced pseudomomentum fluxes, when the polar vortex is disturbed, are related to GWs with small intrinsic group velocity (wave capture), and they would change nonlocally nearby large-scale vortex structures without substantially changing local mean flows.

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