Gravity Wave Investigations over Comandante Ferraz Antarctic Station in 2017: General Characteristics, Wind Filtering and Case Study

This work presents the characteristics of gravity waves observed over Comandante Ferraz Antarctic Station (EACF: 62.1° S, 58.4° W). A total of 122 gravity waves were observed in 34 nights from March to October 2017, and their parameters were obtained by using the Fourier Transform spectral analysis. The majority of the observed waves presented horizontal wavelength ranging from 15 to 35 km, period from 5 to 20 min, and horizontal phase speed from 10 to 70 ± 2 m·s−1. The propagation direction showed an anisotropic condition, with the slower wave propagating mainly to the west, northwest and southeast directions, while the faster waves propagate to the east, southeast and south. Blocking diagrams for the period of April–July showed a good agreement between the wave propagation direction and the blocking positions, which are eastward oriented while the waves propagate mainly westward. A case study to investigate wave sources was conducted for the night of 20–21 July, wherein eight small-scale and one medium-scale gravity waves were identified. Reverse ray tracing model was used to investigate the gravity wave source, and the results showed that six among eight small-scale gravity waves were generated in the mesosphere. On the other hand, only two small-scale waves and the medium-scale gravity wave had likely tropospheric or stratospheric origin, however, they could not be associated with any reliable source.

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

Atmospheric Measurement Techniques ◽

10.5194/amt-12-457-2019 ◽

2019 ◽

Vol 12 (1) ◽

pp. 457-469 ◽

Cited By ~ 2

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.

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Gravity wave transmission diagram

Annales Geophysicae ◽

10.5194/angeo-33-1479-2015 ◽

2015 ◽

Vol 33 (12) ◽

pp. 1479-1484 ◽

Cited By ~ 5

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.

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

10.5194/amt-2018-322 ◽

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.

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Seasonal characteristics of small- and medium-scale gravity waves in the mesosphere and lower thermosphere over the Brazilian equatorial region

Annales Geophysicae ◽

10.5194/angeo-36-899-2018 ◽

2018 ◽

Vol 36 (3) ◽

pp. 899-914 ◽

Cited By ~ 3

Author(s):

Patrick Essien ◽

Igo Paulino ◽

Cristiano Max Wrasse ◽

Jose Andre V. Campos ◽

Ana Roberta Paulino ◽

...

Keyword(s):

Gravity Waves ◽

Source Region ◽

Lower Thermosphere ◽

Atmospheric Composition ◽

Small Scale ◽

Wave Source ◽

Medium Scale ◽

Seasonal Characteristics ◽

Mesosphere And Lower Thermosphere ◽

The Waves

Abstract. The present work reports seasonal characteristics of small- and medium-scale gravity waves in the mesosphere and lower thermosphere (MLT) region. All-sky images of the hydroxyl (NIR-OH) airglow emission layer over São João do Cariri (7.4∘ S, 36.5∘ W; hereafter Cariri) were obtained from September 2000 to December 2010, during a total of 1496 nights. For investigation of the characteristics of small-scale gravity waves (SSGWs) and medium-scale gravity waves (MSGWs), we employed the Fourier two-dimensional (2-D) spectrum and keogram fast Fourier transform (FFT) techniques, respectively. From the 11 years of data, we could observe 2343 SSGW and 537 MSGW events. The horizontal wavelengths of the SSGWs were concentrated between 10 and 35 km, while those of the MSGWs ranged from 50 to 200 km. The observed periods for SSGWs were concentrated around 5 to 20 min, whereas the MSGWs ranged from 20 to 60 min. The observed horizontal phase speeds of SSGWs were distributed around 10 to 60 m s−1, and the corresponding MSGWs were around 20 to 120 m s−1. In summer, autumn, and winter both SSGWs and MSGWs propagated preferentially northeastward and southeastward, while in spring the waves propagated in all directions. The critical level theory of atmospheric gravity waves (AGWs) was applied to study the effects of wind filtering on SSGW and MSGW propagation directions. The SSGWs were more susceptible to wind filtering effects than MSGWs. The average of daily mean outgoing longwave radiation (OLR) was also used to investigate the possible wave source region in the troposphere. The results showed that in summer and autumn, deep convective regions were the possible source mechanism of the AGWs. However, in spring and winter the deep convective regions did not play an important role in the waves observed at Cariri, because they were too far away from the observatory. Therefore, we concluded that the horizontal propagation directions of SSGWs and MSGWs show clear seasonal variations based on the influence of the wind filtering process and wave source location. Keywords. Atmospheric composition and structure (airglow and aurora) – electromagnetics (wave propagation) – history of geophysics (atmospheric sciences)

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

Annales Geophysicae ◽

10.5194/angeo-24-3229-2006 ◽

2006 ◽

Vol 24 (12) ◽

pp. 3229-3240 ◽

Cited By ~ 19

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.

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Gravity wave penetration into the thermosphere: sensitivity to solar cycle variations and mean winds

Annales Geophysicae ◽

10.5194/angeo-26-3841-2008 ◽

2008 ◽

Vol 26 (12) ◽

pp. 3841-3861 ◽

Cited By ~ 80

Author(s):

D. C. Fritts ◽

S. L. Vadas

Keyword(s):

Solar Cycle ◽

Gravity Wave ◽

Gravity Waves ◽

Spatial Scales ◽

Phase Speed ◽

Wave Structure ◽

Lower Atmosphere ◽

Viscous Effects ◽

Wave Source ◽

Wave Phase

Abstract. We previously considered various aspects of gravity wave penetration and effects at mesospheric and thermospheric altitudes, including propagation, viscous effects on wave structure, characteristics, and damping, local body forcing, responses to solar cycle temperature variations, and filtering by mean winds. Several of these efforts focused on gravity waves arising from deep convection or in situ body forcing accompanying wave dissipation. Here we generalize these results to a broad range of gravity wave phase speeds, spatial scales, and intrinsic frequencies in order to address all of the major gravity wave sources in the lower atmosphere potentially impacting the thermosphere. We show how penetration altitudes depend on gravity wave phase speed, horizontal and vertical wavelengths, and observed frequencies for a range of thermospheric temperatures spanning realistic solar conditions and winds spanning reasonable mean and tidal amplitudes. Our results emphasize that independent of gravity wave source, thermospheric temperature, and filtering conditions, those gravity waves that penetrate to the highest altitudes have increasing vertical wavelengths and decreasing intrinsic frequencies with increasing altitude. The spatial scales at the highest altitudes at which gravity wave perturbations are observed are inevitably horizontal wavelengths of ~150 to 1000 km and vertical wavelengths of ~150 to 500 km or more, with the larger horizontal scales only becoming important for the stronger Doppler-shifting conditions. Observed and intrinsic periods are typically ~10 to 60 min and ~10 to 30 min, respectively, with the intrinsic periods shorter at the highest altitudes because of preferential penetration of GWs that are up-shifted in frequency by thermospheric winds.

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Characteristics of mesospheric gravity waves near the magnetic equator, Brazil, during the SpreadFEx campaign

Annales Geophysicae ◽

10.5194/angeo-27-461-2009 ◽

2009 ◽

Vol 27 (2) ◽

pp. 461-472 ◽

Cited By ~ 48

Author(s):

M. J. Taylor ◽

P.-D. Pautet ◽

A. F. Medeiros ◽

R. Buriti ◽

J. Fechine ◽

...

Keyword(s):

Gravity Wave ◽

Gravity Waves ◽

Magnetic Equator ◽

Small Scale ◽

Medium Scale ◽

Source Regions ◽

High Quality Image ◽

Short Period ◽

Spread F ◽

Radio Measurements

Abstract. As part of the SpreadFEx campaign, coordinated optical and radio measurements were made from Brazil to investigate the occurrence and properties of equatorial Spread F, and to characterize the regional mesospheric gravity wave field. All-sky image measurements were made from two sites: Brasilia and Cariri located ~10° S of the magnetic equator and separated by ~1500 km. In particular, the observations from Brasilia provided key data in relatively close proximity to expected convective sources of the gravity waves. High-quality image measurements of the mesospheric OH emission and the thermospheric OI (630 nm) emission were made during two consecutive new moon periods (22 September to 9 November 2005) providing extensive data on the occurrence and properties of F-region depletions and regional measurements of the dominant gravity wave characteristics at each site. A total of 120 wave displays were observed, comprising 94 short-period events and 26 medium-scale gravity waves. The characteristics of the small-scale waves agreed well with previous gravity wave studies from Brazil and other sites. However, significant differences in the wave propagation headings indicate dissimilar source regions for the Brasilia and Cariri datasets. The observed medium-scale gravity wave events constitute an important new dataset to study their mesospheric properties at equatorial latitudes. These data exhibited similar propagation headings to the short-period events, suggesting they originated from the same source regions. Medium-scale waves are generally less susceptible to wind filtering effects and modeling studies utilizing these data have successfully identified localized regions of strong convection, mainly to the west of Brasilia, as their most likely sources (Vadas et al., 2009).

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Observation of mesospheric gravity waves at Comandante Ferraz Antarctica Station (62° S)

Annales Geophysicae ◽

10.5194/angeo-27-2593-2009 ◽

2009 ◽

Vol 27 (6) ◽

pp. 2593-2598 ◽

Cited By ~ 16

Author(s):

J. V. Bageston ◽

C. M. Wrasse ◽

D. Gobbi ◽

H. Takahashi ◽

P. B. Souza

Keyword(s):

Gravity Waves ◽

Weather Conditions ◽

Propagation Direction ◽

Cyclonic Activity ◽

Wave Source ◽

Cold Fronts ◽

Wave Velocities ◽

Orographic Forcing ◽

Sky Imager ◽

The Waves

Abstract. An airglow all-sky imager was operated at Comandante Ferraz Antarctica Station (62.1° S, 58.4° W), between April and October of 2007. Mesospheric gravity waves were observed using the OH airglow layer during 43 nights with good weather conditions. The waves presented horizontal wavelengths between 10 and 60 km and observed periods mainly distributed between 5 and 20 min. The observed phase speeds range between 5 m/s and 115 m/s; the majority of the wave velocities were between 10 and 60 m/s. The waves showed a preferential propagation direction towards the southwest in winter (May to July), while during spring (August to October) there was an anisotropy with a preferential propagation direction towards the northwest. Unusual mesospheric fronts were also observed. The most probable wave source could be associated to orographic forcing, cold fronts or strong cyclonic activity in the Antarctica Peninsula.

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Optimization of Gravity Wave Source Parameters for Improved Seasonal Prediction of the Quasi-Biennial Oscillation

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-19-0077.1 ◽

2019 ◽

Vol 76 (9) ◽

pp. 2941-2962

Author(s):

Cory A. Barton ◽

John P. McCormack ◽

Stephen D. Eckermann ◽

Karl W. Hoppel

Keyword(s):

Gravity Wave ◽

Optimal Parameter ◽

Forecast Error ◽

Source Parameters ◽

Phase Speed ◽

Time Interval ◽

Quasi Biennial Oscillation ◽

Wave Source ◽

Forecast Lead Time ◽

Biennial Oscillation

Abstract A methodology is presented for objectively optimizing nonorographic gravity wave source parameters to minimize forecast error for target regions and forecast lead times. In this study, we employ a high-altitude version of the Navy Global Environmental Model (NAVGEM-HA) to ascertain the forcing needed to minimize hindcast errors in the equatorial lower stratospheric zonal-mean zonal winds in order to improve forecasts of the quasi-biennial oscillation (QBO) over seasonal time scales. Because subgrid-scale wave effects play a large role in driving the QBO, this method leverages the nonorographic gravity wave drag (GWD) parameterization scheme to provide the necessary forcing. To better constrain the GWD source parameters, we utilize ensembles of NAVGEM-HA hindcasts over the 2014–16 period with perturbed source parameters and develop a cost function to minimize errors in the equatorial lower stratosphere compared to analysis. Thus, we may determine the set of GWD source parameters that yields a forecast state that most closely agrees with observed QBO winds over each optimization time interval. Results show that the source momentum flux and phase speed spectrum width are the most important parameters. The seasonal evolution of optimal parameter value, specifically a robust semiannual periodicity in the source strength, is also revealed. Changes in optimal source parameters with increasing forecast lead time are seen, as the GWD parameterization takes on a more active role as QBO driver at longer forecast lengths. Implementation of a semiannually varying source function at the equator provides RMS error improvement in QBO winds over the default constant value.

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Numerical Modeling of Nonlinear Interactions of Spectral Components of Acoustic-Gravity Waves in the Middle and Upper Atmosphere

10.5194/egusphere-egu2020-76 ◽

2020 ◽

Author(s):

Nikolai M. Gavrilov ◽

Sergej P. Kshevetskii

Keyword(s):

Gravity Waves ◽

Upper Atmosphere ◽

Jet Flows ◽

Small Scale ◽

Nonlinear Interactions ◽

Mean Flow ◽

Wave Source ◽

Acoustic Gravity Waves ◽

The Mean ◽

Wave Modes

Acoustic-gravity waves (AGWs) measuring at big heights may be generated in the troposphere and propagate upwards. A high-resolution three-dimensional numerical model was developed for simulating nonlinear AGWs propagating from the ground to the upper atmosphere. The model algorithms are based on the finite-difference analogues of the main conservation laws. This methodology let us obtaining the physically correct generalized wave solutions of the nonlinear equations. Horizontally moving sinusoidal structures of vertical velocity on the ground are used for the AGW excitation in the model. Numerical simulations were made in an atmospheric region having horizontal dimensions up to several thousand kilometers and the height extention up to 500 km. Vertical distributions of the mean temperature, density, molecular viscosity and thermal conductivity are specified using standard models of the atmosphere.Simulations were made for different horizontal wavelengths, amplitudes and speeds of the wave sources at the ground. After &#8220;switch on&#8221; the tropospheric wave source, an initial AGW pulse very quickly (for several minutes) could propagate to heights up to 100 km and above. AGW amplitudes increase with height and waves may break down in the middle and upper atmosphere. Wave instability and dissipation may lead to formations of wave accelerations of the mean flow and to producing wave-induced jet flows in the middle and upper atmosphere. Nonlinear interactions may lead to instabilities of the initial wave and to the creation of smaller-scale perturbations. These perturbations may increase temperature and wind gradients and could enhance the wave energy dissipation.In this study, the wave sources contain a superposition of two AGW modes with different periods, wavelengths and phase speeds. Longer-period AGW modes served as the background conditions for the shorter-period wave modes. Thus, the larger-scale AGWs can modulate amplitudes of small-scale waves. In particular, interactions of two wave modes could sharp vertical temperature gradients and make easier the wave breaking and generating&#160; turbulence. On the other hand, small-wave wave modes might increase dissipation and modify the larger-scale modes.This study was partially supported by the Russian Basic Research Foundation (# 17-05-00458).

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