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

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

Atmosphere ◽

10.3390/atmos11080880 ◽

2020 ◽

Vol 11 (8) ◽

pp. 880

Author(s):

Gabriel Augusto Giongo ◽

José Valentin Bageston ◽

Cosme Alexandre Oliveira Barros Figueiredo ◽

Cristiano Max Wrasse ◽

Hosik Kam ◽

...

Keyword(s):

Gravity Wave ◽

Gravity Waves ◽

Phase Speed ◽

Propagation Direction ◽

Small Scale ◽

Wave Source ◽

Medium Scale ◽

Reliable Source ◽

The Fourier Transform

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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Atmospheric general circulation and waves simulated by a Venus AORI GCM with topographical and radiative forcings

10.5194/egusphere-egu21-3657 ◽

2021 ◽

Author(s):

Masaru Yamamoto ◽

Takumi Hirose ◽

Kohei Ikeda ◽

Masaaki Takahashi

Keyword(s):

Gravity Waves ◽

General Circulation ◽

Circulation Model ◽

Stationary Wave ◽

Static Stability ◽

Small Scale ◽

Mean Flow ◽

Short Period ◽

Low Latitudes ◽

Thermal Tides

General circulation and waves are investigated using a T63 Venus general circulation model (GCM) with solar and thermal radiative transfer in the presence of high-resolution surface topography. This model has been developed by Ikeda (2011) at the Atmosphere and Ocean Research Institute (AORI), the University of Tokyo, and was used in Yamamoto et al. (2019, 2021). In the wind and static stability structures similar to the observed ones, the waves are investigated. Around the cloud-heating maximum (~65 km), the simulated thermal tides accelerate an equatorial superrotational flow with a speed of ~90 m/swith rates of 0.2&#8211;0.5 m/s/(Earth day) via both horizontal and vertical momentum fluxes at low latitudes. Over the high mountains at low latitudes, the vertical wind variance at the cloud top is produced by topographically-fixed, short-period eddies, indicating penetrative plumes and gravity waves. In the solar-fixed coordinate system, the variances (i.e., the activity of waves other than thermal tides) of flow are relatively higher on the night-side than on the dayside at the cloud top. The local-time variation of the vertical eddy momentum flux is produced by both thermal tides and solar-related, small-scale gravity waves. Around the cloud bottom, the 9-day super-rotation of the zonal mean flow has a weak equatorial maximum and the 7.5-day Kelvin-like wave has an equatorial jet-like wind of 60-70 m/s. Because we discussed the thermal tide and topographically stationary wave in Yamamoto et al. (2021), we focus on the short-period eddies in the presentation.

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Stratospheric gravity waves at Southern Hemisphere orographic hotspots: 2003–2014 AIRS/Aqua observations

Atmospheric Chemistry and Physics ◽

10.5194/acp-16-9381-2016 ◽

2016 ◽

Vol 16 (14) ◽

pp. 9381-9397 ◽

Cited By ~ 30

Author(s):

Lars Hoffmann ◽

Alison W. Grimsdell ◽

M. Joan Alexander

Keyword(s):

Gravity Wave ◽

Southern Hemisphere ◽

Antarctic Peninsula ◽

Gravity Waves ◽

General Circulation ◽

Wave Activity ◽

Small Scale ◽

Mountain Wave ◽

Kerguelen Islands ◽

The Antarctic

Abstract. Stratospheric gravity waves from small-scale orographic sources are currently not well-represented in general circulation models. This may be a reason why many simulations have difficulty reproducing the dynamical behavior of the Southern Hemisphere polar vortex in a realistic manner. Here we discuss a 12-year record (2003–2014) of stratospheric gravity wave activity at Southern Hemisphere orographic hotspots as observed by the Atmospheric InfraRed Sounder (AIRS) aboard the National Aeronautics and Space Administration's (NASA) Aqua satellite. We introduce a simple and effective approach, referred to as the “two-box method”, to detect gravity wave activity from infrared nadir sounder measurements and to discriminate between gravity waves from orographic and other sources. From austral mid-fall to mid-spring (April–October) the contributions of orographic sources to the observed gravity wave occurrence frequencies were found to be largest for the Andes (90 %), followed by the Antarctic Peninsula (76 %), Kerguelen Islands (73 %), Tasmania (70 %), New Zealand (67 %), Heard Island (60 %), and other hotspots (24–54 %). Mountain wave activity was found to be closely correlated with peak terrain altitudes, and with zonal winds in the lower troposphere and mid-stratosphere. We propose a simple model to predict the occurrence of mountain wave events in the AIRS observations using zonal wind thresholds at 3 and 750 hPa. The model has significant predictive skill for hotspots where gravity wave activity is primarily due to orographic sources. It typically reproduces seasonal variations of the mountain wave occurrence frequencies at the Antarctic Peninsula and Kerguelen Islands from near zero to over 60 % with mean absolute errors of 4–5 percentage points. The prediction model can be used to disentangle upper level wind effects on observed occurrence frequencies from low-level source and other influences. The data and methods presented here can help to identify interesting case studies in the vast amount of AIRS data, which could then be further explored to study the specific characteristics of stratospheric gravity waves from orographic sources and to support model validation.

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Flexural–Gravity Waves on Floating Stratified Ice

Journal of Glaciology ◽

10.3189/s0022143000005207 ◽

1983 ◽

Vol 29 (101) ◽

pp. 133-141

Author(s):

Edwin S. Robinson

Keyword(s):

Gravity Wave ◽

Gravity Waves ◽

Wave Dispersion ◽

Dispersion Curves ◽

Homogeneous Fluid ◽

Snow Layer ◽

Period Range ◽

Short Period ◽

Flexural Gravity Waves ◽

Flexural Gravity Wave

AbstractFlexural–gravity waves in the 3 ms to 50 ms period range were recorded on floating layers of ice ranging from 6 cm to 52 cm in thickness. These inversely dispersive waves are analogous to Rayleigh waves propagating on a multi-layered structure. Therefore, flexural–gravity wave dispersion curves can be calculated by the well-known Haskell–Thompson method. This approach allows the effects of snow layers and stratification of the ice to be evaluated. In earlier methods of calculating flexural–gravity wave dispersion. the structure was restricted to a single homogeneous solid layer over a homogeneous fluid. The effect of a low-velocity snow layer is to reduce the short-period phase velocity, and to increase the velocity at long periods. Dispersion curves for ice layers with and without a snow cover cross at an intermediate period that increases as ice thickness increases. These effects are measurable in seismic experiments on frozen ponds and lakes.

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Studies on atmospheric gravity wave activity in the troposphere and lower stratosphere over a tropical station at Gadanki

Annales Geophysicae ◽

10.5194/angeo-23-3237-2005 ◽

2005 ◽

Vol 23 (10) ◽

pp. 3237-3260 ◽

Cited By ~ 3

Author(s):

I. V. Subba Reddy ◽

D. Narayana Rao ◽

A. Narendra Babu ◽

M. Venkat Ratnam ◽

P. Kishore ◽

...

Keyword(s):

Gravity Wave ◽

Gravity Waves ◽

Lower Stratosphere ◽

Wave Length ◽

Wave Activity ◽

Lower Atmosphere ◽

Wind Fields ◽

Atmospheric Gravity Wave ◽

Short Period ◽

Atmospheric Gravity

Abstract. MST radars are powerful tools to study the mesosphere, stratosphere and troposphere and have made considerable contributions to the studies of the dynamics of the upper, middle and lower atmosphere. Atmospheric gravity waves play a significant role in controlling middle and upper atmospheric dynamics. To date, frontal systems, convection, wind shear and topography have been thought to be the sources of gravity waves in the troposphere. All these studies pointed out that it is very essential to understand the generation, propagation and climatology of gravity waves. In this regard, several campaigns using Indian MST Radar observations have been carried out to explore the gravity wave activity over Gadanki in the troposphere and the lower stratosphere. The signatures of the gravity waves in the wind fields have been studied in four seasons viz., summer, monsoon, post-monsoon and winter. The large wind fluctuations were more prominent above 10 km during the summer and monsoon seasons. The wave periods are ranging from 10 min-175 min. The power spectral densities of gravity waves are found to be maximum in the stratospheric region. The vertical wavelength and the propagation direction of gravity waves were determined using hodograph analysis. The results show both down ward and upward propagating waves with a maximum vertical wave length of 3.3 km. The gravity wave associated momentum fluxes show that long period gravity waves carry more momentum flux than the short period waves and this is presented.

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Flexural–Gravity Waves on Floating Stratified Ice

Journal of Glaciology ◽

10.1017/s0022143000005207 ◽

1983 ◽

Vol 29 (101) ◽

pp. 133-141 ◽

Cited By ~ 2

Author(s):

Edwin S. Robinson

Keyword(s):

Gravity Wave ◽

Gravity Waves ◽

Wave Dispersion ◽

Dispersion Curves ◽

Homogeneous Fluid ◽

Snow Layer ◽

Period Range ◽

Short Period ◽

Flexural Gravity Waves ◽

Flexural Gravity Wave

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Wind-profiler observations of gravity waves produced by convection at mid-latitudes

Atmospheric Chemistry and Physics ◽

10.5194/acp-6-2825-2006 ◽

2006 ◽

Vol 6 (10) ◽

pp. 2825-2836 ◽

Cited By ~ 8

Author(s):

Y. G. Choi ◽

S. C. Lee ◽

A. J. McDonald ◽

D. A. Hooper

Keyword(s):

Gravity Waves ◽

Vertical Velocity ◽

Small Scale ◽

Wind Profiler ◽

Convective Activity ◽

Velocity Fluctuations ◽

Short Period ◽

Horizontal Momentum ◽

Scale Inhomogeneity

Abstract. This work presents a case study which includes regions of large rapidly varying vertical velocities observed by a VHF wind-profiler at Aberystwyth (52.4° N, 4.1° W). Analysis indicates that this region is associated with gravity waves above the tropopause level and simultaneous regions of convective activity below the tropopause level. This case study also suggests that convective activity can be identified effectively by finding periods of large uncertainties on the derived velocities. These regions are hypothesized to be related to regions of small-scale inhomogeneity in the wind field. Examination suggests that the large vertical velocity fluctuations above these convective regions are short period gravity wave packets as expected from theory. In addition the vertical flux of the horizontal momentum associated with the gravity waves also displays the pattern of reversal observed in previous studies.

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Concurrent observations at the magnetic equator of small-scale irregularities and large-scale depletions associated with equatorial spread F

Journal of Geophysical Research Space Physics ◽

10.1002/2015ja021991 ◽

2015 ◽

Vol 120 (12) ◽

pp. 10,883-10,896 ◽

Cited By ~ 3

Author(s):

Dustin A. Hickey ◽

Carlos R. Martinis ◽

Fabiano S. Rodrigues ◽

Roger H. Varney ◽

Marco A. Milla ◽

...

Keyword(s):

Large Scale ◽

Magnetic Equator ◽

Small Scale ◽

Equatorial Spread F ◽

Spread F

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Diurnal variation of short-period (20–120 min) gravity waves in the equatorial Mesosphere and Lower Thermosphere and its relation to deep tropical convection

Annales Geophysicae ◽

10.5194/angeo-29-623-2011 ◽

2011 ◽

Vol 29 (4) ◽

pp. 623-629 ◽

Cited By ~ 5

Author(s):

N. Venkateswara Rao ◽

Y. Shibagaki ◽

T. Tsuda

Keyword(s):

Gravity Wave ◽

Gravity Waves ◽

Theoretical Calculations ◽

Lower Thermosphere ◽

Tropical Convection ◽

Peak Activity ◽

Medium Frequency ◽

Short Period ◽

Mesosphere And Lower Thermosphere ◽

Mf Radar

Abstract. We study short period gravity waves (20–120 min) in the equatorial Mesosphere and Lower Thermosphere (MLT) using a Medium Frequency (MF) radar at Pameungpeuk (7.4° S, 107.4° E), Indonesia. In particular, we study local time and seasonal variation of the gravity wave variance and its relation to tropical convection. The gravity wave variance at 88 km enhances between 20:00 LT and 07:00 LT, with a peak at 02:00–03:00 LT. The enhancement is mainly observed during February–April and September–October and shows inter-annual variability. Convective activity over the same location persists from 16:00–21:00 LT with a peak activity ~18:00 LT and enhances between November–April. Time delay between the peak of convection and that of gravity wave activity ranges 1–15 h, which is consistent with theoretical calculations and previous reports based on reverse ray tracing analysis.

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Spatial and temporal analysis of high-frequency internal gravity wave signatures in brightness temperature satellite images

10.5194/egusphere-egu21-1609 ◽

2021 ◽

Author(s):

Robert Vicari

Keyword(s):

Water Vapor ◽

Brightness Temperature ◽

Gravity Wave ◽

Gravity Waves ◽

High Frequency ◽

Satellite Images ◽

Internal Gravity Wave ◽

Internal Gravity Waves ◽

Small Scale ◽

Wave Patterns

Highly idealized model studies suggest that convectively generated internal gravity waves in the troposphere with horizontal wavelengths on the order of a few kilometers may affect the lifetime, spacing, and depth of clouds and convection. To answer whether such a convection-wave coupling occurs in the real atmosphere, one needs to find corresponding events in observations. In general, the study of high-frequency internal gravity wave-related phenomena in the troposphere is a challenging task because they are usually small-scale and intermittent. To overcome case-by-case studies, it is desirable to have an automatic method to analyze as much data as possible and provide enough independent and diverse evidence. Here, we focus on brightness temperature satellite images, in particular so-called satellite water vapor channels. These channels measure the radiation at wavelengths corresponding to the energy emitted by water vapor and provide cloud-independent observations of internal gravity waves, in contrast to visible and other infrared satellite channels where one relies on the wave impacts on clouds. In addition, since these water vapor channels are sensitive to certain vertical layers in the troposphere, combining the images also reveals some vertical structure of the observed waves. We propose an algorithm based on local Fourier analyses to extract information about high-frequency wave patterns in given brightness temperature images. This method allows automatic detection and analysis of many wave patterns in a given domain at once, resulting in a climatology that provides an initial observational basis for further research. Using data from the instrument ABI on board the satellite GOES-16 during the field campaign EUREC4A, we demonstrate the capabilities and limitations of the method. Furthermore, we present the respective climatology of the detected waves and discuss approaches based on this to address the initial question.

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