Propagation Of Gravity Waves Research Articles

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

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.

Multilayer hazes over Saturn\u2019s hexagon from Cassini ISS limb images

In June 2015, Cassini high-resolution images of Saturn’s limb southwards of the planet’s hexagonal wave revealed a system of at least six stacked haze layers above the upper cloud deck. Here, we characterize those haze layers and discuss their nature. Vertical thickness of layers ranged from 7 to 18 km, and they extended in altitude ∼130 km, from pressure level 0.5 bar to 0.01 bar. Above them, a thin but extended aerosol layer reached altitude ∼340 km (0.4 mbar). Radiative transfer modeling of spectral reflectivity shows that haze properties are consistent with particles of diameter 0.07–1.4 μm and number density 100–500 cm−3. The nature of the hazes is compatible with their formation by condensation of hydrocarbon ices, including acetylene and benzene at higher altitudes. Their vertical distribution could be due to upward propagating gravity waves generated by dynamical forcing by the hexagon and its associated eastward jet.

The Role of Vertically and Obliquely Propagating Gravity Waves in Influencing the Polar Summer Mesosphere.

Using an 8-year (2007-2014) data set from two different limb-viewing instruments, we evaluate the relative roles of vertically versus obliquely propagating gravity waves (GWs) as sources of GWs in the polar summer mesosphere. Obliquely propagating waves are of interest because they are presumed to be generated by the summer monsoons. In the high-latitude upper mesosphere, the correlation coefficient between the time series of ice water content (IWC) and GW amplitude is 0.48, indicating that the observed GWs enhance polar mesospheric clouds (PMCs). For vertically propagating waves, the correlation coefficient between IWC and stratospheric/lower mesospheric (20-70 km) GW amplitude at the same high latitudes becomes more negative with increasing altitude. This change in correlation from negative in the lower mesosphere to positive at PMC altitudes suggests the presence of another source of GWs. The positive correlation coefficient between the time series of IWC and GW amplitude from 0-50°N, 20-90 km shows a slanted structure suggesting oblique propagation. This slanted structure is more robust in some seasons compared to others, and this interannual variability may be due to the latitudinal gradient of the mesospheric easterly jet where steeper gradients allow for low-latitude tropospheric GWs to be refracted to the high-latitude mesosphere more efficiently. Gravity-Wave Regional or Global Ray Tracer (GROGRAT) ray tracing simulations show that more GWs propagate obliquely compared to vertically propagating waves that reach PMC altitudes. For obliquely propagating waves, GROGRAT simulations indicate that nonorographic tropospheric GWs with faster phase speed (>20 m/s) and longer horizontal wavelength (>400 km) have a higher probability of reaching the polar summer mesosphere.

Variations in the Ionospheric Peak Altitude at Mars in Response to Dust Storms: 13 Years of Observations From the Mars Express Radar Sounder

AbstractPrevious observations have shown that, during Martian dust storms, the peak of the ionosphere rises in altitude. Observational studies of this type, however, have been extremely limited. Using 13 years of ionospheric peak altitude data from the Mars Advanced Radar for Subsurface and Ionosphere Sounding instrument on Mars Express, we study how the peak altitude responded to dust storms during six different Mars years (MY). The peak altitude increased ∼10–15 km during all six events, which include a local dust storm (MY 33), three regional dust storms (MYs 27, 29, and 32), and two global dust storms (MYs 28 and 34). The peak altitude's orbit‐to‐orbit variability was exceptionally large at the apexes of the MY 29 and MY 32 dust seasons and dramatically increased during the MY 28 and MY 34 global dust storms. We conclude that dust storms significantly increase upper atmospheric variability, which suggests that they enhance dynamical processes that couple the lower and upper atmospheres, such as upward propagating gravity waves or atmospheric tides.

Convectively Generated Gravity Waves During Solstice and Equinox Conditions

AbstractPrevious studies suggest that mesospheric concentric wave patterns are more observable in the equinox months than solstice months, despite concentric and semiconcentric waves being readily observed in summer months in the stratosphere. This study uses a 3‐D nonlinear model to simulate the propagation and dissipation of convectively generated gravity waves under averaged equinox and solstice conditions to investigate the influences of wave breaking upon these concentric patterns. It is found that the relatively weak atmospheric winds and shears during the equinox months means that waves can propagate up to the lower thermosphere before breaking. In contrast, strong zonal winds and shears in the summer solstice months lead to in situ breaking in the mesosphere, which causes disruption to the concentric pattern. While the western propagating portion of the concentric pattern is filtered by the stratospheric winds, the eastern propagating portion rapidly transitions to turbulence in the mesosphere making it less likely to observe concentric patterns in the solstice months. The concentric pattern is more complete in the equinox months because the waves are only weakly filtered by winds and relatively little in situ breaking occurs in the mesosphere. However, in situ breaking does not affect the pattern in the stratosphere, where the morphology is primarily dictated by wind filtering. This also helps explain why concentric and semiconcentric patterns are observed in the summer stratosphere but not regularly in the mesosphere.

Formula omitted] gravity with an axion-like particle: Dynamics, gravity waves, late and early-time phenomenology

In this work we investigate several theoretical and phenomenological implications of a scalar -F(R) gravity containing a non-minimal coupling to the scalar curvature. This kind of model is a generalization of axion-F(R) gravity models, so we shall examine several implications of the latter theory. Firstly we study in detail the Einstein frame picture of the model, and also we discuss the dynamics of the cosmological system. By appropriately using the equations of motion, we demonstrate that an arbitrary cosmological evolution can be realized. Also we study the gravitational waves of the theory, and we demonstrate that the speed of their propagation is the same as in F(R) gravity, but there is the possibility of enhancement or dissipation of the gravitational waves, an effect quite similar to the propagation of gravity waves in a viscous fluid. Finally, we examine the energy–momentum tensor and we investigate which quantities related to it are conserved. We also present the constraints imposed by the radiation domination era on the non-minimal coupling of the axion scalar field to the scalar curvature.

An investigation of the properties of flexural-gravity wave propagation in a coupled submerged and floating plate system

The propagation of flexural-gravity waves in a coupled submerged and floating plate system is studied, and the complex flexural gravity wave propagation properties are investigated in the frequency and time domain, The system exhibits two modes of propagation analogous to the surface and internal waves in a two-layer fluid. The effect of the plate properties on the phase velocities of both the faster (floating plate in general) and the slower (submerged plate in general) modes are analysed in detail. Both modes exhibit complex properties, including waves with negative kinetic energy and points of blocking at which no energy can propagate. They also show complex coupling and energy transfer in the time-domain. Furthermore, the dependency of the blocking frequency and the critical opposing current is analysed in both the shallow and deep water limits. The occurrence of blocking in the internal mode under a specific constraint is also demonstrated. As a special case, the influence of the submerged plate’s position and compressive force on the dynamics of the free surface flexural-gravity wave blocking is studied. The characteristics of the phase speed in both modes are studied, and the occurrences/non-occurrences of optima are mathematically proved. Some of the analytic results are illustrated by time-domain simulations which illustrate the complex wave propagation phenomena of this system.

Infrasound and Gravity Waves Over the Andes Observed by a Pressure Sensor on Board a Stratospheric Balloon

AbstractThe study of infrasound (acoustic) and gravity waves sources and propagation in the atmosphere of a planet gives us precious insight on atmosphere dynamics, climate, and even internal structure. The implementation of modern pressure sensors with high rate sampling on stratospheric balloons is improving their study. We analyzed the data from the National Aeronautics and Space Administration Ultra Long Duration Balloon mission (16 May to 30 June 2016). Here, we focus on the balloon's transit of the Andes Mountains. We detected gravity waves that are associated to troposphere convective activity and mountain waves. An increase of the horizontal wavelengths from 50 to 70 km with increasing distance to the mountains is favoring the presence of mountain waves. We also report on the detection of infrasounds generated by the mountains in the 0.01–0.1 Hz range with a pressure amplitude increase by a factor 2 relative background signal. Besides, we characterized the decrease of microbaroms power when the balloon was flying away from the ocean coast. These observations suggest, in a way similar to microseisms for seismometers, that microbaroms are the main background noise sources recorded in the stratosphere even far from the ocean sources. Finally, we observed a broadband signal above the Andes, between 0.45 and 2 Hz, probably associated with a thunderstorm. The diversity of geophysical phenomena captured in less than a day of observation stresses the interest of high rate pressure sensors on board long‐duration balloon missions.

Vertical Propagation of Acoustic Gravity Waves from the Lower Atmosphere during a Solar Eclipse

This paper presents the results of the analysis of a numerical experiment on the generation of acoustic gravity waves (AGWs) in the lower atmosphere and their propagation into the upper atmosphere. The observed variations in atmospheric pressure during the passage of a solar eclipse on March 20, 2015, over Kaliningrad (54° N, 20° E) are considered the be a wave source. The calculation results showed that the passage of a solar eclipse is accompanied in the lower atmosphere by an increase in wave activity in the AGW range with periods of ~4–20 min. In the upper atmosphere, at altitudes of ~200 km, disturbances are formed due to the dissipation of AGWs coming from the lower atmosphere; these disturbances propagate with characteristic periods of ~50 min. The propagation direction of these disturbances was opposite to the propagation direction of the solar eclipse region along the Earth’s surface. The results of the numerical experiment are in qualitative agreement with the results of observations of ionospheric disturbances during the solar eclipse on March 20, 2015.

Traveling Ionospheric Disturbances Characteristics during the 2018 Typhoon Maria from GPS Observations

Typhoons often occur and may cause huge loss of life and damage of infrastructures, but they are still difficult to precisely monitor and predict by traditional in-situ measurements. Nowadays, ionospheric disturbances at a large-scale following typhoons can be monitored using ground-based dual-frequency Global Positioning System (GPS) observations. In this paper the responses of ionospheric total electron content (TEC) to Typhoon Maria on 10 July 2018 are studied by using about 150 stations of the GPS network in Taiwan. The results show that two significant ionospheric disturbances on the southwest side of the typhoon eye were found between 10:00 and 12:00 UTC. This was the stage of severe typhoon and the ionospheric disturbances propagated at speeds of 118.09 and 186.17 m/s, respectively. Both traveling ionospheric disturbances reached up to 0.2 TECU and the amplitudes were slightly different. The change in the filtered TEC time series during the typhoon was further analyzed with the azimuth. It can be seen that the TEC disturbance anomalies were primarily concentrated in a range of between −0.2 and 0.2 TECU and mainly located at 135–300° in the azimuth, namely the southwest side of the typhoon eye. The corresponding frequency spectrum of the two TEC time series was about 1.6 mHz, which is consistent with the frequency of gravity waves. Therefore, the upward propagating gravity wave was the main cause of the traveling ionospheric disturbance during Typhoon Maria.

Self-Acceleration and Instability of Gravity Wave Packets: 3. Three-Dimensional Packet Propagation, Secondary Gravity Waves, Momentum Transport, and Transient Mean Forcing in Tidal Winds.

Dong et al. (2020, https://doi.org/10.1029/2019JD030691) employed a new compressible model to examine gravity wave (GW) self‐acceleration dynamics, instabilities, secondary gravity wave (SGW) generation, and mean forcing for GW packets localized in two dimensions (2D). This paper extends the exploration of self‐acceleration dynamics to a GW packet localized in three dimensions (3D) propagating into tidal winds in the mesosphere and thermosphere. As in the 2D packet responses, 3D GW self‐acceleration dynamics are found to be significant and include 3D GW phase distortions, stalled GW vertical propagation, local instabilities, and SGW and acoustic wave generation. Additional 3D responses described here include refraction by tidal winds, localized 3D instabilities, asymmetric SGW propagation, reduced SGW and acoustic wave responses at higher altitudes relative to 2D responses, and forcing of transient, large‐scale, 3D mean responses that may have implications for chemical and microphysical processes operating on longer time scales.

Aspects of axion F(R) gravity

We provide a compact review on recent developments on axion F(R) gravity. The axion field is a string-theory–originated theoretical particle that is a perfect candidate for low-mass particle dark matter. In this review we present how a viable inflationary phenomenology and a viable late-time evolution can be described by an axion F(R) gravity theory, in which the F(R) gravity part can drive in a geometric way the inflationary and the late-time era, and the axion field behaves as dark matter, with its energy density behaving as a function of the scale factor as . We also briefly discuss the effect of a non-trivial axion Chern-Simons coupling on the inflationary phenomenology of the R2 model. Finally, we briefly discuss the effects of a non-minimal coupling of the axion field with the curvature on neutron stars, and also the propagation of gravity waves in Chern-Simons axion gravity.

Study on concrete through its hardened state properties

Abstract The composition characteristics of concrete, such as water/cement ratio, cement consumption and compressive strength directly affect its handling performance and durability. Thus, the technical standards related to concrete structures recommend technical specification concerning different environmental aggressiveness classes. Therefore, this study followed an experimental method aiming to evaluate the relationship between the characteristics of four different concrete mixes produced in accordance to the specifications of the standards EN 1992-1 and EN 206 for quality of hardened state concrete and its behavior during accelerated tests of carbonation and salt spray. Analyzes of compressive strength, void index, total and capillary water absorption, specific gravity, electrical resistivity and ultrasonic wave propagation velocity were executed. For the statistical treatment, a Multivariate Analysis of Variance (MANOVA) was performed, which provided a simplified analysis of the durable potential of reinforced concrete structures by its characteristics. Results lead to two major groups of behavior, and statistical significant differences in deterioration tests between mixes 1 and 4 for the salt spray test and between mix 4 and the others for the carbonation test.

Oblique Gravity Wave Propagation During Sudden Stratospheric Warmings

AbstractGravity waves (GWs) are important for coupling the mesosphere to the lower atmosphere during sudden stratospheric warmings (SSWs). Here, a minor SSW is internally generated in a simulation with the upper‐atmosphere configuration of the ICOsahedral Nonhydrostatic model. At a horizontal resolution of 20 km the simulation uses no GW drag parameterizations but resolves large fractions of the GW spectrum explicitly, including orographic and nonorographic sources. Consistent with previous studies, the simulated zonal‐mean stratospheric warming is accompanied by zonal‐mean mesospheric cooling. During the course of the SSW the mesospheric GW momentum flux (GWMF) turns from mainly westward to mainly eastward. Waves of large phase speed (40–80 m s ) dominate the eastward GWMF during the peak phase of the warming. The GWMF is strongest along the polar night jet axis. Parameterizations of GWs usually assume straight upward propagation, but this assumption is often not satisfied. In the case studied here, a substantial amount of the GWMF is significantly displaced horizontally between the source region and the dissipation region, implying that the local impact of GWs on the mesosphere does not need to be above their local transmission through the stratosphere. The simulation produces significant vertically misaligned anomalies between the stratosphere and mesosphere. Observations by the Microwave Limb Sounder confirm the poleward tilt with height of the polar night jet and horizontal displacements between mesospheric cooling and stratospheric warming patterns. Thus, lateral GW propagation may be required to explain the middle‐atmosphere temperature evolution in SSW events with significant zonally asymmetric anomalies.

Search for Atmospheric Wave Signatures by Simultaneous Collocated Barometer and Gravimeter Measurements

A spatial distribution model for air density perturbations during the propagation of internal gravity waves (IGWs) is used to derive estimates for gravity perturbations generated by these waves. The estimates show that superconducting gravimeters are capable of detecting IGWs generated by any wave source in the lower atmosphere. Series of barometric and gravimetric measurements at Moxa, Germany (50.6° N, 11.6° E), for 2000–2018 are processed using digital filtering to search for pressure and gravity perturbations with time scales of ~10 min to ~10 h. The annual change in the atmospheric pressure variation with variation scales on the order of and less than 1 h shows a summer maximum, which disappears at higher scales. The summer maximum can be attributed to the effect of IGWs with periods on the order of and less than 1 h from convective clouds that occur in the summer half of the year. The annual change in the gravity variation shows maximums in winter and summer for all the variation scales under consideration. They can be explained by modulating the solar semidiurnal gravitational tide by a semiannual change in the perturbation of the Earth’s gravitational potential.

Ionospheric perturbations initiated due to the forest-fire over Greece as a consequence of lithosphere-atmosphere-ionosphere coupling

A very devastating and long duration wildfire episode occurred in Greece near Athens during 20-25 July 2018. We have investigated particulate matter PM10 and PM2.5; and selected greenhouse gases such as CO2, NO2, SO2, and CH4 which are known to be generated due to the burning of coal, vegetation, and gasoline. There are significant changes in carbon dioxide, methane and carbon monoxide based on the simulations with the chemical transport model. Further, we have checked the ionospheric perturbations during 20-25 July 2018, using the global positioning system (GPS) derived total electron content (TEC) maps over Greece. We have used detrended TEC data to observe the fluctuation in the ionospheric total electron during the presented event. We found that strong ionospheric perturbations have appeared during these events in coincident location to the lower atmospheric anomalies observed in the troposphere and stratosphere. A possible mechanism of the generation of the Atmospheric Gravity Waves (AGW) and Earth’s surface-atmosphere-ionosphere coupling has been discussed. Detrended atmospheric gases/particulate matter density and detrended GPS TEC shows similar variation trend, however, ionospheric changes show significant time delay. This indicates the energy from forest fire region penetrates into ionosphere through the lower atmosphere and gradually triggers fluctuations in the density of the atmospheric elements as well as ionospheric TEC.

A Model for the Generation of Waves in the Ocean by Seismic Bottom Movements in Sigma-Coordinates

This paper describes a model for the generation of waves in the ocean by seismic bottom movements. A specific feature of this model is the use of curvilinear non-orthogonal sigma-coordinates. The results of numerical experiments aimed at studying the mechanisms of the generation of gravity waves by surface seismic waves propagating over the bottom are presented.

Inertial gravity waves observed by a Doppler wind LiDAR and their possible sources

In this paper, we use wind observations by a Doppler wind LiDAR near Delingha (37.4°N, 97.4°E), Qinghai, Northwestern China to study the characteristics of inertial gravity waves in the stratosphere. We focus on 10–12 December 2013, a particularly interesting case study. Most of the time, the inertial gravity waves extracted from the LiDAR measurements were stationary with vertical wavelengths of about 9–11 km and horizontal wavelengths of about 800–1000 km. However, for parts of the observational period in this case study, a hodograph analysis indicates that different inertial gravity wave propagation features were present at lower and upper altitudes. In the middle and upper stratosphere (~30–50 km), the waves propagated downward, especially during a period of stronger winds, and to the northwest–southeast. In the lower stratosphere and upper troposphere (~10–20 km), however, waves with upward propagation and northeast–southwest orientation were dominant. By taking into account reanalysis data and satellite observations, we have confirmed the presence of different wave patterns in the lower and upper stratosphere during this part of the observational period. The combined data sets suggest that the different wave patterns at lower and upper height levels are likely to have been associated with the presence of lower and upper stratospheric jet streams.

On the opposing roles of the Boussinesq and non‐Boussinesq baroclinic torques in surface gravity wave propagation

AbstractHere we suggest an alternative understanding of the surface gravity wave propagation mechanism based on the baroclinic torque, which operates to translate the interfacial vorticity anomalies at the air–water interface. We demonstrate how the non‐Boussinesq term of the baroclinic torque acts against the Boussinesq one to hinder wave propagation. By standard vorticity inversion and mirror imaging, we then show how the existence of the bottom boundary affects the two types of torque. Since the opposing non‐Boussinesq torque results solely from the mirror image, it vanishes in the deep‐water limit and its magnitude is half of the Boussinesq torque in the shallow‐water limit. This reveals that the Boussinesq approximation is valid in the deep‐water limit, even though the density contrast between air and water is large. The mechanistic roles played by the Boussinesq and non‐Boussinesq parts of the baroclinic torque remain obscured in the standard derivation where the time‐dependent Bernoulli equation is implemented instead of the interfacial vorticity equation. Finally, we note on passing that the Virial theorem for surface gravity waves can be obtained solely from considerations of the dynamics at the air–water interface.

Generalized (3+1)-dimensional Boussinesq equation: Breathers, rogue waves and their dynamics

In this work, we consider the generalized (3[Formula: see text]+[Formula: see text]1)-dimensional Boussinesq equation, which can describe the propagation of gravity wave on the surface of water. Based on the Bell polynomial theory, a powerful technique is employed to explicitly construct its bilinear formalism and two-soliton solutions, based on which the new rational solution is well-constructed. Moreover, the extended homoclinic test approach is presented to succinctly construct the breather wave and rogue wave solutions of the Boussinesq equation. Then the main characteristics of these solutions are graphically discussed. More importantly, they reveal that the extreme behavior of the breather wave can give rise to the rogue wave.