Influence Of Gravity Waves Research Articles

Investigation of the influence of gravity waves on the surface thermal signatures and buoyant trajectory of thermal wakes

Thermal wakes discharged by a body moving under the ocean contain large amounts of thermal energy and form a specific temperature profile upon reaching the sea surface. These surface thermal signatures play a vital role in the infrared remote sensing of marine underwater targets. In this study, a model is developed for simulating thermal wakes out of an underwater moving body. The model is based on the 3-D dynamic meshing technique and volume of fluid method, and the surface thermal signatures and buoyant trajectory are analyzed. In addition, a velocity-inlet wave-generating method is coupled with the simulation model, and the influence of gravity waves on the buoyancy and diffusion processes of thermal wakes is investigated. The results show that the velocity-inlet wave-generating method exhibits good performance in wave generation with the period error δT = 0.18%, and wave height error δH = 5.88% (for the second-order Stokes wave). Gravity waves suppress the buoyancy of thermal wakes, resulting in a % increase in the underwater buoyancy distance. The wave enhances the heat transfer of the thermal wake with surrounding water, which causes the surface maximum temperature difference to decrease by 5.6%, and the temperature distribution of the thermal wake becomes more uniform with a broader area.

Модель воздействия гравитационно-волнового излучения релятивистских двойных звездных систем на электрическое поле в тропосфере

A model is proposed which explains the observed effect of gravity-wave influence of relativistic binaries to the Earth’s electric field vertical projection in the near-ground atmosphere layer. The considered mechanism is a perturbation of the Earth’s orbit by the gravity waves which leads to a small displacement between the Earth and the Earth’s atmosphere free electric charge. The proposed model give amplitude estimations of Ez components spectrally localized at the relativistic binaries gravity waves’ frequencies which do not contradict to the observations.

Statistical Study of the Midlatitude Mesospheric Vertical Winds Observed by the Wuhan and Beijing MST Radars in China

AbstractBased on the long‐term observations of the Wuhan and Beijing Mesosphere‐Stratosphere‐Troposphere (MST) radars, the statistic characteristics of the mesospheric vertical winds at midlatitudes are investigated for the first time. The vertical wind data come from the Wuhan MST radar (29.51°N, 114.13°E) during 2012–2017 and from the Beijing MST radar (39.75°N, 116.96°E) during 2012–2014. The subdaily, seasonal, and annual variations of the mesospheric vertical winds at Wuhan and Beijing are presented. No obvious subdaily and seasonal variations are found and the annual variations of the mean vertical winds are downward in most of time. The mean vertical winds at Wuhan become smaller in summer and turn to upward at some heights, while those of Beijing only become smaller in summer. The difference of summer vertical winds over Wuhan and Beijing is closely related to the gravity wave activity. The Wuhan MST radar is located to the east side of the Qinghai‐Tibet plateau and also in the East Asian monsoon region, thus the mesospheric winds over Wuhan may experience more influence of gravity waves compared with those over Beijing. The possible bias sources in the vertical wind measurement of the two MST radars are carefully analyzed and the presented wind velocities are proved to be credible. The measured velocity magnitude is similar to other Very High Frequency radar observations, but much larger than that of the WACCM simulation. The Stokes drift, multicellular circulation structures, the wave influence on the radar echoes are raised as the potential sources for this discrepancy.

Mesospheric winds measured by medium-frequency radar with full correlation analysis: error properties and impacts on studies of wind variance

Abstract. The mesosphere is one of the most difficult parts of the atmosphere to sample; it is too high for balloon measurements and too low for in situ satellites. Consequently, there is a reliance on remote sensing (either from the ground or from space) to diagnose this region. Ground-based radars have been used since the second half of the 20th century to probe the dynamics of the mesosphere; medium-frequency (MF) radars provide estimates of the horizontal wind fields and are still used to analyse tidal structures and planetary waves that modulate the meridional and zonal winds. The variance of the winds has traditionally been linked qualitatively to the occurrence of gravity waves. In this paper, the method of wind retrieval (full correlation analysis) employed by MF radars is considered with reference to two systems in Antarctica at different latitude (Halley at 76∘ S and Rothera at 67∘ S). It is shown that the width of the velocity distribution and occurrence of “outliers” is related to the measured levels of anisotropy in the received signal pattern. The magnitude of the error distribution, as represented by the wind variance, varies with both insolation levels and geomagnetic activity. Thus, it is demonstrated that for these two radars the influence of gravity waves may not be the primary mechanism that controls the overall variance.

The Influence of Gravity Waves on Ice Saturation in the Tropical Tropopause Layer over Darwin, Australia

Gravity waves (GWs) in the tropical tropopause layer (TTL) can help dehydrate the lower stratosphere through rapid cooling events, but observational studies of GWs in the TTL are limited. Using a long-term, high-resolution radiosonde temperature dataset, an atmospheric state classification technique, and wavelet analysis, we characterize temperature perturbations generated by GWs in the TTL over Darwin, Australia across eight atmospheric states. We find a peak in GW power just above the tropical tropopause and a climatological maximum during peak monsoon season. While accounting for a chronic negative temperature bias near the tropical tropopause, we estimate that, in the upper troposphere, GWs impose a 2 K temperature perturbation during non-monsoon states and a 3 K temperature perturbation during the monsoon states, with corresponding values of 5 K and 6 K in the upper TTL. A 3 K negative temperature perturbation will lead to significant perturbations in relative humidity with respect to ice, which has implications for environmental ice number concentrations and TTL cloud fraction.

The Influence of Gravity Waves on the Slope of the Kinetic Energy Spectrum in Simulations of Idealized Midlatitude Cyclones

Abstract The influence of gravity waves generated by surface stress and by topography on the atmospheric kinetic energy (KE) spectrum is examined using idealized simulations of a cyclone growing in baroclinically unstable shear flow. Even in the absence of topography, surface stress greatly enhances the generation of gravity waves in the vicinity of the cold front, and vertical energy fluxes associated with these waves produce a pronounced shallowing of the KE spectrum at mesoscale wavelengths relative to the corresponding free-slip case. The impact of a single isolated ridge is, however, much more pronounced than that of surface stress. When the mountain waves are well developed, they produce a wavenumber to the −5/3 spectrum in the lower stratosphere over a broad range of mesoscale wavelengths. In the midtroposphere, a smaller range of wavelengths also exhibits a −5/3 spectrum. When the mountain is 500 m high, the waves do not break, and their KE is entirely associated with the divergent component of the velocity field, which is almost constant with height. When the mountain is 2 km high, wave breaking creates potential vorticity, and the rotational component of the KE spectrum is also strongly energized by the waves. Analysis of the spectral KE budgets shows that the actual spectrum is the result of continually shifting balances of direct forcing from vertical energy flux divergence, conservative advective transport, and buoyancy flux. Nevertheless, there is one interesting example where the −5/3-sloped lower-stratospheric energy spectrum appears to be associated with a gravity-wave-induced upscale inertial cascade.

Influence of gravity waves on the climatology of high-altitude Martian carbon dioxide ice clouds

Abstract. Carbon dioxide (CO2) ice clouds have been routinely observed in the middle atmosphere of Mars. However, there are still uncertainties concerning physical mechanisms that control their altitude, geographical, and seasonal distributions. Using the Max Planck Institute Martian General Circulation Model (MPI-MGCM), incorporating a state-of-the-art whole atmosphere subgrid-scale gravity wave parameterization (Yiğit et al., 2008), we demonstrate that internal gravity waves generated by lower atmospheric weather processes have a wide-reaching impact on the Martian climate. Globally, GWs cool the upper atmosphere of Mars by ∼10 % and facilitate high-altitude CO2 ice cloud formation. CO2 ice cloud seasonal variations in the mesosphere and the mesopause region appreciably coincide with the spatio-temporal variations of GW effects, providing insight into the observed distribution of clouds. Our results suggest that GW propagation and dissipation constitute a necessary physical mechanism for CO2 ice cloud formation in the Martian upper atmosphere during all seasons.

Influences of Gravity Waves on Convectively Induced Turbulence (CIT): A Review

Thunderstorms are known to produce turbulence. Such turbulence is commonly referred to as convectively induced turbulence or CIT, and can be hazardous to aviation. Although this turbulence can occur both within and outside the convection, out-of-cloud CIT is particularly hazardous, since it occurs in clear air and cannot be seen by eye or onboard radar. Furthermore, due to its small scale and its ties to the underlying convection, it is very difficult to forecast. Guidelines for out-of-cloud CIT avoidance are available, but they are oversimplified and can be misleading. In the search for more appropriate and physically based avoidance guidelines, considerable research has been conducted in recent years on the nature of the phenomenon, and in particular, its connection to gravity waves generated by the convection. This paper reviews the advances in our understanding of out-of-cloud CIT and its relation to convective gravity waves, and provides several detailed examples of observed cases to elucidate some of the underlying dynamics.

Liquid-solid Interaction Seismic Response of an Isolated Overground Rectangular Reinforced-concrete Liquid-storage Structure

In this paper, the liquid-solid interaction dynamic finite element integral models of a reinforced-concrete rectangular liquid-storage structure are established to obtain the liquid-solid interaction seismic response of an isolated overground rectangular reinforced-concrete liquid-storage structure. It is assumed that the liquid is incompressible and the influence of gravity wave on the surface of liquid is considered. Some mechanical properties, such as the liquid sloshing height, wallboard displacement and equivalent stress under seismic action and the seismic response under different liquid level of the single cell liquid-storage structure, are discussed, by considering factors of the nonlinear dynamic characteristic, element selection, seismic input, mesh density, convergence and liquid-solid interaction. The results of numerical examples indicate that: the peak displacements of the isolated structure under different earthquake intensities are basically the same, the displacement of the wallboard and stress increase with the increase of seismic intensity, and the lower the level of the liquid is, the less the amount of liquid is and the greater the shaking amplitude is, the greater the stress and displacement of the wallboard are.

Gravity wave effects on postsunset equatorial F region stability

AbstractThe influence of gravity waves on the stability of the postsunset equatorial F region ionosphere is investigated numerically. For this investigation, we use the output of a direct numerical simulation of waves and turbulence in the mesosphere and lower thermosphere to force a simulation of ionospheric dynamics. Both simulations are cast in three dimensions. The effectiveness of the neutral‐plasma coupling involved is generally thought to depend on the dynamo efficiency and spatial resonance of the forcing, which we evaluate. In our simulations, the postsunset equatorial ionosphere could be deformed by neutral waves after 5–15 min most severely when the wavefronts were aligned approximately with the magnetic meridian, despite the fact that the dynamo efficiency is modest even in that case. However, poor spatial resonance limits the subsequent growth of the deformations in our simulations, and the seeding of interchange instabilities does not occur. The coupled simulations predict the formation of intermediate layers in the equatorial valley region (150–250 km apex altitude) under some circumstances that could serve as telltales in nature of the presence of the kind of neutral forcing we simulate.

Gravity wave influence on NLC: experimental results from ALOMAR, 69° N

Abstract. The influence of gravity waves on noctilucent clouds (NLC) at ALOMAR (69° N) is analysed by relating gravity wave activity to NLC occurrence from common-volume measurements. Gravity wave kinetic energies are derived from MF-radar wind data and filtered into different period ranges by wavelet transformation. From the dataset covering the years 1999–2011, a direct correlation between gravity wave kinetic energy and NLC occurrence is not found, i.e., NLC appear independently of the simultaneously measured gravity wave kinetic energy. In addition, gravity wave activity is divided into weak and strong activity as compared to a 13 yr mean. The NLC occurrence rates during strong and weak activity are calculated separately for a given wave period and compared to each other. Again, for the full dataset no dependence of NLC occurrence on relative gravity wave activity is found. However, concentrating on 12 h of NLC detections during 2008, we do find an NLC-amplification with strong long-period gravity wave occurrence. Our analysis hence confirms previous findings that in general NLC at ALOMAR are not predominantly driven by gravity waves while exceptions to this rule are at least possible.

Impact of Gravity Waves on Marine Stratocumulus Variability

Abstract The impact of gravity waves on marine stratocumulus is investigated using a large-eddy simulation model initialized with sounding profiles composited from the Variability of American Monsoon Systems (VAMOS) Ocean–Cloud–Atmosphere–Land Study Regional Experiment (VOCALS-Rex) aircraft measurements and forced by convergence or divergence that mimics mesoscale diurnal, semidiurnal, and quarter-diurnal waves. These simulations suggest that wave-induced vertical motion can dramatically modify the cloud albedo and morphology through nonlinear cloud–aerosol–precipitation–circulation–turbulence feedback. In general, wave-induced ascent tends to increase the liquid water path (LWP) and the cloud albedo. With a proper aerosol number concentration, the increase in the LWP leads to enhanced precipitation, which triggers or strengthens mesoscale circulations in the boundary layer and accelerates cloud cellularization. Precipitation also tends to create a decoupling structure by weakening the turbulence in the subcloud layer. Wave-induced descent decreases the cloud albedo by dissipating clouds and forcing a transition from overcast to scattered clouds or from closed to open cells. The overall effect of gravity waves on the cloud variability and morphology depends on the cloud property, aerosol concentration, and wave characteristics. In several simulations, a transition from closed to open cells occurs under the influence of gravity waves, implying that some of the pockets of clouds (POCs) observed over open oceans may be related to gravity wave activities.

Dynamical influence of gravity waves generated by the Vestfjella Mountains in Antarctica: radar observations, fine-scale modelling and kinetic energy budget analysis

ABstractGravity waves generated by the Vestfjella Mountains (in western Droning Maud Land, Antarctica, southwest of the Finnish/Swedish Aboa/Wasa station) have been observed with the Moveable atmospheric radar for Antarctica (MARA) during the SWEDish Antarctic Research Programme (SWEDARP) in December 2007/January 2008. These radar observations are compared with a 2-month Weather Research Forecast (WRF) model experiment operated at 2 km horizontal resolution. A control simulation without orography is also operated in order to separate unambiguously the contribution of the mountain waves on the simulated atmospheric flow. This contribution is then quantified with a kinetic energy budget analysis computed in the two simulations. The results of this study confirm that mountain waves reaching lower-stratospheric heights break through convective overturning and generate inertia gravity waves with a smaller vertical wavelength, in association with a brief depletion of kinetic energy through frictional dissipation and negative vertical advection. The kinetic energy budget also shows that gravity waves have a strong influence on the other terms of the budget, i.e. horizontal advection and horizontal work of pressure forces, so evaluating the influence of gravity waves on the mean-flow with the vertical advection term alone is not sufficient, at least in this case. We finally obtain that gravity waves generated by the Vestfjella Mountains reaching lower stratospheric heights generally deplete (create) kinetic energy in the lower troposphere (upper troposphere–lower stratosphere), in contradiction with the usual decelerating effect attributed to gravity waves on the zonal circulation in the upper troposphere–lower stratosphere.

Gravity Wave Mixing and Effective Diffusivity for Minor Chemical Constituents in the Mesosphere/Lower Thermosphere

The influence of gravity waves (GWs) on the distributions of minor chemical constituents in the mesosphere-lower thermosphere (MLT) is studied on the basis of the effective diffusivity concept. The mixing ratios of chemical species used for calculations of the effective diffusivity are obtained from numerical experiments with an off-line coupled model of the dynamics and chemistry abbreviated as KMCM-MECTM (Kuehlungsborn Mechanistic general Circulation Model—MEsospheric Chemistry-Transport Model). In our control simulation the MECTM is driven with the full dynamical fields from an annual cycle simulation with the KMCM, where mid-frequency GWs down to horizontal wavelengths of 350 km are resolved and their wave-mean flow interaction is self-consistently induced by an advanced turbulence model. A perturbation simulation with the MECTM is defined by eliminating all meso-scale variations with horizontal wavelengths shorter than 1000 km from the dynamical fields by means of spectral filtering before running the MECTM.

Influence of Gravity Waves in the Tropical Upwelling: WACCM Simulations

Abstract The annual cycle of tropical upwelling and contributions by planetary and gravity waves are investigated from climatological simulations using the Whole Atmosphere Community Climate Model (WACCM) including three gravity wave drag (GWD) parameterizations (orographic, nonstationary background, and convective GWD parameterizations). The tropical upwelling is estimated by the residual mean vertical velocity at 100 hPa averaged over 15°S–15°N. This is well matched with an upwelling estimate from the balance of the zonal momentum and the mass continuity. A clear annual cycle of the tropical upwelling is found, with a Northern Hemispheric (NH) wintertime maximum and NH summertime minimum determined primarily by the Eliassen–Palm flux divergence (EPD), along with a secondary contribution from the zonal wind tendency. Gravity waves increase tropical upwelling throughout the year, and of the three sources the contribution by convective gravity wave drag (CGWD) is largest in most months. The relative contribution by all three GWDs to tropical upwelling is not larger than 5%. However, when tropical upwelling is estimated by net upward mass flux between turnaround latitudes where upwelling changes downwelling, annual mean contribution by all three GWDs is up to 19% at 70 hPa by orographic and convective gravity waves with comparable magnitudes. Effects of CGWD on upwelling are investigated by conducting an additional WACCM simulation without CGWD parameterization. It was found that including CGWD parameterization increases tropical upwelling not only directly by adding CGWD forcing, but also indirectly by modulating EPD and zonal wind tendency terms in the tropics.

A case study of an elevated stratopause generated in the Whole Atmosphere Community Climate Model

[1] The Whole Atmosphere Community Climate Model (WACCM) is used to study the influence of gravity waves on the generation and evolution of an elevated stratopause following a sudden stratospheric warming (SSW). By comparing WACCM simulations of two Arctic winters, where one is dynamically undisturbed and one is disturbed, we find that intense planetary wave activity during a SSW drives the reversal of the zonal mean wind in the stratosphere. This alters the penetration of eastward propagating, non-orographic gravity waves into the mesosphere, which determine the extent of cooling in the lower mesosphere and upper stratosphere through the adiabatic effects of the gravity wave-driven residual circulation, and play a crucial role in the reformation of the elevated stratopause in the lower mesosphere. Eventually, the forcing due to gravity waves returns to normal wintertime values as the stratospheric zonal wind recovers, and is then associated with the warming and lowering of the elevated stratopause, by wave induced diabatic descent. We find that SSW followed by an elevated stratopause is a climatologically robust phenomenon in free running WACCM with characteristics closely resembling recently observed events in the Arctic.

Study on the layered dusty plasma structures in the summer polar mesopause

Abstract. Traditional hydrodynamic equations are adopted to build a one-dimensional theoretical model to study the effect of gravity wave on layered dusty plasma structures formation and evolution near the polar summer mesospause region associated with polar mesosphere summer echoes (PMSE). The proposed mechanism gives consideration to the charged ice particle motion by the gravity wave modulation, making a significant contribution to the vertical transport of heavy ice particles and convergence into thin layers. And numerical results show that the pattern of the multi-layer structure depends on the ration of the initial ice particles density distribution to the vertical wavelength of the gravity waves, the ice particle size and the wind velocity caused by gravity wave. Also, the variation of ion density distribution under the influence of gravity wave has also been examined. Finally, the electron density depletions (bite-outs) layers has been simulated according to the charge conservation laws, and the results are compared to the ECT02 rocket sounding data, which agree well with the measuring.

Influence of gravity waves and tides on mesospheric temperature inversion layers: simultaneous Rayleigh lidar and MF radar observations

Abstract. Three nights of simultaneous Rayleigh lidar temperature measurements over Gadanki (13.5° N, 79.2° E) and medium frequency (MF) radar wind measurements over Tirunelveli (8.7° N, 77.8° E) have been analyzed to illustrate the possible effects due to tidal-gravity wave interactions on upper mesospheric inversion layers. The occurrence of tidal gravity wave interaction is investigated using MF radar wind measurements in the altitude region 86–90 km. Of the three nights, it is found that tidal gravity wave interaction occurred in two nights. In the third night, diurnal tidal amplitude is found to be significantly larger. As suggested in Sica et al. (2007), mesospheric temperature inversion seems to be a signature of wave saturation in the mesosphere, since the temperature inversion occurs at heights, when the lapse rate is less than half the dry adiabatic lapse rate.

Comparison of mesopause region meteor radar winds, medium frequency radar winds and low frequency drifts over Germany

During 2004 and 2005 measurements of mesospheric/lower thermospheric (80–100 km) winds have been carried out in Germany using three different ground-based systems, namely a meteor radar (36.2 MHz) at the Collm Observatory (51.3°N, 13°E), a MF radar (3.18 MHz) at Juliusruh (54.6°N, 13.4°E) and the LF D1 measurements using a transmitter (177 kHz) at Zehlendorf near Berlin and receivers at Collm with the reflection point at 52.1°N, 13.2°E. This provides the possibility of comparing the results of different radar systems in nearly the same measuring volume. Meteor radar winds are generally stronger than the winds observed by MF and especially by LF radars. This difference is small near 80 km but increases with height. The difference between meteor radar and medium frequency radar winds is larger during winter than during summer, which might indicate an indirect influence of gravity waves on spaced antenna measurements.

Influence of gravity waves on fog structure revealed by a millimeter‐wave scanning Doppler radar

Multiscale band structure in fog influenced by gravity waves and Kelvin‐Helmholtz instability (KHI) is studied based on observations with a millimeter‐wave scanning Doppler radar on 1 August 2000 in Kushiro District, Hokkaido Prefecture, Japan. Band structure in fog having radar reflectivity >−20 dBZ and a scale of ∼1.5 km was observed around 50 m altitude. The band structure was also observed in Doppler velocity. The band structure in both radar reflectivity and Doppler velocity propagated northwestward with a speed of 4.17 m s−1. From linear gravity wave theory it is estimated that the observed gravity waves had a horizontal wavelength of 1.5 km and period of 6 min. The updraft induced by gravity waves is estimated to be 7.8 cm s−1. The increase in liquid water content (LWC) caused by the updraft is 0.035 g m−1, and the increase of radar reflectivity is 2 dBZ. Within the band structure induced by the gravity waves (horizontal scale ∼1.5 km), roll structure with a smaller horizontal scale (∼300–600 m) was also observed in radar reflectivity. A previous study has shown that this smaller‐scale roll structure is caused by shear‐induced KHI. This study shows that both gravity waves and KHI modulated the structure of fog and resulted in the existence of multiscale (1.5 km and 300–600 m scale) fog structure.