Showing papers on "Atmospheric wave published in 2023"

Observation based climatology Martian atmospheric waves perturbation Datasets

Abstract: The Martian atmospheric waves perturbation Datasets (MAWPD) version 2.0 is the first observation-based climatology dataset of Martian atmospheric waves. It contains climatology-gridded temperature, gravity waves, and tides spanning the whole Martian year. MAWPD uses the Data INterpolating Empirical Orthogonal Functions method (DINEOF) reconstruction method for data assimilation with the observational data from the Mars Global Surveyor (MGS), Mars Reconnaissance Orbiter (MRO), Mars Atmosphere and Volatile EvolutioN (MAVEN), Mars Pathfinder (MP), Mars Phoenix Lander (MPL), Mars Exploration Rover (MER) and Mars Express (MEX) temperature retrievals. The dataset includes gridded fields of temperature (Level 1 data) as well as the physical quantities of GWs (Level 2 data, amplitude, and potential energies), SPWs and tides (Level 2 data, amplitude, and phase). The MAWPD, based entirely on multiple reliable observations, provides climatological background atmospheric information of temperature and wave disturbances on Mars. The dataset is not only useful for observation-based scientific studies concerning Martian atmospheric waves, e.g., circulation, dust storms, and wave excitation mechanism, but also for cross-validating with model-based datasets or model results.

Ionospheric disturbances over South America related to Tonga volcanic eruption

Abstract: Abstract On January 15, 2022, we observed various unusual atmospheric wave events over South America: Atmospheric pressure waves (Lamb mode) around 12:30 to 17:30 UT, tsunamis along the Chilean coast at around 17:00 to 19:00 UT, and ionospheric disturbances between 11:30 and 20:00 UT. We understand that these events were generated by the Tonga volcanic eruption that occurred at (20.55°S, 175.39°W) in South Pacific Ocean at 04:15 UT. Several traveling ionospheric disturbances (TIDs), the horizontal wavelengths of 330 to 1174 km and the phase speed of 275–544 m/s were observed before and after the Lamb wave passed over the continent and the arrival of the tsunami on the Chile coast. The observed TID characteristics suggest us that these waves might be generated by the two atmospheric events, Lamb wave and gravity waves induced by the tsunamis. This is the first time to report the signature of ionospheric disturbances over the South American continent generated by the huge volcanic eruption. Graphical Abstract

Statistical Analysis of Hybrid Atmospheric Ducts over the Northern South China Sea and Their Influence on Over-the-Horizon Electromagnetic Wave Propagation

Abstract: Atmospheric ducts are special super-refractive atmospheric structures that can cause over-the-horizon propagation of electromagnetic waves. Different types of atmospheric ducts have different influences on electromagnetic wave propagation. Owing to the complex marine atmospheric environment, different types of atmospheric ducts often occur together. When evaluating the performance of an electromagnetic system near the sea surface, the combined influence of various atmospheric ducts should be considered comprehensively. In this paper, the statistical distribution of atmospheric ducts over the northern South China Sea is analyzed using sounding data and reanalysis data. This paper uses the parabolic equation model to analyze the propagation characteristics of microwaves near the sea surface in the presence of both surface and evaporation ducts. It is found that compared with cases where only one type of atmospheric duct is considered, a hybrid atmospheric duct structure can capture more microwave energy at a lower receiving height. At an antenna height of 5 m, the path loss begins to fluctuate beyond a propagation distance of 50 km, with the maximum fluctuation reaching about 15 dB. Microwave propagation characteristics at different microwave frequencies and antenna heights are also simulated and analyzed.

Numerical modelling of relative contribution of planetary waves to the atmospheric circulation

Abstract: Abstract. Using the general circulation model of the middle and upper atmosphere (MUAM), a number of numerical scenarios were implemented to study the impact of individual planetary waves (PWs) on the global atmospheric circulation, including zonal wind, temperature, and residual meridional circulation (RMC). The calculations were performed for the winter conditions of the Northern Hemisphere (January–February). We show the contribution to the formation of the dynamic and temperature regimes of the MUAM made by equatorial Kelvin waves propagating to the east, as well as atmospheric normal modes (NMs) with periods from 4 to 16 d. In particular, it is demonstrated that the impact of a 5 d PW and an ultra-fast Kelvin wave (UFKW) can change the speed of circulation flows by up to 6 % in the areas of their amplitude maxima. At the same time, this effect can be significantly enhanced in certain periods of time. The presented research results are important for a deeper understanding of the mechanisms of large-scale atmospheric interactions. Despite the obviousness and simplicity of the problem, such work has not been carried out yet.

Direct Observation of Wave-coherent Pressure Work in the Atmospheric Boundary Layer

Abstract: Surface waves grow through a mechanism in which atmospheric pressure is offset in phase from the wavy surface. A pattern of low atmospheric pressure over upward wave orbital motions and high pressure over downward wave orbital motions travels with the water wave, leading to a pumping of kinetic energy from the atmospheric boundary layer into the waves. This pressure pattern persists above the air/water interface, modifying the turbulent kinetic energy in the atmospheric wave-affected boundary layer. Here, we present field measurements of the transfer of energy from wind to waves through wave-coherent atmospheric pressure work. Measured pressure work cospectra are consistent with an existing model for atmospheric pressure work. Measured pressure work energy fluxes reach 0.1-0.2 W m$^{-2}$ during the largest measured wind event (winds reaching 16.5 m s$^{-1}$). The implications for these measurements and their importance to the turbulent kinetic energy budget are discussed.

Atmosphere-ionosphere coupling following the Tonga eruption: global multi-scale ionospheric effects

Abstract: The submarine volcanic eruption at Tonga on 15 January 2022 was a devastated geohazardous rated as VEI (Volcanic Explosivity Index) 5-6, which was the most powerful since the 1883 Krakatoa VEI 6 eruption. The release of enormous amounts of energy into the atmosphere triggered significant geophysical disturbances. In this presentation, we provide various upper atmospheric observations to demonstrate local, regional, and global ionospheric disturbances, including TID global propagation with the most intense, persistent, and consistent wave mode at 300-350 m/s phase speed , EIA deformation and x-cross pattern of EIA crest evolution, equatorial irregularities and bubbles, substantial plasma density depletion. Timing of these and many other observed ionospheric responses was consistent with the Lamb wave arrival, despite of other waves including acoustic and gravity waves as well as tsunami waves were also present in specific regions.  The eruption-excited atmospheric waves produced not only TID global propagation but also modulated the wind dynamos in both E and F regions, driving electrodynamic changes closely associated with EIA and EPBs phenomena at equatorial and low latitudes. These results suggested a new vertical coupling channel through which the intense atmospheric surface disturbance processes can produce far-reaching and long-lasting geospace impacts.

Effects of Atmospheric Coherent Time on Inverse Synthetic Aperture Ladar Imaging through Atmospheric Turbulence

Abstract: Inverse synthetic aperture ladar (ISAL) can achieve high-resolution images for long-range moving targets, while its performance is affected by atmospheric turbulence. In this paper, the dynamic evolution of atmospheric turbulence is studied by using an infinitely long phase screen (ILPS), and the atmospheric coherent time is defined to describe the variation speed of the phase fluctuation induced by atmospheric turbulence. The simulation results show that the temporal decoherence of the echo induced by turbulence causes phase fluctuation and introduces an extra random phase, which deteriorates the phase stability and makes coherent synthesis impossible. Thus, we evaluated its effects on ISAL imaging and found a method to mitigate the impact of turbulence on ISAL images. The phase compensation algorithm could correct the phase variation in different pulses instead of that within the same pulse. Therefore, the relationship between the atmospheric coherent time and pulse duration time (rather than that between the atmospheric coherent time and ISAL imaging time) ultimately determines the ISAL imaging quality. Furthermore, these adverse effects could be mitigated by increasing the atmospheric coherent time or decreasing the pulse duration time, which results in an improvement in the ISAL imaging quality.

Probing gravity waves in the middle atmosphere using infrasound from explosions

Abstract: This study uses low-frequency, inaudible acoustic waves (infrasound) to probe wind and temperature fluctuations associated with breaking gravity waves in the middle atmosphere. Building on an approach introduced by Chunchuzov et al., infrasound recordings are used to retrieve effective sound-speed fluctuations in an inhomogeneous atmospheric layer that causes infrasound backscattering. The infrasound was generated by controlled blasts at Hukkakero, Finland, and recorded at the IS37 infrasound station, Norway in the late summers 2014 – 2017. Our findings indicate that the analyzed infrasound scattering occurs at mesospheric altitudes of 50 – 75 km, a region where gravity waves interact under non-linearity, forming thin layers of strong wind shear. The retrieved fluctuations were analyzed in terms of vertical wave number spectra, resulting in an approximate power law that corresponds to the “universal” saturated spectrum of atmospheric gravity waves. The power law wavenumber range corresponds to vertical atmospheric scales of 33 − 625 m. The fluctuation spectra were compared to theoretical gravity wave saturation theories as well as to independent wind measurements by the Saura medium-frequency radar near Andøya Space Center around 100 km west of IS37, yielding a good agreement in terms of vertical wavenumber spectrum amplitudes and slopes. This suggests that the radar and infrasound-based effective sound-speed profiles represent low- and high-wavenumber regimes of the same “universal” gravity wave spectrum. The results illustrate that infrasound allows for probing fine-scale dynamics not well captured by other techniques, suggesting that infrasound can provide a complementary technique to probe atmospheric gravity waves.

Upward propagation of gravity waves and ionospheric perturbations triggered by the 2022 Hunga-Tonga Volcanic Eruption

Abstract: Abstract Using an atmosphere-ionosphere coupled model (GAIA), atmospheric and ionospheric perturbations triggered by the 2022 Hunga-Tonga volcanic eruption are studied. Our result shows that ionospheric perturbations are caused by neutral wind perturbations associated with gravity waves. Gravity waves with horizontal phase speeds of 200–310 m/s are excited in the troposphere near the Hunga-Tonga volcano, and propagate upward into the thermosphere. While the amplitude of the eruption-generated gravity waves is small in the troposphere (~ 1 m/s), the amplitude of the gravity waves increases exponentially with height because of the exponential decrease of the density, reaching 60‒80 m/s at 300 km height. General features of the TIDs appeared in GNSS-TEC are reproduced fairly well. We can conclude that the eruption-generated gravity waves whose horizontal phase velocity is close to the sound speed play an important role in thermospheric and ionospheric perturbations after the Hunga-Tonga volcano eruption.

Ray-tracing global gravity wave observations in 21 years of AIRS data

Abstract: Gravity waves have a variety of different sources including wind flow over mountains, convection and jet stream instabilities. Yet when working with observations of gravity waves we can only make informed guesses of their sources. In this work we use GROGRAT to backwards ray trace stratospheric observations of gravity waves globally to learn more about their origins.We use observations of temperatures at 40km altitude observed by the AIRS (Atmospheric InfraRed Sounder) instrument on NASA’s Aqua satellite. From these observations we extract temperature perturbations and use the 3D Stockwell transform to derive gravity wave properties such as momentum flux, horizontal wavelength, vertical wavelength. These gravity waves are then backwards ray traced through the ERA5 atmosphere. The significance in this work lies in the volume: we ray trace 21 years (2002-2022) of AIRS data globally, representing by far the largest such observational dataset ever reverse ray-traced.By investigating the lowest traceable altitude of these rays, we can attribute the gravity waves to their sources (orographic gravity waves will originate near the surface whilst convective waves will have a higher origin). We can also investigate the horizontal propagation of orographic gravity waves from specific mountain ranges and how this changes seasonally. This work aims to answer the question: “Where do gravity waves observed by AIRS come from?”

Comment on acp-2022-816

Abstract: Using the general circulation model of the middle and upper atmosphere (MUAM), a number of numerical scenarios were implemented to study the impact of individual planetary waves (PWs) on the global atmospheric circulation, including zonal wind, temperature, and residual meridional circulation. The calculations were performed for the winter conditions of the Northern Hemisphere (January–February). The contribution to the formation of the dynamic and temperature regimes of the middle and upper atmosphere made by equatorial Kelvin waves propagating to the east, as well as atmospheric normal modes with periods from 4 to 16 days is shown. In particular, it is demonstrated that the impact of a 5-day PW and an ultrafast Kelvin wave can change the speed of circulation flows by up to 5 % in the areas of their amplitude maxima. The presented research results are important for a deeper understanding of the mechanisms of large-scale atmospheric interactions. Despite the obviousness and simplicity of the problem, such work has not been carried out at the moment.

Gravity wave signatures in mesospheric/lower thermospheric winds caused by Hunga Tonga-Hunga Ha‘apai volcanic eruption identified by CONDOR and the Nordic Meteor Radar Cluster

Abstract: Gravity waves are a major source of the middle atmospheric short-term variability. The Hunga Tonga-Hunga Ha‘apai volcanic eruption provided a unique opportunity to study gravity wave propagation around the globe from a well-defined source. The eruption triggered several atmospheric signatures including a lamb wave (troposphere/stratosphere/mesosphere) and a package of gravity waves. Here we present results of gravity wave signatures found in mesospheric winds leveraging multi-static meteor radar networks such as the Nordic Meteor Radar Cluster and CONDOR. We were able to identify the eastward and westward propagating gravity waves. Furthermore, it was possible to estimate the intrinsic wave properties such as a horizontal wavelength of approximately 1600-2000 km and an intrinsic phase speed of 200 m/s.

A Comparison of Stratospheric Gravity Waves in a High-Resolution General Circulation Model with 3-D Satellite Observations

Abstract: Atmospheric gravity waves (GWs) play a key role in determining the thermodynamical structure of the Earth’s middle atmosphere. Despite the small spatial and temporal scales of these waves, a few high-top general circulation models (GCMs) that can resolve them explicitly have recently become available. This study compares global GW characteristics simulated in one such GCM, the Japanese Atmospheric GCM for Upper-Atmosphere Research (JAGUAR), with those derived from three-dimensional (3-D) temperatures observed by the Atmospheric Infrared Sounder (AIRS) aboard NASA’s Aqua satellite. The target period is from 15 December 2018 to 8 January 2019, including the onset of a major sudden stratospheric warming (SSW). The 3-D Stockwell transform method is used for GW spectral analysis. The amplitudes and momentum fluxes of GWs in JAGUAR are generally in good quantitative agreement with those in the AIRS observations in both magnitude and distribution. As the SSW event progressed, the GW amplitudes and eastward momentum flux increased at low latitudes in the summer hemisphere in both the model and observation datasets. Case studies demonstrate that the model is able to reproduce comparable wave events to those in the AIRS observations with some differences, especially noticeable at low latitudes in the summer hemisphere. Through a comparison between the model results with and without the AIRS observational filter applied, it is suggested that the amplitudes of GWs near the exits and entrances of eastward jet streaks are underestimated in AIRS observations.

Atmospheric and ionospheric disturbances in Europe induced by Hunga eruption on 15 January 2022

Abstract: The massive explosive eruption of the Hunga Tonga volcano on 15 January generated atmospheric waves that were comparable with those generated by the Krakatoa 1883 eruption. The waves were recorded around the globe and affected also the ionosphere. We focus on observation of atmospheric waves in the troposphere and ionosphere in Europe. The tropospheric waves are studied using a large aperture array of microbarometers and the ionospheric disturbances are detected using continuous Doppler sounding. It is shown that long-period infrasound (periods longer than ~50 s) is observed simultaneously in the troposphere and ionosphere about an hour after the arrival of the first pressure pulse (Lamb wave) in the troposphere. Data analysis confirms propagation approximately along the shorter great circle path both for the infrasound and the Lamb wave. It is suggested that the infrasound propagated into the ionosphere probably due to imperfect refraction in the lower thermosphere. The observation of infrasound in the ionosphere at such large distances from the source (over 16 000 km) is rare and differs from ionospheric infrasound detected at large distances from the epicenters of strong earthquakes, because in the latter case the infrasound is generated locally by seismic waves. An unusually large traveling ionospheric disturbance (TID) observed in Europe and associated with the pressure wave from the Hunga Tonga eruption is also discussed. In addition, a probable observation of wave in the mesopause region approximately 25 min after the arrival of pressure pulse in the troposphere using a 23.4 kHz signal from a transmitter 557 km away is shown.

The propagation of gravity waves in Titan’s stratosphere

Abstract: Gravity waves are ubiquitous and important dynamical processes in planetary atmospheres. But their properties and impact on the lower atmosphere remain unclear for most of planets due to the lack of data. The recent in-situ observation from Huygens reveals gravity wave activity in Titan’s lower stratosphere. This paper investigates the upward propagation of gravity waves from Titan’s lower atmosphere and their thermal effects using a full-wave model. We reproduce the observed temperature perturbations with a superposition of three gravity wave solutions with λx = 50 km and λz = 5.3 km, 8.9 km, and 28 km, with the longer-wavelength one overlooked in previous studies. The simulation suggests that the propagation of gravity waves in Titan’s lower atmosphere is almost non-dissipative and thus has no wave-induced thermal effect on the stratosphere, which is very different from the planetary thermosphere. The temperature minimum at the tropopause leads to a rapid local gravity wave growth, which may be the primary reason for the significant gravity wave signals above 60 km. We also find that the zonal wind may filter out the majority of gravity waves except for those travelling perpendicular to the wind direction, which can propagate upward to above 100 km, as observed by the Huygens probe.

Reply on RC1

Abstract: Abstract. Using the general circulation model of the middle and upper atmosphere (MUAM), a number of numerical scenarios were implemented to study the impact of individual planetary waves (PWs) on the global atmospheric circulation, including zonal wind, temperature, and residual meridional circulation (RMC). The calculations were performed for the winter conditions of the Northern Hemisphere (January–February). We show the contribution to the formation of the dynamic and temperature regimes of the MUAM made by equatorial Kelvin waves propagating to the east, as well as atmospheric normal modes (NMs) with periods from 4 to 16 d. In particular, it is demonstrated that the impact of a 5 d PW and an ultra-fast Kelvin wave (UFKW) can change the speed of circulation flows by up to 6 % in the areas of their amplitude maxima. At the same time, this effect can be significantly enhanced in certain periods of time. The presented research results are important for a deeper understanding of the mechanisms of large-scale atmospheric interactions. Despite the obviousness and simplicity of the problem, such work has not been carried out yet.

A Comparison of Stratospheric Gravity Waves in a High‐Resolution General Circulation Model with 3‐D Satellite Observations

Abstract: Atmospheric gravity waves (GWs) play a key role in determining the thermodynamical structure of the Earth’s middle atmosphere. Despite the small spatial and temporal scales of these waves, a few high-top general circulation models (GCMs) that can resolve them explicitly have recently become available. This study compares global GW characteristics simulated in one such GCM, the Japanese Atmospheric GCM for Upper-Atmosphere Research (JAGUAR), with those derived from three-dimensional (3-D) temperatures observed by the Atmospheric Infrared Sounder (AIRS) aboard NASA’s Aqua satellite. The target period is from 15 December 2018 to 8 January 2019, including the onset of a major sudden stratospheric warming (SSW). The 3-D Stockwell transform method is used for GW spectral analysis. The amplitudes and momentum fluxes of GWs in JAGUAR are generally in good quantitative agreement with those in the AIRS observations in both magnitude and distribution. As the SSW event progressed, the GW amplitudes and eastward momentum flux increased at low latitudes in the summer hemisphere in both the model and observation datasets. Case studies demonstrate that the model is able to reproduce comparable wave events to those in the AIRS observations with some differences, especially noticeable at low latitudes in the summer hemisphere. Through a comparison between the model results with and without the AIRS observational filter applied, it is suggested that the amplitudes of GWs near the entrance or exit of an eastward jet streak are underestimated in AIRS observations.

Comment on acp-2022-816

Abstract: Abstract. Using the general circulation model of the middle and upper atmosphere (MUAM), a number of numerical scenarios were implemented to study the impact of individual planetary waves (PWs) on the global atmospheric circulation, including zonal wind, temperature, and residual meridional circulation (RMC). The calculations were performed for the winter conditions of the Northern Hemisphere (January–February). We show the contribution to the formation of the dynamic and temperature regimes of the MUAM made by equatorial Kelvin waves propagating to the east, as well as atmospheric normal modes (NMs) with periods from 4 to 16 d. In particular, it is demonstrated that the impact of a 5 d PW and an ultra-fast Kelvin wave (UFKW) can change the speed of circulation flows by up to 6 % in the areas of their amplitude maxima. At the same time, this effect can be significantly enhanced in certain periods of time. The presented research results are important for a deeper understanding of the mechanisms of large-scale atmospheric interactions. Despite the obviousness and simplicity of the problem, such work has not been carried out yet.

Probing gravity waves in the middle atmosphere using infrasound from explosions

Abstract: This study uses low-frequency, inaudible acoustic waves (infrasound) to probe wind and temperature fluctuations associated with breaking gravity waves in the middle atmosphere. Building on an approach introduced by Chunchuzov et al., infrasound recordings are used to retrieve effective sound-speed fluctuations in an inhomogeneous atmospheric layer that causes infrasound backscattering. The infrasound was generated by controlled blasts at Hukkakero, Finland and recorded at the IS37 infrasound station, Norway in the late summers 2014 - 2017. Our findings indicate that the analyzed infrasound scattering occurs at mesospheric altitudes of 50 - 75 km, a region where gravity waves interact under non-linearity, forming thin layers of strong wind shear. The retrieved fluctuations were analyzed in terms of vertical wave number spectra, resulting in approximate kz-3 power law that corresponds to the “universal“ saturated spectrum of atmospheric gravity waves. The kz-3 power law wavenumber range corresponds to vertical atmospheric scales of 33 - 625 m. The fluctuation spectra were compared to theoretical gravity wave saturation theories as well as to independent wind measurements by the Saura medium-frequency radar near Andøya Space Center around 100 km west of IS37, yielding a good agreement in terms of vertical wavenumber spectrum amplitudes and slopes. This suggests that the radar and infrasound-based effective sound-speed profiles represent low- and high-wavenumber regimes of the same “universal“ gravity wave spectrum. The results illustrate that infrasound allows for probing fine-scale dynamics not well captured by other techniques, suggesting that infrasound can provide a complementary technique to probe atmospheric gravity waves.

On Tsunami Waves Induced by Atmospheric Pressure Shock Waves After the 2022 Hunga Tonga‐Hunga Ha'apai Volcano Eruption

Abstract: Employing a linear shallow water equation (LSWE) model in the spherical coordinates, this paper investigates the tsunami waves generated by the atmospheric pressure shock waves due to the explosion of the submarine volcano Hunga Tonga–Hunga Ha'apai on 15 January 2022. Using the selected 59 atmospheric pressure records in the Pacific Ocean, an empirical atmospheric pressure model is first constructed. Applying the atmospheric pressure model and realistic bathymetric data in the LSWE model, tsunami generation and propagation are simulated in the Pacific Ocean. The numerical results show clearly the co-existence of the leading locked waves, propagating with the speed of the atmospheric pressure waves (∼1,100 km/hr), and the trailing free waves, propagating with long gravity ocean wave celerity (∼750 km/hr). During the event, tsunamis were reported by 41 Deep-ocean Assessment and Reporting of Tsunamis (DART) buoys in the Pacific Ocean, which require corrections because of the occurrence of atmospheric pressure waves. The numerically simulated tsunami arrival time and the amplitudes of the wave crest and trough of the leading locked waves compare reasonably well with the corrected DART measurements. The comparisons for the trailing waves are less satisfactory, since free waves could also have been generated by other tsunami generation mechanisms, which have not been considered in the present model, and by the scattering of locked waves over changing bathymetry. In this regard, the numerical results show clearly that the deep Tonga trench (∼10 km) amplifies the trailing waves in the Southeast part of the Pacific Ocean via the Proudman resonance condition.

Comparing gravity waves sampled from a kilometre-scale IFS run to AIRS satellite observations

Abstract: Gravity waves are small-scale atmospheric waves which transport energy and momentum. These waves impact the large scale circulation and increasing our understanding of them is therefore important to support improvements to weather and climate models. This presentation focusses on gravity waves in the stratosphere using data from a high resolution run of the European Centre for Medium-Range Weather Forecasts (ECMWF) Integrated Forecasting System (IFS) operated at a kilometre-scale spatial resolution, the Atmospheric Infrared Sounder (AIRS) on NASA’s Aqua satellite and the ECMWF ERA5 reanalysis. For this comparison, the IFS run and ERA5 are resampled using the AIRS observational filter. Data are examined during the first 2 weeks of November, as the high resolution model was initialised on the 1st of this month. Wave properties were found using the 2D+1 S-Transform, a spectral analysis technique, which has been previously applied to AIRS data. Asia and surrounding regions are investigated, because preliminary studies of AIRS data suggested strong gravity wave activity in this region during this time period. Gravity waves can also be seen in the high resolution model and ERA5 data at similar times and locations as those in the observations. Higher amplitude gravity waves can be seen in nighttime AIRS data compared to the resampled models. The horizontal wavelengths in the data sets are generally similar in areas of peak gravity wave activity for nighttime data. Weather models are advancing rapidly and kilometre scales, such as the experimental IFS run, could become operational in the next decade. At these grid scales, gravity waves must be resolved instead of parameterized so the models need to be tested to see if they do this correctly. This work provides information on how a cutting edge model resolves gravity waves compared to observations.

Excitation of mixed Rossby-gravity waves by wave-mean flow interactions on the sphere

Abstract: The equatorial mixed Rossby-gravity wave (MRGW) is an important contributor to tropical variability. Its excitation mechanism capable of explaining the observed MRGW variance peak at synoptic scales remains elusive. This study investigates wave-mean flow interactions as a generation process for the MRGWs using the barotropic version of the global Transient Inertia-Gravity And Rossby wave dynamics model (TIGAR), which employs Hough harmonics as the basis of spectral expansion, thereby representing MRGWs as prognostic variables. High accuracy numerical simulations manifest that interactions between waves emanating from a tropical heat source and zonal mean jets in the subtropics generate MRGWs with the variance spectra resembling the one observed in the tropical troposphere. Quantification of spectral tendencies associated with the MRGW energy growth underscores the significance of wave-mean flow interactions in comparison to excitation mechanisms driven by external forcing and wave-wave interactions. The MRGW growth and amplitude depend on the asymmetry in the zonal mean flow that may explain not only seasonal variability but also differences between the troposphere and the middle atmosphere.

Numerical modeling of relative contribution of planetary waves to the atmospheric circulation

Abstract: Abstract. Using the general circulation model of the middle and upper atmosphere (MUAM), a number of numerical scenarios were implemented to study the impact of individual planetary waves (PWs) on the global atmospheric circulation, including zonal wind, temperature, and residual meridional circulation. The calculations were performed for the winter conditions of the Northern Hemisphere (January–February). The contribution to the formation of the dynamic and temperature regimes of the middle and upper atmosphere made by equatorial Kelvin waves propagating to the east, as well as atmospheric normal modes with periods from 4 to 16 days is shown. In particular, it is demonstrated that the impact of a 5-day PW and an ultrafast Kelvin wave can change the speed of circulation flows by up to 5 % in the areas of their amplitude maxima. The presented research results are important for a deeper understanding of the mechanisms of large-scale atmospheric interactions. Despite the obviousness and simplicity of the problem, such work has not been carried out at the moment.

3D reconstruction of atmospheric gravity waves and derivation of vertical wave parameters with tomography applied to data from two ground-based cameras observing OH airglow

Abstract: Atmospheric gravity waves transport energy and momentum through the atmosphere and can travel large horizontal and vertical distances from the troposphere to the mesosphere and higher. They contribute to atmospheric dynamics and among others drive the meridional pole-to-pole circulation in the mesosphere. Thus, knowing about gravity waves, their spatio-temporal characteristics, their interaction with other waves and the atmospheric background is attracting more and more attention in order to further improve climate and even meteorological models.In the upper mesosphere / lower thermosphere (UMLT) region around an altitude of 80km to 100km, OH airglow can be utilized for passive remote sensing and continuous nightly observations of atmospheric dynamics, especially of gravity waves. The OH airglow layer is a chemiluminescent layer with a strong emission in the short wave infrared spectral range (at about 1500nm) and is located at an altitude of about 86-87km with a layer halfwidth of about 4km. The OH airglow intensity is modulated by traversing atmospheric gravity waves which lead amongst others to a vertical transport of atomic oxygen. Observing the OH airglow with short-wave infrared imagers allows characterizing gravity waves. From these observations the horizontal wave parameters (horizontal wavelength, horizontal direction of propagation, etc.) can be derived.In this study we present measurements of two ground-based FAIM (Fast Airglow IMager) systems, which are cameras sensitive in the short-wave infrared region observing the OH airglow layer with a high temporal resolution. The cameras are located at Oberpfaffenhofen, Germany and Otlica, Slovenia, about 300km apart from each other and are pointing to the same volume at about 87km located in the Alpine Region above Northern Italy. We developed a novel tomographic algorithm to allow for a three-dimensional reconstruction of the airglow layer by combining images from the two viewing angles. In order to solve the highly underdetermined equation system, prior knowledge of the OH airglow layer vertical profile is needed e.g. from multi-year observations of SABER on the TIMED satellite on a statistical basis, or Gaussian and Chapman basis functions. This allows us, among others, to derive the vertical wavelength of the waves, their three-dimensional propagation direction, and their three-dimensional structure. From that knowledge, further wave parameters but also the horizontal wind along the wave propagation can be estimated via the wave’s dispersion relation.We will explain the tomographic reconstruction method, its capabilities and limits and will present a detailed case study showing a 3D-reconstructed gravity wave and the derivation of its parameters.This work received funding from the Bavarian State Ministry of the Environment and Consumer Protection.

Asymptotic Solutions for Equatorial Waves on Venus

Abstract: The atmosphere of Venus exhibits equatorial planetary-scale waves that are suspected to play an important role in its complex atmospheric circulation. Due to its particularly long sidereal day (243 terrestrial days against 24 h for the Earth), the Venusian waves must be described with the momentum equations for a cyclostrophic regime, but efforts to derive analytical wave solutions have been scarce. Following a classic approach for the terrestrial quasi-geostrophic regime, I present analytical solutions for equatorial waves in the atmosphere of Venus, assuming a single layer of a homogeneous incompressible fluid with a free surface and focusing on two asymptotic cases described by the ratio of their non-dimensional frequency and zonal wavenumber. One of the dispersion relations that has been obtained describes waves on a small spatial scale propagating upstream relative to the zonal flow, which is associated with a Rossby-type wave called “centrifugal”. The solutions for the other asymptotic case were interpreted as inertio-surface waves, which describe planetary-scale waves that can propagate “upstream” and “downstream” relative to the zonal winds and have null group velocity. These new wave solutions stress relevant differences between waves in geostrophic and cyclostrophic regimes and may be applicable to Saturn’s moon, Titan, and Venus-like exoplanets.