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Mesospheric gravity-wave (GW) phase velocity spectra and total powers at two Antarctic stations, Davis and Syowa, were derived using OH airglow image data from March to October in 2016. The total p...

Through multi-order structure function analysis and singularity measurement, the Hurst index and intermittent parameter are obtained to quantitatively describe the characteristics of atmospheric disturbance based on the round-trip intelligent sounding system (RTISS) in the lower-middle stratosphere. According to the third-order structure function, small-scale gravity waves are classified into three states: stable, unstable, and accompanied by turbulence. The evolution of gravity waves is reflected by the variation of the third-order structure function over time, and the generation of turbulence is also observed. The atmospheric disturbance intensity parameter RT is defined in this paper and contains both wave disturbance ( \begin{document}$ {H}_{1} $\end{document} ) and random intermittency ( \begin{document}$ {C}_{1} $\end{document} ). RT is considered to reflect the characteristics of atmospheric disturbance more reasonably than either of the above two alone. In addition, by obtaining the horizontal wavenumber spectrum from the flat-floating stage and the vertical wavenumber spectrum from the ascending and descending stages at the height range of 18–24 km, we found that when the gravity wave activity is significantly enhanced in the horizontal direction, the amplitude of the vertical wavenumber spectrum below is significantly larger, which shows a significant impact of gravity wave activity on the atmospheric environment below.

The Hunga Tonga–Hunga Ha′apai volcano eruption was a unique event that caused many atmospheric phenomena around the globe. In this study, we investigate the atmospheric gravity waves in the mesosphere/lower-thermosphere (MLT) launched by the volcanic explosion in the Pacific, leveraging multistatic meteor radar observations from the Chilean Observation Network De Meteor Radars (CONDOR) and the Nordic Meteor Radar Cluster in Fennoscandia. MLT winds are computed using a recently developed 3DVAR+DIV algorithm. We found eastward- and westward-traveling gravity waves in the CONDOR zonal and meridional wind measurements, which arrived 12 and 48 h after the eruption, and we found one in the Nordic Meteor Radar Cluster that arrived 27.5 h after the volcanic detonation. We obtained observed phase speeds for the eastward great circle path at both locations of about 250 m s−1, and they were 170–150 m s−1 for the opposite propagation direction. The intrinsic phase speed was estimated to be 200–212 m s−1. Furthermore, we identified a potential lamb wave signature in the MLT winds using 5 min resolved 3DVAR+DIV retrievals.

Ray path theory is an asymptotic approximation to the wave equations. It represents efficiently gravity wave propagation in nonuniform background flows so that it is useful to develop schemes of gravity wave effects in general circulation models. One of the main limitations of ray path theory to be applied in realistic flows is in caustics where rays intersect and the ray solution has a singularity. Gaussian beam approximation is a higher-order asymptotic ray path approximation that considers neighboring rays to the central one, and thus, it is free of the singularities produced by caustics. A previous implementation of the Gaussian beam approximation assumes a horizontally uniform flow. In this work, we extend the Gaussian beam approximation to include horizontally nonuniform flows. Under these conditions, the wave packet can undergo horizontal wave refraction producing changes in the horizontal wavenumber, which affects the ray path as well as the ray tube cross-sectional area and so the wave amplitude via wave action conservation. As an evaluation of the Gaussian beam approximation in horizontally nonuniform flows, a series of proof-of-concept experiments is conducted comparing the approximation with the linear wave solution given by the WRF Model. A very good agreement in the wave field is found. An evaluation is conducted with conditions that mimic the Antarctic polar vortex and the orography of the southern flank of South America. The Gaussian beam approximation nicely reproduces the expected asymmetry of the wave field. A much stronger disturbance propagates toward higher latitudes (polar vortex) compared to lower latitudes.

The propagating characteristics of the water and muddy waves are one of the concerns of theoretical studies because of the following facts: (1) With the development of the economy in the estuaries, local residents and government paid increasing attention to the ecological environment of the estuarine beaches The propagating characteristics of the water and muddy waves are closely related to the ecological environment, the concern of the government and the residents. (2) The propagating characteristics of the mud are the bottleneck of the study of the coastal and beach dynamics because of the complicated constitutive relation of the mud. The different constitutive models may lead to different explanations of its mechanism. Hence, the proper selection of the model is one of the keys to reveal the true kinematic properties of the mud in the estuaries. This paper first establishes a power law model of the constitutive relation of the mud. Based on this model, a gravity wave theory is proposed. According to the mechanism of the mud wave transportation, the coupled mud-water wave field can be divided into two layers. The upper layer is described as the viscous Newtonian fluid, whereas the lower high-concentration mud layer is described as the power law fluid. Next, the equations of the proposed model are discretized and the calculations are made by using the difference method. Then, the propagating characteristics are discussed, and the dispersion relations of the water and mud waves are analyzed in detail.

Background/Objectives: The ionospheric response to the tropical cyclone (TC) OCKHI of December 2017 in the equatorial region is presented in the study. Methods/Statistical analysis: The ionospheric response includes a change in Total Electron Content (TEC) is utilized using the stations of Tirunelveli and Bangalore. The critical frequency (foF2) from Ionosonde over Tirunelveli station also considered to study the TC effect in the F2 region of ionosphere. Findings: It has been observed that the significant changes in the equatorial ionosphere exhibits during the tropical cyclone (TC) OCKHI. They are: Ionospheric parameter of vertical total electron content (VTEC) varies during the TC (i.e. from Day 332 to Day 336 of the year 2017) as the cyclone center is near to the Tirunelveli (8.7o N, 77.8o E) and the same follows for the IGS station of Bangalore. In addition, ionosonde measurements of foF2 perceived for the local night time support the TEC decrease noted over Tirunelveli when the cyclone attains its peak on 01 December 2017. Novelty/Applications: Using the ionosonde data over the equatorial ionosphere, such behavior may not be reported earlier to the best of my knowledge. The gravity wave induced by the TC Ockhi redistributes the element of the ionosphere due to strong convection and lightning activity. Keywords: TEC; Cyclone; foF2; OCKHI; and gravity waves

We use the Specified Dynamics version of the Whole Atmosphere Community Climate Model Extended (SD-WACCMX) to model the descent of nitric oxide (NO) and other mesospheric tracers in the extended, elevated stratopause phase of the 2013 sudden stratospheric warming (SSW). The dynamics are specified with a high-altitude version of the Navy Global Environmental Model (NAVGEMHA). Consistent with our earlier published results, we find that using a high-altitude meteorological analysis to nudge WACCMX allows for a realistic simulation of the descent of lower-thermospheric nitric oxide down to the lower mesosphere, near 60 km. This is important because these simulations only included auroral electrons and did not consider additional sources of NO from higher-energy particles that might directly produce ionization, and hence nitric oxide, below 80-85 km. This suggests that the so-called energetic particle precipitation indirect effect (EPP-IE) can be accurately simulated, at least in years of low geomagnetic activity, such as 2013, without the need for additional NO production, provided the meteorology is accurately constrained. Despite the general success of WACCMX in bringing uppermesospheric NO down to 55-60 km, a detailed comparison of the WACCMX fields with the analyzed NAVGEMHA H2O and satellite NO and H2O data from the Solar Occultation for Ice Experiment (SOFIE) and the Atmospheric Chemistry Experiment-Fourier Transform Spectrometer (ACE-FTS) reveals significant differences in the latitudinal and longitudinal distributions at lower altitudes. This stems from the tendency for WACCMX descent to maximize at sub-polar latitudes, and while such sub-polar descent is seen in the NAVGEM-HA analysis, it is more transient than in the WACCMX simulation. These differences are linked to differences in the transformed Eulerian mean (TEM) circulation between NAVGEM-HA and WACCMX, most likely arising from differences in how gravity wave forcing is represented. To attempt to compensate for the differing distributions of model vs. observed NO and to enable us to quantify the total amount of upper-atmospheric NO delivered to the stratopause region, we use potential vorticity and equivalent latitude coordinates. Preliminary results suggest both model and observations are generally consistent with NO totals in the range of 0.1-0.25 gigamoles (GM). National Aeronautics and Space Administration, Goddard Space Flight Center [S50029G] Published version This research has been supported by the National Aeronautics and Space Administration, Goddard Space Flight Center (grant no. Interagency Agreement S50029G).

The problem of absorption by a resonator of a gravity wave that propagates on the surface of an incompressible fluid is solved. The resonator is small as compared with the wavelength. For the free fluid surface the resonance, i.e., maximally possible, absorption cross-sections of resonators of various types are found. It is shown that the resonance absorption cross-section depends only on the wavelength. The problem of absorption of a gravity wave propagating in a channel is also considered. It is shown that the joint usage of monopole and dipole resonators ensures the total absorption of wave energy in the channel whose width is not greater than the wavelength.

An undular mesospheric bore event has been recorded over the western Himalayan region in O(1S) 557.7 nm airglow images on a clear and moonless night of 02 October 2018 using a multi-wavelength all-sky imager at Hanle, Leh Ladakh, India (32.77°N, 78.97°E). The bore has a prominent leading dark front followed by trailing waves and it propagates with a mean observed phase velocity of ~31 ± 5 m/s. It also shows a small-scale undulation and clockwise rotation in its phase front. In order to understand the evolution of the bore, vertical temperature profiles from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument onboard TIMED satellite and HWM14 wind maps are used. SABER temperature shows a mesospheric inversion layer prior to the occurrence of the bore event which acted as a thermal duct layer to guide the propagation of the bore. The analyses also suggest that inhomogeneity in the duct depth at different parts of the bore’s horizontal extension could lead the small-scale undulations in the bore phase fronts. The same can also be responsible for the rotation of the bore. Additionally, the peak separation of the bore’s trailing waves suggests that large-scale gravity wave interaction with pre-existing thermal duct could be the potential source for the generation of the undular bore at mesospheric height. Furthermore, the present results indicate that neutral instabilities and weakening duct layer in the path of the bore propagation might have accelerated the faster dissipation of the bore’s energy and consequently suppress its long-distance horizontal propagation.

This paper presents a minimal model of the Madden--Julian Oscillation (MJO), isolating a robust mechanism that leads to the observed characteristic pattern and eastward propagation. A localized heat source due to condensation at the equator leads to a Gill-like pattern in the geopotential, which in turn induces moisture convergence and further condensation. Over a wide range of parameters the moisture convergence is found to be slightly to the east of the heat source. This convergence leads to condensation and hence a heat source that also is east of the original one, thus causing the pattern itself to propagate east. The speed of the ensuing eastward propagation is limited by the ability of the moisture convergence to remain east of the moving condensation heat source. If the pattern moves too quickly, the moisture convergence cannot keep up; the propagation then slows and/or the pattern itself may dissolve. The speed of propagation thus scales with the fluid speed that is induced by the condensation itself, and thus in turn with the strength of the condensational heating, and not with a gravity wave speed. The speed also increases with the distance between the initial heating source and the subsequent condensation. In the real world this distance is determined not only by the location of moisture convergence but also by the complex physics of convection in a conditionally unstable environment, and thus cannot be accurately determined in any simple model. Thus, even though the underlying MJO mechanism is not complicated its reproduction will necessarily depend rather sensitively on model parameters in numerical simulations.

A model is proposed to explain the observed influence of gravity waves of relativistic double stars on the vertical component of the Earth’s electric field in the atmospheric boundary layer. The considered mechanism is the perturbation of the Earth’s orbit by the gravity waves from the relativistic double star systems leading to a small displacement between the Earth and the free electric charge of the Earth’s atmosphere. The proposed model gives estimates of the amplitude of the Ez components spectrally localized at the frequencies of the gravity waves from the relativistic double star systems that do not contradict the observations.

The propagation of evanescent acoustic-gravity waves in the atmosphere with an arbitrary altitude temperature profile is investigated. The possibility of the existence of two types of evanescent wave modes in a vertically nonisothermal atmosphere is shown. The first type is the f-mode in which the dispersion does not depend on the altitude inhomogeneity of temperature and, therefore, is carried out at any altitude level of the nonisothermal atmosphere. The second type is a recently discovered $$\gamma $$ ‑mode in which the dispersion depends on the altitude temperature gradient and can be fulfilled only at certain altitude intervals. The possibility of realizing the f- and $$\gamma $$ - modes in the Earth’s atmosphere is considered, taking into account the model altitude temperature profile. It is shown that these modes can exist at the heights of local temperature extremes in the atmosphere. Moreover, they are realized only in a narrow range of spectral parameters for which the conditions for a decrease in the wave energy above and below the level of their propagation are satisfied. For the f-mode, this energy condition is fulfilled at the altitudes of the local temperature minima, while that for the $$\gamma $$ -mode is at the altitudes of the local maxima. Recommendations are given regarding the possibility of observing these modes in the atmosphere of the Earth and the Sun. In the Earth’s atmosphere, the f-mode can presumably be observed near the mesopause with the characteristic wavelength $${{\lambda }_{x}} \approx 75\,{\text{km}}$$ and in the solar atmosphere at the heights of the chromospheres with $${{\lambda }_{x}} \approx 1600\,{\text{km}}$$ . The period of the f‑mode propagating in the region of the temperature minimum slightly exceeds the Brent-Vaisala period at this altitude. In the Earth’s atmosphere, the $$\gamma $$ -mode can be realized in the regions of maximum temperature, for example, at the height of the stratopause with $${{\lambda }_{x}} \approx 100\,{\text{km}}$$ and a period slightly larger than the Brent-Vaisala period at the altitude of its propagation.

The gravity wave interaction with an array of porous cages in the presence of a seaside submerged quarter-circular porous breakwater (QCPBW) is analyzed within the framework of linearized water wav...

In a companion paper, the Multiscale Gravity Wave Model (MS-GWaM) has been introduced and its application to a global model as a transient subgrid-scale parameterization has been described. This paper focuses on the examination of intermittency of gravity waves (GWs) modeled by MS-GWaM. To introduce the variability and intermittency in wave sources, convective GW sources are formulated, using diabatic heating diagnosed by the convection parameterization, and they are coupled to MS-GWaM in addition to a flow-independent source in the extratropics accounting for GWs due neither to convection nor to orography. The probability density function (PDF) and Gini index for GW pseudomomentum fluxes are assessed to investigate the intermittency. Both are similar to those from observations in the lower stratosphere. The intermittency of GWs over tropical convection is quite high and is found not to change much in the vertical direction. In the extratropics, where nonconvective GWs dominate, the intermittency is lower than that in the tropics in the stratosphere and comparable to that in the mesosphere, exhibiting a gradual increase with altitude. The PDFs in these latitudes seem to be close to the lognormal distributions. Effects of transient GW–mean-flow interactions on the simulated GW intermittency are assessed by performing additional simulations using the steady-state assumption in the GW parameterization. The intermittency of parameterized GWs over tropical convection is found to be overestimated by the assumption, whereas in the extratropics it is largely underrepresented. Explanation and discussion of these effects are included.

We present gravity wave climatologies based on 7 years (2012–18) of lidar and Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) temperatures and reanalysis data at 54° and 69°N in the altitude range 30–70 km. We use 9452 (5044) h of lidar observations at Kühlungsborn [Arctic Lidar Observatory for Middle Atmosphere Research (ALOMAR)]. Filtering according to vertical wavelength (λz < 15 km) or period (τ < 8 h) is applied. Gravity wave potential energy densities (GWPED) per unit volume (EpV) and per unit mass (Epm) are derived. GWPED from reanalysis are smaller compared to lidar. The difference increases with altitude in winter and reaches almost two orders of magnitude around 70 km. A seasonal cycle of EpV with maximum values in winter is present at both stations in nearly all lidar and SABER measurements and in reanalysis data. For SABER and for lidar (with λ < 15 km) the winter/summer ratios are a factor of ~2–4, but are significantly smaller for lidar with τ < 8 h. The winter/summer ratios are nearly identical at both stations and are significantly larger for Epm compared to EpV. Lidar and SABER observations show that EpV is larger by a factor of ~2 at Kühlungsborn compared to ALOMAR, independent of season and altitude. Comparison with mean background winds shows that simple scenarios regarding GW filtering, etc., cannot explain the Kühlungsborn–ALOMAR differences. The value of EpV decreases with altitude in nearly all cases. Corresponding EpV-scale heights from lidar are generally larger in winter compared to summer. Above ~55 km, EpV in summer is almost constant with altitude at both stations. The winter–summer difference of EpV scale heights is much smaller or absent in SABER and in reanalysis data.

Current gravity wave (GW) parameterization (GWP) schemes are using the steady-state assumption, in which an instantaneous balance between GWs and mean flow is postulated, thereby neglecting transient, nondissipative interactions between the GW field and the resolved flow. These schemes rely exclusively on wave dissipation, by GW breaking or near critical layers, as a mechanism leading to forcing of the mean flow. In a transient GWP, without the steady-state assumption, nondissipative wave–mean-flow interactions are enabled as an additional mechanism. Idealized studies have shown that this is potentially important, and therefore the transient GWP Multiscale Gravity Wave Model (MS-GWaM) has been implemented into a state-of-the-art weather and climate model. In this implementation, MS-GWaM leads to a zonal-mean circulation that agrees well with observations and increases GW momentum-flux intermittency as compared with steady-state GWPs, bringing it into better agreement with superpressure balloon observations. Transient effects taken into account by MS-GWaM are shown to make a difference even on monthly time scales: in comparison with steady-state GWPs momentum fluxes in the lower stratosphere are increased and the amount of missing drag at Southern Hemispheric high latitudes is decreased to a modest but nonnegligible extent. An analysis of the contribution of different wavelengths to the GW signal in MS-GWaM suggests that small-scale GWs play an important role down to horizontal and vertical wavelengths of 50 km (or even smaller) and 200 m, respectively.

We assess whether tropical islands tend to warm or cool the troposphere. To this end, we use idealized simulations of the Radiative‐Convective Equilibrium employing a simulation domain that contains flat tropical islands represented by a land surface scheme. Results show more frequent precipitation over land as coastal breezes establish, and gravity waves triggered by afternoon convection propagating away from the islands. These waves horizontally homogenize density and in doing so communicate convectively‐induced temperature anomalies from the islands onto the ocean. What is the influence of the islands on tropospheric temperature? The diurnal surface warming of the islands tends to push the afternoon convection over land towards a warmer moist adiabat, and along with it, the temperature profile of the troposphere. However, at the same time, drying of the land surface pulls it towards a colder moist adiabat. All in all, we find that islands rather cool than warm the troposphere. More specifically, we obtain a weakly colder domain‐mean troposphere during episodes with a larger share of precipitation over land, or when the prescribed land fraction is increased. In particular, we find that the cooling becomes more pronounced over large islands. Overall, the results indicate that the inability of evaporation to keep up with the daytime surface warming over land, in contrast to the ocean, is of key relevance for understanding land effects on the mean climate

Afternoon deep convection over the Maritime Continent islands propagates offshore in the evening to early morning hours, leading to a nocturnal rainfall maximum over the nearby ocean. This work investigates the formation of the seaward precipitation migration off western Sumatra and its intraseasonal and seasonal characteristics using BMKG C-band radar observations from Padang and ERA5 reanalysis. A total of 117 nocturnal offshore rainfall events were identified in 2018, with an average propagation speed of 4.5 m s−1 within 180 km of Sumatra. Most offshore propagation events occur when the Madden–Julian oscillation (MJO) is either weak (real-time multivariate MJO index < 1) or active over the Indian Ocean (phases 1–3), whereas very few occur when the MJO is active over the Maritime Continent and western Pacific Ocean (phases 4–6). The occurrence of offshore rainfall events also varies on the basis of the seasonal evolution of the large-scale circulation associated with the Asian–Australian monsoons, with fewer events during the monsoon seasons of December–February and June–August and more during the transition seasons of March–May and September–November. Low-level convergence, resulting from the interaction of the land breeze and background low-level westerlies, is found to be the primary driver for producing offshore convective rain propagation from the west coast of Sumatra. Stratiform rain propagation speeds are further increased by upper-level easterlies, which explains the faster migration speed of high reflective clouds observed by satellite. However, temperature anomalies associated with daytime convective latent heating over Sumatra indicate that gravity waves may also modulate the offshore environment to be conducive to seaward convection migration.

In this paper, we study the temperatures and gravity wave (GW) activity in the Martian thermosphere during low solar activity. For this purpose, we extracted the GW amplitudes and thermospheric temperatures from CO2 densities measured in situ by the Neutral Gas and Ion Mass Spectrometer (NGIMS) aboard the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. These observations were obtained during the declining phase of solar activity between solar longitude (Ls) =294° in Mars year (MY) 32 and Ls = 242° in MY 35. The observations of the present study show that the temperatures are lower and GW amplitudes are higher at low solar activity. The response of the thermospheric temperatures to solar irradiance is local time dependent such that the noontime and duskside temperatures show significant correlation (correlation coefficient, R > 0.8) with the solar irradiance whereas the temperatures on the dawnside show moderate correlation (R = 0.55). Furthermore, the nominal negative correlation between the gravity wave amplitudes and thermospheric temperatures, which was disturbed during the 2018 global dust event, was restored after the subsidence of the event. Interestingly, the correlation between the thermospheric temperatures and GW activity is also local time dependent with moderate correlation at noon (R = -0.65) and weak correlation at other local times. From the results of the present study, it is inferred that the variability of GW amplitudes in the Martian thermosphere are not necessarily controlled by the temperatures of the underlying atmosphere alone. Other factors, such as the variation of GW amplitudes at the source region and/or changes in the circulation of the underlying atmosphere, are also likely to play a significant role, particularly at the terminator and on the nightside.

Post-sunset ionospheric irregularities are common features of the equatorial ionosphere that affect radio communication and navigation systems; their triggering physical mechanism is not yet fully understood. Atmospheric gravity wave is considered as a seeding mechanism for the occurrence of ionospheric irregularities ( Abdu et al., 2009 ). To understand the effects of atmospheric waves, characteristics of wavelike oscillation from ionospheric total electron content (TEC) fluctuation that can be obtained from superposition of different oscillation modes have been investigated. Decomposing fluctuating TEC into different oscillation modes and investigating oscillation characteristics of each component is also important to get insight about the characteristics of individual atmospheric waves that may cause TEC fluctuation. In this paper we have investigated characteristics of components of fluctuating TEC obtained from SCINDA GPS receiver installed at Bahir Dar, (geographic coordinate, 11.5°N, 37.6° E, and dip latitude of 2.5°N) Ethiopia during April 2012. First Empirical Mode Decomposition (EMD) has been applied to decompose TEC fluctuation into different oscillation modes that are known as Intrinsic Mode Function (IMF). Hilbert-Huang Transform (HHT) and Continuous Wavelet Transform (CWT) have been applied to investigate the characteristics of wave-like oscillations. Applying EMD on fluctuating vTEC corresponding to a GPS satellite, five components are found. Results from HHT and CWT have shown excellent agreement. In addition, it is found out that the median periods of oscillation of those five components are 9, 17, 47, 78, and 118 min. Of these periods, 17 and 47 min respectively are oscillation periods of components of TEC fluctuation with occurrence frequency of 92% and 91% that may be interpreted as the manifestation of two frequently occurring components of atmospheric gravity waves that are likely generated by the motion of solar terminator.

Fringing reefs which are common nearshore islands with coral reef growth have special topography of very steep slope on the fore-reef and mild slope on the wide flat. When incident waves propagate from a very deep water region (from hundreds of meters to thousands of meters of depth) to approaching the reef they abruptly commence a very shallow water (only few centimeters to several meters of depth) and create strong hydrodynamic processes on the reef flat. Due to shallow depth, waves feel the bottom and break in the area of fore-reef slope and reef crest and partial reef flat. Infra-gravity waves (IG), other name as bound long waves or surf beat, which belong to low-frequency wave type (0.002Hz ¸ 0.04Hz) are generated by the varying-breaking point mechanism on the shallow reef flat. On the flat, short wave energy is almost dissipated; low-frequency waves are strongly dominated over the surf zone till swash zone. Wave set-up causing an increase of water level on the flat combines with the run-up at the shoreline which can lead to coastal flooding. Besides, if the reef flat length is in the order of one fourth of wavelength the first oscillation resonant mode with standing wave occurs. This component is resonantly amplified at the shoreline relative to the incident infra-gravity wave energy at the reef crest.

The way the large-scale flow determines the energy of the nonorographic mesoscale inertia–gravity waves (IGWs) is theoretically significant and practically useful for source parameterization of IGWs. The relations previously developed on the f plane for tropospheric sources of IGWs including jets, fronts, and convection in terms of associated secondary circulations strength are generalized for application over the globe. A low-pass spatial filter with a cutoff zonal wavenumber of 22 is applied to separate the large-scale flow from the IGWs using the ERA5 data of ECMWF for the period 2016–19. A comparison with GRACILE data based on satellite observations of the middle stratosphere shows reasonable representation of IGWs in the ERA5 data despite underestimates by a factor of smaller than 3. The sum of the energies, which are mass-weighted integrals in the troposphere from the surface to 100 hPa, as given by the generalized relations is termed initial parameterized energy. The corresponding energy integral for the IGWs is termed the diagnosed energy. The connection between the parameterized and diagnosed IGW energies is explored with regression analysis for each season and six oceanic domains distributed over the globe covering the Northern and Southern Hemispheres and the tropics. While capturing the seasonal cycle, the domain area-average seasonal mean initial parameterized energy is weaker than the diagnosed energy by a factor of 3. The best performance in regression analysis is obtained by using a combination of power and exponential functions, which suggests evidence of exponential weakness.

Full list of authors: Rastinejad, Jillian C.; Gompertz, Benjamin P.; Levan, Andrew J.; Fong, Wen-Fai; Nicholl, Matt; Lamb, Gavin P.; Malesani, Daniele B.; Nugent, Anya E.; Oates, Samantha R.; Tanvir, Nial R.; Postigo, Antonio de Ugarte; Kilpatrick, Charles D.; Moore, Christopher J.; Metzger, Brian D.; Ravasio, Maria Edvige; Rossi, Andrea; Schroeder, Genevieve; Jencson, Jacob; Sand, David J.; Smith, Nathan; Fernandez, Jose Feliciano Agui; Berger, Edo; Blanchard, Peter K.; Chornock, Ryan; Cobb, Bethany E.; De Pasquale, Massimiliano; Fynbo, Johan P. U.; Izzo, Luca; Kann, D. Alexander; Laskar, Tanmoy; Marini, Ester; Paterson, Kerry; Escorial, Alicia Rouco; Sears, Huei M.; Thone, Christina C., Gamma-ray bursts (GRBs) are divided into two populations1,2; long GRBs that derive from the core collapse of massive stars (for example, ref. 3) and short GRBs that form in the merger of two compact objects4,5. Although it is common to divide the two populations at a gamma-ray duration of 2 s, classification based on duration does not always map to the progenitor. Notably, GRBs with short (≲2 s) spikes of prompt gamma-ray emission followed by prolonged, spectrally softer extended emission (EE-SGRBs) have been suggested to arise from compact object mergers6,7,8. Compact object mergers are of great astrophysical importance as the only confirmed site of rapid neutron capture (r-process) nucleosynthesis, observed in the form of so-called kilonovae9,10,11,12,13,14. Here we report the discovery of a possible kilonova associated with the nearby (350 Mpc), minute-duration GRB 211211A. The kilonova implies that the progenitor is a compact object merger, suggesting that GRBs with long, complex light curves can be spawned from merger events. The kilonova of GRB 211211A has a similar luminosity, duration and colour to that which accompanied the gravitational wave (GW)-detected binary neutron star (BNS) merger GW170817 (ref. 4). Further searches for GW signals coincident with long GRBs are a promising route for future multi-messenger astronomy. © 2022, The Author(s), under exclusive licence to Springer Nature Limited., The Fong group at Northwestern acknowledges support by the National Science Foundation under grant nos. AST-1814782 and AST-1909358 and CAREER grant no. AST-2047919. W.F. gratefully acknowledges support by the David and Lucile Packard Foundation. A.J.L. and D.B.M. are supported by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 725246). M.N. and B.P.G. are supported by the ERC under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 948381). M.N. acknowledges a Turing Fellowship. G.P.L. is supported by the UK Science and Technology Facilities Council grant ST/S000453/1. A.R. and E.M. acknowledge support from the INAF research project ‘LBT - Supporto Arizona Italia’. J.F.A.F. acknowledges support from the Spanish Ministerio de Ciencia, Innovación y Universidades through the grant PRE2018-086507. D.A.K. and J.F.A.F. acknowledge support from Spanish National Research Project RTI2018-098104-J-I00 (GRBPhot). W. M. Keck Observatory and MMT Observatory access was supported by Northwestern University and the Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA). Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration (NASA). The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. We wish to recognize and acknowledge the very important cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. Observations reported here were obtained at the MMT Observatory, a joint facility of the University of Arizona and the Smithsonian Institution. On the basis of observations obtained at the international Gemini Observatory (programme ID GN2021B-Q-109), a programme of NOIRLab, which is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation on behalf of the Gemini Observatory partnership: the National Science Foundation (United States), National Research Council (Canada), Agencia Nacional de Investigación y Desarrollo (Chile), Ministerio de Ciencia, Tecnología e Innovación (Argentina), Ministério da Ciência, Tecnologia, Inovações e Comunicações (Brazil) and Korea Astronomy and Space Science Institute (Republic of Korea). Processed using the Gemini IRAF package and DRAGONS (Data Reduction for Astronomy from Gemini Observatory North and South). This work made use of data supplied by the UK Swift Science Data Centre at the University of Leicester. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. This research is based on observations made with the NASA/ESA Hubble Space Telescope obtained from the Space Telescope Science Institute, which is operated by the AURA, Inc., under NASA contract NAS 5-26555. These observations are associated with programme no. 16923. This work is partly based on observations made with the Gran Telescopio Canarias, installed at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias, on the island of La Palma. Partly based on observations collected at the Calar Alto Astronomical Observatory, operated jointly by Instituto de Astrofísica de Andalucía (CSIC) and Junta de Andalucía. Partly based on observations made with the Nordic Optical Telescope, under programme 64-502, owned in collaboration by the University of Turku and Aarhus University, and operated jointly by Aarhus University, the University of Turku and the University of Oslo, representing Denmark, Finland and Norway, respectively, the University of Iceland and Stockholm University at the Observatorio del Roque de los Muchachos, La Palma, Spain, of the Instituto de Astrofísica de Canarias. The LBT is an international collaboration among institutions in the United States, Italy and Germany. LBT Corporation partners are: The University of Arizona on behalf of the Arizona Board of Regents; Istituto Nazionale di Astrofisica, Italy; LBT Beteiligungsgesellschaft, Germany, representing the Max Planck Society, The Leibniz Institute for Astrophysics Potsdam and Heidelberg University; The Ohio State University, representing OSU, University of Notre Dame, University of Minnesota and University of Virginia.

Large wind shears around the mesopause region play an important role in atmospheric neutral dynamics and ionospheric electrodynamics. Based on previous observations using sounding rockets, lidars, radars, and model simulations, large shears are mainly attributed to gravity waves (GWs) and modulated by tides (Liu, 2017). Based on the dispersion and polarization relations of linear GWs and the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) temperature data from 2002 to 2019, a method of deriving GW-perturbed wind shears is proposed. The zonal-mean GW-perturbed shears have peaks (13–17 ms−1 km−1) at around the mesopause region, i.e., at z = 90–100 km at most latitudes and at z = 80–90 km around the cold summer mesopause. This latitude–height pattern is robust over the 18 years and agrees with model simulations. The magnitudes of the GW-perturbed shears exhibit year-to-year variations and agree with the lidar and sounding rocket observations in a climatological sense but are 60 %–70 % of the model results in the zonal-mean sense. The GW-perturbed shears are hemispherically asymmetric and have strong annual oscillation (AO) at around 80 km (above 92 km) at the northern (southern) middle and high latitudes. At middle to high latitudes, the peaks of AO shift from winter to summer and then to winter again with increasing height. However, these GW-perturbed shears may be overestimated because the GW propagation direction cannot be resolved by the method and may be underestimated due to the observational filter, sampling distance, and cutoff criterion of the vertical wavelength of GWs.

In the present manuscript, the time-dependent capillary gravity wave motion in the presence of a current and an undulated permeable bottom is analyzed. The spectral method is used to simulate the time-dependent surface elevation. Also, the Laplace–Fourier transform method is used to obtain the integral form of the surface elevation, and the asymptotic form of the associated highly oscillatory integral is derived using the method of stationary phase. The reflection and transmission coefficients due to the small bottom undulation are obtained using the perturbation method and the Fourier transform method and also alternatively using Green’s function technique and Green’s identity. The nature of wave energy propagation obtained from plane capillary gravity wave motion is verified through time domain simulation and using the spectral method. It is found that, in the case of co-propagating waves, the wave energy propagates faster and also the surface profiles in terms of wave packets move faster for larger values of the Froude number. Also, the maximum value of the reflection and transmission coefficients decreases due to increasing values of the Froude number. For the sinusoidal bottom topography, the Bragg resonance occurs if the ratio of the wave numbers of the wave and the rippled bed is one by two.

Negative temperature perturbations (T′) from gravity waves are known to be favorable to tropical tropopause layer (TTL) clouds, and recent studies have further suggested a possible role of dT′/dz in facilitating TTL cloud formation and maintenance. With a focus on exploring the influence of dT′/dz on TTL clouds, this study utilizes radio occultation temperature retrievals and cloud layers from Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) to understand how gravity wave perturbations modulate cloud occurrence in the tropics. Cloud populations were evaluated in four phases corresponding to positive or negative T′ and dT′/dz. We find that 55 % of TTL clouds are found where T′ and dT′/dz are both negative. Regions of frequent convection are associated with higher cloud populations in the warm phase T′>0. We show that the partitioning of cloud population among wave phases exhibits dependence on background relative humidity. In the phase where T′ and dT′/dz are both negative, the mean cloud effective radius is the smallest of all four phases, but the differences are small. It is shown that the strongest mean negative T′ anomaly is centered on the cloud top, resulting in positive dT′/dz above the cloud top and negative dT′/dz below. This negative T′ anomaly propagates downward with time, characteristic of upward propagating gravity waves. Negative (positive) T′ anomalies are associated with increased (decreased) probability of being occupied by clouds. The magnitude of T′ correlates with the increase or decrease in cloud occurrence, giving evidence that the wave amplitude influences the probability of cloud occurrence. While the decrease in cloud occurrence in the warm phase is centered on the altitude of T′ maxima, we show that the increase in cloud occurrence around T′ minima occurs below the minima in height, indicating that cloud formation or maintenance is facilitated mainly inside negative dT′/dz. Together with existing studies, our results suggest that the cold phase of gravity waves is favorable to TTL clouds mainly through the region where dT′/dz is negative.

We examine the physical processes that led to the meteotsunami observed along the English Channel and North Sea coasts on 29 May 2017. It was most notably reported along the Dutch coast, but also observed on tide gauges from the Channel Islands to the coast of Germany, and also those in eastern England. From an assessment of multiple observations, including rain radar, LIDAR, satellite, surface observations and radiosonde reports we conclude that the event was driven by a rear flank downdraft in association with a mesoscale convective system (MCS). This downdraft, from a medium level or elevated MCS, led to a hydrostatically forced internal or ducted gravity wave below the MCS. The gravity wave was manifested by a marked rise and fall in pressure, a meso-high, which then interacted with the sea surface through Proudman resonance causing a measured wave of close to 0.9 m in amplitude, and an estimated wave run-up on Dutch beaches of 2 m. Through examination of existing research, we show that the basic assumptions here relating to the formation of the Dutch meteotsunami are consistent with previously described physical processes, and confirm the correlation between the speed of the ocean wave and medium level steering winds. This raises the possibility that high-resolution, coupled, weather-ocean numerical weather prediction (NWP) models can be utilised to predict future events. However, deterministic high-resolution NWP models still struggle with modelling convective systems with sufficient precision because of the chaotic nature of the atmosphere and incomplete observations. A way forward is proposed here to improve forecasting through post-processing of NWP model output by overlaying medium level wind fields with ocean bathymetry.

Numerical simulations are carried out using the WRF model to explicitly calculate the ratio of orographic gravity wave drag (GWD) in the presence of a stable boundary layer (BL) to the inviscid drag in its absence, either obtained from inviscid WRF simulations or estimated using an analytical linear model. This ratio is represented as a function of three scaling variables defined as ratios of the BL depth to the orography width, height, and stability height scale of the atmosphere. All results suggest that the GWD affected by the stable BL, D_BL, is inversely proportional to the BL depth h_BL, roughly following D_BL ~ h_BL^(-2). The scaling relations are calibrated and tested using a multilinear regression applied to data from the WRF simulations, for idealised orography and inflow atmospheric profiles derived from reanalysis, representative of Antarctica in austral winter, where GWD is expected to be especially strong. These comparisons show that the scaling relations where the drag is normalised by the analytical inviscid estimate work best. This happens because stable BL effects reduce the amplitude of the waves above the BL, making their dynamics more linear. Knowledge of the BL depth and orography parameters is sufficient to obtain a reasonable correction to the inviscid drag without needing additional information about the wind and stability profiles. Since the drag currently available from numerical weather prediction model parametrizations comes from linear theory uncorrected for BL effects, the results reported here may be applied straightforwardly to improve those parametrizations.

Observations of teleseismic earthquakes using broadband seismometers on the Ross Ice Shelf (RIS) must contend with environmental and structural processes that do not exist for land-sited seismometers. Important considerations are: (1) a broadband, multi-mode ambient wavefield excited by ocean gravity wave interactions with the ice shelf; (2) body wave reverberations produced by seismic impedance contrasts at the ice/water and water/seafloor interfaces and (3) decoupling of the solid Earth horizontal wavefield by the sub-shelf water column. We analyze seasonal and geographic variations in signal-to-noise ratios for teleseismic P-wave (0.5–2.0 s), S-wave (10–15 s) and surface wave (13–25 s) arrivals relative to the RIS noise field. We use ice and water layer reverberations generated by teleseismic P-waves to accurately estimate the sub-station thicknesses of these layers. We present observations consistent with the theoretically predicted transition of the water column from compressible to incompressible mechanics, relevant for vertically incident solid Earth waves with periods longer than 3 s. Finally, we observe symmetric-mode Lamb waves generated by teleseismic S-waves incident on the grounding zones. Despite their complexity, we conclude that teleseismic coda can be utilized for passive imaging of sub-shelf Earth structure, although longer deployments relative to conventional land-sited seismometers will be necessary to acquire adequate data.

In the present study, gravity wave interaction with a series of submerged artificial permeable reefs is analysed within the framework of linearised water wave theory. For wave past porous walls of the artificial reefs, a quadratic pressure drop is assumed to account for the wave energy dissipation due to the changes in wave height. The physical problem is handled for a solution using a numerical model based on the iterative multi-domain boundary element method and the developed numerical model is validated with known results in the literature. The iterative model is compared with the numerical model based on linear pressure drop boundary condition (i.e., Darcy law). The study reveals that the wave transmission reduces with the increase in the number of reef units. It is demonstrated that the transmission coefficient can be reduced to less than 0.5 when the number of reef units is greater than or equal to three for a relative height greater than 0.7, reef porosities less than 20% and for 0.40h

When orographic gravity waves (OGWs) break, they dissipate their momentum and energy and thereby influence the thermal and dynamical structure of the atmosphere. This OGW forcing mainly takes place in the middle atmosphere. It is zonally asymmetric and strongly intermittent. So-called OGW hotspot regions have been shown to exert a large impact on the total wave forcing, in particular in the lower stratosphere (LS). Motivated by this we investigate the asymmetrical distribution of the three-dimensional OGW drag (OGWD) for selected hotspot regions in the specified dynamics simulation of the chemistry-climate model CMAM (Canadian Middle Atmosphere Model) for the period 1979–2010. As an evaluation, we first compare zonal mean OGW fluxes and GW drag (GWD) of the model simulation with observations and reanalyses in the northern hemisphere. We find an overestimation of GW momentum fluxes and GWD in the model's LS, presumably attributable to the GW parameterizations which are tuned to correctly represent the dynamics of the southern hemisphere. In the following, we define three hotspot regions which are of particular interest for OGW studies, namely the Himalayas, the Rocky Mountains and East Asia. The GW drags in these hotspot regions emerge as strongly intermittent, a result that can also quantitatively be corroborated with observational studies. Moreover, a peak-detection algorithm is applied to capture the intermittent and zonally asymmetric character of OGWs breaking in the LS and to assess composites for the three hotspot regions. This shows that LS peak OGW events can have opposing effects on the upper stratosphere and mesosphere depending on the hotspot region. Our analysis constitutes a new method for studying the intermittency of OGWs, thereby facilitating a new possibility to assess the effect of particular OGW hotspot regions on middle atmospheric dynamics.

On Friday, April 13, 2018, a high-amplitude atmospheric inertia–gravity wave packet with surface pressure perturbations exceeding 10 mbar crossed the lake at a propagation speed that neared the long-wave gravity speed of the lake, likely producing Proudman resonance. A set of meteotsunami waves struck the shores near Ludington, Michigan, a coastal community along the sandy dunes of Lake Michigan. During the event, harbor walls were overtopped, damage occurred to shoreline homes and boat docks, and water intake pumps were impacted due to the large change in water level. To fully understand the generation of this event and the impacts to the coastal community, we have carried out atmospheric and hydrodynamic model simulations of the inertia–gravity and meteotsunami waves. Atmospheric simulation of the inertia–gravity waves was performed using a high-resolution model for the Great Lakes region that mimics the National Oceanic and Atmospheric Administration High-Resolution Rapid Refresh operational model. Surface meteorological conditions were supplied to the Lake Michigan-Huron Operational Forecast System, an operational model used for hydrodynamic forecast guidance. This is the first documented case of a meteotsunami generated by an atmospheric inertia–gravity wave in the Great Lakes, and it provides an evaluation of existing and proposed operational infrastructure as it pertains to meteotsunami forecasting in the USA.

A numerical model based on multi-domain boundary element method (BEM) is developed to study the gravity wave interaction with a horizontally submerged wavy porous plate. The boundary condition on t...

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.

The parameterization of orographic gravity wave drag (OGWD) in the Weather Research and Forecasting model is extended by including the second‐order Wentzel‐Kramers‐Brillouin (WKB) corrections to the surface wave momentum flux (SWMF) caused by wind profile shear (WSHR) and curvature (WCUR) effects. Simulations of the atmospheric circulation are performed to study the behavior and impact of WKB corrections. In January, the SWMF is weakened in the Northern Hemisphere (NH) midlatitudes by the WSHR term while WCUR acts to enhance the SWMF over Antarctica. In July, the WSHR corrections are similar to those in January whereas the WCUR term produces corrections of opposite sign in the high latitudes of each hemisphere. The latter is attributed to the increase of near‐surface winds in the cold season which reverses the low‐level wind profile curvature. The seasonal reversal of the WCUR term contradicts previous findings obtained from offline evaluation using reanalysis datasets. This may be due to the different OGWD parameterization schemes used, or suggest a sensitivity to the height where the wind profiles effects are evaluated. Changes in the SWMF can affect the vertical distribution of parameterized OGWD. In January, the OGWD in the NH midlatitudes is decreased in the lower troposphere but increased in the upper troposphere. This is because a reduced SWMF inhibits wave breaking in the lower troposphere. Therefore, more WMF is transported to the upper troposphere which enhances wave breaking there. The increased upper‐tropospheric wave breaking in turn decreases the WMF propagating into the stratosphere where the OGWD is reduced. In July, the reduction of SWMF over Antarctica is more notable than that in the NH midlatitudes in January. Consequently, the OGWD is weakened in the upper troposphere over Antarctica.

The present study deals with the transient flexural gravity wave motion associated with floating elastic plate in the presence of permeable bottom. Integral form of the floating plate deflection is obtained analytically using Laplace–Fourier transform method and the asymptotic solution is derived for large time using stationary phase method. Also, using fast Fourier transform method the time domain simulation of floating plate deflection is obtained. The effect of current, compressive force and porosity parameter on phase and group velocities and floating plate deflection are analyzed. It is observed that in the absence of current, due to the presence of porosity parameter there exist two points where there is a situation of no wave propagation. It is also observed that the current and compressive force have significant effect on transient flexural gravity wave motion whereas the porosity parameter has small impact on the gravity wave motion associated with floating elastic plate. The properties of the roots of the dispersion relation associated with the flexural gravity wave motion in the presence of permeable bed are discussed analytically and numerically.

We used a nonlinear mechanistic global circulation model to analyze the migrating quarterdiurnal tide (QDT) in the middle atmosphere with focus on its possible forcing mechanisms: the absorption of solar radiation by ozone and water vapor, nonlinear tidal interactions, and gravity wave–tide interactions. We show a climatology of the QDT amplitudes, and we examine the contribution of the different forcing mechanisms to the QDT amplitude. To this end, we first extracted the QDT from the model tendency terms and then removed the respective QDT contribution from the different tendency terms. We find that the solar forcing mechanism is the most important one for the QDT; however, the nonlinear and gravity wave forcing mechanisms also play a role in autumn and winter, particularly at lower and middle latitudes in the mesosphere and lower thermosphere. Furthermore, destructive interference between the individual forcing mechanisms is observed. Therefore, tidal amplitudes become even larger in simulations with the nonlinear or gravity wave forcing mechanisms removed.

The offshore extent of Antarctic katabatic winds exert a strong control on sea ice production and the formation of polynyas. In this study, we combine ground-based remotely-sensed and meteorological measurements at Dumont d’Urville (DDU) station, satellite images and simulations with the WRF model to analyze a major katabatic wind event in Adélie Land. Once developed over the slope of the ice sheet, the katabatic flow experiences an abrupt transition near the coastal edge. The transition consists in a sharp increase in the boundary layer depth, a sudden decrease in wind speed and a decrease in Froude number from 3.5 to 0.3. This so-called ‘katabatic jump’ visually manifests as a turbulent ‘wall’ of blowing snow in which updrafts exceed 5 m s −1 . The wall reaches heights of 1000 m and its horizontal extent along the coast is more than 400 km. By destabilizing the boundary-layer downstream, the jump favors the trapping of a gravity wave train with an horizontal wavelength of 10.5 km. The trapped gravity waves exert a drag that significantly slows down the low-level outflow. Moreover, atmospheric rotors form below the first wave crests. The wind speed record measured at DDU in 2017 (58.5 m s −1 ) is due to the vertical advection of momentum by a rotor. A statistical analysis of observations at DDU reveals that katabatic jumps and low-level trapped gravity waves occur frequently over coastal Adélie Land. It emphasizes the important role of such phenomena in the coastal Antarctic dynamics.

The goal of this work is to investigate the gravity wave (GW) characteristics in the low ionosphere using very low frequency (VLF) radio signals. The spatial modulations produced by the GWs affect the conditions of the electron density at reflection height of the VLF signals, which produce fluctuations of the electrical conductivity in the D region that can be detected as variations in the amplitude and phase of VLF narrowband signals. The analysis considered the VLF signal transmitted from the US Cutler, Maine (NAA) station that was received at Comandante Ferraz Brazilian Antarctic Station (EACF, 62.1∘ S, 58.4∘ W), with its great circle path crossing the Drake Passage longitudinally. The wave periods of the GWs detected in the low ionosphere are obtained using the wavelet analysis applied to the VLF amplitude. Here the VLF technique was used as a new aspect for monitoring GW activity. It was validated comparing the wave period and duration properties of one GW event observed simultaneously with a co-located airglow all-sky imager both operating at EACF. The statistical analysis of the seasonal variation of the wave periods detected using VLF technique for 2007 showed that the GW events occurred all observed days, with the waves with a period between 5 and 10 min dominating during night hours from May to September, while during daytime hours the waves with a period between 0 and 5 min are predominant the whole year and dominate all days from November to April. These results show that VLF technique is a powerful tool to obtain the wave period and duration of GW events in the low ionosphere, with the advantage of being independent of sky conditions, and it can be used during the whole day and year-round.

Specified dynamics (SD) schemes relax the circulation in climate models toward a reference meteorology to simulate historical variability. These simulations are widely used to isolate the dynamical contributions to variability and trends in trace gas species. However, it is not clear if trends in the stratospheric overturning circulation are properly reproduced by SD schemes. This study assesses numerous SD schemes and modeling choices in the Community Earth System Model (CESM) Whole Atmosphere Chemistry Climate Model (WACCM) to determine a set of best practices for reproducing interannual variability and trends in tropical stratospheric upwelling estimated by reanalyses. Nudging toward the reanalysis meteorology as is typically done in SD simulations does not accurately reproduce lower-stratospheric upwelling trends present in the underlying reanalysis. In contrast, nudging to anomalies from the climatological winds or anomalies from the zonal-mean winds and temperatures better reproduces trends in lower-stratospheric upwelling, possibly because these schemes do not disrupt WACCM's climatology. None of the schemes substantially alter the structure of upwelling trends – instead, they make the trends more or less AMIP-like. An SD scheme's performance in simulating the acceleration of the shallow branch of the mean meridional circulation from 1980 to 2017 hinges on its ability to simulate the downward shift of subtropical lower-stratospheric wave momentum forcing. Key to this is not nudging the zonal-mean temperature field. Gravity wave momentum forcing, which drives a substantial fraction of the upwelling in WACCM, cannot be constrained by nudging and presents an upper limit on the performance of these schemes.

The Stratospheric Observations of Noctilucent Clouds (SONC) experimental campaign was conducted on the night of 5–6 July 2018 with the aim of photographing noctilucent clouds (NLCs) and studying their large-scale spatial dynamics at scales of 100–1450 km. An automated high-resolution camera (equipped with a wide-angle lens) was lifted by a stratospheric sounding balloon to 20.4 km altitude above the Moscow region in Russia (∼56∘ N, 41∘ E), taking several hundreds of NLC images during the flight that lasted 1.7 h. The combination of a high-resolution camera and large geographic coverage (∼1500 km) has provided a unique technique of NLC observations from the stratosphere, which is impossible to currently achieve from either the ground or space. We have estimated that a horizontal extension of the NLC field as seen from the balloon was about 1450×750 km, whereas it was about 800×550 km as seen from the ground. The NLC field was located in a cold area of the mesopause (136–146 K), which was confirmed by satellite measurements. The southernmost edge of the NLC field was modulated by partial ice voids of 150–250 km in diameter. A medium-scale gravity wave had a wavelength of 49.4±2.2 km and an amplitude of 1.9±0.1 km. The final state of the NLC evolution was represented by thin parallel gravity wave stripes. Balloon-borne observations provide new horizons in studies of NLCs at various scales from metres to thousands of kilometres. Here we present a review paper on our experiment describing the initial results. Detailed studies on the time evolution of the cloud movements will be done in the future.

In the present study, the performance of the GRAPES model in wind simulation over south China was assessed. The simulations were evaluated by using surface observations and two sounding stations in south China. The results show that the GRAPES model could provide a reliable simulation of the distribution and diurnal variation of the wind. It showed a generally overestimated southerly wind speed especially over the Pearl River Delta region and the south of Jiangxi Province as well as the coastal region over south China. GRAPES also exhibited a large number of stations with the opposite surface wind directions over the east of Guangxi and the south of Jiangxi during the nocturnal-to-morning period, as well as an overall overestimation of surface wind over the coastal regions during the afternoon. Although GRAPES could simulate the general evolutional characteristics of vertical wind profile, it underestimated wind speed above 900 hPa and overestimated wind speed below 900 hPa. Though the parameterization scheme of gravity wave drag proved to be an effective method to alleviate the systematic deviation of wind simulation, GRAPES still exhibited large errors in wind simulation, especially in the lower and upper troposphere.

Critical levels, where the wind vanishes in the atmosphere, are of key importance for gravity wave drag parametrization. The reflectivity of these levels to mountain waves is investigated here using a combination of high-resolution numerical simulations and insights from linear theory. A methodology is developed for relating the reflection coefficient R of 2D hydrostatic orographic gravity waves to the extrema of the associated drag as a function of an independent flow parameter. This method is then used to infer the variation of the reflection coefficient with flow nonlinearity. To isolate the effect of critical levels, a wind profile with negative shear is adopted, which is characterized by its Richardson number Ri and the dimensionless mountain height Nh0/U0, based on the mountain height h0, Brunt-Vaisala frequency N and surface incoming wind speed U0. Subject to the assumptions of linear theory, the drag is shown to be modified by wave refraction and reflection. The modulation of the drag by wave reflection is used to derive the reflection coefficient from the drag diagnosed from the numerical simulations. Despite considerable uncertainty, the critical level is found to have an R that first increases with Nh0/U0 for low values of this parameter, and for stronger nonlinearity saturates to a value of about 0.6. The flow configuration in this saturated regime is characterized in the case of high-drag states by constructive wave interference, resembling downslope windstorms. Wave reflection by critical levels enhances the flow nonlinearity and the associated drag amplification, more than doubling it for values of Nh0/U0 as low as 0.12. These results emphasize the need to represent this process in orographic gravity wave drag parametrizations, and suggest a possible way of doing it using a prescribed critical level reflection coefficient, derived using the present methodology.

Based on an advanced numerical model for excited hydroxyl (OH*) we simulate the effects of gravity waves (GWs) on the OH*-layer in the upper mesosphere. The OH* model takes into account (1) production by the reaction of atomic hydrogen (H) with ozone (O3), (2) deactivation by atomic oxygen (O), molecular oxygen (O2), and molecular nitrogen (N2), (3) spontaneous emission, and (4) loss due to chemical reaction with O. This OH* model is part of a chemistry-transport model (CTM) which is driven by the high-resolution dynamics from the KMCM (Kuhlungsborn Mechanistic general Circulation Model) which simulates mid-frequency GWs and their effects on the mean flow in the MLT explicitly. We find that the maximum number density and the height of the OH*-layer peak are strongly determined by the distribution of atomic oxygen and by the temperature. As a results, there are two ways how GWs influence the OH*-layer: (1) through the instantaneous modulation by O and T on short time scales (a few hours), and (2) through vertical mixing of O (days to weeks). The instantaneous variations of the OH*-layer peak altitude due to GWs amount to 5–10 km. Such variations would introduce significant biases in the GW parameters derived from airglow when assuming a constant pressure level of the emission height. Performing a sensitivity experiment we find that on average, the vertical mixing by GWs moves the OH*-layer down by ~2 to 7 km and increases its number density by more than 50%. This effect is strongest at middle and high latitudes during winter where secondary GWs generated in the stratopause region account for large GW amplitudes.

This review summarizes the general developments of the operational mesoscale model system based on the Global/Regional Assimilation and Prediction System-Tropical Monsoon Model (GRAPES-TMM) at the Guangzhou Regional Meteorological Center. GRAPES-TMM consists of the Tropical Regional Atmospheric Model System for the South China Sea (TRAMS, a typhoon model with a horizontal resolution of 9 km), the Mesoscale Atmospheric Regional Model System (MARS, 3km) and the fine-scale Rapid Update Cycling (RUC, 1km) forecasting system. The main advances of model dynamical core and physical processes are summarized, including the development of the 3D reference atmosphere scheme, the coupling scheme between dynamics and model physics, the calculation of nonlinear terms by fractional steps, the gravity wave drag scheme induced by sub-grid orography and a simplified model for landsurface scheme. The progress of model applications is reviewed and evaluated. The results show that the updated 9-3-1 forecasting system provides an overall improved performance on the weather forecasting in south China, especially for typhoon-genesis and typhoon-track forecasting as well as short-range weather forecasting. Capabilities and limitations as well as the future development of the forecasting system are also discussed.

In this research, the roles of gravity waves and planetary waves in the change to middle atmospheric residual circulation during a sudden stratospheric warming period are differentiated and depicted separately by adopting the downward control principle. Our analysis shows clear anomalous poleward residual circulation patterns from the equator to high latitudes in the lower winter stratosphere. At the same time, upward mean flows are identified at high latitudes of the winter upper stratosphere and mesosphere, which turn equatorward in the mesosphere and reach as far as the tropical region, and consequently the extratropical region in the summer hemisphere. The downward control principle shows that anomalous mesospheric residual circulation patterns, including interhemispheric coupling, are solely caused by the change in gravity wave forcing resulting from the reversal of the winter stratospheric zonal wind. Nevertheless, both planetary waves and gravity waves are important to variations in the winter stratospheric circulation, but with opposite effects.