Displays

When an earthquake occurs, it is important to rapidly assess the severity of the consequences. The distribution of shaking intensity around the epicenter, known as the ShakeMap, is a key component in this process and is crucial for guiding first responders to the region. Whereas earthquake source characteristics, e.g., location and magnitude, can be rapidly determined using distant seismic stations, ground motion measurements from stations in the near-source region are needed to generate an adequate ShakeMap. When few or no seismometers exist in the region, ground motions are only estimated and the ShakeMap can be grossly inaccurate.

Besides seismic waves, earthquakes generate infrasound, i.e., inaudible acoustic waves in the atmosphere. Due to the low frequency nature of infrasound, and facilitated by waveguides in the atmosphere, signals propagate over long ranges with limited attenuation and are detected at ground-based stations. Here we show, that acousto-ShakeMaps, indicating the relative shaking intensity, can be rapidly generated using remotely detected infrasound. We illustrate this with infrasound from the 2010 Mw 7.0 Port-au-Prince, Haiti earthquake, detected in Bermuda, over 1700 km away from Haiti.

Such observations are made possible by: (1) An advanced array processing technique that enables the detection of coherent wavefronts, even when amplitudes are below the noise level, and (2) A backprojection technique that maps infrasound detections in time to their origin on the Earth's surface.

Infrasound measurements are conducted globally for the verification of the Comprehensive Nuclear-Test-Ban Treaty and together with regional infrasound networks allow for an unprecedented global coverage. This makes infrasound as an earthquake disaster mitigation technique feasible for the first time.

How to cite: Shani-Kadmiel, S., Averbuch, G., Smets, P., Assink, J., and Evers, L.: The 2010 Haiti Earthquake Disaster: The ShakeMap that could have been..., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7091, https://doi.org/10.5194/egusphere-egu2020-7091, 2020.

Pressure perturbations such as e.g. impulsive acoustic waves can couple into solid earth through the long-known phenomenom of seismo-acoustic coupling. Yet, the associated mechanisms are not always clear. Most studies investigate seismo-acoustic through low-frequency and high amplitude signals generated by e.g. natural or man-made explosions.

We conducted a small-scale field experiment with firecrackers as acoustic sources and hundred 3-component nodal geophones as receivers in a 20m diameter ring layout, some of them co-located with seismically decoupled Hyperion IFS-5111 infrasound sensors. This allowed us to investigate seismo-acousting coupling for higher frequencies and very small (meter scale) offsets.

The large receiver density enabled us to observe and distinguish different wave types induced by acoustic sources, including direct air waves, air-coupled Rayleigh waves, and possibly slow Biot waves. Having co-located seismic and pressure sensors additionally allowed us to investigate the coupling efficiency, which is in the order of 10^-7 and thus similar to many of the low-frequency and large-offset studies. Furthermore, we can deduct soil properties such as rigidity, bulk modulus, and density from the co-located sensors, and efficiently infer near-surface (soil) properties using cheap acoustic sources.

How to cite: Fuchs, F., Novoselov, A., and Bokelmann, G.: Seismo-acoustic ground coupling: Wave types, transfer efficiency, and near-surface structure, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7484, https://doi.org/10.5194/egusphere-egu2020-7484, 2020.

Large meteoroids can be registered in infrasound recordings during their entry into the Earth’s atmosphere. A comprehensive study of 10 large fireball events of the years 2018 and 2019 highlights their detection and characterization using global infrasound arrays of the International Monitoring System (IMS) of the Comprehensive Nuclear-Test-Ban Treaty (CTBT). The study focuses on the observation and event analysis of the fireballs to estimate their respective location, yield, trajectory, and entry behavior. Signal characteristics are derived by applying the Progressive Multi-Channel Correlation method as an array technique. The comparison of the events with a NASA reference database as well as the application of atmospheric propagation modeling allows to draw conclusions about infrasound-based detection capability, localization accuracy, yield estimation, and source characterization. The infrasound technique provides a time- and location-independent remote monitoring opportunity of impacting near-Earth objects (NEOs), either independent or complementary to other fireball observation methods. Additionally, insights about the detection and localization capability of IMS infrasound stations can be gained from using large fireballs as reference events, being of importance for the continuous monitoring and verification of atmospheric explosions in a CTBT context.

How to cite: Pilger, C., Gaebler, P., Hupe, P., Ott, T., and Drolshagen, E.: Global Monitoring and Characterization of Infrasound Signatures by Large Fireballs, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3290, https://doi.org/10.5194/egusphere-egu2020-3290, 2020.

With the advent of civil aviation and growth in air traffic, the problem of volcanic ash encounter has become an issue of importance as a prompt response to volcanic eruptions is required to mitigate the impact of the volcanic hazard on aviation. Many volcanoes worldwide are poorly monitored, and most of the time notifications of volcanic eruptions are reported mainly based on satellite observations or visual observations. Among ground-based volcano monitoring techniques, infrasound is the only one capable of detecting explosive eruptions from distances of thousands of kilometers. On July 3 and August 28, 2019, two paroxysmal explosions occurred at Stromboli volcano. The events, that are similar in terms of energy and size to the peak explosive activity reported historically for the volcano, produced a significant emission of scoria, bombs and lapilli, that affected the whole island and fed an eruptive column that rose almost 5 km above the volcano. The collapse of the eruptive column also produced pyroclastic flows along the Sciara del Fuoco, a sector collapse on the northern flank of the volcano.

Being one of the best-monitored volcanoes of the world, the 2019 Stromboli paroxysmal explosions were observed in real-time and Civil Protection procedures started immediately. However, notification to the Toulouse Volcanic Ash Advisory Centre (VAAC) was not automated, and the VAA was issued only long after the event occurrence. The two explosions produced infrasound signals that were detected by several infrasound stations as far as Norway (IS37, 3380 km) and Azores islands (IS42, 3530 km). Despite of the latency due to the propagation time, infrasound-based notification arrays precedes the Volcanic Ash Advisories (VAAs) issued by Toulouse VACC. Following the same procedure applied for the Volcano Information System developed in the framework of the ARISE project, we show how infrasound array analysis could allow automatic, near-real-time identification of these eruptions with timely reliable source information. We highlight the need for an integration of the CTBT IMS infrasound network with local and regional infrasound arrays capable of providing a timely early warning to VAACs. This study opens new perspectives in volcano monitoring and could represent, in the future, an efficient tool in supporting VAACs activity.

How to cite: Marchetti, E., Ripepe, M., Le Pichon, A., Listowski, C., Ceranna, L., Hupe, P., Pilger, C., Matos, S., Wallenstein, N., Mialle, P., and Hereil, P.: The 2019 July Stromboli volcano paroxysm event: contribution of infrasound to the Volcanic Ash Advisory Centers, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20165, https://doi.org/10.5194/egusphere-egu2020-20165, 2020.

In routine processing of infrasound data of the International Monitoring System, coherent ocean ambient noise with dominant frequencies ranging from 0.1 to 0.5 Hz appears in overlapping frequency bands. These signals, so-called microbaroms, originate from complex wave interactions. In this study, microbarom detections are used as calibration signals, and their amplitudes at the Argentinian infrasound station IS02 are modelled based on operational ocean wave interaction simulations and a semi-empirical attenuation relation. This relation strongly depends on the middle atmosphere (MA) dynamics. Previous studies have shown that the MA wind and temperature are not properly resolved in numerical weather prediction (NWP) models. Therefore, high-resolution soundings of the Compact Rayleigh Autonomous Lidar (CORAL) are incorporated in the modelling. The infrasound data are processed using the progressive Multi-Channel Correlation (PMCC) algorithm.

This sensitivity study focuses on one year of collocated infrasound and lidar measurements in southern Argentina. It highlights the seasonal effects of MA uncertainties on infrasound propagation and detections in 2018.

How to cite: Ceranna, L., Hupe, P., de Carlo, M., and Le Pichon, A.: Modelling infrasonic ocean ambient noise using NWP and lidar observations in southern Argentina, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18581, https://doi.org/10.5194/egusphere-egu2020-18581, 2020.

Recent studies on infrasonic signatures related to atmospheric tides are mostly focused on stratospherically ducted infrasound or on tidal signatures in recorded infrasound signal power.

In the current work, we address microbarom infrasound ducted by mesosphere-lower thermosphere (MLT) waveguides and the associated infrasound apparent velocity (trace velocity) of arrivals at a ground-based array station in northern Norway.

A hypothesis is that the infrasound apparent velocity – which is related to the incidence angle of the wavefront impinging the station – is linked to the altitude of the final refraction of the infrasound waves. This altitude would be affected by the regional MLT tidal pattern.

We apply specialized beamforming and filtering recipes to highlight the MLT-ducted microbarom arrivals and we find semidiurnal patterns in the infrasound apparent velocity measurements.

How to cite: Näsholm, S. P., Vorobeva, E., Le Pichon, A., Orsolini, Y. J., Turquet, A. L., Hibbins, R. E., Espy, P. J., De Carlo, M., Assink, J. D., and Vera Rodriguez, I.: Semidiurnal tidal signatures in microbarom infrasound array measurements, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19035, https://doi.org/10.5194/egusphere-egu2020-19035, 2020.

The International Monitoring System (IMS) of the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) may be used to detect atmospheric explosions and events of interest using infrasound technology. However, ambient noise may affect the detection performance of the station network, and particularly ocean noise known as microbarom, as previously shown by characterizing ambient noise through broadband array processing on IMS data. Indeed, ocean wave interactions generate acoustic noise almost continuously. In this study, we use wave action models and include bathymetry and source directivity effects to model the microbarom sources and perform a global comparison between the synthetic signals obtained from two-dimensional spectrum ocean wave products, and observations. With this study, it is expected to enhance the characterization of the ocean-atmosphere coupling and to discriminate the impact of different features to account for in models. In return, better knowledge of microbarom sources allows to better characterize explosive atmospheric events and to provide information about the middle atmosphere dynamics and disturbances that could be used as model constraints

How to cite: De Carlo, M., Ardhuin, F., Ceranna, L., Hupe, P., Le Pichon, A., and Vergoz, J.: Global comparison between ocean ambient noise modelling and infrasound network observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17475, https://doi.org/10.5194/egusphere-egu2020-17475, 2020.

We use acoustical infrasound from explosions to probe an atmospheric wind component from the ground up to stratospheric altitudes. Planned explosions of old ammunition in Finland generate transient infrasound waves that travel through the atmosphere. These waves are partially reflected back towards the ground from stratospheric levels, and are detected at a receiver station located in northern Norway at 178 km almost due North from the explosion site. The difference between the true horizontal direction towards the source and the back-azimuth direction of the incoming infrasound wave-fronts, in combination with the pulse propagation time, are exploited to provide an estimate of the average cross-wind component in the penetrated atmosphere. 
We perform offline assimilation experiments with an ensemble Kalman filter and these observations, using the ERA5 ensemble reanalysis atmospheric product as background (prior) for the wind at different vertical levels. Information from both sources is combined to obtain analysis (posterior) estimates of cross-winds at different vertical levels of the atmospheric slice between the explosion site and the recording station. The assimilation makes greatest impact at the 12-60 km levels, with some changes with respect to the prior of the order of 0.1-1.0 m/s, which is a magnitude larger than the typical standard deviation of the ERA5 background. The reduction of background variance in the higher levels often reached 2-5%. 
This is the first study demonstrating  techniques to implement assimilation of infrasound data into atmospheric models. It paves the way for further exploration in the use of infrasound  observations (especially natural and continuous sources) to probe the middle atmospheric dynamics and to assimilate these data into atmospheric model products.  

How to cite: Amezcua, J., Nasholm, P., Blixt, M., and Charlton-Perez, A.: Assimilation of atmospheric infrasound data to constrain tropospheric and stratospheric winds, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8244, https://doi.org/10.5194/egusphere-egu2020-8244, 2020.

Observations of the ionosphere with the airglow, GPS-TEC, and HF radar techniques reveal a resonance-kind response of the middle and upper atmosphere to broad-band excitation by earthquakes, volcano eruptions, and convective storms. The resonances occur at such frequencies that an atmospheric wave, which is radiated at the ground level and is reflected from a turning point in the middle or upper atmosphere, upon return to the ground level satisfies boundary conditions on the ground. The "buoyancy" resonances (resonances of atmospheric gravity waves) with periods from several minutes and up to several hours arise in addition to well-known "acoustic" resonances with periods of about 3–4 minutes. The buoyancy resonances occur on the gravity branch of the dispersion relation for the acoustic-gravity waves. Infragravity waves in the ocean covering the same frequency band may serve as an efficient source of excitation of the buoyancy resonances. We have obtained dispersion relations for buoyancy resonances earlier. In this paper we investigate the influence of specific propagation characteristics of the gravity waves (their oblique propagation and dissipative attenuation) on conditions of their observation. We use  asymptotic (WKB and ray tracing) methods to investigate relationship between the gravity wave skip distance and the dimensions of typical infragravity wave packets in the oceans and find that conditions can be met for interaction of the same atmospheric wave packet with the same ocean wave packet. The dissipative attenuation eliminates some of the resonance modes, but still many of them remain intact. We use numerical solutions of the full wave equation to confirm results obtained by asymptotic methods. Calculations of this kind demonstrate a possibility of resonance-like behavior of the gravity waves in situations when partial reflections (caused by extrema of the refractive index) appear in addition to the total reflection. Unlike acoustic resonances, buoyancy resonances exhibit high sensitivity to the wind velocity profile and its variations. Non-stationarity of the atmosphere is an important factor limiting possibilities to observe the buoyancy resonances. Nevertheless, relatively low threshold for meeting all other conditions for their appearance and temporal/geographical diversity of the atmosphere makes it still quite probable to see their manifestations. The resonances correspond to most efficient coupling between the atmosphere and its lower boundary and are promising for detection of such coupling.

How to cite: Zabotin, N. and Godin, O.: Propagation factors influencing observations of resonances of atmospheric gravity waves, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3928, https://doi.org/10.5194/egusphere-egu2020-3928, 2020.

How to cite: Assink, J.: Analysis of the severe weather outbreak of 5 June 2019 in The Netherlands, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19433, https://doi.org/10.5194/egusphere-egu2020-19433, 2020.

How to cite: Le Du, T.: Gravity wave analysis using OH airglow and Rayleigh lidar at the Haute-Provence observatory, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22232, https://doi.org/10.5194/egusphere-egu2020-22232, 2020.

The middle polar atmosphere dynamics is driven by atmospheric waves from the planetary scale to small scale perturbation due to gravity waves. The different atmospheric waves are characterized by their temporal and spatial variability posing challenges to ground-based remote sensing techniques to disentangle and resolve the spatio-temporal ambiguity. Here we present two ground-based remote sensing techniques to resolving spatio-temporal variability at the polar middle atmosphere.

Since 2017 the GROMOS-C radiometer measures ozone and winds at NyÅlesund (78.9°N, 11.9°E) on Svalbard. The radiometer employs four beams in the cardinal directions at 22.5° elevation angle to retrieve ozone profiles and winds at altitudes between 30-75 km. the temporal resolution of the ozone retrievals is 30 minutes. Further, we obtain daily mean winds. Due to the high polar latitude the spatial separation between the beams at stratospheric altitudes covers several degrees in longitude to infer spatial gradients in the ozone densities and their perturbation due to planetary waves.

Another recently established ground-based remote sensing approach to retrieve the spatial characteristic at the mesosphere and lower thermosphere (MLT) is provided by the Nordic meteor radar cluster consisting of the meteor radars at Tromsø, Alta, Esrange, Sodankylä and on Svalbard. Since October 2019 horizontally resolved winds are obtained using a 3DVAR approach with a temporal resolution of 30 minutes and a vertical resolution of 2 km. Here we present preliminary results to infer horizontal wavelength spectra, the tidal variability as well as gravity activity of the winter season 2019/20.

Both datasets are of high value for data assimilation into weather forecast and reanalysis models or for cross-comparisons and validation of meteorological analysis systems (e.g. NAVGEM-HA).

How to cite: Stober, G., Schranz, F., Hall, C., Kozlovsky, A., Lester, M., Tsutsumi, M., Nozawa, S., Belova, E., Kero, J., Hocke, K., and Murk, A.: Resolving spatial dynamics at polar latitudes using the GROMOS-C radiometer on Svalbard and the Nordic meteor radar cluster, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9822, https://doi.org/10.5194/egusphere-egu2020-9822, 2020.

Neutral winds in the mesosphere and lower thermosphere (MLT) have been simultaneously observed by Fabry-Perot interferometer (FPI) and meteor radar (MR) at King Sejong Station (KSS), Antarctica from 2017. Because  the airglow emission height sensitively varies with a solar local time and a season, it is not possible to precisely determine what altitude airglow emission occurs from the traditional assumption of fixed airglow layers. Even though a few previous studies suggested representative heights of airglow emission such as OH band and 557.7 nm line, the true height information of these emission are still unknown. In this study, we try to figure out the temporal dependence of the airglow emissions using the KSS FPI and satellite (SABER/MLS) measurements. We also perform a direct comparison between the FPI and the meteor radar wind measurements considering time-varying airglow emission properties based on a correlation analysis. This study presents how the background wind structure can affect wind estimates from the airglow emissions.

How to cite: Lee, C., Jee, G., Wu, Q., Kim, J.-H., Kam, H., and Kim, Y. H.: Comprehensive comparison of mesospheric wind from Fabry-Perot interferometer and meteor radar at King Sejong Station, Antarctica, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3260, https://doi.org/10.5194/egusphere-egu2020-3260, 2020.

The comparison of ground and ship-based lidar measurements of atmospheric temperature, ozone, and wind to similar measurements made from orbiting satellites is a unique challenge.   In this talk we will discuss general challenges associated with (i) determining coincidence by compensating for geographic and temporal offsets, (ii) satellite-lidar sampling errors, and (iii) comparing results made by different techniques. 

We will show that comparisons of absolute temperature improve when the ground based measurements are compared to a composite satellite profile, created by a weighted average of multiple profiles from one overpass, instead of comparing to the single satellite profile from the closest approach. 

We discuss the importance of including the variation between consecutive satellite profiles for a given overpass in addition to the given satellite instrument uncertainty when calculating the error budget of the comparisons, even when comparing to single satellite profiles. 

We demonstrate how comparing lidar and satellite measurements of events such as small-scale fast moving gravity waves over a particular geographic region can be affected by instrument averaging kernels.

Illustrative examples we will be showing include lidar measurements made during recent instrument validation campaigns at L’Observatoire de Haute Provence (OHP, 43.93 N, 5.71 E), La Réunion (21.17 S, 55.37 E), Hohenpeißenberg Meteorological Observatory (47.80 N, 11.00 E), and onboard the French Navy Research Ship Monge as well as satellite measurements from  the Microwave Limb Sounder (MLS), the Sounding of the Atmosphere by Broadband Emission Radiometry instrument (SABER), Global Ozone Monitoring by Occultation of Stars (GOMOS), and Atmospheric Dynamics Mission Aeolus (Aeolus).

How to cite: Wing, R., Hauchecorne, A., Keckhut, P., Godin-Beekmann, S., Khaykin, S., Martic, M., Steinbrecht, W., McGee, T. J., Sullivan, J., and McCullough, E.: Intercomparisons Between Lidar and Satellite Instruments in the Middle Atmosphere, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11725, https://doi.org/10.5194/egusphere-egu2020-11725, 2020.

The dynamics of the middle atmosphere, between near ground lower troposphere and near Earth space thermosphere is submitted to strong disturbances which impact global circulation and are at the origin of uncertainties in climate and weather models. The lack of observations limits the ability to accurately reproduce these disturbances, while the considered altitude range increases for improving model predictions. Perturbations also affect climate change and environment hazards. ARISE (Atmospheric dynamics Research InfraStructure in Europe) objective is to develop a high resolution platform integrating the infrasound International Monitoring System for the verification of the Comprehensive nuclear-Test-Ban Treaty , the lidar Network for Detection of Atmospheric Composition Changes, associated with multi-instrument reference stations and satellite observations. The research is highly multidisciplinary to cover the full altitude range from polar to equatorial regions submitted to different processes. The main project results and perspectives will be presented. This concern the development of a pilot station for developing synergies, prototypes for improving instrument performances, new tools for applications related to weather and climate using both archived data for applications and near real time data, remote monitoring of extreme events such as volcanoes for civil aviation, stratospheric warming events, severe weather, meteo-tsunamis and meteorites for risk management.

How to cite: Blanc, E.: Dynamics of the middle atmosphere as observed by the ARISE project: scientific highlights and perspectives, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19524, https://doi.org/10.5194/egusphere-egu2020-19524, 2020.

One of the various sources of infrasound signals are lightnings in storms. These moving sources can be detected and tracked at infrasound arrays. We correlate lightning data from Blitzortung with the infrasound detections from the Hungarian infrasound station at Piszkes-teto (PSZI) that has been collecting data since May, 2017. The objective of this study is to track storms and to test the station's capability to detect thunderstorm signals. We invetsigate what conditions affect these detections; in what directions, distances and accuracy can we track storms. We also look at how various noise conditions influence the detection capability of the array.

How to cite: Pásztor, M., Czanik, C., and Bondár, I.: Identitification and tracking of storms via infrasound detections, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-446, https://doi.org/10.5194/egusphere-egu2020-446, 2020.

Atmospheric gravity waves (GWs) transport energy and momentum horizontally and vertically. The dissipation of GWs can modify the atmospheric circulation at different altitude layers. Knowledge about the occurrence of GWs is thus essential for Numerical Weather Prediction (NWP). However, uniform networks for global GW measurements are rare, and satellite observations generally allow to derive GW parameters in the middle and upper atmosphere only. The barometric sensors of the International Monitoring System (IMS) infrasound network can potentially fill this gap of global GW observations at the Earth’s surface. This infrasound network has been established for monitoring the atmosphere to verify compliance with the Comprehensive Nuclear-Test-Ban Treaty.
Two alternative configurations of the Progressive Multi-Channel Correlation Method (PMCC) are discussed for deriving GW detections from the differential pressure data. These configurations focus on GW frequencies equivalent to periods of between 5 min and 150 min. This range covers sources of deep convection, particularly in the tropics, whereas at mid-latitudes, GWs are hard to distinguish from other low-frequency signals, e.g. coherent wind noise. Challenges and perspectives of using the IMS infrasound data for deriving ground-based GW parameters useful for NWP will be discussed.

How to cite: Hupe, P., Ceranna, L., and Le Pichon, A.: Global gravity wave detections at infrasound stations of the International Monitoring System, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1610, https://doi.org/10.5194/egusphere-egu2020-1610, 2020.

Direct excitation of acoustic normal modes in horizontally stratified oceanic waveguides is negligible even for shallow earthquakes because of the disparity between velocities of seismic waves and the sound speed in the water column. T-phases, which propagate at the speed of sound in water, are often reported to originate in the open ocean in the vicinity of the epicenter of an underwater earthquake, even in the absence of prominent bathymetric features or significant seafloor roughness. This paper aims to evaluate the contribution of scattering by hydrodynamic waves into generation of abyssal T-waves. Ocean is modeled as a range-independent waveguide with superimposed volume inhomogeneities due to internal gravity waves and surface roughness due to wind waves and sea swell. Guided acoustic waves are excited by volume and surface scattering of ballistic body waves. The surface scattering mechanism is shown to explain key observational features of abyssal T-waves, including their ubiquity, low-frequency cutoff, presence on seafloor sensors, and weak dependence on the earthquake focus depth. On the other hand, volume scattering due to internal gravity waves proves to be ineffective in coupling the seismic sources to T-waves. The theory is extended to explore a possible role that scattering by gravity waves may play in excitation of infrasonic normal modes of tropospheric and stratospheric waveguides by underwater earthquakes. Model predictions are compared to observations [L. G. Evers, D. Brown, K. D. Heaney, J. D. Assink, P. S. M. Smets, and M. Snellen (2014), Geophys. Res. Lett., 41, 1644–1650] of infrasonic signals generated by the 2004 Macquarie Ridge earthquake.

How to cite: Godin, O.: Gravity waves as a mechanism of coupling oceanic and atmospheric acoustic waveguides to seismic sources, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1782, https://doi.org/10.5194/egusphere-egu2020-1782, 2020.

We present the most interesting cases from observations of short-duration infrasound signals at the array PVCI (50.53°N 14.57°E).  The array is equipped with three sensors and it has an aperture of 200 m. The optimum detection range of the array is 0.02-4 Hz.

On 24 August 2016 at 01:36:32 UTC, a strong earthquake occurred in Central Italy; the epicentre was located at 42.75°N and 13.22°E. The azimuth from PVCI to the epicentre was 187° and the distance was 871 km. At 02:23-02:40 UTC, signals from the azimuths around 195° were recorded at the array. The time interval corresponds to the expected stratospheric signal arrival.

On 3 March 2016 at 21:51-21:53 UTC, PVCI registered signal from the azimuth of 199°. The signal elevation was 30-35°. We assume that the signal source was the bolide EN060316 that entered the atmosphere above Upper Austria and Bavaria. 

Two large accidental explosions occurred in the region recently; both of them were recorded by PVCI and other member stations of the CEEIN network. On 26-27 September 2017, an ammunition depot exploded in Kalynivka, Central Ukraine. Signals from the azimuths of 85-90° were recorded on 26 September 2017 at 21:02-21:05 UTC and at 23:16-23:21 UTC. On 1 September 2018 around 03:15 UTC, an explosion occurred in the refinery near Ingolstadt, Germany. A high amplitude signal arrived at PVCI at 03:30:48 UTC from the azimuth of 243°.

How to cite: Sindelarova, T., Czanik, C., Kozubek, M., Podolska, K., Base, J., and Kouba, D.: Short-duration infrasound signals observed at the array PVCI, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2582, https://doi.org/10.5194/egusphere-egu2020-2582, 2020.

Large aperture array of absolute micro‑barometers located in Western Czechia was used to register distinct infrasound pulses generated by thunderstorm activity. Only cases with a sufficient signal-to-noise ratio on all four micro‑barometers were selected for further processing. Using data from the European lightning detection network and electric field monitor, a corresponding flash was assigned to each set of signals. The position of the infrasound source was calculated from the time delay of signal arrival, assuming propagation of spherical waves from the source. The calculation includes changes in sound speed as a function of temperature variation with altitude. Wind speed value and its variance is also taken into account to estimate the uncertainties. The calculated vertical positions of the infrasound sources are located at the altitudes between 3‑6 km. The horizontal position for most of the selected cases corresponds to the horizontal position of the flash specified by lightning detection network. The recorded infrasound signals followed only intracloud (IC) or mixed (multiple IC+CG) lightning strokes. Thus, the sources of the analyzed infrasound events are most likely IC discharges.

How to cite: Rusz, J., Chum, J., and Baše, J.: Determining the position of the of thunder infrasound source using a large aperture micro barometer array, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2641, https://doi.org/10.5194/egusphere-egu2020-2641, 2020.

The mobile Infrasound Array of the Austrian National Data Centerwhich is a part of the Central and Eastern European Infrasound Network (CEEIN) was installed in a location south of Vienna in April 2019. There data will be collected till April 2020 and the analysis will be conducted using dtkGPMCC-Software which is included in the NDC-in-a-Box-Paketand provided by the Comprehensive Treaty Test Ban Organisation (CTBTO). Several challenges occurred due to the power supply with a fuel cell. After constant problems an upgrade was initialized in July 2019. Results of the analysis since beginning of deployment will be shown in the presentation. Detected signals will be compared both with ground truth information and with observations collected by other Infrasound-stations of CEEIN and IMS-station IS26 located in Germany. 

How to cite: Mitterbauer, U.: Running a temporary mobile Infrasound Array in Austria: Challenges and Detections, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22078, https://doi.org/10.5194/egusphere-egu2020-22078, 2020.

The monitoring network of the Kazakhstani Institute of Geophysical Researches includes seismic and infrasound arrays. The PMCC method helps identifying microseisms in seismic records and microbaroms in infrasound records effectively. Simulation of the microbarom strength, propagation path and signal attenuation are well developed for the moment, and for microseisms as well. However, the bathymetry effect on the source intensity shall be taken into account to model microseisms.

Results of the source parameter simulations and microbaroms and microseisms detections are compared at 7 Kazakhstani seismic and infrasound arrays. These comparisons are also carried out between collocated seismic and infrasound arrays. Similarities and differences between the reconstructed source regions of microseisms and microbaroms are discussed. Beside this study, the advantages of integrating the infrasound and seismic methods have been shown for studying seismoacoustic signals from severe storms.

How to cite: Smirnov, A. and Le Pichon, A.: Similarities and differences of microseism and microbarom source regions reconstructed from the seismo-acoustic Kazakhstani network, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2965, https://doi.org/10.5194/egusphere-egu2020-2965, 2020.

The global International Monitoring System (IMS) network continuously detects coherent ambient infrasound noise between 0.1 and 0.5 Hz. This noise, referred to as microbaroms, is generated by second order non-linear interaction of ocean waves. Various source models have been developed in earlier works; e.g. Brekhovskikh et al. (1973) and Ardhuin & Herbers (2013) who considered a source directivity effect in infinite depth ocean, and Waxler (2007) who investigated the radiation model in finite depth ocean from monopolar sources. De Carlo et al. (2020) proposed a two-dimensional energy spectrum ocean wave model accounting for bathymetry and source directivity effects. First comparisons between the observed and modelled directional microbarom amplitudes at IMS infrasound stations show first order agreement. In order to further evaluate these models, microbarom observations from the Carolina Infrasound secondary payload on board the NASA Ultra Long Duration Balloon flight in 2016 (Bowman and Lees, 2018), that flew over spatially extended microbarom source regions along the Antarctic Circumpolar Current, are compared with the modelled source energy flux. The simulated source strength power spectrum is integrated over an extended source region beneath the balloon and compared with the observed one. The relative importance of modelled source parameters (e.g. bathymetry, launching ray parameters) is assessed. In this presentation, we describe the infrasound observations on the balloon and the supporting microbarom source models, and discuss the implications of these results on the remote estimation of the acoustic energy flux from the ocean surface to the upper atmosphere.

How to cite: Le Pichon, A., De Carlo, M., Bowman, D., and Ardhuin, F.: Evaluating microbarom source models using infrasound recorded on a stratospheric balloon, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19317, https://doi.org/10.5194/egusphere-egu2020-19317, 2020.

Stromboli is one of the most active volcanoes on Earth with a continuous explosive activity and persistent degassing since at least 3-7 AD (Rossi et al., 2000). Being an open conduit volcano, its spectacular basaltic explosions interspersed by lava fountains occurring every ≈10 minutes (Ripepe et al., 2002) make it probably the world's best-know and best-monitored volcano.

On 3^rd July 2019 at the 14:45:43 UTC a paroxysmal explosion occurred with an ash column that rose almost 5 km above the volcano. This very strong explosive event was detected in several IMS infrasound stations, including IS42, located in the Azores islands in the middle of the North-Atlantic, at a distance of about 3,700 km.

We present the long-range infrasound detections that allowed us to locate the source based only in infrasound with an estimated error of less than 55 km from the ground truth event.

Keywords: Stromboli volcano, paroxysm, infrasound, IMS, IS42

How to cite: Matos, S., Wallenstein, N., Marchetti, E., and Ripepe, M.: Location of Stromboli volcano July 2019 paroxysm event based on long-range infrasound detections in several IMS stations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10156, https://doi.org/10.5194/egusphere-egu2020-10156, 2020.

We present the results of the reprocessing a 10-year archive of waveform data recorded with the Romanian infrasound network, by using PMCC signal detector. Starting with 2009, three infrasound stations have been deployed on the Romanian territory by the National Institute for Earth Physics (NIEP): IPLOR 6-element array of 2.5 km aperture, in the central part of the country, BURARI 4-element research array of 1.2 km aperture, in the northern Romania, under the cooperation with Air Force Technical Application Center AFTAC (USA), and I67RO – a temporary PTS portable 4-element array of 0.9 km aperture, in western Romania, for two-year experiment (2016-2018), within a collaboration project with PTS/CTBTO. In 2019, BURARI station has been upgraded to 6-element array with a 0.7 km aperture.

Infrasound data are processed and analyzed on routinely basis at NIEP by using a duo of infrasound detection-oriented software – DTK-GPMCC and DTK-DIVA – packaged into CTBTO NDC-in-a-Box. Since October 2019, a new implementation of PMCC algorithm is available at NIEP, enabling the characterization of the coherent infrasound field in log-spaced frequency with one-third octave bands from 0.1 to 7 Hz. The full data set recorded with the Romanian infrasound stations has been reprocessed by applying the new PMCC algorithm.

The array monitoring performance resulted after the data reprocessing is investigated. Detection capability assessment, types of sources observed, as well the capacity of fusing the detections into support of understanding various infragenic sources are presented. A better characterization of the detected signals in the frequency-azimuth space or frequency trace-velocity space is clearly observed. Infrasonic signals generated by several relevant sources detected with the three arrays deployed on the Romanian territory are shown.

How to cite: Ghica, D., Popa, M., and Ionescu, C.: On the infrasound array monitoring in Romania: reprocessing of the data recorded by the national infrasound network, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5360, https://doi.org/10.5194/egusphere-egu2020-5360, 2020.

Geophysical monitoring observations in Ukraine are performed by the Main Center of Special Monitoring (MCSM), which is a part of the National Space Facilities Control and Test Center, State Space Agency of Ukraine. The MCSM ensures the implementation of the Ukrainian international obligations within the CTBT. It also provides prompt warning and response to emergencies, based on geophysical monitoring results, and runs continuous complex geophysical observations for scientific purposes. 

Infrasound monitoring is one of the types of geophysical monitoring, performed by the MCSM. The infrasound network of Ukraine consists of three observatories, which include mini-arrays of microbarographs (3-4 microbarographs). Standard geometric configuration for an array is a triangle. The aperture of arrays ranges between 200 and 900 meters. There are also three separate observation points, with the only one microbarograph in each. The spacing between these points is hundreds of kilometers. The entire infrasound network is in North-Western Ukraine. One more Ukrainian observatory based in the Antarctic, the Vernadsky Research Base. All microbarographs equipped with wind-protection systems. Microbarographs from the Soviet K-304 acoustic station (0.03-10 Hz, 100 Pa) are currently used in combination with a 4-channel 24-bit digitizer. Besides, Ukraine has created new models of microbarographs with similar technical characteristics. The scheduled upgrade of the sensors is currently underway. There are also plans for installing infrasound arrays in the Eastern and Southern Ukraine. Furthermore, for assessing the possibility of recording large-scale processes in the atmosphere, the pilot plant of the microbarographs on the seismic array nodes PS45 is scheduled for this year. In this case, the distance between the elements of the infrasound array will be around 3-4 kilometers.

Previously mentioned infrasound arrays recorded a wide range of technogenic and natural phenomena, which could be of interest to the scientific community. Among the technogenic ones are explosions at the military arsenals, gas pipeline explosions, plane crashes, and an enormous number of mining blasts. Infrasound signals have also been caused by natural events such as earthquakes, tsunamis, avalanches, hurricanes, thunderstorms, meteorite explosions.

Infrasound data is transmitted to the NDC for processing and storing, using the SeedLink protocol. Registration of the events and events-bulletin is done by an operational on-duty team 24/7. The government authorities responsible for safety are notified immediately in case of emergency events. Data processing realized by using Geotool and WinPMCC, as well as the own software. It also used data from the foreign infrasound arrays for analysis. The Memorandum with the Central and East European Infrasound Network was signed in 2019. For optimizing the on-duty team's, geophysicists-analysts', and experts' work, processing of the infrasound data in the MCSM, as an experiment, has been transferred to the internal MCSM cloud platform. It facilitated access to the information, provided equal opportunities for the processing, and allowed involving experts from other institutions. 

In the future, all of the above allows actively using the infrasound network of Ukraine for running global and regional monitoring and doing researches on the atmosphere and climate.

How to cite: Liashchuk, O., Kariahin, Y., Kolesnykov, L., Andrushchenko, Y., Tolchonov, I., and Poikhalo, A.: The Infrasound Network of Ukraine, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3895, https://doi.org/10.5194/egusphere-egu2020-3895, 2020.

Over the past two decades the German Aerospace Center (DLR) facility near Heilbronn, Germany, has conducted a considerable number of tests of the ARIANE-5 main engine. Infrasound signals from many of these tests (~40%) have been observed at IMS station IS26 at a distance of about 320 km in an easterly direction (99° east-southeast from North). Due to the prevailing weather pattern in Central Europe, nearly all detected tests occurred during the winter months from October to April, when the stratospheric wind points in an eastern direction, while it reverses during the summer season. Except for a single event in May 2012, the summer months (May through September) did not yield any infrasound signal detections from the engine tests. On the other hand, not all tests conducted in winter are observed either, while detection in the spring and fall equinox months of April and October must be considered to occur incidentally.
 
The large database of about 160 engine tests enables us to assess how well propagation modelling based on a standard atmospheric specification such as the ECMWF forecast model conforms with observed detections and non-detections.  While reversal of the stratospheric wind pattern in the summer season eliminates the stratospheric duct towards the eastern direction, the case of non-detections in the winter season may be of a more subtle nature. Besides increases in background noise levels due to heavy winds at the station, the fine structure of the stratospheric duct in the atmospheric model should determine the detection capability at IS26, which could be located inside or outside a shadow zone at a specific time. Ultimately, the standard atmospheric model used may not be an accurate description of the atmosphere in such cases either. This work on a controlled ground truth infrasound source will thus increase our understanding on the relationship between infrasound detection capabilities and atmospheric specifications over the seasons.

How to cite: Koch, K. and Pilger, C.: Infrasound signals from a ground-truth source and implications from atmospheric models: ARIANE engine tests in Southern Germany revisited, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9344, https://doi.org/10.5194/egusphere-egu2020-9344, 2020.

Strong ground motions induced by North Korea’s declared underground nuclear test in September 2017 and a subsequent subsurface collapse excited substantial and characteristic atmospheric acoustic waves (infrasound) that were detected by multiple stations at regional distances. Back-projection method is applied to the detected long-lasting coherent infrasound wavetrains related to the nuclear test. This allows to reconstruct source locations and reveals ground-to-air coupling in a large area over the northeast Korean Peninsula. To understand the excitation of atmospheric acoustic phases from the underground sources, full 3-D seismo-acoustic simulations are performed with pre-defined seismic moment tensor solutions of the underground sources. The simulations quantitatively predict the excitation of epicentral and diffracted acoustic phases developed by direct vertical ground motion at the immediate epicenter and by seismic surface waves propagating through high mountainous regions, respectively. In the atmosphere, the direct acoustic phases propagate spherically at the speed of sound, but the diffracted phases form inclined wavefronts in the atmosphere as the surface wave moves away from the epicenter. On a broad scale, the simulated acoustic coupling shows good agreement with the infrasound radiation patterns determined from the infrasound observations. Additional simulations for the subsequent subsurface collapse event show that an underground cavity collapse can be a potential mechanism for the production of low-frequency acoustic energy that is also detectable at regional distances. Finally, this study highlights the link between ground motions caused by underground sources and infrasound detection, further enabling infrasound as a depth discriminant for subsurface sources.

How to cite: Che, I.-Y., Kim, K., and Le Pichon, A.: Infrasound from the North Korea underground explosion and subsequent collapse on 3 September 2017, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13599, https://doi.org/10.5194/egusphere-egu2020-13599, 2020.

Polar Mesosphere Winter Echoes (PMWE) are radar echoes that originate from the mesosphere at 50-80 km altitude and are observed with VHF radars during equinox and winter seasons. Strong PMWE are relatively rare phenomena, in most cases they are observed when the lower ionosphere displays high ionisation. Interpretations of observational results concerning PMWE are controversial and the origin of the echoes is still under debate. Especially intriguing is that in some cases of strong PMWE, the measured horizontal speeds of the radar reflecting structures can exceed 300 m/s. Radar reflection (scattering) by infrasound waves at frequencies below about 2 Hz was suggested in order to explain these observations. We will give recent examples of PMWE events of high horizontal speed as observed with the 52 MHz MST radar (ESRAD) located at Esrange (68°N, 21ºE) in northern Sweden. Together with this we will analyse infrasound measurements made at ground-based stations near Kiruna (67.5°N, 20.13ºE) and at the infrasound station IS37 (69°N, 18ºE) in Norway during these events. We discuss prospective relations between PMWE and the microbaroms that are generated by ocean swell in the North Atlantic.

How to cite: Belova, E., Kero, J., Näsholm, S. P., Vorobeva, E., Godin, O. A., and Barabash, V.: Polar Mesosphere Winter Echoes and their relation to infrasound, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5055, https://doi.org/10.5194/egusphere-egu2020-5055, 2020.

Like seismic waves traveling through the solid earth, infrasound waves traveling through the atmosphere are also sensitive to the medium properties – in particular to temperature and wind. The exploitation of this information is particularly interesting in regions and altitude ranges where other
measurements are sparse. In this work, we look at the climatology from first-arrival travel-times using a dataset of infrasound observations from northern Scandinavia, this is, in the context of stratospheric temperatures.

The same dataset has recently been exploited to estimate tropospheric and stratospheric cross-winds. This dataset spans 30 years and corresponds to explosions that are due to the destruction of ammunition at a military site in Finland conducted over the months of August and September; hence, it
covers the period of transition from summer to winter stratosphere. The transition between summer and winter stratosphere is clear in the data. However, a significant travel-time variation between years produces inconclusive results when inferring stratospheric temperature trends over the 30 years analyzed. Still, when comparing the travel-times against regional stratospheric temperatures represented in atmospheric re-analysis models, there is a correspondence between models and infrasound data.

How to cite: Vera Rodriguez, I., Näsholm, S. P., Turquet, A. L., and Evers, L. G.: Climatology reflected by infrasound travel-times sampling the stratosphere in its transition between summer and winter, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20269, https://doi.org/10.5194/egusphere-egu2020-20269, 2020.

We analyze dataset of infrasound observations from surface military explosions in northern Finland which occur yearly in August and September since 1988. The transient nature of these events allows for identification of returns reflected (or scattered) both from stratospheric and from mesospheric - lower thermospheric (MLT) altitudes. The  infrasound data were recorded at Norwegian infrasound-array station around 200 km north of the explosion site. In this study, we use the measured travel-time and backazimuth deviation of the arriving infrasound wavefronts to estimate snapshots of the MLT cross-wind averaged along the propagation path. The spatial extent of that averaging process is explored, and the MLT wind estimates retrieved from infrasound data are presented and compared against high-top atmospheric model winds.

How to cite: Vorobeva, E., Näsholm, S. P., Espy, P., Orsolini, Y., and Hibbins, R.: Wind estimates in the mesosphere - lower thermosphere retrieved from infrasound data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10128, https://doi.org/10.5194/egusphere-egu2020-10128, 2020.

The atmosphere and ionosphere are a complex dynamic system, which is affected by sources, caused both by internal processes and external ones. It is known that atmospheric waves propagating from the troposphere to the upper atmosphere make a significant contribution to the state of this system. One of the regular sources of such waves are various tropospheric disturbances caused, for example, by meteorological processes. Numerical modeling is an effective tool for studying these processes and the effects they cause. However, a number of problems arise, while setting up numerical experiments. The first is that most atmospheric models use hydrostatic approximation (which does not allow the resolution of small-scale perturbations) and work for a limited range of heights (which does not allow studying the relationship between the lower and upper atmosphere). This demands an accurate selection of the model in accordance with the stated research goals. The second problem is the difficulty of direct definition of the wave tropospheric sources, that was mentioned before, due to the lack of experimental information for their detailed description. The authors proposed, researched and tested a way to solve this problem. It was shown that the solution of the problem of waves propagation from a certain tropospheric source is completely determined by the pressure field at the surface of the Earth. This work is devoted to solving various problems using this approach.

This study presents the results of calculations of the propagation of infrasound and internal gravity waves from tropospheric disturbances given by pressure variations at the surface of the Earth. The experimental data associated with various meteorological events and the passage of the solar terminator were obtained both directly - by a network of microbarographs in the studied region, and indirectly - based on the data from the LIDAR signal intensity and temperature changes in the coastal region. The calculations were done using the non-hydrostatic numerical model “AtmoSym”. The characteristics of atmospheric waves generated by such sources are estimated. The effect from a tropospheric sources on the state of the upper atmosphere and ionosphere is investigated. The physical processes that determine the change in atmospheric parameters are discussed.  It is shown that the main contribution from wave disturbances generated by meteorological sources belongs to infrasound. Infrasound and internal gravity waves can be sources of travelling wave packets and can also cause a sporadic E-layer.

The study was funded by RFBR and Kaliningrad region according to the research project  19-45-390005 (Y. Kurdyaeva) and  RFBR to the research project  18-05-00184 (O. Borchevkina).

How to cite: Kurdyaeva, Y., Borchevkina, O., and Kshevetskii, S.: Modeling the propagation of atmospheric waves from various tropospheric disturbances and studying their influence on the upper atmosphere, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-459, https://doi.org/10.5194/egusphere-egu2020-459, 2020.