How to cite: Amezcua, J., Näsholm, S. P., and Vera-Rodriguez, I.: Constraining middle and upper atmospheric variables by assimilating measurements from infrasound propagation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6803, https://doi.org/10.5194/egusphere-egu22-6803, 2022.

The International Monitoring System (IMS) was established to monitor for nuclear explosions, and is capable of detecting many different signals of interest (e.g. volcanoes, earthquakes, atmospheric convection etc.) embedded in the station specific ambient noise. The ambient noise can be separated into coherent noise (e.g. microbaroms) and incoherent noise (e.g. wind turbulence). The analysis of the coherent ambient noise was expanded through the use of updated IMS data-sets up to the end of 2020 for all 53 currently certified IMS stations. Monthly reference curves will be presented, which provide a means to determine the deviation from nominal monthly behavior. An example of this use is through the Ambient Noise Stationarity (ANS) factor created for this paper, which provides quick references to the data quality compared to the nominal situations allowing for the identification of either poor data quality, or instances of strong abnormal signals of interest. Further investigation, through use of information about the number of detections can be used to distinguish between poor data quality and strong abnormal signals of interest.

How to cite: Kristoffersen, S., Le Pichon, A., Hupe, P., and Matoza, R.: Updated global reference models of broadband infrasound signals for atmospheric studies and civilian applications, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1902, https://doi.org/10.5194/egusphere-egu22-1902, 2022.

We are presenting a new and novel approach to the detection and parameter estimation of infrasonic signals. Our approach is based on the likelihood function derived from a multi-sensor stochastic model expressed in different frequency channels. Using the likelihood function, we determine, for the detection problem, the Generalized Likelihood Ratio Test (GLRT) and, for the estimation of the slowness vector, the Maximum Likelihood Estimation (MLE). We establish new asymptotic results (i) for the GLRT under the null hypothesis leading to the computation of the corresponding p-value and (ii) for the MLE by focusing on the two wave parameters back-azimuth and horizontal trace velocity. The Multi-Channel Maximum-Likelihood (MCML) detection and estimation method is implemented in the time-frequency domain in order to avoid the presence of interfering signals. Extensive simulations with synthetic signals show that MCML outperforms the state-of-the-art multi-channel correlation detector algorithms like the Progressive Multi-Channel Correlation (PMCC) in terms of detection probability and false alarm rate in poor signal-to-noise ratio scenarios. We also illustrate the use of the MCML on real data from the International Monitoring System (IMS) and show how the improved performances of this new method lead to a refined analysis of events in accordance with expert knowledge.

How to cite: Poste, B., Charbit, M., Le Pichon, A., Listowski, C., Roueff, F., and Vergoz, J.: The Multi-Channel Maximum-Likelihood (MCML) method: a new approach for infrasound detection and wave parameter estimation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1651, https://doi.org/10.5194/egusphere-egu22-1651, 2022.

To fill the gap in infrasound network coverage, the Central and Eastern European Infrasound Network (CEEIN) has been established in 2018 with the collaboration of the Zentralanstalt für Meteorologie and Geodynamik (ZAMG), Vienna, Austria; the Institute of Atmospheric Physics of the Czech Academy of Sciences (CAS IAP), Prague, Czech Republic; the Research Centre for Astronomy and Earth Sciences of the Eötvös Loránd Research Network (ELKH CSFK), Budapest, Hungary; and the National Institute for Earth Physics (NIEP), Magurele, Romania. The Main Centre of Special Monitoring National Center for Control and Testing of Space Facilities, State Agency of Ukraine joined CEEIN in 2019. We present the first CEEIN bulletin (2017-2020) of infrasound-only and seismo-acoustic events, and using ground truth events, we demonstrate how adding infrasound observations to seismic data in the location algorithm improves location accuracy. We show how the CEEIN infrasound arrays improve the detection capability of the European infrasound network and identify coherent noise sources observed at CEEIN stations.

How to cite: Bondár, I., Šindelářová, T., Ghica, D., Mitterbauer, U., Liashchuk, A., Baše, J., Chum, J., Czanik, C., Ionescu, C., Neagoe, C., Pásztor, M., Kouba, D., and Le Pichon, A.: The Central and Eastern European Infrasound Network Bulletin, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3503, https://doi.org/10.5194/egusphere-egu22-3503, 2022.

The mobile Infrasound Array of the Austrian National Data Center which is a part of the Central and Eastern European Infrasound Network (CEEIN) was installed early 2021 at the Trafelberg in Lower Austria. The array aperture is approximately 1000 m. All sites are equipped with Hyperion IFS 3000 sensors and sara® dataloggers. Power is supplied by a fuelcell and solar panels. The data is locally saved and stored on USB sticks, as well it is transferred in real-time to the Headquarter of ZAMG in Vienna. The data is recorded in miniseed format and processed and analyzed manually by using the dtkGPMCC- and dtkDIVA-Software, developed by CEA/DASE (Commissariat à l'Énergie Atomique/Département analyse, surveillance, environment, France). Several challenges occured due to failures of sensors as well of dataloggers. In frame of the SWOT analysis strengths, weaknesses, opportunities and threats of the new installed array were compiled. Results of the analysis will be shown in the presentation.

How to cite: Mitterbauer, U.: Challenges of the Infrasound Array in Austria, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9401, https://doi.org/10.5194/egusphere-egu22-9401, 2022.

Detecting and notifying ongoing volcanic explosive eruptions can support the activities of the Volcanic Ash Advisory Centres (VAAC) in their contribution to the International Airways Volcano Watch. However, local monitoring systems are missing on many active volcanoes. Here, the use of a global monitoring that, even with lower reliability, can allow a fast response. Many studies have shown so far the utility and potential of long-range infrasound monitoring for this aim, but still open questions remain concerning the real efficiency and reliability of such a system.

In this study we investigate the potential of the infrasound network of the International Monitoring System (IMS) of the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) to detect volcanic explosive eruptions at large distances. We apply a procedure based on the Infrasound Parameter (IP) calculated from a single array to selected volcanoes by accounting for realistic infrasound propagation conditions.

The procedure was applied to data recorded by the I06AU infrasound array (Cocos Island) between January 2012 and December 2019 and targeting Indonesian volcanoes at source-to-receiver distances ranging between 1000 and 2000 km, where activity from 11 volcanoes was reported in the period of analysis with an energy spanning from mild explosions to VEI4 eruptions.

The system reliability was evaluated from the ratio between real ones and the total number of notifications provided from I06AU array for each volcano.

The IP was calculated following previous studies and improved with new constraints accounting for the source strength and signal persistency. These allowed us to improve significantly the system reliability for events VEI3 or greater and strongly reduce the number of false alerts. Still, undetected explosive events remain due to unfavorable propagation conditions and unresolved ambiguity due to short spacing among volcanoes with respect to the array. We propose to solve this last issue by considering volcanic sectors rather than single volcanic edifices. Instead of a notification for a single volcano, an alert for an area of interest could be issued to draw the attention and trigger further analysis of satellite images by the VAACs.

This study is performed to improve the Volcanic Information System (VIS) proposed and developed in the framework of FP7 and H2020 ARISE projects.

How to cite: Gheri, D., Marchetti, E., Belli, G., Le Pichon, A., Ceranna, L., Hupe, P., Mialle, P., and Hereil, P.: Monitoring of Indonesian Volcanoes with I06AU infrasound array, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5380, https://doi.org/10.5194/egusphere-egu22-5380, 2022.

The International Monitoring System (IMS), which has been established for the Comprehensive Nuclear-Test-Ban Treaty (CTBT) verification since the late 1990s, is supposed to detect every explosion of at least 1 kt TNT equivalent worldwide. Pressure waves in the infrasound range (between ~0.01 and 20 Hz) can efficiently propagate over long distances, depending on the winds near the stratopause. Therefore, the IMS verification technology monitoring the atmosphere comprises a global infrasound network consisting of up to 60 stations, 53 of which have already been certified. Moreover, research studies and projects have suggested infrasound observations of repeating or persistent sources for probing the winds in the middle atmosphere, where numerical weather prediction models suffer from the lack of continuous observation technologies for data assimilation. One type of repetitive source is active volcanoes. In turn, this natural hazard for civil security can be monitored using infrasound, and prototypes of applications for the release of early volcanic eruption warnings have been established. However, access to raw infrasound data or products of the IMS is limited to specific user groups, which might hinder the utilization of infrasound observations.

In this study, we present IMS infrasound open-access data products for atmospheric studies and civilian applications. For this purpose, 18 years of raw infrasound data (2003-2020) were reprocessed using the Progressive Multi-Channel Correlation method with a one-third octave frequency band configuration between 0.01 and 4 Hz. From the comprehensive detection lists of 53 stations, four products were derived that differ in frequency range and temporal resolution. These are (i) low-frequency infrasound events (0.02-0.07 Hz, 30 min), detections in the microbarom frequency range – in both (ii) a lower (0.15-0.35 Hz) and (iii) a higher (0.45-0.65 Hz) frequency spectrum (both 15 min) – and (iv) observations with relatively high centre frequencies of between 1 and 3 Hz (5 min). Along with several detection parameters, calculated quantities for assessing the relative quality of the products are provided. All four products are provided per station and include detections of volcanic eruptions, while the microbarom products best reflect the middle atmosphere dynamics. The data products are demonstrated by historical and recent examples of natural events that produced infrasound detected at IMS stations. Global compilations of the products highlight the stratospheric circulation effect in the microbarom detections.

How to cite: Hupe, P., Ceranna, L., Le Pichon, A., Matoza, R. S., and Mialle, P.: Infrasound Broadband Bulletin Products of the IMS for Atmospheric Studies and Civilian Applications, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2667, https://doi.org/10.5194/egusphere-egu22-2667, 2022.

Streamer events are induced by breaking of planetary waves near the tropopause. Streamers are significant transient disturbances to the seasonal circulation patterns in the tropopause-stratosphere region at mid latitudes. They modify dynamics of the polar jet stream and of the lower stratosphere.  At streamers’ flanks, strong wind shear occurs and gravity waves can be excited.  Western Europe and the surrounding regions of the North Atlantic are typical regions where streamer events develop.

Long range infrasound propagation is mainly controlled by temperature and wind fields in the atmosphere. Zonal winds in the stratosphere and jet stream near the tropopause belong to key factors that drive infrasound propagation.

A feasibility study on utilisation of ground infrasound measurements in research of streamer events was performed under the ESA’s Aeolus+Inovation project Lidar Measurements to Identify Streamers and Analyse Atmospheric Waves. Three western stations of the Central and Eastern European Infrasound Network WBCI (50.25°N 12.44°E), PVCI (50.53°N 14.57°E), and PSZI (47.92°N 19.89°E) were included in the study of streamer events from February 2020 to March 2021. WBCI is a large aperture array used for observations of low frequency infrasound in the frequency range of 0.0033-0.4 Hz. The stations PVCI and PSZI operate in the infrasound band of 0.05-5 Hz. We focused on statistical comparison of infrasound arrival parameters in periods influenced by streamer events and on calm days.

The presented analysis of the data of the three infrasound stations located in Central Europe did not identify significant first order phenomena related to streamer events. Considering further streamer events and including more stations is necessary to find out if ground infrasound observations could serve for monitoring of streamer events.

How to cite: Sindelarova, T., Kozubek, M., Podolska, K., Bondar, I., Pasztor, M., and Kuchelbacher, L.: Can ground infrasound measurements be a useful complementary technology in studies of streamer events?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-751, https://doi.org/10.5194/egusphere-egu22-751, 2022.

Mediterranean hurricanes, or medicanes, are tropical-like cyclones forming once or twice per year essentially over the waters of Mediterranean Sea. These mesocyclones pose a serious threat to coastal infrastructures and lives, because of their strong winds and intense rainfalls. Infrasound technology has already been employed to investigate acoustic signatures of severe weather events. In order to characterize medicane infrasound detections, we use data from the International Monitoring System (IS48 infrasound station, Tunisia), processed with a multi-channel correlation algorithm. For four different medicanes, high and/or low frequency detections are corresponding to these events, and non-detected cases are also discussed. These detections are discussed by considering other datasets such as satellite observations, a surface lightning detection network, and products mapping the intensity of the swell. While convective systems and lightning seem to be the main sources of detections above 1 Hz, hotspots of swell related to the medicanes are evidenced in the 0.1-0.5 Hz range.

How to cite: Forestier, E., Listowski, C., Dafis, S., Le Pichon, A., Farges, T., De Carlo, M., Vergoz, J., and Claud, C.: Infrasound Signatures of Mediterranean Hurricanes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3907, https://doi.org/10.5194/egusphere-egu22-3907, 2022.

Every day, around one thousand thunderstorms occur around the world producing about 45 lightning flashes per second. One prominent infrasound station of the International Monitoring System of the Comprehensive Nuclear-Test-Ban Treaty Organization for studying lightning activity is IS17 in Ivory Coast where the lightning rate is relatively high. Infrasound is defined as acoustic waves with frequencies below 20 Hz, the lower limit of human hearing. Statistical results are presented in this paper based on infrasound measurements from 2004 to 2019. One-to-one association between infrasound detections from 0.5 to 5 Hz and lightning flashes detected by the World Wide Lightning Location Network within 500 km from the infrasound station is systematically investigated. Most of the infrasound signals detected at IS17 in this frequency band are due to thunder, even if the thunderstorms are located up to 500 km away from the station. A decay of the thunder amplitude with the flash distance, d, is found to scale as d to the power of -0.717 for flashes within 100 km from the station, which holds for direct and tropospheric waveguide propagation. Interestingly, the stratospheric detections reflect a pattern in the annual azimuth variation, which is consistent with the equatorial stratospheric Semi-Annual Oscillation.

How to cite: Farges, T., Hupe, P., Le Pichon, A., Ceranna, L., and Diawara, A.: Infrasound thunder detections across 15 years over Ivory Coast: localization, propagation, and link with the stratospheric semi-annual oscillation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1620, https://doi.org/10.5194/egusphere-egu22-1620, 2022.

Between 0.1 and 0.6 Hz, the coherent ambient infrasound noise is dominated worldwide by signals originating from the ocean, the so-called microbaroms. With an energy peaking around 0.2 Hz, microbaroms signals are generated by second order non linear interactions between wind-waves at the ocean surface and are able to propagate all around the globe through the stratosphere and thermosphere. Monitoring these signals allows characterizing the source activity and probing the properties of their propagation medium, the middle atmosphere, assuming that the source is well modelled. A new theoretical description of the mechanism signal generation connecting the amplitude of the pressure signal to the height and frequency wave oscillation has been proposed by De Carlo et al. (2020). This model has been evaluated quantitatively through systematic comparisons with worldwide observations (De Carlo et al., 2021). This model has been implemented by the Laboratoire d’Océanographie Physique et Spatiale (LOPS) research unit of IFREMER in the DATARMOR HPC center (11088 cores - 426 Tflops) which allows big data hosting and intensive computation. We present a technical overview of the ARROW product and its implementation framework for both hindcast and real-time production. In the context of the future verification of the Comprehensive nuclear Test Ban Treaty (CTBT), ARROW offers an opportunity to target infrasonic signals of specific interest interfering with the global ambient coherent noise. This product, based on a state-of-the-art numerical wave model, paves the way for improved medium-range weather forecasting, by building a global and time-dependent reference database used as input to develop innovative remote sensing methods. 

How to cite: De Carlo, M., Accensi, M., Ardhuin, F., and Le Pichon, A.: ARROW (AtmospheRic InfRasound by Ocean Waves): a new real-time product for global ambient noise monitoring., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7564, https://doi.org/10.5194/egusphere-egu22-7564, 2022.

Mesospheric temperature inversions are subject to investigations due to the links with multiscale dynamics such as planetary wave and gravity waves. Knowing the impact on climatological inversions also requires understanding the phenomena occurring before, through, and after a mesospheric inversion. We use data obtained during a measurement campaign over Maïdo observatory in La Réunion Island and focus on a specific event occurring in the night between the 9^th and the 10^th of October 2017. Among the several observations available, LIDAR measurements provided vertical profiles of temperature and gravity waves potential energy completed by high vertical resolution radiosoundings. The airglow layer observed by an InGaAs camera shows the evolution of gravity wave structures at about 87 km between 0.9 and 1.7 µm. Gravity wave parameters such as horizontal wavelengths or intensity emission variations are extracted, along with potential energy compared with LIDAR data. We use atmospheric models (ERA5, WACCM, WRF) and specific tools (NEMO, GROGRAT) to add supplementary information about the night selected. We present here the first results related to the gravity waves and energy exchanges in the frame of the temperature inversion.

How to cite: Hauchecorne, A., Bellisario, C., Chane-Ming, F., Keckhut, P., Simoneau, P., Trémoulou, S., Litowski, C., Berthet, G., Jégou, F., and Khaykin, S.: Case study of a mesospheric inversion over Maïdo observatory through a multi-instrumental observation., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5593, https://doi.org/10.5194/egusphere-egu22-5593, 2022.

Global scale infrasound observations confirm that the detection capability of the International Monitoring System (IMS) deployed to monitor compliance with the Comprehensive Nuclear-Test ban Treaty (CTBT) is highly variable in space and time. Previous studies estimated the radiated source energy from remote observations using empirical yield-scaling relations accounting for the along-path stratospheric winds. However, these relations simplified the complexities of infrasound propagation as the wind correction applied does not account for an accurate description of the middle atmosphere along the propagation path. In order to reduce the variance in the calculated transmission loss, massive frequency and range-dependent full-wave propagation simulations are carried out, exploring a wide range of realistic atmospheric scenarios. Model predictions are further enhanced by incorporating fine-scale atmospheric structures derived from a two-dimensional horizontal wave number spectrum model. A cost-effective approach is proposed to estimate the transmission losses at distances up to 8,000 km along with uncertainties derived from multiple gravity wave realizations. In the context of the future verification of the CTBT, this approach helps advance the development of network performance simulations in higher resolution and the evaluation of middle atmospheric models at a global scale with limited computational resources.

How to cite: Le Pichon, A., Ceranna, L., and Listowski, C.: Evaluating long range middle atmospheric variability for global infrasound monitoring, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1879, https://doi.org/10.5194/egusphere-egu22-1879, 2022.

Gravity Waves (GW) alter the propagation path of acoustic energy in the middle atmospheric waveguide and complexify the large scale picture where infrasound (IS) propagation is mainly driven by the seasonal changes in stratospheric winds. Thus, GW affect the detection capability of the IS station network of the International Monitoring System (IMS) established to monitor the compliance with the Comprehensive Nuclear-Test-Ban Treaty (CTBT). Atmospheric models explicitly resolving a part of the GW spectrum are relevant tools to be considered for investigating the effect of GW on infrasound propagation, given increasing computing means made available by HPC facilities. Parabolic equation simulations allow accounting for the partial reflections induced by GW. They can be used to quantify the impact of GW on infrasound transmission loss, for instance. Here, we use atmospheric specification fields obtained in the framework of the Dynamics of the Atmospheric General Circulation Modeled on Nonhydrostatic Domains (DYAMOND). DYAMOND is an international project, initiated by the Max Planck Institute for Meteorology (MPIM) and the University of Tokyo. It describes a framework for the intercomparison of high-resolution global models. It mainly focuses on the troposphere, but some models were run with a high enough top so that GW are resolved up to the stratosphere. Lidar observations are used to validate the model at Observatoire de Haute Provence (France) and we investigate the potential energy of GW activity across the IMS. By filtering out small-scale perturbations (GW) in atmospheric specifications and comparing parabolic equation simulations with and without GW, respectively, we quantify the impact of GW on the main atmospheric waveguide. We focus on the transmission loss derived at the surface, and more particularly in the shadow zones, for different national or IMS infrasound stations during the (northern hemisphere) winter.

How to cite: Listowski, C., Stephan, C., Le Pichon, A., Hauchecorne, A., Kim, Y.-H., Achatz, U., and Bölöni, G.: Quantifying the impact of gravity waves on infrasound propagation using high-resolution global models for atmospheric specifications, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3619, https://doi.org/10.5194/egusphere-egu22-3619, 2022.

Infrasound observations and complimentary numerical simulations have shown that infrasound propagation is strongly influenced by topography within approximately 10 km from the source. Recent computational efforts using ray theory have shown that topographic influence extends over hundreds of km and is especially strong when considering propagation through the troposphere. Wind and temperature gradients also have a strong influence on propagation at these distances, which suggests that both topography and 3-D atmospheric structure need to be accounted for in long range waveform modeling. Here we show preliminary results from numerical simulations of linear acoustic propagation through a moving, inhomogeneous atmosphere using an in-development 3-D finite difference time-domain (FDTD) propagation code. We compare our synthetic waveforms in two and three dimensions with existing community infrasound propagation codes and discuss future developments, including open source licensing. Lastly, we present preliminary results from applying this code to the Humming Roadrunner experiments and similar data sets.

How to cite: Bishop, J. W., Blom, P. S., and Fee, D.: Infrasound Propagation with Realistic Terrain and Atmospheres Using a Three-Dimensional Finite-Difference Time-Domain Method, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13054, https://doi.org/10.5194/egusphere-egu22-13054, 2022.