In-situ measurements of atmospheric variables are key to the validation and improvement of current models of the Martian climate, particularly of the planetary boundary layer. This highly dynamical region, whose thickness and altitude vary, is governed by unique thermodynamical, physical and chemical exchanges between the troposphere and surface. However, only sparse data is available in this location, as information is collected mostly by a few surface probes and during occasional spacecraft descent and landing. 

Recently, the seismometers of the InSight lander recorded short low-frequency, dispersed waveforms on six occasions. These signals were shown to be impact-generated guided infrasound waves. They were excited by the atmospheric entry and surface impact of bolides, and propagated  in a low-altitude atmospheric waveguide. The location of their source, i.e., the impact crater, is well characterized by orbital imaging and the origin time by joint seismic and acoustic analysis. The deformation of the ground by the propagating infrasound wave allowed their detection by InSight seismometers.

Using analytical modeling, we show that the signal group velocity depends on the vertical profile of the effective sound speed in the Martian boundary layer. These impact-generated signals provide a unique opportunity to probe the atmosphere at these low altitudes. Here, we conduct a Bayesian inversion of effective sound speed up to  ~2000 m altitude using the group velocity measured for events S0981c, S0986c and S1034a. We compare these results with estimates of effective sound speed profiles provided by the Mars Climate Database based on global circulation models. We show that the differences between inverted and modeled profiles can be attributed to a local variation in wind in the impact → station direction, with amplitude smaller than 2 m/s, and that the infrasound data generally validates the Mars Climate Database results for each date and location.

How to cite: Froment, M., Xu, Z., Lognonné, P., Larmat, C., Garcia, R. F., Drilleau, M., Delbridge, B. G., Spiga, A., Kawamura, T., and Beucler, E.: Probing the Martian atmospheric boundary layer using impact-generated seismo-acoustic signals, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8572, https://doi.org/10.5194/egusphere-egu24-8572, 2024.

Inferring a model of the wind, pressure, velocity in the atmosphere is an inverse problem, for which the state of the art methods use the travel times of acoustic waves.
We aim to solve such an inverse problem by adding more information and using a full waveform (in this case pressure variation) as infrasound observation.
In particular, we place our study in the context of an inversion of infrasound due to an explosion (or quake) in a domain, without gravity, without attenuation but with the wind as a non isotropic parameter. The addition of wind is important because wind can have an significant impact on the waveform (like the wave guide). 
To this end, we adapted the adjoint method developed in seismology to a fluid in movement : sensitivity kernels have been computed in the case of acoustics waves in the presence of wind (linearised Navier-Stokes equations).
The sensitivity kernels play the role of a gradient in an optimization framework that recovers the variation of atmospheric parameters (density, wind, pressure, speed).
Sensitivity kernels have been studied on simple and more realistic cases in 1d and 2d.
We validated the sensitivity kernels acquired by the adjoint method by comparing them with those obtained by auto-differentiation. Discontinuities near the source and receivers are observed in the sensitivity kernels. We studied the influence of source frequency on the kernels and on these discontinuities.
These encouraging results on sensitivity kernels led us to test initial synthetic inversion in 1d and 2d.
We proposed an analysis of the efficiency of the inversion depending on the choice of parametrization, conjugate gradient method and regularization term.

How to cite: Gerier, S., Martin, R., and Garcia, R.: Development of a full waveform inversion method for acoustic waves in the presence of wind: application to synthetic and realistic cases , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7749, https://doi.org/10.5194/egusphere-egu24-7749, 2024.

We present an improvement of the Multi-Channel Maximum-Likelihood (MCML) method [1]. This 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 (GLR) with a p-value threshold to discriminate signal of interest and noise. For the estimation of the slowness vector, we determine the Maximum Likelihood Estimation (MLE). Comparisons with synthetic and real datasets show that MCML, when implemented in the time-frequency domain, outperforms state-of-the-art detection algorithms in terms of detection probability and false alarm rate in poor signal-to-noise ratio scenarios. Mathematical extension of MCML is implemented in order to detect overlapping coherent signals in the same time frequency domain. This extension is based on the spectral matrix content. Taking into account the last detected source, the array response in the spectral matrix is iteratively subtracted to estimate a subsequent source of weaker energy. We show that the implemented approach allows detecting overlapping signals in the same time frequency window under various scenarios with varying signal-to-noise ratio (SNR), frequency bands and array geometry. Compared with the original method based on multiple maxima selection on the monosource likelihood function, the new approach yields improved wave parameter estimates. Results are illustrated by synthetics and real data recorded by stations part of the International Monitoring System (IMS).

[1] B. Poste et al. (2022), The Multi-Channel Maximum-Likelihood (MCML) method: a new approach for infrasound detection and wave parameter estimation, Geophysical Journal International, https://doi.org/10.1093/gji/ggac377

How to cite: Poste, B., Abed-Meraim, K., Charbit, M., Le Pichon, A., Listowski, C., Roueff, F., and Vergoz, J.: The Multi-Channel Maximum-Likelihood (MCML) method: towards a cost-effective multisource estimation algorithm, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3150, https://doi.org/10.5194/egusphere-egu24-3150, 2024.

Detecting and promptly reporting ongoing volcanic eruptions is crucial in supporting Volcanic Ash Advisory Centers (VAACs) in their mission to inform about ash clouds that may endanger aviation. Nevertheless, many active volcanoes lack local monitoring systems. Long-range infrasound monitoring, which holds the potential to detect and notify volcanic explosive events, could offer valuable insights. Numerous studies have already emphasized the utility of long-range infrasound data for this purpose, which led to the proposal of several monitoring approaches. 
The Volcanic Information System (VIS), developed in the framework of the FP7 and H2020 ARISE projects, is one of the most recent approaches for reporting ongoing eruptive events in near real-time based on process data from a single infrasound array. However, uncertainties still persist regarding its effectiveness and reliability. VIS is based on the Infrasound Parameter, IP, a detection algorithm originally developed for local monitoring and later adapted to long-range volcanic infrasound observations.
In this study, we investigate the efficiency of VIS considering 10 years (2010-2019) of data provided by 16 infrasound arrays of the International Monitoring System (IMS) established and provisionally operated by the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO). These 16 arrays are located in the most active volcanic regions of the world, encompassing multiple eruptions that range in energy from mild explosions to eruption classified with a VEI (Volcanic Explosivity Index) ≥ 4. To evaluate the reliability of the VIS algorithm and estimate the rate of false alerts (false positives), we compared the notifications provided for the entire period of analysis with reports from the Global Volcanism Program (GVP). 
Our results show that VIS is well designed for long-lasting (> few minutes), large (VEI >3) eruptions, such as Sub-Plinian/Plinian events or highly sustained Vulcanian/Strombolian explosions, while it typically misses single transient events. In terms of ranges, its reliability is strongly azimuth-dependent, with the best results at IMS range (up to 2000 km) achieved under favourable propagation conditions while limited to shorter distances (~1000 km) otherwise. Despite that improvements are possible by azimuthal deflation with the computational of 3D ray-tracing, unresolved ambiguity often remains due to the short angular distances between volcanoes with respect to the array. This issue can be solved by considering volcanic sectors rather than single edifices. In this context, we show that the VIS reliability significantly increases and might provide critical information to the VAACs, automatically and in near real-time, to trigger an independent analysis of ongoing volcanic eruptions.
This study was financially supported by the National Recovery and Resilience Plan, Mission 4 Component 2 - Investment 1.4 - NATIONAL CENTER FOR HPC, BIG DATA AND QUANTUM COMPUTING - funded by the European Union - NextGenerationEU - CUPB83C22002830001.

How to cite: Gheri, D., Belli, G., Marchetti, E., Boulenger, V., Le Pichon, A., Hupe, P., Näsholm, P., and Mialle, P.: Long range monitoring of explosive volcanoes with IMS infrasound arrays: testing the VIS, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17819, https://doi.org/10.5194/egusphere-egu24-17819, 2024.

The mobile Infrasound Array ISCO of the Austrian National Data Center at GeoSphere Austria is a part of the Central and Eastern European Infrasound Network (CEEIN). It was installed early 2021 at the Trafelberg, with the premises of the Conrad Observatory in Lower Austria. In 2022 and 2023 a multitude of signals caused by production blasts of a quarry in a distance of 16 km to the array were detected at the station ISCO. Approximately 20 signals were selected, analyzed and compared not only with the data of the seismic station CONA at the Conrad Observatory but also with the recordings of the Macro Seismic Sensor Network, a local low cost sensor network. Blasting parameters were provided by the operator. In addition, video recordings for the blast process and photogrammetric surveys of the blasted rock mass are available for selected events. This data provides information about the source mechanism for the recorded infrasound signals. Analysis of waveform showed that envelopes of the investigated signals are bell-shaped. Values of peak-to-peak amplitudes range between 0.16 and 0.38 Pascal, the half widths of the envelopes vary from 1 to 3 seconds and the frequency range covers 0.25 to 6.35 Hertz. Products of the peak-to-peak amplitudes and half widths show a significant correlation (R2 = 0.6) with the total explosive charge of the blasts.

Data assessment indicates that the change of rock volume caused by the explosion generates the infrasound signal. The videos of the blasting process show an initial expansion of the blasted rock mass, followed by the deposition in front of the blasting area. We interpret the primary increase of volume and the subsequent compaction during the deposition as the source mechanism of the infrasound signal. Numerical modelling of the volume changes during the overall blasting process allows for the calculation of the infrasound source and Green’s functions.

How to cite: Mitterbauer, U., Brückl, E., Carniel, P., and Mertl, S.: Infrasound signals generated by production blasts in a nearby quarry, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16177, https://doi.org/10.5194/egusphere-egu24-16177, 2024.

Nightglow radiation is a very good marker of high-altitude dynamics. After a first detection of a tsunami signature by a camera in the O+ emission (red airglow at 250km) in 2011, only a few other tsunami detections have been recorded and none have been observed in OH SWIR emission, which is the brightest of all the nightglow emissions and the only compatible for shorter periods signals, such as seismic waves. On the other hand, these acoustic waves associated with earthquakes are systematically detected by other ionospheric instruments (GPS, radar), they have never been directly observed by an airglow camera.  Can they be also detected by airglow?

We present here our strategy for such proof of concept. If achieved, it will provide unique access to seismic waves propagation where ground instruments are not available:  oceans, which cover more than 70% of the Earth's surface, but also to provide the harsh planetary environment of Venus, where airglow also exists and where it is not possible to send spacecraft to the ground.

The recent development of SWIR cameras and the first detection of infrasound in OH radiation in 2020 opened the way for these detections. To better understand the continuous dynamics of the OH layer, we have deployed a first camera at La Réunion island in May 2023. Another one will be installed on the Japanese island of Oshima in February-March 2024 to try to detect the signature of a seismic event if one occurs during the course of this scientific study. The presentation details our methodology for observing the airglow OH perturbations, from the instrument specifications to the first results of almost one year-acquisition at la Réunion and the expected events that we will observe from Japan.

How to cite: Froissart, P.-Y., Lognonné, P., Simoneau, P., and Nishida, K.: OH airglow SWIR observations: high temporal resolution acquisition for ionospheric seismology proof of concept, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8096, https://doi.org/10.5194/egusphere-egu24-8096, 2024.

Lower ionosphere is the theater of interactions between the ionized atmosphere and homogeneous atmosphere. Some phenomena such as gravity and acoustic waves which originate from the homogeneous atmosphere also impact the ionosphere and are suspected to be the source of sporadic disturbances in the E-region. Our goal is to correlate these disturbances to acoustic and gravity waves through modelling and ionosphere sounding. We first present the first steps towards this goal, a bi-dimensionnal, inviscid and compressible acoustic-gravity wave model coupled to a nightglow emission model (NEMO).  Then subsequent cross-comparisons with acoustic and gravity waves seen in the OH nightglow emission layer using an infrared sensor and MRA (Multi-Resolution Analysis) are discussed. These comparisons will help to improve the model’s rendering of wave impacts on their transportation medium, before extending the model’s range to ionospheric heights and properties.

How to cite: Jaffré, E., Bellisario, C., Keckhut, P., Froissart, P.-Y., Trémoulu, S., Chane-Ming, F., Simoneau, P., Hauchecorne, A., and Saillant, S.: Gravity wave model validation using nightglow emission observations for lower ionosphere disturbance modelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9840, https://doi.org/10.5194/egusphere-egu24-9840, 2024.

We present the first continuous observations of the three-dimensional winds in the mesosphere and lower thermosphere (MLT) of the northern hemisphere midlatitudes using the composite data from the first multistatic meteor radar network in China. Our continuous observations started in 2022. In the summer of 2023, typhoon Doksuri passed through China and resulted in intense rainfalls. To reveal the impact of the typhoon on the MLT region, we focus on the variability in the three-dimensional wind fields. The horizontal winds are retrieved using an improved Volume Velocity Processing (VVP) with coordinate transformation and non-linear constraints to minimize errors, and the vertical winds are retrieved from the horizontal divergence with magnitudes of less than 1m/s. We found that on the day when the typhoon passed through our meteor radar network, the horizontal winds strengthened southwest and contained small-scale waves, and the vertical winds showed no significant change.

How to cite: Zeng, J., Stober, G., Yi, W., Xue, X., and Dou, X.: 3-dimensional winds and impacts of the typhoon observed in the MLT region using the Chinese multistatic meteor radar network, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8908, https://doi.org/10.5194/egusphere-egu24-8908, 2024.

In this study, the neutral density and horizontal wind observed by the four meteor radars, as well as the temperature measured by the Microwave Limb Sounder (MLS) onboard the Aura satellite are used to examine the response of neutral density, wind, and temperature in the MLT region to the stratospheric sudden warmings (SSWs) during 2005 to 2021 in the Northern Hemisphere. The four meteor radars include the Svalbard (78.3°N, 16°E) and Tromsø (69.6°N, 19.2°E) meteor radars at high latitudes and the Mohe (53.5°N, 122.3°E) and Beijing (40.3°N, 116.2°E) meteor radars at middle latitudes.

The superposed epoch analysis results indicate that 1) the neutral density over Svalbard and Tromsø at high latitude increased at the beginning of SSWs and decreased after the zonal mean stratospheric temperature reached the maximum. However, the neutral density over Mohe at midlatitudes decreased in neutral density at the beginning of SSW and increase after the zonal mean stratospheric temperature reached the maximum. 2) The zonal wind at high latitudes show a westward enhancement at the beginning of SSWs and then shows an eastward enhancement after the stratospheric temperature reaches maximum. However, the zonal wind at midlatitudes shows an opposite variation to at high latitudes, with an eastward enhancement at the onset and changing to westward enhancements after the stratospheric temperature maximum. The meridional winds at high and midlatitudes show a southward enhancement after the onset of SSW and then show a northward enhancement after the stratospheric temperature maximum. 3) In general, the temperature in the MLT region decreased throughout SSWs. However, as the latitudes decrease, the temperature cooling appears to lag a few days to the higher latitudes, and the degree of cooling will decrease relatively.

How to cite: Yi, W., Zhou, B., Xue, X., Zeng, J., Li, G., Gulbrandsen, N., and Tsutsumi, M.: Impact of Sudden Stratospheric Warmings on the Neutral Density, Temperature and Wind in the MLT region, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16288, https://doi.org/10.5194/egusphere-egu24-16288, 2024.