AS4.9 | Infrasound, acoustic-gravity waves, and atmospheric dynamics

AS4.9

EDI

The field of infrasonic research, the science of low-frequency acoustic waves, has expanded to include acoustic-gravity waves and developed into a broad interdisciplinary field encompassing academic disciplines of geophysics and recent technical and basic scientific developments. The International Monitoring System (IMS) infrasound network for nuclear test ban verification and regional infrasound arrays deployed around the globe have demonstrated their capacity for detecting and locating various natural and anthropogenic disturbances in the atmosphere. Infrasound and acoustic-gravity waves are capable of traveling up to thermospheric altitudes and over enormous ranges, where the wind and temperature structure controls their propagation. Recent studies have offered new insights on quantitative relationships between infrasonic observations and atmospheric dynamics, and therefore open a new field for atmospheric remote sensing.

New studies using lidar, radar, microwave spectrometer, and mesospheric airglow observations complemented by satellite measurements help better determine the interaction between atmospheric layers from the ground to the mesosphere and the influence of atmospheric waves on the mean flow. It is expected that further developing multi-instruments platforms would improve gravity wave parameterizations and enlarge the science community interested in operational infrasound monitoring. In a higher frequency range, the infrasound monitoring system also offers a unique opportunity to provide, in near-real time, continuous relevant information about natural hazards with high societal impact, such as large volcanic eruptions, surface earthquakes, meteoroids, and bright fireballs.

We invite contributions on recent studies characterizing infrasound sources or large-scale atmospheric phenomena, including presentations utilizing acoustic waves to probe the atmosphere. Results and advances in acoustic propagation modeling and innovative instrumentation, which also encompasses the extension of regional array networks, are welcome. We also invite studies of the role that infrasound and acoustic-gravity waves play in the coupled Earth’s crust – ocean – atmosphere system and, in particular, in ionospheric manifestations of physical processes in the ocean and in the solid Earth. Contributions highlighting data products and services for civilian and scientific applications utilizing or supplementing infrasound observations are particularly encouraged.

Convener: Alexis Le Pichon | Co-conveners: Patrick HupeECSECS, Alain Hauchecorne, Elisabeth Blanc, Gunter Stober
PICO
| Thu, 27 Apr, 08:30–12:30 (CEST)
 
PICO spot 5
Thu, 08:30

PICO: Thu, 27 Apr | PICO spot 5

08:30–08:35
Instrumentation and processing
08:35–08:37
|
PICO5.1
|
EGU23-15769
|
On-site presentation
Jelle Assink

In order to reduce the observation of wind and turbulence on infrasound sensors, wind noise reduction filters are in place at most infrasound stations. The use of such filters is essential to obtain low background noise levels, which in turn facilitates detection of low signal-to-noise (SNR) infrasound signals. Most filters operate by spatially integrating the pressure field in the vicinity of an infrasound sensor. While the turbulent pressure (partially) de-correlates over the spatial length scale of the filter, the infrasound wave remains coherent. Infrasound arrays that are part of the International Monitoring System make use of advanced pipe array structures that have been designed for long-term deployments. The response is of these systems is stable and well understood. In contrast, many experimental infrasound arrays have relied on the use of porous hoses for wind noise reduction. Porous hoses appear to be efficient, yet cost-effective solutions for short term deployments. Over longer timescales, however, it is known that the response of the hoses can vary significantly and that the hoses can degrade over time.

 

In this work, we investigate the varying response of the porous hoses at the De Bilt Infrasound Array in the Netherlands, using a reference infrasound sensor without hoses. Since a weather station is co-located with the infrasound array, this allows us to study the relationship between the response of the hoses and various meteorological parameters. It is found that under dry conditions, the hoses act as a low-pass filter with a corner frequency around 1.8 Hz, which is consistent with earlier work. We shows that the higher frequency signals with sufficient SNR can be reasonably well reconstructed after a deconvolution step. Under wet conditions however, the hoses become highly absorptive. This can affect observations down to 0.1 Hz. The excess attenuation can be attributed to the presence of rain and/or dew. Although these effects appear to be reversible to some degree, this work shows that care must be taken in the interpretation of data from infrasound arrays that make use of porous hoses.

How to cite: Assink, J.: How does the weather affect the response of porous hose wind noise reduction systems?, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-15769, https://doi.org/10.5194/egusphere-egu23-15769, 2023.

08:37–08:39
|
PICO5.2
|
EGU23-8239
|
ECS
|
On-site presentation
Samuel Kristoffersen, Alexis Le Pichon, Paul Vincent, Michaela Schwardt, and Franck Larsonnier

Infrasound signals can be detected using a time-delay of arrival approach to derive the back azimuth and trace velocity of the coherent wave. For these calculations, it is necessary to have a calibrated measure of the pressure. Although the calibration of microbarometers can be performed in a laboratory setting with specific metrological means such as those developed by the CEA, it is much more difficult to determine the transfer function of the wind noise reduction systems (WNRS), designed to reduce the wind associated noise. In-situ calibration of these WNRS’s can be performed (as described by Gabrielson*) using a co-located reference sensor and comparing the response to that of the array sensor (considering only highly coherent signals) to determine the relative response of the WNRS. System defects, such as flooded pipes or blocked inlets, have significant impacts on the response, which in turn would influence the calculated infrasonic wave parameters. These defects can be characterized using in-situ calibration measurements. To demonstrate the importance of these measurements, experiments were undertaken at the infrasound station IS26, using a temporary detector whose defects on the WNRS can be produced. This will allow for the effects on real infrasound detections to be quantified and corrected using in-situ calibrations. Comparisons between models of these defects and experimental results allow for the characterization of their effects on infrasound parameter measurements and improvements of the models and WNRS designs.

* Thomas B. Gabrielson, “In situ calibration of atmospheric-infrasound sensors including the effects of wind-noise-reduction pipe systems”, The Journal of the Acoustical Society of America 130, 1154-1163 (2011) https://doi.org/10.1121/1.3613925

How to cite: Kristoffersen, S., Le Pichon, A., Vincent, P., Schwardt, M., and Larsonnier, F.: Correcting infrasound wave parameter estimations using in-situ calibration on defective wind-noise reduction systems, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-8239, https://doi.org/10.5194/egusphere-egu23-8239, 2023.

08:39–08:41
|
PICO5.3
|
EGU23-6647
|
ECS
|
On-site presentation
Benjamin Poste, Maurice Charbit, Alice Janela Cameijo, Alexis Le Pichon, Constantino Listowski, François Roueff, and Julien Vergoz

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. We evaluate the capability of MCML to detect overlapping coherent signals in the same time frequency domain, depending on various scenarios with varying signal-to-noise ratio (SNR), frequency bands and array geometry. We quantify the performance of deep learning method to discriminate between interfering coherent signals by predicting the number of sources in a given time-frequency cell using synthetics and real data recorded by stations part of the International Monitoring System (IMS).

 

[1] B Poste, M Charbit, A Le Pichon, C Listowski, F Roueff, J Vergoz (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., Charbit, M., Janela Cameijo, A., Le Pichon, A., Listowski, C., Roueff, F., and Vergoz, J.: The Multi-Channel Maximum-Likelihood (MCML) method: towards a multisource detection and wave parameter estimations using deep learning, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-6647, https://doi.org/10.5194/egusphere-egu23-6647, 2023.

08:41–08:43
|
PICO5.4
|
EGU23-5212
|
On-site presentation
maurice charbit, alexis le pichon, benjamin poste, françois roueff, and julien vergoz
In the area of infrasonic monitoring system, an important task is to clustering the various cells containing a
signal of interest to a reduced event number. Indeed, to each time-frequency cell is attached a source direction of arrivals,
many of which arise from the same physical event spanning over a large time-frequency window. In PMCC (Progressive
Multi-Channel Cross-Correlation) the clustering is based on ad hoc rules and metrics provided by a large empirical expertise.

In this study we present a new approach based on a statistical model, associated to the multichannel maximum-
likelihood (MCML). More specifically, for each time-frequency cell, the MCML provides the estimations of the slowness
vector and of the signal-to-noise ratio (SNR), and the p-value computed from the generalized likelihood ratio (GLR).
These quantities are collected within a large window, typically 10 Hz by 1 hour. To reduce the computational time, only
the cells with p-values below a threshold are considered. The proposed mixture model (MM) is based on the following
4-dimensional vector: the time location, the log of the frequency location and the two components of the slowness vector.
 
Each cluster is modeled by a distribution, chosen in a flexible catalog that can still be improved. Today the catalog
consists of Gaussian distribution, uniform distribution and mixture of Gaussian and uniform. A few examples: short
time event is modeled by a 4D Gaussian, permanent event in a given frequency band, as microbarom or wind turbine, is modeled by
a 2D Gaussian for the DOA, a full time uniform distribution for the time location and a uniform distribution in the
known frequency band. For the DOA modeled by a Gaussian, the covariance is taken as the asymptotic covariance of
the MCML, using the estimated SNR in the corresponding cell. Moreover we introduce a specific cluster to trap falsely
detected signals, modeled by a full uniform distribution in the four dimensions.

The estimation of the parameters of the MM is performed by the so-called Expectation Maximization algorithm.
Then the maximum a posteriori provides the final clustering. We also present an estimation of the number of events
based on the Bayesian information criterion (BIC). Many real observations are considered to illustrate the method.

The main advantages of the proposed method are (i) taking into account the p-value for selecting the cells to cluster,
(ii) the flexibility of the model catalog, (iii) the statistical interpretation of the results.
 

How to cite: charbit, M., le pichon, A., poste, B., roueff, F., and vergoz, J.: Event clustering for infrasound monitoring system, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-5212, https://doi.org/10.5194/egusphere-egu23-5212, 2023.

08:43–08:45
|
PICO5.5
|
EGU23-12236
|
ECS
|
On-site presentation
Quentin Brissaud, Erik Myklebust, Ben Dando, Bettina Goertz-Allmann, Andreas Köhler, Johannes Schweitzer, and Tormod Kvaerna

The real-time seismo-acoustic monitoring of military conflicts can provide a unique alternative to conventional ground reports and sparse satellite coverage. The pressure waves generated by an explosion travel through the atmosphere and subsurface as sound and seismic waves, and their signature can be recorded by arrays of seismometers for ground motion or microbarometers for sound propagation. However, standard monitoring techniques can be both computationally expensive when localizing signals over large regions and/or prone to false detections when signals have low amplitudes. In this contribution we propose a Machine-Learning (ML) based solution to detect seismic and infrasound arrivals and locate sources close to real time. To validate our model we leverage the seismic data collected during the Russia-Ukraine conflict started in February 2022 using the Ukrainian primary station of the International Monitoring System (IMS), the Malin array (AKSAG). We test both the accuracy and computational efficiency of our approach against a threshold-based migration stacking model developed for near-real time monitoring in Ukraine. We hope that this first-ever ML detector of both seismic and acoustic phases could be employed for real-time monitoring of conflicts around the world across different network geometries and noise conditions.

How to cite: Brissaud, Q., Myklebust, E., Dando, B., Goertz-Allmann, B., Köhler, A., Schweitzer, J., and Kvaerna, T.: Seismic and infrasound monitoring of military conflicts using machine learning, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-12236, https://doi.org/10.5194/egusphere-egu23-12236, 2023.

Source studies
08:45–08:47
|
PICO5.6
|
EGU23-13242
|
Highlight
|
On-site presentation
Elisabeth Blanc, Alexis Le Pichon, Thomas Farges, Constantino Listowski, and Pierrick Mialle

The infrasound International Monitoring System (IMS, ) is a unique tool for atmospheric observations due to its high capacity for long-range detection and localisation. Its development, starting in the nineties, motivated technological innovations in sensors, array stations, network configuration and automatic detection algorithms. The rapidly increasing number of certified stations detected a large diversity of anthropic and natural infrasound events, well identified thanks to their accurate description. Numerical simulations, based on propagation laws and atmospheric models, determined the IMS specifications for infrasound monitoring. They were revisited at the end of the 2000s, integrating an improved representation of the variable atmospheric environment, showing the high performances of the network. Data analyses clearly demonstrated that most uncertainties originate from the middle atmosphere disturbances, which control the infrasound waveguides and are under-represented in models. Unexpectedly, relevant atmospheric parameters were identified in infrasound signals from well-known sources such as volcanoes, opening new infrasound remote sensing possibilities. The association of the infrasound IMS to complementary multi-instrument platforms provided new middle atmosphere data, needed for the determination of uncertainties in atmospheric models and infrasound simulations for more precise event analyses. New methods are developed for middle atmospheric remote sensing from IMS infrasound ocean swell noise observations. Such global observations could be relevant for future data assimilation systems used in numerical weather prediction models. A remote volcano information system is developed to provide in the future notification to civil aviation in case of large eruptions of non-instrumented volcanoes. Large-scale climatology systems, such as the inter-tropical convergence zone (ITCZ) of the winds and the semi-annual oscillation (SAO) of stratospheric winds were recently identified. They can provide relevant information about the evolution of climate related parameters. This shows the high IMS potential for weather, climate and civil safety applications.

How to cite: Blanc, E., Le Pichon, A., Farges, T., Listowski, C., and Mialle, P.: 25 years of infrasound monitoring: achievements and challenges, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-13242, https://doi.org/10.5194/egusphere-egu23-13242, 2023.

08:47–08:49
|
PICO5.7
|
EGU23-5764
|
On-site presentation
Daniela Ghica and Constantin Ionescu

Simultaneous observations of infrasonic and seismic signals recorded with the Romanian seismo-acoustic arrays (BURAR, BURARI and IPLOR) are used to forensic tracking the repetitive explosion sources generated by the bombing and shelling taking place in Ukraine since 24 February 2022. Seismo-acoustic signature (signal shape and amplitude, frequency content, energy spectrum) analyzed are characterized by impulsive energetic signals. Events reported in the bulletins provided by IDC/CTBTO are used as reference for associating infrasound and seismic detections of the Romanian arrays. Infrasound signals observed with BURAR seismic array are added to better characterize the type of events in this region. Seismo-acoustic data are analyzed by using processing capabilities of the DTK-GPMCC and DTK-DIVA software embedded in NDC-in-a-Box package.
Infrasonic detections are strongly influenced both by seasonally dependent stratospheric winds and local turbulence-induced pressure fluctuations, i.e., level of wind-generated background noise increases with station altitude. Directions of IPLOR and BURARI infrasonic detections are estimated and the locations are obtained by cross-bearing the derived back azimuths. Deviating effects of zonal cross winds along the propagation path through the atmosphere affect the observed back azimuths: rays which arrive at BURARI are deflected towards the East with approx. 5o, whilst at IPLOR, the azimuthal deviation is negligible (below 1o).
The propagation path of infrasonic signals is analyzed by applying infraGA 2D ray tracer through NRL-G2S atmospheric model. Stratospheric and thermospheric infrasound phases are identified to be observed at BURARI and IPLOR stations.
lease insert your abstract HTML here.

How to cite: Ghica, D. and Ionescu, C.: Analysis of infrasound and seismic signals recorded from repetitive explosion sources at near-regional distance, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-5764, https://doi.org/10.5194/egusphere-egu23-5764, 2023.

08:49–08:51
|
PICO5.8
|
EGU23-3838
|
On-site presentation
Daniel Stich, Josué Casado Rabasco, José María Madiedo, Juan Luis Guerrero Rascado, and Jose Morales

With the densification of seismic networks, recordings of atmospheric infrasound events through ground coupled signals are becoming more numerous. In particular, there’s an increasing probability of detecting direct arrivals at near distances from the source. Here, we analyze a meteor event with absolute magnitude m = −17 on December 11th 2016 that was recorded coincidentally along a dense seismic broadband transect near Granada, Spain. Using 44 near-field detections and the ERA5 atmospheric temperature and wind speed model, we can locate the acoustic source at 38 km height, consistent with the triangulation of the meteor terminal explosion from camera recordings.

The waveforms recorded along the seismic transect reveal important differences between nearby stations, emphasizing the importance of local conditions for acoustic wave propagation and acousto-seismic coupling. A common component of all waveforms are ~0.5 s long N-waves, inherited from the atmospheric shock wave, however waveform attributes such as peak velocity amplitudes and frequencies, signal duration and signal energy show variations of one order of magnitude. Also, the three-component signal polarization shows large variability among stations, suggesting that waveform complexity and the repetitions of N-waves reflects the interaction with local topography, in addition to multipathing through the small-scale structure of the atmosphere along the path. Our observations shed light on various causes of complexity in the conversion of the free-atmosphere acoustic wavefield to ground motion, and point to the difficulties involved in estimating the original pressure signal from acousto-seismic data.

How to cite: Stich, D., Casado Rabasco, J., Madiedo, J. M., Guerrero Rascado, J. L., and Morales, J.: Meteor infrasound recordings at a dense seismic broadband transect in Spain, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-3838, https://doi.org/10.5194/egusphere-egu23-3838, 2023.

08:51–08:53
|
PICO5.9
|
EGU23-2444
|
Highlight
|
Virtual presentation
Elizabeth Silber, Miro Ronac Giannone, and Daniel Bowman

The Earth’s atmosphere is continuously bombarded by extraterrestrial objects (generally referred to as meteoroids) of various sizes and velocities (11.2–72.5 km/s). Such high kinetic energy interactions with exponentially increasing higher density atmosphere result in a visual phenomenon known as a meteor. Optically very bright events, or fireballs, are typically produced by objects larger than about 10 cm in diameter. A rare class of fireballs are earthgrazers which enter the atmosphere at an extremely shallow angle. Depending on their size and velocity, some earthgrazers return to space after a relatively short hypersonic flight through the upper regions of the atmosphere. Due to a variety of factors, including the lack of dedicated observational resources, there are only a handful of documented observations of earthgrazing fireballs in the last 50 years. Nevertheless, this category of extraterrestrial objects is of significant interest to the scientific community for a range of practical reasons, such as the analogous relationship with artificial platforms capable of reaching the boundary of the outer atmosphere. In general, typical fireballs are capable of generating shockwaves that can decay to very low frequency acoustic waves, also known as infrasound. Theoretically, the resulting shockwaves and subsequent infrasound from earthgrazers should have distinct signatures. In principle, fireballs can serve as natural laboratories for testing regional and global infrasound monitoring capabilities and provide an important leverage towards improving high-altitude source detection, characterization and geolocation efforts. Infrasound signatures from earthgrazers should further enhance our understanding of infrasonic signals generated in the upper atmopshere. We report infrasound detection of a rare earthgrazing fireball that was observed by casual witnesses and all-sky cameras across Europe on 22 September 2020. It entered at 03:53:40 UTC over northern Europe, and its luminous path extended from Germany to the UK. Despite the high-altitude trajectory (~100 km), the earthgrazer generated a pressure wave that reached the ground at low frequencies detectable by infrasonic instruments. Three infrasound stations of the Royal Netherlands Meteorological Institute (KNMI) network detected the signal. The airwave swept one of the arrays at a particularly high trace velocity (>1 km/s), indicative of a near-vertical arrival angle from a high-altitude cylindrical line source. 
SNL is managed and operated by NTESS under DOE NNSA contract DE-NA000352.

How to cite: Silber, E., Ronac Giannone, M., and Bowman, D.: Infrasonic observations of a rare earthgrazing fireball, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-2444, https://doi.org/10.5194/egusphere-egu23-2444, 2023.

08:53–08:55
|
PICO5.10
|
EGU23-3173
|
On-site presentation
Thomas Farges, Pierre Letournel, Alexis Le Pichon, and Constantino Listowski

Lightning emits electromagnetic (radio and optical) or acoustic waves, commonly called thunder. In recent years, studies have shown the contribution of acoustic measurements for the 3D reconstruction of cloud-to-ground or intracloud discharges. These acoustic reconstructions are in good agreement with LMA measurements and classical lightning location systems. Recent developments allow to infer the acoustic power of the source and its variability from one flash to another as well as within a flash.

In spring 2022, we set up a measurement campaign where four dense microphone arrays were deployed in the southeast of France. These arrays were composed of nine sensors distributed in a 3x3 matrix of a 20 meter square area. The signals were sampled at 100 Hz and time-stamped with the GPS reference. A thunderstorm occurred on April 23, 2022 and was observed by three of these four arrays. Comparisons with detections at a four array elements of comparable aperture highlights the contribution of denser networks in terms of detection and location capabilities. The storm of April 23 passed between two arrays 14 km apart. This campaign is a very good opportunity to demonstrate how lightning locations can be reconstructed by combining detection results at two acoustic arrays. We detail these new contributions in our presentation.

 

How to cite: Farges, T., Letournel, P., Le Pichon, A., and Listowski, C.: 3D Acoustic reconstruction of lightning by two dense acoustic networks 14 km apart, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-3173, https://doi.org/10.5194/egusphere-egu23-3173, 2023.

08:55–08:57
|
PICO5.11
|
EGU23-6609
|
On-site presentation
Constantino Listowski, Edouard Forestier, Stavros Dafis, Thomas Farges, Marine De Carlo, Florian Grimaldi, Alexis Le Pichon, Julien Vergoz, Philippe Heinrich, and Chantal Claud

Infrasound detections of Mediterranean cyclones known as medicanes (for « Mediterranean hurricanes ») are demonstrated in low- and high- frequency ranges, respectively. We summarize the main findings of a recently published study [1]. We use data from the infrasound station IS48 of the International Monitoring System, in Tunisia, to investigate the infrasound signatures of these meso-cyclones, using a multi-channel correlation algorithm. We discuss cases of detections and non-detections, based on the state of the middle atmosphere and of the wind noise measured at the station. Detections and likely sources are discussed in light of other datasets, comprising satellite observations of deep convection [2] and cloud-to-ground lightning detections from a ground-based network. Detections of infrasound emitted by the cyclone-related swell are modelled using a microbarom source model [3] and are in agreement with observations, comforting the identification of the lower frequency sources. This multi-technology and modelling approach allows to discuss the various sources at plat that may contribute to the monitoring of such extreme meteorological events.

[1] Listowski, C.; Forestier, E.; Dafis, S.; Farges, T.; De Carlo, M.; Grimaldi, F.; Le Pichon, A.; Vergoz, J.; Heinrich, P.; Claud, C. Remote Monitoring of Mediterranean Hurricanes Using Infrasound. Remote Sens. 2022, 14, 6162. https://doi.org/10.3390/rs14236162

[2] Dafis, S.; Claud, C.; Kotroni, V.; Lagouvardos, K.; Rysman, J. Insights into the convective evolution of Mediterranean tropical-like cyclones. Q. J. R. Meteorol. Soc. 2020, 146, 4147–4169.

[3] De Carlo, M.; Accensi, M.; Ardhuin, F.; Le Pichon, A. ARROW (AtmospheRic InfRasound by Ocean Waves): A new real-time product for global ambient noise monitoring. In Proceedings of the EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022

 

How to cite: Listowski, C., Forestier, E., Dafis, S., Farges, T., De Carlo, M., Grimaldi, F., Le Pichon, A., Vergoz, J., Heinrich, P., and Claud, C.: Swell and thunder : infrasound signatures of Mediterranean hurricanes, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-6609, https://doi.org/10.5194/egusphere-egu23-6609, 2023.

08:57–08:59
|
PICO5.12
|
EGU23-14786
|
Virtual presentation
Oleksandr Liashchuk, Yurii Andrushchenko, and Yurii Otruba

At the Ukrainian Antarctic Akademik Vernadsky station deployed a significant multidisciplinary complex of equipment, some of which has been providing data to the scientific community for more than half a century. In addition to existing measuring instruments, a small aperture infrasound array was installed at the Vernadsky Station in 2021. The distance between the Chaparral Physics Model 64Vx sensors is 100 meters. The shape of the array is in the form of a triangle with a central element. The signal from the sensor goes by wire to a four-channel 24-bit ADC and then to the SeisComP server, where the data archive is formed in the miniSEED format. Since 2022, data has been transmitted in real time via the SeedLink protocol via satellite internet to the National Data Center, where it is processed.

During the observation, a large number of interesting regional and global signals associated with the calving of icebergs, avalanches, tsunamis, and storm processes were recorded by the array. At the beginning of 2022, together with the global infrasound network, signals from the eruption of the Hunga volcano, Tonga, were also recorded at the infrasound array of the Vernadsky station.

During registration, some technical issues were discovered that need to be upgraded, in particular, to improve the noise reduction and power systems. It is also necessary to increase the aperture of the array.

In general, the infrasonic array showed good survivability and the ability to record a wide range of phenomena in the Antarctic Peninsula region. Processing of its data in combination with data from neighboring infrasound arrays of the International Monitoring System CTBTO in a number of cases makes it possible to locate and identify the source of the signal. In addition, the current observational experience can be used in the installation of the IMS infrasound station in the Antarctic Peninsula region, as previously planned.

How to cite: Liashchuk, O., Andrushchenko, Y., and Otruba, Y.: Small aperture infrasound array in the Antarctic Peninsula region - the first observations experience, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-14786, https://doi.org/10.5194/egusphere-egu23-14786, 2023.

08:59–09:01
|
PICO5.13
|
EGU23-17492
|
ECS
|
On-site presentation
Sandro Matos, Maria do Céu Jesus, and Nicolau Wallenstein and the CIVISA team²

Located in the middle of the North Atlantic Ocean, São Jorge is a volcanic island that belongs to the central group of the Azores Archipelago, Portugal. Very steep, with 54 km long and 7 km wide, São Jorge is different from all the other archipelago’s islands, being itself a WNW-ESE oriented fissure volcanic system composed of four volcanic units.

Since March 19, 2022, a seismovolcanic crisis has been ongoing beneath the active Manadas Volcanic Fissure System on the western half of the island, where historical eruptions occurred in 1580 and 1808. This unrest, characterized by the occurrence of several thousands of low magnitude earthquakes and some ground deformation, is being monitored by IVAR/CIVISA teams using several techniques (seismology, geodesy, infrasound, ground water geochemistry and CO2 and 222Rn emissions).

Infrasound detections were based on data from the IMS IS42 infrasound station located on the Graciosa Island (Azores) and a portable infrasound array (SJ1) that was deployed in the northwestern part of the island at ~7 km from the main epicentral area.

We describe the actual procedures to correlate seismic and infrasonic data, based on epicentral locations and infrasound back-azimuths and the main results obtained so far.

How to cite: Matos, S., do Céu Jesus, M., and Wallenstein, N. and the CIVISA team²: The use of infrasound monitoring in the 2022 São Jorge Island (Azores) seismovolcanic crisis, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-17492, https://doi.org/10.5194/egusphere-egu23-17492, 2023.

09:01–09:03
|
PICO5.14
|
EGU23-13253
|
ECS
|
On-site presentation
Patrick Hupe, Lars Ceranna, Alexis Le Pichon, Robin S. Matoza, and Pierrick Mialle

We present recent and planned updates of the infrasound data products of all certified infrasound stations of the International Monitoring System, which was established in the late 1990s for verification of the Comprehensive Nuclear-Test-Ban Treaty (CTBT). The updates extend the four data products initially published for the 2003 to 2020 period (https://doi.org/10.5194/essd-14-4201-2022) by two years and thus complete a 20-year period.

Our intention for these data products is to facilitate using this unique global infrasound dataset for scientific applications. The products open up the IMS observations to user groups who do not have access to IMS data or are unfamiliar with data processing using the Progressive Multi-Channel Correlation (PMCC) method. We demonstrate the updated data products based on recent and global infrasound sources such as volcanic eruptions and ocean ambient noise and highlight the provided detection and quality parameters.

How to cite: Hupe, P., Ceranna, L., Le Pichon, A., Matoza, R. S., and Mialle, P.: IMS infrasound data products for atmospheric studies and civilian applications – 2021 and 2022 updates, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-13253, https://doi.org/10.5194/egusphere-egu23-13253, 2023.

09:03–10:15
Coffee break
Probing the atmosphere and propagation modelling
10:45–10:55
|
PICO5.1
|
EGU23-3555
|
Highlight
|
On-site presentation
Claudia Stephan

As we enter the age of exascale computing, more and more global scale simulations with horizontal grid spacings in the range of 1-10 km become available. Yet, not the full spectrum of gravity waves (GWs) is resolved and new challenges emerge, some of which are directly linked to the representation of convection, which is only partially resolved, but the most important source of GWs in the tropics.

Unlike most climate models that use parameterizations for GWs, the DYAMOND simulations reproduce detailed, satellite-observed features of the global GW momentum flux (GWMF) distribution including the zonal mean. This can be attributed to realistic GWs from convection, orography and storm tracks. Yet, the GWMF magnitudes differ substantially among simulations. Differences in the strength of convection may help explain differences in the GWMF between simulations of the same model in the summer low latitudes where convection is the primary source. For ICON, simulations with explicit convection show 30-50% larger zonal-mean momentum fluxes in the summer hemisphere subtropics than simulations with parameterized convection. Explicit convection is associated with stronger updrafts and GW sources.

Since any kind of observations can only see a fraction of the GW spectrum, we also analyzed the spectra of the horizontal motions associated with inertia GWs and Rossby waves, respectively. A fundamental characteristic of the atmosphere is the distribution of wave energy across different horizontal scales. Observations and numerical modelling have supported the idea of a canonical energy spectrum. Horizontal kinetic energy scales with the horizontal wavenumber k as k**-3 at large scales with a transition towards k**-5/3 at mesoscales.

The simulations produce the expected canonical shape of the spectra, which is encouraging given that some models are stripped down to a minimum set of physical parameterizations. Yet, total energy levels, spectral slopes at sub-synoptic scales, and spectral crossing scales differ significantly. The contribution of inertia GWs to the total wave energy differs by factors of up to two between the simulations. The crossing scales between the inertia GW and Rossby wave spectra also differ by a factor of about two between the simulations and depend mostly on the ratio of integrated wave energies, rather than on spectral slope or details of the spectral shape. The spectra exhibit little variability in time and can serve as an almost instantaneous diagnostic.

How to cite: Stephan, C.: Stratospheric gravity waves in high-resolution global models, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-3555, https://doi.org/10.5194/egusphere-egu23-3555, 2023.

10:55–10:57
|
PICO5.2
|
EGU23-7121
|
Highlight
|
On-site presentation
Sven Peter Näsholm, Javier Amezcua, Jelle D. Assink, Evgenia Belova, Erik Mårten Blixt, Quentin Brissaud, Mari Dahl Eggen, Patrick J. Espy, Robert Hibbins, Johan Kero, Tormod Kvaerna, Alexis Le Pichon, Yvan J. Orsolini, Ismael Vera Rodriguez, Antoine Turquet, and Ekaterina Vorobeva

The MADEIRA project (Middle Atmosphere Dynamics: Exploiting Infrasound Using a Multidisciplinary Approach at High Latitudes) is a four-year basic research project finishing in the spring 2023, funded by the Research Council of Norway. 

Its primary objective has been in elucidating the 30-60 km altitude range over large spatial scales using wind and temperature constraints from infrasound data collected at Arctic stations. Wave propagation modelling and infrasound interpretation from well-characterized sources provide remote atmospheric sensing. These data are more continuous in space and time than from many other direct measurement techniques. An aim has been to constrain high-top atmospheric models and explore stratosphere-mesosphere coupling with meteor radar wind measurements sampling the 70-100 km altitude range in combination with the infrasonic data. Another ambition has been to develop real-time diagnostic tools for the stratospheric polar vortex circulation and extreme events like Sudden Stratospheric Warmings. 

Thanks to this project, the research teams have got the opportunity to explore several aspects and building blocks related to infrasound-based middle atmospheric probing and to work towards an assimilation of such datasets into atmospheric models. This paper reviews key research output from the project and highlights accomplishments in the domains of, e.g.: Tropospheric and stratospheric cross-wind estimation using infrasound from explosions; Assimilation of atmospheric infrasound data to constrain tropospheric and stratospheric winds; Atmospheric wind and temperature profile inversion in an ensemble model context; Microbarom radiation and propagation model benchmarking; Speeding up infrasound transmission loss estimation using deep learning; Probing internal middle atmospheric gravity waves; Using a machine learning and stochastics-founded model to provide near real-time stratospheric polar vortex diagnostics.

This project has included several high risk / high gain components and we highlight results that maybe could be labelled as unexpected successes, but we also discuss challenging research obstacles that occurred in our journey.

How to cite: Näsholm, S. P., Amezcua, J., Assink, J. D., Belova, E., Blixt, E. M., Brissaud, Q., Eggen, M. D., Espy, P. J., Hibbins, R., Kero, J., Kvaerna, T., Le Pichon, A., Orsolini, Y. J., Vera Rodriguez, I., Turquet, A., and Vorobeva, E.: Summarizing the research of the MADEIRA project - Middle atmosphere dynamics: exploiting infrasound using a multidisciplinary approach at high latitudes, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-7121, https://doi.org/10.5194/egusphere-egu23-7121, 2023.

10:57–10:59
|
PICO5.3
|
EGU23-6993
|
ECS
|
Virtual presentation
Ekaterina Vorobeva, Jelle Assink, Igor Chunchuzov, Toralf Renkwitz, Patrick Espy, and Sven Peter Näsholm

This study uses ground-based recordings of low-frequency, inaudible acoustic waves (infrasound) to probe the wind and temperature fluctuations associated with internal gravity waves breaking in the middle atmosphere. Building on the approach introduced by Chunchuzov et al., the recorded waveforms are used to retrieve the effective sound speed fluctuations in an inhomogeneous atmospheric layer of infrasound backscattering. The retrieval procedure was applied to infrasound from controlled blasts related to the disposal of military explosives in Hukkakero, Finland and recorded at the IS37 station in Norway over a four-year period from 2014 to 2017. Our findings indicate that infrasound scattering occurs in the lower mesosphere between 50 and 75 km in altitude in a region where gravity waves interact due to strong nonlinear effects and form thin layers with strong wind shears. The retrieved effective sound speed fluctuations were then analysed in terms of the vertical wave number spectra. The analysis revealed that the spectra follow a kz–3 power law that corresponds to the "universal" saturated spectrum of atmospheric gravity waves within kz ∈ [2.1·103; 2.7·102] cycles/m. Based on this wavenumber range, we estimate the outer and inner vertical scale of atmospheric inhomogeneities that infrasound is sensitive to as Linner= 33 – 37 m, Louter = 382 – 625 m.  

Furthermore, the spectra of the retrieved effective sound speed fluctuations were compared to theoretical linear and nonlinear gravity wave saturation theories as well as to independent wind measurements made by the Saura MF radar near the Andøya Space Center in Norway. The comparison showed a good agreement in terms of the amplitude and slopes of the vertical wavenumber spectra in both cases. The overall agreement allows us to suggest that the Saura radar and infrasound-based effective sound speed profiles represent the low- and high-wavenumber regimes of the same "universal" gravity wave spectrum. These results illustrate that the use of infrasound makes it possible to probe fine-scale motions that are not well captured by other techniques. The latter suggests that infrasound observations can be used as a complementary technique to probe internal gravity waves in the middle- and upper atmosphere. 

How to cite: Vorobeva, E., Assink, J., Chunchuzov, I., Renkwitz, T., Espy, P., and Näsholm, S. P.: Using infrasound from explosions for probing internal gravity waves in the middle atmosphere, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-6993, https://doi.org/10.5194/egusphere-egu23-6993, 2023.

10:59–11:01
|
PICO5.4
|
EGU23-3534
|
On-site presentation
Alexis Le Pichon, Constantino Listowski, Patrick Hupe, and Lars Ceranna

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 4,000 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., Listowski, C., Hupe, P., and Ceranna, L.: Evaluating long range middle atmospheric variability for global infrasound monitoring, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-3534, https://doi.org/10.5194/egusphere-egu23-3534, 2023.

11:01–11:03
|
PICO5.5
|
EGU23-7085
|
ECS
|
Virtual presentation
Pierre Letournel, Constantino Listowski, Marc Bocquet, Alexis Le Pichon, Alban Farchi, Julien Vergoz, and Marine De Carlo

Oceanic ambient noise (microbaroms) records are examined to retrieve information on the state of the middle atmosphere. We present an approach to compare ground-based infrasound observations with simulated infrasound detections obtained by combining a microbarom source model [1] with a semi-empirical attenuation law. Comparisons using this continuous and global infrasound source are presented for large time periods to assess performances on both seasonal and finer time scales. Infrasound detections obtained with a cross-correlation algorithm (PMCC) as well as with the new MCML (MultiChannel Maximum Likelihood) method [2] are considered. The sensitivity of simulated infrasound detections to the middle atmosphere model and to the propagation model (the transmission loss parametrisation) is evaluated. We discuss how this method may help to assess the performance of an atmospheric model in the middle atmosphere, as well as to select best members in an ensemble reanalysis.

 

[1] 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.


[2] B Poste, M Charbit, A Le Pichon, C Listowski, F Roueff, J Vergoz, The multichannel maximum-likelihood (MCML) method: a new approach for infrasound detection and wave parameter estimation, Geophysical Journal International, Volume 232, Issue 2, February 2023, Pages 1099–1112, https://doi.org/10.1093/gji/ggac377

How to cite: Letournel, P., Listowski, C., Bocquet, M., Le Pichon, A., Farchi, A., Vergoz, J., and De Carlo, M.: Evaluating atmospheric models in the stratosphere using oceanic infrasound ambient noise., EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-7085, https://doi.org/10.5194/egusphere-egu23-7085, 2023.

11:03–11:05
|
PICO5.6
|
EGU23-11344
|
On-site presentation
Christophe Bellisario, Pierre Simoneau, Ewen Jaffré, Philippe Keckhut, and Alain Hauchecorne

The infrared emission lines observed between 80 and 100 km known as nightglow allow the investigation of dynamic phenomena such as gravity waves acting on local temperature and density. Swenson and Gardner (1998) introduced the cancellation factor as the link between the nightglow intensity observed and the local temperature. In a previous study, we investigated local changes in spectral intensity using the main source of the nightglow OH. The variations showed dependencies on vibrational levels due to the differences in their reaction coefficients. We now extend the sensitivity study by performing 3D spatial tests. We briefly describe the nightglow evolution model (NEMO), which is developed on a pressure level grid where the gravity wave perturbation is applied. Inherent parameters of the perturbation such as spatial wavelengths are confronted to their impacts on the nightglow layer. In addition, spectral integration over infrared InGaAs camera is applied to allow comparisons with measurement campaigns.

How to cite: Bellisario, C., Simoneau, P., Jaffré, E., Keckhut, P., and Hauchecorne, A.: Sensitivity of the cancellation factor spectral variations for temperature investigation in the mesospheric nightglow layer, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-11344, https://doi.org/10.5194/egusphere-egu23-11344, 2023.

11:05–11:07
|
PICO5.7
|
EGU23-11941
|
ECS
|
On-site presentation
Witali Krochin, Gunter Stober, Axel Murk, Roland Albers, and Tobias Plüss

Continuous temperature measurements in the stratosphere (12-50 km) and the mesosphere (50-80 km) are crucial for the deeper
understanding of the physical processes in the middle atmosphere and our understanding of the vertical coupling between the
different atmospheric layers. Several studies have shown the importance of atmospheric waves such as planetary waves, tides,
and gravity waves, their propagation and breaking at these altitudes, and its effect on the global circulation.


Investigating these effects requires long-term measurements with high temporal resolution and altitude coverage. Satellite data
covers the required altitude range but provides limited temporal resolution due to its fixed orbital geometry. Active measurement
techniques such as LIDAR are usually limited to nighttime and only a few instruments have daytime capability and therefore
are unsuitable for continuous observations. Ground-based microwave radiometry provides a robust observational method that
is independent of the daytime, almost independent of the weather conditions, and that permits to perform continuous soundings
from 20-60 km altitude.


TEMPERA (TEMPErature RAdiometer) is a ground-based radiometer developed at the University of Bern in 2013. It measures
microwave radiation spectra from atmospheric oxygen in a range between 52 GHz and 53 GHz. Atmospheric temperature profiles can be retrieved from these spectra. In the last 9 years, the accuracy and performance of this instrument were continuously
improved. The latest version of TEMPERA has a temporal resolution of one measurement per 30 min and temperature profiles
can be retrieved up to an altitude of about 50 km.


The reason for the altitude limitation is the Zeeman effect, which occurs due to the interaction of the atmospheric oxygen with
the Earths magnetic field. The polarisation of atmospheric radiation affected by the Zeeman effect depends on the orientation
of the propagation direction to the magnetic field. Therefore the altitude range for temperature retrievals could be further
improved by decomposing the measured radiation in its polarisation components. In addition, the inclusion of the Zeeman
effect in the retrieval algorithm provides the ability to retrieve the Earths magnetic field from measurements of atmospheric
microwave emissions.


The microwave group from the Institute of Applied Physics of the University of Bern, is currently developing a temperature
radiometer (TEMPERA-C), which is based on the former instrument (TEMPERA), but allows a fully polarymetric analysis of
the atmospheric emission spectra. In my talk I will present the technical details of TEMPERA-C as for example the challenges
in the calibration process. Furthermore I will present calibrated measurements of circular polarized atmospheric emission
spectra as well as temperature retrievals and discuss the effect of the Earth’s magnetic field on these measurements.

How to cite: Krochin, W., Stober, G., Murk, A., Albers, R., and Plüss, T.: Temperature retrievals from a ground-based, fully polarymetric, 50 GHz radiometer, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-11941, https://doi.org/10.5194/egusphere-egu23-11941, 2023.

11:07–11:09
|
PICO5.8
|
EGU23-8117
|
ECS
|
On-site presentation
Pedro Da Costa, Philippe Keckhut, and Alain Hauchecorne

Global observations from space are not numerous and show some disagreements with ground-based NDACC lidars that are not fully explained or do not provide the required vertical resolution to reproduce large fluctuations (20-40 K) due to mesospheric inversions. Comparisons with ERA5 also confirm the lack of variability in the mesosphere. Temperature observations in the mesosphere are biased by migrating atmospheric solar tides with large amplitudes requiring more frequent measurements. Such observations can be easily handled by a constellation of cubesats.

Temperature profiles can be derived by existing satellite missions that were not initially designed for this purpose. This opportunity has been recently tested and processed using GOMOS/ENVISAT observations allowing to provide new and accurate temperature measurements in the mesosphere during 8 years of operation. OMPS/NPP is another limb sensor with a different technical implementation that can expend de 8 years duration of GOMOS to now providing more than 20 years of mesospheric temperature data.

How to cite: Da Costa, P., Keckhut, P., and Hauchecorne, A.: Limb temperature observations in the mesosphere with OMPS, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-8117, https://doi.org/10.5194/egusphere-egu23-8117, 2023.

11:09–11:11
|
PICO5.9
|
EGU23-7641
|
Highlight
|
On-site presentation
Philippe Keckhut, Alexis Mariaccia, Alain Hauchecorne, Mathieu Ratynski, and Sergey Khaykin

It is known that propagation of atmospheric waves and their dissipation are responsible for the small and large disturbances governing the variability observed in the mesosphere (50-90 km). One of the main phenomena caused by these waves is the so-called mesospheric inversion layer (MIL) referring to a vertical layer of ~10 km where there is an enhanced temperature (15-50 K) lasting many days over thousands of kilometers in the mesosphere. Additionally, as perturbations in the mesosphere are crucial issues in aeronautics for the safe reentry of space shuttles or missiles, the study of MILs have aroused a large interest. However, the understanding of MIL’s formation mechanisms is still not fully complete as MILs’ impact on wind behavior has never been observed accurately in the middle atmosphere preventing to determine the shear profile or study how gravity waves propagate from the stratosphere to the thermosphere. Though numerous studies have suggested the important role of gravity waves in the MIL’s apparition. For instance, Hauchecorne and Maillard (1990) have simulated MIL’s formation by the breaking of gravity waves inside and above the MIL making decrease wind above the mesospheric jet, generating turbulence.

In this context, we report here, for the first time, an investigation of co-located temperature-wind observations in the altitude range 30-90 km during MIL events. According to these observations, the temperature inversion within the MIL is associated with a wind deceleration occurring in the same altitude range, confirming an inter-connection and arguing in favor of the role of gravity wave in the occurrence of MIL phenomenon.

How to cite: Keckhut, P., Mariaccia, A., Hauchecorne, A., Ratynski, M., and Khaykin, S.: New observations showing temperature-wind interconnection during mesospheric inversion layer events, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-7641, https://doi.org/10.5194/egusphere-egu23-7641, 2023.

11:11–11:13
|
PICO5.10
|
EGU23-6931
|
ECS
|
On-site presentation
Guochun Shi and Gunter Stober

Sudden stratospheric warmings (SSWs) have significant impacts on the Arctic ozone. In this study, MERRA-2 provides the characteristics of the zonal-mean zonal wind and temperature influenced by the planetary waves during major SSWs. We present an analysis of ozone variations in the stratosphere over Ny-Ålesund, Svalbard (79°N, 12°E) based on the ground-based microwave radiometer GROMOS-C during the major SSW events that occurred from 2015 to 2022. The results are compared with Aura-MLS observations and MERRA-2 simulations. GROMOS-C captures the high variability of stratospheric ozone fluctuations during SSWs at polar latitudes very well. The stratospheric ozone dramatically increases after SSW onset day, which lasts up to two months. The polar vortex is disturbed or weakened by SSW resulting in the meridional transport of ozone from the mid-latitude into the polar regions. Therefore, this study assists in understanding the relationship between the interannual variability of stratospheric ozone and the occurrence of SSWs and has significant implications for stratospheric ozone trends in the northern polar regions.

How to cite: Shi, G. and Stober, G.: Analysing ozone variability at northern polar latitude during sudden stratospheric warming events using ground-based microwave radiometer, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-6931, https://doi.org/10.5194/egusphere-egu23-6931, 2023.

11:13–11:15
|
PICO5.11
|
EGU23-11977
|
ECS
|
Highlight
|
Virtual presentation
Mari Eggen, Alise Danielle Midtfjord, Ekaterina Vorobeva, Fred Espen Benth, Patrick Hupe, Quentin Brissaud, Yvan Orsolini, Alexis Le Pichon, Constantino Listowski, and Sven Peter Näsholm

Acoustic waves below the frequency limit of human hearing - infrasound - can travel for thousands of kilometres in the atmosphere. The global propagation signature of infrasound is highly sensitive to the wind structure of the stratosphere. 

This work exploits processed continuous data from three high-latitude infrasound stations to characterize an aspect of the stratospheric polar vortex. Concretely, a mapping is developed which takes the infrasound data from these three stations as input and outputs an estimate of the polar cap zonal mean wind averaged over 60-90 degrees in latitude at the 1 hPa pressure level. This stratospheric diagnostic information is relevant to, for example, sudden stratospheric warming assessment and sub-seasonal prediction.

The considered acoustic data is within a low-frequency regime globally dominated by so-called microbarom infrasound, which is continuously radiated into the atmosphere due to nonlinear interaction between counter-propagating ocean surface waves. 

We trained a stochastics-based machine learning model (delay-SDE-net) to map between a time series of five years (2014-2018) of processed infrasound data and the ERA5 (reanalysis-based) daily average polar cap wind at 1 hPa for the same period. The ERA5 data was hence treated as ground-truth. In the prediction, the delay-SDE-net utilizes time-lagged inputs and their dependencies, as well as the day of the year to account for seasonal differences. In the validation phase, the input was the 2019 and 2020 infrasound time series, and the model inference results in an estimate of the daily average polar cap wind time-series. This result was then compared to the ERA5 representation of the stratospheric diagnostic time-series for the same period. 

The applied machine learning model is based on stochastics and allows for an interpretable approach to estimate the aleatoric and epistemic prediction uncertainties. It is found that the mapping, which is only informed of the trained model, the day of year, and the infrasound data from three stations, generates a 1 hPa polar cap average wind estimate with a prediction error standard deviation of around 10 m/s compared to ERA5.

Focus should be put on the winter months because this is when the coupling between the stratosphere and the troposphere can mostly influence the surface conditions and provide additional prediction skill, in particular during strong and weak stratospheric polar vortex regimes. The infrasound data is available in real-time, and we discuss how the developed approach can be extended to provide near real-time stratospheric polar vortex diagnostics.

How to cite: Eggen, M., Midtfjord, A. D., Vorobeva, E., Benth, F. E., Hupe, P., Brissaud, Q., Orsolini, Y., Le Pichon, A., Listowski, C., and Näsholm, S. P.: Using a machine learning and stochastics-founded model to provide near real-time stratospheric polar vortex diagnostics based on high-latitude infrasound data, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-11977, https://doi.org/10.5194/egusphere-egu23-11977, 2023.

11:15–11:17
|
PICO5.12
|
EGU23-769
|
ECS
|
On-site presentation
Zongbo Xu and Philippe Lognonné

The air-ground coupling is the conversion of the atmospheric pressure perturbation to the ground motion. This coupling includes the pressure static loading and the acoustic-to-seismic conversion. Studying this coupling can aid investigating the shallow subsurface using the pressure drops and monitoring explosive sources in the atmosphere (like meteorites). However, the theory link of the possible coupling scenarios is missing for 1D elastic media. We demonstrate that by utilizing the compliance, the ratio between the ground motion and the atmospheric pressure perturbation on the ground surface, we can analytically model the coupling scenarios: the static loading, the air-coupled Rayleigh wave, leaky mode, and the acoustic-to-body-wave conversion.

How to cite: Xu, Z. and Lognonné, P.: A theoretical review of the air-ground coupling of 1D elastic media, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-769, https://doi.org/10.5194/egusphere-egu23-769, 2023.

11:17–12:30