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, 23–28 Apr 2023, EGU23-15769, https://doi.org/10.5194/egusphere-egu23-15769, 2023.

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, 23–28 Apr 2023, EGU23-8239, https://doi.org/10.5194/egusphere-egu23-8239, 2023.

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, 23–28 Apr 2023, EGU23-6647, https://doi.org/10.5194/egusphere-egu23-6647, 2023.

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, 23–28 Apr 2023, EGU23-5212, https://doi.org/10.5194/egusphere-egu23-5212, 2023.

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, 23–28 Apr 2023, EGU23-12236, https://doi.org/10.5194/egusphere-egu23-12236, 2023.

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, 23–28 Apr 2023, EGU23-13242, https://doi.org/10.5194/egusphere-egu23-13242, 2023.

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 11^th 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, 23–28 Apr 2023, EGU23-3838, https://doi.org/10.5194/egusphere-egu23-3838, 2023.

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, 23–28 Apr 2023, EGU23-2444, https://doi.org/10.5194/egusphere-egu23-2444, 2023.

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, 23–28 Apr 2023, EGU23-3173, https://doi.org/10.5194/egusphere-egu23-3173, 2023.

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, 23–28 Apr 2023, EGU23-6609, https://doi.org/10.5194/egusphere-egu23-6609, 2023.

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, 23–28 Apr 2023, EGU23-14786, https://doi.org/10.5194/egusphere-egu23-14786, 2023.

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, 23–28 Apr 2023, EGU23-17492, https://doi.org/10.5194/egusphere-egu23-17492, 2023.

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, 23–28 Apr 2023, EGU23-3555, https://doi.org/10.5194/egusphere-egu23-3555, 2023.

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, 23–28 Apr 2023, EGU23-3534, https://doi.org/10.5194/egusphere-egu23-3534, 2023.

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, 23–28 Apr 2023, EGU23-7085, https://doi.org/10.5194/egusphere-egu23-7085, 2023.

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, 23–28 Apr 2023, EGU23-11344, https://doi.org/10.5194/egusphere-egu23-11344, 2023.

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, 23–28 Apr 2023, EGU23-11941, https://doi.org/10.5194/egusphere-egu23-11941, 2023.

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, 23–28 Apr 2023, EGU23-8117, https://doi.org/10.5194/egusphere-egu23-8117, 2023.

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, 23–28 Apr 2023, EGU23-7641, https://doi.org/10.5194/egusphere-egu23-7641, 2023.

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, 23–28 Apr 2023, EGU23-6931, https://doi.org/10.5194/egusphere-egu23-6931, 2023.

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, 23–28 Apr 2023, EGU23-769, https://doi.org/10.5194/egusphere-egu23-769, 2023.