ALBERT

Description: Monitoring stations around the globe routinely detect microbarom signals with a dominant frequency of ∼0.2 Hz from regions of marine storminess. International Monitoring System (IMS) infrasound array IS59 in Kailua-Kona, Hawaii recorded clear signals in close proximity of Hurricanes Felicia and Neki of 2009 for a first-hand investigation of the detailed source mechanism through a hindcast analysis. A spectral wave model describes the tropical cyclone and ambient sea states through a system of two-way nested grids with forcing from a blended data set of global, regional, and cyclonic winds. The computed wave conditions are validated with altimetry measurements and utilized in an acoustic model to estimate the intensity and spatial distribution of the microbarom source. The model results elucidate origins of infrasound signals from the tropical cyclone waves as well as their interactions with the ambient conditions consisting of swells, wind seas, and storm waves from nearby systems. The positive correlation between the IS59 observations and the theoretical microbarom estimates, and the saturation of recorded signals from high-energy sources support the use of infrasound signals for inference of tropical cyclone waves.

Description: Varied acoustic signals were recorded at Kīlauea Volcano in mid-2007, coincident with dramatic changes in the volcano's activity. Prior to this time period, Pu'u 'Ō'ō crater produced near-continuous infrasonic tremor and was the primary source of degassing and lava effusion at Kīlauea. Collapse and draining of Pu'u 'Ō'ō crater in mid-June produced impulsive infrasonic signals and fluctuations in infrasonic tremor. Fissure eruptions on 19 June and 21 July were clearly located spatially and temporally using infrasound arrays. The 19 June eruption from a fissure approximately mid-way between Kīlauea's summit and Pu'u 'Ō'ō produced infrasound for ∼30 minutes—the only observed geophysical signal associated with the fissure opening. The infrasound signal from the 21 July eruption just east of Pu'u 'Ō'ō shows a clear azimuthal progression over time, indicative of fissure propagation over 12.9 hours. The total fissure propagation rate is relatively slow at 164 m/hr, although the fissure system ruptured discontinuously. Individual fissure rupture times are estimated using the acoustic data combined with visual observations.

Description: Microbaroms are continuous infrasonic signals with a dominant frequency around 0.2 Hz produced by ocean surface waves. Monitoring stations around the globe routinely detect strong microbaroms in the lee of tropical cyclones. We utilize a parametric wind model and a spectral wave model to construct the tropical cyclone wave field and a theoretical acoustic source model to describe the intensity, spatial distribution, and dynamics of microbarom sources. This approach excludes ambient wave conditions and facilitates a parametric analysis to elucidate the source mechanism within the storm. A stationary tropical cyclone produces the strongest microbarom signals at the center, where the waves generated by the cyclonic winds converge. As the tropical cyclone moves forward, the converging wave field becomes less coherent and lags and expands behind the storm center. The models predict a direct relation between the storm forward speed and the location of maximum microbarom source intensity consistent with the infrasonic observations from Hurricane Felicia 2009 in the North Central Pacific.

Description: The dynamics and consequences of host–parasite coevolution depend on the nature of host genotype-by-parasite genotype interactions (G × G) for host and parasite fitness. G × G with crossing reaction norms can yield cyclic dynamics of allele frequencies (“Red Queen” dynamics) while G × G where the variance among host genotypes differs between parasite genotypes results in selective sweeps (“arms race” dynamics). Here, we investigate the relative potential for arms race and Red Queen coevolution in a protist host–parasite system, the dinoflagellate Alexandrium minutum and its parasite Parvilucifera sinerae . We challenged nine different clones of A. minutum with 10 clones of P. sinerae in a fully factorial design and measured infection success and host and parasite fitness. Each host genotype was successfully infected by four to ten of the parasite genotypes. There were strong G × Gs for infection success, as well as both host and parasite fitness. About three quarters of the G × G variance components for host and parasite fitness were due to crossing reaction norms. There were no general costs of resistance or infectivity. We conclude that there is high potential for Red Queen dynamics in this host–parasite system. We investigate the relative potential for arms race and Red Queen coevolution in a protist host–parasite system by dissecting the nature of host geontype-by-parasite genotype interactions (G × G). G × Gs were mainly a result of crossing reaction norms, indicating high potential for Red Queen dynamics.

Description: Based on the application of OB considerations (Part I) to various major thermal barrier coating (TBC) compositions and two types of important calcium–magnesium–alumino–silicates (CMAS)—desert sand and fly ash—the 2 ZrO 2 · Y 2 O 3 solid solution (ss) TBC composition, with high CMAS-resistance potential, is chosen for studying molten-CMAS/TBC interactions. It is demonstrated that 2ZrO 2 ·Y 2 O 3 (ss) air plasma sprayed (APS) TBCs are highly resistant to high-temperature attack by both sand-CMAS and fly-ash-CMAS. Despite the differences in the compositions of the two CMASs, the overall CMAS-attack mitigation mechanisms in both cases appear to be similar, viz reaction between 2ZrO 2 ·Y 2 O 3 (ss) APS TBC and the CMAS, and the formation of main reaction products of Y-depleted c - ZrO 2 and nonstoichiometric Ca – Y apatite. Large differences in the OBs (ΔΛ) between the 2ZrO 2 ·Y 2 O 3 (ss) and the CMASs are good predictors of ready reaction between this TBC and these CMASs. While the details of the CMAS-mitigation mechanisms can depend critically on various other aspects, the OB difference (ΔΛ) calculations could be used for the initial screening of CMAS-resistant TBC compositions.

Description: The higher operating temperatures in gas-turbine engines enabled by thermal barrier coatings (TBCs) engender new materials issues, viz silicate particles (sand, volcanic ash, fly ash) ingested by the engine melt on the hot TBC surfaces and form calcium–magnesium–alumino–silicate (CMAS) glass deposits. The molten CMAS glass degrades TBCs, leading to their premature failure. In this context, we have used the concept of optical basicity (OB) to provide a quantitative chemical basis for the screening of CMAS-resistant TBC compositions, which could also be extended to environmental barrier coatings (EBCs). By applying OB difference considerations to various major TBC compositions and two types of important CMASs—desert sand and fly ash—the 2 ZrO 2 · Y 2 O 3 solid solution (ss) TBC composition, with the potential for high CMAS-resistance, is chosen for this study. Here, we also demonstrate the feasibility of processing of 2ZrO 2 ·Y 2 O 3 (ss) air-plasma sprayed (APS) TBC using commercially developed powders. The resulting TBCs with typical APS microstructures are found to be single-phase cubic fluorite, having a thermal conductivity 〈0.9 W·(m·K) −1 at elevated temperatures. The accompanying Part II paper presents results from experiments and analyses of high-temperature interactions between 2ZrO 2 ·Y 2 O 3 (ss) APS TBC and the two types of CMASs.

Description: [1]  Three large-scale infrasound calibration experiments were conducted in 2009 and 2011 to test the IMS infrasound network and provide ground-truth data for infrasound propagation studies. Here we provide an overview of the deployment, detonation, atmospheric specifications, infrasound array observations, and propagation modeling for the experiments. The experiments at the Sayarim Military Range, Israel had equivalent TNT yields of 96.0, 7.4, and 76.8 tonnes (t) of explosives on 26 August 2009, 24 January 2011, and 26 January 2011, respectively. Successful international collaboration resulted in the deployment of numerous portable infrasound arrays in the region to supplement the IMS network and increase station density. Infrasound from the detonations is detected out to ~3500 km to the northwest in 2009 and ~6300 km to the northeast in 2011, reflecting the highly anisotropic nature of long-range infrasound propagation. For 2009, the moderately strong stratospheric wind jet results in a well-predicted set of arrivals at numerous arrays to the west-northwest. A second set of arrivals is also apparent, with low celerities and high frequencies. These arrivals are not predicted by the propagation modeling and result from unresolved atmospheric features. Strong eastward tropospheric winds (up to ~70 m/s) in 2011 produce high amplitude tropospheric arrivals recorded out to 〉1000 km to the east. Significant eastward stratospheric winds (up to ~80 m/s) in 2011 generate numerous stratospheric arrivals and permit the long-range detection (i.e. 〉1000 km). No detections are made in directions opposite the tropospheric and stratospheric wind jets for any of the explosions. Comparison of predicted transmission loss and observed infrasound arrivals gives qualitative agreement. Propagation modeling for the 2011 experiments predicts lower transmission loss in the direction of the downwind propagation compared to the 2009 experiment, consistent with the greater detection distance. Observations also suggest a more northerly component to the stratospheric winds for the 2009 experiment and less upper atmosphere attenuation. The Sayarim infrasound calibration experiments clearly demonstrate the complexity and variability of the atmosphere, and underscore the utility of large-scale calibration experiments with dense networks for better understanding infrasound propagation and detection. Additionally, they provide a rich dataset for future scientific research.

Description: [1]  Atmospheric pressure waves were recorded within five hours after the 2011 great Tohoku earthquake (Mw = 9.0) by sensitive microbarographs at four regional stations and eight International Monitoring System (IMS) stations at distances up to 6,700 km. While its apparent phase velocity between the regional stations is 341 m/s, the global stations indicate weak dispersive wave trains with low frequencies between 1.6 and 4.8 mHz, propagating with an average phase velocity around 364 m/s. The low-frequency waves may be interpreted as acoustic-gravity waves excited by upheaval and depression of the sea surface in the source region due to coseismic uplift and subsidence of the sea bottom during this great thrust earthquake. Assuming the source dimension and the average coseismic vertical displacements of the sea surface, referenced to tsunami observations, we calculate synthetic waveforms for some of the far-field stations, by incorporating a standard sound-velocity structure in the atmosphere up to an altitude of 220 km. The synthetics provide reasonable explanations to the general features of the observed waveforms, suggesting possible ranges for the source parameters generating these acoustic-gravity waves. Our analysis suggests that the average initial upheaval of the sea surface in the central zones of the source region may exceed 4 - 6 m, and the rise time of the coseismic deformation may be in the range between 3 and 4 min. In the eastern narrow zone adjacent to the Japan Trench, the deformation has significantly higher initial amplitude and shorter rise time.

Description: [1]  Monitoring stations around the globe routinely detect microbarom signals with a dominant frequency of ∼0.2 Hz from regions of marine storminess. International Monitoring System (IMS) infrasound array IS59 in Kailua-Kona, Hawaii recorded clear signals in close proximity of Hurricanes Felicia and Neki of 2009 for a first-hand investigation of the detailed source mechanism through a hindcast analysis. A spectral wave model describes the tropical cyclone and ambient sea states through a system of two-way nested grids with forcing from a blended data set of global, regional, and cyclonic winds. The computed wave conditions are validated with altimetry measurements and utilized in an acoustic model to estimate the intensity and spatial distribution of the microbarom source. The model results elucidate origins of infrasound signals from the tropical cyclone waves as well as their interactions with the ambient conditions consisting of swells, wind seas, and storm waves from nearby systems. The positive correlation between the IS59 observations and the theoretical microbarom estimates, and the saturation of recorded signals from high-energy sources support the use of infrasound signals for inference of tropical cyclone waves.

Description: [1]  The 2011 Mw 9.0 Tohoku earthquake generated infrasound that was recorded by nine infrasonic arrays. Most arrays recorded a back azimuth variation with time due to the expanse of the source region. We use ray tracing to predict group velocities and backazimuth wind corrections. A Japan accelerometer network recorded ground shaking in unprecedented spatial resolution. We back projected infrasound from arrays IS44 (Kamchatka) and IS30 (Tokyo) to the source region and compare these results with acceleration data. IS44 illuminates the complex geometry of land areas that experienced shaking. IS30 illuminates two volcanoes and a flat area around the city of Sendai, where the maximum accelerations occurred. The arrays and epicentral region define three source-receiver profiles. The observed broadband energy transmission loss (TL) follows an exponential decay law. The best-fitting model, which has parameters that are interpreted to include the effects of geometric spreading, scattering, and the maximum ratio of the effective sound speed in the stratosphere to that at the ground (accounts for stratospheric wind speed), yields a 65% variance reduction relative to predictions from a traditional TL relationship. This model is a simplified versionof the model of [47], which yields an 83% variance reduction for a single frequency, implying fine-scale atmospheric structure is required to explain the TL for stratospheric upwind propagation. Our results show that infrasonic arrays are sensitive to ground acceleration in the source region of megathrust earthquakes. The TL results may improve infrasonic amplitude scaling laws for explosive yield.