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No abstract is available for this article.

Book review: Over the seawall: tsunamis, cyclones, drought, and the delusion of controlling nature
Jasper Verschuur
Nat. Hazards Earth Syst. Sci., 24, 2705–2706, https://doi.org/10.5194/nhess-24-2705-2024, 2024

Limitations in wavelet analysis of non-stationary atmospheric gravity wave signatures in temperature profiles
Robert Reichert, Natalie Kaifler, and Bernd Kaifler
Atmos. Meas. Tech., 17, 4659–4673, https://doi.org/10.5194/amt-17-4659-2024, 2024
Imagine you want to determine how quickly the pitch of a passing ambulance’s siren changes. If the vehicle is traveling slowly, the pitch changes only slightly, but if it is traveling fast, the pitch also changes rapidly. In a similar way, the wind in the middle atmosphere modulates the wavelength of atmospheric gravity waves. We have investigated the question of how strong the maximum wind may be so that the change in wavelength can still be determined with the help of wavelet transformation.

Applicability of the inverse dispersion method to measure emissions from animal housings
Marcel Bühler, Christoph Häni, Albrecht Neftel, Patrice Bühler, Christof Ammann, and Thomas Kupper
Atmos. Meas. Tech., 17, 4649–4658, https://doi.org/10.5194/amt-17-4649-2024, 2024
Methane was released from an artificial source inside a barn to test the applicability of the inverse dispersion method (IDM). Multiple open-path concentration devices and ultrasonic anemometers were used at the site. It is concluded that, for the present study case, the effect of a building and a tree in the main wind axis led to a systematic underestimation of the IDM-derived emission rate probably due to deviations in the wind field and turbulent dispersion from the ideal assumptions.

Abstract

Idealized general circulation models (GCMs) suggest global-mean precipitation ceases to increase with warming in hot climates because evaporation is limited by the available solar radiation at the surface. We investigate the extent to which this generalizes in comprehensive GCMs. We find that in the Community Atmosphere Model, global-mean precipitation increases approximately linearly with global-mean surface temperatures up to about 330 K, where it peaks at 5 mm day−1. Beyond 330 K, global-mean precipitation decreases substantially despite increasing surface temperatures because of increased atmospheric shortwave absorption by water vapor, which decreases the shortwave radiation available for evaporation at the surface. Precipitation decreases in the tropics and subtropics but continues to increase in the extratropics because of continuously strengthening poleward moisture transport. Precipitable water increases everywhere, resulting in longer water-vapor residence times and implying more episodic precipitation. Other GCMs indicate global-mean precipitation might exhibit a smaller maximum rate and begin to decrease at lower surface temperatures.

Abstract

As a key factor influencing the cloud life cycle and radiative properties, liquid-ice mass partitioning remains a major source of uncertainties in modeling mixed-phase clouds. One of the unresolved problems is that liquid-ice mixing is highly inhomogeneous, but it has not been well understood and quantified for parameterization. In this study, the liquid-ice mixing homogeneity (χ) is quantified using the information-theoretic entropy based on airborne measurements. It is demonstrated that χ is positively correlated with the condensed water content (CWC). Cloud regions with low χ are consist of liquid and ice clusters. With the increase in χ, the size and frequency of continuous mixed-phase clusters increase. For a given CWC, χ is lower at relatively warm temperatures as sedimentation of large ice crystals can enhance the inhomogeneity. The strong positive relationship between CWC and χ indicates CWC should be considered when parameterizing the liquid-ice mixing in models.

Abstract

Regional floods result from various flood generation mechanisms. Traditional analyses mainly link flooding to extreme rainfall, with limited input from soil moisture. Total water storage (TWS) is a holistic measure of basin wetness, including additional storage components from surface water, snow, and groundwater. Utilizing a new 5-day Gravity Recovery and Climate Experiment and its Follow On (GRACE(-FO)) data set, we investigated the linkage between short-term TWS anomaly (TWSA) and regional flooding. The 5-day TWSA solutions revealed flood signals missed by monthly TWSA solutions. Global basins exhibit distinct storage-discharge co-evolution patterns, offering new insights into flood mechanisms and propensity. Our bivariate event analyses show the annual maximum river discharges co-occur more often with the TWSA maxima than with precipitation in many basins. Further analyses revealed TWSA's time-lagged effect on river discharge, particularly in basins susceptible to floods triggered by saturation-excess runoff. The 5-day TWSA provides a new source of information for enhancing global flood preparedness.

No abstract is available for this article.

Abstract

The 1999 basaltic eruption of Shishaldin volcano (Alaska) displayed a transition between Subplinian and Strombolian activity. Strombolian bubbles indicate the presence of a periodically unstable foam at the top of magma reservoir. In contrast, a long foam, whose rupture led to the eruptive column, was also able to collect in the conduit. Laboratory experiments show that long foams can be produced in a conduit by the spreading of a stable foam accumulated at the top of the reservoir. The existence of a Taylor bubble at the onset of the Subplinian phase, also reproduced by my laboratory experiments, suggests that the foam in the reservoir was just at the transition between stable and unstable. This constrains the bubble diameter prior to the Subplinian phase to be 0.034–0.038 mm when using the foam dimensionless analysis and the underlying gas flux (0.52–0.80 m3/s). The increase in bubble diameter and potentially gas flux prior to the Strombolian activity, 0.81–1.4 m3/s, is sufficient to explain the foam in transition to be unstable. The radius of the magma reservoir is small, 200–210 m, as expected. The bubble diameter is the smallest of those estimated for classical basaltic eruptions (Etna, Kı̄lauea, Erta 'Ale), while the gas flux is among the largest. A dilute suspension of small and isolated bubbles cannot explain the large gas flux at Shishaldin. This implies numerous bubbles with a gas volume fraction ≥0.63−2%, a regime for which the bubbles form bubble clusters. The diameter of these bubble clusters, 3.0–5.4 mm, is sufficient to explain large gas fluxes.

Abstract

Despite significant progress in studying subduction earthquake cycles, the vertical deformation is still not well understood. Here, we use a generic viscoelastic earthquake-cycle model that has recently been validated by horizontal observations to explore the dynamics of vertical earthquake-cycle deformation. Conditioned on two dimensionless parameters (i.e., the ratio of earthquake recurrence interval T to mantle Maxwell relaxation time t M (T/t M ) and the ratio of downdip seismogenic depth D to elastic upper-plate thickness H c (D/H c )), the modeled viscoelastic deformation exhibits significant spatiotemporal deviations from the simple time-independent elastic solution. Caution thus should be exercised in interpreting fault kinematics with vertical observations if ignoring Earth's viscoelasticity. By systematically exploring these two parameters, we further investigate three metrics that characterize the predicted vertical deformation: the coastal pivot line (CPL), the uplift zone (UZ) landward above the downdip seismogenic extent, and the secondary subsidence zone (SSZ) in the back-arc region. We find that these metrics can all be time-dependent, subject to D/H c and T/t M . The CPL location and the UZ width are mainly controlled by D/H c and T/t M , respectively. The presence of the SSZ is prevalent during the interseismic phase due to viscous mantle flow driven by ongoing plate convergence. Contemporary vertical deformation in Nankai and Cascadia is largely consistent with the model predictions and features differences mainly related to contrasting D/H c values in the two margins. These findings suggest that vertical crustal deformation bears fruitful information about subduction-zone dynamics and is potentially useful for inversions of key subduction-zone parameters, deserving properly designed monitoring.

Abstract

Fault normal stress (σ n ) changes dynamically during earthquakes. However, the impact of these changes on fault strength is poorly understood. We explore the effects of rapidly varying σ n by conducting rotary-shear experiments on simulated fault gouges at 1 μm/s, under well-drained, hydrothermal conditions. Our results show both elastic and anelastic (time-dependent but recoverable) changes in gouge layer thickness in response to step changes and sinusoidal oscillations in σ n . In particular, we observe dilation associated with marked weakening during ongoing σ n -oscillations at frequencies >0.1 Hz. Moreover, recovery of shear stress after such oscillations is accompanied by transient (anelastic) compaction. We propose a microphysically based friction model that explains most of the observations made, including the effects of temperature and step versus sinusoidal perturbation modes. Our results highlight that σ n -oscillations above a specific frequency threshold, controlled by the loading regime and frictional properties of the fault, may enhance seismic hazards.

Abstract

Saturn Kilometric Radiation (SKR), being the dominant radio emission at Saturn, has been extensively investigated. The low-frequency extension of SKR is of particular interest due to its strong association with Saturn's magnetospheric dynamics. However, the highly anisotropic beaming of SKR poses challenges for observations. In most cases, the propagation of SKR is assumed to follow straight-line paths. We explore the propagation characteristics of SKR across different frequencies in this study. An extended equatorial shadow region for low-frequency SKR is identified, resulting from the merging of the Enceladus plasma torus and the previously known equatorial shadow zone. Ray-tracing simulations reveal that low-frequency (≲ $\lesssim $100 kHz) SKR is unable to enter the shadow region and is instead reflected toward high latitudes. In contrast, high-frequency SKR (≳ $\gtrsim $100 kHz) generally propagates without hindrance. Observations suggest that some low-frequency SKR can enter the shadow region through reflection by the magnetosheath or leakage from the plasma torus.

Abstract

An expression of Rayleigh-Taylor (R-T) instability growth rate based on the field-line integrated theory is newly established. This expression can be directly utilized in ionosphere models with magnetic flux tube structure based on Modified Apex Coordinates. The R-T instability growth rates are calculated using the thermospheric and ionospheric conditions based on the coupled Whole Atmosphere Model and Ionosphere Plasmasphere Electrodynamic model (WAM-IPE). The parameters used in this calculation include the field-line integrated conductivities and currents, which consider the Quasi-Dipole Coordinates and the modifications to the equations of electrodynamics. Detailed description of the new formulas and comprehensive analyses of diurnal, longitudinal, and seasonal variations of the R-T instability growth rate are carried out. The dependencies of growth rates on pre-reversal enhancement (PRE) vertical drifts and solar activity are also examined. The results show that pronounced R-T growth rates are captured between 18 and 22 local time (LT) when strong PRE occurs in the equatorial ionosphere. The simulated R-T growth rate increases with increasing solar activity levels and demonstrates strong correlations with the angle between the sunset terminator and the geomagnetic field line. These results are consistent with plasma irregularity occurrence rates shown in various satellite observations, suggesting that the newly developed R-T growth rate calculation can effectively capture the probability of irregularities by considering the changes along magnetic flux-tubes in the ionosphere. Since the WAM-IPE is running in operation at National Oceanic and Atmospheric Administration Space Weather Prediction Center, the new calculations can be potentially implemented in the near future to provide forecasted information of the R-T growth rate.

Abstract

The mechanisms by which clouds impact the variability of the mid-latitude atmosphere are poorly understood. We use an idealized, dry atmospheric model to investigate the relationship between Atmospheric Cloud Radiative Effects (ACRE) and annular mode persistence. We force the model with time-varying diabatic heating that mimics the observed ACRE response to the Southern Annular Mode (SAM). Realistic ACRE forcing reduces annular mode persistence by 5 days (−16%), which we attribute to a weakening of low-frequency eddy forcing via modified low-level temperature gradients, though this effect is partly compensated by reduced frictional damping due to zonal wind anomalies becoming more top-heavy. The persistence changes are nonlinear with respect to the amplitude of ACRE forcing, reflecting nonlinearities in the response of the eddy forcing. These results highlight the ACRE's impact on low-frequency eddy forcing as the dominant cause of changes in annular mode persistence.

Abstract

Pressure and stress perturbations associated with volcanic activity and geothermal production can modify the porosity and permeability of volcanic rock, influencing hydrothermal convection, the distribution of pore fluids and pressures, and the ease of magma outgassing. However, porosity and permeability data for volcanic rock as a function of pressure and stress are rare. We focus here on three porous tuffs from Krafla volcano (Iceland). Triaxial deformation experiments showed that, despite their very similar porosities, the mechanical behavior of the three tuffs differs. Tuffs with a greater abundance of phyllosilicates and zeolites require lower stresses for inelastic behavior. Under hydrostatic conditions, porosity and permeability decrease as a function of increasing effective pressure, with larger decreases measured at pressures above that required for cataclastic pore collapse. During differential loading in the ductile regime, permeability evolution depends on initial microstructure, particularly the initial void space tortuosity. Cataclastic pore collapse can disrupt the low-tortuosity porosity structure of high-permeability tuffs, reducing permeability, but does not particularly influence the already tortuous porosity structure of low-permeability tuffs, for which permeability can even increase. Increases in permeability during compaction, not observed for other porous rocks, are interpreted as a result of a decrease in void space tortuosity as microcracks surrounding collapsed pores connect adjacent pores. Our data underscore the importance of initial microstructure on permeability evolution in volcanic rock. Our data can be used to better understand and model fluid flow at geothermal reservoirs and volcanoes, important to optimize geothermal exploitation and understand and mitigate volcanic hazards.

Abstract

The induced polarization (IP) method holds a strong potential to better characterize the critical zone of our planet especially in areas characterized by multi-phase flow. Power-law relationships between the bulk, surface, and quadrature conductivities versus the pore water saturation are potentially useable to map the subsurface water content distribution. However, the saturation exponents n and p in these power-law relationships have been observed to vary with the texture of geomaterials and the wettabilities of pore fluids. Traditional experimental setups in the laboratory do not allow to independently visualize the pore fluid distribution. Therefore, the physical interpretations of the two saturation exponents have remained unclear. We developed a novel milli-fluidic micromodel using clay-coated glass beads that exhibit excellent visibility and high IP response. Through laboratory experiments, we simultaneously determined the micromodel complex conductivity and acquired the corresponding pore-scale fluid distributions generated by drainage and imbibition through such class of porous materials. Finite-element simulations of complex conductivity based on the upscaling of the complex surface conductance of grains were conducted to determine the saturation exponents under ideal pore fluid distributions. Results indicate that saturation exponents n and p vary depending on the ganglia size of the insulating fluids. The saturation exponents n and p exhibit power-law relationships with the change rate of pore water connectivity with saturation, which is calculated through the computation of the derivative of Euler characteristics. These findings provide a new physical explanation to the relationships between the saturation exponents and the microscopic fluid distributions within the geomaterials.

Abstract

The shortwave cloud radiative effect (SWCRE) is important for the Arctic surface radiation budget and is a major source of inter-model spread in simulating Arctic climate. To better understand the individual contributions of various radiative processes to changes in SWCRE, we extend the existing Approximate Partial Radiative Perturbation (APRP) method by adding the absorptivity for the upward beam, considering differences in reflectivity between upward and downward beams, and analyzing the cloud masking effect resulting from changes in surface albedo. Using data from CMIP model experiments, the study decomposes the SWCRE over the Arctic surface and analyzes inter-model differences in quadrupled CO2 simulations. The study accounts for the influence of surface albedo, cloud amount, and cloud microphysics in the response of SWCRE to Arctic warming. In the sunlit season, CMIP models exhibit a strong, negative SWCRE with a large inter-model spread. Arctic clouds dampen the surface albedo feedback by reflecting incoming solar radiation and further decrease the shortwave radiation reflected by surface, a fraction of which is scattered back to the surface by clouds. Specifically, this accounts for the majority of the inter-model spread in SWCRE. In addition, increased (decreased) cloud amount and cloud liquid water reduce (increase) incoming shortwave fluxes at the surface, but they are found to be not critical to the Arctic surface radiation budget and its inter-model variation. Overall, the extended APRP method offers a useful tool for analyzing the complex interactions between clouds and radiative processes, accurately decomposes the individual SWCRE responses at the Arctic surface.

Abstract

Although blind normal faults are common in subduction environments, their rheology, kinematics and interaction with the upper crust are poorly constrained. A month-long shallow normal faulting sequence in the Ibaraki-Fukushima prefectural border (IFPB), northeast Japan, which followed the M w 9.0 Tohoku-Oki earthquake (TOE) and culminated in the M w 6.7 Iwaki earthquake, provides a window into megathrust-to-normal fault interaction. Stress change calculations indicate that direct triggering by the TOE co- and post-seismic slip does not provide a plausible explanation for the IFPB earthquake sequence. In quest for an alternative triggering mechanism, we analyzed post-TOE GNSS data from eastern IFPB. A key step in this analysis is the removal of the large-scale post-TOE displacement field, after which a distinct highly-localized strain along the coastline becomes apparent. The accumulation of this strain was mostly aseismic, and migrated with time prior to the Iwaki earthquake in a manner that correlates well with post-TOE local seismicity. We attribute the pre-Iwaki earthquake strain accumulation to aseismic slip along low-angle seaward dipping blind normal fault, activated by the TOE. Stresses transferred by this slip episode accelerated the failure along the IFPB shallow normal faults. This indirect triggering of the Iwaki earthquake sequence by the TOE highlights the complexity of stress transfers in subduction environments.

Abstract

In this study, based on the OI135.6 nm night airglow data of the FY-3D Ionospheric Photometer (IPM) during the 2018–2021 geomagnetically quiet period, the global wavenumber 4 longitudinal structure of the equatorial ionization anomaly (EIA) at 2:00 local time was discovered, and the component of the wavenumber 4 was extracted from these structures. Compared with the OI135.6 nm night airglow data of the Special Sensor Ultraviolet Spectrographic Imager (SSUSI) F18 during 2011–2014, there were significant differences in the variation pattern of the relative amplitude of the two versus solar activity and the seasonal variation in the proportion of the component of the wavenumber 4. Based on the neutral wind speed observation results of the Michelson Interferometer for Global High-Resolution Thermospheric Imaging on board the Ionospheric Connection Explorer (ICON) from 2020 to 2021, the longitudinal structures of the 4 ionospheric waves after midnight are related to the cross-equatorial meridional wind. We believe that the wavenumber 4 longitudinal structures after midnight originate from the semidiurnal eastward-propagating with zonal wavenumber 2 (SE2) nonmigrating tide in the cross-equatorial neutral wind rather than the diurnal eastward-propagating with zonal wavenumber 3 (DE3) nonmigrating tide in from the zonal wind, which modulates the daytime wavenumber 4 longitudinal structures.

Abstract

This work investigates seasonal and interhemispheric variations of the afternoon auroral responses to the interplanetary magnetic field (IMF) B y effects. The auroral observations are adopted from the global ultraviolet imager instrument on board the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite during 2002–2007. The results show that in both summer and winter solstices, the stronger afternoon auroral intensity is associated with negative IMF B y (B y  < 0) in the northern hemisphere, and with B y  > 0 in the southern hemisphere. This suggests stronger contributions from the upward field-aligned currents (FACs), which can be induced by the B y -associated north-south oriented electric field and the B y -associated flow shear in the ionosphere. In addition, the strongest afternoon aurora occurs in summer in each hemisphere. In summer, the absolute difference between the auroral peak intensity under the two B y polarities is greater and occurs earlier than in winter, which may be related to changes in FACs and conductivity from winter to summer. Differently, in equinoxes stronger auroral intensity favors B y conditions associated with more frequent occurrence of southward IMF B z , such as B y  < 0 and B y  > 0 conditions in March and in September, respectively. Therefore, in equinoxes the effects of the favorable B y , which were seen in solstices, are masked. We suggest that these are caused by the Russell-McPherron effect, which leads to more southward B z conditions, resulting in more energy deposited and subsequent stronger aurora in polar ionosphere. These results contribute to our deeper understanding of the asymmetrical phenomena in the Earth's magnetosphere-ionosphere induced by IMF B y .