The delivery of low-abundance, bioactive trace elements to the surface ocean by aerosol mineral dust is a major planetary control over marine primary production and hence the global carbon cycle. Variations in atmospheric dust have established links to global climate over geologic timescales and to regional biogeographic shifts over seasonal timescales. Constraining atmospheric dust variability is thus of high value to understanding oceanographic systems, especially vast, constitutively low-nutrient subtropical gyre ecosystems and high-nutrient/low-chlorophyll ecosystems where availability of the trace element iron is a dominant ecological control. Here we leverage the MERRA-2 reanalysis product to examine over four decades of surface-level atmospheric mineral dust variability in a domain of the subtropical North Pacific centered at ocean Station ALOHA. This study region has been sampled regularly since the mid-1980s and was the site of the Hawaii Aerosol Time-Series (HATS) project in 2022-2023. Two nearly semi-annual dust pulses evident in the long-term data are described and constrained. We look for evidence of shifts in total and seasonal atmospheric dust abundances and in the onset timing of the dominant spring/summer pulse, finding year-to-year variations but little evidence for long-term trends. We observe significant and complex monthly relationships between the Pacific Decadal Oscillation (PDO) index and both dust and precipitation, offering new insights into the role of timing for increased or diminished dust delivery. We observe that 2022 was among the dustiest years for the study domain in the preceding two decades and, by contrast, that 2023 exhibited a significant early-spring lull in dust.

Seven years of data collected at the Atmospheric Radiation Measurement (ARM)’s Eastern North Atlantic (ENA) site are analyzed to understand the controls of Cloud Condensation Nuclei (CCN) concentrations in the region. Day-night differences in the aerosol data as segregated by wind direction demonstrated the aerosol observations to be impacted by local emissions when the wind direction (wdir) is between 90° and 310° (measured clockwise from the North where air is coming from). Data collected during marine conditions (wdir<90° or wdir>310°) showed the CCN concentrations to be higher in the summer months as compared to the winter months. CCN budget analysis revealed advection and precipitation scavenging being primarily responsible for modulating the CCN concentrations at the site on monthly timescales, with rain rates driving the precipitation scavenging term. High (greater than 75th percentile) and low (lower than 25th percentile) CCN events were identified for each month to characterize the sub-monthly variability of CCN concentrations. Low CCN events had deeper clouds, stronger rain rates, and lower free-tropospheric aerosol mass at the ENA site as compared to the high CCN events. Analysis of satellite data of air-parcels 48 hours prior to their arrival at the ENA site demonstrated the air parcels during low CCN events to encounter higher cloudiness, stronger rain rates, and higher cloud top heights as compared to the high CCN events. The results presented herein provide key constraints for model evaluation studies and climatological studies conducted at the ENA site.

The current paper investigates the shallow layers of the lunar regolith at the Chang'E-4 landing site. Four layers between 0-10 meters were identified using lunar penetrating radar. Based on these outputs, a revised stratigraphic model is suggested for the post-Imbrian ejecta at the Von Karman crater. The layers were previously unseen due to the smooth boundaries between them. The revised model was inferred using an advanced hyperbola-fitting scheme. Applying conventional hyperbola-fitting to non-homogeneous media results in errors and inaccuracies that are often wrongly assumed to be negligible. We propose a novel hyperbola-fitting scheme that is not constrained to homogeneous media and can be applied subject to any arbitrary one-dimensional permittivity distribution. Via this approach, we can estimate the permittivity profile of an investigated area and detect layered structures that were previously transparent to electromagnetic waves due to the gradational dielectric properties at their interfaces.

In case of earthquakes and crustal movement, the concentration of impounding load over a large region of crust can cause disturbances to the stratum. In order to quantitatively investigate crack initiation, propagation and coalescence processes of jointed stratum based on thermal variations caused by concentrated mechanical loading, a series of indention tests were performed on granite specimens. In the experiment, fracture process and resulting infrared radiation fields of specimens were respectively recorded by synchronized digital image correlation system and infrared camera. Then, thermal characteristics of mixed shear-tensile and tensile conical crack were analyzed. Experimental results indicate that the highlighted temperature localization is mainly caused by shear deformation within the localized fracture process zone. It is shown that in the initiation process, the abnormities in the temperature concentration factors are caused by the frictional-thermal effect for mixed mode crack and the thermoelastic effect for tensile mode crack. Subsequently, in the propagation process, these two crack types followed newly proposed criteria, namely, the maximum temperature gradient criterion for mixed mode crack and the minimum temperature gradient criterion for tensile mode crack. In addition, the intensity of temperature concentrations in crack initiation stage and coalescence stage are more pronounced than that of crack propagation stage. These thermal effects strongly correlated with the stress states in the cracking process. The new findings from the infrared radiation temperature distributions improve our understanding of fracturing process of rock mass. Furthermore, it will provide some fundamental references for geophysical prospecting in jointed rock mass.

A document by Mark Looper. Click on the document to view its contents.

In this study, to generate bioelectricity to power the monitoring sensors and to improve sediment simultaneously is discussed in Yamaguchi bay located in the south part of the Honshu island, Japan through sediment microbial fuel cell (SMFC). To supply energy to the geoenvironmental monitoring sensors is a serious problem, as traditional batteries and solar cells are often inconvenient due to the limitations of recharging and weather conditions, respectively. Four different sediments were used in the laboratory to generate bioelectricity and to improve sulfide contamination simultaneously by SMFCs. The acid volatile sulfide (AVS) was determined to check the improvement of the geo-environment of the sediments as it was the main source of contamination in the intertidal zone (tidal flat). Various factors which affected the voltage generation have been studied. Voltage values showed almost twice when two anodes were used instead of a single anode. Higher temperature showed the higher voltage due to increased activity of the bacteria in the higher temperature. AVS values reduced quickly when the closed circuit was used. All the marine sediments showed the decreasing trend of AVS value with time and reached at the 0.2 mg/g-dry mud indicating the geoenvironmental improvement of the marine sediments within 14 days . Field test showed the higher value of voltage comparing to the laboratory test by using the similar sized SMFCs.

Fracture geometry, density, and distribution control fluid and thermal transport in low porosity rocks, as well as their seismic attributes. The creation of cracks throughout the matrix can result in large and disparate reductions in P- and S-wave velocities with negligible porosity development, which breaks the classic velocity-porosity relationship. Properly interpreting these signatures in seismic surveys from stimulated geothermal, oil, and gas reservoirs or seismogenic areas requires a rock physics model that uses realistic elastic properties of fractures. Conventional models for cracked rocks employ specific inclusion shapes such as spheroids with small aspect ratios. However, all these exhibit the same normal-to-shear compliance ratio -- regardless of aspect ratio -- and therefore impact the bulk and shear moduli in the same qualitative way. As such they are inadequate for describing many of the complementary evolutions of P- and S-wave velocities that transpire with the generation of cracks. Using a differential model of dimensionless compliances, we analyze published velocities for granite, basalt, and limestone to quantify typical compliance ratios and find that it is often different from that assumed in conventional crack models, which then affects crack density estimates. We also investigate how the total normal and shear compliances change due to certain thermo-hydro-chemo-mechanical processes that generate large crack densities, and conclude that the final ratios often still deviate from that of conventional models. Finally, we demonstrate how the model can be used to describe scatter in both P- and S-wave velocity-porosity trends. Implications for energy extraction and seismic monitoring are discussed.

Strong ground motions from large earthquakes are capable of damaging near-surface sediments and promoting notable reductions in their seismic velocity structures. These velocity reductions can be monitored using either body waves or surface waves from repeatable seismic sources, such as repeating earthquakes or ambient seismic noise. Here we compile a decade-long catalog of repeating earthquakes since the 2004 Mw 9.2 Sumatra Earthquake, and monitor the temporal velocity changes from Rayleigh waves (δVLR) and Love waves (δVLQ). We observe a δVLR of –0.16% and δVLR/δVLQ ratio of ~6, inconsistent with velocity reductions in isotropic media. To reconcile the observations, we carry out analyses of sensitivity kernels of surface waves in isotropic and vertical transversely isotropic (VTI) media and forward waveform modeling. The modeling reveals that the observed large δVLR/δVLQ ratio can be explained by strong dbV (–4%) and weak dbH (–0.615%) reductions and an increase in radial anisotropy in the near surface. These changes are best explained by a 2% increase in crack density of aligned horizontal cracks in overpressured sediments near the compressive subduction zone environment. Temporal variations of δVLR/δVLQ ratios after consecutive great earthquakes are consistent with laboratory experiments under cyclic loading.

A document by John Louie. Click on the document to view its contents.

The exchange of kinetic and electromagnetic energy by precipitation and/or outflow, and through field-aligned currents are two aspects of the ionosphere-magnetosphere coupling. A thorough investigation of these processes is required to better understand magnetospheric dynamics. Building on our previous study using DMSP spectrometer data, here we use Swarm vector field magnetometer data to describe the auroral oval morphology in terms of east-west magnetic field perturbations. We define a threshold for detecting magnetic fluctuations based on the power spectral density of ΔBEW and derive the disturbed magnetic field occurrence probability (dBOP) at low [0.1–1Hz] and high [2.5–5Hz] frequencies. High-frequency distributions of dBOP reveal a dayside-nightside asymmetry, whereas low-frequency dBOP exhibits a persistent morphological asymmetry between the dawn-to-noon and the dusk-to-midnight sectors, peaking at dawn. Notably, weak solar wind conditions are associated with an increase in the dBOP asymmetric patterns. At low frequency in particular, while the dBOP seems to be primarily constant at dawn, the dusk dBOP decreases during quiet times, inducing a relatively larger dawn-dusk asymmetry in such conditions. We find that the dBOP distributions at low frequencies exhibit features similar to those present in distributions of the auroral electron precipitation occurrence probability, suggesting that the low-frequency dBOP constitutes a reasonable proxy for the large-scale auroral oval. Our interpretation is that the dBOP at low frequencies reflects a quasi-steady state circulation of energy, while the high-frequency dBOP reflects the regions of rapid changes in the magnetosphere. The dBOP is therefore a crucial source of information regarding the magnetosphere-ionosphere coupling.

Emulators of Earth System Models (ESMs) are complementary to ESMs by providing climate information at lower computational costs. Thus far, the emulation of spatially resolved climate extremes has only received limited attention, even though it is one of the most impactful aspects of climate change. Here, we propose a method for the emulation of local annual maximum temperatures, with a focus on reproducing essential statistical properties such as correlations in space and time. We test different emulator configurations and find that driving the emulations with global mean surface temperature offers an optimal compromise of model complexity and performance. We show that the emulations can mimic the temporal evolution and spatial patterns of the underlying climate model simulations and are able to reproduce their natural variability. The general design and the good performance for annual maximum temperatures suggests that the proposed methodology can be applied to other climate extremes.

We describe a new phenomenon in atmospheric physics – 222Rn progeny circulation during thunderstorms. The enhancement of the natural gamma radiation during thunderstorms was measured with precise gamma ray spectrometers. Results of measurements performed at Aragats mountain in Armenia during summer 2020 demonstrate the Rn progeny lifted to the atmosphere by a near-surface electric field are returned back to the ground by rain precipitation. Thus, thunderstorms not only return negative charge to the Earth by lightning flashes but, also maintain Rn progeny circulation in the atmosphere; it this way, significantly enlarging natural gamma radiation above the Earth surface and Radon concentration in the atmosphere.

Nitrate aerosol has become an increasingly important component of fine particles. While the formation and evolution of nitrate in airborne particles are extensively investigated, little is known about the formation of nitrate in clouds. Here we present a detailed investigation on the in-cloud formation of nitrate based on the size-resolved mixing state of nitrate in the individual cloud residual and cloud-free particles by single particle mass spectrometry, and the mass concentrations of nitrate in the cloud water and PM2.5 at a mountain site (1690 m a.s.l.) in southern China. The results show a significant enhancement of nitrate mass fraction in cloud water and relative intensity of nitrate in the mass spectra of the cloud residual particles, underlining a critical role of in-cloud processing in the formation of nitrate. Based on the size distribution of relative intensity of nitrate in individual particles, we exclude the gas phase scavenging of HNO3 and the facilitated activation of nitrate-containing particles as the major contribution for the enhanced nitrate. Regression analysis and theoretical calculations further reveal that nitrate is highly related (R2 = ~0.6) to the variation of [NOx][O3], temperature and droplet surface area in clouds. Accounting for droplet surface area greatly enhances the predictability of the observed nitrate compared with using [NOx][O3] and temperature. Our results indicate a critical role of in-cloud formation of nitrate via N2O5 hydrolysis, even during the daytime, attributed to the diminished light in clouds. The detailed observation would benefit future investigations of the evolution and oxidative impacts of nitrate.

The changing characteristics of the frozen ground (FG) are essential indicators of climate change. The soil temperature (ST) on the Tibetan Plateau (TP) during 1987- 2018 was simulated using the coupled model of RegCM4.7-CLM4.5. The results show that there is a significant warming trend in the ST on the TP, and the warming trend is higher in October-May (0.040 ℃∙decade−1) than in June-September (0.026 ℃∙decade−1), with the maximum value in February (0.058 ℃∙decade−1). Spatially, the warming is most significant in the Three River Source Region (0.15~0.20 ℃∙decade−1) and near the Himalayas and Kunlun Mountains (0.20~25 ℃∙decade−1), with the warming trend greater in winter and spring than in summer and autumn. Air temperature (AT), total precipitation (TPR), maximum snow depth (MSD), and maximum frozen ground depth (MFD) can significantly affect the ST variation. The AT (R=0.851) and TPR (R=0.411) can accelerate the soil warming, while the MSD (R=-0.381) and the MFD (R=-0.770) can decelerate the soil warming. The AT has a strong influence on the ST in all four seasons, while the effect of the TPR is strongest in autumn (R=0.836). The retarding effects of the MSD and the MFD are strongest in summer (R=-0.772 and -0.35 respectively). Both the observation data and numerical simulation analyses indicate that the FG on the TP shows a degradation trend, and the consequent hydrological, ecological, and climatic effects deserve sufficient attention.

• We present a two-dimensional Discrete Element Method model that simulates host rock fracturing during the inflation of a magmatic laccolith. • The host rock toughness and stiffness along with source depth control spatial fracture distribution between two end-members. • At a constant injection rate, the vertical displacement maximum and lateral extent show sudden changes in response to host rock fracturing.

Many regions worldwide have replaced quotas, as a means to controlling irrigation-water usage, with a hybrid policy that integrates private quotas and uniform prices. This paper characterizes the political equilibrium in a game in which farmers lobby for lower prices and larger quotas. We show that combining the two instruments reinforces the robustness of each against political distortion; consequently, a hybrid policy that follows a quotas-only regime reduces water usage. However, the social welfare rank of the hybrid policy versus the quotas-only and price-only counterparts is an empirical question. We use the equilibrium conditions to derive a structural discrete/continuous choice model that enables estimating the agricultural sector’s lobbying power and the level of political organization used to reduce prices. We employ the model to data from Israel during the 1980s; during that period, quotas were set at a village-specific level and prices were set at a region-specific level, thereby generating the variability required to estimate the model’s parameters. We obtain empirical support for the reinforcement hypothesis and evidence of strong political influence, but also evidence of considerable free-riding regarding price reduction. Simulations of political equilibria under the quotas-only, price-only and hybrid regimes indicate a domination of the latter in terms of social welfare.

The turbulent static pressure spectrum Epp(kx) as a function of longitudinal wavenumber kx in the roughness sublayer of forested canopies is of interest to a plethora of problems such as pressure pumping from snow or forest floor. Long term static pressure measurements above a sub-arctic forested canopy during the winter and spring were collected and analyzed for three snow cover conditions: trees and ground covered with snow, trees are snow free but the ground is covered with snow, and snow free cover. In all three cases, it is shown that Epp(kx) obeys the attached eddy hypothesis at low wavenumbers (1/δ

A document by Tolulope O. Odunola. Click on the document to view its contents.