Frost weathering is a major control of rockwall erosion in alpine environments. Previous frost cracking model approaches used air temperatures as a proxy for rock temperatures to drive frost weathering simulations on rockwall and on mountain scale. Unfortunately, the thermal rockwall regime differs from air temperature due to topographic effects on insolation and insulation, which affects frost weathering model results and the resulting erosion patterns. To provide a more realistic model of the rockwall regime, we installed six temperature loggers along an altitudinal gradient in the Swiss Alps including two logger pairs at rockwalls with opposing aspects. We used the recorded rock surface temperatures to model rock temperatures in the upper 10 m of the rockwalls and as input data to run four different frost cracking models. We mapped fracture spacing and rock strength to validate the model results. Our results showed that frost cracking models are sensitive to thermal, hydraulic and mechanical parameters that affect frost cracking magnitude, while frost cracking patterns in terms of peak location and affected rock mass were consistent. Thermo-mechanical models incorporate rock strength and hydraulic properties and provided a frost cracking depth pattern at rockwall scale that reflects better measured rock strength and fracture spacing of the simulated rock masses. On mountain scale, these models showed a pattern of increasing frost cracking with altitude, which is contrary to purely thermal models but consistent with observations of existing rockfall studies.

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.

We present indirect measurements of size-resolved ultrafine particle composition conducted during the Ocean–Atmosphere–Sea Ice–Snowpack (OASIS) Campaign in Utqiagvik, Alaska, during March 2009. This study focuses on measurements of size-resolved particle hygroscopicity and volatility measured over two periods of the campaign. During a period that represents background conditions in this location, particle hygroscopic growth factors (HGF) at 90% relative humidity ranged from 1.45-1.51, which combined with volatility measurements suggest a mixture of ~30% ammoniated sulfates and ~70% oxidized organics. Two separate regional ultrafine particle growth events were also observed during this campaign. Event 1 coincided with elevated levels of H2SO4 and solar radiation. These particles were highly hygroscopic (HGF=2.1 for 35 nm particles), but were almost fully volatilized at 160 °C. The air masses associated with both events originated over the Arctic Ocean. Event 1 was influenced by the upper marine boundary layer, while Event 2 spent more time closer to the surface and over open ocean leads, suggesting marine influence in growth processes. Event 2 particles were slightly less hygroscopic (HGF=1.94 for 35nm and 1.67 for 15nm particles), and similarly volatile. We hypothesize that particles formed during both events contained 60-70% hygroscopic salts by volume, with the balance for Event 1 being sulfates and oxidized organics for Event 2. These observations suggest that primary sea spray may be an important initiator of ultrafine particle formation events in the Arctic late-winter, but a variety of processes may be responsible for condensational growth.

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.

Icefalls are steep ice flow features that form over steps in bedrock elevation. With their high driving stresses, icefalls have long been assumed to have a constant ice flowspeed. This assumption has not been thoroughly tested as methods using satellite feature tracking rapidly loose coherence and long-term GPS installations on the ground are unlikely to be retrievable. In this study, we test the hypothesis that the Vaughan Lewis Icefall in Southeast Alaska experiences daily velocity variations with daily variations in subglacial hydrology. Using high resolution tiltmeters, we observe change in ice surface tilt across eight days at two sites near the glacier centerline. We find daily variation in ice surface tilt, suggesting there are variations in daily ice flowspeed velocity. A weak and lagged correlation with air temperature suggests that velocity variations may be due to daily variations in subglacial hydrology. Future modeling efforts focused on describing ice flow over icefalls should consider adding daily or seasonal velocity variations. These results additionally have implications for theoretical models of ogive formation, which could result from seasonal flow speed variations across icefalls.

An obvious interdecadal change is measured in the super cyclones (SCs, categories 4 and 5) that occur from Oct-Nov over the Bay of Bengal (BoB). This change may be modulated by the interdecadal Pacific oscillation (IPO). A La Niña-like difference between the 1977–1998 (IP1) and 1999–2014 (IP2) periods forces a local Hadley circulation in the eastern tropical Indian Ocean by strengthening the Walker circulation, causing a plummeting upper-level temperatures and ultimately creating favorable thermodynamic conditions to enhance the cyclone intensity. Meanwhile, an equatorial downwelling Kelvin wave caused by heating and westerly wind differences enters the BoB rim along the coast and aptly intensifies the cyclone such that the downwelling Kevin wave and Rossby wave generated by its reflection deepen the thermocline in the BoB. The favorable atmospheric and oceanic conditions in IP2 jointly and preferentially form far more SC activities from Oct-Nov over the BoB compared to IP1.

This study presents a novel enhancement for Lagrangian particle transport modeling by integrating Coherent Structures theory. Lagrangian transport modeling is frequently utilized to forecast the trajectories of floating particles in the ocean despite the unstable nature of geophysical velocity fields that inevitably result in large trajectory errors. Current particle tracking methodologies often rely on deploying numerous particles and incorporating diffusion mechanisms into models to estimate particle probabilities across different locations. However, this approach can result in significant disparities in the final particle locations, thereby posing challenges in scenarios such as search and rescue operations and oil spill containment. To address these limitations, this study leverages dynamical systems and Eulerian Coherent Structures to improve particle tracking accuracy and diminish uncertainty.

The close connection between the total lightning flash rate and storm updraft has been well recognized. In this study, we assessed the benefit of such a relationship in convective-scale data assimilation (DA) for model initialization. A lightning DA scheme to update model kinematic states was developed in the Weather Research and Forecasting Data Assimilation (WRFDA) three-dimensional variational (3DVar) system. This scheme combines total lightning observations with model-based prescribed vertical velocity profiles to retrieve kinematic information useful to DA. With the availability of space-borne lightning imagers in recent years, total lightning data observations from the Lightning Mapping Imager (LMI) on board the FY-4A geostationary satellite were assimilated in combination with radar DA. A detailed analysis of the impact of the lightning DA scheme on convective precipitation forecasting was conducted using a squall line case over Beijing on 13 July 2017. The results showed that the assimilation of LMI data further improves the analyses of dynamical conditions from assimilating radar radial winds. Although the microphysical states are identical due to the assimilation of reflectivity, updrafts directly form at lightning observation locations via lightning DA and hence improve the convective-scale dynamical balance. The quantitative verification of short-term convective forecasts indicated that the lightning DA adds value to current radar DA by improving the precipitation forecast skill. The new lightning DA scheme was further applied to a heavy rainfall case in 2018, and the results confirmed the effective and robust improvement in storm forecasting.

Active faulting and Deep-seated Gravitational Slope Deformation (DGSD) constitute common geological hazards in mountain belts worldwide. In the Italian central Apennines, km-thick carbonate sedimentary sequences are cut by major active normal faults which shape the landscape generating intermontane basins. Geomorphological observations suggest that the DGSDs are commonly located in the fault footwalls. We selected five mountain slopes affected by DGSD and exposing the footwall of active seismic normal faults exhumed from 2 to 0.5 km depth. We combined field structural analysis of the slopes with microstructural investigation of the slipping zones from the slip surfaces of both DGSDs and major faults. The collected data show that DGSDs exploit pre-existing surfaces formed both at depth and near the ground surface by tectonic faulting and, locally, by gravitational collapse. At the microscale, the widespread compaction of micro-grains (e.g., clasts indentation) forming the cataclastic matrix of both normal faults and DGSDs is consistent with clast fragmentation, fluid-infiltration and congruent pressure-solution mechanisms active at low ambient temperatures and lithostatic pressures. These processes are more developed in the slipping zones of normal faults because of the larger displacement accommodated. We conclude that in carbonate rocks of the central Apennines, DGSDs commonly exploit pre-existing tectonic faults/fractures and, in addition, localize slip along newly formed fractures that accommodate deformation mechanisms similar to those associated to tectonic faulting. Furthermore, the exposure of sharp slip surfaces along mountain slopes in the central Apennines can result from both surface seismic rupturing and DGSD or by a combination of them.

We present a statistical investigation of the seasonal effect on hemispheric asymmetry in the auroral currents during low (Kp $<$ 2) and high (Kp $\geq$ 2) geomagnetic activity. Five years of magnetic data from the Swarm satellites has been analysed by applying the spherical elementary current system (SECS) method. Bootstrap resampling has been used to remove the seasonal differences between the hemispheres in the dataset. In general, the currents are larger in the Northern Hemisphere (NH) than in the Southern Hemisphere (SH). Asymmetry is larger during low than high Kp, and during winter and autumn than summer and spring. The NH/SH ratio for FACs in winter, autumn, spring and summer are 1.17 $\pm$ 0.05, 1.14 $\pm$ 0.05, 1.07 $\pm$ 0.04 and 1.02 $\pm$ 0.04, respectively. The largest asymmetry is observed during low Kp winter, when the excess in the NH currents is 21$\pm$5\% in FAC, 14 $\pm$ 3\% in curl-free (CF), and 10$\pm$3\% in divergence-free (DF) current. We also find that evening sector (13-24 MLT) contributes more to the high NH/SH ratio than the morning (01-12 MLT) sector. The physical mechanisms producing the hemispheric asymmetry are not presently understood. We calculated the background ionospheric conductances during low Kp conditions from the IRI, NRLMSISE and CHAOS models. The results indicate that only a small part of the hemispheric asymmetry can be explained by variations in the solar induced conductances.

Solar-wind forecasting is critical for predicting events which can affect Earth's technological systems.  Typically, forecasts combine coronal model outputs with heliospheric models to predict near-Earth conditions. Ensemble forecasting generates sets of outputs to create probabilistic forecasts which quantify forecast uncertainty, vital for reliable/actionable forecasts. We adapt meteorological methods to create a calibrated solar-wind ensemble and probabilistic forecast for ambient solar wind, a prerequisite for accurate coronal mass ejection (CME) forecasting. Calibration is achieved by adjusting ensemble inputs/outputs to align the ensemble spread with observed event frequencies. We produce hindcasts in near-Earth space using coronal-model output over Solar Cycle 24, as input to Heliospheric Upwind eXtrapolation with time dependence (HUXt) solar-wind model. Making spatial perturbations to the coronal model output at 0.1~AU, we produce ensembles of inner-boundary conditions for HUXt, evaluating how forecast accuracy was impacted by the scales of perturbations applied. We found optimal spatial perturbations described by Gaussian distributions with variances of 20 degrees latitude and 10 degrees longitude; these might represent spatial uncertainty within the coronal model. This produced probabilistic forecasts better matching observed frequencies.  Calibration improved forecast reliability, reducing the Brier score by 9% and forecast decisiveness increasing AUC ROC score by 2.5%. Improvements were subtle but systematic. Additionally, we explored statistical post-processing to correct over-confidence bias, improving forecast actionability. However, this method, applied post-run, does not affect the solar-wind state used to propagate CMEs. This work represents the first formal calibration of solar-wind ensembles, laying groundwork for comprehensive forecasting systems like a calibrated multi-model ensemble.

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.

Lithospheric flexure at subduction zones is a major contributor to induce outer rise earthquakes. Here, we modeled the bending deformation of the subducting plate at the southern Mariana using a 3-D plate flexural model. Intraplate stresses were investigated, with the along-strike variable boundary loadings. In order to match the observations of plate geometry, boundary vertical loading near the Challenger Deep has to be set twice of that in other areas. We also compared results between 2-D and 3-D models and found that the difference on estimating plate stress can exceed 20% when there is an along-strike variation in plate bending. Finally, we found that the sharp lateral variation in the σ and the σ corresponded to an outer rise earthquake cluster at the southern Mariana subduction zone, indicating that along-strike variation in σ and σ may be a significant mechanism to cause non-uniform distribution of outer rise earthquakes.

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

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.

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

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.

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.