Sediment grain size links sediment production, weathering, and fining from fractured bedrock on hillslopes to river incision and landscape relief. Yet, models of sediment grain size delivery to rivers remain unconstrained due to a scarcity of field data. We analyzed how bedrock fracture spacing and hillslope weathering influence landscape-scale patterns in surface sediment grain size across gradients of erosion rate and hillslope bedrock exposure in the San Gabriel Mountains (SGM) and northern San Jacinto Mountains (NSJM) of California, USA. Using ground-based structure-from-motion photogrammetry models of 50 bedrock cliffs, we showed that fracture density is ~5× higher in the SGM than the NSJM. 274 point count surveys of surface sediment grain size measured in the field and from imagery show a drainage area control on sediment grain size, with systematic downslope coarsening on hillslopes and in headwater colluvial channels transitioning to downstream fining in fluvial channels. In contrast to prior work and predictions from a hillslope weathering model, grain size does not increase smoothly with increasing erosion rate. For soil-mantled landscapes, sediment grain size increases with increasing erosion rates; however, once bare bedrock emerges on hillslopes, sediment grain size in both the NSJM and SGM becomes insensitive to further increases in erosion rate and hillslope bedrock exposure, and instead reflects fracture spacing contrasts between the NSJM and SGM. We interpret this threshold behavior to emerge in steep landscapes due to efficient delivery of coarse sediment from bedrock hillslopes to channels and the relative immobility of coarse sediment in fluvial channels.

The 2020 Mw 6.8 Elazig earthquake was the largest along the Eastern Anatolian Fault (EAF) in over a century, providing valuable insights into its rupture behavior. We use satellite geodesy and seismology to detail the mainshock rupture, postseismic deformation and aftershocks. The mainshock propagated mostly westwards at 2 km/s from a nucleation point on an abrupt 10° fault bend. Only one end of the rupture corresponds to an established EAF segment boundary, and the earthquake may have propagated into the slip zone of the 1874 M 7.1 Golcuk Golu earthquake. It exhibits a pronounced (80%) shallow slip deficit, only a small proportion of which is recovered by early aseismic afterslip. The slow rupture velocity, shallow slip deficit and low afterslip are characteristic of earthquakes hosted by faults of low-to-intermediate structural maturity, indicating that faults continue to evolve in important ways even as they accrue cumulative off sets of tens of kilometers

Examination of the radiation budget at the surface of the Earth shows that there are three factors affecting the surface temperature; the amount of solar radiation absorbed by the atmosphere and by the surface respectively, and the amount of leakage of infrared radiation emitted from the surface directly into space. If there were no leakage, the upwelling infrared radiation from the Earth’s surface would be equal to the incoming solar radiation absorbed by the atmosphere plus twice the solar radiation absorbed by the surface. This results from the summation of a sequence of equal upward and downward re-emissions of infrared radiation absorbed by the atmosphere following the initial absorption of solar radiation. At current levels of solar absorption, this would result in total upwelling radiation of approximately 398.6 W/m2, or a maximum surface temperature of 16.4°C. Allowing for leakage of infrared radiation through the atmospheric window, the resulting emission from the Earth’s surface is reduced to around 396 W/m2, corresponding to the current average global surface temperature of around 15.9°C. Absorption of solar and infrared radiation by greenhouse gases is determined by the absorption bands for the respective gases and their concentrations. Absorption of incoming solar radiation is largely by water vapor and ozone, and an increase in absorption would reduce not increase the surface temperature. Moreover, it is probable that all emitted infrared radiation that can be absorbed by greenhouse gases, primarily water vapor, with a small contribution from carbon dioxide and ozone, is already fully absorbed, and the leakage of around 5.5 % corresponds to the part of the infrared red spectrum that is not absorbed by greenhouse gases. The carbon dioxide absorption bands, which represent a very small percentage of the infrared spectrum, are most likely fully saturated. In these circumstances, increased concentrations of greenhouse gases, and carbon dioxide in particular, will have no effect on the emitted radiation. The surface temperature is probably at the thermodynamic limit for the current luminosity of the sun. Satellite based measurements since 1979 suggest that any global warming over the past 150 years may be due to an increase in total solar irradiance, which we are still a decade or two from being able to confirm.

Quantifying energy dissipation due to wave breaking remains an essential but elusive goal for studying and modeling air-sea fluxes of heat, gas, and momentum. Previous observations have shown that lifetimes of bubble plumes and surface foam are directly related to the dissipated energy. Specifically, the foam decay time can be used to estimate the timescale of the subsurface bubble plume and the energy dissipated in the breaking process. A mitigating factor is that the foam decay time can be significantly affected by the surfactant concentration. Here we present an experimental investigation of a new technique that exploits the thermal signature of cooling foam to infer wave breaking dynamics. The experiments were conducted in a laboratory wave tank using artificial seawater with and without the addition of a surfactant. We show that the time from the start of the breaking process to the onset of cooling scales with the bubble plume decay time and the dissipated energy, and is not significantly affected by the presence of additional surfactants. We confirm observations from the field of the spatial variability of the temperature of foam generated by an individual breaking event, which has implications for inferring the spatial variability of bubble plume depth.

Previous studies of wind-blown sand have considered either fully erodible or non-erodible soils, but the transport over sparsely sand-covered soils is still poorly understood. The quantitative modeling of this transport is important for the parametrization of Aeolian processes under low sand availability. Here we show, by means of particle-based numerical simulations, that the Aeolian sand transport rate Q scales with the wind shear velocity u∗ as Q = a.[1 + b . (u∗/u∗t − 1)] .√(d/g) . ρf. (u∗² − u∗t²), where u∗t is the minimal threshold u∗ for sustained transport, d is particle size, g is gravity and ρf is air density, while u∗t and the empirical parameters a and b depend on the sand cover thickness. Our model explains the transition from the quadratic to cubic scaling of Q with u∗ as soil conditions change from fully erodible to rigid and provides constraints for modeling Aeolian transport under low sand availability.

The Brazilian Amazon provides important hydrological cycle functions, including precipitation regimes that bring water tothe people and environment and are critical to moisture recycling and transport, and represents an important variable forclimate models to simulate accurately. This paper evaluates the performance of 13 Coupled Model Intercomparison Projectphase 6 (CMIP6) models. This is done by discussing results from spatial pattern mapping, Taylor diagram analysis and Taylorskill score, annual climatology comparison, and Empirical Orthogonal Function (EOF) analysis. Precipitation analysis shows1) This region displays a more uniform spatial distribution of precipitation with higher rainfall in the north-northwest anddrier conditions in the south. Models tend to underestimate northern values or overestimate the central to northwest averages.2) Southern Amazon has a more defined dry season (June, July, and August) and wet season (December, January, andFebruary) and models are able to simulate this well. Northern Amazon dry season tends to occur in August, September, andOctober and the wet season occurs in March, April, and May, and models are not able to capture the climatology as well.Models tend to produce too much rainfall at the start of the wet season and tend to either over- or under-estimate the dryseason, although ensemble means typically display the overall pattern more precisely. 3) EOF analysis of models are able tocapture the dominant mode of variability, which was the annual cycle or SAMS. 4) When all evaluation metrics are taken intoaccount the models that perform best are CESM2, MIROC6, MRIESM20, SAM0UNICON, and the ensemble mean. Thispaper supports research in determining the most up to date CMIP6 model performance of precipitation regime for 1981-2014for the Brazilian Amazon. Results will aid in understanding future projections of precipitation for the selected subset ofglobal climate models and allow scientists to construct reliable model ensembles, as precipitation plays a role in many sectorsof the economy, including the ecosystem, agriculture, energy, and water security.

A growing number of studies are concluding that the resilience of the Arctic sea ice cover in a warming climate is essentially controlled by its thickness. Satellite radar and laser altimeters have allowed us to routinely monitor sea ice thickness across most of the Arctic Ocean for several decades. However, a key uncertainty remaining in the sea ice thickness retrieval is the error on the sea surface height (SSH) which is conventionally interpolated at ice floes from a limited number of lead observations along the altimeter’s orbital track. Here, we use an objective mapping approach to determine sea surface height from all proximal lead samples located on the orbital track and from adjacent tracks within a neighborhood of 10s of kilometers. The patterns of the SSH signal’s zonal, meridional, and temporal decorrelation length scales are obtained by analyzing the covariance of historic CryoSat-2 Arctic lead observations, which match the scales obtained from an equivalent analysis of high-resolution sea ice-ocean model fields. We use these length scales to determine an optimal SSH and error estimate for each sea ice floe location. By exploiting leads from adjacent tracks, we can increase the SSH precision estimated at orbital crossovers by a factor of three. In regions of high SSH uncertainty, biases in CryoSat-2 sea ice freeboard can be reduced by 25% with respect to coincident airborne validation data. The new method is not restricted to a particular sensor or mode, so it can be generalized to all present and historic polar altimetry missions.

A single week-long warm event in midwinter in Svalbard flooded an inefficient en- and subglacial drainage system and led to a 2.5x velocity increase that remained in effect for the remainder of the winter - more than 3 months. Because of the long winter season, changes in winter velocity have a large impact on the annual average velocity. As the climate warms and surface melt and rain events increase during winter months, sustained high winter glacier velocities are likely to occur more often. Increasing glacier velocity near the terminus leads to additional ice entering the fjord, and an increase of ice dynamics contribution to sea level rise during winter.

Tropical mountain glaciers are an important water resource and highly impacted by recent climate change. Tropical mountain glaciation also occurred in the recent and deep past, which presents opportunities for better validating paleoclimate simulations in continental interiors and mountainous regions but requires bridging global model scales (100s of km) with the ~ 1–10 km scale of glaciers when paleotopography is poorly known. Here we hindcast tropical mountain glaciation in pre-industrial time by using global climate model meteorology to force standalone simulations in its land component that use high resolution topography to resolve selected tropical mountain glaciers. These simulations underestimate observed equilibrium line altitudes (ELA) by 249 ± 330 m, but the simulated ELA and snow lines capture observed inter-mountain ELA variability. Error in large-scale model precipitation and ELA reconstruction uncertainty are the main contributors to this bias.

We investigate the solar events of late solar cycle 24 in July 2017 observed by a number of spacecraft in the inner heliosphere widely separated in heliolongitude and radial distance. These include spacecraft at L1 point, STEREO-A, near Earth satellites, and MAVEN (near Mars). The GRASP payload onboard Indian GSAT-19 satellite provides a new vantage point for Solar Energetic Particle (SEP) observations near Earth. There were two major Coronal Mass Ejections (CMEs) and a Stream Interaction Region (SIR) event in July 2017, which is a period during the deep descending phase of the historically weak solar cycle 24. The 16 July CME was Earth directed and the 24 July CME was STEREO-A and Mars directed. Earth and Mars were on the opposite sides of the solar disk, while Mars and STEREO-A were aligned with respect to the nominal Parker spiral field. The 24 July event was stronger and wider in heliolongitude. This CME-driven shock had magnetic connectivity to Earth, which produced an SEP event at Earth ~two days later. The spectral indices of the event observed directly at STEREO-A and at the remote location of ACE was found to be similar. The 16 July SIR event was observed by both MAVEN and STEREO-A. Higher particle intensities (a factor of 6 enhancement for 1 MeV protons) are observed by MAVEN (at 1.58 AU) compared to STEREO-A (at 0.96 AU). Also a spectral hardening is observed while comparing the spectral indices at these two locations, indicating proton acceleration at the SIR forward shock during the radial propagation of 0.62 AU in the interplanetary space.

There are a large number of tectonic shortening structures distributed across the planet Mercury, which are interpreted as the product of lithospheric deformation mainly attribute to secular cooling of the planetary interior. As the largest single volcanic deposit on Mercury, the northern smooth plains (NSP) is dominated by thrust fault-related landforms, showing particularity in their geomorphic features and requires an assumed weak layer at a shallow depth to account for the thin-rooted deformation in the lithosphere. However, there is a lack of proper mechanical model to account for such layer in the lithosphere beneath the NSP. In this work, we propose a new mechanical model allowing for a mechanically discontinuous lithosphere by introducing the semi-brittle deformation style, with detailed model configurations. Our work simulates a compressive dynamic process to mimic the formation for thrust fault-related landforms in the NSP of 3.8 billion years ago through 2-D numerical simulations. This simulation lasts for 70 million years, resulting in a concentrated and high strain rate region (i.e., weak layer) at shallow depth in the crust and geomorphically consistent surface topography with commonly observed thrust fault-related landforms. Geomorphically steady surface relief suggests that these shortening landforms were formed in a short period of time on geological time scales, and have maintained their basic geomorphic features to present day. The potential influence of the topography at the crust-mantle boundary on the surface relief is also recognized. Additional set of numerical simulations emphasizes that a larger topography facilitates the formation for higher surface relief.

We use the Space Weather Modeling Framework (SWMF) Geospace configuration to simulate a total of 122 storms from the period 2010-2019. With the focus on the storm main phase, each storm period was run for 54 hours starting from 6 hours prior to the start of the Dst depression. The simulation output of ground magnetic variations were compared with ground magnetometer station data provided by SuperMAG to statistically assess the Geospace model regional magnetic perturbation prediction performance. Our results show that the regional predictions at mid-latitudes are quite accurate, but the high-latitude regional disturbances are still difficult to predict.

Increased interest in combining compound flood hazards and social vulnerability has driven recent advances in flood impact mapping. However, current methods to estimate event specific compound flooding at the household level require high performance computing resources frequently not available to local stakeholders. Government and non-government agencies currently lack methods to repeatedly and rapidly create flood impact maps that incorporate local variability of both hazards and social vulnerability. We address this gap by developing a methodology to estimate a flood impact index at the household level in near-real time, utilizing high resolution elevation data to approximate event specific inundation from both pluvial and fluvial sources in conjunction with a social vulnerability index. Our analysis uses the 2015 Memorial Day flood in Austin, Texas as a case study and proof of concept for our methodology. We show that 37% of the Census Block Groups in the study area experience flooding from only pluvial sources and are not identified in local or national flood hazard maps as being at risk. Furthermore, averaging hazard estimates to cartographic boundaries masks household variability, with 60% of the Census Block Groups in the study area having a coefficient of variation around the mean flood depth exceeding 50%. Comparing our pluvial flooding estimates to a 2D physics-based model, we classify household impact accurately for 92% of households. Our methodology can be used as a tool to create household compound flood impact maps to provide computationally efficient information to local stakeholders.

The subduction zone along the northern Tonga Trench has the highest plate convergence rate in the world, but limited records of its seismic and tsunamigenic activities. In 2009, a tsunami generated by an MW 8.1 earthquake doublet caused severe impacts in the region including damage and loss of life on the south shores of Upolu and Savaii Islands, Samoa. Here we use numerical modeling aided by recorded data and eyewitness accounts to evaluate which of the published source models in the Tonga Trench region most suitably represents the 2009 event for use in hazard assessment around Samoa. We show that only a few of the published sources are suitable to reproduce large inundation observed in Samoa and none reproduces runup as high as observed in areas that were most severely impacted on the southeast Upolu coast. The distribution and intensity of inundation is dependent on local topographic and bathymetric features, configuration of coastal geomorphology, and trapping of short-period waves over the reef flats. For one of the sources, comparison of the relative contributions of the normal and thrust faulting components of the doublet to the southeast Upolu inundation indicates that the initial intraplate normal faulting dominated the east-northeastward tsunami propagation and inundation compared with the subsequent interplate thrust faulting. Overall, two key source models are discussed and identified for future refinement.

The recently developed Micromagnetic Tomography (MMT) technique combines advances in high resolution scanning magnetometry and micro X-ray computed tomography. This allows precise recovery of magnetic moments of individual magnetic grains in a sample using a least-squares inversion approach. Here we investigate five factors, which are governing the mathematical validity of MMT solutions: grain concentration, thickness of the sample, size of the sample’s surface, noise level in the magnetic scan, and sampling interval of the magnetic scan. To compute the influence of these parameters, we set up series of numerical models in which we assign dipole magnetizations to randomly placed grains. Then we assess how well their magnetizations are resolved as function of these parameters. We expanded the MMT inversion to also produce the covariance and standard deviations of the solutions, and use these to define a statistical uncertainty ratio and signal strength ratio for each solution. We show that the magnetic moments of a majority of grains under the inspected conditions are solved with very small uncertainties. However, increasing the grain density and sample thickness carry major challenges for the MMT inversions, demonstrated by uncertainties larger than 100% for some grains. Fortunately, we can use the signal strength ratio to extract grains with the most accurate solutions, even from these challenging models. Hereby we have developed a quick and objective routine to individually select the most reliable grains from MMT results. This will ultimately enable determining paleodirections and paleointensities from large subsets of grains in a sample using MMT.

In steep wildfire-burned terrains, intense rainfall can produce large volumes of runoff that can trigger highly destructive debris flows. The ability to accurately characterize and forecast debris-flow hazards in burned terrains, however, remains limited. Here, we augment the Weather Research and Forecasting Hydrological modeling system (WRF-Hydro) to simulate both overland and channelized flows and assess postfire debris-flow hazards over a regional domain. We perform hindcast simulations using high-resolution weather radar-derived precipitation and reanalysis data to drive non-burned baseline and burn scar sensitivity experiments. Our simulations focus on January 2021 when an atmospheric river triggered numerous debris flows within a wildfire burn scar in Big Sur – one of which destroyed California’s famous Highway 1. Compared to the baseline, our burn scar simulation yields dramatic increases in total and peak discharge, and shorter lags between rainfall onset and peak discharge. At Rat Creek, where Highway 1 was destroyed, discharge volume increases eight-fold and peak discharge triples relative to the baseline. For all catchments within the burn scar, we find that the median catchment-area normalized discharge volume increases nine-fold after incorporating burn scar characteristics, while the 95th percentile volume increases 13-fold. Catchments with anomalously high hazard levels correspond well with post-event debris flow observations. Our results demonstrate that WRF-Hydro provides a compelling new physics-based tool to investigate and potentially forecast postfire hydrologic hazards at regional scales.

Very-long-period (VLP) volcano seismicity often represents subsurface magma movement, and thus provides insight into magma system geometry and magma properties. We develop a fully automated signal processing workflow using wavelet transforms to detect and assess period, decay rate, and ground motions of resonant VLP signals. We then generate and analyze a catalog of VLP seismicity over the 2008-2018 open-vent summit eruptive episode at Kilauea Volcano, Hawaii USA. VLP seismicity occurred throughout this eruption that involved a persistent lava-lake, multiple intrusions and rift zone eruptions, and a climactic caldera collapse. We characterize trends in two dominant magma resonances: the fundamental eigenmode of the shallow magma system is a vertical oscillation of the magma column in the conduit and lava-lake, and higher frequency eigenmodes largely consist of lateral lava-lake sloshing. VLP seismicity was mainly triggered by lava-lake surface perturbations, and less commonly from depth. Variation in periods and quality factors occurred on timescales from hours to years. VLP seismicity exhibited varying correlations over time with other datasets such as ground tilt, SO2 emissions, and lava-lake elevation. Variation in VLP properties also occurred over days to months preceding and following intrusions and rift zone eruptions. Changes in VLP ground motions over various timescales indicate evolution of shallow magma system geometry, which contributed to the variation in resonance. However much of the variation on timescales less than months is likely from changing magma density and viscosity, reflecting a variable shallow magmatic outgassing and convective regime within the open conduit over the ten year eruption.

A negative shortwave cloud feedback associated with higher extratropical liquid water content in mixed-phase clouds is a common feature of global warming simulations, and multiple mechanisms have been hypothesized. A set of process-level experiments performed with an idealized global climate model (a dynamical core with passive water and cloud tracers and full Rotstayn-Klein single-moment microphysics) show that the common picture of the liquid water path (LWP) feedback in mixed-phase clouds being controlled by the amount of ice susceptible to phase change is not robust. Dynamic condensate processes—rather than static phase partitioning—directly change with warming, with varied impacts on liquid and ice amounts. Here, three principal mechanisms are responsible for the LWP response, namely higher adiabatic cloud water content, weaker liquid-to-ice conversion through the Bergeron-Findeisen process, and faster melting of ice and snow to rain. Only melting is accompanied by a substantial loss of ice, while the adiabatic cloud water content increase gives rise to a net increase in ice water path (IWP) such that total cloud water also increases without an accompanying decrease in precipitation efficiency. Perturbed parameter experiments with a wide range of climatological LWP and IWP demonstrate a strong dependence of the LWP feedback on the climatological LWP and independence from the climatological IWP and supercooled liquid fraction. This idealized setup allows for a clean isolation of mechanisms and paints a more nuanced picture of the extratropical mixed-phase cloud water feedback than simple phase change.