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.

Old descriptive diaries are important sources of daily weather conditions before modern instrumental measurements became available. A previous study demonstrated the potential of reconstructing historical weather at high temporal resolution by assimilating cloud cover converted from descriptive diaries. However, cloud cover often exhibits a non-Gaussian distribution, which violates a basic assumption of most data assimilation schemes. In this study, we applied a Gaussian transformation (GT) approach for cloud cover data assimilation and conducted observing system simulation experiments (OSSEs) using 15 randomly selected observation points over Japan. We performed experiments to assimilate cloud cover with large observational errors using the Global Spectral Model (GSM) and a local ensemble transform Kalman filter (LETKF). Without GT, temperature and zonal and meridional wind exhibited deterioration compared to the experiment assimilating no observations. By contrast, the 2-month root mean square error (RMSE) of zonal wind, meridional wind, temperature, and specific humidity at mid-troposphere were improved by 8.7%, 5.1%, 4.2%, and 1.4%, respectively, through GT. Among two-dimensional variables, the 2-month RMSE of total cloud cover, surface pressure, rainfall, and downward solar radiation were improved by 2.2%, 5.2%, 27.6%, and 4.3%, respectively. We further demonstrated that the effect of GT was more pronounced on clear days. Our results show the potential of GT in high-resolution historical weather reconstruction using old descriptive diaries.

In this letter, we present the results of a conjunction between the SAMPEX satellite and a THEMIS all-sky imager in Gillam, Canada—showing a high correlation between relativistic, >1 MeV, electron microbursts and a type of pulsating aurora called patchy aurora. The correlation was 0.8, and is not serendipitous. While the relationship between pulsating aurora and 10-100s keV microbursts has been previously predicted, here we show a strong association between keV and MeV electron dynamics—possibly spanning two orders of magnitude. Importantly, this result shows that the dynamics of relativistic radiation belt electrons are at times intimately tied to keV electron precipitation, and can not be studied in isolation.

The heat energy necessary to melt the recently reported 28 trillions tonnes of ices disappeared between 1994 and 2017 was estimated. This heat energy was compared to an estimate of anthropogenic heat energy released in the world during the same period. Both heat energies being of the same order of magnitude, it was concluded that anthropogenic heat energy was sufficient to have caused the melting of a large part of the disappeared ices. Ice melting was not the only source of anthropogenic heat absorption. It is shown that interphase equilibria between ice-liquid-vapour physical forms of water acted as thermal buffers. If more and more anthropogenic heat has to be absorbed in the future, interphase equilibria will move water from ices and liquid to vapour and clouds. In parallel, atmosphere and ocean turbulences that contribute in dispatching solar heat over the world should be enhanced because of the extra heat to manage. The role assigned to anthropogenic heat and water interphase equilibria will be confirmed if ices continue to disappear increasingly while global CO2 production decreases as expected in the future.

Space plasmas are composed of charged particles that play a key role in electromagnetic dynamics. However, to date, there has been no direct measurement of the distribution of such charges in space. In this study, three schemes for measuring charge densities in space are proposed. The first scheme is based on electric field measurements by multiple spacecraft. This method is applied to deduce the charge density distribution within Earth’s magnetopause boundary layer using Magnetospheric MultiScale constellation (MMS) 4-point measurements, and indicates the existence of a charge separation there. The second and third schemes proposed are both based on electric potential measurements from multiple electric probes. The second scheme, which requires 10 or more electric potential probes, can yield the net charge density to first-order accuracy, while the third scheme, which makes use of seven to eight specifically distributed probes, can give the net charge density with second-order accuracy. The feasibility, reliability, and accuracy of these three schemes are successfully verified for a charged-ball model. These charge density measurement schemes could potentially be applied in both space exploration and ground-based laboratory experiments.

The composition of impurities in ice controls the stability of liquid water and thus the distribution of potential aqueous habitats. We present a framework for modeling the brine volume fraction in impure water ice as a polynomial function of temperature and bulk ice salinity, inspired by models originally developed for sea ice. We applied this framework to examine the distribution of brine within the thermally conductive layer of Europa’s ice shell, considering binary (NaCl and MgSO4) and multi-ion “analog” (Cl-dominated and SO4-dominated) endmember impurity compositions. We found the vertical extent of brine in a conductive ice layer, expressed as a fraction of the total layer thickness, to be <12% for NaCl, <2% for MgSO4, and <18% for both the analog endmember impurity compositions, suggesting that the depth where brine is stable in an ice shell is more sensitive to composition when only two ionic species are present. For the same temperature and bulk ice salinity, the brine volume fraction is higher in a Cl-dominated ice shell than a SO4-dominated ice shell. Pressure, governed by the ice thickness, was found to have only a minor effect on the vertical extent of brine within an ice shell, relative to temperature and bulk salinity. The minimum stable bulk ice shell salinity formed through freezing of an ocean was found to be insensitive to composition and ultimately governed by the magnitude of the assumed percolation threshold.

Along the lateral margins of floating ice shelves in Greenland and Antarctica, ice flow past confining margins and pinning points is often accompanied by extensive rifting. Rifts in zones of marginal decoupling (“detachment zones’) typically propagate inward from the margins and result in many of Earth’s largest calving events. Velocity maps of detachment zones indicate that flow through these regions is spatially transitioning from confined to unconfined shelf flow. We employ the software package \textit{icepack} to demonstrate that longitudinally decreasing marginal resistance reproduces observed transitions in flow regime, and we show that these spatial transitions are accompanied by near-margin tension sufficient to explain full-thickness rifts. Thus, we suggest that zones of progressive decoupling are a primary control on ice shelf calving. The steadiness of detachment zone positions may be a good indicator of ice shelf vulnerability, with migratory or thinning detachment zones indicating shelves at risk of dynamic speedup and increased fracture.

Infrasound observations are increasingly used to constrain properties of volcanic eruptions. In order to better interpret infrasound observations, however, there is a need to better understand the relationship between eruption properties and sound generation. Here we perform two-dimensional computational aeroacoustic simulations where we solve the compressible Navier-Stokes equations for pure-air with a large-eddy simulation approximation. We simulate idealized impulsive volcanic eruptions where the exit velocity is specified and the eruption is pressure-balanced with the atmosphere. Our nonlinear simulation results are compared with the commonly-used analytical linear acoustics model of a compact monopole source radiating acoustic waves isotropically in a half space. The monopole source model matches the simulations for low exit velocities (<100 m/s or M ~ 0.3 where M is the Mach number); however, the two solutions diverge as the exit velocity increases with the simulations developing lower peak amplitude, more rapid onset, and anisotropic radiation with stronger infrasound signals recorded above the vent than on Earth’s surface. Our simulations show that interpreting ground-based infrasound observations with the monopole source model can result in an underestimation of the erupted volume for eruptions with sonic or supersonic exit velocities. We examine nonlinear effects and show that nonlinear effects during propagation are relatively minor for the parameters considered. Instead, the dominant nonlinear effect is advection by the complex flow structure that develops above the vent. This work demonstrates the need to consider anisotropic radiation patterns and jet dynamics when interpreting infrasound observations, particularly for eruptions with sonic or supersonic exit velocities.

Slow earthquakes are mainly distributed in the vicinity of seismogenic zones of megathrust earthquakes and relationships between both types of earthquakes are expected. We examined the activity of very low frequency earthquakes (VLFEs), classified as one type of slow earthquake, around Japan because they have the potential to clarify detailed spatiotemporal slip behaviors at the plate boundaries. The distribution of the shallow VLFE activity rate is heterogeneous along trench axes and exhibits an anticorrelation relationship with the spatial distribution of the interplate coupling ratio, whereas deep VLFEs are distributed only in weakly coupled areas and the spatial variation of the activity rate is small. Furthermore, VLFEs are mainly hosted by low seismic velocity anomalies. Thus, slow earthquakes can be triggered by decreased effective stress due to the high pore fluid pressure within regions with weak interplate coupling and their activity can be an indicator of interplate slip behavior.

Shear attenuation provides insights into the physical and chemical state of the upper mantle. Yet, observations of attenuation are infrequent in the oceans, despite recent proliferation of arrays of ocean-bottom seismometers (OBS). Studies of attenuation in marine environments must overcome unique challenges associated with strong oceanographic noise at the seafloor and data loss during OBS recovery in addition to untangling the competing influences of elastic focusing, local site amplification, and anelastic attenuation on surface-wave amplitudes. We apply Helmholtz tomography to OBS data to simultaneously resolve array-averaged Rayleigh wave attenuation and maps of site amplification at periods of 20–150 s. The approach explicitly accounts for elastic focusing and defocusing due to lateral velocity heterogeneity using wavefield curvature. We validate the approach using realistic wavefield simulations at the NoMelt Experiment and Juan de Fuca (JdF) plate, which represent endmember open-ocean and coastline-adjacent environments, respectively. Focusing corrections are successfully recovered at both OBS arrays, including at periods < 35 s at JdF where coastline effects result in strong multipathing. When applied to real data, our observations of Rayleigh wave attenuation at NoMelt and JdF revise previous estimates. At NoMelt, we observe a low attenuation lithospheric layer (Q_μ>1500) overlying a highly attenuating asthenospheric layer (Q_μ~50–70). At JdF, we find a broad peak in attenuation (Q_μ~50–60) centered at a depth of 100–130 km. We also report strong local site amplification at the JdF Ridge (>10% at 31 s period), which can be used to refine models of crust and shallow mantle structure.

Southern Hemisphere (SH) Stratospheric Sudden Warmings (SSWs) result in smaller Antarctic ozone holes and are linked to extreme midlatitude weather on subseasonal to seasonal timescales. Therefore, it is of interest how often such events occur and whether we should expect more events in the future. Here, we use a pair of novel multi-millennial simulations with a stratosphere-resolving coupled ocean-atmosphere climate model to show that the frequency of SSWs, such as observed 2002 and 2019, is about one in 22 years for 1990 conditions. In addition, we show that we should expect the frequency of SSWs - and that of more moderate vortex weakening events - to strongly decrease by the end of this century.

A comprehensive catalogue of historical earthquakes, with accurate epicentres and harmonised magnitudes is a crucial resource for seismic hazard mapping. Here we update and combine catalogues from several sources to compile a catalogue of earthquakes in and near Iceland, in the years 1900–2019. In particular the epicentres are based on local information, whereas the magnitudes are based on teleseismic observations, primarily from international on-line catalogues. The most reliable epicentre information comes from the catalogue of the Icelandic Meteorological Office, but this is complemented with information from several technical reports, scientific publications, and newspaper articles. The catalogue contains 1281 moment magnitude (MW) ≥ 4 events and the estimated completeness magnitude is MW 5.5 in the first years, going down to MW 4.5 for recent years. The largest magnitude is MW 7.0. Such merging of local data and teleseismic catalogues has not been done before for Icelandic earthquakes, and the result is an earthquake map with much more accurate locations than earlier maps. The catalogue also lists additional 5640 earthquakes on the Mid-Atlantic Ridge, north of 43°, with both epicentres and magnitudes determined teleseismically. When moment magnitudes are not available, proxy MW values are computed using chi-squared-regression, normally on the surface-wave magnitude, but exceptionally on the body-wave magnitude. Magnitudes MW ≥ 4.5 have associated uncertainty estimates. The actual combined seismic moment released in the Icelandic earthquakes is found to be consistent with the moment estimated using a simple plate motion model, indicating that the seismic activity of the catalogue period might be typical for any 120 year timespan. The catalogue is named ICEL-NMAR and it is available online on http://data.mendeley.com.

Due to EC’s easy recordability and the existence of a strong correlation between EC and discharge in certain catchments, EC is a potential predictor of discharge. This potential has yet to be widely addressed. In this paper, we investigate the feasibility of using EC as a proxy for long-term discharge monitoring in a small karst catchment where EC always shows a negative correlation with the spring’s discharge. Given their complex relationship, a special machine learning architecture, LSTM (Long Short Term Memory), was used to handle the mapping from EC to discharge. The results indicate, based on LSTM, that the spring’s discharge can be predicted well with EC, particularly in storms when the dilution dominates the EC dynamic; however, the prediction may have relatively large uncertainties in the small or middle recharge events. A small number of discharge observations are sufficient to obtain a robust LSTM for the long-term discharge prediction from EC, indicating the practicality of recording EC in ungauged catchments for indirect discharge monitoring. Our study also highlights that the random or fixed-interval discharge measurement strategy, which covers various climate conditions, is more informative for LSTM to give robust predictions. While our study is implemented in a karst catchment, the method is also suitable for non-karst catchments where there is a strong correlation between EC and discharge.

Basal properties beneath ice streams and glaciers are known to be a control for ice flow dynamics, hence knowledge of them is crucial for predicting sea level due to changes in glacial dynamics. Basal properties, processes and topography also drive the formation of subglacial landforms. Bed properties beneath Rutford Ice Stream (West Antarctica) have previously been described using seismic acoustic impedance measurements at a sparse spatial coverage. Here, we derive bed properties in a 15 x 17 km grid of surface radar data with coverage and sampling much higher than previous seismic studies. Bed reflection amplitudes in surface radar data were calibrated using sediment porosities (ranging from 0.4 – 0.5) derived from seismic acoustic impedance. We find the bed properties are spatially variable, consisting of low porosity material in some areas and soft sediment in other areas. Comparison of seismic and surface radar data imply the low porosity material to be a consolidated sediment or sedimentary rock. Mega-scale glacial lineations (MSGLs) are ubiquitous on the bed and consist of soft, high porosity, probably deforming sediment, consistent with previous interpretations of MSGLs. We find some MSGLs have high reflectivity on their crest, interpreted as water bodies overlying high porosity sediment, whereas the trough around and the upstream end of some landforms consist of low porosity material. Integrating these different observations, we place constraints on possible explanations for the occurrence of water on the crest of landforms.

The freshwater alga Spirogyra grevilleana was used in an experimental biofiltration system to reduce levels of Escherichia coli, nitrates, and phosphates. Water collected from a 2.32 ha lake in Atlanta, Georgia, USA was pumped at a constant rate ( m3 hr-1) through the algal filtration devices with low and high concentrations of S. grevilleana. Effluent water was tested over time for E. coli, nitrate, phosphate, dissolved oxygen, and pH levels. Both concentrations of S. grevilleana reduced E. coli by 100% and significantly reduced nitrate concentrations (30% ± 13%) and phosphate concentrations (23% ± 5%) while maintaining dissolved oxygen and pH at normal levels. Utilizing S. grevilleana in an algal filtration device could potentially provide a sustainable, flexible, and low-cost method of E. coli reduction in freshwater lakes worldwide. Initial results indicate that the use of S. grevilleana in conjunction with an algal filtration device is potentially capable of creating potable water.

Extreme precipitation events are intensifying due to a warming climate, which, in some cases, is leading to increases in flooding. Detection of flood extent is essential for flood disaster management and prevention. However, it is challenging to delineate inundated areas through most publicly available optical and short-wavelength radar data, as neither can “see” through dense forest canopies. The 2018 Hurricane Florence produced heavy rainfall and subsequent record-setting riverine flooding in North Carolina, USA. NASA/JPL collected daily high-resolution full-polarized L-band Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) data between September 18th and 23rd. Here, we use UAVSAR data to construct a flood inundation detection framework through a combination of polarimetric decomposition methods and a Random Forest classifier. Validation of the established models with compiled ground references shows that the incorporation of linear polarizations with polarimetric decomposition and terrain variables significantly enhances the accuracy of inundation classification, and the Kappa statistic increases to 91.4% from 64.3% with linear polarizations alone. We show that floods receded faster near the upper reaches of the Neuse, Cape Fear, and Lumbee Rivers. Meanwhile, along the flat terrain close to the lower reaches of the Cape Fear River, the flood wave traveled downstream during the observation period, resulting in the flood extent expanding 16.1% during the observation period. In addition to revealing flood inundation changes spatially, flood maps such as those produced here have great potential for assessing flood damages, supporting disaster relief, and assisting hydrodynamic modeling to achieve flood-resilience goals.