The Lithium Nevada Corp. Thacker Pass Project has a measured resource of 242M tonnes at 0.29% Li (~0.7M tonnes Li). The deposit is the southernmost of five known lenses hosted within intracaldera tuffaceous sediments along the west side of the McDermitt caldera, which formed by eruption of 16.4 Ma peralkaline-metaluminous tuff. Analyses of 9880 core samples (~1.5-m thick) give a mean of ~ 2500 ppm Li, with some >8800 ppm. Entire sedimentary sections in the southern and western parts of the caldera basin have high Li (1500+ ppm). Pre-caldera rocks, the McDermitt Tuff, late caldera volcanics, and unaltered tuffaceous sediments have relatively low Li (5 -140 ppm). Sediment deposition was mainly subaqueous in the closed caldera basin. Li-rich fill may have been deposited from airborne sources. Claystone comprises most of the Thacker Pass deposit and dominates Li-rich intervals. The rest is mostly feldspar-rich ash. X-ray diffraction (XRD) data from six core holes across the deposit show consistent lateral mineral zoning. A Li-rich zone (mean >4,000 ppm) mainly contains illitic clay and underlies a zone of lower Li with smectite + analcime. Based on XRD peak locations and chemistry, the closest analogs to the illitic clay are Li micas (e.g. tainiolite). Montmorillonitic clay and a basal silicified zone underlie the illitic zone. Some transitional rock of mixed-layer clay between the illite and smectite zones also has high Li. All clay has similar optical properties but SEM images show illite forms tiny hexagonal plates and smectite has no resolvable crystallinity. Calcite, albite, K-feldspar, and quartz occur in all zones, dolomite and fluorite near the top of the illite zone, and pyrite and bitumen in unoxidized rock. The Li-rich zone has relatively high K, Rb, Mo, As, and Sb. Secondary Kspar in the Li-rich zone gave an 40Ar/39Ar age of 14.87±0.05 Ma. No origin fully explains known characteristics. The presence of illite suggests a moderate temperature hydrothermal system. Release of Li from tuffaceous sediments and transport by alkaline groundwater are consistent with most mineralogy (characteristic of closed hydrologic system diagenesis) and with the Kspar date that long postdates caldera magmatism. Release of 10 ppm Li from the likely 50-200 km3 of intracaldera sediments would contribute ~1-4M tonnes Li.

Air composition of the Lewis-Clark Valley (LCV) was studied over a two-year period to investigate the effects of a local pulp paper mill on ambient air and to assess potential health risk to the community. Lewiston, Idaho and Clarkston, Washington are twin cities in the Snake River Valley bordering North-Central Idaho and Southeastern Washington, with a population of over 50,000 including the surrounding areas. The paper mill is located in North Lewiston and releases malodorous sulfur air pollutants in the LCV. The neighboring Nez Perce Tribe has conducted a couple of air studies, in 2006-2007 and the summer of 2016-17, but to date no longer term study has taken place. Our current study utilized active air sampling via sorbent tubes followed by thermal desorption gas chromatography-mass spectrometry (TD-GC-MS) analysis to measure over 50 volatile organic compounds, hazardous air pollutants, and sulfides in ambient air (adapted from EPA Method TO-17). Seasonal, diurnal, and spatial variations in air composition were explored. In addition, monthly averaged passive air samples were collected for comparison at nearby urban areas – Boise, ID, Coeur d’Alene, ID, and Spokane, WA in 2018. In the LCV, dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) were the primary sulfur compounds detected, with concentrations highest adjacent to the paper mill. However, concentrations varied considerably depending on time of day, season, location and meteorology. Seasonal observations include DMS, benzene and chloroform peaking in the summer months, while DMDS peaks in the winter. Diurnal trends show DMS and chloroform with higher values during the morning hours than later in the day. The long-term monthly samples show benzene decreasing from winter to spring, with LCV levels comparable to Coeur d’Alene and Spokane, and Boise slightly higher. In most cases, benzene levels exceed those recommended for ambient air in the state of Idaho. Sources and potential health implications will be discussed.

Immersion freezing is an important heterogeneous ice nucleation process in mixed-phase clouds. Many researches on immersion freezing focus on the parameterization using the classical nucleation theory. However, the ice nucleating abilities of the atmospheric aerosol particles are not well understood, and therefore cause difficulties of the parameterization of immersion freezing. In this study, we investigate the ice nucleating ability of Marigold pollen from the Beijing area by doing drop immersion freezing experiments in the laboratory. Marigold pollen are first mixed with pure water. A population of drops with a volume of 10 mL from the mixture are then put on a PE film in a chamber with a cooling rate of about 0.5 °C min-1. We find that the median freezing temperature of drops with pollen as ice nuclei is -17 °C. The contact angle parameterization of immersion freezing using the classical nucleation theory is also given in this study. We use the single-θ and the θ-pdf parameterization schemes to explain the data. The results show that the θ-pdf parameterization scheme is better for describing the ice nucleating behavior of the pollen in Beijing.

As a national strategic resource, trade activities of potassium resources（K） have changed its state of ownership. Futures and spot trading forms in the international market are mainly primary processed ore and deep-processed products. So, K trade can be replaced by the potassium salt trade. Its international trade will affect a country’s strategic resource management, and increase national resource security risks. Thence, it is necessary to study the evolution of international trade in K. This paper has constructed a weighted and directed complex network model of K trade using UN Comtrade 2000-2016 data and analyzed the scale and activity of international trade of K, trade relations, trade flow distribution and the importance of countries. By analyzing the international trade data of K in 224 countries, it is found that trade is active year by year and K is becoming more significant. From network density and diameter, resource allocation is more convenient. The network cluster is growing. It shows that some countries form trade groups. The correlation coefficient of degrees is less than 0, indicating that the trade relationship between small and major trade countries is enhancing. And, the reciprocal coefficient is between 0.1 and 0.35, showing that the trade order is poor. Moreover, it presents a state that the greater the country’s degree, the smaller the difference in trade flow distribution. So, resource flows in countries with more trade relations can promote a balanced distribution of K. Finally, from countries’ trade influence and hub status, Canada is a leading trade country, and the US, the Russian Federation, China and Brazil are trade-led countries. They are the main source of K flows. China, the Netherlands, the US, France and India are important hubs. So, countries should strengthen bilateral trade relations. So as to ensure the SD of international trade in K, major trading countries should focus on the exploit of K and improve the level of production and processing tech. Countries should also enhance their hub role to facilitate the flow of K. China, as a large country in agriculture and K demand, should increase self-sufficiency to reduce import dependence risks. Besides, attention should be paid to market changes in major trading countries and to reducing risks by adding the number of trade countries.

There have been numerous calls to promote reproducible research. This growing awareness coincides with major advances in data/code sharing technologies. Yet authors, journals, institutions, and funders still need to act to advance more reproducible research. Here, we suggest to view reproducibility as a continuum that includes the 1) availability of data, models, code, and directions to use the digital artifacts, 2) replication of results, and 3) reproducibility of findings. We present a simple survey tool to assess where a peer-reviewed journal article lies on the continuum. We use the tool to assess 360 random sampled articles of the 1,989 articles published in 2017 in six well-regarded hydrology and water resources journals. 49% of sampled articles had some materials available online, but just 5.6% made available all the data, models, code, and directions. For 1.6% of articles, we generated results that replicated some or all of the published results. Assessments took 5 to 14 minutes per article to determine the availability of digital artifacts and 25 to 86 minutes to replicate results (25-75% range). The availability of data, models, code, and directions differed by journal and journal policy towards data availability. From the 360 article sample, we estimate that 0.6% to 6.8% of all articles published in the six journals in 2017 can be replicated using their published artifacts (95% confidence interval). These results suggest several practices to improve the reproducibility of published research. First, authors should provide directions to use their data, models, and code in addition to the digital artifacts. Second, on author submission, journals should use a tool like ours to assess the submission’s position on the reproducibility continuum. Third, journals should formulate policies that require authors to state the intended reproducibility of their work and place relevant information in an easy-to-find article location. Fourth, journals, institutions, and funders should highlight work whose digital artifacts, results, and findings are available, replicable, and reproducible.

The past 2 decades of research has demonstrated the value of co-production as a process that creates information that is usable to decision makers. However, research has also shown that those organizations that are already larger, more technically-capable, and located closer to the sources of new information are more likely to engage in co-production with boundary organizations. The question then arises of how smaller entities, who may actually have greater need for capacity, can benefit from investments in new science aimed at improving decision making for water management. In this project we conducted 5 case studies of the information use preferences and practices among small-scale water systems (small municipalities and Water Conservancy Districts) in the Upper Colorado River Basin to understand the opportunities and constraints for the uptake of new sources of information. Like previous work, results indicated that scale, skill, understandability, and lack of capacity limited the use of available information. Furthermore, entities did not engage in co-production with knowledge-related boundary organizations to any extent. However, small water providers did consistently mention the value of contact with other water systems in the area, and the value of being able to reach out to certain key individuals who were looked to as trusted sources of opinion on current information products and trends. Managers emphasized the importance of experience in operating a water system and involvement in operations as critical factors that engendered trust in these key individuals. Finally, certain water systems were seen as leaders in the local area, and constantly mentioned as sources of information and innovative ideas. These findings suggest the importance of both key individual practitioners in pioneering and disseminating new information, as well as more broadly the role of a community of practice in reaching small water providers. Implications for boundary organizations and emerging networks are discussed.

Mixed phase clouds, consisting of ice particles and super cooled liquid droplets, predominantly found in Arctic, are poorly represented in various climate models. A unique tethered balloon campaign carrying 4π radiometer, a cloud particle imager, and a meteorological package on board was conducted in Ny-Ålesund, Norway, located high in the Arctic at 78.91°N, 11.91°E during May-June 2008. The radiometric and cloud observations at 500nm and 800nm were collected during a month long experimental campaign. A state-of-the-art discrete ordinate radiative transfer model was used to estimate optimal cloud optical properties. These optical properties are contrasted with those of the cloud parameterization in the new NOAA-GFDL AM4 model that is presently being used in the Coupled Model Intercomparison Project 6 (CMIP6). The improved simulation of cloud optical properties will aid in understanding cloud radiation feedbacks and better representation of clouds in global climate model.

Dense acquisition are more and more available in exploration and earthquake seismology. Tomographic approaches can now consider not only travel times but also the wavefront itself across the seismic network (Zhang and Thurber, 2003; Yuan et al., 2016). For dense controlled-source seismic experiments, double differences of travel times between receivers in a common-shot gather (resp between sources in a common-receiver gather) are estimated, namely the horizontal component of the slowness vector at source and receiver positions designed as slopes. These slopes associated with the two-way traveltimes are interpreted as a reflection/diffraction from a small reflector segment or diffractor are used in tomographic inversion (Lambaré, 2008; Tavakoli F. et al., 2017). Picking of locally-coherent events leads to dense volumetric dataset and hence higher-resolution tomographic results (Guillaume et al., 2008). The reflection setting introduces implicitly another class of unknowns which are scatterer positions. Resulting inverse problem is awkward due to the intrinsic coupling between velocities and scatterer positions. The first choice alternates positions and wavespeeds. The second performs the joint estimation of the two parameter classes. The third one relies on the projection of the scatterer positions subspace onto the wavespeed subspace leading to a reduced-space inversion. This reduced-space formulation can be implemented in the slope tomography using adjoint-state method. Two focusing equations, which depend on two observables among the three available ones (two-way traveltime and one slope in 2D), gives exact solutions of positions which are injected as constraints in the slope tomography (Chauris et al., 2002). These constraints explicitly enforce the positions in the velocity estimation problem, which reduces now to a mono-variate inverse problem by minimization of single-slope residuals, not yet used. 2D synthetic (see figure) and real data case studies show faster convergence toward more accurate minimizer achieved by this variable projection method compared to the alternated and joint strategies. This method, which can be extended to 3D configurations, draws also interesting perspective for the joint hypocenter-velocity inversion problem in earthquake seismology.

Since mid-2008, automated radio monitoring networks such as the Reverse Beacon Network (RBN) and the Weak Signal Propagation Reporting Network (WSPRNet) have been observing and logging global amateur radio high frequency (HF, 3-30 MHz) communications. These networks are built and operated by amateur radio operators for amateur radio purposes, but the data are also useful for the study of ionospheric space weather and ionospheric science. Ham Radio Science Citizen Investigation (HamSCI) members will present global observations of over 1.9 billion radio reports on the 1.8, 3.5, 7, 14, 21, and 28 MHz amateur radio bands. The observations span an 11-year period from 2009-2020. We find a correlation between HF propagation path characteristics and the solar EUV output through the F10.7 index, along with solar cycle effects, seasonal effects, and sporadic E signatures. We will also discuss impacts of operator behavior and sampling effects caused by the distribution of amateur radio transmitting and receiving stations.

Triton is one of the few satellites in the Solar System which shows an ongoing geological activity, with plumes and geysers whose origin is still controversial [1]. Its surface is relatively young, as shown by the paucity of craters detected on its surface [2]. Our knowledge of this moon comes from the Voyager 2 mission, which obtained several images, covering about 40% of Triton’s surface [3]. However, few studies were focused principally on surficial geomorphology, and those are mostly limited to the cantaloupe region and surrounding areas. Triton’s crust is composed predominantly by solid nitrogen (N2) but several other ices have been detected [3]. Crater counting has revealed that the surface is very young and likely it went through a resurfacing process in the past. In fact, a very small number of craters has been detected, and these usually exhibit a typical bowl-like shape [2]. Geological features on Triton include regions, called terrains, such as cantaloupe terrains or plains, which show different textures. Usually, plains are categorized within smooth, walled and terraced plains [3]. The latter are the flattest areas on Triton, a characteristic which has been explained by evoking a lava-like or other viscous liquid infill. Their central depressions also present a cluster of irregular pits, which have been interpreted as drainage pits or eruptive vents [3]. These peculiar morphologies seem to indicate the presence of a viscous fluid on the surface in a remote epoch, which may imply potential climatic and atmospheric changes during Triton’s geological history. In this work we analyse an area located at NW of Tuonela Planitia, which shows several depressions rimmed by sharp margins. Two of these depressions are named Kulilu Cavus and Mah Cavus [4]. Cavi are elliptical-shaped depressions, distributed in an ordered trend, which constitute the cantaloupe terrain [3]. Diapirism is the main candidate process to explain these collapsed depressions [3] but other hypotheses, such as cryovolcanism or impact cratering [5], have also been proposed. Methodology A new geological map has been realized. We used Voyager 2 imagery named c1139533 [6] (600 m/px), properly calibrated, filtered and georeferenced using the Integrated Software for Imagers and Spectrometers (ISIS4) [7]. We mapped the different geological units and main features according to differences in surface morphology (fig.1). We also produced a DEM of the study area, using the open-source suite of tools NASA Ames Stereo Pipeline (ASP) [8]. We applied the photoclinometry-based “shape-from-shading” (SfS) tool to produce the DEM. Since SfS needs an input DEM generated preferably with stereo images, and we do not have such data for Triton, we used the methodology proposed by Lesage et al. 2021[9]. We analysed four different cross sections to measure the relative height of Kulilu Cavus, Mah Cavus and two other depressions, as well as their associated terraces (fig.2). Discussion Geologic

Ice motion in land terminating regions of the Greenland Ice Sheet is controlled in part by meltwater input into moulins. Moulins, large near-vertical shafts that deliver supraglacial water to the bed, modulate local and regional basal water pressure and ice flow by influencing subglacial drainage efficiency on daily to seasonal timescales. Our previous modeling work found that the geometry of a moulin near the water line has substantial effect on subglacial water pressure variations. Here, we develop a new physically based moulin model which can help constrain moulin shape across the ice sheet and its influence on hydraulic head oscillation, and inform the englacial void parameter used in glacier hydrology modeling. The Moulin Shape (MouSh) model (in Matlab and Python) provides new insight into the evolution of subsurface moulin size and shape at hourly to multi-year timescales. The modeled moulin is initialized as a vertical cylinder. The moulin walls melt back above and below the water line due to the dissipation of turbulent energy, open or close due to viscous and elastic deformation, and freeze inward in winter when cold air temperatures and an absence of meltwater allow refreezing. We combine MouSh modeling results with geometric data from two moulins in Pâkitsoq, western Greenland, which we mapped to the water line. The moulins have heterogeneous shapes and volumes in the top 100 m. This suggests that the size and shape of the upper portion is controlled by local and regional pre-existing fractures, which provide preferential paths for water flow and melting, creating stochastic karst-like conduit shapes. Modeling results show that moulin geometry below the water line is influenced by the hydraulic head, which controls the depth-dependent elastic and viscous closure rates, and by the roughness of the walls, which enhances melt-out rates that oppose moulin closure. We show that subglacial water pressure across the ice sheet is likely influenced by moulin geometry, underscoring the need for including moulins in subglacial models.

The Eastern Himalayan region, along with its neighboring area is known to be the part of the ‘Alpine-Himalayan global seismic belt’, a seismically active area of the world. In the past (1897, 1905, 1934, and 1950) four great earthquakes have triggered in this region with a magnitude higher than Mw=8.0. The 2011 (Mw= 6.9) Sikkim and 2015 (Mw= 7.8) Gorkha Nepal earthquakes call attention to the need for a more accurate understanding of seismic characteristics in the Eastern Himalayan region. In the present study, analysis of spatial variation of seismic activity in the Eastern Himalayas and its surroundings is done by analyzing the variation of seismic parameters and fractal dimension (Dc). Considering the seismicity data and tectonic features, the eastern part of the Himalayas is divided into eight seismic source zones. For the comparison of the seismicity between each seismic source zone, seismic parameters like average seismic activity rate at threshold magnitude (λo), maximum possible earthquake magnitude (Mmax), and ‘b-value’ are calculated. Seismic parameters of seismic zones are calculated by considering the incompleteness of earthquake catalogue, for that sub-catalogue is prepared for each seismic zone, which is complete to the different threshold of magnitude. The seismotectonic stress variations in Eastern Himalayas are indicated by the estimated values of b and Dc. The calculated seismic parameters can be used directly for seismic hazard analysis of the study area. Keywords:Eastern Himalayas; Seismicity; Fractal dimension; Seismic source zone

The hydrological behavior and freshwater availability in any typical river basin are highly dependent upon precipitation making it the most crucial input variable for hydrological modelling. Precipitation as an input variable to hydrological models is available in gridded form with various spatiotemporal resolution. The variations in the model inputs could be subjected to uncertainties in the hydrological model simulation, which further affect the estimation of blue water flow (BWF) and green water flow (GWF) of a river basin. In this study, we investigated the effects of three gridded precipitation datasets [Watch forcing data ERA-Interim (WFDEI); Princeton datasets; Indian Meteorological Department (IMD)] on streamflow pattern, BWF, and GWF using a semi-distributed hydrological model [Soil and Water Assessment Tool (SWAT)] and a lumped rainfall-runoff model [Hydrological Simulation model (HYSIM)] in the Damodar river basin situated in eastern India. Both the models are simulated at daily time steps with the calibration of ten years (1994 – 2004) and validation of five years (2005 – 2010) at catchment outlet (Durgapur barrage) using three precipitation datasets. The performance of all the three precipitation products is evaluated on the basis of streamflow simulation for both HYSIM and SWAT model at the basin outlet using the performance indicators viz., Nash-Sutcliffe efficiency (NSE), coefficient of determination (R2) and percent bias (PBIAS). The seasonal and annual variation in precipitation values of the WFDEI, Princeton, and IMD dataset could attribute to the significant variations in the performance indicators. Subsequently, the best performance in streamflow simulation is achieved by HYSIM model compared to SWAT with IMD precipitation input. Both models showed remarkable differences in BWF and GWF estimation due to changes in precipitation inputs. The results also indicate that BWF is more sensitive to precipitation than GWF as BWF is directly generated from precipitation. All the above observations suggest that the choice of appropriate precipitation datasets is essential to examine the catchment hydrological behavior, and it further helps policymakers to make critical water management decisions.

Accurate field data are required to predict elevated runoff and sediment transport to aid post-fire planning. This is especially significant at the small catchment scale, where these runoff processes occur disproportionately, occurring at a higher magnitude and higher frequency. Sources of elevated runoff include soil hydrophobicity, in-channel sediment loading through dry ravel, extensive rill networks, and exposed bare soil. Recovery of these processes are related to vegetation conditions before, during, and after fire. This can be quantified using satellite-based vegetation indices to understand the recovery of the burned area and resulting hydrologic response. The main objective was to demonstrate potential for ECOsystem Spaceborne Thermal Radiometer Experiment on Space Station (ECOSTRESS) evaporation measurements in post-fire hydrology by linking to hydrologic signatures (flashiness index and runoff-ratio) to highlight changes and improve vegetation assessments after fire. A case study of the 2018 Holy Fire is presented using a control catchment and a burned catchment. Results show that areas containing higher proportions of montane hardwood and montane hardwood conifers burned at high soil burn severity, a result of the normal to moderately dry period (2012-2016, 2018) that decreased annual evapotranspiration and increased water stress leading up to fire. For 1-year post-fire, ECOSTRESS measured the highest variation between burned and control during the peak dry months (3 to 4 mm/day), which explained the comparatively higher dry-season flows observed for the burned catchment. Summer field visit also showed vegetation regrowth that consisted of mostly annual grasses following a moderately wet year. Preliminary results were adequate; however, not enough time has passed for the system to fully recover, and thus, we present a Google Earth Engine application to help track recovery.

One obstacle to space weather research is the practical challenge of accessing relevant data. Space weather data are housed in disparate repositories, each with its own unique focus, be it solar, magnetospheric, atmospheric, or earth-based. Much of the effort spent acquiring data could instead be spent on space weather research and education. To address this problem, the Space Weather Technology, Research, and Education Center (SWx TREC), at the University of Colorado, Boulder, in collaboration with the Laboratory for Atmospheric and Space Physics (LASP), has developed the Space Weather Data Portal (https://lasp.colorado.edu/space-weather-portal), a tool built by and for the space weather community. Through the Data Portal, previously dispersed space weather data are in one unified place, accessible to scientists, students, and curious individuals. The focus is on the users and their ability to discover, display, compare, overplot, and download relevant data. A user can filter for past events then easily display and download data related to that event, from the moment it occurs on the Sun, as it travels through space and the atmosphere, to the impacts it has on the Earth. Analysis of space weather events via the Data Portal has proved useful for forecaster training and online learning. The community-created Event Library is a short-cut to curated data collections that provide narratives for context and serve as launch pads for further space weather exploration. This presentation will highlight contributions to the Data Portal from the community: datasets, event markers, timelines, and narrated data collections. Your contributions are encouraged as new resources and improvements are deployed every few weeks. Through this iterative, collaborative process, the Data Portal aims to increase awareness of space weather and its impacts and decrease the time between research and real-world applications.

Observational records of rapidly varying magnetic fields strongly constrain our understanding of core flow dynamics and Earth’s dynamo. Archeomagnetic analyses of densely sampled artefacts from the Near-East have suggested that the intensity variation during the first millennium BC was punctuated with two geomagnetic spikes with rates of change of intensity exceeding 1 μT/y, whose extreme behaviour is challenging to explain from a geodynamo perspective. By applying a new transdimensional Bayesian method designed to capture variations on both long and short timescales, we show that the data considered only at the fragment (thermal-unit) level require a complex intensity variation with six spikes, each with a duration between ~30-100 years. However, the nature of the inferred intensity evolution and the number of spikes detected are fragile and highly dependent on the specific treatment of the archeomagnetic data. No spikes are observed when the data are considered only at the level of a group of fragments from the same archeological context, with a minimum of three different artefacts per context. Furthermore, the number of spikes decreases to zero when increasing the error budget for the intensity within reasonable levels of 3-6 μT and the data age uncertainty up to 50 years. Thus, depending on the choices made, the Near-Eastern data are compatible with a broad range of time-dependence, from six spikes at one extreme to zero spikes on the other, the latter associated with much more modest rates of change of ~0.2-0.3 μT/y, comparable to secular variation at other periods and in other regions.

It is accepted that the Perseids Meteor Shower each August is related to the comet Swift Tuttle. It is apparent that the outgassing as the comet travels spreads a cloud of dust along its 133 year long orbital path, and that as the Earth passes through the dust each year, the larger particles burn in the atmosphere creating the meteor shower. Fireballs are also common at the same time, associated with Comet Swift Tuttle. Fireballs are much larger objects than expected from comets outgassing, but the timing and association with the Perseids and Comet Swift Tuttle is significant enough to comfortably assign a large number of mid August fireballs to a relationship with Swift Tuttle. William Cooke of NASA’s Meteoroid Environment Office has plotted the orbits of the fireballs associated with Swift Tuttle as shown in the attached image. They show a large range of orbits, with only one common factor: They all intersect Earth’s orbit in mid-August. Some have very short periods and others long periods. The image shown in this abstract is a diagram of the orbital paths of the fireballs presented by NASA. Studies with iSALE impact hydrocode show that comets hitting Earth at low angles such as 5 degrees or less can skip and continue on a new path at similar speeds to the original orbital speeds. Such a skip will cause part of the comet to drag across the surface of Earth, and both portions of the comet and portions of the Earth’s surface will be carried into space at above Earth escape velocities. Such an occurrence would send some fragments at high speeds similar to or higher than the speed of the comet, and other fragments would be tossed at slower speeds, all depending on the location of the fragments during the impact event. It would be expected that such fragments would travel away from Earth on a wide range of orbits, with the common feature of all of the orbits being the initiation point of the event: the skip impact of Swift Tuttle with Earth. It is proposed that Comet Swift Tuttle has previously impacted Earth at a low angle, causing a skip event which sent fragments of the comet and of the Earth into the wide range of orbits seen in the fireball orbits associated with the Perseids Meteor Showers. The .gif image shows a graphic rendition of such a skip impact. The third image shows the calculated orbits of the resultant debris. The debris from a skip impact produces the same range of orbits as determined by NASA.

Woody plants vary greatly from tall trees to branching shrubs with increasing dryness. Variations in plant allometry are driven by both biotic and abiotic factors, reflecting different plant adaption strategies in different environments. While much is known about the response of plant functional traits to declining rainfall, less is known about how aboveground allometry (e.g. canopy size, height, stems, branching) of woody plants might respond to increasing dryness, limiting our ability to predict changes in woody plants and associated ecosystem functions under future climate change scenarios. Here, we explore how aboveground allometry of different woody genera responds to increasing dryness at 150 sites long an extensive aridity gradient from humid to arid areas. We used regression analyses and Structural Equation Modelling to explore the variation in woody allometry with increasing aridity, and the abiotic (resource availability) and biotic (competition) mechanisms driving such changes. Our results showed that plant height declined, but branching, and canopy width and depth increased with increasing aridity. Woody responses to dryness varied among genera, with increasing aridity associated with wider canopies in Eucalyptus and Callitris, thicker stems in Acacia, but no clear differences in Allocasuarina. Biotic and abiotic factors exerted different effects on the allometry of different genera, with Eucalyptus and Callitris spp. constrained by resource availability, while Acacia and Allocasuarina spp. were regulated mainly by competition. Our results highlight the genus-specific responses in allometric changes and driving mechanisms (resource availability cf. competition) with increasing dryness. Rather than merely shrinking, plants would allocate resources to either canopies or stems to cope with increasing dryness. Under predicted hotter and drier climates, increasing stem or canopy size, and altering branching might be a useful strategy for woody plants to compensate for biomass reduction and maintain ecosystem functions while growing shorter as dryness increases.