As seismic data from the lower crust becomes more readily available, it is import ant to link seismic properties to the ongoing processes within lower crustal evolution. It includes high temperature, pre- and post-migmatisation solid state deformation as well as melt-present deformation condition. We selected two tonalitic migmatites with variable former melt content (one metatexite and one diatexite) from the lower crustal Daqingshan area, northern North China Craton (NCC) to assess the link between seismic properties and rock structure and rheology. Field observation along with microstructural features suggest that the character of hornblende and plagioclase within the residuum of the metatexite can be used to derive information regarding the pre-migmatisation deformation. Residuum’s plagioclase CPO (crystallographic preferred orientation) is consistent with high temperature dislocation creep as the main deformation mechanism; similarly, hornblende shows a strong CPO related to dislocation creep. During syn-melt (melt present) conditions, phenocrysts of plagioclase in the metatexite’s neosome and K-feldspar and peritectic hornblende in the diatexite’s neosome are present. The rheology of the rock was dominated by melt; hence is inferred to follow Newtonian flow. After melt crystallization deformation is minor but again dominated by dislocation creep. For seismic properties (seismic velocity, anisotropy, Vp/Vs ratio, etc.), in pre- and post-melt conditions, migmatites have normal values. While in syn-melt condition, seismic velocities have a greater decrease, Vp/Vs ratios have a great increase, seismic anisotropies are unusually high.

Lower-viscosity fluids are commonly believed to be able to create more complex fractures in hydraulic fracturing, however, the mechanism remains stubbornly unclear. We use a new grain-scale model with accurate coupling of hydrodynamic forces to simulate the propagation of fluid-driven fracturing. The results clarify that fracturing fluid with a lower viscosity does not always create more complex fractures. The heterogeneity in the rock exerts the principal control on systematic evolution of fracture complexity. In homogeneous rock, low viscosity fluids result in low breakdown pressure, but viscosity exerts little influence on fracture complexity. However, in heterogeneous rock, lower viscosity can lead to more complex network of fracturing. A regime map shows the dependence of fracture complexity on the degree of rock heterogeneity where low viscosity fracturing fluid more readily permeates weak defects and creates complex fracture networks.

Historical volcanic eruptions in Canary Islands have traditionally been considered as quiet eruptions, mostly effusive and with scant explosions (VEI 1-2), attending to the general characteristics of this volcanism. Nevertheless, the geological record of these eruptions shows abundant signs of moderately explosive activity with PDC desposits and bombs and blocks of considerable size outcropping in the islands. Scientific studies of Canarian historical volcanism have been focused on the analysis of the volcanic processes and the assessment of related hazards, paying special attention to the monitoring of volcanic activity in the last few years. However, there is hardly any data of their effects on the population, like number of victims, affected people, displaced, emigrated, damage to the crops, lands, animals, etc. In general, there is also no accurate information on the actions of authorities or on the crises management. The knowledge of the impacts caused by volcanic eruptions provides very significant information to be prepared for future eruptions, and can be found in documentary sources, both handwritten and printed and graphic, in official or private documentation. The analysis of these historical chronicles has shed light on these aspects not previously considered neither by the authorities nor the scientist or general public. The results of this research examining the historical chronicles shows that, contrary to what is generally believed, historical eruptions in Canary Islands did cause several impacts both on the population (dead, injured or missing, displaced and evacuated), and on the economy (damage to crops, livestock, buildings, roads and various infrastructures). The historical documents also highlight that there was indeed crisis management, both from the political and scientific authorities in most of the eruptions. From all these we can conclude that no social interpretation has been made about the legacy of historical eruptions in Canary Islands nor about the impact they had. We should implement this knowledge in the prevention and emergency plans made by the authorities for a better management of future eruptions, considering the population increase in the Canary Islands from ca. 360000 inhabitants in 1900 up to ca. 2.13 millions in 2018, plus some millions of tourists (15.5 in 2018).

In this paper, we present the results obtained in the determination of the true North direction on Mars by using a gnomon on the InSight mission and compare the measurements with either the North determination from the Inertial Measurement Unit and Imaging analysis. The obtained measurement has been use to populate the SEIS orientation information in the archived SEIS data. Images taken during December 2018 and January 2019 allows to determine the gnomon shadow position and length over a target. By calculating the Sun local coordinates using planetary ephemeris VSOP87, the images are used to estimate the true North direction on the landing site. By using eight different images, we obtain the true North direction with an accuracy up to $2.5^{\circ}$, which is confirmed by the IMU and Imaging analysis. The true North direction is also confirmed by an image taken near local noon, when the sun crosses the meridian. The North determination precision is then discussed in view of the seismic determination of the back-azimuth.

The Heliospheric Imagers on board NASAs twin STEREO spacecraft show that coronal mass ejections (CMEs) can be visually complex structures. To explore this complexity, we created a web-based citizen science project in collaboration with the UK Science Museum, in which participants were shown pairs of differenced CME images, taken by the inner cameras of the Heliospheric Imagers (HI-1) on board the twin NASA STEREO spacecraft between 2008 and 2016. Participants were asked to decide which image in each pair appeared the most complicated. 4,028 volunteers conducted 246,692 comparisons of 20,190 image pairs, with each pair being classified by 12 independent users. A Bradley-Terry model was then applied to these data to rank the CMEs by their visual complexity. This complexity ranking revealed that the annual average visual complexity values follow the solar activity cycle, with a higher level of complexity being observed at the peak of the cycle, and the average complexity of CMEs observed by HI1-A was significantly higher than the complexity of CMEs observed by HI1-B. Visual complexity was found to be associated with CME size and brightness, but the differences between HI1-A and HI1-B images suggest that complexity may be influenced by the scale-sizes of structure in the CMEs. Whilst it might not be surprising that the complexity observed in these CME images follows the trend observed in sunspots and the solar cycle; these results demonstrate that there is a quantifiable change in the structure of CMEs seen in the inner heliosphere.

Reverse Time Migration (RTM) Surface Offset Gathers (SOGs) are demonstrated to deliver more superior residual dip information than ray-based approaches. It appears more powerful in complex geological settings, such as salt areas. Still, the computational cost of constructing RTM SOGs is a big challenge in applying it to 3D field data. To tackle this challenge, we propose a novel method using dips of local events as a guide for RTM gather interpolation. The residual-dip information of the SOGs is created by connecting local events from depth-domain to time-domain via ray tracing. The proposed method is validated by a synthetic experiment and a field example. It mitigates the computational cost by an order of magnitude while producing comparable results as fully computed RTM SOGs.

Key Points: • In-situ stress and natural gas saturation affects fracture process and sediment mechanical properties • Mixed fracture mode tends to be induced while micro fractures and craters were created due to phase change of gas hydrate • Hydraulic fracturing most likely makes pathways favorable for natural gas hydrate Abstract: The utilization of natural gas hydrate (NGH) as fuel is beneficial for meeting increasing energy demands. Hydraulic fracturing is a promising technology for developing NGH resources. Tri-axial fracturing experiments are combined with acoustic emission monitoring to study the feasibility of slickwater fracturing on NGH samples. The results reveal that the NGH samples with high gas hydrate saturation show better fracability; The fluid invasion zone can be found for samples with low gas hydrate saturation, indicating that micro fractures are created inside the sediment. In addition, the fracture morphology is more complex under the strike-slip fault regime than under the normal fault regime for all NGH samples, while a lower horizontal stress difference can increase the fracture complexity and breakdown pressure. The AE monitoring results shows mixed fracture modes exist during NGH fracturing, while the ratio of the tensile and shear fracture mode decrease with a large stress difference. Moreover, the post injection propagation can be observed due to the temperature related mechanical properties of the NGH sample; thus, the phase change of the solid gas hydrate is another important fracture mechanism for NGH fracturing, although the extent of the phase change’s influence on the fracture behavior is closely related to the hydrate distribution and saturation. The fracture mechanical stability observation shows a more rapid strength decrease and large deformation and failure for the NGH samples with high gas hydrate saturations, although the effectiveness is high; thus, it is necessary to balance natural gas production with the geological risk before fracturing.

Knowledge of snow/firn density is important for deriving ice sheet mass change from satellite altimetry and for surface mass balance modeling. However, snow/firn densities are largely unknown over the Greenland ice sheet (GrIS) away from isolated direct measurements in boreholes. Density assumptions are widely used when converting volume change from satellite altimetry into mass change, which could introduce errors. Here we extract the inter-annual anomalies of mass change from Gravity Recovery And Climate Experiment (GRACE) data and the refined ice elevation change through the repeat-track analysis of Environmental Satellite (Envisat) altimetry data retrieved using both the ICE1 and ICE2 waveform retracking algorithms. By combining these two types of inter-annual anomalies (GRACE+ICE1 and GRACE+ICE2), we investigate the inter-annually changing snow/firn density estimates over the GrIS during the 2003–2009 period. Our results demonstrate that satellite-derived density is relatively greater over Western GrIS, with magnitude falling between 300 “kg” ⁄“m” ^“3” and 917 “kg” ⁄“m” ^“3” occupying more than 71% of the GrIS. At the regional scale, GRACE+ICE1 derived density agrees well with that from density profiles of 9 ice cores at Summit Station, Central GrIS, with relative errors less than 5%. Satellite-derived densities are further compared with that from 110 ice cores mostly along the central ice divide. The percentage of GRACE+ICE1 derived densities with relative errors less than 20% exceeds 84%, as opposed to 41% for GRACE+ICE2. Satellite-derived densities could possibly underestimate the inter-annually varying snow/firn density over Southern GrIS. This study may provide constraints on the currently applied density assumptions for the GrIS.

The direct and indirect effects of global emissions of black carbon (BC) on the evolution of Arctic climate has been well documented. The significance of within-Arctic emissions of BC is less certain. In light of this, an ensemble of scenarios are developed that simulate the hypothetical diversion of 75% of current and projected shipping traffic from the Suez Canal to the Northern Sea Route (NSR). This experiment shows that BC from ships results in a small change in climate forcing that does not influence the Arctic-wide trajectory of change. However, the shift in forcing from the Suez route to the NSR not only influences regional evolution of sea ice cover, but also results in regional feedbacks that in some locations amplify (e.g. Greenland Sea) and in other locations damp (e.g. Labrador Sea) the sea ice retreat under anthropogenic climate change. The primary mechanism underlying these regional effects is a shift in circulation rather than direct thermodynamic forcing. The most significant impacts are distal from the emissions sources, which is likely to have policy implications as the expansion of industrial and transportation activities into the Arctic is considered.

Harmful algal blooms (HABs), in particular those consisting of the cyanobacteria \textit{Microcystis}, are becoming increasingly more common across the globe. Despite the growing body of evidence that suggests vertical heterogeneity of \textit{Microcystis} can be a precursor to HAB formation, the abiotic drivers of vertical distribution of \textit{Microcystis} are poorly understood in the field environment. The prediction of subsurface cyanobacteria is also pertinent because subsurface concentrations are not easily recognizable to the public or lake system managers, creating an unnoticed safety hazard. High-frequency temporal and vertical data were collected from an Eulerian research station anchored in a stratified and eutrophic lake for five months. Data show that the magnitude of the subsurface \textit{Microcystis} concentration peak and the center of gravity of the deep cyanobacteria layer are statistically significantly mediated by the thermal structure of the lake. The peak subsurface cyanobacteria biovolume scales linearly with the thermocline depth and temperature, whereas the center of gravity of the subsurface cyanobacteria biovolume scales linearly with the mixed layer depth and temperature. Furthermore, our data suggest there is a seasonal evolution of the subsurface cyanobacteria center of gravity that could potentially indicate timing of HAB onset. Based on easily measured parameters associated with the vertical lake temperature profile and meteorological conditions, we provide evidence of predictable trends in subsurface cyanobacteria variables.

Sea surface temperature (SST) observations made at ships are distributed irregularly in space and time and are affected by systematic biases and random errors. Such observations are often “binned”: split into samples, contained within “bins” - grid boxes of a space-time grid (1oX1o monthly bins are used here), and their statistics are computed. Bin averages often serve as gridded representations of such data, thus requiring reliable uncertainty estimates, which for ship observations are particularly important because of their domination in the early observational records. Here ship SST observations for 1992–2010 are compared with an independent high-resolution satellite-based SST data set. To remove systematic biases, seasonal means were subtracted from the difference between bin-averaged data sets. In more than 66%(50%) of locations with binned temporal coverage exceeding 50%(66%), the magnitude of remaining anomalies agreed within 20%(10%) with random error model estimates. Separate estimates for sampling and measurement error components were obtained.

The SAMI3/ESF (Sami3 is also a model of the ionosphere/equatorial spread $F$) code is used to simulate the growth of equatorial plasma bubbles in the presence of a background wind field based on measured winds. The measured winds exhibit the well-known ‘midnight temperature maximum’ (MTM) pattern, in which an equatorward wind occurs simultaneously with a cessation in the zonal wind. The MTM is often preceded by strong equatorward winds (about 100 m/s). The circumstance where the MTM winds are symmetric across the equator is considered; here the meridional wind component in the southern hemisphere is the reverse of the northern meridional wind. The timing of the wind pattern relative to the imposition of a seed for the ESF instability is explored. We find that the simultaneous occurrence of a seed wave and a strong converging meridional wind pattern can produce post-midnight ESF. We further find that the seed wave and the sudden cessation of the zonal winds can also produce post-midnight ESF. The MENTAT (Magnetic mEridional NeuTrAl Thermospheric) code verifies the occurrence of converging meridional wind patterns such as those simulated here, based on ionosonde data. Results suggest that regional-scale wind measurements would aid in the prediction signal-disrupting ionospheric bubbles.

Rising temperatures and an acceleration of the hydrological cycle due to climate change are increasing river discharge, causing permafrost thaw, glacial melt, and a shift to a groundwater-dominated system in the Arctic. These changes are funnelled to coastal regions of the Arctic Ocean where the implications for the distributions of nutrients and biogeochemical constituents are unclear. In this study, we investigate the impact of terrestrial runoff on marine biogeochemistry in Inuit Nunangat (the Canadian Arctic Archipelago) --- a key pathway for transport and modification of waters from the Arctic Ocean to the North Atlantic --- using sensitivity experiments from 2002-2020 with an ocean model of manganese (Mn). The micronutrient Mn traces terrestrial runoff and the modification of geochemical constituents of runoff during transit. The heterogeneity in Arctic runoff composition creates distinct terrestrial fingerprints of influence in the ocean: continental runoff influences Mn in the southwestern Archipelago, glacial runoff dominates the northeast, and their influence co-occurs in central Parry Channel. Glacial runoff carries micronutrients southward from Nares Strait in the late summer and may help support longer phytoplankton blooms in the Pikialasorsuaq polynya. Enhanced glacial runoff may increase micronutrients delivered downstream to Baffin Bay, accounting for up to 18% of dissolved Mn fluxes seasonally and 6% annually. These findings highlight how climate induced changes to terrestrial runoff may impact the geochemical composition of the marine environment, and will help to predict the extent of these impacts from ongoing alterations of the Arctic hydrological cycle.

All rivers undergo changes in channel geometry downstream systematically. A river adjusts its channel geometry (width,depth,cross-sectional area)within the limitations imposed by discharge, channel lithology. As not much studies on channel geometry on large monsoon-fed rivers. Therefore, in this study an attempt will be made to understand the fluvial geomorphological characteristics and variation for 2 decades of major Indian Peninsular River namely Krishna, in terms of channel geometry, discharge. Present study focusses on channel geometry changes downstream for a large Peninsular River . The Krishna River is the third largest river in India.Cross-sectional data for a downstream gauging sites during 1990-2010is downloaded from India Water Resources Information System (India-WRIS) WebGIS. portal. Channel Geometry parameters in terms of Channel Cross-Section Area,Width,Depth,Wetted Perimeter,Hydraulic Radius,Form Ratio are derived from the data involving 9 sites on main river. The Graphs indicate as the maximum discharge increases with corresponding increase in Cross-Sectional Area,Width,Depth,Wetted Perimeter,Form Ratio,Velocity,Hydraiulic Radius is observed with corresponding decrease in Mean Velocity downstream.Channel forms upstream to downstream becomes less steep.APower-log regression equation carried out to evaluate the level of confidence between the parameters.

The seasonal diurnal variability of atmospheric CO2 and driving factors are studied using its continuous isotopic fractionation (δ13C and δ18O) over Shadnagar, a sub-urban location of India with high precision in-situ data from November 2018 to October 2019. The annual averaged atmospheric CO2 concentrations and 13C-CO2 and 18O-CO2 are 415.03±9.77 ppm, -11.18±1.73 ‰ and 9.1±13.35 ‰. Seasonal amplitudes of atmospheric CO2 was observed in summer monsoon (17.30 ± 9.29 ppm) and the minimum was noticed in winter (7.19 ± 0.11 ppm) indicating strong seasonality at the study site. To characterize the atmospheric CO2 sources/sinks, an improved model of Miller and Tans was implemented by plotting ΔCO2 against Δ(CO2 × δ13C) respectively during day and night. An averaged seasonal δ13C source/sink signature (δs) is -32.84 ‰ in the day time and -26.09‰ in night time representing the source of atmospheric CO2 is related to combustion and dominance of C3 ecosystem respiration respectively. The seasonal relationship between δ18O and δ13C is strongly correlated during pre-monsoon ( ‘r’ = 0.93 to 0.95) than post monsoon (‘r’ = 0.07 to 0.13), which might be due to high vapour pressure deficit. A Lagrangian back-trajectory model confirms the influence of the Indian Summer Monsoon on the variability of atmospheric CO2 concentration during the summer monsoon season.

Forest management can enhance forest resiliency against natural disturbances such as fire, drought, or disease. Mechanical thinning, followed by a prescribed burn, is a useful technique to achieve a desired forest structure, usually maximizing large tree basal area or decreasing fuel loads, meant to protect against wildfire or reduce water stress in the western US. Changing forest structure can alter ecosystem function by reducing competition and exposing soil, modifying microclimates and creating suitable conditions for shrubs and grasses to encroach. Typically, forest treatments are expected to make the remaining trees more productive through competitive release, and an open canopy helps the understory to thrive. This enhanced plant water use often contradicts the expected result of increased streamflow following thinning. In mountainous terrain, water yield is further complicated by hillslope-scale processes of subsurface lateral flow and groundwater recharge. This research seeks to understand how management-derived forest structure influences hillslope-scale forest regrowth and water yield. We apply a spatially-distributed ecohydrologic model (RHESSys) to an experimental hillslope in the Sierra Nevada, CA. We incorporate multi-temporal Lidar observations and U.S. Forest Service Forest Inventory & Analysis (FIA) survey data to estimate post-thinning regrowth in treated plots in the watershed, which is used to verify RHESSys accuracy of vegetation regrowth. Then, we run long-term virtual thinning experiments to understand how the combination of thinning and prescribed burns in upslope and riparian sites separately and concurrently influences regrowth and water fluxes in these sites. We expect that an intermediate forest density will yield the most co-benefits in terms of carbon sequestration and water yield. However, these patterns will likely be modified along a hillslope, such that riparian forest stands will be less sensitive to the competitive release that thinning provides, whereas dense upslope forests will be highly sensitive to treatment since they are more water-limited. Water yield is likely to be confounded by multiple factors, including topography, whether a burn follows thinning to remove understory fluxes, and interactions between upslope thinning and processes of lateral flow and groundwater recharge when increased riparian water use compensates for additional upslope subsidies.

Stochastic precipitation generators (SPGs) are often used to produce synthetic precipitation series for water resource management. Typically, an SPG assumes a stationary climate. We present an hourly precipitation generation algorithm for non-stationary conditions informed by the Global Climate Model (GCM) forecasted average monthly temperature (AMT). The physical basis for precipitation formation is considered explicitly in the design of the algorithm using hourly Pressure Change Events (PCE) to define the relationship between hourly precipitation and AMT. The algorithm consists of a multi-variable Markov Chain and a moving window driven by time, temperature, and pressure change. We demonstrate the methodology by generating a 100-year, continuous, synthetic hourly precipitation time series using GCM AMT projections for the Northeast US. When compared with historical observations, the synthetic results suggest that future precipitation in this region will be more variable, with more frequent mild events and fewer but intensified extremes, especially in warm seasons. The synthetic time series suggests that there will be less precipitation in the summers, while winters will be wetter, consistent with other research on climate change projections for the northeast US. This SPG provides physically plausible weather ensembles for water resource studies involving climate change.

The Low-level Jet (LLJ) in the Yangtze River Basin during the Meiyu season is analyzed and studied mostly as the atmospheric circulation background of precipitation, which cannot adequately reflect the characteristics of the jet itself. In this paper a fusion of sounding observations and precipitation data from Wuhan Station during the Meiyu season in 2010 are used to analyze the characteristics of the LLJ in the middle reaches of the Yangtze River. The results show that: the vertical structure of the LLJ is characterized by the predominance of a Boundary-layer Jet (BLJ) with an occurrence height concentrated in the 300-1200 m. The BLJ occurs most frequently at 22:00 at night, but most strongly at 01:00 at night, with resultant wind velocities exceeding 14 m/s. A Synoptic-system-related Low-Level Jet (SLLJ) occurs most frequently at 07:00 during the day, but most strongly at 10:00, with resultant wind velocities exceeding 12 m/s. For both the BLJ and SLLJ, the wind direction is characterized by southwesterly winds. However, the wind direction of the SLLJ is more westerly relative to the BLJ, and the northeasterly direction of the SLLJ occurs significantly more frequently. The analysis of four typical cases of heavy precipitation in the middle reaches of the Yangtze River shows that before the onset of heavy precipitation, a LLJ exists in the precipitation center and at its south side. The SLLJ is dominated by southwesterly winds, and the BLJ has more southerly wind component with the BLJ developing earlier than the SLLJ.