bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantifying the effects of the M7.8 November 14, 2016 earthquake on rainfall-induced landslide triggering and reactivation, Kaikoura, New Zealand
Authors: Rosser Brenda , Jones Katie , Massey Chris , Ashraf Salman , Strawbridge Georgia , Morris Samuel
Published: March 2020

The 2016 Mw 7.8 Kaikoura Earthquake in Canterbury, New Zealand produced one of the most complex fault ruptures observed in the historical period and produced strong ground shaking. As a consequence, over twenty-nine thousand landslides were triggered over a total area of about 10,000 km2 with the majority concentrated in a smaller area of about 3,600 km2 (Massey et al 2018). In addition, hillslopes in the affected area were severely damaged by tension cracking and dilation. Large volumes of landslide debris generated during the earthquake remain stored in the landscape and the potential for rainfall to trigger landslides on the failed and partially failed hillslopes is anticipated to be elevated for the foreseeable future. Despite this little is known about the increase in landslide hazard and the timeframe over which this hazard will be elevated.

We used airborne LiDAR captured immediately after the earthquake (November 2016), and at six consecutive dates between November 2017 and April 2019  to develop high resolution surface change models to construct an inventory of rainfall-induced landslides and reactivated landslides following the earthquake. The results were compared with landslide inventories for a series of significant storm events between 1880 and 2019 which were compiled from various sources, including mapping from available aerial photography and satellite imagery collected between 1961 and 2019.

Analysis of the landslide inventories indicates that rainfall triggering thresholds for landslides on these highly cracked and dilated slopes is lower than before the earthquake which has resulted in a significant increase in landslide frequency for a given rainfall amount through the initiation of new landslides on weakened slopes, reactivation of existing landslides and reworking of landslide debris stored on the landscape. Most of the landslides triggered by rainfall following the earthquake were highly mobile debris flows that were strongly coupled to the channel network. Preliminary results suggest that the highest rates of post-earthquake landslide initiation (for both new and reactivated landslides) occurred in the first major storm event following the earthquake and the rate has reduced with time since the earthquake. Maximum landslide size (area) also decreased with time following the earthquake. Quantification of rates of post-EQ rainfall-induced landsliding using LiDAR differencing and aerial photo interpretation will further our understanding of post-earthquake landscape recovery.
Assessment of grassland degradation in alpine meadow using visible vegetation indices by UAV on Qinghai-Tibetan Plateau
Authors: Han Wangya , Su Xukun , Liu Guohua
Published: March 2020

Grassland degradation is a global ecological problem, and grassland on the Qinghai-Tibetan Plateau (QTP) is suffering serious and continuous degradation. Due to the vulnerability of grassland ecosystem on the QTP and its sensitivity to global climate change, alpine grassland degradation needs more attention. In this study, we extracted 7 visible vegetation indices by using an unmanned aerial vehicle (UAV) with visible light sensors. We used random forest model and stepwise multiple regression establishing the relationship between visible vegetation indices and filed degradation index to assess alpine meadow degradation. The result showed that ExG (Excess Green Index) was effective in the simulation with an R2 value of 0.53. The degradation distributions of 50 field sites were obtained at 10cm spatial resolution. This study with visible vegetation indices by UAV provides an effective approach for monitoring grassland degradation at low altitude. The high resolution contributes to more refined grassland management.
Driving mechanisms of sea-level variability in the U.S. mid-Atlantic during the last millennium
Authors: Walker Jennifer , Kopp Robert , Khan Nicole , Shaw Timothy , Cahill Niamh , Barber Don , Brain Matt , Clear Jennifer , Corbett Reide , Horton Benjamin
Published: March 2020

Last millennium relative sea-level (RSL) changes along the U.S. Atlantic coast are spatially variable. Glacial isostatic adjustment (GIA) has been a significant driving factor in RSL rise during the last millennium, producing maximum rates of vertical land motion in the mid-Atlantic region due to its proximity to the margin of the former Laurentide Ice Sheet. However, there is uncertainty surrounding the influence of other regional and local processes on RSL changes such as ocean and atmosphere circulation dynamics; gravitational, rotational, and deformational signals associated with ice mass and distribution changes; sediment compaction; and tidal range change.

Here, we examined the high spatial density of high-resolution RSL records along a ~200 km stretch of coastline from New York City to southern New Jersey to distinguish between local, regional, and global scale drivers. We produced a new high-resolution (decimeter vertical, decadal temporal) RSL record of the last millennium in northern New Jersey and integrated it into an updated global database of instrumental and proxy sea-level records of the Common Era. We used a spatiotemporal empirical hierarchical model to estimate past RSL and rates of RSL change and their associated uncertainties in the context of broader regional changes by decomposing the records into global, regional linear, regional non-linear, and local components.

We found that RSL in northern New Jersey continuously rose over the last 1000 years at a rate of 1.2 ± 0.2 mm/yr (2σ) from 1000 to 1700 CE before increasing to 1.3 ± 0.7 mm/yr from 1700-1800 CE to 1.8 ± 0.6 mm/yr from 1800-1900 CE to 3.0 ± 0.6 mm/yr from 1900-2000 CE. Most of the RSL rise during the past 1000 years is attributed to regional-scale linear processes that we interpret primarily as GIA. The linear component of the RSL records exhibits a north to south gradient, with a greater contribution of RSL rise in southern New Jersey and a smaller contribution in New York City. The regional-scale non-linear contribution from the records have a magnitude <10 cm and are nearly identical because they fall within the same regional scale determined by the spatiotemporal model. The rate of the regional non-linear component fluctuated between -0.1 and 0.1 mm/yr until the late 19th century when it increased to a rate of 0.6 ± 0.1 mm/yr in the late 20th century. These trends are likely explained by a combination of physical processes, including the evolving mass of the Greenland Ice Sheet, steric effects, or ocean mass changes from atmospheric circulation and ocean currents. The local-scale contribution is <10 cm at all sites, but varies in magnitudes and rates of change, which may be due to sediment compaction or tidal range change.
Determination of Drought Threshold for Agricultural Land-use using Satellite Image Analysis Techniques
Authors: Kim Jieun , Yu Jaehyung , Seo Sang Kee , Baek Jin-Hee , Jeon Byung Chil
Published: March 2020

The climate change causes major problems in natural disasters such as storms and droughts and has significant impacts on agricultural activities. Especially, global warming changed crops cultivated causing changes in agricultural land-use, and droughts along with land-use change accompanied serious problems in irrigation management. Moreover, it is very problematic to detect drought impacted areas with field survey and it burdens irrigation management. In South Korea, drought in 2012 occurred in western area while 2015 drought occurred in eastern area. The drought cycle in Korea is irregular but the drought frequency has shown an increasing pattern. Remote sensing approaches has been used as a solution to detect drought areas in agricultural land-use and many approaches has been introduced for drought monitoring. This study introduces remote sensing approaches to detect agricultural drought by calculation of local threshold associated with agricultural land-use. We used Landsat-8 satellite images for drought and non-drought years, and Vegetation Health Index(VHI) was calculated using red, near-infrared, and thermal-infrared bands. The comparative analysis of VHI values for the same agricultural land-use between drought year and non-drought year derived the threshold values for each type of land-use. The results showed very effective detection of drought impacted areas showing distinctive differences in VHI value distributions between drought and non-drought years.
Dynamic modeling of the 1999 Chi-Chi (Mw7.6) earthquake: New insights on energy partition in large earthquakes by incorporating in-situ stress measurements into the constitutive relationship from kinematic modeling
Authors: Liao Jolan , Ma Kuo-Fong , Specht Sebastian , Oglesby David
Published: March 2020

The September 20, 1999 (UTC) Mw7.6 Chi-Chi earthquake in Taiwan was a devastating event of historic proportions. Although this event caused severe damage, it also provided a large data set of high-quality near-field strong motion acceleration records from the Taiwan Strong Motion Instrumentation Program. Despite ongoing advances in kinematic modeling in the last two decades, some questions remain unresolved.  One of those questions is the seismic energy partition in radiated energy and fracture energy. We address this question by investigating the dynamic rupture behavior of this event. We constructed a 3D dynamic rupture model which is constrained by the well resolved spatiotemporal slip distribution and in-situ stress measurements from fault-zone drilling. In our model, we consider the fault ruptures with both spatially uniform and non-uniform frictional behavior and perform a series of numerical experiments with different sets of input variables (e.g., slip-weakening distance, dc, and initial stress on fault plane) based on a slip-weakening friction law. We examined the parameters controlling the slip patterns as the result from kinematic modeling. For the constraints of the input variables, we first derived the constitutive relationship between slip and stress change on the subfaults from the temporal and spatial slip distribution of the kinematic models by Ji et al. (2003), and then determined the dynamic parameters (e.g., apparent slip-weakening distance, dc', and the ratio of strength excess and stress drop,  S). Our initial normal stress on the fault plane is based on the geophysical logging analysis of the Taiwan Chelungpu-fault Drilling Project. Our optimal model can simulate a rupture similar to the kinematic model  by Ji et al. (2003) and suggests that the final slip distribution is mainly controlled by the spatial distribution of the normal stress. We require a downscaling (α) of the apparent slip-weakening distance, αdc', from the derived constitutive law of the kinematic model to allow a dynamic rupture propagation with large slip velocity comparable to the observations. With the downscaled slip-weakening distance, αdc', and a heterogeneous stress distribution, the slip-weakening curves from our optimal model suggests the downscaling in radiated seismic energy and fracture energy accordingly .
C-dots as non-toxic, non-destructive novel tracers to measure biochemical cycles in the soil-plant-atmosphere continuum
Authors: Hafner Benjamin D. , Singh Kanishka , Bauerle Taryn L.
Published: March 2020

Tracers provide a way to determine, follow and quantify biochemical cycles and energy fluxes within the soil-plant-atmosphere continuum (SPAC). Thereby, different tracers, such as dyes, carbonyl sulfite or stable isotopes are employed. One major disadvantage of many tracers is, that very often, plants have to be destructively harvested to analyze the tracer concentration, making it difficult to measure continuous fluxes. Additionally, for stable isotope studies, fractionation or exchange effects can make interpretation and quantification of biogeochemical fluxes difficult. Novel tracers that are already frequently used in animal systems, are fluorescent C-dots. These nanoparticles (5-50 nm diameter) provide a non-destructive imaging option using “in vivo imaging systems” (IVIS). We examined a first approach to apply and measure C-dots as possible tracers in tree saplings of three species (Picea glauca, Pinus strobus, Tsuga canadensis). Roots were excavated from soils and exposed to 20 µmol/l liquid silica-based nanoparticles (diameter of 5.1 nm) labeled with a near-infrared fluorophore, cyanine 5.5 (excitation maximum 646 nm, emission maximum 662 nm). Subsequent continuous IVIS imaging showed real-time uptake and transport of the C-dots by the trees. Respective fluorescence intensity revealed the concentration of C-dots in each of the tissues at measured time steps. Subsequent cross-sectioning of roots, stems and leaves elucidated the internal transport pathway of the C-dots inside the saplings’ tissues. Finally, measurements of stomatal conductance, photosynthesis, transpiration rate, stem hydraulic conductivity and pre-dawn leaf water potentials in comparison to control saplings revealed no phytotoxic effect by the C-dots on plant functioning. In conclusion, C-dots provide a non-toxic new technique for measuring biochemical cycles within the SPAC. Future applications include high resolution tracing of water flow cycles and turnover times within the SPAC, compound specific analyses of root exudation or determining mechanisms of pest influences on plant metabolism.
Northwest U.S. crustal seismic anisotropy suggests crustal flow driven by vertical loads in the underlying mantle
Authors: Humphreys Eugene , Castellanos Jorge , Clayton Robert , Perry-Houts Jonathan , Kim YoungHee , Niday Bart , Stanciu Christian
Published: March 2020

Azimuthal anisotropy in the NW U.S. crust is derived using 3-17 s Rayleigh waves derived using ambient noise from about 300 broadband stations. Velocity is resolved between all station pairs in close proximity, and velocity as a function of azimuth is determined for each station. Azimuthal anisotropy orientations point strongly toward tomographically-imaged high-velocity structures in the underlying mantle, but show no relation to the underlying mantle anisotropy field. We suggest that the crustal anisotropy is decoupled from lateral tectonic forces and is created by upper mantle vertical loading, which in turn generates lateral pressure gradients that drive channelized flow in the ductile mid and lower crust. This idea is tested with geodynamic modeling. Using reasonable values for crustal viscosity and mantle buoyancy structure, we find that the local buoyancy sources within the upper mantle will drive the viscous crustal flow in a manner that reproduces well the imaged crustal anisotropy. We conclude that mantle vertical loading, acting independently from mantle flow, can actively control crustal deformation on a scale of several hundred kilometers.
Hands on geochemistry as a means to promote equality, diversity, and inclusion in geoscience
Authors: Bierman Paul , Corbett Lee
Published: March 2020

Geochemistry has become central to geoscience research; yet, many students have no access to geochemical laboratories because such labs are expensive to build, maintain, and run. Sophisticated geochemical and isotopic techniques require specialized training and technical support. As a result, most of these lab tend to exist only at well-funded, large, graduate-focused institutions. All of these factors cause isotope techniques to be available to only a small subset of the student and faculty population – often white, well off and male.

Since 2018, our cosmogenic nuclide clean laboratory at the University of Vermont has been supported by the US National Science Foundation as a community facility for cosmogenic nuclide sample preparation; our primary goal is to increase access to such specialized techniques isotopic techniques. During our first year under NSF funding, we hosted 36 individual users and several group tours. Visitors came for weeks to months at a time to process their own samples and learn laboratory methods. Our visitors included 12 faculty members, 3 professionals, 13 graduate students, and 8 undergraduate students; they represented 27 different institutions across 16 American states and 4 other countries. We have sought to optimize safety and laboratory training procedures, enabling us to host visitors regardless of their previous experience working in a laboratory setting. We work with visitors collaboratively and are involved in their projects from inception to publication, thereby including researchers who have had no experience with isotopes, laboratory science, or geochronology. The diversity of our visitors far exceeds that of US Geoscience as a whole and includes many woman and demographics currently under-represented in Geoscience faculty ranks.

However, challenges to facilitating a diverse community still exist. Although all training and mentoring costs are covered by the US NSF, visitors to the Community Cosmogenic Facility pay a per-sample fee to cover consumables, pay for AMS analyses, and cover their own travel, all of which restrict access. Certain interested users come from countries for which obtaining a US visa is challenging or impossible; similarly, users may not be able to travel to Vermont for financial or personal reasons. We are exploring additional possibilities for awarding our own internal grants in order to be more inclusive, and also seek to develop robust online content so that collaborators can learn from afar. Increasing diversity, inclusivity, and access in isotopic techniques is a work in progress, which we will continue address in the coming years.

 
Influence of Saharan Dust and Other Aerosols on Hurricane Nadine (2012) as Revealed by the Comparison of Ensemble Model Results and NASA HS3 Data
Authors: Shi Jainn , Braun Scott , Tao Zhining , Sippel Jason
Published: March 2020

This presentation will focus on simulations of the early stages of Hurricane Nadine (2012), which interacted with the SAL and never intensified beyond a minimal hurricane. Given the complexity of aerosol effects on cloud microphysics and radiation and their subsequent effects on deep convective clouds, there is a need to assess the combined microphysical and radiative effects of aerosols. We use the Goddard Space Flight Center version of the Weather Research and Forecasting model with interactive aerosol-cloud-radiation physics to study the influence of the SAL and other aerosols (sea salt and black/organic carbon) on Nadine via a series of model sensitivity runs. The results from the control experiment with all aerosols will be compared to the dropsonde and CPL aerosol lidar backscatter data collected during the NASA Hurricane and Severe Storm Sentinel (HS3) field campaign. Comparison of model results and dropsonde data shows evidence of the intrusion of Saharan air into the storm core. Simulation results also show the possible intrusion of biomass-burning aerosols that originated from forest fires in the Northwestern United States a few days before Nadine reached hurricane strength. In addition, we will also present results from three sets of 30-member ensemble simulations: 1) without aerosol coupling, 2) with all aerosols, and 3) with only dust aerosol, to study the aerosol impact on Nadine.
Regional and Seasonal Influence of Cloud Radiative Effects on CMIP6 Model Climate Sensitivity
Authors: De Bithi , Tselioudis George
Published: March 2020

Recent analyses of Coupled Model Intercomparison Project phase 6 (CMIP6) models have shown higher climate sensitivities than previously reported, and this increase has been preliminary attributed to the simulation of anomalous Shortwave Cloud Radiative Effect (SWCRE) over the southern midlatitude regions. In this work, we further explore how the seasonal and annual SWCRE over different regions of the globe influence the model climate sensitivities. Our study suggests a significant contribution of SWCRE on climate sensitivities in both northern and southern midlatitudes; and the relationship remains robust across the seasons. Additionally, we assess the underlying physics of the inter-model spread to diagnose model biases. The results will contribute to quantify the severity of the Equilibrium Climate Sensitivity, as simulated by the CMIP6 models.
The relative importance of environmental factors on the interannual variability of carbon fluxes in the boreal forest
Authors: El-Amine Mariam , Roy Alexandre , Legendre Pierre , Sonnentag Oliver
Published: March 2020

As climate change will cause a more pronounced rise of air temperature in northern high latitudes than in other parts of the world, it is expected that the strength of the boreal forest carbon sink will be altered. To better understand and quantify these changes, we studied the influence of different environmental controls (e.g., air and soil temperatures, soil water content, photosynthetically active radiation, normalized difference vegetation index) on the timing of the start and end of the boreal forest growing season and the net carbon uptake period in Canada. The influence of these factors on the growing season carbon exchanges between the atmosphere and the boreal forest were also evaluated. There is a need to improve the understanding of the role of the length of the growing season and the net carbon uptake period on the strength of the boreal forest carbon sink, as an extension of these periods might not necessarily result in a stronger carbon sink if other environmental factors are not optimal for carbon sequestration or enhance respiration.

Here, we used 31 site-years of observation over three Canadian boreal forest stands: Eastern, Northern and Southern Old Black Spruce in Québec, Manitoba and Saskatchewan, respectively. Redundancy analyses were used to highlight the environmental controls that correlate the most with the annual net ecosystem productivity and the start and end of the growing season and the net carbon uptake period. Preliminary results show that the timing at which the air temperature becomes positive correlates the most strongly with the start of the net carbon uptake period (r = 0.70, p < 0.001) and the start of the growing season (r = 0.55, p < 0.01). Although the increase of the normalized difference vegetation index also correlates with the start of these periods, a thorough examination of this result shows that the latter happens well before the former. No dependency between any environmental control and the end of the net carbon uptake period was identified. Also, the annual net ecosystem productivity is highly correlated with the length of the net carbon uptake period (r = 0.54, p < 0.01). Other environmental controls such as annual precipitations, the mean annual soil temperature or the maximum yearly normalized difference vegetation index have a smaller impact on the annual net ecosystem productivity. By extending the dataset to include forest stands that represent a wider climate and permafrost variability, we will examine the generalizability of these results.
Within-day and between-day chlorophyll a dynamics during summer in Guanting Reservoir, Beijing, China
Authors: Weiwei Jiang , Jingshan Yu
Published: March 2020

Recognizing intra- and inter-daily dynamics of Chlorophyll a (Chl-a) and its related environmental variables in consecutive days play an important role in assessing and managing water quality and eutrophication. In this study, the water temperature, nutrients, Chl-a concentration  and meteorological factors were collected at six sampling times in Guanting reservoir during summer. Chl-a concentration generally decreased from last May to primary September. At both test times, thermal stratification and mixing in the water column controlled the variation of maximum Chl-a concentration layer at both temporal and vertical scale. The position of the maximum Chl-a concentration layer between days generally followed the same dynamics as thermocline. Daily stratifications were temporary and maximum Chl-a concentration layer varies downwelling by wind driven; hence, the vertical distribution of Chl-a concentration was homogenized at night. Surface Chl-a concentration decreased during the day and increased at night, except on rainy days. The results of Person correlations and principal component analysis indicated that raw surface and daily average Chl-a concentration generally changed as a negative function of solar radiation, wind speed, water temperature and air temperature. However, when a five hour time lag is considered, the relationship between surface Chl-a concentration, water temperature and all meteorological factors became significantly positive.
The Polar Wind Modulated by the Spatial Inhomogeneity of the Strength of the Earth’s Magnetic Field
Authors: Li Kun , Förster Matthias , Rong Zhaojin , Haaland Stein , Kronberg Elena , Cui Jun , Chai Lihui , Wei Yong
Published: March 2020

When the geomagnetic field is weak, the small mirror force allows precipitating charged particles to deposit energy in the ionosphere. This leads to an increase in ionospheric outflow from the Earth’s polar cap region, but such an effect has not been previously observed because the energies of the ions of the polar ionospheric outflow are too low, making it difficult to detect the low-energy ions with a positively charged spacecraft. In this study, we found anti-correlation between ionospheric outflow and the strength of the Earth’s magnetic field. Our results suggest that the electron precipitation through the polar rain can be a main energy source of the polar wind during periods of high levels of solar activity. The decreased magnetic field due to spatial inhomogeneity of the Earth’s magnetic field and its effect on outflow can be used to study the outflow in history when the magnetic field was at similar levels.
C-dots as a novel silica-based fluorescent nanoparticle tracer to investigate plant hydraulics
Authors: Singh Kanishka , Hafner Benjamin , Knighton James , Walter M. Todd , Bauerle Taryn
Published: March 2020

Forest cover exerts a significant control on the partitioning of precipitation between evapotranspiration and surface runoff. Thus, understanding how plants take up and transpire water in forested catchments is essential to predict flooding potential and hydrologic cycling. A growing literature underscores the importance of integrating whole-plant hydraulics, including such processes as the spatial variability of root distribution and the temporally dynamic nature of root water uptake by depth in understanding the relationship between changes in vegetation and hydrology. The analysis of stable isotopes of water (18O and 2H) sourced from soils and plant tissue has enabled the estimation of tree root water uptake depths and water use strategies. Despite the general acceptance of stable water isotopic data to estimate plant hydraulic dynamics, this methodology imposes assumptions that may produce spurious results. For example, end member mixing analysis neglects time-delays during tree-water storage. Also, it is likely that hydraulic redistribution processes of plants, which transport water across soil depths and both into and out of plant tissue, modify δ18O and δ2H; the isotopic signature of a collected sample may thus reflect a history of transport and exposure to fractionating processes not accounted for in analysis. We tested the feasibility of C-dots, core-shell silica polyethylene-glycol coated fluorescent nano-particles (5.1 nm diameter) in 20 µmol/l solution with H2O labeled with a near-infrared fluorophore, cyanine 5.5 (excitation maximum of 646 nm, emission maximum of 662 nm), as an alternative to stable water isotopes in the investigation of plant hydraulics. We examined the absorption and transport of C-dots through soil, as well as roots and aerial structures of Eastern hemlock (Tsuga canadensis), Eastern white pine (Pinus strobus), and white spruce (Picea glauca) saplings (n = 12 each) via an IVIS-200 luminescence in-situ imaging system. We compared the fluid mechanics, residence times and mixing schemes of C-dots with 2H-labeled water during transport within these plant species to establish the nanoparticles as a viable alternative through a split-root hydraulic redistribution experiment under moderate and severe drought conditions. We present a residence-time distribution to elucidate the mixing scheme of C-dot solution and calibration curves to aid future studies. This research is the premier assessment of this nanoparticle as an alternative tracer to stable water isotopes, and as such may yield insights for broader applications.
Mapping Drainage Canals in Southeast Asian Peatlands and their Implications for Peatland Degradation
Authors: Dadap Nathan , Cobb Alexander , Hoyt Alison , Rao Krishna , Harvey Charles , Konings Alexandra
Published: March 2020

Drainage canal networks associated with agricultural land use are a major contributor to peatland degradation in Southeast Asia. These canals are used to control water table depth and make the soil suitable for planting, but their presence has the negative impact of drying out peat soils near the ground surface. Drier soils in turn cause elevated fire risk, increased carbon release to the atmosphere, and subsidence. Although canals directly impact local peat hydrology, the effect of drainage intensity (i.e. canal density) in peatlands has not been quantitatively investigated, due to a lack of reliable canal maps in the region.

In this study, we trained a machine learning model to identify drainage canals and map their density throughout Southeast Asian peatlands using remote sensing imagery. Specifically, a fully convolutional neural network was applied to RGB 5m resolution Basemap imagery from Planet. Training data was generated by hand-labeling canals from satellite images, and validation of canal density was performed via comparison to independently labeled maps. A map of canal density was then produced across ISEA peatlands using images from 2017. We compared canal density with land use type and found that mean canal density is highest in industrial plantations. We also compared canal density with fire occurrence and subsidence data. This new dataset has potential applications for studies of peatland hydrology, land use change, and fire risk.
A numerical approach for understanding the main parameters and processes influencing the soil organic matter decay in wildfire events
Authors: Aedo Sebastián A. , Bonilla Carlos A.
Published: March 2020

High temperatures reached at topsoil during wildfires can induce changes in physical, chemical, and biological soil properties. In the end, these changes are related to the loss of soil organic matter (SOM) and control the post-fire soil management decision. Therefore, the objectives of this study were: (1) to develop a numerical model to predict the SOM decay during wildfires, and (2) to study which are the main parameters that control the soil response. The model couples the energy balance for soil heating, and the species conservation for water and SOM using high temperature-induced vaporization and combustion kinetics. Fluid flow was neglected; however, radiative energy conducted through pores was included as a function of the volumetric pore radius. The soil thermal evolution showed values of r2>0.92 when the radiative term in the thermal conductivity was neglected, and r2>0.98 when the volumetric pore radius was adjusted. The results showed that the main parameters that control the soil response were soil texture, soil water content, volumetric pore radius, and oxygen availability. Also, soil response depends on the surface temperature and exposure time. Soil water content enhances the thermal properties and determines the amount of heat consumed during vaporization because of the high enthalpy of this endothermic reaction. On the other hand, neglecting oxygen flux leads to restricted oxidation, limiting the SOM decay. In terms of texture, silty soils showed the lower soil response, clay and loamy soils an intermediate response, and sandy soils had a higher response. Also, the volumetric pore radius enhances the soil thermal conductivity at high temperatures, leading to higher temperatures near the soil surface. These results suggest that the normalized SOM decay does not depend on the initial SOM content.
Mechanisms of delayed monsoon onset with warming
Authors: Bordoni Simona , Hui Katrina
Published: March 2020

Comprehensive general circulation models (GCMs) in the CMIP3/CMIP5 archive project a delay in the timing of monsoon onset, as the climate warms in response to greenhouse gas (GHG) concentration increases. It has been argued that surface latent heat flux, and its differing response to GHG perturbations over land and over ocean, plays an important role in the redistribution of rainfall from early to late in the warm season in monsoon regions. However, similar phase delays in tropical precipitation have been shown to occur even in warming aquaplanet simulations forced by sea surface temperature perturbations. An alternative explanation invokes energetic arguments, in which elevated latent energy demand in the hemisphere warming up seasonally, as dictated by the Clausius–Clapeyron relation, drives a shift of tropical rainfall towards the opposite hemisphere, manifesting itself as a seasonal delay in the onset of the rainy season. 

 

In this study, we explore mechanisms of delayed monsoon onset with warming in aquaplanet simulations with an idealized GCM spanning a wide range of climates. In earlier work, we have in fact shown how monsoons with rapid circulation and precipitation changes at the beginning of the warm season can be simulated even without any land-sea contrast, provided that the lower boundary has sufficiently low thermal inertia. As the climate is warmed, we find that the onset of the monsoon is progressively delayed to later pentads in the summer season, in agreement with results from the comprehensive GCMs. However, the end of the monsoon season varies less strongly with climate, resulting in a progressive shortening of the overall monsoon season as the climate is warmed. The atmospheric energy balance is examined to separate possible influences of changes in surface fluxes, atmospheric energy storage and gross moist stability on the circulation's seasonality. Radiative-convective equilibrium experiments with the same GCM are also examined, to explore if and to what extent the delayed monsoon onset can indeed result from increases in the effective heat capacity of the atmospheric column with warming, through changes in its latent energy component. 
The Gutenberg-Richter law based on rupture dynamics
Authors: Zhang Zhenguo , Zhang Wenqiang , Xu Jiankuan , Chen Xiaofei
Published: March 2020

Earthquakes recorded by instruments obey the Gutenberg-Richter law, which expresses the dependence of earthquake frequency on magnitude. The Gutenberg-Richter law reveals the physics of earthquake sources and is important for analyzing the seismicity of active fault systems and vulnerable areas. Based on rupture dynamics, for the first time, we obtain a power-law distribution for the relationship between earthquake frequency and magnitude. The weight of an earthquake relies on its rupture area and recurrence interval. Our derived frequency-magnitude distribution agrees with the Gutenberg-Richter law, which is summarized from global and regional earthquake catalogs. This work provides a new way to understand the Gutenberg-Richter law and the physics of earthquake sources.
Hydrological Variability and its Response to Climate Change in Turpan basin
Authors: Du Lijuan
Published: March 2020

The Turpan basin is one of the most arid and water insecure regions in China. The mountain snowmelt is the primary source of water. To assess the impact of climate change on stream flow, this study examined the long-term trends and change points of hydro-meteorological variables and explored the possible correlation between them at annual and seasonal scales. A set of non-parametric statistical tests including Mann-Kendall, Kendall’s tau, Sen’s slope estimator, and Pettitt test was applied, and change point of the hydro-meteorological variables. This study provided valuable information in understanding the changing properties of the stream flow in the basin and insights for a better integrated water resources management planning.
A Methodological Framework to Combine Multiple Precipitation Datasets for Improving Streamflow Simulations: A test study in the Saskatchewan River basin, Canada
Authors: Wong Jefferson , Yassin Fuad , Famiglietti James
Published: March 2020

Obtaining reliable precipitation measurements and accurate spatiotemporal distribution of precipitation remains as a challenging task for driving Hydrologic-Land Surface Models (H-LSMs) and better hydrological simulations and predictions. To further improve the accuracy of precipitation estimation for hydrological applications, the idea of generating a hybrid dataset by combining existing precipitation products has become a more appealing approach in recent years. The reliability of the hybrid dataset is evaluated against in-situ climate stations and error characteristics are calculated to compare to the existing products. However, the robustness of the hybrid dataset in representing spatial details could be problematic when evaluated only using a sparse network of in-situ observations at regional or basin scales. This study aims to develop a methodological framework that combines multiple precipitation products based on evaluation against not only climate stations but also streamflow stations that are spatially representative across large river basin. The framework is illustrated using a Canadian H-LSM named MESH (Modélisation Environmentale communautaire - Surface Hydrology) in the Saskatchewan River basin, Canada over the period of 2002 to 2012. Five existing precipitation datasets are considered as the candidates for generating the hybrid dataset. The framework consists of three components. The first component evaluates each precipitation candidate against the local gauge data for benchmarking, runs each candidate through MESH with 10 km spatial resolution and default parameterization, and calculates the overall streamflow performance in each sub-basins with equal weighting of three evaluation metrics. The second component generates the hybrid dataset by combining the best performing candidates (annual or seasonal) at sub-basin scale. The third component assesses the performance of the hybrid dataset at downstream gauge stations along the mainstream as a validation mechanism for comparison with the performance of the candidate datasets. Results shows that the hybrid dataset is able to perform equally well with the existing precipitation products in the headwater while improve the streamflow performance downstream. The successful application of the framework in this river basin could build the foundation and the confidence in applying the combination method to data-limited river basins in northern Canada.
Simulating mixed-phase cloud properties with ICON around the CAPRICORN field campaign at the kilometre scale
Authors: Ramadoss Veeramanikandan , Protat Alain , Huang Yi , Siems Steven , Possner Anna
Published: March 2020

Stratocumulus clouds are low-level boundary layer clouds that cover 23% of the ocean surface on a global average, with a mean coverage of 25% to 40% in the mid-latitude oceans. These clouds affect Earth's radiative balance due to their strong radiative cooling effect. Many climate models underestimate the reflection of short wave radiation over the Southern Ocean (SO) which results in a positive mean bias of 2K in the annual mean SST in the mid-latitudes of the southern hemisphere. The organization, cloud field properties and the cloud radiative effects of these clouds occur at the lee of cold front in the SO are analyzed in this study. At this conference, we will present preliminary results.
Real case simulations are performed in this study by using ICON - LAM (Icosahedral Nonhydrostatic - Limited Area Model) with two-way nesting domains of resolutions 4.9 km to 2.4 km to 1.2 km. The initial and lateral boundary conditions for the model are derived from IFS meteorological data. CAPRICORN (Clouds, Aerosols, Precipitation, Radiation, and Atmospheric Composition over the Southern Ocean) field campaign that took place during March and April 2016 has continuously observed the open-cell and stratocumuli using shipborne radars and lidars on 26 and 27 March 2016 at the lee of a cold front between 47ºS 144ºE and 45ºS 146ºE (South of Tasmania). The results are evaluated quantitatively and qualitatively with the shipborne observations and HIMAWARI satellite retrievals respectively.
Fifty years of sustainable no-tillage agriculture in the semi-arid Canadian Prairies
Authors: Adl Sina , Kumar Manoj , Paupescu Lucia
Published: March 2020

Fifty years of sustainable no-tillage agriculture in the semi-arid Canadian Prairies 

Agriculture collapsed in the Canadian Prairies during the multi-year drought of 1926-1934. Two changes to local agriculture practice became critical in the recovery of top-soil and agricultural yield. One was abandonment of summer fallow, the other was adoption of no-tillage techniques pioneered in this region. We have obtained soil samples from commercial fields in cereal production (up to one century), from long-term experimental field-plots at research stations, from undisturbed prairies, and from secondary grasslands converted from agriculture. The data provides a chronosequence of fields about 40 years in continuous no-tillage, to contrast against fields in traditional tillage, against secondary grasslands, and undisturbed native prairie. For all samples, we measured free-living nitrogen fixation capacity (15N) in the laboratory, aggregate size distribution, microbial nitrogen fixing community (nif gene), and both bacteria (16S DNA) and eukaryote (18S DNA) diversity. We reconstructed eukaryote community structure and food web structure for the fields. Our results indicate that despite decades of continuous no-tillage, free-living nitrogen fixing capacity remains far below undisturbed prairies, but improved from ploughed fields. Soil aggregate size distribution remains lower in continuous no-tillage, but grasslands contain more larger-sized aggregates enabling more nitrogen fixation. Biodiversity indices follow a pattern of reduced diversity with increased disturbance from agriculture. Biodiversity improves with years into no-tillage or abandonment to secondary grasslands. Overall, we had anticipated a greater recovery of biodiversity, food web complexity, and of free-living nitrogen fixation in decades old continuous no-tillage fields, compared to continuous tillage. Nonetheless, the region of Canadian prairies in no-tillage has been resilient to cyclical droughts, and has accumulated soil organic carbon since adoption of no-tillage. The results are significant because about 95% of the area in cereal crops (~10 million Ha) is in no-tillage, and significant soil organic matter has accumulated in the agroecosystem to contribute to carbon storage to mitigate climate change. 
Linking marine fog variability in Atlantic Canada to changes in large-scale atmospheric and marine features
Authors: Duplessis Patrick , Zhang Minghong , Perrie William , Isaac George A , Chang Rachel Y W
Published: March 2020

Marine and coastal fog forms mainly from the cooling of warm and moist air advected over a colder sea surface. Atlantic Canada is one of the foggiest regions of the world due to the strong temperature contrast between the two oceanic currents in the vicinity. Recurring periods of low visibility notably disrupt off-shore operations and marine traffic, but also land and air transportation. On longer time-scales, marine fog variability also has a significant impact on the global radiative budget. Clouds, including fog, are the greatest source of uncertainty in the current climate projections because of their complex feedback mechanisms. Meteorological records indicate a significant negative trend in the occurrence of foggy conditions over the past six decades at most airports in Atlantic Canada, with large internal variability, including interannual and interdecadal variations. Using the airport observations, reanalysis data and climate model outputs, we investigated the various variabilities on the trend, at interannual and interdecadal scales, and attempted to address what caused these changes in fog frequency. Our results show that the strength and position of the North Atlantic Subtropical High as well as the sea-surface temperature of the cold and warm waters near Atlantic Canada were highly correlated with fog occurrence. We applied the derived fog indices on climate model outputs and projected the fog trends and variability in the different future climate scenarios. The results from this study will be compared with those obtained from other methods and the implications will be discussed.
Characterizing secondary ice production events in mixed-phase clouds using ground-based polarimetric radar
Authors: Kedzuf Nicholas , Chiu J. Christine , Chandrasekar Venkatachalam , Westbrook Christopher
Published: March 2020

Secondary ice production processes are widely proposed as the pathway by which observed cloud ice number concentration can markedly exceed what is expected from primary ice nucleation alone. These processes play a critical, yet poorly constrained, role in the lifecycle of mixed-phase clouds. Presently, main constraints on secondary ice production come from airborne observations, but the transiency of such observations makes it difficult to paint a complete picture of these processes. Here, we develop a novel method for retrieving ice number concentration in a Lagrangian reference frame, allowing us to unearth information not accessible from existing aircraft observations. Our retrieval method employs an iterative ensemble approach, advanced ice crystal models, and the traditional suite of polarimetric radar observables. We will present examples from the Atmospheric Radiation Measurement (ARM) program Mobile Facility deployment in Finland and evaluations against in-situ observations from the UK Parameterizing Ice Clouds using Airborne obServationS and triple-frequency dOppler radar data (PICASSO) field campaign. We will also present a climatology of cloud ice number concentration from the Finland campaign, shedding light on the spatiotemporal evolution, process rates, and trigger requirements of secondary ice production events.