bluuebunny/crossref_metadata_2025 huggingface dataset:
Climate as the great equalizer of continental-scale erosion
Authors: Jepson Gilby , Carrapa Barbara , Gillespie Jack , Feng Ran , DeCelles Peter , Tabor Clay , Zhu Jiang
Published: March 2021

Central Asia is one of the most tectonically active and orographically diverse regions in the world and is the location of the highest topography on Earth resulting from major plate tectonic collisional events. Yet the role of tectonics versus climate on erosion remains one of the greatest debates of our time. We present the first regional scale analysis of 2526 published low-temperature thermochronometric dates from Central Asia spanning the Altai-Sayan, Tian Shan, Tibet, Pamir, and Himalaya. We compare these dates to tectonic processes (proximity to tectonic boundaries, crustal thickness, seismicity) and state-of-the-art paleoclimate simulations in order to constrain the relative influences of climate and tectonics on the topographic architecture and erosion of Central Asia. Predominance of pre-Cenozoic ages in much of the interior of central Asia suggests that significant topography was created prior to the India-Eurasia collision and implies limited subsequent erosion. Increasingly young cooling ages are associated with increasing proximity to active tectonic boundaries, suggesting a first-order control of tectonics on erosion. However, areas that have been sheltered from significant precipitation for extensive periods of time retain old cooling ages. This suggests that ultimately climate is the great equalizer of erosion. Climate plays a key role by enhancing erosion in areas with developed topography and high precipitation such as the Tian Shan and Altai-Sayan during the Mesozoic and the Himalaya during the Cenozoic. Older thermochronometric dates are associated with sustained aridity following more humid periods.
Some future projections from coupling the U.K. Earth System Model to the Antarctic ice sheets
Authors: Siahaan Anthony
Published: March 2021

A UKESM climate model which is coupled annually to the BISICLES ice sheet model to enable a two way interactions in Antarctica has been developed 
and run through a small ensemble of four SSP1-1.9 & SSP5-8.5 scenario members. Under the extreme anthropogenic forcing, all the initial condition 
ensemble members develop strong melting under the cold & large Ross and Filchner-Ronne ice-shelves, where it starts after the first half of simulation 
period for the former and in the last decade of the run for the latter. Despite that, during the 85 years timescale of these scenario runs, the stronger radiative forcing has positive effects on the ice-sheet mass gain through increasing precipitation on grounded ice regions which offsets the impact of basal melting in ice discharge across the grounding lines.
Assessment of Cold-Season Precipitation Estimates Derived from Daily Satellite Precipitation Products over CONUS
Authors: Prat Olivier , Nelson Brian , Leeper Ronald , Embler Scott
Published: March 2021

We evaluate the ability of different daily gridded satellite precipitation products (SPPs) to capture cold season precipitation. The satellite precipitation products considered are from the NOAA/Climate Data Record program (CMORPH-CDR, PERSIANN-CDR, GPCP) and from the NASA/Global Precipitation Measurement (IMERG). The evaluation is performed at the daily scale (sub-daily when possible) over CONUS for the period 2007-2018. The daily precipitation measurements at the ground and the atmospheric conditions (temperature, relative humidity) are obtained from the US Climate Reference Network (USCRN). The USCRN network (including associated local networks) is constituted of about 240 stations. Among those USCRN stations, 70 are located above between latitudes 40-60N, and 65 are located above an altitude of 1500m. The USCRN network provides sub-hourly (5-min), hourly, and daily precipitation measurements from shielded gauges in addition to air temperature and wind speed information at 1.5-m. The evaluation is performed by using the usual statistical toolbox; contingency analysis, accuracy, false alarm ratio (FAR), probability of detection (POD), probability of false detection (POFD), Kling–Gupta efficiency (KGE), Pearson’s correlation coefficient, biases, correlations, variability ratio, etc. Although, this work focusses on cold precipitation, the performance of each product will be also compared to their respective performance for warm precipitation (seasonal and/or as a function of the corresponding station atmospheric conditions). This long-term evaluation (11-years) could be helpful in quantifying errors and biases of SPPs with respect to cold season precipitation and provide an objective basis for rainfall retrieval algorithm improvement.
Modeling the formation and eruption of coronal structures by linking data-driven magnetofrictional and MHD simulations
Authors: Daei Farhad , Pomoell Jens , Kilpua Emilia , Price Daniel , Kumari Anshu , Good Simon
Published: March 2021

The time-dependent magnetofrictional model (TMFM) is a prevalent approach that has proven to be a very useful tool in the study of the formation of unstable structures in the solar corona. In particular, it is capable of incorporating observational data as initial and boundary conditions and requires shorter computational time compared to MHD simulations. To leverage the efficiency of data-driven TMFM and also to simulate eruptive events in the MHD framework, one can apply TMFM up to a certain time before the expected eruption(s) and then go on with simulation in the full or ideal MHD regime in order to more accurately capture the eruption process. However, due to the different evolution processes in these two models, using TMFM snapshots in an MHD simulation is non-trivial with several issues that need to be addressed, both physically and numerically.

 

In this study, we showcase our progress in using magnetofrictional model results as input to dynamical MHD simulations. In particular, we discuss the incompatibility of the TMFM output to serve as the initial condition in MHD, and show our methods of mitigating this.

As our benchmark test-case, we study the evolution of NOAA active region 12673, which was previously studied using data-driven TMFM by Price et al. (2019).
Impact induced electric field signals observed by the Solar Orbiter/RPW
Authors: Morooka Michiko , Khotyaintsev Yuri , Eriksson Anders , Edberg Niklas , Johansson Erik , Maksimovic Milan , Bale Stuart , Chust Thomas , Krasnoselskikh Volodya , Kretzschmar Matthieu , Lorfèvre Eric , Plettemeier Dirk , Souček Jan , Steller Manfred , Štverák Štěpán , Trávníček Pavel , Vaivads Andris , Vecchio Antonio
Published: March 2021

A large-amplitude impact-induced like electric field signal is often observed by the Radio and Plasma Wave (RPW) Instrument onboard Solar Orbiter. The signal has a sharp increase followed by an exponential decay, typically observed when spacecraft experiences a dust impact. The amplitude can reach several V/m. The impact dust size can be estimated from the electric field amplitude and is similar to the characteristic dust size near the sun expected from the zodiacal-light observations. On the other hand, the signal's decay time is the order of second, unusually long compared to the dust impact signals previously reported by the other spacecraft. We will show the characteristics of these signals and discuss the origin.
Variability and meandering of the East Australian Current jet at 27oS
Authors: Sloyan Bernadette , Chapman Christopher , Cowley Rebecca , Moore Thomas
Published: March 2021

The East Australian Current (EAC) is the complex and highly energetic western boundary current of the South Pacific Ocean gyre. Low frequency (>2 year) variability of the EAC reflects the changes in the wind and buoyancy forcing over the South Pacific. However, local and regional wind and buoyancy forcing drives higher frequency variability (< 1-2 year) of the EAC. Due to the narrow shelf, the EAC-jet  meandering has an immediate impact on the continental shelf circulation. Here we use the IMOS EAC mooring array between May 2015 to September 2019 and satellite observational data to quantify the quantify the EAC variability and assess the potential drives and impact of the on-shelf meandering of the EAC jet on the properties of the Coral and Tasman Seas.

 

We find that there is considerable variability of Sea Surface Height (SSH) and Sea Surface temperature (SST) that at times co-vary, but at  other times the anomalies are opposed. We compare the surface anomalies with the EAC velocity and transport timeseries. The mean along-slope velocity vectors show poleward velocity dominates from 0-1500 m at the five mooring locations from the 500 m isobath to the deep abyssal basin with the strongest southward flow at the continental shelf. The variance ellipses show that the largest variability in EAC transport is in the along-shore direction. This indicates that the EAC variability is dominated by the movement of the EAC on- and off-shore. The EAC thus maintains its jet structure as it meanders onshore and offshore adjacent to the continental slope. While the mean along-shore velocity vectors provide a picture of the mean EAC, the time-series shows that the EAC has a complex and highly variable structure. Strong southward flow is associated with off-shore flow (positive across-slope velocity). While mostly measuring the EAC core we see times where the flow is northward (positive along-slope velocity). This northward velocity is due to the shelf flow extending from the coast to the shelf, and is generally associated with on-shore flow (negative across-slope velocity). These changes in the direction and strength of the velocity are driven by cyclonic eddies inshore of the jet, and have significant influence on the exchange between the open and shelf ocean.
Are iodic acid measurements by chemical ionization unambiguous?  
Authors: Lewis Thomas , Gomez Martin Juan Carlos , Blitz Mark , Saiz-Lopez Alfonso , Plane John
Published: March 2021

Field observations of IO3− and HIO3−-containing cluster anions by chemical ionization–atmospheric pressure interface–time-of-flight mass spectrometry (CI-API-ToF-MS) have been reported1. These observations, which employ nitrate (NO3−) reagent ions for reaction with the analytes, have been interpreted as resulting from atmospheric gas-phase iodic acid (HOIO2) and molecular cluster formation via HOIO2 addition steps. CI-API-ToF-MS chamber measurements with alternative ionization schemes have also reported signals that could be attributed to gas-phase HOIO and HOIO2. However, well-established chemical kinetics and thermochemistry do not indicate any straightforward route to gas-phase iodine oxyacids and HOIO2 particle formation in the atmosphere. This does not only hinder the ability of chemical models for linking iodine emissions and particle formation, but also calls into question the interpretation of these CI-API-ToF-MS measurements. It has been proposed that water plays an important role in generating gas phase and HOIO2-containing molecular clusters, but recent flow tube experiments have established extremely low upper limits to the rate constants of possible reactions between iodine oxides (IOx and IxOy) and water. In this presentation, we discuss experimental and theoretical kinetics and thermochemistry of proposed routes to gas-phase HOIO and HOIO2 in the atmosphere as well as potential ion-molecule reactions turning iodine oxides into IO3- ions in the CI-API-ToF-MS inlet. We show that there is an important ambiguity in the interpretation of IO3- and other signals observed with CI instruments as a result of barrierless reactions between IxOy and the reagent ions. Experiments for solving this ambiguity and reconciling conflicting results are proposed.
Last Glacial Maximum to near present 10Be chronology of the Universidad glacier fluctuations in the Subtropical Chilean Andes (34° S): paleoclimate implications  
Authors: Fernández Hans , García Juan-Luis , Nussbaumer Samuel U. , Geiger Alessa , Gärtner-Roer Isabelle , Tikhomirov Dmitry , Egli Markus
Published: March 2021

The geochronological and geomorphological reconstruction of glacier fluctuations is required to assess the timing and structure of climate changes of the last glacial cycle in the subtropical Andes of Chile. The scarcity of data in this region limits the knowledge related to the timing of glacial landscape changes during this long-term period. To provide a new framework to better understand the climate history of the semiarid Andes of Chile, we have reconstructed the glacial history of the Universidad glacier (34° S).

Our mapping shows the existence of four moraine belts (UNI I to UNI IV, from outer to inner) that are spatially unequally distributed along the 13 km of the valley between ~2500 and ~1400 m a.s.l. We applied 10Be cosmogenic surface exposure dating to 26 granodioritic boulders on moraines and determined the age of the associated glacial advances. UNI I moraine represents the distal glacier advance between 20.8±0.8 and 17.8±0.8 kyr ago (number of 10Be samples = 11). Other two significative glacier advances terminated one and four km up-valley from the UNI I moraine, respectively, formed 16.1±0.9 kyr (n=1) (UNI II) and 14.6±1 to 10±0.5 kyr ago (n=3) (UNI III). A sequence of six distinct and smaller moraine ridges has been identified in the proglacial area. They are part of last significative glacier advances labeled as UNI IV. The four distal ridges have been dated to between 645-150 years ago (n=11), while the most proximal moraines coincide with mid-20th century and 1997 aerial photographs.

The results indicate that the Universidad glacier advanced during the Last Glacial Maximum (LGM) (UNI I). Deglaciation was punctuated by glacier readvances during the Late Glacial when the UNI II and UNI III moraines were deposited. Finally, UNI IV moraine shows six glacier fluctuations developed between the 14th and 20th centuries.

Our data suggest that the glacier advances by the Universidad glacier were triggered by intensified southern westerly winds bringing colder and wetter conditions to subtropical latitudes in the SE Pacific. Moreover, our data indicate that more or less in-phase Late-Glacial advances along the tropical and extratropical Andes occurred. We discuss different climate forcings that explain these glacier changes. Finally, we illustrate the influence of the “Little Ice Age” in the Semiarid Andes.
Transient methane emissions in the Permian Basin
Authors: Cusworth Daniel , Duren Riley , Thorpe Andrew , Dennison Philip , Downey Nicole , Green Robert , Olson-Duvall Winston , Chapman John , Eastwood Michael , Asner Greg , Heckler Joseph , Miller Charles
Published: March 2021

The Permian Basin is the largest and fastest growing oil and gas (O&G) producing region in the United States. Methane (CH4), a powerful greenhouse gas, is emitted from both routine and abnormal or avoidable operating conditions in the Permian Basin, including O&G production, distribution, and processing. The time scales over which these emissions persist is uncertain, and this uncertainty can lead to large discrepancies in bottom-up emission accounting. Here, we conducted an extensive airborne campaign across the majority (55,000 km2) of the Permian Basin with imaging spectrometers to quantify individual CH4 point sources at the facility scale. We revisited each source multiple times and found that CH4 sources exhibited 26% persistence on average. Persistence-averaged CH4 emissions follow a heavy-tailed distribution, with 20% of facilities constituting 60% of the total point source budget. We quantified the total CH4 flux in the region (point + area sources) through an inverse analysis with satellite observations, and find that point sources make up 50% of the regional CH4 budget. Sector attribution of plumes shows that 50% of detected emissions result from O&G production, 38% from gathering, and 12% from processing plants. Imaging spectroscopy allows for identification of flares, and we find that 12% of CH4 plume emissions were associated with either active or inactive flares, and often emitting above 1000 kg CH4 h-1, even under active flaring. These results show that regular plume-scale monitoring in heterogeneous O&G basins is necessary to understand the high intermittency of operations and resulting emissions.
Climate change impact on photovoltaic potential in Poland
Authors: Zdunek Malgorzata
Published: March 2021

Due to global warming and the worldwide depletion of fossil fuel resources, there is a growing need to transform the energy system toward greater use of renewable sources. In Poland, poor air quality constitutes an additional argument for the necessity of such transition. High levels of pollutants concentrations in many locations, especially in urban and suburban areas are caused by emissions from individual heating systems running on fossil fuels.

 Data from recent years show that renewable generation forms the largest share of the total generation mix in Europe. Regarding new installation, solar and wind energy dominate renewable capacity expansion, jointly accounting for example in 2019 for 90% of all net renewable additions. However, along with the increase in the penetration of these energy sources also increases the sensitivity of the power system to weather and climatic conditions.

The study presents the impact of climate change up to the year 2100 on the photovoltaic power generation potential (Pvpot) in Poland. For determination of Pvpot index a set of high-resolution climate models projections, made available within the EURO-CORDEX initiative was used. Maps showing spatial distribution of absolute values of Pvpot in future climate (30-year average for 2071-2100) and relative changes with respect to current climate (30-year average for 2006-2035) are presented, separately for RCP4.5 and RCP8.5 scenario. The influence of meteorological conditions (temperature, wind and solar radiation) on PV module performance is taken into account by applying two different formula (Ciulla et. al, 2014 and Davy and Troccoli, 2012). Furthermore, two options for module orientation are considered: horizontal and inclined at an optimal angle.
Why Does Western Indian Ocean Circulation Connectivity Matter?
Authors: Kelly Stephen , Popova Ekaterina , Jacobs Zoe
Published: March 2021

Marine circulation connectivity describes the pathways and timescales over which spatially separated parts of the ocean are connected by oceanic currents. In the Western Indian Ocean (WIO), these pathways and associated timescales are characterised by pronounced seasonal and interannual variability, including monsoon-driven reversal of surface currents in the northern part of the basin.

Understanding the connectivity timescales in the WIO – and their variability – is important for a multitude of reasons. Ecological connectivity between coral reefs is necessary to maintain their biodiversity, understanding downstream connectivity from marine resource exploitation sites is important to understand which areas are likely to be affected, and circulation connectivity is a key concern when designing marine conservation measures. For example, establishing an effective network of marine protected areas (MPAs) requires that they are connected on ecologically relevant timescales (e.g. the duration of species’ pelagic larval stages), but gaps in the existing MPA network mean that decisions need to be undertaken about which areas to prioritise for future protection. Therefore, knowledge of the advective pathways connecting the WIO over these timescales is essential for effective management of the region.

Here, a Lagrangian particle tracking method is used in conjunction with a 1/12° resolution ocean model to elucidate the advective pathways mediated by major surface currents in the WIO. Model experiments are performed with virtual particles released into several major WIO currents and tracked for 100 days, and the resulting trajectories are analysed. Significant variability was found, with advective pathways and timescales sensitive to both season and year of release. The main differences are associated with the different monsoon regimes driving changes in connectivity timescales, and reversing direction of advective pathways in the north of the WIO. In addition to this seasonal variability, interannual changes are explored. Case studies of anomalous connectivity pathways / timescales are presented and discussed in the context of extremes in forcing and larger scale variability, including the Indian Ocean Dipole.  
Warming effects on soil CO2 efflux in the tropical Andes: Insights from an experimental thermosequence with dominant tree species.
Authors: Ocampo Montoya Elizabeth , Nottingham Andrew T. , Villegas Palacio Juan Camilo , Mercado Lina M. , Restrepo Zorayda , Meir Patrick
Published: March 2021

Tropical forests, while only occupying 12% to 15% of the Earth's surface, contain about 25% of the world's carbon biomass, with soils representing the second largest reservoir. Yet, recent studies have suggested that, in response to changing environmental conditions, in future decades tropical forests can switch from carbon sinks to carbon sources, with profound implications for the global carbon cycle. Most of these conclusions result from studies in lowland humid forests. However, other tropical forests, such as those occurring in the Andes are also important determinants of regional-to-global biogeochemical functioning, and their sensitivity to future warming has been less studied than in lowland forests. In this study, we explore intra and interspecific thermal sensitivity of soil respiration and its components (autotrophic and heterotrophic) in 15 dominant tree species in the tropical Andes, through an experimental thermosecuence in the Colombian Andes that uses elevation as a proxy for warming. In this thermosequence, a common garden experiment was set up and individuals from 15 dominant species were planted in three sites that represent a temperature gradient: the higher elevation site (2452 masl) corresponds to the base condition; the mid-elevation site (1326 masl) represents a warming of 8°C; and the lower site (575 masl) and it represents a warming of 12°C. Our results indicate consistently higher respiration values with increased temperature both within and between tree species. We used 𝑸10 values (the factor by which soil respiration increases for every 10-degree rise in temperature) to determine the temperature sensitivity of soil respiration. More specifically, for a warming of 5°C there is a temperature coefficient of 𝑸10 = 2 and for a warming of 9°C and there is a temperature coefficient 𝑸10 = 3, this means that for the greater increase temperature the soil respiration can increase faster. Notably, our results show that not all species respond equally to augmented temperatures, highlighting the potential for differential effects of increased temperature and more generally, of environmental change in the compositions and function of these strategic ecosystems. Collectively, our results are relevant for the management and adaptation of ecosystems, particularly tropical Andean forest, and for the refinement of ecological models that support projections of global environmental change and carbon cycle. 
Ionospheric Plasma Transported into the Martian Magnetosheath
Authors: Andersson Laila , Thaller Scott , Fowler Christopher , DiBraccio Gina , Poh Kai
Published: March 2021

How the heavy ionospheric ions escape the Martian atmosphere is still not solved. Missions such as the Mars Express (MEX) satellite have observed significant heavy ions (O2+ and Co2+) on the night side of the terminator. The hot oxygen corona when ionized gives rise to the pickup ions but they are of lighter mass.  With the more comprehensive instrumentation on the MAVEN mission, it is clear that cold heavy ions are transported down the tail of the planet. However, there has not yet been a good explanation of how heavy ions can reach into the Martian sheath in high density concentrations. In December 2020 the MAVEN satellite was observing on the dusk side tailward of the terminator with an orbital configuration allowing the density changes and the ion compositions to be followed. In this presentation the focus is on three subsequent orbits where a channel of heavy ions with high densities reaches out into the sheath. In this presentation we will argue for different possible processes that could explain the observations.
Equilibrium Spin-up of Cold and Warm Permafrost Models
Authors: Ross Cameron , Beddoe Ryley , Siemens Greg
Published: March 2021

Initialization (spin-up) of a numerical ground temperature model is a critical but often neglected step for solving heat transfer problems in permafrost. Improper initialization can lead to significant underlying model drift in subsequent transient simulations, distorting the effects on ground temperature from future climate change or applied infrastructure.  In a typical spin-up simulation, a year or more of climate data are applied at the surface and cycled repeatedly until ground temperatures are declared to be at equilibrium with the imposed boundary conditions, and independent of the starting conditions.

Spin-up equilibrium is often simply declared after a specified number of spin-up cycles. In few studies, equilibrium is visually confirmed by plotting ground temperatures vs spin-up cycles until temperatures stabilize; or is declared when a certain inter-cycle-temperature-change threshold is met simultaneously at all depths, such as ∆T ≤ 0.01oC per cycle. In this study, we investigate the effectiveness of these methods for determining an equilibrium state in a variety of permafrost models, including shallow and deep (10 – 200 m), high and low saturation soils (S = 100 and S = 20), and cold and warm permafrost (MAGT = ~-10 oC and >-1 oC). The efficacy of equilibrium criteria 0.01oC/cycle and 0.0001oC/cycle are compared. Both methods are shown to prematurely indicate equilibrium in multiple model scenarios.  Results show that no single criterion can programmatically detect equilibrium in all tested models, and in some scenarios can result in up to 10oC temperature error or 80% less permafrost than at true equilibrium.  A combination of equilibrium criteria and visual confirmation plots is recommended for evaluating and declaring equilibrium in a spin-up simulation.

Long-duration spin-up is particularly important for deep (10+ m) ground models where thermal inertia of underlying permafrost slows the ground temperature response to surface forcing, often requiring hundreds or even thousands of spin-up cycles to establish equilibrium. Subsequent transient analyses also show that use of a properly initialized 100 m permafrost model can reduce the effect of climate change on mean annual ground temperature of cold permafrost by more than 1 oC and 3 oC under RCP2.6 and RCP8.5 climate projections, respectively, when compared to an identical 25 m model. These results have important implications for scientists, engineers and policy makers that rely on model projections of long-term permafrost conditions.
Spatial and temporal variability of the Antarctic Slope Current in an eddying ocean-sea ice model
Authors: Huneke Wilma , Morrison Adele , Hogg Andy
Published: March 2021

 The basal melt rate of Antarctica's ice shelves is largely controlled by heat delivered from the Southern Ocean to the Antarctic continental shelf. The Antarctic Slope Current (ASC) is an almost circumpolar feature that encircles Antarctica along the continental shelf break in an anti-clockwise direction. Because the circulation is to first order oriented along the topographic slope, it inhibits exchange of water masses between the Southern Ocean and the Antarctic continental shelf and thereby impacts cross-slope heat supply. Direct observations of the ASC system are sparse, but indicate a highly variable flow field both in time and space. Given the importance of the circulation near the shelf break for cross-shelf exchange of heat, it is timely to further improve our knowledge of the ASC system. This study makes use of the global ocean-sea ice model ACCESS-OM2-01 with a 1/10 degree horizontal resolution and describes the spatial and temporal variability of the velocity field. We categorise the modelled ASC into three different regimes, similar to previous works for the associated Antarctic Slope Front: (i) A surface-intensified current found predominantly in East Antarctica, (ii) a bottom-intensified current found downstream of the dense shelf water formation sites in the Ross, Weddell, and Prydz Bay Seas, and (iii) a reversed current found in West Antarctica where the eastward flowing Antarctic Circumpolar Current impinges onto the continental shelf break. We find that the temporal variability of the Antarctic Slope Current varies between the regimes. In the bottom-intensified regions, the variability is set by the timing of the dense shelf water overflows, whereas the surface-intensified flow responds to the sub-monthly variability in the wind field.
When does gap filling of trait data confound taxonomic and functional analyses? 
Authors: Joswig Julia , Kattge Jens , Kraemer Guido , Mahecha Miguel , Rüger Nadja , Schaepman Michael , Schrodt Franziska , Wirth Christian , Schuman Meredith
Published: March 2021

Data on plant traits are increasingly used to understand relationships between biodiversity and ecosystem processes. Large trait databases are sparse because they are compiled from many smaller and usually more local databases. This sparsity severely limits the potential for both multivariate and global data analyses, and so "gap-filling" (imputation) approaches are commonly used to predict missing trait data prior to analysis. Data imputation can result in large biases and circularity; yet, no best practice has evolved for the appropriate use of gap-filled data. Here, we use the TRY database, the largest global database of plant traits, in combination with the commonly used gap-filling algorithm, BayesianHierarchical Probabilistic Matrix Factorization (BHPMF), to address opportunities and problems introduced by gap-filling. BHPMF is the gap-filling method of choice for both TRY, and the large and widely used database sPLOT. It predicts missing trait data using the taxonomic hierarchy and observed patterns of trait variance and trait-trait correlations. We use three metrics: root mean square error estimates, coefficient of variation to assess univariate deviation, and silhouette indices to assess multivariate deviation and clustering strength. We show that gap-filling results in deviation of these metrics calculated for groupings at lower taxonomic levels (intra-specific and intra-genera), but less so at higher taxonomic levels (family) and for functional groups. Trait-trait correlations are preserved at all levels. The strength of deviations depends both on the percentage of gaps, and on data characteristics, e.g. intra-taxa variability. Gap-filling with dataset-external trait data generally ameliorates prediction error, but the deviations of intra-taxonomic variation measures depend on the content of the added data. We conclude that BHPMF gap-filling introduces little bias if specifically used for analyses of traits within functional groups, including growth forms and plant functional types (PFTs), as well as trait-trait correlations. However, we generally discourage their use for analyses of taxonomic groupings at or below the family level. In summary, our study supports decisions on when and how to integrate BHPMF gap-filled trait data in future studies. We conclude with selected best practices when using sparse databases.
Photoelectron transport and associated Far Ultraviolet emissions: Model simulation and comparison with observations
Authors: Liang Jun , Sydorenko Dmytro , Donovan Eric , Rankin Robert
Published: March 2021

Photoelectrons are produced by solar Extreme Ultraviolet radiation and contribute significantly to the ionization and heat balances in planetary upper atmospheres. They are also the source of dayglow emissions, whose intensities may become comparable to weak or moderate dayside auroras. Proper modeling of photoelectrons and dayglow components is desirable for global auroral imaging, one of the core objectives of the SMILE mission. In many previous studies and model simulations, the transport effects of photoelectrons are neglected, so that the photoelectron distribution is controlled by a balance between local production and energy degradation. However, photoelectrons, when generated, can move along the magnetic field line. In particular, some of the photoelectrons may precipitate into the conjugate dark hemisphere and induce auroral-like emissions there, which was reported in realistic observations [Kil et al., 2020]. As a part of the SMILE Ultraviolet imager (UVI) model platform, we have recently developed an auroral/dayglow model that takes into account the interhemispheric transport of photoelectrons and/or secondary electrons, as well as their interaction with the ionosphere/thermosphere. In this study, we report the model simulation of the photoelectron generation and transport, and their induced UV emissions in both the dayside and nightside atmosphere. The simulation results are found to be in reasonable agreement with the realistic SSUSI/GUVI observations.
Role of Longitudinal Lithological Contrast On the Channel Evolution of Piedmont Rivers
Authors: Qin Jintang , Li Kechang , Chen Jie , Li Shenghua
Published: March 2021

The cut-and-fill terrace sequence, resulted from aggradation and incision cycles of alluvial rivers on the piedmont of active orogens, is a common tectonic geomorphological feature observed across different continents under different climatic regimes. Such aggradation and incision cycles are identified on both the orbital and sub-orbital cycles, which poses a question about their origins. Efforts have been put into disentangling the contributions from tectonics, climate and other autogenic sources. In this study, we investigated it by exploring the cut-and-fill terrace sequences along the Jingou River on the northern piedmont of Chinese Tianshan, where numerous terraces are seen along tens of alluvial rivers flowing through the fold-and-thrust belt. More than ten terrace flights, are observed where Jingou River flows across the active Huoerguosi anticline. We collected sediment samples for OSL dating to decipher the building and abandonment processes of these terraces and made topographic measurements to evaluate the paleo-slope of this section of Jingou River. Detailed field survey of sedimentary structure and luminescence dates unambiguously unveil the aggradation and incision cycles on sub-orbital cycles since the last interglacial. Down-cutting of no less than 80 meters is identified during the last ten thousands of years. We tentatively evaluated the possible roles of regional climatic variation, anticline deformation and the autogenic processes. Of all these factors, we detailedly investigated the role of longitudinal contrast of lithologies along the river due to the deformation of the Huoerguosi anticline, which always promotes the channel incision.
No mafic layer in 80 km thick Tibetan crust
Authors: Wang Gaochun , Hans Thybo , Artemieva Irina M.
Published: March 2021

All models of the magmatic and plate tectonic processes that create continental crust predict the presence of a mafic lower crust. It has been suggested that the lower crust does not need to be basaltic, but until now all seismic observations show high P-wave velocity, which requires that the bulk composition of the lower crust must include at least 20-40% of mafic rocks. Earlier proposed crustal doubling in Tibet and the Himalayas by underthrusting of the Indian plate requires the presence of a mafic layer with high seismic P-wave velocity (Vp>7.0 km/s) above the Moho. Our new seismic data demonstrates that some of the thickest crust on Earth in the middle Lhasa Terrane has exceptionally low velocity (Vp<6.7 km/s) throughout the whole 80 km thick crust. Observed deep crustal earthquakes throughout the crustal column and thick lithosphere from seismic tomography imply low temperature crust. The calculated typical velocity versus depth curves for different crustal lithologies and temperature regimes imply the composition of the lower crust is felsic. Therefore, the whole crust must consist of felsic rocks as any mafic layer would have high velocity unless the temperature of the crust were high. Our results form basis for alternative models for the formation of extremely thick juvenile crust with predominantly felsic composition in continental collision zones.

 
High Spatial Resolution Mapping of Glaciers Mass Variations over the Gulf of Alaska Using Spatial Concentration Functions and Monthly GRACE and GRACE-FO Data 
Authors: Doumbia Cheick , Rousseau Alain N.
Published: March 2021

The spatial resolutions of GRACE solutions (level-2 dampened by truncation and/or filtering and level-3 called MASCON) are generally too coarse (~300km) to estimate regional changes in the terrestrial water storage (TWS) components. Focusing methods such as constrained forward approach and spatial concentration functions could improve the spatial distribution estimates of concentrated masses (e.g. glaciers, lakes). In this study, we apply spatial concentration functions to create high resolution monthly time-series of glaciers mass changes over the Gulf Of Alaska (GOA). Spatial weighting functions are based on heterogeneous glaciers mass distribution maps called a priori. First, we use three a priori of different spatial resolutions and sources to create different spatial functions. Second, we compare the amplitude of glaciers mass variations with others GRACE TWS components over the GOA, using the same spatial functions, to improve the discrimination of glaciers mass distribution. Third, we use a variety of GRACE solutions with different processing assumptions given identical resolution characteristics to estimate the uncertainties associated with our methodological framework. To analyze the accuracy of our assessments, we also compare trends resulting from the spatial concentration functions and the constrained forward approach. Then, we compare our estimates with three released MASCON solutions and published results over: (i) the GOA, (ii) the Saint-Elias Mountains and (iii) the Upper Yukon watershed. The results indicate that the spatial functions are sensitive to glaciers mass distribution. The signal from the glaciers dominate the GRACE TWS over the GOA. All solutions used, provide comparable glaciers mass variations. The two focusing methods give similar trends, but the constrained forward approach is time-consuming. The results obtained here could provide to be useful to further our understanding of the contribution of the GOA’s glaciers to sea-level rise and to river flows at the regional scale.
The hydrochemical genesis of groundwater brines of the Eastern arm of the Makgadikgadi basin.
Authors: Motswaiso Fiona , Wang Jiajie , Nakamura Kengo , Watanabe Noriaki , Komai Takeshi
Published: March 2021

Hydrochemistry of groundwater brines of the eastern part of the large playa deposit in the Makgadikgadi basin in northern Botswana has been analyzed. Brine samples were collected from 37 production and monitoring wells in this area. Brine samples for analysis were filtered to 0.45 and analyzed for major and minor anions and cations as well as trace species. The results of the hydrochemical analysis revealed that the major element chemistry of these samples from the area is dominated by Na and Cl with minor components of K, CO3, HCO3, and SO4, and depleted in Ca and Mg, which is typical of seawater or coastal water. The brine type is Na-Cl type. However, the exact mechanism of the genesis of the brines is still ambiguous, hence comparison curves of Na/C1 against seawater concentration factor (SCF) and Ca/Mg against (SCF) in order to ascertain the brine genesis geochemically were employed. The relationship between the current results to previous seawater freezing and evaporation experiments by other researchers indicated that the brines were formed by seawater evaporation. Observed variations in hydrogeochemistry and salinity with depth support the results of previous studies indicating downward infiltration of brackish waters and evaporative and/or mixing processes. With respect to minor and trace element analysis, A comparison of measured concentrations of trace elements to their concentration in seawater when normalized against the concentration of chloride, it can be seen that the saline groundwater brines in the area are enriched in a number of trace elements including W, Th, Se, Pb while depleted in Sr. Enrichments in all of these elements which would be expected to exhibit conservative behavior in the brines suggest that the origin of the brine is not restricted to the simple evaporation of seawater or but to a combination of end members enriched in these elements such as riverine and groundwater inputs.
How morphologic variability, a novel metric derived from supervised landform classification, can offer insights into the processes governing fault scarp morphology in jointed rock 
Authors: Brigham Cassandra , Crider Juliet
Published: March 2021

Fault scarps are steps in the landscape created by surface-rupturing faults. Study of their morphology can supply paleoseismic information, such as the timing and size of past events, but the form of a single fault scarp can show great variability along the length of the scarp, complicating its interpretation. We developed a methodology to quantify this variability: scarp-normal profiles are extracted from point clouds, their shape is automatically classified using a supervised learning algorithm, and these classification results are used to calculate the morphologic variability metric, a measure of the frequency and degree of change in profile form along strike.

Using point clouds derived from structure-from-motion photogrammetry, we computed the morphologic variability along thirteen jointed-bedrock fault scarps from four field sites, located in southwestern Iceland, northern and central California, and southeastern Hawai’i. Quantifiable characteristics such as climate, vegetation, lithology, fault throw, and fracture spacing change either internally along a single scarp or between these four sites.

In an individual scarp, we make pairwise comparisons between measurements of a characteristic and the morphologic variability: a strong correlation between the two indicates that this characteristic is an important driver of scarp form. For example, in the young Icelandic scarps, scarp throw is correlated with morphologic variability, suggesting that the initial slip distribution along a fault contributes to the variability in the profile forms of younger scarps. We also compute the fracture intensity and orientation along the scarps and hypothesize that increased fracture spacing leads to decreased morphologic variability.

To understand variation between sites, we make pairwise comparisons between the average values of morphologic variability of the scarps and site-specific characteristics. For example, maximum scarp throw is negatively correlated with average morphologic variability, suggesting that scarp profile form evolves towards a common morphology as scarps mature.

We show that the morphologic variability metric is a useful tool to understand the agents responsible for changes in scarp form, an essential step in accurately interpreting any paleoseismic information that might be present. Morphologic variability is a metric that can be determined for any other type of linear landform (e.g. coastal bluffs or cross-channel profiles) and our approach of linking morphologic variability to process is applicable to a wide array of geomorphic questions.
The statistical research on the Kinetic- scale magnetic hole in magnetosheath
Authors: Yue Zongshun , Liu Ji , Yao Shutao , Shi Quanqi , Guo Ruilong , Tian Anmin , Bai Shichen
Published: March 2021

Kinetic- scale magnetic hole (KSMH) is a kind of structure whose spatial scale is only or smaller than the ion gyroradius and the magnetic field intensity shows rapid decrease in the observation. Recently, with the improvement of high spatio-temporal resolution measurements, previous studies have revealed some physical processes at the small scale, like electron energization, energy dissipation, wave-particle interaction and the turbulence. However, these studies on KSMHs have not touched on the generation and evolution of these structures due to limitations in the analysis methods used. In this work, using a series of KSMHs events observed by MMS and a new method to analyze the size of the hole, we are studying the relationship between the size of KSMHs and their spatial position in the magnetosheath statistically, and try to find the headstream of this type of structures and reveal their evolution process when they propagate with plasma flow.
Electron Pitch Angle Distributions in the Compressional Pc5 Waves
Authors: Ma Xiao , Tian Anmin , Shi Quanqi , Bai Shichen , Liu Ji , Guo Ruilong , Yao Shutao
Published: March 2021

In the two flanks of the Earth’s magnetosphere, the compressional Pc5 waves are often observed. Previous study suggests that these waves are usually excited by plasma pressure anisotropy such as drift mirror instability. Interestingly, whistler mode waves are often observed in the magnetic trough regions of the compressional Pc5 waves. In this study, we use 10 years (2007-2016) THEMIS A data to study the electron distributions in the compressional Pc5 waves associated with the whistler mode waves. We find three typical electron pitch angle distributions (PADs) in these compressional waves: cigar-shape, donut-shape and pancake-shape. They predominantly occur at tens to hundreds eV, several keV and >10 keV, respectively. The interaction effects between the electrons and whistler waves inside the magnetic troughs are stressed in understanding the formation of these PADs.
Precipitation variability from drop scale to urban scale in the Dallas-Fort Worth metro region
Authors: Chandra Chandrasekar V , Ma Yingzhao
Published: March 2021

Precipitation variability from drop scale to regional scale is not fully understood, except we know there is variability at all scales.  The Center for Collaborative Adaptive Sensing of the Atmosphere (CASA) Dallas-Fort Worth (DFW) urban demonstration network consists of a high-resolution, dual-polarized X-band radar network and a National Weather Service S-band radar system for areal coverage as well as a network of in-situ instruments including tipping bucket gauges, and disdrometers in the DFW international airport. Based on the CASA DFW monitoring platform, we have been exploring the rainfall variability across the airport scale of a large airport such as DFW.  We study the variability of precipitation within the airport grounds and the corresponding impact on airport monitoring and regulatory compliance issues. We also extend this variability analysis across the DFW metro which is also considered a large metro region. The particle size distribution and its small-scale variability are analyzed on both heavy and light rainfall events. As for the catchment scale, the spatial heterogeneity of precipitation in the DFW international airport is specially explored. As for the regional scale, the DFW metropolis is used, and its precipitation variability and trends are demonstrated under the DFW urban radar network. Finally, hydrological response to precipitation variability during the rainstorm event in the DFW international airport is discussed. These observations provide an insight into the relation between space time variability of precipitation and practical response activities in an important region such as airport grounds.  

 