bluuebunny/crossref_metadata_2025_split huggingface dataset:
Evaluating Different Machine Learning Methods for Upscaling Evapotranspiration from Flux Towers to the Regional Scale
Authors: Xu Tongren , Guo Zhixia , Liu Shaomin , He Xinlei , Meng Yangfanyu , Xu Ziwei , Xia Youlong , Xiao Jingfeng , Zhang Yuan , Ma Yanfei , Song Lisheng 
Published: August 2018

AbstractEvapotranspiration (ET) is a vital variable for land‐atmosphere interactions that links surface energy balance, water, and carbon cycles. The in situ techniques can measure ET accurately but the observations have limited spatial and temporal coverage. Modeling approaches have been used to estimate ET at broad spatial and temporal scales, while accurately simulating ET at regional scales remains a major challenge. In this study, we upscale ET from eddy covariance flux tower sites to the regional scale with machine learning algorithms. Five machine learning algorithms are employed for ET upscaling including artificial neural network, Cubist, deep belief network, random forest, and support vector machine. The machine learning methods are trained and tested at 36 flux towers sites (65 site years) across the Heihe River Basin and are then applied to estimate ET for each grid cell (1 km × 1 km) within the watershed and for each day over the period 2012–2016. The artificial neural network, Cubist, random forest, and support vector machine algorithms have almost identical performance in estimating ET and have slightly lower root‐mean‐square error than deep belief network at the site scale. The random forest algorithm has slightly lower relative uncertainty at the regional scale than other methods based on three‐cornered hat method. Additionally, the machine learning methods perform better over densely vegetated conditions than barren land or sparsely vegetated conditions. The regional ET generated from the machine learning approaches captured the spatial and temporal patterns of ET at the regional scale.
Continuous Assimilation of Lightning Data Using Time‐Lagged Ensembles for a Convection‐Allowing Numerical Weather Prediction Model
Authors: Wang Haoliang , Liu Yubao , Zhao Tianliang , Liu Yuewei , Xu Mei , Shen Si , Jiang Yin , Yang Honglong , Feng Shuanglei 
Published: August 2018

AbstractIn this study, a lightning data assimilation method based on the time‐lagged ensembles for predicting severe convection is presented. With the lightning data assimilation scheme, the background error covariances are computed using time‐lagged ensembles, which consist of deterministic forecasts from eight forecast cycles initialized every 3 hr. Pseudo‐observations of graupel mixing ratio (qg) are retrieved from total lightning rates by utilizing empirical vertical profiles obtained from the simulation results of the previous forecast cycles, and the corresponding observation errors are estimated according to the uncertainties in the lightning observations and the empirical vertical profiles of qg. The increments of the model state variables are computed with the Kalman gain matrices and are continuously ingested into the Weather Research and Forecasting model via nudging terms acting on the prognostic equations over each time step during model integration. The effect of the lightning data assimilation scheme on convection analysis and forecast was assessed through a case study of a severe convective event, which took place in the Guangdong of China. Assimilating lightning data recovered many of the observed convective cells, suppressed the spurious convection, and corrected the displacement errors of the convective systems. Quantitative verifications indicate that forecast skills were improved mainly in the convective regions with the impact of assimilating lightning data on stratiform regions being overall less effective.
Disentangling Impacts of Dynamic and Thermodynamic Components on Late Summer Rainfall Anomalies in East Asia
Authors: Oh Hyoeun , Ha Kyung‐Ja , Timmermann Axel 
Published: August 2018

AbstractThis study has examined relative contributions of dynamic and thermodynamic components to East Asian summer monsoon (EASM), compared to the others over Asia. We have decomposed of moisture budget into the dynamic and thermodynamic components composing of interannual variability of the EASM. As represented by the moisture budget, the Asian monsoon is mostly caused by changes in winds (dynamic component); interestingly, changes in moisture (thermodynamic component) play an important role in monsoon rainfall anomalies only for East Asia (27.09%). In terms of the dynamic component over East Asia, strong continental heating, resulting in enhanced land‐sea contrast, is identified as crucial to a local development of winds toward East Asia, and it ultimately strengthens a meridional wind, which is accompanied by the western North Pacific subtropical high. In addition, the negative winter North Atlantic Oscillation could induce the enhanced moisture advection term of the dynamic component over East Asia through barotropic Rossby wave propagation. The thermodynamic component has a localized effect on net precipitation at midlatitudes, with an enhanced wave train pattern with a zonal wavenumber‐5, which reinforces the Okhotsk high. These distinct large‐scale circulation patterns together create favorable conditions for heavy rainfall over East Asia when the two components are positively in‐phase. Here we have also described that the extreme heavy rainfall is noticeable when the Eurasian blocking occurs. This study is expected to improve the detailed predictability of the EASM by understanding the two components to prevent disaster risks in terms of extreme rainfall.
The Life Cycles of Ice Crystals Detrained From the Tops of Deep Convection
Authors: Jensen Eric J. , van den Heever Susan C. , Grant Leah D. 
Published: August 2018

AbstractExtensive anvil cirrus clouds generated by deep convection have important impacts on the Earth's radiation budget and climate. We use growth‐sedimentation trajectory calculations to investigate the life cycles of anvil ice crystals as they are advected downwind from their convective source. Temperature, water vapor, and wind fields from a cloud‐resolving model simulation of an isolated cumulonimbus cloud are used to drive the calculations. Ice crystals are initialized in the main upper‐level detrainment zone with a size distribution based on in situ measurements made in a convective core at about 12 km. Advection, deposition growth, and sedimentation of thousands of sample ice crystals are tracked over about 2.5 hr; neither aggregation of ice crystals nor radiative effects are included. Results support the importance of deposition growth and gravitational size sorting in the evolution of the anvil cirrus. Most ice crystals initialized with maximum dimensions larger than about 200 μm fall out of the anvil and sublimate in subsaturated air below within about 2 hr. Few small ice crystals are present in the lower part of the mature anvil. Vapor deposition growth accounts for about 50% of the ice mass remaining after about 2 hr. Ice crystals larger than about 50 μm in the mature anvil have grown substantially by deposition of vapor. This result is consistent with the predominance of bullet rosette habits observed in mature anvils. Variations in ice crystal fall speeds and growth rates associated with ice crystal habit assumptions have little impact on the ice crystal life cycles.
Variations of Thunderstorm Charge Structures in West Texas on 4 June 2012
Authors: Chmielewski Vanna C. , Bruning Eric C. , Ancell Brian C. 
Published: August 2018

AbstractThis study documents an environment for which small changes therein significantly impacted electrification and for which current theories of electrification lacked the ability to discriminate storm polarity. Thirty single‐cell and multicell storms from 1900 to 2200 UTC on 4 June 2012 over a 150‐ by 100‐km West Texas region were examined. Some of these storms had anomalous charge structures (primarily positive charge in the midlevels at −10 °C to −30 °C or 6.3 to 8.8 km above MSL locally) and some normal (primarily negative at midlevels), even though they existed concurrently and did not statistically differ in overall flash sizes, flash rates, radar volume, or echo top height. Overall, the normal storms ingested lower equivalent potential temperature surface air and were estimated to experience lower convective available potential energy than the anomalous storms, as observed in other studies. They were, however, estimated to have smaller warm cloud depth and surface dew point temperatures, contrary to expectations. Significant overlap between the storm environments suggested that lower instability may have contributed to some storms becoming normally electrified, but it was not a sufficient condition. Additionally, there had been previous convection in the region dominated by normal‐polarity storms. A Weather Research and Forecasting ensemble suggested that the previous convection moistened the midlevels of the atmosphere near cloud base. We propose that future studies investigate dry‐air entrainment as an additional, intertwined environmental factor that could decrease droplet sizes and effective warm rain processes, promoting positive graupel charging in the midlevels and anomalous charge structures.
Spectral Trends of the Surface Regolith in Lunar Craters
Authors: Sim Chae Kyung , Kim Sungsoo S. 
Published: August 2018

AbstractUsing topography‐corrected reflectance maps of the Moon, we present a new methodology for quantifying the spectral distribution of craters in the 750 nm reflectance and 950 nm/750 nm reflectance ratio space (R‐C space) and investigate how the spectral trend changes as the crater matures and degrades. Considering more than 3,495 craters across the Moon, we calculate three parameters to describe spectral trends of the pixels in each crater: 95th‐percentile length, clockwise rotation angle from the horizontal line, and statistical skewness along the principal axis of the distribution, as well as median values of the reflectance and the reflectance ratio. We find that the shape of the spectral trend of a crater in R‐C space becomes shorter, steeper, and more skewed toward the upper left as it optically matures and topographically degrades. Skewness shows a similar relationship to topographical degradation in both mare and highland craters. The skewness is useful in age estimation because it can be calculated easily from reflectance data and is applicable to craters of large size or in low‐iron‐content regions where a topographic model is currently not available. Using these three parameters, one can define the representative trends of a group of craters. We show representative trends of craters with various iron contents at different latitudes. The trends are parallel to one another, with offset controlled by latitude and radial rotation controlled by local iron content; these observations integrate the results of previous studies that reported the two behaviors individually.
A Climate Index Optimized for Longshore Sediment Transport Reveals Interannual and Multidecadal Littoral Cell Rotations
Authors: Anderson Dylan , Ruggiero Peter , Antolínez José A. A. , Méndez Fernando J. , Allan Jonathan 
Published: August 2018

AbstractA recent 35‐year endpoint shoreline change analysis revealed significant counterclockwise rotations occurring in north‐central Oregon, USA, littoral cells that extend 10s of kilometers in length. While the potential for severe El Niños to contribute to littoral cell rotations at seasonal to interannual scale was previously recognized, the dynamics resulting in persistent (multidecadal) rotation were unknown, largely due to a lack of historical wave conditions extending back multiple decades and the difficulty of separating the timescales of shoreline variability in a high energy region. This study addresses this question by (1) developing a statistical downscaling framework to characterize wave conditions relevant for longshore sediment transport during data‐poor decades and (2) applying a one‐line shoreline change model to quantitatively assess the potential for such large embayed beaches to rotate. A climate INdex was optimized to capture variability in longshore wave power as a proxy for potential LOngshore Sediment Transport (LOST_IN), and a procedure was developed to simulate many realizations of potential wave conditions from the index. Waves were transformed dynamically with Simulating Waves Nearshore to the nearshore as inputs to a one‐line model that revealed shoreline rotations of embayed beaches at multiple time and spatial scales not previously discernible from infrequent observations. Model results indicate that littoral cells respond to both interannual and multidecadal oscillations, producing comparable shoreline excursions to extreme El Niño winters. The technique quantitatively relates morphodynamic forcing to specific climate patterns and has the potential to better identify and quantify coastal variability on timescales relevant to a changing climate.
Climate Variability Controls on CO2 Consumption Fluxes and Carbon Dynamics for Monsoonal Rivers: Evidence From Xijiang River, Southwest China
Authors: Zhong Jun , Li Si‐Liang , Liu Jing , Ding Hu , Sun Xiaole , Xu Sheng , Wang Tiejun , Ellam Rob M. , Liu Cong‐Qiang 
Published: August 2018

AbstractThe feedbacks of climate variability on CO2 consumption fluxes and carbon dynamics are thought to play an important role in moderating the global carbon cycle. High‐frequency sampling campaigns and analyses were conducted in this study to investigate temporal variations of river water chemistry and the impacts of climate variability on CO2 consumption fluxes and carbon dynamics for the Xijiang River, Southwest China. Physical processes modify biogeochemical processes, so major ions display different responses to changing discharge. The annual CO2 consumption rate is (6.8 ± 0.2) × 106 ton/year by carbonate weathering and (2.4 ± 0.3) × 106 ton/year by silicate weathering. The annual CO2 consumption flux is much higher than most world rivers, and strong CO2 consumption capacities are observed in catchments in Southwest China. Lower negative δ13CDIC values are found in the high‐flow season which corresponds with high temperatures compared to those in the low‐flow season. High discharge will accelerate material transport, and high temperatures will increase primary production in the catchment, both of which can be responsible for the shift of δ13CDIC values in the high‐flow season. Increased mineral weathering and biological carbon influx in the catchment are the main factors controlling carbon dynamics. Overall, these findings highlight the sensitivity of CO2 consumption fluxes and carbon dynamics in response to climate variability in the riverine systems.
Identifying Critical Climate Periods for Vegetation Growth in the Northern Hemisphere
Authors: Chen Chen , He Bin , Guo Lanlan , Zhang Yafeng , Xie Xiaoming , Chen Ziyue 
Published: August 2018

AbstractVegetation‐climate relationships have been extensively investigated in previous studies, yet the critical seasons and corresponding climate factors influencing annual vegetation growth in a changing climate remain unclear. Relying on Global Inventory Modeling and Mapping Studies NDVI3g data and climate data from 1982 to 2013, this study explored the responses of vegetation growth to climate changes in the Northern Hemisphere (NH), with an emphasis on vegetation changes and legacy effects during different seasons. We further identified the most critical season in terms of vegetation growth. We found an apparent seasonal shift in the influence of climate change on vegetation growth in the NH. In addition, we observed legacy effects of climate change on vegetation growth throughout the seasons. Winter temperatures exerted a positive impact on vegetation growth during the following spring in Europe and central North America. Spring precipitation was an important factor for summer vegetation growth in dry areas. Using partial least squares regression, the relative importance of seasonal climatic factors on annual vegetation growth conditions were determined. This study finds that the vegetation in more than 40% of the NH is controlled by temperature, especially spring temperatures (12.8%). Precipitation and solar radiation were the dominant climate factors influencing vegetation growth in 29.9% and 29.1% of vegetated regions, respectively. Furthermore, compared with the period from 1983 to 1997, the influence of seasonal solar radiation on vegetation growth increased in the NH during the period from 1998 to 2013. This phenomenon was accompanied by reductions in the influence of spring and summer temperatures.
Carbon Dioxide and Methane Dynamics in a Small Boreal Lake During Winter and Spring Melt Events
Authors: Denfeld B. A. , Klaus M. , Laudon H. , Sponseller R. A. , Karlsson J. 
Published: August 2018

AbstractIn seasonally ice‐covered lakes, carbon dioxide (CO2) and methane (CH4) emission at ice‐off can account for a significant fraction of the annual budget. Yet knowledge of the mechanisms controlling below lake‐ice carbon (C) dynamics and subsequent CO2 and CH4 emissions at ice‐off is limited. To understand the control of below ice C dynamics, and C emissions in spring, we measured spatial variation in CO2, CH4, and dissolved inorganic and organic carbon from ice‐on to ice‐off, in a small boreal lake during a winter with sporadic melting events. Winter melt events were associated with decreased surface water DOC in the forest‐dominated basin and increased surface water CH4 in the mire‐dominated basin. At the whole‐lake scale, CH4 accumulated below ice throughout the winter, whereas CO2 accumulation was greatest in early winter. Mass‐balance estimates suggest that, in addition to the CO2 and CH4 accumulated during winter, external inputs of CO2 and CH4 and internal processing during ice‐melt could represent significant sources of C gas emissions during ice‐off. Moreover, internal processing of CO2 and CH4 worked in opposition, with production of CO2 and oxidation of CH4 dominating at ice‐off. These findings have important implications for how small boreal lakes will respond to warmer winters in the future; increased winter melt events will likely increase external inputs below ice and thus alter the extent and timing of CO2 and CH4 emissions to the atmosphere at ice‐off.
Historical Reanalysis: What, How, and Why?
Authors: Slivinski Laura C. 
Published: August 2018

AbstractHistorical reanalyses combine observations of past weather with simulations from modern numerical weather prediction models to provide a consistent, global history of the weather. Recently, a new reanalysis was released that allows observations of the ocean to impact the atmosphere and vice versa. “CERA‐20C: A Coupled Reanalysis of the Twentieth Century” by P. Laloyaux et al. (2018, https://doi.org/10.1029/2018MS001273) describes the first coupled centennial reanalysis, thereby providing more balanced estimates of the ocean‐atmosphere system and allowing for a broader range of studies of the entire Earth system. Results suggest that similar methods could also be leveraged to improve modern weather forecasts.
An X Band Radio Channel Model for Propagation Through the Solar Corona
Authors: Stocker A. J. , Siddle D. R. , Warrington E. M. , Mariotti G. , Silvestri D. , Zeqaj A. , Tortora P. , Argyriou A. , De Vicente J. , Abello R. , Mercolino M. 
Published: August 2018

AbstractSpacecraft communication systems operating at X band are strongly affected when the propagation path passes close to the Sun (which can be characterized by the Sun‐Earth‐Probe, SEP, angle). In this paper, a channel model that can generate a time series of signal amplitude and phase, and hence the signal in‐phase and quadrature values, is presented. For X band, the channel model reproduces the observations well for SEP > 0.8°. While the model has not been experimentally validated at SEP angles below 0.8°, the behavior is consistent with measurements reported in the literature and is therefore likely to be suitable for use, with caution, in that region too.
Mantle Flow and Deforming Continents: From India‐Asia Convergence to Pacific Subduction
Authors: Jolivet Laurent , Faccenna Claudio , Becker Thorsten , Tesauro Magdala , Sternai Pietro , Bouilhol Pierre 
Published: August 2018

AbstractThe formation of mountain belts or rift zones is commonly attributed to interactions between plates along their boundaries, but the widely distributed deformation of Asia from Himalaya to the Japan Sea and other back‐arc basins is difficult to reconcile with this notion. Through comparison of the tectonic and kinematic records of the last 50 Ma with seismic tomography and anisotropy models, we show that the closure of the former Tethys Ocean and the extensional deformation of East Asia can be best explained if the asthenospheric mantle transporting India northward, forming the Himalaya and the Tibetan Plateau, reaches East Asia where it overrides the westward flowing Pacific mantle and contributes to subduction dynamics, distributing extensional deformation over a 3,000‐km wide region. This deep asthenospheric flow partly controls the compressional stresses transmitted through the continent‐continent collision, driving crustal thickening below the Himalayas and Tibet and the propagation of strike‐slip faults across Asian lithosphere further north and east, as well as with the lithospheric and crustal flow powered by slab retreat east of the collision zone below East and SE Asia. The main shortening direction in the deforming continent between the collision zone and the Pacific subduction zones may in this case be a proxy for the direction of flow in the asthenosphere underneath, which may become a useful tool for studying mantle flow in the distant past. Our model of the India‐Asia collision emphasizes the role of asthenospheric flow underneath continents and may offer alternative ways of understanding tectonic processes.
Evidence for an Early Silurian Synorogenic Basin Within the Metamorphic Hinterland of the North Atlantic Caledonides: Insights From the U‐Pb Zircon Geochronology of the Funzie Conglomerate, Shetland, Scotland
Authors: Biejat S. , Strachan R. A. , Storey C. D. , Lancaster P. J. 
Published: August 2018

AbstractThe spectacular kilometer‐thick Funzie Conglomerate is a deformed and metamorphosed high‐energy sedimentary deposit that occurs in Shetland (Scottish Caledonides). Its age and tectonic significance in relation to Early Ordovician (485–475 Ma) and Late Ordovician (450–445 Ma) accretionary orogenic events and the culminating Silurian (430–425 Ma) continental collision and closure of the Iapetus Ocean have hitherto been unknown. U‐Pb zircon dating indicates that the clast population of the conglomerate was derived from easterly sources comprising Neoproterozoic metasedimentary rocks and the northern extension of the Ordovician‐Silurian Midland Valley Arc that formed during Iapetus closure. A lower age limit of 440 Ma is indicated by the ages of the youngest matrix detrital zircon grains and the youngest granitic clast. Deformation and metamorphism of the conglomerate is attributed to sinistrally oblique extension at ca. 430 Ma that excised at least 10 km of crustal section. Sedimentation of the conglomerate is therefore constrained to a 10‐myr time span (440–430 Ma). The tectonic setting is interpreted as a synorogenic basin that received detritus from, and was buried by, advancing thrust nappes during the Early Silurian collision of Laurentia and Baltica. Tectonic burial was followed rapidly by ductile deformation during oblique extensional unroofing of the metamorphic pile and accounts for preservation of the Funzie Conglomerate as a rare example of a synorogenic basin within the metamorphic hinterland of the North Atlantic Caledonides.