bluuebunny/crossref_metadata_2025 huggingface dataset:
Relationships among phenology, climate and biomass across subtropical forests in Argentina
Authors: Blundo Cecilia , Gasparri Nestor I. , Malizia Agustina , Clark Matthew , Gatti Genoveva , Campanello Paula I. , Grau H. Ricardo , Paolini Leonardo , Malizia Lucio R. , Chediack Sandra E. , MacDonagh Patricio , Goldstein Guillermo
Published: April 2018

Phenology is a key ecosystem process that reflects climate–vegetation functioning, and is an indicator of global environmental changes. Recently, it has been suggested that land-use change and timber extraction promote differences in forest phenology. We use remote-sensing data to describe regional leaf phenological patterns in combination with field data from 131 plots in old-growth and disturbed forests distributed over subtropical forests of Argentina (54–65°W). We assessed how climate is related to phenological patterns, and analysed how changes in forest structural characteristics such as stock of above-ground biomass relate to the observed phenological signals across the gradient. We found that the first three axes of a principal component analysis explained 85% of the variation in phenological metrics across subtropical forests, ordering plots mainly along indicators of seasonality and productivity. At the regional scale, the relative importance of forest biomass in explaining variation in phenological patterns was about 15%. Climate showed the highest relative importance, with temperature and rainfall explaining Enhanced Vegetation Index metrics related to seasonality and productivity patterns (27% and 47%, respectively). Within forest types, climate explains the major fraction of variation in phenological patterns, suggesting that forest function may be particularly sensitive to climate change. We found that forest biomass contributed to explaining a proportion of leaf phenological variation within three of the five forest types studied, and this may be related to changes in species composition, probably as a result of forest use.
A survey of incentive engineering for crowdsourcing
Authors: Muldoon Conor , O’Grady Michael J. , O’Hare Gregory M. P.
Published: April 2018

With the growth of the Internet, crowdsourcing has become a popular way to perform intelligence tasks that hitherto would be either performed internally within an organization or not undertaken due to prohibitive costs and the lack of an appropriate communications infrastructure. In crowdsourcing systems, whereby multiple agents are not under the direct control of a system designer, it cannot be assumed that agents will act in a manner that is consistent with the objectives of the system designer or principal agent. In situations whereby agents’ goals are to maximize their return in crowdsourcing systems that offer financial or other rewards, strategies will be adopted by agents to game the system if appropriate mitigating measures are not put in place. The motivational and incentivization research space is quite large; it incorporates diverse techniques from a variety of different disciplines including behavioural economics, incentive theory, and game theory. This paper specifically focusses on game theoretic approaches to the problem in the crowdsourcing domain and places it in the context of the wider research landscape. It provides a survey of incentive engineering techniques that enable the creation of apt incentive structures in a range of different scenarios.
Inhabitation in simply typed lambda-calculus through a lambda-calculus for proof search
Authors: ESPÍRITO SANTO JOSÉ , MATTHES RALPH , PINTO LUÍS
Published: April 2018

A new approach to inhabitation problems in simply typed lambda-calculus is shown, dealing with both decision and counting problems. This approach works by exploiting a representation of the search space generated by a given inhabitation problem, which is in terms of a lambda-calculus for proof search that the authors developed recently. The representation may be seen as extending the Curry–Howard representation of proofs by lambda terms. Our methodology reveals inductive descriptions of the decision problems, driven by the syntax of the proof-search expressions, and produces simple, recursive decision procedures and counting functions. These allow to predict the number of inhabitants by testing the given type for syntactic criteria. This new approach is comprehensive and robust: based on the same syntactic representation, we also derive the state-of-the-art coherence theorems ensuring uniqueness of inhabitants.
A. J. BROWN, “PHILLIPS’S CURVE,” AND ECONOMIC NETWORKS IN THE 1950S
Authors: Button Kenneth
Published: April 2018

This paper examines the role of the English economist Arthur (A. J.) Brown in the 1950s debate surrounding the wage-rate change/unemployment relationship. While the publication of William (Bill) Phillips’s 1958 paper and the subsequent moniker of the “Phillips Curve” attracted a wealth of attention, Brown’s book on the subject, The Great Inflation, and his later work on inflation have received much less. Here, the focus is on redressing this situation somewhat by looking at Brown’s work to see how much it predates Phillips’s paper, and what differences there are to it. We also consider this within the changing institutional structure of English economic networks in the 1950s that led to a relatively rapid acceptance of Phillips’s analysis and, in many cases, to a strong, ordinal interpretation of the Phillips Curve that overshadowed Brown’s work.
GROWTH OPTION AND DEBT MATURITY WITH EQUITY DEFAULT SWAPS IN A REGIME-SWITCHING FRAMEWORK
Authors: Luo Pengfei , Yang Zhaojun
Published: April 2018

We consider a firm with assets-in-place and a growth option. There is a funding gap for the expansion investment, which is covered by entering into an equity-for-guarantee swap or fee-for-guarantee swap. We explicitly derive all contingent claim prices with the pricing and timing of the growth option taking business cycle and debt maturity into account. For short-term loan, we produce an explanation why Chinese government suggests that guarantee fee rate should be approximately the fraction 50% of the interest rate of bank loans with the same maturity, but for long-term debt, we show this fraction is too small.
Design and demonstration of acoustically optimized, fully-printed, BST MIM varactors for high power matching circuits
Authors: Kienemund Daniel , Bohn Nicole , Fink Thomas , Abrecht Mike , Bigler Walter , Binder Joachim R. , Jakoby Rolf , Maune Holger
Published: April 2018

This work addresses the piezoelectric induced reduction of quality factor in fully-printed metal-insulator-metal (MIM) barium strontium titanate (BST) thick film varactors designed for high power operation. An acoustically optimized varactor design is presented and compared to a non-optimized high-power varactor. The design is utilized to present a narrowband acoustic suppression technique based on defined weights. The acoustically optimized varactor consists of 162 varactor cells in a capacitive matrix. The cells in the matrix are interconnectable allowing for a variable unbiased capacitance and power rating. Due to this setup, surface acoustic waves are interrupted, and the reduced size of the cells allows for a reduced BST layer thickness, shifting the acoustic resonance away from the operational frequency. Therefore, an inverted behavior in comparison to the high-power varactor is observed with an increasing quality factor with biasing voltage. Compared to the high-power varactor, the acoustically optimized varactor design shows a 40% increased quality factor in biased state. By applying the narrowband acoustic suppression technique, an increase in quality factor of 145% is achieved compared to the unsuppressed design. In comparison to the high-power varactor, the acoustical suppressed design shows an increase in quality factor of 480% at the first acoustic resonance frequency.
How to Survey About Electoral Turnout? Additional Evidence
Authors: Morin-Chassé Alexandre
Published: April 2018

Post-election surveys measure voter turnout in a variety of ways. The Canadian Election Study (CES) simply asks respondents whether or not they voted. However, existing research shows that some abstainers report having voted when they in fact did not (Granberg and Holmberg, 1991; Selb and Munzert, 2013). If this misreporting is correlated with other traits, analysis based on the data can be biased. One possible solution to reduce the incentive to overreport is to reframe the turnout question.
Field‐Aligned Currents in Saturn's Nightside Magnetosphere: Subcorotation and Planetary Period Oscillation Components During Northern Spring
Authors: Bradley T. J. , Cowley S. W. H. , Provan G. , Hunt G. J. , Bunce E. J. , Wharton S. J. , Alexeev I. I. , Belenkaya E. S. , Kalegaev V. V. , Dougherty M. K.
Published: April 2018

We newly analyze Cassini magnetic field data from the 2012/2013 Saturn northern spring interval of highly inclined orbits and compare them with similar data from late southern summer in 2008, thus providing unique information on the seasonality of the currents that couple momentum between Saturn's ionosphere and magnetosphere. Inferred meridional ionospheric currents in both cases consist of a steady component related to plasma subcorotation, together with the rotating current systems of the northern and southern planetary period oscillations (PPOs). Subcorotation currents during the two intervals show opposite north‐south polar region asymmetries, with strong equatorward currents flowing in the summer hemispheres but only weak currents flowing to within a few degrees of the open‐closed boundary (OCB) in the winter hemispheres, inferred due to weak polar ionospheric conductivities. Currents peak at ~1 MA rad−1 in both hemispheres just equatorward of the open‐closed boundary, associated with total downward polar currents ~6 MA, then fall across the narrow auroral upward current region to small values at subauroral latitudes. PPO‐related currents have a similar form in both summer and winter with principal upward and downward field‐aligned currents peaking at ~1.25 MA rad−1 being essentially collocated with the auroral upward current and approximately equal in strength. Though northern and southern PPO currents were approximately equal during both intervals, the currents in both hemispheres were dual modulated by both systems during 2012/2013, with approximately half the main current closing in the opposite ionosphere and half cross field in the magnetosphere, while only the northern hemisphere currents were similarly dual modulated in 2008.
Multivariable Comprehensive Analysis of Two Great Geomagnetic Storms of 2015
Authors: Kashcheyev A. , Migoya‐Orué Y. , Amory‐Mazaudier C. , Fleury R. , Nava B. , Alazo‐Cuartas K. , Radicella S. M.
Published: April 2018

During the year 2015 two great geomagnetic storms (Dst < −200 nT) occurred on 17 March and 22 June. These two geomagnetic storms have similarities. They occurred during the same decreasing phase of the sunspot cycle 24. The interplanetary and magnetospheric environments were calm before the beginning of the storms. Both events were due to Coronal Mass Ejections and High‐Speed Solar Wind. Variations of the solar wind velocity and the Bz component of the interplanetary magnetic field were also similar. Two key features that are different for these storms are UT time of the beginning (04:45 UT for 17 March and 18:33 UT for 22 June) and season (equinox and solstice). The comparison of the impact of the storms on the Earth ionosphere and magnetosphere has been performed using diverse parameters including global ionospheric maps of vertical total electron content, data from individual Global Navigation Satellite System receivers, ionosondes, magnetometers, and instruments from different space missions. Visualizing global ionospheric map data as the difference of vertical total electron content between consecutive days allowed understanding better the effect of the storms as a function of time of the beginning of the storm and of the season. It is shown that the presence or absence of scintillations in Global Navigation Satellite System signals during these two storms in African longitude sector is clearly related to the local time at a given station at the beginning of the storm.
Simulation and Quasi‐Linear Theory of Whistler Anisotropy Instability
Authors: Lee Sang‐Yun , Lee Ensang , Seough Jungjoon , Lee Jung‐gi , Hwang Junga , Lee Jae‐Jin , Cho Kyung‐Suk , Yoon Peter H.
Published: April 2018

The whistler anisotropy (or electromagnetic electron cyclotron) instability may be operative in many geomagnetic and heliospherical environments, including the radiation belt, solar wind, and the solar corona. The present investigation carries out a comparative analysis between the two‐dimensional particle‐in‐cell simulation of weakly growing whistler anisotropy instability and the velocity moment‐based two‐dimensional quasi‐linear theory under the assumption of bi‐Maxwellian electron distribution function. It is shown that the simplified quasi‐linear theory provides a qualitative agreement with the more rigorous particle‐in‐cell simulation, but some discrepancies are also found. Possible causes for the differences in either method are discussed, and future improvements on the theory are suggested. Potential applicability of the present finding in the context of the space and astrophysics is discussed.
A Distributed Lag Autoregressive Model of Geostationary Relativistic Electron Fluxes: Comparing the Influences of Waves, Seed and Source Electrons, and Solar Wind Inputs
Authors: Simms Laura , Engebretson Mark , Clilverd Mark , Rodger Craig , Lessard Marc , Gjerloev Jesper , Reeves Geoffrey
Published: April 2018

Relativistic electron flux at geosynchronous orbit depends on enhancement and loss processes driven by ultralow frequency (ULF) Pc5, chorus, and electromagnetic ion cyclotron (EMIC) waves, seed electron flux, magnetosphere compression, the “Dst effect,” and substorms, while solar wind inputs such as velocity, number density, and interplanetary magnetic field Bz drive these factors and thus correlate with flux. Distributed lag regression models show the time delay of highest influence of these factors on log10 high‐energy electron flux (0.7–7.8 MeV, Los Alamos National Laboratory satellites). Multiple regression with an autoregressive term (flux persistence) allows direct comparison of the magnitude of each effect while controlling other correlated parameters. Flux enhancements due to ULF Pc5 and chorus waves are of equal importance. The direct effect of substorms on high‐energy electron flux is strong, possibly due to injection of high‐energy electrons by the substorms themselves. Loss due to electromagnetic ion cyclotron waves is less influential. Southward Bz shows only moderate influence when correlated processes are accounted for. Adding covariate compression effects (pressure and interplanetary magnetic field magnitude) allows wave‐driven enhancements to be more clearly seen. Seed electrons (270 keV) are most influential at lower relativistic energies, showing that such a population must be available for acceleration. However, they are not accelerated directly to the highest energies. Source electrons (31.7 keV) show no direct influence when other factors are controlled. Their action appears to be indirect via the chorus waves they generate. Determination of specific effects of each parameter when studied in combination will be more helpful in furthering modeling work than studying them individually.
Statistical Behavior of the Longitudinal Variations of the Evening Topside Mid‐Latitude Trough Position in both Northern and Southern Hemispheres
Authors: Yang Na , Le Huijun , Liu Libo , Zhang Ruilong
Published: April 2018

Based on the nighttime ionosphere ion density data from the Defense Meteorological Satellite Program (DMSP) satellites in 1996–2016, we statistically analyzed the longitudinal variation of the mid‐latitude trough position in the Northern and Southern hemispheres. The results show significant difference in the longitudinal variation of the trough position between the Northern and Southern hemispheres. In the Northern hemisphere, the trough position in the two longitudinal sectors of 60°W and 120°E is always located at higher latitudes than that in the other longitudinal sectors under most of time and solar and geomagnetic conditions. The longitudinal variation of trough position in the Northern hemisphere is mainly affected by season, solar activity level, and geomagnetic activity level. In the Southern hemisphere, the trough position in the western hemisphere is located at lower latitude than that in the eastern hemisphere in winter and at low solar activity level in equinox. At medium and high solar activity levels in equinox, the southern trough structure in the western hemisphere can't be identified, which also occurs in summer. The change in geomagnetic activity would cause the same movement of trough position in the Southern hemisphere in all longitude sectors at low solar activity level. Thus, the longitudinal variation of trough position in the Southern hemisphere is mainly affected by season and solar activity level. The longitudinal variation of the trough position may be associated with the longitudinal variation of the ion density at the equatorward/poleward side of the trough in the Northern and Southern hemispheres.
Van Allen Probes Observations of Drift‐Bounce Resonance and Energy Transfer Between Energetic Ring Current Protons and Poloidal Pc4 Wave
Authors: Oimatsu S. , Nosé M. , Takahashi K. , Yamamoto K. , Keika K. , Kletzing C. A. , Smith C. W. , MacDowall R. J. , Mitchell D. G.
Published: April 2018

A poloidal Pc4 wave and proton flux oscillations are observed in the inner magnetosphere on the dayside near the magnetic equator by the Van Allen Probes spacecraft on 2 March 2014. The flux oscillations are observed in the energy range of 67.0 to 268.8 keV with the same frequency of the poloidal Pc4 wave. We find pitch angle and energy dispersion in the phase difference between the poloidal magnetic field and the proton flux oscillations, which are features of drift‐bounce resonance. We estimate the resonance energy to be ~120 keV for pitch angle (α) of 30° or 150° and 170–180 keV for α = 50° or 130°. To examine the direction of energy flow between protons and the wave, we calculate the sign of the gradient of proton phase space density (df/dW) on both the inbound and outbound legs of the orbit. We find the gradient to be outward on both legs, which means that energy is transferred from the protons to the wave. During the poloidal Pc4 wave event, the Dst* index shows a measurable increase of ~6.7 nT. We estimate the total energy loss of the ring current from the recovery of the Dst* index and from the variation of proton flux by the drift‐bounce resonance. We suggest that energy transfer from the ring current protons to the poloidal Pc4 wave via the drift‐bounce resonance contributes to up to ~85% of the increase of the Dst* index.
Was Magnetic Storm the Only Driver of the Long‐Duration Enhancements of Daytime Total Electron Content in the Asian‐Australian Sector Between 7 and 12 September 2017?
Authors: Lei Jiuhou , Huang Fuqing , Chen Xuetao , Zhong Jiahao , Ren Dexin , Wang Wenbin , Yue Xinan , Luan Xiaoli , Jia Mingjiao , Dou Xiankang , Hu Lianhuan , Ning Baiqi , Owolabi Charles , Chen Jinsong , Li Guozhu , Xue Xianghui
Published: April 2018

In this study, multiple data sets from Beidou geostationary orbit satellites total electron contents (TECs), ionosonde, meteor radar, magnetometer, and model simulations have been used to investigate the ionospheric responses in the Asian‐Australian sector during the September 2017 geomagnetic storm. It was found that long‐duration daytime TEC enhancements that lasted from 7 to 12 September 2017 were observed by the Beidou geostationary orbit satellite constellation. This is a unique event as the prominent TEC enhancements persisted during the storm recovery phase when geomagnetic activity became quiet. The Thermosphere‐Ionosphere Electrodynamics Global Circulation Model predicted that the TEC enhancements on 7–9 September were associated with the geomagnetic activity, but it showed significant electron density depletions on 10 and 11 September in contrast to the observed TEC enhancements. Our results suggested that the observed long‐duration TEC enhancements from 7 to 12 September are mainly associated with the interplay of ionospheric dynamics and electrodynamics. Nevertheless, the root causes for the observed TEC enhancements seen in the storm recovery phase are unknown and require further observations and model studies.
Process‐Based Model Evaluation Using Surface Energy Budget Observations in Central Greenland
Authors: Miller Nathaniel B. , Shupe Matthew D. , Lenaerts Jan T. M. , Kay Jennifer E. , de Boer Gijs , Bennartz Ralf
Published: April 2018

Energy exchange at the Greenland ice sheet surface governs surface temperature variability, a factor critical for representing surface melt. Physical processes link driving forces to subsequent surface energy budget responses, including radiative, turbulent, and ground heat fluxes, and ultimately control surface temperature evolution. A reanalysis product (ERA‐Interim, ERA‐I), operational model (Climate Forecast System version 2, CFSv2), and climate model (Community Earth System Model, CESM) are evaluated using a comprehensive set of surface energy budget observations and process‐based relationships obtained at Summit, Greenland. Simulated downwelling longwave radiation is underestimated, which is linked to a deficiency of liquid‐bearing clouds. Lower than observed surface albedo, especially in ERA‐I, compensates for summer deficiencies in downwelling longwave radiation. In winter, such deficiencies are compensated by an overestimation of the sensible heat flux. Process‐based relationships convey that all three models underestimate the response of surface temperature to changes in radiative forcing, primarily due to an overactive ground heat flux response in ERA‐I, turbulent heat fluxes in CFSv2, and sensible heat flux in CESM. Cross comparison of three distinct models indicates that the ground heat flux response for ERA‐I, CFSv2, and CESM is too high, too low, and comparatively accurate, respectively, signifying the benefit of using an advanced representation of snow properties. Relatively small biases in CESM surface albedo suggest that advances in the representation of cloud microphysics result in more realistic radiative forcing. These results provide insight into model strengths and deficiencies, indicating the importance of representing physical processes when portraying cloud impacts on surface temperature variability.
Radiance‐Based Evaluation of WRF Cloud Properties Over East Asia: Direct Comparison With FY‐2E Observations
Authors: Yao Bin , Liu Chao , Yin Yan , Zhang Peng , Min Min , Han Wei
Published: April 2018

Radiance‐based comparison between model‐simulated and satellite‐observed atmosphere shows its unique advantage for model evaluation. This study couples a fast radiative transfer model, namely, the community radiative transfer model, and the Weather Research and Forecasting (WRF) to generate synthetic satellite observed infrared (IR) brightness temperatures (BTs) over East Asia. Simulated IR BTs are used to evaluate WRF cloud properties by direct comparison with observations from the Visible and Infrared Spin‐Scan Radiometer (onboard the FengYun‐2E geostationary satellite). A deep cyclone over North China is investigated as our case study. The simulated and observed BTs in the 6.8‐μm channel demonstrate agreement with an averaged bias of <3 K, whereas the performances in two IR window channels are relatively poor with averaged BT differences almost 10 K. For typical precipitation regions, BT differences between the 6.8‐ and 10.8‐μm channels indicate that the WRF simulation underestimates low‐ to midlevel clouds but reproduces high‐level clouds better. Overall, the WRF has solid capabilities to capture the cloud characteristics broadly, whereas some limitations are shown in the cloud temporal and variation cloud cover, especially 3 days after the WRF initialization.
The Dust Direct Radiative Impact and Its Sensitivity to the Land Surface State and Key Minerals in the WRF‐Chem‐DuMo Model: A Case Study of Dust Storms in Central Asia
Authors: Li Longlei , Sokolik Irina N.
Published: April 2018

The instantaneous direct radiative forcing is a basis for estimating the aerosol's climate effect, which is still one of the most uncertain factors. In this study, we incorporate eight minerals into a dust emission model that is coupled with the regional model. The model is used to estimate the direct radiative impact at the top of the atmosphere and at the surface by mineral dust. In addition, multiple tests are performed to investigate the sensitivity of the forcing to some key parameters (such as the surface albedo and key minerals, e.g., hematite and calcite). Based on our simulations of a dust event in Central Asia, the net instantaneous direct forcing (solar + infrared), averaged over the Aral Sea basin on 7 May 2007, are approximately in a range of (−8.05, −0.47) W/m2 at the top of the atmosphere. In comparison to the forcing estimated based on the default complex index, incorporation of dust minerals introduced a less cooling effect at the top of the atmosphere. We found that for a given clay‐to‐silt ratio, the net instantaneous forcing and the forcing in the solar band are sensitive to the surface albedo and hematite variation in the silt fraction. The forcing in the infrared band, however, is insensitive to these parameters, but it is sensitive to calcite and quartz in the silt fraction. Our results highlight the importance of accurately predicting the size‐resolved content of hematite and the surface albedo change to quantify the radiative forcing of mineral dust.
Comparison of Fire Radiative Power Estimates From VIIRS and MODIS Observations
Authors: Li Fangjun , Zhang Xiaoyang , Kondragunta Shobha , Csiszar Ivan
Published: April 2018

Satellite‐based active fire data are a viable tool to understand the role of global fires in the biosphere and atmosphere. The Moderate Resolution Imaging Spectroradiometer (MODIS) sensors on Aqua and Terra satellites are nearing the end of their lives. The Visible Infrared Imaging Radiometer Suite (VIIRS) sensor on the Suomi National Polar‐orbiting Partnership satellite and the subsequent Joint Polar Satellite System series is expected to extend the MODIS active fire record. Thus, understanding the similarities of and discrepancies between the two data sets during their overlap period is important for existing applications. This study investigated the dependence of the MODIS and VIIRS fire characterization capabilities on satellite view zenith angle and the relationship between the two sensors' fire radiative power (FRP) from individual fire clusters to fire data on continental and global scales. The results indicate that the VIIRS fire characterization capability is similar across swath, whereas MODIS is strongly dependent on view zenith angle. Statistical analyses reveal that the VIIRS and MODIS FRP relationship varies between different spatial scales. In fire clusters, MODIS and VIIRS FRP estimates are very comparable, except for large boreal forest fires where VIIRS FRP is approximately 47% smaller. At the continental scale, the contemporaneous FRP retrievals from MODIS and VIIRS are generally comparable and strongly correlated, but VIIRS FRP is slightly larger and their differences vary across seasons. At global 1° × 1° grids, the FRP difference between the two sensors is, on average, approximately 20% in fire‐prone regions but varies significantly in fire‐limited regions.
The Impacts of Chinese Wind Farms on Climate
Authors: Sun Hongwei , Luo Yong , Zhao Zongci , Chang Rui
Published: April 2018

As a renewable energy resource, wind energy has developed fast in recent years, and its impacts on climate have received widespread attention. In this study, a new wind farm fleet scenario is designed based on Chinese wind farm data from the Chinese Wind Energy Association and Chinese cumulative wind power capacity data from the Global Wind Energy Council. A mesoscale numerical model is used to simulate the impacts of wind farms on climate. The results indicate that the wind farms in the designed scenario could impact the local and regional climate in China, causing changes in both lower‐level atmosphere (changes within ±0.5 K for 2‐m temperature) and upper‐level atmosphere (changes within ±30 m2/s2 for 500‐hPa geopotential height) over several specific areas. The momentum sink and the turbulent kinetic energy source generated by wind farms are first separated to evaluate their respective contributions to the impacts of wind farms on climate.
Denali Ice Core Methanesulfonic Acid Records North Pacific Marine Primary Production
Authors: Polashenski David J. , Osterberg Erich C. , Koffman Bess G. , Winski Dominic , Stamieszkin Karen , Kreutz Karl J. , Wake Cameron P. , Ferris David G. , Introne Douglas , Campbell Seth , Lewis Gabriel M.
Published: April 2018

The high‐nutrient, low‐chlorophyll region of the northeastern (NE) subarctic Pacific is one of the most biologically productive marine ecosystems in the world, supporting fisheries worth over $5 billion annually. Phytoplankton are the primary producers in this ecosystem and are also a major source of biogenic sulfur emissions, important in Earth's climate system. However, variability in marine primary production through time is not well constrained. Here we establish methanesulfonic acid (MSA) concentrations in the Denali ice core as a proxy for marine primary production in the NE Pacific. Using Hybrid Single‐Particle Lagrangian Integrated Trajectory (HYSPLIT; Stein et al., 2015, https://doi.org/10.1178/BAMS-D-14-00110.1) modeling, we identify moisture source regions for the core site and correlate Sea‐Viewing Wide Field‐of‐View Sensor‐derived chlorophyll a concentrations with ice core MSA. From 1998 to 2007 we find that areas of significant positive correlation overlap with the HYSPLIT‐inferred moisture source region in the western Gulf of Alaska on an annual basis (r = 0.85, p < 0.001). We identify an MSA response to a localized bloom related to ash deposition from a 2009 Mt. Redoubt eruption. An anomalous upwelling‐driven bloom in spring 2008 did not impact the ice core MSA record due to unfavorable transport conditions. Despite this, we observe that bloom events are rarely missed in the MSA record, which we attribute to the consistent and high snow accumulation rate at the ice core drill site. Our findings suggest that Denali ice core MSA is a reliable recorder of changes in marine primary production through time in the NE subarctic Pacific.
Burned Area Comparisons Between Prescribed Burning Permits in Southeastern United States and Two Satellite‐Derived Products
Authors: Huang Ran , Zhang Xiaoyang , Chan Daniel , Kondragunta Shobha , Russell Armistead G. , Odman M. Talat
Published: April 2018

Prescribed burning (PB) is one of the most prominent sources of PM2.5 (particulate matter with an aerodynamic diameter less than 2.5 μm) in the southeastern United States. The PB emissions estimates may have significant uncertainty because they are based on the burned areas reported to the state agencies when burners apply for burn permits. When no permit records are available, satellite‐derived products could be used as a substitute tool to provide burned area data. In order to evaluate burned areas from satellite‐derived products, we conducted a comparison between PB permit records and two satellite‐derived products, Blended Polar Geo Biomass Burning Emissions Product and Global Fire Emissions Database, in Georgia and Florida. The comparison results indicate that both satellite‐derived products underestimate seriously the burned areas compared to permit record data. They can capture a cluster of fires better than isolated fires but may misinterpret those small fires together as one big fire. Overall, current satellite‐derived products have limitations in estimating the burned areas of small fires and still need improvements.
The Total Drainable Water Storage of the Amazon River Basin: A First Estimate Using GRACE
Authors: Tourian M. J. , Reager J. T. , Sneeuw N.
Published: April 2018

In the Amazon River basin, water stored for months to years in the soils and subsurface provide a persistent resource that regulates local and global climate via teleconnections and provides water to plants in times of little rain. While Gravity Recovery and Climate Experiment (GRACE) satellites have provided the hydrological community with large advances in the understanding of large river basin dynamics and for water resources monitoring applications, the relative storage measurements from GRACE satellites have not yet been utilized for the quantification of total available freshwater on landmasses. In this study, we quantify the total drainable water storage (TDWS) in the Amazon basin by characterizing the relationship between the water storage anomaly of a large catchment and its base flow. Previous studies have shown that these two hydrological parameters behave like a linear time‐independent system over a catchment like the Amazon dominated by fully humid tropical climate. This linear relationship allows us to determine a zero water storage level, at which the storage‐driven discharge becomes zero. We quantify the TDWS of the Amazon basin as 1,766 km3 and estimate an average 2 month residence time for stored waters. An independent analysis over nine major subbasins confirms our estimate for the entire basin. We show that our estimated TDWS values for individual subbasins, varying between 15 and 654 km3, follow two different linear relationships with their mean annual input. Through these relationships we also quantify the storage‐driven portion of the streamflow and the total streamflow for Amazon and its subbasins. Furthermore, we estimate surface water storage variation of the Amazon River system by combining the water level time series from satellite altimetry and surface water extent time series from satellite imagery. Our results show that 61% of total basin water storage variation occurs in the surface water compartment. In addition, we find that 65% of the TDWS is available in its surface water system.
An Empirical Model of Radiation Belt Electron Pitch Angle Distributions Based On Van Allen Probes Measurements
Authors: Zhao H. , Friedel R. H. W. , Chen Y. , Reeves G. D. , Baker D. N. , Li X. , Jaynes A. N. , Kanekal S. G. , Claudepierre S. G. , Fennell J. F. , Blake J. B. , Spence H. E.
Published: April 2018

Based on over 4 years of Van Allen Probes measurements, an empirical model of radiation belt electron equatorial pitch angle distribution (PAD) is constructed. The model, developed by fitting electron PADs with Legendre polynomials, provides the statistical PADs as a function of L‐shell (L = 1–6), magnetic local time, electron energy (~30 keV to 5.2 MeV), and geomagnetic activity (represented by the Dst index) and is also the first empirical PAD model in the inner belt and slot region. For megaelectron volt electrons, model results show more significant day‐night PAD asymmetry of electrons with higher energies and during disturbed times, which is caused by geomagnetic field configuration and flux radial gradient changes. Steeper PADs with higher fluxes around 90° pitch angle and lower fluxes at lower pitch angles for higher‐energy electrons and during active times are also present, which could be due to electromagnetic ion cyclotron wave scattering. For hundreds of kiloelectron volt electrons, cap PADs are generally present in the slot region during quiet times and their energy‐dependent features are consistent with hiss wave scattering, while during active times, cap PADs are less significant especially at outer part of slot region, which could be due to the complex energizing and transport processes. The 90°‐minimum PADs are persistently present in the inner belt and appear in the slot region during active times, and minima at 90° pitch angle are more significant for electrons with higher energies, which could be a critical evidence in identifying the underlying physical processes responsible for the formation of 90°‐minimum PADs.
MHD Stability of Magnetotail Configurations With a Bz Hump
Authors: Birn J. , Merkin V. G. , Sitnov M. I. , Otto A.
Published: April 2018

Using two‐dimensional magnetohydrodynamic (MHD) simulations, we explore the stability of magnetotail configurations that include a local enhancement of Bz (a “Bz hump”). We demonstrate that hump configurations can become unstable within the constraints of ideal MHD, even when strict boundary conditions v = 0 are imposed at all boundaries, consistent with the constraints of the ideal MHD energy principle. Necessary conditions for instability are that the boundaries on the earthward and high‐latitude sides are far enough away, that the background pressure, equivalent to the lobe pressure, is small enough, and that the Bz enhancement or entropy reduction is strong enough. The unstable evolution then bears strong similarity to the evolution of observed and simulated dipolarized flux bundles and dipolarization fronts, presumed or simulated to be the consequence of reconnection. The Bz humps, which for sufficiently low background pressure correspond to entropy depletions, move faster for lower background density and penetrate closer toward Earth when they are initiated closer to Earth or when the background pressure is lower, similar to 3‐D low‐entropy flux tubes, which are affected by ballooning‐/interchange‐type modes.
On the Relationship Between E Region Scintillation and ENSO Observed by FORMOSAT‐3/COSMIC
Authors: Chang Loren C. , Chiu Pei‐Yun , Salinas Cornelius Csar Jude H. , Chen Shih‐Ping , Duann Yi , Liu Jann‐Yenq , Lin Chien‐Hung , Sun Yan‐Yi
Published: April 2018

Global Navigation Satellite System radio occultation signals often show extremely strong levels of scintillation when passing through the ionospheric E region. This is related to sporadic E(Es)—dense layers of metallic ions that can form in the E region, influencing terrestrial and satellite radio propagation. In our report on the 2007–2014 variation of E region S4 amplitude fluctuation indices measured by the FORMOSAT‐3/Constellation Observing System for Meteorology Ionosphere and Climate (COSMIC) satellite constellation, we find that the spatial and temporal variation of the maximum S4 index in the E region is proportionate to the occurrence rate of extreme scintillation and by extension, sporadic E. We also find that the monthly median extreme S4 amplitude fluctuation index in the E region midlatitudes shows a dependence on variation of the El Niño–Southern Oscillation (ENSO) in the troposphere that has not been previously reported. The ENSO‐related variation of the E region median extreme S4 indices varies closely with the tropopause height, with both parameters lagging the Oceanic Niño Index by roughly 1 to 2 months, while also displaying a similar spectrum of periodicities. This similarity is especially strong in the southern midlatitudes. These results indicate that ENSO signatures can be transmitted to Es formation mechanisms, potentially through modulation of vertically propagating atmospheric tides that alter lower thermospheric wind shears. The end result is the modulation of the interannual variation of extreme Es values by ENSO.
Spatial Distribution of Plasma Sheet Entropy Reduction Caused by a Plasma Bubble: Rice Convection Model Simulations
Authors: Wang Chih‐Ping , Gkioulidou Matina , Lyons Larry R. , Wolf Richard A.
Published: April 2018

We conduct simulations based on the Rice Convection Model to evaluate the spatial distributions of total flux tube entropy (S) in the near‐Earth plasma sheet resulting from an earthward moving plasma bubble, and their dependences on two parameters: (1) the bubble's initial magnetic local time location and (2) strength of large‐scale convection. The plasma and magnetic field changes caused by the simulated bubble as it moves earthward qualitatively agree with an observed event. The simulated large‐scale convection is weaker in the premidnight than postmidnight sector because auroral conductance becomes lower toward dusk. The S reduction region resulting from the bubble expands azimuthally at smaller radial distances. The dawnward expansion is due to electric drift, while the duskward expansion is a result of proton's magnetic drift. The S within the bubble is not conserved as the bubble moves because particles of different energies within the bubble drift apart. The radial and azimuthal extents of the S reduction vary with the bubble's initial magnetic local time location. The S reduction region caused by a premidnight bubble extends substantially closer to the Earth and azimuthally wider than does a postmidnight bubble. This difference is mainly due to the weaker convection in the premidnight sector. Comparing with those under strong convection, the bubble plasma is colder under weak convection so that the bubble transport is affected more by electric drift. The S reductions under weak convection are much more confined in their azimuthal width and do not extend as far inward.
Effects of Geomagnetic Storms on the Postsunset Vertical Plasma Drift in the Equatorial Ionosphere
Authors: Huang Chao‐Song
Published: April 2018

It has been observed that geomagnetic storms cause suppression of the occurrence of equatorial spread F or plasma bubbles in the evening sector. In this study, we use ion drift data measured by the Communication/Navigation Outage Forecasting System satellite over 6 years (2008–2014) to derive the dependence of the vertical ion drift at the prereversal enhancement peak on the strength of magnetic storms (the Dst index). It is found that the average vertical ion drift does not change much for Dst in the range between 0 and −60 nT but decreases approximately linearly with the increasing magnitude of Dst for Dst < −60 nT. The net decrease in the average vertical ion drift is ~30 m/s when Dst changes from −60 to −90 nT. This result is derived when the ion drift data during the storm main phase are excluded, so the decrease of the vertical ion drift is caused by storm time disturbance dynamo. A possible interpretation of this phenomenon is that geomagnetic activity must be strong enough (e.g., Dst < −60 nT) so disturbance winds can reach the equatorial region and change plasma drifts there. The storm time disturbance dynamo becomes dominant in the equatorial ionospheric dynamics near the end of the storm main phase, ~4.7 hr after the storm onset. The postsunset vertical ion drift is significantly decreased during the early stage of the storm recovery phase but becomes almost fully recovered when Dst increases close to −60 nT.
Multistage Triaxial Tests on Laboratory‐Formed Methane Hydrate‐Bearing Sediments
Authors: Choi Jeong‐Hoon , Dai Sheng , Lin Jeen‐Shang , Seol Yongkoo
Published: April 2018

A sound understanding of the geomechanical behavior of hydrate‐bearing sediments (HBSs) is essential not only for assessing reservoir and wellbore stability during methane gas production but also for projecting the impact of global warming on the stability of geological settings that contain hydrates. This study experimentally investigated the geomechanical responses of laboratory‐formed methane‐HBS to triaxial shearing under drained conditions. The hydrate pore habit formed in the sediments is noncontact‐cementing, which is different from contact‐cementing or grain‐coating hydrate pore habits formed when the excessive gas method is used. The multistage triaxial test method, which shears a single specimen under different confinements, was employed to examine its applicability in measuring geomechanical properties of the HBS. Conventional single‐stage triaxial tests were also performed to serve as baselines. The results show that both the strength and stiffness of HBS increase with increased hydrate saturation and confining stress. Shear dilatancy increases with increased hydrate saturation and decreased confining stress. The peak strength and peak/postpeak shear dilation measured using the multistage tests are comparable to those using the single‐stage tests. However, the stiffness measured in later stress stages in the multistage tests was enhanced by the stress‐strain history of earlier stages. Therefore, the multistage test offers an efficient way of measuring the strength and volumetric response of the HBS with a much smaller number of specimens than the single‐stage test. This benefits the geomechanical characterization of the HBS, as obtaining the pressure cores is extremely costly and preparing lab samples is usually sophisticated and time consuming.
Genetic validation of bipolar disorder identified by automated phenotyping using electronic health records
Authors: Chen Chia-Yen , Lee Phil H. , Castro Victor M. , Minnier Jessica , Charney Alexander W. , Stahl Eli A. , Ruderfer Douglas M. , Murphy Shawn N. , Gainer Vivian , Cai Tianxi , Jones Ian , Pato Carlos N. , Pato Michele T. , Landén Mikael , Sklar Pamela , Perlis Roy H. , Smoller Jordan W.
Published: April 2018

Bipolar disorder (BD) is a heritable mood disorder characterized by episodes of mania and depression. Although genomewide association studies (GWAS) have successfully identified genetic loci contributing to BD risk, sample size has become a rate-limiting obstacle to genetic discovery. Electronic health records (EHRs) represent a vast but relatively untapped resource for high-throughput phenotyping. As part of the International Cohort Collection for Bipolar Disorder (ICCBD), we previously validated automated EHR-based phenotyping algorithms for BD against in-person diagnostic interviews (Castro et al. Am J Psychiatry 172:363–372, 2015). Here, we establish the genetic validity of these phenotypes by determining their genetic correlation with traditionally ascertained samples. Case and control algorithms were derived from structured and narrative text in the Partners Healthcare system comprising more than 4.6 million patients over 20 years. Genomewide genotype data for 3330 BD cases and 3952 controls of European ancestry were used to estimate SNP-based heritability (h2g) and genetic correlation (rg) between EHR-based phenotype definitions and traditionally ascertained BD cases in GWAS by the ICCBD and Psychiatric Genomics Consortium (PGC) using LD score regression. We evaluated BD cases identified using 4 EHR-based algorithms: an NLP-based algorithm (95-NLP) and three rule-based algorithms using codified EHR with decreasing levels of stringency—“coded-strict”, “coded-broad”, and “coded-broad based on a single clinical encounter” (coded-broad-SV). The analytic sample comprised 862 95-NLP, 1968 coded-strict, 2581 coded-broad, 408 coded-broad-SV BD cases, and 3 952 controls. The estimated h2g were 0.24 (p = 0.015), 0.09 (p = 0.064), 0.13 (p = 0.003), 0.00 (p = 0.591) for 95-NLP, coded-strict, coded-broad and coded-broad-SV BD, respectively. The h2g for all EHR-based cases combined except coded-broad-SV (excluded due to 0 h2g) was 0.12 (p = 0.004). These h2g were lower or similar to the h2g observed by the ICCBD + PGCBD (0.23, p = 3.17E−80, total N = 33,181). However, the rg between ICCBD + PGCBD and the EHR-based cases were high for 95-NLP (0.66, p = 3.69 × 10–5), coded-strict (1.00, p = 2.40 × 10−4), and coded-broad (0.74, p = 8.11 × 10–7). The rg between EHR-based BD definitions ranged from 0.90 to 0.98. These results provide the first genetic validation of automated EHR-based phenotyping for BD and suggest that this approach identifies cases that are highly genetically correlated with those ascertained through conventional methods. High throughput phenotyping using the large data resources available in EHRs represents a viable method for accelerating psychiatric genetic research.