bluuebunny/crossref_metadata_2025_split huggingface dataset:
Assessing Phytoplankton Nutritional Status and Potential Impact of Wet Deposition in Seasonally Oligotrophic Waters of the Mid‐Atlantic Bight
Authors: Sedwick P. N. , Bernhardt P. W. , Mulholland M. R. , Najjar R. G. , Blumen L. M. , Sohst B. M. , Sookhdeo C. , Widner B. 
Published: March 2018

AbstractTo assess phytoplankton nutritional status in seasonally oligotrophic waters of the southern Mid‐Atlantic Bight, and the potential for rain to stimulate primary production in this region during summer, shipboard bioassay experiments were performed using natural seawater and phytoplankton collected north and south of the Gulf Stream. Bioassay treatments comprised iron, nitrate, iron + nitrate, iron + nitrate + phosphate, and rainwater. Phytoplankton growth was inferred from changes in chlorophyll a, inorganic nitrogen, and carbon‐13 uptake, relative to unamended control treatments. Results indicated the greatest growth stimulation by iron + nitrate + phosphate, intermediate growth stimulation by rainwater, modest growth stimulation by nitrate and iron + nitrate, and no growth stimulation by iron. Based on these data and analysis of seawater and atmospheric samples, nitrogen was the proximate limiting nutrient, with a secondary limitation imposed by phosphorus. Our results imply that summer rain events increase new production in these waters by contributing nitrogen and phosphorus, with the availability of the latter setting the upper limit on rain‐stimulated new production.
Snowmelt‐Driven Trade‐Offs Between Early and Late Season Productivity Negatively Impact Forest Carbon Uptake During Drought
Authors: Knowles John F. , Molotch Noah P. , Trujillo Ernesto , Litvak Marcy E. 
Published: March 2018

AbstractFuture projections of declining snowpack and increasing potential evaporation are predicted to advance the timing of snowmelt in mountain ecosystems globally with unknown implications for snowmelt‐driven forest productivity. Accordingly, this study combined satellite‐ and tower‐based observations to investigate the forest productivity response to snowpack and potential evaporation variability between 1989 and 2012 throughout the Southern Rocky Mountain ecoregion, United States. Our results show that early and late season productivity were significantly and inversely related and that future shifts toward earlier and/or reduced snowmelt could decrease snowmelt water use efficiency and thus restrict productivity despite a longer growing season. This was explained by increasing snow aridity, which incorporated evaporative demand and snow water supply, and was modified by summer precipitation to determine total annual productivity. The combination of low snow accumulation and record high potential evaporation in 2012 resulted in the 34 year minimum ecosystem productivity that could be indicative of future conditions.
Regional Climate Sensitivity‐ and Historical‐Based Projections to 2100
Authors: Hébert Raphaël , Lovejoy Shaun 
Published: March 2018

AbstractReliable climate projections at the regional scale are needed in order to evaluate climate change impacts and inform policy. We develop an alternative method for projections based on the transient climate sensitivity (TCS), which relies on a linear relationship between the forced temperature response and the strongly increasing anthropogenic forcing. The TCS is evaluated at the regional scale (5° by 5°), and projections are made accordingly to 2100 using the high and low Representative Concentration Pathways emission scenarios. We find that there are large spatial discrepancies between the regional TCS from 5 historical data sets and 32 global climate model (GCM) historical runs and furthermore that the global mean GCM TCS is about 15% too high. Given that the GCM Representative Concentration Pathway scenario runs are mostly linear with respect to their (inadequate) TCS, we conclude that historical methods of regional projection are better suited given that they are directly calibrated on the real world (historical) climate.
Volcanic Thunder From Explosive Eruptions at Bogoslof Volcano, Alaska
Authors: Haney Matthew M. , Van Eaton Alexa R. , Lyons John J. , Kramer Rebecca L. , Fee David , Iezzi Alexandra M. 
Published: March 2018

AbstractLightning often occurs during ash‐producing eruptive activity, and its detection is now being used in volcano monitoring for rapid alerts. We report on infrasonic and sonic recordings of the related, but previously undocumented, phenomenon of volcanic thunder. We observe volcanic thunder during the waning stages of two explosive eruptions at Bogoslof volcano, Alaska, on a microphone array located 60 km away. Thunder signals arrive from a different direction than coeruptive infrasound generated at the vent following an eruption on 10 June 2017, consistent with locations from lightning networks. For the 8 March 2017 eruption, arrival times and amplitudes of high‐frequency thunder signals correlate well with the timing and strength of lightning detections. In both cases, the thunder is associated with lightning that continues after significant eruptive activity has ended. Infrasonic and sonic observations of volcanic thunder offer a new avenue for studying electrification processes in volcanic plumes.
The 4D‐var Estimation of North Korean Rocket Exhaust Emissions Into the Ionosphere
Authors: Ssessanga Nicholas , Kim Yong Ha , Choi Byungyu , Chung Jong‐Kyun 
Published: March 2018

AbstractWe have developed a four‐dimensional variation data assimilation technique (4D‐var) and utilized it to reconstruct three‐dimensional images of the ionospheric hole created during Kwangmyongsong‐4 rocket launch. Kwangmyongsong‐4 was launched southward from North Korea Sohae space center (124.7°E, 39.6°N) at 00:30 UT on 7 February 2016. The data assimilated were Global Positioning System total electron content from the South Korean Global Positioning System‐receiver network. Due to lack of publicized information about Kwangmyongsong‐4, the rocket was assumed to inherit its technology from previous launches (Taepodong‐2). The created ionospheric hole was assumed to be made by neutral molecules, water (H2O) and hydrogen (H2), deposited in exhaust plumes. The dispersion model was developed based on advection and diffusion equation, and a simple asymmetric diffusion model assumed. From the analysis, using the adjoint technique, we estimated an ionospheric hole with the largest depletion existing around 6–7 min after launch and gradually recovering within ~30 min. These results are in agreement with temporal total electron content analyses of the same event from previous studies. Furthermore, Kwangmyongsong‐4 second stage exhaust emissions were estimated as 1.9 × 1026 s−1 of which 40% was H2 and the rest H2O.
Source Energy Spectrum of the 17 May 2012 GLE
Authors: Pérez‐Peraza Jorge , Márquez‐Adame Juan C. , Miroshnichenko Leonty , Velasco‐Herrera Victor 
Published: March 2018

AbstractAmong the several GLEs (ground level enhancements) that have presumptuously occurred in the period 2012–2015, the 17 May 2012 is that which is more widely accepted to be a GLE, in view of the high number of high‐latitude neutron monitor stations that have registered it. In spite of the small amplitude, it was more prominent of the predicted GLE's of the present decade (Pérez‐Peraza & Juárez‐Zuñiga, 2015, https://doi.org/10.1088/0004-637X/803/1/27). However, the lack of latitude effect makes it difficult to study the characteristics of this event in the high‐energy extreme of the spectrum. Nevertheless, several outstanding works have been able to derive observational spectra at the top of the Earth atmosphere for this peculiar GLE. Some of these works find that the flow of protons is characterized by two components. Quite a great number of works have been published in relation with observational features obtained with different instrumentation, but the source phenomena, regarding the generation processes and source physical parameters, have not been scrutinized. The main goal of this work is to look at such aspects by means of the confrontation of the different approaches of the observational spectra with our analytical theoretical spectra based on stochastic acceleration and electric field acceleration from reconnection processes. In this way, we derive a set of parameters which characterize the sources of these two GLE components, leading us to propose possible scenarios for the generation of particles in this particular GLE event.
Nearshore Flow Patterns in a Complex, Tidally Driven System in Summer: Part I. Model Validation and Circulation
Authors: Conlon LeAnn M. , Xue Huijie , Morello Scott L. , Yund Philip O. 
Published: March 2018

AbstractCirculation models are often validated with respect to temporal rather than spatial variability, yet spatial variability is often very important for many questions subsequently addressed with the models. We validated a high‐resolution nearshore circulation model using both temporal and spatial data sets and used the model to investigate small‐scale nearshore flow patterns along the complex eastern Maine coast. The Finite Volume Coastal Ocean Model (FVCOM) was run from April to September 2014. In the temporal comparison, the model captured variation in sea level (model skill of 0.98) and the seasonal warming trend (model skill of 0.94). Temperature fluctuations were largely due to horizontal temperature divergence, implying the sensitivity to the forcing at the open boundary. To evaluate spatial variation in performance, we calculated model skill for current profile transects, which ranged from 0.99 to 0.60 in the east/west direction and 0.99 to 0.62 in the north/south direction. The combination of temporal and spatial validation improved confidence in the model's ability to recreate realistic flow patterns. Residual currents across the entrance to the bays showed flows that move out of the bays via the upper western side and into the bays in the lower water column before surfacing on the eastern side. As the coastal current passed by headlands and islands, eddies formed in the wake of several of them. Residual flows varied among months and location along the shelf. This model is a valuable first step in understanding how particulates move through such a complex and variable nearshore region.
Transformation of Deep Water Masses Along Lagrangian Upwelling Pathways in the Southern Ocean
Authors: Tamsitt V. , Abernathey R. P. , Mazloff M. R. , Wang J. , Talley L. D. 
Published: March 2018

AbstractUpwelling of northern deep waters in the Southern Ocean is fundamentally important for the closure of the global meridional overturning circulation and delivers carbon and nutrient‐rich deep waters to the sea surface. We quantify water mass transformation along upwelling pathways originating in the Atlantic, Indian, and Pacific and ending at the surface of the Southern Ocean using Lagrangian trajectories in an eddy‐permitting ocean state estimate. Recent related work shows that upwelling in the interior below about 400 m depth is localized at hot spots associated with major topographic features in the path of the Antarctic Circumpolar Current, while upwelling through the surface layer is more broadly distributed. In the ocean interior upwelling is largely isopycnal; Atlantic and to a lesser extent Indian Deep Waters cool and freshen while Pacific deep waters are more stable, leading to a homogenization of water mass properties. As upwelling water approaches the mixed layer, there is net strong transformation toward lighter densities due to mixing of freshwater, but there is a divergence in the density distribution as Upper Circumpolar Deep Water tends become lighter and dense Lower Circumpolar Deep Water tends to become denser. The spatial distribution of transformation shows more rapid transformation at eddy hot spots associated with major topography where density gradients are enhanced; however, the majority of cumulative density change along trajectories is achieved by background mixing. We compare the Lagrangian analysis to diagnosed Eulerian water mass transformation to attribute the mechanisms leading to the observed transformation.
Influence of Barrier Wind Forcing on Heat Delivery Toward the Greenland Ice Sheet
Authors: Fraser Neil J. , Inall Mark E. 
Published: March 2018

AbstractA high‐resolution numerical hydrodynamic model of Kangerdlugssuaq Fjord and the adjacent southeast Greenland shelf region was constructed in order to investigate the dynamics of fjord‐shelf exchange. Recent studies have suggested that rapid exchange flows, driven by along‐shelf barrier wind events, are the dominant agent of exchange between fjord and shelf. These events are prone to occur during the winter, when freshwater forcing is minimal and observations of the fjord interior are scarce. Subglacial freshwater discharge was held at zero, so that any buoyancy‐driven overturning circulation was driven by melting alone. The model described a geostrophically balanced background flow transporting water masses between the fjord mouth and the glacier terminus, indicating that rotational effects are of order‐one importance. Barrier wind events were found to trigger coastally trapped internal wave activity within fjord, temporarily enhancing exchange and vertical mixing, and causing warm water to oscillate in the along‐fjord direction. These internal waves were also found to enhance the background flow via Stokes' drift. Heat delivery through the fjord mouth was smaller than that recorded in summer observations, however the system is more effective at delivering this heat to the head of the fjord. There exists the potential for wintertime melting at the ice‐ocean interface to be significant to the same order as summertime melting.
Observation‐Driven Estimation of the Spatial Variability of 20th Century Sea Level Rise
Authors: Hamlington B. D. , Burgos A. , Thompson P. R. , Landerer F. W. , Piecuch C. G. , Adhikari S. , Caron L. , Reager J. T. , Ivins E. R. 
Published: March 2018

AbstractOver the past two decades, sea level measurements made by satellites have given clear indications of both global and regional sea level rise. Numerous studies have sought to leverage the modern satellite record and available historic sea level data provided by tide gauges to estimate past sea level rise, leading to several estimates for the 20th century trend in global mean sea level in the range between 1 and 2 mm/yr. On regional scales, few attempts have been made to estimate trends over the same time period. This is due largely to the inhomogeneity and quality of the tide gauge network through the 20th century, which render commonly used reconstruction techniques inadequate. Here, a new approach is adopted, integrating data from a select set of tide gauges with prior estimates of spatial structure based on historical sea level forcing information from the major contributing processes over the past century. The resulting map of 20th century regional sea level rise is optimized to agree with the tide gauge‐measured trends, and provides an indication of the likely contributions of different sources to regional patterns. Of equal importance, this study demonstrates the sensitivities of this regional trend map to current knowledge and uncertainty of the contributing processes.
Investigation of Lightning Flash Locations in Isolated Convection Using LMA Observations
Authors: Fuchs Brody R. , Rutledge Steven A. 
Published: March 2018

AbstractUsing Lightning Mapping Arrays (LMAs), lightning flash locations in three dimensions have been investigated using multiple methods. Approximately 500,000 flashes were analyzed to reveal the variability of lightning initiation and propagation within convective storms. These flashes were produced by over 4,000 isolated convective storms during one warm season across diverse weather regimes in northern Alabama, Washington, D.C., central Oklahoma, and northeastern Colorado. Lightning locations are analyzed within the context of radar reflectivities and examined for vertical variability. Results show that storms in Colorado preferentially produced flashes at lower altitudes and in regions of higher reflectivity compared to the other regions. The regional differences in flash altitudes are largely attributed to the prevalence of anomalous polarity storms (middle‐ or low‐level dominant positive charge) in Colorado, as anomalous storms produced a majority of flashes at lower altitudes compared to storms with normal polarity charge structures (middle‐level negative charge). Conversely, anomalous storms are exceedingly rare in the other regions of study. The differences in flash altitudes are coincident with discrepancies between annual average densities estimated by satellite observations and LMA. Specifically, large differences in annual average flash density estimates exist in northeastern Colorado, which are not present in the other regions, suggesting that the lower altitude flashes in Colorado may be more difficult to detect by satellites.
Intralake Heterogeneity of Thermal Responses to Climate Change: A Study of Large Northern Hemisphere Lakes
Authors: Woolway R. Iestyn , Merchant Christopher J. 
Published: March 2018

AbstractLake surface water temperature (LSWT) measurements from various sources illustrate that lakes are warming in response to climate change. Most previous studies of geographical distributions of lake warming have tended to utilize data with limited spatial resolution of LSWTs, including single‐point time series. Spatially resolved LSWT time series are now available from satellite observations, and some studies have investigated previously the intralake warming patterns in specific lakes (e.g., North American Great Lakes). However, across‐lake comparisons of intralake warming differences have not yet been investigated at a large, across‐continental scale, thus limiting our understanding of how intralake warming patterns differ more broadly. In this study, we analyze up to 20 years of satellite data from 19 lakes situated across the Northern Hemisphere, to investigate how LSWT changes vary across different lake surfaces. We find considerable intralake variability in warming trends across many lakes. The deepest areas of large lakes are characterized by a later onset of thermal stratification, a shorter stratified warming season and exhibit longer correlation timescales of LSWT anomalies. We show that deep areas of large lakes across the Northern Hemisphere as a result tend to display higher rates of warming of summer LSWT, arising from a greater temporal persistence in deep areas of the temperature anomalies associated with an earlier onset of thermal stratification. Utilization of single‐point LSWT trends to represent changes in large lakes therefore suppresses important aspects of lake responses to climate change, whereas spatially resolved LSWT measurements can be exploited to provide more comprehensive understanding.
Stable Isotopes of Precipitation During Tropical Sumatra Squalls in Singapore
Authors: He Shaoneng , Goodkin Nathalie F. , Kurita Naoyuki , Wang Xianfeng , Rubin Charles Martin 
Published: March 2018

AbstractSumatra Squalls, organized bands of thunderstorms, are the dominant mesoscale convective systems during the intermonsoon and southwest monsoon seasons in Singapore. To understand how they affect precipitation isotopes, we monitored the δ value of precipitation daily and continuously (every second and integrated over 30 s) during all squalls in 2015. We found that precipitation δ18O values mainly exhibit a “V”‐shape pattern and less commonly a “W”‐shape pattern. Variation in δ18O values during a single event is about 1 to 6‰ with the lowest values mostly observed in the stratiform zone, which agrees with previous observations and modeling simulations. Reevaporation can significantly affect δ values, especially in the last stage of the stratiform zone. Daily precipitation is characterized by periodic negative shifts in δ value, largely associated with the squalls rather than moisture source change. The shifts can be more than 10‰, larger than intraevent variation. Initial δ18O values of events are highly variable, and those with the lowest values also have the lowest initial values. Therefore, past convective activities in the upwind area can significantly affect the δ18O, and convection at the sampling site has limited contribution to isotopic variability. A significant correlation between precipitation δ18O value and regional outgoing longwave radiation and rainfall in the Asian monsoon region and western Pacific suggests that regional organized convection probably drives stable isotopic compositions of precipitation. A drop in the frequency of the squalls in 2015 is related to weak organized convection in the region caused by El Niño.
Effects of Cryospheric Change on Alpine Hydrology: Combining a Model With Observations in the Upper Reaches of the Hei River, China
Authors: Chen R. , Wang G. , Yang Y. , Liu J. , Han C. , Song Y. , Liu Z. , Kang E. 
Published: March 2018

AbstractCryospheric changes have great effects on alpine hydrology, but these effects are still unclear owing to rare observations and suitable models in the western cold regions of China. Based on long‐term field observations in the western cold regions of China, a cryospheric basin hydrological model was proposed to evaluate the cryospheric effects on streamflow in the upper Hei River basin (UHR), and the relationship between the cryosphere and streamflow was further discussed with measured data. The Norwegian Earth System Model outputs were chosen to project future streamflow under scenarios Representative Concentration Pathways (RCP)2.6, RCP4.5, and RCP8.5. The cryospheric basin hydrological model results were well validated by the measured precipitation, streamflow, evapotranspiration, soil temperature, glacier and snow cover area, and the water balance of land cover in the UHR. The moraine‐talus region contributed most of the runoff (60%), even though it made up only about 20% of the area. On average, glacier and snow cover, respectively, contributed 3.5% and 25.4% of the fresh water to the streamflow in the UHR between 1960 and 2013. Because of the increased air temperature (2.9°C/54a) and precipitation (69.2 mm/54a) over the past 54 years, glacial and snowmelt runoff increased by 9.8% and 12.1%, respectively. The increase in air temperature brought forward the snowmelt flood peak and increased the winter flow due to permafrost degradation. Glaciers may disappear in the near future because of their small size, but snowmelt would increase due to increases in snowfall in the higher mountainous areas, and the basin runoff would increase slightly in the future.