bluuebunny/crossref_metadata_2025_split huggingface dataset:
Integrated Orbit Determination of FengYun‐3C, BDS, and GPS Satellites
Authors: Li Xingxing , Zhang Keke , Zhang Qian , Zhang Wei , Yuan Yongqiang , Li Xin 
Published: August 2018

AbstractAiming at weather forecast and global climate research, the satellite FengYun‐3C (FY‐3C), as the new generation of China's weather satellites, was launched in 2013. It carries the Global Navigation Satellite Systems Occultation Sounder instrument, a BDS + GPS receiver, to fulfill the demand of orbit determination and occultation. In this contribution, we develop an integrated orbit determination of FY‐3C, BDS, and GPS satellites by joint processing of onboard FY‐3C and ground data during 2013–2017. Four processing schemes, BDS, GPS, BDS + GPS, and BDS (without Geostationary Earth Orbit [GEO]) + GPS, are designed to investigate the capability of BDS for the integrated precise orbit determination and the benefit of BDS and GPS fusion. Regional and global networks are also employed to analyze the influence of station distribution on the orbit determination. The results show that with a regional network, both BDS and GPS orbits present a significant improvement after including FY‐3C data. For the BDS + GPS one‐step solution, GPS orbits are improved by 20% compared with the two‐step solution, while the improvement can reach 42%, 27%, and 27% for BDS GEO, Inclined Geosynchronous Satellite Orbit, and Medium Earth Orbit, respectively. The precision improvement of FY‐3C is respectively 26%, 44%, and 30% in along, cross, and radial components. For a global network, the orbit precision of the BDS + GPS solution is improved by 4% for GPS and 5%, 16%, and 19% for BDS GEO, Inclined Geosynchronous Satellite Orbit, and Medium Earth Orbit, respectively. For FY‐3C, the orbit improvement can reach 7%. The validation with satellite laser ranging also demonstrates the benefit of the integrated orbit determination. Such a high‐quality orbit will potentially benefit meteorological studies and applications.
Lithospheric Structure of Greenland From Ambient Noise and Earthquake Surface Wave Tomography
Authors: Pourpoint Maeva , Anandakrishnan Sridhar , Ammon Charles J. , Alley Richard B. 
Published: August 2018

AbstractWe present a high‐resolution shear wave velocity model of Greenland's lithosphere from regional and teleseismic Rayleigh waves recorded by the Greenland Ice Sheet Monitoring Network supplemented with observations from several temporary seismic deployments. To construct Rayleigh wave group velocity maps, we integrated signals from regional and teleseismic earthquakes with several years of ambient seismic noise and used the dispersion to constrain crustal and upper‐mantle seismic shear wave velocity structure. Specifically, we used a Markov Chain Monte Carlo technique to estimate 3‐D shear wave velocities beneath Greenland to a depth of 200 km. Our model reveals four prominent anomalies: a deep high‐velocity feature extending from southwestern to northwestern Greenland that may be the signature of a thick cratonic keel, a corridor of relatively low upper‐mantle velocity across central Greenland that could be associated with lithospheric modification from the passage of the Iceland plume beneath Greenland or interpreted as a tectonic boundary between cratonic blocks, an upper‐crustal southwest‐northeast trending boundary separating Greenland into two regions of contrasting tectonic and crustal properties, and a midcrustal low‐velocity anomaly beneath northeastern Greenland. The nature of this midcrustal anomaly is of particular interest given that it underlies the onset of the Northeast Greenland Ice Stream and raises interesting questions regarding how deeper processes may impact the ice stream dynamics and the evolution of the Greenland Ice Sheet.
Implications of Eddy Cancellation for Nutrient Distribution Within Subtropical Gyres
Authors: Doddridge Edward W. , Marshall David P. 
Published: August 2018

AbstractThe role of mesoscale eddies within the nutrient budget of subtropical gyres remains poorly understood and poorly constrained. We explore a new mechanism by which mesoscale eddies may contribute to these nutrient budgets, namely eddy cancellation. Eddy cancellation describes the rectified effect of mesoscale eddies acting to oppose the Eulerian‐mean Ekman pumping. We present an idealized axisymmetric two‐layer model of a nutrient in a wind‐driven gyre and explore the sensitivity of this model to variations in its parameter values. We find that the residual Ekman pumping velocity has a substantial impact on nutrient concentration, as does mode water thickness. These results suggest the response to both residual Ekman pumping and mode water thickness is nonmonotonic: for small values of these parameters the nutrient concentration decreases as the parameter increases. However, beyond a critical value, further increases in Ekman pumping or mode water thickness increase nutrient concentration throughout our highly idealized model. A thin mode water layer promotes vertical diffusion of nutrients from the abyss, while a thicker mode water layer increases productivity by reducing the parametrized particulate flux through the thermocline. The impact of mode water thickness is modulated by the residual Ekman pumping velocity: strong Ekman pumping suppresses the influence of mode water thickness on nutrient concentrations. We use satellite and in situ measurements to assess the influence of mode water thickness on primary productivity and find a statistically significant relationship; thicker mode water correlates with higher productivity. This result is consistent with a small residual Ekman pumping velocity.
Drivers of Ice Algal Bloom Variability Between 1980 and 2015 in the Chukchi Sea
Authors: Selz Virginia , Saenz Benjamin T. , van Dijken Gert L. , Arrigo Kevin R. 
Published: August 2018

AbstractSea ice provides an important habitat for the ice algae that fuel upper trophic levels in early spring, prior to phytoplankton bloom development. In the Chukchi Sea, the ice environment has experienced large‐scale changes in snow cover, ice thickness and extent, and timing of ice advance and retreat. Using a 1‐D coupled physical‐biological ice‐ecosystem model and observed distributions of sea ice, we investigated how changing ice conditions may have impacted ice algal bloom dynamics for the central Chukchi Sea between 1980 and 2015. Model results suggest that over this 35‐year time period, annual ice algal net primary production (NPP) decreased by 22%. Modeled snow and ice melt, as well as satellite‐derived ice retreat, occurred progressively earlier in the spring from 1980 to 2015, even though modeled ice and snow thicknesses showed no temporal trends. Over time, ice algal blooms ended earlier in spring due to earlier onset of ice melt and ice retreat. Results suggest that the length of the ice season sets the upper bound on annual ice algal NPP, with late melt years corresponding to highest NPP. Linear regression results suggest that within early versus late melt year groupings, snow plays a secondary, yet important role in determining annual ice algal NPP. As sea ice thins and melts earlier in spring, future snow dynamics will be an important factor determining the onset of the ice algal bloom and thus the duration of the bloom in an early melt, shortened ice season scenario.
Tracing the Three Atlantic Branches Entering the Arctic Ocean With 129I and 236U
Authors: Casacuberta N. , Christl M. , Vockenhuber C. , Wefing A.‐M. , Wacker L. , Masqué P. , Synal H.‐A. , Rutgers van der Loeff M. 
Published: August 2018

AbstractThis study presents the data on 129I and 236U concentrations in seawater samples and sea ice cores obtained during two expeditions to the Arctic Ocean that took place onboard R/V Polarstern (PS94) and R/V Lance (N‐ICE2015) in summer 2015. Carbon‐14 was also measured in the deep water samples from the Nansen, Amundsen, and Makarov Basins. The main goal was to investigate the distribution of 129I and 236U in a transect from the Norwegian Coast to the Makarov Basin to fully exploit the potential of combining 129I and 236U as a dual tracer to track Atlantic waters throughout the Arctic Ocean. The use of the 129I/236U and 236U/238U atom ratios allowed identifying a third Atlantic branch that enters the Arctic Ocean (the Arctic Shelf Break Branch) following the Norwegian Coastal Current that carries a larger proportion of the European reprocessing plants signal compared to Fram Strait Branch Water and Barents Sea Branch Water. The combination of 129I and 236U also allowed quantifying the different proportions of the La Hague stream, the Scottish stream, and Atlantic waters forming the three Atlantic branches of the Arctic Ocean Boundary Current. The results show that the 129I/236U atom ratio can now be used to identify the different Atlantic branches entering the Arctic Ocean. New input functions for 129I, 236U, and 129I/236U have also been described for each branch, which can be further used for calculation of transit time distributions of Atlantic waters.
A Comparison of Cloud Microphysical Properties Derived From MODIS and CALIPSO With In Situ Measurements Over the Wintertime Southern Ocean
Authors: Ahn Eunmi , Huang Yi , Siems Steven T. , Manton Michael J. 
Published: August 2018

AbstractIn situ observations of cloud effective radius (reff), droplet number concentration (Nd), and thermodynamic phase from 11 wintertime flights over the Southern Ocean (43–45°S, 145–148°E) are compared to products from MODerate‐resolution Imaging Spectroradiometer (MODIS) and Cloud‐Aerosol Lidar with Orthogonal Polarization. The in situ observations were in close alignment with A‐train overpasses for a 30‐min window. For open mesoscale cellular convection, which was predominantly observed, clouds were commonly found to be intermittently drizzling, patchy, and mixed phase. Compared to the in situ observations of the cloud thermodynamic phase, the Cloud‐Aerosol Lidar with Orthogonal Polarization and MODIS cloud phase optical property products consistently underestimated the occurrence of mixed‐phase clouds, whereas the MODIS infrared‐based phase product showed a better qualitative agreement despite a frequent classification of uncertainty. The MODIS reff_2.1 overestimated the in situ reff for nondrizzling clouds (by ~13 μm on average) and, to a lesser extent, for lightly drizzling cases. Conversely, MODIS reff_2.1 underestimated the in situ reff for heavily drizzling cases by ~10 μm on average. The overestimation of reff is much greater than that for the stratocumulus over the Southeast Pacific shown in other studies. An examination on subpixel heterogeneity, droplet size variability, a bimodal distribution, and solar zenith angle suggests that all of these factors have measurable impacts on the MODIS reff bias. The MODIS Nd is largely consistent with the in situ observations. However, the Nd of the two high Nd cases (closed mesoscale cellular convection) are highly underestimated. An error analysis suggests that the Nd biases are likely a result of a compensating error effect.
Investigating Sources of Mercury's Crustal Magnetic Field: Further Mapping of MESSENGER Magnetometer Data
Authors: Hood L. L. , Oliveira J. S. , Galluzzi V. , Rothery D. A. 
Published: August 2018

AbstractOne hundred six low‐altitude passes of magnetometer data from the last 2 months of the MErcury Surface, Space ENvironment, GEochemistry, and Ranging mission have been applied to produce a map of the crustal magnetic field at a constant altitude of 40 km covering latitudes of 35–75∘ N and longitudes of 270–90∘ E. Some anomalies correlate significantly with impact basins/craters (e.g., Rustaveli and Vyasa), while other basins/craters have no obvious anomalies. A possible interpretation that is consistent with lunar evidence is that some impactors delivered more ferromagnetic Fe–Ni metal to the interior subsurfaces and ejecta fields of the craters/basins that they produced. The amount of metallic iron that could plausibly be delivered is limited by the diameter and mass of an impactor that would yield a crater with observed diameters (e.g., 200 km for Rustaveli). This in turn limits the maximum amplitude of anomalies that could be induced by impactor‐added iron in the present‐day Mercury global field to relatively low values. It is therefore concluded that if impactor‐added iron is the source of the observed crater‐associated anomalies, then they must be almost entirely a consequence of ancient remanent magnetization. A broad magnetic anomaly occurs over the northern rise, a topographically high region with an associated strong free air gravity anomaly. A possible interpretation of the latter anomaly is that an early major impact preconditioned the region for a later mantle uplift event.
Episodic and Declining Fluvial Processes in Southwest Melas Chasma, Valles Marineris, Mars
Authors: Davis J. M. , Grindrod P. M. , Fawdon P. , Williams R. M. E. , Gupta S. , Balme M. 
Published: August 2018

AbstractThere is abundant evidence for aqueous processes on Noachian terrains across Mars; however, key questions remain about whether these processes continued into the Hesperian as the martian climate became less temperate. One region with an extensive Hesperian sedimentary record is Valles Marineris. We use high‐resolution image and topographic data sets to investigate the fluvial systems in the southwest Melas basin, Valles Marineris, Mars. Fluvial landforms in the basin exist across a wide area, and some are preserved as inverted channels. The stratigraphy of the basin is complex: Fluvial landforms are preserved as planview geomorphic features and are also interbedded with layered deposits in the basin. The fluvial morphologies are consistent with formation by precipitation‐driven runoff. Fluvial processes in the basin were episodic, suggesting multiple wet and dry periods. During dry periods, mantling material accumulated, and significant volumes of sediment were eroded, inverting fluvial channels. During wet periods, inverted channels and mantling material infilling valleys were incised by further fluvial erosion. These trends for episodic fluvial processes are similarly reflected in the central depression of the southwest Melas basin, previously described as a paleolake. Ultimately, fluvial processes in the basin gradually shut down, becoming geographically restricted, and then ceased entirely. We show that branching valley networks are also present on the plateaus above Melas and Ius Chasma, which converge on the heads of tributary canyons. These suggest that precipitation‐driven runoff processes also extended onto the plateaus of Valles Marineris.
Hydrologic and Edaphic Controls on Soil Carbon Emission in Dongting Lake Floodplain, China
Authors: Deng Zhengmiao , Li Youzhi , Xie Yonghong , Peng Changhui , Chen Xinsheng , Li Feng , Ren Yijie , Pan Baihan , Zhang Chengyi 
Published: August 2018

AbstractWetlands play a critical role in mitigating carbon emission. However, little is known about soil carbon emission and their environmental controls from inland floodplain wetlands. This study aimed to determine the effects of hydrologic and edaphic controllers (water table depth [WTD], soil temperature [Ts], and soil water content [SWC]) on soil C emission in Dongting Lake wetland, China. One‐year emissions were measured in Carex meadow and mudflat using static chambers during 2013 to 2014, including nonflooded season (NFs) and flooded season (Fs). The results showed that soil C emission in the Carex meadow and mudflat was 307.8 and 264.3 g C·m−2·year−1, respectively, and 50–66% of soil C were emitted during NFs. Compared with NFs, CO2 emission was significantly decreased by 57% but CH4 emission was significantly increased by 38 times during Fs in the Carex meadow. Stepwise regression combined with structural equation model analysis showed that CO2 and CH4 flux were mainly influenced by Ts during NFs, and they were controlled by water temperature (Tw) during Fs. During NFs, CO2 flux increased with increasing Ts and SWC but decreased significantly when SWC was over 66% and 52% in the Carex meadow and mudflat, respectively. CH4 flux showed an emission pulse at SWC and Ts of 65% and 17.2 °C, respectively. These results indicate that flooding significantly inhibited soil CO2 emission but stimulated CH4 emission. The continuous decrease of flooding days caused by anthropogenic disturbances may induce soil C loss in Dongting Lake wetlands.
Partitioning Eddy Covariance Water Flux Components Using Physiological and Micrometeorological Approaches
Authors: Perez‐Priego Oscar , Katul Gabriel , Reichstein Markus , El‐Madany Tarek S. , Ahrens Bernhard , Carrara Arnaud , Scanlon Todd M. , Migliavacca Mirco 
Published: August 2018

AbstractEddy covariance (EC) provides ecosystem‐scale estimates of photosynthesis (Ph) and evapotranspiration (ET; the sum of plant transpiration [T] and evaporation [Es]). Separating ET into its components is becoming necessary for linking plant‐water use strategies to environmental variability. Based on optimality principles, a data‐model based approach for partitioning ET was proposed and independently tested. Short‐term responses of canopy‐scale internal leaf‐to‐ambient CO2 (χ) were predicted based on a big‐leaf representation of the canopy accounting for the influence of boundary‐layer conductance. This representation allowed investigating stomatal behavior in accordance with the Ph estimates. With the objective of minimizing the carbon cost of transpiration, a novel optimization approach was implemented to develop solutions for an optimal stomatal conductance model as the basis to derive T. The Es was then calculated as a residual between the observed ET and modeled T. The proposed method was applied to long‐term EC measurements collected above a Mediterranean tree‐grass ecosystem. Estimated Es agreed with independent lysimeter measurements (r = 0.69). They also agreed with other partitioning methods derived from similarity theory and conditional sampling applied to turbulence measurements. These similarity schemes appeared to be sensitive to different χ parameterization. Measured Es was underestimated by 30% when χ was assumed constant (= 0.8). Diel and seasonal χ patterns were characterized in response to soil dryness. A surprising result was a large Es/ET throughout the seasons. The robustness of the results provides a new perspective on EC ET partitioning, which can be utilized across a wide range of climates and biomes.
Multiyear Trends in Solute Concentrations and Fluxes From a Suburban Watershed: Evaluating Effects of 100‐Year Flood Events
Authors: Coble Ashley A. , Wymore Adam S. , Shattuck Michelle D. , Potter Jody D. , McDowell William H. 
Published: August 2018

AbstractAnthropogenic activities have increased solute concentrations and fluxes in rivers globally. Increases in salt, dissolved organic carbon, and inorganic nutrients have been attributed to changes in atmospheric deposition, road salt and fertilizer application, and urbanization. Extremely large flood events, which are increasing in frequency and duration, could also alter river chemistry by flushing various solute reservoirs within watersheds and effectively “resetting” the linkages between land and river. We evaluated changes in concentrations and fluxes of inorganic nutrients, dissolved organic matter, and salts and major ions across 12 to 15 years in a rural‐suburban watershed in New Hampshire, USA. During this period, the human imprint on the landscape (impervious surfaces and population density) increased, but two 100‐year flood events also occurred. We found that concentrations and fluxes of chloride and potassium, fluxes of all other major ions, and concentrations of dissolved organic carbon declined over time, but concentrations and fluxes of inorganic nutrients and dissolved organic nitrogen were unchanged. The minor declines in concentrations were of similar magnitude to declines previously observed in other watersheds that did not experience extreme flood events. We observed a shift in nitrate (NO3−) concentration‐discharge behavior from enrichment in the years prior to and including the floods to chemostasis after the floods, but for both time periods NO3− concentrations were weakly related to discharge. Our results suggest a limited role of extreme events in the biogeochemistry of urbanizing watersheds and emphasize the importance of long‐term records and multiple analytical approaches to understand the dynamics of complex watersheds.
Incorporation of Microbial Functional Traits in Biogeochemistry Models Provides Better Estimations of Benthic Denitrification and Anammox Rates in Coastal Oceans
Authors: Zhang Xiaoli , Zhang Qianqian , Yang Anjing , Hou Lijun , Zheng Yanling , Zhai Weidong , Gong Jun 
Published: August 2018

AbstractMarine benthic nitrogen (N) cycling may vary widely across space and seasons; it is thus needed to make high‐resolution estimations of these important ecosystem processes with a reasonable number of variables. In this study, we determined the benthic denitrification and anammox potentials in two basins, the Bohai Sea and the North Yellow Sea of China in May and November, and evaluated models in predicting these functions with environmental factors and/or microbial gene‐based functional traits. We found that denitrification generally dominated the N loss (54–98%), and that the denitrification rate varied greatly between basins and seasons. The anammox rate was generally higher in the Bohai Sea than in the North Yellow Sea in both seasons, and it made a greater contribution in November (22%) than in May (16%). Among the measured environmental factors, chlorophyll a in bottom waters and sedimentary organic carbon content were the most influential for predicting denitrification and anammox rates, respectively. On the other hand, the alpha diversities and gene abundances of involved bacteria were poorly correlated with the function potentials, indicating that these functional traits could not well explain the functions alone. Upon the incorporation of two gene copy number ratios [nosZ/(nirS + nirK) and nirK/bacterial 16S rRNA genes] into the environmental factor‐parameterized models, however, we found that the predictive powers of the regression models for total N loss, denitrification and anammox rates, and contributions of anammox increased substantially, indicating that taking microbial functional traits into account could make estimations of these N‐cycling functions in coastal ecosystems more accurate.
Space Weather on the Surface of Mars: Impact of the September 2017 Events
Authors: Hassler D. M. , Zeitlin C. , Ehresmann B. , Wimmer‐Schweingruber R. F. , Guo J. , Matthiä D. , Rafkin S. , Berger T. , Reitz G. 
Published: August 2018

AbstractAlthough solar activity is declining as the Sun approaches solar minimum, a series of large solar storms occurred in September 2017 that impacted both Earth and Mars. This was the largest event seen on the surface of Mars by the Radiation Assessment Detector on the Mars Science Laboratory Curiosity rover since landing in 2012 and was also observed as Ground Level Enhancement 72 on Earth, making it the first event observed to produce a Ground Level Enhancement on two planets at the same time. We present Radiation Assessment Detector observations of the surface radiation environment since 2012 and discuss the impact of the September 2017 events on this environment and its implications for human exploration and for mitigating the risk of space radiation and space weather events for future manned missions to Mars.