bluuebunny/crossref_metadata_2025_split huggingface dataset:
An Improved Second‐Moment Closure Model for Langmuir Turbulence Conditions: Model Derivation and Validation
Authors: Yu W. , Song J. B. , Cao A. Z. , Yin B. S. , Guan S. D. 
Published: October 2018

AbstractIn this study, an improved second‐moment closure model, the so‐called k‐ω model, which takes into consideration the Langmuir turbulent effect in the transport equations of turbulent kinetic energy and turbulent frequency, was developed. The Langmuir turbulent effect was also included in the vertical eddy viscosity and diffusivity coefficient. Langmuir turbulence production, as well as buoyancy production, anisotropic production, and vorticity production induced by velocity shear, was included in the pressure covariance parameterization to derive the stability function. The Langmuir effect and relatively complete pressure covariance parameterization inclusion can account for the influences of Langmuir turbulence and stratification in the vertical eddy viscosity and vertical eddy diffusion coefficients. Based on the modified model, one‐dimensional numerical experiments for horizontally homogeneous flows were carried out. The results indicate that the modified model is more accurate than other models in terms of the vertical eddy viscosity, vertical turbulence velocity variance, kinetic energy, and mean velocity profile compared with the large eddy simulation results. The simulated sea surface temperature (SST) and mixed layer depth of the modified model were compared with observations at Ocean Station Papa. When considering Langmuir turbulent effects, the modified model overcomes the shortcoming that the simulated SST is higher than the observed SST. Numerical results indicate that the k‐ω model performs better than the k‐kl model, although both models consider the Langmuir turbulent effect in the simulation of upper mixing motions.
A Diel Method of Estimating Gross Primary Production: 1. Validation With a Realistic Numerical Model of Chesapeake Bay
Authors: Scully Malcolm E. 
Published: October 2018

AbstractA method for estimating gross primary production (GPP) is presented and validated against a numerical model of Chesapeake Bay that includes realistic physical and biological forcing. The method statistically fits a photosynthesis‐irradiance response curve using the observed near‐surface time rate of change of dissolved oxygen and the incoming solar radiation, yielding estimates of the light‐saturated photosynthetic rate and the initial slope of the photosynthesis‐irradiance response curve. This allows estimation of GPP with 15‐day temporal resolution. The method is applied to the output from a numerical model that has high skill at reproducing both surface and near‐bottom dissolved oxygen variations observed in Chesapeake Bay in 2013. The rate of GPP predicted by the numerical model is known, as are the contributions from physical processes, allowing the proposed diel method to be rigorously assessed. At locations throughout the main stem of the Bay, the method accurately extracts the underlying rate of GPP, including pronounced seasonal variability and spatial variability. Errors associated with the method are primarily the result of contributions by the divergence in turbulent oxygen flux, which changes sign over the surface mixed layer. As a result, there is an optimal vertical location with minimal bias where application of the method is most accurate.
A Diel Method of Estimating Gross Primary Production: 2. Application to 7 Years of Near‐Surface Dissolved Oxygen Data in Chesapeake Bay
Authors: Scully Malcolm E. 
Published: October 2018

AbstractA diel method for estimating gross primary production (GPP) is applied to nearly continuous measurements of near‐surface dissolved oxygen collected at seven locations throughout the main stem of Chesapeake Bay. The data were collected through the Chesapeake Bay Interpretive Buoy System and span the period 2010–2016. At all locations, GPP exhibits pronounced seasonal variability consistent temperature‐dependent phytoplankton growth. At the Susquehanna Buoy, which is located within the estuarine turbidity maximum, rates of GPP are negatively correlated with uncalibrated turbidity data consistent with light limitation at this location. The highest rates of GPP are located immediately down Bay from the estuarine turbidity maximum and decrease moving seaward consistent with nutrient limitation. Rates of GPP at the mouth (First Landing Buoy) are roughly a factor of 3 lower than the rates in the upper Bay (Patapsco). At interannual time scales, the summer (June–July) rate of GPP averaged over all stations is positively correlated (r2 = 0.62) with the March Susquehanna River discharge and a multiple regression model that includes spring river discharge, and summer water temperature can explain most (r2 = 0.88) of the interannual variance in the observed rate of GPP. The correlation with river discharge is consistent with an increase in productivity fueled by increased nutrient loading. More generally, the spatial and temporal patterns inferred using this method are consistent with our current understanding of primary production in the Bay, demonstrating the potential this method has for making highly resolved measurements in less well studied estuarine systems.
On the Mechanism of the Generation and Interannual Variations of the Summer Upwellings West and Southwest Off the Hainan Island
Authors: Li Yineng , Peng Shiqiu , Wang Jia , Yan Jing , Huang Hu 
Published: October 2018

AbstractThe generation and interannual variations of the upwellings west and southwest off the Hainan Island (hereafter denoted as UWHI and USWHI, respectively) detected from satellite‐derived sea surface temperature as well as the mechanism behind them are investigated using a 3‐D high‐resolution ocean model with a set of sensitivity experiments. The model is able to reproduce the upwellings with significant variations in the seasonal and interannual time scales. Results of sensitivity experiments show that the joint effect of tidal mixing and stratification is the main cause of the generation of both UWHI and USWHI in summer, and the offshore pattern of the upwelling centers is closely associated with that of high mixing rate centers where currents interact with steep bathymetry. In addition, the circulation changes induced by the joint effect of tidal mixing and stratification have significant impacts on the upwellings, especially on USWHI. For the interannual variations of both UWHI and USWHI, the changes of the along‐shore winds, the tidal mixing, and the boundary currents are the main causes of the variations; the weak tidal mixing, enhanced along‐shore winds, and strong boundary currents result in the weakest upwellings there in 1998, with the enhanced along‐shore wind being the largest contributor.
Seasonal Variability of the Mauritania Current and Hydrography at 18°N
Authors: Klenz T. , Dengler M. , Brandt P. 
Published: October 2018

AbstractExtensive field campaigns in the Mauritanian upwelling region between 2005 and 2016 provide the database for analyzing the seasonal variability of the eastern boundary circulation (EBC) and associated water mass distribution at 18°N. The data set includes shipboard upper ocean current, hydrographic, and oxygen measurements from nine research cruises conducted during upwelling (December to April) and relaxation (May to July) seasons. During the upwelling season, the EBC closely resembles a classical eastern boundary current regime, with a poleward undercurrent flowing beneath an equatorward coastal jet. In contrast, elevated poleward flow exceeding 30 cm/s and extending from the surface down to 250‐m depth is observed during the relaxation season. The pronounced seasonal variability of the across‐shore structure of the EBC can be related to local wind forcing and is in general agreement with Sverdrup balance. The EBC transport is correlated to the wind stress curl leading the transport by 7 days. The short lead time suggests a fast response of locally forced waves adjusting the EBC to wind forcing. The seasonal and vertical water mass distribution is presented based on hydrographic observations. The meridional oxygen distribution and corresponding water mass partitioning into South and North Atlantic Central Water masses reveal a possible northerly ventilation pathway in the deeper layers of the central water stratum. Our results suggest that the poleward surface flow and the poleward undercurrent both are a consequence of the cyclonic wind stress curl forcing and thus propose to name it the Mauritania Current.
Wintertime Gas‐Particle Partitioning and Speciation of Inorganic Chlorine in the Lower Troposphere Over the Northeast United States and Coastal Ocean
Authors: Haskins Jessica D. , Jaeglé Lyatt , Shah Viral , Lee Ben H. , Lopez‐Hilfiker Felipe D. , Campuzano‐Jost Pedro , Schroder Jason C. , Day Douglas A. , Guo Hongyu , Sullivan Amy P. , Weber Rodney , Dibb Jack , Campos Teresa , Jimenez Jose L. , Brown Steven S. , Thornton Joel A. 
Published: October 2018

AbstractThe formation of photolabile chlorine reservoirs depend on how much chloride is available in the particle to react, which requires the chlorine partitioning to the particle in the troposphere to be well understood. However, limited measurements of gas and particle composition necessary to constrain this chemistry exist. We present measurements from the Wintertime Investigation of Transport, Emissions, and Reactivity (WINTER) aircraft campaign that show inorganic tropospheric chlorine compounds (Cly) measured in the lower troposphere are dominated by HCl and PM4 particulate chloride (pCl−), with contributions from trace chlorine species like nitryl chloride (ClNO2), hypochlorous acid (HOCl), and molecular chlorine (Cl2). We observed elevated Cly mixing ratios over the ocean (540–625 pptv) compared to over land (178–225 pptv). Observations show 0–20% (0–0.2 μg/m3) of measured chlorine partitions into particles with a diameter less than 1 μm under typical WINTER conditions. The thermodynamic model, ISORROPIA II, overpredicts submicron pCl− by a factor of 2 but is brought into agreement, assuming a small fraction of unmeasured, refractory sea salt <0.1 μg/m3 exists. The model‐measurement disagreement could also be caused by an effective equilibrium constant for HCl that is too large. We derive a lower‐limit equilibrium function (Keq = 2.5 × 106 exp[5,208(1/T − 1/T0)] mol2·kg−2·atm−1) that lowers the model value's temperature dependency. This work provides constraints on Cly in the troposphere, addresses the sensitivity of chlorine partitioning to minor changes in environmental variables, and highlights the remaining questions interfering with our ability to correctly model pCl− concentrations.
Radiosondes Show That After Decades of Cooling, the Lower Stratosphere Is Now Warming
Authors: Philipona Rolf , Mears Carl , Fujiwara Masatomo , Jeannet Pierre , Thorne Peter , Bodeker Greg , Haimberger Leopold , Hervo Maxime , Popp Christoph , Romanens Gonzague , Steinbrecht Wolfgang , Stübi Rene , Van Malderen Roeland 
Published: October 2018

AbstractSince the mid‐twentieth century, radiosonde and satellite measurements show that the troposphere has warmed and the stratosphere has cooled. These changes are primarily due to increasing concentrations of well‐mixed greenhouse gases and the depletion of stratospheric ozone. In response to continued greenhouse gas increases and stratospheric ozone depletion, climate models project continued tropospheric warming and stratospheric cooling over the coming decades. Global average satellite observations of lower stratospheric temperatures exhibit no significant trends since the turn of the century. In contrast, an analysis of vertically resolved radiosonde measurements from 60 stations shows an increase of lower stratospheric temperature since the turn of the century at altitudes between 15 and 30 km and over most continents. Trend estimates are somewhat sensitive to homogeneity assessment choices, but all investigated radiosonde data sets suggest a change from late twentieth century cooling to early 21st century warming in the lower stratosphere, which is consistent with a reversal from ozone depletion to recovery from the effects of ozone‐depleting substances. In comparison, satellite observations at the radiosonde locations show only minor early 21st century warming, possibly due to the compensating effects of continued cooling above the radiosonde altitude range.
Comparison of the Fast and Slow Climate Response to Three Radiation Management Geoengineering Schemes
Authors: Duan Lei , Cao Long , Bala Govindasamy , Caldeira Ken 
Published: October 2018

AbstractGeoengineering has been proposed as a backup approach to rapidly cool the Earth and avoid damages associated with anthropogenic climate change. In this study, we use the NCAR Community Earth System Model to conduct a series of slab‐ocean and prescribed sea surface temperature simulations to investigate the climate response to three proposed radiation management geoengineering schemes: stratospheric aerosol increase (SAI), marine cloud brightening (MCB), and cirrus cloud thinning (CCT). Our simulations show that different amounts of radiative forcing are needed for these three schemes to compensate global mean warming induced by a doubling of atmospheric CO2. With radiative forcing defined in terms of top‐of‐atmosphere energy imbalances in prescribed sea surface temperature simulations with land temperature adjustments, radiative forcing efficacy for SAI is about 15% smaller than that of CO2, and the efficacy for MCB and CCT is about 10% larger than that of CO2. In our simulations, different forcing efficacies are associated with different feedback processes for these forcing agents. Also, these geoengineering schemes produce different land‐ocean temperature change contrasts. The apparent hydrological sensitivity, that is, change in equilibrium global mean precipitation per degree of equilibrium temperature change, differs substantially between CO2, SAI, MCB, and CCT forcings, which is mainly a result of different precipitation responses during fast adjustment. After removing the component of fast adjustment, the northward movement of the Intertropical Convergence Zone in response to these forcing agents is tightly related with changes in the interhemispheric energy exchange and hemispheric temperature gradient.
Long‐Range Correlation Analysis of Soil Temperature and Moisture on A'rou Hillsides, Babao River Basin
Authors: Zhang Ting , Shen Shi , Cheng Changxiu , Song Changqing , Ye Sijing 
Published: October 2018

AbstractStudying the tendency of soil temperature and moisture can provide scientific support for setting soil parameters for land surface hydrological model. Previous research has shown that there is long‐range correlation of soil temperature or moisture; however, driving factors of long‐range correlation variations and the cross correlation between temperature and moisture under multiple timescales have rarely been discussed. To explore the driving factors, we compared long‐range correlation between shady and sunny slopes. Adaptive fractal analysis was utilized to analyze long‐range cross correlation (LRCC) and long‐range correlation (LRC). Experimental data were collected between 9 August 2013 and 3 December 2014 at A'rou observation stations, Babao River Basin. Results show that two slopes have some common characteristics. (1) Soil temperature and moisture display the consistent change. (2) The persistence intensity of moisture, temperature, and their interaction intensity change at 9, 6, and 6‐day timescales, respectively. (3) LRC and LRCC indices demonstrate the stratification heterogeneity. Results also show that LRC and LRCC indices on two slopes have differences. The soil system was stratified into three layers to explain these differences over large timescales. (1) At 4‐ to 20‐cm depth, with significant influence of solar radiation and evapotranspiration on sunny slope, moisture shows weaker persistence. There is stronger antipersistence of temperature and stronger hydrothermal interaction on sunny slope. (2) At 20‐ to 80‐cm depth, there is weaker persistence of soil moisture on shady slope because of unstable groundwater and side runoff supply. (3) At 80‐ to 160‐cm depth, with seasonal melt‐water effect on sunny slope, persistence of moisture was considerably weaker.
Temporal Trends in Absolute and Relative Extreme Temperature Events Across North America
Authors: Sheridan Scott C. , Lee Cameron C. 
Published: October 2018

AbstractIn this research, we define extreme temperature events using a recently defined excess heat factor, based on the exceedance of apparent temperature beyond the 95th percentile along with an acclimatization factor, to define extreme heat events (EHE). We extend the calculation to assess cold and develop relative metrics to complement the absolute metrics, where extremeness is based on conditions relative to season. We thus examine extreme cold events (ECE), relative extreme heat events, and relative extreme cold events in addition to EHE. We present a climatology of these variables for North America, followed by analyses of trends from 1980 to 2016. While EHE and ECE are found in the core of summer and winter, respectively, relative events tend to have a broader seasonality. Trends in relative extreme heat events and EHE are upward, and relative extreme cold events and ECE are downward; the relative events are changing more rapidly than the absolute events.
Thermal and Microphysical Effects of Ice Clouds on Torrential Rainfall Over Northern China
Authors: Zhu Haoran , Xu Huiyan , Li Xiaofan 
Published: October 2018

AbstractIce clouds are an important part of precipitation systems and their thermal (radiative and latent heat) and microphysical effects may impact rainfall. In this study, the thermal and microphysical effects of ice clouds on rainfall are investigated through the diagnostic analysis of rainfall and heat budgets of a torrential rainfall simulation in north China during July 2013. During evening, the maximum reduction in rainfall caused by the inclusion of the thermal effects of ice clouds is mainly associated with the inclusion of latent‐heat effects of ice clouds, which suppresses instability and upward motions. During early morning, the maximum increase in rainfall caused by the inclusion of the thermal effects of ice clouds is mainly related to the inclusion of radiative effects of ice clouds, which enhances radiative cooling in the upper troposphere and suppresses radiative cooling in the lower troposphere and thus increases instability and upward motions. The inclusion of microphysical effects of ice clouds increases rainfall directly by the inclusion of deposition and indirectly by the increase in condensation.
Measurement of Ionospheric Total Electron Content Using Single‐Frequency Geostationary Satellite Observations
Authors: Cooper C. , Mitchell C. N. , Wright C. J. , Jackson D. R. , Witvliet B. A. 
Published: October 2018

AbstractThe ionized upper portion of the atmosphere, the ionosphere, affects radio signals traveling between satellites and the ground. This degrades the performance of satellite navigation, surveillance, and communication systems. Techniques to measure and mitigate ionospheric effects and in particular to measure the total electron content (TEC) are therefore required. TEC is usually determined by analyzing the differential delay experienced by dual‐frequency signals. Here we demonstrate a technique which enables TEC to be derived using single‐frequency signals passing between geostationary satellites and terrestrial Global Positioning System (GPS) receivers. Geostationary satellites offer the key advantage that the raypaths are not moving and hence are easier to interpret than standard GPS TEC. Daily TEC time series are derived for three ground receivers from Europe over the year 2015. The technique is validated by correlation analysis both between pairs of ground receiver observations and between ground receivers and independent ionosonde observations. The correlation between pairs of receivers over a year shows good agreement. Good agreement was also seen between the TEC time series and ionosonde data, suggesting the technique is reliable and routinely produces realistic ionospheric information. The technique is not suitable for use on every GPS receiver type because drift in derived TEC values was observed for profiles calculated using receivers without links to highly stable clocks. The demonstrated technique has the potential to become a routine method to derive TEC, helping to map the ionosphere in real time and to mitigate ionospheric effects on radio systems.
Detection of Stress Anomaly Produced by Interaction of Compressive Fault Steps in the West Bohemia Swarm Region, Czech Republic
Authors: Vavryčuk Václav , Adamová Petra 
Published: October 2018

AbstractObservations of the 2008–2014 seismic activity in West Bohemia, Czech Republic, provide evidence of interaction of compressive fault steps that created local stress anomaly and triggered a seismic sequence with exceptional properties. The West Bohemia is a geothermal area, characterized by persistent fluid‐driven seismicity in the form of earthquake swarms. The focal zone is formed by two weak and fluid‐eroded parallel strike‐slip faults with a step of about 200 m. The fault segments were activated successively by the 2008 and 2011 swarms with magnitudes of the strongest events of 3.8 and 3.7, respectively. In 2014, a fracture linking both segments was formed or activated by a mainshock‐aftershock sequence. The aftershock decay was very fast, and the focal mechanism of the strongest event with magnitude of 4.2 was inconsistent with the regional background stress. The stress inversion of 957 focal mechanisms revealed a stress anomaly characterized by interchanging theσ2andσ3principal stress axes in the area of fault interaction. The modeling of the Coulomb stress change confirmed that the stress anomaly could completely disturb the regional background stress and produce the rotation of the principal stress axes retrieved from focal mechanisms. The faults activated or newly formed within the compressive stress anomaly were of high strength, which caused the anomalous mainshock‐aftershock character of the 2014 activity and the rapid aftershock decay. Linking the two previously active isolated faults during the 2014 activity increased the expected moment magnitude Mwof a possible strongest earthquake from 5.0 to 5.4.
Edge-emitting polariton laser and amplifier based on a ZnO waveguide
Authors: Jamadi O. , Reveret F. , Disseix P. , Medard F. , Leymarie J. , Moreau A. , Solnyshkov D. , Deparis C. , Leroux M. , Cambril E. , Bouchoule S. , Zuniga-Perez J. , Malpuech G. 
Published: October 2018

AbstractWe demonstrate edge-emitting exciton-polariton (polariton) laser operation from 5 to 300 K and polariton amplifiers based on polariton modes within ZnO waveguides. The guided mode dispersion below and above the lasing threshold is directly measured using gratings placed on top of the sample, fully demonstrating the polaritonic nature of the lasing modes. The threshold is found to be smaller than that expected for radiative polaritons in planar ZnO microcavities below 150 K and comparable above. These results open up broad perspectives for guided polaritonics by enabling easier and more straightforward implementation of polariton integrated circuits that exploit fast propagating polaritons, and, possibly, topological protection.