bluuebunny/crossref_metadata_2025_split huggingface dataset:
Traveling planetary‐scale waves in the lower thermosphere: Effects on neutral density and composition during solar minimum conditions
Authors: Sassi Fabrizio , Liu Han‐Li , Emmert John T. 
Published: January 2016

AbstractThe effects of breaking of traveling, planetary scale Rossby waves (TPWs) in the lower thermosphere are investigated with respect to the mixing of neutral constituents. We use numerical simulations of the Whole Atmosphere Community Climate Model, eXtended version, whose meteorology below 92 km is constrained by atmospheric specifications obtained from operational weather forecast/data assimilation system. The Fourier spectra show that the amplitude of TPWs with periods between 3 and 10 days are statistically significant in some years; the amplitude and phase of the band‐pass filtered behavior is consistent with the behavior of the 5 day wave. A wavelet analysis using the S‐transform shows that large variations with periods between 3 and 10 days can occur in relatively narrow temporal windows (20–30 days) during boreal winter. The momentum flux entering the lower thermosphere during the times of TPW amplification is shown to be large, and the amplifications of the TPWs in the thermosphere are not always associated with stratospheric sudden warming. The subtropical zonal accelerations are consistent with Rossby wave encountering a surf zone at low latitudes, resulting in wave breaking. The zonal acceleration is shown to be associated with a meridional diffusion, which is largest in the lower thermosphere where the wave activity and the wave breaking are also large. The ultimate effect on neutral density and composition is a meridional, down‐gradient mixing; although this horizontal diffusion is largest below 110 km, the effects on the composition are amplified with increasing altitude, due to the diffusive separation of the thermosphere.
Generation of magnetosonic waves over a continuous spectrum
Authors: Chen Lunjin , Sun Jicheng , Lu Quanming , Gao Xinliang , Xia Zhiyang , Zhima Zeren 
Published: January 2016

AbstractMagnetosonic waves, also known as equatorial noise emission, were found to have discrete frequency structures, which is consistent with instability caused by proton ring distribution. Nonetheless, nondiscrete structure, i.e., a broadband spectrum over a continuous frequency range, has been reported. We investigate the question whether proton ring distribution can generate nondiscrete spectra for perpendicularly propagating magnetosonic waves. We propose discrete and nondiscrete characteristics of the local instability for explaining the observation of discrete, continuous, and mixed spectra. The criterion for transition from discrete and continuous instability is given, γ >∼ Ωh/2, where γ is wave growth rate and Ωh is proton cyclotron frequency. The condition is verified by particle‐in‐cell simulation using more realistic electron‐to‐proton mass ratio and speed of light than in previous studies. Such criterion of generating a continuous spectrum can be tested against simultaneous in situ measurement of wave and particle. We also find that the modes at low Ωh harmonics, including the fundamental Ωh, can be still excited through nonlinear wave‐wave coupling, even when they are neutral modes (γ = 0) according to the linear kinetic theory. Comparison with magnetosonic waves in cold plasma limit and electromagnetic ion Bernstein mode is also discussed.
Diel vertical migration of zooplankton at the S1 biogeochemical mooring revealed from acoustic backscattering strength
Authors: Inoue Ryuichiro , Kitamura Minoru , Fujiki Tetsuichi 
Published: January 2016

AbstractWe examined the diel vertical migration of zooplankton by using the backscatter strength obtained from moored acoustic Doppler current profilers at mooring site S1 in the North Pacific subtropical gyre. There was seasonal variability in the vertical distribution and migration of the high‐backscatter layers in that they became deeper than the euphotic zone (<100 m) in winter and were confined above this depth in other seasons. Seasonal changes in daylight hours also affected the timing of the diel migration. We found that lunar cycles affected vertical distributions of zooplankton near the surface by changing the light intensity. Physical events, such as mixed‐layer deepening and restratification and the passage of a mesoscale eddy, also affected zooplankton behavior possibly by changing food environment in the euphotic zone. Since the comparison with net samples indicated that the backscatter likely represents the bulk biomass, the accuracy of biomass estimates based on net samples could be influenced by the high temporal variability of zooplankton distributions.
Seasonal variations of seawater pCO2 and sea‐air CO2 fluxes in a fringing coral reef, northern South China Sea
Authors: Yan Hongqiang , Yu Kefu , Shi Qi , Tan Yehui , Liu Guohui , Zhao Meixia , Li Shu , Chen Tianran , Wang Yinghui 
Published: January 2016

AbstractEvidence based on four field surveys conducted between July 2009 and April 2011 indicates that both sea surface partial pressures of CO2 (pCO2) and sea–air CO2 fluxes at Luhuitou fringing reef in Sanya, Hainan Island, northern South China Sea (SCS) are subject to significant seasonal variations. The diurnal variation of seawater pCO2 ranges from 264 to 579 μatm in summer, which is much larger than that in autumn (152–335 μatm), in winter (84–260 μatm), and in spring (114–228 μatm). The sea‐air CO2 flux in summer (∼9.6 mmol CO2 m−2 d−1) is also larger than that in other seasons (i.e.,∼3 mmol CO2 m−2 d−1 in spring, ∼3.5 mmol CO2 m−2 d−1 in autumn, and ∼2.7 mmol CO2 m−2 d−1 in winter). The atmospheric pCO2 in this reef shows small diurnal and seasonal variations. The integration of the time‐series pCO2 data shows that the reef area is a weak source of atmospheric CO2 at ∼0.54 mol CO2 m−2 yr−1. Further analyses indicate that the seasonal variations of the surface seawater pCO2 in Luhuitou fringing reef are mainly affected by seasonally‐dependent biological metabolic processes (organic processe and inorganic process), and that the organic process play a more important role than the inorganic process. Seasonal sea surface temperature (SST) variations and hydrodynamic processes may also have some influence on seawater pCO2 variation.
Tides in the mesopause region over Antarctica: Comparison of whole atmosphere model simulations with ground‐based observations
Authors: Akmaev R. A. , Forbes J. M. , Lübken F.‐J. , Murphy D. J. , Höffner J. 
Published: January 2016

AbstractAlmost a quarter century ago first optical and radar observations from the South Pole revealed rich dynamics unexpected from classical tidal theory. A strong semidiurnal wind oscillation was detected near the mesopause implying substantial deviations from the classical view that the semidiurnal variation is dominated by the migrating tide. Subsequent systematic observations exhibited large seasonal variations of both the diurnal and semidiurnal tide with dramatic reduction in amplitude from summer to winter. First numerical simulations with a realistic general circulation model extending into the lower thermosphere indicated the presence of nonmigrating tides with substantial amplitudes in the polar regions. However, direct model‐data comparisons have been limited to idealized linear models. Here whole atmosphere model (WAM) simulations for January and July are compared with available wind climatologies based on multiyear radar observations at different locations in Antarctica as well as with first summertime lidar measurements of temperature. The diurnal tide simulation agrees well with most of the independent radar and satellite wind observations in both seasons. The strong semidiurnal tide comprised of migrating and nonmigrating components is well reproduced in summer, while in winter the model tends to overestimate the amplitudes over the continental edge. Besides model validation, a self‐consistent numerical solution also enables cross validation of observations made with different instruments at different locales.
Modeling the weekly cycle of NOx and CO emissions and their impacts on O3 in the Los Angeles‐South Coast Air Basin during the CalNex 2010 field campaign
Authors: Kim S.‐W. , McDonald B. C. , Baidar S. , Brown S. S. , Dube B. , Ferrare R. A. , Frost G. J. , Harley R. A. , Holloway J. S. , Lee H.‐J. , McKeen S. A. , Neuman J. A. , Nowak J. B. , Oetjen H. , Ortega I. , Pollack I. B. , Roberts J. M. , Ryerson T. B. , Scarino A. J. , Senff C. J. , Thalman R. , Trainer M. , Volkamer R. , Wagner N. , Washenfelder R. A. , Waxman E. , Young C. J. 
Published: January 2016

AbstractWe developed a new nitrogen oxide (NOx) and carbon monoxide (CO) emission inventory for the Los Angeles‐South Coast Air Basin (SoCAB) expanding the Fuel‐based Inventory for motor‐Vehicle Emissions and applied it in regional chemical transport modeling focused on the California Nexus of Air Quality and Climate Change (CalNex) 2010 field campaign. The weekday NOx emission over the SoCAB in 2010 is 620 t d−1, while the weekend emission is 410 t d−1. The NOx emission decrease on weekends is caused by reduced diesel truck activities. Weekday and weekend CO emissions over this region are similar: 2340 and 2180 t d−1, respectively. Previous studies reported large discrepancies between the airborne observations of NOx and CO mixing ratios and the model simulations for CalNex based on the available bottom‐up emission inventories. Utilizing the newly developed emission inventory in this study, the simulated NOx and CO mixing ratios agree with the observations from the airborne and the ground‐based in situ and remote sensing instruments during the field study. The simulations also reproduce the weekly cycles of these chemical species. Both the observations and the model simulations indicate that decreased NOx on weekends leads to enhanced photochemistry and increase of O3 and Ox (=O3 + NO2) in the basin. The emission inventory developed in this study can be extended to different years and other urban regions in the U.S. to study the long‐term trends in O3 and its precursors with regional chemical transport models.
Linking the morphology of fluvial fan systems to aquifer stratigraphy in the Sutlej‐Yamuna plain of northwest India
Authors: van Dijk W. M. , Densmore A. L. , Singh A. , Gupta S. , Sinha R. , Mason P. J. , Joshi S. K. , Nayak N. , Kumar M. , Shekhar S. , Kumar D. , Rai S. P. 
Published: January 2016

AbstractThe Indo‐Gangetic foreland basin has some of the highest rates of groundwater extraction in the world, focused in the states of Punjab and Haryana in northwest India. Any assessment of the effects of extraction on groundwater variation requires understanding of the geometry and sedimentary architecture of the alluvial aquifers, which in turn are set by their geomorphic and depositional setting. To assess the overall architecture of the aquifer system, we used satellite imagery and digital elevation models to map the geomorphology of the Sutlej and Yamuna fan systems, while aquifer geometry was assessed using 243 wells that extend to ∼200 m depth. Aquifers formed by sandy channel bodies in the subsurface of the Sutlej and Yamuna fans have a median thickness of 7 and 6 m, respectively, and follow heavy‐tailed thickness distributions. These distributions, along with evidence of persistence in aquifer fractions as determined from compensation analysis, indicate persistent reoccupation of channel positions and suggest that the major aquifers consist of stacked, multistoried channel bodies. The percentage of aquifer material in individual boreholes decreases down fan, although the exponent on the aquifer body thickness distribution remains similar, indicating that the total number of aquifer bodies decreases down fan but that individual bodies do not thin appreciably, particularly on the Yamuna fan. The interfan area and the fan marginal zone have thinner aquifers and a lower proportion of aquifer material, even in proximal locations. We conclude that geomorphic setting provides a first‐order control on the thickness, geometry, and stacking pattern of aquifer bodies across this critical region.
Comparison of equatorial Pacific sea surface temperature variability and trends with Sr/Ca records from multiple corals
Authors: Alpert Alice E. , Cohen Anne L. , Oppo Delia W. , DeCarlo Thomas M. , Gove Jamison M. , Young Charles W. 
Published: January 2016

AbstractCoral Sr/Ca is widely used to reconstruct past ocean temperatures. However, some studies report different Sr/Ca‐temperature relationships for conspecifics on the same reef, with profound implications for interpretation of reconstructed temperatures. We assess whether these differences are attributable to small‐scale oceanographic variability or “vital effects” associated with coral calcification and quantify the effect of intercolony differences on temperature estimates and uncertainties. Sr/Ca records from four massive Porites colonies growing on the east and west sides of Jarvis Island, central equatorial Pacific, were compared with in situ logger temperatures spanning 2002–2012. In general, Sr/Ca captured the occurrence of interannual sea surface temperature events but their amplitude was not consistently recorded by any of the corals. No long‐term trend was identified in the instrumental data, yet Sr/Ca of one coral implied a statistically significant cooling trend while that of its neighbor implied a warming trend. Slopes of Sr/Ca‐temperature regressions from the four different colonies were within error, but offsets in mean Sr/Ca rendered the regressions statistically distinct. Assuming that these relationships represent the full range of Sr/Ca‐temperature calibrations in Jarvis Porites, we assessed how well Sr/Ca of a nonliving coral with an unknown Sr/Ca‐temperature relationship can constrain past temperatures. Our results indicate that standard error of prediction methods underestimate the actual error as we could not reliably reconstruct the amplitude or frequency of El Niño–Southern Oscillation events as large as ± 2°C. Our results underscore the importance of characterizing the full range of temperature‐Sr/Ca relationships at each study site to estimate true error.
Validation of an operational product to determine L1 to Earth propagation time delays
Authors: Cash M. D. , Witters Hicks S. , Biesecker D. A. , Reinard A. A. , de Koning C. A. , Weimer D. R. 
Published: January 2016

AbstractWe describe the development and validation of an operational space weather tool to forecast propagation delay times between L1 and Earth using the Weimer and King (2008) tilted phase front technique. A simple flat plane convection delay method is currently used by the NOAA Space Weather Prediction Center (SWPC) to propagate the solar wind from a monitoring satellite located at L1 to a point upstream of the magnetosphere. This technique assumes that all observed solar wind discontinuities, such as interplanetary shocks and interplanetary coronal mass ejection boundaries, are in a flat plane perpendicular to the Sun‐Earth line traveling in the GSE X direction at the observed solar wind velocity. In reality, these phase plane fronts can have significantly tilted orientations, and by relying on a ballistic propagation method, delay time errors of ±15 min are common. In principle, the propagation time delay product presented here should more accurately predict L1 to Earth transit times by taking these tilted phase plane fronts into account. This algorithm, which is based on the work of Weimer and King (2008), is currently running in real time in test mode at SWPC as part of the SWPC test bed. We discuss the current algorithm performance, and via our detailed validation study, show that there is no significant difference between the two propagation methods when run in a real‐time operational environment.
Use of a flux‐based field capacity criterion to identify effective hydraulic parameters of layered soil profiles subjected to synthetic drainage experiments
Authors: Nasta Paolo , Romano Nunzio 
Published: January 2016

AbstractThis study explores the feasibility of identifying the effective soil hydraulic parameterization of a layered soil profile by using a conventional unsteady drainage experiment leading to field capacity. The flux‐based field capacity criterion is attained by subjecting the soil profile to a synthetic drainage process implemented numerically in the Soil‐Water‐Atmosphere‐Plant (SWAP) model. The effective hydraulic parameterization is associated to either aggregated or equivalent parameters, the former being determined by the geometrical scaling theory while the latter is obtained through the inverse modeling approach. Outcomes from both these methods depend on information that is sometimes difficult to retrieve at local scale and rather challenging or virtually impossible at larger scales. The only knowledge of topsoil hydraulic properties, for example, as retrieved by a near‐surface field campaign or a data assimilation technique, is often exploited as a proxy to determine effective soil hydraulic parameterization at the largest spatial scales. Comparisons of the effective soil hydraulic characterization provided by these three methods are conducted by discussing the implications for their use and accounting for the trade‐offs between required input information and model output reliability. To better highlight the epistemic errors associated to the different effective soil hydraulic properties and to provide some more practical guidance, the layered soil profiles are then grouped by using the FAO textural classes. For the moderately heterogeneous soil profiles available, all three approaches guarantee a general good predictability of the actual field capacity values and provide adequate identification of the effective hydraulic parameters. Conversely, worse performances are encountered for the highly variable vertical heterogeneity, especially when resorting to the “topsoil‐only” information. In general, the best performances are guaranteed by the equivalent parameters, which might be considered a reference for comparisons with other techniques. As might be expected, the information content of the soil hydraulic properties pertaining only to the uppermost soil horizon is rather inefficient and also not capable to map out the hydrologic behavior of the real vertical soil heterogeneity since the drainage process is significantly affected by profile layering in almost all cases.
Estimating transmissivity from single‐well pumping tests in heterogeneous aquifers
Authors: Pechstein Armin , Attinger Sabine , Krieg Ronald , Copty Nadim K. 
Published: January 2016

AbstractAlthough aquifers are naturally heterogeneous, the interpretation of pumping tests is commonly performed under the assumption of aquifer homogeneity. This yields interpreted hydraulic parameters averaged over a domain of uncertain extent which disguises their relation to the underlying heterogeneity. In this study, we numerically investigate the sensitivity of the transient drawdown at the pumping well, to nonuniform distributions of transmissivity in confined aquifers. Frechet kernels and their time derivative are used to estimate two spatially averaged transmissivities, denoted the equivalent and interpreted transmissivity, Teq and Tin, respectively, for the case of single‐well pumping tests. Interrelating Teq and Tin is achieved by modeling Tin in terms of a distance dependent, radially heterogeneous field. In weakly heterogeneous aquifers, Teq approximates TPW, the local transmissivity at the pumped well. With increasing degree of heterogeneity, Teq deviates from TPW as pumping propagates. Tin starts at TPW, approaching the spatial geometric mean of transmissivity during late pumping times. Limits of the proposed spatial weighting functions are investigated by treating the interpreted storativity, Sest, as an indicator for flow connectivity. It is shown numerically that the spatial weights for Teq and Tin agree well to the underlying heterogeneity if
. Finally, implications for applying the concepts of Teq and Tin to heterogeneous domains, and, for real world applications are discussed. It is found that time‐dependent spatial averages of Tin agree well with estimates of the interpreted transmissivity from the Continuous‐Derivation method.
Hydrodynamics and sediment transport in a meandering channel with a model axial‐flow hydrokinetic turbine
Authors: Hill Craig , Kozarek Jessica , Sotiropoulos Fotis , Guala Michele 
Published: January 2016

AbstractAn investigation into the interactions between a model axial‐flow hydrokinetic turbine (rotor diameter, dT = 0.15 m) and the complex hydrodynamics and sediment transport processes within a meandering channel was carried out in the Outdoor StreamLab research facility at the University of Minnesota St. Anthony Falls Laboratory. This field‐scale meandering stream with bulk flow and sediment discharge control provided a location for high spatiotemporally resolved measurements of bed and water surface elevations around the model turbine. The device was installed within an asymmetric, erodible channel cross section under migrating bed form and fixed outer bank conditions. A comparative analysis between velocity and topographic measurements, with and without the turbine installed, highlights the local and nonlocal features of the turbine‐induced scour and deposition patterns. In particular, it shows how the cross‐section geometry changes, how the bed form characteristics are altered, and how the mean flow field is distorted both upstream and downstream of the turbine. We further compare and discuss how current energy conversion deployments in meander regions would result in different interactions between the turbine operation and the local and nonlocal bathymetry compared to straight channels.
Representing spatial variability of forest snow: Implementation of a new interception model
Authors: Moeser D. , Mazzotti G. , Helbig N. , Jonas T. 
Published: January 2016

AbstractA new interception model was integrated in a snowmelt model and for the first time the spatial variability of forest snow was effectively represented due to the inclusion of new forest structure metrics. The model was tested at 1273 field points surrounding Davos, Switzerland, that feature an extremely wide range of canopy and forest structure. The behavior of the new model was compared against a widely applied interception model. Due to the inclusion of novel forest structure parameters (mean distance to canopy and total gap area) in the new model, simulated interception mimicked the horizontal layout of canopy structure, while the standard interception model yielded fairly homogeneous interception estimations even under highly heterogeneous canopy conditions. The large variance of estimated interception between points using the new model translated into significant effects on under‐canopy snow water equivalent and snow depth. Precipitation conditions were also analyzed, and further differences between the models were related to storm intensity. In climates characterized by large storm events, the new interception model provides significantly higher interception estimations (i.e., lower under‐canopy snow) than the standard model, whereas in climates characterized by small storms events, the new model yields lower interception estimations (i.e., higher under‐canopy snow) in areas with moderately sized to large canopy gaps.