bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of effective saturated hydraulic conductivity in an agricultural field using Karhunen‐Loève expansion with the Markov chain Monte Carlo technique
Authors: Das N. N. , Mohanty B. P. , Efendiev Y.
Published: June 2010

Process‐based soil hydrologic models require input of saturated hydraulic conductivity (Ksat). However, model users often have limited access to measured data and thus use published or estimated values for many site‐specific hydrologic and environmental applications. We proposed an algorithm that uses the Karhunen‐Loève expansion (KLE) in conjunction with the Markov chain Monte Carlo (MCMC) technique, which employs measured soil moisture values to characterize the saturated hydraulic conductivity of an agricultural field at a 30 m resolution. The study domain is situated in the Walnut Creek watershed, Iowa, with soybean crop (in 2005) and well‐defined top (atmospheric) and bottom (groundwater) boundary conditions. The KLE algorithm parameterizes and generatesKsatfields with random correlation lengths that are used in the SWMS_3D model for predicting the soil moisture dynamics for two different scenarios: (1) the van Genuchten soil hydraulic parameters (exceptKsat) are constant and are based on the soil type of the grid block within the domain, and (2)Ksatis correlated with the van Genuchten parameterαasKsat∝α2. The predicted soil moisture fields for both the scenarios are evaluated with the measured soil moisture in the MCMC algorithm for acceptance (or rejection) of theKsatfields. The acceptedKsatfields are evaluated against the laboratory‐measuredKsatat specific locations as well as with a largeKsatdata set measured in situ in a nearby field with similar hydrologic conditions, and the comparisons show reasonably good agreement. The KLE‐MCMC algorithm was further tested in the same study domain for another year (2002) having different vegetation (corn) and local forcings. The algorithm shows potential to characterize the effective saturated hydraulic conductivity fields at 30 m resolution using inexpensive and more regularly measured soil moisture measurements. Further studies are required to incorporate variability in different hydroclimatic regions and diverse topography to extend the application of this algorithm.
The 8.2 ka event: Abrupt transition of the subpolar gyre toward a modern North Atlantic circulation
Authors: Born A. , Levermann A.
Published: June 2010

Climate model simulations of the 8.2 ka event show an abrupt strengthening of the Atlantic subpolar gyre that allows us to connect two major but apparently contradictory climate events of the early Holocene: the freshwater outburst from proglacial lakes and the onset of Labrador Sea water formation. The 8.2 ka event is the largest climatic signal of our present interglacial with a widespread cooling in the North Atlantic region about 8200 years before present. It coincides with a meltwater outburst from North American proglacial lakes that is believed to have weakened the Atlantic meridional overturning circulation and northward heat transport, followed by a recovery of the deep ocean circulation and rising temperatures after a few centuries. Marine proxy data, however, date the onset of deep water formation in Labrador Sea to the same time. The subsequent strengthening of the slope current system created a regional signal recorded as an abrupt and persistent surface temperature decrease. Although similarities in timing are compelling, a mechanism to reconcile these apparently contradictory events was missing. Our simulations show that an abrupt and persistent strengthening of the Atlantic subpolar gyre provides a plausible explanation. The intense freshwater pulse triggered a transition of the gyre circulation into a different mode of operation, stabilized by internal feedbacks and persistent after the cessation of the perturbation. As a direct consequence, deep water formation around its center intensifies. This corresponds to the modern flow regime and stabilizes the meridional overturning circulation, possibly contributing to the Holocene's climatic stability.
Longitudinal variation of tides in the MLT region: 2. Relative effects of solar radiative and latent heating
Authors: Zhang Xiaoli , Forbes Jeffrey M. , Hagan Maura E.
Published: June 2010

Part 2 of our study examines the relative importance of radiative heating and latent heating in accounting for vertically propagating tides that impose longitude variability on mesosphere‐lower thermosphere (MLT) winds, temperatures, and densities. Our results are based upon numerical simulations using the Global‐Scale Wave Model (GSWM) and new tidal heating rates derived from International Satellite Cloud Climatology Project (ISCCP) radiative fluxes (see part 1), Tropical Rainfall Measuring Mission (TRMM) latent heating profiles, and TRMM rainfall rates. Contrary to previous results and general perceptions, we demonstrate that radiative heating is more important than latent heating in accounting for MLT longitude variability due to tides although latent heating causes some large nonmigrating tidal oscillations such as DE3. Through comparison with TIMED SABER temperature measurements, the model results are shown to approximate many observed features of this longitude variability.
Modeling radiation belt radial diffusion in ULF wave fields: 1. Quantifying ULF wave power at geosynchronous orbit in observations and in global MHD model
Authors: Huang Chia‐Lin , Spence Harlan E. , Singer Howard J. , Hughes W. Jeffrey
Published: June 2010

To provide critical ULF wave field information for radial diffusion studies in the radiation belts, we quantify ULF wave power (f = 0.5–8.3 mHz) in GOES observations and magnetic field predictions from a global magnetospheric model. A statistical study of 9 years of GOES data reveals the wave local time distribution and power at geosynchronous orbit in field‐aligned coordinates as functions of wave frequency, solar wind conditions (Vx, ΔPd and IMF Bz) and geomagnetic activity levels (Kp, Dst and AE). ULF wave power grows monotonically with increasing solar wind Vx, dynamic pressure variations ΔPd and geomagnetic indices in a highly correlated way. During intervals of northward and southward IMF Bz, wave activity concentrates on the dayside and nightside sectors, respectively, due to different wave generation mechanisms in primarily open and closed magnetospheric configurations. Since global magnetospheric models have recently been used to trace particles in radiation belt studies, it is important to quantify the wave predictions of these models at frequencies relevant to electron dynamics (mHz range). Using 27 days of real interplanetary conditions as model inputs, we examine the ULF wave predictions modeled by the Lyon‐Fedder‐Mobarry magnetohydrodynamic code. The LFM code does well at reproducing, in a statistical sense, the ULF waves observed by GOES. This suggests that the LFM code is capable of modeling variability in the magnetosphere on ULF time scales during typical conditions. The code provides a long‐missing wave field model needed to quantify the interaction of radiation belt electrons with realistic, global ULF waves throughout the inner magnetosphere.
Modeling radiation belt radial diffusion in ULF wave fields: 2. Estimating rates of radial diffusion using combined MHD and particle codes
Authors: Huang Chia‐Lin , Spence Harlan E. , Hudson Mary K. , Elkington Scot R.
Published: June 2010

Quantifying radial transport of radiation belt electrons in ULF wave fields is essential for understanding the variability of the trapped relativistic electrons. To estimate the radial diffusion coefficients (DLL), we follow MeV electrons in realistic magnetospheric configurations and wave fields calculated from a global MHD code. We create idealized pressure‐driven MHD simulations for controlled solar wind velocities (hereafter referred to as pressure‐driven Vx simulations) with ULF waves that are comparable to GOES data under similar conditions, by driving the MHD code with synthetic pressure profiles that mimic the pressure variations of a particular solar wind velocity. The ULF wave amplitude, in both magnetic and electric fields, increases at larger radial distance and during intervals with higher solar wind velocity and pressure fluctuations. To calculate DLL as a function of solar wind velocity (Vx = 400 and 600 km/s), we follow 90 degree pitch angle electrons in magnetic and electric fields of the pressure‐driven Vx simulations. DLL is higher at larger radial distance and for the case with higher solar wind velocity and pressure variations. Our simulated DLL values are relatively small compared to previous studies which used larger wave fields in their estimations. For comparison, we scale our DLL values to match the wave amplitudes of the previous studies with those of the idealized MHD simulations. After the scaling, our DLL values for Vx = 600 km/s are comparable to the DLL values derived from Polar measurements during nonstorm intervals. This demonstrates the use of MHD models to quantify the effect of pressure‐driven ULF waves on radiation belt electrons and thus to differentiate the radial diffusive process from other mechanisms.
A comparison of different source location methods for ELF transients by using the parent lightning discharges with known positions
Authors: Nakamura T. , Sekiguchi M. , Hobara Y. , Hayakawa M.
Published: June 2010

Different kinds of direction finding methods (azimuth and range determinations) have been proposed so far in order to locate ELF transients. As for the azimuth determination, we have used the Lissajous method and goniometer and Poynting vector methods, which are found to be not so much different. The biggest problem is the range (or source‐to‐observer distance) estimation, which is principally based on the use of wave impedance. By using the known positions of parent lightning discharges during the European sprite campaign, we have compared different methods ((1) cross‐correlation over a wide frequency range between the measured and theoretical wave impedances, (2) the use of peak frequency in the observed wave impedance, (3) Jones and Kemp method (the use of maxima and minima in the frequency spectrum of wave impedance), (4) the use of oscillation frequency in the wave impedance variation), and it is found that the best one is the use of Jones and Kemp method with an error of 0.33 Mm for the nine events with sufficient S/N ratio from the analyzed 11 events. This has been based on the FFT analysis. However, for the remaining two events with small time separation, we have tried the use of wavelet analysis, which improved the range determination significantly. Finally, we recommend a combined use of Jones and Kemp method and wavelet analysis for locating ELF transients.
Hybrid simulations of plasma transport by Kelvin‐Helmholtz instability at the magnetopause: Density variations and magnetic shear
Authors: Cowee M. M. , Winske D. , Gary S. P.
Published: June 2010

Two‐dimensional hybrid (kinetic ions and massless fluid electrons) simulations of the Kelvin‐Helmholtz instability (KHI) for a magnetopause configuration with a varying density jump and magnetic shear across the boundary are carried out to examine how the transport of magnetosheath plasma into the magnetosphere is affected by these conditions. Low magnetic shear conditions where the magnetosheath magnetic field is within 30° of northward is included in the simulations because KHI is thought to be important for plasma transport only for northward or near‐northward interplanetary magnetic field orientations. The simulations show that coherent vortices can grow for these near‐northward angles and that they are sometimes more coherent than for pure northward conditions because the turbulence which breaks down these vortices is reduced when there are magnetic tension forces. With increasing magnetic shear angle and increasing density jump, the growth rate is reduced, and the vortices do not grow to as large of a size, which reduces the plasma transport. By tracking the individual particle motions, diffusion coefficients can be obtained for the system, where the diffusion is not classical in nature but instead has a time dependence resulting from both the increasingly large‐scale vortex motion and the small‐scale turbulence generated in the breakdown of the instabilities. Results indicate that diffusion on the order of 109 m2/s could possibly be generated by KHI on the flanks of the magnetosphere.
Reconnection and flows in the Jovian magnetotail as inferred from magnetometer observations
Authors: Vogt Marissa F. , Kivelson Margaret G. , Khurana Krishan K. , Joy Steven P. , Walker Raymond J.
Published: June 2010

In Jupiter's magnetosphere, events such as flow bursts and changes to the magnetic field are thought to be driven predominantly by internal processes. Analysis of energetic particle data has established that flow bursts are associated with magnetic reconfiguration in the Jovian magnetotail. Here we use magnetometer data throughout the Jovian magnetotail to identify events that we relate to reconnection and flow. Using quantitative criteria, we have identified 249 reconnection events that are characterized by reversals or significant increases in Bθ, the north‐south component of the magnetic field, over background levels. We discuss the distribution of the events, their occurrence rate, and location inside or outside of a putative neutral line, as functions of radial distance and local time. Using the sign of Bθ as a proxy for the flow direction, we establish the location of a statistical separatrix and find that its radial distance varies with local time. Where particle signatures of events in our data set have also been analyzed, they generally show increases of anisotropy. However, we have identified scores of additional events that have not been previously identified in the particle data; many of these new events occur in the premidnight local time sector. Finally, we examine our events for the 2–3 day periodicity that has been reported for flow bursts and auroral polar dawn spots and find that this periodicity is present only intermittently and is not statistically significant.
Fore‐arc deformation and underplating at the northern Hikurangi margin, New Zealand
Authors: Scherwath M. , Kopp H. , Flueh E. R. , Henrys S. A. , Sutherland R. , Stagpoole V. M. , Barker D. H. N. , Reyners M. E. , Bassett D. G. , Planert L. , Dannowski A.
Published: June 2010

Geophysical investigations of the northern Hikurangi subduction zone northeast of New Zealand, image fore‐arc and surrounding upper lithospheric structures. A seismic velocity (Vp) field is determined from seismic wide‐angle data, and our structural interpretation is supported by multichannel seismic reflection stratigraphy and gravity and magnetic modeling. We found that the subducting Hikurangi Plateau carries about 2 km of sediments above a 2 km mixed layer of volcaniclastics, limestone, and chert. The upper plateau crust is characterized by Vp = 4.9–6.7 km/s overlying the lower crust with Vp > 7.1 km/s. Gravity modeling yields a plateau thickness around 10 km. The reactivated Raukumara fore‐arc basin is >10 km deep, deposited on 5–10 km thick Australian crust. The fore‐arc mantle of Vp > 8 km/s appears unaffected by subduction hydration processes. The East Cape Ridge fore‐arc high is underlain by a 3.5 km deep strongly magnetic (3.3 A/m) high‐velocity zone, interpreted as part of the onshore Matakaoa volcanic allochthon and/or uplifted Raukumara Basin basement of probable oceanic crustal origin. Beneath the trench slope, we interpret low‐seismic‐velocity, high‐attenuation, low‐density fore‐arc material as accreted and recycled, suggesting that underplating and uplift destabilizes East Cape Ridge, triggering two‐sided mass wasting. Mass balance calculations indicate that the proposed accreted and recycled material represents 25–100% of all incoming sediment, and any remainder could be accounted for through erosion of older accreted material into surrounding basins. We suggest that continental mass flux into the mantle at subduction zones may be significantly overestimated because crustal underplating beneath fore‐arc highs have not properly been accounted for.
Energy radiation from intermediate‐ to large‐magnitude earthquakes: Implications for dynamic fault weakening
Authors: Malagnini Luca , Nielsen Stefan , Mayeda Kevin , Boschi Enzo
Published: June 2010

The amount of energy radiated from an earthquake can be measured using recent methods based on earthquake coda signals and spectral ratios. Such methods are not altered by either site or directivity effects, with the advantage of a greatly improved accuracy. Several studies of earthquake sequences based on the aforementioned measurements showed evidence of a breakdown in self‐similarity in the moment to energy relation. Radiated energy can also be used as a gauge to estimate the average dynamic stress drop on the fault. Here we compute the dynamic stress drop, infer the coseismic friction and estimate the coseismic heating resulting from the frictional work during events from different main shock‐aftershock earthquake sequences. We relate the dynamic friction to the maximum temperature rise estimated on the faults for each earthquake. Our results are strongly indicative that a thermally triggered dynamic frictional weakening is present, responsible for the breakdown in self‐similarity. These observations from seismic data are compatible with recent laboratory evidence of thermal weakening in rock friction under seismic slip rates, associated with various physical processes such as melting, decarbonation, and dehydration.
Energetics of strain localization in a model of seismic slip
Authors: Hermundstad A. M. , Daub E. G. , Carlson J. M.
Published: June 2010

We quantify the energy dissipated to heat and to local disorder in a sheared layer of granular fault gouge. Local disorder is modeled using shear transformation zone theory, a continuum model of nonaffine deformation in amorphous solids that resolves spontaneous localization of strain. Strain localization decreases the total energy dissipated during slip. In addition, a fraction of this energy is dissipated to increasing local disorder as the material is sheared, thereby decreasing the amount of energy dissipated as thermal heat. We quantify the heat dissipated per unit area as a function of total slip in the presence and absence of strain localization and test the parameter dependence of these calculations. We find that less heat is dissipated per unit area compared to results obtained using a traditional heuristic energy partition.
Estimation of hydraulic conductivity and water table map in a large‐scale laboratory model by means of the self‐potential method
Authors: Straface Salvatore , Rizzo Enzo , Chidichimo Francesco
Published: June 2010

The goal of this paper is to estimate the position of the water table and hydraulic conductivity of a homogeneous porous medium by means of the self‐potential method. The hydrogeophysical experiments were carried out at the Hydrogeosite Laboratory of the Istituto di Metodologie per l'Analisi Ambientale, Consiglio Nazionale delle Ricerche (Marsico Nuovo, Italy); the laboratory is a large‐scale model sized 10 × 7 × 3 m3that is filled with a homogeneous medium made up of quartz‐rich sand with a medium‐high hydraulic conductivity in the order of 10−5m s−1. Self‐potential signals generated by the groundwater flow, during a pumping test, were measured on the ground surface, on both the pumping and the recovery phases. A novel methodology to estimate the hydraulic conductivity from self‐potential measurements is proposed. Hydraulic conductivity very close to that calculated from hydraulic data, by means of Neuman‐type curves, has been obtained by solving the electrical flow equation through a linear least squares method. Moreover, a kriging with external drift geostatistical methodology has been proposed to estimate the hydraulic head distribution. The advantages given by this geostatistical method are that (1) hydraulic head distribution can be estimated without any previous electrokinetic coupling coefficient calculation and (2) the method is valid for either linear or nonlinear relationships between self‐potential and hydraulic head gradients. An original finding of this work is that the relationship between self‐potential signals and drawdown, around a pumping well, is not always linear: linearity applies only when the groundwater velocity is low, but high nonlinearity occurs when hydraulic head gradient rises up. Kriging with the external drift method could be used for the inversion of the hydraulic conductivity distribution, in a real heterogeneous aquifer, by means of an appropriate conditioning technique.
Simulating dimethylsulphide seasonality with the Dynamic Green Ocean Model PlankTOM5
Authors: Vogt M. , Vallina S. M. , Buitenhuis E. T. , Bopp L. , Le Quéré C.
Published: June 2010

We study the dynamics of dimethylsulphide (DMS) and dimethylsulphoniopropionate (DMSP) using the global ocean biogeochemistry model PlankTOM5, which includes three phytoplankton and two zooplankton functional types (PFTs). We present a fully prognostic DMS module describing intracellular particulate DMSP (DMSPp) production, concentrations of dissolved DMSP (DMSPd), and DMS production and consumption. The model produces DMS fields that compare reasonably well with the observed annual mean DMS fields, zonal mean DMS concentrations, and its seasonal cycle. Modeled ecosystem composition and modeled total chlorophyll influenced mean DMS concentrations and DMS seasonality at mid‐ and high latitudes, but did not control the seasonal cycle in the tropics. The introduction of a direct, irradiation‐dependent DMS production term (exudation) in the model improved the match between modeled and observed DMS seasonality, but deteriorated simulated zonal mean concentrations. In PlankTOM5, exudation was found to be most important for DMS seasonality in the tropics, and a variable DMSP cell quota as a function of light and nutrient stress was more important than a PFT‐specific minimal DMSPp cell quota. The results suggest that DMS seasonality in the low latitudes is mostly driven by light. The agreement between model and data for DMS, DMSPp, and DMSPd is reasonable at the Bermuda Atlantic Time Series Station, where the summer paradox is observed.
On the corrections of ERA‐40 surface flux products consistent with the Mediterranean heat and water budgets and the connection between basin surface total heat flux and NAO
Authors: Pettenuzzo D. , Large W. G. , Pinardi N.
Published: June 2010

This is a study of heat fluxes and heat budget of the Mediterranean Sea using the European Centre for Medium‐Range Weather Forecasts (ECMWF) 45 year reanalysis data set ERA‐40. The simple use of the ERA‐40 surface flux components fails to close the budget and, in particular, the shortwave radiation flux is found to be underestimated with respect to observed data by about 10%. The heat flux terms are recomputed and corrected in order to close the heat and freshwater budgets of the Mediterranean basin over the period 1958 to 2001, thus producing a corrected ERA‐40 surface flux data set. Various satellite and in situ observational data are used to construct spatially varying corrections to the ERA‐40 products needed to compute the air‐sea fluxes. The corrected interannual and climatological net surface heat and freshwater fluxes are −7 W/m2 and −0.64 m/yr, respectively, which are regarded as satisfactorily closing the Mediterranean heat and water budgets. It is also argued that there is an important contribution from large heat losses associated with a few severe winters over the Mediterranean Sea. This is shown to be related to wind regime anomalies, which strongly affect the latent heat of evaporation that is mainly responsible for the interannual modulation of the total heat flux. Furthermore, the surface total heat flux anomaly time series is compared with the North Atlantic Oscillation (NAO) index, and the result is a positive correlation with ocean warming for positive NAO index periods and ocean cooling associated with negative index periods.
Tyrrhenian Sea circulation and water mass fluxes in spring 2004: Observations and model results
Authors: Vetrano A. , Napolitano E. , Iacono R. , Schroeder K. , Gasparini G. P.
Published: June 2010

Hydrological and current measurements, collected in the Tyrrhenian Sea during May–June 2004, are analyzed with an inverse box model (IBM) to establish the mean circulation patterns of the basin during spring 2004. These patterns are compared with those provided by a high‐resolution, primitive equation model (the Princeton ocean model, or POM) implemented over the area to simulate the mean basin circulation during the survey. The good agreement between the two circulation fields, despite the differences and the respective limitations of the employed methods, represents solid evidence for the reliability of the estimated dynamical structures. Moreover, the POM reveals the short spatial variability of the basin not always resolved by IBM because of the low spatial resolution of the in situ measurements. The comparative study indicates the Tyrrhenian basin as an extremely active region of the Mediterranean Sea, characterized by a rich mesoscale dynamics. This work provides, for the first time after more than 25 years, a novel qualitative assessment of the Tyrrhenian Sea spring circulation, together with a robust quantitative estimation of the water mass stream fluxes inside the basin and of the exchanges with the adjacent regions.
Evaporative dense water formation and cross‐shelf exchange over the northwest Australian inner shelf
Authors: Shearman R. Kipp , Brink Kenneth H.
Published: June 2010

High‐resolution surveys of oceanographic and atmospheric conditions made during the winter over the inner shelf off northwest Australia are used to examine the coastal ocean response to large outgoing heat and freshwater fluxes. Relatively cool, low‐humidity air blows off the Australian continent out over the tropical continental shelf, resulting in a large mean latent heat flux (−177 W m−2) that overwhelms insolation and, along with the outgoing long‐wave radiation, results in substantial net cooling (−105 W m−2) and evaporative freshwater flux (0.6 cm d−1). The inner shelf is characterized by increasingly cool, salty, and dense waters onshore, with a strong front near the 25 m isobath. The front is evident in satellite sea surface temperature (SST) imagery along the majority of the northwest Australian shelf, exhibiting a complex filamentary and eddy structure. Cross‐shelf buoyancy fluxes estimated from the mean, two‐dimensional heat and salt budgets are comparable to parameterizations of cross‐shelf eddy driven fluxes; however, the same fluxes can be achieved by cross‐shelf transports in the bottom boundary layer of about 0.5 m2 s−1 (and an overlying return flow).
Empirical‐statistical downscaling of reanalysis data to high‐resolution air temperature and specific humidity above a glacier surface (Cordillera Blanca, Peru)
Authors: Hofer Marlis , Mölg Thomas , Marzeion Ben , Kaser Georg
Published: June 2010

Recently initiated observation networks in the Cordillera Blanca (Peru) provide temporally high‐resolution, yet short‐term, atmospheric data. The aim of this study is to extend the existing time series into the past. We present an empirical‐statistical downscaling (ESD) model that links 6‐hourly National Centers for Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR) reanalysis data to air temperature and specific humidity, measured at the tropical glacier Artesonraju (northern Cordillera Blanca). The ESD modeling procedure includes combined empirical orthogonal function and multiple regression analyses and a double cross‐validation scheme for model evaluation. Apart from the selection of predictor fields, the modeling procedure is automated and does not include subjective choices. We assess the ESD model sensitivity to the predictor choice using both single‐field and mixed‐field predictors. Statistical transfer functions are derived individually for different months and times of day. The forecast skill largely depends on month and time of day, ranging from 0 to 0.8. The mixed‐field predictors perform better than the single‐field predictors. The ESD model shows added value, at all time scales, against simpler reference models (e.g., the direct use of reanalysis grid point values). The ESD model forecast 1960–2008 clearly reflects interannual variability related to the El Niño/Southern Oscillation but is sensitive to the chosen predictor type.
Characterization of aerosol associated with enhanced small particle number concentrations in a suburban forested environment
Authors: Ziemba L. D. , Griffin R. J. , Cottrell L. D. , Beckman P. J. , Zhang Q. , Varner R. K. , Sive B. C. , Mao H. , Talbot R. W.
Published: June 2010

Two elevated particle number/mass growth events associated with Aitken‐mode particles were observed during a sampling campaign (13–29 September 2004) at the Duke University Free‐Air CO2 Enrichment facility, a forested field site located in suburban central North Carolina. Aerosol growth rates between 1.2 and 4.9 nm hr−1 were observed, resulting in net increases in geometric mean diameter of 21 and 37 nm during events. Growth was dominated by addition of oxidized organic compounds. Campaign‐average aerosol mass concentrations measured by an Aerodyne quadrupole aerosol mass spectrometer (Q‐AMS) were 1.9 ± 1.6 (σ), 1.6 ± 1.9, 0.1 ± 0.1, and 0.4 ± 0.4 μg m−3 for organic mass (OM), sulfate, nitrate, and ammonium, respectively. These values represent 47%, 40%, 3%, and 10%, respectively, of the measured submicron aerosol mass. Based on Q‐AMS spectra, OM was apportioned to hydrocarbon‐like organic aerosol (HOA, likely representing primary organic aerosol) and two types of oxidized organic aerosol (OOA‐1 and OOA‐2), which constituted on average 6%, 58%, and 36%, respectively, of the apportioned OM. OOA‐1 probably represents aged, regional secondary organic aerosol (SOA), while OOA‐2 likely reflects less aged SOA. Organic aerosol characteristics associated with the events are compared to the campaign averages. Particularly in one event, the contribution of OOA‐2 to overall OM levels was enhanced, indicating the likelihood of less aged SOA formation. Statistical analyses investigate the relationships between HOA, OOA‐1, OOA‐2, other aerosol components, gas‐phase species, and meteorological data during the campaign and individual events. No single variable clearly controls the occurrence of a particle growth event.
A 10 year climatology of cloud fraction and vertical distribution derived from both surface and GOES observations over the DOE ARM SPG site
Authors: Xi Baike , Dong Xiquan , Minnis Patrick , Khaiyer Mandana M.
Published: June 2010

Analysis of one decade of radar‐lidar and Geostationary Operational Environmental Satellite (GOES) observations at the Department of Energy (DOE) Atmospheric Radiation Measurement Program (ARM) Southern Great Plains (SGP) site reveals that there is excellent agreement in the long‐term mean cloud fractions (CFs) derived from the surface and GOES data, and the CF is independent of temporal resolution and spatial scales for grid boxes of size 0.5° to 2.5°. When computed over a a 0.5 h (4 h) period, cloud frequency of occurrence (FREQ) and amount when present (AWP) derived from the point surface data agree very well with the same quantities determined from GOES for a 0.5° (2.5°) region centered on the DOE ARM SGP site. The values of FREQ (AWP) derived from the radar‐lidar observations at a given altitude increase (decrease) as the averaging period increases from 5 min to 6 h. Similarly, CF at a given altitude increases as the vertical resolution increases from 90 to 1000 m. The profiles of CF have distinct bimodal vertical distributions, with a lower peak between 1 and 2 km and a higher one between 8 and 11 km. The 10 year mean total CF, 46.9%, varies seasonally from a summer minimum of 39.8% to a maximum of 54.6% during the winter. The annual mean CF is 1%–2% less than that from previous studies, ∼48%–49%, because fewer clouds occurred during 2005 and 2006, especially during winter. The differences in single‐ and multilayered CFs between this study and an earlier analysis can be explained by the different temporal resolutions used in the two studies, where single‐layered CFs decrease but multilayered CFs increase from a 5 min resolution to a 1 h resolution. The vertical distribution of nighttime GOES high cloud tops agrees well with surface observations, but during the daytime, fewer high clouds are retrieved by the GOES analysis than seen from the surface observations. The FREQs for both daytime and nighttime GOES low cloud tops are significantly higher than surface observations, but the CFs are in good agreement.
Descent from the polar mesosphere and anomalously high stratopause observed in 8 years of water vapor and temperature satellite observations by the Odin Sub‐Millimeter Radiometer
Authors: Orsolini Yvan J. , Urban Joachim , Murtagh Donal P. , Lossow Stefan , Limpasuvan Varavut
Published: June 2010

Using newly analyzed mesospheric water vapor and temperature observations from the Sub‐Millimeter Radiometer instrument aboard the Odin research satellite over the period 2001–2009, we present evidence for an anomalously strong descent of dry mesospheric air from the lower mesosphere into the upper stratosphere in the winters of 2004, 2006, and 2009. In the three cases, the descent follows the recovery of the upper stratospheric polar vortex from a major midwinter stratospheric sudden warming. It is also accompanied by the rapid formation of an anomalously warm polar mesospheric layer, i.e., an elevated polar stratopause, near 75 km, and its slower descent to prewarming level (near 1 hPa) over 1.5–2 months. These three winters stand out in the current record of Odin/Sub‐Millimeter Radiometer observations started in July 2001.
Crustal structure beneath the Montserrat region of the Lesser Antilles island arc
Authors: Sevilla Winchelle Ian , Ammon Charles J. , Voight Barry , De Angelis Silvio
Published: June 2010

We use receiver function analysis to estimate the first‐order subsurface seismic structure in the vicinity of the island of Montserrat, located in the northern Lesser Antilles arc and home of the active Soufrière Hills Volcano. Near‐surface complexity in the island structure inhibits our ability to resolve lateral variations in seismic structure, so we average the signals from eight stations in two directions to produce a first‐order regional seismic velocity model. Although we are unable to resolve a precise sharpness of the crust‐mantle transition, we can limit its thickness to less than ∼4 km. Lateral variations in shallow structure complicate a receiver function based estimate of Poisson's ratio, but the data indicate that in both directions sampled by the receiver functions, the lower crustal Poisson's ratio is greater than 0.27 and more likely in the range 0.29–0.30. We estimate a mean crustal thickness of ∼30 km, and the observations suggest that the crust may be slightly thinner northwest of the island (∼26–30 km) than it is to the south (∼30–34 km). The high P wave speed and Poisson's ratio indicate a generally mafic lower crust, with rocks of intermediate composition not precluded in the upper part of the lower crust. We did not find evidence for a thick high‐speed lower crust (>7.4 km/s) as has been inferred in some other arcs.
Convective heat transfer in planetary dynamo models
Authors: King Eric M. , Soderlund Krista M. , Christensen Ulrich R. , Wicht Johannes , Aurnou Jonathan M.
Published: June 2010

The magnetic fields of planets and stars are generated by the motions of electrically conducting fluids within them. These fluid motions are thought to be driven by convective processes, as internal heat is transported outward. The efficiency with which heat is transferred by convection is integral in understanding dynamo processes. Several heat transfer scaling laws have been proposed, but the range of parameter space to which they apply has not been firmly established. Following the plane layer convection study by King et al. (2009), we explore a broad range of buoyancy forcing (Ra) and rotation strength (E−1) to show that heat transfer (Nu) in spherical dynamo simulations occurs in two distinct regimes. We argue that heat transfer scales as Nu ∼ Ra6/5 in the rapidly rotating regime and Nu ∼ Ra2/7 in the weakly rotating regime. The transition between these two regimes is controlled by the competition between the thermal and viscous boundary layers. Boundary layer scaling theory allows us to predict that the transition between the regimes occurs at a transitional Rayleigh number, Rat = E−7/4. Furthermore, boundary layer control of heat transfer is shown to relate to the interior temperature profiles of the models. In the weakly rotating regime, the interior fluid is nearly adiabatic. In the rapidly rotating regime, adverse mean temperature gradients abide, irrespective of the Reynolds number (Re). Extrapolating our results to Earth's core, we estimate that core convection resides in the rapidly rotating regime, with Ra ≈ 2 × 1024 (Ra/Rat ≈ 0.02), corresponding to a superadiabatic density variation of Δρ/ρo ≈ 10−7, which is significantly below the sensitivity of present seismic observations.
Where is the real transform boundary in California?
Authors: Platt John P. , Becker Thorsten W.
Published: June 2010

The zone of highest geodetically defined strain rate in California does not everywhere coincide with the surface trace of the San Andreas Fault (SAF). To determine whether this reflects the pattern of long‐term, permanent deformation, we analyzed the velocity field on swaths across the transform, located so as to avoid intersections among the major fault strands. Slip rates and flexural parameters for each fault were determined by finding the best fit to the velocity profile using a simple arctan model, representing the interseismic strain accumulation. Our slip rates compare well with current geologic estimates, which suggests that the present‐day velocity field is representative of long‐term motions. We find that the transform is a zone of high strain rate up to 80 km wide that is straighter than the SAF and has an overall trend closer to the relative plate motion vector than the SAF. Most sections of the SAF take up less than half of the total slip rate, and slip is transferred from one part of the system to another in a way that suggests that the SAF should not be considered as a unique locator of the plate boundary. Up to half of the total displacement takes place on faults outside the high strain rate zone, distributed over several hundred kilometers on either side. Our findings substantiate previous suggestions that the transform has the characteristics of a macroscopic ductile shear zone cutting the continental lithosphere, around which stress and strain rate decrease on a length scale controlled by the length of the transform.
An improved parameterization of wind‐blown sand flux on Mars that includes the effect of hysteresis
Authors: Kok Jasper F.
Published: June 2010

Saltation, the wind‐driven hopping motion of sand grains, forms dunes and ripples, and ejects fine dust particles into the atmosphere on Mars. Although the wind speed at which saltation is initiated, the “fluid threshold,” has been studied extensively, the wind speed at which saltation is halted, the “impact threshold,” has been poorly quantified for Mars conditions. I present an analytical model of the impact threshold, which is in agreement with measurements and numerical simulations for Earth conditions. For Mars conditions, the impact threshold is approximately an order of magnitude below the fluid threshold, in agreement with previous studies. Saltation on Mars can thus be sustained at wind speeds an order of magnitude less than required to initiate it, leading to the occurrence of hysteresis. I include the effect of hysteresis into an improved parameterization of sand transport on Mars.
Reflected ions at interplanetary shocks
Authors: Richardson J. D.
Published: June 2010

This paper shows that the shock dissipation mechanism changes profoundly from the inner to outer heliosphere and that pickup ions are responsible for shock dissipation beyond 35 AU. We make the first study of reflected ions in ICME sheaths downstream of interplanetary shocks observed by Voyager 2 from 1–80 AU. A reflected ion population was present in 12 of 14 ICME sheaths inside 35 AU and in 0 of 6 sheaths outside 35 AU. Reflected ions comprised from 0–47% of the downstream ions. The ratio of the reflected to thermal ion temperature ranges from 2.6 to 9.3. The percent of reflected ions increases with sonic Mach number and the ratio of the reflected to thermal ion temperature increases with the speed jump at the shock. Energetic neutral atoms created from the heated pickup ions may be observable by IBEX.
Resistance and resilience of benthic biofilm communities from a temperate saltmarsh to desiccation and rewetting
Authors: McKew Boyd A , Taylor Joe D , McGenity Terry J , Underwood Graham J C
Published: July 2010

Periods of desiccation and rewetting are regular, yet stressful events encountered by saltmarsh microbial communities. To examine the resistance and resilience of microbial biofilms to such stresses, sediments from saltmarsh creeks were allowed to desiccate for 23 days, followed by rewetting for 4 days, whereas control sediments were maintained under a natural tidal cycle. In the top 2 mm of the dry sediments, salinity increased steadily from 36 to 231 over 23 days, and returned to seawater salinity on rewetting. After 3 days, desiccated sediments had a lower chlorophyll a (Chl a) fluorescence signal as benthic diatoms ceased to migrate to the surface, with a recovery in cell migration and Chl a fluorescence on rewetting. Extracellular β-glucosidase and aminopeptidase activities decreased within the first week of drying, but increased sharply on rewetting. The bacterial community in the desiccating sediment changed significantly from the controls after 14 days of desiccation (salinity 144). Rewetting did not cause a return to the original community composition, but led to a further change. Pyrosequencing analysis of 16S rRNA genes amplified from the sediment revealed diverse microbial responses, for example desiccation enabled haloversatile Marinobacter species to increase their relative abundance, and thus take advantage of rewetting to grow rapidly and dominate the community. A temporal sequence of effects of desiccation and rewetting were thus observed, but the most notable feature was the overall resistance and resilience of the microbial community.
Extending Use of the NRT to Preschool-Age Children With and Without Specific Language Impairment
Authors: Deevy Patricia , Weil Lisa Wisman , Leonard Laurence B. , Goffman Lisa
Published: July 2010

Purpose

The purpose of this study was to assess the diagnostic accuracy of the Nonword Repetition Test (NRT; Dollaghan & Campbell, 1998) using a sample of 4- and 5-year-olds with and without specific language impairment (SLI) and to evaluate its feasibility for use in universal screening.

Method

The NRT was administered to 29 children with SLI and 47 age-matched children with typical development. Diagnostic accuracy was computed using alternative scoring methods, which treated out-of-inventory phonemes either as errors or as unscorable. To estimate accuracy in a universal screening context, the probability of identifying a child at risk for language impairment was computed using the prevalence of SLI (7%) as the base rate.

Results

Diagnostic accuracy was acceptable using both scoring methods. The resulting likelihood ratios (LR+ = 22.66, 19.43; LR− = .05, .05) were similar to those reported for older children. The probability of accurate detection of children with SLI in the general population increased from 7% to 61%. However, this value suggests that many false positives could be expected.

Conclusion

The NRT yielded results similar to those reported for older children. However, despite its strengths, the NRT is not sufficient for screening the general population of 4- and 5-year-olds.
Measurement and simulation of jet mass caused by a high-aspect ratio hole perturbation
Authors: Keiter P. A. , Elliott J. B. , Blue B. E. , Cooley J. H. , Edwards J. , Kyrala G. A. , Robey H. F. , Spears B. , Wilson D. C.
Published: June 2010

Inertial confinement fusion (ICF) capsule performance can be negatively impacted by the presence of hydrodynamic instabilities. To perform a gas fill on an ICF capsule, current plans involve drilling a small hole and inserting a fill tube to inject the gas mixture into the capsule. This introduces a perturbation on the capsule, which can seed hydrodynamic instabilities. The small hole can cause jetting of the shell material into the gas, which might adversely affect the capsule performance. We have performed simulations and experiments to study the hydrodynamic evolution of jets from high-aspect ratio holes, such as the fill tube hole. Although simulations using cold materials overpredict the amount of mass in the jet, when a plausible amount of preheat (<1 eV) is introduced, the simulations are in better agreement with the experiment.
A simple double-focusing electrostatic ion beam deflector
Authors: Kreckel H. , Bruhns H. , Miller K. A. , Wåhlin E. , Davis A. , Höckh S. , Savin D. W.
Published: June 2010

We have developed an electrostatic, double-focusing 90° deflector for fast ion beams consisting of concentric cylindrical plates of differing heights. In contrast to standard cylindrical deflectors, our design allows for focusing of an incoming parallel beam not only in the plane of deflection but also in the orthogonal direction. The optical properties of our design resemble those of a spherical capacitor deflector while it is much easier and more cost effective to manufacture.
Development of a synthetic phase contrast imaging diagnostic
Authors: Rost J. C. , Lin L. , Porkolab M.
Published: June 2010

A “synthetic diagnostic” has been developed to calculate the expected experimental response of phase contrast imaging (PCI), a scattering diagnostic used to measure density fluctuations in laboratory plasmas, to a tokamak discharge modeled with the GYRO nonlinear gyrokinetic code [J. Candy and R. Waltz, J. Comput. Phys. 186, 545 (2003)]. The synthetic PCI includes the spatial response of the experimental diagnostic, primarily implemented as a line integral of plasma density along the beam path, and the minimum and maximum wavenumber response resulting from the detection scheme. The synthetic PCI can be used for comparisons between GYRO and experiment as well as studies of the PCI response.
An exact solution to Maxwell’s equations including an evanescent field for a gapped three layered optical system
Authors: Kitsunezaki Naofumi , Mizusawa Jun-ichi , Kitsunezaki Akio
Published: June 2010

We have investigated the electromagnetic characteristics of an optical configuration consisting of two dielectric regions of the same n>1 with a thin flat gap of air/vacuum of width d between them. Based on an analytical and exact solution to Maxwell’s equations including an evanescent field in the vacuum gap, we have obtained the transmission property of a four terminal optical circuit that consists of two input lights aimed toward the gap from both sides of the dielectric regions and two output lights from the gap, where all of the four terminals have the same angle to a plane that is vertical to the boundary plane between the dielectric and the vacuum. The results show several unique possible applications of the optical circuit elements such as a variable ratio power splitter, phase to amplitude field modulator, and optical mode selector.