bluuebunny/crossref_metadata_2025 huggingface dataset:
Summer breakout of trapped bottom dense water from the northern Adriatic
Authors: Vilibić Ivica , Beg Paklar Gordana , Žagar Nedjeljka , Mihanović Hrvoje , Supić Nastjenjka , Žagar Mark , Domijan Nenad , Pasarić Miroslava
Published: October 2008

The paper deals with an intriguing dense‐water breakout episode in mid‐August 2004 which has been observed in the bottom layers of the oil rig located in the middle of the northern Adriatic. Various data (temperature series and vertical T‐S profiles, currents, meteorological measurements, and satellite images) have been analyzed in order to understand conditions which preceded, were active, and followed the breakout episode. A stationary bottom pool of dense water, generated during the previous winter, has been suspected to be a source of the dense water observed during the breakout, with a permanent position established by a stationary northern Adriatic cyclonic‐anticyclonic gyre system. The breakout lasted for 3 days, advecting the bottom waters more than 2°C colder than residing waters at the oil rig site. The main result of modeling experiments concerns the generative force for the observed breakout which was found to be a mesoscale storm that occurred over the open north Adriatic on 8 August 2004. The storm has been reproduced by the Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS®) atmospheric model which was then used to force the Princeton Ocean Model (POM) at the surface. Results of simulations reveal the capability of the storm to break the thermohaline fronts through the wind‐induced baroclinic transport and downwelling at the exposed shorelines. This is the first study in the Adriatic which evaluates the impact of mesoscale summer storm to the sea, driving bottom layer circulation through the convergence/divergence dynamics in addition to the direct impact on the sea surface through the wind stress forcing.
Warm pool thermodynamics from the Arabian Sea Monsoon Experiment (ARMEX)
Authors: Sengupta Debasis , Parampil Sindu R. , Bhat G. S. , Murty V. S. N. , Ramesh Babu V. , Sudhakar T. , Premkumar K. , Pradhan Y.
Published: October 2008

Before the onset of the south Asian summer monsoon, sea surface temperature (SST) of the north Indian Ocean warms to 30–32°C. Climatological mean mixed layer depth in spring (March–May) is 10–20 m, and net surface heat flux (Qnet) is 80–100 W m−2 into the ocean. Previous work suggests that observed spring SST warming is small mainly because of (1) penetrative flux of solar radiation through the base of the mixed layer (Qpen) and (2) advective cooling by upper ocean currents. We estimate the role of these two processes in SST evolution from a two‐week Arabian Sea Monsoon Experiment process experiment in April–May 2005 in the southeastern Arabian Sea. The upper ocean is stratified by salinity and temperature, and mixed layer depth is shallow (6 to 12 m). Current speed at 2 m depth is high even under light winds. Currents within the mixed layer are quite distinct from those at 25 m. On subseasonal scales, SST warming is followed by rapid cooling, although the ocean gains heat at the surface: Qnet is about 105 W m−2 in the warming phase and 25 W m−2 in the cooling phase; penetrative loss Qpen is 80 W m−2 and 70 W m−2. In the warming phase, SST rises mainly because of heat absorbed within the mixed layer, i.e., Qnet minus Qpen; Qpen reduces the rate of SST warming by a factor of 3. In the second phase, SST cools rapidly because (1) Qpen is larger than Qnet and (2) advective cooling is ∼85 W m−2. A calculation using time‐averaged heat fluxes and mixed layer depth suggests that diurnal variability of fluxes and upper ocean stratification tends to warm SST on subseasonal timescale. Buoy and satellite data suggest that a typical premonsoon intraseasonal cooling event occurs under clear skies when the ocean is gaining heat through the surface. In this respect, premonsoon SST cooling in the north Indian Ocean is different from that due to the Madden‐Julian oscillation or monsoon intraseasonal oscillation.
AIRS views transport from 12 to 22 July 2004 Alaskan/Canadian fires: Correlation of AIRS CO and MODIS AOD with forward trajectories and comparison of AIRS CO retrievals with DC‐8 in situ measurements during INTEX‐A/ICARTT
Authors: McMillan W. W. , Warner J. X. , Comer M. McCourt , Maddy E. , Chu A. , Sparling L. , Eloranta E. , Hoff R. , Sachse G. , Barnet C. , Razenkov I. , Wolf W.
Published: October 2008

We present observations of transport of tropospheric carbon monoxide (CO) obtained by the Atmospheric Infrared Sounder (AIRS) on board NASA's Aqua satellite during the Intercontinental Chemical Transport Experiment–North America (INTEX‐A) field campaign in the summer of 2004, part of the International Consortium for Atmospheric Research on Transport and Transformation (ICARTT). In situ measurements from NASA's DC‐8 provide crucial assessment of AIRS midtropospheric (400–500 mbar) CO retrievals. For the nine best INTEX‐A profiles, convolution of the in situ profiles with AIRS verticality functions demonstrates version 4 AIRS CO retrievals between 400 and 500 mbar are biased high by approximately 8% with a standard deviation slightly less than 5%. The 400–500 mbar region is the only portion of the version 4 AIRS CO retrievals that can be validated as presented here. In some cases, AIRS CO retrievals may be sensitive to CO in the lower to midtroposphere (800–500 mbar). Focusing on one major episode, we investigate transport of CO from a large fire outbreak in the Alaskan/Canadian Yukon region from 11 to 14 July 2004 and follow it downwind to the southeastern United States and Europe by 22 July 2004. Comparison of AIRS CO maps and forward trajectories from fire locations reveals substantial variations in fire emissions especially emission injection height. Any useful forecast model must control for such fire emission variabilities to predict correctly the downwind impact. To match the forward trajectory analyses with AIRS CO observations requires some fires to have directly injected emissions to at least 500 mbar and perhaps as high as 300 mbar. Ground‐based lidar observations show smoke plume altitudes from 3 to 11 km over Wisconsin and from 1 to 4 km over Maryland in agreement with the forward trajectories. The Wisconsin lidar profiles on the afternoon of 18 July 2004 constrain the altitude of CO‐rich smoke observed by AIRS and MODIS to lie between 2 and 5.5 km above the surface, roughly 800 to 500 mbar. We find that changes in the correlation between AIRS CO and MODIS AOD reflect changes in the CO vertical distribution during this event. This finding is confirmed by in situ measurements, meteorological analyses, and forward trajectory analyses.
Transient hydrodynamics within intercratonic sedimentary basins during glacial cycles
Authors: Bense V. F. , Person M. A.
Published: October 2008

The hydrodynamic consequences of a glaciation/deglaciation cycle within an intercratonic sedimentary basin on subsurface transport processes is assessed using numerical models. In our analysis we consider the effects of mechanical ice sheet loading, permafrost formation, variable density fluids, and lithospheric flexure on solute/isotope transport, groundwater residence times, and transient hydraulic head distributions. The simulations are intended to apply, in a generic sense, to intercratonic sedimentary basins that would have been near the southern limit of the Laurentide Ice Sheet during the last glacial maximum (∼20 ka B.P.), such as the Williston, Michigan, and Illinois basins. We show that in such basins fluid flow and recharge rates are strongly elevated during glaciation as compared to nonglacial periods. Furthermore, our results illustrate that steady state hydrodynamic conditions in these basins are probably never reached during a 32.5 ka cycle of advance and retreat of a wet‐based ice sheet. Present‐day hydrogeological conditions across formerly glaciated areas are likely to still reflect the impact of the last glaciation and associated processes that ended locally more than 10 ka B.P. Our results reveal characteristic spatial patterns of underpressure and overpressure that occur in aquitards and aquifers, respectively, as a result of recent glaciation. The calculated emplacement of low salinity, isotopically light glacial meltwater along basin margins is roughly consistent with observations from formerly glaciated basins in North America. The modeling presented in this study will help to improve the management of groundwater resources in formerly glaciated basins as well as to evaluate the viability on geological timescales of nuclear waste repositories located at high latitudes.
Bounding higher‐order ionosphere errors for the dual‐frequency GPS user
Authors: Datta‐Barua S. , Walter T. , Blanch J. , Enge P.
Published: October 2008

Civil signals at L2 and L5 frequencies herald a new phase of Global Positioning System (GPS) performance. Dual‐frequency users typically assume a first‐order approximation of the ionosphere index of refraction, combining the GPS observables to eliminate most of the ranging delay, on the order of meters, introduced into the pseudoranges. This paper estimates the higher‐order group and phase errors that occur from assuming the ordinary first‐order dual‐frequency ionosphere model using data from the Federal Aviation Administration's Wide Area Augmentation System (WAAS) network on a solar maximum quiet day and an extremely stormy day postsolar maximum. We find that during active periods, when ionospheric storms may introduce slant range delays at L1 as high as 100 m, the higher‐order group errors in the L1–L2 or L1–L5 dual‐frequency combination can be tens of centimeters. The group and phase errors are no longer equal and opposite, so these errors accumulate in carrier smoothing of the dual‐frequency code observable. We show the errors in the carrier‐smoothed code are due to higher‐order group errors and, to a lesser extent, to higher‐order phase rate errors. For many applications, this residual error is sufficiently small as to be neglected. However, such errors can impact geodetic applications as well as the error budgets of GPS Augmentation Systems providing Category III precision approach.
Rain rates, drop size information, and precipitation type, obtained from one‐way differential propagation phase and attenuation along a microwave link
Authors: Holt A. R. , Cummings R. J. , Upton G. J. G. , Bradford W. J.
Published: October 2008

We report measurements of total path differential phase along a 23 km microwave link in northwest England, in addition to measurements of total path attenuation at 17.6 GHz and 12.8 GHz, with the latter at both horizontal and vertical polarizations. Since the differential phase measurements are one‐way, they do not contain backscatter differential phase (unlike radar measurements of differential phase). We show that differential phase is sensitive to atmospheric effects, but that it can help identify both snow and sleet (a mixture of melting particles and rain) near the ground. Additionally, we found that it gave unexpectedly accurate path‐averaged rain rates. We also report measurements from a second, 15 km, link operating at 22.9 GHz and 14.1 GHz. There is evidence from this link, which had no topographic constraints on its beam width, that differential phase can be affected by interference possibly caused by scattering from the terrain. The measurements give some information about the path‐average drop size distribution being experienced by the link.
Regeneration of Fe(II) during EIFeX and SOFeX
Authors: Croot P. L. , Bluhm K. , Schlosser C. , Streu P. , Breitbarth E. , Frew R. , Van Ardelan M.
Published: October 2008

Investigations into Fe(II) cycling during two Southern Ocean mesoscale iron enrichment experiments, SOFeX and EIFeX, clearly show the importance of Fe(II) to iron speciation during these experiments. In both cases the added Fe(II) persisted significantly longer than its expected oxidation time indicating a significant Fe reduction process at work. During EIFeX diel studies showed a strong photochemically induced cycle in Fe(II) production in sunlit surface waters. Our results suggest that the photochemical cycling of iron may also be important in unfertilized waters of the Southern Ocean.
Strong Indian Ocean sea surface temperature signals associated with the Madden‐Julian Oscillation in late 2007 and early 2008
Authors: Vialard J. , Foltz G. R. , McPhaden M. J. , Duvel J. P. , de Boyer Montégut C.
Published: October 2008

A moored buoy was recently deployed at 8°S, 67°E in the shallow thermocline region of the Indian Ocean known as “Seychelles‐Chagos Thermocline Ridge” (SCTR), where the Madden Julian Oscillation (MJO) is associated with strong sea surface temperature (SST) variability. We use observations from this mooring to describe the oceanic signature of two MJOs between November 2007 and February 2008. The four‐month average upper ocean heat balance was largely between heating by atmospheric forcing (2.0 ± 0.3°C/month) and a significant cooling by subsurface processes (−2.2 ± 0.8°C/month), consistent with climatological Ekman pumping in the region. The two MJO events resulted in strong intraseasonal SST variations (1.5 to 2°C in ∼20 days) in the SCTR. At the mooring site, atmospheric fluxes dominated the upper ocean heat balance at the MJO timescale, with the net surface heat flux into the ocean decreasing from an average 105 W m−2 during suppressed phases to 15 W m−2 during active phases of the MJO. It is difficult to establish if MJO‐induced variations of subsurface processes also contributed to the cooling because of large uncertainty in this term. Lateral advection had no systematic fluctuations on MJO timescales, but cannot be neglected at the mooring site.
Transitional nonlinear elastic behaviour in dense granular media
Authors: Brunet Thomas , Jia Xiaoping , Johnson Paul A.
Published: October 2008

Nonlinear sound propagation in a stressed glass bead pack is investigated via amplitude measurements of harmonic generation. We evidence two distinct regimes of sound‐matter interaction: reversible and irreversible, as a function of the ratio rs between dynamic strain and static one. In the reversible regime, the higher harmonics generated agree well with a mean‐field model based on the Hertz contact theory, and the coefficient of nonlinearity β deduced from the measured amplitude of second‐harmonic is consistent with that deduced from the acoustoelastic measurement. Beyond a certain threshold (rs > 3%), the interaction of sound wave with granular matter becomes irreversible, accompanied by a small compaction of the medium.
Recent in‐situ observations of magnetic reconnection in near‐Earth space
Authors: Paschmann Götz
Published: October 2008

The paper presents a brief review of recent in‐situ observations of reconnection in space, with emphasis on results pertaining to the question of anti‐parallel versus component reconnection, the implied spatial and temporal scales, the location of the reconnection sites, particle acceleration, reconnection rates, the dependence on plasma β, and the properties of the diffusion region.
CloudSat adding new insight into tropical penetrating convection
Authors: Luo Zhengzhao , Liu Guangyuan Y. , Stephens Graeme L.
Published: October 2008

Collocated observations of cloud‐top height and cloud‐profiling information from CloudSat and cloud‐top temperature from MODIS are analyzed to determine where convective cloud top occurs in relation to the cold point tropopause and to characterize the internal vertical structure of these deep convective clouds. Three types of penetrating convection identified as cold‐low (CL), cold‐high (CH), and warm‐high (WH) are defined according to the cloud‐top temperature and height in comparison to the cold point tropopause height and temperature: It is suggested that CL, CH and WH types correspond to, respectively, the incipient, mature and dissipating stage of the convective lifecycle. Multiple lines of evidence, including characteristics of CloudSat radar profiles, test against the undiluted ascent hypothesis, and examination of convective system size, all lend support to this interpretation.
Distinctive effects of interplanetary electric field and substorm on nighttime equatorial F layer: A case study
Authors: Chakrabarty D. , Sekar R. , Sastri J. H. , Ravindran Sudha
Published: October 2008

A geomagnetic storm event is identified wherein the base of the equatorial F layer (h′F) over dip equator moved unusually upward till premidnight hours and descended thereafter. The h′F variation is linearly correlated with the variation in the smoothed auroral electrojet index (AE) which varies slowly. The fast fluctuations (residuals) with periodicity ∼42 min in the vertical plasma drift are found to be causally related with the fast fluctuations in the dawn‐to‐dusk component of interplanetary electric field (IEFy) and interestingly, not with the fast fluctuations in AE. However, during the interval when a substorm was triggered in association with sharp transitions in IEFy polarity, the drift fluctuations follow the AE fluctuations and are out of phase with IEFy fluctuations. The investigation demonstrates distinctive effects of IEFy and substorm‐related current systems on the zonal electric field over dip equator in the premidnight hours during geomagnetic storms.
Comparisons of satellites liquid water estimates to ECMWF and GMAO analyses, 20th century IPCC AR4 climate simulations, and GCM simulations
Authors: Li Jui‐Lin F. , Waliser D. , Woods C. , Teixeira J. , Bacmeister J. , Chern J. , Shen B.‐W. , Tompkins A. , Tao W.‐K. , Köhler M.
Published: October 2008

To assess the fidelity of general circulation models (GCMs) in simulating cloud liquid water, liquid water path (LWP) retrievals from several satellites with passive sensors and the vertically‐resolved liquid water content (LWC) from the CloudSat are used. Comparisons are made with ECMWF and MERRA analyses, GCM simulations utilized in the IPCC 4th Assessment, and three GCM simulations. There is considerable disagreement amongst the LWP estimates and amongst the modeled values. The LWP from GCMs are much larger than the observed estimates and the two analyses. The largest values in the CloudSat LWP occur over the boundary‐layer stratocumulus regions; this feature is not as evident in the analyses or models. Better agreement is found between the two analyses and CloudSat LWP when cases with surface precipitation are excluded. The upward vertical extent of LWC from the GCMs and analyses is greater than CloudSat estimates. The issues of representing LWC and precipitation consistently between satellite‐derived and model values are discussed.
Representation of the measured geosynchronous plasma environment in spacecraft charging calculations
Authors: Davis V. A. , Mandell M. J. , Thomsen M. F.
Published: October 2008

Historically, the characterization of the magnetospheric environment has limited our ability to determine spacecraft surface charging levels. One difficulty lies in the common practice of fitting the plasma data to a Maxwellian or Double Maxwellian distribution function, which may not represent the data well for use in spacecraft charging simulations. We use electron and ion flux spectra measured by the Los Alamos National Laboratory (LANL) Magnetospheric Plasma Analyzer (MPA) during eclipse in September 2001 to examine how the use of different spectral representations of the charged particle environment in computations of spacecraft potentials during magnetospheric substorms affects the accuracy of the results. We examine charging and noncharging flux spectra and the relationships between the density and temperature moments. We then calculate the spacecraft potential (zero net current) using both the measured fluxes and several different fits to these fluxes. The potential computed using the measured fluxes and secondary and backscattered fluxes computed for graphite carbon, with a constant fraction of 81% of secondary electrons escaping, is within a factor of three of the measured potential for 87% of the data. Potentials calculated using a Kappa function fit to the electron flux and a Maxwellian function fit to the ion flux agree with measured potentials nearly as well. Alternative spectral representations give less accurate estimates. The use of all the components of the net flux, along with spacecraft specific average material properties, gives a better estimate of the spacecraft potential than the measured flux from a single high‐energy channel.
Estimation of magnetopause motion from low‐energy neutral atom emission
Authors: Hosokawa K. , Taguchi S. , Suzuki S. , Collier M. R. , Moore T. E. , Thomsen M. F.
Published: October 2008

A new method for deriving the position of the dayside equatorial magnetopause directly from the measured intensity of energetic neutral atom (ENA) emissions is presented. This approach makes it possible to track the position of the magnetopause using data observed by the low‐energy neutral atom (LENA) imager on board the Imager for Magnetopause‐to‐Aurora Global Exploration (IMAGE) spacecraft. The model is applied to data recorded during a period of high solar wind dynamic pressure on 13 April 2001. In this interval, significant ENA flux was observed originating from the dayside low‐latitude magnetosheath. This ENA flux is primarily the result of enhanced charge exchange between the increased solar wind plasma and exospheric hydrogen neutrals. The temporal variation in the estimated magnetopause position is compared with in situ measurements of magnetopause crossings by the LANL‐01A spacecraft in geosynchronous orbit and the results of a recent empirical magnetopause model. It is demonstrated that the subsolar distance of the magnetopause was successfully tracked for a period of more than 1 h. In this particular case example, the dayside magnetopause is closer to the Earth and fluctuates on a shorter timescale than predicted by the previous empirical model based on in situ data. It is also revealed that the subsolar magnetopause can move with speeds of 100–200 km s−1 in response to marked dynamic pressure changes, and during periods of stable dynamic pressure can fluctuates with speeds of up to 50 km s−1.
Topside ionospheric scale heights retrieved from Constellation Observing System for Meteorology, Ionosphere, and Climate radio occultation measurements
Authors: Liu Libo , He Maosheng , Wan Weixing , Zhang Man‐Lian
Published: October 2008

The vertical scale height (VSH) in the topside ionosphere can be derived from electron density profiles. In this study, the electron density profiles retrieved from the COSMIC/FORMOSAT‐3 (a Constellation Observing System for Meteorology, Ionosphere, and Climate mission; C/F3 for short) ionospheric radio occultation (IRO) observations have been collected to investigate the local time, seasonal, latitudinal, and longitudinal variations of the VSH. With the postprocessed C/F3 IRO electron density profiles during the interval from day of year (DOY) 194 in 2006 to DOY 60 in 2008, we conduct an analysis on the behaviors of VSH at an altitude of 400 km. There are appreciable latitudinal variations in VSH. A new finding is a significant peak around dip equator during daytime in four seasons. Away from the equatorial peak, it is obvious that the VSH generally increases at higher latitudes. The equatorial VSH undergoes a significant diurnal variation with a local noon maximum. The peak shifts to sunrise time with increasing dip latitude, and the values of daytime VSH become comparable with those at nighttime at low latitude in both hemispheres, which is somewhat different from the feature revealed from Arecibo incoherent scatter radar observations. One of the crucial findings in our results is the most outstanding feature of VSH, that is, the presence of a substantial longitudinal structure in equatorial regions. A wave‐like longitudinal feature is found in equatorial VSH during the daytime in four seasons, while it becomes weaker or absent at other local time intervals and at higher latitudes. This investigation also confirms that the behaviors of VSH are not strongly consistent with those of the neutral or plasma‐scale heights.
Cross‐ripple patterns and wave directional spectra
Authors: Cheel Richard A. , Hay Alex E.
Published: October 2008

Rotary sonar images of the seafloor during SandyDuck97 are used to investigate the geometry of the cross‐rippled bed state relative to the directional properties of the incident waves. The sonar imagery indicates that the cross‐ripple pattern is a quasi‐regular diamond‐shaped lattice constructed of variable length ladder‐like tiles, each with shorter‐wavelength ripples residing within the troughs of the longer‐wavelength component. The longer‐wavelength crests were oriented at approximately ±30° with respect to the incident wave direction. Most wave directional spectra were not bimodal in direction and, for the small number (17%) which were, the distribution of the angular separations of the two peaks was very broad and indicated no preferred value. Thus, contrary to some previous suggestions in the literature, these results indicate not only that cross ripples do not require waves propagating from two different directions for their formation but also that for most of the occurrences during this experiment, cross ripples formed when the incident wave field was unimodal in direction. Finally, the orientation angles of the long‐crested ripple components exhibit no dependence on mean current velocity.
Tracer‐based assessment of the origin and biogeochemical transformation of a cyclonic eddy in the Sargasso Sea
Authors: Li Qian P. , Hansell Dennis A. , McGillicuddy Dennis J. , Bates Nicholas R. , Johnson Rodney J.
Published: October 2008

Mechanisms of nutrient supply in oligotrophic ocean systems remain inadequately understood and quantified. In the North Atlantic Subtropical Gyre, for example, the observed rates of new production are apparently not balanced by nutrient supply via vertical mixing. Mesoscale eddies have been hypothesized as a mechanism for vertical nutrient pumping into the euphotic zone, but the full range and magnitude of biogeochemical impacts by eddies remain uncertain. We evaluated a cyclonic eddy located near Bermuda for its effect on water column biogeochemistry. In the density range σθ 26.1 to 26.7, an eddy core with anomalous salinity, temperature, and biogeochemical properties was observed, suggesting that the eddy was not formed with local water (i.e., not formed of the waters surrounding the eddy at the time of observations), hence complicating efforts to quantify biogeochemical processes in the eddy. We combined conservative hydrographic tracers (density versus potential temperature and salinity) and quasi‐conservative biogeochemical tracers (density versus NO, PO, and total organic carbon) to propose the origin of the eddy core water to have been several hundred kilometers to the southeast of the eddy location at sampling. By comparing the observed eddy core's biogeochemical properties with those near the proposed origin, we estimate the net changes in biogeochemical properties that occurred. A conservative estimate of export was 0.5 ± 0.34 mol N m−2 via sinking particles, with export occurring prior to our period of direct observation. Our results suggest that biogeochemical signals induced by mesoscale eddies could survive to be transported over long distances, thus providing a mechanism for lateral fluxes of nutrients and AOU (apparent oxygen utilization). Given that the proposed source area of this eddy is relatively broad, and the eddy‐mixing history before our sampling is unknown, uncertainty remains in our assessment of the true biogeochemical impact of mesoscale eddies in the gyre.
Influence of convective processes on the isotopic composition (δ18O and δD) of precipitation and water vapor in the tropics: 1. Radiative‐convective equilibrium and Tropical Ocean–Global Atmosphere–Coupled Ocean‐Atmosphere Response Experiment (TOGA‐COARE) simulations
Authors: Bony Sandrine , Risi Camille , Vimeux Françoise
Published: October 2008

Cumulus convection constitutes a key process in the control of tropical precipitation and the vertical transport of atmospheric water. To better understand the influence of convective processes on the isotopic composition of precipitation and water vapor, water stable isotopes (H218O and HDO) are introduced into a single column model including the Emanuel convective parameterization. This paper analyzes unidimensional simulations of the tropical atmosphere in a state of radiative‐convective equilibrium, and simulations forced by data from the Tropical Ocean–Global Atmosphere–Coupled Ocean‐Atmosphere Response Experiment (TOGA‐COARE). This study shows that deep convective atmospheres are associated with robust isotopic features such as an isotopic composition of the air below the tropical tropopause layer (around 12–13 km) close to the typical values observed in the lower tropical stratosphere, and an isotopic enrichment of the upper tropospheric water that starts well below the tropopause. It highlights the critical role of condensate lofting and convective detrainment in these features, and the role of convective unsaturated downdrafts in the control of the isotopic composition of precipitation. Finally, it shows that the so‐called “amount effect” primarily reveals the influence of large‐scale atmospheric circulation changes on the isotopic composition of the precipitation, and that temperature changes not associated with circulation changes lead to an “anti–amount effect”. The detailed analysis of the physical processes underlying the “amount effect” is presented in a companion paper.
Influence of convective processes on the isotopic composition (δ18O and δD) of precipitation and water vapor in the tropics: 2. Physical interpretation of the amount effect
Authors: Risi Camille , Bony Sandrine , Vimeux Françoise
Published: October 2008

In the tropics, the proportion of heavier water isotopes in precipitation is anticorrelated with the precipitation amount. The physical processes underlying this so‐called amount effect are still poorly understood and quantified. In the present study, stable water isotopes (H218O and HDO) have been introduced in a single column model including the Emanuel convection parameterization. We investigate the physical processes underlying the amount effect and propose a methodology to quantify their relative contributions. We focus on convective processes, since the idealized framework of the single column models does not allow us to consider the effects of large‐scale horizontal advections of air masses of different isotopic signatures. We show that two kinds of processes predominantly explain the amount effect: first, the reevaporation of the falling rain and the diffusive exchanges with the surrounding vapor; and second, the recycling of the subcloud layer vapor feeding the convective system by convective fluxes. This highlights the importance of a detailed representation of rain evaporation processes to simulate accurately the isotopic composition of precipitation in the tropics. The variability of the isotopic composition on different timescales (from days to months) is also studied using a unidimensional simulation of the Tropical Ocean–Global Atmosphere–Coupled Ocean‐Atmosphere Response Experiment (TOGA‐COARE) campaign. The amount effect is best observable at intraseasonal or longer timescales. The period of time over which convective activity significantly affects the isotopic composition of precipitation is related to the residence time of water within atmospheric reservoirs.
Artificial modification of polar mesospheric winter echoes with an RF heater: Do charged dust particles play an active role?
Authors: La Hoz C. , Havnes O.
Published: October 2008

An investigation of polar mesosphere winter echoes (PMWE) has been carried out with the mesosphere‐stratosphere‐troposphere Mobile Rocket and Radar Observatory (MST MORRO) radar operating at 56 MHz. MORRO has been deployed recently at the European Incoherent Scatter (EISCAT) installation near Tromsø in northern Norway, home of two other large incoherent scatter radars and an RF heating facility. The main object of the investigation is to examine whether, and if so, how, RF heating influences PMWE. In particular, an experimental confirmation of the overshoot effect would indicate the presence of charged dust particles. On 11 February 2008 we measured several weak and variable PMWE layers and we used the RF heater with an on period of 20 s and off period of 100 s to modulate the radar scatter from the layers. We chose one layer, which for 44 min was the strongest and most stable layer, for further analysis. The signal intensity variation during an averaged on/off heater period shows the expected weakening of the signal intensity when heating is turned on followed by a significant small recovery of the signal during the on phase and a corresponding small overshoot of the signal strength of about 13–15% over the background level when heating is switched off. The recovery and overshoot are attributable to charge accumulation on the dust particles due to electron heating. The overshoot characteristic curve shows that a considerable increase in the electron temperature did take place during heating and that charged dust particles should be present, probably with radii of some nanometers.
Gas transfer rate and CO2 flux between an unproductive lake and the atmosphere in northern Sweden
Authors: Jonsson A. , Åberg J. , Lindroth A. , Jansson M.
Published: October 2008

Measurements of the gas transfer rate of CO2 between lake water and the atmosphere present a critical problem for the understanding of lake ecosystem carbon balances and landscape carbon budgets. We present calculations of the gas transfer rate of CO2 from direct measurements of the CO2 flux using an eddy covariance system and concurrent measurements of the concentration of CO2 in the surface water in a lake in boreal zone of northern Sweden. The measured gas transfer rate was different, and in general larger than, rates obtained with the most commonly used models for prediction of the gas transfer rate in lakes. The normalized gas transfer rate (k600EC) was well predicted from the wind speed at 10 m height if data were bin classed into wind classes of 1 m/s for winds above 1 m/s. Unbinned data were also correlated to wind speed but also to water temperature, water temperature/air temperature ratio and to incoming photosynthetic active radiation (PAR). These relationships could reflect effects of both physico‐chemical reactions and biological activity.
Sorting out PtdIns(4,5)P2 and clathrin-coated vesicles in plants
Authors: Brearley Charles
Published: October 2008

Phosphoinositides and their binding proteins are regulators of many aspects of the vesicle-trafficking processes that underlie cellular physiology in animal cells. Relatively little is known, by comparison, of the contribution of phosphoinositides to membrane-trafficking phenomena in plants. A study in this issue of the Biochemical Journal by König et al. reports for the first time in this kingdom the association of PtdIns(4,5)P2 with an endomembrane fraction enriched for clathrin. This work is discussed in the context of current evidence for constitutive and evoked endocytosis of membrane protein cargoes in plants.
Low extended defect density nonpolar m-plane GaN by sidewall lateral epitaxial overgrowth
Authors: Kim Kwang-Choong , Schmidt Mathew C. , Wu Feng , McLaurin Melvin B. , Hirai Asako , Nakamura Shuji , DenBaars Steven P. , Speck James S.
Published: October 2008

Sidewall lateral epitaxial overgrowth (SLEO) is demonstrated by metal organic chemical vapor deposition for nonpolar {11¯00} m-plane GaN films. m-plane GaN films were grown by metal organic chemical vapor deposition on m-plane 6H SiC substrates with an AlN initiation layer. Subsequently, an SiO2 stripe dielectric pattern was formed with 2μm window openings parallel to the [112¯0] a-direction and an 8μm mask and then the m-plane GaN was etched through the window openings to reveal Ga-face (0001) and N-face (0001¯) sidewalls. The SLEO growth was achieved in two growth steps—lateral growth from the sidewalls and subsequent growth through and then over the dielectric mask openings. In comparison to planar m-plane GaN films grown on 6H SiC, the threading dislocation density was reduced from low 1010to3×108cm−2 and the stacking fault density was reduced by one order of magnitude.
General in situ chemical etching synthesis of ZnO nanotips array
Authors: Wang H. Q. , Li G. H. , Jia L. C. , Wang G. Z. , Li L.
Published: October 2008

In this letter, we present a general solution based in situ chemical etching strategy to synthesize ZnO nanotips arrays. The in situ chemical etching can generate nanotips with controllable tip morphologies on various substrates, and the nanotips density is tunable via etching ZnO nanorods with different root diameters. The preferential etching along c axis and the curvature dependence of the NH3 molecule absorption on the nanorod tip are considered responsible for the formation of ZnO nanotips. This general in situ chemical etching method will significantly advance the research in the ZnO nanotips based nanodevice.
Structural properties of nitrogenated amorphous carbon films: Influence of deposition temperature and radiofrequency discharge power
Authors: Lazar G. , Bouchet-Fabre B. , Zellama K. , Clin M. , Ballutaud D. , Godet C.
Published: October 2008

The structural properties of nitrogenated amorphous carbon deposited by radiofrequency magnetron sputtering of graphite in pure N2 plasma are investigated as a function of the substrate temperature and radiofrequency discharge power. The film composition is derived from x-ray photoemission spectroscopy, nuclear reaction analysis and elastic recoil detection measurements and the film microstructure is discussed using infrared, Raman, x-ray photoemission and near edge x-ray absorption fine structure spectroscopic results. At low deposition temperature and low radiofrequency power, the films are soft, porous, and easily contaminated with water vapor and other atmospheric components. The concentration of nitrogen in the films is very large for low deposition temperatures (∼33.6at.% N at 150°C) but decreases strongly when the synthesis temperature increases (∼15at.% N at 450°C). With increasing deposition temperature and discharge power values, the main observed effects in amorphous carbon nitride alloys are a loss of nitrogen atoms, a smaller hydrogen and oxygen contamination related to the film densification, an increased order of the aromatic sp2 phase, and a strong change in the nitrogen distribution within the carbon matrix. Structural changes are well correlated with modifications of the optical and transport properties.
Direct numerical simulation of turbulence in injection-driven plane channel flows
Authors: Venugopal Prem , Moser Robert D. , Najjar Fady M.
Published: October 2008

Compressible turbulent flow in a periodic plane channel with mass injecting walls is studied as a simplified model for core flow in a solid-propellant rocket motor with homogeneous propellant and other injection-driven internal flows. In this model problem, the streamwise direction was asymptotically homogenized by assuming that at large distances from the closed end, both the mean and rms of turbulent fluctuations evolve slowly in the streamwise direction when compared to the turbulent fluctuations themselves. The Navier–Stokes equations were then modified to account for this slow growth. A direct numerical simulation of the homogenized compressible injection-driven turbulent flow was then conducted for conditions occurring at a streamwise location situated 40 channel half-widths from the closed off end and at an injection Reynolds number of approximately 190. The turbulence in this model flow was found to be only weakly compressible, although significant compressibility existed in the mean flow. As in nontranspired channels, turbulence resulted in increased near-wall shear for the mean streamwise velocity. When normalized by the average rate of turbulence production, the magnitudes of near-wall velocity fluctuations were similar to those in the log region of nontranspired wall-bounded turbulence. However, the sharp peak in streamwise velocity fluctuations observed in nontranspired channels was absent. While streaks and inclined vortices were observed in the near-wall region, their structure was very similar to those observed in the log region of nontranspired channels. These differences are attributed to the absence of a viscous sublayer in the transpired case which in turn is the result of the fact that the no-slip condition for the transpired case is an inviscid boundary condition. That is, unlike nontranspired walls, with transpiration, zero tangential velocity boundary conditions can be imposed at the wall for the Euler (inviscid) equations. The results of this study have important implications on the ability of turbulence models to predict this flow.
Intracavity harmonic generation in figure-8 undulator free electron lasers
Authors: Dattoli G. , Ottaviani P. L. , Pagnutti S.
Published: October 2008

We consider a free electron laser oscillator employing an exotic undulator provided by a figure-8, a device having the orthogonal field component oscillating with a period one-half of the radial component. The harmonic spectrum of such an oscillator device is fairly reach. We have indeed emission on odd and even harmonics with orthogonal polarizations. The intracavity nonlinear coherent harmonic generation follows the harmonic undulator spectrum and in addition allows the possibility of obtaining robust and very short pulses at different wavelengths.
Polarization-electric field hysteresis of ferroelectric PVDF films: Comparison of different measurement regimes
Authors: Wegener Michael
Published: October 2008

Polarization-electric field hysteresis is an important property of ferroelectric materials. Different experimental procedures and measurement regimes are demonstrated and frequently used in order to determine this hysteresis behavior. For the characterization of the poling behavior of ferroelectric polymers it is common to analyze the poling current and separate current contributions, which are based on charging the sample capacitance as well as on conductivity. Experimentally this can be realized with two different measurement regimes, either poling of the sample with bipolar cycles or with a sequence of bipolar and unipolar cycles of the applied electric field. Here, we demonstrate the comparison of both measurement routines by performing poling experiments on the same ferroelectric PVDF sample.
Operating lifetime recovery in organic light-emitting diodes having an azaaromatic hole-blocking/electron-transporting layer
Authors: Jarikov Viktor V. , Klubek Kevin P. , Liao Liang-Sheng , Brown Christopher T.
Published: October 2008

Azaaromatic compounds (AACs) are widely used in organic light-emitting diodes (OLEDs), especially as efficient electron transporters. Yet, the operating lifetime of OLEDs is always compromised when AACs are involved in anything more than electron transport (e.g., hole blocking). We show (i) the operating lifetime of OLEDs incorporating AACs as a hole-blocking/electron-transporting layer (HBETL) depends strongly on the charge-conducting ability and excited state energy of the light-emitting layer (LEL) materials and (ii) shifting the charge recombination zone away from the LEL∣HBETL interface deeper into the LEL can recover the lost lifetime. Thus, a pure red fluorescent OLED is demonstrated having 5.3 V drive voltage, 6.5% external quantum efficiency, 6.6 cd/A electroluminescent yield, and ∼125 000 h half-life, all at 20 mA/cm2. This device utilizes an AAC as HBETL followed by an aluminum triquinolate (Alq) ETL doped with Li metal. Alternatively, the lifetime recovery might be assigned to the presence of the n-dopant (Li) at the LEL∣HBETL interface (e.g., effected by diffusion of Li) because such presence stabilizes a wide range of OLEDs, e.g., those based on Alq mixed with polycyclic aromatic hydrocarbons and those based on 9,10-diarylanthracenes. Yet, this rationale is discarded in view of a strong deleterious interaction between the triazine-based AAC used in this work and n-dopants.
Internal photoemission of electrons from Ta-based conductors into SiO2 and HfO2 insulators
Authors: Shamuilia S. , Afanas’ev V. V. , Stesmans A. , Schram T. , Pantisano L.
Published: October 2008

The origin of annealing-induced variations in the effective work function of Ta-based conductors (TaC, Ta2C, and TaNx) at interfaces with SiO2 and HfO2 dielectrics is investigated using the spectroscopy of internal photoemission (IPE) of electrons. Two physical mechanisms were considered that could affect the Ta-based metal/oxide barrier: (a) oxidation of the metal conductor after thermal treatment by oxygen supplied from the oxide layer, resulting in a variation in the density of electron states inside the metal emitter, and (b) annealing-induced variations in the barrier at the interface. Field-dependent and differential IPE experiments allowed us to identify the latter as the dominant mechanism causing the barrier instability after thermal treatment in nonoxidizing ambient. The incorporation of negatively charged centers in the near-interface oxide layers is the most likely explanation for the significant increase (∼0.6 eV) of the barrier height after annealing, leading us to the hypothesis that Ta may diffuse into the oxide layer, and thereby be at the origin of the negative charge creation.
Applications and assessment of QM:QM electronic embedding using generalized asymmetric Mulliken atomic charges
Authors: Parandekar Priya V. , Hratchian Hrant P. , Raghavachari Krishnan
Published: October 2008

Hybrid QM:QM (quantum mechanics:quantum mechanics) and QM:MM (quantum mechanics:molecular mechanics) methods are widely used to calculate the electronic structure of large systems where a full quantum mechanical treatment at a desired high level of theory is computationally prohibitive. The ONIOM (our own N-layer integrated molecular orbital molecular mechanics) approximation is one of the more popular hybrid methods, where the total molecular system is divided into multiple layers, each treated at a different level of theory. In a previous publication, we developed a novel QM:QM electronic embedding scheme within the ONIOM framework, where the model system is embedded in the external Mulliken point charges of the surrounding low-level region to account for the polarization of the model system wave function. Therein, we derived and implemented a rigorous expression for the embedding energy as well as analytic gradients that depend on the derivatives of the external Mulliken point charges. In this work, we demonstrate the applicability of our QM:QM method with point charge embedding and assess its accuracy. We study two challenging systems—zinc metalloenzymes and silicon oxide cages—and demonstrate that electronic embedding shows significant improvement over mechanical embedding. We also develop a modified technique for the energy and analytic gradients using a generalized asymmetric Mulliken embedding method involving an unequal splitting of the Mulliken overlap populations to offer improvement in situations where the Mulliken charges may be deficient.