bluuebunny/crossref_metadata_2025 huggingface dataset:
Oversampling of sedimentary series collected by giant piston corer: Evidence and corrections based on 3.5‐kHz chirp profiles
Authors: Széréméta Nadia , Bassinot Franck , Balut Yvon , Labeyrie Laurent , Pagel Maurice
Published: January 2004

The depth‐scale accuracy of marine sedimentary series collected by coring is of key importance for the precise calculation of sedimentation rates and fluxes. For three giant piston cores collected during the InterPole MD99‐114/International Marine Past Global Changes Study (IMAGES) V cruise (MD99‐2227, MD99‐2246, and MD99‐2251), the 3.5‐kHz chirp profiles recorded on board are compared to synthetic seismograms computed from physical property logs measured on cores. In each case, the perfect match of main deep reflectors requires a significant upward shift of the water‐sediment (W/S) interface in the synthetic seismograms with respect to the 3.5‐kHz profiles. Since no drastic perturbation of the physical property logs is observed, this upward shift is interpreted as resulting from a significant sediment oversampling in the upper part of the cores. The affected depth intervals are consistent with the thickness of the perturbed zones observed in penetrometry and anisotropy of magnetic susceptibility records (∼10–15 m). To retrieve the true in situ sediment thickness, a linear depth correction is applied between consecutive acoustic reflectors to achieve a perfect match between the synthetic seismogram and the corresponding 3.5‐kHz profiles. Depth correction laws (amount of material excess as a function of initial depth) are deduced from this resynchronization procedure. First estimations of upper core oversampling rates range from 30% (core MD99‐2227) to 37% (core MD99‐2246). Moreover, we observe that some undersampling may also exist in the lower part of the sediment cores.
An improved ionospheric model for the Wide Area Augmentation System
Authors: Cormier D. , Altshuler E.
Published: January 2004

We provide an enhanced model of the errors induced by deviations of ionospheric delays from those estimated by the planar model used by the GPS‐based Wide Area Augmentation System (WAAS). To a first approximation the nominal ionospheric spatial decorrelation of vertical equivalent signal delays, σdecorrnom, is roughly constant over the whole of the WAAS service volume. However, significant gains may be achieved by including a more detailed description of σdecorrnom as a function of various metrics such as geomagnetic latitude, time of day, as well as the quality of the planar fit as characterized by the radius, relative centroid of the fit, and the density of delay data. We take the first step in the development of this more sophisticated model by determining which of these parameters is best suited for use as a metric for determining σdecorrnom. This allows us to construct a first‐order model of the ionospheric decorrelation which depends on the local density of ionospheric pierce points. Our preliminary study indicates that this first‐order model will result in a better than 20% reduction in the values of broadcast grid ionospheric vertical errors (GIVEs) within the coterminous United States. We also observe a better than 50% reduction in trips of the ionospheric irregularity detector in the Alaska region, which will lead to significant improvements to continuity, although this comes at the cost of a roughly 20% increase in the median GIVE in the Alaska region.
Ionospheric scintillation monitoring and mitigation using a software GPS receiver
Authors: Ganguly Suman , Jovancevic Aleksandar , Brown Andrew , Kirchner Michael , Zigic Slavisa , Beach Theodore , Groves Keith M.
Published: January 2004

Scintillations are caused by ionospheric irregularities and affect the amplitude, phase, dispersion, and related parameters of GPS signals. Both L1 and L2 are affected in a somewhat uncorrelated fashion. Adequate understanding of the effects that ionospheric scintillation has on GPS signals is essential in order to produce a GPS receiver that is immune to the degradation of signal caused by these scintillation‐related effects. Access to the internal workings of commercial GPS receivers is not provided to users. However, in order to understand, control, and mitigate scintillation effects, it is necessary to have access to tracking loops and associated components such as local oscillator. The software GPS receiver developed by the Center for Remote Sensing, Inc. allows the user to access its internal workings; hence facilitating advanced development of GPS receivers under different conditions. In this paper we present the results of analysis of GPS signals under scintillating conditions. Raw signals under conditions of ionospheric scintillation at Ascension Island have been processed using our software GPS receiver in order to derive the scintillation parameters. The receiver has been configured to provide stable operation during scintillation. We describe the receiver architecture, particularly the portion involving the tracking filters and related components, and demonstrate their performances under scintillating conditions. The software‐based approach used by us allows receiver implementations which are suitable for ionospheric monitoring as well as for reliable operation during scintillating conditions. The improved architecture may be used for several other applications.
Assimilation of radio occultation measurements into background ionospheric models
Authors: Angling M. J. , Cannon P. S.
Published: January 2004

Data assimilation processes aim to combine measurement data with background models in an optimal way. In anticipation of the availability of global radio occultation (RO) measurements, a computationally practical data assimilation technique for combining RO data with background ionospheric models has been implemented, and simulations have been conducted to assess the utility of the technique. In simulations where tomographic images provide the truth data and the Parameterized Ionospheric Model (PIM) provides the background, a fourfold decrease in the electron density error at 300 km altitude was achieved. A global assimilation simulation has also been conducted using the International Reference Ionosphere as the truth data. For a constellation of eight RO satellites, a factor of four decrease in the vertical total electron content RMS error has been demonstrated. The same simulation also results in a factor of three decrease in the NmF2 RMS error and a halving of the hmF2 RMS error.
Mark 4 VLBI correlator: Architecture and algorithms
Authors: Whitney A. R. , Cappallo R. , Aldrich W. , Anderson B. , Bos A. , Casse J. , Goodman J. , Parsley S. , Pogrebenko S. , Schilizzi R. , Smythe D.
Published: January 2004

The Mark 4 VLBI correlator is a station‐based system designed to process data from up to 16 stations at an aggregate data rate of 1 Gbps/station. It is compatible with data recorded on Mark 3A, Mark 4, and VLBA tape‐based data‐acquisition systems, as well as the new disc‐based Mark 5 system which also supports both real‐time and quasi‐real‐time data‐transmission over high‐speed networks. The system incorporates an XF algorithm implemented in a custom‐VLSI chip that can be flexibly configured to cross‐correlate VLBI data from one to four baselines of a single 2‐bits/sample channel at 64 Mbps/channel/station. Each chip also incorporates integral phase generators, rotators and vernier‐delay management circuitry. Each of the sixteen Correlator Boards in the system contains 32 correlator chips and can process up to 8192 complex lags that can be flexibly traded off between baselines, lags and channels. Innovative algorithms allow station‐model information to be injected periodically into the data stream from each channel of each station to drive the correlation process. The correlator control software allows up to four independent multistation scans to be processed simultaneously to significantly improve processing efficiency.
Sudden ionospheric delay decorrelation and its impact on the Wide Area Augmentation System (WAAS)
Authors: Sparks L. , Komjathy A. , Mannucci A. J.
Published: January 2004

In the absence of selective availability, the ionosphere represents the largest source of positioning error for single‐frequency users of the Global Positioning System (GPS). In differential GPS systems such as the Wide Area Augmentation System (WAAS), vertical ionospheric delays are modeled at regularly spaced intervals in geographic latitude and longitude. The broadcast bound on the error at each of these points is designated the grid ionospheric vertical error (GIVE). Higher performance standards planned for future implementations of WAAS require a reduction in the magnitude of the GIVE broadcast under nominal conditions. Achieving this reduction depends upon a better understanding of the decorrelation of ionospheric delay, in both space and time. In this paper we focus on temporal decorrelation. We report a methodology for assessing the impact on WAAS posed by a sudden increase in the level of ionospheric disturbance. The methodology is based upon forming an estimate of the probability PD that a WAAS user will confront a sudden increase in the level of ionospheric disturbance following a period of relative calm. We have determined a limiting upper bound of PD to be 4 × 10−7, which lies well within the margin needed to meet WAAS integrity requirements.
Conductive incubation and the origin of dome‐and‐keel structure in Archean granite‐greenstone terrains: A model based on the eastern Pilbara Craton, Western Australia
Authors: Sandiford Mike , Van Kranendonk Martin J. , Bodorkos Simon
Published: January 2004

The Archean East Pilbara Granite‐Greenstone Terrane (EPGGT) of the Pilbara Craton in Western Australia preserves a prolonged record of voluminous mafic‐dominated volcanism and felsic plutonism, commencing at circa 3515 Ma and ultimately resulting in the development of spectacular “dome‐and‐keel” structures. Early crustal growth was dominated by basaltic magmatism and the regional development of a 12–18 km thick greenstone sequence by circa 3335 Ma, overlying widespread 3470–3430 Ma tonalite‐trondhjemite‐granodiorite (TTG) suites emplaced into the middle crust. Stratigraphic and structural relationships imply that voluminous granitoid plutonism and crustal‐scale dome‐and‐keel formation in the southeastern EPGGT was not initiated until circa 3325 Ma but proceeded rapidly over the interval 3325–3308 Ma. This scenario is consistent with a “conductive incubation” period of 10–100 Myr duration, following the burial of radiogenic granitic crust beneath the accumulated greenstone pile. For heat production parameters appropriate to the 3515–3308 Ma EPGGT, we show that the burial of 3470–3430 Ma granitoid‐rich crust beneath the ≥3335 Ma Euro Basalt and its precursors led to long‐term crustal temperature increases of 170–234°C at 35 km depth, with a corresponding reduction in effective viscosity of 2–5 orders of magnitude. In combination with the greenstone‐over‐granitoid density inversion, the changes in effective viscosity of the mid to deep crust due to the burial of heat sources may have provided the crucial trigger for the initiation of dome‐and‐keel formation. Similarly, cooling and strengthening of the crust during syndoming exhumation of the heat production potentially terminated large‐scale dome‐and‐keel amplification.
Constructing subsurface structures of the Chelungpu fault to investigate mechanisms leading to abnormally large ruptures during the 1999 Chi‐Chi earthquake, Taiwan
Authors: Wang Chien‐Ying , Li Chien‐Li , Lee Hsiang‐Chun
Published: January 2004

The Chelungpu fault, a NS oriented thrust fault, was activated by the 1999 Chi‐Chi earthquake (Mw = 7.6), Taiwan. At its northern end, the fault turned east causing an extra 15 km EW branch, which experienced abnormal 9 m surface rupturing. In this paper, we used shallow reflection seismics to investigate the subsurface structure, attempting to find the relationship between the structure and large ruptures. Over 90 short seismic lines were distributed throughout a 10 km × 20 km area. Approximate 3D subsurface structures can be constructed by carefully compiling all seismic profiles with well data. The revealed structural pattern shows that the Chinshui shale, the key‐bed layer on which the Chelungpu fault slips, arises toward the north and becomes quite shallow under the EW branch. This structural variation is believed to be the main factor causing the abnormal rupturing of the Chelungpu fault.
Nonstationary impact of ENSO on Euro‐Atlantic winter climate
Authors: Greatbatch Richard J. , Lu Jian , Peterson K. Andrew
Published: January 2004

Previous studies have suggested a lack of robustness over the Euro‐Atlantic sector in the extratropical teleconnection response to ENSO. We use a simple AGCM to show that during the 20 years before and after the late 1970's, the ENSO signal leaving the tropics has the character of a wave train that is similar to the PNA, but is much stronger and penetrates further poleward in the post 1970s period. We also find that the synchronous extratropically‐forced model response is almost the reverse in the post‐ compared to the pre‐late 1970s period. We argue that the change in the signal leaving the tropics is due to the sensitivity of the tropically‐forced signal to changes in the spatial pattern of the tropical forcing. The extent to which the extratropically‐forced response is itself dependent on the tropical forcing, or simply the result of chance, is not clear.
Luminosity characteristics of multiple dart leader/return stroke sequences measured with a high‐speed digital image system
Authors: Wang D. , Takagi N. , Liu X. , Watanabe T. , Chihara A.
Published: January 2004

Using a newly‐developed high‐speed digital optical system, we measured the luminosity profiles of four leader/return stroke sequences within a flash occurred on a high tower. By analyzing those profiles, we obtained two simple expressions to characterize the light pulse decay features of subsequent return strokes along the channel bottom 210 m. These expressions can be extended to return stroke pulse currents and be easily included in return stroke modeling. In addition, we found that the peak light intensity of a leader and its following return stroke at various heights correlates positively in the channel bottom 210 m.
Estimates of slip weakening distance for different dynamic rupture models
Authors: Tinti Elisa , Bizzarri Andrea , Piatanesi Alessio , Cocco Massimo
Published: January 2004

We model the dynamic propagation of a 2‐D in‐plane crack obeying to either slip weakening (SW) or rate‐ and state‐dependent friction laws (R&S). We compare the value of slip weakening distance (Dc), adopted or estimated from the traction versus slip curves, with the critical slip distance measured as the slip at the time of peak slip velocity (D′c). The adopted friction law and the constitutive parameters control the slip acceleration as well as the timing and the amplitude of peak slip velocity. Our simulations with R&S show that the direct effect of friction and the friction behavior at high slip rates affect the timing of peak slip velocity and thus control the ratio D′c/Dc. The difference observed in this study between the Dc values and the inferred D′c can range between few percent up to 50%.
Correlation of solar wind entropy and oxygen ion charge state ratio
Authors: Pagel A. C. , Crooker N. U. , Zurbuchen T. H. , Gosling J. T.
Published: January 2004

Both proton specific entropy and solar wind composition have been recognized in the past as markers of boundaries between what was originally slow and fast solar wind during the declining phase of the solar cycle, when the solar wind alternates between the two regimes. During the rising phase, when boundaries between regimes are not apparent, ACE SWICS and SWEPAM data from 1998–1999 show that O7+/O6+ and proton specific entropy are well‐correlated over the full range of complicated time variations. The correlation holds in spite of the fact that unlike O7+/O6+, entropy is not a constant of the solar wind flow. At solar maximum however, particularly in 2000, the correlation between entropy and O7+/O6+ degrades. While the correlation inside known interplanetary coronal mass ejections (ICMEs) is much worse throughout 1998–2001, the correlation outside ICMEs also worsens at solar maximum, possibly owing to unidentified transient outflows. Outside ICMEs and shocks, entropy structures have decorrelation times of 5–40 hours and both ln(O7+/O6+) and entropy have Gaussian distributions, consistent with their correlation. We conclude that except at solar maximum, the processes affecting entropy in nontransient solar wind act at time scales much smaller than the scales found here and that entropy is a good a proxy for O7+/O6+.
Coastal ocean optical influences on solar transmission and radiant heating rate
Authors: Chang Grace C. , Dickey Tommy D.
Published: January 2004

An extensive set of physical and optical measurements is utilized to characterize the processes and quantify parameters that contribute to the variability of solar transmission, sea surface albedo, and radiant heating rate (RHR). This study is among the first to utilize multidisciplinary observations coupled with radiative transfer simulations to investigate the impact of optical properties on solar transmission, albedo, and heating in nearshore coastal waters. The data were collected from a shallow‐water coastal mooring as part of the Hyperspectral Coastal Ocean Dynamics Experiment (HyCODE) in summer 2001. Over the 41‐day time series, the average loss in solar radiation was 274 W m−2 for mean surface radiation of 365 W m−2 (average solar transmission of 21%). Quantitative coherence and principle component analyses suggest that cloud cover, chlorophyll concentration (Chl), and colored dissolved organic matter (CDOM) have the greatest impacts on solar transmission variability on timescales of ∼1 week. Radiative transfer simulations show that Chl, absorption, and attenuation have the most significant impact on solar transmission, whereas solar angle and cloud cover greatly influence albedo.
Coastal transition zone off Chile
Authors: Hormazabal Samuel , Shaffer Gary , Leth Ole
Published: January 2004

Seven years of subsurface current observations at deep‐sea and continental slope moorings off Chile (30°S), satellite sea surface anomaly, and satellite wind stress are used to examine space, time, and propagation characteristics of the mesoscale eddy activity in the coastal transition zone off Chile. This zone off Chile extends from the coast to ∼600–800 km offshore and can be separated into two latitudinal regions. The first region, between 29° and 39°S off central Chile, is characterized by high eddy kinetic energy and strong but variable equatorward wind stress. The second region, between 19° and 29°S off northern Chile, is characterized by low eddy kinetic energy and weak but persistent equatorward wind stress. Low‐frequency mesoscale variability off central Chile is mainly associated with baroclinic instability of coastal currents and westward propagation of Rossby waves from the eastern boundary and is strongly modulated over El Niño/La Niña cycles. Application of a new rotary wavelet spectrum method to the recording current meter data and the use of current estimates from satellite altimeter data show that mesoscale eddies and meanders in the coastal transition zone fluctuate with periods centered on 120 days and with length scales centered on ∼200 km. Cross‐rotary wavelet analyses of currents and wind stress indicate that fluctuations of coastal currents with periods longer than 220 days propagated westward as free Rossby waves during 1995–1996 and as forced Rossby waves during 1999–2001.
Middle‐atmospheric response to a future increase in humidity arising from increased methane abundance
Authors: MacKenzie I. A. , Harwood R. S.
Published: January 2004

The response of the middle atmosphere to an increase in humidity arising from a possible future increase in CH4 is examined in a general circulation model with interactive H2O and O3. A chemical parameterization allows the middle‐atmospheric H2O change to evolve naturally from an imposed change in tropospheric CH4. First, a simulation of the year 2060 using postulated loadings of the radiatively active gases is compared with a control simulation of the present‐day atmosphere. Then, the particular contribution of the CH4 (and hence H2O) change to the observed difference is isolated by repeating the 2060 simulation without the projected CH4 change. Under the Intergovernmental Panel on Climate Change Special Report on Emission Scenarios (SRES) B2 scenario, the middle atmosphere in 2060 cools by up to ∼5 K relative to 1995, with the CH4‐derived increase in H2O accounting for ∼10% of the change. The cooling is accompanied by a strengthened general circulation, intensified dynamic heating rates, and a reduction in the mean age of middle‐atmospheric air. The component of the circulation change attributable solely to the H2O change differs somewhat from the net response: The H2O change causes a greater increase in the descent rate in the north than in the south, ages the stratospheric air, and has a distinct effect on age/N2O correlations. Around 20% of the increased prevalence of polar stratospheric clouds (PSCs) in 2060 is due to the microphysical effect of the extra H2O, with the remainder attributable to the reduced vortex temperatures. Although the PSC increase facilitates release of reactive chlorine, this positive impact on chemical O3 destruction is outweighed by the negative impact of the reduced total chlorine in 2060. Nonetheless, the H2O increase does make the 2060 Arctic O3 loss ∼15% greater than it would otherwise be.
Impact of desertification and global warming on soil carbon in northern China
Authors: Qi Feng , Wei Liu , Yansui Liu , Yanwu Z. , Yonghong S.
Published: January 2004

While the global rise in mean day/night and seasonal air temperatures (ATE) of recent decades is well documented, its influence on levels of soil‐sequestered organic carbon, and on emission rates of CO2and other greenhouse gases emanating therefrom, is only beginning to garner serious attention. This has resulted in a limited but growing understanding, particularly in the context of the lands of the Chinese subcontinent, of the mechanisms underlying such emissions. Some 340 soil samples from 12 different sandy land regions in China were analyzed for soil organic carbon (SOC) content. Stepwise regression identified correlations between SOC and a number of climatic factors measured at the sampling sites: winter, summer, nighttime and daytime ATE, and precipitation. In desertified lands, net SOC losses showed a direct correlation with precipitation but no significant relationship with mean ATE. However, in northwest and northeast China, decreases in SOC were linked to rises in day/night and seasonal ATE, while in north central China they were linked to a rise in mean ATE. Between 1900 and 1998, mean ATE in the northwest, northeast, and north central regions rose by 0.14E, 0.28E, and 0.15E decade−1, respectively. Meanwhile, precipitation dropped by 25 mm decade−1across these regions. In this study, day/night and seasonal ATE showed differing levels of significance with respect to their linear relationships with SOC content. Driven by rises in day/night and seasonal ATE, long‐term alterations to global ecosystemic processes, particularly the carbon cycle, may quantitatively and qualitatively alter the flora of desertified ecosystems. Our study suggests that, over the last 40 years, anthropogenic factors, precipitation, and rises in ATE (particularly nighttime and winter) have contributed 47%, 26%, and 20%, respectively, of greenhouse gas emissions from SOC. It is apparent that for China's desertified lands, human activity is the primary causative factor in the release of SOC‐derived greenhouse gases to the atmosphere, while geography and climatic extremes individually play a lesser role.
Model simulations of the northern extravortex ozone column: Influence of past changes in chemical composition
Authors: Marchand M. , Bekki S. , Lefèvre F. , Hauchecorne A. , Godin‐Beekmann S. , Chipperfield M. P.
Published: January 2004

A high‐resolution three‐dimensional chemistry transport model is used to evaluate the contributions of different mechanisms (in situ chemistry, import of chemically activated or ozone‐depleted polar air) to the extravortex chemical ozone loss during the winter‐spring period and to show how their efficiencies might have changed in the last 2 decades. Two extreme, but somewhat typical, present‐day winters are considered: the 1999–2000 winter (cold with a stable and persistent vortex) and the 2001–2002 winter (warm with an weak and distorted vortex). An ozone budget analysis is performed for the partial ozone column between 350 and 600 K using a combination of geographical and chemical ozone tracers. The results suggest that the interannual variability in the seasonal ozone loss at midlatitudes is mainly driven by the import of ozone‐depleted polar air. The contribution from the import of chemically activated polar air is not found to be significant. The magnitudes of the polar contributions (entirely driven by the halogen cycles) differ by about a factor 4 between the simulations. The polar contribution is found to be responsible for 60% of the total extravortex ozone loss for the exceptional 1999–2000 Arctic winter. In contrast, the magnitude of the in situ destruction (dominated by HOx and NOx cycles) varies little from one winter to the other one. The evolution of the atmospheric chemical composition since 1980 may account for an additional midlatitude ozone loss of 3 to 10 Dobson units depending on the winter considered (representing up to about 40% of the observed midlatitude ozone trends). The polar contribution is found to increase by a factor 2 to 3 in the last 2 decades, whereas the in situ destruction increases by about 20% only.
Evidence for a late Holocene warm and humid climate period and environmental characteristics in the arid zones of northwest China during 2.2 ∼ 1.8 kyr B.P.
Authors: Bao Yang , Braeuning Achim , Yafeng Shi , Fahu Chen
Published: January 2004

Natural archives like ice cores, tree rings, river and lake sediments, lake terraces, and paleosols and also historical documents witness aspects of climate change in northwestern China during the Western and Eastern Han Dynasties (206 B.C.–220 A.D.). Reconstructions of decadal averages of annual mean temperature and precipitation fluctuations were derived from variations of δ18O and net accumulation rates in the Guliya ice core. They revealed a period of higher temperatures and higher precipitation than today, which affected vast areas of northwestern China during the period of interest until the fifth century A.D. These conditions resulted in a marked increase in the discharge of big endorheic river systems, such as the Tarim, the Keriya and the Manas rivers. As a consequence, water levels in appendant terminal lakes rose, e.g., at Lop Nor, Manas Lake, and Baijian Hu. Lake surface areas expanded, and lake desalting occurred also at lakes in intermontane basins, such as Balikun Hu and Qinghai Lake. The warm and moist conditions during the Western and Eastern Han Dynasties might have been responsible for the large‐scale agricultural production and the local socioeconomic boom that is documented by the occurrence of the famous ruin groups of Loulan, Niya, and Keriya. The following desiccation phase led to a deterioration of water resources, and most oases tended to dry out and were finally abandoned. The appearance, development, flourishing, and final abandonment of each great ruin group are closely associated with regional climate change at that time.
Estimation of instantaneous TOA albedo at 670 nm over ice clouds from POLDER multidirectional measurements
Authors: Sun Wenbo , Loeb Norman G. , Kato Seiji
Published: January 2004

An algorithm that determines the 670‐nm top‐of‐atmosphere (TOA) albedo of ice clouds over ocean using Polarization and Directionality of the Earth's Reflectance (POLDER) multidirectional measurements is developed. A plane‐parallel layer of ice cloud with various optical thicknesses and light scattering phase functions is assumed. For simplicity, we use a double Henyey‐Greenstein phase function to approximate the volume‐averaged phase function of the ice clouds. A multidirectional reflectance best‐fit match between theoretical and POLDER reflectances is used to infer effective cloud optical thickness, phase function and TOA albedo. Sensitivity tests show that while the method does not provide accurate independent retrievals of effective cloud optical depth and phase function, TOA albedo retrievals are accurate to within ∼3% for both a single layer of ice clouds or a multilayer system of ice clouds and water clouds. When the method is applied to POLDER measurements and retrieved albedos are compared with albedos based on empirical angular distribution models (ADMs), zonal albedo differences are generally smaller than ∼3%. When albedos are compared with those on the POLDER‐I ERB and Cloud product, the differences can reach ∼15% at small solar zenith angles.
Adsorption of organic compounds pertinent to urban environments onto mineral dust particles
Authors: Falkovich Alla H. , Schkolnik Gal , Ganor Eliezer , Rudich Yinon
Published: January 2004

The interaction of mineral dust particles from the Sahara with semivolatile organic compounds over an urban region in Israel's coastal plain was studied. Dust samples were collected during numerous dust storm events in 2000 and 2001, under varying meteorological conditions. Organic compounds adsorbed on collected mineral dust particles were analyzed using an integrated, multitechnique study that employed a scanning electron microscope equipped with an energy dispersion system (SEM‐EDS) and bulk aerosol analysis by gas chromatography/mass spectrometry (GC/MS) and ion chromatography (IC). The SEM‐EDS analysis exemplifies the coexistence of inorganic and organic species on individual mineral dust particles. Using the GC/MS and IC analysis, specific tracers for urban air pollution and photodegradation products of agriculture emissions have been identified, and their size distributions have been obtained. Redistribution of semivolatile organics such as polycyclic aromatic hydrocarbons (PAH) and pesticides from submicron to larger particle size fractions, governed by the mineral dust transport trajectory and size distributions, was observed. Nonvolatile species, such as anhydrous sugars and large PAH, do not redistribute between the phases because of their low vapor pressure. The concentrations of short chain carboxylic acids increased with higher ambient relative humidity, suggesting water‐assisted uptake onto the mineral particles.
Analyses of firn gas samples from Dronning Maud Land, Antarctica: Study of nonmethane hydrocarbons and methyl chloride
Authors: Kaspers K. A. , van de Wal R. S. W. , de Gouw J. A. , Hofstede C. M. , van den Broeke M. R. , van der Veen C. , Neubert R. E. M. , Meijer H. A. J. , Brenninkmeijer C. A. M. , Karlöf L. , Winther J.‐G.
Published: January 2004

Firn air was sampled on the Antarctic plateau in Dronning Maud Land (DML), during the Norwegian Antarctic Research Expedition (NARE) 2000/2001. In this paper, we describe the analyses for methyl chloride and nonmethane hydrocarbons (NMHCs) in these firn air samples. For the first time, the NMHCs ethane, propane, and acetylene have been measured in Antarctic firn air, and concentration profiles for these gases have been derived. A one‐dimensional numerical firn air diffusion model was used to interpret the measured profiles and to derive atmospheric concentrations as a function of time. The atmospheric trends we derived for the NMHC and methyl chloride at DML cover the period from 1975 to 2000. Methyl chloride shows a decreasing trend of 1.2 ± 0.6 ppt per year (annual mean concentration 548 ± 32 ppt). For ethane we found an increasing trend of 1.6 ± 0.6 ppt per year (annual mean concentration 241 ± 12 ppt). The concentrations of propane and acetylene appear to be constant over the period 1975–2000, with annual mean concentrations of 30 ± 4 ppt for propane and 24 ± 2 ppt for acetylene.
Photostationary state deviation–estimated peroxy radicals and their implications for HOx and ozone photochemistry at a remote northern Atlantic coastal site
Authors: Yang J. , Honrath R. E. , Peterson M. C. , Parrish D. D. , Warshawsky M.
Published: January 2004

Measurements of NO, NO2, O3, and ultraviolet irradiance made at Cape Norman, Newfoundland (51.6°N, 55.9°W), during February–April 1996 were used to examine peroxy radical photochemistry and the local photochemical ozone tendency. Deviations from NO‐NO2‐O3 photostationary state (the PSSD method) were used to estimate peroxy radical (PO2) mixing ratios. Potential biases in the PSSD method and the methods used to apply it in an unbiased manner are discussed. PO2 levels reached 77 ± 8 pptv (midday mean ±2σ of the mean), significantly higher than observed in previous studies at remote marine locations. [PO2] was well correlated with ()1/2, indicating that the dominant radical source was photolysis by ultraviolet radiation in the wavelength region of O3 photolysis and the dominant sink of PO2 was recombination. However, the variation of [PO2] with ()1/2 (d[PO2]/d()1/2) was significantly higher than expected at this site during spring. Significant radical production in addition to that from net O3 photolysis, possibly related to snow photochemistry in the upwind region, is suggested as the cause. However, the measurements needed to test this hypothesis were not made in this study, and we suggest future HOx measurements in remote midlatitude, snow‐covered regions. The net photochemical ozone production at this site during springtime was calculated to be minimal (generally small and negative, and always less than or equal to +0.1 ppbv/h). These small values indicate that in situ photochemical ozone production is negligible at this site during spring; if [HO2]/[PO2] is large, net ozone destruction may contribute up to ∼10% of mean ozone levels per day.
Testing the impact of clouds on the radiation budgets of 19 atmospheric general circulation models
Authors: Potter Gerald L. , Cess Robert D.
Published: January 2004

We compare cloud‐radiative forcing (CRF) at the top‐of‐the atmosphere from 19 atmospheric general circulation models, employing simulations with prescribed sea‐surface temperatures, to observations from the Earth Radiation Budget Experiment (ERBE). With respect to 60°N to 60°S means, a surprising result is that many of the 19 models produce unusually large biases in Net CRF that are all of the same sign (negative), meaning that many of the models significantly overestimate cloud radiative cooling. The primary focus of this study, however, is to demonstrate a diagnostic procedure, using ERBE data, to test if a model might produce, for a given region, reasonable CRF as a consequence of compensating errors caused either by unrealistic cloud vertical structure, cloud optical depth or cloud fraction. For this purpose we have chosen two regions, one in the western tropical Pacific characterized by high clouds spanning the range from thin cirrus to deep convective clouds, and the other in the southeastern Pacific characterized by trade cumulus. For a subset of eight models, it is found that most typically produce more realistic regionally‐averaged CRF (and its longwave and shortwave components) for the southeastern region as opposed to the western region. However, when the diagnostic procedure for investigating cloud vertical structure and cloud optical depth is imposed, this somewhat better agreement in the southeastern region is found to be the result of compensating errors in either cloud vertical structure, cloud optical depth or cloud fraction. The comparison with ERBE data also shows large errors in clear‐sky fluxes for many of the models.
Transport and freeze‐drying in the tropical tropopause layer
Authors: Jensen Eric , Pfister Leonhard
Published: January 2004

We use a Lagrangian, one‐dimensional cloud model to simulate ice cloud formation and dehydration along trajectories in the tropical tropopause layer (TTL). Time‐height curtains of temperature along the trajectory paths are extracted from meteorological analyses. The temperatures are adjusted near the tropopause such that the spatial average cold point temperature matches tropical radiosonde measurements. Temperature perturbations due to Kelvin waves, Rossby gravity waves, and high‐frequency gravity waves are superimposed. The cloud model tracks the growth and sedimentation of individual ice crystals. Ice number densities in the cloud simulations without waves range from <0.001 to ∼0.2 cm−3; when clouds form, they dehydrate the air but generally do not reduce the water vapor mixing ratio down to ice saturation. Wave‐driven temperature perturbations result in higher cloud frequencies and cause higher ice number densities (>1 cm−3) and smaller crystals (1–10 μm radius), resulting in less sedimentation but still effective dehydration overall. Inclusion of wave‐driven temperature oscillations decreases the final TTL H2O mixing ratio somewhat primarily because the wave perturbations decrease the tropical average cold point tropopause temperature by ∼0.75 K. Ultimately, air rising through the TTL is effectively dehydrated with or without wave perturbations. In general, the model results suggest that the final water vapor mixing ratios are primarily controlled by the minimum temperatures encountered by parcels and that they are relatively insensitive to factors such as the wave‐driven temperature variability, the supersaturation threshold for ice nucleation, and the rate of ascent through the tropopause layer. However, the frequency and geographical distribution of cloud formation is very sensitive to these parameters. On average, the clouds dehydrate the air along trajectories down to mixing ratios ∼10–40% higher than the temperature minimum saturation mixing ratio. The simulations predict efficient freeze‐drying of air by cloud formation within the TTL: For the December–January 1995/1996 period simulated the average final H2O mixing ratios at the tropopause (370–380 K potential temperature) range from 2.5 to 3.2 ppmv. These values are somewhat lower than the estimates of the stratospheric water vapor entry value from satellite and in situ measurements; hence an additional source of water (such as injection by deep convection) may be required to explain the observed tropical tropopause humidity.
Enhanced upper stratospheric ozone: Sign of recovery or solar cycle effect?
Authors: Steinbrecht W. , Claude H. , Winkler P.
Published: January 2004

Ozone data measured since 1987 in the 35‐ to 45‐km altitude region by differential absorption laser‐radar (DIAL) at Hohenpeissenberg (47.8°N, 11.0°E) confirm the long‐term ozone decline observed by the satellite‐borne Stratospheric Aerosol and Gas Experiment (SAGE) and Halogen Occultation Experiment (HALOE) instruments, as well as interannual ozone fluctuations. Analysis of the DIAL data indicates that the amplitude of ozone variations related to the 11‐year solar cycle might reach up to 7%, much larger than 4% reported in other studies. Higher ozone values observed in the years 2001 to 2003 might, therefore, be a consequence of the ending solar maximum and not necessarily indicate a beginning recovery of upper stratospheric ozone. Much clearer evidence for a recovery is expected in a few years, near the end of the solar minimum starting now.
Amorphous and crystalline ice on the Galilean satellites: A balance between thermal and radiolytic processes
Authors: Hansen Gary B. , McCord Thomas B.
Published: January 2004

The water ice on the three outermost Galilean satellites of Jupiter has a lattice structure that can vary from crystalline to amorphous. Amorphous ice is crystallized by heating, while crystalline ice is amorphized through disruption by particle radiation. We determine ice lattice order using infrared spectra from the Near Infrared Mapping Spectrometer on the Galileo Jupiter orbiter. The shape of the reflectance peak near 3.1 μm is diagnostic of the lattice order in the top micrometers of the surface. A narrow, temperature‐sensitive band near 1.65 μm, from ∼1 mm depth, is missing for amorphous ice. Spectral averages of >100 pixels were used for Europa and Callisto, because of high radiation noise and small ice amounts, respectively. Model comparisons show that the surface ice is predominantly amorphous on Europa and predominantly crystalline on Callisto, while both types of ice are found on Ganymede. The distribution of Ganymede ice properties shows a broad global pattern of more amorphous ice in the high‐latitude Jovian‐facing hemisphere and in the low‐latitude trailing hemisphere. The ice at ∼1 mm depth on all three satellites is predominantly crystalline. The radiation flux increases by ∼300 times between Callisto and Europa, while the thermal crystallization rate may vary over five orders of magnitude among the three satellites (being the fastest at Callisto). The occurrence of crystalline and amorphous ice suggests a balance between the disruption and crystallization, with Callisto dominated by thermal crystallization and Europa by radiative disruption, and with nearly equal rates between the two processes at Ganymede.
Powder snow avalanches: Approximation as non‐Boussinesq clouds with a Richardson number–dependent entrainment function
Authors: Ancey C.
Published: January 2004

This paper presents an investigation into non‐Boussinesq particle‐driven gravity currents such as powder snow avalanches and pyroclastic flows. For a finite‐volume current to maintain its non‐Boussinesq character (i.e., a substantial density difference with its surroundings) and therefore high velocities, it must counterbalance the entrainment of surrounding fluid by entraining particles from the bed. A number of theoretical models have assumed that the volume growth rate of such currents is controlled by the local slope and the density ratio between the current and the ambient fluid. An alternative assumption, according to which the volume growth rate is controlled solely by the overall Richardson number, is examined here. Both assumptions were used successively in the same theoretical model, primarily developed by A. G. Kulikovskiy and E. I. Sveshnikova, then by P. Beghin. The model predictions were compared to laboratory experiments (release of a finite volume down an inclined channel, with particle entrainment from the bed) and field data (a well‐documented large powder snow avalanche in Switzerland). In both cases, the assumption of a slope‐dependent volume growth rate received little support, whereas assuming that the entrainment coefficient is controlled by the Richardson number makes it possible to describe the velocity and volume variations fairly well, except for highly concentrated particle‐driven currents in the laboratory.
Local and global statistics of clear‐air Doppler radar signals
Authors: Muschinski Andreas
Published: January 2004

A refined theoretical analysis of the clear‐air Doppler radar (CDR) measurement process is presented. The refined theory builds on the Fresnel‐approximated (as opposed to Fraunhofer‐approximated) radio wave propagation theory, and turbulence statistics like locally averaged velocities, local velocity variances, local dissipation rates, and local structure parameters are allowed to vary randomly within the radar's sampling volume and during the dwell time. A local version of the moments theorem and the random Taylor hypothesis are used to derive first‐principle formulations of all higher moments of the Doppler cross‐spectrum. The mth moment is written as a convolution integral of a spectral sampling function and a generalized, mth‐order refractive‐index spectrum or, alternatively, as a convolution integral of a lag‐space sampling function and a spatial cross‐covariance function of the local refractive‐index fluctuations and their local mth‐order time derivatives. Closed‐form expressions of the first three moments (i.e., m = 0, 1, 2) of the Doppler spectrum for the monostatic, single‐signal case are derived. This refined theory, or “local sampling theory,” enables one to correctly interpret CDR observations that are collected under conditions where the applicability of the traditional “global sampling theory” is questionable. The commonly used global sampling assumptions (Bragg‐isotropy, homogeneity, and stationarity of all turbulence statistics within the sampling volume and during the dwell time) may be invalid for small‐scale intermittency in the mixed layer, for refractive‐index sheets corrugated by gravity waves or instabilities, and for layered turbulence in the stably stratified atmosphere.
Conservative and reactive solute transport in constructed wetlands
Authors: Keefe Steffanie H. , Barber Larry B. , Runkel Robert L. , Ryan Joseph N. , McKnight Diane M. , Wass Roland D.
Published: January 2004

The transport of bromide, a conservative tracer, and rhodamine WT (RWT), a photodegrading tracer, was evaluated in three wastewater‐dependent wetlands near Phoenix, Arizona, using a solute transport model with transient storage. Coupled sodium bromide and RWT tracer tests were performed to establish conservative transport and reactive parameters in constructed wetlands with water losses ranging from (1) relatively impermeable (15%), (2) moderately leaky (45%), and (3) significantly leaky (76%). RWT first‐order photolysis rates and sorption coefficients were determined from independent field and laboratory experiments. Individual wetland hydraulic profiles influenced the extent of transient storage interaction in stagnant water areas and consequently RWT removal. Solute mixing and transient storage interaction occurred in the impermeable wetland, resulting in 21% RWT mass loss from main channel and storage zone photolysis (10%) and sorption (11%) reactions. Advection and dispersion governed solute transport in the leaky wetland, limiting RWT photolysis removal (1.2%) and favoring main channel sorption (3.6%). The moderately leaky wetland contained islands parallel to flow, producing channel flow and minimizing RWT losses (1.6%).
Modeling the effect of development on internal phosphorus load in nutrient‐poor lakes
Authors: Nürnberg Gertrud K. , LaZerte Bruce D.
Published: January 2004

A steady state lake phosphorus (P) mass balance model was used to predict the equilibrium P concentration (annual, volume‐weighted average) of the lake water from natural and anthropogenic, external and internal P inputs. Internal P load was modeled as the product of sediment release rates and anoxic factors. Both these components were predicted from lake P concentration computed from external load to create a link between external and internal load components. Such estimates allow the modeling and setting of objectives of several hundred lakes on the Canadian Shield. In particular, estimates of predevelopment lake P concentration made by removing all anthropogenic inputs were compared with postdevelopment conditions in which additional loading was added to the model. This was accomplished by determining how much development would increase external as well as internal phosphorus load and ultimately annual average lake P concentrations. By comparing proposed lake development scenarios with existing or predevelopment scenarios, it can be determined whether water quality objectives will be exceeded.