bluuebunny/crossref_metadata_2025 huggingface dataset:
A theoretical model for O5+ (O7+) ions in the fast solar wind
Authors: Chen Yao , Esser Ruth , Hu You Qiu
Published: December 2002

We present a theoretical model for O5+ (O7+) ions as test particles in the fast solar wind using a previous turbulence‐driven four‐fluid model to establish the background solar wind, which consists of electrons, protons, alpha particles, and O6+ ions. The O5+ (O7+) ions in our model and the O6+ ions in the background are driven by the same mechanism, say, the resonant cyclotron interaction or an exponential heating addition. The ionization and recombination processes of O ions are taken into account. It is shown that the differential flow speeds between O6+ and O5+ or O7+, which are found to be in the range of 0.3–2, play very different roles in the formation of O charge states. This is due to discrepancy between the freezing‐in distances of the two ion species. O7+ forms predominantly below 1.2 RS too close to the Sun to develop a differential streaming between O ions. O5+, on the other hand, freezes‐in at about 1.8 RS where differential flows are well developed and therefore important for the formation of O5+ ions.
A physical reconstruction of cosmic ray intensity since 1610
Authors: Usoskin Ilya G. , Mursula Kalevi , Solanki Sami K. , Schüssler Manfred , Kovaltsov Gennady A.
Published: December 2002

The open solar magnetic flux has been recently reconstructed by Solanki et al. [2000, 2002] for the last 400 years from sunspot data. Using this reconstructed magnetic flux as an input to a spherically symmetric quasi‐steady state model of the heliosphere, we calculate the expected intensity of galactic cosmic rays at the Earth's orbit since 1610. This new, physical reconstruction of the long‐term cosmic ray intensity is in good agreement with the neutron monitor measurements during the last 50 years. Moreover, it resolves the problems related to previous reconstruction for the last 140 years based on linear correlations. We also calculate the flux of 2 GeV galactic protons and compare it to the cosmogenic 10Be level in polar ice in Greenland and Antarctica. An excellent agreement between the calculated and measured levels is found over the last 400 years.
Interpretation of Pioneer 10 Ly‐α based on heliospheric interface models: Methodology and first results
Authors: Gangopadhyay P. , Izmodenov Vlad , Gruntman Mike , Judge D. L.
Published: December 2002

The very local interstellar medium (VLISM) neutral hydrogen and proton densities are still not precisely known even after 3 decades of deep space research and the existence of the EUV and other diagnostic data obtained by Pioneer 10/11, Voyager 1/2, and other spacecraft. The EUV data interpretation, in particular, has suffered because of inadequate neutral hydrogen‐plasma models, difficulty of calculating the multiply scattered Lyman α glow, and calibration uncertainties. Recently, all these difficulties have been significantly reduced. In the present work we have used the latest state‐of‐the‐art supersonic VLISM neutral hydrogen‐plasma and Monte Carlo radiative transfer model, incorporating neutral density, temperature, and velocity variations, actual solar line shape, realistic redistribution function, Doppler and aberration effects. This work presents the methodology of the radiative transfer code and the first results of the comparison of the model predictions with the Pioneer 10 data. Monte Carlo radiative transfer calculations were carried out for five neutral hydrogen‐plasma models and compared with Pioneer data. The first results are quite encouraging. We found that the VLISM ionization ratio is between 0.2 and 0.5 and that the VLISM neutral hydrogen density is <0.25 cm−3. The present calculation suggests that the Pioneer 10 photometer‐derived intensities (Rayleighs) need to be increased by a factor of 2. If this model‐derived calibration is used, then the difference between Pioneer 10 and Voyager 2 intensity values is reduced to ∼2.2. The model, neutral hydrogen density = 0.15 cm−3 and proton density = 0.07 cm−3, is found to best fit the Pioneer 10 data.
Active photometry of atmospheric compositions by microwave breakdown plasma spectroscopy
Authors: Iinuma K. , Suto H. , Uchida S. , Takayama K.
Published: December 2002

A laboratory technique of pulsed microwave breakdown plasma spectroscopy (MBS) has been developed for simultaneous, quantitative, in situ, and remote diagnostics of atmospheric compositions. This technique, based upon a concept proposed by Papadopoulos et al. [1994], enables for remote photometry of the atomic/molecular spectra emitted from the microwave breakdown plasma of the atmosphere mixed with various kinds of trace gases and air pollutants at relevant breakdown spots in open space. Two different breakdown methods, the single beam method and the dual beam intersection method, have been tested using a small test chamber, a pulsed 9.4 GHz/100 kW magnetron tube, and a high‐resolution wavelength/time resolution spectroscopy system. Major 50 lines of atomic/molecular spectra emitted from N2, O2, Cl, F, CN, and OH radical in the plasma of model/real atmosphere have been assigned and compared with the emission candidates in the stratosphere predicted by Papadopoulos et al. Very many strong emission lines including, for example, 837.6 nm (4p4D07/2 → 4s4P5/2) of Cl(I) and 777.4 nm (3p5P1,2,3 → 3s5S02) of O(I) can be observed, most of which have not been expected yet in their theoretical approach. Also, the controllability of the pulsed microwave breakdown power as well as the quantitative detection limit of trace gases has been examined both experimentally and theoretically.
Solar wind‐magnetosphere‐ionosphere coupling: Signal arrival time and perturbation relations
Authors: Song P. , Vasyliūnas V. M.
Published: December 2002

On the basis of a simple one‐dimensional model, we describe the sequence of the perturbations of different quantities from the magnetopause to the ionosphere after reconnection at the magnetopause has been switched on. Reconnection produces perturbations in the electric field, current, magnetic field, and plasma velocity. These perturbations extend over a broad frequency range, and each frequency band propagates at its group velocity to the ionosphere. The first perturbations to arrive at the ionosphere are mainly electromagnetic oscillations carried by the highest frequencies, whose front can propagate as fast as the speed of light if reconnection has switched on sufficiently suddenly, although it may propagate at the whistler‐mode speed if reconnection switches on only on the whistler‐mode timescale. The front of oscillations predominantly in the current arrives next, at the whistler‐mode speed. Perturbations predominantly in the magnetic field and the velocity as well as nonoscillatory (step‐function) changes of all the quantities arrive last, at the Alfvén speed. The ionosphere starts responding after the arrival of the electromagnetic front, although the dominant changes occur after the arrival of the Alfvén front.
Lower hybrid drift wave turbulence and associated electron transport coefficients and coherent structures at the magnetopause boundary layer
Authors: Shukla P. K. , Mamun A. A.
Published: December 2002

It is well known that at the Earth's magnetopause there is much scale size turbulence whose origin is not yet fully understood. Our objective here is to present a detailed investigation of short‐wavelength (in comparison with the ion gyroradius) lower hybrid drift (LHD) wave turbulence that is generated by sheared electron flows and ion beams. We employ here a hybrid approach, in which the ions are treated kinetically while the cold electrons are described by means of a fluid model, and derive the linear dispersion relation. The latter is analyzed analytically and numerically for different realistic situations. Introducing the mixing length hypothesis and mode coupling processes, we deduce the saturated wave spectra for nonthermal LHD wave fluctuations. The latter produce the anomalous resistivity and cross‐field particle diffusion in a nonuniform magnetoplasma. It is shown that the nonlinear equations governing the dynamics of weakly interacting LHD waves admit stationary solutions in the form of vortices which can also trap particles and transport them to large distances. The present study is relevant for understanding the properties of nonthermal fluctuations and associated transport processes and coherent vortex structures at the magnetopause current layer.
Seasonal and diurnal variation of Dst dynamics
Authors: O'Brien T. P. , McPherron R. L.
Published: December 2002

In recent years the debate over the causes of seasonal and diurnal variations in magnetic activity has been revived. Popular explanations rely primarily on the orientation of the terrestrial magnetic dipole relative to heliospheric topology. We investigate the signatures of this geometry in the dynamics of Dst, the ring current index. We show that the Russell‐McPherron effect is present; however, enhancements in Dst, as measured by the Dst index, exhibit a seasonal and diurnal pattern that is significantly different from the Russell‐McPherron (RM) effect. Specifically, the dynamics of Dst, which accommodate the RM effect, demonstrate seasonal and diurnal variations associated with ψ the magnetic colatitude of the subsolar point. Specifically, it is primarily the diurnal signature that distinguishes between various mechanisms for semiannual variations. We suggest that these variations are most consistent with the hypothesis that ψ modulates the depth of penetration of the magnetosheath field into the magnetopause and thereby the amount of magnetic merging and the strength and orientation of magnetopause currents.
Cloud components of the Intertropical Convergence Zone
Authors: Gu Guojun , Zhang Chidong
Published: December 2002

This study explores the roles of different synoptic‐scale cloud systems in the making of the Intertropical Convergence Zone (ITCZ). Outgoing longwave radiation (OLR) data are used to represent both the mean ITCZ and cloud systems. An OLR threshold of 205 W m−2 is used to distinguish daily mean deep convective clouds from nondeep clouds. Zonally moving synoptic‐scale cloud systems are identified through a cloud‐tracking method. Mean OLR of the ITCZ is decomposed into five components: westward and eastward moving synoptic‐scale deep convective clouds, random (nonpropagating) deep convective clouds, nondeep clouds, and clear‐sky backgrounds. Hypothetical ITCZs, each composed of one of the cloud components and the clear‐sky background, are constructed and compared. The largest synoptic‐scale cloud constituents of the ITCZ are nondeep clouds and deep clouds with no persistent tendency of zonal propagation. Each of the two comprises about 40–45% of total cloud signals in the ITCZ. A weak ITCZ could exist solely because of westward propagating, synoptic‐scale, deep‐convective clouds. In reality, these westward propagating clouds contribute 25–40% of deep convective clouds and 10–20% of total clouds in the ITCZ. Contributions from eastward propagating synoptic‐scale clouds are much smaller (8% of the deep convective clouds and less than 5% of total clouds in the ITCZ). An ITCZ without any zonally propagating synoptic‐scale deep convective clouds would be diffused in latitude. The cloud compositions in the ITCZ and other tropical convective zones are compared. Their discrepancies indicate fundamental characteristics in large‐scale environments for the cloud components in different regions.
Understanding the 30‐year Barbados desert dust record
Authors: Mahowald Natalie M. , Zender Charles S. , Luo Chao , Savoie Dennis , Torres Omar , del Corral John
Published: December 2002

Atmospheric mineral aerosols influence climate and biogeochemistry, and thus understanding the impact of humans on mineral aerosols is important. Our longest continuous record of in situ atmospheric desert dust measurements comes from Barbados, which shows fluctuations of a factor of 4 in surface mass concentrations between the 1960s and the 1980s [Prospero and Nees, 1986]. Understanding fluctuations this large should help us understand how natural and anthropogenic factors change mineral aerosol sources, transport, distributions, and deposition, although we are limited in our ability to interpret the results as there is a quantitative record only at one location. We test the hypothesis that dry topographic lows (and not disturbed sources such as cultivated areas or new desert regions) are the sources of desert dust, using a hierarchy of models as well meteorological data sets to look at decadal scale changes in the North Atlantic desert dust. We find that the inclusion of a disturbed source improves our simulations in many (but not all) comparisons. Unfortunately, we are severely limited by the accuracy of the available data sets and models in making definitive statements about the role of disturbed sources or anthropogenic activity in changing the atmospheric desert dust cycle. Processes that might change the size or intensity of desert dust sources in North Africa (such as new sources due to desertification or land use) may be difficult to distinguish from topographic low sources in models due to their similar geographical locations and impact on atmospheric aerosol distributions.
Black carbon radiative heating effects on cloud microphysics and implications for the aerosol indirect effect 2. Cloud microphysics
Authors: Nenes Athanasios , Conant William C. , Seinfeld John H.
Published: December 2002

This work examines the effect of black carbon (BC) radiative heating on cloud droplet formation. Changes in cloud droplet concentration and cloud albedo due to the presence of black carbon are computed for different cases of aerosol size distributions, meteorological conditions, BC mixing state, and aerosol composition. We examine the effect of three new mechanisms (that result from BC heating) that can affect cloud droplet number and lifetime. Two of these mechanisms act to increase cloud droplet number or lifetime: (1) the ability of BC to decrease the collection efficiency of giant cloud condensation nuclei (CCN) and (2) the delayed growth of low‐Sc CCN that allow higher‐Sc CCN to form droplets. These two mechanisms complement each other in terms of increasing cloud droplet number, since it is shown that the former is most efficient at strong updrafts and the latter is most efficient at low updraft velocities. A third mechanism identified, gas‐phase heating (which is different from the so‐called “semi‐direct effect”), in our simulations acts to decrease LWC, and thus albedo; however, the droplet number concentration does not change significantly due to dynamic readjustments in cloud supersaturation. The simulations indicate that the mixing state of BC with the CCN population can have an important influence on the effect of BC heating on the droplet population. Although additional work is necessary to fully assess the effects of BC heating on cloud microphysics and climate, this work shows that these effects are more complex than currently thought.
Sequential assimilation of stratospheric chemical observations in a three‐dimensional model
Authors: Chipperfield M. P. , Khattatov B. V. , Lary D. J.
Published: December 2002

We describe a technique to assimilate chemical observations in a three‐dimensional (3‐D) chemical transport model (CTM). The method uses the established sequential technique of Khattatov et al. [2000], but here, it is applied simultaneously to many observed species. Following the assimilation, care is taken to preserve compact correlations between all modeled long‐lived tracers and the total abundance of reactive families (e.g., inorganic chlorine). This way, the observations of long‐lived tracers and family members constrain many other species in the model. In this paper, we apply the technique to the assimilation of O3, CH4, H2O, and HCl from the Halogen Occultation Experiment (HALOE) in 1992. Despite the poor coverage of HALOE, the assimilation of species with long photochemical lifetimes is a useful global constraint on the model. Results of the assimilation model have been tested by comparison with Atmospheric Trace Molecule Spectroscopy Experiment (ATMOS) profiles of O3, CH4, H2O, HCl, and N2O. Direct comparison of the assimilated species shows that the assimilation model performs better in reproducing the independent observations. Comparison of the nonassimilated species (N2O) shows that assimilation has generally improved the comparison, especially in the midlatitude lower stratosphere.
A potential source of atmospheric sulfur from penguin colony emissions
Authors: Xie Zhou‐Qing , Sun Li‐Guang , Wang Jian‐Jun , Liu Bai‐Zhan
Published: December 2002

Samples of fresh penguin excrements and lake sediments composed of aged penguin excrements were collected on an Antarctic Peninsula island. Gases emitted from these samples were collected and analyzed for volatile organosulfur compounds. No dimethyl sulfide (DMS) was found. However, dimethyl trisulfide (DMTS), dimethyl tetrasulfide (DMTTS), and dimethyl pentasulfide (DMPS) were found among the numerous organic compounds emitted from fresh penguin droppings. These sulfur compounds account for as mush as 13.5% of the emitted gases, but they have not been reported previously in atmospheric gases and therefore may represent a hitherto undetected source of atmospheric sulfur. To evaluate the potential contribution of this non‐DMS biogenic source to the atmospheric sulfur reservoir at high southern latitudes, measurements of various chemical species in aerosols at several coastal Antarctic locations were analyzed and compared. The locations include Zhongshan Station (China) and Dumont D'Urville (France) in east Antarctica. Tentative calculations based on assumptions of similar aerosol sources and composition at these locations show that in areas downwind from large penguin colonies up to 5.5 × 10−5 nmol m−3 sulfur may be attributed to penguin emissions on a per‐penguin basis. Depending on the size of penguin population at a given location, sulfur from this non‐DMS source may account for 5–15% of the total non‐sea‐salt (nss) sulfur in these areas. Such high contributions may significantly impact the atmospheric sulfur burden and alter the sulfur budget in the high southern latitudes.
Atmospheric chemistry of CF3CFHOCF3: Reaction with OH radicals, atmospheric lifetime, and global warming potential
Authors: Takahashi Kenshi , Matsumi Yutaka , Wallington Timothy J. , Hurley Michael D.
Published: December 2002

Smog chamber/FTIR techniques were used to study the OH radical initiated oxidation of CF3CFHOCF3 in 700 torr of air diluent at 296 K. Relative rate techniques were used to measure k1(OH + CF3CFHOCF3) = (1.4 ± 0.3) × 10−15 cm3 molecule−1 s−1. The atmospheric lifetime of CF3CFHOCF3 is estimated to be 40 years. The IR spectrum of CF3CFHOCF3 was measured and used to estimate a global warming potential (relative to CO2, 100 year time horizon) for CF3CFHOCF3 of 4500. Results are discussed with respect to the previous literature data.
Simulation of the tropospheric sulfur cycle in a global model with a physically based cloud scheme
Authors: Rotstayn Leon D. , Lohmann Ulrike
Published: December 2002

The treatment of the sulfur cycle in the CSIRO global climate model (GCM) is described. It is substantially based on the scheme developed previously for the European Center/Hamburg (ECHAM) model, but the treatment of wet scavenging has been completely rewritten to better reflect the different properties of liquid and frozen precipitation, and the treatment of these in the model's cloud microphysical scheme. The model is able to reproduce the observed finding that wet deposition of sulfur over Europe and North America is larger in summer than in winter, but the seasonal cycle of sulfate over Europe is not well simulated. The latter is improved when the amplitude of the seasonal cycle of European emissions is increased. Below‐cloud scavenging makes an important contribution in our scheme: On omitting it, the global sulfate burden increases from 0.67 to 0.93 Tg S. On reverting to the less efficient scavenging treatment used in ECHAM, the global sulfate burden again increases from 0.67 to 0.93 Tg S, and excessive sulfate concentrations are obtained in Europe and North America. Some deficiencies in the simulation are investigated via further sensitivity tests. In particular, during the Arctic winter, the modeled sulfur dioxide (SO2) concentrations are too large, and the modeled sulfate concentrations are too small (as in most global sulfur‐cycle models). Recent laboratory experiments suggest that SO2 oxidation in ice clouds is nonnegligible. We obtain a much improved Arctic simulation when a simple treatment of SO2 oxidation in ice clouds is included.
Simulations of the quasi‐biennial oscillation and its effect on stratospheric H2O, CH4, and age of air with an interactive two‐dimensional model
Authors: McCormack J. P. , Siskind D. E.
Published: December 2002

A zonally averaged photochemical–dynamical model of the middle atmosphere is used to simulate the quasi‐biennial oscillation (QBO) and its effect on the distributions of stratospheric H2O, CH4, and age of air. Changes in planetary wave amplitudes of ±25% cause 2–3 month changes in QBO period. Comparable changes in prescribed tropical heating have a smaller effect on the QBO period. The response of tropical upwelling, and QBO period, to changes in extratropical forcing depends on the magnitude and location of the imposed changes. In the Southern Hemisphere, where the planetary wave forcing is smaller than in the Northern Hemisphere, increased forcing produces stronger equatorial upwelling and a longer QBO period. In the Northern Hemisphere, increased forcing produces weaker upwelling and a shorter QBO period due to the larger amplitude waves becoming saturated. Overall, the effect of the QBO is to produce a slightly younger mean age of air near the tropical stratopause due to the model not exactly reproducing the strength and duration of the observed westerly wind shear. The QBO in lower stratospheric H2O, but not CH4, results primarily from meridional circulation anomalies superimposed upon background gradients in H2O mixing ratio that are maintained by the annual cycle in lower stratospheric H2O. QBO modulation of horizontal eddy transport plays a much smaller role. A realistic annual cycle in equatorial H2O mixing ratio at the model tropopause produces a QBO variation in lower stratospheric H2O of 0.1–0.2 ppmv. The effect of the QBO on model tropical tropopause temperatures doubles the amplitude of the water vapor QBO at 20 km.
On error estimation in atmospheric CO2 inversions
Authors: Engelen Richard J. , Denning A. Scott , Gurney Kevin R.
Published: December 2002

This paper explores various sources of error in atmospheric CO2 synthesis inversions using global circulation models. The estimation of prior, observation, model transport, and representation errors is described, and the latter two error sources are explored in more detail. Not accounting for these errors will act as a hard constraint on the inversion and will produce incorrect solutions to the problem as is shown in some example inversions. The magnitude of these errors falls generally between about 10% and 100% in the retrieved fluxes but can be even larger. This makes it highly desirable to avoid hard constraints and apply any prior information we have about the surface fluxes as a weak constraint to the inversion problem.
Sources of nonmigrating tides in the tropical middle atmosphere
Authors: Oberheide J. , Hagan M. E. , Roble R. G. , Offermann D.
Published: December 2002

Temperature measurements from the Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) experiment taken during the U.S. Space Shuttle mission STS‐66 in November 1994 provide a variety of zonally symmetric and asymmetric tidal signatures in the altitude range from 40–90 km. The most prominent zonally asymmetric tidal pattern is identified to be the westward propagating nonmigrating diurnal tide of zonal wavenumber 2 (s = −2). This mode has an amplitude of approximately half the amplitude of the migrating (s = −1) component of the diurnal tide. The observational findings are compared to model results from the Global Scale Wave Model (GSWM) and from the Thermosphere Ionosphere Mesosphere Electrodynamics General Circulation Model (TIME‐GCM). GSWM and TIME‐GCM account for different tidal sources and therefore allow an analysis of the tidal forcing responsible for the observed signatures. The GSWM tidal forcing in the model version used is based upon latent heat release associated with tropical deep convection while nonmigrating tides in the TIME‐GCM are predominantly forced by nonlinear interactions between the migrating diurnal tide and stationary planetary waves. It is shown that the latter mechanism forces a large part of the s = −2 mode while the stationary, zonally uniform (s = 0) diurnal nonmigrating tide is mainly driven by latent heat release. This result suggests that dynamical models for the mesosphere/lower thermosphere (MLT) region need to account for the tropospheric latent heat source and stationary planetary wave activity in order to predict realistic longitudinal diurnal tidal variability.
Basic characteristics of canopy turbulence in a homogeneous rice paddy
Authors: Hong Jinkyu , Kim Joon , Miyata Akira , Harazono Yoshinobu
Published: December 2002

To assess the interactions of key ecosystems with the overlying atmosphere, it is fundamental to understand the turbulence structure within and above their canopies. Rice is a staple crop particularly in Asia, and, yet, information on canopy turbulence of this vital food resource is limited by the scarcity of field measurement. The purpose of this study was to examine whether rice canopy shows an organized turbulence structure and, if so, whether such coherent structure scales to the patterns found in other canopies. Using the field data obtained during the 1996 International Rice Experiment (IREX96), we computed turbulence statistics such as mean, standard deviation, covariance, skewness, kurtosis, and turbulence length scales. When appropriately scaled with canopy height and friction velocity, these turbulence statistics showed coherent structures, which agreed well within the ranges of those reported for other canopies. Both quadrant and spectrum analyses confirmed that the intermittent and energetic eddies with length scale of the order of canopy height dominated the transfer processes within and above rice canopy. Such results were further substantiated by the countergradient fluxes observed during the IREX96. Furthermore, within‐canopy turbulence became more intermittent under stable conditions.
Role of NO3 in sulfate production in the wintertime northern latitudes
Authors: Feingold Graham , Frost Gregory J. , Ravishankara A. R.
Published: December 2002

The production of sulfate via multiphase chemistry is usually assumed to be dominated by oxidation of S(IV) by O3 and H2O2. The former reaction is pH dependent and negligibly small for pH less than about 5, while oxidation via H2O2 is independent of pH. Another oxidant that may play a role in sulfate formation is NO3 [Sander et al., 1995; Mozurkewich, 1995; Rudich et al., 1998]. Although it is commonly assumed to be far less important than O3 and H2O2, it has been hypothesized that it may account for significant oxidation under certain conditions, such as relatively low mixing ratios of O3 and <150 pptv of H2O2. These conditions may be met in the nighttime Northern Hemisphere winters when H2O2 production is small and NOx concentrations are sufficient to produce adequate concentrations of NO3. We explore the importance of NO3 in multiphase sulfate production using a simple cloud model. It is shown that the relative importance of NO3 is very sensitive to the assumed value of the Henry's Law equilibrium constant of NO3 as well as the assumed catalytic chain length for NO3 oxidation of S(IV). Using the recently measured value of 0.6 M atm−1 [Rudich et al., 1996], and a catalytic chain length of 8, it is shown that NO3 enhances sulfate production by about 10–30% relative to calculations where NO3 is absent. It is noted that NO3 may contribute even more if additional sources of NOx are present and/or H2O2 is removed via precipitation.
Impact of fires on surface albedo dynamics over the African continent
Authors: Govaerts Y. M. , Pereira J. M. , Pinty B. , Mota B.
Published: December 2002

The seasonal variation analysis of a land surface albedo data set derived from 1‐year Meteosat observations reveals the high sensitivity of albedo to anthropogenic biomass burning activities during the dry season. At the beginning of this season, a rapid decrease of albedo is observed over fire‐prone areas. These low albedo values last during the entire dry season, increasing slowly at the end of this season. This paper focuses on a quantitative estimation of biomass burning impact on albedo seasonal variations. To this end, a conceptual method is proposed to detect pixels whose albedo seasonal cycle is affected by biomass burning. The performance of this approach is evaluated over the central Africa region, where the Experiment for Regional Sources and Sinks of Oxidants (EXPRESSO) field campaign took place in November 1996. Our results compare favorably with maps of fire‐affected areas derived from NOAA advanced very high resolution radiometer (AVHRR) observations. When applied over the entire African continent, the Northern Hemisphere appears much more affected by fire‐induced albedo decrease than the Southern Hemisphere. At a regional scale, Northern Hemisphere fires are responsible for a relative decrease of the albedo as large as 25% with respect to nonburnt areas. The amplitude of this large‐scale darkening phenomenon might locally affect the wind regime and associated rainfall.
Lagrangian estimate of global stratosphere‐troposphere mass exchange
Authors: Seo Kyong‐Hwan , Bowman Kenneth P.
Published: December 2002

Seasonal variations of the mass flux between the stratosphere and troposphere are investigated using a Lagrangian framework. Monthly three‐dimensional trajectories are calculated for 1996 and 1997 from the United Kingdom Meteorological Office assimilated data. Mass exchange shows nearly the same annual variations as previous Eulerian studies: (1) the northern net downward flux across the extratropical tropopause shows a primary maximum in late spring and early summer and secondary in winter, which is consistent with observational measurements, (2) the southern net downward flux has a peak only in winter, and (3) the extratropical and tropical air exchange across the upper boundary of the middleworld exhibits a pronounced annual variation with a wintertime maximum and summertime minimum. The occurrence of the largest downward flux over the western edges of the Pacific and Atlantic and near the Mediterranean suggests that tropopause folding and baroclinic disturbances in midlatitude storm tracks are the primary agent for the intrusion of stratospheric air into the troposphere. Tropical upward transport occurs in association with the monsoon anticyclones, and the greatest diabatic injection into the tropical stratosphere takes place over the summer hemisphere subtropics according to the seasonal variation of the Hadley circulation. Comparison of the Lagrangian flux estimate across the 100‐hPa surface with the estimate by the downward control mechanism using the residual mean meridional circulation shows reasonable correspondence.
Correlations among the optical properties of cirrus‐cloud particles: Microphysical interpretation
Authors: Reichardt J. , Reichardt S. , Hess M. , McGee T. J.
Published: December 2002

Cirrus measurements obtained with a ground‐based polarization Raman lidar at 67.9°N in January 1997 reveal a strong positive correlation between the particle optical properties, specifically depolarization ratio δpar and extinction‐to‐backscatter (lidar) ratio Spar, for δpar < ∼40%, and an anticorrelation for δpar > ∼40%. Over the duration of the measurements, both particle properties vary systematically. This effect is particularly pronounced in the case of δpar, which decreases significantly with time. The analysis of lidar humidity and radiosonde temperature data shows that the measured optical properties stem from scattering by dry solid ice particles, while scattering by supercooled droplets, or by wetted or subliming ice particles, can be excluded. For the microphysical interpretation of the lidar measurements, ray‐tracing computations of particle scattering properties have been used. The comparison with the theoretical data suggests that the observed cirrus data can be interpreted in terms of size, shape, and growth of the cirrus particles, the latter under the assumption that the lidar measurements of consecutive cloud segments can be mapped on the temporal development of a single cloud parcel moving along its trajectory: Near the cloud top in the early stage of cirrus development, light scattering by nearly isometric particles that have the optical characteristics of hexagonal columns (short, column‐like particles) is dominant. Over time, the ice particles grow, and as the cloud base height extends to lower altitudes characterized by warmer temperatures they become morphologically diverse. For large Spar and depolarization values of ∼40%, the scattering contributions of column‐ and plate‐like particles are roughly the same. In the lower ranges of the cirrus clouds, light scattering is predominantly by plate‐like ice particles. This interpretation assumes random orientation of the cirrus particles. Simulations with a simple model suggest, however, that the positive correlation between Spar and δpar, which is observed for depolarization ratios <40% mainly at low cloud altitudes, can be alternatively explained by horizontal alignment of a fraction of the cirrus particle population.
Average summer peak UV‐B in central Texas, 1995–2001
Authors: Roeder Robert C.
Published: December 2002

This paper develops the statistical treatment necessary to calculate the error bars associated with the average summer peak UV‐B irradiance (ASPUV), a measure of annual solar UV‐B irradiance similar to the “summertime peak UV Index” introduced by McKenzie et al. These errors include the effects of autocorrelation among daily average values of the solar UV‐B irradiance at local noon as measured by a variance inflation factor (VIF), which increases the variance of the ASPUV beyond its value for no autocorrelation by amounts ranging from 14% to 52% depending on the year. Including the VIF in the error estimates of the ASPUV allows one to gauge the significance of possible changes in this quantity. As an example, the treatment is applied to broadband radiometric measurements carried out at Georgetown, TX (30.6°N, 97.7°W) and it is found that from summer 1995 to summer 2001 the ASPUV has decreased, the values for 1995 and 2001 differing by about 3 standard deviations.
Hydrogen cyanide in comet C/1996 B2 Hyakutake
Authors: Magee‐Sauer Karen , Mumma Michael J. , DiSanti Michael A. , Dello Russo Neil
Published: December 2002

Spectral emission from HCN in C/1996 B2 Hyakutake was detected on UT 1996 March 24.4 (rh = 1.06 AU, Δ = 0.106 AU), using the CSHELL infrared spectrometer at the NASA Infrared Telescope Facility. A Boltzmann analysis of eight ro‐vibrational lines in the ν3 band returned a rotational temperature (83 ± 9 K) for a region centered on the nucleus. The global HCN production rate was (4.50 ± 0.81) × 1026 molecules s−1. The HCN abundance relative to water is then (0.18 ± 0.04)%, based on direct measurements of H2O made on the same night with the same instrument and reduced with the same data processing algorithms. The measured spatial distribution for HCN is consistent with its release at the nucleus; no significant contribution from a distributed source is required within ∼600 km of the nucleus. We use these data to obtain insights regarding the origin of HCN in this comet.
Influence of ionospheric conductivity on parameters of a radio wave at a reflection point
Authors: Krasnov V. M.
Published: December 2002

A generalized solution of the problem of radio wave reflection in a linear conductive layer indicates the following: (1) the height of radio wave reflection depends on the value of the conductivity gradient; (2) only a fraction of the energy of an incident wave is propagating downwards from a reflection point; (3) Doppler frequency depends critically on temporary changes of layer conductivity; (4) the angle of incidence is not equal to the reflection angle at the height of radio wave reflection.
Combination of interferon alfa-2b and ribavirin in liver transplant recipients with histological recurrent hepatitis C
Authors: Firpi Roberto J. , Abdelmalek Manal F. , Soldevila-Pico Consuelo , Reed Alan , Hemming Alan , Howard Richard , van der Werf William , Lauwers Gregory , Liu Chen , Crawford James M. , Davis Gary L. , Nelson David R.
Published: December 2002

Recurrent hepatitis C virus (HCV) infection is an important cause of fibrosis and cirrhosis after liver transplantation (LT), with histological recurrence developing in at least 50% of patients within the first year. The aim of this study is to assess the safety and efficacy of interferon alfa-2b plus ribavirin in treating histological recurrent HCV after LT. Since 1998, patients with HCV with significant histological recurrence (fibrosis ≥ 3 and/or histological activity index ≥ 5) or progressive cholestatic disease after LT were treated with interferon alfa-2b (3 million units subcutaneously three times weekly) plus ribavirin (800 to 1,000 mg/d) for 12 months. Immunosuppression was tapered to cyclosporine/FK506 monotherapy. HCV RNA was assessed at entry, week 24, end of treatment, and 6 months after therapy. The primary end point was loss of HCV RNA 6 months after therapy, whereas the secondary end point was histological response. Fifty-four patients met criteria for treatment and have completed follow-up. Patients were mainly men (71% men; mean age, 51 ± 5 years) with genotype 1 infection (88%) and high viral load (mean HCV RNA, 38 ± 9 mEq/mL). Dose modification was required in 72% of patients because of cytopenia or side effects. Intent-to-treat analysis showed that serum HCV RNA was undetectable in 19 patients (35%) week 24, 21 patients (38%) week 48, and 16 patients (30%) at the 6-month follow-up. Paired liver biopsy results (before and within 6 months after treatment) were available for 35 patients. Patients who achieved viral eradication had no significant progression of fibrosis after 1 year of therapy. In summary, combination therapy is a reasonable antiviral option for recurrent HCV infection for established post-LT hepatitis and appears to prevent histological progression of disease if viral eradication is successful.
Role of echocardiography in detecting portopulmonary hypertension in liver transplant candidates
Authors: Cotton Cynthia L. , Gandhi Sanjay , Vaitkus Paul T. , Massad Malek G. , Benedetti Enrico , Mrtek Robert G. , Wiley Thelma E.
Published: December 2002

Portopulmonary hypertension (PPHTN) is a recognized complication of end-stage liver disease that adversely affects the outcome of orthotopic liver transplantation (OLT). There are limited data on the role of Doppler echocardiography in assessing pulmonary artery systolic pressure (PASP) in this population. The purpose of our study was to examine the accuracy of Doppler echocardiography in evaluating pulmonary artery pressures in liver transplant candidates. Clinical and demographic data were gathered retrospectively for 78 liver transplant candidates (48 men and 30 women, mean age 51 ± 9.6 yr) who had PASP determined both by right heart catheterization (RHC) and echocardiography. Paired sample t-test was used to compare mean PASP by echocardiography and RHC. Correlation of PASP between echocardiography and RHC was determined using Pearson’s linear correlation. Positive and negative predictive values for echocardiography for PASP > 50 mmHg are reported as compared with RHC. The mean PASP by echocardiography (43.2 ± 12.3 mm Hg) was significantly higher than mean PASP by RHC (33.7 ± 15.5 mm Hg; P < .001). Regarding PASP, there was a significant but weak correlation between echocardiography and RHC (r = 0.46, P = .01). The positive and negative predictive values of echocardiography for identifying clinically significant pulmonary hypertension (PASP > 50 mm Hg) were 37.5% and 91.9%, respectively. Echocardiography is a useful tool in estimating PASP in liver transplant candidates. Patients with apparently elevated PASP by echocardiography should undergo invasive assessment by RHC before being excluded from liver transplant.
Management and outcome of major bile duct injuries after laparoscopic cholecystectomy: From therapeutic endoscopy to liver transplantation
Authors: Nordin Arno , Halme Leena , Mäkisalo Heikki , Isoniemi Helena , Höckerstedt Krister
Published: December 2002

Laparoscopic cholecystectomy is associated with a higher rate of bile duct injuries than an open cholecystectomy. The annual incidence of bile duct injuries has remained almost constant and these injuries tend to be more serious, making demands on the method of repair. We wanted to report the management and outcome of major bile duct injuries after laparoscopic cholecystectomy in patients referred to a hepatobiliary and liver transplantation unit. Eighteen patients (14 women), with a median age of 53.5 years were referred to the liver surgery unit with a major bile duct injury after laparoscopic cholecystectomy. The injury was identified after a median of 3 days (range, 0 to 25 days) after operation and the median time interval to referral was 79 days (0 to 2270 days). Fourteen patients had undergone surgery before referral. By the time of referral, four patients had developed end-stage cirrhosis, necessitating liver transplantation. Three of them had undergone bilioenteric drainage operations at the referring institute. Of the remaining 14 patients, three were managed by therapeutic endoscopic procedures. Ten patients were managed with Roux-en-Y hepaticojejunostomy. One died of septic complications before the repair. A median time for hospitalization in our unit was 33 days (range, 10 to 164 days). At present, 16 patients are alive. One patient died of Kaposi’s sarcoma 7 months after liver transplantation. A long interval between bile duct injury and referral was associated with the development of end-stage liver disease. Surgery of biliary lesions is demanding, and surgical experience with multidisciplinary approach, including therapeutic endoscopy and liver transplantation, is necessary for successful outcome.
Hepatocellular carcinoma: Can it be considered a controversial indication for liver transplantation in centers with high rates of hepatitis C?
Authors: Moya Angel , Berenguer Marina , Aguilera Victoria , Juan Fernando San , Nicolás David , Pastor Miguel , López-Andujar Rafael , Rayón Miguel , Orbis Francisco , Mora Julio , de Juan Manuel , Carrasco Domingo , Vila Juan-José , Prieto Martín , Berenguer Joaquín , Mir José
Published: December 2002

Hepatocellular carcinoma (HCC) is still considered a controversial indication for liver transplantation (LT), mainly because of long waiting times and underlying viral cirrhosis. The goal was to evaluate the outcome of LT in 104 patients with HCC and cirrhosis, mainly hepatitis C virus (HCV)-related, in a center with a short waiting time (median, 105 days). Four groups were formed according to the HCC and HCV status: HCV positive with HCC (group 1, n = 81), HCV negative with HCC (group 2, n = 23), HCV positive without HCC (group 3, n = 200), and HCV negative without HCC (group 4, n = 207). Predictive factors of tumor recurrence were demographics, tumor related (size or number of nodules, capsule, bilobar involvement, vascular or lymphatic invasion, clinical and pathologic TNM staging, pre-LT percutaneous ultrasound-guided ethanol injection or transarterial chemoembolization, α-fetoprotein levels), donor and surgery related, and year of transplantation. The same variables and “tumor recurrence (yes/no)” were applied to evaluate the effect on survival. The median follow up was 29 months (range, 0 to 104 months). Patient survival was 70% at 1 year and 59% at 5 years for group 1, 87% at 1 year and 77% at 5 years for group 2, 81% at 1 year and 64% at 5 years for group 3, and 88% at 1 year and 77% at 5 years for group 4 (P = .013). Survival was significantly lower in patients with HCC than in those without (74% and 63% versus 85% and 70%, at 1 and 5 years, respectively; P = .05). The causes of death in those with and without HCC were tumor recurrence (24%) and recurrent HCV (8%) versus sepsis (34%) and recurrent HCV (14%). HCC recurrence occurred in 12 patients (11.5%) at a median of 14 months (range, 3 to 60 months) with a probability increasing from 8% at 1 year to 16% at 5 years. In patients with HCC, tumor recurrence was associated with vascular invasion (P = .0004) by multivariate analysis; variables predictive of survival were donor old age (P = .01), viral-related etiology (P = .02), and tumor recurrence (P = .001). Although LT still remains an adequate indication for HCC in centers with high prevalence of HCV infection and short waiting times, both tumor and HCV-related recurrent diseases hamper significantly the outcomes of these patients.
Aspergillus osteomyelitis after liver transplantation
Authors: Kaneko Junichi , Sugawara Yasuhiko , Makuuchi Masatoshi
Published: December 2002

A 57-year-old woman underwent liver transplantation and developed osteomyelitis in the femur attributable to Aspergillus fumigatus. The patient was treated successfully with amphotericin B and 5-fluorocytosine for 30 days, and then switched to itraconazole for 12 months. Plasma (1->3)-beta-D-glucan levels decreased significantly after the chemotherapy. Early diagnosis by (1->3)-beta-D-glucan measurement and extended treatment with itraconazole can improve the prognosis of invasive Aspergillus infection.
The optimal number of donor biopsy sites to evaluate liver histology for transplantation
Authors: Frankel Wendy L. , Tranovich Jason G. , Salter Laura , Bumgardner Ginny , Baker Peter
Published: December 2002

Macrovesicular steatosis (MaS), fibrosis, and inflammation have been associated with poor graft function after liver transplantation. We evaluated histological variation in livers to determine the optimal number of biopsies to estimate pathological characteristics in livers for transplantation. Specimens from autopsies performed during 3 months in 16- to 70-years-olds without known liver disease or drug and/or alcohol abuse were examined. Eight needle biopsies were performed, and hematoxylin and eosin-stained slides were evaluated. Percentages of MaS and microvesicular steatosis (MiS) were determined, and inflammation and fibrosis were scored as 0 to 4. MaS correlated positively with MiS, and inflammation correlated positively with fibrosis, whereas patient weight showed a significant correlation with liver weight and body mass index. No patient characteristic showed a significant correlation with histological findings. Subjects 55 years and older showed no increase in pathological findings compared with those younger than 55 years. When any site was compared with the average of the other sites, Spearman’s ρ correlation ranged from 0.89 to 0.95 for MaS, 0.89 to 0.94 for MiS, 0.54 to 0.80 for inflammation, and 0.66 to 0.80 for fibrosis. Two biopsies explained 95% of variations for MaS and MiS and 85% for inflammation and fibrosis. There was no significant difference between findings in the right and left lobes of livers. These findings suggest that no single site best predicts pathological findings, and there is little variation among sites. In borderline cases of MaS, significant pathological characteristics may be found in additional biopsies. Therefore, we recommend two biopsy sites to evaluate donor livers with suspicious clinical histories.