bluuebunny/crossref_metadata_2025 huggingface dataset:
Potential calibration errors in carbonyl sulfide permeation devices: Implications for atmospheric studies
Authors: Fried Alan , Henry Bruce , Sewell Scott
Published: February 2004

Ambient in situ measurements of the important sulfur gas carbonyl sulfide (OCS) very frequently rely on permeation devices based on weight loss measurements (gravimetry) as the method of calibration. Both time series studies as well as measurements of OCS sources and sinks typically employ this approach. Although this calibration approach is based upon fundamental quantities, its accuracy directly depends upon the purity of the permeating effluent. The present study describes a systematic investigation of four permeation wafers and their time history based on gravimetry, direct absorption spectroscopy employing a tunable diode laser absorption spectrometer (TDLAS), and two different ratio approaches. Gravimetric determinations for two of the devices, which employed fluorinated ethylene propylene (FEP) Teflon wafers as the permeating medium, indicated mass loss rates which decayed exponentially with time. This is in contrast to the direct absorption and ratio measurements, which were significantly lower at the start (37% in one case and 19% in the other) and displayed a small linear drop with time. We present evidence for the presence of a CO2 impurity in FEP permeation devices, either from the starting material or the breakdown of OCS. This impurity copermeates along with OCS but at a much faster rate, giving rise to an apparent exponential decay in the OCS rate. Calculations based on fundamental permeability parameters for CO2 in FEP Teflon and typical levels of CO2 impurity (0.1 to 2%) in the starting material yield results that are consistent with the present interpretation. Two other permeation wafers, which employed polytetrafluoroethylene (PTFE) Teflon membranes, exhibited completely different behavior; all the measurement methods indicated similar results and showed a linearly decreasing permeation rate with time. The CO2 impurity problem prevalent in FEP wafers is insignificant in PTFE wafers because the permeability of PTFE is at least 21 times higher. It is possible that the high pressure inside the membrane (POCS = 17.7 atm at 40°C) alters the crystalline PTFE structure with time, resulting in a real decrease in permeation rate. Although more studies are needed to further confirm and extend these findings, the effects observed here suggest that ambient OCS measurements could in some circumstances be systematically high by as much as 37%. Such errors can produce erroneous temporal trends and/or inconsistencies between ambient measurements carried out by different laboratories.
Emission factors of hydrocarbons, halocarbons, trace gases and particles from biomass burning in Brazil
Authors: Ferek Ronald J. , Reid Jeffrey S. , Hobbs Peter V. , Blake Donald R. , Liousse Catherine
Published: February 2004

Airborne measurements of the emissions of gases and particles from 19 individual forest, cerrado, and pasture fires in Brazil were obtained during the Smoke, Clouds, and Radiation‐Brazil (SCAR‐B) study in August‐September 1995. Emission factors were determined for a number of major and minor gaseous and particulate species, including carbon dioxide, carbon monoxide, sulfur dioxide, nitrogen oxides, methane, nonmethane hydrocarbons, halocarbons, particulate (black and organic) carbon, and particulate ionic species. The magnitude of the emission factors for gaseous species were determined primarily by the relative amounts of flaming and smoldering combustion, rather than differences in vegetation type. Hydrocarbons and halocarbons were well correlated with CO, which is indicative of emissions primarily associated with smoldering combustion. Although there was large variability between fires, higher emission factors for SO2and NOχwere associated with an increased ratio of flaming to smoldering combustion; this could be due to variations in the amounts of sulfur and nitrogen in the fuels. Emission factors for particles were not so clearly associated with smoldering combustion as those for hydrocarbons. The emission factors measured in this study are similar to those measured previously in Brazil and Africa. However, particle emission factors from fires in Brazil appear to be roughly 20 to 40% lower than those from North American boreal forest fires.
Snow‐albedo feedback and the spring transition in a regional climate system model: Influence of land surface model
Authors: Lynch Amanda H. , McGinnis David L. , Bailey David A.
Published: February 2004

Using the Arctic regional climate system model (ARCSYM), we investigate the spring seasonal transition and mechanisms controlling snowmelt over a domain covering the northern half of Alaska. Annual simulations for 1992 comparing the Biosphere‐Atmosphere Transfer Scheme (BATS) and the land surface model scheme (LSM) show that the BATS experiment enters the spring transition with respect to the large‐scale atmospheric regime approximately one month earlier than observed climate and the LSM experiment transitions a month later than observed, even though the air temperature in the LSM experiment is generally warmer than in the BATS experiment. A more detailed examination reveals that each simulation commences and completes the snowmelt period at about the same time but that the LSM snowmelt is more rapid than in the BATS experiment. Controlling the snowmelt is the initial snowpack depth and the surface energy budget, both of which involve a complex series of feedbacks between shortwave and longwave radiation, cloud, surface turbulent fluxes, and vegetation. The snowmelt over tundra regions dominates the more rapid snowmelt seen in the LSM simulation. It is determined that the most crucial differences between the BATS and the LSM schemes are the partitioning of net ground heat flux between patches of snow and bare ground and the formulation of snow albedo.
Variations of cloud droplet concentrations and the optical properties of clouds due to changing hygroscopicity: A model study
Authors: Kulmala Markku , Toivonen Anne , Mattila Timo , Korhonen Pekka
Published: February 2004

The effects of the availability of gaseous nitric acid, hydrochloric acid, and ammonia on cloud droplet formation have been studied using an adiabatic air parcel model including detailed multicomponent condensation. The used preexisting lognormal particle distribution is bimodal in size and in hygroscopicity: four lognormal distributions were used. In each mode particles were assumed to be internally mixed; that is, they were composed partly of salt and partly of an insoluble substance. According to the simulations made, a clear positive correlation between condensable species concentrations and the number of activated cloud droplets exists. Thus trace gases can also influence the optical thickness and reflectance of clouds. The simulations show that ammonia enhances the condensation rate of acids and thus also their effect on the cloud droplet activation significantly. The change in optical thickness varies as a function of the number concentration of preexisting particles, having a maximum (Δτ/τ = 1.6) near a concentration of 1000–2000 cm−3.
OH measurements during the First Aerosol Characterization Experiment (ACE 1): Observations and model comparisons
Authors: Mauldin R. L. , Frost G. J. , Chen G. , Tanner D. J. , Prevot A. S. H. , Davis D. D. , Eisele F. L.
Published: February 2004

Airborne measurements of the hydroxyl radical, OH, performed during the First Aerosol Characterization Experiment (ACE 1), using the Selected Ion Chemical lonization Mass Spectrometry (SICIMS) technique are presented. Adaptations of the previous ground‐based technique for measurement aboard an aircraft platform are discussed, including an inlet for the straightening and slowing of the airflow, calibration, and measurement considerations at changing pressure altitudes. Steady state model calculations of the concentration of OH, [OH], throughout the entire mission were generally in good agreement, with a slight bias toward an overestimate of the measured [OH]. The largest discrepancies between measured and modeled values occurred for measurements in the boundary layer, and those in and around clouds, with the model overestimating the [OH] by ∼40% in the boundary layer or inside clouds, and underestimating it by ∼30% near clouds. The low model [OH] near clouds can be attributed to underestimating the actinic flux calculated from Eppley radiometer measurements. The model overestimates in the boundary layer and inside clouds may in part be due to a lack of heterogeneous losses of HOx species in the model. Models developed at the National Oceanic and Atmospheric Administration Aeronomy Laboratory and at Georgia Institute of Technology produce similar results with differences being attributed to the methods of calculating photolysis rates. Calculations of high noon [OH] for a flight out of Hobart using the O(1D) quantum yields from Talukdar et al. [1998] produce 17% higher values than those calculated using the currently recommended Jet Propulsion Laboratory values.
Stratospheric aerosols observed by lidar over northern Greenland in the aftermath of the Pinatubo eruption
Authors: di Sarra A. , Bernardini L. , Cacciani M. , Fiocco G. , Fuà D.
Published: February 2004

Lidar observations were carried out from Thule (76.5°N, 68.8°W), Greenland, during the period September 1991 to February 1996. The measurements were carried out with relative continuity throughout the solar year, with the exception of the summer 1992. A total of over 300 profiles of the stratospheric aerosol backscattering and depolarization were obtained. The buildup and decay of the volcanic aerosols, originated from the eruption of Mount Pinatubo (June 1991, Philippines), were followed in detail. Maxima of the backscatter ratio, around 6, were recorded in March 1992. The aerosol decay, mainly controlled by gravitational sedimentation and stratosphere‐troposphere exchange, shows a strong modulation induced by dynamical phenomena: an annual oscillation of the aerosol integrated backscattering, with a winter maximum at altitudes below 20 km, distinctly appears. Subsidence during winter and, possibly, upward motion during summer lead to a consistently different winter‐to‐summer aerosol vertical distribution. Discontinuities in the evolution of the aerosol backscattering may be related to the influence of the quasi‐biennial oscillation (QBO) on the poleward transport and on the mean diabatic circulation. The QBO appears also to affect the stratosphere‐troposphere exchange during winter. By fitting the decreasing phase of the volcanic aerosol integrated backscattering with an analytical expression given by an exponential decrease and an annual oscillation, an e‐folding time of approximately 9.4 months is derived. The e‐folding time varies however with time and depends on altitude. A distinct transition occurs in early summer 1994, with a fast decrease of the aerosol load below 20 km. The observation of backscattering values larger than in the pre‐Pinatubo period still in early 1996 above 20 km seems to be consistent with modifications of the particle size distribution at these altitudes. Upper limit estimates for the diabatic descent in and outside the polar vortex could also be derived from the lidar observations in the winter months.
Seven years of continuous methane observations at a remote boreal site in Ontario, Canada
Authors: Worthy D. E. J. , Levin I. , Trivett N. B. A. , Kuhlmann A. J. , Hopper J. F. , Ernst M. K.
Published: February 2004

A 7‐year record (1990–1996) of continuous atmospheric methane (CH4) measurements is presented from a remote midcontinental monitoring station at Fraserdale, Ontario (49°53′N, 81°34′W). Ninety‐six air samples per day were measured with a fully automated gas chromatograph with flame ionization detection. Five‐day Lagrangian back trajectories over the 7‐year period were used to establish a climatology in the region of the station. The site is predominantly influenced by air flow from northern and high‐latitude regions and therefore uniquely positioned to monitor wetland emissions. During winter, CH4 concentration time series from Fraserdale often match the short‐term variability observed at the high Arctic monitoring station at Alert, Northwest Territories (82°27′N, 61°31′W). During summer, due to diurnal changes of vertical mixing in the boundary layer, large diurnal cycles in CH4 mixing ratio up to 150 ppb are observed. The data selected for the afternoon, when the boundary layer is well‐mixed, are representative of a larger spatial scale. The mean annual cycle of CH4 at Fraserdale determined using these selected data is significantly different from annual cycles at other mid‐ and high‐northern latitude sites thus providing key information for global atmospheric CH4 models. In late summer the annual cycle at Fraserdale shows a distinct secondary maximum in CH4. This is the result of advection of air with enhanced CH4 due to emissions from the extensive wetland areas to the north and northwest. The average growth rate (using selected data) for the period was 5.6 ppb yr−1 with a growth rate pattern that is slightly different and out of phase with growth rate changes observed at other high‐latitude observing sites by 2 to 6 months.
Measurement and modeling of particle nitrate formation
Authors: Makar P. A. , Wiebe H. A. , Staebler R. M. , Li S. M. , Anlauf K.
Published: February 2004

Nighttime measurements of particle number distribution and mass composition, and concentrations of NO2, O3, NH3, and HNO3, were made at night at a rural site in Ontario in August of 1992. A simple model of particle growth was constructed to simulate the observed rapid growth of aerosol mass in the 0.2 to 0.5 μm diameter range. Both measurements and model results indicate that the growth of accumulation mode aerosol mass was due to condensation of the nitrate radical, HNO3, and NH3 onto particles, with the formation of particle ammonium nitrate. The results show that the reaction of O3 with NO2 in the isolated nocturnal boundary layer can lead to the production of gas‐phase nitric acid. When this occurs in the presence of local ammonia emissions and preexisting particles, rapid growth of particle ammonium nitrate takes place. The model results show that most of the observed variations can be accounted for by a coupled system of equations including dynamical and thermodynamic effects. The dynamical approach to equilibrium is sufficiently fast that the gas‐phase nitric acid concentrations are more sensitive to the magnitude of the thermodynamic equilibrium concentration than the dynamical time constant. A simple parameterization for the effects of sulphate on particle nitrate formation was developed and shown to provide a good estimate of the equilibrium concentration of gas‐phase nitric acid.
The effect of organic coatings on the cloud condensation nuclei activation of inorganic atmospheric aerosol
Authors: Cruz Celia N. , Pandis Spyros N.
Published: February 2004

Atmospheric aerosols have mixed chemical composition, with a variety of inorganic (e.g., sulfate, nitrate, ammonium, and sodium) and organic species often present in a single particle. In the present study, we investigate experimentally the cloud condensation nuclei (CCN) activation of submicron aerosol consisting of an inorganic core (e.g., ammonium sulfate) coated by an organic film, at typical atmospheric supersaturations. We use two types of organic coatings on the (NH4)2SO4 particles. The first is glutaric acid, a CCN active organic found in the atmosphere, and the second species is dioctylphthalate (DOP), a nonhygroscopic organic. The CCN activation of (NH4)2SO4‐glutaric acid particles was measured at a supersaturation of 0.3%, for different inorganic core sizes and organic film thickness. We found that a coating of glutaric acid increases the CCN activation of an (NH4)2SO4 particle and that this behavior can be predicted by Köhler theory. The deviation from Köhler theory for the mixed aerosol was determined by comparing theoretical and experimental CCN activation diameters for the particles and was found to be within experimental error. A thick coating of DOP (at least 70% by mass) did not hinder the activation of (NH4)2SO4 particles at supersaturations of 0.5 and 1.0%. The values for the measured activation diameters for the DOP coated (NH4)2SO4 particles were within the experimental error determined by the pure inorganic experiments, indicating that DOP was most likely acting as inert mass during activation.
A one‐dimensional sectional model to simulate multicomponent aerosol dynamics in the marine boundary layer: 1. Model description
Authors: Fitzgerald James W. , Hoppel William A. , Gelbard Fred
Published: February 2004

A one‐dimensional, multicomponent sectional model has been developed to simulate the temporal and vertical variations of the aerosol size distribution and composition in the marine boundary layer (MBL). An important aspect of the model is its ability to handle the transport of aerosols in an atmosphere with humidity gradients with no numerical diffusion caused by the swelling and shrinking of the particles as they move through the humidity gradients. This is achieved by rewriting the aerosol general dynamical equation (GDE) in terms of dry radius thus transferring all variations in radius caused by temporal and spatial humidity variations to the rate coefficients appearing in the equations. The model then solves the new GDE in fixed dry size sections, with the humidity dependence of the processes now included in variable coefficients. This procedure also results in correct gradient transport. A limiting assumption is that the particles equilibrate instantaneously with the ambient water vapor. This assumption limits the maximum particle size which can be treated in the model to ambient (wet) radii less than about 30 μm. All processes currently believed to be important in shaping the MBL size distribution are included in the current version of the model. These include generation of sea‐salt aerosol at the ocean surface, nucleation of new particles, coagulation, growth due to condensation of gas‐phase reaction products, growth due to sulfate formation during cloud processing, precipitation scavenging, surface deposition, turbulent mixing, gravitational settling, and exchange with the free troposphere. Simple gas‐phase chemistry which includes the oxidation of dimethylsulfide and SO2 to sulfate is incorporated in the current version of the model.
Electric field measurements with an airplane: A solution to problems caused by emitted charge
Authors: Mo Q. , Ebneter A. E. , Fleischhacker P. , Winn W. P.
Published: February 2004

The growth of electrical energy in a thundercloud prior to a lightning flash can be studied by measuring the electric field. The use of airplanes to measure the electric field has been a problem because the intense electric field of a thunderstorm causes electric breakdown in air at sharp metallic points and edges. The electrical charge produced by the breakdown can be confused with the charge in the thunderstorm itself, causing large errors in the measurement. Electric field sensors on the fuselage of a single‐engine airplane can give erroneous measurements when the electric field amplitude is as low as 10 kV/m. However, new electric field sensors in pods under the wings away from the fuselage appear to give correct measurements up to about 150 kV/m, the most intense field we have encountered. A flight around a rainshaft beneath a thunderstorm shows how the electric field, deduced from the new pod meters under the wings, differs from the field deduced from meters on the fuselage.
Breakup of levitated frost particles
Authors: Bacon Neil J. , Swanson Brian D. , Baker Marcia B. , Davis E. James
Published: February 2004

We have studied the sublimation and breakup of single 100–200 μm frost particles levitated electrically at temperatures in the range −2°C to −30°C. Breakup rates were largely independent of temperature and humidity in this range but strongly dependent on particle shape. Irregular particles of high aspect ratio were most likely to break up. Sublimation (evaporation) was accompanied by an increasing aspect ratio. A linearized sublimation model, presented in the appendix, accounts for the observation that thin neck regions were not subject to enhanced sublimation rates. Estimates of the forces involved in breakup suggest that the breaking strength of these frost particles is considerably less than that of bulk ice. We discuss possible implications of our results for ice particle multiplication in clouds.
Influence of different water masses and biological activity on dimethylsulphide and dimethylsulphoniopropionate in the subantarctic zone of the Southern Ocean during ACE 1
Authors: Jones Graham B. , Curran Mark A. J. , Swan Hilton B. , Greene Richard M. , Griffiths F. Brian , Clementson Lesley A.
Published: February 2004

Measurements of salinity, temperature, phytoplankton biomass and speciation, dissolved nitrate, dimethylsulfide (DMS) in seawater and air, and dimethylsulfoniopropionate (DMSP), were made in the subantarctic zone of the Southern Ocean from 40°‐54°S, and 140°‐153°E during the southern hemisphere marine First Aerosol Characterization Experiment (ACE 1). DMSP concentrations were highest in subtropical convergence zone (STCZ) waters, intermediate in subantarctic waters, and lowest in polar waters. DMSP appeared to decrease at frontal regions between these major water masses. In subantarctic waters, high levels of DMSP were generally associated with an increase in dinoflagellate biomass and low microzooplankton grazing rates. Lower DMSP concentrations occurred in polar waters when the diatom biomass and grazing rates were high. DMS levels measured onSouthern Surveyorranged from not detectable (nd) to 5.6 nM (mean 1.7 nM), with below average levels in subantarctic waters (mean 1.25 nM), and above average levels (mean = 1.93 nM) in polar waters. Pulses of DMS occurred asSouthern Surveyortraveled south into polar waters, with a large pulse (mean = 2.3 nM) highlighted as the vessel traveled back into subantarctic waters (46°‐47°S, 148°‐151°E) in early December. By using the dissolved DMSP (DMSPd) to DMS ratio as an index of the bacterial conversion of DMSPd to DMS some evidence was found that, in polar waters, increased microzooplankton (MZP) grazing in diatom dominated waters, may lead to above average concentrations of DMS. This does not appear to be the case when the biomass was dominated by dinoflagellates in subantarctic waters.
NOAA 11 Solar Backscatter Ultraviolet, model 2 (SBUV/2) instrument solar spectral irradiance measurements in 1989–1994: 2. Results, validation, and comparisons
Authors: DeLand Matthew T. , Cebula Richard P.
Published: February 2004

Accurately measuring long‐term solar UV variability is an experimental challenge because instrument response degradations are typically large enough to obscure solar change. For satellite instruments, one solution is a series of regular comparisons with a well‐calibrated reference. The NOAA 11 Solar Backscatter Ultraviolet, model 2 (SBUV/2) instrument made solar spectral irradiance measurements between 170 and 400 nm from December 1988 to October 1994, covering the maximum and most of the decline of solar cycle 22. The NOAA 11 irradiance data were corrected for long‐term instrument sensitivity changes using comparisons with coincident flights of the Shuttle SBUV (SSBUV) instrument. The NOAA 11 data show a decrease of 7.0(±1.8)% in smoothed 200–208 nm irradiance from Cycle 22 maximum in mid‐1989 to October 1994, near solar minimum. The long‐term decrease in solar irradiance at 250 nm was ∼3.5(±1.8)%. Longward of 300 nm, no solar variations were observed to within the 1% accuracy of the data. The NOAA 11 measurements overlap observations from the Upper Atmosphere Research Satellite (UARS) Solar Stellar Irradiance Comparison Experiment (SOLSTICE) and Solar Ultraviolet Spectral Irradiance Monitor (SUSIM) instruments from October 1991 to October 1994, providing the first opportunity to compare three coincident long‐term solar UV irradiance data sets. We find reasonable agreement between the NOAA 11, SOLSTICE, and SUSIM results at all wavelengths in the 170–400 nm region. Power spectral analysis gives consistent results for all three instruments on solar rotational timescales, and reveals the evolution of solar rotation periodicity and strength during a solar cycle. We find significant differences between instruments in both period and spectral location when the spectral irradiance data are analyzed on intermediate (50–250 days) timescales. The NOAA 11 spectral irradiance data provide a valuable complement to the UARS solar data, and capture the entire maximum of solar cycle 22.
Simulation of impacts of climatological MSU data processing methods using NCEP/NCAR reanalysis data
Authors: Wu Zhen‐Jia , McAvaney Bryant
Published: February 2004

The Microwave Sounding Units (MSUs) aboard TIROS‐N/NOAA satellites have played an important role in providing long‐term global climate information. However, mainly due to the “limb‐correction” and the “intrascan averaging” procedures in the data processing, changes to the characteristics of the data may have occurred. In this paper we investigate this possibility in two parts. In the first part we have chosen to revisit the radiative transfer theory and to re‐derive the (effective) radiative transfer equation for the processed MSU data under more general conditions. We find that the weighting function of the processed MSU deviates from the original at nadir and that the normalization condition, which ensures the total weight of contributions to the total observed radiance from different sources sums up to unity, is breached. In the later part of the paper we generate simulations of climatological MSU‐2 before and after data processing using a line‐by‐line radiative transfer code of Shah and Rind [1995] with the monthly mean output of the National Centers for Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR) reanalysis project [Kalnay et al, 1996] for the period 1982–1994. These simulations are examined and compared with the processed MSU‐2 observations available in the public domain. We find that a systematic reduction of contrast between land and ocean MSU‐2 brightness temperatures can result from the limb‐correction procedure. The temporal variances are affected by the greater‐than‐unity limb‐correction coefficients, especially in the tropical region. A reduction of the spatial variances over the land region, as was reported earlier by Basist et al. [1995], can be caused by the intrascan averaging treatment in the processing. We suggest that a better approach in future MSU data processing may be to use the nadir data directly without averaging with the other off nadir data and, in addition, that the off‐nadir data should be “navigated” and be processed into separate data sets.
Diffusion coefficients for HCl and HBr in 30 wt % to 72 wt % sulfuric acid at temperatures between 220 and 300 K
Authors: Klassen Jane K. , Hu Zhengjie , Williams Leah R.
Published: February 2004

Diffusion in sulfuric acid plays a role in heterogeneous stratospheric processes. Knowledge of diffusion coefficients is required to determine the partitioning of heterogeneous reactions between the bulk and the surface of sulfate aerosol particles. Diffusion coefficients are also needed to analyze time‐dependent uptake data to obtain solubilities. In order to provide quantitatively accurate diffusion coefficients, the experimental challenges of measuring solute diffusion in strong electrolyte environments must be overcome. We use a modified diaphragm cell technique and report diffusion coefficients for HCl and HBr in sulfuric acid solutions from 220 to 300 K. We find that the temperature and viscosity dependence of these measurements follows the equation D = cT/η, where η is viscosity, yielding c = 7.8 × 10−8 cm2 cP/s K for HCl and c = 7.9 × 10−8 cm2 cP/s K for HBr. An empirical equation for predicting diffusion coefficients for other species in sulfuric acid is also presented.
Estimation of aerosol transport from biomass burning areas during the SCAR‐B experiment
Authors: Trosnikov Igor V. , Nobre Carlos A.
Published: February 2004

A transport model for the estimation of tracers spreading from biomass burning areas has been developed on the basis of the semi‐Lagrangian technique. The model consists of a three‐dimensional Lagrangian form transport equation for tracers and uses the quasi‐monotone local cubic‐spline interpolation for calculation of unknown values at irregular points. A mass‐conserving property of the model is based on the flux‐corrected transport method using the algorithm of Priestley. The transport of the smoke particles from Amazonia was simulated for the period from August 20 to 29, 1995. During this period the air mass located below 2 km moved to the south and carried the smoke particles until 30°S.
An overview of GOES‐8 diurnal fire and smoke results for SCAR‐B and 1995 fire season in South America
Authors: Prins Elaine M. , Feltz Joleen M. , Menzel W. Paul , Ward Darold E.
Published: February 2004

The launch of the eighth Geostationary Operational Environmental Satellite (GOES‐8) in 1994 introduced an improved capability for diurnal fire and smoke monitoring throughout the western hemisphere. In South America the GOES‐8 automated biomass burning algorithm (ABBA) and the automated smoke/aerosol detection algorithm (ASADA) are being used to monitor biomass burning. This paper outlines GOES‐8 ABBA and ASADA development activities and summarizes results for the Smoke, Clouds, and Radiation in Brazil (SCAR‐B) experiment and the 1995 fire season. GOES‐8 ABBA results document the diurnal, spatial, and seasonal variability in fire activity throughout South America. A validation exercise compares GOES‐8 ABBA results with ground truth measurements for two SCAR‐B prescribed burns. GOES‐8 ASADA aerosol coverage and derived albedo results provide an overview of the extent of daily and seasonal smoke coverage and relative intensities. Day‐to‐day variability in smoke extent closely tracks fluctuations in fire activity.
Radiative effects of sub‐mean free path liquid water variability observed in stratiform clouds
Authors: Marshak Alexander , Davis Anthony , Wiscombe Warren , Cahalan Robert
Published: February 2004

A unique 4‐cm‐resolution data set of stratocumulus cloud liquid water content (LWC) made possible, for the first time, the generation of credible models of cloud LWC down to centimeter‐scales, well below the photon mean free path (mfp) which is typically tens of meters. These models are exploited to study the errors in the usual assumption of LWC homogeneity within three‐dimensional (3D) radiative transfer grid boxes, by doing Monte Carlo computations for 30‐m cubes resolved down to 10‐cm scales. Cloud models with and without vertical variability are compared. We found that vertically homogeneous but horizontally variable cloud structure produces cloud radiation biases of 3–5% relative to the assumption of complete homogeneity. The addition of vertical variability similar to the horizontal variability reduces these biases well below 1%. We therefore conclude that 3D cloud models resolved down to the mfp scale (20–30 m for marine stratocumulus clouds), with an incorrect assumption of homogeneity below that scale are sufficient for modeling radiative properties averaged over mfp and larger scales in both visible and near‐infrared spectral regions. This conclusion is restricted to only the overcast cases.
Model sensitivity studies of Arctic ozone depletion
Authors: Chipperfield M. P. , Pyle J. A.
Published: February 2004

We have used an off‐line chemical transport model (CTM) to diagnose the expected chemical ozone destruction in the Arctic winters of 1993/1994 to 1996/1997, and to investigate the sensitivity of the model‐calculated loss to meteorological variability, chlorine and bromine loadings, denitrification, dehydration, and increased stratospheric H2O. The model was integrated on a single isentropic surface at 475 K (about 18 km or 50 hPa altitude) using analyses from the European Centre for Medium‐Range Weather Forecasts. The CTM produces local depletions of up to 45% in the polar vortex in the cold winter of 1995/1996. In winter 1996/1997 the large‐scale temperatures cold enough for polar stratospheric clouds did not start until early January which delayed chlorine activation. However, because the cold temperatures persisted well into March, the local O3 depletion in the model vortex was around 40% in late March. The sensitivity experiments using 1994/1995 meteorology show that the chlorine loading is much more important than bromine for controlling the polar ozone loss given the expected abundances, but the ClO + BrO ozone loss cycles are calculated to be more important than ClO + ClO. Accordingly, the local relative efficiency factor we calculate from the model (α) is large, especially in the polar region where it is around 60 for current day halogen loadings. Denitrification can increase Arctic ozone depletion through a delay in chlorine deactivation. However, very strong denitrification early in the winter causes less O3 depletion in the model, with the current heterogeneous chemistry scheme, due to enhanced recovery into HCl and inefficient chlorine reactivation. The additional inclusion of dehydration reduces the modeled Arctic O3 depletion, due to decreased heterogeneous processing rates, and the reduced occurrence of equilibrium nitric acid trihydrate particles. The modeled Arctic O3 depletion increases slightly (by 2–4% of the initial O3) using 1994/1995 meteorology when the stratospheric H2O loading is increased. This is due to slightly more polar stratospheric cloud (PSC) activity in this cold winter, although this effect would be potentially more important in a warmer winter where PSC processing was marginal.
“Spider” lightning in intracloud and positive cloud‐to‐ground flashes
Authors: Mazur Vladislav , Shao Xuan‐Min , Krehbiel Paul R.
Published: February 2004

The nature of visible, horizontally stratified lightning channels propagating over large distances near the cloud base during the decaying stage of a storm (also called “spider” lightning) was investigated. The study was effectuated through the use of the coordinated observations of a VHF interferometer, a high‐speed image‐intensified video system, measurements of electric and magnetic fields, and optical transients. Spider‐lightning events were found to be negative leaders similar to stepped leaders in negative cloud‐to‐ground flashes, with a similar average speed of propagation horizontally of 2–4 × 105 m s−1. Being slow negative leaders, spider‐lightning events are part of intracloud flashes and positive cloud‐to‐ground flashes occurring prior to and during the inverted (fair weather polarity) phase of the End of the Storm Oscillation in the ground electric field. Spider lightning is characterized by both the pulsing luminosity at the tips of its branched channels and the continuous luminosity (for tens to hundreds of milliseconds) which is maintained by the continuing current flow. The interferometer produced mapping of radiation sources closely resembling the spider‐lightning channels (negative leaders) but only a weak trace of radiation sources associated with positive leaders to ground. Both the video images and a few radiation sources of positive leaders were obtained within 1 ms of the leader's ground attachment. The interferometer, however, failed to map fast negative leaders that occurred intermittently during the spider‐lightning events.
Sampling errors for meteorological fields observed by low Earth orbiting satellites
Authors: Li Ta‐Hsin , North Gerald R.
Published: February 2004

This paper investigates the sampling errors in the spherical harmonic coefficients of meteorological fields derived from observations made by polar‐orbiting satellites. The sampling errors are attributed not only to the spatial gaps of satellite orbits but also to the nonsimultaneousness of satellite sampling. As a result, the mean‐square error is found to consist of aliased powers from spatial waves as well as temporal frequencies. In addition to analytical results, a simple energy balance model is employed in a numerical study that produces interesting numerical results. In particular, the root‐mean‐square error for estimating the daily global average surface temperature anomaly using 16 polar orbits is found to be 0.06°C or less if the temporal scale of decorrelation is equal to 30 days or longer; it can be as high as 1.12°C if the temporal scale is decreased to 1 day.
A simple model of the ice particle size distribution in noctilucent clouds
Authors: Klostermeyer J.
Published: February 2004

A timescale analysis indicates that at noctilucent cloud (NLC) heights near 83 km, the growth and decay of ice particles and their transport by tide‐ and gravity‐wave‐associated vertical velocity components are the dominant processes that determine the particle size distribution. Other processes including sedimentation are of minor importance, so that the formation of NLCs should, in general, not depend on atmospheric conditions at the mesopause, in agreement with recent findings from simultaneous lidar and rocket experiments. Then a simple NLC model can be constructed consisting essentially of a partial differential equation which describes the temporal behavior of the particle size distribution in particle parcels moving with the wave‐associated air velocity. Contrary to previous ones, the present model yields a steady state oscillation within an integration time of 1 day because the optically active ice particles have lifetimes of a few hours only. NLC simulations yield particle concentrations, mean radii, and scatter ratios which are in good agreement with observational results. The model also predicts an occasional coexistence of small populations of optically active particles and large populations of microscopic particles, which may be of basic importance for the interpretation of recent observations indicating a more or less tight coupling between NLCs and simultaneously occurring polar mesosphere summer echoes.
Upper tropospheric water vapor from GEOS reanalysis and UARS MLS observation
Authors: Chen Minghang , Rood Richard B. , Read William G.
Published: February 2004

The upper tropospheric water vapor (UTWV) from the reanalysis produced by the Goddard Earth Observing System (GEOS) Data Assimilation System is compared with the retrieved UTWV from the measurements of the Microwave Limb Sounder (MLS) aboard the Upper Atmosphere Research Satellite (UARS). The UTWV from the GEOS reanalysis is in fair agreement with the UTWV retrieved from the UARS MLS observation. Both data sets show high tropical UTWV closely related with the tropical deep convection. There is, however, clear evidence of overestimation of UTWV in the GEOS reanalysis, especially for the summer season (July 1992). The GEOS overestimation is more significant after considering the MLS retrieval bias. The reasons for the GEOS overestimation are discussed. For interannual variations between 1992 and 1993, the reanalysis and the observation consistently show significant changes in UTWV resulting from sea surface temperature anomalies associated with the El Niño‐Southern Oscillation phenomenon.
The effect of varying the source spectrum of a gravity wave parameterization in a middle atmosphere general circulation model
Authors: Manzini E. , McFarlane N. A.
Published: February 2004

Climate simulations of the middle atmosphere circulation with general circulation models are now starting to include parameterizations of the momentum flux deposition due to unresolved gravity wave spectra. A current uncertainty in the application of such parameterizations is the specification of the imposed gravity wave spectrum. The aim of this work is to quantify the effect of varying within a realistic range the source spectrum of a gravity wave parameterization in a general circulation model. Results from two simulations with the gravity wave spectrum launched at two different heights, the surface and the 110‐hPa pressure level, respectively, are compared. Noteworthy differences found in the simulated middle atmosphere response include the following (1) The average temperature in the southern winter upper stratosphere is about 40 K warmer in the experiment with the surface as the launching height, virtually eliminating the typical cold polar bias that affects many general circulation models. (2) Stronger easterlies in the subtropical summer mesosphere, again in the experiment with the surface as the launching height. Diagnostics of the parameterized gravity waves indicate that in the experiment with the surface as the launching height, the net zonal momentum flux transported by the gravity waves is negative just above the troposphere at middle latitudes. This negative net momentum flux facilitates the deceleration of the mesospheric winter westerlies. The meridional circulation induced by such deceleration is thereafter responsible for the substantial polar winter warming. In contrast, in summer the negative net momentum flux limits the upper mesospheric deceleration of the easterlies. In the experiment with launching height at 110‐hPa, the gravity wave net momentum flux is instead zero by construction at the launching height.
Changes in ultraviolet radiation due to stratospheric and tropospheric ozone changes since preindustrial times
Authors: Sabziparvar Ali A. , de F. Forster Piers M. , Shine Keith P.
Published: February 2004

This paper estimates global changes in ultraviolet radiation since preindustrial times, resulting from anthropogenic stratospheric and tropospheric ozone changes. A sophisticated radiative transfer scheme is employed to calculate changes in the diurnally integrated UVB (defined here as 280–320 nm) and erythemally weighted (EER) irradiance reaching the Earth's surface. Stratospheric ozone changes are obtained from combining total ozone mapping spectrometer satellite data with Dobson ground‐based instrument data. Tropospheric ozone changes are estimated from the University of Oslo three‐dimensional chemical transport model. These ozone trend data are combined in three ways to calculate the associated ultraviolet trend and estimate its uncertainty. We show that in low latitudes a significant (up to 5% for UVB and 9% for EER) decrease in surface UV may have occurred, due to tropospheric ozone increases. Large UV increases are found at high latitudes, with up to 60% increases in October and 20% increases in April. The possible effects of soot and sulphate aerosol changes on the UV are also briefly examined; increased aerosol amounts may have decreased surface UVB and EER by up to 7% locally and about 2% on a global average.
Large‐scale aerosol source apportionment in Amazonia
Authors: Artaxo Paulo , Fernandas Eduardo T. , Martins José V. , Yamasoe Márcia A. , Hobbs Peter V. , Maenhaut Willy , Longo Karla M. , Castanho Andrea
Published: February 2004

Aerosol particles were collected aboard two Brazilian Bandeirante EMB 110 planes, and the University of Washington Convair C‐131A aircraft during the Smoke, Clouds, and Radiation‐Brazil (SCAR‐B) field project in the Amazon Basin in August and September 1995. Aerosols were collected on Nuclepore and Teflon filters. Aerosol size distribution was measured with a MOUDI cascade impactor. Sampling was performed mostly over areas heavily influenced by biomass burning smoke. Particle‐induced X ray emission (PIXE) was used to measure concentrations of up to 20 elements (Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Br, Rb, Sr, Zr, and Pb). Black carbon (BC) and gravimetric mass analysis were also performed. Instrumental neutron activation analysis (INAA) determined the concentrations of about 15 elements on the Teflon filters. Electron probe X ray microanalysis (EPMA) was used to analyze individual aerosol particles. The average aerosol mass concentration was 105 μg m−3, with a maximum of 297 μg m−3. Black carbon (BC) averaged 5.49 μg m−3, or 1–7% of the aerosol mass load. Five aerosol components were revealed by absolute principal factor analysis: (1) a biomass burning component (responsible for 54% of the aerosol mass and associated with BC, K, Cl, Zn, I, S, Br, Rb, aerosol mass concentration, and other elements); (2) a soil dust aerosol component (15.6% of the aerosol mass); (3) a natural biogenic component (18.7% of the aerosol mass and associated with P, K, S, Ca, Sr, Mg, Mn, Cu and Zn); (4) a second soil dust (5.7% of the aerosol mass and enriched in Si, Ti, and Fe); and (5) a NaCl aerosol component (5.9% of the aerosol mass with Na, Cl, Br, and iodine). Electron microscopy analysis of individual aerosol particles confirmed these five aerosol types. Organic material dominated the aerosol mass and the number concentration of airborne particles. Aerosol size distributions show that the fine mode accounts for 78% of the aerosol mass, centered at 0.33 μm aerodynamic diameter. The coarse mode accounts for 22% of the mass, centered at about 3.2 μm. Black carbon size distributions show a consistent picture, with a mass median diameter centered at about 0.175‐0.33 μm aerodynamic diameter. This study suggests that for modeling the optical properties of aerosol in the Amazon Basin, it is essential to use a model that includes the optical and physical properties of at least two aerosol components other than the biomass burning aerosol, namely, natural biogenic aerosol and soil dust.
A two‐dimensional model with input parameters from a general circulation model: Ozone sensitivity to different formulations for the longitudinal temperature variation
Authors: Smyshlyaev Sergei P. , Dvortsov Victor L. , Geller Marvin A. , Yudin Valery A.
Published: February 2004

Net heating and temperature derived from the middle atmospheric version of the National Center for Atmospheric Research's Community Climate Model (MA CCM2) history tapes are used to evaluate three different approaches to account for zonal temperature asymmetries in the calculation of gas phase and heterogeneous chemical reaction rate constants and polar stratospheric cloud (PSC) surface area in a two‐dimensional chemistry transport model (2‐D CTM). The first method uses the daily (and monthly) averaged three‐dimensional (3‐D) temperature distribution derived from the MA CCM2 to calculate chemical and heterogeneous reaction rates at each 3‐D grid point, followed by zonal averaging (pseudo‐3‐D method). The second method uses 3‐D daily temperature statistics from the MA CCM2 to calculate the monthly averaged probability function (stochastic approach). The third method is based on a planetary wave superposition on the zonally averaged temperature (wave approach). The sensitivity of the gas phase reactions to the longitudinal temperature asymmetry is small, while the sensitivity of the heterogeneous reaction rates is comparable to the ozone response to aircraft emissions. All three methods of accounting for longitude temperature asymmetry give similar PSC morphologies in the southern hemisphere, in good agreement with climatological data and independent model calculations. In the northern hemisphere, where the CCM2 winter temperatures at high latitudes are known to be warmer than those observed, the PSCs predicted by the pseudo‐3‐D and wave methods are much scarcer than those observed or calculated by other authors using climatological temperatures. For the same reason, all other methods employed in the present study failed to predict any PSCs in the northern hemisphere.