bluuebunny/crossref_metadata_2025 huggingface dataset:
Aspects of atmospheric pollutant origin and deposition revealed by multielemental observations at a rural location in eastern Canada
Authors: Barrie L. A.
Published: February 2008

During autumn 1984, at a location in central Ontario, a study of the elemental composition of aerosols and precipitation was undertaken to determine the feasibility of making daily multielemental measurements on a routine basin, to probe the potential for gaining insight into pollutant origin from multielemental composition, and to estimate trace element deposition to an acid‐sensitive watershed. The concentrations of Ti, Br, Mn, In, Na, V, Al, Ca, Se, As, Sb, Pb, Fe, Mg, Cu, Zn, and Cd in aerosol and of Pb, Mg, Ca, As, Br, I, Mn, and V in precipitation were measurable routinely, using neutron activation, X ray fluorescence, and plasma emission spectroscopy. Standard high volume samplers for total aerosols below 15 μm diameter as well as dichotomous samplers and Andersen impactors for size fractionation were operated simultaneously with two wet‐only precipitation collectors. Aerosol data revealed four components: one soil (Mg‐Ti‐Al‐Ca‐Fe) and three anthropogenic (Se‐Sb‐Pb‐Cd‐Br; Mass‐Cu‐SO4=; In‐As). Ranked in order of increasing mass fraction in 2.1‐ to 10‐μm diameter particles are the elements Pb, S, Se, Br, As, Cl, Na, V, In, Cu, Mn, Al, Ba, Ti, and Ca. A comparison of air parcel origin on high‐ and low‐concentration days, using 3‐day back trajectories, revealed major source regions of SO4=, Pb, In, As, and Al. The element In is an excellent tracer of smelter emissions to the north. Although the estimated mean ratio of In/Se in smelter emissions from central Ontario is close to that used in the regional aerosol apportionment model of Rahn and Lowenthal, its variability is greater than they propose. In 21 precipitation events, strong correlations were found between H+‐SO4 =, Ca++‐Mg++, NO3−‐NH4+‐Cl−‐V, and Pb‐Br. The mass ratio of Br/Pb was higher in precipitation (0.47) than in aerosols (0.27), possibly because of precipitation scavenging of HBr gas in addition to Br in aerosols. In ascending order, the estimated dry‐deposited fraction of total deposition of Br, Pb, Mg, Mn, Ca, S, V, and As ranged from 10 to 42%.
Mixing rates calculated from potential vorticity
Authors: Newman Paul A. , Schoeberl Mark R. , Plumb R. Alan , Rosenfield Joan E.
Published: February 2008

The flux and the gradient of potential vorticity are used to calculate horizontal mixing coefficients (Kyy and Kyz). It is found that the mid‐latitude to polar mixing coefficients depend on the use of nongeostrophic winds. Geostrophic winds yield Kyy values which are largely negative near the polar region, implying counter‐gradient transport of potential vorticity by eddies, while nongeostrophic winds yield Kyy values which are mostly positive. Typically, large Kyy values (in excess of 106 m2 s−1) are found in the middle to upper stratosphere during winter in the northern hemisphere, the middle to upper stratosphere during spring in the southern hemisphere, and the troposphere for both northern and southern hemispheres. As an alternative procedure, Kyy values have also been calculated using the momentum balance between the flux of potential vorticity and the residual circulation. These residual circulation balanced Kyy values in the upper stratosphere are much larger than those determined from the potential vorticity fluxes and gradients. This difference may be a result of breaking gravity waves in the upper stratosphere and lower mesosphere.
Sulfur dioxide at the Venus cloud tops, 1978–1986
Authors: Esposito Larry W. , Copley M. , Eckert R. , Gates L. , Stewart A. I. F. , Worden H.
Published: February 2008

Ultraviolet spectroscopy from the Pioneer Venus Orbiter shows a decline in the cloud top abundance of SO2 from about 100 ppb to about 10 ppb in the period 1978–1986. A consistent decline in polar haze has occurred over the same period, with the correlation coefficient between these two observables of r = 0.8. Star calibrations determine the instrument sensitivity to within 10%, which rules out the possibility that this is an instrumental effect. Systematic errors could increase the SO2 abundance to twice the inferred values in later orbits. Tracking of SO2 features and power spectral analysis give rotation periods for the longer‐lived features of 3.6–5.2 days, consistent with cloud‐tracked winds observed at other wavelengths. The behavior of SO2 and polar haze can be plausibly explained by episodic injection of SO2 into the cloud top regions, for example, by active volcanism.
Radar interferometer observations of mesospheric echoing layers at Jicamarca
Authors: Kudeki Erhan
Published: February 2008

VHF radar observations at Jicamarca show that the most intense mesospheric echoes at the equator are returned from thin horizontal layers with lifetimes ranging from tens of minutes to many hours. A few such layers may be present at a time, typically separated in altitude by a few kilometers. Interferometric studies of radar returns from these layers indicate that the characteristic widths of the corresponding Doppler spectra are usually determined by the spatial integration effect due to finite size scattering volumes. Radar returns from lower mesospheric layers appear to be due to randomly distributed scatterers convected through the observation volume by nonturbulent wind fields. The scatterers in question may possibly be specularity points or glints on corrugated refractive index surfaces. Higher mesospheric layer echoes, however, imply the existence of turbulent flow fields in the vertical plane, with dominant eddy motions at scale sizes comparable with the scattering volume dimensions of about a kilometer.
Seasonal trends of ozone in equatorial Africa: Experimental evidence of photochemical formation
Authors: Cros Bernard , Delmas Robert , Nganga Dominique , Clairac Bernard , Fontan Jacques
Published: February 2008

Surface ozone measurements obtained at Brazzaville, Congo (4°20′S, 15°20′E), from 1983 to 1986 are summarized. In addition, results from aircraft surveys (1985 and 1986) from Brazzaville to the Atlantic coast and results from a shipboard expedition (1986) along the Atlantic coast at the Equator are presented. On the basis of the data, there appears to exist a seasonal cycle with the highest values in early spring (southern) which compare with the mid‐latitude values observed in the northern hemisphere. The data suggest that during the dry season, emission of precursor gases from biomass burning leads to high ozone values in the boundary layer. Ozone mixing ratios approached levels as high as 100 parts per billion by volume in a layer residing just above the monsoon. In the wet season, the data suggest that biogenic, organic emissions may act as precursors to photochemical ozone production and may contribute to the fairly high ozone burden of the lower troposphere over Equatorial Africa.
Sensitivity of regional predictability to flow characteristics
Authors: Horel John D. , Roads John O.
Published: February 2008

A two‐level spherical quasi‐geostrophic model is used to assess the dependence of model skill upon initial conditions. The medium‐frequency variability of a 3600‐day control run of perpetual January conditions is found to exhibit many features of the observed wintertime circulation in the Pacific sector. In particular, the frequency of occurrence and characteristics of quasi‐stationary regimes, periods when the planetary circulation is more persistent than usual, are similar to those observed. A total of 856 predictability experiments are performed by introducing small initial errors to the control run. Quasistationary flow patterns in the Pacific sector are no easier to predict than transient flow patterns. In addition, forecasts begun during quasi‐stationary periods are no more successful than those begun during transient episodes. An index of the dominant medium‐frequency variability of the control run, a north‐south dipole in the eastern Pacific, is used to assess the dependence of model skill on the strength of the zonal flow across the Pacific Ocean. We found a slight asymmetry in forecast skill, such that forecasts begun during episodes of above‐normal zonal flow are more successful than those begun during episodes of below‐normal zonal flow. These results are consistent with recent analyses of European Centre for Medium Range Weather Forecasts model forecast skill.
The effect of cirrus clouds on 118‐GHz brightness temperatures
Authors: Weinman J. A.
Published: February 2008

A microwave radiative transfer model that describes the effect of scattering by cirrus clouds on the brightness temperatures that may be measured by a geostationary temperature‐sounding radiometer has been developed. The model assumes that cirrus clouds are situated at an altitude where the temperature is ∼230 K above completely absorbing land surfaces. It is shown that the brightness temperature at 118.75±3.9 GHz is depressed by 0.3–0.4 K g−1 m−2 of ice. The channels that operate at frequencies closer to 118.75 GHz are less affected by cirrus clouds. The brightness temperature reduction is most pronounced in warm temperate and tropical conditions.
Cloud field classification based upon high spatial resolution textural features: 1. Gray level co‐occurrence matrix approach
Authors: Welch R. M. , Sengupta S. K. , Chen D. W.
Published: February 2008

Standard cloud algorithms rely on multispectral signatures to identify high, medium, and low clouds. In contrast, the present study classifies stratocumulus, cumulus, and cirrus clouds, using textural features alone, derived from a single high‐resolution Landsat Multispectral Scanner near‐infrared channel. Applying stepwise linear discriminant analysis, classification accuracies of 92–95%, with standard deviations of about 1.5%, are achieved using the random subregion hold‐out pattern. Accuracies of 83–88%, with standard deviations of about 7%, are achieved using the random scene hold‐out pattern. The theoretical accuracy of the approach is estimated by treating the simulation on a non‐parametric basis, using the bootstrap method. It is significant that the present method is capable of distinguishing high cirrus clouds from low clouds strictly on the basis of spatial brightness patterns. In fact, cirrus has the highest classification accuracy with this approach. The largest probability of misclassification is associated with confusion between stratocumulus breakup regions and fair‐weather cumulus. The present study is based upon textural features computed from Gray Level Co‐occurrence Matrix (GLCM) statistics defined at various pixel displacement distances. It is found that textural features defined at pixel separations of 0.5 km produce classification accuracies equal to or better than those defined at separations of 57 m. Some slight improvement (2–3%) in classification accuracy is achieved by inclusion of textural features defined at multiple pixel separations. In general, stratocumulus classification is improved by inclusion of additional features defined at pixel separations d < 0.25 km, cirrus by features at d ≃ 1 km, and cumulus by features at d ≳ 2 km.
Emission of NO from savanna soils during rainy season
Authors: Johansson Christer , Sanhueza Eugenio
Published: February 2008

Emission of NO from soil was measured in a woodland savanna of Venezuela during the rainy season. Fluxes obtained using closed chamber and gradient techniques were found to agree to within around 30%. The emission varied by up to a factor 4 from one site to another and increased dramatically after rain. An estimate of the total rainy season (7 months) emission range from 0.2 to 1.2 g N m−2. Adding to this our earlier estimate, based on measurements during the dry season, gives an annual emission of 0.3–1.3 g N m−2. These results suggest that NO emission from savanna soils should play an important role in the photochemistry of the tropical region. The NOx concentrations varied diurnally, with up to 20 parts per billion by volume (ppbv) during stable conditions during nighttime. Daytime concentrations, which may be considered representative of a large part of the boundary layer, were found to be around 1 ppbv.
SAGE II aerosol correlative observations: Profile measurements
Authors: Osborn M. T. , Rosen J. M. , McCormick M. P. , Wang Pi‐Huan , Livingston J. M. , Swissler T. J.
Published: February 2008

Profiles of Stratospheric Aerosol and Gas Experiment (SAGE) II aerosol extinction measurements are compared with dustsonde‐ and lidar‐derived aerosol extinction profiles during five correlative experiments between November 1984 and July 1986. Six‐channel dustsonde measurements of particle concentration are used to construct a size distribution, then converted to extinction using Mie theory. The two‐wavelength lidar backscatter data are converted to extinction, using model extinction to backscatter values constrained by the standard dustsonde two‐channel ratio. A set of wavelength‐dependent refractive indices is calculated and used in the conversion of both the dustsonde and lidar data to extinction. The November 30, 1984, intercomparison period provided near‐ideal conditions for SAGE II validation. A six‐channel dustsonde and two‐wavelength aircraft lidar system were nearly coincident with the SAGE II measurement. All four profiles of aerosol extinction at 1.02 μm agree very well from the tropopause to 28 km. Selected altitudes were also compared at all four SAGE II aerosol wavelengths: 1.02, 0.525, 0.453, and 0.385 μm. The remaining four intercomparisons vary in quality, but they are very good, considering the time and space gradients and other problems involved. Therefore the SAGE II lower stratospheric aerosol extinction measurements are consistent with dustsonde and lidar measurements for the conditions present during November 1984 to July 1986.
European validation of SAGE II aerosol profiles
Authors: Ackerman M. , Brogniez C. , Diallo B. S. , Fiocco G. , Gobbi P. , Herman M. , Jäger M. , Lenoble J. , Lippens C. , Mégie G. , Pelon J. , Reiter R. , Santer R.
Published: February 2008

A SAGE II validation program has been performed in Europe using ground‐based lidars and balloon‐borne polarimetric and photographic experiments. Between the tropopause height and about 23 km, good agreement is found between the SAGE II 1.02‐μm extinction profiles and the lidar profiles, using for the conversion of backscattering into extinction an aerosol model consistent with the SAGE II spectral extinction. The extinction profiles deduced from the limb photographs at 0.44 and 0.375 μm present a good agreement with the SAGE II profiles at 0.453 and 0.385 μm, respectively. The size distribution retrieved from the near‐infrared polarimetric observations leads to a spectral variation of the extinction in good agreement with SAGE II data in the same altitude range. Above 23–25 km the observations are scarce and the data of poorer quality because of the low aerosol content. The 1.02‐μm extinction profiles seem to agree with the ruby lidar and the limb photograph profiles. But any conclusion concerning the short‐wavelength profiles and the size distribution at these high altitudes would be risky.
The role of cloud microphysical processes in climate: An assessment from a one‐dimensional perspective
Authors: Liou Kuo‐Nan , Ou Szu‐Cheng
Published: February 2008

The potential link between cloud microphysical processes and climate is investigated and theorized. We base our theory on results simulated from a one‐dimensional climate model with an interactive cloud formation and precipitation program. This cloud program includes temperature‐dependent parameterization equations for condensation, evaporation, and precipitation derived from growth equations for water droplets. We show that the cloud liquid water content is directly related to precipitation processes, which are governed by the mean cloud particle radius. In particular, we illustrate that the rate of precipitation generation is directly proportional to the fourth power of this radius. A doubling of CO2 is used as the radiative forcing. If the perturbed mean cloud particle radii for model high, middle, and low clouds are less than the climatological mean values, precipitation decreases because of the presence of smaller cloud particles, leading to an increase in the cloud liquid water content. Cloud solar albedo effects are enhanced, resulting in a reduction of temperature increases due to CO2 doubling (negative feedback). If, however, the perturbed mean cloud particle radii are larger than the climatological mean values, the availability of larger cloud particles would increase precipitation, leading to a decrease in the cloud liquid water content. The temperature increase in the case of CO2 doubling is amplified because of a reduction of cloud solar albedo effects (positive feedback). In the model the particle sizes are not directly related to radiative transfer, but they are indirectly related through precipitation and condensation processes, which determine the cloud liquid water content. We hypothesize that there are uncertainties in cloud microphysical processes and that a possible key to climate stability due to external radiative perturbations is the availability of larger or smaller cloud droplets (in reference to the climatological mean values). Smaller cloud droplets may be produced by additional condensation nuclei over the oceans as a result of greenhouse warming and pollution over land. The existence of larger cloud droplets could be caused by the removal of cloud‐forming nuclei, resulting from enhanced precipitation due to greenhouse perturbations. It is critically important to have a global climatology of the cloud particle radii for various cloud types in the investigation of the role of clouds in climate.
The kinetic isotope effect in the reaction of H2 with OH
Authors: Ehhalt D. H. , Davidson J. A. , Cantrell C. A. , Friedman I. , Tyler S.
Published: February 2008

Atmospheric hydrogen, H2, is removed to a large extent by reaction with OH. That reaction is expected to show a large kinetic isotope effect, enriching the deuterated hydrogen molecule, HD, in the atmospheric H2. We measured the kinetic fractionation factor using a static system with a UV‐irradiated mixture of O3, H2O and O2 to produce OH, H2 with a natural D content, and standard isotope mass spectrometry to measure the D/H ratio in the hydrogen. At room temperature the fractionation factor was found to be α = 1.65 ± 0.05 (±1σ), where a is the ratio between the rate constants of the H2 and HD reactions with OH. A calculation based on BEBOVIB‐IV gave exactly the same result and was extended to include the corresponding kinetic fractionation factors of other isotopic H2 molecules and their temperature dependence. The possible applications of the obtained fractionation factors to the tropospheric HD and HT balance and the resulting information for the H2 cycle are briefly illustrated.
The roles of dynamical and chemical processes in determining the stratospheric concentration of ozone in one‐dimensional and two‐dimensional models
Authors: Ko Malcolm K. W. , Sze Nien‐Dak , Weisenstein Debra K.
Published: February 2008

The local concentration of stratospheric ozone in any region of the stratosphere is set by a balance among photochemical production and transport into the region versus local photochemical removal and export out of the region. In a given region of the atmosphere, however, different terms (or processes) may dominate, resulting in various modes of balance. Such modes include balances between chemical production and chemical removal (the photochemical equilibrium state), chemical production and export, import and chemical removal, or strict balance between the transport terms. In this study, we analyze the results from a two‐dimensional model to determine the principal modes of balance for different regions of the stratosphere. The analysis showed that except near the poles, ozone is in photochemical equilibrium above 35 km. In the lower stratosphere, equatorward of 50°, concentration of ozone is neither photochemically controlled nor transport controlled, but is set by a balance between transport and chemical processes. The low abundance of O3 in the tropics is a result of the balance between photochemical production and transport out of the region. The seasonal behavior at high latitudes, as evident from the springtime maxima, results from a balance between photochemical removal and transport into the region. It is this “mixed” mode of balance that distinguishes two‐dimensional models from the one‐dimensional models in which the bulk of the O3 content is chemically controlled. The budget analysis has implications for assessing the response of ozone in two‐dimensional models to changes in the photochemical environment. This response is contrasted with that of one‐dimensional models to highlight the limitation of one‐dimensional model studies.
Secular increase of the vertical column abundance of methane derived from IR solar spectra recorded at the Jungfraujoch station
Authors: Zander R. , Demoulin Ph. , Ehhalt D. H. , Schmidt U.
Published: February 2008

Using all of the pertinent infrared solar spectra recorded at the Jungfraujoch Station, Switzerland, in 1951, 1975, and in 1984–1987, the increase of the vertical column abundance of methane, CH4, above that station has been reevaluated. The results are based on equivalent widths measurements of both the R0 and the R5 transitions of the 2v3 band of CH4 at 6015.66 and 6067.09 cm−1 and on the CH4–v3 band absorption characteristics between 2905.0 and 2908.8 cm−1. The data between 1984 and 1987 provide a full seasonal cycle. They demonstrate a significant annual variation in the column abundance of CH4 of ±10% around the mean. They also show variability on shorter time scales. The mean cumulative rate of increase of the total vertical column abundance of CH4 above the Jungfraujoch is found to be (0.7 ± 0.1)% yr−1 between 1951 and 1986. Using a realistic CH4 concentration profile throughout the troposphere and the stratosphere, we deduce volume mixing ratios at the altitude of the Jungfraujoch, equal to 1.28±0.08 and 1.64±0.09 ppm, for 1951 and for 1985–1987, respectively.
A divergent and rotational kinetic energy budget for January and July
Authors: Lambert Steven J.
Published: February 2008

Rotational and divergent kinetic energy (K) exchanges are studied using a budget which partitions the global K into four components: zonal divergent K, zonal rotational K, eddy divergent K, and eddy rotational K. Vertically integrated results are given for the energies, the exchanges between them, and the conversions from available potential energy (APE) using the National Meteorological Center global operational analyses for the five Januarys and the five Julys from 1983 to 1987. Both the January and the July results show that the flow of energy is generally from eddy APE to eddy divergent K and then to eddy rotational K. From the eddy rotational K, energy flows to zonal rotational K and then to zonal divergent K. The conversion of zonal APE to zonal divergent K is seasonally dependent. In January the conversion is indirect (APE is converted to divergent K) and in July it is in the opposite sense. The results also indicate that the amounts of divergent energy in the atmosphere are small compared to the amounts of rotational energy even though the sources and sinks of divergent energy are relatively large, supporting the idea suggested by previous studies that the divergent K plays a “catalytic” role in the conversion of APE to rotational K.
Diagnostic studies of the Antartctic vortex during the 1987 Airborne Antarctic Ozone Experiment: Ozone miniholes
Authors: McKenna D. S. , Jones R. L. , Austin J. , Browell E. V. , McCormick M. P. , Krueger A. J. , Tuck A. F.
Published: February 2008

During the Airborne Antarctic Ozone Experiment (AAOE) localized rapid reductions in total ozone, called “miniholes”, were observed by the Total Ozone Mapping Spectrometer (TOMS) within the main ozone hole. Evolving too rapidly to be the result of chemical destruction, miniholes must be the result of atmospheric transport. An important question then is “Do miniholes represent large‐scale transport of ozone poor air into the vortex?” In this paper we examine the genesis and evolution of miniholes, and we demonstrate by the calculation of air parcel trajectories that miniholes are not the result of irreversible transport of ozone‐poor air into the polar vortex. We show instead that minihole genesis can be attributed, in large part, to synoptic‐scale tropospherically forced reversible advection (both horizontal and vertical) of low‐ozone air below the level of the main ozone depletion, resulting from the poleward penetration of an anticyclone below the main vortex. We then examine the implications of the disturbed flows associated with minihole formation. Employing differential infrared absorption laser (DIAL) data, Stratospheric Measurement (SAM) II retrievals, and United Kingdom Meteorological Office (UKMO) global analysis fields and trajectories, we highlight two aspects of minihole formation, which have important implications for both theories of photochemical ozone destruction and vortex isolation. We conclude that tropospheric forcing which reduces the ozone column through advection also forces the formation of Polar Stratospheric Clouds (PSC)s (type I and II) throughout a substantial depth of atmosphere, resulting in a large portion of the air in the vortex being exposed to heterogeneous chemistry as it passes through individual quasi‐stationary PSC regions. Finally we conclude that synoptic‐scale transport associated with these events can lead to the exchange of vortex air with air from lower latitudes. The lower limit on the mass exchange over the period of ozone depletion is estimated to be 4% of the total depleted mass, with large uncertainties.
A model of the effect of cumulus clouds on the redistribution and transformation of pollutants
Authors: Cho H. R. , Niewiadomski M. , Iribarne J. V. , Melo O.
Published: February 2008

A one‐dimensional time‐dependent cumulus model was developed to study the effects of convective clouds on air pollutants. The model contains two drafts, core and periphery, surrounded by a stagnant environment. There are exchanges between the two drafts and between cloud and environment, both by dynamic entrainment/detrainment and by turbulence. Application to a “base case” with given initial conditions and producing a cloud 7 km thick is analyzed. Microphysical exchanges involved mainly cloud water, rain, and graupel. The warm rain mechanism seems to dominate, including a frozen drop stage. At lower temperatures the ice mechanism is also effective. Only a minor fraction of the SO2 entering the cloud becomes oxidized and is partly rained out to the ground as sulfate. Although H2O2 is the main and faster oxidant, O3 also contributes in a rather large proportion. Oxidation of NOx with subsequent dissolution of the acids is negligible, unless the OH radical concentration in the air is very high. Production and deposition of acidity depends on SO2 concentration in a very nonlinear way, but approximately linearly on H2O2 concentration. The acidity concentration of precipitation varies substantially under different regions of the cloud. Consideration of solutes in solid phase is shown to appreciably influence the results. The model was also applied to small, 2‐km‐thick cumuli, and the results compared with those of a three‐dimensional model and with observations, with reasonable agreement.
Mathematical modeling of acid deposition due to radiation fog
Authors: Pandis Spyros N. , Seinfeld John H.
Published: February 2008

A Lagrangian model has been developed to study acidic deposition due to radiation fog. The model couples submodels describing the development and dissipation of radiation fog, the gas‐phase chemistry and transfer, and the aqueous‐phase chemistry. The model is applied to a radiation fog episode in Bakersfield in the San Joaquin Valley of California over the period January 4–5, 1985. Model predictions for temperature profile, fog development, liquid water content, gas‐phase concentrations of SO2, HNO3, and NH3, pH, aqueous‐phase concentrations of SO42−, NH4+, and NO3−, and finally deposition rates of the above ions are compared with the observed values. The deposition rates of the major ions are predicted to increase significantly during the fog episode, the most notable being the increase of sulfate deposition. Pathways for sulfate production that are of secondary importance in a cloud environment may become significant in a fog. Expressing the mean droplet settling velocity as a function of liquid water content is found to be quite influential in the model's predictions.
Calculations on the electrical development of a small thunderstorm
Authors: Latham J. , Dye J. E.
Published: February 2008

Data obtained in airborne studies of a small thundercloud (Gardiner et al., 1985; Dye et al., 1986) have been examined in terms of the noninductive mechanism (Jayaratne et al., 1983; Saunders and Jayarante, 1986; Baker et al., 1987). Crude calculations are consistent with the observation that only a few percent of ice hydrometeors carry detectable charges. They reproduce the observed particle charges reasonably well. They suggest that this mechanism can explain the observed electrical development, and predict that most of the charge in thunderstorms is carried on particles greater than about 0.2 mm in size.
Long‐term variations in thunder‐day frequencies in Japan
Authors: Kitagawa N.
Published: February 2008

The frequencies of thunder days in various regions in Japan have been investigated for the past 100 years. During this period the temporal variation of winter thunder‐day frequencies along the Japan Sea coast and that of summer thunder‐day frequencies on the inland area of the Kanto Plain shows some characteristic features. The former indicates a negative and the latter a positive correlation with the temperature variation of the northern hemisphere. While the variation of thunderstorm activities in most parts of Japan is controlled by local weather and climate changes, the above two categories of thunderstorm activities appear to be affected by global‐scale temperature variation.
A parametric estimation of systematic errors in networks of magnetic direction finders
Authors: Passi Ranjit M. , López Raúl E.
Published: February 2008

We consider the problem of estimating systematic errors in a network of magnetic direction finders using bearing data from a historical record containing a large number of lightning flash observations. It is clear that this problem is linked with the flash location estimation problem and that the two are statistically confounded in the sense that the effect of one cannot be separated from the other. We formalize mathematically a connection between the two problems to arrive at a self‐consistent system. In this paper we parameterize the site errors as two‐cycle sinusoidal functions and show that the estimation equations can be described by a model which separates into linear and nonlinear parameters. We take advantage of this separation to decouple large‐dimensional equations into smaller dimensional equations. Through these equations we show the link between the site error and flash location estimation problems. Validation of our modeling procedures is done by heuristic arguments and analysis of residuals. The latter reveals that not all of the residuals have been explained by sinusoidal site errors but that some residuals might result from the geometry of the network. This appears to be an important problem and is presently under study. Also, there is a need to test the site error estimation algorithm developed in this paper against some ground truth.
Visible and near‐ultraviolet spectroscopy at McMurdo Station, Antarctica: 6. Observations of BrO
Authors: Carroll M. A. , Sanders R. W. , Solomon S. , Schmeltekopf A. L.
Published: February 2008

Observations of the evening twilight BrO abundance over McMurdo Station, Antarctica during austral spring, 1987, are described. The observed variation of the slant column abundance with increasing solar zenith angles suggests that most of the BrO is located near 15 km. The total vertical column abundance observed during 1 week of measurements yielded an average value of 2.5×1013 cm−2, assuming the room temperature absorption cross sections measured by Cox et al. (1982). These values are consistent with BrO mixing ratios of about 5–15 parts per trillion by volume distributed from 150 to 20 mbar. If the differential absorption cross section of BrO increases by 30% at temperatures characteristic of the Antarctic lower stratosphere, as indicated by Sander and Watson (1981), then the BrO measurements reported in this paper should be decreased by 30%.
The global geochemistry of bomb‐produced tritium: General circulation model compared to available observations and traditional interpretations
Authors: Koster Randal D. , Broecker Wallace S. , Jouzel Jean , Suozzo Robert J. , Russell Gary L. , Rind David , White James W. C.
Published: February 2008

Observational evidence suggests that of the tritium produced during nuclear bomb tests that has already reached the ocean, more than twice as much arrived through vapor impact as through precipitation. In the present study, the Goddard Institute for Space Studies 8°×10° atmospheric general circulation model is used to simulate tritium transport from the upper atmosphere to the ocean. The simulation indicates that tritium delivery to the ocean via vapor impact is about equal to that via precipitation. The model result is relatively insensitive to several imposed changes in tritium source location, in model parameterizations, and in model resolution. Possible reasons for the discrepancy are explored.
The seasonal variation of water vapor and ozone in the upper mesosphere: Implications for vertical transport and ozone photochemistry
Authors: Bevilacqua Richard M. , Strobel Darrell F. , Summers Michael E. , Olivero John J. , Allen Mark
Published: February 2008

Ground‐based microwave techniques have supplied the only long‐term measurements of water vapor in the mesosphere. We review the entire current data base, which consists of measurements obtained in three separate experiments over an 8‐year period. The data from all three experiments indicate that the water vapor seasonal variation at mid‐latitudes in the upper mesosphere is dominated by an annual component with low mixing ratios in winter and high mixing ratios in summer. This suggests that the vertical distribution of water vapor in the upper mesosphere (up to 80 km) is controlled by advective rather than diffusive processes. This is consistent with the low mesospheric Kzz values (≈ 105 cm2 s−1) deduced from the vertical gradient of the microwave water vapor measurements by Strobel et al. (1987). However, it is difficult to reconcile the predominantly annual water vapor variation with the semiannual variation in ozone at 78 km observed by the Solar Mesosphere Explorer. We perform a series of one‐dimensional photochemical/vertical transport model calculations which verify that (within the context of the hydrogen/oxygen chemistry considered in the model), the seasonal variation of water vapor cannot be the mechanism for the semiannual ozone variation. This variation is either a manifestation of some heretofore unknown ozone photochemical mechanism, or it could be driven by a seasonal variation in the vertical transport of atomic oxygen from the thermosphere. One possible vertical transport scenario for producing the semiannual ozone variation (while retaining the annual water vapor variation) is described.
The effects of fire on biogenic emissions of methane and nitric oxide from wetlands
Authors: Levine Joel S. , Cofer Wesley R. , Sebacher Daniel I. , Rhinehart Robert P. , Winstead Edward L. , Sebacher Shirley , Hinkle C. Ross , Schmalzer Paul A. , Koller Albert M.
Published: February 2008

Enhanced emissions of methane (CH4) and nitric oxide (NO) were measured following three controlled burns in a Florida wetlands in 1987 and 1988. Wetlands are the major global source of methane resulting from metabolic activity of methanogenic bacteria. Methanogens require carbon dioxide, acetate, or formate for their growth and the metabolic production of methane. All three water‐soluble compounds are produced in large concentrations during biomass burning. Postfire methane emissions exceeded 0.15 g CH4 m−2 d−1. Nitric oxide is produced by nitrifying bacteria using ammonium as the substrate. Ammonium is also produced in large concentrations during biomass burning. Preburn and postburn measurements of soil nutrients indicate significant postburn increases in soil ammonium, from 8.35 to 13.49 parts per million (ppm) in the upper 5 cm of the Juncus marsh and from 8.83 to 23.75 ppm in the upper 5 cm of the Spartina marsh. Soil nitrate concentrations were found to decrease in both marshes after the fire. These measurements indicate that the combustion products of biomass burning exert an important “fertilizing” effect on the biosphere and on the biogenic production of environmentally significant atmospheric gases. These findings are particularly important since global biomass burning appears to be far more widespread and extensive than previously believed.
Global impact of the Antarctic ozone hole: Chemical propagation
Authors: Prather Michael , Jaffe Andrew H.
Published: February 2008

A model is presented for the chemical mixing of stratospheric air over spatial scales from tens of kilometers to meters. Photochemistry, molecular diffusion, and strain (the stretching of air parcels due to wind shear) are combined into a single one‐dimensional model. The model is applied to the case in which chemically perturbed air parcels from the Antarctic stratosphere are transported to mid‐latitudes and strained into thin ribbon‐like filaments until they are diffusively mixed with the ambient stratosphere. We find that the parcels may be treated as evolving in chemical isolation until the final mixing. When parcels reach a transverse thickness of 50–100 m in the lower stratosphere, they are rapidly dispersed by the combination of molecular diffusion and strain. The rapidity of the final mixing implies a lower limit to the vertical scales of inhomogeneities observed in the lower stratosphere. For this sensitivity study we consider four types of Antarctic air: a control case representing unprocessed polar air; heterogeneous processing by polar stratospheric clouds (PSCs) that has repartitioned the Clx and NOy families; processing that also includes denitrification and dehydration; and all processing plus 90% ozone depletion. Large abundances of ClO, resulting initially from heterogeneous processing of stratospheric air on PSCs, are sustained by extensive denitrification. (One exception is the case of Antarctic air with major ozone depletion in which ClO is converted rapidly to HCl upon release of small amounts of NOx as a result of the extremely nonlinear Clx‐NOy chemical system.) ClO concentrations in the mid‐latitude stratosphere should be enhanced by as much as a factor of 5 due to the mixing of air processed around the Antarctic vortex and will remain elevated for most of the following season. Chemical propagation of the Antarctic ozone hole occurs in two phases: rapid loss of ozone in the heterogeneously processed parcels as they evolve in isolation, and more slowly, a relative recovery of ozone over the following months. Another important effect is the transport of denitrified Antarctic air reducing NOx and hence the total catalytic destruction of ozone throughout the southern mid‐latitudes. In Antarctic air that has already been depleted of ozone within the vortex, little additional loss occurs during transport, and the propagation of chemically perturbed air acts partially to offset the deficit at mid‐latitudes caused by dynamical dilution of the ozone hole. In air which has not experienced substantial ozone loss, chemical propagation can generate a net ozone deficit of order 2–3% at mid‐latitudes.
Spectral ultraviolet intensity measurements at 45°S: 1980 and 1988
Authors: Bittar A. , McKenzie R. L.
Published: February 2008

The spectral distribution of solar ultraviolet (UV) radiation received at the surface in the New Zealand region was first measured in October 1980. We present these results, together with results from a second campaign in November 1988. Ozone amounts were similar over the two observation periods. The measurements agree with calculated irradiances, and there is no evidence of unexplained changes over the intervening period. The sensitivity of UV irradiance to ozone changes is demonstrated in the spectral range 300 to 340 nm.
An interactive chemical dynamical radiative two‐dimensional model of the middle atmosphere
Authors: Brasseur G. , Hitchman M. H. , Walters S. , Dymek M. , Falise E. , Pirre M.
Published: February 2008

This paper describes a new two‐dimensional model of the stratosphere and the mesosphere in which dynamics, radiation and chemistry are treated interactively. The transport equations are expressed in the transformed Eulerian framework. Momentum deposition associated with Rossby wave absorption and gravity wave breaking and related eddy diffusion coefficients are parameterized as a function of the mean zonal state of the atmosphere. Diabatic heating and cooling is derived from the detailed National Center for Atmospheric Research community climate model radiative code. The distributions of chemically active species belonging to the oxygen, hydrogen, nitrogen and chlorine families are calculated for present‐day conditions. By applying near the tropopause a different dynamical forcing in each hemisphere, the model produces significant hemispheric asymmetries in dynamical quantities (e.g., temperature) and trace gas densities (e.g., column ozone), in good agreement with climatological values. It is shown that the calculated distributions of source gases, such as nitrous oxide and methane, are very sensitive to the calculated (and parameterized) dynamical quantities and that species produced in the atmosphere, like carbon monoxide and odd nitrogen, can provide interesting information on the role of atmospheric transport. A major problem that remains to be elucidated is the underestimation by most models of the ozone density in the upper stratosphere. Because of the many feedback mechanisms included in its formulation, the model is well adapted to study the effects of human or natural perturbations. The response of the atmosphere to perturbations resulting from increasing emissions of CO2 and chlorofluorocarbons is considered.
Simulated transport of NOy to Hawaii during August: A synoptic study
Authors: Moxim Walter J.
Published: February 2008

Using data sets generated by the Geophysical Fluid Dynamics Laboratory general circulation/transport model's U.S.‐Canada combustion nitrogen source experiment, a detailed analysis of the simulated transport mechanisms producing the observed August NOy, maximum at Hawaii is presented. Combustion nitrogen is not simply advected from the United States to Hawaii by the winds circulating around the climatological subtropical anticyclone. Rather, its transport results from a complicated three‐way interaction of surface advection from source regions, enhanced vertical diffusion due to dry convection, and winds in the “free troposphere.” Backward trajectories from Hawaii using model pressure and isentropic surfaces were insufficient in explaining the transport. Model‐consistent three‐dimensional trajectories revealed that the transport originated in the “free troposphere” along a path from northern Baja to the Texas Gulf coast. Combustion nitrogen from the source regions of southern California and as distant as the Texas Gulf area is advected along the surface toward the arid areas of Baja, the desert southwest, northern Mexico, and west Texas. Dry convection then vertically mixes the air to pressures of 800–650 mbar, where the subsiding wind flow from the east‐northeast transports the NOy to Hawaii. Observed wind fields and heights of dry convection are compared to the model where data are available.
Wind velocity measurements in the neutral boundary layer above hilly prairie
Authors: Sugita Michiaki , Brutsaert Wilfried
Published: February 2008

The Flint Hills region in eastern Kansas is characterized by strongly dissected rolling to hilly terrain with on average about 25 m of relief between steep ridges and valleys, and with ridges typically separated by distances of the order of 600 m. Intensive radiosonde observations during summer and fall of 1987 allowed the determination of some aspects of the wind regime in the region. For an assumed ground‐surface reference of 330 m above sea level (asl), analysis of neutral profiles yielded a value z0 = 1.05(±0.51) m, approximately; this value was obtained with an assumed displacement height d0 = 25.7z0, as suggested by the density of the terrain roughness. The corresponding logarithmic law was found to hold over the height range 50(±19) m < z − d0 < 202(±101) m (where z is above the same ground surface level). Good agreement (r = 0.92) was obtained between the u* values derived from these wind profiles and values determined independently from the corresponding humidity profiles. Some large wind speeds were observed; for instance, the resulting mean surface shear stress was u* = 0.82(±0.24) m/s.
An intercomparison of airborne nitric acid measurements
Authors: Gregory G. L. , Hoell J. M. , Huebert B. J. , Van Bramer S. E. , LeBel P. J. , Vay S. A. , Marinaro R. M. , Schiff H. I. , Hastie D. R. , Mackay G. I. , Karecki D. R.
Published: February 2008

Results from an airborne intercomparison of techniques to measure tropospheric levels of nitric acid are discussed. The intercomparison was part of the National Aeronautics and Space Administration's Global Tropospheric Experiment and was conducted during the summer of 1986. Instruments intercompared included a denuder tube collection system (DENUDER) with chemiluminescent detection, a niylon filter collection system (FILTER) with ion chromatography detection, and a tunable diode laser (TDLAS) multipath absorption system. Intercomparison of investigators' calibration standards were also performed as part of the test protocol. While results were somewhat “soft” and data sparse, these tests suggested that the TDLAS measurements might be high compared to the other techniques. Airborne intercomparisons were conducted predominately in the free troposphere and included encounters with marine and continental air masses. While the intercomparisons included mixing ratios to 1000 parts per trillion by volume (pptv), the majority of the results were for mixing ratios of <300 pptv. The TDLAS participated in an intercomparison of NO2 instruments (major focus) that was also conducted during the same flights. As a result the TDLAS data set is limited. Further, a significant fraction of the nitric acid measurements were below the TDLAS detection limit (75 pptv as configured for these tests). While the lack of simultaneous measurements from the three instruments limits the conclusions that can be drawn, it is clear that there can be substantial disagreement among the three techniques, even at mixing ratios above their respective detection limits. Equally clear is that at mixing ratios below 150 pptv there is very little correlation between their results. Based on these observations, an overall conclusion from the intercomparison is that none of the HNO3 techniques can be identified to unambiguously (e.g., 20% accuracy) provide measurements of HNO3 at levels often encountered in the free troposphere (e.g., 100 pptv). However, at the more elevated levels of HNO3 (e.g., >150 pptv), both the FILTER and DENUDER techniques reported the same levels of nitric acid, while as suggested by the results from the standards intercomparison, the TDLAS reported higher nitric acid values than the other two techniques.