bluuebunny/crossref_metadata_2025 huggingface dataset:
Vertical transport of anthropogenic soot aerosol into the middle atmosphere
Authors: Pueschel R. F. , Verma S. , Rohatschek H. , Ferry G. V. , Boiadjieva N. , Howard S. D. , Strawa A. W.
Published: September 2002

Gravito‐photophoresis, a sunlight‐induced force acting on particles which are geometrically asymmetric and which have uneven surface distribution of thermal accommodation coefficients, explains vertical transport of fractal soot aerosol emitted by aircraft in conventional flight corridors (10–12 km altitude) into the mesosphere (>80 km altitude). While direct optical effects of this aerosol appear nonsignificant, it is conceivable that they play a role in mesospheric physics by providing nuclei for polar mesospheric cloud formation and by affecting the ionization of the mesosphere to contribute to polar mesospheric summer echoes.
Nonmethane hydrocarbon measurements in the North Atlantic Flight Corridor during the Subsonic Assessment Ozone and Nitrogen Oxide Experiment
Authors: Simpson I. J. , Sive B. C. , Blake D. R. , Blake N. J. , Chen T.‐Y. , Lopez J. P. , Anderson B. E. , Sachse G. W. , Vay S. A. , Fuelberg H. E. , Kondo Y. , Thompson A. M. , Rowland F. S.
Published: September 2002

Mixing ratios of nonmethane hydrocarbons (NMHCs) were not enhanced in whole air samples collected within the North Atlantic Flight Corridor (NAFC) during the fall of 1997. The investigation was conducted aboard NASA's DC‐8 research aircraft, as part of the Subsonic Assessment (SASS) Ozone and Nitrogen Oxide Experiment (SONEX). NMHC enhancements were not detected within the general organized tracking system of the NAFC, nor during two tail chases of the DC‐8's own exhaust. Because positive evidence of aircraft emissions was demonstrated by enhancements in both nitrogen oxides and condensation nuclei during SONEX, the NMHC results suggest that the commercial air traffic fleet operating in the North Atlantic region does not contribute at all or contributes negligibly to NMHCs in the NAFC.
Sulfur chemistry in the National Center for Atmospheric Research Community Climate Model: Description, evaluation, features, and sensitivity to aqueous chemistry
Authors: Barth M. C. , Rasch P. J. , Kiehl J. T. , Benkovitz C. M. , Schwartz S. E.
Published: September 2002

Sulfur chemistry has been incorporated in the National Center for Atmospheric Research Community Climate Model in an internally consistent manner with other parameterizations in the model. The model predicts mixing ratios of dimethylsulfide (DMS), SO2, SO42−, H2O2. Processes that control the mixing ratio of these species include the emissions of DMS and SO2, transport of each species, gas‐ and aqueous‐phase chemistry, wet deposition, and dry deposition of species. Modeled concentrations agree quite well with observations for DMS and H2O2, fairly well for SO2, and not as well for SO42−. The modeled SO42− tends to underestimate observed SO42− at the surface and overestimate observations in the upper troposphere. The SO2 and SO42− species were tagged according to the chemical production pathway and whether the sulfur was of anthropogenic or biogenic origin. Although aqueous‐phase reactions in cloud accounted for 81% of the sulfate production rate, only ∼50–60% of the sulfate burden in the troposphere was derived from cloud chemistry. Because cloud chemistry is an important source of sulfate in the troposphere, the importance of H2O2 concentrations and pH values was investigated. When prescribing H2O2 concentrations to clear‐sky values instead of predicting H2O2, the global‐averaged, annual‐averaged in‐cloud production of sulfate increased. Setting the pH of the drops to 4.5 also increased the in‐cloud production of sulfate. In both sensitivity simulations, the increased in‐cloud production of sulfate decreased the burden of sulfate because less SO2 was available for gas‐phase conversion, which contributes more efficiently to the tropospheric sulfate burden than does aqueous‐phase conversion.
Seasonal and interannual variability of the budgets of N2O and CCl3F
Authors: Wong Sun , Prather Michael J. , Rind David H.
Published: September 2002

The 6‐year wind archives from the Goddard Institute for Space Studies/Global Climate‐Middle Atmosphere Model (GISS/GCMAM) were input to the GISS/Harvard/Irvine Chemical Transport Model (G/H/I CTM) to study the seasonal and interannual variability of the budgets and distributions of nitrous oxide (N2O) and trichlorofluoromethane (CCl3F), with the corresponding chemical loss frequencies recycled and boundary conditions kept unchanged from year to year. The effects of ozone feedback and quasi‐biennial oscillation (QBO) were not included. However, the role of circulation variation in driving the lifetime variability is investigated. It was found that the global loss rates of these tracers are related to the extratropical planetary wave activity, which drives the tropical upward mass flux. For N2O a semiannual signal in the loss rate variation is associated with the interhemispheric asymmetry in the upper stratospheric wave activity. For CCl3F the semiannual signal is weaker, associated with the comparatively uniform wave episodes in the lower stratosphere. The loss rates lag behind the wave activity by about 1–2 months. The interannual variation of the general circulation model generated winds drives the interannual variation of the annually averaged lifetime. The year‐to‐year variations of the annually averaged lifetimes can be about 3% for N2O and 4% for CCl3F.
A Lagrangian view of stratospheric trace gas distributions
Authors: Schoeberl M. R. , Sparling L. C. , Jackman C. H. , Fleming E. L.
Published: September 2002

As a result of photochemistry, some relationship between the stratospheric age of air or mean age and the amount of tracer contained within an air sample is expected. The existence of such a relationship allows inferences about transport history to be made from observations of chemical tracers. This paper lays down the conceptual foundations for the relationship between age and tracer amount for long‐lived tracers, developed within a Lagrangian framework. Although the photochemical loss depends not only on the age of the parcel but also on its path, we show that under the “average path approximation” that the path variations are less important than parcel age. The average path approximation then allows us to develop a formal relationship between the age spectrum and the tracer distribution. Using this relationship, tracer‐tracer correlations can be interpreted as the result of mixing which connects parts of the “single‐path photochemistry curve,” a universal path‐independent curve that describes the photochemical loss in terms of the total photon exposure. This geometric interpretation of mixing gives rise to constraints on trace gas correlation curves as can be seen in the atmospheric trace molecule spectroscopy observations.
Derivation of UV‐A irradiance from pyranometer measurements
Authors: McArthur L. J. B. , Fioletov V. E. , Kerr J. B. , McElroy C. T. , Wardle D. I.
Published: September 2002

Two statistical models have been developed from 6 years of simultaneous measurements of global radiation by pyranometers, UV‐A by a Brewer spectrophotometer and from total ozone, dew point temperature and snow cover data at Toronto. The models estimate instantaneous UV‐A irradiance at 324 nm from pyranometer data with an uncertainty as low as 3.5% (1σ) for summer sunny conditions and between 6–10% for cloudy conditions. These uncertainties are reasonably small when compared with the uncertainty of UV‐A and global solar irradiance measurements (2–3%). The uncertainty is reduced when daily and longer‐term averages are considered. The major source of error in the models is likely linked to rare occurrences of absorbing aerosols in the atmosphere. The models were also tested on a 6‐year, independent record from Edmonton. The uncertainties at Edmonton are 30–45% larger than at Toronto for the instantaneous data, approximately 20% larger for daily integrated values.
Numerical study of surface ozone in China during summer time
Authors: Yang Xin , Wang Mingxing , Li Xingsheng
Published: September 2002

On the basis of meteorological fields provided by a mesoscale nonhydrostatic model (MM5), a three‐dimensional regional chemical model (RADM) is applied to China to address the photochemical reaction mechanisms of surface ozone, with respect to ozone precursors such as NOx and NMHC. The behaviors of surface ozone in the Tibetan Plateau are much different than that in eastern China. Physical factors rather than photochemical factors may play important roles in determining surface ozone. Several model experiments are conducted to focus on these questions. Some results can be obtained as follows: (1) In polluted areas, the surface ozone is primarily dependent on its precursors (NOx, NMHC, etc.) and has highly nonlinear sensitivities to their perturbation. However, in clean areas photochemistry is not the controlling factor. Surface ozone on the Tibetan Plateau is sensitive to ozone perturbation in upper layers, suggesting that ozone above the planetary boundary layer may be a greater influence upon surface ozone. (2) The variations in OH and HO2 caused by perturbations in the precursors are very complicated, and the feedback effect of ozone is very important. There is a nearly linear relationship between percentage differences in HO2 and O3 for NMHC emission reduction, and a similar linear relationship also appears between percentage differences in OH and O3 for NOx emission reduction. (3) During summer midday time, the ratio of O3 to NO2/NO has a constant value.
Uptake on fractal particles: 1. Theoretical framework
Authors: Coelho Daniel , Bekki Slimane , Thovert Jean‐Francois , Adler Pierre M.
Published: September 2002

We develop a detailed framework for calculating uptake rates of gases on fractal particles. Aggregates with a fractal dimension between 1.6 and 2.6 are generated numerically. Three‐dimensional simulations of uptake on these aggregates are performed for a large range of conditions. The numerical results can be expressed by a single physically based formula as a function of the usual parameters (gas phase diffusion coefficient, uptake coefficient) and of morphological parameters (aggregate gyration radius, size of the monomers composing the aggregate, fractal dimension). The expression for the uptake flux on an aggregate is generalized to a lognormal distribution of aggregates. The results for an isolated aggregate are compared to calculations used for spherical particles. The importance of accounting for the fractal character of aggregates in the calculation of the uptake flux is highlighted. The magnitude of the errors also depends on which aggregate equivalent size is used as the characteristic radius for mass transfer.
Sensitivity of model assessments of high‐speed civil transport effects on stratospheric ozone resulting from uncertainties in the NOx production from lightning
Authors: Smyshlyaev Sergei P. , Geller Marvin A. , Yudin Valery A.
Published: September 2002

Lightning NOx production is one of the most important and most uncertain sources of reactive nitrogen in the atmosphere. To examine the role of NOx lightning production uncertainties in supersonic aircraft assessment studies, we have done a number of numerical calculations with the State University of New York at Stony Brook‐Russian State Hydrometeorological Institute of Saint‐Petersburg two‐dimensional model. The amount of nitrogen oxides produced by lightning discharges was varied within its quoted uncertainty from 2 to 12 Tg N/yr. Different latitudinal, altitudinal, and seasonal distributions of lightning NOx production were considered. Results of these model calculations show that the assessment of supersonic aircraft impacts on the ozone layer is very sensitive to the strength of NOx production from lightning. The high‐speed civil transport produced NOx leads to positive column ozone changes for lightning NOx production less than 4 Tg N/yr, and to total ozone decrease for lightning NOx production more than 5 Tg N/yr for the same NOx emission scenario. For large lightning production the ozone response is mostly decreasing with increasing emission index, while for low lightning production the ozone response is mostly increasing with increasing emission index. Uncertainties in the global lightning NOx production strength may lead to uncertainties in column ozone up to 4%. The uncertainties due to neglecting the seasonal variations of the lightning NOx production and its simplified latitude distribution are about 2 times less (1.5–2%). The type of altitude distribution for the lightning NOx production does not significally impact the column ozone, but is very important for the assessment studies of aircraft perturbations of atmospheric ozone. Increased global lightning NOx production causes increased total ozone, but for assessment of the column ozone response to supersonic aircraft emissions, the increase of lightning NOx production leads to column ozone decreases in response to aircraft emissions.
The signature of cyclonic PV filaments in the lower stratosphere
Authors: Richter Harald , Atkinson Roger J.
Published: September 2002

The perturbation temperature and wind fields induced by a given zonally invariant potential vorticity (PV) filament in an isothermal atmosphere with uniform westerly background flow is investigated using a two‐dimensional isentropic semigeostrophic model. Such PV filaments are commonplace in the lower midlatitude and polar stratosphere during winter and spring. The model is formulated in isentropic geostrophic coordinates because this formulation greatly simplifies the equations of motion describing the system. Given the potential vorticity distribution, the dynamics of the filament problem are obtained by inverting a single nonlinear elliptic equation. The model diagnoses relatively cool air below and relatively warm air above cyclonic filaments. In the case of anticyclonic filaments, air above the filament is cooler and air below the filament is warmer than the ambient air. The thermal perturbations in an isothermal atmosphere are sensitive to vertical gradients in PV, while the zonal along‐filament flow associated with PV filaments is sensitive to quasi‐horizontal PV gradients. If the PV anomaly marking the stratospheric filament is weak compared to ambient PV values, the magnitude of the thermal perturbations in the isothermal atmosphere is a linear function of the magnitude of the PV anomaly. In principle, it is possible to remotely detect the thermal signature of PV filaments using a Microwave Temperature Profiler (MTP), for example. This instrument, mounted aboard an aircraft flying in the lower stratosphere, can measure vertical profiles of the thermal structure below and above the flight track.
Fully equivalent operational models for atmospheric chemical kinetics within global chemistry‐transport models
Authors: Wang S. W. , Levy H. , Li G. , Rabitz H.
Published: September 2002

A major portion of the computational effort in simulations by three‐dimensional (3‐D) chemistry‐transport models is consumed in chemical kinetics calculations which repeatedly solve coupled ordinary differential equations. To address this burden, this paper introduces a high‐speed fully equivalent operational model (FEOM) for chemical kinetics calculations. The FEOM consists of a hierarchical correlated‐function expansion capturing the input‐output relationships of chemical kinetics. As an initial test of the FEOM approach for chemical kinetics calculations in 3‐D models, this paper develops the FEOMs for CO‐CH4‐NOy‐H2O chemistry to obtain the time‐dependent chemical ozone production and destruction rates in global chemistry‐transport model (GCTM) simulations. The FEOMs are constructed for all GCTM model levels, all 12 months of the year, every 10° of latitude, for two types of surface albedo, and for all tropospheric values of H2O, CO, NOx, and O3. It is shown that the simulated global ozone fields using the FEOMs in the GCTM ozone simulation are at least as accurate and in some cases better than those obtained by using four‐dimensional interpolative look‐up tables. Future work will expand the FEOM approach to more detailed chemical schemes, including nonmethane hydrocarbon chemistry in 3‐D chemistry‐transport model simulations.
Comparison of daily UV doses estimated from Nimbus 7/TOMS measurements and ground‐based spectroradiometric data
Authors: Kalliskota Sari , Kaurola Jussi , Taalas Petteri , Herman Jay R. , Celarier Edward A. , Krotkov Nikolay A.
Published: September 2002

During recent years, methods have been developed for estimating UV irradiance reaching the Earth's surface using satellite‐measured backscattered UV radiances. The NASA‐developed method is based on radiative transfer calculations and satellite measurements of parameters affecting UV radiation: extraterrestrial solar irradiance, atmospheric ozone, cloud reflectivity, aerosol amounts, and ground albedo. In this work a comparison is made between daily UV erythemal doses estimated from Nimbus‐7/TOMS measurements (from 1991 to May 1993) and those calculated from ground‐based spectroradiometer data. Three stations operated by the National Science Foundation were chosen for this comparison: Ushuaia, Argentina (for 573 days), Palmer, Antarctica (for 450 days), and San Diego, California, (for 149 days). These stations were selected to illustrate the differences between ground‐based measurements using the same type of instrument, SUV‐100 double monochromator spectroradiometers, and satellite estimates of surface UV irradiance under three different environmental conditions (mountains and snow, nearly continuous snow cover, and midlatitude urban sea level conditions). Averaging the measured and TOMS‐estimated doses over periods from 1 week to 1 month improves the agreement. The daily or monthly mean bias increases during months when there is snow/ice on the surface. TOMS has a larger estimate of the UV irradiance by 25% at San Diego (no snow), in agreement with the summer‐month analysis of Toronto irradiances [Herman et al., 1999]. TOMS underestimates the average daily‐UV dose at Ushuaia (monthly mean bias of −13%) and at Palmer (−35%) consistent with snow/ice with cloud effects not being properly accounted for in the TOMS algorithm. When the reflectivity at all three sites is low (no snow), the TOMS irradiance estimate is larger than the SUV‐100 measurements consistent with previously analyzed Brewer data at Toronto. The effects of local fog or clouds smaller than the satellite field of view and undetected UV‐absorbing aerosols near the ground are discussed. In addition to uncertainties in radiometric calibrations of the spectrometers, none of the SUV‐100 data are corrected for deviations of diffuser‐transmittance from true cosine response.
Reduction of solar UV by clouds: A comparison between satellite‐derived cloud effects and ground‐based radiation measurements
Authors: Matthijsen J. , Slaper H. , Reinen H. A. J. M. , Velders G. J. M.
Published: September 2002

Assessment of the effects of ozone depletion on biologically effective solar UV at ground level has been greatly advanced through the use of remote sensing data. Satellite data on atmospheric properties allow the construction of geographically distributed surface UV radiation maps based on radiative transfer calculations. In this respect, clouds play a dominant but rather complex role. We compared the reduction of daily UV doses due to clouds, as derived from satellite cloud data, with the reduction derived from routine ground‐based measurements of global solar radiation (i.e., broadband total solar irradiances with wavelengths between 0.3 and 2.8 μm). An empirical relationship is used to link the reduction due to clouds of global solar radiation and UV radiation. The abundance of global solar radiation measurements (data from over 125 stations in 30 satellite grid cells) for the European region ensured a sound basis for the data analysis for the period considered (May, June, and July of 1990, 1991, and 1992). Approximately 6500 daily UV‐reduction factors, defined as the ratio of daily UV doses calculated with and without clouds, were thus obtained applying both methods. The daily UV‐reduction factors (and 10‐day averaged UV reduction factors) from the two independent sources correlated well, with r2 = 0.83 (r2 = 0.89), and had a standard deviation of 0.06 (0.03). Over 90% of the satellite‐derived results agreed within a range of ±0.14 (±0.07) with the ground‐based measurement‐derived results. We evaluated sources of uncertainty related to spatial and temporal resolution, and optical properties, and estimated their consequences and range. Among these different sources the largest uncertainties are caused by the sampling error, i.e., grid‐cell average versus station average, which is on average 0.10 for daily UV‐reduction factors. Information on the atmospheric optical properties during the measurements may reduce the stated range of uncertainty from ±0.14 to ±0.07. The variation of the measurements from station to station is then the limiting factor. We concluded that the reduction of daily UV based on satellite‐derived cloud cover and cloud optical thickness relates well with the UV reduction due to clouds derived from ground‐based global solar radiation measurements.
A process‐oriented model of N2O and NO emissions from forest soils: 1. Model development
Authors: Li Changsheng , Aber John , Stange Florian , Butterbach‐Bahl Klaus , Papen Hans
Published: September 2002

To predict emissions of nitrous oxide (N2O) and nitric oxide (NO) from forest soils, we have developed a process‐oriented model by integrating several new features with three existing models, PnET, Denitrification‐Decomposition (DNDC), and a nitrification model. In the new model, two components were established to predict (1) the effects of ecological drivers (e.g., climate, soil, vegetation, and anthropogenic activity) on soil environmental factors (e.g., temperature, moisture, pH, redox potential, and substrates concentrations), and (2) effects of the soil environmental factors on the biochemical or geochemical reactions which govern NO and N2O production and consumption. The first component consists of three submodels for predicting soil climate, forest growth, and turnover of soil organic matter. The second component contains two submodels for nitrification and denitrification. A kinetic scheme, a so‐called “anaerobic balloon,” was developed to calculate the anaerobic status of the soil and divide the soil into aerobic and anaerobic fractions. Nitrification is only allowed to occur in the aerobic fraction, while denitrification occurs only in the anaerobic fraction. The size of the anaerobic balloon is defined by the simulated oxygen partial pressure which is calculated based on oxygen diffusion and consumption rates in the soil. As the balloon swells or shrinks, the model dynamically allocates substrates (e.g., dissolved organic carbon, ammonium, nitrate, etc.) into the aerobic and anaerobic fractions. With this approach, the model is able to predict both nitrification and denitrification in the same soil at the same time. This feature is important for soils where aerobic and anaerobic microsites often exist simultaneously. With the kinetic framework as well as its interacting functions, the PnET‐N‐DNDC model links ecological drivers to trace gas emissions. Tests for validating the new model are published in a companion paper [Stange et al., this issue].
Spatial and temporal variability of nitrogen oxide and methane fluxes from a fertilized tree plantation in Costa Rica
Authors: Weitz A. M. , Keller M. , Linder E. , Crill P. M.
Published: September 2002

Nitric oxide (NO), nitrous oxide (N2O), and methane (CH4) are naturally produced and consumed by soil biogeochemical processes. Naturally high variation between trace gas fluxes may temporarily increase due to agricultural management. We studied spatial and temporal variability of fluxes in the context of a 3‐year field experiment established to identify and quantify N2O fluxes and controlling factors using automated field measurements. We measured trace gas fluxes, soil temperature, and moisture from fertilized and unfertilized balsa (Ochroma lagopus) plantations. Combining spatial and temporal sampling we evaluate if automatically measured time series of N2O emissions are representative of overall mean fluxes from fertilized loam under balsa. Soil trace gas fluxes were measured manually at 36 randomly distributed sampling locations per plot. Mean plot emissions were evaluated against fluxes measured by seven chambers commonly used for routine bimonthly manual measurements and against N2O emissions measured by two automated chambers at 4.6‐hour sampling intervals. Trace gas fluxes were highly variable over 40 × 40 m plots. Nitrogen oxide fluxes were mainly spatially independent. Fertilization increased nitrogen oxide emissions but did not introduce spatial dependency of flux data. Within about 6 weeks fluxes approached pre‐fertilization level again. Given high spatial variation of nitrogen oxide fluxes we find that automatically measured N2O fluxes represent the nature of the flux response well and are in the range of fluxes indicated by spatial sampling. When soils were relatively dry fertilization inhibited CH4 uptake.
Comparison of water vapor measurements from POLINAT 2 with ECMWF analyses in high‐humidity conditions
Authors: Ovarlez Joëlle , van Velthoven Peter , Sachse Glen , Vay Stephanie , Schlager Hans , Ovarlez Henri
Published: September 2002

During the Pollution From Aircraft in the North Atlantic Flight Corridor (POLINAT 2) experiment, water vapor content was measured during 12 flights of the Deutsches Zentrum fuer Luft und Raumfahrt Falcon research aircraft by means of a frost‐point hygrometer. The last three flights were coordinated with the flights of the NASA DC8 aircraft, taking part in the Subsonic Assessment Ozone and Nitrogen Oxide Experiment (SONEX). The measurements were generally performed in high‐humidity and cloudy environments. Synthesized profiles of humidity and cloud cover along the flight tracks were retrieved from the European Centre for Medium‐Range Weather Forecasts analyses. It is shown that the measurements of supersaturation are generally correlated to the occurrence of clouds as indicated by the model cloud cover product. However, there are large discrepancies between the mixing ratio from the analyses and the measurements: the model underestimates the water vapor content. Some reasons for this underestimation are put forward, and the consequences for the investigation of the occurrence of contrail formation and persistence, when using such analyses, are pointed out.
Trends, spectral characteristics, and rainfall relationships of low‐latitude sea surface temperatures at different longitudes
Authors: Kane R. P.
Published: September 2002

The sea surface temperature (SST) data for low latitudes in the Pacific, Atlantic, and Indian Oceans for 1950–1996 (47 years) showed different seasonal variation patterns at different longitudes. When the seasonal patterns were subtracted from the monthly values, the deseasoned residuals showed considerable anomalies (interannual variability). In the Pacific the main features were the El Niño events. In the Atlantic, North and South Atlantic SST showed dissimilar anomalies, and these did not have any fixed lag or lead relationships with the Pacific events. The same was true for the low‐latitude Indian Ocean SST. The correlation of Pacific SST with Atlantic or Indian Oceans' SST was less than ∼0.65, yielding a common variance (square of the correlation) of less than ∼40%. Thus, whereas SST anomalies might have some common origin, the manifestation of SST anomalies at different longitudes was erratic, with no preference for any longitude to start with, nor any definite sequence of occurrence in the Pacific relative to the Atlantic or Indian Oceans. A spectral analysis showed that all regions had quasi‐biennial, quasi‐triennial, and higher periodicities, but the exact values of these periodicities differed significantly at different longitudes. All parameters had long‐term trends. These were mostly nonuniform, almost negligible in the first half (1950–1973) and mostly upward in the second half (1973–1996), indicating warming in recent decades, which is also reflected in decreases in snow cover area in the Northern Hemisphere. Rainfalls in various regions are considerably influenced by local SST regimes. For northeast Brazil, Atlantic SST influence is overpowering and often operates independently of the Pacific SST (El Niños). Hence the emphasis given in mass media (press, radio, and television) to the role of El Niño events only in influencing the rainfalls may turn out to be misleading, as seems to have happened for the 1997 El Niño. This El Niño started in early 1997 but did not have any significant influence on rainfall in northeast Brazil and India. It continued strongly in 1998, causing a severe drought in northeast Brazil but no drought in India.
Ozone production and transport near Nashville, Tennessee: Results from the 1994 study at New Hendersonville
Authors: Baumann K. , Williams E. J. , Angevine W. M. , Roberts J. M. , Norton R. B. , Frost G. J. , Fehsenfeld F. C. , Springston S. R. , Bertman S. B. , Hartsell B.
Published: September 2002

During the summer of 1994 the photochemical production of ozone and the relation of this production to the photochemical precursors were studied at a suburban ground site near Nashville, Tennessee. The study, which was carried out as part of the Southern Oxidant Study (SOS), investigated the ozone produced by urban outflow during one period of high photochemical activity around July 1, 1994. Estimates of the instantaneous rate of in situ ozone production, P(O3), are inferred from deviations of the photostationary state (PSS) for clear‐sky conditions. The biggest contributor to the large errors in P(O3) are the systematic errors in the derived, not measured, j(NO2) levels. Ozone entrainment from aloft has been quantified by simple subtraction of calculated production and loss terms from the observed rate of ozone change. The uncertainty of this derived transport term was estimated to a factor of 2 at best and 2 orders of magnitude at worst. Entrainment provides a substantial contribution to the observed increase of [O3] (∼20 ppbv h−1) in the mornings between 0700 and 1000 Central Standard Time (CST being 1 hour behind LT) when advection can be neglected. An average entrainment velocity of 1.5–2 cm s−1 agreed within 30 to 50% with a result found from another, completely independent study. P(O3) dominates the observed [O3] increase from 1000 CST until early afternoon, when entrainment weakens and even turns into an effective ozone loss term due to cloud venting processes. The July 1 case clearly demonstrates that the morning ozone entrainment occurs on a more regional scale covering the entire study area, whereas the midday ozone exceedance was spatially more confined to the area covered by the advective outflow of the chemically processed Nashville urban plume. The data show that the entrained [O3]‐rich air aloft is the remnant of the previous day's local ozone buildup and subsequent nocturnal advective redistribution.
Investigations of potassium, lithium, and sodium emission in the nightglow and OH cross calibration
Authors: Slanger T. G. , Osterbrock D. E.
Published: September 2002

Sky spectra from the high‐resolution echelle spectrometer (HIRES) on the Keck I telescope have been analyzed to obtain information on the potassium, lithium, and sodium resonance line emission in the nightglow. Relative intensity calibration is carried out against OH band intensities, and absolute values are obtained by utilizing new averaged intensities of the OH 9–4 band. The D1 line of potassium, at 7699 Å, is shown to be present, as previously speculated by Swider [1987]. Its average intensity is 1.0 R, twice as large as predicted. Any lithium line emission at the resonance wavelengths near 6708 Å is obscured by the PP(3) line of the 12‐9 emission band of the O2 (b1Σg+−X3Σg−) Atmospheric Band system. However, as that line has an intensity of ∼60 mR, our estimated upper limit on the Li line intensities is ∼15 mR. The intensity that we extract for the Na(D1) line, averaged over 4 years, is 20 R. Although there is no solar scattering contribution to the Na and K data, the Na D2/D1 line intensity ratio is substantially smaller than reported earlier for nightglow conditions. Observing that the Na/K D1 line intensity ratio is an order of magnitude smaller than the typical [Na]/[K] concentration ratio leads to the conclusion that the maximum efficiency for production of mesospheric Na(2P) is 0.1.
Rainfall characteristics (δ18O, δ2H, ΔT and ΔHr) in western Africa: Regional scale and influence of irrigated areas
Authors: Taupin Jean‐Denis , Coudrain‐Ribstein Anne , Gallaire Robert , Zuppi Gian Maria , Filly Annick
Published: September 2002

A summary of previous isotopic studies of rainfall in western Africa (0°‐17°N; 0°‐15°E) together with the isotopic analyses of rainfall events from 15 stations in 1989 shows that (1) the Gulf of Guinea is the main source of water vapor in the Sudan‐Sahelian zone (minimum of monthly mean of δ18O contemporaneous with the heart of the monsoon), (2) the reevaporated water from previous local rainfalls is an important source of water vapor of subsequent rainfalls (lack of continental effect, where the majority of rain events present isotopic signature either evaporated or fed by evaporated water), and (3) no isotopic data support the Indian Ocean as a source of vapor. Isotopic ratios combined with variations of temperature and relative humidity associated with rain events in 1989 mirror the increasing aridity from south to north and from west to east. However, a Sahelian station, Birni N'Konni, presents all the features of a humid station with a large contribution of continental vapor (60% of rain events with d > 10‰, −2 K < ΔT <2 K and ΔHr < 10%). This observation can be attributed to continental vapor originating from irrigated fields 100 km upstream of the dominant monsoon currents, in the Sokoto valley of Nigeria. This is corroborated by the difference in the evolution of rainfall amounts and relative humidity at Niamey and Birni N'Konni since 1951, signaling an important effect of land use changes on regional climate conditions.
A study of size‐segregated aerosol chemistry in the Antarctic atmosphere
Authors: Teinilä Kimmo , Kerminen Veli‐Matti , Hillamo Risto
Published: September 2002

During austral summer 1998, aerosol particles were sampled at the Finnish station Aboa in continental Antarctica. The collected aerosol samples were analyzed for major inorganic ions, methane sulphonate, and dicarboxylates. Measured ions composed on average about one third of the total gravimetric mass in fine particulate matter (particle diameter < 2 μm). Particulate sulphate, ammonium, and methane sulphonate were internally mixed and found predominantly in the submicron size range. The submicron mass size distribution of these three ions had a dominant mode peaking at ∼ 0.3 μm of particle aerodynamic diameter, another mode peaking at 0.6 μm, and an identifiable Aitken mode below 0.2 μm. The mass size distribution of sodium, a tracer for sea salt particles, peaked in most samples slightly below 2 μm; in addition, it had a submicron mode between ∼0.5 and 1.0 μm and a mode with great variability between 3 and 10 μm. The overall concentration of sea salt was 1–2 orders of magnitude lower than concentrations measured in coastal Antarctica. Particulate nitrate was found almost entirely in the supermicron size range, the most likely formation pathway being the interaction of nitric acid or some other reactive nitrogen compound with sea‐salt particles in the Antarctic atmosphere. The only dicarboxylate above the analytical limit of detection was oxalate, which was distributed in about equal quantities between the submicron and supermicron size ranges. The average total particle number concentration varied in the range 235–955 cm−3 between the samples and showed no obvious correlation with any aerosol species. The great majority of these particles (> 80–90%) were shown to be smaller than ∼ 0.1 μm in diameter.
Aerosol number‐to‐volume relationship and relative humidity in the eastern Atlantic
Authors: Hegg Dean A. , Jonsson Haflidi
Published: September 2002

Measurements acquired from the Office of Naval Research (ONR) Pelican research aircraft during the second Aerosol Characterization Experiment (ACE 2) are analyzed to derive values for the dry (RH = 40%) aerosol number‐to‐volume ratio in the submicron size range. This ratio is found to be relatively constant, with a mean value of 168±21 μm−3, in agreement with previous studies elsewhere. The impact of ambient relative humidity (RH) on the dry number‐to‐volume is also quantified and a procedure for estimating the dry from the ambient ratio established. Finally, the feasibility of a remote retrieval of the aerosol number concentration in the submicron size range, essentially the cloud condensation nucleus concentration active at a nominal 0.2% supersaturation, is partially assessed.
Case studies of the vertical structure of the direct shortwave aerosol radiative forcing during TARFOX
Authors: Redemann J. , Turco R. P. , Liou K. N. , Hobbs P. V. , Hartley W. S. , Bergstrom R. W. , Browell E. V. , Russell P. B.
Published: September 2002

The vertical structure of aerosol‐induced radiative flux changes in the Earth's troposphere affects local heating rates and thereby convective processes, the formation and lifetime of clouds, and hence the distribution of chemical constituents. We present observationally based estimates of the vertical structure of direct shortwave aerosol radiative forcing for two case studies from the Tropospheric Aerosol Radiative Forcing Observational Experiment (TARFOX) which took place on the U.S. east coast in July 1996. The aerosol radiative forcings are computed using the Fu‐Liou broadband radiative transfer model. The aerosol optical properties used in the radiative transfer simulations are calculated from independent vertically resolved estimates of the complex aerosol indices of refraction in two to three distinct vertical layers, using profiles of in situ particle size distributions measured aboard the University of Washington research aircraft. Aerosol single‐scattering albedos at 450 nm thus determined range from 0.9 to 0.985, while the asymmetry factor varies from 0.6 to 0.8. The instantaneous shortwave aerosol radiative forcings derived from the optical properties of the aerosols are of the order of −36 W m−2 at the top of the atmosphere and about −56 W m−2 at the surface for both case studies.
Comparison of the Madden‐Julian oscillation (MJO) during the TOGA COARE IOP with a 15‐year climatology
Authors: Chen Baode , Yanai Michio
Published: September 2002

During the Tropical Ocean‐Global Atmosphere (TOGA) Coupled Ocean‐Atmosphere Response Experiment (COARE) intensive observing period (IOP) (November 1992 to February 1993), two pronounced Madden‐Julian oscillation (MJO) events were observed and have been intensively studied. To provide a necessary climatological basis for the case study as well as to evaluate how typical the COARE MJO cases are and to what degree conclusions made from these cases can be generalized, we compare the MJOs that occurred during the COARE IOP with a 15‐year climatology. In this paper, along with a description of the characteristics of large‐scale background including flow patterns, OLR and SST, the emphasis is placed on the intensity and propagation of the oscillations exhibited in organized convection and atmospheric circulation. Moreover, the maintenance of perturbation kinetic energy (PKE) associated with 30‐ to 60‐day variability containing the MJOs is compared as well. The COARE IOP occurred in a lingering period between the persistence and the rejuvenation of the warm ENSO episode of 1992–1993. The intraseasonal oscillations in the convective activity and large‐scale circulation are intensified during the IOP, and the maximum intensification is located in the region of central Pacific. Two MJO events in the COARE IOP are typical in terms of phase propagation. The major features of the energy transformation processes, such as the predominant role of the generation of the perturbation available potential energy (PAPE) by convective heating and its conversion into the PKE in the maintenance of the MJOs, found in the COARE IOP, are also displayed in the climatology indicating the generality of the results obtained from the COARE case study.
A new gas chromatograph‐isotope ratio mass spectrometry technique for high‐precision, N2O‐free analysis of δ13C and δ18O in atmospheric CO2 from small air samples
Authors: Ferretti D. F. , Lowe D. C. , Martin R. J. , Brailsford G. W.
Published: September 2002

A new gas Chromatograph‐isotope ratio mass spectrometry (GC‐IRMS) technique for the first N2O‐free, high‐precision (<0.05‰) isotopic analysis of δ13C and δ18O in atmospheric CO2 from small air samples has been developed. On‐line GC separation of CO2 and N2O from a whole air sample is combined with IRMS under elevated ion source pressures. A specialized open split interface is an integral part of the inlet system and ensures a continuous flow of either sample gas or pure helium to the IRMS. The analysis, including all flushing, uses a total amount of 45 mL of an air sample collected at ambient pressure. Of this, three 0.5 mL aliquots are injected onto the GC column, each providing ∼0.8 nmol CO2 in the IRMS source. At this sample size, δ13C precision obtained is at the theoretical shot noise limit. For typical ambient air samples collected in the Southern Hemisphere, demonstrated precisions for δ13C, δ18O, and the CO2 mixing ratio (all measured simultaneously) are 0.02‰, 0.04‰, and 0.4 ppm, parts per million (ppm) respectively. Since these data are achieved from small air samples without contamination by atmospheric N2O or the use of cryogen, the technique will be a valuable tool in global carbon cycle research.
Sea level pressure variability in the Amundsen Sea region inferred from a West Antarctic glaciochemical record
Authors: Kreutz K. J. , Mayewski P. A. , Pittalwala I. I. , Meeker L. D. , Twickler M. S. , Whitlow S. I.
Published: September 2002

Using European Center for Medium‐Range Weather Forecasts (ECMWF) numerical operational analyses, sea ice extent records, and station pressure data, we investigate the influence of sea level pressure variability in the Amundsen Sea region on a West Antarctic (Siple Dome) glaciochemical record. Empirical orthogonal function analysis of the high‐resolution Siple Dome multivariate ice core chemical time series record (SDEOF1) documents lower tropospheric transport of sea‐salt aerosols to the site. During 1985–1994 the SDEOF1 record of high (low) aerosol transport corresponds to anomalously low (high) sea level pressure (SLP) in the Amundsen Sea region. Spatial correlation patterns between ECMWF monthly SLP fields and the annual SDEOF1 record suggest that a majority of sea‐salt aerosol is transported to Siple Dome during spring (September, October, and November). Analysis of zonal and meridional wind fields supports the SLP/SDEOF1 correlation and suggests the SDEOF1 record is sensitive to changes in regional circulation strength. No relationship is found between sea ice extent and the SDEOF1 record for the period 1973–1994. To investigate the SDEOF1 record prior to ECMWF coverage, a spring transpolar index (STPI) is created, using normalized SLP records from the New Zealand and South America/Antarctic Peninsula sectors, and is significantly correlated (at least 95% c.l.) with the SDEOF1 record on an annual (r = 0.32, p < 0.001) and interannual (3 years; r = 0.51, p < 0.001) basis. Dominant periodicities (3.3 and 7.1 years) in the annual SDEOF1 record (1890–1994 A.D.) suggest that a portion of the recorded interannual variability may be related tropical/extratropical ENSO teleconnections. Changes in the periodic structure of the full (850–1994 A.D.) Siple Dome record suggests a shift in SLP forcing during the Little Ice Age (∼1400–1900 A.D.) interval.
Northern midlatitude stratospheric ozone dilution in spring modeled with simulated mixing
Authors: Knudsen Bjørn M. , Grooß Jens‐Uwe
Published: September 2002

Measurements have shown a substantial decrease in Northern midlatitude ozone, which has only partially been explained by chemical models. The large ozone depletions determined for the Arctic vortex in recent winters will ultimately spread out and dilute the midlatitudes and thus contribute to the observed decrease. Here we have followed the ozone‐depleted air inside the Arctic vortex in 1995 and 1997 during April and May with high‐resolution reverse domain‐filling (RDF) trajectory calculations. The resulting average midlatitude (30°–60°N) stratospheric ozone dilution in May is 2.9% and 2.6% of the 1979 column ozone in 1995 and 1997, respectively, or about 40% of the observed depletion. Nearly realistic mixing was introduced by a regridding procedure between successive 7‐day long RDF calculations. Low‐resolution grid point models give too much mixing, causing an overestimate of the calculated dilution. A recovery of about 12% of the midlatitude dilution in May 1997 is calculated with a photochemical box model, but is not included in the number given above.
Sensitivity of the National Oceanic and Atmospheric Administration multilayer model to instrument error and parameterization uncertainty
Authors: Cooter Ellen J. , Schwede Donna B.
Published: September 2002

The response of the National Oceanic and Atmospheric Administration multilayer inferential dry deposition velocity model (NOAA‐MLM) to error in meteorological inputs and model parameterization is reported. Monte Carlo simulations were performed to assess the uncertainty in NOAA‐MLM deposition velocity Vd estimates for ozone (O3), sulfur dioxide (SO2), and nitric acid (HNO3) associated with measurements of meteorological variables (including temperature, humidity, radiation, wind speed, wind direction, and leaf area index). Summer daylight scenarios for grass, corn, soybean, oak, and pine were considered. Model sensitivity to uncertainty in the leaf area index (LAI), minimum stomatal resistance, and soil moisture parameterizations was explored. For SO2 and HNO3, instrument error associated with the measurement of wind speed and direction resulted in the greatest Vd error. Depending on vegetation type, the most important source of uncertainty due to instrument error for the Vd of O3 was LAI. Of the model parameterizations studied, accurate estimation of temporal aspects of the annual LAI profile and the characterization of soil moisture supply and demand are most important to model‐estimated Vd uncertainty. Considered individually, these factors can result in SO2 and HNO3 Vd estimate uncertainty of ±25% and O3 estimate uncertainty greater than 60%. For single plant species settings, reductions in estimate uncertainty should be possible with minor algorithmic modification, inclusion of more species‐appropriate LAI profiles, and careful application of remote sensing technology.