bluuebunny/crossref_metadata_2025 huggingface dataset:
A description of the global sulfur cycle and its controlling processes in the National Center for Atmospheric Research Community Climate Model, Version 3
Authors: Rasch Philip J. , Barth Mary C. , Kiehl Jeffrey T. , Schwartz Stephen E. , Benkovitz Carmen M.
Published: September 2002

We examine the balance between processes that contribute to the global and regional distributions of sulfate aerosol in the Earth's atmosphere using a set of simulations from the National Center for Atmospheric Research Community Climate Model, Version 3. The analysis suggests that the seasonal cycle of SO2 and SO42− are controlled by a complex interplay between transport, chemistry and deposition processes. The seasonal cycle of these species is not strongly controlled by temporal variations in emissions but by seasonal variations in volume of air processed by clouds, mass of liquid water serving as a site for aqueous chemistry, amount of oxidant available for the conversion from SO2 to SO42−, vertical transport processes, and deposition. A tagging of the sulfate by emission region (Europe, North America, Asia, and rest of world [ROW]), chemical pathway (gaseous versus in‐cloud), and type of emissions (anthropogenic versus biogenic) is used to differentiate the balance of processes controlling the production and loading from this material. Significant differences exist in the destiny of SO2 molecules emitted from the several regions. An SO2 molecule emitted from the ROW source region has a much greater potential to form sulfate than one emitted from, for example, Europe. A greater fraction of the SO2 molecules is oxidized that originate from ROW compared with other areas, and once formed, the sulfate has a longer residence time (that is, it is not readily scavenged). The yield of sulfate from ROW sources of SO2 is a factor of 4 higher than that of Europe. A substantially higher fraction of the SO2 emitted over Europe is oxidized to sulfate through the ozone pathway compared to other regions. The analysis suggests that there are significant differences in the vertical distribution, and horizontal extent, of the propagation of sulfate emitted from the several source regions. Sulfate from Asian source regions reaches the farthest from its point of origin and makes a significant contribution to burdens in both hemispheres, primarily from plumes reaching out in the upper troposphere. Sulfate from other source regions tends to remain trapped in their hemisphere of origin.
Levels and pattern of alkyl nitrates, multifunctional alkyl nitrates, and halocarbons in the air over the Atlantic Ocean
Authors: Fischer Ralf G. , Kastler Jürgen , Ballschmiter Karlheinz
Published: September 2002

The Albatross Campaign was a research cruise of the German research vessel RV Polarstern (cruise ANT XFV/1) in October and November 1996 across the Atlantic Ocean. The cruise started in Bremerhaven, Germany, reached the polar region at 67°N, followed the 30°W meridian longitude, crossed the equatorial region, and ended at 50°S at Punta Quilla, Argentina. A second cruise leg closer to the African continent started from Capetown, South Africa, passed the Canary Island, and ended through the English Channel at Bremerhaven, Germany, in May/June 1998. Measurements of atmospheric levels of C1–C13 alkyl mononitrates, 24 alkyl dinitrates (C3–C6), 19 hydroxy alkyl nitrates (C2–C6), and benzyl nitrate, as well as the halocarbons tetrachloroethene, hexachloroethane, and bromoform are presented in this work. The halocarbons are used to assess the origin of the air parcels analyzed. Levels and patterns of multifunctional alkyl nitrates in the marine air are described here for the first time. The air masses include polluted air from the northern Europe, as well as highly degraded air masses of the South Atlantic trade wind region that represent global baseline levels. Two independent analytical methods were used in combination to cover the whole range of organic nitrates. First, the low‐volume adsorptive enrichment of organic traces on Tenax, followed by thermodesorption cold trap HRGC‐ECD and thermodesorption cold trap HRGC‐(EI)MSD was used. Second, high‐volume adsorptive enrichment of organic traces on silica gel was applied followed by solvent desorption, NP‐HPLC group separation, and HRGC‐(EI)‐MSD. Short‐chain alkyl nitrates (C4–C6) showed mixing ratios in the range of 0.2–2.5 parts per trillion by volume (pptv), with a local minimum for the tropical regions and significantly lower ratios for the Southern Hemisphere. The mixing ratio of the sum of 36 long‐chain alkyl mononitrates (C7–C13) ranged from 0.02–0.43 pptv, the mixing ratio of the sum of 23 alkyl dinitrates (C3–C6) ranged from 0.005–1.08 pptv, and the mixing ratio of the sum of 7 hydroxy alkyl nitrates (C2–C4) ranged from 0.005–1.07 pptv, respectively. The average alkyl nitrate concentration in ambient air of central Europe (Ulm, Germany) turned out to be a factor of 10–100 higher than in the marine samples. The low concentrations in marine air reflect chemical and physical loss processes during long‐range transport of the air starting from the continents. Our results are compared with earlier field studies to complete the data set of global occurrence of alkyl nitrates in the troposphere.
Interrelationships between aerosol characteristics and light scattering during late winter in an Eastern Mediterranean arid environment
Authors: Ichoku Charles , Andreae Meinrat O. , Andreae Tracey W. , Meixner Franz X. , Schebeske Guenther , Formenti Paola , Maenhaut Willy , Cafmeyer Jan , Ptasinski Jacek , Karnieli Arnon , Orlovsky Leah
Published: September 2002

An intensive field campaign involving measurement of various aerosol physical, chemical, and radiative properties was conducted at Sde Boker (also written as Sede Boqer) in the Negev Desert of Israel, from 18 February to 15 March 1997. Nephelometer measurements gave average background scattering coefficient values of about 25 Mm−1 at 550 nm wavelength, but strong dust events caused the value of this parameter to rise up to about 800 Mm−1. Backscattering fractions did not depend on aerosol loading and generally fell in the range of 0.1 to 0.25, comparable to values reported for marine and Arctic environments. Chemical analysis of the aerosol revealed that in the coarse size range (2–10 μm equivalent aerodynamic diameter (EAD)), calcium (Ca) was by far the most abundant element followed by silicon (Si), both of which are indicators for mineral dust. In the fine size fraction (<2 μm EAD), sulfur (S) generally was the dominant element, except during high dust episodes when Ca and Si were again the most abundant. Furthermore, fine black carbon (BC) correlates with S, suggesting that they may have originated from the same sources or source regions. An indication of the short‐term effect of aerosol loading on radiative forcing was provided by measurements of global and diffuse solar radiation, which showed that during high‐turbidity periods (strong dust events), almost all of the solar radiation reaching the area is scattered or absorbed.
Potential importance of the reaction CO+HNO3
Authors: Lary D. J. , Shallcross D. E.
Published: September 2002

CO has a strong thermodynamic potential for reducing HNO3 to HONO. If the reaction of HNO3 with CO does proceed via heterogeneous catalysis on sulfuric acid aerosols in our atmosphere, then this data assimilation study shows that the model is better able to reproduce the observed NOx/HNO3 ratio even with a γ value as low as 1×10−4. This is particularly true in the upper troposphere and lower stratosphere. We would like to highlight the possibility that elements such as iron deposited in the lower stratosphere by meteorites may be catalyzing this and other reactions within sulfate aerosols.
The Nonmethane Hydrocarbon Intercomparison Experiment (NOMHICE): Task 3
Authors: Apel E. C. , Calvert J. G. , Gilpin T. M. , Fehsenfeld F. C. , Parrish D. D. , Lonneman W. A.
Published: September 2002

The Nonmethane Hydrocarbon Intercomparison Experiment (NOMHICE) was designed to evaluate current analytical methods used to determine mixing ratios of atmospheric nonmethane hydrocarbons (NMHCs). A series of planned experiments, or tasks, were implemented to test the analytical methods in a graduated fashion. Tasks 1 and 2 involved relatively simple standard gas mixtures prepared by the National Institute for Standards and Technology (NIST). Results are presented here for task 3 in which a complex mixture containing 60 commonly observed NMHCs at concentrations of 1–30 parts per billion by volume (ppbv) in nitrogen diluent gas was prepared and distributed for analysis to 29 participating laboratories throughout the world. Reference mixing ratios were determined jointly by scientists from the National Center for Atmospheric Research (NCAR) and from the U.S. Environmental Protection Agency (EPA). Participants were asked to identify and quantify the hydrocarbons present in the mixture and submit their results to NCAR‐NOMHICE scientists. The results were encouraging overall. Some laboratories performed extremely well during this exercise whereas other laboratories experienced problems in either identification or quantification or both. It is evident from the comparison of the NCAR‐NOMHICE results with both the EPA analysis and the top 11 analyses in the study that very good agreement is achievable between laboratories for mixtures in this concentration range. Some of the largest analytical discrepancies were from laboratories that used in‐house standards for their calibration and/or syringe sample injection techniques. A major conclusion from this study is that the use of high‐quality gas phase standards, introduced into the measurement instrument in a similar manner to air samples, is an important prerequisite for an accurate analysis.
Airborne spectral measurements of surface reflectivity at ultraviolet and visible wavelengths
Authors: Webb Ann R. , Stromberg I. M. , Li H. , Bartlett L. M.
Published: September 2002

Spectral reflectivities at ultraviolet and visible wavelengths (290–500 nm) have been measured from an airborne platform (Cessna light aircraft) at several heights in the boundary layer, and at ground level, using an Optronic Laboratories 742 spectroradiometer with specially adapted input optics. Ground level measurements of vegetation and man‐made surfaces show a general increase in reflectivity with wavelength. Airborne measurements over vegetation and ocean (from heights of 700–5500 ft) show an increase in effective reflectivity with the height at which measurements were made and also a reversal in spectral character, so reflectivity decreases with increasing wavelength at height. This suggests significant backscattering from the boundary layer air which rapidly dominates the surface influence for low‐albedo surfaces.
Observations of HOx and its relationship with NOx in the upper troposphere during SONEX
Authors: Faloona Ian , Tan David , Brune William H. , Jaeglé Lyatt , Jacob Daniel J. , Kondo Y. , Koike M. , Chatfield Robert , Pueschel Rudolf , Ferry Guy , Sachse Glen , Vay Stephanie , Anderson Bruce , Hannon John , Fuelberg Henry
Published: September 2002

Simultaneous measurements of the oxides of hydrogen and nitrogen made during the NASA Subsonic Assessment, Ozone and Nitrogen Oxide Experiment (SONEX) afforded an opportunity to study the coupling between these two important families throughout the free troposphere and lowermost stratosphere. Moreover, the suite of measurements made during the campaign was unprecedented in its completeness, thus providing a uniquely detailed picture of the radical photochemistry that drives oxidation and ozone production in this part of the atmosphere. On average, observed hydrogen oxides (HOx = OH + HO2) agree well with both instantaneous and diel steady‐state models; however, there is a persistent deviation of the observations that correlates with the abundance of nitrogen oxides (NOx = NO + NO2) in the sampled air mass. Specifically, the observed HOx tends to exceed the model predictions in the presence of high NOx concentrations, by as much as a factor of 5 (> 500 pptv NOx), and is sometimes as little as half that expected by steady state at lower NOx levels. While many possibilities for these discrepancies are discussed, it is argued that an instrumental artifact is not probable and that the discrepancy may bespeak a shortcoming of our understanding of HOx chemistry. The consistently elevated HOx in the presence of elevated NOx leads directly to greater ozone production than expected, thereby extending the NOx‐limited regime of the upper troposphere. These results could thus have bearing on the predicted impacts of increasing NOx emissions into this region of the atmosphere from, for example, the growth of global air traffic.
Modeling heterogeneous sulphate production in maritime stratiform clouds
Authors: O'Dowd Colin D. , Lowe Jason A. , Clegg Nicola , Smith Michael H. , Clegg Simon L.
Published: September 2002

A size‐resolved droplet physico chemical model linked to a Lagrangian parcel framework was developed and used to study the heterogeneous sulphate production process in marine stratiform clouds. This model study provides a rigorous approach to cloud chemistry processing by treating the effects of non ideal chemistry on both aqueous phase equilibration and droplet growth using the Pitzer method to overcome many of the shortcomings of alternative thermodynamic methods. In addition, the current study uses a multi modal representation of sea‐salt aerosol, rather than the single mode used in most previous work. The results of the model simulations showed a distribution of sulphate production across the aerosol size range that was non linear and that a significant fraction (≈ 75–90%) of the sulphate was produced in droplets formed on sea‐salt aerosol particles. The number of sea‐salt particles affected both the total amount of sulphate produced and the fraction produced on cloud droplets formed around non‐sea‐salt sulphate aerosol. Dissolved ozone and hydrogen peroxide were both important as oxidant species, although the ozone‐driven oxidation pathway was dominant in droplets formed on sea‐salt aerosol particles. The rate of sulphate production was found to be a non linear function of the gaseous sulphur dioxide concentration at cloud base and only very weakly dependent on sulphate nuclei concentration. A comparison of sulphate production in cloud and below cloud indicates that sulphate production in sea‐salt nuclei is not limited by the carbonate buffer and that in‐cloud production can exceed, many times, that of cloud‐free production due to the “virtual” buffering capacity of the cloud. The use of non ideal solution effects appear important, particularly for clean‐to‐moderately polluted SO2 concentrations (<500 parts per trillion) and when sea‐salt nuclei are present, resulting in at least 40% lower sulphate production when compared to ideal solution simulations.
Comparison of TOVS‐derived land surface variables with ground observations
Authors: Lakshmi Venkataraman , Susskind Joel
Published: September 2002

The Tiros Operational Vertical Sounder (TOVS) Pathfinder Path A retrieved surface skin temperature, surface air temperatures, and surface specific humidity are compared with data obtained from three large‐scale field campaigns: the First ISLSCP (International Satellite Land Surface Climatology Project) Field Experiment (FIFE), the Hydrologic Atmospheric Pilot Experiment (HAPEX) in the Sahel, and the Boreal Ecosystem‐Atmosphere Study (BOREAS). The long‐term estimates of surface skin temperatures, surface air temperatures, and surface vapor pressure were unbiased, and the standard deviations of the errors were about 4°C, 3.5°C, and 3.5 mbar, respectively. The monthly mean variables obtained from the TOVS data at four times of the day (corresponding to the AM and PM overpass for each of two satellites) exhibited realistic diurnal and seasonal cycles when compared with corresponding ground observations.
Emission inventory development and processing for the Seasonal Model for Regional Air Quality (SMRAQ) project
Authors: Houyoux Marc R. , Vukovich Jeffrey M. , Coats Carlie J. , Wheeler Neil J. M. , Kasibhatla Prasad S.
Published: September 2002

This paper describes the experiences and insights gained from inventory preparation and emissions processing for the Seasonal Model for Regional Air Quality (SMRAQ) project. The emission inventory was derived from the 1990 and 1995 Ozone Transport Assessment Group (OTAG) inventories. Here we outline the emissions processing strategy used for the May‐to‐September simulation, summarize the inventory characteristics and corrections made on the OTAG inventories, and describe the quality assurance steps taken as part of the processing. We then provide spatial maps and daily total time series charts of the hourly, gridded emissions of nitrogen oxides (NOx), reactive organic gases (ROG), and carbon monoxide (CO). Large peaks from electric utility point sources and urban mobile sources characterize the NOx emissions, and the NOx emissions in nonpeak regions are primarily mobile‐source emissions. ROG emissions are dominated by biogenic isoprene production in the southern United States, and they have a strong seasonal variability. CO emissions are characterized by less variability, with area and mobile sources dominating the inventory. We compare ratios of season‐average nonmethane organic gases to NOx between the emission inventory and the Photochemical Assessment Monitoring Stations (PAMS) data, and these comparisons show poor correlation between the inventory and ambient ratios.
Scavenging of acidic gases (HCOOH, CH3COOH, HNO3, HCl, and SO2) and ammonia in mixed liquid‐solid water clouds at the Puy de Dôme mountain (France)
Authors: Voisin Didier , Legrand Michel , Chaumerliac Nadine
Published: September 2002

In order to study scavenging processes of chemical species in mixed phase clouds, in‐cloud field measurements were conducted in December 1997 at the Puy de Dôme mountain (center of France, 1465 m above sea level). Soluble species including NH+4, Cl−;, NO3−3, SO−4, HCOO−, CH3COO−, and C2O−4 present in the different phases (supercooled water droplets, rimed snowflakes, interstitial gases, and aerosols) of cold clouds have been investigated. Conducted in parallel to microphysical studies of clouds (liquid water and ice contents, and size distribution of hydrometeors), these chemical investigations allow us to examine the partitioning of strong (HNO3 and HCl) and weak (SO2, HCOOH, and CH3COOH) acids as well as ammonia between interstitial air and the condensed phases (liquid and solid water particles) in mixed clouds present during winter at midlatitude regions. From that, we discuss the processes by which these key atmospheric species are taken up from the gas phase by the condensed phases (liquid and ice) in these cold clouds. We examine several factors which are of importance in driving the final composition of cloud ice. They include the partitioning of species between gaseous and supercooled liquid phases, the amount of rimed ice collected by snowflakes, and the retention of gas during shock freezing of supercooled droplets onto ice particles. Strong acids (HCl and HNO3) as well as NH3, being sufficiently soluble in water, are mainly partitioned into supercooled water droplets. Furthermore, being subsaturated in liquid droplets, these species are well retained in rimed ice. For these species, riming is found to be the main process driving the final composition of snowflakes, direct incorporation from the gas phase during growth of snowflakes remaining insignificant because of low concentrations in the gas phase. For light carboxylic acids the riming process mainly determines the composition of the snowflakes, but an additional significant contribution by gas incorporation during the growth of snowflakes cannot be excluded. SO2 is also present at significant levels in the interstitial air and is poorly retained in ice during riming of supercooled water droplets. However, hydroxymethanesulfonate (HMSA) was likely present in supercooled liquid droplets, making it difficult to evaluate by which mechanism S(IV) (i.e., HMSA plus SO2) has been incorporated into snowflakes.
Three‐dimensional climatological distribution of tropospheric OH: Update and evaluation
Authors: Spivakovsky C. M. , Logan J. A. , Montzka S. A. , Balkanski Y. J. , Foreman‐Fowler M. , Jones D. B. A. , Horowitz L. W. , Fusco A. C. , Brenninkmeijer C. A. M. , Prather M. J. , Wofsy S. C. , McElroy M. B.
Published: September 2002

A global climatological distribution of tropospheric OH is computed using observed distributions of O3, H2O, NOt (NO2 +NO + 2N2O5 + NO3 + HNO2 +HNO4), CO, hydrocarbons, temperature, and cloud optical depth. Global annual mean OH is 1.16×106 molecules cm−3 (integrated with respect to mass of air up to 100 hPa within ±32° latitude and up to 200 hPa outside that region). Mean hemispheric concentrations of OH are nearly equal. While global mean OH increased by 33% compared to that from Spivakovsky et al. [1990], mean loss frequencies of CH3CCl3 and CH4 increased by only 23% because a lower fraction of total OH resides in the lower troposphere in the present distribution. The value for temperature used for determining lifetimes of hydrochlorofluorocarbons (HCFCs) by scaling rate constants [Prather and Spivakovsky, 1990] is revised from 277 K to 272 K. The present distribution of OH is consistent within a few percent with the current budgets of CH3CCl3 and HCFC‐22. For CH3CCl3, it results in a lifetime of 4.6 years, including stratospheric and ocean sinks with atmospheric lifetimes of 43 and 80 years, respectively. For HCFC‐22, the lifetime is 11.4 years, allowing for the stratospheric sink with an atmospheric lifetime of 229 years. Corrections suggested by observed levels of CH2Cl2 (annual means) depend strongly on the rate of interhemispheric mixing in the model. An increase in OH in the Northern Hemisphere by 20% combined with a decrease in the southern tropics by 25% is suggested if this rate is at its upper limit consistent with observations of CFCs and 85Kr. For the lower limit, observations of CH2Cl2 imply an increase in OH in the Northern Hemisphere by 35% combined with a decrease in OH in the southern tropics by 60%. However, such large corrections are inconsistent with observations for 14CO in the tropics and for the interhemispheric gradient of CH3CCl3. Industrial sources of CH2Cl2 are sufficient for balancing its budget. The available tests do not establish significant errors in OH except for a possible underestimate in winter in the northern and southern tropics by 15–20% and 10–15%, respectively, and an overestimate in southern extratropics by ∼25%. Observations of seasonal variations of CH3CCl3, CH2Cl2, 14CO, and C2H6 offer no evidence for higher levels of OH in the southern than in the northern extratropics. It is expected that in the next few years the latitudinal distribution and annual cycle of CH3CCl3 will be determined primarily by its loss frequency, allowing for additional constraints for OH on scales smaller than global.
On the relationship between relative humidity and particle backscattering coefficient in the marine boundary layer determined with differential absorption lidar
Authors: Wulfmeyer Volker , Feingold Graham
Published: September 2002

A ground‐based water‐vapor differential absorption lidar (DIAL) has been applied to investigate aerosol properties in the convective marine boundary layer. The high resolution and accuracy of this instrument enables measurement of the particle backscattering coefficient βpar and the absolute humidity under a single boundary layer cloud, so the hygroscopic growth of the aerosol can be investigated in a single profile over a large range of the relative humidity RH. Arguing that the convective boundary layer was adiabatic and using the DIAL absolute humidity measurements, the relation βpar(RH) has been determined. This relation is compared with a simple aerosol model. Assuming that the simplifications are valid, it follows that βpar(RH) is mainly sensitive to variations in the mass fraction of soluble material ε of an internally mixed aerosol. Applying this model to the experimental data, we found ε was in the range of 0.05–0.27 during the measurements. These values are consistent with those from in situ particle analyses at other anthropogenically influenced sites. These rather low soluble mass fractions have strong implications for the magnitude of both aerosol direct and indirect effects.
A seasonal deuterium excess signal at Law Dome, coastal eastern Antarctica: A southern ocean signature
Authors: Delmotte Marc , Masson Valérie , Jouzel Jean , Morgan Vin I.
Published: September 2002

The snow isotopic composition (δ18O and δD) of two shallow cores from the high accumulation summit region of Law Dome, east Antarctica, was measured at monthly resolution over the 1980–1992 period. While the δ18O or δD signals clearly reflect the local temperature cycle, the deuterium excess (d = δD ‐ 8δ18O) is shifted with respect to δ18O cycle by a 4 months lag. Interpretation of this phase lag is investigated using both an Atmospheric General Circulation Model (AGCM), which includes the water isotopic cycles, and a simple isotopic model, which better describes the microphysical processes within the cloud. Using this dual approach, we show that the seasonality of δ18O and d at Law Dome summit results from a combination of the southern ocean temperature cycle (shifted by 2–3 months with respect to the local insolation) and seasonal moisture origin changes due to a strong contribution of the local ocean when ice free. Both approaches are consistent with a dominant temperate to subtropical moisture origin. We thus demonstrate from our present‐day subseasonal study that the record of d in the Dome Summit South (DSS) deep ice core represents a potential tool for identifying changes in Southern Ocean temperatures and/or sea ice cover at the scale of the past thousand years.
Stratospheric residence time and its relationship to mean age
Authors: Hall Timothy M. , Waugh Darryn W.
Published: September 2002

Transport inaccuracies in stratospheric models are a major source of uncertainty in predicting the environmental impact of trace gases with stratospheric source, such as emissions from high‐flying aircraft. Because there are no observed tracers of stratospheric aircraft emissions, a direct evaluation of the models' transport of the emissions is not possible. Here we examine the relationship between the stratospheric residence time τR for tracers of midlatitude stratosphere source and the mean age Γ, a transport diagnostic for which observations are available and have been used to evaluate stratospheric models. Employing a representation of the stratosphere that includes the basic kinematic features of the global circulation, we find that τR and Γ are correlated over a range of plausible circulations, but that the correlation is imperfect. A major (but not sole) limitation on Γ as a proxy for τR is the midlatitude tropopause height ZM. Elevating ZM reduces τR significantly, while Γ is only weakly affected. The relationship between τR and Γ seen among the participants of a recent stratospheric model intercomparison is consistent with this analysis.
Tropospheric reactive odd nitrogen over the South Pacific in austral springtime
Authors: Talbot R. W. , Dibb J. E. , Scheuer E. M. , Bradshaw J. D. , Sandholm S. T. , Singh H. B. , Blake D. R. , Blake N. J. , Atlas E. , Flocke F.
Published: September 2002

The distribution of reactive nitrogen species over the South Pacific during austral springtime appears to be dominated by biomass burning emissions and possibly lightning and stratospheric inputs. The absence of robust correlations of reactive nitrogen species with source‐specific tracers (e.g., C2H2 [combustion], CH3Cl [biomass burning], C2Cl4 [industrial], 210Pb [continental], and 7Be [stratospheric]) suggests significant aging and processing of the sampled air parcels due to losses by surface deposition, OH attack, and dilution processes. Classification of the air parcels based on CO enhancements indicates that the greatest influence was found in plumes at 3–8 km altitude in the distributions of HNO3 and peroxyacetyl nitrate (PAN). Here mixing ratios of these species reached 600 parts per trillion by volume (pptv), values surprisingly large for a location several thousand kilometers removed from the nearest continental areas. The mixing ratio of total reactive nitrogen (the NOy sum), operationally defined in this paper as measured (NO + HNO3 + PAN + CH3ONO2 + C2H5ONO2) + modeled (NO2), had a median value of 285 pptv within these plumes compared with 120 pptv in nonplume air parcels. Particle NO−3 was not included in this analysis of the NOy sum due to its 10‐ to 15‐min sampling time resolution, but, in general, it was <10% of the NOy sum. Comparison of the two air parcel classifications for NOy and alkyl nitrate distributions showed no perceivable plume influence, but recycling of reactive nitrogen may have masked this direct effect. In the marine boundary layer, the NOy sum averaged 50 pptv in both air parcel classifications, being somewhat isolated from the polluted conditions above it by the trade wind inversion. In this region, however, alkyl nitrates appear to have an important marine source where they comprise 20–80% of the NOy sum in equatorial and high‐latitude regions over the South Pacific.
Characterization of aerosols from simulated SAGE III measurements applying two retrieval techniques
Authors: Anderson J. , Brogniez C. , Cazier L. , Saxena V. K. , Lenoble J. , McCormick M. P.
Published: September 2002

We investigated the retrieval of aerosol properties and the extinction due to aerosols at the ozone and water vapor channels from simulated measurements at variations of the planned Stratospheric Aerosol and Gas Experiment (SAGE) III aerosol channels. The aerosol quantities surface area, volume, and effective radius are retrieved through the application of two distinct algorithms in the form of the randomized‐minimization‐search technique (RMST) and the constrained linear inversion (CLI) method. These aerosol quantities are important as inputs in climate, photochemical, and radiative forcing models and are useful in comparing diverse measurements. Ten analytical size distributions fitted to aerosol populations measured in situ are used with a Mie scattering code in conjunction with a Monte Carlo technique to simulate SAGE III measurements. These models consist of variations of prevolcanic and postvolcanic size distributions that exhibit various spectral shapes. Neither the complex components nor the uncertainties of the refractive indices are considered. We developed an objective scheme to estimate the systematic, random, and total uncertainties of each retrieved quantity that considers the contribution of the particles that lie outside the retrieved size range. Results, based on the 10 selected aerosol models, indicate that in the seven‐eight SAGE III channel retrievals, both algorithms obtain estimated total errors in the range 8–50% for the surface area with an average total error (R*) of ∼25%; for the volume the range is 5–25% with an R* of ∼12%, and for the effective radius, the range is 6–36% with an R* of 20% though both inversion techniques are applied in different size ranges. The inversion of the six longest channels to study aerosol properties in both the lower stratosphere and the upper troposphere leads to RMST R* values of ∼32, ∼15, and ∼20% and CLI R* values of ∼48, ∼22, and ∼31% for the surface area, volume, and effective radius, respectively. In the seven wavelength retrievals, both algorithms retrieved the extinction coefficients at the unused channel to within their measurement uncertainties except at the 0.385 and 1.550 μm channels located at the tail ends of the SAGE III aerosol extinction spectrum. The calculated extinction due to aerosols at the water vapor channel at 0.940 μm and the ozone channel at 0.600 μm produced R* values of <10 and <15% for both techniques. We have shown that the application of either technique, when properly tailored to the SAGE III system, not only can obtain useful aerosol information in most cases but also can estimate reasonably the extinction due to aerosols at other wavelengths within the SAGE III wavelength range.
Properties of the 1979 SAM II Antarctic 1.0‐μm extinction coefficients: Implications of dehydration and seasonal evolution of the Antarctic polar vortex
Authors: Wang Pi‐Huan , Kent Geoffrey S. , Powell Kathleen A. , Yue Glenn K. , Poole Lamont R. , McCormick M. Patrick
Published: September 2002

The present study investigates the 1.0‐μm extinction coefficient measurements obtained in the Antarctic region in 1979 from the Stratospheric Aerosol Measurement (SAM) II, with particular focus on the background aerosol properties. Correlative meteorological information from the National Centers for Environmental Prediction is incorporated in this investigation. The results indicate that the data frequency distribution of the background aerosol extinction coefficient in the local summer and fall can be adequately modeled by using a single‐mode normal distribution, and that a binormal distribution is needed for modeling the distribution in the local winter and spring because of the different characteristics of the aerosols inside and outside the polar vortex. In general, the vertical distribution of the aerosol mean extinction coefficient exhibits two regions of different seasonal variation. Above 16 km the extinction coefficient is the highest during the local summer, and the lowest during the local spring inside the polar vortex. Below 16 km the aerosol seasonal variation is more complex, but the winter enhancement of the aerosol extinction coefficient inside the Antarctic polar vortex is clearly evident. As the season changes from winter to spring, the results inside the Antarctic polar vortex also indicate a reduction in aerosol optical depth in the stratosphere, but no significant changes in the upper troposphere. The present study further indicates that the bottom of the winter polar vortex in Antarctica is located at an altitude as low as 8 to 9 km, which is about 4 to 5 km lower than the bottom of the Arctic polar vortex. This difference may be attributable to the different strengths of the winter polar vortex and the planetary wave activities between the two hemispheres. In summary, the properties of the Antarctic background aerosol are very consistent with the effect of polar stratospheric clouds on the aerosol vertical distribution through their formation, sedimention, and evaporation, and with the seasonal evolution of the polar vortex. Finally, the result of the present study provides valuable opportunities for fully utilizing the multiyear SAM II tropospheric and stratospheric measurements to investigate the aerosol climatology and long‐term variations in the Arctic and Antarctic regions.
Mössbauer and thermoluminescence studies of meteorites from Frontier Mountain, Antarctica
Authors: Calogero Sandro , Stievano Lorenzo , Benoit Paul H.
Published: September 2002

Mössbauer and thermoluminescence (TL) data have elucidated the terrestrial histories of five equilibrated chondrites, of petrologic types 5 and 6, collected on blue ice fields near Frontier Mountain in Antarctica. Mössbauer spectroscopy substantially reflects the destruction of iron‐bearing species with formation of finely divided aggregates of iron oxides or oxyhydroxides. TL sensitivity reflects the possible coating of the feldspar grains due to the iron oxide mobility during progressive weathering.
New results and implications for lunar crustal iron distribution using sensor data fusion techniques
Authors: Clark P. E. , McFadden L. A.
Published: September 2002

Remote measurements of the Moon have provided iron maps, and thus essential constraints for models of lunar crustal formation and mare basalt petrogenesis. A bulk crustal iron map was produced for the equatorial region from Apollo gamma‐ray (AGR) spectrometer measurements, and a global iron variation map from recent Clementine spectral reflectance (CSR) measurements. Both iron maps show bimodal distribution, but have significantly different peak values and variations. In this paper, CSR data have been recalibrated to pyroxene in lunar landing site soils. A residual iron map is derived from the difference between AGR (bulk) and recalibrated CSR (pyroxene) iron abundances. The most likely interpretation is that the residual represents ferrous iron in olivine. This residual iron is anticorrelated to basin age, with older basins containing less olivine, suggesting segregation of basin basalt sources from a progressively fractionating underlying source region at the time of basin formation. Results presented here provide a quantitative basis for (1) establishing the relationship between direct geochemical (gamma‐ray, X‐ray) and mineralogical (near‐IR) remote sensing data sets using sensor data fusion techniques to allow (2) simultaneous determination of elemental and mineralogical component distribution on remote targets and (3) meaningful interpretation of orbital and ground‐based spectral reflectance measurements. When calibrated data from the Lunar Prospector mission are available, mapping of bulk crustal iron and iron‐bearing soil components will be possible for the entire Moon. Similar analyses for data from the Near Earth Asteroid Rendezvous (NEAR) mission to asteroid 433 Eros will constrain models of asteroid formation.
Thermal infrared spectroscopy of Europa and Callisto
Authors: Mills Franklin P. , Brown Michael E.
Published: September 2002

The trailing hemispheres of Europa and Callisto were observed at 9–13 μm, and a spectrum of Europa with better spectral resolution and a better signal‐to‐noise ratio than was previously possible has been derived. The ratio spectrum of the two satellites has a signal‐to‐noise ratio of approximately 30 for a spectral resolving power of approximately 50. The disk‐integrated, effective color temperature ratio for the two satellites is consistent with broadband, thermal infrared photometry from previous ground‐based studies and from the Galileo photopolarimeter radiometer. The ratio spectrum was combined with the average Voyager 1 spectrum of Callisto to obtain a 9–13 μm spectrum of Europa with a signal‐to‐noise ratio that is a factor of 10 better than that in the average Voyager spectrum of Europa. After convolving the measured spectrum to the expected width of water ice emissivity features, ∼1 μm, no spectral features that could be attributed to water ice on the surface of Europa are apparent at the 0.6–0.7% level. The absence of spectral features attributable to water ice is consistent with the proposal that the equatorial region of Europa that was observed may be composed primarily of a heavily hydrated mineral. The absence of water ice features may also be the result of a large fractional abundance of fine particles, such as that found on the surface of the Moon.
Noble gas abundance and isotope ratios in the atmosphere of Jupiter from the Galileo Probe Mass Spectrometer
Authors: Mahaffy P. R. , Niemann H. B. , Alpert A. , Atreya S. K. , Demick J. , Donahue T. M. , Harpold D. N. , Owen T. C.
Published: September 2002

The Galileo Probe Mass Spectrometer provided the first data on the noble gas mixing and isotope ratios in the Jovian atmosphere. These measurements and the comparison with solar values constrain models of Jupiter's formation. Significant refinements to the initially reported abundances of argon, krypton, and xenon have been enabled through post‐encounter laboratory calibrations using a refurbished engineering unit mass spectrometer nearly identical to the flight unit. The abundances relative to hydrogen for argon, krypton, and xenon are respectively 2.5±0.5, 2.7±0.5, and 2.6±0.5 times the solar ratios. The mixing ratios of He and Ne found in these studies are consistent with previously reported values of 0.8 and 0.1 times solar respectively. The Jovian 36Ar/38Ar ratio is 5.6±0.25 and the 20Ne/22Ne ratio is 13±2, consistent with the solar values of 5.77 and 13.81, respectively, that are derived from lunar mineral grain analysis. The distribution of xenon isotopes at Jupiter also resembles the solar distribution.
Evolution of a previously thickened thermochemical lithosphere: Application to Venus
Authors: Dupeyrat L. , Ansan V. , Insergueix D.
Published: September 2002

Magellan images have revealed areas with high topography on Venus like Maxwell Montes, interpreted as the result of a lithospheric thickening, associated to a global compressional stress regime. In addition to compressional structures, Maxwell Montes displays younger extensional structures and magmatism at its summit. We present a numerical model to explore the main factors that may explain the chronology of compressional and magmatic events observed on Maxwell Montes. In particular, this study aims to quantify the process of destabilization of a thickened lithosphere by taking into account thermal and chemical instabilities. Indeed, the contribution of basaltic/eclogitic rocks and depleted mantle rocks is not negligible in mantle dynamical models. The initial situation in the upper mantle is represented in a two‐dimensional cartesian domain by a stationary state of thermal convection. The thermal lithosphere is then instantaneously thickened and buoyant tracers of depleted mantle and basalt are placed in the lithospheric mantle and crust, respectively. This material distribution controls both the thermal evolution of the lithosphere and its recycling after thickening. Assuming a continuous and slow basalt/eclogite transformation, the lithosphere acts as an insulating layer during 100 Myr before an effective recycling can occur. For an instantaneous basalt/eclogite transformation, combination of basaltic crust and depleted upper mantle prevents recycling of the lithosphere during the first few millions years. The recycling is all the more enhanced as the basalt transforms to eclogite because it is an ongoing process. It is twice as fast (20 Myr) as the recycling of a purely thermal lithosphere (40 Myr) but the recycled rocks of a thermochemical lithosphere represent less than the recycled rocks of a thermal one because of the great stability of the depleted layer. This results in a thermochemical lithosphere thicker by several tens of kilometers. At an upper mantle scale, this chemical diversity favors the mixing of chemical heterogeneities and the perturbation of internal dynamics. This involves the impingement of a hot depleted diapir at the base of the lithospheric root. For a sufficiently hot mantle, a partial melting zone is trapped inside the lithospheric root and induces magmatism about 80–100 Myr after the lithospheric recycling. This could explain the late volcanic flows observed in Maxwell Montes. Detailed modeling of a thermochemical lithosphere also could explain the formation and evolution of Maxwell Montes as evidenced by volcanic and tectonic features.
Paleoceanographic change during the last deglaciation, east Sea of Korea
Authors: Kim Jung‐Moo , Kennett James P. , Park Byong‐Kwon , Kim Dae Choul , Kim Gil Young , Roark E. Brendan
Published: September 2002

Foraminiferal assemblage and stable isotopic data are presented for three Quaternary piston cores from Ulleung Basin, East Sea of Korea ((ESK) Japan Sea) near the Korean Peninsula. Major changes in both temperature and salinity strongly affected surface and deep waters of the ESK during the transition from the Last Glacial Maximum (LGM) to the middle Holocene. Local environmental effects dominated during the LGM and the Bølling/Allerød (B/A) when the ESK became semi‐isolated from the Pacific Ocean. Regional/global influences dominated following the B/A, after sufficient reconnection with the Pacific. This is reflected in the foraminiferal δ18O record which was largely salinity‐controlled before the Younger Dryas (YD) and temperature‐controlled after the YD. Paleoceanographic changes in the ESK during the last deglaciation reflect sequential reconnection with the Pacific Ocean, through gateways, first (B/A) in the north (Tsugaru Strait) and later (Holocene) in the south (Korea Strait).
Role of increased marine silica input on paleo‐pCO2 levels
Authors: Harrison Kevin G.
Published: September 2002

Changing the supply of silica to the ocean may alter pCO2 levels. The increase in dust delivered to the ocean during glacial times increased the availability of silica for biological uptake. The increased silica levels shifted species composition: Diatom populations increased and coccolith populations decreased. Decreasing the population of coccoliths decreased the flux of calcite to the sediments, which, in turn, lowered pCO2 levels enough to explain the glacial‐interglacial pCO2 transition. Furthermore, the contemporary increase in dust delivered to the ocean's mixed layer may be removing significant amounts of carbon dioxide from the atmosphere at present. To set the stage, this silica hypothesis is compared with the iron fertilization and nitrogen fixation hypotheses.
Evidence for a reduction in the carbonate ion content of the deep sea during the course of the Holocene
Authors: Broecker Wallace S. , Clark Elizabeth , McCorkle Daniel C. , Peng Tsung‐Hung , Hajdas Irena , Bonani Georges
Published: September 2002

The paleo carbonate ion proxy proposed by Broecker et al. [1999] is applied in a search for trends in the Holocene acidity of waters in the transition zone between North Atlantic Deep Water and Antarctic Bottom Water (AABW). A clear signal emerges that the carbonate ion content of waters in this zone declined during the past 8000 years. In order to determine whether this decline represents a strengthening of the northward penetrating tongue of low CO3= content AABW or a global reduction of CO3=ion, measurements were made on a core from the Ontong Java Plateau in the western equatorial Pacific. Evidence for a similar decline in CO3=ion over the course of the Holocene was obtained lending support of the latter explanation. Such a drop is consistent with the recent finding by Indermühle et al. [1999] that the CO2 content of the atmosphere (as recorded in the Taylor Dome Antarctica ice core) rose by 20–25 ppm during the past 8000 years.
A simulation of the Atlantic meridional circulation during Heinrich event 4 using reconstructed sea surface temperatures and salinities
Authors: Paillard Didier , Cortijo Elsa
Published: September 2002

With a simplified two‐dimensionnal Atlantic Ocean model, we investigate the response of the deep ocean circulation to reconstructed sea surface salinity and temperature used as surface boundary conditions at two time slices: just before and during Heinrich event 4. In contrast to previous studies, we do not make any assumption about freshwater input. Our model results suggest that the recorded estimations of surface hydrological changes during an Heinrich event are able to induce a drastic slowdown, or even a collapse, of the overall Atlantic thermohaline circulation. This is, to some extent, consistent with records of the deep sea ventilation at these times.