bluuebunny/crossref_metadata_2025 huggingface dataset:
Dominant wave directions and significant wave heights from synthetic aperture radar imagery of the ocean
Authors: Plant William J. , Zurk L. M.
Published: February 2004

We show that quasi‐linear theory accounts for dominant wave directions observed in synthetic aperture radar (SAR) imagery of the ocean for range‐to‐velocity (R/V) ratios up to 70 s. We also show that when used in combination with Alpers and Hasselmann's [1982] model of signal‐to‐noise ratios in SAR imagery, this theory yields significant wave heights in good agreement with those actually observed. We have found that the apparent dominant wave direction in SAR imagery taken at a 45° incidence angle can differ from the true wave direction by as much as 40° under certain conditions. To understand such differences, we simulated SAR image spectra using quasi‐linear theory, a surface wave spectrum measured by a buoy but with a variable angular spread, coherence times calculated from line‐of‐sight velocity spreads, and modulation transfer functions based on a functional form developed from Bragg scattering theory and data obtained during the SAR X Band Ocean Nonlinearities‐Forschungsplatform Nordsee (SAXON‐FPN) experiment. We carried out these simulations for a 45° incidence angle, L, C, and X bands, both horizontal/horizontal (HH) and vertical/vertical (VV) polarization, three different flight altitudes, and a variety of flight directions to compare the predicted apparent wave directions with those observed in the SAR imagery collected during SAXON‐FPN. The difference between the SAR‐derived dominant wave direction and the one measured by the buoy could be predicted well as a function of the true wave direction relative to the flight direction. The parameters of the quasi‐linear theory that produced the best fit to the directional data differed somewhat from those measured by tower‐based radars during SAXON‐FPN, however. Significant wave heights obtained using the parameters that best fit the directional data were in good agreement with those measured by the buoy. The SAR‐derived wave heights were consistently higher than the measured ones, however, unless the full system bandwidth was used in determining the clutter level, that is, unless bandwidth reductions due to azimuthal presumming and multilook averaging were removed. Finally, the prediction and observation of spectral splitting in SAR spectra of azimuthally traveling waves are also reported.
Modeling the quasi biennial oscillation's influence on isentropic tracer transport in the subtropics
Authors: O'Sullivan Donal , Chen Ping
Published: February 2004

Tracer transport in the lower stratosphere is investigated using an off‐line semi‐Lagrangian transport model and winds from a mechanistic three dimensional middle atmosphere model, interpolated to the 650 K isentropic surface, over a winter season. By comparing two simulations, the effect of the quasi‐biennial oscillation's (QBO's) easterly or westerly wind phases on low‐latitude transport is examined, especially regarding the formation of an apparent subtropical transport barrier at the equatorward edge of the surf zone. The tracer field is diffused less than potential vorticity (PV) and shows sharper gradients and finer structures developing over the winter. In both QBO phases the winter extratropical surf zone is bounded by large tracer gradients equatorward of about 15° latitude. The inability of quasi‐stationary Rossby waves to propagate into QBO easterlies leads to a much sharper edge forming between the rapidly stirred extratropical surf zone and the relatively unstirred tropics during the easterly QBO phase than occurs during the westerly QBO phase. In the westerly phase some Rossby wave activity can propagate across the equatorial westerlies and break on reaching the summer hemisphere easterly winds, causing mixing there. Simulations using a tracer initially confined to the tropics show that more tropical air is mixed out to the winter extratropics by Rossby wave stirring when the QBO phase is easterly, despite the sharper band of stronger tracer (or PV) gradient which separates the tropics and the winter extratropics in this phase. While air was mixed out of the tropics in both QBO phase simulations, neither QBO phase simulation showed extratropical air being irreversibly mixed into the tropics. These results are related to observations of the tropical reservoir of stratospheric aerosols, especially the dynamics and transport of its winter hemisphere boundary.
Cross‐isentropic stratosphere‐troposphere exchange of mass and water vapor
Authors: Yang Hu , Tung Ka Kit
Published: February 2004

Since cross‐isentropic mass fluxes are directly related to net diabatic heating, mass fluxes into the “overworld” across the 385 K and 444 K isentropes are calculated using a comprehensive radiative transfer code. Ozone, methane, water vapor, and nitrous oxide data from instruments aboard the Upper Atmospheric Research Satellite (UARS) and temperature data from United Kingdom Meteorological Office (UKMO) are used for this study. Water vapor budget for the stratosphere is calculated as an independent check on the validity of the calculated mass exchange rate. The total upward mass flux is found to be strongest in northern winter and weakest in northern summer, with an annual mean flux of 73 and 119 × 108 kg/s across the 444 K and 385 K isentropes, respectively, giving a turnover time of 1.6 years for the overworld.
Isotopic measurements of precipitation on central Asian glaciers (southeastern Tibet, northern Himalayas, central Tien Shan)
Authors: Aizen Vladimir , Aizen Elena , Melack John , Martma Tonu
Published: February 2004

The glacial regions of central Asia considered in our study are influenced by tropical monsoons and western extratropical cyclones. Isotopic δ18O and δD data were obtained over 3 years in three climatic regions: Gongga massif of southeastern Tibet (windward slope of summer monsoon), Xixibangma massif on the northern slope of the Himalayas (leeward of summer monsoon), and the massifs of Pobeda‐Khan Tengry in the central Tien Shan (exposed to western airstreams). The survey reported here provides information from atmospheric precipitation, snow pits and a 23 m ice core. The significant differences of oxygen isotopic ratios (from −25.1 per mil to −9.5 per mil) indicate that the Indian and Pacific Oceans as well as the Atlantic Ocean are sources of moisture on the northern slope of the Himalayas and southeastern Tibet. Sharply changing isotopic ratios in precipitation corresponded to changing wind direction and were associated with different sources of air masses on the northern slope of the Himalayas and southeastern Tibet. Steady isotopic ratios in atmospheric precipitation and the absence of changing δ18O composition in a 23 m ice core suggest only one source of moisture in central Tien Shan. The relatively heavier oxygen isotopic ratios in atmospheric precipitation and ice core indicate the moisture from which the precipitation was derived originated over the Caspian or Mediterranean seas. Within the Eurasian continent, air masses developed over the Atlantic Ocean advance farther than those from the Pacific and Indian Oceans.
Simultaneous measurements of stratospheric HOx, NOx, and Clx: Comparison with a photochemical model
Authors: Chance K. , Traub W. A. , Johnson D. G. , Jucks K. W. , Ciarpallini P. , Stachnik R. A. , Salawitch R. J. , Michelsen H. A.
Published: February 2004

We report simultaneous measurements of the stratospheric concentration profiles of OH, HO2, H2O2, H2O, O3, HNO3, NO2, N2O, HCl, HOCl, and ClO during a midlatitude balloon flight in 1989. Measurements were made over almost an entire diurnal cycle by the Smithsonian Astrophysical Observatory Far‐Infrared Spectrometer (FIRS‐2) and the Jet Propulsion Laboratory Balloon Microwave Limb Sounder (BMLS). We analyze these measurements using a photochemical model constrained by observations of long‐lived gases. Measured HOx species (OH and HO2) and H2O2 show fair agreement with theory throughout the diurnal cycle. Measurements of HNO3 are higher than theory near the concentration peak, while the levels of NO2 are consistent with the model at most altitudes. Measurements of ClO and HOCl are less than predicted concentrations, suggesting a source of HCl in addition to the reaction of Cl with CH4. Possibilities for such a source include a minor HCl + O2 product channel for the reaction of ClO with OH and a minor HCl + O3 channel for the reaction of ClO with HO2.
Actinometric and radiometric measurement and modeling of the photolysis rate coefficient of ozone to O(1D) during Mauna Loa Observatory Photochemistry Experiment 2
Authors: Shetter Richard E. , Cantrell Christopher A. , Lantz Kathleen O. , Flocke Siri J. , Orlando John J. , Tyndall Geoffrey S. , Gilpin Timothy M. , Fischer Chris A. , Madronich Sasha , Calvert Jack G. , Junkermann Wolfgang
Published: February 2004

The in situ photolysis rate coefficient of O3 to O(1D) has been measured at Mauna Loa Observatory using a new actinometric instrument based on the reaction of O(1D) with N2O and with a hemispherical radiometer. One minute averaged photolysis rate coefficients were determined with an overall uncertainty of approximately ±11% at the 1 σ level for the actinometer and ±15% at the 1 σ level for the radiometer. Over 120 days of data were collected with varying cloud cover, aerosol loadings, and overhead ozone representing the first set of long term measurements. Clear sky solar noon values vary between approximately 3.0 × 10−5 and 4.5 × 10−5 sec−1. Modeling of the photolysis rate coefficients was done using a discrete ordinate radiative transfer scheme and results were compared with the actinometric measurements. The quantum yields for O(1D) production are reevaluated from existing data and reported here. The comparisons were done using the quantum yields for the photolysis of ozone recommended by DeMore et al. [1994], the newer evaluation of Michelsen et al. [1994], and also with reevaluated values in this paper. An analysis of the measured photolysis rate coefficient of O3 to O(1D) and model simulations of the photolysis rate coefficient data from clear days during the study provides added insight into the choice of quantum yield data for use in photochemical models of the troposphere.
UV controlling factors and trends derived from the ground‐based measurements taken at Belsk, Poland, 1976–1994
Authors: Krzyścin Janusz W.
Published: February 2004

Monthly means of UV erythemal dose at ground level from the Robertson‐Berger (RB) sunburn meter (1976–1992) and the UV‐Biometer model 501 MED meter (1993–1994) located at Belsk (21°E, 52°N), Poland, are examined. The monthly means are calculated from all‐sky daily means of UV erythemal dose. Ancillary measurements of column ozone (by Dobson spectrophotometer), sunshine duration (by Campbell‐Stokes heliograph), and total (sun and sky) radiation (by a pyranometer) are considered to explain variations in the UV data. A multiple regression model is proposed to study trends in the UV data. The model accounts for the UV erythemal dose changes induced by total ozone, sunshine duration (surrogate for cloud cover variations), or total solar radiation (surrogate for combined cloud cover and atmospheric turbidity impact on the UV radiation), trends due to instrument drift, step changes in the data, and serial correlations. A strong relationship between monthly all‐sky UV erythemal dose changes and total ozone (and total solar radiation) is found. Calculations show that an erythemal radiative amplification factor (RAF) due to ozone under all skies is close to its clear‐sky value (about 1). However, the model gives evidence that the RAF due to ozone is smaller for cloudier (and/or more turbid) atmospheres than long‐term reference. Total solar radiation change of 1% is associated with a change of 0.7% in the UV erythemal dose. Modeled trends in the Belsk's UV data, inferred from the model using ozone and total solar radiation as the UV forcing factors, are 2.3% ± 0.4% (1σ) per decade in the period 1976–1994. The large increase in the UV erythemal dose, of the order of 4% per decade due to ozone depletion (−3.2% per decade), is partially compensated by a decreasing tendency (−2.8% per decade) in total solar radiation. The model estimates the trend in the UV data of the order of 0.1% per decade (not statistically significant) due to superposition of the instrument drift and long‐term effects related to other UV influencing factors (not parameterized by the model).
Quantifying the effect of oxidation on landfill methane emissions
Authors: Czepiel P. M. , Mosher B. , Crill P. M. , Harriss R. C.
Published: February 2004

Field, laboratory, and computer modeling methods were utilized to quantitatively assess the capability of aerobic microorganisms to oxidize landfill‐derived methane (CH4) in cover soils. The investigated municipal landfill, located in Nashua, New Hampshire, was operating without gas controls of any type at the time of sample collection. Soil samples from locations of CH4 flux to the atmosphere were returned to the laboratory and subjected to incubation experiments to quantify the response of oxidation in these soils to temperature, soil moisture, in situ CH4 mixing ratio, soil depth, and oxygen. The mathematical representations of the observed oxidation reponses were combined with measured and predicted soil characteristics in a computer model to predict the rate of CH4 oxidation in the soils at the locations of the measured fluxes described by Czepiel et al. [this issue]. The estimated whole landfill oxidation rate at the time of the flux measurements in October 1994 was 20%. Local air temperature and precipitation data were then used in conjunction with an existing soil climate model to estimate an annual whole landfill oxidation rate in 1994 of 10%.
Nonlinearities in the gas phase chemistry of the troposphere: Oscillating concentrations in a simplified mechanism
Authors: Poppe D. , Lustfeld H.
Published: February 2004

The nonlinear coupling of atmospheric trace constituents can, at least in principle, cause concentrations to oscillate with time. This is demonstrated for a simplified scheme encompassing only the tropospheric gas phase chemistry of CO, O3, HOx, and NOx. Oscillating concentrations with a common period of about 33 days were found for all chemical compounds under the forcing by time independent sources for CO and NO. Linear stability analysis shows that the periodic solution is locally stable. The periodicity is found for a large domain of NO and CO source strengths. The presence of methane destroys the oscillation. This finding limits the applicability for problems of the real atmosphere. The source strengths of NO and CO necessary to produce undamped oscillations in the model are much larger than the corresponding globally averaged source strengths. In the polluted boundary layer, however, the source strengths of NO and CO could very well be encountered. Evaluation of the Lyapunov exponents and of the dependence on the initial conditions indicates that the periodic solution is attained independent of the initial conditions, usually within a few days. Thus even if the meteorological and source strength conditions do not persist for the time of a whole period, parts of it may still be observable.
Estimation of angular distribution models from radiance pairs
Authors: Green Richard N. , Hinton Patricia O'Rawe
Published: February 2004

A new approach to constructing angular distribution models (ADMs) from satellite data has been developed. The ADMs model the radiance anisotropy and are used to convert satellite measured radiance to flux at the top of the atmosphere. The radiance pairs method (RPM) processes radiance pairs that view approximately the same area at the same time. By ratioing the paired radiances, the flux or field strength is eliminated, producing ratios of anisotropies which are taken as the data source for the ADMs. The ADMs are modeled as random functions, and the RPM estimates the mean of the ADM. The RPM is compared to the standard method of sorting by angular bins (SAB) and is shown to remove questionable assumptions, converge faster, and give better accuracy than the SAB method. Both methods were applied to the same Nimbus 7 ERB data and resulted in statistically different longwave ADMs.
Model studies of chlorine deactivation and formation of ClONO2 collar in the Arctic polar vortex
Authors: Chipperfield M. P. , Lutman E. R. , Kettleborough J. A. , Pyle J. A. , Roche A. E.
Published: February 2004

We have investigated the processes which lead to the deactivation of active chlorine (ClO+2Cl2O2) and the formation of ClONO2 in and around the Arctic polar vortex. By using a range of three‐dimensional and trajectory models, forced by meteorological analyses for the 1991/1992 winter, we have been able to separate processes associated with the model formulation and resolution, from true chemical processes. The rate of ClO deactivation can be overestimated in a three‐dimensional model due to numerical diffusion from a poor transport scheme or to low resolution. In our experiments we found that vertical resolution is at least as important as horizontal resolution. The use of isentropic levels reduced the spurious vertical mixing by providing a true separation between horizontal and vertical motion. Increasing the horizontal resolution of the model reduced mixing and produced a sharper, narrower ClONO2 collar region with slightly higher maximum values. The domain‐filling trajectories produce a ClONO2 collar structure with no mixing between parcels. These results show that it is in situ chemical deactivation of ClO and not mixing which produces the ClONO2 collar. Results from the high‐resolution isentropic simulations and domain‐filling trajectories have been compared with Cryogenic Limb Array Etalon Spectrometer data and diagnosed for the chemical cause of ClO deactivation. The models generally reproduce the observed features of the collar region but underestimate the highest ClONO2 mixing ratios. As the polar lower stratosphere is heavily denoxified the cause of the ClONO2 recovery is release of NO2 from HNO3. For this process, reaction of HNO3 with OH can be as important as photolysis at high solar zenith angles.
Airborne heterodyne measurements of stratospheric ClO, HCl, O3, and N2O during SESAME 1 over northern Europe
Authors: de Valk J. P. J. M. M. , Goede A. P. H. , de Jonge A. R. W. , Mees J. , Franke B. , Crewell S. , Küllmann H. , Urban J. , Wohlgemuth J. , Chipperfield M. P. , Lee A. M.
Published: February 2004

Vertical distributions of ClO, HCl, N2O, and O3 have been retrieved from airborne observations of pressure‐broadened emission spectra in the frequency range of 620 to 690 GHz. Observations were made in February 1994 in the Arctic stratosphere above northern Europe with the Airborne Submillimeter SIS Radiometer (ASUR) during the Second European Stratospheric Arctic and Mid‐latitude Experiment (SESAME) 1 campaign. ASUR is the first airborne submillimeter experiment to employ the new superconductor‐insulator‐superconductor (SIS) receiver technology for stratospheric ozone research. Owing to meteorological conditions, all observations were made outside the polar vortex. The retrieved volume mixing ratio (VMR) profiles show a good agreement with observations made by the submillimeter limb sounder (SLS) operated by the Jet Propulsion Laboratory (JPL) (Pasadena) and the Kern Forschungs Anlage (KFA) (Jülich). A comparison between retrieved VMR profiles and profiles obtained from the SLIMCAT three‐dimensional stratospheric chemistry model also shows a good agreement. Two ClO emission lines, at 649 and 686 GHz, respectively, are shown to be equally adequate lines for observation purposes. An anticorrelation has been found between the N2O and HCl VMR values, and also between the N2O and ClO VMR values. The correlations between N2O and HCl do not show the relatively low HCl VMR values correlated to relatively low N2O values as shown by Webster et al. [1994].
Examining the relationship among atmospheric aerosols and light scattering and extinction in the Grand Canyon area
Authors: Malm William C. , Molenar John V. , Eldred Robert A. , Sisler James F.
Published: February 2004

During the winter and summer months of 1990 a special study called Project MOHAVE (measurement of haze and visual effects) was carried out with the principle objective of attributing aerosol species to extinction and scattering and the aerosol species to sources and/or source regions. The study area included much of southern California and Nevada, Arizona, and Utah; however, the intensive monitoring sites and primary focus of the study was on the Colorado Plateau of northern Arizona, southern Nevada, and Utah. This paper reports on the apportionment of various aerosol species to measured fine and coarse mass concentrations and these species to scattering and extinction. The study is unique in that a number of “ambient” integrating nephelometers were operated to measure the ambient scattering coefficient, while transmissometers were used to measure atmospheric extinction. Comparison of measured scattering, extinction, and aerosol species concentration, both statistically and theoretically, allows for an estimate of scattering and absorption efficiencies. Analysis suggests that using elemental carbon, derived from thermal optical techniques, to estimate absorption may significantly underestimate absorption. Using elemental carbon, absorption is estimated to be 5% of extinction, while direct measurements of absorption suggest that it is about 30% of measured extinction. Furthermore, because light absorption by soil is usually not accounted for, soil extinction is underestimated by about 30%.
Lifetime and emission estimates of 1,1,2‐trichlorotrifluorethane (CFC‐113) from daily global background observations June 1982–June 1994
Authors: Fraser P. , Cunnold D. , Alyea F. , Weiss R. , Prinn R. , Simmonds P. , Miller B. , Langenfelds R.
Published: February 2004

Observations every two hours of CCl2FCClF2 at Mace Head, Ireland (February 1987–June 1994); Cape Meares, Oregon (April 1984–June 1989); Ragged Point, Barbados (October 1985–June 1994); Cape Matatula, Samoa (October 1985–June 1989 and January 1992–June 1994); and Cape Grim, Tasmania (June 1982–June 1994) are reported. The observations from Cape Grim have been extended back to 1978 using archived air samples. The global atmospheric abundance of CCl2FCClF2 is indicated to have been growing exponentially between 1978 and 1987 with an e‐folding time of approximately 7.6 years; it has been growing less rapidly since that time. On January 1, 1994, the mean inferred northern hemispheric mixing ratio in the lower troposphere was 84.4 ± 0.4 ppt and the southern hemispheric value was 80.6 ± 0.4 ppt; the global growth rate in 1991–1993 is estimated to have averaged approximately 3.1 ± 0.1 ppt/year. The differences between the northern and southern hemispheric concentrations are calculated to be consistent with the almost entirely northern hemispheric release of this gas. The annual release estimates of CCl2FCClF2 by industry, which include estimates of eastern European emissions, fairly consistently exceed those deduced from the measurements by approximately 10% from 1980 to 1993. The uncertainties in each estimate is approximately 5%. This difference suggests that up to 10% of past production might not yet have been released. The measurements indicate that atmospheric releases of CCl2FCClF2 have been decreasing rapidly since 1989 and in 1993 amounted to 78 ± 27 × 106 kg or 42 ± 15% of the 1985–1987 emissions.
Interpretation of nitric oxide profile observed in January 1992 over Kiruna
Authors: Kondo Y. , Kawa S. R. , Lary D. , Sugita T. , Douglass Anne R. , Lutman E. , Koike M. , Deshler T.
Published: February 2004

NO mixing ratios measured from Kiruna (68°N, 20°E), Sweden, on January 22, 1992, revealed values much smaller than those observed at midlatitude near equinox and had a sharper vertical gradient around 25 km. Location of the measurements was close to the terminator and near the edge of the polar vortex, which is highly distorted from concentric flow by strong planetary wave activities. These conditions necessitate accurate calculation, properly taking into account the transport and photochemical processes, in order to quantitatively explain the observed NO profile. A three‐dimensional chemistry and transport model (CTM) and a trajectory model (TM) were used to interpret the profile observations within their larger spatial, temporal, and chemical context. The NOy profile calculated by the CTM is in good agreement with that observed on January 31, 1992. In addition, model NOy profiles show small variabilities depending on latitudes, and they change little between January 22 and 31. The TM uses the observed NOy values. The NO values calculated by the CTM and TM agree with observations up to 27 km. Between 20 and 27 km the NO values calculated by the trajectory model including only gas phase chemistry are much larger than those including heterogeneous chemistry, indicating that NO mixing ratios were reduced significantly by heterogeneous chemistry on sulfuric acid aerosols. Very little sunlight to generate NOx from HNO3 was available, also causing the very low NO values. The good agreement between the observed and modeled NO profiles indicates that models can reproduce the photochemical and transport processes in the region where NO values have a sharp horizontal gradient. Moreover, CTM and TM model results show that even when the NOy gradients are weak, the model NO depends upon accurate calculation of the transport and insolation for several days.
A critical analysis of Stratospheric Aerosol and Gas Experiment ozone trends
Authors: Wang H. J. , Cunnold D. M. , Bao X.
Published: February 2004

A latitudinally dependent reference height error in Stratospheric Aerosol and Gas Experiment (SAGE) I ozone profiles is inferred from two separate analyses: first, by essentially comparing the mean height of the stratospheric ozone layer between SAGE I and SAGE II measurements and second, by examining SAGE I/II differences above the ozone peak using solar backscattered ultraviolet (SBUV) profiles as transfer standards. Both approaches yield a reference height error in the tropics of approximately 200 m and midlatitude errors of approximately 400 m. Comparisons between SAGE II and SBUV measurements also suggest that SAGE II ozone concentrations are too small at altitudes above approximately 40 km for a few days following high beta angle conditions and that anomalous differences, related to SAGE II, exist in several Januaries. When these periods are filtered out, the SAGE I measurements are corrected for the reference height errors, and the SAGE II measurements are corrected for aerosol interference [Cunnold et al., 1996a], the SAGE I/II ozone trends are found to be in good agreement with the SBUV and total ozone mapping spectrometer trends and with the Hohenpeissenberg ozonesonde results. The SAGE I/II deduced ozone trend from 1979 to 1991 shows an almost negligible ozone loss in the tropical upper stratosphere but an increasingly negative trend, with latitude maximizing at − 1.2%/yr at 2 mbar at 60°S (the highest latitude reported). In the lower stratosphere, decreases of approximately 1%/yr are reported at 68 mbar, and the column ozone decreases at midlatitudes are almost all related to losses below 30 mbar. In the tropics, SAGE I/II suggests stratospheric ozone losses of approximately 0.2%/yr. The solar cycle ozone dependence in the upper stratosphere is less than that previously reported in SBUV analyses, with a local maximum response in the ozone concentration of approximately 3% at midlatitudes at approximately 41 km altitude. In the lower stratosphere, SAGE results confirm previous reports of a sensitivity of approximately a 1.5% change over the solar cycle but indicate that this change is mostly occurring just below the ozone concentration peak.
Concurrent measurements of black carbon aerosol and carbon monoxide at Mace Head
Authors: Jennings S. G. , Spain T. G. , Doddridge B. G. , Maring H. , Kelly B. P. , Hansen A. D. A.
Published: February 2004

Continuous measurements of white light attenuation (ATN) through a quartz fiber filter (related to aerosol black carbon content) and of carbon monoxide (CO) carried out over the period December 1991 through July 1992 at the Mace Head atmospheric field research station (53°19′N, 9°54′W) near Carna, County Galway on the west coast of Ireland are presented. Isentropic air flow back trajectories, condensation nuclei concentration data, and meteorological data were generated as part of the Atmosphere/Ocean Chemistry Experiment. Use is made of this supporting data together with synoptic weather charts in the analysis of the measurements. Measurements of ATN and CO are reported for unmodified marine air from the North Atlantic which yield ATN and ATN/CO values in the range 1–4 × 10−3 m−3 and 1–4 × 10−5 m−3 ppbv−1. Increasing values of ATN and ATN/CO are obtained for polluted transatlantic air, modified marine air, and polluted air from the UK and/or Europe. The covariance of ATN and CO obtained for these air masses suggests a common source. Transport of air from west of the African Saharan region to Mace Head is accompanied by a rise in optical attenuation purported to be due to absorbing desert dust aerosol without a concurrent rise in CO.
Ice flow and mass continuity of Shumsky Glacier in the Djungarski Alatau Range of Kazakhstan, Central Asia
Authors: Cherkasov Piotr A. , Ahmetova Galia S. , Hastenrath Stefan
Published: February 2004

The glaciological monitoring program on the Shumsky Glacier in the Djungarski Alatau Range of southeastern Kazakhstan has included measurements of horizontal surface ice flow velocity, net balance, and emergence velocity at a network of more than 200 stakes during 1967–1991, as well as mappings of the ice surface topography by double‐theodolite triangulation and determination of ice thickness and of bedrock topography by radio echo sounding in 1984. These observations are here evaluated together to deduce the long‐term average dynamic behavior of Shumsky Glacier. The glacier extends between 3100 and 4400 m with a total area of 3 km2 and length of nearly 4 km. Maximum surface velocity is 20 m yr−1 and maximum volume flux 9 × 105 m3 yr−1, located near the equilibrium line altitude around 3680 m. The ice‐volume‐equivalent net balance is +0.5 m yr−1 in the average over the accumulation area, changing to about −1.5 m yr−1 near the terminus. The submergent flow in the accumulation area changes to emergence of 1 m yr−1 in the lower glacier. The rate of ice thinning is less than 0.1 m yr−1 in the middle glacier, increases to 2.5 m yr−1 near the terminus, and averages 0.12 m yr−1 for the glacier as whole. In fact, the Shumsky glacier differs little from equilibrium, being in a more favorable location that the other glaciers of the Djungarski Alatau. However, trends toward slower ice flow, more negative net balance, and faster rate of ice thinning indicate response to a progressively adverse climatic environment.
Aircraft section measurements of meteorology and ozone in northern Namibia during SAFARI‐92
Authors: Jury Mark R. , Brunke Ernst , Schormann Mark
Published: February 2004

Ozone and meteorological data obtained via instrumented aircraft surveys over tropical southwestern Africa in the period October 8–12, 1992, are analyzed as part of the international Southern African Fire‐Atmosphere Research Initiative (SAFARI) program. Twice‐daily aircraft flights recorded measurements of wind, turbulence, temperature, dewpoint, and ozone at 1 Hz from 1–12 km in a series of successive profiles extending from 12° to 24°E along 18°S latitude. Wind patterns derived from aircraft and the European Centre for Medium‐Range Weather Forecasts (ECMWF) highlight a quasi‐permanent anticyclone in the midtroposphere over central southern Africa. Light meridional flow prevailed in the 3–7 km layer. Ozone values were in the range 40–60 parts per billion by volume (ppbv) from 1 to 4 km across the aircraft section and <20 ppbv in the surface marine layer off the west coast. In the continental air, ozone increased with height to 90 ppbv above 7 km. As a dry trough passed eastward, ozone values declined 30% in the layer above 4 km. Aircraft results indicate the presence of a potential recirculation mechanism around the midtropospheric anticyclone. Recirculation would facilitate photochemical reduction to ozone of regional pyrogenic emissions, following vertical mixing by turbulent diurnal heating. A persistent dry stable layer from 6 to 9 km may accumulate pollutants over tropical southern Africa, while upper westerly troughs could eject some of the continental air eastward.
An overview of the Tropospheric OH Photochemistry Experiment, Fritz Peak/Idaho Hill, Colorado, fall 1993
Authors: Mount George H. , Williams Eric J.
Published: February 2004

An extensive study of tropospheric photochemical trace species, including the hydroxyl radical OH was conducted in the Colorado Rocky Mountains from early August to early October 1993. Many of the parameters that influence the abundance of OH in the atmosphere, including j(O3 and NO2), formaldehyde, nonmethane hydrocarbons, NOx, ozone, H2O, aerosols, and others, were measured simultaneously with OH. Instrumentation for measurement of OH included a long‐path spectroscopic technique and several in situ techniques: ion‐assisted mass spectrometry, laser‐induced resonance fluorescence, and a liquid scrubber/liquid chromatographic method. Instrument comparisons between long‐path and in situ measurements were conducted for OH, O3, CH2O, NO2, and H2O, and these measurements provide a valuable insight into the chemistry of the region. The complete data set provided a robust set of inputs to a zero‐dimensional model for exploring OH photochemistry. Independently measured OH concentrations were in agreement within one standard error much of the time, thus giving confidence that hydroxyl is being measured correctly. OH concentrations were typically low during clean continental airflow with concentrations rarely above 4×106 cm−3. During occasions of polluted airflow from the Denver‐Boulder metropolitan areas, values of OH rose as high as 1.2×107 cm−3. The nearly complete suite of trace gases measured simultaneously with the hydroxyl radical severely constrained the models and provided numerous opportunities to compare relations between species (e.g. OH versus NOx, OH/HO2, RO2 versus NOx). Modeled hydroxyl results using the complete species suite were about a factor of 1.5 higher than measured OH concentrations suggesting that the photochemistry may not be well understood. The campaign data provide new insights into the chemistry of the lower troposphere. This paper provides an overview of the campaign and brief descriptions of results from individual experiments. Details are provided in the accompanying papers in this issue.
Photochemical trajectory modeling studies of the North Atlantic region during August 1993
Authors: Wild Oliver , Law Katharine S. , McKenna Daniel S. , Bandy Brian J. , Penkett Stuart A. , Pyle John A.
Published: February 2004

A Lagrangian photochemical trajectory model has been used to assess the factors affecting O3 production during transport of polluted air masses across the North Atlantic Ocean. Sensitivity studies have been performed along idealized trajectories, and it is found that the potential impact of North American emission sources is maximized by transport of air at high altitudes, in drier conditions and in conditions where mixing of the air with background air masses is relatively limited. Measurements taken from the NCAR King Air aircraft as part of the North Atlantic Regional Experiment (NARE) August 1993 intensive have been used to initialize forward trajectories, calculated using European Centre for Medium‐Range Weather Forecasting analyzed wind fields, from eastern North America to assess O3 production over the Atlantic during this period. The effects of dilution of a polluted air parcel with air from the upper troposphere have also been studied, and the contribution of photochemical O3 production to the air mass composition is found to be smaller than that of dilution, particularly for long trajectories and for conditions where dilution is relatively rapid or involves air from the stratosphere. Measurements taken from the Meteorological Research Flight Hercules aircraft over the eastern Atlantic as part of the Oxidizing Capacity of the Tropospheric Atmosphere campaign have been examined in the light of these studies. A backward trajectory analysis has been performed from one of the vertical profiles taken off the coast of Portugal on August 31, 1993, to assess the origin of the different air masses intercepted. While the lower levels are characteristic of air from the European boundary layer advected over the ocean, the upper levels show strong evidence for anthropogenic influence from North American sources, with elevated levels of O3, NOy, CO, and aerosol. Although it cannot be concluded that this air mass definitely originated from over North America, the measured concentrations are shown to be consistent with those for an air mass from this source region experiencing some mixing with air masses in the upper troposphere.
The effect of dynamical mixing in a simple model of the ozone hole
Authors: Edouard S. , Legras B. , Zeitlin V.
Published: February 2004

The role of the horizontal dynamical mixing on the ozone destruction by chlorine in the polar stratosphere is investigated. We use a one‐dimensional high‐resolution model to represent the microstructure of chemical species distribution on which the effective reactivity depends. The chemical model is idealized by only considering two species, ozone and chlorine (assumed to be under the active form ClO). Ozone destruction is proportional to the square of chlorine content. We compare the effects of a chaotic type of mixing, represented as a Bernoulli map over the unit interval, with purely diffusive mixing, which is used in most parameterizations of turbulence. The comparison is done for various values of the chemical reactivity constant. Owing to the nonlinearity of the chemical reaction, reactivity decreases with mixing if the chemical constant is small, while it increases with mixing for large values of the chemical constant. In any situation, large discrepancies in the ozone destruction are observed between chaotic and diffusive mixing, indicating the need for a better representation of the mixing processes in studies of stratospheric chemistry.
Chemical composition of single aerosol particles at Idaho Hill: Positive ion measurements
Authors: Murphy D. M. , Thomson D. S.
Published: February 2004

The chemical compositions of single aerosol particles larger than 0.3 μm optical diameter were measured at Idaho Hill using a laser ionization mass spectrometer. The mass spectrometer can analyze either positive or negative ions; this paper covers the positive ion results. Potassium, iron, and organics were among the most common positive ions in the spectra of particles at Idaho Hill. Organic ions were the largest contributor to the ion current from accumulation mode particles and were also significant in larger particles. Iron was present mostly in coarse mode particles. Potassium was bimodal, with large amounts of K in coarse mode particles and large amounts in particles near 0.3 μm in west winds but not in east winds. Boron was observed in a number of particles. A wide variety of metals were also observed including lead, tin, and vanadium. Lead was less common in polluted air. Silver, copper, zinc, nickel, molybdenum, rhenium, and thallium were also observed in a few particles. Ammonium ions and cluster ions were more abundant in upslope conditions. Amines seem to be evident in many of the spectra, especially in east winds. Elemental carbon was observed in 2 to 3% of the particles. Almost all of the particles contained some nonvolatile material.
Atmospheric non‐sea‐salt sulfate, nitrate and methanesulfonate over the China Sea
Authors: Gao Y. , Arimoto R. , Duce R. A. , Chen L. Q. , Zhou M. Y. , Gu D. Y.
Published: February 2004

To characterize atmospheric particulate non‐sea‐salt (nss) sulfate, nitrate, methanesulfonate (MSA), and selected trace elements over the China Sea, aerosol sampling was conducted at Qingdao and Xiamen, which are on the coast of China, and over offshore regions of the East China Sea. The atmospheric concentrations of nss sulfate and nitrate were much higher along the coast of the China Sea than over remote oceans, with mean values of 10 to 12 μg m−3 for nss sulfate and 5.6 to 7.7 μg m−3 for nitrate. The mean concentrations of atmospheric MSA ranged from 0.029 to 0.066 μg m−3 over the China Sea; these are comparable to values from other coastal sites and remote oceans. Both MSA and nss sulfate are concentrated in particles ≤0.5 μm in diameter, while nitrate shows a bimodel distribution. There was no clear correlation between nss sulfate and MSA concentrations, with the ratios of nss sulfate to MSA (60–870) being substantially higher than those over remote oceans. Based on a biogenic nss‐sulfate/MSA ratio of 18 obtained from the remote North Pacific, the estimated anthropogenic sulfate accounts for 81–97% of the total nss sulfate over the China Sea. Results of factor analyses suggest that coal combustion is the dominate source for anthropogenic sulfate over the basin of the China Sea. Oil combustion appears to be an additional important contributor for anthropogenic sulfate in the region of the East China Sea, but this feature does not exist in the South China Sea region. Pyrometallurgical nonferrous metal smelting is among the additional sources for nss sulfate in this region.
Meteorological mechanisms for transporting O3 over the western North Atlantic Ocean: A case study for August 24–29, 1993
Authors: Moody J. L. , Davenport J. C. , Merrill J. T. , Oltmans S. J. , Parrish D. D. , Holloway J. S. , Levy H. , Forbes G. L. , Trainer M. , Buhr M.
Published: February 2004

A large‐scale view of O3 transport over the western North Atlantic Ocean (WNAO) in summer illustrates distinct sources of O3, and separate transport mechanisms are important at different vertical levels in the troposphere. The week‐long period presented covers a sequence of O3 sondes released from Bermuda and encompasses two surface O3 events in the month‐long NARE intensive. O3 and CO peaked at Chebogue Point on the evening of August 25 and after midnight on the morning of August 28. At Sable Island, peaks occurred during early morning of August 26 and late morning of August 28. These events occurred under W‐SW winds associated with advancing low‐pressure systems that transported anthropogenic pollutants over the WNAO. The concentrations dropped with the passage of a trough or a cold front. Evidence suggests the surface was occasionally isolated from polluted air during favorable transport with pollutants lifted in warm sector flow riding over a wedge of cool, thermodynamically stable air. In addition to surface O3, the O3‐sonde profile over Bermuda on the morning of August 27 showed a deep layer of O3 from 6 to 12 km. Using back trajectories and two tracers (isentropic potential vorticity and water vapor), we illustrate that stratospheric ozone exchanged into the upper troposphere in conjunction with surface cyclogenesis was advected through the middle to upper troposphere over the midlatitudes with the potential to reach lower altitudes through subsidence in regions of anticyclonic motion.
Analysis of UARS data in the southern polar vortex in September 1992 using a chemical transport model
Authors: Chipperfield M. P. , Santee M. L. , Froidevaux L. , Manney G. L. , Read W. G. , Waters J. W. , Roche A. E. , Russell J. M.
Published: February 2004

We have used a new, isentropic‐coordinate three‐dimensional chemical transport model to investigate the decay of ClO and evolution of other species in the Antarctic polar vortex during September 1992. The model simulations cover the same southern hemisphere period studied in a companion data paper by Santee et al. [this issue]. The model is initialized using the available data from the Microwave Limb Sounder (MLS) and Cryogenic Limb Array Etalon Spectrometer (CLAES) on the Upper Atmosphere Research Satellite (UARS). During the model initialization chemical inconsistencies in the UARS data became evident. Fields of odd nitrogen (NOy) derived from CLAES N2O underestimated the sum of the direct observations of the major NOy species. Results from the model integrations at 465 K and 585 K are sampled in the same way as the various UARS instruments and compared to the observations both directly and by considering average quantities in the inner and edge vortex regions. Sampling the observed species in the same way as the UARS instruments is important in removing any spurious trends due, for example, to changing solar zenith angle. While the model can reproduce the magnitude of the MLS ClO observations at 585 K, this is not possible at 465 K. The model partitions too much ClO into Cl2O2 to reproduce the observed ClO which is around 2.0 parts per billion by volume (ppbv) averaged within the polar vortex. The model also underestimates CLAES ClONO2 in the inner vortex at 465 K due to heterogeneous processing. The observations require that effectively all of the inorganic chlorine is in the form of ClO and ClONO2 in the inner vortex at this altitude. In the basic model run, the decay of ClO produces ClONO2 which is not observed by CLAES. Our results indicate the potential importance of the speculative reaction between OH and ClO producing HCl for the recovery of HCl in the Antarctic spring. By including this reaction, the decay of model ClO into HCl is enhanced, yielding better agreement with HCl data from the Halogen Occultation Experiment (HALOE) data. Similar results can also be obtained by including the reaction between HO2 and ClO to produce HCl with a 3% channel. The model generally reproduces the observed O3 destruction during September. The most significant discrepancy for O3 is in the inner vortex at 465 K where the model underestimates the observed O3 loss rate, especially when the effects of vertical motion are included.
Ground‐based measurements of NOx and total reactive oxidized nitrogen (NOy) at Sable Island, Nova Scotia, during the NARE 1993 summer intensive
Authors: Wang T. , Carroll M. A. , Albercook G. M. , Owens K. R. , Duderstadt K. A. , Markevitch A. N. , Parrish D. D. , Holloway J. S. , Fehsenfeld F. C. , Forbes G. , Ogren J.
Published: February 2004

Measurements of NO, NO2, and total reactive oxidized nitrogen (NOy) were added to ongoing measurements of aerosols, CO, and O3 at Sable Island (43°55′N, 60°01′W), Nova Scotia, during the North Atlantic Regional Experiment (NARE) 1993 summer intensive. Ambient levels of NOx and NOy were found to be highly variable, and elevated levels can be attributed to the transport of polluted continental air or presumably to relatively fresh emissions from sources upwind (e.g., ship traffic). The median values for NOx and NOy are 98 and 266 parts per trillion by volume (pptv), respectively. A multiday pollution episode occurred during which elevated NOx and NOy were observed with enhanced levels of O3, CO, and condensation nuclei. Air masses of recent tropical marine origin characterized by low and constant levels of O3 and CO were sampled after Hurricane Emily. The correlation between ozone and CO is reasonably good, although the relation is driven by the single pollution episode observed during the study. The correlation of O3 with NOy and with NOy‐NOx is complicated by the presumed NOy removal processes in the marine boundary layer. Examination of the radiosonde data and comparisons of the surface data with those obtained on the overflying aircraft provide clear indications of vertical stratification above the site.