bluuebunny/crossref_metadata_2025 huggingface dataset:
A method for estimating the extent of denitrification of arctic polar vortex air from tracer‐tracer scatter plots
Authors: Esler J. G. , Waugh D. W.
Published: October 2002

A method for estimating the extent of denitrification of Arctic polar vortex air is proposed. Previous estimates of denitrification using tracer‐tracer scatter plots have not allowed for mixing‐induced changes in tracer‐tracer relationships in a sufficiently general way. This difficulty is overcome by constructing an artificial “reference tracer” from a linear combination of other long‐lived tracers. The reference tracer is designed so that, as far as possible, it has a linear canonical relationship with NOy in midlatitudes. A linear relationship is unaffected by mixing, so denitrification is apparent as deviations of vortex measurements from the linear midlatitude relationship. The method is first demonstrated using data from a chemical transport model in which no denitrification processes are present. It is then applied to balloon, aircraft and shuttle‐borne measurements made before and during the breakdown of the Arctic vortex in 1992–1993 and 1996–1997. In each case the method indicates that little or no denitrification had occurred in any of the vortex air encountered. When the method is applied to the southern hemisphere vortex in 1994, by contrast, denitrified air is clearly seen to be present around 19–23 km in the vortex.
Evaluation of inlets used for the airborne measurement of formaldehyde
Authors: Wert B. P. , Fried A. , Henry B. , Cartier S.
Published: October 2002

The performance of three aircraft inlets used for sampling gas‐phase formaldehyde (CH2O) was evaluated. These 1.5 m long inlets were operated with the National Center for Atmospheric Research Tunable Diode Laser Absorption Spectrometer (TDLAS) at flow rates between 7 and 9 standard liters per minute. Laboratory tests were performed on the 1997 North Atlantic Regional Experiment (NARE 97) TDLAS inlet, involving a wide range of sample temperatures (−40° to 25°C), pressures (250–625 torr), relative humidities (<1 to 85%), and CH2O concentrations (0–25 ppbv). Standard additions on ambient air were performed in the field with another inlet. Sampling artifacts were not observed in either case at CH2O levels less than about 10 ppbv to within the measurement precision (25–120 parts per trillion by volume (1 min, 1σ)) and/or accuracy of standard generation (±6%). Desorption associated with the Herriott Cell was measured under highly polluted conditions, and was largely corrected for by subtracting a frequently acquired instrument background. Inlet shielding and heating minimized error due to liquid water collection. Common inlet materials such as PFA Teflon and silica‐coated steel efficiently transmitted CH2O.
Lidar observations of polar stratospheric clouds over northern Greenland in the period 1990–1997
Authors: di Sarra A. , Cacciani M. , Fiocco G. , Fuà D. , Jørgensen T. S.
Published: October 2002

Observations of the stratosphere were carried out at Thule (76.5°N, 68.8°W), Greenland, in the period 1990–1997 with an elastic backscatter/depolarization lidar. Polar stratospheric clouds (PSCs) were never detected during the winters 1991, 1992, 1993, and 1994. Small nondepolarizing PSCs could have been masked, however, by the large volcanic aerosol cloud that was in the stratosphere during 1992, 1993, and 1994. During 1995, 1996, and 1997, PSCs were observed on a total of 32 days. The evolution of the PSCs during each winter was mainly modulated by the behavior of the polar vortex. PSC signatures were often detected in regions where, assuming a 5 ppmv concentration of water vapor and a 10 ppbv concentration of nitric acid, condensation was not possible. Thus larger concentrations of these gases, or significant differences between the true and the radiosonde/analysis temperatures, were experienced. All observed PSCs could be classified as type I PSCs. Type Ia PSCs, sometimes found as stable homogeneous layers, were common. These layers formed when the air mass temperature reached the frost point during the days preceding the passage over Thule. Type Ib PSCs were generally associated with an articulated cloud structure, consisting of several layers of type Ib and type Ia particles. Circumstantial indications suggest that the development of these articulated clouds is associated with oscillations in the temperature profile, and with rapid temperature changes along the isentropic trajectories. The behavior of the depolarization ratio appears to depend on the minimum temperature experienced by the air mass during the past few days, and possibly on the condensation of ice prior to the PSC observation. The properties of a large type Ib PSC have been studied by means of a ternary solution model, and theoretical calculations of the backscattering. The measured cloud properties are not satisfactorily described by the ternary solution model, and a droplet composition with a water fraction larger than expected may be implied. The type Ib PSC properties are, however, consistent with a cloud composed of a large number of small particles, with a narrow size distribution. In a single case a cloud exhibiting relatively large backscatter ratio and depolarization, classified as type Ic, was detected; the isentropic trajectory of the air mass shows that the particles probably reached the frost point a few days before arriving at Thule. Theoretical calculations of the backscatter ratio from this cloud indicate that it was probably constituted of a relatively large number of submicron to micron‐sized crystals.
Ground‐based FTIR observations of chlorine activation and ozone depletion inside the Arctic vortex during the winter of 1999/2000
Authors: Mellqvist J. , Galle B. , Blumenstock T. , Hase F. , Yashcov D. , Notholt J. , Sen B. , Blavier J.‐F. , Toon G. C. , Chipperfield M. P.
Published: October 2002

The time evolution and latitudinal distribution of ozone and chlorine species (HCl, ClONO2, and ClO) in the Arctic and midlatitude stratosphere have been studied for the winter of 1999/2000. This has been done by the use of ground‐based solar absorption Fourier Transform Infrared (FTIR) measurements from four locations: Harestua (60.2°N, 10.8°E), Kiruna (67.8°N, 20.4°E), Esrange (67.9°N, 21.1°E), and Ny Ålesund (79°N, 12°E). The measurements were normalized with the inert tracer HF to minimize the effects of transport, combined using the concept of equivalent latitude and interpreted using the 3D model SLIMCAT. By late January, there was strong chlorine activation with 33% of the available inorganic chlorine column (HCl + ClONO2) being lost, with amounts of ClO greatly enhanced. By the middle of March, the ClO had been deactivated to ClONO2, which exceeded its original fractional abundance (41%), but HCl stayed low (39%) and the ClO columns were still enhanced. The strong and sustained chlorine activations caused considerable accumulated ozone column loss of (12 ± 7)% and (31 ± 4)% by the beginning of February and March, respectively. The model showed only (5 ± 3)% and (23 ± 5)% column loss for the same time periods. By comparison, the 1998/1999 winter measurements showed no significant loss of column ozone but a 10% loss in the model.
Redistribution of reactive nitrogen in the Arctic lower stratosphere in the 1999/2000 winter
Authors: Koike M. , Kondo Y. , Takegawa N. , Lefevre F. , Ikeda H. , Irie H. , Hunton H. D. E. , Viggiano A. A. , Miller T. M. , Ballenthin J. O. , Sachse G. W. , Anderson B. E. , Avery M. , Masui Y.
Published: October 2002

Total reactive nitrogen (NOy) in the Arctic lower stratosphere was measured from the NASA DC‐8 aircraft during the SAGE III Ozone Loss and Validation Experiment (SOLVE) in the winter of 1999/2000. NOy‐N2O correlations obtained at altitudes of 10–12.5 km in December 1999 and January 2000 are comparable to the reported reference correlation established using the MkIV balloon measurements made during SOLVE prior to the onset of denitrification. Between late February and mid‐March, NOy values obtained from the DC‐8 were systematically higher than those observed in December and January by up to 1 part per billion by volume, although a compact correlation between NOy and N2O was maintained. Greater increases in NOy were generally observed in air masses with lower N2O values. The daily minimum temperatures at 450–500 K potential temperature (∼20–22 km) in the Arctic fell below the ice saturation temperature between late December and mid‐January. Correspondingly, intense denitrification and nitrified air masses were observed from the ER‐2 at 17–21 km and below 18 km, respectively, in January and March. The increases in NOy observed from the DC‐8 in late February/March indicate that influence from nitrification extended as low as 10–12.5 km over a wide area by that time. We show in this paper that the vertical structure of the temperature field during the winter was a critical factor in determining the vertical extent of the NOy redistribution. Results from the Reactive Processes Ruling the Ozone Budget in the Stratosphere (REPROBUS) three‐dimensional chemistry transport model, which reproduced the observed general features only when the NOy redistribution process is included, are also presented.
Analysis of hot spot directional signatures measured from space
Authors: Bréon Francois‐Marie , Maignan Fabienne , Leroy Marc , Grant Ian
Published: October 2002

Reflectance measurements from the spaceborne Polarization and Directionality of Earth Reflectances (POLDER) instrument are used to analyze the so‐called hot spot directional signature in the backscattering direction. The hot spot is measured with an angular resolution better than half a degree using the directional capabilities of the radiometer, with some assumptions on the spatial homogeneity of the surface. The analysis yields the first quantitative observation of the hot spot signature of vegetated surfaces, with such angular resolution. The measurements show that the hot spot reflectance is a function of the phase angle ξ rather than a function of a parameter Δ, often used in hot spot modeling, that quantifies the horizontal distance between Sun and view directions. The observed directional signature is very accurately fitted by a linear ratio of the phase angle, as predicted by a simple theory of radiative transfer within the canopy foliage. Most of the measured hot spot half widths are between 1° and 2°. Some dispersion occurs for the cases belonging to the forest and desert International Geosphere‐Biosphere Program (IGBP) classes, in the range 1° to 5°. Theory predicts that the width is independent of wavelength. Our measurements indicate that the widths at 670 and 865 nm are very close, but with a significant scatter in regards to the rather small variability. The distribution of the width as a function of the IGBP surface classification shows a variability within the classes that is larger than between the classes, except for the “evergreen broadleaf” class. The hot spot reflectance amplitude is generally on the order of 0.10–0.20 at 865 nm and 0.03–0.18 at 670 nm, although the full range of values is wider. For thick canopies, it may be interpreted in terms of foliage element (leaf) reflectance. Retrieved values are on the order of 0.4 in the near infrared and in the range 0.05–0.20 at 670 nm. At 440 nm, the amplitude of the signature is very small, as is expected from the small surface reflectance. This confirms that the atmospheric contribution to the reflectance increase at the backscattering direction is negligible.
Sensitivity of zenith total delay accuracy to GPS orbit errors and implications for near‐real‐time GPS meteorology
Authors: Ge Maorong , Calais Eric , Haase Jennifer
Published: October 2002

Global Positioning System (GPS) measurements have been demonstrated to provide precipitable water vapor (PWV) estimates with a level of accuracy that is comparable to that of radiosondes and microwave radiometers. GPS measurements therefore have the potential to become a significant source of data for operational weather forecasting, provided that PWV (or the intermediate zenith total delay (ZTD)) can be made available in near real‐time with a minimum accuracy degradation. Despite the recent decrease in the latency and increase in accuracy provided by the International GPS Service (IGS) ultrarapid predicted GPS orbit products, we show that the accuracy of these orbits continues to be a limiting factor for the accuracy of near real‐time GPS‐derived atmospheric estimates. In this work, a coefficient matrix is derived from the normal equations of the least squares adjustment model for the GPS observables that maps the orbital parameter errors into ZTD errors. This is used to analyze the sensitivity of GPS derived tropospheric errors to an extensive set of parameters, including their time dependence, in a computationally efficient manner. We show that ZTD errors are dominated by biases in the orbital semimajor axis, with minor contributions from the inclination and argument of perigee, and that this error increases significantly after the fourth to fifth hour of the prediction window. We implemented a GPS data processing strategy based on an iterative estimation of the three most critical orbital parameters (semimajor axis, inclination and argument of perigee) together with the ZTD parameters. We tested this strategy in a 3500 × 3500 km network of 15 GPS sites in western Europe providing hourly data files. We show that the standard deviation improvement compared to a strategy based only on the orbit quality index provided with the predicted orbit products is on the order of 20%. The analysis of one month of data in near‐real‐time shows a bias lower than 1 mm ZTD and a standard deviation lower than 6 mm ZTD compared to using the most precise IGS final orbits. We also show that this strategy is robust and capable of dealing with very large orbit errors appropriately. We demonstrate that the same quality is achievable with a 1500 × 1500 km network which has positive implications for decentralized processing strategies. The near real‐time processing methodology described here meets the current timeliness requirements of operational meteorology (30 mn to 2 hours, depending on the application), while ensuring a level of accuracy similar to that provided in postprocessed mode with precise final IGS orbits (1 mm ZTD bias, 6 mm ZTD RMS). The method we propose can also be considered as an “on‐the‐fly” orbit quality control for near real‐time GPS applications.
Products of reaction of OH radicals with α‐pinene
Authors: Aschmann Sara M. , Atkinson Roger , Arey Janet
Published: October 2002

Products of the gas‐phase reaction of α‐pinene with OH radicals in the presence of NO have been investigated using gas chromatography with flame ionization detection to quantify pinonaldehyde and in situ atmospheric pressure ionization mass spectrometry in the negative ion mode to quantify selected other products as their NO2− adducts by utilizing C6‐dihydroxycarbonyls and C6‐hydroxynitrates formed in situ from the reaction of OH radicals with 1‐hexene as an internal standard. The products quantified, and their molar formation yields, were: pinonaldehyde, 28 ± 5%; molecular weight 184 product (dihydroxycarbonyl), 19% (with an estimated uncertainty of a factor of ∼2); molecular weight 200 product, 11% (with an estimated uncertainty of a factor of ∼2). Together with a very approximate yield from our API‐MS analyses for the formation of organic nitrates (∼1%) and literature data for acetone (plus coproducts), ∼65–70% of the reaction products and pathways are accounted for.
Measurement of prenucleation molecular clusters in the NH3, H2SO4, H2O system
Authors: Hanson D. R. , Eisele F. L.
Published: October 2002

The molecular cluster ions HSO4−(H2SO4)n−1(NH3)m corresponding to the neutral species (H2SO4)n(NH3)m for n = 2 to 6 and m = 0 to n−1 have been observed at temperatures up to ∼285 K. A transverse chemical ionization apparatus was located inside a cooled flow tube where water, sulfuric acid, and ammonia vapors mixed and formed clusters. The complexities of the experimental technique and the interpretation of the results are extensively discussed. Typical NH3 and H2SO4 concentrations were 2 × 109 cm−3, i.e, ∼100 pptv at atmospheric pressure. For these conditions, cluster concentrations were estimated to be a few times 106 cm−3 and the critical, particle‐forming cluster likely contained 2 H2SO4 molecules at 275 K. The results are consistent with the species (H2SO4)2NH3 playing an important role in the formation of new particles in the atmosphere.
Impact of improved near‐infrared water vapor line data in simulations with the ECHAM4 general circulation model
Authors: Lohmann Ulrike , Bennartz Ralf
Published: October 2002

Recently, two new water vapor line absorption data sets have become available. First, the HITRAN 2000 data set provides updated information on several water vapor absorption lines in the near infrared. Second, an independent study initiated by the European Space Agency (ESA) created a new line data set for the spectral range between 8592 and 20000 cm−1. We investigate the impact of these new data in the near infrared as compared to HITRAN‐92 on the absorption of solar radiation in the ECHAM4 general circulation model. Owing to the increased water vapor absorption in the new parameterizations, the global annual mean atmospheric absorption of solar radiation in ECHAM4 is increased under all skies between 3.2 and 3.7 W m−2 and between 5.0 and 5.7 W m−2 under clear skies for the different data sets. While the dynamics barely change, the hydrological cycle is slightly weaker, the cloud cover has decreased by 0.4% and the precipitation by 0.06 to 0.08 mm d−1 when the new data sets are used.
Gas/aerosol partitioning: 1. A computationally efficient model
Authors: Metzger Swen , Dentener Frank , Pandis Spyros , Lelieveld Jos
Published: October 2002

A computationally efficient model to calculate gas/aerosol partitioning of semivolatile inorganic aerosol components has been developed for use in global atmospheric chemistry and climate models. We introduce an approximate method for the activity coefficient calculation that directly relates aerosol activity coefficients to the ambient relative humidity, assuming chemical equilibrium. We demonstrate that this method provides an alternative for the computationally expensive iterative activity coefficient calculation methods presently used in thermodynamic gas/aerosol models. The gain of our method is that the entire system of the gas/aerosol equilibrium partitioning can be solved noniteratively, a substantial advantage in global modeling. We show that our equilibrium simplified aerosol model (EQSAM) yields results similar to those of current state‐of‐the‐art equilibrium models.
European pollution outbreaks during ACE 2: Microphysical particle properties and single‐scattering albedo inferred from multiwavelength lidar observations
Authors: Müller Detlef , Ansmann Albert , Wagner Frank , Franke Kathleen , Althausen Dietrich
Published: October 2002

We present vertically resolved physical particle properties and the single‐scattering albedo at 532 nm of pollution plumes advected from the European continent out over the Atlantic Ocean. The parameters follow from the inversion of optical data, which were obtained from six‐wavelength aerosol lidar observations near Sagres (37°N, 9°W), Portugal, in the framework of Aerosol Characterization Experiment 2 (ACE 2) (June–July 1997). Particle effective radii were 0.15 ± 0.06 μm, volume concentrations ranged from 6 to 27 μm3cm−3, and surface area concentrations were 80 to 1200 μm2cm−3. The particles in general showed negligible absorption, with the mean imaginary part of the wavelength‐independent complex refractive index being at 0.009i± 0.010i. The mean real part was 1.56 ± 0.07. A mean value of 0.95 ± 0.06 was obtained for the single‐scattering albedo at 532 nm. The numbers indicate that the major contributor to the observed pollution was nonabsorbing ammonium‐sulfate‐like material. A very small fraction was contributed by absorbing sootlike material. Correlation analysis showed that effective radius was well correlated with the Ångström exponents of the underlying extinction spectra. Furthermore, correlations of the single‐scattering albedo with the particle extinction‐to‐backscatter ratio and with the imaginary part of the complex refractive index were found. This result shows that the first two parameters contain information about the chemical state of the observed particles.
CHASER: A global chemical model of the troposphere 1. Model description
Authors: Sudo Kengo , Takahashi Masaaki , Kurokawa Jun‐ichi , Akimoto Hajime
Published: October 2002

We present a new global three‐dimensional chemical model for the troposphere, named chemical atmospheric general circulation model (AGCM) for study of atmospheric environment and radiative forcing (CHASER). This model, developed in the framework of the Center for Climate System Research/National Institute for Environment Studies (CCSR/NIES) AGCM, is aimed to study tropospheric photochemistry and its influences on climate. The chemical component of the model simulates the O3‐HOx‐NOx‐CH4‐CO photochemical system and oxidation of nonmethane hydrocarbons through 88 chemical and 25 photolytic reactions with 47 chemical species in its present configuration. The model includes emission sources, dry and wet deposition, as well as chemical transformations. Meteorological processes such as transport due to advection, convection, and other subgrid‐scale mixing are simulated “on‐line” by the dynamical component of the CCSR/NIES AGCM. A detailed evaluation of the model results is presented in a companion paper [Sudo et al., 2002]. An evaluation of the transport scheme adopted in the model suggests that the model is capable of simulating transport associated with convection and boundary layer mixing as well as large‐scale advection. The model capability to simulate dry and wet deposition was also evaluated by conducting a simulation of atmospheric lead. The simulated lead distributions are consistent with those observed at the surface, showing the validity of the deposition parameterization adopted in the model.
Air mass motion, temperature, and humidity over the Arabian Sea and western Indian Ocean during the INDOEX intensive phase, as obtained from a set of superpressure drifting balloons
Authors: Ethé Christian , Basdevant Claude , Sadourny Robert , Appu K. S. , Harenduprakash L. , Sarode P. R. , Viswanathan G.
Published: October 2002

During the Indian Ocean Experiment (INDOEX) Intensive Field Phase, 17 superpressure balloons drifting at lower tropospheric levels were launched from Goa to sample the motion and meteorological characteristics of polluted air masses originating from the Indian subcontinent. The mass flow, as expected, is attracted to the Intertropical Convergence Zone (ITCZ), which is reached in about 7 days. Successive trajectories show evidence of shifts in the flow regime, consistent with Meteosat‐5 imagery and illustrative of the Madden–Julian oscillation. Balloons also show evidence of coastal anticyclonic circulations off the western coast of India, linked to both the orography of the Ghâts and the diurnal coastal wind mesoscale wind systems. These mesoscale circulations may be important in the transport of anthropogenic or mineral pollutants across the coast. The meteorological data gathered on board the balloons were systematically compared with European Centre for Medium‐Range Weather Forecasts (ECMWF) analyses interpolated in time and space at the balloons' successive locations every half‐hour. The agreement is generally good in terms of wind velocities, temperature, and humidity. However, above the marine boundary layer, balloon data seem to indicate a cold bias of analyzed temperatures and a northeasterly bias of horizontal winds. The underestimation of variability in the analyzed winds can be partly explained by mesh size smoothing in the analysis system.
Methyl chloride and other chlorocarbons in polluted air during INDOEX
Authors: Scheeren H. A. , Lelieveld J. , de Gouw J. A. , van der Veen C. , Fischer H.
Published: October 2002

Methyl chloride (CH3Cl) is the most abundant, natural, chlorine‐containing gas in the atmosphere, with oceans and biomass burning as major identified sources. Estimates of global emissions suffer from large uncertainties, mostly for the tropics, partly due to a lack of measurements. We present analyses of whole‐air canister samples for selected nonmethane hydrocarbons and chlorocarbons. The samples were collected from an aircraft during the Indian Ocean Experiment (INDOEX) campaign over the northern Indian Ocean in February and March 1999. The CH3Cl results are correlated to selected nonmethane hydrocarbons and in situ measurements of carbon monoxide (CO) and acetonitrile (CH3CN). We relate high mixing ratios of ∼750 pmol mol−1of CH3Cl to biomass burning, as observed in polluted air masses from India and Southeast Asia. We infer a relatively high enhancement ratio relative to CO, ΔCH3Cl/ΔCO ≈1.74 ± 0.21 × 10−3mol mol−1. The CH3Cl levels relate to the extensive biofuel use in India and Southeast Asia, notably the burning of agricultural waste and dung with a comparatively high chlorine content. It appears that CH3Cl emissions from biofuel consumption in India and Southeast Asia have been underestimated in the past. Furthermore, we observed enhanced dichloromethane (CH2Cl2) and trichloromethane (CHCl3) levels, correlating with high CO, acetylene (C2H2) and CH3Cl, indicating that biomass burning is a small but significant source of these species.
Near equatorial CO and O3 profiles over the Indian Ocean during the winter monsoon: High O3 levels in the middle troposphere and interhemispheric exchange
Authors: Williams J. , Fischer H. , Wong S. , Crutzen P. J. , Scheele M. P. , Lelieveld J.
Published: October 2002

Between January and March 1999, a Citation jet aircraft equipped with a variety of chemical instrumentation took part in the Indian Ocean Experiment (INDOEX). During the winter monsoon (December–March), the Intertropical Convergence Zone (ITCZ) over the Indian Ocean lies between 10°S and the equator, effectively dividing the polluted Northern Hemisphere from the relatively pristine Southern Hemisphere. Analyzed here are four vertical profiles (0.5–12.5 km) of CO, O3 mixing ratios, and relative humidity, north and south of the ITCZ. From these profiles and accompanying back‐trajectory analyses, we identify two possible mechanisms for the influx of dry, ozone‐rich stratospherically influenced air observed in the middle tropical troposphere. The first involves rapid advection and subsidence of air associated with the subtropical jet stream in the Northern Hemisphere. The second is associated with subsidence ahead of a tropical cyclone in the Southern Hemisphere. Moreover, high mixing ratios of CO in Northern Hemisphere boundary layer air and the Southern Hemisphere middle atmosphere are interpreted as a case of interhemispheric exchange, leading to elevated levels of pollutants in the 8‐ to 10‐km altitude range of the Southern Hemisphere.
Size distributions and modal parameters of aerosol constituents in northern Finland during the European Arctic Aerosol Study
Authors: Ricard V. , Jaffrezo J.‐L. , Kerminen V.‐M. , Hillamo R. E. , Teinilä K. , Maenhaut W.
Published: October 2002

Size resolved aerosol components (major ions, selected organic acids, and crustal elements) were investigated with 12‐stage impactors during the summers 1997 and 1998 and winter 1997–1998 at Sevettijärvi in Finnish Lapland. Concentrations are compared with those obtained with simultaneous measurements with bulk sampling and show agreement within 15%. The samples were classified depending on their degree of marine and continental origin. Modal parameters (aerodynamic diameters and dispersion) were identified from the size distribution of each species. In general, the aerosol comprises two submicron modes (condensation mode at 0.30 ± 0.05 μm and droplet mode at 0.65 ± 0.15 μm) and one or two supermicron modes (the first one between 3.5 and 4.5 μm associated with marine species and the second one between 5 and 6 μm associated with crustal species). The results suggest internal mixing of nss sulfate, ammonium, and organic acids in the submicron modes, and differences between the classes of air masses allow to draw hypotheses on the formation processes involved for each species. The results for the supermicron modes indicate interactions of nss sulfate, ammonium, nitrate, and organic acids with the marine and crustal particles, which increase from the marine to the continental classes. During summer and winter the supermicron mass fraction largely decreases from the marine air masses to continental ones.
Diagnostic analysis of atmospheric moisture and clear‐sky radiative feedback in the Hadley Centre and Geophysical Fluid Dynamics Laboratory (GFDL) climate models
Authors: Allan Richard P. , Ramaswamy V. , Slingo A.
Published: October 2002

The interannual variability of the hydrological cycle is diagnosed from the Hadley Centre and Geophysical Fluid Dynamics Laboratory (GFDL) climate models, both of which are forced by observed sea surface temperatures. The models produce a similar sensitivity of clear‐sky outgoing longwave radiation to surface temperature of ∼2 W m−2 K−1, indicating a consistent and positive clear‐sky radiative feedback. However, differences between changes in the temperature lapse‐rate and the height dependence of moisture fluctuations suggest that contrasting mechanisms bring about this result. The GFDL model appears to give a weaker water vapor feedback (i.e., changes in specific humidity). This is counteracted by a smaller upper tropospheric temperature response to surface warming, which implies a compensating positive lapse‐rate feedback.
Analysis of moisture variability in the European Centre for Medium‐Range Weather Forecasts 15‐year reanalysis over the tropical oceans
Authors: Allan Richard P. , Slingo A. , Ramaswamy V.
Published: October 2002

We compare European Centre for Medium‐Range Weather Forecasts 15‐year reanalysis (ERA‐15) moisture over the tropical oceans with satellite observations and the U.S. National Centers for Environmental Prediction (NCEP) National Center for Atmospheric Research 40‐year reanalysis. When systematic differences in moisture between the observational and reanalysis data sets are removed, the NCEP data show excellent agreement with the observations while the ERA‐15 variability exhibits remarkable differences. By forcing agreement between ERA‐15 column water vapor and the observations, where available, by scaling the entire moisture column accordingly, the height‐dependent moisture variability remains unchanged for all but the 550–850 hPa layer, where the moisture variability reduces significantly. Thus the excess variation of column moisture in ERA‐15 appears to originate in this layer. The moisture variability provided by ERA‐15 is not deemed of sufficient quality for use in the validation of climate models.
Comparison of ScaRaB, GOES 8, aircraft, and surface observations of the absorption of solar radiation by clouds
Authors: Pope Shelly K. , Valero Francisco P. J. , Collins William D. , Minnis Patrick
Published: October 2002

Data obtained by the Scanner for Radiation Budget (ScaRaB) instrument on the Meteor 3 satellite have been analyzed and compared to satellite (GOES 8), aircraft (Radiation Measurement System, RAMS), and surface (Baseline Solar Radiation Network (BRSN), Solar and Infrared Observations System (SIROS), and RAMS) measurements of irradiance obtained during the Atmospheric Radiation Measurements Enhanced Shortwave Experiment (ARESE). It is found that the ScaRaB data covering the period from March 1994 to February 1995 (the instrument's operational lifetime) indicate excess absorption of solar radiation by the cloudy atmosphere in agreement with previous aircraft, surface, and GOES 8 results. The full ScaRaB data set combined with BSRN and SIROS surface observations gives an average all‐sky absorptance of 0.28. The GOES 8 data set combined with RAMS surface observations gives an average all‐sky absorptance of 0.26. The aircraft data set (RAMS) gives a mean all‐sky absorptance of 0.24 (for the column between 0.5 and 13 km).
Climate forcings in Goddard Institute for Space Studies SI2000 simulations
Authors: Hansen J. , Sato M. , Nazarenko L. , Ruedy R. , Lacis A. , Koch D. , Tegen I. , Hall T. , Shindell D. , Santer B. , Stone P. , Novakov T. , Thomason L. , Wang R. , Wang Y. , Jacob D. , Hollandsworth S. , Bishop L. , Logan J. , Thompson A. , Stolarski R. , Lean J. , Willson R. , Levitus S. , Antonov J. , Rayner N. , Parker D. , Christy J.
Published: October 2002

We define the radiative forcings used in climate simulations with the SI2000 version of the Goddard Institute for Space Studies (GISS) global climate model. These include temporal variations of well‐mixed greenhouse gases, stratospheric aerosols, solar irradiance, ozone, stratospheric water vapor, and tropospheric aerosols. Our illustrations focus on the period 1951–2050, but we make the full data sets available for those forcings for which we have earlier data. We illustrate the global response to these forcings for the SI2000 model with specified sea surface temperature and with a simple Q‐flux ocean, thus helping to characterize the efficacy of each forcing. The model yields good agreement with observed global temperature change and heat storage in the ocean. This agreement does not yield an improved assessment of climate sensitivity or a confirmation of the net climate forcing because of possible compensations with opposite changes of these quantities. Nevertheless, the results imply that observed global temperature change during the past 50 years is primarily a response to radiative forcings. It is also inferred that the planet is now out of radiation balance by 0.5 to 1 W/m2 and that additional global warming of about 0.5°C is already “in the pipeline.”
Methyl iodide: Atmospheric budget and use as a tracer of marine convection in global models
Authors: Bell N. , Hsu L. , Jacob D. J. , Schultz M. G. , Blake D. R. , Butler J. H. , King D. B. , Lobert J. M. , Maier‐Reimer E.
Published: October 2002

We simulate the oceanic and atmospheric distribution of methyl iodide (CH3I) with a global 3‐D model driven by assimilated meteorological observations from the Goddard Earth Observing System of the NASA Data Assimilation Office and coupled to an oceanic mixed layer model. A global compilation of atmospheric and oceanic observations is used to constrain and evaluate the simulation. Seawater CH3I(aq) in the model is produced photochemically from dissolved organic carbon, and is removed by reaction with Cl− and emission to the atmosphere. The net oceanic emission to the atmosphere is 214 Gg yr−1. Small terrestrial emissions from rice paddies, wetlands, and biomass burning are also included in the model. The model captures 40% of the variance in the observed seawater CH3I(aq) concentrations. Simulated concentrations at midlatitudes in summer are too high, perhaps because of a missing biological sink of CH3I(aq). We define a marine convection index (MCI) as the ratio of upper tropospheric (8–12 km) to lower tropospheric (0–2.5 km) CH3I concentrations averaged over coherent oceanic regions. The MCI in the observations ranges from 0.11 over strongly subsiding regions (southeastern subtropical Pacific) to 0.40 over strongly upwelling regions (western equatorial Pacific). The model reproduces the observed MCI with no significant global bias (offset of only +11%) but accounts for only 15% of its spatial and seasonal variance. The MCI can be used to test marine convection in global models, complementing the use of radon‐222 as a test of continental convection.
A three‐dimensional model of molecular hydrogen in the troposphere
Authors: Hauglustaine D. A. , Ehhalt D. H.
Published: October 2002

The global distribution and budget of atmospheric molecular hydrogen (H2) is simulated with a global Chemistry‐Transport Model (CTM). Surface emissions include technological sources (industry, transportation and other fossil fuel combustion processes), biomass burning, nitrogen fixation in soils, and oceanic activity and totals 39 Tg/yr. The photochemical production (31 Tg/yr) from formaldehyde photolysis accounts for about 45% of the total source of H2. Soil uptake (55 Tg/yr) represents a major loss process for H2 and contributes for 80% to the total destruction. H2 oxidation by OH in the troposphere contributes the remainder. The global burden of H2 in the atmosphere is 136 Tg. Its overall lifetime in the atmosphere is 1.9 years. H2 is rather well‐mixed in the free troposphere. However, its distribution shows a significant seasonal variation in the lower troposphere where soil uptake dominates. This loss process shows a strong temporal variability and is maximum over the northern hemisphere landmass during summer. Strong vertical gradients result from this surface uptake. In these regions, H2 varies by more than 30% between the maximum mixing ratio in winter and the summer minimum. Our results stress the important role played by the tropics in the budget of H2. In these regions a strong seasonal cycle is also predicted due to the annual variation in biomass burning emissions, soil uptake, and rapid transport by convection of H2 depleted air masses from the boundary layer to the upper troposphere. A comparison with the observed H2 distribution allows to test some of the model predictions. Good agreement is found for the global burden and the annually averaged latitudinal gradient in the southern hemisphere and the tropics. A detailed comparison of the seasonal cycles of H2 in surface air indicates that the use of the net primary productivity to prescribe the seasonal and geographical pattern of soil uptake in the model leads to an underestimate of the deposition velocity during winter and spring over the continents in the northern hemisphere.
Seasonally resolved Alpine and Greenland ice core records of anthropogenic HCl emissions over the 20th century
Authors: Legrand Michel , Preunkert Susanne , Wagenbach Dietmar , Fischer Hubertus
Published: October 2002

The continuous highly resolved records of Cl−, Na+, and Ca2+ in ice cores from Col du Dôme (4250 m elevation, French Alps) and Summit (3240 m elevation, central Greenland) are used to reconstruct the history of atmospheric HCl pollution over Europe and Greenland since the early 20th century. The evaluation of the HCl amount in summer snow deposits at high‐elevation Alpine sites is complex since continental emissions (soils, halide evaporites, and possibly manure‐fertilized fields) account for 80% of the chloride budget and only one fifth of Cl− is related to HCl. During the preindustrial era the HCl content of summer Alpine snow layers fluctuated between 0 and 6 ng g−1, likely in relation with a highly variable interannual biomass burning activity in western Europe. From 1925 to 1960 the HCl levels were slightly higher (3–9 ng g−1), mainly due to growing coal burning emissions in western Europe. In the late 1960s a sharp increase of HCl levels (up to 17 ng g−1) took place as a result of the setup of waste incineration in western Europe, this process contributing 3–4 times more than coal combustion to the HCl budget of summer Alpine snow layers deposited between 1970 and 1990. In winter, sea spray emissions dominate (∼78%) the total Cl− level of Alpine snow layers. The HCl trend in these snow layers remained limited to ∼2 ng g−1 over the 20th century, likely in relation to waste incineration after 1965. In Greenland snow layers most of particulate Cl− originates from sea spray, 1/3 to 2/3 of Cl− being present as HCl in spring and summer, respectively. The Greenland HCl ice core records indicate a preindustrial HCl level close to 4 ng g−1, which is found to be mainly due to the sea‐salt dechlorination, while the contribution of passive volcanic HCl emissions at high northern latitudes can be neglected. The input from sea‐salt dechlorination has been enhanced by a factor of 2–3 during the second half of the 20th century similarly to the increase of the atmospheric acidity in response to growing NOx and SO2 anthropogenic emissions.
Laboratory investigations of the response of Brewer‐Mast ozonesondes to tropospheric ozone
Authors: Tarasick David W. , Davies Jonathan , Anlauf Kurt , Watt Maurice , Steinbrecht Wolfgang , Claude Hans J.
Published: October 2002

The Brewer‐Mast ozonesonde was used at Canadian stations from 1966 until 1980, when the Canadian network switched to the electrochemical concentration cell sonde. While the sondes appear to agree relatively well in the stratosphere, there is an evident discrepancy of 10–20% in tropospheric measurements [e.g., Tarasick et al., 1995, Figure 4]. Comparison of Brewer‐Mast sondes with a calibrated ozone source yields some interesting insight into this discrepancy. Sonde response is strongly dependent on the preflight preparation procedures employed. Although sondes prepared via procedures introduced in the 1980s [Claude et al., 1987] perform quite well, when prepared according to the procedures used in Canada in the 1970s, Brewer‐Mast sondes indicate 10–30% lower ozone than the calibrator. The following points are noted in particular: (1) a new Brewer‐Mast sonde shows a large (∼15%) increase in sensitivity between successive experiments; (2) especially at low (<100 ppb) O3 levels, the response even of previously flown sondes increases slowly with time; and (3) sondes show an additional slow increase of response with time that is apparently caused by ozone reactions with the phosphate buffer. The overall response curve indicated by 1, 2, and 3 implies that after correction to the observed total ozone, the earlier part of a flight would yield values that are too low, while the latter part would be too high. By applying a varying ozone input, simulating the typical variation in absolute ozone concentration experienced by a sonde in flight, we show that this can explain both the average correction factor (1.255) for the Canadian Brewer‐Mast record and the 10–20% discrepancy in tropospheric measurements.
Establishing the relationship between the CERES window and total channel measured radiances for conditions involving deep convective clouds at night
Authors: Kratz David P. , Priestley Kory J. , Green Richard N.
Published: October 2002

Characterizing the stability of the Clouds and the Earth's Radiant Energy System (CERES) instrument is critical to obtaining accurate measurements of the radiative energy budget of the Earth's atmosphere‐surface system. Composed of three broadband radiometers, the CERES instrument measures radiances in the shortwave (>2000 cm−1), infrared window (835–1250 cm−1), and total regions of the spectrum. Such a choice of radiometers does not allow for a straightforward three channel intercomparison of the CERES measurements. We observed, however, the outgoing infrared spectra of high, cold, optically thick clouds were fairly representative of blackbody emission. This observation suggested a potential relationship between the infrared window radiometer and longwave portion of the total radiometer. Using nighttime measurements made by the CERES instrument aboard the Tropical Rainfall Measuring Mission (TRMM) spacecraft during the first eight months of 1998, we were able to determine a highly correlated relationship between the infrared window and total channel radiances for conditions corresponding to high, cold, optically thick clouds. Comparisons were then made between the measurements and reference line‐by‐line calculations. From these comparisons, a quantified relationship was derived between the total and window channel radiances which could accurately reproduce one set of results from the other. Such a relationship has allowed for the establishment of a three channel intercomparison for the CERES instrument with an accuracy of ∼1% for the case of high, cold, optically thick clouds. An independent relationship based upon the tropical mean is shown to produce results which support the three channel analysis for the deep convective cloud systems.
Regional marine boundary layer aerosol size distributions in the Indian, Atlantic, and Pacific Oceans: A comparison of INDOEX measurements with ACE‐1, ACE‐2, and Aerosols99
Authors: Bates Timothy S. , Coffman Derek J. , Covert David S. , Quinn Patricia K.
Published: October 2002

Aerosol number size distributions were measured aboard the R/V Ronald H. Brown during the Indian Ocean Experiment (INDOEX) 1999 Intensive Field Phase (IFP) using a differential mobility particle sizer (DMPS) and an aerodynamic particle sizer (APS), covering a size range from 0.02 to 7 μm geometric diameter at 55% relative humidity (RH). The Indian Ocean marine boundary layer (MBL) aerosol number size distributions measured during the 1999 IFP were categorized into eight air mass source regions based on air mass back trajectories. The number and volume size distributions in these eight regions were distinctly different as a result of the different aerosol sources, meteorological conditions during transport, and time spent in the MBL. The aerosol sampling and data reduction during INDOEX were similar to that used during the Aerosol Characterization Experiment (ACE)‐1 (Mid‐Pacific Ocean 37°N to 32°S and Southern Ocean south of Tasmania, Australia), ACE‐2 (North Atlantic Ocean west of Portugal and North Africa), and Aerosols99 (Atlantic Ocean transit from Norfolk, USA to Cape Town, South Africa) thus facilitating comparisons of the number and volume size distributions from these different experiments. The combined data set, summarized in this paper, provides regional aerosol parameters for comparison with global climate models and satellite retrieval algorithms.
Tropical ozone as an indicator of deep convection
Authors: Folkins Ian , Braun Christopher , Thompson Anne M. , Witte Jacquelyn
Published: October 2002

The climatological ozone profile in the tropics is shaped like an “S,” with a minimum at the surface, a maximum at 330 K (∼6.5 km), another minimum at 345 K (∼11.2 km), and a subsequent increase toward the tropopause. These features can be reproduced by a very simple model whose only free parameter is the mean ozone mixing ratio of air detraining from deep convective clouds. To first order, the climatological ozone profile in the tropics arises from a balance between vertical advection, deep convection, and chemistry. The 345 K ozone minimum is coincident with a lapse rate minimum. Both minima are associated with a large increase in convective outflow at 345 K followed by a quasi‐exponential decrease. The increase in ozone above 345 K is caused mainly by decreased injection of low‐ozone air from the boundary layer. The model tends to underestimate ozone between 340 and 365 K (∼9–15 km). This is most likely due either to an underestimate by the model of in situ ozone production or to eddy transport of ozone from the lowermost stratosphere into the upper tropical troposphere across the subtropical jet. The magnitudes of both these processes are poorly constrained by measurements. In the case of ozone production this is mainly due to a lack of measurements of HOx precursors such as acetone and CH3OOH between 11 and 16 km.