bluuebunny/crossref_metadata_2025 huggingface dataset:
Large‐scale stratospheric ozone photochemistry and transport during the POLARIS Campaign
Authors: Pierce R. Bradley , Al‐Saadi Jassim A. , Fairlie T. Duncan , Olson Jennifer R. , Eckman Richard S. , Grose William L. , Lingenfelser Gretchen S. , Russell James M.
Published: September 2002

Measurements from the Halogen Occultation Experiment (HALOE) on board the UARS satellite and assimilated winds, temperatures, and diabatic heating rates from the NASA Goddard data assimilation office (DAO) are used with the NASA Langley Research Center (LaRC) Lagrangian photochemical model to compute 3‐D air parcel trajectories with photochemistry for all Northern Hemisphere HALOE observations during the period March‐September 1997. Results from ensemble means of the photochemical trajectory calculations provide a global perspective for the interpretation of constituent measurements made from the ER‐2 and balloon platforms during the POLARIS aircraft campaign. Lagrangian photochemical predictions are shown to compare favorably with ER‐2, balloon, Total Ozone Mapping Spectometer (TOMS), and subsequent coincident HALOE observations. Model predictions show large‐scale photochemical ozone loss in high latitudes at ER‐2 flight altitudes of over 10% per month in June and July, in good agreement with steady state photochemical calculations constrained with ER‐2 observations of radical and long‐lived species. Largest summertime photochemical ozone losses (over 1.4 ppmv/month) are found to occur poleward of 60°N above 30 mbar, in good agreement with steady state photochemical calculations constrained with observations from the balloon‐borne Fourier transform infrared solar absorption spectrometer (MkIV) instrument. Summertime polar photochemical ozone losses are driven largely by NOx chemistry and are largest for air parcels with high NOx/NOy ratios that have experienced continuous sunlight for several days. Differences between predicted net changes in ozone and changes due to photochemistry are used to estimate residual changes due to transport processes. Photochemical and residual transport tendencies tend to be of similar magnitude but opposite sign. Photochemical loss of ozone tends to outweigh positive transport tendencies in high latitudes, while upwelling of low ozone below the tropical ozone maximum moderates photochemical production there. The estimated transport tendencies are generally consistent with expectations based on transformed Eulerian circulation derived from the DAO assimilated data and the mean ozone distribution. A net (photochemical plus transport) ozone decrease of over 0.2 ppmv/month is predicted throughout the middle and lower stratosphere poleward of 70°N during the summer months.
Simulations of the Last Glacial Maximum ice sheet surface climate: Implications for the interpretation of ice core air content
Authors: Krinner G. , Raynaud D. , Doutriaux C. , Dang H.
Published: September 2002

This paper reports on analyses of the surface pressure, surface wind, and seasonality of temperature and precipitation in the central parts of Greenland and Antarctica as simulated by different general circulation models (GCMs) for the present and for the Last Glacial Maximum (LGM) climates. These parameters, in addition to the mean surface temperature, influence the air content of the ice either directly or through their influence on the pore volume. To correctly interpret the air content of the ice in terms of past ice sheet elevation changes, the variations of these parameters must therefore be known. Most of the simulations discussed here have been carried out within the framework of the Paleoclimate Modeling Intercomparison Project. Moreover, a stretched grid GCM has been used with a high resolution over the ice sheets. We show that not taking into account changes of surface pressure at constant altitude between the LGM and today leads to an overestimation of past ice sheet elevation up to 150 m, while wind speed changes are too weak to have a significant influence on ice core air content. The results concerning changes of the amplitude or phase of the seasonal variations of precipitation and temperature are somewhat ambiguous. Most, but not all, of the models suggest an intensification of the seasonal cycle of surface temperatures over central Greenland, and, to a lesser extent, over central East Antarctica. Neglecting these changes might lead to an underestimation of past elevation by up to 140 m for the Greenland ice sheet, but this number is subject to large uncertainties.
Trends in lower stratospheric zonal winds, Rossby wave breaking behavior, and column ozone at northern midlatitudes
Authors: Hood L. , Rossi S. , Beulen M.
Published: September 2002

Statistical trend analyses of National Centers for Environmental Prediction (NCEP) gradient zonal winds for the months of February and March demonstrate that the zonal mean meridional wind shear for these months in the midlatitude lower stratosphere has tended to become more anticyclonic with time over the period from 1979 to 1998. Such a tendency favors the increased occurrence at these latitudes of anticyclonic, poleward, Rossby wave breaking events that transport low potential vorticity (PV), ozone‐poor air from the subtropical upper troposphere to the midlatitude lower stratosphere while favoring the decreased occurrence of equatorward breaking, cyclonic events. Composite mean differencing and statistical trend analyses of NCEP‐derived PV on the 330 K isentropic surface show that zonal mean PV values at midlatitudes in February and March have decreased with time, consistent with the expected trends in Rossby wave breaking behavior. Similar analyses of Total Ozone Mapping Spectrometer (TOMS) total ozone for the same 2 months show that total ozone trends correlate geographically with PV trends. Regression relationships between 330 K PV and total ozone deviations derived from monthly mean measurements on the Northern Hemisphere are applied to estimate that as much as 40% of the zonal mean total ozone decline at midlatitudes in February during the analysis period may be attributed to long‐term trends in Rossby wave breaking behavior. As much as 25% of the midlatitude ozone trend in March may be attributed to such trends in wave‐breaking behavior. At specific longitudes the contribution to ozone trends from this source (as well as long‐term changes in quasi‐stationary wave amplitudes and phases) can be well over 50%.
Vertical distributions of cloud condensation nuclei spectra over the summertime northeast Pacific and Atlantic Oceans
Authors: Hudson James G. , Xie Yonghong
Published: September 2002

More than 80 hours of airborne cloud condensation nuclei (CCN) measurements made during the first phase of the First International Satellite Cloud Climatology Project (ISCCP) Regional Experiment (FIRE 1) in the northeast Pacific and the Atlantic Stratocumulus Transition Experiment (ASTEX) in the northeast Atlantic are presented and analyzed. The complete CCN spectra from 0.6% to 0.02% supersaturation and condensation nuclei concentrations are presented. Substantial direct continental/anthropogenic influence in ASTEX resulted in an obvious division into maritime and continental components, which had 5 times higher concentrations. Boundary layer FIRE 1, ASTEX maritime, and previously published summertime Southern Ocean number concentration measurements with the same instrument were comparable (110, 197, and 165 cm−3, respectively, at 0.6% supersaturation; 45, 60, and 48 cm−3 at 0.1% supersaturation, and 18, 19, and 20 cm−3 at 0.02% supersaturation).
Comparison of tropospheric NO3 radical measurements by differential optical absorption spectroscopy and matrix isolation electron spin resonance
Authors: Geyer A. , Alicke B. , Mihelcic D. , Stutz J. , Platt U.
Published: September 2002

Despite the importance of NO3 in the nighttime atmosphere only two techniques, Differential Optical Absorption Spectroscopy (DOAS) and Matrix Isolation Electron Spin Resonance (MIESR) have been applied to its detection in ambient air to date. Here we report the results of the first intercomparisons of these techniques in the atmosphere carried out at rural sites in Germany, at Deuselbach in 1983 and near Berlin in 1998. The simultaneously measured NO3 mixing ratios, which were in the range from 9 to 20 ppt and at one measurement near 100 ppt, were in good agreement within the error limits. A regression analysis yields a linear relationship between the DOAS and MIESR data with a correlation coefficient of R = 0.99 and a slope of 0.83±0.03 (1σ error) at a negligible intercept of 0.33±0.73 ppt (1σ error). The deviation from unity is within the total systematic error of both measurement techniques. This result shows the reliability of the two techniques over the past 15 years.
Homogenization of the Belsk UV‐B series (1976–1997) and trend analysis
Authors: Borkowski Janusz L.
Published: September 2002

An analysis of the ultraviolet radiation measurements taken at Belsk by Robertson‐Berger meter and Brewer spectrophotometer over the period 1976–1997 is performed. In the Robertson‐Berger data series, a mean level shift that can be attributed to change in calibration procedure was detected. In the examination of the series, a wavelet analysis was used. To determine the magnitude of the shift, a relationship between UV radiation and total ozone for a clear sky was applied. The results showed that for the Robertson‐Berger data, over the period 1984–1992, the correction factor of 1.14 should be applied. The trend in the whole observational period was 6.1±2.9% per decade. In the estimation of the trend uncertainty, the autocorrelation in the noise and shift of the level in the data was taken into account. The UV‐B trend depends mainly on the trend of ozone, and the response of UV‐B to ozone changes is most evident for the variations of the ozone content at a large timescale.
Trend in total atmospheric deposition fluxes of aluminium, iron, and trace metals in the northwestern Mediterranean over the past decade (1985–1997)
Authors: Ridame Céline , Guieu Cécile , Loÿe‐Pilot Marie‐Dominique
Published: September 2002

The total atmospheric deposition of aluminium (Al), cadmium (Cd), copper (Cu), iron (Fe), manganese (Mn), nickel (Ni), lead (Pb), and zinc (Zn) on the northwestern coast of Corsica (Pirio) was sampled for two years, and their respective concentrations were measured during that period. The sampling station was chosen for its isolation from any local and regional sources of contamination. The year‐to‐year variability of the total atmospheric deposition was found to be high (up to a factor of 2). Using Al as the crustal reference indicates that Pb, Cd, and Zn are mainly associated with man‐made aerosols (>85%), and Fe is mainly associated with crustal aerosols (>70 %). However, our results indicate that Saharan dust is a potential source of “natural” lead, especially in the case of a major input of dust to the northwestern Mediterranean. To determine the spatiotemporal variability of the trace metals over the northwestern Mediterranean Sea, the observed fluxes were compared to those found in the past decade using the same methodology. The comparison indicated a relative homogeneity of Cu and Ni fluxes over the northwestern Mediterranean and over the past decade. The decrease found in Al and Fe since 1985 (by a factor of 4 to 6) can be related to the decrease in Saharan dust fallout. The limitation in the use of lead additives in gasoline may have resulted in a decrease in the European atmospheric lead emissions by a factor of about 6 since 1985 and in a maximum decrease in the total atmospheric flux by a factor of 12 at most if the natural interannual variability of atmospheric deposition in this region is taken into account. So the recorded decrease in the atmospheric lead flux since 1985 (by a factor of ∼30) reveals a slight local contamination at the earlier Corsican station. In the case of Cd and Zn, there was a decrease by a factor of 30 and 23, respectively, between the data obtained at La Tour du Valat (July 1988 to June 1989) and those at Pirio (March 1996 to March 1997); such a decrease cannot be the consequence of either a reduction in emissions in Europe as a whole (the factor being at most 4), or the distance from the emission sources. Hence, we can confirm that Zn and Cd fluxes at La Tour du Valat and Zn fluxes at Cap Ferrat were not representative of a long‐range transport to the Mediterranean but the result of a local/regional contamination. The large decrease observed for metals (Cd, Zn, and Pb) mainly mobilized by human activities, results from a combination of the actual diminution of the concentrations due to a reduction in the emissions and the occurrence of local/regional contamination for some elements at some sampling sites.
Product study and mechanisms of the reactions of α‐pinene and of pinonaldehyde with OH radicals
Authors: Nozière Barbara , Barnes Ian , Becker Karl‐Heinz
Published: September 2002

The reactions of α‐pinene and of its main oxidation product, pinonaldehyde (3‐acetyl‐2,2‐dimethyl‐cyclobutyl‐ethanal), with OH radicals have been studied in the laboratory using Fourier transform infrared spectroscopy for real‐time monitoring of the gas‐phase chemical species and a Scanning Mobility Particle Sizer system (3071 A, TSI) for the study of the secondary aerosol formation. All gas‐phase molar yields were quantified using calibrated reference of the pure compound, except for the nitrates products. The results were: for the α‐pinene experiments in the presence of NOx, pinonaldehyde, (87±20)%; total nitrates (18±9)%; formaldehyde, (23±9)%; acetone (9±6)%; for the α‐pinene experiments in the absence of NOx: pinonaldehyde, (37±7)%; formaldehyde, (8±1)%; acetone, (7±2)%; for the pinonaldehyde experiments in the presence of NO, formaldehyde (152±56)% and acetone (15±7)%. The aerosol measurements showed that the condensed products accounted for the missing carbon in the gas‐phase balance. The partitioning of the products into the condensed phase was found to be potentially significant under experimental conditions but less than 10% for initial α‐pinene concentrations lower than 1013 molecule cm−3 and hence negligible under atmospheric conditions in the absence of aerosol seeds. On the basis of these results a comprehensive mechanism for the gas‐phase reaction of α‐pinene with OH in the presence of NOx has been proposed, including quantitative values for all the involved branching ratios.
Semiannual cycles of pollution at Bermuda
Authors: Huang Suilou , Rahn Kenneth A. , Arimoto Richard , Graustein William C. , Turekian Karl K.
Published: September 2002

To identify the sources and determine the transport pathways for aerosol during the Atmosphere/Ocean Chemistry Experiment (AEROCE), we examined the temporal variations of trace elements in daily aerosol samples collected at Bermuda from 1988 to 1994. Crustal (e.g., Al) and marine (e.g., Na) elements showed annual cycles with summer and winter maxima, respectively. In contrast, pollution‐derived elements (e.g., Sb) showed unusual semiannual cycles with strong spring maxima and weaker fall maxima, which to the best of our knowledge, have not been previously documented. The seasonality in trace element concentrations was mainly transport‐driven: The spring maxima of pollutants were caused by rapid westerly transport from North America, and the fall maxima were caused by North American air slowly transported to Bermuda by large high‐pressure systems that stagnated over the lower mid‐Atlantic states. Low concentrations of pollution elements in winter resulted from the southwestward extension of the Bermuda‐Azores high‐pressure system that brought marine air to Bermuda from the east or northeast while hindering transport from North America and Africa. The summer minima in pollutants were associated with air transported from the eastern Atlantic and Africa. The variations of the trace gases O3 and CO and two naturally occurring radionuclides, 210Pb and 7Be, showed semiannual cycles similar to those of the pollution‐derived trace elements.
Assimilation of Measurement of Air Pollution from Space (MAPS) CO in a global three‐dimensional model
Authors: Lamarque J.‐F. , Khattatov B. V. , Gille J. C. , Brasseur G. P.
Published: September 2002

Observations of carbon monoxide (CO) by the Measurement of Air Pollution from Space (MAPS) instrument onboard the space shuttle were assimilated into a global three‐dimensional chemistry‐transport model using the Physical‐space Statistical Analysis System approach. The assimilation considerably improved the calculated distribution of CO in the troposphere. On the global scale, the adjustment of the CO field resulting from the assimilation procedure was large at the beginning of the assimilation, suggesting discrepancies in the initial conditions of the model. As the model integration/assimilation progressed with time, transport caused the model to drift. This drift limited to a few days the “memory” of CO from its adjustment toward the observations. The assimilation of CO significantly influenced the distribution of other chemical species, even over the limited time periods (∼10 days) analyzed.
Emissions of formaldehyde, acetic acid, methanol, and other trace gases from biomass fires in North Carolina measured by airborne Fourier transform infrared spectroscopy
Authors: Yokelson R. J. , Goode J. G. , Ward D. E. , Susott R. A. , Babbitt R. E. , Wade D. D. , Bertschi I. , Griffith D. W. T. , Hao W. M.
Published: September 2002

Biomass burning is an important source of many trace gases in the global troposphere. We have constructed an airborne trace gas measurement system consisting of a Fourier transform infrared spectrometer (FTIR) coupled to a “flow‐through” multipass cell (AFTIR) and installed it on a U.S. Department of Agriculture Forest Service King Air B‐90. The first measurements with the new system were conducted in North Carolina during April 1997 on large, isolated biomass fire plumes. Simultaneous measurements included Global Positioning System (GPS); airborne sonde; particle light scattering, CO, and CO2; and integrated filter and canister samples. AFTIR spectra acquired within a few kilometers of the fires yielded excess mixing ratios for 10 of the most common trace gases in the smoke: water, carbon dioxide, carbon monoxide, methane, formaldehyde, acetic acid, formic acid, methanol, ethylene, and ammonia. Emission ratios to carbon monoxide for formaldehyde, acetic acid, and methanol were each 2.5±1%. This is in excellent agreement with (and confirms the relevance of) our results from laboratory fires. However, these ratios are significantly higher than the emission ratios reported for these compounds in some previous studies of “fresh” smoke. We present a simple photochemical model calculation that suggests that oxygenated organic compounds should be included in the assessment of ozone formation in smoke plumes. Our measured emission factors indicate that biomass fires could account for a significant portion of the oxygenated organic compounds and HOxpresent in the tropical troposphere during the dry season. Our fire measurements, along with recent measurements of oxygenated biogenic emissions and oxygenated organic compounds in the free troposphere, indicate that these rarely measured compounds play a major, but poorly understood, role in the HOx, NOx, and O3chemistry of the troposphere.
Network for the Detection of Stratospheric Change Fourier transform infrared intercomparison at Table Mountain Facility, November 1996
Authors: Goldman A. , Paton‐Walsh C. , Bell W. , Toon G. C. , Blavier J.‐F. , Sen B. , Coffey M. T. , Hannigan J. W. , Mankin W. G.
Published: September 2002

An intercomparison of four Fourier transform infrared (FTIR) spectrometers, operated side by side by Jet Propulsion Laboratory (JPL), National Center for Atmospheric Research, and National Physical Laboratory groups, using two different spectral fitting algorithms, was conducted at JPL's Table Mountain Facility (TMF) during November 1996. A “blind” comparison of retrieved vertical column amounts, of preselected trace gases in preselected microwindows (mw), and subsequent reanalysis of the results are described. The species analyzed are N2 (3 mw), HF (1 mw), HCl (1 mw), CH4 (1 mw), O3 (2 mw), N2O (2 mw), HNO3 (2 mw), and CO2 (1 mw). The column agreements from the “blind” phase were within 0.5–2%, except that for HNO3, HF, and O3 the disagreement of the results was up to 10%, 5%, and 4%, respectively. It was found that several systematic effects were neglected in the “blind” phase analysis. Taking these into account in the postanalysis reduced the disagreements to 0.5–1.0% for most cases, and to less than 4%, 3%, and 1% for HNO3, HF, and O3 respectively. It was concluded that zero off‐sets caused by detector nonlinearity were the main cause of the large errors in HNO3 and other gases (i.e., CO2) retrieved from the HgCdTe spectra. At shorter wavelengths (i.e., HF) we conclude that incomplete modeling of the instrument line shapes (ILS) was the main cause of column differences larger than 1%.
Upper tropospheric SO2 conversion into sulfuric acid aerosols and cloud condensation nuclei
Authors: Laaksonen Ari , Pirjola Liisa , Kulmala Markku , Wohlfrom Karl‐Heinz , Arnold Frank , Raes Frank
Published: September 2002

We have investigated the potential of upper tropospheric cloud condensation nuclei (CCN) formation from sulfur dioxide. This process involves three steps including SO2 conversion to gaseous sulfuric acid (GSA), homogeneous bimolecular nucleation of GSA and water vapor leading to new aerosol particles, and new aerosol particle growth via mutual coagulation and GSA‐H2O condensation. Our investigation includes both measurements of SO2 and GSA as well as model calculations of SO2 conversion to new aerosol particles in the presence of preexisting aerosols which act as a competing sink for GSA. The model reproduces the measured abundance ratio GSA‐SO2 reasonably well. Furthermore, the model predicts that efficient upper tropospheric CCN formation from SO2 may, in fact, occur under certain plausible conditions. These conditions are explored utilizing the factor FCCN, defined as a ratio of the source and sink terms of gaseous sulfuric acid. In particular, a threshold FCCN value for efficient CCN formation is calculated with the model.
Latitudinal variations of trace gas concentrations in the free troposphere measured by solar absorption spectroscopy during a ship cruise
Authors: Notholt J. , Toon G. C. , Rinsland C. P. , Pougatchev N. S. , Jones N. B. , Connor B. J. , Weller R. , Gautrois M. , Schrems O.
Published: September 2002

The latitudinal variations of atmospheric trace gas column abundances have been measured during a ship cruise between 57°N and 45°S on the central Atlantic. The measurements were performed in October 1996 using high‐resolution solar absorption spectroscopy in the infrared. The analysis method employed permits the retrieval of the total column densities of 20 different trace gases and for a few compounds the vertical mixing ratio profiles. For CH4 an interhemispheric difference of 3% was observed. The total columns of the shorter‐lived trace gases CO and C2H6, analyzed between 57°N and 45°S, reveal a slight maximum in the tropics and a substantial increase north of 45°N. The total columns of C2H2 and HCN, detectable between 30°N and 30°S, reveal a maximum in the tropics of the Southern Hemisphere. For CH2O, studied between 57°N and 45°S, a well‐pronounced maximum is observed in the tropics. The profile retrieval gives high mixing ratios for CO, C2H6, and O3 north of 40°N in the lower troposphere. In the tropics high concentrations are found for all three compounds in the entire troposphere, even above 12 km. The measurements have been used to estimate averaged mixing ratios of the trace gases for the free troposphere between 0 and 12 km. In the tropics the data give high values: for example, more than 200 pptv for HCN, 750 pptv for CH2O, 100 ppbv for CO and 100 pptv for C2H2. These values are comparable to or higher than what has been observed at midlatitudes, indicating the importance of biomass burning emissions on the tropospheric composition.
Influence of valley winds on transport and dispersion of airborne pollutants in the Freiburg‐Schauinsland area
Authors: Kalthoff N. , Horlacher V. , Corsmeier U. , Volz‐Thomas A. , Kolahgar B. , Geiß H. , Möllmann‐Coers M. , Knaps A.
Published: September 2002

The change of the concentration of trace gases in a natural environment depends on both chemical and meteorological conditions. To quantify the contribution of meteorological processes, such as transport and dispersion, chemical and meteorological processes must be assessed separately. In June 1996 the Schauinsland Ozone Precursor Experiment (SLOPE) was carried out to investigate the behavior of ozone and its precursors as a function of time in a valley between Freiburg in the Rhine Valley and Schauinsland in the Black Forest [Volz‐Thomas et al., this issue]. The main purpose of this contribution is to calculate the influence of transport and dispersion on the change of the concentration of airborne pollutants in a propagating air mass. Therefore (1) an inert tracer, SF6, was released, and (2) meteorological measurements were performed to investigate the valley wind regimes and the evolution of the mixed layer. Here are the main results of the experiment: Clear‐sky conditions caused upvalley winds to be generated in the various valleys in the morning. These upvalley winds led to the transport of polluted air and SF6 from Freiburg through the Zarten Basin and the side valley(Großes Tal) up to the Schauinsland hill. The propagation through the Großes Tal took 90± 5 min, which gives a propagation rate of approximately 1.3 m s−1. The dilution factor for SF6 between the entrance and the outlet of the valley was approximately 9. This dilution factor could not only be explained by the continuous growth of the boundary layer during the propagation time of the tracer from the entrance to the outlet of the valley, but additionally by flow splitting and mountain venting [Fiedler et al., this issue].
Fate of long‐lived trace species near the northern hemispheric tropopause: 2. Isotopic composition of carbon dioxide (13CO2, 14CO2, and C18O16O)
Authors: Zahn Andreas , Neubert Rolf , Platt Ulrich
Published: September 2002

CO2 samples collected by aircraft near the winter midlatitude and high‐latitude Northern Hemispheric tropopause were measured for their stable isotope (13C/12C, 18O/16O) and radioisotope (14C/12C) ratios. The strongly varying CO2 and δ13C(CO2) values spanning 21ppm and 1.1‰, respectively, as well as the low 13C/12C ratio of the source/sink system responsible for these variations (inferred by applying a simple “Keeling relationship”) point to frequent transport of polluted air masses to the tropopause. This hypothesis is supported by the often depleted 14C/12C ratios in CO2, marking contributions of up to 9ppm (14C‐free) fossil fuel combustion derived CO2. The oxygen isotope ratio δ18O(CO2) was found to correlate negatively with the CO2 mixing ratio (R ≈ −0.8), which demonstrates that even the δ18O(CO2) data can, as a first approach, be interpreted in terms of a Keeling relation. However, the apparent δ18O(CO2) source/sink signature was found to drop from −(11±3)‰ south of the polar front down to −(27±4)‰ north of it. The low Arctic δ18O(CO2) values can be explained by the assumption that in the wintertime Arctic about double the amount of CO2 isotopically exchanges with 18O‐depleted soil water as is net released by the entire biosphere. A vertical δ18O(CO2) gradient of 0.5‰ km−1 was observed above the tropopause. This δ18O(CO2) increase in the stratosphere is most likely due to oxygen isotope exchange between CO2 and electronically excited oxygen O(1D), the isotope composition of which is controlled by that of O3, in the stratosphere known to be strongly enriched in the heavy oxygen isotopes. The typical δ18O(CO2) gradient is assumed to be lower compared to measured because our high‐altitude samples were affected by chemically disturbed polar vortex air.
Tropospheric water vapor measurements over the North Atlantic during the Subsonic Assessment Ozone and Nitrogen Oxide Experiment (SONEX)
Authors: Vay S. A. , Anderson B. E. , Jensen E. J. , Sachse G. W. , Ovarlez J. , Gregory G. L. , Nolf S. R. , Podolske J. R. , Slate T. A. , Sorenson C. E.
Published: September 2002

Fast‐response tunable diode laser measurements of water vapor were made over the North Atlantic during the Subsonic Assessment Ozone and Nitrogen Oxide Experiment (SONEX) conducted in the fall of 1997. Resulting water vapor mixing ratios, in conjunction with air temperature and pressure measurements obtained by the DC‐8's Data Acquisition and Distribution System (DADS), were used to calculate the prevalence of ice‐saturated conditions (relative humidity with respect to ice >100% or frost saturation) in the upper troposphere over the SONEX sampling region. Additionally, Appleman theory was applied to the data to determine the subset of ice‐saturated regions which would support formation of contrails. Results suggest that studies to determine the potential climate or radiative impact of contrails and aviation‐induced cirrus clouds should not only consider the climatology of frost‐saturated regions, but should also address whether ambient conditions can support contrail formation within these regions. A separate discussion within the paper describes an in‐flight intercomparison between the SONEX diode laser hygrometer and the Pollution From Aircraft Emissions in the North Atlantic Flight Corridor (POLINAT 2) cryogenic hygrometer and shows that the instruments perform to within their stated accuracies (∼10%) over a range of mixing ratios and altitudes.
Possible role of power plant plume emissions in fostering O3 exceedence events in Atlanta, Georgia
Authors: St. John James C. , Chameides William L.
Published: September 2002

Shortly after 12 noon on August 15, 1995, the second highest 1‐hour averaged O3 mixing ratio on record in Atlanta was observed at a monitoring site located to the west and generally upwind of the downtown core. Analysis of relevant data suggest that the peak mixing ratio at the site was caused by a highly localized and transient event: the intersection of a plume emanating from a nearby power plant with the monitoring site. In addition to representing an exceedence of the 1‐hour‐120‐ppbv U.S. National Ambient Air Quality Standard (NAAQS), the O3 mixing ratios observed at the site would have also been in excess of the new 8‐hour‐80‐ppbv NAAQS. Without more extensive observational data it is not possible to assess spatial and temporal frequency of this type of event, although SO2 data from downtown Atlanta, and modeling studies suggest that there may be significant influence by these plumes on the measurement of O3 at Atlanta monitoring sites.
A three‐dimensional total odd nitrogen (NOy) simulation during SONEX using a stretched‐grid chemical transport model
Authors: Allen Dale , Pickering Kenneth , Stenchikov Georgiy , Thompson Anne , Kondo Yutaka
Published: September 2002

The relative importance of various odd nitrogen (NOy) sources including lightning, aircraft, and surface emissions on upper tropospheric total odd nitrogen is illustrated as a first application of the three‐dimensional Stretched‐Grid University of Maryland/Goddard Chemical‐Transport Model (SG‐GCTM). The SG‐GCTM has been developed to look at the effect of localized sources and/or small‐scale mixing processes on the large‐scale or global chemical balance. For this simulation the stretched grid was chosen so that its maximum resolution is located over eastern North America and the North Atlantic; a region that includes most of the Subsonic Assessment (SASS) Ozone and Nitrogen Oxide Experiment (SONEX) flight paths. The SONEX period (October‐November 1997) is simulated by driving the SG‐GCTM with assimilated data from the Goddard Earth Observing System‐Stratospheric Tracers of Atmospheric Transport Data Assimilation System (GEOS‐STRAT DAS). A new algorithm is used to estimate the lightning flash rates needed to calculate NOyemission by lightning. This algorithm parameterizes the flash rate in terms of upper tropospheric convective mass flux. Model‐calculated upper tropospheric NOyand NOymeasurements from the NASA DC‐8 aircraft are compared. Spatial variations in NOywere well captured especially with the stretched‐grid run; however, model‐calculated peaks due to “stratospheric” NOyare occasionally too large. The lightning algorithm reproduces the temporally and spatially averaged total flash rate accurately; however, the use of emissions from observed lightning flashes significantly improves the simulation on a few days, especially November 3, 1997, showing that significant uncertainty remains in parameterizing lightning in chemistry and transport models. Aircraft emissions contributed ∼15% of the upper tropospheric NOyaveraged along SONEX flight paths within the North Atlantic Flight Corridor with the contribution exceeding 40% during portions of some flights.
Effects of specifying bottom boundary conditions in an ensemble of atmospheric GCM simulations
Authors: Zwiers Francis W. , Wang Xiaolan L. , Sheng Jian
Published: September 2002

Interannual variability in an ensemble of six 47‐year climate simulations with specified time‐varying sea surface temperature (SST) and sea ice extent is analyzed. Variability is compared with that in a 250‐year control simulation with climatological SST and sea ice extent. The simulations were performed with the Canadian Climate Centre second generation General Circulation Model. An analysis of variance approach was combined with rotated Empirical Orthogonal Function analysis to assess the influence of the prescribed boundary conditions on the simulated atmospheric circulation structure and variability and to identify potentially predictable spatially coherent modes of variation. The quantities analyzed are seasonal mean 500 hPa geopotential (Z500) and mean sea level pressure (Pmsl). The prescribed boundary conditions increase the variability of the simulated atmosphere and modulate its large‐scale circulation structure. The effects on Z500 are found to be strongest in DJF and MAM and weakest in SON. The prescribed boundary conditions have a significant effect over the extratropical land areas, especially over northern North America, in El Niño‐Southern Oscillation (ENSO) years, but have little influence in non‐ENSO years. The variability of several of the leading spatial modes is significantly affected by the prescribed boundary conditions. In contrast with some previous studies, we find that the simulated North Atlantic Oscillation is not affected by the prescribed boundary forcing.
Cloud processing of continental aerosol particles: Experimental investigations for different drop sizes
Authors: Krämer Martina , Beltz Norbert , Schell Dieter , Schütz Lothar , Sprengard‐Eichel Cornelia , Wurzler Sabine
Published: September 2002

Atmospheric aerosol particles are activated and grow into drops during the formation of a cloud. Subsequently, they are delivered from the dissipating cloud drops back to the atmosphere. During the cloud lifetime, the drops scavenge water‐soluble trace gases, leading to an increase in size and solubility of the particles emerging from the evaporating cloud drops. This processing of aerosol particles by clouds has an influence on the microphysics of the following cloud and its probability to rain as well as on the cooling effect of the direct and indirect aerosol forcing of climate. To measure the cycling history (particle activation and gas scavenging in drops followed by processing of the activated particles followed by emerging processed particles) of continental aerosol particles passing through cloud drops of different sizes, a new method is developed and applied during three field experiments carried out on the Mount Kleiner Feldberg/Ts., Germany, in 1990, 1993, and 1995. The typical droplet spectra of most of the observed stratus clouds is weakly bimodal, with mode 1 at drop sizes between 3 and 5 μm and mode 2 between 5 and 10 μm radius. Cloud drops in this overall size range are subject to growth only by condensation, while coalescence can be neglected. Therefore the observed processing is related solely to gas scavenging and in‐cloud chemical reactions. We found that the processing of particles is different for the two modes of the cloud drop size spectrum: Small activated particles mostly grow to the small drops of mode 1, while larger particles can grow further to the larger drops of mode 2. Likewise, the mass of scavenged gas is, on average, lower for the small than for the larger drops. Vice versa, the ratio of scavenged gas to particle mass, the parameter quantifying the particle processing, is, on average, found to be higher in the small drop mode containing the smaller particles. The reason is that the degree of processing is mainly inversely linked to the mass of the activated particles. Therefore the strongest modification of particles takes place in smaller drops and affects mainly the smaller activated particles (r ap ≤ 0.1 μm). Their radii can increase by up to a factor of 3 and, consequently, their nucleation as well as radiative properties change significantly. The consequence for the aerosol climate forcing is that the cooling can be, to an unknown extent, intensified with increasing atmospheric amount of water‐soluble trace gases such as HNO3, NH3, and SO2, counteracting the warming effect of the greenhouse gases.
Effects of satellite scanning configurations on derived gridded fields
Authors: Lait Leslie R.
Published: September 2002

Various configurations of a scanning satellite instrument are simulated by sampling realistic fields of nitrous oxide. Synoptic grids are computed from the resulting simulated orbital data and compared to the original sampled data fields. Results are compared with those obtained by flying a simulated satellite over low‐resolution fields and fields that are static in time. Although increasing the number of instrument scan positions does provide more information along an orbital swath, using more than three to five scan positions does not significantly increase the accuracy of global synoptic grids using the gridding techniques described here.
Remote sensing of cloud properties using MODIS airborne simulator imagery during SUCCESS: 1. Data and models
Authors: Baum Bryan A. , Kratz David P. , Yang Ping , Ou S. C. , Hu Yongxiang , Soulen Peter F. , Tsay Si‐Chee
Published: September 2002

We investigate methods to infer cloud properties such as cloud optical thickness, thermodynamic phase, cloud particle size, and cloud overlap by comparing cloud and clear‐sky radiative transfer computations to measurements provided by the Moderate Resolution Imaging Spectroradiometer (MODIS) airborne simulator (MAS). The MAS scanning spectroradiometer was flown on the NASA ER‐2 during the Subsonic Aircraft Contrail and Cloud Effects Special Study (SUCCESS) field campaign during April and May 1996. The MAS bands chosen for this study correspond to wavelengths of 0.65, 1.63, 1.90, 2.15, 3.82, 8.52, 11, and 12 μm. Clear‐sky absorption due to water vapor, ozone, and other trace gases is calculated using a set of correlated k‐distribution routines developed specifically for these MAS bands. Scattering properties (phase function, single‐scattering albedo, and extinction cross section) are derived for water droplet clouds using Mie theory. Scattering properties for ice‐phase clouds are incorporated for seven cirrus models: cirrostratus, cirrus uncinus, cold cirrus, warm cirrus, and cirrus at temperatures of T = −20°C, −40°C, and −60°C. The cirrus are composed of four crystal types: hexagonal plates, two‐dimensional bullet rosettes, hollow columns, and aggregates. Results from comparison of MAS data from a liquid water cloud with theoretical calculations indicate that estimates of optical thickness and particle size are reasonably consistent with one another no matter which spectral bands are used in the analysis. However, comparison of MAS data from a cirrus cloud with theoretical calculations shows consistency in optical thickness but not with particle size among the various band combinations used in the analysis. The methods described in this paper are used in two companion papers to explore techniques to infer cloud thermodynamic phase and cloud overlap.
Effect of biomass burning, convective venting, and transport on tropospheric ozone over the Indian Ocean: Reunion Island field observations
Authors: Randriambelo Tantely , Baray Jean‐Luc , Baldy Serge
Published: September 2002

Relationships between vertical distribution of tropospheric ozone at Reunion Island (21°S‐55°E), satellite (NOAA advanced very high resolution radiometer) observations of fires, smoke plumes, and convective events in southeastern Africa and Madagascar, and analyses of meteorological situations (European Centre for Medium‐Range Weather Forecasts) are presented. This study is based on 7 years (1992 to 1999) of 2‐monthly PTU‐O3 radiosoundings at Reunion. Results show, for the first time, that during 1995 tropospheric ozone content rose above average and that this year should be set apart as atypical. Stratospheric contributions are also ruled out using an identification method based on considerations of ozone, humidity, vertical stability, and meteorological conditions. The seasonal variation of ozone profiles during typical years and without the stratospheric contribution suggests that ozone contamination from biomass burning is a maximum during October in the whole free troposphere. During August, before the deep convection period, but already within the fire period, only the middle troposphere is contaminated by ozone inputs. By contrast, through November to December, well within the deep convection period, all the higher troposphere is contaminated. The comprehensive study of the observations in 1993, taken as a typical year, highlights the roles of convection and transport in contamination of remote oceanic regions. August contamination of the middle troposphere by about 70 ppbv of ozone is contrasted to October enhancement of the whole free troposphere by about 100 ppbv of ozone after the spreading of deep convective events. Fire satellite data further indicate that column integrated contamination level mainly depends on biomass burning intensity. Through August to October the fourfold increase of ozone concentration is comparable with the fivefold augmentation of fires. The redistribution of ozone with altitude depends on the convection intensity near source regions in accordance with convection detection and backtrajectory analysis.
Implications of subsonic aircraft NOx emissions for the chemistry of the lowermost stratosphere: Model studies on the role of bromine
Authors: Hendricks J. , Lippert E. , Petry H. , Ebel A.
Published: September 2002

The role of inorganic bromine compounds in the chemistry of the midlatitude lowermost stratosphere is examined. Model studies are perfomed using a chemistry box model. Special emphasis is layed on investigating the implications of bromine chemistry on the atmospheric effects of subsonic aircraft NOx emissions. The simulations suggest that the presence of bromine constituents leads to an effective denoxification, an activation of HOx, and a significant ozone depletion in the background lowermost stratosphere. Bromine chemistry has the potential to induce large increases in the modeled ozone production caused by aircraft NOx emissions in the lowermost stratosphere. The modeled effect strongly depends on the availability of inorganic bromine compounds, on aerosol loading, and on the NOx background concentration. The hydrolysis reaction of BrONO2 on sulfate aerosols and the reaction of BrO with HO2 appear to be the key reactions driving the simulated impact of bromine chemistry on the aircraft‐induced ozone changes.
Statistical significance of trends and trend differences in layer‐average atmospheric temperature time series
Authors: Santer B. D. , Wigley T. M. L. , Boyle J. S. , Gaffen D. J. , Hnilo J. J. , Nychka D. , Parker D. E. , Taylor K. E.
Published: September 2002

This paper examines trend uncertainties in layer‐average free atmosphere temperatures arising from the use of different trend estimation methods. It also considers statistical issues that arise in assessing the significance of individual trends and of trend differences between data sets. Possible causes of these trends are not addressed. We use data from satellite and radiosonde measurements and from two reanalysis projects. To facilitate intercomparison, we compute from reanalyses and radiosonde data temperatures equivalent to those from the satellite‐based Microwave Sounding Unit (MSU). We compare linear trends based on minimization of absolute deviations (LA) and minimization of squared deviations (LS). Differences are generally less than 0.05°C/decade over 1959–1996. Over 1979–1993, they exceed 0.10°C/decade for lower tropospheric time series and 0.15°C/decade for the lower stratosphere. Trend fitting by the LA method can degrade the lower‐tropospheric trend agreement of 0.03°C/decade (over 1979–1996) previously reported for the MSU and radiosonde data. In assessing trend significance we employ two methods to account for temporal autocorrelation effects. With our preferred method, virtually none of the individual 1979–1993 trends in deep‐layer temperatures are significantly different from zero. To examine trend differences between data sets we compute 95% confidence intervals for individual trends and show that these overlap for almost all data sets considered. Confidence intervals for lower‐tropospheric trends encompass both zero and the model‐projected trends due to anthropogenic effects. We also test the significance of a trend in d(t), the time series of differences between a pair of data sets. Use of d(t) removes variability common to both time series and facilitates identification of small trend differences. This more discerning test reveals that roughly 30% of the data set comparisons have significant differences in lower‐tropospheric trends, primarily related to differences in measurement system. Our study gives empirical estimates of statistical uncertainties in recent atmospheric temperature trends. These estimates and the simple significance testing framework used here facilitate the interpretation of previous temperature trend comparisons involving satellite, radiosonde, and reanalysis data sets.
Analysis of tropospheric transport in the Pacific Basin using the adjoint technique
Authors: Vukićević Tomislava , Hess Peter
Published: September 2002

An adjoint sensitivity analysis is performed within a regional episodic chemical transport model covering the Pacific Basin. The analysis is performed with respect to the concentration over Hawaii of a soluble and insoluble chemically inert species, with the same emissions as NOx. The sensitivity is examined at times of elevated tracer mixing ratio at 300, 680, and 900 mbar. The sensitivity to the average mixing ratio at 680 mbar is also examined. The meteorological conditions of April and May 1992 are used for the transport. The adjoint analysis includes the effect of the entire model transport function. It provides a method to analyze the transport of modeled emissions to Hawaii, including the effect of various emission regions, and the associated transport pathways and timescales. The boundary layer mixing ratio at Hawaii is most sensitive to local emissions, with emissions from North America and Asia also contributing to the modeled concentration. In the free troposphere the concentration over Hawaii is most sensitive to emissions from Asia. The adjoint also allows modeled processes to be ranked by their importance in determining the concentration of a species at a particular location. At Hawaii, emissions are ranked first and second in order of importance for the insoluble and soluble species, respectively. For the soluble species the solution is most sensitive to the modeled wet deposition by nonconvective rain. Free tropospheric mixing is generally next in order of importance. Deep convection is important in some locations, particularly for the 300 mbar concentrations. Boundary layer processes, including dry deposition, are generally not important to the free tropospheric solution at Hawaii.