bluuebunny/crossref_metadata_2025 huggingface dataset:
Emission of nitrogen monoxide from African tropical ecosystems: Control of emission by soil characteristics in humid and dry savannas of West Africa
Authors: Le Roux X. , Abbadie L. , Lensi R. , Serça D.
Published: February 2004

Heterogeneity of soil characteristics and potential microbial activities were measured in several humid tropical West African ecosystems and in one dry savanna ecosystem in order to explain the high spatial variability of NO fluxes observed in the field. At the landscape scale, the variability of NO emission rates in the humid zone is mainly a function of topographic position and vegetation type. The highest NO fluxes occur in the downslope nutrient‐rich environment (forest) which exhibits high denitrification potential and high total mineral N accumulation. NO fluxes are low in humid savanna environments which exhibit no detectable potential denitrification. Local structures such as mounds colonized by hypogeous termites exhibit an accelerated nitrogen cycling relative to their surroundings. Ammonium is quickly converted to nitrate; the soil has high potential rates of denitrification with correspondingly high NO emissions. NO fluxes are also high in dry savanna soils with high nitrification potentials but low denitrification potentials, suggesting that NO at these sites was produced during nitrification rather than denitrification. These results underscore the importance of considering the mechanisms driving spatial variability and the need to account for them in large‐scale extrapolations. Among the soil characteristics studied, denitrification potentials provide a reliable indication of high NO fluxes for the humid sites, but not for the dry sites.
Remote sensing of ClO and HCl over northern Scandinavia in winter 1992 with an airborne submillimeter radiometer
Authors: Wehr T. , Crewell S. , Künzi K. , Langen J. , Nett H. , Urban J. , Hartogh P.
Published: February 2004

In February and March 1992 stratospheric ClO and HCl over northern Scandinavia were observed with the submillimeter‐wave atmospheric sounder (SUMAS), as part of the European Arctic Stratospheric Ozone Experiment (EASOE). SUMAS is operated on board the German research aircraft Falcon and observes thermal emission lines in the frequency range 620–650 GHz. In this paper the instrument design and techniques to retrieve volume mixing ratios (VMR) from the measurement will be discussed. Results from the EASOE campaign will be presented including a detailed error analysis. A comparison of the retrieved profiles in the lower stratosphere indicates a strong decrease of ClO abundances from February to March, whereas no corresponding increase in HCl is observed.
Length scale composition of moisture flux in a continental, convective boundary layer
Authors: Grossman Robert L.
Published: February 2004

A multivariate conditional sampling method introduced in a companion paper is extended to investigate length scale contribution to turbulent fluxes. The method is briefly introduced. A model of convective processes thought to be active over the continental boundary layer during the First International Land Surface Climatology Project Field Experiment (FIFE) is used to interpret the conditional sampling results. The conditional sampling scheme is used to investigate moisture flux data obtained near the surface and near the inversion during the morning transition (a period of rapid mixed layer growth) and the afternoon's fully developed mixed layer (a period of slow mixed layer growth). Length scale distributions associated with the primary conditional sampling pair, vertical wind speed, and virtual potential temperature (a surrogate for density) were highly skewed with a predominance of shorter lengths relative to the longer ones. There was little difference in the length scale distributions for near‐surface and near‐inversion legs, nor were there obvious differences between morning and afternoon. The contribution of length scales to the moisture flux showed that the bulk of the flux was associated with the relatively fewer longer length scale events and not with the predominance of shorter lengths. In general, the length scale decomposition showed the bulk of the moisture flux to be associated with longer lengths (greater than 300 m) near the inversion compared to the length scales of the near‐surface flux. While there was little difference in the moisture flux distribution between morning and afternoon in the near‐surface layer, there were substantial differences in the near‐inversion distribution. Although these observations are consistent with cospectral decomposition of turbulent fluxes, the magnitudes of cospectral wavelengths were much longer compared to this analysis. Importantly, the near‐surface flux has a substantial contribution from downward moving coherent structures originating in the inversion layer. Length scales greater than 200 m are a significant portion of this inversion contribution to the near‐surface flux, a fact that must be taken into account in the determination of the surface flux “footprint”.
Halogen Occultation Experiment ozone channel validation
Authors: Brühl Christoph , Drayson S. Roland , Russell James M. , Crutzen Paul J. , McInerney Joseph M. , Purcell Patrick N. , Claude Hans , Gernandt Hartwig , McGee Thomas J. , McDermid Iain S. , Gunson Michael R.
Published: February 2004

The HALogen Occultation Experiment (HALOE) instrument on UARS observes vertical profiles of ozone and other gases of interest for atmospheric chemistry using the solar occultation technique. A broadband radiometer in the 9.6‐μm band is used for ozone measurements. Version 17 ozone retrieved by HALOE is intercompared successfully with about 400 profiles of other sounders, including ozonesondes, lidars, balloons, rocketsondes, and other satellites. Usually, the HALOE data are within the error range of the correlative measurements between about 100 and 0.03 mbar atmospheric pressure. Between about 30 and 1 mbar, HALOE agrees typically within 5%, with a tendency to be low. In the first year of data, larger errors sometimes occur in the lower stratosphere due to the necessary correction for Pinatubo aerosol effects, but these differences do not exceed 20%. The data show internal consistency for sunrise and sunset events at the same locations. Some examples of observed ozone distributions, including polar regions, are given.
Aerosol measurements during the Mauna Loa Photochemistry Experiment 2
Authors: Bodhaine Barry A.
Published: February 2004

Aerosol measurements have been made continuously at Mauna Loa Observatory (MLO) from 1974 to the present. Condensation nucleus (CN) concentration has been measured using automatic CN counters, and aerosol scattering extinction (σsp) has been measured using a four‐wavelength nephelometer. The Mauna Loa Observatory Photochemistry Experiment (MLOPEX) was conducted in 1991–1992 to study intensively many important variables in the field of atmospheric chemistry. Because of a strong diurnal cycle in nearly everything measured at MLO, caused by an upslope‐downslope wind system, it is important to develop data‐editing criteria that can safely identify background conditions as opposed to other conditions when the site may be contaminated by local sources. Ordinarily, background conditions occur during nighttime downslope wind conditions, and contaminated conditions occur during daytime upslope wind conditions. However, occasionally unusual weather conditions or contamination caused by a local source such as the Mauna Loa caldera can confuse the issue. It is recommended that background aerosol data be chosen during 0000–0800 Hawaiian standard time (HST) to generally avoid upslope wind conditions, and that wind direction and speed, CN, and SO2 data be used if available to further eliminate local pollution episodes. In addition, all data should be examined by a human editor, if possible, in order to recognize certain episodes that may not fit automated criteria.
Evidence for anthropogenic impact on number concentration and sulfate content of cloud‐processed aerosol particles over the North Atlantic
Authors: Van Dingenen Rita , Raes Frank , Jensen Niels R.
Published: February 2004

Aerosol properties were measured during two transects over the North Atlantic between Halifax (Nova Scotia, Canada) and the Moroccan coast. Measurements of the chemical composition of total aerosol, of the black carbon concentration and of the number size distributions with particle diameter Dp in the range 16 nm < Dp < 1 μm were made. The e‐folding lifetime of the black carbon aerosol, coming from the northeast American continent and transported eastward over the ocean, was estimated to be 15 hours. The non‐sea‐salt (nss) fraction of the sulfate concentrations encountered during this campaign spans a 3 order of magnitude range (0.02 μm m−3 to 19 μm m−3) and shows a high correlation with black carbon. The measured bimodal aerosol size distributions were analysed in order to yield number concentrations of the nuclei and the accumulation mode (ACM), the latter being interpreted as cloud‐processed particles and thus as cloud condensation nuclei (CCN). A strong positive correlation was found between ACM number concentration and nss‐sulfate load over the whole concentration range, i.e. for clean to polluted air masses. Furthermore, our regression between nss‐sulfate and ACM number concentration also agrees well with results from other investigators where CCN or cloud droplet concentrations were related to nss‐sulfate at a variety of geographical locations and degrees of pollution. The composite data set shows that the nss‐sulfate‐CCN relationship from baseline conditions to anthropogenically conditioned aerosol, happens via a smooth transition which can be described by a linear regression on a logarithmic scale.
Dimethylsulfide in marine air at Cape Grim, 41°S
Authors: Ayers G. P. , Bentley S. T. , Ivey J. P. , Forgan B. W.
Published: February 2004

Atmospheric dimethylsulfide measurements made in marine air at Cape Grim, Tasmania, have been combined with a simple photochemical box model to provide estimates of monthly mean flux of dimethylsulfide from the Southern Ocean upwind of Cape Grim. The flux estimates for midsummer agree remarkably well with the independent estimates made for the latitude of Cape Grim based on oceanic surface water data and simple sea‐air transport models. However, for midwinter the flux estimates made here, based on atmospheric dimethlysidfide data, are as much as an order of magnitude lower than those made elsewhere based on oceanic surface water data.
Comparative lidar study of the optical, geometrical, and dynamical properties of stratospheric post‐volcanic aerosols, following the eruptions of El Chichon and Mount Pinatubo
Authors: Chazette P. , David C. , Lefrère J. , Godin S. , Pelon J. , Mégie G.
Published: February 2004

The spatiotemporal evolution of aerosols formed from precursors injected into the stratosphere by major volcanic eruptions, such as those of El Chichon in 1982 and Mount Pinatubo in 1991, has been studied using a ground‐based lidar system located at the Observatoire de Haute‐Provence (OHP) in southern France (44°N, 5°E). From the inversion of the lidar signals the optical, geometrical and dynamical properties of the particles have been determined as a function of time after the eruption. In immediate post‐volcanic conditions, when the optical thickness of particles in the stratosphere is largely enhanced, an estimate of the aerosols backscatter phase function has been evaluated directly from the lidar measurements, using a size‐distribution model adjusted to in situ balloon measurements. The precision of this determination lies in the ±15% range. Values of the mean radius of the particles, of their integrated content, surface areas, and sedimentation velocities are then derived from the systematic lidar measurements performed at OHP. These values are compared for the two major volcanic eruptions which have occurred over the last decade. Although the injection of sulphur dioxide was twice as large for the Mount Pinatubo eruption as compared to the El Chichon case, the diffusion of the cloud in the two hemispheres due to the interaction of the particular phase of the quasi‐biennal oscillation with several other dynamical processes at the time of the eruption, led to the observation of similar values for the aerosol content over the Observatoire de Haute‐Provence in the months just following the two events. However, the residence time of the particles in atmospheric layers below 20 km are 4 months longer after the Mount Pinatubo eruption, caused by the observed difference in the initial vertical distribution of the aerosol cloud.
Seasonal variation of N2O and CH4 fluxes in differently managed arable soils in southern Germany
Authors: Flessa H. , Dörsch P. , Beese F.
Published: February 2004

Agricultural practices are assumed to contribute significantly to the increase in atmospheric nitrous oxide (N2O) concentrations observed in the last decades, and they might influence the consumption of atmospheric methane (CH4) by soil. The aim of this study was to quantify the effects of management intensity, soil type, and frost periods on the emission of N2O and the consumption of CH4 in rotations in southern Germany. Fluxes of N2O and CH4 were monitored over 12 months, using a closed chamber technique. The extensively managed system was cropped to sunflower and fertilized with farmyard manure (12 t ha−1). The intensively managed field was planted with spring wheat and fertilized with a total of 190 kg N ha−1 given as calcium ammonium nitrate (30 kg N) and urea‐NH4NO3 solution (160 kg N). Variation in the N2O emissions with time was extremely high, with flux rates ranging from 0 to 2700 μg m−2 h−1. The N2O fluxes were influenced by soil properties, management practices, and weather. The highest release rates were measured in the winter during thawing of the frozen soil. During the growing season, N2O emission was highest after heavy precipitation. No strong relationship was found between N2O emission rates and soil factors such as soil temperature, soil moisture, and soil nitrate content. Annual fluxes of N2O from the extensively managed field were 9.4 and 12.9 kg N2O‐N ha−1 yr−1 for a sandy soil and a clay soil, respectively. Total N2O‐N losses from the intensively fertilized field amounted to 9.6 kg ha−1 yr−1 for a silty soil with a tendency to waterlogging during wintertime and to 16.8 kg ha yr−1 for a loamy colluvial soil. Up to 46% of the annual N2O evolution was emitted during December and January when frost/thaw cycles induced extremely high N2O production. The application of urea‐NH4NO3 solution significantly increased N2O emission rates. Of the 160 kg N applied, 2.9 kg N or 1.8% was lost as N2O within a period of 8 weeks. Rates of CH4‐C uptake varied from 0 to 17 μg m−2 h−1. Soil temperature correlated positively and soil moisture correlated negatively with the CH4 consumption. Stepwise multiple linear regression, including these soil factors, explained up to 44% of the variation in CH4 fluxes. Annual CH4‐C uptake was rather similar for the intensively and extensively managed Eutrochrepts, ranging from 348 to 395 g ha−1. Significantly higher CH4‐C consumption of 567 g ha−1 yr−1 occurred in the colluvial soil (Typic Udifluvent). N fertilizers had no effect on the CH4 flux rates.
Sulfur dioxide as a source of condensation nuclei in the upper troposphere of the Pacific Ocean
Authors: Thornton D. C. , Bandy A. R. , Blomquist B. W. , Davis D. D. , Talbot R. W.
Published: February 2004

The NASA Pacific Exploratory Mission‐West A (PEM‐West A) experiment in 1991 covered large portions of the northwestern Pacific Ocean troposphere and a transect of the subtropical troposphere of the North Pacific Ocean. Sulfur dioxide consistently increased with altitude from the surface to 11 km except for a few cases of anthropogenic inputs confined to the planetary boundary layer. Using the PEM West A data set for SO2, sulfate, and calculated OH over the central Pacific Ocean, we have estimated the impacts of the SO2 on the formation of condensation nuclei and the lifetimes of SO2 and sulfate for this region.
Intercomparison of Umkehr and differential absorption lidar stratospheric ozone measurements
Authors: Hahn J. F. , McElroy C. T. , Hare E. W. , Steinbrecht W. , Carswell A. I.
Published: February 2004

A comparison of stratospheric ozone measurements using the Umkehr and differential absorption lidar (DIAL) techniques is presented. The ozone observations were made in Toronto, Canada (43.8°N, 79.5°W), using a Brewer ozone spectrophotometer and a DIAL co‐owned by York University, the Institute for Space and Terrestrial Science, and the Atmospheric Environment Service. DIAL and Umkehr comparisons were made between January 1, 1991, and November 30, 1993. Our measurements show that under conditions of low aerosol loading, the Umkehr and DIAL ozone measurements overlap within their respective confidence intervals. After the Mount Pinatubo eruption the presence of aerosol affects both measurement techniques. The Umkehr retrievals are 20–40% lower than corresponding DIAL data at altitudes of 28 km and above. Below 28 km the DIAL data are ∼35% lower than the Umkehr measurements. We apply aerosol corrections to the Umkehr data and observe overlap between DIAL and Umkehr measurements for altitudes greater than 28 km to within their respective error intervals throughout the entire period of observation.
Effect of fertilizer application on NO and N2O fluxes from agricultural fields
Authors: Harrison Roy M. , Yamulki Sirwan , Goulding K. W. T. , Webster C. P.
Published: February 2004

Losses of fertilizer as NO and N2O were studied at Broadbalk field, Rothamsted Experimental Station in England, on which subplots have been subject to differing constant levels of fertilizer application for many years. Fluxes of NO and N2O were measured using open‐ and closed‐chamber techniques, respectively. Fluxes from unfertilized soil ranged from 0.3 to 4.8 ng N m−2 s−1 for NO and 0.23 to 3.0 ng N m−2 s−1 for N2O. The corresponding fluxes from the plot with the highest fertilizer application (92 kg N ha−1 yr−1 as NH4NO3) ranged from 0.5 to 64 ng N m−2 s−1 for NO and 0.4 to 240 ng N m−2 s−1 for N2O. Application of increasing amounts of fertilizer substantially enhanced emission rates of both NO and N2O. However, the amount of increase was controlled by competition between the crop and the microorganisms for the available soil nutrients, and loss of N2O to the atmosphere increased sharply at superoptimal levels of fertilizer application. The fertilizer‐derived NO and N2O emissions represented approximately 90% of the total emission of these gases during the 25−day sampling period after fertilizer application. The results suggest that while increasing the amount of fertilizer increases both NO and N2O fluxes simultaneously, the NO/N2O emission ratio decreases. Results from laboratory experiments showed that the magnitude of the fertilizer loss as N2O was strongly affected by the form of the applied fertilizer.
Improved stratospheric and mesospheric sounder validation: General approach and in‐flight radiometric calibration
Authors: Rodgers C. D. , Wells R. J. , Grainger R. G. , Taylor F. W.
Published: February 2004

This paper introduces a series of papers describing the validation of data products from the improved stratospheric and mesospheric sounder (ISAMS) on the Upper Atmosphere Research Satellite. ISAMS is a limb‐sounding infrared gas‐correlation radiometer, measuring thermal emission from a range of constituents. The constituents measured are ozone, water vapor, methane, nitrous oxide, nitric oxide, nitrogen dioxide, nitrogen pentoxide, nitric acid, carbon monoxide, and aerosol. Atmospheric temperature and composition data were obtained for approximately 180 days between September 26, 1991, and July 29, 1992, with near‐global coverage. The instrument and the retrieval process are briefly described, together with aspects of the validation process relevant to all data products, including the radiometric calibration and the analysis of the calibrated radiances to produce data on a standard time‐altitude grid.
Southern hemisphere midlatitude ground‐based measurements of ClONO2: Method of analysis, seasonal cycle and long term‐trend
Authors: Reisinger Andreas R. , Jones Nicholas B. , Matthews W. Andrew , Rinsland Curtis P.
Published: February 2004

We report the first long‐term analysis of the total column of ClONO2 from ground‐based infrared solar absorption measurements recorded at Lauder, New Zealand (45°S, 170°E, 370 m above sea level (asl)). Between September 1990 and August 1994 the ClONO2 total column averaged 1.22(±0.4)×1015 cm−2 (1σ standard deviation), in good agreement with previous airborne and spaceborne measurements at southern hemisphere midlatitudes. The monthly mean ClONO2 column over Lauder shows a clear seasonal cycle with a peak amplitude of 22(±3)% of the yearly mean (1σ standard error) with the seasonal maximum occurring in early September. This is the first measured seasonal variation of ClONO2. Within the error limits, the derived September 1990 to August 1994 total column increase rate of 1.3(±2)% per year (1σ standard error) is consistent with determinations of the recent growth rate of atmospheric chlorine.
The vertical distribution of ozone measured at Brazzaville, Congo during TRACE A
Authors: Nganga Dominique , Minga Alexis , Cros Bernard , Biona C. Bouka , Fishman Jack , Grant William B.
Published: February 2004

The distribution of ozone in the African tropical region is examined for measurements made between late June 1990 and early October 1992 in support of the NASA Global Tropospheric Experiment/Transport and Atmospheric Chemistry Near the Equator‐Atlantic (GTE/TRACE A) experiment conducted at Brazzaville (4°17′S, 15°15′E;) in September and October 1992. A set of ozone data has been obtained in the troposphere and the stratosphere to above 30 km using balloon‐borne electrochemical concentration cell ozonesondes. The analysis of the tropospheric data confirms the seasonal trends of ozone in these latitudes, which shows, in particular, the presence of an ozone‐enriched layer located between 1‐ and 4‐km altitude during the dry season of each hemisphere. A more detailed analysis of the data set for September–October 1992 shows a behavior of ozone which suggests the presence of two periods of biomass burning in the dry season of the southern hemisphere. In addition, this study shows that the dry season of the northern hemisphere has a limited influence on tropospheric ozone at large distances.
Temperature‐dependent daily variability of precipitable water in special sensor microwave/imager observations
Authors: Gutowski William J. , Lindemulder Elizabeth A. , Jovaag Kari
Published: February 2004

We use retrievals of atmospheric precipitable water from satellite microwave observations and analyses of near‐surface temperature to examine the relationship between these two fields on daily and longer timescales. The retrieval technique producing the data used here is most effective over the open ocean, so the analysis focuses on the southern hemisphere's extratropics, which have an extensive ocean surface. For both the total and the eddy precipitable water fields, there is a close correspondence between local variations in the precipitable water and near‐surface temperature. The correspondence appears particularly strong for synoptic and planetary scale transient eddies. More specifically, the results support a typical modeling assumption that transient eddy moisture fields are proportional to transient eddy temperature fields under the assumption of constant relative humidity.
Reducing biases in estimates of precipitation over the United States: Phase 3 adjustments
Authors: Groisman Pavel Ya. , Easterling David R. , Quayle Robert G. , Golubev Valentin S. , Krenke Aleksander N. , Mikhailov Andrey Yu.
Published: February 2004

Adjustment procedures for reducing the bias in precipitation point measurements of standard U.S. rain gauges are discussed. The procedures presented here employ information about wind speed variations over the gauge orifice during precipitation events and extensive metadata files which trace the history of precipitation measurements at each site throughout the period of instrumental observations (gauge type, exposure, and site climatology). The metadata required for this more sophisticated method has been compiled for about 1500 U.S. stations. A description of this metadata is provided, and examples of the application of this adjustment procedure are shown. However, reconstruction of precipitation over rough terrain from a network of adjusted point precipitation values still remains a problem for further studies.
A three‐dimensional simulation of the ozone annual cycle using winds from a data assimilation system
Authors: Douglass Anne R. , Weaver Clark J. , Rood Richard B. , Coy Lawrence
Published: February 2004

The wind fields from the NASA Goddard stratospheric data assimilation procedure are used in a three‐dimensional chemistry and transport model to produce an ozone simulation for the year September 11, 1991 to September 10, 1992. Photochemical production and loss are taken from the Goddard two‐dimensional model. The calculated ozone is compared with observations from the total ozone mapping spectrometer (TOMS) onboard Nimbus 7 and the microwave limb sounder on the upper atmospheric research satellite. Although the model total ozone is about 50 Dobson units (DU; =2.69 × 10−16 molecules cm−2) lower than TOMS in the tropics and up to 70 DU higher than TOMS in middle to high latitudes, the simulated ozone fields reproduce many of the features in the observations. Even at the end of this integration, the synoptic features in the modeled total ozone are very similar to TOMS observations, indicating that the model maintains realistic values for the horizontal and vertical gradients, at least in the lower stratosphere. From this good comparison between model and observations on timescales ranging from days to months, we infer that the transport driven by the assimilated wind fields closely approximates the actual atmospheric transport. Therefore the assimilated winds are useful for applications which may be sensitive to the lower stratospheric transport.
A tracer calibration of back trajectory analysis at the Grand Canyon
Authors: A. de P Vasconeelos Luis. , D. W. Kahl Jonathan , Liu Desong , Macias Edward S. , White Warren H.
Published: February 2004

The potential of routine back trajectory analyses to locate sources of contaminants in air at Grand Canyon is investigated with data on methylchloroform (CH3CCl3) concentrations collected during the Subregional Cooperative Electric Utility, Department of Defense, National Park Service, and Environmental Protection Agency Study (SCENES). Following a now‐standard approach, the distribution of back trajectory segment endpoints over a latitude longitude grid is examined as a function of measured concentrations at the fixed monitoring site. Grid cells in which segment endpoints are preferentially associated with high concentrations are then identified as candidate emissions sources. The method correctly identifies southern California as a source of CH3CCl3. An objective rationale is developed for screening out chance associations, attributable to statistical fluctuations, and the results are evaluated for real and hypothetical tracers with known, simple distributions.
Three‐dimensional distribution of nonmenthane hydrocarbons and halocarbons over the northwestern Pacific during the 1991 Pacific Exploratory Mission (PEM‐West A)
Authors: Blake Donald R. , Chen Tai‐Yih , Smith Tyrrel W. , Wang Charles J.‐L. , Wingenter Oliver W. , Blake Nicola J. , Rowland F. S. , Mayer Edward W.
Published: February 2004

A total of 1667 whole air samples were collected onboard the NASA DC‐8 aircraft during the 6‐week Pacific Exploratory Mission over the western Pacific (PEM‐West A) in September and October 1991. The samples were assayed for 15 C2‐C7 hydrocarbons and six halocarbons. Latitudinal (0.5°S to 59.5°N) and longitudinal (114°E to 122°W) profiles were obtained from samples collected between ground level and 12.7 km. Thirteen of the 18 missions exhibited at least one vertical profile where the hydrocarbon mixing ratios increased with altitude. Longitude‐latitude color patch plots at three altitude levels and three‐dimensional color latitude‐altitude and longitude‐altitude contour plots exhibit a significant number of middle‐upper tropospheric pollution events. These and several lower tropospheric pollution plumes were characterized by comparison with urban data from Tokyo and Hong Kong, as well as with natural gas and the products from incomplete combustion. Elevated levels of nonmethane hydrocarbons (NMHC) and other trace gases in the upper‐middle free troposphere were attributed to deep convection over the Asian continent and to typhoon‐driven convection near the western Pacific coast of Asia. In addition, NMHCs and CH3CCl3 were found to be useful tracers with which to distinguish hydrocarbon and halocarbon augmented plumes emitted from coastal Asian cities into the northwestern Pacific.
Assessment of dimethylsulfide sea‐air exchange rate
Authors: Putaud Jean‐Philippe , Nguyen Ba Cuong
Published: February 2004

The concentrations of dimethylsulfide (DMS) in surface seawater and in the atmosphere at three heights above sea level (1, 6, and 20 m) were measured in June 1992 in the Atlantic Ocean south of the Azores Islands (34–37°N, 23–26°W) at stations of the “Surface of Oceans: Fluxes and Interactions With the Atmosphere” cruise (SOFIA). Simultaneous meteorological and micrometeorologicai measurements were also made. Sea surface temperature and wind speed were used to estimate sea‐air exchange coefficients, according to two parameterizations of the piston velocity Kw reported by Liss and Merlivat [1986] and by Smethie et al. [1985]. The Liss and Merlivat's [1986] parameterization leads to values of Kw smaller by 40% on average than Smethie et al.'s [1985] parameterization, the difference depending on wind speed. Kw values were used to calculate the DMS flux from an air‐sea exchange model, with DMS concentrations measured in and above the seawater. Friction velocity, air temperature and heat flux were used to compute the eddy diffusion coefficient Kz as a function of altitude. In the cases where the DMS concentration decreased between 1 and 6 m, DMS flux in the 1–6 m layer was calculated from Kz and DMS atmospheric gradients according to the gradient‐transfer approach. DMS flux values obtained from the sea‐air exchange model and from the gradient‐transfer approach appear to be significantly correlated (R = 0.7, n = 15). The slopes of regressions suggest that the Liss and Merlivat's [1986] and Smethie et al.'s [1985] parameterizations of Kw both lead to DMS sea‐air fluxes lower than that calculated by the gradient‐transfer approach by a factor of 1.6 to 1.9 ± 0.5 and 1.1 to 1.4 ± 0.4, respectively.
Global radiolocation in the lower ELF frequency band
Authors: Burke C. P. , Jones D. Llanwyn
Published: February 2004

A system for recording large‐amplitude discrete extremely low frequency atmospherics (ELF “events” or “Q bursts”) produced by global lightning activity is described. The location of the source lightning flashes for some 261 events has been deduced from these data. In the data set, about 75% of the signals were produced by positive flashes and 25% were produced by negative flashes. The analysis technique depends on the fact that in the lower ELF band (5–45Hz), signals can be detected which have made multiple circulations of the globe. The range of the sources was found by modelling the data using a least squares fit to the complex wave impedance computed using the well‐established propagation theory applicable to the Earth‐ionosphere spherical‐shell waveguide. The source bearings were deduced from two orthogonal components of the magnetic field vector using the usual goniometric technique. The data show that the majority of the sources of ELF events are located in low‐latitude regions, an average of 7.4 Mm away from the observing station situated in the UK. The use of such a system to monitor worldwide thunderstorm activity, so far as this relates to ELF events observed in the band 5–45 Hz, is demonstrated.
Assessment of ozone photochemistry in the western North Pacific as inferred from PEM‐West A observations during the fall 1991
Authors: Davis D. D. , Crawford J. , Chen G. , Chameides W. , Liu S. , Bradshaw J. , Sandholm S. , Sachse G. , Gregory G. , Anderson B. , Barrick J. , Bachmeier A. , Collins J. , Browell E. , Blake D. , Rowland S. , Kondo Y. , Singh H. , Talbot R. , Heikes B. , Merrill J. , Rodriguez J. , Newell R. E.
Published: February 2004

This study examines the influence of photochemical processes on ozone distributions in the western North Pacific. The analysis is based on data generated during NASA's western Pacific Exploratory Mission (PEM‐West A) during the fall of 1991. Ozone trends were best described in terms of two geographical domains: the western North Pacific rim (WNPR) and the western tropical North Pacific (WTNP). For both geographical regions, ozone photochemical destruction, D(O3), decreased more rapidly with altitude than did photochemical formation, F(O3). Thus the ozone tendency, P(O3), was typically found to be negative for z < 6 km and positive for z > 6–8 km. For nearly all altitudes and latitudes, observed nonmethane hydrocarbon (NMHC) levels were shown to be of minor importance as ozone precursor species. Air parcel types producing the largest positive values of P(O3) included fresh continental boundary layer (BL) air and high‐altitude (z > 7 km) parcels influenced by deep convection/lightning. Significant negative P(O3) values were found when encountering clean marine BL air or relatively clean lower free‐tropospheric air. Photochemical destruction and formation fluxes for the Pacific rim region were found to exceed average values cited for marine dry deposition and stratospheric injection in the northern hemisphere by nearly a factor of 6. This region was also found to be in near balance with respect to column‐integrated O3 photochemical production and destruction. By contrast, for the tropical regime column‐integrated O3 showed photochemical destruction exceeding production by nearly 80%. Both transport of O3 rich midlatitude air into the tropics as well as very high‐altitude (10–17 km) photochemical O3 production were proposed as possible additional sources that might explain this estimated deficit. Results from this study further suggest that during the fall time period, deep convection over Asia and Malaysia/Indonesia provided a significant source of high‐altitude NOx to the western Pacific. Given that the high‐altitude NOx lifetime is estimated at between 3 and 9 days, one would predict that this source added significantly to high altitude photochemical O3 formation over large areas of the western Pacific. When viewed in terms of strong seasonal westerly flow, its influence would potentially span a large part of the Pacific.
Vertical ozone distribution in the marine atmosphere over the central Atlantic Ocean (56°S – 50°N)
Authors: Weller R. , Lilischkis R. , Schrems O. , Neuber R. , Wessel S.
Published: February 2004

The vertical ozone distribution over the Atlantic Ocean has been measured in situ by shipborne ozone soundings during three RV Polarstern meridional transects in January/February 1993, October/November 1993, and May/June 1994. The low ozone column densities measured by Nimbus 7 and Meteor 3 satellites in 1993 could be confirmed by our investigations. We observed distinct differences in the vertical distribution pattern of tropospheric ozone between the northern and the southern hemisphere: The ozone mixing ratio gradients were flat in the northern hemisphere and ozone mixing ratios in the free troposphere never did exceed 80 parts per billion by volume (ppbv) up to the tropopause, while the southern hemisphere exhibited a pronounced vertical gradient. Extremely dry air masses with enhanced ozone amounts up to 120 ppbv have been found in the tropical free troposphere of the southern hemisphere between 0° and 20°S. The vertical ozone stratification in the troposphere of the southern hemisphere was dominated by this large‐scale feature. Photochemical ozone production as a consequence of the emissions of natural fires or intrusions of stratospheric air masses are the most probable sources for these ozone‐rich layers. On the basis of our results, a stringent differentiation between both alternatives could not be given.
The role of water vapor and convection during the Central Equatorial Pacific Experiment from observations and model simulations
Authors: Lohmann U. , Roeckner E. , Collins W. D. , Heymsfield A. J. , McFarquhar G. M. , Barnett T. P.
Published: February 2004

Field measurements from the Central Equatorial Pacific Experiment (CEPEX) conducted from March 7 to April 5, 1993, are used to study the link between water vapor, convection, and sea surface temperature (SST) in a region of particular importance to global climate. The data are compared with results from a general circulation model (GCM). Three high‐resolution simulations were carried out with slightly different initial conditions using European Centre for Medium Range Weather Forecasts (ECMWF) analyses from March 1, 1993, and forced with the observed SST as lower boundary condition. Radiosondes released between the equator and 5°S show a dry region east of the dateline collocated with a clear sky region observed from the Japanese Geostationary Meteorological Satellite (GMS) in the first 2 weeks of CEPEX, which both vanish in the second 2 weeks. The model is able to reproduce this change in convective activity. Moreover, a comparison of the anomalies of the relative humidity profiles grouped according to SST and infrared brightness temperature (IRBT) indicates that the GCM correctly simulates the observed behavior. The atmosphere is relatively moist when the SST is warm and low IRBTs occur at the same time, that is, when convection takes place, and dryer than on average for the opposite case. In general, however, the model is too dry in the midtroposphere and too wet in the upper troposphere. Very good agreement is found between the simulated and observed ice water content, in particular with respect to its increase with in cloud temperature.
Using atmospheric electrical conductivity as an urban air pollution indicator
Authors: Guo Y. , Barthakur N. N. , Bhartendu S.
Published: February 2004

The atmospheric electrical conductivity as an air pollution indicator was investigated through correlation analyses based on 2 years of daily averaged observations of the atmospheric electrical conductivity, the weather classification index, and the concentrations of aerosol particles, carbon monoxide, sulfur dioxide, and nitrogen dioxide at a single site in downtown Toronto from 1973 to 1974. The main findings are the following: (1) The electrical conductivity was negatively and almost linearly correlated to the individual pollutant concentrations. (2) The effects of the individual gaseous pollutants (i.e., carbon monoxide, sulfur dioxide, and nitrogen dioxide) on the electrical conductivity were superimposable with unequal weighting factors. (3) The multicorrelation of the electrical conductivity versus the superimposed concentration of the gaseous pollutants and the particulate pollutant concentration (i.e., aerosol particles) was significant, suggesting that the atmospheric electrical conductivity can be used as a composite air pollution indicator for detecting total air pollution. (4) The weather conditions did not seem to have any significant impact on the above correlation, although they had influenced both electrical conductivity and pollutant concentrations.
Ozone and aerosol correlated observations at Thule, Greenland, in the period 1991–1994
Authors: di Sarra A. , Cacciani M. , Fiocco G. , Fuà D. , Jørgensen T. S. , Knudsen B. , Larsen N. , Mikkelsen I. S.
Published: February 2004

Ozonesonde launches and ground‐based lidar observations have been carried out at Thule, Greenland, during the winters 1991–1992, 1992–1993 and 1993–1994 following the Mt. Pinatubo eruption. The profiles thus obtained show large amounts of aerosols of volcanic origin in the lower stratosphere, and negatively correlated laminated structures in the ozone and in the aerosol content. The presence of these structures is confined to the region below approximately 18 km. The laminae are probably due to the spatial and temporal modulation induced by the dynamics at the edge of the polar vortex: large differences exist in the aerosol and ozone concentration inside and outside the vortex. Averages of the correlation coefficient between the deviations of ozone and aerosol from their seasonal averages, calculated in 4‐km height intervals for the quasi‐simultaneous observations, are consistently negative in the 13‐ to 19‐km region during the three winters. Minima of the average correlation coefficient occur at 18.5 km with −0.56 during 1991–1992, at 18 km (−0.69) during 1992–1993 and at 14.5 km (−0.38) during 1993–1994. Short‐term trajectory analysis do not provide firm evidence for chemical phenomena occurring on the surface of polar stratospheric clouds or volcanic aerosol: such possible actions appear to be masked by the dynamical phenomena.
Precipitation development and electrification in Florida thunderstorm cells during Convection and Precipitation/Electrification Project
Authors: Ramachandran Rahul , Detwiler Andrew , Helsdon John , Smith Paul L. , Bringi V. N.
Published: February 2004

Precipitation development and electrification in Florida thunderstorms are observed using an instrumented aircraft and a multiparameter radar. A low concentration of raindrops initially develops in the updraft, and these raindrops begin to freeze when they are carried above the 0°C level. High concentrations of ice particles and downdrafts soon appear in the −5° to −10°C regions of the cloud, where the aircraft penetrated, as do electric fields in the range of tens of kilovolts per meter. In a cell with relatively weak updrafts, drops start to freeze at temperatures just below 0°C. Although significant electric fields are measured by the aircraft, no lightning is observed in this cell. In more vigorous cells, drops first begin to freeze at temperatures between −5°C and −10°C. The electric fields measured by the aircraft in these cells are similar in magnitude to those in the weaker cell, but lightning is observed in these more vigorous cells. The net charge in convective regions at altitudes just above the aircraft penetration levels, 6–7 km, appears to be negative.
Validation of measurements of water vapor from the Halogen Occultation Experiment (HALOE)
Authors: Harries J. E. , Russell J. M. , Tuck A. F. , Gordley L. L. , Purcell P. , Stone K. , Bevilacqua R. M. , Gunson M. , Nedoluha G. , Traub W. A.
Published: February 2004

The Halogen Occultation Experiment (HALOE) experiment is a solar occultation limb sounder which operates between 2.45 and 10.0 μm to measure the composition of the mesosphere, stratosphere, and upper troposphere. It flies onboard the Upper Atmosphere Research Satellite (UARS) which was launched in September 1991. Measurements are made of the transmittance of the atmosphere in a number of spectral channels as the Sun rises or sets behind the limb of the atmosphere. One of the channels, at 6.60 μm, is a broadband filter channel tuned to detect absorption in the ν2 band of water vapor. This paper describes efforts to validate the absolute and relative uncertainties (accuracy and precision) of the measurements from this channel. The HALOE data have been compared with independent measurements, using a variety of observational techniques, from balloons, from the ground, and from other space missions, and with the results of a two‐dimensional model. The results show that HALOE is providing global measurements throughout the stratosphere and mesosphere with an accuracy within ±10% over most of this height range, and to within ±30% at the boundaries, and to a precision in the lower stratosphere of a few percent. The H2O data are combined with HALOE measurements of CH4 in order to test the data in terms of conservation of total hydrogen, with most encouraging results. The observed systematic behavior and internal consistency of the HALOE data, coupled with these estimates of their accuracy, indicate that the data may be used for quantitative tests of our understanding of the physical and chemical processes which control the concentration of H2O in the middle atmosphere.
Long‐term daily mean mixing ratios of O3, PAN, HNO3, and particle nitrate at a rural location in eastern Canada: Relationships and implied ozone production efficiency
Authors: Bottenheim Jan W. , Sirois Alain
Published: February 2004

Temporal trends (long‐term, annual, and daily) for concurrent observations of O3, PAN, HNO3, and pNO3− (particle nitrate) are derived. Correlations between these compounds and the meteorological parameters temperature and precipitation are outlined using a partial correlation analysis and a principal component analysis. Long‐term trends are observed for the nitrogen oxides that do not appear to be due to eastern North American sources. No long‐term trend in O3 is found, and a decrease in the efficiency of its production as function of nitrogen oxide abundance is indicated which may be caused by a decrease in the levels of hydrocarbons. Annual cycles of O3 and PAN show similarity with a spring peak and a summer minimum. These compounds are positively correlated at all times but especially so in the spring, independent of the annual cycle, and it is inferred that a common mechanism drives the spring maximum. HNO3 and pNO3− do not show a similar spring maximum: HNO3 maximizes in the summer and pNO3− in the winter. On a day‐to‐day basis, PAN and O3 show almost identical autocorrelation which is greater than that for HNO3 and pNO3−, probably due to the variance introduced by precipitation scavenging of the latter. HNO3 and temperature correlate negative in the winter and positive in the summer with O3 reflecting the different production mechanisms of HNO3. Positive correlation between HNO3 and PAN is seen suggesting that part of their variance is due to their common precursor NOx, while the negative correlation between PAN and temperature is probably reflecting the thermal instability of PAN. The results are used to infer the seasonal variation in the O3 production efficiency as a function of nitrogen oxide abundance. A slight negative value is derived for the winter, and only during the period May to August is O3 expected to be produced efficiently.
Measurement of horizontal electric fields associated with distant cloud‐to‐ground strokes
Authors: Michishita Koji , Ishii Masaru , Hojo Jun‐Ichi
Published: February 2004

A broadband sensor for the horizontal component of the electric field associated with lightning discharges was developed. The vertical electric field component contaminating the output of this sensor was, on the average, only about 0.5% of the output. Simultaneous measurement of both vertical and horizontal electric field components, associated with lightning striking at more than 16 km away, confirms that the horizontal electric field is accurately evaluated from the measured vertical electric field with the help of the wave tilt formula, irrespective of the propagation path or the polarity of the cloud‐to‐ground stroke. From this simultaneous measurement, it is possible to estimate the effective conductivity and permittivity of the ground in the vicinity of the measuring site. These local electrical parameters are independent of those of the ground beneath the propagation path, which are estimated by comparing the attenuated electromagnetic waves propagated over land with relatively unattenuated electromagnetic waves propagated over seawater. The estimation becomes easier by measuring the horizontal electric field, as it is more sensitive to the attenuation.