bluuebunny/crossref_metadata_2025 huggingface dataset:
Systematic variations in the concentration of NOx (NO Plus NO2) at Niwot Ridge, Colorado
Authors: Parrish D. D. , Hahn C. H. , Fahey D. W. , Williams E. J. , Bollinger M. J. , Hübler G. , Buhr M. P. , Murphy P. C. , Trainer M. , Hsie E. Y. , Liu S. C. , Fehsenfeld F. C.
Published: February 2008

Measurements of the concentrations of NO and NO2 were made in the rural troposphere during a year's period in 1980–1981, during the summers of 1983, 1984, and 1987, and during the fall of 1984. The field site was located near Niwot Ridge, Colorado, at an elevation of 3 km. NO was measured with a chemiluminescence instrument, and NO2 was photolyzed to NO and measured by the same instrument. The performance of this instrument is discussed in detail. Aspects of the NOx (sum of NO and NO2) concentrations discussed include the overall distribution, the seasonal and diurnal cycles, the interannual variations, and the correlation with meteorological parameters. The meteorological dependence of [NOx] elucidates the mechanisms that transport NOx to the site. Even though the Denver urban area lies downwind from the site with respect to the prevailing winds, it is NOx from that area that predominates and is responsible for the enhanced acidic deposition and elevated ozone levels at the site. The valley‐mountain flow that is primarily responsible for this transport also may be an important mechanism for transporting anthropogenic pollution from the planetary boundary layer to the free troposphere. The major photochemical loss processes of NOx are reaction of NO2 with hydroxyl radicals to form HNO3 and the formation of PAN (peroxyacetyl nitrate) and perhaps other organic nitrates in the summer and reaction of NO2 with O3 to form NO3, N2O5, and further oxidized species in the winter.
Multifractals, universality classes and satellite and radar measurements of cloud and rain fields
Authors: Lovejoy Shaun , Schertzer Daniel
Published: February 2008

The extreme variability of cloud and rain fields poses serious problems in quantitative use of remotely sensed satellite and radar data. We show how to characterize this variability using scale invariant (sensor resolution independent) codimension functions which are exponents characterizing the probability distributions. These codimension functions in turn form a three parameter universality class. We review the properties of these multifractal measures and empirically evaluate the codimension functions as well as the universality classes for infrared and visible satellite cloud images using the new probability distribution/multiple scaling technique, refining previously published results and relating these to the established lognormal rain and cloud phenomenologies. We then show how to solve the radar observers' problem for multifractal radar reflectivity factors and to estimate the codimension function of rain from the radar. Finally, we reexamine some earlier (monofractal) analysis techniques in the light of our findings.
Rain estimation from satellites: Effect of finite field of view
Authors: Chiu Long S. , North Gerald R. , Short David A. , McConnell Alan
Published: February 2008

Nonuniform rain rates within a field of view (FOV) and a nonlinear rain rate‐microwave temperature (R‐T) relation lead to a bias in the estimation of areal average rain rate from spaceborne microwave measurements. This bias is estimated from rain rate data collected during the Global Atmospheric Research Program Atlantic Tropical Experiment (GATE) using an R‐T relation which is derived from the model results of Wilheit et al. (1977). The bias is about 25% (30%) for a footprint size of 8 km and increases to about 40% (45%) for a footprint size of 40 km for phase I (II) of GATE. In the large FOV limit of 280‐km footprint size, the bias is 48% (50%). An experiment was performed in which the biases calculated from phase I were applied to phase II for different rain rate categories. The empirical correction works quite well. An approximate formula which takes account of the effect of spatial inhomogeneity within the FOV and a nonlinear R‐T relation is derived. To first order, the two effects multiply to produce the bias. The bias formula is applied to rain field models. For a rain field model where the autocorrelation function is defined by an exponential, the dependence of the bias on the ratio of the FOV size and the e‐folding scale is very similar to those calculated from the GATE data. For a Poisson process rain field model the bias formula shows an inverse dependence on the probability of rain. In this context, the lower percent bias for phase I of GATE can be understood in terms of the higher probability of rain during the same period.
Dependence of Antarctic surface mass balance on temperature, elevation, and distance to open ocean
Authors: Giovinetto M. B. , Waters N. M. , Bentley C. R.
Published: February 2008

The latest compilations of surface mass balance, mean annual surface temperature, and elevation for the Antarctic ice sheet, derived from data sets of approximately 1500, 700, and 105 points, respectively, have been used to obtain areally integrated means for 24 ice drainage systems and 329 grid point values covering the whole ice sheet. Monthly summaries of remotely sensed sea ice data for 1973–1976 have been used to obtain mean annual distance to open ocean. Linear and second‐order regression analyses of surface balance on (1) temperature for the entire ice sheet, (2) elevation for the conterminous grounded ice, and (3) distance to the open ocean for the ice shelves (including ice rises and attached islands) have been made using both system means and grid point values. These analyses show correlation coefficients of between 0.63 and 0.81, and they provide bases for descriptive models of the present Antarctic ice sheet, as well as for predictive models of the response of the ice sheet to air temperature changes and variations in meridional mass and energy transfers. Extrapolation to other ice sheets, past and present, may be possible but should be made cautiously. Linear models are recommended for paleoclimatic reconstructions of ice sheets in upper mid‐latitudes, and second‐order models are recommended for those in high latitudes. System means are shown to be reliable for these purposes. Incidental results are new estimates of the mean annual surface temperature for the whole ice sheet (−36°C) and mean surface elevation for the conterminous grounded ice (2290 m).
The influence of termites on atmospheric trace gases: CH4, CO2, CHCl3, N2O, CO, H2, and light hydrocarbons
Authors: Khalil M. A. K. , Rasmussen R. A. , French J. R. J. , Holt J. A.
Published: February 2008

Based on field studies of mounds of Australian termites we estimate that on a global scale termites emit about 12 × 1012 g/yr of methane (< 20 tg/yr) and about 4 ×1015 g CO2/yr (< 8 pg/yr). Most of the detailed results are based on studies of the species Coptotermes lacteus. We found that in mid‐latitudes the emissions vary seasonally. As much methane is emitted in the summers as in all other seasons combined. The soils a few meters from the mounds consumed methane at an average rate of 40 μg/m2/h. We found no evidence of net emissions of CO and found that H2 is consistently consumed by the mounds and the soils near the mounds. All six species studied produced chloroform. The concentrations of chloroform inside the mounds of C. lacteus were a thousand times greater than ambient levels, but our calculations show that termites are not likely to be a significant global source of chloroform. Finally, we used the results of our study, and others before us, to construct a view of the role of termites in the global carbon cycle.
The confluence zone of the intense katabatic winds at Terra Nova Bay, Antarctica, as derived from airborne sastrugi surveys and mesoscale numerical modeling
Authors: Bromwich David H. , Parish Thomas R. , Zorman Christian A.
Published: February 2008

The surface wind field inland of the intense coastal katabatic wind regime at Terra Nova Bay, Antarctica, has been studied both observationally and numerically. Airborne surveys of wind‐induced features on the snow surface have been used to construct the time‐averaged winter surface airflow pattern. The surface motion field has also been simulated by a mesoscale primitive equation model using terrain slopes with a horizontal resolution of 32 km. Both methods of analysis demonstrate that the intense katabatic airstream at Terra Nova Bay is forced by converging air currents in the continental interior. The broadscale confluence zone becomes organized into two regions within about 180 km of the coast. The primary route for katabatic mass transport into the Terra Nova Bay area is Reeves Glacier valley, but an important secondary source is provided by airflow down David Glacier. The former is generated by the Coriolis‐induced concentration of mass transport on the left side (looking downwind) of the broadscale confluence zone as well as by the near‐coastal mountain deflection of airflow into the valley head. The confluence zone feeding into David Glacier valley stretches over 100 km into the interior and is forced by the broadscale terrain configuration of the ice sheet. Source areas for the two airstreams diner with Reeves Glacier valley being fed by cold air formed well into the interior, whereas the airflow down David Glacier is sustained by radiative cooling over lower parts of the ice sheet which are much closer to the Ross Sea. Evaluation of the observational and modeling results reveals both the strengths and weaknesses of each approach. Airborne surveys of sastrugi orientations are a highly successful method for establishing the detailed pattern of surface airflow. However, a systematic examination of sastrugi dimensions suggests that such work could also be carried out using SPOT‐type satellite observations, which is a more cost‐effective approach than aircraft surveying. The double‐jet structure of katabatic airflow into the Terra Nova Bay area is well represented by the primitive equation modeling, but much finer grids are needed to resolve the near‐coastal drainage details.
Global ocean‐to‐atmosphere dimethyl sulfide flux
Authors: Erickson David J. , Ghan Steven J. , Penner Joyce E.
Published: February 2008

The global ocean‐to‐atmosphere flux of dimethyl sulfide (DMS) is calculated on a monthly basis with 4.5°×7.5° latitude/longitude spatial resolution. An atmospheric general circulation model, the National Center for Atmospheric Research (NCAR) Community Climate Model 1 (CCM1) is used to drive algorithms pertinent to the air‐sea exchange of DMS. The cloud and radiation package in the CCM1 provides estimates of the solar radiation impinging on the surface ocean, which is then related to the flux of DMS from the ocean to the atmosphere on the basis of the empirical data of Bates et al. (1987a). The computed DMS flux values vary globally from 0.5 to 5.5 μmol m−2d−1. A globally integrated ocean‐to‐atmosphere flux of 15 Tg S yr−1(as DMS) is computed. This value is probably a lower limit since there is no explicit simulation of global primary productivity presently in the model. The DMS flux is implicitly lower in chronically cloudy regions, such as the Inter‐Tropical Convergence Zone and in low‐radiation regions such as the high‐latitude winter hemispheres. To examine the global applicability of the solar radiation‐DMS flux relationship, the DMS flux fields are scaled by the independently computed transfer velocity fields so as to obtain global maps of surface ocean DMS concentration at the resolution of the model. The computed surface ocean DMS concentrations vary from 2 to 150 nL L−1, with highest values predicted near equatorial regions and adjacent to summer hemisphere polar regions, areas with relatively low climatological wind speeds. The oceanic DMS concentrations computed here agree with the experimental data in those regions not impacted by high biological productivity. In those areas of relatively high oceanic productivity the solar radiation‐DMS flux relationship underestimates the ocean‐to‐atmosphere DMS flux and the subsequently computed surface ocean DMS concentrations.
Potential impact of the northern hemisphere Quaternary ice sheets on the frequencies of the astroclimatic orbital parameters
Authors: Dehant Véronique , Loutre Marie‐France , Berger André
Published: February 2008

The Earth's orbital elements involved in the astronomical theory of paleoclimates are the eccentricity, the obliquity, and the climatic precession. The sensitivity of their frequencies to the dynamical ellipticity of the Earth is investigated for the Quaternary period. According to the model used, the modification of the distribution of the masses on and inside the Earth during full glacial conditions has only a weak influence on the moments of inertia of the Earth and consequently on the astronomical periods.
Spectroscopic observations of atmospheric trace gases over Kitt Peak: 1. Carbon dioxide and methane from 1979 to 1985
Authors: Wallace L. , Livingston W.
Published: February 2008

We have analyzed atmospheric spectra obtained with the Fourier transform spectrometer on Kitt Peak, in Arizona, for absorption by CO2 and CH4. During the period 1979–1985 we find that the CO2 total column amount was increasing at a rate of 0.4%/yr and that CH4 was increasing at a rate of 1.1%/yr. This is in substantial agreement with air sampling measurements from other sites. In addition, a weak seasonal variation of ∼2% is detected in CO2, but none is seen in CH4.
Comparison of ozone profiles from ground‐based lidar, electrochemical concentration cell balloon sonde, ROCOZ‐A rocket ozonesonde, and Stratospheric Aerosol and Gas Experiment satellite measurements
Authors: McDermid I. S. , Godin S. M. , Barnes R. A. , Parsons C. L. , Torres A. , McCormick M. P. , Chu W. P. , Wang P. , Butler J. , Newman P. , Burris J. , Ferrare R. , Whiteman D. , McGee T. J.
Published: February 2008

A series of coordinated atmospheric ozone profile measurements was made during October and November 1988. The instruments making observations and their locations were as follows. The Jet Propulsion Laboratory (JPL) and Goddard Space Flight Center differential absorption lidar systems were located at the JPL‐Table Mountain Facility 34.4°N, 117.7°W. The electrochemical concentration cell balloon sondes and the rocket ozonesondes were both launched from Point Mugu Naval Air Station at 34.2°N, 119.2°W. Stratospheric Aerosol and Gas Experiment (SAGE II) satellite measurements were at various latitudes and longitudes but only measurements made within 1000 km of both of the above sites were considered for this intercomparison study. It was found that at least for the time of year of the study, SAGE II measurements agreed only when they were made much closer than 1000 km (<500 km) from the other sites, and this is explained in terms of the large latitudinal gradient observed in the ozone concentration profile. Agreement to 5% was seen between the instruments, over the altitude range from 20 to 50 km, when the measurements were made close together in both time and space.
Reference NO2 calibration system for ground‐based intercomparisons during NASA's GTE/CITE 2 mission
Authors: Fried Alan , Nunnermacker Linda , Cadoff Barry , Sams Robert , Yates Nathan , Dorko William , Dickerson Russell , Winstead Edd
Published: February 2008

An NO2 calibration system, based upon a permeation device and a two‐stage dynamic dilution system, was designed, constructed, and characterized at the National Bureau of Standards. In this system, calibrant flow entering the second stage was controlled without contacting a metal flow controller, and permeation oven temperature and flow were continuously maintained, even during transport. The system performance and the permeation emission rate were characterized by extensive laboratory tests based on gravimetry, chemiluminescence detection, and tunable diode laser absorption spectroscopy. This system was capable of accurately delivering known NO2 concentrations in the ppbv and sub‐ppbv concentration range with a total uncertainty of approximately 10%. Upon completion of these tests the calibration system was placed on board NASA's research aircraft at both the Wallops Island and Ames research facilities. There it was employed as the reference standard in NASA's Global Tropospheric Experiment/Chemical Instrumentation Test and Evaluation 2 mission in August 1986, as discussed in a companion paper (Gregory et al., this issue).
Ozone in the marine boundary layer over the Pacific and Indian Oceans: Latitudinal gradients and diurnal cycles
Authors: Johnson James E. , Gammon Richard H. , Larsen Jimmy , Bates Timothy S. , Oltmans Samuel J. , Farmer J. Carl
Published: February 2008

Ozone concentrations in the atmospheric boundary layer of the Pacific and Indian Oceans were measured on four separate oceanographic research cruises (July 1986, May to August 1987, April to May 1988). These measurements show a distinct zone of near zero (≤3 ppb) ozone concentration in the central equatorial Pacific in April–May, with ozone increasing in this region over the next 4 months. The seasonal observed change in the latitudinal gradient of ozone is consistent with previous ozone measurements at Hilo and Samoa by Oltmans and Komhyr [1986] and predictions from an atmospheric general circulation model study [Levy et al., 1985]. A significant diurnal cycle of ozone was found in almost all locations with a maximum near sunrise, a minimum in the late afternoon, and a peak‐to‐peak amplitude of 1 to 2 ppb (10–20%), similar to that predicted by a photochemical model in the low NOx limit [Thompson and Lenschow, 1984].
An improved return stroke model with specified channel‐base current
Authors: Diendorfer G. , Uman M. A.
Published: February 2008

An improved return stroke model that is both physically oriented and has a relatively straightforward mathematical basis is proposed. The current at the channel base is specified, and a time‐dependent discharging of the charge stored on the leader channel determines the channel current as a function of height and time. The discharging process is separated into (1) the exponential discharge of the leader head and leader core with a relatively short time constant, less than 1 μs, which we call the “breakdown” time constant, and (2) the exponential discharge of the charge stored around the leader core with a longer time constant, of the order of microseconds. If a typical measured channel‐base current is assumed and if the discharge time constants are properly chosen, electric and magnetic field wave shapes calculated with the model exhibit all the significant characteristics of measured fields. From a comparison of calculated and measured field wave shapes, we find a ratio of the breakdown time constant to the channel‐base current rise time between 1 and 5. Comparison of typical characteristics of field wave shapes from natural and from artificially initiated (triggered) lightning indicates a faster discharging process for triggered lightning. Depending on the breakdown time constant, the return stroke speed determined using the well‐known formula for the transmission‐line model, with inputs being the peak electric field and peak current from the present model, are in the range from about 50 percent to 90 percent of the return stroke speed assumed in the present model. The corresponding transmission‐line model speeds determined from the peak derivatives of the electric field and current are in the range from about 140 percent to 160 percent of the assumed return stroke speed. These results supply some indication of why transmission‐line model speeds determined from the ratio of measured peak current and field derivatives in triggered lightning are greater than the speeds determined from the ratio of measured peak currents and fields. For a given channel‐base current, the initial peak electric field and field derivative derived from the model increases as the height above ground of the strike point increases. The new model can therefore explain the differences in the data obtained from the triggered lightning studies at Kennedy Space Center in 1985 and in 1987 as being due to the different height of the triggering structures in those two years. If natural lightning strikes an elevated object, the increase of the initial electric field and field derivative can result in an additional substantial error in determining the peak current and peak current derivative from the transmission‐line model.
Variance in trace constituents following the final stratospheric warming
Authors: Hess Peter
Published: February 2008

Temporal variances in the concentration of trace species are examined within the northern hemisphere stratosphere following the final warming. Variances are computed utilizing an annual cycle run of a tracer transport model and stratospheric balloon observations. The model uses winds generated with a general circulation model to transport N2O. Regions of significant N2O variance are produced immediately following the modeled final warming as zonally inhomogeneous N2O anomalies are created during the warming, then advected passively about the pole by easterly winds. Diffusion rapidly dissipates these anomalies and decreases the associated stratospheric tracer variance to very low levels by June. On monthly timescales the 10 day normal mode explains up to 50% of the modeled variance of N2O during summer. On these timescales potential temperature exhibits less variability than N2O, as horizontal parcel displacements are relatively ineffective at inducing potential temperature variability. An examination of balloon observations of N2O and other long lived trace species, between 40° and 50°N, indicates that the primary component of the tracer variance during June is on an interannual time scale. We attribute this interannual variability to stratospheric variability during the winter and early spring months imprinted onto the distributions of long lived tracers. Potential temperature does not exhibit much interannual variability because it does not retain a memory of the previous winter's circulation.
The NO3 radical decomposition and NO3 scavenging in the troposphere
Authors: Davidson J. A. , Cantrell C. A. , Shetter R. E. , McDaniel A. H. , Calvert J. G.
Published: February 2008

Studies designed to measure the apparent first order decay of the NO3 radical are reported here: NO3 (+M) → NO + O2 (+M) (R1). Two techniques were employed: (1) direct absorption measurements of [NO2] and [NO3] were made in the visible in a mixture of N2O5 in nitrogen; and (2) NO3 was followed indirectly through measured infrared absorptions of NO2 and N2O5 and calculated from the N2O5 equilibrium relation. Rate data were obtained in experiments over a range of temperatures (313–347 K) and pressures of added N2 (5–2000 torr). Rate coefficient data obtained in experiments at PN2 < 40 torr show no detectable increase with increase in PN2 within the large uncertainty, and the observed temperature dependence is qualitatively similar to that derived by Johnston et al. (1986) from experiments at 760 torr. However, the data obtained using the indirect method at PN2 > 40 torr show an apparent increase in k1 with PN2, and a negative temperature coefficient which is attributed to a wall‐catalyzed decomposition of NO3, presumably to form NO and O2 by the stoichiometry of reaction (R1). Although our observations on the kinetics of reaction (R1) are only qualitative, they support those of Johnston et al. The occurrence of a first order, homogeneous decomposition of NO3 in the atmosphere can explain most of Noxon's (1983) observations of NO3 scavenging in the troposphere. However, his reported loss of NOx during the nighttime hours requires, in addition, a contribution from some other, unidentified reaction pathway. Alternatives for this removal mechanism are discussed in view of our current knowledge.
Airborne aerosol inlet passing efficiency measurement
Authors: Huebert B. J. , Lee G. , Warren W. L.
Published: February 2008

We have evaluated the aerosol passing efficiency of a variety of inlet systems during three experiments on the National Center for Atmospheric Research Electra. During the Dynamics and Chemistry of the Marine Stratocumulus (DYCOMS) program, we found discrepancies between concentrations in cloud water and the air below cloud, which we attribute to curved‐inlet aerosol losses. In the First ISCCP Regional Experiment (FIRE) program, the same curved inlet passed significantly less material than a straight one. In the Particulate Matter Airborne Sampling Inlet Experiment (PASIN), we analyzed the material deposited within one inlet tube to establish an efficiency reference. Six different inlets were used simultaneously with six filter samplers to evaluate the effects of tube diameter, radius of curvature, and surface coating. The PASIN filters collected different amounts of material when they should have been sampling the same aerosol. Extraction of the 1‐inch metal reference tube routinely found that 50–90% of the aerosol material had been deposited in the tube. None of the inlets had an average bulk efficiency greater than about 50% for the aerosol species we measured. In the commonly used 1‐inch ID curved tube inlet, only 10–20% of marine sodium made it to the filter. High turbulence in the diffuser cone may be responsible for much of the observed loss. It is possible that many of the existing aircraft‐derived aerosol data in the literature are serious underestimates of actual ambient concentrations. We suggest some changes in strategy to improve the collection of aerosols from aircraft.
Sources of variation in nitrous oxide flux from Amazonian ecosystems
Authors: Matson P. A. , Vitousek P. M. , Livingston G. P. , Swanberg N. A.
Published: February 2008

Nitrous oxide flux and soil nutrient characteristics were measured in three undisturbed tropical ecosystem types, in cleared and burned areas, and in areas of forest converted to pasture near Manaus, Brazil. Nitrogen mineralization, nitrification, and soil nitrogen pools were high in upland forests on clay soils (terra firme) and low in the sand‐type and floodplain (varzea) soils. Nitrous oxide flux followed the same pattern, with an average flux of 1.9 ng cm−2 h−1 in terra firme, 0.3 in sand types, and 0.1 in varzea. Flux from recently cleared and burned areas did not differ from terra firme forest, but pastures had significantly elevated fluxes (10.3 ng cm−2 h−1). These data were combined with satellite data‐based areal estimates of land cover classes to estimate total N2O‐N flux from the intensive study area used by the Amazon Boundary Layer Experiment. Total N2O‐N flux from the area was 22.9 kg h−1; pastures covered 11% of the area but accounted for over 40% of the flux.
Sources and sinks of formic, acetic, and pyruvic acids over central Amazonia: 2. Wet season
Authors: Talbot R. W. , Andreae M. O. , Berresheim H. , Jacob D. J. , Beecher K. M.
Published: February 2008

We have determined the gas phase concentrations of formic (HCOOH), acetic (CH3COOH), and pyruvic (CH3C(O)COOH) acids in the forest canopy, boundary layer, and free troposphere over the central Amazon Basin during the April–May segment of the 1987 wet season. At 150‐m altitude in the boundary layer the daytime average concentrations were 430±225, 340±155, and 25± 5 ppt for HCOOH, CH3COOH, and CH3C(O)COOH, respectively. These values were fivefold lower than those observed in the 1985 dry season. Concentrations measured near canopy top were not significantly different from boundary layer values (P = 0.10), while concentrations in the lower canopy were significantly less. Concentrations in the free troposphere (5 km) were lower than in the boundary layer and averaged 170±40, 210±40, and 15±15 ppt for HCOOH, CH3COOH, and CH3C(O)COOH, respectively. Fivefold enhancements of CH3C(O)COOH concentrations were observed in convective outflows at 5‐ to 6‐km altitudes. Aerosol carboxylate concentrations were usually below our detection limit of 5–10 ppt. Preliminary branch enclosure measurements indicated significant direct emission of carboxylic acids by vegetation. A one‐dimensional photochemical model for the canopy and the boundary layer was used to examine the contributions from various sources to the carboxylic acid budgets. Model results indicate that direct emissions from vegetation can account for most of the concentrations observed in the canopy. These emissions peak during the daytime hours, and 24‐hour average upward fluxes at canopy top are 4.4×109, 3.7×109, and 2.8×108 molecules cm−2 s−1 for HCOOH, CH3COOH, and CH3C(O)COOH, respectively. However, direct emissions from vegetation can account for only a small fraction of the observed carboxylic acid concentrations in the boundary layer, suggesting a large contribution from atmospheric sources. The atmospheric reactions previously suggested in the literature as sources of carboxylic acids (gas phase decomposition of isoprene, CH3CO3 + peroxy, aqueous phase oxidation of CH2O) appear to be too slow to explain the observed concentrations. Other atmospheric reactions, so far unidentified, could make a major contribution to the carboxylic acid budgets.
Aerosol characteristics and sources for the Amazon Basin during the wet season
Authors: Artaxo Paulo , Maenhaut Willy , Storms Hedwig , Van Grieken René
Published: February 2008

As a part of the NASA Global Tropospheric Experiment (GTE), aerosols were sampled in the tropical rain forest of the Amazon Basin during the Amazon Boundary Layer Experiment (ABLE 2B) in April and May 1987, in the wet season, when no forest burning occurs. Fine (dp < 2.0 μm) and coarse (2.0 < dp < 15 μm) aerosol fractions were collected using stacked filter units, at three sites under the forest canopy and at three levels of a tower inside the jungle. Particle‐induced X ray emission (PIXE) was used to measure concentrations of 22 elements (Na, Mg, Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Br, Rb, Sr, Zr, and Pb). Morphological and trace element measurements of individual particles were carried out by automated electron probe X ray microanalysis. Gravimetric analysis was performed to obtain the fine and coarse aerosol mass concentration. Absolute factor analysis was used to interpret the large data set of the trace element concentrations and to obtain elemental source profiles. Hierarchical cluster analysis was used to derive groups of individual particles. The concentrations of soil dust related elements (Al, Si, Ti, Fe, Mn) were 5 times larger in the wet season compared to the 1985 ABLE 2A dry season experiment. Biogenic aerosol related elements in the fine fraction showed lower concentrations in the wet season. Fine aerosol mass concentration averaged only 2.1±0.7 μg m−3, while the average coarse mass concentration was 6.1±1.8 μg m −3. Sulphur concentrations averaged 76±14 ng m −3 in the fine fraction and 37±9 ng m −3 in the coarse fraction. Biogenic aerosol‐related elements were dominant under the forest canopy, while soil dust dominated at the top of the forest canopy. Only two factors explained about 90% of the data variability for the fine and coarse aerosol fractions. These were soil dust (represented mainly by Al, Si, Ti, Mn, and Fe) and biogenic aerosol (represented by K, P, Cl, S, Zn, and the aerosol mass concentration). Source profiles showed a homogeneous aerosol distribution with similar elemental compositions at the different sampling sites. Enrichment factor calculations revealed a soil dust elemental profile similar to the average bulk soil composition, and a biogenic component similar to the plant bulk elemental composition. Total aerosol mass source apportionment showed that biogenic particles account for 55–95% of the airborne concentrations. The analysis of individual aerosol particles showed that the biogenic particles consist of leaf fragments, pollen grains, fungi, algae, and other types of particles. Several groups of particles with K, Cl, P, S, and Ca as minor elements could easily be identified as biogenic particles on the basis of their morphology. Considering the vast area of tropical rain forests and the concentrations measured in this work, it is possible that biogenic particles can play an important role in the global aerosol budget and in the global biogeochemical cycles of various elements.
Lightning return stroke current models with specified channel‐base current: A review and comparison
Authors: Nucci C. A. , Diendorfer G. , Uman M. A. , Rachidi F. , Ianoz M. , Mazzetti C.
Published: February 2008

We compare five lightning return stroke current models that exhibit a simple relationship between the current at the return stroke channel‐base and the current along the return stroke channel, namely the Bruce‐Golde (BG) model, the transmission line (TL) model, the Master, Uman, Lin, and Standler (MULS) model, the Traveling Current Source (TCS) model, and the Modified Transmission Line (MTL) model, by assuming a common current wave shape at the channel base and then calculating the channel currents and charges and the resultant electric and magnetic fields. There are basically two characteristics that distinguish the models, namely, (1) the treatment of the return stroke wave front and (2) the spatial and temporal distribution of charge removed from the leader channel. The simpler BG model can be used as an excellent approximation to the TCS model. The latter reduces to the former when the current injected downward by the traveling current source has an infinite speed. The MULS model is equivalent to the MTL model when the MULS uniform current is assumed to be zero. The BG and TCS models produce sharper initial field peaks than do the TL, MTL, and MULS models. The ratio of the peak field derivative to the peak current derivative is near the ratio of the peak field to the peak current for the MULS and MTL models and is equal for the TL model, whereas for the BG and TCS models the ratio of the peak derivatives is about twice the ratio of the peak field to peak current. The TL model is unrealistic for long‐time field calculations due to the fact that no net charge is removed from the channel. The other four models produce overall fields which are reasonable approximations to measured fields from natural lightning even though, for the assumed channel‐base current, the BG and TCS models do not reproduce the observed distant‐field zero crossing and the MTL and MULS models do not reproduce the magnetic “hump” observed after the initial field peak at close range. None of the models can reproduce the fine structure observed in the measured fields.
Effects of autocorrelation and temporal sampling schemes on estimates of trend and spatial correlation
Authors: Tiao G. C. , Reinsel G. C. , Xu Daming , Pedrick J. H. , Zhu Xiaodong , Miller A. J. , DeLuisi J. J. , Mateer C. L. , Wuebbles D. J.
Published: February 2008

This paper is concerned with temporal data requirements for the assessment of trends and for estimating spatial correlations of atmospheric species. We examine statistically three basic issues: (1) the effect of autocorrelations in monthly observations and the effect of the length of data record on the precision of trend estimates, (2) the effect of autocorrelations in the daily data on the sampling frequency requirements with respect to the representativeness of monthly averages for trend estimation, and (3) the effect of temporal sampling schemes on estimating spatial correlations of atmospheric species in neighboring stations. Our principal findings are (1) the precision of trend estimates depends critically on the magnitude of auto‐correlations in the monthly observations, (2) this precision is insensitive to the temporal sampling rates of daily measurements under systematic sampling, and (3) the estimate of spatial correlation between two neighboring stations is insensitive to temporal sampling rate under systematic sampling, but is sensitive to the time lag between measurements taken at the two stations. These results are based on methodological considerations as well as on empirical analysis of total and profile ozone and rawinsonde temperature data from selected ground stations.
Heavy metals in the near‐surface aerosol over the Atlantic Ocean from 60° south to 54° north
Authors: Völkening Joachim , Heumann Klaus G.
Published: February 2008

The participate heavy metal concentrations of Cr, Fe, Ni, Cu, Zn, Cd, Tl, and Pb were determined in the atmosphere over the Atlantic Ocean from 60°S to 54°N with the definitive method of isotope dilution mass spectrometry. The samples were collected during an expedition with the German polar research ship Polarstern. The sampling and the sample treatment were carried out under strict contamination control. Fe was used as a reference element for the influence of crustal material calculating the corresponding enrichment factors EF(Fe) for the other metal traces. The heavy metal concentrations varied up to more than 3 orders of magnitude, which represents the different natural and anthropogenic sources and influences on the composition of the marine aerosol. Tl showed the lowest abundance of all heavy metals with concentrations of less than 20 pg m−3 for all samples except those from the area around the English Channel. The concentration ranges for the other elements were Cr = < 0.08–9 ng m−3, Fe = < 2.6–7500 ng m−3, Ni = < 0.05–10 ng m−3, Cu = < 0.02–20 ng m−3, Zn = < 0.09–450 ng m−3, Cd = < 0.003–3.5 ng m−3, and Pb = < 0.05–200 ng m−3. The lowest element concentrations were usually measured in the remote areas of the South Atlantic, whereas the highest ones were detected around the English Channel. However, at some sampling sites over the North Atlantic, very low Cd and Pb values in the range of 6–20 pg m−3 and < 0.5 ng m−3, respectively, were determined, which could be attributed to Arctic air masses by their corresponding backward trajectories. Due to high Fe concentrations, a substantial influence of crustal material was observed in the atmosphere southeast of the South American continent, in the South Atlantic area of the southeast trades, and over the North Atlantic west of North Africa. EF(Fe) values for the most part less than 10 for Cr and Ni and less than 50 for Cu indicate that the influence of crustal material for these metals is much higher than for Zn, Cd, and Pb where EF(Fe) values between 500 and 5000 had often been determined. This is due to anthropogenic and biological influences. The anthropogenic influence was clearly identified, e.g., over the South Atlantic near the La Plata area, in the English Channel, and over the North Sea, whereas a substantial biological influence could be observed over the South Atlantic in the area of the southeast trades.
Concentrations, sources, and fluxes of trace elements in the remote marine atmosphere of New Zealand
Authors: Arimoto Richard , Ray Barbara J. , Duce Robert A. , Hewitt Alan D. , Boldi Robert , Hudson Andrew
Published: February 2008

The concentrations of trace elements were determined for aerosol particle, dry deposition, and precipitation samples collected from Ninety Mile Beach on the North Island of New Zealand. Major objectives for the studies, which were conducted as part of the SEAREX (Sea/Air Exchange) Program, were to investigate the concentrations, sources and geochemical cycling of trace elements in the westerly wind field over the South Pacific Ocean. Many of the trace elements were associated with natural materials such as atmospheric sea salt or mineral aerosol. The mean concentration of atmospheric sea salt (∼7.9 μg m −3) was 5 to 30% higher than that predicted by models based on relationships between salt concentrations and wind speed. Mineral aerosol particles were transported through the atmosphere from Australia, and the concentration of atmospheric dust (∼200 ng m −3) was lower than the expected long‐term average due to the fact that the sampling at Ninety Mile Beach was conducted during the climatological low‐dust season. Estimates of the atmospheric deposition rates suggest that eolian material constitutes a significant fraction of the nonbiogenic deep‐sea sediments of the region. Certain trace elements, including Ag, Cd, Cu, I, Mo, Pb, Sb, Se, Ni, and Zn, were enriched over the concentrations expected from natural sources. Anthropogenic emissions from Australia and New Zealand evidently affected the concentrations of several of these elements on local to regional scales.
Aerosol spectral optical depths: Jet fuel and forest fire smokes
Authors: Pueschel R. F. , Livingston J. M.
Published: February 2008

The Ames autotracking airborne sun photometer was used to investigate the spectral optical depth between 380 and 1020 nm of smokes from a jet fuel pool fire and a forest fire in May and August 1988, respectively. Results show that the forest fire smoke exhibited a stronger wavelength dependence of optical depths than did the jet fuel fire smoke at optical depths less than unity. At optical depths greater than or equal to 1, both smokes showed neutral wavelength dependence, similar to that of an optically thin stratus deck. These results verify findings of earlier investigations and have implications both on the climatic impact of large‐scale smokes and on the wavelength‐dependent transmission of electromagnetic signals.
Graphic correlation of oxygen isotope stratigraphy application to the Late Quaternary
Authors: Prell Warren L. , Imbrie John , Martinson Douglas G. , Morley Joseph J. , Pisias Nicklas G. , Shackleton Nicholas J. , Streeter Harold F.
Published: February 2008

A geological time scale is only as useful as the stratigraphy to which it is tied. The stratigraphy of deep‐sea sediments of the Brunhes chron is largely based on the 19 oxygen isotope stages defined by Emiliani (1955) and Shackleton and Opdyke (1973). To improve the reliability and precision of this isotope stratigraphy, we have applied the technique of graphic correlation (Shaw, 1964) to isotopic events that can be consistently recognized on a global scale. Accordingly, we have devised a numerical taxonomy of isotope stratigraphy to include not only the 19 stage boundaries but also 56 isotopic events that are recorded as δ18O maxima or minima within these stages. Because samples are taken at discrete intervals, each event is recorded as a depth range which depends both on the sampling density and the structure of the isotopic record. Graphic correlation proceeds by selecting a reference section (V28‐238) and then graphing the depth range of isotopic events that are common to both sections. The overlapping ranges define correlation boxes, within which the true event must lie. The line of correlation must pass through all correlation boxes. Surprisingly, empirical tests have shown that correlation between stratigraphic sections can be accomplished as a series of straight line segments. The number of segments required and their slopes and offsets identify changes in accumulation rate, stratigraphic gaps, and zones of deformation. The line of correlation relates any level in a given core to the standard section and enables all isotopic records to be recast on the basis of a common depth scale. In this form, isotopic records can be stacked (averaged) to construct a global average record that can be used to differentiate between global and local isotopic variations. Preliminary results with 13 deep‐sea cores suggest that correlation may be precise to within a few centimeters and will provide an accurate and reliable method for the application of time scales in the Brunhes chron.
Pliocene‐Pleistocene evolution of the North Pacific Ocean‐Atmosphere system, interpreted from fossil diatoms
Authors: Sancetta Constance , Silvestri ShayMaria
Published: February 2008

The relative abundance of diatom taxa in 216 core tops has been quantified and compared, using cluster analysis, with assemblages in six cores located beneath different water masses of the North Pacific Ocean. All but one sequence span at least 1.5 m.y., (early Pleistocene to Holocene), and one extends to 2.6 Ma. The quantitative abundance of each taxon and the space‐time occurrence of each cluster are interpreted as tracers of oceanographic conditions. In addition to high‐frequency (glacial‐interglacial) oscillations, the records display rapid steplike changes at 2.4 Ma, 1.6–1.5 Ma, 1.0 Ma, 0.8–0.7 Ma, and 0.35 Ma. Two secondary transitions, recorded only in the northwestern cores, occur at 2.0 Ma and 1.1 Ma. We conclude that both the high‐frequency oscillations and the stepwise transitions reflect variations in extent of subarctic water masses, under the influence of the Siberian high‐pressure and Aleutian low‐pressure atmospheric cells. We further conclude that (1) the subarctic water mass has developed progressively and attained its modern structure only in the late Pleistocene; (2) some stages of this evolution may have occurred earlier in the eastern subarctic; (3) the Holocene is an atypical “warm” extreme, so that the present is not a very good key to the past; (4) there were several glaciations between 2.4 and 2.0 Ma; and (5) the Subtropical Gyre is more conservative than the Subarctic Gyre, and major changes in the region have been due to forcing from the north. We propose a conceptual model of oscillating metastable climatic modes, maintained by internal feedback; and suggest that steplike changes may occur when one set of boundary conditions is temporarily exceeded.
Tertiary oxygen isotope synthesis, sea level history, and continental margin erosion
Authors: Miller Kenneth G. , Fairbanks Richard G. , Mountain Gregory S.
Published: February 2008

Tertiary benthic and planktonic foraminiferal oxygen isotope records are correlated to a standard geomagnetic polarity time scale, making use of improved chronostratigraphic control and additional Oligocene isotope data. Synchronous changes in both benthic and planktonic δ18O values which occurred in the Oligocene to Miocene (36–5.2 Ma) are interpreted, in part, to represent ice growth and decay. The inferred ice growth events correlate with erosion on passive continental margins as interpreted from seismic and chronostratigraphic records. This association is consistent with a link between Oligocene to Miocene erosional events and rapid (>15 m/m.y.) glacioeustatic lowerings of about 50 m. High benthic foraminiferal δ18O values suggest the presence of continental ice sheets during much of the Oligocene to Recent (36–0 Ma). Substantially ice‐free conditions probably existed throughout the Paleocene and Eocene (66–36 Ma). The mechanisms and rates of sea level change apparently were different between the early and late Tertiary, with glacioeustatic changes restricted to the past 36 m.y. Pre‐Oligocene erosion on passive continental margins was caused by eustatic lowerings resulting from global spreading rate changes. We apply a model which suggests that large areas of the continental shelves were subaerially exposed during such tectonoeustatic lowstands, stimulating slope failure and submarine erosion. The different mechanisms and rates of eustatic change may have caused contrasting erosional patterns between the early and late Tertiary on passive continental margins. This speculation needs to be confirmed by examination of data from several passive margins.