bluuebunny/crossref_metadata_2025 huggingface dataset:
Land use impacts on atmospheric carbon monoxide consumption by soils
Authors: King Gary M.
Published: February 2004

Seasonal analyses of in situ CO fluxes from forested and agricultural soils in Maine and Georgia, and more limited comparisons in Hawai'i indicated that agricultural land use consistently enhanced CO consumption. Soils at an agricultural site in Maine consumed approximately 1.9 g CO m−2 yr−1 while uptake in a nearby mixed forest was about 70% lower, 0.6 g CO m−2 yr−1. A similar trend was observed for sites in Georgia, where annual uptake by agricultural sites was approximately 1.0 g CO m−2 while net emission (about −0.5 g CO m−2) was observed for neighboring pine stands. Net CO fluxes in Maine and Georgia were generally aseasonal. Accordingly, seasonal changes in temperature and water content played variable but often minimal roles as determinants of net fluxes and gross CO uptake and production. However, comparisons among sites suggested that soil organic matter contents were an important control of the magnitude of CO fluxes. In particular net CO consumption for a given soil type increased with decreasing organic matter content associated with forest to agriculture transitions in land use. Although interactions among soil organic matter and various microbiological, physical and chemical parameters in soils are complex, changes in organic matter at the sites described here appear to affect net CO fluxes primarily by reducing the relative rate of abiological CO production
Comparative analysis of black carbon in soils
Authors: Schmidt Michael W. I. , Skjemstad Jan O. , Czimczik Claudia I. , Glaser Bruno , Prentice Ken M. , Gelinas Yves , Kuhlbusch Thomas A. J.
Published: February 2004

Black carbon (BC), produced by incomplete combustion of fossil fuels and vegetation, occurs ubiquitously in soils and sediments. BC exists as a continuum from partly charred material to highly graphitized soot particles, with no general agreement on clear‐cut boundaries of definition or analysis. In a comparative analysis, we measured BC forms in eight soil samples by six established methods. All methods involved removal of the non‐BC components from the sample by thermal or chemical means or a combination of both. The remaining carbon, operationally defined as BC, was quantified via mass balance, elemental composition or by exploiting benzenecarboxylic acids as molecular markers or applying 13C MAS NMR (magic angle spinning nuclear magnetic resonance) spectroscopy. BC concentrations measured for individual samples vary over 2 orders of magnitude (up to a factor of 571). One possible explanation for this wide range of results is that the individual BC methods rely on operational definitions with clear‐cut but different boundaries and developed for specific scientific questions, whereas BC represents a continuum of materials with widely contrasting physicochemical properties. Thus the methods are inherently designed to analytically determine different parts of the continuum, and it is crucial to know how measurements made by different techniques relate to each other. It is clear from this preliminary comparative analysis that a collection of BC reference materials should be established as soon as possible 1 ) to ensure long‐term intralaboratory and interlaboratory data quality and 2) to facilitate comparative analyses between different analytical techniques and scientific approaches
Emissions of greenhouse gases from the tropical hydroelectric reservoir of Petit Saut (French Guiana) compared with emissions from thermal alternatives
Authors: Delmas Robert , Galy‐Lacaux Corinne , Richard Sandrine
Published: February 2004

Greenhouse gas (GHG) emissions of CH4 and CO2, resulting from decomposition of flooded organic matter from the hydroelectric reservoir of Petit Saut in the tropical rain forest of French Guiana have been monitored since reservoir impoundment in January 1994. This data set along with complementary data taken from older reservoirs in forested regions of the southern Ivory Coast provides an estimate of long‐term GHG emission trends from a tropical reservoir. The trends are used to calculate the contribution of this reservoir to global warming on a 100 year timescale, assumed to be consistent with the life cycle of the reservoir. Calculations are based on the concept of global warming potential (GWP). Natural emission of greenhouse gases (CH4 and N2O) from soils of the reservoir before impoundment is estimated through field measurements and literature data. Then net GHG emissions from the reservoir on a 100 hundred year timescale (30 million tons of equivalent CO2, with an uncertainty range of 7–54 Mt CO2eq) are compared with predicted emissions from thermal power plants of equivalent power (115 MW). The final comparison takes into account the actual energy production of the dam power station at only 50% of the installed capacity. Emission from this reservoir, whose power density is low (0.315 MW km−2 flooded), would be similar to emissions from a gas power plant (33 Mt CO2eq) producing the same energy amount and less than emissions from other thermal alternatives, among which the most polluting are coal plants. Such a result, however, strongly depends on the choice of the integration time.
Does carbon 13 track anthropogenic CO2 in the southern ocean?
Authors: McNeil B. I. , Matear R. J. , Tilbrook B.
Published: February 2004

A multiparametric linear regression technique was used for waters in the Southern Ocean to estimate the change in both δ13CDIC (Δδ13CDIC) and dissolved inorganic carbon (DIC) (ΔDIC) between 1978 and 1998, due to the accumulation of anthropogenic CO2. The observed decrease in Δ13CDIC at the surface, the Suess effect, was −0.015 ± 0.003‰ yr−1 in the Sub‐Antarctic Zone and −0.005 ± 0.003‰ yr−1 in the Antarctic Zone, similar to values reported for the southern Indian Ocean [Gruber et al; 1999; Sonnerup et al., 2000]. To compare the Δδ13CDIC with ΔDIC, we used the ratio of these two anomalies (ΔRC=–Δδ13CDIC/ΔDIC‰ (μmol; kg−1)−1). Along the section, ΔRC ranged from 0.015 ± 0.005 at 42°S to 0.007 ± 0.005‰ (μmol; kg−1)−1 at 54°S. The spatial variability in ΔRC in the Southern Ocean reflects different timescales for processes controlling the uptake of 13C from those controlling the uptake of 12C and indicates that Δδ13CDIC decouples from ΔDIC poleward of the Sub‐Antarctic Zone. The variations of ΔRC along the section suggest that the δ13CDIC anomaly is not a good predictor of the anthropogenic CO2 inventory in the Southern Ocean. Some methods for determining anthropogenic CO2 uptake both on the global and regional scale assume the penetration depths of Δδ13CDIC to be the same as ΔDIC, which implies a constant value for ΔRC in the ocean at ∼0.016‰ (μmol; kg−1)−1 [Heimann and Maier‐Reimer, 1996; Ortiz et al., 2000; Bauch et al., 2000]. The use of a constant ΔRC and the observed Δδ13CDIC to estimate anthropogenic CO2 could lead to an underestimate in the inventory of anthropogenic CO2 for the Southern Ocean by ∼50%.
Chemical discrimination of Columbia River basalt flows
Authors: Hooper Peter R.
Published: February 2004

The homogeneity and distinctive chemical composition of individual Columbia River basalt flows are illustrated in a series of chemical plots, and the procedure for flow identification is outlined. The unique characterization of many individual eruptions permits units to be mapped from feeder dike to flow margins across the Columbia Plateau for hundreds of kilometers, and so provides critical constraints on the physical and chemical evolution of this continental flood basalt province.
Ecological and environmental factors affecting alkenone distributions in seawater and sediments
Authors: Volkman John K.
Published: February 2004

The use of alkenones to estimate past sea surface temperatures has gained wide acceptance, but there are still some issues that need to be resolved before alkenone proxies can be used confidently in all environmental settings. A particular concern is defining what seawater temperature is recorded by the alkenone distributions preserved in sediments. Does it, for example, reflect a seasonal average or a snapshot of bloom conditions or some other combination of environmental effects? This paper reviews some of the environmental and ecological factors that might affect alkenone distributions and, in particular, the influence of depth and seasonality on alkenone production in the water column.
Does iron fertilization lead to rapid carbon export in the Southern Ocean?
Authors: Charette Matthew A. , Buesseler Ken O.
Published: February 2004

The Southern Ocean has the potential to influence climate due to its large inventory of excess macronutrients such as nitrate and phosphate. It has been hypothesized that if the supply of the micronutrient iron increased, it would lead to enhanced uptake of atmospheric CO2 and hence the sequestration of carbon via sinking particles [Martin, 1990]. While much has been learned about iron limitation and low phytoplankton biomass in high‐nutrient, low‐chlorophyll regions [Martin, 1991; Coale et al., 1996], less is known about the effect of Fe on particle export. Here we present results from the first detailed study of particle export during a mesoscale iron fertilization experiment (the Southern Ocean Iron Release Experiment (SOIREE)). Measurements of the natural tracer thorium‐234 indicate negligible particle export within 14 days after the initial infusion of iron. We attribute this lack of response to colder water temperatures that promote slower cell metabolism in phytoplankton and hence slower secondary responses of herbivores and particle aggregation.
Residence time of osmium in the oceans
Authors: Oxburgh Rachel
Published: February 2004

Estimates of osmium residence time in the oceans that are based on oceanic mass balance calculations (35–50 kyr) appear irreconcilable with those inferred from the recent evolution of the osmium isotope composition of seawater (3–4 kyr). It is argued that the osmium budget of the oceans is currently close to steady state and thus that the estimates made by the two methods should agree. As the inventory of osmium in the oceans is relatively well constrained, these disparate residence time estimates imply wildly different osmium input fluxes to the oceans. An osmium residence time of 8–10 kyr is proposed by evaluating the uncertainties and limitations of both methods, and it is argued that osmium inputs to the ocean are currently underestimated by a factor of ∼3. This reflects in part the underestimation of the river input of osmium to the oceans owing to a bias within the existing data set and in part the probable existence of sources of osmium to the oceans that have not yet been identified. The very short residence time of 3–4 kyr inferred from the postglacial change in seawater composition (assuming a single step change in input flux) is rejected as it implies unreasonably high osmium input fluxes to the oceans. It is concluded that a postglacial spike in osmium flux, associated with a meltwater event, must have driven part of the change in seawater composition. However, it is also shown that such a spike cannot be the dominant cause of the most recent shift in seawater 187Os/188Os.
Vailulu'u undersea volcano: The New Samoa
Authors: Hart S. R. , Staudigel H. , Koppers A. A. P. , Blusztajn J. , Baker E. T. , Workman R. , Jackson M. , Hauri E. , Kurz M. , Sims K. , Fornari D. , Saal A. , Lyons S.
Published: February 2004

Vailulu'u Seamount is identified as an active volcano marking the current location of the Samoan hotspot. This seamount is located 45 km east of Ta'u Island, Samoa, at 169°03.5′W, 14°12.9′S. Vailulu'u defines the easternmost edge of the Samoan Swell, rising from the 5000‐m ocean floor to a summit depth of 590 m and marked by a 400‐m‐deep and 2‐km‐wide summit crater. Its broad western rift and stellate morphology brand it as a juvenile progeny of Ta'u. Seven dredges, ranging from the summit to the SE Rift zone at 4200 m, recovered only alkali basalts and picrites. Isotopically, the volcano is strongly EM2 in character and clearly of Samoan pedigree (87Sr/86Sr: 0.7052–0.7067; 143Nd/144Nd: 0.51267–0.51277; 206Pb/204Pb: 19.19–19.40). The 210Po‐210Pb data on two summit basalts indicate ages younger than 50 years; all of the recovered rocks are extremely fresh and veneered with glass. An earthquake swarm in early 1995 may attest to a recent eruption cycle. A detailed nephelometry survey of the water column shows clear evidence for hydrothermal plume activity in the summit crater. The water inside the crater is very turbid (nephelometric turbidity unit (NTU) values up to 1.4), and a halo of “smog” several hundred meters thick encircles and extends away from the summit for at least 7 km. The turbid waters are highly enriched in manganese (up to 7.3 nmol/kg), providing further evidence of hydrothermal activity. Vailulu'u is similar to Loihi (Hawaii) in being an active volcanic construct at the eastern end of a hotspot chain; it differs importantly from the Hawaiian model in its total lack of tholeiitic basalt compositions.
Representations of Seismicity
Authors: Kennett B. L. N.
Published: February 2004

Some alternative representations for seismicity are introduced based on the use of the hue, saturation, and brightness model of color representation. Depth information is conveniently coded by hue and magnitude by saturation. The approach can be used for individual events or to provide useful summary properties of seismicity. The cumulative effects of many events can be combined by converting body wave magnitude into an equivalent energy or strain release and then summing the energy or strain contributions in a particular cell, finally converting back to an effective magnitude over a 10‐year period for plotting. Time averaging improves the reliability of the information and can provide a clearer picture of the balance between seismic events at different depths.
Alkyl nitrate measurements during STERAO 1996 and NARE 1997: Intercomparison and survey of results
Authors: Stroud Craig A. , Roberts James M. , Williams Jonathan , Goldan Paul D. , Kuster William C. , Ryerson Thomas B. , Sueper Donna , Parrish David D. , Trainer Michael , Fehsenfeld Frederick C. , Flocke Frank , Schauffler Sue M. , Stroud Verity R. F. , Atlas Elliot
Published: February 2004

Alkyl nitrates were measured over the northeastern plains of Colorado during the Stratospheric Tropospheric Exchange: Radiation, Aerosols and Ozone (STERAO) 1996 campaign and over the North Atlantic during the North Atlantic Regional Experiment (NARE) 1997. Alkyl nitrate measurements were performed by two different laboratories enabling an intercomparison of analytical techniques. A weighted bivariate linear regression analysis of comparable samples (National Oceanic and Atmospheric Administration versus National Center for Atmospheric Research) for the four alkyl nitrates measured by both techniques (2‐propyl nitrate, 1‐propyl nitrate, 2‐butyl nitrate, and 3‐pentyl nitrate) suggests there is neither a significant calibration difference nor a systematic offset. The precision of the measurements is indicated by the scatter in the correlations. Good precision is observed for the 2‐butyl nitrate measurements (square of the correlation coefficient, R2 = 0.90). However, relatively small values of R2 and relatively large uncertainties in the determination of the slopes and intercepts (2σ confidence intervals) for 2‐propyl nitrate, 1‐propyl nitrate, and 3‐pentyl nitrate suggest significant imprecision when compared to ambient mixing ratios for at least one of the measurement techniques. Vertical profiles during NARE 1997 show high levels of alkyl nitrates in well‐defined photochemical pollution layers of continental origin. A comparison of alkyl nitrate to hydrocarbon ratios with a sequential reaction scheme model suggests our understanding of C4–C5 alkyl nitrate photochemistry is adequate to reproduce the observations. Air masses with larger ratios of alkyl nitrate to hydrocarbons were observed during NARE 1997 than STERAO 1996, consistent with the NARE 1997 measurements being in the more remote North Atlantic. These results suggest that information related to the photochemical age of an air mass can be derived from alkyl nitrate to hydrocarbon ratios.
Constraints on the seasonal cycle of stratospheric water vapor using in situ measurements from the ER‐2 and a CO photochemical clock
Authors: Weinstock E. M. , Hintsa E. J. , Kirk‐Davidoff D. B. , Anderson J. G. , Andrews A. E. , Herman R. L. , Webster C. R. , Loewenstein M. , Podolske J. R. , Bui T. P.
Published: February 2004

We use in situ measurements of CO obtained in the tropics from 1995 to 1997 on the NASA ER‐2 aircraft and a simple photochemical model to calculate the elapsed time between the entry of air into the stratosphere and the observation, which we define as the photochemical “age” of the air. Assuming this age represents the transit time of the air mass from a boundary at 390 K to its measured altitude, we calculate boundary condition values of CO2 derived from in situ measurements of this species from 400 to 480 K. We validate the approach by comparing these CO2 boundary values with an independent representation of the boundary condition from observations of CO2 in air that had recently entered the stratosphere (as indicated by simultaneous measurements of N2O, CO, and potential temperature). For five of the six flights, differences between CO2 boundary condition values determined using the photochemical age of the air and those derived from independent measurements can be accounted for with isentropic mixing of midlatitude stratospheric air into the tropics. Having validated the photochemical ages of the sampled stratospheric air, we use the same analysis of in situ water data to provide water vapor boundary condition values that constrain the seasonal cycle of water vapor entering the stratosphere. On the basis of these constraints we evaluate the seasonal cycle of entry‐level water vapor derived from tropical tropopause temperatures from the radiosonde network between 10°S and 10°N. We conclude that while average saturation mixing ratios provide a suitable boundary condition for water vapor entering the stratosphere, the uncertainties in saturation mixing ratios derived from radiosonde temperatures and the lack of coverage prevents distinguishing between ascent preferentially occurring over the western equatorial Pacific or throughout the tropics. With the assumption that vertical diffusion and midlatitude mixing have a negligible effect on the calculated age, ascent velocities can be inferred from the photochemical ages. These ascent velocities show a seasonal cycle that is inconsistent with our current understanding of the dynamics driving the stratospheric circulation and with independent estimates of tropical vertical ascent rates.
GOES 10 cloud optical property retrievals in the context of vertically varying microphysics
Authors: Miller S. D. , Stephens G. L. , Austin R. T.
Published: February 2004

An optimal estimation approach is applied to the physical retrieval of single‐layer cloud optical properties (optical depth and effective radius) using multispectral imager channels on the western Geostationary Operational Environmental Satellite (GOES 10). The retrieval includes diagnostic information pertaining to uncertainty and dependence on a priori assumptions required by the forward model. Satellite retrievals of 0.65‐μm cloud optical depth and effective radius (micrometers) for marine stratocumulus (in both drizzle and drizzle‐free conditions) during the CloudSat Antecedent Validation Experiment and tropical cirrus during the Atmospheric Radiation Measurement (ARM)‐Unmanned Aerospace Vehicle spring flight series are examined together with data from the NASA/Jet Propulsion Laboratory Airborne Cloud Radar (ACR), the ARM Cloud Detection Lidar, and the Colorado State University Scanning Spectral Polarimeter (SSP) instruments. Optical depths are found to be consistent between GOES and SSP after taking into account the degradation of responsivity in GOES channel 1. Colocated ACR/GOES observations support past evidence that passive satellite detection of drizzle size droplets (in terms of a significant positive bias in the retrieved effective radius) may be possible under certain conditions. The ability of a dual lidar/radar active observing system to provide independent information over different cloud particle size regimes is illustrated and speaks to the vertical variability of cloud microphysics. The GOES estimate of effective radius was found to be more representative of the upper 0.5 km of the cirrus clouds examined.
Ozone photochemistry and the role of peroxyacetyl nitrate in the springtime northeastern Pacific troposphere: Results from the Photochemical Ozone Budget of the Eastern North Pacific Atmosphere (PHOBEA) campaign
Authors: Kotchenruther Robert A. , Jaffe Daniel A. , Jaeglé Lyatt
Published: February 2004

In the spring of 1999 airborne measurements of NO, O3, peroxyacetyl nitrate (PAN), CO, CH4, H2O, volatile organic compounds, aerosols (particle count, light scattering, and light absorption), NO2 photolysis frequency, and standard meteorological variables were made off the coast of Washington State as part of the Photochemical Ozone Budget of the Eastern North Pacific Atmosphere (PHOBEA) experiment. These measurements were used to constrain a photochemical box model to calculate the ozone photochemical tendency, T(O3), in this region. T(O3) in marine flow from the remote Pacific was found to be weakly ozone destroying from the surface up to 8 km. Values of T(O3) increased from −0.83 ppbv d−1 in the 0–2 km layer to −0.11 ppbv d−1 in the 6–8 km layer. These results are compared to T(O3) from other photochemistry experiments in the springtime Pacific. We also used the model to investigate the impacts of PAN decomposition on the mixing ratio of NOx (defined here as NO+NO2+NO3+2N2O5+ HNO2 +HNO4) and on T(O3). PAN decomposition was found to contribute from 11 to 30% toward NOx production and to enhance T(O3) by 0.13 to 0.41 ppbv d−1. The impacts of PAN decomposition were further investigated in a case study where measurements were made in a strongly subsiding air mass. In this air mass, PAN induced perturbations to IMOx and T(O3) reached 20.1 pptv and 1.45 ppbv d−1, respectively, more than three times that found in marine background average. Finally, we estimate how T(O3) in the northeast Pacific atmosphere may change as a result of increasing anthropogenic NOx emissions from Asia. The calculations suggest that while O3 mixing ratios in the northeast Pacific are likely to increase, T(O3) will remain close to its current value as a result of offsetting factors.
Exploring polar stratospheric cloud and ozone minihole formation: The primary importance of synoptic‐scale flow perturbations
Authors: Teitelbaum H. , Moustaoui M. , Fromm M.
Published: February 2004

The formation of polar stratospheric clouds (PSCs) is sometimes attributed to cooling induced by mountain waves. Some examples of PSCs explained by this mechanism are found in the literature. Other studies show that the cooling producing PSCs is of synoptic scale. In this paper we use data from Polar Ozone Aerosol Measurement (POAM) II and from TIROS Operational Vertical Sounder (TOVS) showing coincident occurrences of PSCs and ozone miniholes over the sea and land. Using European Centre for Medium‐Range Weather Forecasts (ECMWF) analyses, we show that when both PSCs and localized ozone minima appear, they are associated primarily with anticyclonic potential vorticity anomalies near the tropopause. The flow anomaly penetrates upward and downward, inducing an upward displacement of isentropic surfaces above and a downward displacement below, the upward and downward penetration being consistent with the deformation scale. These flow anomalies result in synoptic‐scale quasi‐adiabatic uplift through the lower stratosphere. The adiabatic cooling of the air masses creates the conditions for PSC formation. Coincidentally, the ozone partial pressure decreases, and the localized ozone minimum appears. Our purpose in this paper is to show that the primary PSC formation mechanism in the Arctic is the same as for minihole formation: synoptic‐scale dynamics. We show three multiday sequences of PSCs and localized ozone minima. We reveal the robustness of the PSC/dynamics link by showing multiyear, monthly statistics of POAM II PSC sighting fraction compared with PSC formation temperature and isentropic geopotential.
Effects of postdepositional processes on snow composition of a subtropical glacier (Cerro Tapado, Chilean Andes)
Authors: Ginot Patrick , Kull Christoph , Schwikowski Margit , Schotterer Ulrich , Gäggeler Heinz W.
Published: February 2004

In order to study the effects of postdepositional processes on snow chemistry a surface snow experiment was performed on the Cerro Tapado summit glacier in northern Chile, a subtropical glacier site presumably influenced by strong sublimation. Chemical species irreversibly trapped in the snow were significantly enriched in the surface layer by sublimation of the water matrix (Cl−, SO42−, and K+) and by sublimation and dry deposition (Ca2+, Mg2+, Na+, CH3SO3−, and C2O42−). Species present in a volatile form, such as HCOOH, CH3COOH, and HNO3, were released from the snow. This indicates that not only particular meteorological conditions influence the modification of snow composition but so does the chemical form of the studied species (salts or volatile). From the enrichment in concentrations of irreversibly deposited chemical species the sublimation rate was quantified as 1.9 mm weq d−1, which agrees with the sublimation rates determined by lysimeters and by mass balance modeling.
Polarization of the moonlit clear night sky measured by full‐sky imaging polarimetry at full Moon: Comparison of the polarization of moonlit and sunlit skies
Authors: Gál József , Horváth Gábor , Barta András , Wehner Rüdiger
Published: February 2004

Using 180° field of view (full‐sky) imaging polarimetry, the patterns of the degree and angle of polarization of the moonlit clear night sky were measured in every half an hour throughout the night at full Moon. The patterns were compared with those of the sunlit sky. The observed patterns including the positions of the Arago and Babinet neutral points of the moonlit night sky and sunlit day sky are practically identical if the zenith angle of the Moon is the same as that of the sun. The possible biological relevance of the polarization pattern of the moonlit night sky in the polarization vision and orientation of night‐active insects is briefly discussed.
UARS Microwave Limb Sounder upper tropospheric humidity measurement: Method and validation
Authors: Read W. G. , Waters J. W. , Wu D. L. , Stone E. M. , Shippony Z. , Smedley A. C. , Smallcomb C. C. , Oltmans S. , Kley D. , Smit H. G. J. , Mergenthaler J. L. , Karki M. K.
Published: February 2004

The methodology and validation of upper tropospheric humidity (UTH) measurements by the Microwave Limb Sounder (MLS) on the Upper Atmosphere Research Satellite (UARS) are described. The MLS instrument was not specifically designed to measure UTH, but its measurement is achieved by modeling the radiance signal from a window channel as the instrument field of view is scanned through the troposphere. UTH is retrieved as a piecewise‐linear function in relative humidity with respect to ice (% RHi) with breakpoints at 147, 215, 316, and 464 hPa. MLS version 4.9 is believed to be the most accurate version to date; its estimated global‐averaged accuracy (precision) is 23(21), 22(10), 22(8), and 50(19) %RHi at 147, 215, 316, and 464, hPa respectively. The validation of UTH is established by its consistency with (1) climatological fields, (2) coincident comparisons with in situ Vaisala RS80 balloon sondes, frostpoint hygrometers and Measurement of Ozone and Water Vapor by Airbus In‐Service Aircraft measurements, (3) cirrus observations, and (4) meteorological dynamics and assimilation fields. MLS climatological UTH is morphologically consistent with Stratospheric Aerosol and Gas Experiment II and Vaisala zonal climatologies. Comparisons with coincident in situ data show a wide range of agreement. Relative to the other in situ instruments, V4.9 MLS humidities agree on average within 11% at 147 hPa, 3–36% dry at 215 hPa, and 14–39% dry at 316 and 464 hPa. The standard deviation of the individual comparisons about the mean between MLS UTH and the other techniques is approximately 25%RHi at all heights. Humidity measurements in cirrus are compared with UARS Cryogenic Limb Array Etalon Spectrometer (CLAES) extinction measurements and an MLS cirrus detection algorithm. CLAES extinction measurements from 316 to 147 hPa which indicate the presence of cirrus correspond well with MLS UTH measurements greater than ∼100 %RHi. Global MLS UTH distributions appear consistent with those expected from upper tropospheric dynamics and with the Goddard Data Assimilation Office humidity fields.
Regional inventory of nitric oxide and nitrous oxide emissions for forest soils of southeast Germany using the biogeochemical model PnET‐N‐DNDC
Authors: Butterbach‐Bahl Klaus , Stange Florian , Papen Hans , Li Changsheng
Published: February 2004

Though it has been shown recently that forest ecosystems affected by high rates of atmospheric N input are significant sources of N trace gases, reliable regional estimates of the source strength of such forests are missing. In this study, the biogeochemical model Photosynthesis and Evapotranspiration‐Nitrification‐Denitrification and Decomposition (PnET‐N‐DNDC), which simulates processes involved in N trace gas production and emission in forest soils on a daily scale, was used to calculate a regional inventory of N trace gas emissions from forest soils in southeast Germany for the year 1997. Prior to its use the model was further validated for climate and site sensitivity using multiyear observations of N trace gas fluxes at the Höglwald Forest site, Germany, and at forest sites in the Netherlands. On a regional scale the model estimates for Bavaria, Germany, that NO and N2O emissions from forest ecosystems in the year 1997 were ∼4.21 kt NO‐N yr−1 and ∼6.64 kt N2O‐N yr−1, respectively. Compared with total annual NOx emissions from combustion processes in Bavaria, total emissions of NO from forest soils are of minor importance [4.6%]. However, in summer, NO emissions from forest soils were of significant importance [8.8–22.0%] for the total regional NOx burden, since NO emissions showed a strong seasonal pattern with highest emissions during summer. Also, with regard to N2O, huge seasonal variations were found. Because of high N2O emissions during periods of freezing and thawing of forest soils, N2O fluxes in the winter period of 1997 also contributed significantly on the regional scale to total annual N2O emissions [∼38%]. Sensitivity analysis revealed that the accuracy of the N trace gas inventory strongly depended on the quality of regional input data, since the regional estimates of N trace gas fluxes calculated by PnET‐N‐DNDC were very sensitive to changes in soil texture, soil carbon content, site fertility, and, especially for NO emissions, to changes in soil pH.
On the potential influence of ice nuclei on surface‐forced marine stratocumulus cloud dynamics
Authors: Harrington Jerry Y. , Olsson Peter Q.
Published: February 2004

The mixed phase cloudy boundary layer that occurs during off‐ice flow in the marine Arctic was simulated in an environment with a strong surface heat flux (nearly 800 W m−2). A two‐dimensional, eddy‐resolving model coupled to a detailed cloud microphysical model was used to study both liquid phase and mixed phase stratocumulus clouds and boundary layer (BL) dynamics in this environment. Since ice precipitation may be important to BL dynamics, and ice nuclei (IN) concentrations modulate ice precipitation rates, the role of IN in cloud and BL development was explored. The results of several simulations illustrate how mixed phase microphysical processes affect the evolution of the cloudy BL in this environment. In agreement with past studies, BLs with mixed phase clouds had weaker convection, shallower BL depths, and smaller cloud fractions than BLs with clouds restricted to the liquid phase only. It is shown that the weaker BL convection is due to strong ice precipitation. Ice precipitation reduces convective strength directly by stabilizing downdrafts and more indirectly by sensibly heating the BL and inhibiting vertical mixing of momentum thereby reducing surface heat fluxes by as much as 80 W m−2. This feedback between precipitation and surface fluxes was found to have a significant impact on cloud/BL morphology, producing oscillations in convective strength and cloud fraction that did not occur if surface fluxes were fixed at constant values. Increases in IN concentrations in mixed phase clouds caused a more rapid Bergeron‐Findeisen process leading to larger precipitation fluxes, reduced convection and lower cloud fraction. When IN were removed from the BL through precipitation, fewer crystals were nucleated at later simulation times leading to progressively weaker precipitation rates, greater cloud fraction, and stronger convective BL eddies.
Objective estimation of the probability density function for climate sensitivity
Authors: Andronova Natalia G. , Schlesinger Michael E.
Published: February 2004

The size and impacts of anthropogenically induced climate change (AICC) strongly depend on the climate sensitivity, ΔT2x. If ΔT2x is less than the lower bound given by the Intergovernmental Panel on Climate Change (IPCC), 1.5°C, then AICC may not be a serious problem for humanity. If ΔT2x is greater than the upper bound given by the IPCC, 4.5°C, then AICC may be one of the most severe problems of the 21st century. Here we use a simple climate/ocean model, the observed near‐surface temperature record, and a bootstrap technique to objectively estimate the probability density function for ΔT2x. We find that as a result of natural variability and uncertainty in the climatic radiative forcing, the 90% confidence interval for ΔT2x is 1.0°C to 9.3°C. Consequently, there is a 54% likelihood that ΔT2x lies outside the IPCC range.
Ground‐based measurements of tropospheric CO, C2H6, and HCN from Australia at 34°S latitude during 1997–1998
Authors: Rinsland Curtis P. , Meier Arndt , Griffith David W. T. , Chiou Linda S.
Published: February 2004

High spectral resolution (0.004 cm−1) infrared solar absorption measurements of CO, C2H6, and HCN have been recorded with the Fourier transform spectrometer located at the Network for the Detection of Stratospheric Change complementary station at the University of Wollongong, Australia (34.45°S, 150.88°E, 30 m above sea level). The time series covers March 1997 to February 1998. Profile retrievals with maximum sensitivity in the upper troposphere show distinct seasonal cycles for all three molecules with maxima during October‐December 1997. Best fits to the time series of daily averages yield peak 0.03–14 km columns (molecules cm−2) of 1.54×1018for CO, 8.56×1015for C2H6, and 6.56×1015for HCN during austral spring. Mixing ratio profiles of all three molecules during this time show maxima in the upper troposphere. Isentropic back trajectories suggest the elevated CO, C2H6, and HCN columns above Wollongong originated from southern Africa or South America with no significant contribution from the intense tropical Asian emissions during the strong El Niño event of 1997–1998.
N2O and O3 relationship in the lowermost stratosphere: A diagnostic for mixing processes as represented by a three‐dimensional chemistry‐transport model
Authors: Bregman A. , Lelieveld J. , van den Broek M. M. P. , Siegmund P. C. , Fischer H. , Bujok O.
Published: February 2004

A three‐dimensional chemistry‐transport model has been used to investigate N2O and O3 distributions in the lowermost stratosphere at middle and high latitudes in the Northern Hemisphere. The model results are compared with detailed in situ aircraft observations, performed in the winters of 1994–1995 and 1996–1997 and spring 1996, as part of the Stratosphere Troposphere Experiment by Aircraft Measurements (STREAM) II and III. In addition, observations performed earlier in the winter of 1997 during the Polar Stratospheric Aerosol Experiment (POLSTAR) I mission have been included. It is shown that slopes from the observed N2O‐O3 relationships can be used to characterize air masses in the lowermost stratosphere and to test a global tropospheric‐stratospheric chemistry‐transport model. The calculated slopes are consistent with the general view of the N2O‐O3 distribution in the lower stratosphere. However, examining the lowermost stratosphere in detail, the model occasionally calculates significantly steeper slopes than observed. The observed shallower slopes reflect the presence of polar vortex air. Depending on the strength and the persistence of the polar vortex during winter, confined polar stratospheric air masses reach the tropopause, even during late spring at midlatitudes. This is consistent with the view that stratosphere‐troposphere exchange and vortex erosion take place along isentropic surfaces from the polar reservoir.
Description and performance of the UIUC 24‐layer stratosphere/troposphere general circulation model
Authors: Yang Fanglin , Schlesinger Michael E. , Rozanov Eugene
Published: February 2004

This paper describes the 24‐layer stratosphere/troposphere general circulation model (24‐L ST‐GCM) developed by the Climate Research Group of the University of Illinois at Urbana‐Champaign (UIUC). The model's dynamical and physical processes, similar to those of its ancestors, are briefly described. The newly implemented parameterizations of longwave and solar radiation, cloud‐radiation interaction, subgrid‐scale orographic gravity wave drag, and aerosol radiative forcing are described in more detail. Sensitivity tests using simplified one‐dimensional column models and the 24‐L ST‐GCM are carried out to evaluate these implementations. A 15‐year simulation with prescribed climatological sea‐surface temperatures and sea‐ice extents has been performed. To determine the model's strengths and weaknesses, the simulated results are compared with observations. The model simulates well the geographical distributions of surface‐air temperature and precipitation and their seasonal variations. The simulated cloud cover and cloud radiative forcing have the observed magnitudes and latitudinal variations, except near 60°S where the model underestimates the cloud cover by ∼20–30%. It is found that the large‐scale cloud distribution and the cloud‐top altitude depend on the respective critical relative humidities for the onset of large‐scale precipitation and penetrating convection. The model captures reasonably well the observed features of atmospheric temperature and zonal wind in both the stratosphere and troposphere in all seasons, with the exception of the northern stratospheric polar‐night jet. The simulated Transformed‐Eulerian‐Mean residual circulation in the stratosphere has comparable magnitudes and distributions to those obtained by data assimilation and other general circulation models (GCMs). The two‐cell Brewer‐Dobson circulation is captured. The use of an orographic‐type gravity wave drag parameterization is responsible for an abnormally warm northern polar stratosphere in winter, which is contrary to most other GCMs.
Stratospheric balloon measurements of electric fields associated with thunderstorms and lightning in Brazil
Authors: Saba M. M. F. , Pinto O. , Pinto I. R. C. A. , Mendes O.
Published: February 2004

Measurements of electric fields associated with thunderstorms and lightning were obtained during two balloon flights carrying double‐probe electric field detectors launched from Cachoeira Paulista (22°44′S, 44°56′W), Brazil, on January 26, 1994, and March 23, 1995. From data obtained in 1994, a linear relationship between the quasi‐dc vertical electric field peak amplitude and the decay time constant of lightning signatures was found for negative flashes. The results are compared to similar data for intracloud flashes. Based on electric field data obtained in 1995 and on the present knowledge about the differences between positive cloud‐to‐ground and intracloud flashes, two methods to distinguish them at balloon altitudes are presented: The first is based on an estimate of the destroyed charge in the event; the second is based on the peak amplitude ratio between the vertical quasi‐dc and the VLF electric field. The behavior of the vertical quasi‐dc electric field before and after large cloud‐to‐ground lightning flashes is discussed and attributed to the existence of a shielding layer around the thunderstorm. This shielding layer is associated with a threefold or greater decrease in the conductivity inside the cloud. An abrupt variation observed in the quasi‐dc electric field possibly associated with the occurrence of positive flashes was observed and attributed to the formation of a transient shielding layer just above the thunderstorm, which could be produced by the near‐breakdown field inside the cloud.
Importance of structure in the longer‐term dynamics of landscapes
Authors: Shugart H. H.
Published: February 2004

When one is attempting to simulate the dynamic response of the vegetation over short timescales (days to as long as years), it is efficacious to ignore the change in the vertical and the horizontal structure of natural vegetation. At longer timescales, for example, the timescales associated with monitoring and predicting interannual variation in the vegetation, structural dynamics can strongly alter the process‐based predictions of such features as ecosystem productivity. There are ecosystem models that have the capability of simulating structural change, and these models have been tested to some degree using large‐scale remotely sensed information. This paper reviews types of ecological modeling approaches used for evaluations of terrestrial vegetation change at large‐area and longer‐than‐annual timescale. It then provides examples of results from models that simulate structural change. Finally, examples of ecosystem dynamics that change with spatial scale are presented.
Measurements of landscape‐scale fluxes of carbon dioxide in the Peruvian Amazon by vertical profiling through the atmospheric boundary layer
Authors: Kuck Laura R. , Smith Tyrell , Balsley Ben B. , Helmig Detlev , Conway Thomas J. , Tans Pieter P. , Davis Kenneth , Jensen Michael L. , Bognar John A. , Arrieta Rosaura Vazquez , Rodriquez Rodolfo , Birks John W.
Published: February 2004

Vertical profiles of carbon dioxide were measured within and above the atmospheric boundary layer at a tropical forest site in the Peruvian Amazon during July 1996 using a tethered balloon sampling platform. Flask samples were collected within and above the mixed layer and analyzed off‐site for carbon dioxide by nondispersive infrared spectrophotometry. Ozone and temperature vertical profiles were used to determine the boundary layer heights and growth rates. The mean values for methane, carbon monoxide, hydrogen, carbon‐13, and oxygen‐18 ratios were determined within and above the mixed layer. Daytime carbon dioxide flux values were calculated using the budget method. Nocturnal fluxes were estimated by integrating the carbon dioxide mixing ratios as a function of height from the ground to the inversion layer and dividing the total accumulated carbon dioxide by the time since sunset. The daytime carbon dioxide flux of −13 ± 2 μmol C m−2 s−1 and the nocturnal flux of +5.0 ± 1.0 μmol C m−2 s−1 are in good agreement with previous studies in the Brazilian Amazon.
An interpretation of trace gas correlations during Barrow, Alaska, winter dark periods, 1986–1997
Authors: Harris J. M. , Dlugokencky E. J. , Oltmans S. J. , Tans P. P. , Conway T. J. , Novelli P. C. , Thoning K. W. , Kahl J. D. W.
Published: February 2004

Positive correlations among CO, CO2, and CH4 during winter–spring have been observed at Barrow, Alaska, for many years. We examine these, as well as negative correlations between O3 and these gases, during the winter dark period. Because biogenic and photochemical processes are limited within this environment, we believe that pollution is driving these relationships. The dearth of mixing processes within the Arctic basin, the strong stability of the winter boundary layer, and lack of sunlight (and hence low OH) contribute to the winter–spring maxima in CO, CO2, and CH4. We hypothesize that the negative correlation of O3 with these gases is the result of O3 titration by NO and NO2 (NOx) in industrial plumes, which leads to the destruction of one to two molecules of O3 per NO emitted. Using the empirical slopes of O3/CO2 and O3/CO determined from 12 years of Barrow data, we derived emission factors, ΔNOx/ΔCO2 and ΔNOx/ΔCO, assuming −1.5 O3/NO because of titration. Comparing these with published emission factors for NOx, CO2, and CO from industrial processes, we found good agreement. This pollution signature is regionally widespread, although air parcels transported from the direction of Siberia have the highest mixing ratios of pollutant gases. Possible scenarios leading to these trace gas relationships are explored.
Modeling trace gas concentrations at Cape Grim using the CSIRO Division of Atmospheric Research Limited Area Model (DARLAM)
Authors: Kowalczyk Ewa A. , McGregor John L.
Published: February 2004

The CSIRO Division of Atmospheric Research Limited Area Model (DARLAM) is used to study the emission and transport of trace gases in the atmosphere. Two simulations are performed, one for radon, which has relatively simple surface emissions, and another for CO2, which has more complex spatial and temporal distributions of surface fluxes. For this study, DARLAM was initialized from observed atmospheric conditions. Diurnally varying surface fluxes from photosynthesis and respiration were included as functions of temperature, incoming solar radiation, and vegetation type. Industrial sources of CO2 and an Australian inventory of radon fluxes were also included. This study provides an evaluation of the model's trace gas transport capability by comparing Cape Grim measurements with the modeled concentrations of radon and CO2. Correlations calculated using 3‐hour averaging are generally high for radon (0.6–0.8), and lower for CO2 (0.2–0.6). An objective verification technique of categorical forecasting is used to show that the model can satisfactorily forecast the occurrence of radon events. The quality of the model CO2 simulation is less satisfactory. Extra simulations suppressing either island or mainland sources are used to identify whether the air is of island, oceanic, or mainland origin. Further simulations suppressing industrial or biospheric sources are then used to show that the model can handle isolated industrial sources, but biospheric sources and sinks are not handled well at present. We conclude that insufficient accuracy in the spatial and temporal representation of the biospheric CO2 sources and sinks is the main reason for the model's less satisfactory CO2 simulation.