bluuebunny/crossref_metadata_2025 huggingface dataset:
Temperature‐ and composition‐dependent infrared optical constants for sulfuric acid
Authors: Niedziela R. F. , Norman M. L. , Miller R. E. , Worsnop D. R.
Published: February 2004

Complex refractive indices have been retrieved directly from the FT‐IR extinction spectra of laboratory‐generated, binary sulfuric acid/water aerosols over a range of temperatures and compositions relevant to the atmosphere of Earth. The refractive indices are strongly dependent upon both temperature and composition, due to changes in the equilibrium between sulfate and bisulfate ions and the resultant change in the corresponding solvation interactions. The present results have important implications for determining the composition of sulfuric acid aerosols by remote sensing applications.
Evidence for control of Atlantic subtropical humidity by large scale advection
Authors: Pierrehumbert Raymond T. , Roca Rémy
Published: February 2004

The interplay between large scale dynamics and tropospheric moisture is investigated. A simple conceptual model of the sources and sinks of humidity is used to reconstruct, using a backward Lagrangian trajectory technique, the water vapor distribution in the tropical and subtropical free troposphere. Satellite data in the water vapor channel from both Meteosat‐3 and Meteosat‐4 satellites are then used to validate the model following a model‐to‐satellite approach over the whole Atlantic ocean. There is excellent agreement between simulations and observations in the drier regions, but the simulated brightness temperature exhibits a warm bias within and near moist, convective regions. This bias is most probably due to the neglect of cloud effects in reconstructing the simulated brightness temperature, rather than to a dry bias in the simulation. A second advective simulation, performed with monthly mean rather than full transient winds, led to a substantially drier subtropics. This calculation demonstrates the importance of synoptic scale transient eddies in determining the humidity of the subtropical dry zones. It is speculated on this basis that discontinuous changes in synoptic eddy activity could provide a mechanism for rapid global climate changes.
On different moisture variables in the constitutive equation for condensation growth of cloud drops
Authors: Wacker Ulrike , Herbert Fritz
Published: February 2004

The irreversible H2O‐transfer between a drop and moist air is described on the basis of the diffusion model for condensational drop growth. Depending on the chosen form of the flux‐gradient relationship to approach the irreversible vapour diffusion flux, distinct equations for the growth rate follow, all of which are equally in accord with thermodynamics. They differ in the formulation of the driving force and in the choice of the relevant moisture variable as well as in the correction term due to thermal effects. Considering all assumptions entering the approaches of the condensational drop growth rate, arguments are provided that the most relevant form of the growth equation should be that depending linearly on the mass fraction of water vapour in air as representative moisture variable.
Interplanetary magnetic field periodicity of ∼153 days
Authors: Cane H. V. , Richardson I. G. , von Rosenvinge T. T.
Published: February 2004

We report on the finding of a 153‐day periodicity in the magnetic field strength and solar wind speed measured at 1 AU during the years 1978–1982. The period and the occurence epoch are consistent with the “154‐day” periodicity previously reported for events occurring at the Sun. In particular, the variations in the field strength and the occurence rate of energetic (tens of MeV) solar particle events are in phase. The similar periodicities in the interplanetary field and solar phenomena are consistent with a global phenomenon. Whereas this periodicity is quite strong for the magnetic field magnitude, there is only a weak periodicity for the individual field components. The field magnitude shows essentially no periodicity at this period during the previous and following solar maxima. The lack of persistence, and of significant harmonic components of the observed periodicity, does not support the proposal of a solar “clock” mechanism. The most significant variations in the complete near‐earth magnetic field data base (1963–1997) with periods of less than 200 days occur at 166 and 146 days.
Evidence for a substantial role for dilution in northern mid‐latitude ozone depletion
Authors: Knudsen Bjørn M. , Lahoz William A. , O'Neill Alan , Morcrette Jean‐Jacques
Published: February 2004

Satellite measurements have shown a significant decline in ozone at mid‐latitudes, and this has only partially been explained by chemical models. Here we show that the large ozone depletion in the Arctic vortex in spring 1997 leads to a dilution of northern mid‐latitude ozone after break‐up of the vortex of about 3% or more than 1/3 of the observed change in TOMS total ozone at 30–60°N from May 1979 to May 1997. The dilution in spring 1993–96 is crudely estimated to be 2–4%. These results indicate that dilution plays a substantial role in the mid‐latitude ozone depletion in spring and summer, when the harmful effects of increases in UV radiation are largest.
Impact of El Chichon and Pinatubo on ozonesonde profiles in north extratropics
Authors: Angell James K.
Published: February 2004

The impact of El Chichon and Pinatubo volcanic eruptions on ozonesonde‐derived ozone values in 8–16, 16–24 and 24–32 km layers is estimated for north polar and temperate zones, and the north temperate regions of North America, Europe and Asia, by minimizing the influence of solar cycle and trend, and adjusting for the quasi‐biennial variation in ozone by use of the superposed epoch method. Based on this procedure, in north temperate 8–16 and 16–24 km layers the impact of El Chichon is a significant 10% ozone decrease 3–4 seasons after eruption, the impact of Pinatubo a significant 15% ozone decrease 7 seasons after eruption. In the 24–32 km layer the respective ozone decreases are 2% and 5%, the latter significant. In the north polar zone the ozone decreases following Pinatubo are a significant 20% and 10% in 8–16 and 16–24 km layers, but there are marginally significant ozone increases of 5% in the 24–32 km layer following both eruptions.
Formation of North Pacific Intermediate Water in Meteorological Research Institute ocean general circulation model: 2. Transient tracer experiments
Authors: Yamanaka Goro , Kitamura Yoshiteru , Endoh Masahiro
Published: February 2004

Spreading of North Pacific Intermediate Water (NPIW) is investigated using transient tracers, such as chlorofluorocarbons (CFCs), tritium‐type tracers, and dye tracers. Tracer advection and diffusion are calculated based on flow and density fields obtained using an Meteorological Research Institute (MRI) ocean general circulation model for the North Pacific Ocean. Historical CFCs simulation generally agrees well with observed distributions. The subsurface CFCs maximum, the most striking feature of observed CFCs distribution in the North Pacific, is well reproduced by the model. Tritium‐type tracers with a sink due to radioactive decay and a source restoring to a uniform value, are used to determine the path of NPIW spreading. Two tracer source regions are assumed: the subarctic sea surface and the Okhotsk Sea. Tracers flowing from source regions spread southward with paths different in the 26.4–26.7 σθ surfaces, which outcrop only in the subarctic gyre, and in the 26.8–27.4 σθ surfaces, which do not outcrop in the North Pacific. In the 26.4–26.7 σθ surfaces, tracers are mostly advected eastward by the clockwise intermediate layer circulation, and eventually reach the subtropical gyre mostly in the eastern North Pacific. In the 26.8–27.4 σθ surfaces, however, tracers are carried southeastward by isopycnal eddy diffusion into the subtropical gyre beneath the Kuroshio Extension flow. Transient dye tracers whose source varies over time are used to estimate timescale of the NPIW spreading, defined as a time span over which an assumed temporal peak of the source reaches the basin interior. This timescale is free from contamination by mixing with surrounding waters. It is found that the timescale increases with density, <10 years at 26.4 σθ (advection timescale) to 15–25 years at 27.2 σθ (diffusion timescale).
Improved atmospheric trace gas measurements with an aircraft‐based tandem mass spectrometer: Ion identification by mass‐selected fragmentation studies
Authors: Reiner Thomas , Möhler Ottmar , Arnold Frank
Published: February 2004

We have built and employed an aircraft‐borne triple quadrupole mass spectrometer (TQMS) for fragmentation studies of mass‐selected ions in the upper troposphere and lower stratosphere. The fragmentation studies included both ambient and artificially produced ions relevant for the measurement of atmospheric trace gases by ion molecule reaction mass spectrometry (IMRMS) and led to an unambiguous identification of the chemical composition of important ions used for IMRMS measurements. Among these are the product ions of ion molecule reactions of CO3−(H2O)n and H3O+(H2O)n ions with HNO3, SO2, acetone, HCN, and methyl cyanide. These reactions have been studied in the laboratory, and ions having the same masses as the expected product ions have been previously observed in atmospheric IMRMS spectra. The present fragmentation studies are the first to actually identify the chemical composition of these ions during aircraft measurements in the upper troposphere and lower stratosphere and demonstrate that these ions can reliably be used for atmospheric trace gas measurements. Furthermore, the fragmentation studies gave indications for the existence and the possible identification of previously unknown ions. Among these the tentative identification of CO3−H2O2 offers the possibility for sensitive measurements of H2O2 by IMRMS. The fragmentation studies were accompanied by IMRMS measurements of atmospheric trace gases using the TQMS. Altitude profiles of HNO3, SO2, and lower limits for H2O2 are shown.
Airborne aerosol measurements in the tropopause region and the dependence of new particle formation on preexisting particle number concentration
Authors: de Reus Marian , Ström Johan , Kulmala Markku , Pirjola Liisa , Lelieveld Jos , Schiller Cornelius , Zöger Martin
Published: February 2004

Airborne measurements of aerosol particles and trace gases were performed at midlatitudes in the Stratosphere‐Troposphere Experiment by Aircraft Measurements (STREAM‐96) campaign during late spring in the free troposphere and lower stratosphere. The results show a consistent relation between particle number concentration and water vapor mixing ratio, suggesting a minimum particle number concentration below which nucleation of particles is very likely to occur. Numerical simulations, using a coupled atmospheric chemistry and aerosol nucleation model, support this hypothesis. The model calculations indicate that new particle formation is very sensitive to the preexisting particle number concentration in the tropopause region.
Heterogeneous reaction of N2O5 on sodium nitrate aerosol
Authors: Wahner Andreas , Mentel Thomas F. , Sohn Martin , Stier Jutta
Published: February 2004

The heterogeneous reactive uptake coefficients of N2O5 on metastable and deliquescent aerosols were determined in a large aerosol chamber at different humidities to 0.0018±0.0004, 0.0032±0.0006, and 0.023±0.005 at 48, 62, and 88% relative humidity and 293±2 K. The uptake coefficients at the lower two relative humidities are ∼1 order of magnitude smaller than the uptake coefficients of N2O5 on other aqueous surfaces. This effect is explained by the ionic hydrolysis mechanism of N2O5 and the influence of the significantly enhanced recombination reaction NO2+ + NO3− ⇒ N2O5 due to the large molality of NO3− in the metastable aerosols. About 70% of the heterogeneously hydrolyzed N2O5 are found to be released as HNO3 into the gas phase. The results present experimental support for the ionic hydrolysis mechanism of N2O5. The low reaction probabilities lead to lower heterogeneous NOx turnover in specific areas of the atmosphere as assumed so far.
Implications of the new ozone National Ambient Air Quality Standards for compliance in rural areas
Authors: Saylor Rick D. , Chameides William L. , Cowling Ellis B.
Published: February 2004

The U.S. Environmental Protection Agency (EPA) has recently promulgated new National Ambient Air Quality Standards (NAAQS) for ozone (O3). The new standard is based on an 8‐hour average O3 concentration instead of a 1‐hour average, as was the previous standard. Analysis of O3 concentrations measured at rural sites in the eastern United States in the Aerometric Information Retrieval System (AIRS) network, the Southern Oxidant Study's Spatial Ozone Network (SON), and EPA's Clean Air Status and Trends Network (CASTNet) during 1993–1995 indicates that 30–50% of these sites would have been noncompliant under the new standard, as compared with only 2–12% under the old standard. These results suggest that the new standard will thus require a major shift in emphasis in the nation's pollution control strategy from an urban‐centered focus to a more regional emphasis. This in turn will require the development of a more comprehensive, truly rural air quality monitoring network in coming years.
Intercomparison among chamber, tower, and aircraft net CO2 and energy fluxes measured during the Arctic System Science Land‐Atmosphere‐Ice Interactions (ARCSS‐LAII) Flux Study
Authors: Oechel Walter C. , Vourlitis George L. , Brooks Steven , Crawford Timothy L. , Dumas Edward
Published: February 2004

Measurements of net ecosystem CO2 exchange (NEE) and energy balance were made using chamber‐, tower‐, and aircraft‐based measurement techniques in Alaskan arctic tundra ecosystems during the 1994–1995 growing seasons (June‐August). One of our objectives was to quantify the interrelationships between the NEE and the energy balance measurements made from different sampling techniques. Qualitative and quantitative intercomparisons revealed that on average the correspondence between the mass and energy fluxes measured by these sampling methods was good despite potential spatial and temporal mismatches in sampling scale. Quantitative comparisons using least squares linear regression analyses with the tower‐based measurements of NEE as the independent variable indicate that the chamber‐ and aircraft‐based NEE measurements were generally lower relative to the tower‐based measurements (slope =0.76–0.86). Similarly, tower‐aircraft comparisons of latent (Le) and sensible (H) heat exchange indicated that the aircraft‐based measurements were lower than the tower‐based measurements (slope =0.72–0.80). Qualitative comparisons, however, indicate that the correspondence among the chamber‐, tower‐, and aircraft‐measured fluxes varied both seasonally and interannually, suggesting the lack of a consistent bias between the sampling techniques. The results suggest that differences observed between the chamber, tower, and aircraft flux measurements were primarily due to the failure to account for the spatial distribution of surface types in the tower and aircraft sampling footprint, problems involved in the comparison of temporal and spatial averages, and temporal (e.g., seasonal and interannual) variance in rates of mass and energy flux for a given point. Other potential sources of variance include the underestimation of nocturnal NEE by the tower‐based eddy covariance system, and the periodic occurrence of an elevated CO2 plume in the atmosphere over the Prudhoe Bay oil field. Even with these potential sources of variation, the results reveal that the various methods give comparable estimates of NEE and energy flux within a range of temporal or spatial variability.
Tropical and global scale interactions among water vapor, atmospheric greenhouse effect, and surface temperature
Authors: Inamdar Anand K. , Ramanathan V.
Published: February 2004

We employ a multitude of global data sets to extend recent analyses of atmospheric greenhouse effect and its dependence on surface temperature (Ts) and vertical water vapor distribution. The new data encompasses a global domain including both the continents and the oceans as well as both the ascending and descending branches of the Walker and Hadley cells and the extratropical storm track regions. We adopt the radiometric definition of the atmospheric greenhouse effect, Ga, which is the difference between the surface longwave emission and the outgoing longwave radiation. We derive the global average greenhouse effect over both oceans and land areas. The east to west variations of the normalized atmospheric greenhouse effect (ga) and precipitable water (w) are just as strong as the north to south variations, thus illustrating the strong role of the dynamics in w and ga. Between 60°N and 60°S the lowest values of ga (0.11–0.15) are found over the Saharan and other deserts; while the largest values (0.35–0.40) are found over the warm oceans with a deep convective atmosphere. The coupling between Ga, and the vertical distribution of atmospheric water vapor and temperature, is examined from monthly mean annual cycle. When averaged from the southern to the northern latitudes, these quantities exhibit a statistically significant annual cycle. The annual cycle of Ts, about 1 K for the tropics (30°N to 30°S) and about 4 K for the globe, is large enough to obtain a statistically significant estimate for the sensitivity parameter dGa/dTs. It is as large as 5.5–6 W m−2 K−1 for tropical mean conditions (30°N to 30°S) and reduces to a global mean value of 3.5 W m−2 K−1 (with a 2σ range of 2.9–4.1 W m−2 K−1). Consistent with earlier studies, the tropics exhibit a strong positive coupling between Ts, Ga, and water vapor distribution with large increases in the midtroposphere humidity. However, poleward of 30°N, water vapor increases are about half as much as that in the tropics, and the sensitivity parameter dGa/dTs decreases. This is because poleward of 30°, the annual cycle is dominated by land surface temperature changes which are not so effective as sea surface temperature changes in enhancing the water vapor greenhouse effect. Irrespective of the region (ocean or land) or the latitude domain (tropics or extratropics), the data presented here do not offer any support for the suggestion that increases in tropical or global mean surface temperature would lead to a decrease in water vapor greenhouse effect by drying the middle to upper troposphere. If any, the global scale sensitivity derived from the annual cycle is consistent with the magnitude of the positive feedback obtained by general circulation models.
Alteration processes in volcanic soils and identification of exobiologically important weathering products on Mars using remote sensing
Authors: Bishop Janice L. , Fröschl Heinz , Mancinelli Rocco L.
Published: February 2004

Determining the mineralogy of the Martian surface material provides information about the past and present environments on Mars which are an integral aspect of whether or not Mars was suitable for the origin of life. Mineral identification on Mars will most likely be achieved through visible‐infrared remote sensing in combination with other analyses on landed missions. Therefore, understanding the visible and infrared spectral properties of terrestrial samples formed via processes similar to those thought to have occurred on Mars is essential to this effort and will facilitate site selection for future exobiology missions to Mars. Visible to infrared reflectance spectra are presented here for the fine‐grained fractions of altered tephra/lava from the Haleakala summit basin on Maui, the Tarawera volcanic complex on the northern island of New Zealand, and the Greek Santorini island group. These samples exhibit a range of chemical and mineralogical compositions, where the primary minerals typically include plagioclase, pyroxene, hematite, and magnetite. The kind and abundance of weathering products varied substantially for these three sites due, in part, to the climate and weathering environment. The moist environments at Santorini and Tarawera are more consistent with postulated past environments on Mars, while the dry climate at the top of Haleakala is more consistent with the current Martian environment. Weathering of these tephra is evaluated by assessing changes in the leachable and immobile elements, and through detection of phyllosilicates and iron oxide/oxyhydroxide minerals. Identifying regions on Mars where phyllosilicates and many kinds of iron oxides/oxyhydroxides are present would imply the presence of water during alteration of the surface material. Tephra samples altered in the vicinity of cinder cones and steam vents contain higher abundances of phyllosilicates, iron oxides, and sulfates and may be interesting sites for exobiology.
Farewell
Authors: Jakosky Bruce
Published: February 2004

My term as Editor of the Journal of Geophysical Research‐Planets comes to an end with this issue. While it might seem useful for me to take stock of the state of the journal after having served for four years, I am not going to. Rather, it is much more appropriate for the planetary science community as a whole to do so. Certainly there has been a lot of discussion during my term as Editor as to whether the journal should exist. Questions have been raised both philosophically based on the nature of planetary science and its relation to other geophysical fields, and programmatically based on the number of papers that are published, their quality, and the role of the journal in planetary science. It is appropriate for any community to continually take stock of its journals, as well as of its societies and especially of its relevance; it is fundamentally important that it not be afraid to take whatever actions are appropriate for the future of the field.
Using chemical tracers to assess ocean models
Authors: England Matthew H. , Maier‐Reimer Ernst
Published: February 2004

Chemical tracers can be used to assess the simulated circulation in ocean models. Tracers that have been used in this context include tritium, chlorofluorocarbons, natural and bomb‐produced radiocarbon, and to a lesser extent, oxygen, silicate, phosphate, isotopes of organic and inorganic carbon compounds, and certain noble gases (e.g., helium and argon). This paper reviews the use of chemical tracers in assessing the circulation and flow patterns in global and regional ocean models. It will be shown that crucial information can be derived from chemcial tracers that cannot be obtained from temperature‐salinity (T‐S) alone. In fact, it turns out that a model with a good representation of T‐S can have significant errors in simulated circulation, so checking a model’s ability to capture chemical tracer patterns is vital. Natural chemical tracers such as isotopes of carbon, argon, and oxygen are useful for examining the model representation of old water masses, such as North Pacific and Circumpolar Deep Water. Anthropogenic or transient tracers, such as tritium, chlorofluorocarbons, and bomb‐produced 14C, are best suited for analyzing model circulation over decadal timescales, such as thermocline ventilation, the renewal of Antarctic Intermediate Water, and the ventilation pathways of North Atlantic Deep Water and Antarctic Bottom Water. Tracer model studies have helped to reveal inadequacies in the model representation of certain water mass formation processes, for example, convection, downslope flows, and deep ocean currents. They show how coarse models can chronically exaggerate the spatial scales of open‐ocean convection and deep currents while underestimating deep flow rates and diffusing downslope flows with excessive lateral mixing. Higher‐resolution models typically only resolve thermocline ventilation because of shorter integration times, and most resort to high‐latitude T‐S restoring to simulate reasonable interior water mass characteristics. This can be seen to result in spuriously weak chemical tracer uptake at high latitudes due to suppressed convective overturn and vertical motion. Overall, the simulation of chemical tracers is strongly recommended in model assessment studies and as a tool for analyzing water mass mixing and transformation in ocean models. We argue that a cost‐effective approach is to simulate natural radiocarbon to assess long‐timescale processes, and CFCs for decadal to interdecadal ocean ventilation.
Specification of channel filters for an interferometric radiometer
Authors: Bará J. , Camps A. , Corbella I. , Torres F.
Published: February 2004

Differences among the channels that form an interferometric radiometer result in amplitude and phase errors in the cross correlations measured from the signals collected by each pair of antennas (visibility samples). Since point source calibration of a satellite‐embarked instrument operating in a radio astronomy protected band is, in principle, not possible, and although separable phase errors can be corrected, the nonseparable ones produce an irrecoverable loss of information and have to be kept below specified limits. Preliminary work performed by the authors established basic requirements on the channel transfer function so as to meet these strict specifications imposed by proper calibration and inversion procedures. These requirements were set, from a simple filter model, in terms of three basic parameters: center frequency, bandwidth, and overall group delay. The purpose of this work is, for any kind of filter, to translate these requirements into a given insertion loss mask that must be satisfied by all filters so as to keep nonseparable error terms under certain specified bounds. The numerical results and computer simulations presented are based on the specifications of MIRAS, a two‐dimensional aperture synthesis radiometer currently under study by the European Space Agency, and its proposed in‐orbit calibration procedure.
Quantifying the effects of uncertainty on optimal groundwater bioremediation policies
Authors: Minsker Barbara S. , Shoemaker Christine A.
Published: February 2004

This paper describes a method for quantifying the economic and environmental effects of uncertainty in biological parameter values on optimal in situ bioremediation design. The range of uncertainty in model results associated with a range of input parameter values is quantified for both individual parameter errors and errors in combinations of parameters. Three measures of sensitivity are presented that quantify different aspects of the effects of model error on an implemented optimal policy. Numerical results are presented for an example site contaminated with phenol, with parameter ranges derived from values reported in the literature. For the example site, Ks (the substrate half‐velocity coefficient in the Monod kinetic equation for biodegradation) was found to be the most sensitive biological parameter and this sensitivity was asymmetric; i.e., reductions in the value of Ks have a much greater effect than increases in the value of Ks. The methodology applied in this paper could also be applied to other water resource management problems, allowing the user to quantify the effects of wide ranges of possible parameter values on model results. The method is particularly useful for computationally intensive optimization models, as it requires a manageable number of model runs, and for the many situations where insufficient data are available to permit accurate estimation of probability distributions.
Implications of interannual variability in atmospheric circulation on modeled CO2 concentrations and source estimates
Authors: Dargaville R. J. , Law R. M. , Pribac F.
Published: February 2004

The impact of the interannual variability (IAV) of atmospheric transport on atmospheric CO2 observations is often ignored in carbon cycle studies. We use 8 years of analyzed European Centre for Medium‐Range Weather Forecasts (ECMWF) wind fields from 1985–1992 to demonstrate the effect of IAV of the circulation on modeled CO2 concentrations for fossil and biosphere CO2 sources. The wind fields are used to drive the Melbourne University Tracer Model. The modeled annual mean CO2 values at observing locations show little IAV in the fossil case. In the biosphere case the IAV of the annual mean is considerably larger, especially in the high northern latitudes. Simulated baseline selection using modeled radon concentrations does not reduce the IAV. In both cases, surface layer interhemispheric differences show small interannual variations indicating small changes in interhemispheric transport. Source fields from a mass balance inversion using 1985–1992 ECMWF winds are compared with those from inversions using a single year of winds repeated for each year of observations. We find differences in semi‐hemispheric sources of up to 0.6 Gt C yr−1 at some times. However, 8 year mean sources show smaller differences, mostly less than 0.2 Gt C yr−1 at regional scales. This indicates that the variability in the circulation is a second order factor in determining the sources from inversion calculations.
Distribution and sea‐air fluxes of biogenic trace gases in the eastern Atlantic Ocean
Authors: Baker A. R. , Turner S. M. , Broadgate W. J. , Thompson A. , McFiggans G. B. , Vesperini O. , Nightingale P. D. , Liss P. S. , Jickells T. D.
Published: February 2004

A number of atmospherically important trace gases (dimethyl sulphide (DMS), methyl iodide (CH3I), and nonmethane hydrocarbons (NMHCs)) were measured simultaneously in the eastern Atlantic Ocean during May 1997. This investigation was part of the U.K. Atmospheric Chemistry Studies in the Oceanic Environment (ACSOE) Community Research Program and covered a 200 by 200 nautical mile (1 nautical mile is 1.852 km) area to the west of the Mace Head Atmospheric Research Station on the coast of Ireland. Different spatial and temporal patterns were observed for each of the gases, showing that distinct sources dominate their production in this region: specific species of phytoplankton (DMS), macroalgae (CH3I), total phytoplankton biomass (isoprene), and photochemistry (ethene). Sea‐to‐air fluxes of the gases are calculated for near and offshore domains, and their temporal variations are discussed. A simple photochemical box model has been used to assess the contributions of the gas fluxes to the levels of the gases observed at Mace Head. Results show that the area studied may constitute a substantial source of DMS, a weak source of CH3I, a small source of ethene at night, and an insignificant source of isoprene to atmospheric levels of these gases measured at Mace Head in western Ireland.
Interannual variability of the oceanic sink of CO2 from 1979 through 1997
Authors: Le Quéré Corinne , Orr James C. , Monfray Patrick , Aumont Oliver , Madec Gurvan
Published: February 2004

We have estimated the interannual variability in the oceanic sink of CO2with a three‐dimensional global‐scale model which includes ocean circulation and simple biogeochemistry. The model was forced from 1979 to 1997 by a combination of daily to weekly data from the European Centre for Medium‐Range Weather Forecast and the National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis as well as European Remote Sensing satellite observations. For this period, the ocean sink of CO2 is estimated to vary between 1.4 and 2.2 Pg C yr−1, as a result of annually averaged interannual variability of ±0.4 Pg C yr−1 that fluctuates about a mean of 1.8 Pg C yr−1. Our interannual variability roughly agrees in amplitude with previous ocean‐based estimates but is 2 to 4 times less than estimates based on atmospheric observations. About 70% of the global variance in our modeled flux of CO2 originated in the equatorial Pacific. In that region, our modeled variability in the flux of CO2 generally agreed with that observed to ±0.1 Pg C yr−1. The predominance of the equatorial Pacific for interannual variability is caused by three factors: (1) interannual variability associated with El Niño events occurs in phase over the entire basin, whereas elsewhere positive and negative anomalies partly cancel each other out (e.g., for events such as Antarctic Circumpolar Wave and the North Atlantic Oscillation); (2) dynamic processes dominate in the equatorial Pacific, whereas dynamic, thermodynamic, and biological processes partly cancel one another at higher latitudes; and (3) our model underestimates the variability in ocean dynamics and biology at high latitudes.
Global significance of nitrous‐oxide production and transport from oceanic low‐oxygen zones: A modeling study
Authors: Suntharalingam P. , Sarmiento J. L. , Toggweiler J. R.
Published: February 2004

Recent studies of marine nitrons oxide have focused attention on the suboxic and low‐oxygen zones associated with ocean basin eastern boundaries. It has been suggested that complex N2O cycling mechanisms in these regions may provide a net source to the oceanic interior and a significant portion of the ocean‐atmosphere flux. In this study we evaluate the global significance of N2O formation in these regions. N2O is treated as a nonconserved tracer in an ocean general circulation model; a simple source function is developed which models N2O production as a function of organic matter remineralization and local oxygen concentration. Model results are evaluated against both surface and deep observational data sets. The oceanic oxygen minimum zones are predominantly found in the upper water column of tropical latitudes and overlain by regions of strong upwelling in the surface ocean. Simulations of increased N2O production under low‐oxygen conditions indicate that the majority of the N2O thus formed escapes directly to the atmosphere and is not subject to significant meridional transport. Results indicate that while enhanced N2O production in these regions cannot be held accountable for the majority of the sea‐air flux and interior distribution, it may, however, have significance for the local distribution and provide as much as 25–50% of the global oceanic source.
Spatial distribution of melt conduits in the mantle beneath oceanic spreading ridges: Observations from the Ingalls and Oman ophiolites
Authors: Kelemen Peter B. , Braun Michael , Hirth Greg
Published: February 2004

Ophiolites are on‐land exposures of igneous crust and residual upper mantle formed beneath submarine spreading ridges. Upper mantle outcrops in ophiolites provide insight into focusing of melt transport from a ∼100 km wide region of partial melting into an ∼5 km wide zone of igneous crustal accretion beneath the ridges. Dunite veins, composed of the minerals olivine and spinel, mark conduits for melt transport through at least the uppermost 30 km of the mantle. New data in this paper, on dunite veins in the Ingalls ophiolite, central Washington Cascades, show a power law relationship between frequency and width, in which frequency/m ≈0.02 width−3 over a size interval from ∼0.1 to 2 m. There may be several ways to generate this relationship, but we favor the hypothesis that the dunites represent a coalescing melt transport network. This conclusion is broadly consistent with the related hypothesis that mantle melt extraction occurs in a fractal, branching network, and with recent results on formation of a coalescing network of dissolution channels via flow of a solvent through a partially soluble, compacting porous medium.
Coccolith Sr/Ca as a new indicator of coccolithophorid calcification and growth rate
Authors: Stoll Heather M. , Schrag Daniel P.
Published: February 2004

Polyspecific coccolith separates from core top sediments in the eastern equatorial Pacific show variations of ∼15% in Sr/Ca ratios across the equatorial upwelling zone, with Sr/Ca highest at the equator and decreasing off‐axis. These variations cannot be due to changes in the Sr/Ca of seawater, which varies by less than 2% in the surface ocean. Variations in Sr/Ca of coccolith sediments are similar to variations in primary productivity and alkenone‐estimated coccolithophorid growth rates in overlying surface waters and to CaCO3 rain rates measured in sediment traps. Because of these relationships and because calcification rate exerts a strong control on Sr/Ca in abiogenic calcites, we suggest that the observed Sr/Ca variations in coccoliths may be strongly controlled by coccolithophorid growth and calcification rates, although temperature may also influence coccolith Sr/Ca to a lesser degree. Changes in dissolution intensity and coccolith assemblages appear to exert a minor influence, if any, on coccolith Sr/Ca in these sediment core tops. If further work confirms relationships between coccolith Sr/Ca and coccolithophorid productivity, Sr/Ca records of past changes in coccolithophorid productivity may be useful in reconstructing past variations in the rain ratio of organic to carbonate carbon, an important control on deep ocean pH and partitioning of CO2 between the atmosphere and ocean. In addition, coccolith Sr/Ca might provide an independent record of past changes in coccolithophorid growth rates, which in combination with data on the carbon isotopic fractionation in coccolithophorid organic matter may permit more reliable calculations of past dissolved CO2 in the surface ocean.
H2O and CO2 in magmas from the Mariana arc and back arc systems
Authors: Newman Sally , Stolper Edward , Stern Robert
Published: February 2004

We examined the H2O and CO2 contents of glasses from lavas and xenoliths from the Mariana arc system, an intraoceanic convergent margin in the western Pacific, which contains an active volcanic arc, an actively spreading back arc basin, and active behind‐the‐arc cross‐chain volcanoes. Samples include (1) glass rims from Mariana arc, Mariana trough, and cross‐chain submarine lavas; (2) glass inclusions in arc and trough phenocrysts; and (3) glass inclusions from a gabbro + anorthosite xenolith from Agrigan (Mariana arc). Glass rims of submarine arc lavas contain 0.3–1.9 wt % H2O, and CO2 is below detection limits. Where they could be compared, glass inclusions in arc phenocrysts contain more H2O than their host glasses; most arc glasses and phenocryst inclusions contain no detectable CO2, with the exception of those from a North Hiyoshi shoshonite, which contains 400–600 ppm. The glass inclusions from the Agrigan xenolith contain 4–6% H2O, and CO2 is below the detection limit. Glasses from the cross‐chain lavas are similar to those from the arc: H2O contents are 1.4–1.7 wt %, and CO2 is below detection limits. Volatile contents in Mariana trough lava glass rims are variable: 0.2–2.8 wt % H2O and 0–300 ppm CO2. Glass inclusions from trough phenocrysts have water contents similar to the host glass, but they can contain up to 875 ppm CO2. Volatile contents of melt inclusions from trough and arc lavas and from the xenolith imply minimum depths of crystallization of ∼1–8 km. H2O and CO2 contents of Mariana trough glasses are negatively correlated, indicating saturation of the erupting magma with a CO2‐H2O vapor at the pressure of eruption (∼400 bars for these samples), with the vapor ranging from nearly pure CO2 at the CO2‐rich end of the glass array to nearly pure H2O at the H2O‐rich end. Degassing of these magmas on ascent and eruption leads to significant loss of CO2 (thereby masking preeruptive CO2 contents) but minimal disturbance of preeruptive H2O contents. For submarine Mariana arc magmas, depths were low enough that degassing on ascent and eruption led to loss of both H2O and CO2; as a result, H2O contents are positively correlated with water depth for these samples. The H2O contents of primitive Mariana trough magmas richest in the slab‐derived component (i.e., the most “arc‐like” magmas) are ∼2 wt %. Although evolved glasses with up to 4–6 wt % H2O are present among Mariana arc samples, we interpret the glass inclusion data as indicating that primitive Mariana arc liquids contain 1–3 wt % H2O. The preeruptive H2O contents of primitive cross‐chain seamount liquids are >1–2 wt %.
Modeled impact of cirrus cloud increases along aircraft flight paths
Authors: Rind D. , Lonergan P. , Shah K.
Published: February 2004

The potential climate impact of contrails and alterations in the lifetime of background cirrus due to subsonic aircraft water and aerosol emissions has been investigated in a set of experiments using the GISS GCM connected to a q‐flux ocean. Cirrus clouds at a height of 12–15km, with an optical thickness of 0.33, were input to the model “x” percentage of clear‐sky occasions along subsonic aircraft flight paths. The percentage x is varied from 0.05 to 6%. Two types of experiments were performed: one with the percentage of cirrus cloud increase independent of flight density along the flight paths, the other with the percentage related to the density of fuel expenditure. The overall climate impact was similar with the two approaches, due to the feedbacks of the climate system. Fifty years were run for each of the eight experiments, with the following conclusions based on the stable results from years 31–50. The equilibrium global mean response shows that altering high‐level clouds by 1% changes the global mean temperature by 0.43°C. The global temperature response is highly linear (linear correlation coefficient of 0.996) for high cloud cover changes between 0.1 and 5%. The warming is amplified in the Northern Hemisphere, more so with greater cloud cover change. The temperature effect maximizes around 10km, more so as the overall warming increases (warming greater than 4°C occurs there with a 4.8% increase in upper level clouds). The surface temperature response is dominated by the feedbacks and shows little geographic relationship to the high cloud input outside of the hemispheric difference. Considering whether these effects would be observable, changing upper level cloud cover by as little as 0.4% produces warming greater than 2 standard deviations in the microwave sounding unit (MSU) channels 4, 2, and 2r (although the effect would be most noticeable in the upper troposphere channel 3 were standard deviations available). Given estimates of current aircraft impacts, this would require some increase relative to present‐day effects, but a signal should be clear given the projections for 2050 aircraft. In comparison to increased CO2 experiments, in these runs the Northern Hemisphere clearly warms more relative to the Southern Hemisphere, and warming due to cloud height changes exceeds that due to the water vapor feedback. Despite the simplified nature of these experiments, the results emphasize the sensitivity of the modeled climate to high‐level cloud cover changes and thus the potential ability of aircraft to influence climate by altering clouds in the upper troposphere.
Preliminary estimation of horizontal fluxes of cloud liquid water in relation to subtropical moisture budget studies employing ISCCP, SSMI, and GEOS‐1/DAS data sets
Authors: Shay‐El Yuval , Alpert Pinhas , da Silva Arlindo
Published: February 2004

Special Sensor Microwave/Imager (SSM/I) retrievals of cloud liquid water, International Satellite Cloud Climatology Project (ISCCP) cloud estimates, and winds from the Goddard EOS (GEOS‐1/DAS) assimilation are employed to evaluate vertically integrated cloud liquid water (CLW) transport for 1992. First, GEOS‐1/DAS multiyear data are used to confirm an earlier finding of a paradoxical net moisture sink over the Arabian‐Iraqi desert [Alpert and Shay‐El, 1993]. The negative vertically integrated moisture flux divergence over this region is balanced mainly by the negative incremental analysis updates (IAU) of moisture. Moisture fluxes reveal strong convection but without precipitation in a shallow Hadley‐type cell. Vertical profiles indicate that the moisture removal process is associated with middle and high clouds and probably with CLW flux divergence. The CLW fluxes are estimated explicitly and globally from ISCCP and SSM/I by using linear regression methods. Areas of significant CLW divergence are found over the eastern coasts of both the United States and Asia, in the vicinity of the Gulf Stream and Kuroshio currents, as earlier conjectured by Peixoto [1973]. In both the Arabian‐Iraqi desert and over the Sahara, divergence of a vertically integrated CLW flux opposes the convergence of a vertically integrated horizontal moisture flux, thus explaining at least partially the paradoxical net sink and source in these regions. However, the magnitude of the annual CLW flux estimates as calculated here is, in general, too small to play any significant role in the vertically integrated water budget, except perhaps along coastal regions and over dry subtropical deserts where precipitation minus evaporation is relatively small.
Mars Descent Imager (MARDI) on the Mars Polar Lander
Authors: Malin M. C. , Caplinger M. A. , Carr M. H. , Squyres S. , Thomas P. , Veverka J.
Published: February 2004

The Mars Descent Imager, or MARDI, experiment on the Mars Polar Lander (MPL) consists of a camera characterized by small physical size and mass (∼6×6×12 cm, including baffle; <500 gm), low power requirements (<2.5 W, including power supply losses), and high science performance (1000×1000 pixel, low noise). The intent of the investigation is to acquire nested images over a range of resolutions, from 8 m/pixel to better than 1 cm/pixel, during the roughly 2 min it takes the MPL to descend from 8 km to the surface under parachute and rocket‐powered deceleration. Observational goals will include studies of (1) surface morphology (e.g., nature and distribution of landforms indicating past and present environmental processes); (2) local and regional geography (e.g., context for other lander instruments: precise location, detailed local relief); and (3) relationships to features seen in orbiter data. To accomplish these goals, MARDI will collect three types of images. Four small images (256×256 pixels) will be acquired on 0.5 s centers beginning 0.3 s before MPL's heatshield is jettisoned. Sixteen full‐frame images (1024×1024, circularly edited) will be acquired on 5.3 s centers thereafter. Just after backshell jettison but prior to the start of powered descent, a “best final nonpowered descent image” will be acquired. Five seconds after the start of powered descent, the camera will begin acquiring images on 4 s centers. Storage for as many as ten 800×800 pixel images is available during terminal descent. A number of spacecraft factors are likely to impact the quality of MARDI images, including substantial motion blur resulting from large rates of attitude variation during parachute descent and substantial rocket‐engine‐induced vibration during powered descent. In addition, the mounting location of the camera places the exhaust plume of the hydrazine engines prominently in the field of view.
Autonomous identification of carbonates using near‐IR reflectance spectra during the February 1999 Marsokhod field tests
Authors: Gazis P. R. , Roush T.
Published: February 2004

An autonomous system has been developed to identify the presence of carbonates in near‐IR reflectance spectra (0.35–2.5 μm). This system consists of a set of feature‐extraction algorithms that operate in conjunction with a rule‐based system to identify carbonates on the basis of presence and characteristics of absorption bands near 2.33 and 2.5 μm. This autonomous system was tested during the February 1999 Marsokhod field operations. While performance was compromised to some extent by noise problems associated with the spectrometer, the autonomous system successfully rejected all noisy spectra. Among the nonnoisy spectra that it accepted, it identified carbonates with a success rate of 70% compared with the performance of the field team, a success rate of 82–90% compared with the performance of the remote science team, and a false positive rate of 0%.