bluuebunny/crossref_metadata_2025 huggingface dataset:
Biological enhancement at cyclonic eddies tracked with GOES Thermal Imagery in Hawaiian waters
Authors: Seki Michael P. , Polovina Jeffrey J. , Brainard Russell E. , Bidigare Robert R. , Leonard Carrie L. , Foley David G.
Published: February 2004

In November 1999, ship and satellite platforms were used to track, target and map the vertical and horizontal structure of two cyclonic eddies in the lee of Hawaii. Depth‐integrated nitrate+nitrite levels within the photic zone of the eddy cores were 3‐ to 15‐ fold higher than those observed for control stations. The depth and magnitude of the deep chlorophyll maximum were significantly elevated in the more mature of the two eddies. HPLC analyses revealed that the enhanced chlorophyll was largely contributed by chromophyte microalgae. Modeled primary productivity rates were up to twofold higher at the stations within the eddies.
Modeling coastal aerosol transport and effects of surf‐produced aerosols on processes in the marine atmospheric boundary layer
Authors: Vignati Elisabetta , de Leeuw Gerrit , Berkowicz Ruwim
Published: February 2004

The Coastal Aerosol Transport (CAT) model was developed to study the evolution of aerosol particle size distributions and composition in the coastal environment. The model simulates such processes as particle production at the sea surface, mixing of particles through the boundary layer by turbulent diffusion, gravitational settling, and dry deposition. The model is initialized at the shoreline with continental and/or surf aerosol. An empirical source function was developed which better accounts for the production of submicron particles than current formulations. Continental and sea spray particles are treated separately to account for effects of processes depending on chemical composition. CAT has been tested by comparison with independent data sets as regards the prediction of particle size distributions, the wind speed dependence of sea‐salt aerosol mass concentrations, and the evolution of sea spray aerosol plumes generated over the surf zone. The model was applied to study effects of sea spray aerosol produced in the surf zone on sea spray concentrations, the composition of continental/sea spray aerosol mixture, the uptake of nitric acid by sea spray aerosol, and the effect of the latter process on nitric acid profiles. The results lead to the conclusion that surf‐produced aerosol cannot be neglected in studies of processes involving sea spray aerosol in the coastal atmospheric boundary layer.
Emissions of greenhouse gases and other airborne pollutants from charcoal making in Kenya and Brazil
Authors: Pennise David M. , Smith Kirk R. , Kithinji Jacob P. , Rezende Maria Emilia , Raad Tulio Jardim , Zhang Junfeng , Fan Chengwei
Published: February 2004

Airborne emissions from charcoal‐making kilns commonly used in Kenya and Brazil were measured during typical operating conditions. Emission factors were determined for carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), carbon monoxide (CO), total nonmethane hydrocarbons, nitrogen oxides (NOx) and total suspended particulates (TSP) along with charcoal production efficiency and charcoal and fuelwood carbon and energy contents. The conversion of wood carbon to charcoal carbon ranged from 37 to 69%, depending on kiln type. Emission factors, expressed as grams of pollutant per kilogram of charcoal produced, for the eight kilns ranged from 543 to 3027 for CO2, 32–62 for CH4, 143–373 for CO, 24–124 for total nonmethane organic compounds, 0.011–0.30 for N2O, 0.0054–0.13 for NOx, and 13–41 for TSP. On average, fuelwood carbon was approximately diverted as follows: 51% to charcoal, 27% to CO2, and 13% to products of incomplete combustion (PIC). Due to the higher global warming potentials (GWPs) of PIC relative to CO2on a carbon atom basis, such kilns can produce rather large net greenhouse gas emissions, even when the wood is harvested renewably. Based on published GWPs for CO2, CH4, and N2O only, we estimate that 0.77–1.63 kg C‐CO2(carbon as carbon dioxide equivalents) is emitted per kilogram of charcoal produced. We estimate that the total primary global warming commitment (GWC) of Kenyan and Brazilian charcoal‐making kiln emissions is about 2.7 and 7.5 million tons (Mt) C‐CO2, respectively. For comparison, the primary GWC from fossil fuel use in the United States is almost 1700 Mt C‐CO2.
Interaction between antecedent planetary‐scale envelope soliton blocking anticyclone and synoptic‐scale eddies: Observations and theory
Authors: Luo Dehai , Huang Fei , Diao Yina
Published: February 2004

The conditions of 30 blocking events were examined at the time of onset over the 1993/1994–1996/1997 cold season (November to March). The antecedent synoptic‐scale eddies in 83.3% of the total events are shown to induce a large‐scale low/high eddy forcing pattern upstream of the incipient block, and the mean basic westerly flow is weak, 76.7% of which possesses cyclonic shear. It appears that both the antecedent synoptic‐scale eddies that induce a low/high eddy forcing pattern and the weak background westerly flow (zonal wave number O) that allows quasi‐stationary preblock ridge are two necessary preconditions for the onset of blocking anticyclone, but the cyclonic shear of the background westerly flow is a favorable preblock environment. In addition, a theoretical model, represented by the superposition of dipole and monopole envelope Rossby solitons with weak orographic forcing for zonal wave number 2, is proposed to confirm these observations. It is found that the dipole envelope soliton is dominant and exhibits a quasi‐2‐week oscillation during the interaction between an antecedent blocking anticyclone and upstream synoptic‐scale eddies. The monopole soliton tends to break up, indicating that blocking anticyclone circulation is dominated by the amplification of dipole component associated with synoptic‐scale eddies. Finally, the evolution of time‐dependent eddy feedback is shown to control the direction of planetary‐scale potential vorticity transports induced by transient eddies, which is an indicator of the onset, maintenance, and decay of blocking. Moreover, the changes of amplified blocking anticyclone and synoptic‐scale eddies obtained theoretically are also in agreement with those of observed blocking and synoptic eddies.
Decadal power in land air temperatures: Is it statistically significant?
Authors: Thejll Peter A.
Published: February 2004

The geographical distribution and properties of the well‐known 10–11 year signal in terrestrial temperature records is investigated. By analyzing the Global Historical Climate Network data for surface air temperatures we verify that the signal is strongest in North America and is similar in nature to that reported earlier by R. G. Currie. The decadal signal is statistically significant for individual stations, but it is not possible to show that the signal is statistically significant globally, using strict tests. In North America, during the twentieth century, the decadal variability in the solar activity cycle is associated with the decadal part of the North Atlantic Oscillation index series in such a way that both of these signals correspond to the same spatial pattern of cooling and warming. A method for testing statistical results with Monte Carlo trials on data fields with specified temporal structure and specific spatial correlation retained is presented.
On the accuracy of Total Ozone Mapping Spectrometer retrievals over tropical cloudy regions
Authors: Newchurch M. J. , Liu X. , Kim J. H. , Bhartia P. K.
Published: February 2004

Motivated by the desire to accurately derive tropospheric ozone from Total Ozone Mapping Spectrometer (TOMS) measurements, we investigate several aspects of these observations in the presence of highly reflecting clouds. Using the collocated Temperature Humidity InfraRed (THIR) measurements of cloud‐top pressures, we identify three TOMS algorithm errors resulting from the inaccurate assignment of cloud‐top pressure. The most significant error results from the inappropriate tropospheric ozone amount added below cloudy scenes to complete the total ozone column. After accounting for the cloud‐height errors, we find significant total ozone column excesses of 10–15 Dobson units (DU) (1 DU = 2.6867×1016 molecules cm−2) over high‐altitude, highly reflecting clouds compared with clear area observations. After accounting for additional algorithm errors involving the tropospheric ozone climatology and considering potential dynamical, photochemical, and NIMBUS‐7/Earth Probe calibration errors, approximately 4–9 DU excesses over cloudy scenes remain. We speculate that the TOMS algorithm approximation of clouds as opaque Lambertian reflecting surfaces may account for a significant portion of these unexplained excesses. The excess ozone due to calibration error and unknown sources will affect the tropospheric ozone derived from TOMS measurements using clear/cloudy difference techniques.
Role of the equatorial Kelvin wave in stratosphere‐troposphere exchange in a general circulation model
Authors: Fujiwara Masatomo , Takahashi Masaaki
Published: February 2004

Large‐scale disturbances which cause the variations of ozone and water around the equatorial tropopause are investigated with a general circulation model incorporating a simplified ozone photochemistry, realistic topography, and seasonal cycle of the sea surface temperature. Eastward moving large‐scale equatorial gravity waves are found to be dominant to modulate the minor constituents' distribution around the equatorial tropopause. A case over the Indian Ocean in the northern summer was investigated in detail. The disturbance had the characteristics of the equatorial Kelvin wave at the tropopause level, coupled with organized active convections in the troposphere. Associated with the downward displacement (and suppressed‐convection) phase of this system, dry, ozone‐rich stratospheric air moved downward into the upper troposphere. At the opposite phase, physical and dynamical processes above the organized active convections prevented the lower stratosphere from accumulating excess water. Thus the dryness around the equatorial tropopause is maintained during the passage of such a system. Analysis of 4‐year integration data reveals that such disturbances are especially active over the Indian Ocean during the northern summer through autumn. This is probably related to the development of the summer monsoon circulation over south Asia. This model has also simulated the zonal wave one structure of tropical tropospheric ozone and suggested the important contribution of convective transport to the structure.
Comparison of boreal ecosystem model sensitivity to variability in climate and forest site parameters
Authors: Potter Christopher S. , Wang Shusen , Nikolov Ned T. , McGuire A. David , Liu Jane , King Anthony W. , Kimball John S. , Grant Robert F. , Frolking Steven E. , Clein Joy S. , Chen Jing M. , Amthor Jeffrey S.
Published: February 2004

Ecosystem models are useful tools for evaluating environmental controls on carbon and water cycles under past or future conditions. In this paper we compare annual carbon and water fluxes from nine boreal spruce forest ecosystem models in a series of sensitivity simulations. For each comparison, a single climate driver or forest site parameter was altered in a separate sensitivity run. Driver and parameter changes were prescribed principally to be large enough to identify and isolate any major differences in model responses, while also remaining within the range of variability that the boreal forest biome may be exposed to over a time period of several decades. The models simulated plant production, autotrophic and heterotrophic respiration, and evapotranspiration (ET) for a black spruce site in the boreal forest of central Canada (56°N). Results revealed that there were common model responses in gross primary production, plant respiration, and ET fluxes to prescribed changes in air temperature or surface irradiance and to decreased precipitation amounts. The models were also similar in their responses to variations in canopy leaf area, leaf nitrogen content, and surface organic layer thickness. The models had different sensitivities to certain parameters, namely the net primary production response to increased CO2 levels, and the response of soil microbial respiration to precipitation inputs and soil wetness. These differences can be explained by the type (or absence) of photosynthesis‐CO2 response curves in the models and by response algorithms of litter and humus decomposition to drying effects in organic soils of the boreal spruce ecosystem. Differences in the couplings of photosynthesis and soil respiration to nitrogen availability may also explain divergent model responses. Sensitivity comparisons imply that past conditions of the ecosystem represented in the models' initial standing wood and soil carbon pools, including historical climate patterns and the time since the last major disturbance, can be as important as potential climatic changes to prediction of the annual ecosystem carbon balance in this boreal spruce forest.
Influence of cloud feedback on annual variation of global mean surface temperature
Authors: Tsushima Yoko , Manabe Syukuro
Published: February 2004

The goal of this study is to estimate the cloud radiative feedback effect on the annual variation of the global mean surface temperature using radiative flux data from the Earth Radiation Budget Experiment. We found that the influence of the cloud feedback upon the change of the global mean surface temperature is quite small, though the increase of the temperature is as much as 3.3 K from January to July. On a global scale, we found no significant relationship between either solar reflectivity of clouds or effective cloud top height and the annual cycle of surface temperature. The same analysis was repeated using the output from three general circulation models, which explicitly predict microphysical properties of cloud cover. On a global scale, both solar cloud reflectivity and cloud top height increase significantly with the increase of surface temperature, in contrast to the observation. The comparative analysis conducted here could be used as an effective test for evaluating the cloud feedback process of a model.
A study of the dynamics of the equatorial lower stratosphere by use of ultra‐long‐duration balloons: 1. Planetary scales
Authors: Vial F. , Hertzog A. , Mechoso C. R. , Basdevant C. , Cocquerez P. , Dubourg V. , Nouel F.
Published: February 2004

In the late southern winter of 1998, Centre National d'Études Spatiales (CNES), the French Space Agency, released six 10‐m‐diameter, superpressure balloons from a location near Quito, Ecuador. Three balloons collapsed soon after launching, but the remaining three drifted westward for a few weeks at altitudes between 19 and 20 km. Two of those balloons crossed the Pacific Ocean before falling above the “maritime continent,” while the other completed a revolution around the Earth and crossed the Pacific for a second time before its final fall. Despite the small number and the relatively short duration of the flights, the balloons provided a unique in situ data set for the lower equatorial stratosphere. This part 1 of a two‐part paper describes this data set and analyzes outstanding features in the planetary scales. Part 2 focuses on gravity‐wave scale. It is argued that balloon trajectories over the Pacific are primarily determined by the westward drift during the easterly phase of the equatorial quasi‐biennial oscillation (QBO) and the meridional velocity field of a mixed Rossby‐gravity (Yanai) wave with an apparent period of 4 days and zonal wave number 4. This wave appears to have two episodes of amplification during the balloon flights. It is also argued that the balloons show evidence of oscillations with periods between 2 and 4 days and of a Kelvin wave with an apparent period close to 10 days and zonal wave number 1. In this way, the balloon behavior provided a pictorial view of air parcel trajectory in the equatorial lower stratosphere. It is stated that larger balloon campaigns can provide excellent in situ data sets for studies on the dynamics and composition of the middle atmosphere.
Detection and characterization of boreal coniferous forests from remote sensing data
Authors: Widlowski Jean‐Luc , Pinty Bernard , Gobron Nadine , Verstraete Michel M.
Published: February 2004

Advanced radiation transfer models capable of representing the reflectance of the coupled surface and atmosphere system have been used to generate look‐up tables of simulated remote sensing measurements at the top of the atmosphere for typical conditions of forest cover and atmospheric composition found in northern Europe. These simulations were evaluated against actual observations under identical viewing and illumination geometries, available for the blue, red, and near‐infrared spectral bands of the VEGETATION instrument to retrieve the most likely of a set of predefined solutions to the inverse problem. The accumulation of results over multiple days in the summer of 1999 permitted the establishment of maps showing the likelihood of identifying the predefined forest types, their corresponding structural characteristics, as well as the associated atmospheric optical depth on the day of retrieval. The proposed methodology is completely generic and thus can easily be prototyped for different biomes and instruments.
The biogeochemical controls of the δ15N and δ18O of N2O produced in landfill cover soils
Authors: Mandernack Kevin W. , Rahn Thomas , Kinney Chad , Wahlen Martin
Published: February 2004

We document an enrichment of both the δ18OAtm.O2 and δ15NAtm.N2 values of soil‐derived N2O collected from landfill cover soils relative to tropospheric N2O. The isotopic values of N2O vary from −5.1‰ to +l9.4‰ and from +19.0‰ to +33.5‰ for δ 15NAtm.N2 and δ18OAtm.O2,, respectively. A tight linear correlation for δ18OAtm.O2 versus δ15NAtm.N2 is apparent, reflecting coupled microbial processes that produce N2O that may be isotopically enriched or depleted in relation to tropospheric N2O. Several explanations are provided to explain this correlation, including evidence for NH3 limitation during nitrification, which would be expected to diminish isotopic fractionation and consequently result in more enriched isotopic values of N2O. Desiccation effects on nitrification were also observed, which contribute to NH3 limitation and thus could influence the isotopic signature of N2O. Our results indicate that the N2O isotopic composition from soils may vary greatly depending on the season and soil moisture conditions and may at times be enriched in 15N and 18O relative to tropospheric N2O.
Soil‐atmosphere nitrogen oxide fluxes: Effects of root disturbance
Authors: Keller Michael , Weitz Antje M. , Bryan Brynne , Rivera Maria M. , Silver Whendee L.
Published: February 2004

Chambers are the most common method used to sample soil‐atmosphere fluxes of trace gases. Working in tree plantations in Costa Rica and in subtropical forest in Puerto Rico, we performed controlled experiments in order to evaluate whether installation of the chamber bases into the soil affects the soil‐atmosphere flux of nitrogen oxides. Installation of chambers severed roots. We found a short‐term disturbance effect related to chamber installation. Fluxes of nitrogen oxides increased by as much as a factor of 4 during a period of about 1 month following chamber installation in the soil. Within 6 weeks of chamber base installation, fluxes fell to control levels. Given the timescale of disturbance and recovery, root mortality and decomposition is the most likely cause of the observed effect.
Significance of HOx and peroxides production due to alkene ozonolysis during fall and winter: A modeling study
Authors: Ariya Parisa A. , Sander Rolf , Crutzen Paul J.
Published: February 2004

In an attempt to identify new mechanisms for the generation of oxidants during fall and winter, we carried out a modeling investigation in which ozonolysis reactions of alkenes that were primarily anthropogenic in origin were considered. Our results indicate that the ozonolysis reactions of these molecules can be the major sources of HOx, H2O2, and organic peroxides during the night and therefore especially during dark seasons. These O3‐initiated oxidation reactions produce more peroxy radicals than those initiated by HO or NO3. This increase in RO2 also results in an increase in HO, HO2, and H2O2. The direct HO formation pathways by ozonolysis of alkenes can form more HO radicals than that from the reaction of O(1D) + H2O during the dark seasons. This additional source of HO can augment significantly atmospheric oxidation. H2O2 formation by ozonolysis also appears to be the most important dark season tropospheric sources of this oxidant. Our modeling results suggest that the existence of pollutant hydrocarbons and trace amount of biogenically produced terpenes can also lead to important production of HOx, H2O2, and organic peroxides. Substantially enhanced gas‐phase production of H2O2 and organic peroxides due to ozonolysis reactions can cause significant liquid‐phase oxidation of S(IV) to S(VI), and hence the role of ozonolysis reactions can be important for the sulfur conversion studies.
Seasonal characteristics of tropospheric ozone production and mixing ratios over East Asia: A global three‐dimensional chemical transport model analysis
Authors: Mauzerall Denise L. , Narita Daiju , Akimoto Hajime , Horowitz Larry , Walters Stacy , Hauglustaine Didier A. , Brasseur Guy
Published: February 2004

We examine seasonal and geographical distributions of tropospheric ozone production and mixing ratios over East Asia with a global three‐dimensional chemical transport model called Model of Ozone and Related Tracers, version 1 (MOZART 1). Net ozone production within the East Asian boundary layer exhibits three distinct seasonal cycles depending on region (north of 20°N, 5–20°N and south of 5°N). North of 20°N, net ozone production over East Asia from spring through autumn is found to have a maximum extending from 25°N–40°N and from central eastern China to Japan, resulting from the strong emission and transport of anthropogenic O3 precursors. In winter, maximum O3 production in this region occurs between 20°N and 30°N. This is a region of long‐range transport. Over the Indochina peninsula, between 5°N and 20°N, net O3 production is controlled by the seasonal cycle between wet and dry seasons and has a maximum at the end of the dry season due to emissions from biomass burning. South of 5°N, in the true tropics, O3 mixing ratios are relatively constant throughout the year and do not exhibit a seasonal cycle. A spring‐summer maximum of net O3 production is found throughout the troposphere in East Asia. We estimate an annual net O3 production in East Asia of 117 Tg/yr. Both model results and analysis of measurements of O3/CO correlations over East Asia and Japan show strong variability as a function of both photochemical activity and seasonal meteorology, and indicate ozone export off the coast of East Asia in spring. An upper estimate of O3 export from East Asia to the Pacific Ocean in the mid‐1980s of 3.3 Gmol/d (58 Tg/yr) is obtained.
Modeled Arctic ozone depletion in winter 1997/1998 and comparison with previous winters
Authors: Guirlet M. , Chipperfield M. P. , Pyle J. A. , Goutail F. , Pommereau J. P. , Kyrö E.
Published: February 2004

We have used a three‐dimensional stratospheric model to investigate Arctic ozone depletion in the three winters from 1995/1996 to 1997/1998, winters with quite different dynamical conditions. We have diagnosed the chemical depletion from the model and compared the model ozone with ground‐based and sonde measurements. In winter 1997/1998 the lower stratosphere was generally much warmer than the previous two cold winters. However, the occurrence of low temperatures in December 1997 did cause chlorine activation and ozone loss in the model. In fact, despite the very different meteorological conditions for these three winters, by mid‐February the model‐calculated mean vortex loss was similar in each year at around 20% at 480 K. Larger differences in the calculated loss occurred when low temperatures persisted into March; this seems a prerequisite for very large loss. By late March the model‐calculated mean vortex column loss was 53 Dobson units (DU) in 1998, 71 DU in 1996, and 80 DU in 1997. A first effort at a detailed day‐to‐day validation of a chemical transport model by comparison with ozone measurements is presented. The model reproduces the mean column observations to within about ±10%, although the bias varies in magnitude and changes sign in different years. The agreement between the model and ozonesonde profiles in the lower stratosphere varies from year to year and during the course of a particular winter/spring. In winter 1997/1998, the model agrees well with sonde profiles at the 480 K and 555 K levels with a positive mean difference (ozonesonde values minus model values) with amplitude of less than 6%. In contrast, in winter 1996/1997, the mean difference is negative and the amplitude is less than 15%. In winter 1995/1996 the mean difference is negative and the amplitude reaches 43%. The differences in 1995/1996 and 1996/1997 result despite good agreement between model and observations in midwinter, and they develop following the large chemical losses which occurred in those winters. We suggest that a major contribution to the model/observation differences for those two winters is a model underestimation of the chemical ozone loss.
Aerosol properties at a midlatitude northern hemisphere continental site
Authors: Koloutsou‐Vakakis S. , Carrico C. M. , Kus P. , Rood M. J. , Li Z. , Shrestha R. , Ogren J. A. , Chow J. C. , Watson J. G.
Published: February 2004

Measurements of chemical, physical, and optical properties of ambient aerosol particles were obtained at Bondville, Illinois. This research was completed to increase the spatial and temporal resolution of measured aerosol. Results from measurements describe (1) the physical and chemical characteristics of the aerosol and (2) the dependence of light scattering and backscattering on wavelength of light λ, controlled relative humidity RH, and aerosol particle chemical composition. Formulations for the hygroscopic growth factor f(RH), and backscatter ratio b, as functions of λ and RH and estimates of the upscatter fraction
, and Ångström exponent å are also provided. For aerosol sampled at the site from January to December 1995, the mean gravimetric mass concentration for particles with aerodynamic diameter (dpa)≤1 μm had an arithmetic mean and standard deviation of 10.6±6.5 μg/m3, respectively. Ion chromatography (IC) speciated 53% of the total gravimetric mass for particles with dpa≤1 μm. Most of the IC‐identified material (88.0±13.5%) consisted of NH4+ and SO42−. Material not identified with IC was primarily elemental and organic carbon. The total aerosol light‐scattering coefficient at λ = 550 nm and RH≤40% was 51.6±43.2 Mm−1 for dpa≤10 μm and 42.0±34.9 Mm−1 for dpa≤1 μm. Mean values of f(RH = 82.5%, λ) for total scattering ranged between 1.4 and 1.5 and for back scattering between 1.1 and 1.2. Mean values of b(λ) ranged from 0.11 to 0.18 for RH<40% and from 0.09 to 0.14 for RH = 82.5%. Mean values of
ranged from 0.21 to 0.30 depending on λ, RH, and the particle size distribution. Mean values of å ranged between 1.8 and 2.4 for RH<40% and 1.8 and 2.1 for RH = 82.5%. These measured properties are now available for use in models to reduce uncertainties when quantifying direct aerosol radiative forcing at a continental site influenced by aerosol with anthropogenic origin.
Validation of the Austrian forecast model for solar, biologically effective UV radiation‐UV index for Vienna
Authors: Schmalwieser Alois W. , Schauberger Günther
Published: February 2004

Since October 1995, a daily forecast of the UV index, as the irradiance of the biologically effective ultraviolet radiation, for the next day is published for Austria, Europe, and world wide. The Austrian forecast model as well as the input parameters are described. By connecting the UV index with the sensitivity of the photobiological skin types, a recommendation is given to select an appropriate sun protection factor of a sunscreen to avoid overexposure of the skin. The validation of the Austrian forecast model is done by measurements of the biologically effective ultraviolet radiation collected between July 1996 and July 1998 at Vienna (48°N, 16°E), Austria. The forecast quality is evaluated by comparing the Austrian model with two statistical models used in Canada and the Netherlands. By using the underestimation of the UV index as criteria in the sense of radiation protection, the Austrian model shows a 12% underestimation over the whole year.
Effective radiative properties of bounded cascade absorbing clouds: Definition of an effective single‐scattering albedo
Authors: Szczap Frédéric , Isaka Harumi , Saute Marcel , Guillemet Bernard , Ioltukhovski Andrey
Published: February 2004

We applied the equivalent homogeneous cloud approximation (EHCA) to the bounded cascade inhomogeneous absorbing clouds and defined their effective radiative properties. It is found that we have to introduce an effective single‐scattering albedo in addition to an effective optical depth to treat the inhomogeneous absorbing clouds under the plane‐parallel homogeneous cloud assumption. For an inhomogeneous absorbing cloud, a pair of the effective parameters can be estimated from each one of three possible pairs taken from the area‐averaged reflectance, transmittance and absorptance. We found that the behavior of these effective properties was quite similar to those observed for the inhomogeneous non absorbing clouds except that two effective parameters were to be examined instead of only one effective parameter for the nonabsorbing clouds. Empirical relations for both the effective optical depth and the single‐scattering albedo were given as a function of the local mean optical depth and relative local cloud inhomogeneity. We showed that the effective single‐scattering albedo could not be properly introduced under the effective thickness approximation (ETA), which indicates an important conceptual difference between the EHCA and the ETA. Finally, we discussed possible consequences of the effective single‐scattering albedo, defined in this study, with respect to the anomalous absorption phenomenon.
Potential of multiangular spectral measurements to characterize land surfaces: Conceptual approach and exploratory application
Authors: Gobron Nadine , Pinty Bernard , Verstraete Michel M. , Martonchik John V. , Knyazikhin Yuri , Diner David J.
Published: February 2004

New sensors exhibiting advanced technical specifications motivate the development of improved algorithms to take advantage of the enhanced performances of these sensors. In the particular case of the Multiangle Imaging Spectroradiometer (MISR) instrument, the angular sampling of the scattered radiance field, coupled with high spatial resolution and accurate radiometric calibration, justifies the implementation of physically based algorithms to optimally interpret the data and extract high‐level information. This paper proposes a new approach to the reliable and accurate characterization of vegetated areas on the basis of data gathered in space and to the delivery of improved products to meet increasingly demanding user requests. An exploratory study based on advanced very high‐resolution radiometer (AVHRR) data shows the potential of approaches based on advanced models but also points out the limitations associated with the use of data from monodirectional instruments. By contrast, a preliminary investigation conducted with synthetic MISR‐like multiangular data illustrates the potential of analyzing data of high radiometric quality with advanced models to move toward a more complete characterization of terrestrial surfaces.
The relative importance of solar activity and anthropogenic influences on the ion composition, temperature, and associated neutrals of the middle atmosphere
Authors: Beig Gufran
Published: February 2004

The changes arising from variations in solar activity and human activities on atmospheric composition and thermal structure of the middle atmosphere, especially in the ion composition, are assessed using interactive one‐ and two‐dimensional chemical models of the stratosphere, mesosphere, and lower thermosphere. The changes from anthropogenic activities are less in magnitude but permanent in nature, and changes due to variations in the solar activity are comparatively higher but periodic. Our results may have bearing and could explain some of the results reported in recent literature on observed lower ionospheric data and strengthen the global change concept in this region. Model response to available observations is quite reasonable, and a good agreement on temperature trend and ionization parameters is found. The impact of increasing concentrations of several greenhouse gases (anthropogenic origin) and variations in solar activity on the ion composition, temperature, and neutral species (of interest to ionization) is examined in two different modeling studies. In each case, the effect of the other forcing is filtered out. A cooling of the order of −10°K in the mesosphere and a maximum of −14°K in the stratosphere is predicted for the double‐CO2 scenario. A decreasing trend in nitric oxide number density from −40% to −95% with altitude is noticed for the double‐CO2 case contrary to an increasing trend (10% to 140%) for high solar activity (HSA) as compared to low solar activity (LSA) conditions in the mesosphere and the lower thermosphere. As a result of changes in temperature and in the concentrations of NO, O2, H2O, O, CH3CN, a decreasing trend of −50% for the double‐CO2 case and an increasing trend of 60% for HSA as compared to LSA are predicted in NO+ ion number density near the mesopause for the tropics. The variations in water cluster ions are negligible in the stratosphere but reach to −50% in the lower thermosphere for the double‐CO2 scenario. The total ion density varies from −30% at 40 km to +30% at 90 km for HSA as compared to LSA conditions and from −5% to 12% from the stratosphere to the mesosphere for the double‐CO2 scenario.
Identification of sources of aerosol particles in three locations in eastern Botswana
Authors: Chimidza S. , Moloi K.
Published: February 2004

Airborne particles have been collected using a dichotomous virtual impactor at three different locations in the eastern part of Botswana: Serowe, Selibe‐Phikwe, and Francistown. The particles were separated into two fractions (fine and coarse). Sampling at the three locations was done consecutively during the months of July and August, which are usually dry and stable. The sampling time for each sample was 12 hours during the day. For elemental composition, energy‐dispersive x‐ray fluorescence technique was used. Correlations and principal component analysis with varimax rotation were used to identify major sources of aerosol particles. In all the three places, soil was found to be the main source of aerosol particles. A copper‐nickel mine and smelter at Selibe‐Phikwe was found to be not only a source of copper and nickel particles in Selibe‐Phikwe but also a source of these particles in far places like Serowe. In Selibe‐Phikwe and Francistown, car exhaust was found to be the major source of fine particles of lead and bromine.
Relevance of mountain wave cooling for the formation of polar stratospheric clouds over Scandinavia: Mesoscale dynamics and observations for January 1997
Authors: Dörnbrack Andreas , Leutbecher Martin , Reichardt Jens , Behrendt Andreas , Müller Klaus‐Peter , Baumgarten Gerd
Published: February 2004

The effect of mesoscale mountain wave‐induced temperature anomalies on the formation potential of polar stratospheric clouds above northern Scandinavia is analyzed with a one‐month mesoscale model integration. The simulation results are contrasted with synoptic‐scale analyses and compared with remote sensing and in situ observations. The mesoscale mass flux of air parcels with temperatures below the threshold for cloud formation through a control volume is compared with its synoptic‐scale counterpart. A classification of the synoptic‐scale flow into periods of large and small mountain wave activity in the stratosphere is proposed. The derived classification will be used for a climatology of stratospheric mountain wave activity above Scandinavia.
Vertical short‐scale structures in the upper tropospheric and lower stratospheric temperature and ozone at la Réunion Island (20.8°S 55.3°E)
Authors: Chane‐Ming Fabrice , Molinaro Franck , Leveau Jean , Keckhut Philippe , Hauchecorne Alain , Godin Sophie
Published: February 2004

The distribution and the nature of vertical short‐scale structures observed in ozone and temperature are investigated in the upper troposphere and the lower stratosphere at La Reunion Island located in the vicinity of the southern subtropical barrier by using wavelet‐based methods. A climatology of dominant wavelike patterns with short vertical wavelengths reveals the presence of localized structures on both the ozone and the temperature perturbations, extracted from ozonesonde and temperature data, up to the middle stratosphere. Some case studies are presented to identify the nature of short‐scale structures with 1‐ to 5‐km vertical wavelengths in the troposphere and the stratosphere. A climatology of short‐scale structures induced by gravity waves and the horizontal advection shows that short‐scale structures are mainly detected in the middle and upper troposphere and in the lower stratosphere. The weak value of the coefficient R(z) that links the ozone and temperature perturbations induced by gravity waves is a major limit to detecting such short‐scale structures above 21‐km altitude. Some structures with vertical wavelengths ranging from 1 to 5 km are attributed to gravity waves produced by convection in summer and the subtropical jet in winter, or quasi‐horizontal large‐scale motions from both sides of the subtropical barrier.
Impact of climate variability on the vegetation water stress
Authors: Ridolfi Luca , D'Odorico P. , Porporato A. , Rodriguez‐Iturbe I.
Published: February 2004

An important parameter in the assessment of the impact that conditions of limited soil water availability have on vegetation is the average length of the intervals during the growing season in which soil moisture is below some critical levels. These levels are related to the plant tolerance to water stress. The interannual rainfall variability induces important fluctuations on the average duration and frequency of the periods of water stress with important effects on the spatial and temporal structure of plant ecosystems. It is shown that the nonlinearities embedded in the dynamics controlling the soil water balance may drastically enhance the effects of the fluctuations present in the climatic forcing. Interannual climate variability leads to stronger year‐to‐year changes on the mean duration and frequency of periods of soil water deficit as well as to the emergence of preferential states in the probability distributions of these two variables. The sensitivity of these statistical properties is studied with respect to the characteristics of climate, soil, and vegetation.
In situ ozone production under free tropospheric conditions during FREETEX ’98 in the Swiss Alps
Authors: Zanis P. , Monks P. S. , Schuepbach E. , Carpenter L. J. , Green T. J. , Mills G. P. , Bauguitte S. , Penkett S. A.
Published: February 2004

The second Free Tropospheric Experiment (FREETEX ’98) took place at the Jung‐fraujoch Observatory (3580 m above sea level), Switzerland, in March/April 1998. A number of trace gases and photolysis parameters were measured, including peroxy radicals (HO2+RO2), the photolysis rate coefficients j(NO2) and j(O1D), O3, NOx, NOy, HCHO, peroxyacetylnitrate (PAN), CO, CN, and hydrocarbons. The average midday concentration of HO2+RO2 observed during the campaign is 13±3 parts per trillion by volume (pptv). The peroxy radical concentrations measured during FREETEX '98 are discussed in terms of the respective NO measurements and box model calculations. By screening out polluted and cloudy conditions during FREETEX ’98, 8 relatively clean days are selected. These 8 days represent near free tropospheric conditions. The average midday concentration of HO2+RO2 observed during these 8 days is 17±5 pptv and the modeled diurnal cycle of [HO2]+[CH3O2] simulated by a photochemical box model shows very good agreement with the mean diurnal cycle of the peroxy radicals over these 8 days. The in situ net ozone production rate is calculated for each day during FREETEX '98 using the peroxy radical, j(O1D), NO, H2O, and O3 measurements. The mean net ozone production rate during the 8 relatively clean selected days is 0.09 ppbv h−1. If more stringent criteria are applied, 3 free tropospheric days can be selected with a mean net ozone production rate of 0.05±0.01 ppbv h−1, indicating the positive role of in situ photochemistry during springtime in the free troposphere over the Alps and supporting the previous results of the first FREETEX campaign in April/May 1996. Using the experimental data, it is estimated that the ozone compensation point, that is, the point where photochemical ozone production equals destruction, occurs at 24±9 pptv of NO in good agreement with theoretical calculations.
Vibrational level distribution of O2(b1∑+g, v = 0–15) in the mesosphere and lower thermosphere region
Authors: Slanger T. G. , Cosby P. C. , Huestis D. L. , Osterbrock D. E.
Published: February 2004

We have determined the vibrational distribution of emission from the O2(b1∑+g) state in the terrestrial nightglow. Previous nightglow studies have been limited to detecting emission from the v = 0 level, but the high sensitivity and resolution available in sky spectra taken with the Keck I telescope and the associated High Resolution Echelle Spectrometer (HIRES) have made it possible to observe O2(b1∑+g) levels up to v = 15. Apart from emission from v = 0, which is intense above the atmosphere due to ineffective quenching, the vibrational‐level‐dependent intensity distribution is bimodal, with maxima at v = 3–4 and v = 12, and a deep minimum at v = 8. Excluding the v = 0 level, the total system intensity is of the order of 150 rayleighs. The O2(b1∑+g) vibrational levels seem to fall into two categories: v = 0, 1 and v≥2. The intensity of emission from the latter group tends to follow the intensity of the OH Meinel system, while that of the former group does not. We consider the possibility that at least a portion of the v≥2 group derives from OH chemistry, and also discuss the possible role of sodium chemistry.
Analysis of gas‐aerosol partitioning in the Arctic: Comparison of size‐resolved equilibrium model results with field data
Authors: Fridlind A. M. , Jacobson M. Z. , Kerminen V.‐M. , Hillamo R. E. , Ricard V. , Jaffrezo J.‐L.
Published: February 2004

Size‐resolved aerosol mass and gas concentrations were measured during the European Arctic Aerosol Study (EAAS). A thermodynamic equilibrium model was applied to the data in order to (1) test whether gas‐aerosol equilibrium appeared to be obtained by NH3, HNO3, HCl, HCOOH, and CH3COOH, and (2) test the sensitivity of gas‐aerosol equilibrium to several nonvolatile organic acids that were measured. Model results indicated that all submicrometer, accumulation‐mode aerosols appeared to be near equilibrium with NH3. Supermicrometer, coarsemode aerosols of recent marine origin appeared to be out of equilibrium with HNO3 and closer to equilibrium with HCl, while continentally influenced aerosols sometimes appeared to be near equilibrium with both HNO3 and HCl. However, the observed gas‐aerosol partitioning of HCOOH and CH3COOH could not be explained by effective Henry's law partitioning, consistent with other studies. Nonvolatile organic acids measured were methanesulfonate, oxalate, succinate, and glutarate. Sensitivity tests indicated that methanesulfonate retained ∼30% of NH4+ under marine conditions but had <3% impact on other species and under other conditions. Whereas oxalic acid was predicted to be ∼15–30% dissociated in the aerosol solution, succinic and glutaric acids were predicted to be <10% dissociated, limiting their ability to influence gas‐aerosol partitioning. Together, the three dicarboxylic acids were responsible for retaining 0–2% of predicted NH4+ and displacing 0–6% of predicted Cl− and NO3−. Model results were sensitive to the assumed mixing state of the aerosols, as well as the degree of aerosol size resolution represented by the model.
Cloud‐aerosol interactions during autumn over Beaufort Sea
Authors: Pinto James O. , Curry Judith A. , Intrieri Janet M.
Published: February 2004

Cloud and aerosol properties were observed by aircraft in autumn over the Beaufort Sea during the 1994 Beaufort and Arctic Storms Experiment (BASE). The microphysical properties (particle size, concentration, mass, and phase) and vertical structure of autumn clouds are examined as a function of height and minimum in‐cloud temperature, Tmin. Below 2 km, liquid clouds were observed at Tmin between −5° and −9°C, mixed‐phase clouds were observed between −5° and −20°C, and clear‐sky ice crystal precipitation was observed at Tmin as warm as −14°C. Between 2 and 5 km all clouds were mixed‐phase and typically consisted of a thin layer of liquid with ice extending well below the liquid layer. These mixed‐phase clouds were found at Tmin as low as −32°C. All clouds observed above 5.5 km were composed entirely of ice at Tmin as warm as −33°C. The concentration of ice crystals is observed to increase exponentially with decreasing Tmin. The Hallet‐Mossop ice multiplication process did not appear to be an important in the production of ice crystals in the mixed‐phase cloud observed in this study. The atmosphere was relatively clean with condensation nuclei (CN) concentrations rarely exceeding 300 cm−3. The smallest CN concentrations (as low as 50 cm−3) were observed in the boundary layer and just above the surface where precipitation and nucleation scavenging have cleansed the air. Thin layers of very large CN concentrations were often observed within and just above low‐level clouds possibly resulting from gas‐to‐particle conversion which requires clean and humid air typical of lower Arctic atmosphere.
A multisensor diagnostic satellite cloud property retrieval scheme
Authors: Miller S. D. , Stephens G. L. , Drummond C. K. , Heidinger A. K. , Partain P. T.
Published: February 2004

Active sensor data, in the form of lidar and radar cloud vertical boundaries, are used as a priori information to passive sensor satellite retrievals of cloud optical depth and effective particle radius. Correct placement of cloud in the vertical eliminates the need to approximate cloud height from multispectral passive techniques and is shown to improve uncertainties in nighttime retrievals of thin cirrus in excess of 30%. The new method is exemplified by two casen studies using imager data from GOES but remains valid for any passive/active remote sensing application. A strength of this method is its ability to diagnose components of the retrieval uncertainty and thereby quantify retrieval performance. Errors associated with the forward model and measurement uncertainties, and an independent validation of the retrieval, are discussed.