bluuebunny/crossref_metadata_2025 huggingface dataset:
An advective‐diffusive isotopic evaporation‐condensation model
Authors: He Hui , Smith Ronald B.
Published: December 2003

A one‐dimensional advective‐diffusive model is developed for the evaporation process across an evaporating surface, providing a general theory of fractionation during evaporation and condensation. The model configuration is based on the Craig‐Gordon linear evaporation model. We improve the model by allowing advection and diffusion to exist in the skin layer beneath the evaporating surface. The model is based on two fundamental physical principles, Henry's law and Fick's law. The model solutions show that diffusion of isotopes in both the atmosphere and the condensed phase plays an essential role in controlling the isotope flux ratio δF, which is a measurable quantity. There are several dimensionless parameters that control the isotopic fractionation during evaporation. The most important parameter is N, which takes into account the evaporation rate and the depth of the advective‐diffusive layer and represents the relative magnitude of the rate of advection versus the rate of diffusion. Assuming rapid surface exchange, the water vapor is always in isotopic equilibrium with the liquid water at the interface. Under the slow evaporation limit, i.e., N → 0, the back flux from the atmosphere to the liquid water reservoir is not negligible compared with the upward flux; hence the net flux ratio must take into account information from the atmosphere such as the mixing ratio and the isotope ratios of water vapor. When N is large, the back flux becomes negligible, so the upward flux dominates the net flux and brings only the information of the liquid water reservoir into the net flux; therefore the flux ratio approaches the isotope ratio of the liquid water reservoir. The model also justifies itself by matching with independent theoretical results from earlier studies. Vapor condensation onto ice is also included as a special case in the model.
Hydrologic effects of frozen soils in the upper Mississippi River basin
Authors: Cherkauer Keith A. , Lettenmaier Dennis P.
Published: December 2003

The variable infiltration capacity (VIC) macroscale hydrologic model was modified to improve its performance in cold regions by adding frozen soil and energy balance snow accumulation and ablation algorithms. Frozen soil penetration was determined by solving thermal fluxes through the soil column. Infiltration and runoff response parameterizations were modified to reflect the simulated ice content of the soil. The revised model was tested using point data from the University of Minnesota Rosemount Agricultural Experiment Station and subsequently applied to two subcatchments in the upper Mississippi River basin. The point tests showed that the model was able to reproduce observations of the snowpack, soil liquid water content, and freezing and thawing front depths. Comparisons of simulated discharge from the two subbasins showed that the frozen soil algorithm reduced infiltration during winter and spring thaws and increased rapid runoff response. However, the magnitude of the increased runoff response is relatively modest, at the scale of the two upper Mississippi subbasins tested.
Modeling the river‐basin response to single‐storm events simulated by a mesoscale meteorological model at various resolutions
Authors: Yu Zhongbo , Lakhtakia M. N. , Barron E. J.
Published: December 2003

The link between the Penn State/NCAR Mesoscale Meteorological Model (MM5) and the Hydrologic Model System (HMS) was implemented to simulate the river‐basin response to single‐storm events. Three MM5‐domain setups, a single domain (36 km grid increment), one nest (36 + 12 km grid increments), and two nests (36 + 12 + 4 km grid increments) were used to simulate two single‐storm events from April 1986 and May 1988 over the Susquehanna River basin (SRB). The MM5‐simulated precipitation at various resolutions and the analyzed observed precipitation were used to drive the hydrologic simulation of direct surface runoff for the SRB and two subbasins (the upper west branch and the upper north branch) and of streamflow for the upper west branch. The streamflow simulation driven with the observed precipitation was first calibrated to the observed streamflow. The simulated streamflow with the observed precipitation and the MM5‐simulated precipitation at various resolutions were compared to the observed streamflow. The discrepancies in modeling the streamflow response and the direct surface runoff with the MM5‐simulated precipitation at various resolutions were evaluated. The simulated results improved as the resolution of the MM5‐simulated precipitation increased. The MM5 simulations for all three domain setups captured the general pattern of the storm systems. On the basis of the quality of the simulated results and the required computing time, the MM5 setup with two nests appears to be the most appropriate to provide the simulated precipitation for the hydrologic simulation of single‐storm events over the SRB.
Application of a laboratory gas exchange chamber for assessment of in situ mercury emissions
Authors: Gustin M. Sexauer , Rasmussen P. , Edwards G. , Schroeder W. , Kemp J.
Published: December 2003

The potential for the use of a laboratory gas exchange system to estimate of mercury emissions from naturally and anthropogenically mercury‐enriched areas was assessed by comparison of mercury fluxes measured from the same substrate in situ and in the laboratory. In general, mercury emissions measured with the laboratory chamber for daytime conditions were of the same magnitude as mean mercury emissions measured in situ with field chambers. Mercury emissions measured with both the field chamber and laboratory chamber were lower than those measured with micrometeorological methods. Within the controlled experimental regime of the laboratory chamber, data were developed that demonstrated that substrate mercury concentrations and light are important parameters in controlling mercury emissions. However, with light and other parameters interacting with the soil, the correlation between mercury fluxes and substrate mercury concentrations declined. Mercury emissions from a variety of substrates in the dark were ∼25% of those emissions measured in the light at the same soil surface temperature.
A new measurement technique of peroxyacetyl nitrate at parts per trillion by volume levels: Gas chromatography/negative ion chemical ionization mass spectrometry
Authors: Tanimoto Hiroshi , Hirokawa Jun , Kajii Yoshizumi , Akimoto Hajime
Published: December 2003

A new technique for measuring peroxyacetyl nitrate (PAN) at parts per trillion by volume (pptv) levels has been developed using gas chromatography with negative ion chemical ionization mass spectrometry (GC/NICI MS). Four fragment ions, CH3C(O)O− (mass‐to‐charge ratios (m/z) = 59), NO−3 (m/z = 62), CH3C(O)OO− (m/z = 75), and NO−2 (m/z = 46), were identified by NICI mass spectra. NO−3 (m/z = 62) was used in selected ion monitoring (SIM) mode among these fragment ions, since it gave the best signal‐to‐noise (S/N) ratio, and a potential interference from isopropyl nitrate (IPN) was excluded. Optimization of mass spectrometry and use of capillary gas chromatography enabled us to detect PAN at a retention time of 2.6±0.1 min in ambient air mixing ratio range. The present detection limit is 15±4 pptv (S/N = 3), which is comparable to those of previously published GC/ECD methods, with good linearity at pptv levels. The instrumental accuracy and precision are estimated to be ±20% and ±15%, respectively. Other PAN analogs (i.e., peroxypropionyl nitrate and peroxymethacryloyl nitrate) were also measured within 10 min. Exploratory ambient air measurements were made at our laboratory in a suburban area of Tokyo, Japan. These results demonstrated the performance of GC/NICI MS for ambient air measurements.
Nevada STORMS project: Measurement of mercury emissions from naturally enriched surfaces
Authors: Gustin M. Sexauer , Lindberg S. , Marsik F. , Casimir A. , Ebinghaus R. , Edwards G. , Hubble‐Fitzgerald C. , Kemp R. , Kock H. , Leonard T. , London J. , Majewski M. , Montecinos C. , Owens J. , Pilote M. , Poissant L. , Rasmussen P. , Schaedlich F. , Schneeberger D. , Schroeder W. , Sommar J. , Turner R. , Vette A. , Wallschlaeger D. , Xiao Z. , Zhang H.
Published: December 2003

Diffuse anthropogenic and naturally mercury‐enriched areas represent long‐lived sources of elemental mercury to the atmosphere. The Nevada Study and Tests of the Release of Mercury From Soils (STORMS) project focused on the measurement of mercury emissions from a naturally enriched area. During the project, concurrent measurements of mercury fluxes from naturally mercury‐enriched substrate were made September 1–4, 1997, using four micrometeorological methods and seven field flux chambers. Ambient air mercury concentrations ranged from 2 to nearly 200 ng m−3 indicating that the field site is a source of atmospheric mercury. The mean daytime mercury fluxes, during conditions of no precipitation, measured with field chambers were 50 to 360 ng m−2 h−1, and with the micrometeorological methods were 230 to 600 ng m−2 h−1. This wide range in mercury emission rates reflects differences in method experimental designs and local source strengths. Mercury fluxes measured by many field chambers were significantly different (p<0.05) but linearly correlated. This indicates that field chambers responded similarly to environmental conditions, but differences in experimental design and site heterogeneity had a significant influence on the magnitude of mercury fluxes. Data developed during the field study demonstrated that field flux chambers are ideal for assessment of the physicochemical processes driving mercury flux and development of an understanding of the magnitude of the influence of individual factors on flux. In general, mean mercury fluxes measured with micrometeorological methods during daytime periods were nearly 3 times higher than mean fluxes measured with field flux chambers. Micrometeorological methods allow for derivation of a representative mercury flux occurring from an unconstrained system and provide an assessment of the actual magnitude and variability of fluxes occurring from an area.
Project to Intercompare Regional Climate Simulations (PIRCS): Description and initial results
Authors: Takle Eugene S. , Gutowski William J. , Arritt Raymond W. , Pan Zaitao , Anderson Christopher J. , da Silva Renato Ramos , Caya Daniel , Chen Shyh‐Chin , Giorgi F. , Christensen Jens Hesselbjerg , Hong Song‐You , Juang Hann‐Ming Henry , Katzfey Jack , Lapenta William M. , Laprise Rene , Liston Glen E. , Lopez Philippe , McGregor John , Pielke Roger A. , Roads John O.
Published: December 2003

The first simulation experiment and output archives of the Project to Intercompare Regional Climate Simulations (PIRCS) is described. Initial results from simulations of the summer 1988 drought over the central United States indicate that limited‐area models forced by large‐scale information at the lateral boundaries reproduce bulk temporal and spatial characteristics of meteorological fields. In particular, the 500 hPa height field time average and temporal variability are generally well simulated by all participating models. Model simulations of precipitation episodes vary depending on the scale of the dynamical forcing. Organized synoptic‐scale precipitation systems are simulated deterministically in that precipitation occurs at close to the same time and location as observed (although amounts may vary from observations). Episodes of mesoscale and convective precipitation are represented in a more stochastic sense, with less precise agreement in temporal and spatial patterns. Simulated surface energy fluxes show broad similarity with the First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE) observations in their temporal evolution and time average diurnal cycle. Intermodel differences in midday Bowen ratio tend to be closely associated with precipitation differences. Differences in daily maximum temperatures also are linked to Bowen ratio differences, indicating strong local, surface influence on this field. Although some models have bias with respect to FIFE observations, all tend to reproduce the synoptic variability of observed daily maximum and minimum temperatures. Results also reveal the advantage of an intercomparison in exposing common tendencies of models despite their differences in convective and surface parameterizations and different methods of assimilating lateral boundary conditions.
Ground‐based measurements of stratospheric ClO over Spitzbergen in the Arctic spring of 1997
Authors: Nagar V. C. , McDonald M. K. , de Zafra R. L.
Published: December 2003

We have measured stratospheric chlorine monoxide (ClO) at Ny Ålesund (79°N), on the Arctic island of Spitzbergen, during the spring of 1997 as part of a ground‐based millimeter‐wave radiometer intercomparison campaign. The presence of ClO in the stratosphere is a direct result of the catalytic destruction of ozone by chlorine and can provide a good measure of this process. Spitzbergen remained well inside the strong, cold polar spring vortex of 1997 during most of our observation period, which ran from February 7 through March 17. Measurements show a strong enhancement of lower stratospheric ClO from mid‐February through mid‐March, in substantial agreement with other measurements, and consistent with increasing daily exposure to photolytic processes liberating active chlorine. A comparison of these results with ClO observations made at McMurdo Station (78°S), Antarctica, during the austral spring of 1997 shows ClO amounts in the Arctic stratosphere that were comparable to Antarctic stratospheric values when temperatures and solar exposures were similar over a relatively short time.
Influences of atmospheric transport pathways on radionuclide activities in aerosol particles from over the North Atlantic
Authors: Arimoto R. , Snow J. A. , Graustein W. C. , Moody J. L. , Ray B. J. , Duce R. A. , Turekian K. K. , Maring H. B.
Published: December 2003

Data for 7Be (produced in the upper troposphere and lower stratosphere (UT/LS)) and 210Pb (a tracer of continental emissions) activities in daily aerosol samples from over the North Atlantic were combined with meteorological information to investigate how the composition of aerosol particles varied in relation to transport pathways and precipitation scavenging. The strongest UT/LS influences (highest 7Be/ 210Pb ratios) occurred in winter, but differences in nuclide activities among sites reflect heterogeneity over the basin. High values for a radionuclide loading index (RLI) at Bermuda were matched to northwesterly air mass trajectories, while low RLIs, due at least in part to precipitation scavenging, occurred under easterly flow. The activities of both nuclides and the RLI at Bermuda were lower on rainy versus nonrainy days, but there was no evidence that a day‐of‐the‐week cycle was imposed on radionuclide activities by precipitation scavenging.
Trace gas emissions from laboratory biomass fires measured by open‐path Fourier transform infrared spectroscopy: Fires in grass and surface fuels
Authors: Goode Jon G. , Yokelson Robert J. , Susott Ronald A. , Ward Darold E.
Published: December 2003

The trace gas emissions from six biomass fires, including three grass fires, were measured using a Fourier transform infrared (FTIR) spectrometer coupled to an open‐path, multipass cell (OP‐FTIR). The quantified emissions consisted of carbon dioxide, nitric oxide, water vapor, carbon monoxide, methane, ammonia, ethylene, acetylene, isobutene, methanol, acetic acid, formic acid, formaldehyde, and hydroxyacetaldehyde. By including grass fires in this study we have now measured smoke composition from fires in each major vegetation class. The emission ratios of the oxygenated compounds, formaldehyde, methanol, and acetic acid, were 1–2% of CO in the grass fires, similar to our other laboratory and field measurements but significantly higher than in some other studies. These oxygenated compounds are important, as they affect O3 and HOx chemistry in both biomass fire plumes and the free troposphere. The OP‐FTIR data and the simultaneously collected canister data indicated that the dominant C4 emission was isobutene (C4H8) and not 1‐butene. The rate constant for the reaction of isobutene with the OH radical is 60% larger than that of 1‐butene. We estimate that 67±9% of the fuel nitrogen was volatilized with the major nitrogen emissions, ammonia, and nitric oxide, accounting for 22±8%.
Toward a parameterization of mesoscale fluxes and moist convection induced by landscape heterogeneity
Authors: Liu Yongqiang , Weaver Christopher P. , Avissar Roni
Published: December 2003

A growing body of evidence from modeling and observations indicates that mesoscale circulations generated by land‐surface wetness heterogeneities result in substantial vertical fluxes of sensible heat and moisture. These fluxes are believed to have a strong impact on large‐scale mean atmospheric variables such as temperature, humidity, cloudiness, and precipitation. Currently, however, this type of mesoscale convective process is not considered in general circulation models (GCMs). In this study, we develop a parameterization for these landscape‐forced fluxes, similar to what might eventually be implemented into a GCM. In addition, we investigate the relationship between the parameterized mesoscale flux and the convective condensation associated with these circulations as a first step toward directly including clouds and precipitation forced by surface heterogeneity effects as one component of a comprehensive GCM convective scheme. To generate the data necessary for this development, we perform a number of simulations with a state‐of‐the‐art mesoscale model to determine the sensitivity of the fluxes and condensation to a variety of background atmospheric conditions and land‐surface wetness distributions. We use similarity theory to determine the dependence of the mesoscale sensible heat and moisture fluxes on the parameters relevant to the problem, and we create parameterized vertical flux profiles by fitting with Chebyshev polynomials. The parameterized fluxes are tested against an independent, three‐dimensional (3‐D) simulation of mesoscale development over a heterogeneous landscape, and general good agreement is found. We propose an empirical form for domain‐averaged condensation on the basis of a linear relationship with parameterized mesoscale moisture flux and also demonstrate a reasonable agreement with the results from the 3‐D simulation. The methodology of this study, i.e., the use of a numerical model in the preliminary stages of parameterization development, is advantageous for situations where the necessary observational data set is nonexistent. The use of model simulations to fully explore the parameter space of this type of problem should then lead to observational campaigns that focus on only those key processes and variables which are relevant for the further refinement of a given parameterization.
Oxidized nitrogen chemistry and speciation in the Antarctic troposphere
Authors: Jones A. E. , Weller R. , Minikin A. , Wolff E. W. , Sturges W. T. , McIntyre H. P. , Leonard S. R. , Schrems O. , Bauguitte S.
Published: December 2003

Understanding the NOy budget at high latitudes is important for our knowledge of present‐day clean air chemistry and essential for reliable interpretation of existing ice core nitrate data. However, measurements of NOy components at high latitudes have been limited, and no measurements have attempted to address the budget of NOy. Here we report on a campaign conducted in the austral summer of 1997 at the German Antarctic research station, Neumayer, with first Antarctic measurements for NOy in addition to light alkyl nitrates, NO, HNO3 and p−NO3−. Inorganic nitrate has generally been assumed to be the dominant component of NOy in Antarctica, although this idea has not previously been tested. However, our results show that for this coastal station, methyl nitrate was present in much higher concentration than inorganic nitrate (median CH3ONO2 = 38 pptv, HNO3 = 5 pptv). It has been suggested earlier that some alkyl nitrates might have a marine source. If this suggestion is correct, the implication arises that the oceans are an important source of NOy to the Antarctic troposphere and that their role in determining nitrate concentrations in ice must be considered.
Stratospheric age spectra derived from observations of water vapor and methane
Authors: Johnson David G. , Jucks Kenneth W. , Traub Wesley A. , Chance Kelly V. , Toon Geoffrey C. , Russell James M. , McCormick M. Patrick
Published: December 2003

The stratospheric age spectrum is useful both as a diagnostic for testing models of stratospheric transport and as a tool for calculating the response of the stratosphere to changes in tropospheric composition. Although the age spectrum of an individual air parcel is not an observable quantity, it is possible to estimate a zonal mean age spectrum from long‐term observations of a conserved tracer with sufficient temporal variability. We have constructed a conserved tracer by combining satellite and balloon‐borne observations of water vapor and methane from 1986 to 1998. After discussing the possible roles of tropical sea surface temperatures and the quasi‐biennial oscillation in determining stratospheric humidity, we use the observations to estimate the zonal mean age spectrum in the tropics and northern midlatitudes. The estimated age spectrum peaks at progressively greater lag times as the altitude increases above the tropopause, in agreement with model calculations. The mean age of air calculated from the derived age spectrum in the lower stratosphere is in good agreement with ages calculated from measurements of SF6, but the satellite record is still too short to calculate reliable ages from the age spectrum in the middle and upper stratosphere.
Infrared solar spectroscopic measurements of free tropospheric CO, C2H6, and HCN above Mauna Loa, Hawaii: Seasonal variations and evidence for enhanced emissions from the Southeast Asian tropical fires of 1997–1998
Authors: Rinsland C. P. , Goldman A. , Murcray F. J. , Stephen T. M. , Pougatchev N. S. , Fishman J. , David S. J. , Blatherwick R. D. , Novelli P. C. , Jones N. B. , Connor B. J.
Published: December 2003

High spectral resolution (0.003 cm−1) infrared solar absorption measurements of CO, C2H6, and HCN have been recorded at the Network for the Detection of Stratospheric Change station on Mauna Loa, Hawaii, (19.5°N, 155.6°W, altitude 3.4 km). The observations were obtained on over 250 days between August 1995 and February 1998. Column measurements are reported for the 3.4–16 km altitude region, which corresponds approximately to the free troposphere above the station. Average CO mixing ratios computed for this layer have been compared with flask sampling CO measurements obtained in situ at the station during the same time period. Both show asymmetrical seasonal cycles superimposed on significant variability. The first 2 years of observations exhibit a broad January‐April maximum and a sharper CO minimum during late summer. The C2H6and CO 3.4–16 km columns were highly correlated throughout the observing period with the C2H6/CO slope intermediate between higher and lower values derived from similar infrared spectroscopic measurements at 32°N and 45°S latitude, respectively. Variable enhancements in CO, C2H6, and particularly HCN were observed beginning in about September 1997. The maximum HCN free tropospheric monthly mean column observed in November 1997 corresponds to an average 3.4–16 km mixing ratio of 0.7 ppbv (1 ppbv = 10−9per unit volume), more than a factor of 3 above the background level. The HCN enhancements continued through the end of the observational series. Back‐trajectory calculations suggest that the emissions originated at low northern latitudes in southeast Asia. Surface CO mixing ratios and the C2H6tropospheric columns measured during the same time also showed anomalous autumn 1997 maxima. The intense and widespread tropical wild fires that burned during the strong El Niño warm phase of 1997–1998 are the likely source of the elevated emission products.
Atmospheric signals and characteristics of accumulation in Dronning Maud Land, Antarctica
Authors: Noone David , Turner John , Mulvaney Robert
Published: December 2003

With the planned European Programme for Ice Coring in Antarctica in Dronning Maud Land it is important to understand the processes leading to accumulation for successful interpretation of core data. Because it is impractical to obtain precipitation observations with a large spatial coverage and on a daily timescale in Antarctica, model‐generated precipitation must be considered for a comprehensive study of the region. However, without observational data it is difficult to check the veracity of the model data. Precipitation data from the European Centre for Medium‐Range Weather Forecasts reanalysis project shows that 89% of days have low (under 0.2 mm) precipitation resulting in 31% of the annual total. At the other extreme, less than 1% of days have high (over 1 mm) precipitation, which results in 20% of the annual total. It is reasoned that the changes in the frequency of extreme precipitation events could alter the trace record in ice cores and lead to a bias in reconstructed paleotemperatures. Case studies reveal that high‐precipitation days have amplified upper level planetary waves directing warm moist air to the region. Associated with this is the presence of a cyclone in or at the northeast extreme of the Weddell Sea. Commonly, the longwaves provide a blocked anticyclone in the South Atlantic to form a dipolar channeling of the air mass. The accumulation variability is linked to the variability in the intensity of these storms and their tracks. It is seen that this is related to the El Niño‐Southern Oscillation and a semiannual cycle.
Infrared spectroscopic study of the deliquescence and efflorescence of ammonium sulfate aerosol as a function of temperature
Authors: Onasch Timothy B. , Siefert Ronald L. , Brooks Sarah D. , Prenni Anthony J. , Murray Benjamin , Wilson Margaret A. , Tolbert Margaret A.
Published: December 2003

The deliquescence and efflorescence phase transitions of ammonium sulfate aerosols have been studied as a function of relative humidity (RH) over the temperature range from 234 K to 295 K. Polydisperse submicrometer ammonium sulfate particles produced by atomization were monitored in a temperature‐controlled flow tube system using Fourier transform infrared spectroscopy. The relative humidity in the aerosol flow was controlled using a sulfuric acid bath conditioner and the addition of a known flow of dry nitrogen. The relative humidity was measured using a dew point hygrometer and infrared absorption features. The deliquescence transition was observed to be nearly independent of temperature, changing from 80% RH at 294.8 K to 82% RH at 258.0 K near the ice saturation line, in good agreement with previous results. The relative humidity at the efflorescence transition also increased slightly (32% to 39%) with decreasing temperature (294.8 K to 234.3 K). These results suggest that once a crystalline ammonium sulfate particle deliquesces, the droplet can exist as a metastable solution droplet over a broad region of temperature and water pressures under the conditions in the upper troposphere. The persistence of metastable ammonium sulfate solution droplets may have important implications for cirrus cloud formation and heterogeneous reaction rates in the upper troposphere.
Oceanographic context of the First Aerosol Characterization Experiment (ACE 1): A physical, chemical, and biological overview
Authors: Griffiths F. B. , Bates T. S. , Quinn P. K. , Clementson L. A. , Parslow J. S.
Published: December 2003

The First Aerosol Characterization Experiment (ACE 1) intensive experiment, conducted between November 14 and December 15, 1995, covered an oceanographically complex region, including the subtropical (ST), Subtropical Convergence Zone (STCZ), Subantarctic (SA), and polar water masses. Oceanographic and atmospheric sampling to identify the chemical and biological communities that might affect biologically produced, aerosol precursors in these water masses was carried out from the RV Discoverer and FRV Southern Surveyor. Sea surface temperature was not a good indicator of water mass during ACE 1. The physical structure east of 147.5°E was more complex than west of this longitude. Nutrient concentrations (nitrate, silicate) in the mixed layer increased, but ammonia concentrations decreased from ST to polar waters. Ammonia concentrations in surface waters exceeded >5 μM, and ammonia fluxes peaked at 12 μM m−2 d−1 in ST water near Cape Grim between November 27 and 30. Seawater dimethyl sulfide (DMSSW) concentrations averaged 1.7±1.1 nM with maximum values near 6 nM in ST waters. The flux of dimethyl sulfide to the atmosphere averaged 4.7±5.0 μM m−2 d−1, with peak fluxes (>40 μM m−2 d−1) in SA water. DMSSW increased significantly only in SA waters during the experiment. Surface chlorophyll‐a concentrations measured from the FRV Southern Surveyor ranged between 0.3 and 0.6 mg m−3. Surface chlorophyll‐a concentrations along the Discoverer cruise track were similar, but 5 phytoplankton blooms (>1 mg m−3) were found. Integrated column chlorophylls ranged from 29.4 mg m−2 in SA water to 53.2 mg m−2 in ST water. Modeled primary production rates were ranged between 409 mg carbon m−2 d−1 in the polar front to 3180 mg carbon m−2 d−1 in ST water near Cape Grim. Mixed layer phytoplankton growth rates, estimated from net primary production, were 0.31 d−1 in the SAF to 1.07 d−1 in STCZ water east of Tasmania. Grazing dilution experiments showed microzooplankton grazing and phytoplankton growth rates were tightly coupled, with net growth rates ranging from ‐ 0.13 d−1 to 0.22 d−1. During the ACE 1 intensive period, the surface waters were in transition from the deeply mixed, winter conditions to the shallowly stratified, spring conditions. The spring phytoplankton bloom was just beginning in the northern water masses, and isolated blooms were present at several locations in SA surface waters. The low standing stocks of chlorophyll and tightly coupled grazing rates may have been responsible for the low concentrations of DMS and NH3 in the region, and the generally low fluxes of these compounds to the atmosphere during the ACE 1 intensive experiment.
Atmospheric processes influencing measured carbon monoxide in the NASA Measurement of Air Pollution From Satellites (MAPS) experiment
Authors: Newell Reginald E. , Zhu Yong , Connors Vickie S. , Reichle Henry G. , Novelli Paul C. , Gormsen Barbara B.
Published: December 2003

The Measurement of Air Pollution From Satellites (MAPS) experiment measured global distributions of carbon monoxide (CO) while on board the space shuttle during April 9–19 and September 30 to October 11, 1994. This paper examines selected examples of the meteorological processes that contributed to the observed signals. We first examine and relate the mean distribution of MAPS‐measured CO, surface station‐measured CO, streamlines, and divergent winds averaged over the two missions. Tropical high CO values were associated with boundary layer convergence regions, particularly in October, that enable CO associated with biomass burning to reach the free troposphere where it can be detected by the nadir viewing gas filter 4.7 μm radiometer. CO values over northern middle latitudes show evidence of fossil fuel pollution especially in April. Southern middle and high latitudes in April suggest photochemical control, while in October these regions are strongly influenced by the tropical biomass burning. Next, we consider events on 1 day near the center of each mission and show that in one of these cases, low CO measurements are associated with high potential vorticity, which suggests that the air samples originated from the stratosphere. Finally, we modify the two mean patterns, both within 23 days of the equinox, to illustrate the possible separation of the natural photochemical CO pattern from the CO pollution patterns. This procedure brings out the intercontinental and transcontinental transport of pollution in April northern hemisphere middle and high latitudes as well as, less markedly, in the October maps. It also accentuates the biomass burning contribution in October and shows pollution to extend southeastward from South America into the South Atlantic and also from Australia into the South Pacific. The separation is made possible by having CO measurements with global coverage.
Historical record of carbonaceous particle concentrations from a European high‐alpine glacier (Colle Gnifetti, Switzerland)
Authors: Lavanchy V. M. H. , Gäggeler H. W. , Schotterer U. , Schwikowski M. , Baltensperger U.
Published: December 2003

Historical records of the concentrations of black carbon (BC) and elemental carbon (EC), as well as of water insoluble organic carbon (OC) and total carbon (TC) covering the time period ∼1755–1975 are presented. Concentrations were obtained from an ice core of a European high‐alpine glacier, using an optical and a thermal method. Concentrations were found to vary between 7 and 128 μg L−1 for BC, between 5 and 130 μg L−1 for EC, between 53 and 484 μg L−1 for OC, and between 66 and 614 μg L−1 for TC. From preindustrial (1755–1890) to modern times (1950–1975) BC, EC, OC, and TC concentrations increased by a factor of 3.7, 3.0, 2.5, and 2.6, respectively. The sum of BC emissions of Germany, France, Switzerland, and Italy, calculated from fossil fuel consumption, and the EC concentration record correlate well (R2 = 0.56) for the time period from 1890 to 1975; this indicates that the ice core record reflects the emissions of western Europe. High pre‐1860 concentrations indicate that by that time BC emissions to the atmosphere were already significant.
Impact of tropospheric aerosol absorption on ozone retrieval from backscattered ultraviolet measurements
Authors: Torres O. , Bhartia P. K.
Published: December 2003

The impact of tropospheric aerosols on the retrieval of column ozone amounts using space‐borne measurements of backscattered ultraviolet radiation is examined. Using radiative transfer calculations, we show that the radiative effects of UV‐absorbing aerosols produce spurious ozone column reductions. The magnitude of the total ozone underestimation depends on the aerosol type, optical depth, and aerosol layer height. Desert dust can produce errors as large as 10%. Smaller errors are produced by carbonaceous aerosols that result from biomass burning. Ozone retrieval errors associated with nonabsorbing aerosols are typically ±1% of the total ozone amount depending on aerosol optical depth and viewing geometry. Though the error is produced by complex interactions between ozone absorption (both stratospheric and tropospheric), aerosol scattering, and aerosol absorption, a surprisingly simple correction procedure reduces the error to ∼1% for a variety of aerosols and for a wide range of aerosol loading. Comparison of the corrected Total Ozone Mapping Spectrometer (TOMS) data with operational data indicates that though the zonal mean total ozone derived from TOMS is not significantly affected by these errors, localized effects in the tropics can be large enough to affect seriously the studies of tropospheric ozone that are currently undergoing using the TOMS data.
A reference model for middle atmosphere ozone in 1992–1993
Authors: Wang H. J. , Cunnold D. M. , Froidevaux L. , Russell J. M.
Published: December 2003

An ozone climatology for the period April 1992 to March 1993 and covering pressures from 0.1 to 100 hPa and from 80°N to 80°S is derived from satellite‐based measurements by the Stratospheric Aerosol and Gas Experiment (SAGE), the Halogen Occultation Experiment (HALOE), and the Microwave Limb Sounder (MLS). At pressures <1 hPa, separate distributions are given for daytime and nighttime conditions. From 0.46 to 32 hPa the accuracy of the distribution is estimated to be 5%, and the precision is also ∼5%. Estimates of atmospheric variability are provided on the basis of standard deviations of the measurements within months. Distributions of ozone monthly means and standard deviations are also given in a potential temperature, equivalent latitude coordinate system. This data set is included in the UARS reference atmosphere, and it is accessible through that web site.
Measurements of middle atmospheric water vapor from low latitudes and midlatitudes in the northern hemisphere, 1995–1998
Authors: Nedoluha Gerald E. , Bevilacqua Richard M. , Gomez R. Michael , Hicks Brian C. , Russell James M.
Published: December 2003

We present middle atmospheric water vapor measurements made at 22 GHz using two Naval Research Laboratory Water Vapor Millimeter‐wave Spectrometers (WVMS2 and WVMS3). We include measurements from an intercomparison campaign at Table Mountain, California (34.4°N, 242.3°E), and measurements obtained since March 1996 from Table Mountain and from Mauna Loa, Hawaii (19.5°N, 204.4°E). The mesospheric data from Mauna Loa show both a mixing ratio peak at a higher altitude and smaller seasonal variations than those from the WVMS instrument at Table Mountain. These differences are qualitatively consistent with the changes in mixing ratio and the increase in mesospheric variability expected with decreasing latitude. The latitudinal variation in the mixing ratio profile observed in the WVMS data is very similar to that observed by the Halogen Occultation Experiment (HALOE) in the upper stratosphere and lower mesosphere. The WVMS measurements generally show higher water vapor mixing ratios than HALOE does in the upper stratosphere and lower mesosphere but smaller mixing ratios in the upper mesosphere. The winter of 1997–1998 shows an unusually large decrease in mesospheric water vapor, a result that is consistent with measurements from HALOE throughout the Northern Hemisphere for this winter. There appears to be a slight overall decrease in water vapor for all seasons over the period of the WVMS observations from Mauna Loa. The relatively small seasonal variations, combined with the small amount of tropospheric water vapor above Mauna Loa, make this an ideal site for the monitoring of multiyear trends in water vapor.
A comparison between simulated and observed ozone mixing ratios in eastern North America
Authors: Sirois Alain , Pudykiewicz Janusz A. , Kallaur Alexander
Published: December 2003

The successful computer simulation of physical processes consists of two complementary stages: (1) the development of a numerical model that represents the physical process and (2) its evaluation. Although less often discussed, the second stage is as important as the first one. In the second stage, the goal is to verify as much as possible that the model cannot only reproduce the observations but that it does it for the right reasons. Techniques that take that factor into account are presented in the present paper. They include the use of spectral and cross‐spectral analysis and the fitting of time series models to the observed and simulated data. The time series models used are composed of five components describing the long‐term, episodic, diurnal variations as well as an autoregressive and a random component. To evaluate the numerical model, the components of the observed and simulated values within the same grid cell are compared. The different techniques described in the paper are illustrated by evaluating the chemical tracer model (CTM) model described by Pudykiewicz et al. [1997]. The model was run for the period between June 15, 1995, 0000 UTC and August 16, 1995, 0000 UTC. Hourly mean O3 mixing ratios were generated for each cell within the model domain. The numerical results were compared to data at 322 sites across the model domain from the NARSTO‐NE database. The paper also presents suggested modifications to the CTM model to improve it.
Observations of convective and dynamical instabilities in tropopause folds and their contribution to stratosphere‐troposphere exchange
Authors: Cho John Y. N. , Newell Reginald E. , Bui T. Paul , Browell Edward V. , Fenn Marta A. , Mahoney Michael J. , Gregory Gerald L. , Sachse Glen W. , Vay Stephanie A. , Kucsera Tom L. , Thompson Anne M.
Published: December 2003

With aircraft‐mounted in situ and remote sensing instruments for dynamical, thermal, and chemical measurements we studied two cases of tropopause folding. In both folds we found Kelvin‐Helmholtz billows with horizontal wavelength of ∼900 m and thickness of ∼120 m. In one case the instability was effectively mixing the bottomside of the fold, leading to the transfer of stratospheric air into the troposphere. Also, we discovered in both cases small‐scale secondary ozone maxima shortly after the aircraft ascended past the topside of the fold that corresponded to regions of convective instability. We interpreted this phenomenon as convectively breaking gravity waves. Therefore we posit that convectively breaking gravity waves acting on tropopause folds must be added to the list of important irreversible mixing mechanisms leading to stratosphere‐troposphere exchange.
Impact of the ECMWF reanalysis soil water on forecasts of the July 1993 Mississippi flood
Authors: Viterbo Pedro , Betts Alan K.
Published: December 2003

We reexamine the impact of soil water on the precipitation for the United States for July 1993 (the time of the Mississippi flood), previously discussed by Beljaars et al. [1996], using soil moisture from the European Centre for Medium‐Range Weather Forecasts (ECMWF) reanalysis (ERA). Ensembles of three precipitation forecasts for the month of July, initialized on July 1, 2, and 3, using different initial soil water fields, are compared with the 12 to 24 hour ERA precipitation forecasts for the month and the observed precipitation. Both the 12 to 24 hour forecasts and the July integrations depict the July mean anomaly field well, although the mid‐West precipitation maximum is displaced northward in both the ECMWF short and long‐term forecasts. The July 1993 ERA soil water anomaly does not account for the anomalous July precipitation, but replacing the July 1, 1993, soil water with the much drier soil water from June 1988 reduces the July 1993 ensemble forecast precipitation by about 40%. It is probable that soil water nudging has reduced the variability of soil water in the ERA fields.
Improved general circulation models of the Martian atmosphere from the surface to above 80 km
Authors: Forget François , Hourdin Frédéric , Fournier Richard , Hourdin Christophe , Talagrand Olivier , Collins Matthew , Lewis Stephen R. , Read Peter L. , Huot Jean‐Paul
Published: December 2003

We describe a set of two “new generation” general circulation models of the Martian atmosphere derived from the models we originally developed in the early 1990s. The two new models share the same physical parameterizations but use two complementary numerical methods to solve the atmospheric dynamic equations. The vertical resolution near the surface has been refined, and the vertical domain has been extended to above 80 km. These changes are accompanied by the inclusion of state‐of‐the‐art parameterizations to better simulate the dynamical and physical processes near the surface (boundary layer scheme, subgrid‐scale topography parameterization, etc.) and at high altitude (gravity wave drag). In addition, radiative transfer calculations and the representation of polar processes have been significantly improved. We present some examples of zonal‐mean fields from simulations using the model at several seasons. One relatively novel aspect, previously introduced by Wilson [1997], is that around northern winter solstice the strong pole to pole diabatic forcing creates a quasi‐global, angular‐momentum conserving Hadley cell which has no terrestrial equivalent. Within such a cell the Coriolis forces accelerate the winter meridional flow toward the pole and induce a strong warming of the middle polar atmosphere down to 25 km. This winter polar warming had been observed but not properly modeled until recently. In fact, thermal inversions are generally predicted above one, and often both, poles around 60–70 km. However, the Mars middle atmosphere above 40 km is found to be very model‐sensitive and thus difficult to simulate accurately in the absence of observations.
Dynamics of dust ejected from Enceladus: Application to the Cassini dust detector
Authors: Spahn Frank , Thiessenhusen Kai‐Uwe , Colwell Joshua E. , Srama Ralf , Grün Eberhard
Published: December 2003

The satellite Enceladus is obviously the main source of Saturn's E ring. Up to now, different mechanisms of how particles are delivered from this satellite have been suggested. In this paper, we try to answer the question of whether these different launch processes can be distinguished by the cosmic dust analyzer (CDA) aboard the Cassini spacecraft. To this aim, the dynamics of dust particles just launched from the surface of Enceladus is studied numerically. We have integrated the equations of motion for a wide range of initial conditions including ejecta from interplanetary and E ring impactors onto Enceladus. According to our simulations, Cassini will encounter a significant dust stream about the time of closest approach to Enceladus. The duration and intensity of this expected enhanced impact rate onto the CDA depends on the way the particles are ejected from the satellite. The counting rate yields information about the distribution of ejecta sources on the surface of Enceladus. For instance, an anisotropy of the ejecta between the leading and the trailing hemispheres of Enceladus should be detectable, and impactors of different origin should be distinguishable. Furthermore, the vertical component of the ejecta velocities can explain the vertical extent of the E ring.
Quantitative compositional analysis using thermal emission spectroscopy: Application to igneous and metamorphic rocks
Authors: Feely Kimberly C. , Christensen Philip R.
Published: December 2003

The mineral composition of a suite of igneous and metamorphic rocks was determined using the thermal infrared emission spectra of these rocks in a linear spectral deconvolution algorithm. This algorithm assumes that the infrared spectrum of each rock is a linear mixture of the component mineral spectra weighted by volume abundance. A diverse suite of 36 common rock‐forming and accessory minerals was used in the deconvolution. The model was tested by comparing the mineralogy derived from the infrared spectrum with petrographically estimated abundances for 45 igneous and 51 metamorphic rock samples. The mineral abundances derived from these two techniques agree to within ±7–15% for the primary minerals feldspar, pyroxene, quartz, and calcite/dolomite and ±9–17% for secondary minerals such as micas and amphiboles. These differences are comparable to the error for traditional thin section mode estimates, which are ±5–15% for major minerals and ≤5% for minor minerals. The detection limit for the primary and secondary minerals found in the rocks analyzed ranged from 5 to 10%. Each major rock type studied here was easily distinguished by its spectral characteristics. The best results, in both the qualitative determination of the rock type and dominant minerals and the quantitative reproduction of absorption features and mineral composition, were obtained for igneous rock samples. For metamorphic rocks, pelite and quartzo‐feldspathic samples gave slightly better results than calcareous or mafic samples. A controlled analysis, in which the end‐member suite was reduced based on an initial estimate of the rock type, only improved the results by several percent for most primary and secondary minerals. The quality of the obtained results demonstrates that a linear deconvolution of infrared emission spectra provides an accurate, rapid technique for determining the quantitative mineral composition of rock samples in a laboratory and has application to future in situ measurements.