bluuebunny/crossref_metadata_2025 huggingface dataset:
A three‐dimensional model of atmospheric CO2 transport based on analyzed winds: Model description and simulation results for TRANSCOM
Authors: Taguchi Shoichi
Published: February 2004

A three‐dimensional tracer transport model is used to investigate the temporal trend and the annual cycle of atmospheric CO2. The model transport was driven by a semi‐Lagrangian scheme, using winds from 1992, analyzed at the European Centre for Medium‐Range Weather Forecasts. A simple planetary boundary layer (PBL) formulation was used to investigate the sensitivity of the model results. Two source/sink distributions were used independently: fixed emissions of 5.3 Gt C/yr, estimated from fossil fuel consumption (fossil run), and a source representing net exchange with the terrestrial biosphere (vegetation run). This terrestrial flux represents a growing season net flux of 14.5 Gt C. The simulated interhemispheric difference between the mean surface concentrations, in terms of north pole minus south pole, is about 4 ppm for the fossil run and 2 ppm for the vegetation run. These results suggest that the so‐called missing sink should be found in the northern hemisphere. On the other hand, the interhemispheric difference in the vegetation run was changed by 40%, while the fossil run changed by only 4% when the instantaneous PBL height was replaced by monthly averages of PBL height. This result suggests that the monthly average PBL height can be used in place of the instantaneous PBL height only in limited cases, if it is scaled with an appropriate factor.
An intercomparison of ground‐based UV‐visible sensors of ozone and NO2
Authors: Vaughan G. , Roscoe H. K. , Bartlett L. M. , O'Connor F. M. , Sarkissian A. , Van Roozendael M. , Lambert J‐C , Simon P. C. , Karlsen K. , Høiskar B. A. Kåstad , Fish D. J. , Jones R. L. , Freshwater R. A. , Pommereau J‐P. , Goutail F. , Andersen S. B. , Drew D. G. , Hughes P. A. , Moore D. , Mellqvist J. , Hegels E. , Klupfel T. , Erle F. , Pfeilsticker K. , Platt U.
Published: February 2004

An intercomparison of zenith‐sky UV‐visible spectrometers was held at Camborne, UK, for 2 weeks in September 1994. Eleven instruments participated, from nine different European institutes which were involved with the Second European Stratospheric Arctic and Mid‐latitude Experiment (SESAME) campaign. Four instruments were of the Systeme d'Analyse d'Observations Zénithales (SAOZ) type, while the rest were particular to the institutes involved. The results showed that the SAOZ instruments were consistent to within 3% (10 DU) for ozone and 5% for NO2. For ozone the results from these instruments agreed well with total ozone measurements by Dobson and Brewer spectrophotometers and integrated ozonesondes when the air mass factors for the SAOZ were calculated using the ozonesonde profiles. Differences of up to 10% in ozone and 30% in NO2 were found between different instruments. In some cases these differences are attributable to the different absorption cross sections used in the analysis of the spectra, but other discrepancies remain to be investigated. A prominent source of error identified in the campaign was uncertainty in the derivation of the amount of absorber in the reference spectrum, which can contribute an error of up to 3% (10 DU) in ozone and 1.5×1014 molecules cm−2 in NO2.
Stratospheric temperature measurements by two collocated NDSC lidars during UARS validation campaign
Authors: Singh Upendra N. , Keckhut Philippe , McGee Thomas J. , Gross Michael R. , Hauchecorne Alain , Fishbein Evan F. , Waters Joe W. , Gille John C. , Roche Aidan E. , Russell James M.
Published: February 2004

The NASA Goddard Space Flight Center (GSFC) mobile lidar system was deployed at the Observatoire de Haute Provence (OHP), during an Upper Atmosphere Research Satellite (UARS)/Network for Detection of Stratospheric Change (NDSC) correlative measurement campaign (July–August 1992). The objective of this campaign was twofold: to intercompare two independent lidars and to provide ground‐based UARS correlative ozone and temperature validation measurements. This paper, for the first time, presents a coincident temperature intercomparison between two independently operating temperature lidar systems of similar capabilities. Systems and retrieval algorithms have been described and discussed in terms of error sources. The comparison of the two analyses have shown very similar results up to the upper mesosphere. The statistical mean differences of 0.5 K in the stratosphere and about 2 K in the mesosphere suggests insignificant bias throughout except below 35 km, where one of the data sets is contaminated by the volcanic aerosols from the eruption of Mount Pinatubo. Profiles of the root‐mean‐square (RMS) of the differences are in good agreement with random error estimates, except around 35–40 km where RMS is larger. These measurements can be used as the ground reference for UARS temperature validation. However, the spatial‐temporal coincidence between satellite and lidar needs to be carefully considered for meaningful validation.
The Polar Ozone and Aerosol Measurement instrument
Authors: Glaccum W. , Lucke R. L. , Bevilacqua R. M. , Shettle E. P. , Hornstein J. S. , Chen D. T. , Lumpe J. D. , Krigman S. S. , Debrestian D. J. , Fromm M. D. , Dalaudier F. , Chassefière E. , Deniel C. , Randall C. E. , Rusch D. W. , Olivero J. J. , Brogniez C. , Lenoble J. , Kremer R.
Published: February 2004

The second Polar Ozone and Aerosol Measurement instrument (POAM II) is a spaceborne experiment designed to measure the vertical profiles of ozone, water vapor, nitrogen dioxide, aerosol extinction, and temperature in the polar stratosphere and upper troposphere with a vertical resolution of about 1 km. Measurements are made by the solar occultation technique. The instrument package, which has a mass of less than 25 kg, is carried on the Satellite Pour l'Observation de la Terre (SPOT) 3 spacecraft and has a design lifetime of 3–5 years. POAM II has provided data on the south polar ozone hole, north and south polar ozone phenomena, the spatial and temporal variability of stratospheric aerosols and polar stratospheric clouds, and has detected polar mesospheric clouds.
Global CF2Cl2 measurements by UARS cryogenic limb array etalon spectrometer: Validation by correlative data and a model
Authors: Nightingale R. W. , Roche A. E. , Kumer J. B. , Mergenthaler J. L. , Gille J. C. , Massie S. T. , Bailey P. L. , Edwards D. P. , Gunson M. R. , Toon G. C. , Sen B. , Blavier J.‐F. , Connell P. S.
Published: February 2004

The cryogenic limb array etalon spectrometer (CLAES) onboard the Upper Atmosphere Research Satellite (UARS) has obtained the first global measurements of CF2Cl2 over six seasons, for which 388 days have been processed in data version 7 for the period from January 9, 1992, to May 5, 1993. The CLAES measurements provide a near‐global view of this stratospheric species, greatly extending the altitude, latitude, and seasonal coverage of previous measurements. This work evaluates CLAES version 7 data set quality. To arrive at estimates of experimental error, we compared the CLAES CF2Cl2 profiles with all of the available correlative data from balloon and space‐borne sensors, and we looked at the repeatability of multiple profiles in the same location. In addition, we carried out empirical estimates of experimental error based on knowledge of instrument characteristics, and we performed consistency checks using the Lawrence Livermore National Laboratory two‐dimensional (LLNL‐2D) model and the CLAES N2O data set. Both the range of mean differences between CLAES and the available correlative data and the empirical estimates of the instrument systematic error indicate a CF2Cl2 profile systematic error of 14% over the range of 18.7 through 32 km and 22% for 33–35 km and 16–18 km. These systematic errors are applicable in the spring through fall seasons for the midlatitude region and all seasons in the tropical region. The CF2Cl2 estimated random errors, which are close to the observed data repeatability, are 32 to 11 pptv between 17 and 32 km and translate to an average 9% in the low to midstratosphere. The altitude range of best confidence for the CF2Cl2 mixing ratio profiles is 18.7 to 32 km (∼68 to 10 mbar), to which we assign an accuracy (root‐sum‐square of systematic and random errors) of ∼17%. In the tropics the profiles from 16 to about 26 km may sometimes be biased low by up to 14% due to a data processing algorithm constraint. The CLAES CF2Cl2 global fields show generally good spatial correlation and exhibit the major morphological and seasonal features seen in other global tracer field data. Overall, the results of this validation exercise indicate that the CLAES version 7 CF2Cl2 data set, within the limitations discussed in the paper, can be used for quantitative and qualitative studies of stratospheric structure and dynamics.
SAFARI‐92 characterization of biomass and fire behavior in the small experimental burns in the Kruger National Park
Authors: Trollope W. S. W. , Trollope L. A. , Potgieter A. L. F. , Zambatis N.
Published: February 2004

As one of the ground component projects in the South African Fire‐Atmosphere Research Initiative (SAFARI‐92) the herbaceous fuel loads, comprising mainly fine grass fuels, were characterized before and after the application of controlled burns to small experimental plots, approximately 7 ha in size, situated in moist savanna in the Pretoriuskop section of the Kruger National Park. The grass fuel loads were estimated before and after the controlled fires with a disk pasture meter (DPM) which comprises a circular aluminium disk fitted with a measuring rod and which relates the settling height of the disk to the quantity of grass material holding it off the ground. One hundred readings were recorded in each plot before and after the burns, and these data were used to estimate the quantity of fine fuel consumed during the fires. Surveys were conducted to describe the botanical composition and structure of the grass sward and tree and shrub vegetation in the plots prior to burning. The fuel moisture, air temperature, relative humidity, and wind speed and direction were recorded for each fire. Fire behavior parameters comprising rate of spread, fire intensity, and flame height were estimated for the head and back fires occurring during each burn. The results showed that the fine fuel loads on the plots varied greatly ranging from 323 to 4495 kg ha−1. Generally, the behavior of the head fires was more variable than the back fires with fire intensities varying from 93 to 3644 kJ s−1 m−1 for the former and 20 to 160 kJ s−1 m−1 for the latter.
An extended data set of river discharges for validation of general circulation models
Authors: Perry G. D. , Duffy P. B. , Miller N. L.
Published: February 2004

Using existing measurements of streamflow data, we present a new data set of river discharges to the ocean, for use in validating climate models. This data set includes annual mean discharges for 981 rivers, representing approximately 824,500 m3/s of global river discharge. This is about 65% of contemporary estimates of continental precipitation minus continental evaporation (P‐E). Using our new data set, we present a self‐consistent water budget over continents. We find that rivers with annual mean discharges between about 250 m3/s and about 20,000 m3/s closely follow a power law size distribution. We estimate the total flow from rivers smaller than 250 m3/s by assuming they obey the same power law size distribution. Under this assumption, the estimated total flow from these rivers is about 33% of P‐E. Including an existing estimate of soil moisture entering the ocean underground, our estimated total flow into the ocean is within about 2% of contemporary estimates of continental P‐E. Our data set is available in digital format.
Mesoscale model simulations of TRACE A and preliminary regional experiment for storm‐scale operational and research meteorology convective systems and associated tracer transport
Authors: Wang Y. , Tao W.‐K. , Pickering K. E. , Thompson A. M. , Kain J. S. , Adler R. F. , Simpson J. , Keehn P. R. , Lai G. S.
Published: February 2004

A tropical mesoscale convective system (MCS) during the Transport and Atmospheric Chemistry Near the Equator‐Atlantic (TRACE A) experiment and a midlatitude squall line during Preliminary Regional Experiment for Storm‐scale Operational and Research Meteorology (PRESTORM) were simulated with the National Center for Atmospheric Research/Pennsylvania State University (NCAR/PSU) MM5 model. For the TRACE A case the model simulation predicted locations of convection systems fairly accurately compared with satellite images and the rainfall pattern from rain gauge data. For the PRESTORM case the model simulation captured many observed features such as the rainfall field and wind circulation pattern. Model simulated wind fields were used to transport an inert tracer (CO) in the mesoscale systems. Tracer transport in the two convective systems (TRACE A‐tropical MCS versus PRESTORM midlatitude squall line) are substantially different over 24‐hour simulation periods and over the regional scale (about 2000 × 2000 km domains). The time‐evolving tracer fields in the upper troposphere are different in the tropical MCS and midlatitude squall line regimes as a consequence of different propagation speeds of the two convective systems. The nearly “stationary” tropical MCS produced regions of large upper tropospheric CO mixing ratios that had moved very little in the horizontal by the end of the 24‐hour simulation. The enhanced upper tropospheric CO region propagates with the “fast‐moving” squall line in the midlatitude case. Model transport and redistribution of CO agrees well with aircraft measurements in the TRACE A case. Significant subgrid‐scale (parameterized) upward transport (48% with Grell scheme, 41% with Kain‐Fritsch scheme) occurred in the TRACE A case. The subgrid upward transport in the PRESTORM event was even greater, accounting for 64% of total upward transport. Downward transport in both events was dominated by grid‐scale motions.
Sorption of vapor phase octanoic acid onto deliquescent salt particles
Authors: Wagner Jeff , Andrews Elisabeth , Larson Susan M.
Published: February 2004

Single NaCl and (NH4)2SO4 particles (Dp = 30–50 μm) have been suspended and exposed to airstreams containing octanoic acid vapor and controlled amounts of water vapor. Sorption of vapor phase organic onto the coated droplets was found to occur at a rate that was independent of the relative humidity, the particle size, and the phase (solid or droplet) of the salt. These results are only comparable with atmospheric studies to a limited extent, however, since both the organic vapor concentrations and the particle sizes in this research were generally larger than their atmospheric counterparts. Because of the relatively large coating scale of the experiment, the measured sorption rate is thought to correspond to octanoic acid sorbing onto bulk octanoic coatings around the salt particles, and the average observed uptake coefficient was found to be γavg = (6.7 ± 3.0) × 10−2. Imperfect surface accommodation was hypothesized as a source for the nonunity uptake coefficient, and the accommodation coefficient in this case was found to be αavg = (3.5−2.0+8.2) × 10−4. Formation of organic surfactant layers did not cause the hydrophilic salts to become completely hydrophobic. The organic tended to slow the salts' deliquescence rates, however, which suggests that organic components may effectively limit water uptake by salt aerosols in competitive atmospheric conditions.
Heterogeneous chemistry in the smoke plume from the 1991 Kuwait oil fires
Authors: Herring John A. , Ferek Ronald J. , Hobbs Peter V.
Published: February 2004

During late spring of 1991, airborne measurements in the smoke plume from the Kuwait oil fires indicated that SO2 was removed from the gas phase at rates of ∼6 to 8% h−1 and that NOx was removed at rates of ∼7 to 23% h−1. Photochemical calculations indicate that homogeneous chemical reactions were responsible for only a small fraction of this removal. Also, indirect evidence suggests that heterogeneous removal of SO2 on black carbon (or soot) and salt aerosols produced by the fires was relatively slow. The highest rates of SO2 and NOx removal were associated with high concentrations of atmospheric soil dust. This was likely due to heterogeneous oxidation of the SO2 and NOx on the surfaces of soil dust particles. The removal of SO2 and NOx on soil dust was probably accelerated by the alkaline nature of the dust. Heterogeneous reactions on soil dust particles proceeded more rapidly in regions of dispersed smoke than in the core of the plume; this was probably due to the depletion of the available surface area of the soil dust in regions of dense smoke. On the basis of smoke samples collected during the experiment we estimate that the quasi‐second‐order reaction rate for SO2 is (9 ± 4) × 10−8 (μg soil dust m−3)−1 s−1. For a soil dust concentration of 200 μg m−3 this implies a removal rate for SO2 on soil dust of 6.5% h−1.
Impact of biomass burning emissions on the composition of the South Atlantic troposphere: Reactive nitrogen and ozone
Authors: Singh H. B. , Herlth D. , Kolyer R. , Chatfield R. , Viezee W. , Salas L. J. , Chen Y. , Bradshaw J. D. , Sandholm S. T. , Talbot R. , Gregory G. L. , Anderson B. , Sachse G. W. , Browell E. , Bachmeier A. S. , Blake D. R. , Heikes B. , Jacob D. , Fuelberg H. E.
Published: February 2004

In September/October 1992 an instrumented DC‐8 aircraft was employed to study the composition and chemistry of the atmosphere over the southern tropical Atlantic Ocean. Analysis of measurements, which included tracers of biomass combustion and industrial emissions, showed that this atmosphere was highly influenced by biomass burning emissions from the South American and African continents. Marine boundary layer was generally capped off by a subsidence inversion and its composition to a large degree was determined by slow entrainment from aloft. Insoluble species (such as PAN, NO, hydrocarbons, CO) were enhanced throughout the troposphere. Soluble species (such as HNO3, HCOOH, H2O2) were minimally elevated in the upper troposphere in part due to scavenging during cloud (wet) convection. Ozone mixing ratios throughout the South Atlantic basin were enhanced by ≈20 ppb. These enhancements were larger in the eastern South Atlantic (African emissions) compared to the western South Atlantic (South American emissions). In much of the troposphere, total reactive nitrogen (NOy) correlated well with tracers of biomass combustion (e.g., CH3Cl, CO). Although NOx(NO + NO2) correlated reasonably with these tracers in the lower (0–3 km) and middle troposphere (3–7 km), these relationships deteriorated in the upper troposphere (7–12 km). Stratospheric intrusions were found to be a minor source of upper tropospheric NOxor HNO3. Sizable nonsurface sources of NOx(e.g., lightning) as well as secondary formation from the NOyreservoir species (such as HNO3, PAN, and organic nitrates) must be invoked to explain the NOxabundance present in the upper troposphere. It is found that HNO3, PAN, and NOxwere able to account for most of the NOy, in the middle troposphere (3–7 km); but a significant shortfall was present in the upper troposphere (7–12). This shortfall was also most pronounced in air masses with low HNO3. The reasons for the upper tropospheric reactive nitrogen shortfall is probably due to instrumental uncertainties and the presence of unidentified organic and inorganic nitrogen species.
Transport and processing of O3 and O3 precursors over the North Atlantic: An overview of the 1993 North Atlantic Regional Experiment (NARE) summer intensive
Authors: Fehsenfeld F. C. , Daum P. , Leaitch W. R. , Trainer M. , Parrish D. D. , Hübler G.
Published: February 2004

In the summer of 1993, airborne and ground‐based measurements of O3 and O3 precursors were made in the North Atlantic region. These studies were made by an international team of scientists collaborating as part of the North Atlantic Regional Experiment, an activity of the International Global Atmospheric Chemistry project of the International Geosphere‐Biosphere Program. Previous measurements [cf. Fehsenf eld et al, this issue] have indicated that the amount of O3 produced from anthropogenic sources is greater than that reaching the lower troposphere in this region from the stratosphere and that ozone derived from anthropogenic pollution has a hemisphere wide effect at northern temperate latitudes. In this special issue the recently acquired data are used to better quantify the contribution of continental sources to the ozone levels over the North Atlantic. The aim of this overview is to provide the operational and logistical context of the study and to introduce the principal findings and conclusions that have been drawn from the results.
Comparison of analyzed stratospheric temperatures and calculated trajectories with long‐duration balloon data
Authors: Knudsen B. M. , Rosen J. M. , Kjome N. T. , Whitten A. T.
Published: February 2004

The Polar Vortex Balloon Experiment (POVORBEX) has flown eight long‐duration flights 1992 to 1995 in the arctic winter stratosphere at about 50 mbar. European Centre for Medium‐Range Weather Forecasts (ECMWF) analyses are compared with the balloon temperatures and winds, which are accurate and independent, and substantial differences are found. For example, the average temperature difference is 2.4 K. These temperature differences have important implications for the potential for polar stratospheric clouds, which play a vital role in the destruction of ozone. Large differences are also found between the observed and calculated trajectories. For the longest flight, which lasted almost 6 days, the calculated trajectory end point is off by 2700 km (23% of the trajectory length). For the other seven POVORBEX flights, which lasted about ½–3 days, the calculated end point is off by 156–544 km (5–19% of the trajectory length for six of the flights). The main causes of these differences are discrepancies between real and ECMWF analyzed winds and temperatures and the large distance between the model levels at this altitude.
On the age of stratospheric air and inorganic chlorine and bromine release
Authors: Daniel J. S. , Schauffler S. M. , Pollock W. H. , Solomon S. , Weaver A. , Heidt L. E. , Garcia R. R. , Atlas E. L. , Vedder J. F.
Published: February 2004

We estimate the average transport time from the tropical tropopause to various regions of the northern hemisphere lower stratosphere (stratospheric age) using simultaneous mixing ratio measurements of CFC‐115 and CO2 measured by the Whole Air Sampler (WAS) during Airborne Arctic Stratospheric Expedition II (AASE II). Our inferred ages are consistent with those presented in previous studies. We discuss sources of uncertainties that affect age estimates in general, as well as specific uncertainties arising from inferring ages using CO2 and CFC‐115 abundances. We infer inorganic chlorine (Cly) and bromine (Bry) at various lower stratospheric locations using the WAS organic chlorine and bromine measurements in combination with modeled tropospheric halocarbon trends and with our estimated ages. Inferred Cly and Bry abundances generally increase with increasing latitude and altitude. For our analyzed locations inside the polar vortex, we estimate a maximum Cly abundance of about 2.7 parts per billion by volume (ppbv) and a maximum Bry abundance of about 13.7 parts per trillion by volume (pptv). The locations of these maxima correspond to an average N2O mixing ratio of about 100 ppbv, and to a fractional dissociation of organic chlorine and bromine of 0.85 and 0.90, respectively. Finally, we discuss the expected future limitations of using CFC‐115 to estimate stratospheric age due to the production limitations prescribed by the amendments and adjustments to the Montreal Protocol.
Carbonaceous particles in the atmosphere: A historical perspective to the Fifth International Conference on Carbonaceous Particles in the Atmosphere
Authors: Penner Joyce E. , Novakov T.
Published: February 2004

Carbonaceous aerosol species together with sulfates, other water‐soluble inorganic compounds, and mineral particles play an important role in a variety of environmental effects. Carbonaceous particles contribute to the extinction of visible light by both scattering and absorption, thus influencing visibility degradation and radiative transfer through the atmosphere. These particles may serve as sites for condensation of water vapor and organic compounds. Components of carbonaceous material may contribute to atmospheric chemical processes because of their chemical and catalytic properties. Many of the original results in this field of research were first presented at the International Conferences on Carbonaceous Particles in the Atmosphere held in Berkeley (1978 and 1987) and in Linz and Vienna, Austria (1983 and 1991, respectively). At the fifth conference, August 23–26, 1994, at Lawrence Berkeley Laboratory, 85 papers were presented. This volume contains papers accepted for publication after peer review. In this introduction we attempt to provide an overview of research on carbonaceous particles from the 1950s to mid‐1970s, which provided the backdrop for the first conference. We follow this by outlining research accomplishments and evolution of emphasis (as evidenced by the material presented at these conferences) and by summarizing the present state of this field of research.
Intraseasonal oscillations and associated spatial‐temporal structures of precipitation over China
Authors: Wang Xiaolan L. , Corte‐Real João , Zhang Xuebin
Published: February 2004

On the basis of daily rainfall series for 122 stations well covering eastern China (east of 97°E), intraseasonal oscillations of the monsoonal precipitation and the associated spatial‐temporal structures were explored by performing multichannel singular spectrum analysis. Three oscillations with quasi‐periods of 43, 21, and 12 days were found to be robust, being confined to the region south of 40°N latitude. The spatial‐temporal structures, i.e., the propagation of rainfall anomalies, associated with these quasi‐periodicities are presented. Also, some information about the amplitudes of these oscillations is provided by using composite analysis.
Model studies of the meteorology and chemical composition of the troposphere over the North Atlantic during August 18–30, 1993
Authors: Flatøy Frode , Hov Øystein , Gerbig Christoph , Oltmans Samuel J.
Published: February 2004

A mesoscale chemistry transport model driven by meteorological data from a numerical weather prediction model is used to calculate ozone, carbon monoxide, oxides of nitrogen, and other chemical species over the North Atlantic for a 13‐days period (August 18–30, 1993). The model has a circumpolar grid so that the boundary condition problems are minimized, and the influence of North American emissions on the chemical composition of the troposphere over the North Atlantic and Europe is calculated. During the first part of the period there is a zonal flow across the North Atlantic in the free troposphere; later, there is a strong north‐south as well as vertical component in the advection field. The variability in the concentrations of ozone in the free troposphere is mainly caused by dynamical processes, while the chemical modification is small over an integration time of less than two weeks. A continental plume off the North American continent extending 2000 km or more into the North Atlantic is identified toward the end of the calculation period. There is then a maximum in the concentration of ozone around 1 km above the sea surface, with a much lower concentration in the marine boundary layer close to the ocean surface. Measurements from the U.K. Meteorological Office Hercules C‐130 in the free troposphere off the Atlantic Provinces, across the Atlantic Ocean, and around the Azores together with ozone soundings from the Azores, Bermuda, and Iceland were used for model comparison. The calculations indicate that in the free troposphere the initial conditions as well as the upper boundary conditions are important for ozone distribution. In the upper troposphere the net change in the chemical formation rate of ozone due to a change in the NOx concentration is quite independent of the absolute value of the ozone concentration itself and, consequently, the choice of boundary conditions for ozone is not so important in this context. In the lower troposphere the change in the net chemical formation rate of ozone, which follows from a change in the concentration of NOx, shows a marked dependence on the concentration of ozone.
Physical and chemical observations in marine stratus during the 1993 North Atlantic Regional Experiment: Factors controlling cloud droplet number concentrations
Authors: Leaitch W. R. , Banic C. M. , Isaac G. A. , Couture M. D. , Liu P. S. K. , Gultepe I. , Li S.‐M. , Kleinman L. , Daum P. H. , MacPherson J. I.
Published: February 2004

Airborne observations from 14 flights in marine stratus over the Gulf of Maine and Bay of Fundy in August and September of 1993 are examined for the relationships among the cloud droplet number concentrations (Nd), the out‐of‐cloud aerosol particle number concentrations (Na), the major ion concentrations in the cloud water, and turbulence in cloud. There was a wide range of aerosol concentrations, but when low stratus and the main anthropogenic plume from eastern North America were in the same area the plume overrode the cloud. The Nd increased with increasing Na and cloud water sulfate concentration (cwSO4=), but the relationships were very weak. The separation of the data between smooth and lightly turbulent air substantially improved the ability to explain the variance in the Nd by either of these two quantities. Also, the relative increase in Nd for increases in Na and cwSO4= was greater for lightly turbulent air than for smooth air. The estimated minimum size of particles activated in these clouds ranged from 0.14 μm to 0.31 μm, corresponding to average supersaturations of <0.1%. The minimum size tended to be lower for lightly turbulent air and smaller Na. The results for lightly turbulent air agree well with previously reported parameterizations of the impact of aerosols on Nd, but the results for smooth air do not agree. In general, more knowledge of the physical factors controlling the Nd in stratiform clouds, such as turbulence, is needed to improve not only our ability to represent Nd but also to increase our understanding of the impact of the aerosol particles on the Nd and climate.
Vertical ozone distribution over southern Africa and adjacent oceans during SAFARI‐92
Authors: Diab R. D. , Thompson A. M. , Zunckel M. , Coetzee G. J. R. , Combrink J. , Bodeker G. E. , Fishman J. , Sokolic F. , McNamara D. P. , Archer C. B. , Nganga D.
Published: February 2004

A set of four ozonesonde stations located at Ascension Island, Brazzaville, Okaukuejo, and Irene, operational during the TRACE A and SAFARI‐92 experiments has provided an opportunity to investigate the vertical distribution of ozone over southern Africa and adjacent oceans. All stations display a springtime maximum in tropospheric ozone. Enhanced tropospheric ozone, which occurs between June and September at Brazzaville and between July and October at Ascension Island, is linked to dry season biomass burning. The influence of tropical biomass burning is delayed until September at Okaukuejo when a sharp increase in tropospheric ozone is experienced. The biomass burning influence at Irene is less because of its more southerly location. A general tropospheric enhancement is observed at all stations. It is manifest as an enriched layer in the upper troposphere at Okaukuejo (9–12 km) and Brazzaville (11–14 km) and in the lower troposphere (2–8 km) at Ascension Island. At Ascension Island lower tropospheric ozone values are about 20 parts per billion by volume greater than elsewhere and the tropospheric component here accounts for about 18% of the total column ozone. A series of tethersonde soundings conducted at hourly intervals at Okaukuejo revealed ozone to be well mixed in the lower boundary layer during the day, but to display marked vertical stratification at night.
Airborne observations of strong biogenic NOx emissions from the Namibian savanna at the end of the dry season
Authors: Harris G. W. , Wienhold F. G. , Zenker T.
Published: February 2004

We report the observation of substantial emissions of NOx from a several‐hundred‐square‐kilometer region of savanna in northern Namibia in September 1992. The estimated emission rates lie near the high end of the range of values reported from flux chamber studies on various tropical savanna soils and appear to be associated with a light rainfall event which occurred 4 days prior to the observations. If our measurements are typical for this situation, then biogenic emission of NOx following sporadic rainfall events during and at the end of the dry season may be an important regional source rivaling that arising from savanna burning and may have important consequences for regional scale ozone formation.
Simulations of Antarctic climate using a limited area model
Authors: Walsh Kevin , McGregor John L.
Published: February 2004

A limited area model is nested within the European Centre for Medium‐Range Weather Forecasts (ECMWF) analyses and climate simulations are performed for July at a resolution of 125 km for a domain located over the continent of Antarctica. The model displays negative biases of mean sea level pressure off the coast of East Antarctica, and positive biases in other oceanic regions close to the coast of the continent. Biases of surface air temperature are generally modest over the continent; the quality of the temperature simulation is more difficult to assess over the areas of sea ice close to the coast, as the ECMWF analyses do not include an open water fraction. The model simulation of snow accumulation is good; the observed positive gradient of accumulation between the center of Antarctica and the coast is reproduced well, although precipitation is generally too high over regions of significant orography. Comparison between simulations performed with and without oceanic leads shows that leads increase sensible and latent heat fluxes over regions of sea ice, and increase accumulation over the continent of Antarctica. The effects of the introduction of leads into the limited area model are consistent with the results of similar general circulation model (GCM) sensitivity tests previously performed.
A meteorological overview of the TRACE A period
Authors: Bachmeier A. Scott , Fuelberg Henry E.
Published: February 2004

General meteorological conditions over the South Atlantic basin during the Transport and Atmospheric Chemistry Near the Equator‐Atlantic (TRACE A) experiment period are described. TRACE A occurred during one of the longest continuous El Nino‐Southern Oscillation (ENSO) events of the twentieth century. Effects of this ENSO event included warmer than normal temperatures concurrent with a severe drought in southern Africa and warm, dry conditions over northeastern Brazil. Large‐scale flow patterns are described, and the TRACE A period is compared to climatological normals. Significant meteorological features affecting the TRACE A flights included a northward moving middle‐latitude cold frontal system over Brazil, eastward moving middle‐latitude frontal waves crossing the South Atlantic basin and southern Africa, and deep convection over central Africa. The Brazilian cold front helped induce organized convective systems which led to vertical transports of biomass burning related chemical species. A well‐defined middle‐latitude frontal wave was traversed during the transit flight from Rio de Janeiro to Johannesburg, along with the penetration of a tropopause fold of stratospheric air. Deep surface‐based mixed layers and frequent diurnal convection over central Africa were responsible for vertical transports over that continent. Middle‐latitude frontal waves that crossed the southern region of Africa slightly displaced the shear axes and col zones that often were present off the west coast of central Africa.
Influence of atmospheric circulation types on space‐time distribution of intense rainfall
Authors: Mamassis Nikos , Koutsoyiannis Demetris
Published: February 2004

The influence of the prevailing weather situation on the temporal evolution and geographical distribution of intense rainfall is studied, as a potential tool to improve rainfall prediction. A classification scheme of the atmospheric circulation over the east Mediterranean territory is used for the analysis. The study area is the Sterea Hellas region (central Greece) with an area of about 25,000 km2. Daily data from 71 rain gages and hourly data from three rain recorders over a 20 year period are used. From these data sets, the intense rainfall events were extracted and analyzed. Several empirical and statistical methods (also including the available tools of a Geographical Information System) are used for the analysis and comparison of rainfall distribution both in time and in space. The analysis shows that the contribution of the concept of weather types to the quantitative point rainfall prediction in short timescale is small, and only the estimation of the probability of occurrence of an intense event is feasible. On the contrary, the relation between the spatial distribution of rainfall and the atmospheric circulation patterns is significant and may be used for improving the forecasting of the geographical distribution of rainfall.
Calculation of the global land surface energy, water and CO2 fluxes with an off‐line version of SiB2
Authors: Zhang C. , Dazlich D. A. , Randall D. A. , Sellers P. J. , Denning A. S.
Published: February 2004

Global land surface fluxes of energy and CO2 have been simulated using an off‐line version of a biosphere‐atmosphere model, SiB2, forced with analyzed or observed atmospheric boundary layer mean potential temperature, water vapor mixing ratio, and wind, surface downward solar and thermal radiation, and precipitation. The off‐line model is called SiBDRV. Soil and vegetation boundary conditions were specified from satellite data and other sources. The European Centre for Medium‐Range Weather Forecasts (ECMWF) data assimilation system products were used to derive the atmospheric and radiative forcings. Precipitation was based on station observations. The SiBDRV results were compared with corresponding simulation results produced by the Colorado State University general circulation model (CSU GCM), with the ECMWF assimilation system output and with observations. Differences between the surface energy budget components and the surface climatology produced by SiBDRV and the ECMWF assimilation system are due to differences in the land surface parameterizations between the two models. SiBDRV produced lower surface latent heat fluxes and larger sensible heat fluxes than the ECMWF data assimilation, partly due to large canopy resistent term explicitly formulated by SiB2 and possible precipitation differences between the SiBDRV precipitation forcing and the ECMWF data. Differences between the SiBDRV and the CSU GCM results are due to the different climates associated with the ECMWF assimilation system output, which is strongly constrained by assimilated observations, and by the CSU GCM, which is run in pure simulation mode. More specifically, the major reasons for the surface energy and CO2 budget differences between the SiBDRV and the GCM are greater incoming solar radiation in the GCM and differences in the precipitation patterns. The simulated global annual carbon uptake by the terrestrial biosphere is similar in SiBDRV and the GCM. The annual gross primary productions of SiBDRV (116 Gt) and the GCM (113 Gt) agree well with other studies, using either ecological process models or empirical regression models. SiBDRV takes up 10 and 5% more CO2 than the GCM in January and July, respectively. The seasonally varying land surface CO2 fluxes estimated by the SiBDRV and the GCM both compare reasonably well with the results of other calculations.
Effect of peroxy radical reactions on the predicted concentrations of ozone, nitrogenous compounds, and radicals
Authors: Kirchner Frank , Stockwell William R.
Published: February 2004

The reactions of organic peroxy radicals with NO, HO2, organic peroxy radicals, and NO3 along with the formation and decomposition of peroxyacetyl nitrate are all important for the modeling of atmospheric chemistry. Recent laboratory measurements of the rate constants for peroxy radical‐peroxy radical reactions show that there are large differences between these rate constants. We present methods of estimating organic peroxy radical self‐reaction rate constants from an empirical expression. These self‐reaction rate constants may be used to estimate the rates of peroxy radical cross reactions. There are also new data available on the rate constants for peroxyacetyl nitrate formation, decomposition, the reaction of acetyl peroxy radicals and other organic peroxy radicals with NO, and the reactions of NO3 with organic peroxy radicals. To estimate the importance of these reactions, these new data along with revisions to the product yields for organic peroxy radical‐organic peroxy radical reactions were implemented in the mechanism of Stockwell et al. [1990]. The revised mechanism yields significantly different concentrations of peroxyacetyl nitrate, higher organic hydroperoxides and peroxyacetic acid concentrations. Nighttime concentrations of organic peroxy radicals, HO2, HO, and NO3 are also strongly affected by organic peroxy radical‐organic peroxy radical reactions and the reactions of organic peroxy radicals with NO3. Our results suggest that the reactions of organic peroxy radicals with NO3 are more important than organic peroxy radical‐organic peroxy radical reactions in the nighttime atmosphere.
GOMETRAN: A radiative transfer model for the satellite project GOME, the plane‐parallel version
Authors: Rozanov V. V. , Diebel D. , Spurr R. J. D. , Burrows J. P.
Published: February 2004

The Global Ozone Monitoring Experiment (GOME) is a new, nadir‐viewing instrument on the European Space Agency satellite ERS 2 which was launched in April 1995. With diode‐array detector technology, spectra of the upwelling radiance are measured simultaneously at thousands of wavelengths in the UV, visible, and near‐IR regions. Inversion of these measurements by appropriate algorithms allows the retrieval of the distribution of gaseous and particulate constituents, which modulate the radiance by absorption, emission, or scattering processes. Such a retrieval algorithm requires an accurate radiative transfer model to describe the propagation of light through the atmosphere. The model GOMETRAN has been specially designed to fulfill the needs of GOME, but it applies generally to other downward looking space instrumentation in the UV, visible, or near‐IR. In this paper the model is described in the plane‐parallel version, and the optimization of computational parameters and comparisons with other radiative transfer models is presented.
Information content and wavelength selection for multispectral radiometers
Authors: Box G. P. , Box M. A. , Krücker J.
Published: February 2004

When choosing the wavelengths for a multispectral radiometer, it is important to consider the information content of the proposed measurement set. Eigenanalysis provides valuable information about the number of independent pieces of information which can be obtained from a proposed set of measurement wavelengths. This method has been used to determine a suitable measurement wavelength set for an instrument: we recommend seven channels between 0.368 and 2.23 μm. The interdependence of measurements means that one measurement may often be predicted from the others to within the experimental accuracy. Eigenanalysis provides a means of making such predictions and has been applied in this paper to predict the aerosol optical thickness at 0.61 μm from optical thickness measurements at other wavelengths. This would allow the ozone contribution to optical thickness to be extracted from this measurement.
Water soluble dicarboxylic acids and related compounds in Antarctic aerosols
Authors: Kawamura Kimitaka , Sempéré Richard , Imai Yoshie , Fujii Yoshiyuki , Hayashi Masahiko
Published: February 2004

Antarctic aerosols collected at Syowa Station were studied for water soluble organic compounds by employing a water extraction and dibutyl ester derivatization and using a capillary gas chromatography (GC) and GC/mass spectrometry (GC/MS). Total carbon and nitrogen were also determined. A homologous series of α,ω‐dicarboxylic acids (C2–C11), ω‐oxocarboxylic acids (C2–C9), and α‐dicarbonyls (C2–C3) were detected, as well as pyruvic acid and aromatic (phthalic) diacid. Succinic (C4) or oxalic (C2) acid was found to be the dominant diacid species, followed by azelaic (C9), adipic (C6), or malonic (C3) acid. Concentration range of the total diacids was 5.9–88 ng m−3, with an average of 29 ng m−3. Highest concentrations were observed in the summer sample with a predominance of succinic acid (61.5 ng m−3), which comprised approximately 70% of the total diacids and accounted for 3.5% of total aerosol carbon (1020 ng m−3). The succinic acid (C4) is likely produced by photooxidation of 4‐oxocarboxylic acids, which are present in the atmosphere as intermediates of the photooxidation of unsaturated fatty acids. These results indicate that the Antarctic organic aerosols originate from marine‐derived lipids and are transformed largely by photochemical oxidations. ω‐Oxocarboxylic acids (C2–C9, 0.36–3.0 ng m−3) also showed the highest concentration in the summer sample, again suggesting a secondary production in the atmosphere of the Antarctic and in the Southern Ocean.
The global tropospheric distribution of NOx estimated by a three‐dimensional chemical tracer model
Authors: Kraus Annette B. , Rohrer Franz , Grobler Ellen S. , Ehhalt Dieter H.
Published: February 2004

The global distribution of NOx in the troposphere is calculated using a simple three‐dimensional chemical tracer model. This model includes a simplified chemistry scheme for the tracers NOx ≡ NO + NO2 and HNO3, which are redistributed by advection, dry and wet convection, and large‐scale diffusion. The sources of NOx considered are fossil fuel combustion, emissions from soil microbial activity, biomass burning, lightning discharges, emissions by aircraft, and downward transport from the stratosphere. Dry and wet deposition act as final sinks. At northern middle and high latitudes the calculated tropospheric NOx content is dominated by the surface sources, fossil fuel combustion in particular. In the tropical free troposphere, lightning discharges provide about 80% of the total NOx throughout the year. The zonally averaged fractional contribution of aircraft emissions strongly depends on the season. The largest contribution of this source, over 60%, occurs during January in the upper troposphere between 45°N and 60°N. The NO mixing ratios determined by the model show good overall agreement with vertical profiles measured during the Stratospheric Ozone Experiment (STRATOZ) III aircraft campaign.