bluuebunny/crossref_metadata_2025 huggingface dataset:
Temperature profiles in radiative‐convective equilibrium above surfaces at different heights
Authors: Molnar Peter , Emanuel Kerry A.
Published: September 2002

Soundings of temperature and specific humidity calculated assuming radiative‐convective equilibrium over surfaces at different heights show only small variations in surface temperature and specific humidity with surface height. Calculated surface temperatures decrease at ∼2°C km−1, with all other parameters held fixed. Calculated temperatures aloft in the upper troposphere above surfaces at different heights differ by 10°–20°C; those above surfaces at 3000–5000 m are significantly warmer. These differences support the contention that an elevated terrain can force significant atmospheric circulation through its effect on equilibrium temperatures, as occurs in the case of the Tibetan Plateau forcing the south Asian monsoon.
Radiative forcing due to sulfate aerosols from simulations with the National Center for Atmospheric Research Community Climate Model, Version 3
Authors: Kiehl J. T. , Schneider T. L. , Rasch P. J. , Barth M. C. , Wong J.
Published: September 2002

The direct and indirect radiative forcing due to sulfate aerosols is calculated in a version of the National Center for Atmospheric Research (NCAR) Community Climate Model (CCM3). This model includes a sulfur chemistry model and predicts the mass of sulfate. New optical properties are presented that account for the hygroscopic growth effects on both extinction optical depth and asymmetry parameter. These new properties enhance the sulfate direct forcing for relative humidities above 90% compared to previous results. The global annual mean forcing is −0.56 W m−2. The forcing due to the indirect cloud albedo effect is studied using four different methods to relate cloud drop number concentration to sulfate mass. One method assumes the presence of background aerosols that can also act as a source of cloud condensation nuclei. This effect reduces the magnitude of the indirect effect by 40% to −0.4 W m−2. This sensitivity study indicates the importance of the presence of other aerosols that can nucleate cloud drops. The seasonal cycle of the indirect effect is different from that of the direct effect, as the maximum of the indirect effect occurs in the Northern Hemisphere springtime, while that of the direct effect is largest in the Northern Hemisphere summer. The four different methods of accounting for the indirect effect result in a large uncertainty in the global annual mean net forcing due to sulfates and greenhouse gases, 0.05 to 1.42 W m−2. It is argued that a less empirical and more physically based approach is required to account for the indirect effect in climate models.
Ground‐based observations of Arctic O3 loss during spring and summer 1997
Authors: Toon G. C. , Blavier J.‐F. , Sen B. , Salawitch R. J. , Osterman G. B. , Notholt J. , Rex M. , McElroy C. T. , Russell J. M.
Published: September 2002

Ground‐based solar absorption spectra were measured from Fairbanks, Alaska (65°N, 148°W) from March to September 1997 by the Jet Propulsion Laboratory (JPL) MkIV Fourier transform infrared (FTIR) spectrometer. The derived column abundances of O3 declined by 35% over this period (20% in April and May, and 15% during the summer), whereas those of HF, a long‐lived tracer, changed by less than 5%. High‐latitude, summertime balloon observations reveal similar shapes for the volume mixing ratio profiles of O3 and HF in the lower stratosphere, where most of their column abundance resides. Vertical transport should therefore have similar effects on the column abundances of O3 and HF. Data from the Halogen Occultation Experiment (HALOE) show a poleward decrease in the O3/HF ratio at all stratospheric altitudes, so that any reductions in column O3 due to horizontal meridional transport would have been accompanied by even larger reductions in column HF. Therefore the observed column O3 decrease must be the result of chemical loss processes. Column measurements of other atmospheric gases show a summertime maximum in the NOx/NOy column ratio and little change in the chlorine partitioning. We conclude that most of the reduction in column O3 over Fairbanks from March to September 1997 was likely driven by NOx chemistry. These conclusions are supported by the similar behavior of column abundances measured by another ground‐based FTIR spectrometer based in Ny Ålesund, Spitsbergen, (79°N, 12°E).
Solubility of acetone in low‐temperature (210–240 K) sulfuric acid solutions
Authors: Klassen Jane K. , Lynton Julia , Golden David M. , Williams Leah R.
Published: September 2002

The solubility of acetone in low‐temperature sulfuric acid solutions was studied in a low‐pressure Knudsen cell reactor. The time dependence of the uptake coefficient was analyzed to give effective Henry's law coefficients for acetone in 48–68 wt % sulfuric acid solutions between 210 and 240 K. The measured solubilities suggest that very little acetone will be partitioned into sulfate aerosol particles in the upper troposphere. Addition of ammonium sulfate to the sulfuric acid reduced the solubility slightly. No evidence was observed for reaction of dissolved acetone with itself or with nitric acid under the conditions of these experiments.
Results from the 1995 Stratospheric Ozone Profile Intercomparison at Mauna Loa
Authors: McPeters R. D. , Hofmann D. J. , Clark M. , Flynn L. , Froidevaux L. , Gross M. , Johnson B. , Koenig G. , Liu X. , McDermid S. , McGee T. , Murcray F. , Newchurch M. J. , Oltmans S. , Parrish A. , Schnell R. , Singh U. , Tsou J. J. , Walsh T. , Zawodny J. M.
Published: September 2002

In August 1995, multiple instruments that measure the stratospheric ozone vertical distribution were intercompared at the Mauna Loa Observatory, Hawaii, under the auspices of the Network for the Detection of Stratospheric Change. The instruments included two UV lidar systems, one from the Jet Propulsion Laboratory and the other from Goddard Space Flight Center, electrochemical concentration cell balloon sondes, a ground‐based microwave instrument, Dobson‐based Umkehr measurements, and a new ground‐based Fourier transform infrared instrument. The Microwave Limb Sounder instrument on the Upper Atmosphere Research Satellite provided correlative profiles of ozone, and there was one close overpass of the Stratospheric Aerosol and Gas Experiment II (SAGE II) instrument. The results show that much better consistency among instruments is being achieved than even a few years ago, usually to within the instrument uncertainties. The different measurement techniques in this comparison agree to within ±10% at almost all altitudes, and in the 20–45 km region most agreed within ±5%. The results show that the current generation of lidars is capable of accurate measurement of the ozone profile to a maximum altitude of 50 km. SAGE II agreed well with both lidar and balloon sonde down to at least 17 km. The ground‐based microwave measurement agreed with other measurements from 22 km to above 50 km. One minor source of disagreement continues to be the pressure‐altitude conversion needed to compare a measurement of ozone density versus altitude with a measurement of ozone mixing ratio versus pressure.
Particle production in the lowermost stratosphere by convective lifting of the tropopause
Authors: de Reus Marian , Ström Johan , Hoor Peter , Lelieveld Jos , Schiller Cornelius
Published: September 2002

Aircraft measurements of aerosol particles and trace gases were performed in the upper free troposphere and lower stratosphere during the Stratosphere and Troposphere Experiment by Aircraft Measurements (STREAM‐96) campaign from Shannon airport, Ireland. During one measurement flight, ultrafine particle number densities up to 104 cm−3 (STP) were observed in the lowermost stratosphere. Concurrent with these very high number densities of ultrafine particles, high accumulation mode particle number densities were observed over the same geographical location in the free troposphere, which were attributed to convective transport in the troposphere. The observations suggest that adiabatic cooling of the stratospheric air, as a result of the convective transport in the troposphere that lifted the tropopause and the air in the lowermost stratosphere, was responsible for triggering the formation of new particles. However, also aircraft emissions could have contributed to the enhancement in ultrafine particles.
A comparison of cloud top heights computed from airborne lidar and MAS radiance data using CO2 slicing
Authors: Frey Richard A. , Baum Bryan A. , Menzel W. Paul , Ackerman Steven A. , Moeller Christopher C. , Spinhirne James D.
Published: September 2002

Data from two instruments onboard the National Aeronautics and Space Administration (NASA) ER‐2 high‐altitude aircraft have been utilized in the largest validation study to date in assessing the accuracy of the CO2‐slicing cloud height algorithm. Infrared measurements of upwelling radiance from the MODIS (Moderate‐Resolution Imaging Spectroradiometer) airborne simulator (MAS) were used to generate cloud top heights and then compared to those derived from the Cloud Lidar System (CLS), operating with dual polarization at 0.532 μm. The comparisons were performed for 10 flight days during the Subsonic Aircraft Contrail and Cloud Effects Special Study (SUCCESS) field experiment during April and May 1996 which included various single‐layer and multilayer cloud conditions. Overall, the CO2‐slicing method retrieved cloud heights to within ±500 m and to within ±1500 m of the lidar heights in 32 and 64% of the cases, respectively. From a simulation of cloud height errors as a function of various error sources in the CO2‐slicing algorithm, it was concluded that the problem of multilayer clouds is secondary to that of proper specification of clear‐sky radiances.
Regional and global distributions and lifetimes of sulfate aerosols from Mexico City and southeast China
Authors: Barth M. C. , Church A. T.
Published: September 2002

To learn what possible influence a megacity and an industrial region, both of which have poor air quality, have on the global scale, sulfate aerosol derived from Mexico City and from southeast China is examined. It is found that the highest values of sulfate from Mexico City mostly travel westward and northward. Sulfate from southeast China travels eastward, and its distribution encircles the Earth in summer and autumn. Mexico City, which emits ∼1% of the global anthropogenic sulfur emissions, contributes ∼1% to the global sulfate burden. Southeast China, which emits 11.6% of the global anthropogenic sulfur emissions, contributes 9% to the global sulfate burden, a nonlinear response between emissions and burden. When the anthropogenic sulfur emissions are doubled in the two regions, the sulfate burden derived from Mexico City approximately doubles, but the sulfate burden from southeast China more than doubles. An examination of the sulfate budget indicates that for sulfate derived from southeast China more sulfate is produced via gas‐phase reaction, thus allowing the sulfate to be less susceptible to wet deposition. We qualitatively analyze black carbon aerosol from Mexico City and southeast China and determine that hydrophilic black carbon has a lifetime similar to sulfate aerosol when the emitted black carbon is assumed to be of hydrophilic form. When the emitted black carbon is hydrophobic and its transfer rate to the hydrophilic form is 1.9 days, which is the same as the global sulfur dioxide lifetime, the lifetime of hydrophilic black carbon is 3.5 days longer than sulfate. The difference between the two types of aerosol is attributed to the aqueous production pathway of sulfate and consequently its availability to rain out. If the transfer rate is 5 days, then hydrophilic black carbon is found in regions with little cloud activity thus increasing its lifetime to 10 days or more.
Consistency tests on UV spectral irradiance measurements using modeling and a broadband instrument
Authors: Pachart Eric , Lenoble Jacqueline , Brogniez Colette , Masserot Dominique , Bocquet Jean Louis
Published: September 2002

The UV spectroradiometer used at the University of Lille is presented, and its characterization and calibration are described. In order to detect possible shifts between calibrations, two different consistency tests are regularly performed on cloudless days. The erythemal dose rate obtained by integrating the weighted spectrum is compared to broadband measurements and modeling results. A Sun photometer provides the aerosol optical depth necessary as an input to the radiative transfer model. Results of these tests are presented for some cases; the general agreement is within 5%, which corresponds to the expected uncertainties.
Inverse modeling of the global CO cycle: 2. Inversion of 13C/12C and 18O/16O isotope ratios
Authors: Bergamaschi Peter , Hein Ralf , Brenninkmeijer Carl A. M. , Crutzen Paul J.
Published: September 2002

Following a three‐dimensional inverse modeling study on atmospheric CO mixing ratios [Bergamaschi et al., this issue], we present the expansion of our model for the treatment of the stable isotope ratios 13C/12C and 18O/16O in carbon monoxide. The individual isotopomers were included in the model as independent tracers, and the inversion scheme was extended, allowing the simultaneous optimization (with respect to observational data) of modeled atmospheric mixing and isotope ratios. Observational data of 13C/12C and 18O/16O ratios were taken from a set of five globally distributed sites, all of which exhibit pronounced seasonal cycles and which as a whole clearly define large latitudinal gradients. Incorporation of 13C/12C ratios in the inversion resulted in a clear constraining of the total amount of CO arising from CH4 oxidation. The present study suggests an average CO yield of 86% (80–88%), provided that (1) the reaction of CH4+Cl has no significant impact on the δ 13C of the resulting CO and (2) CO from the ocean helps to balance the δ13C in the Southern Hemisphere. Otherwise, a further reduced CO yield would be necessary, as low as 71% in case of an average kinetic isotope effect of 1.013 [Lowe et al., 1999] or 69% in case of a δ13C value of −25.0‰ for the oceanic source. Despite a lack of experimental investigations on 18O/16O in CO arising from CH4 or nonmethanehydrocarbons (NMHC) oxidation, inclusion of 18O/16O into the inversion gives further significant constraints on the global CO cycle. It is shown that apart from the large technological CO source, additional sources with dominant emissions in the Northern Hemisphere are required, such as biogenic emissions (either direct or via oxidation of biogenic NMHCs) or anthropogenic NMHCs, in order to reproduce observed atmospheric 18O/16O ratios. The extended inversion scheme allows CO budgets to be derived, which reproduce, within two standard deviations of observational data, simultaneously CO mixing ratios (from the National Oceanic and Atmospheric Administration Climate Monitoring and Diagnostics Laboratory network), 13C/12C, and 18O/16O ratios. Incorporation of stable isotopes renders inversion results much more robust compared to inversions of CO mixing ratios only.
Simulation of the dynamics and composition of secondary and marine inorganic aerosols in the coastal atmosphere
Authors: von Salzen Knut , Schlünzen K. Heinke
Published: September 2002

Results of an extended version of the three‐dimensional Eulerian Mesoscale Transport, Chemistry, and Stream Model (METRAS) for simulating size‐segregated inorganic aerosols are presented. The extended version of METRAS includes aerosol transport by advection, diffusion, gravitational settling, and dry deposition. Aerosols are produced by homogeneous nucleation and by sea spray. They are modified by condensation and evaporation of inorganic aerosol precursor gases. Altogether, 73 inorganic and organic gas species are treated in the model by taking into account transport, deposition, emissions, and gas‐phase reactions. The model is applied to simulate the mixing of marine and continental air in the coastal atmosphere over the German Bight. The simulation results give evidence for the importance of the uptake of nitric acid and ammonia by sea‐salt aerosol for the dynamics of nitrogen compounds in the coastal atmosphere. As a result of the mixing of polluted continental air masses with marine air masses, the pH of the sea‐salt aerosol reaches values as low as pH = 2.1.
Absolute intensities for the O2 1.27 μm continuum absorption
Authors: Maté B. , Lugez C. , Fraser G. T. , Lafferty W. J.
Published: September 2002

Collision‐induced absorption coefficients for the 1.27 μm band of O2 have been measured at a resolution of 0.5 cm−1 and an optical path length of 84 m using a Fourier transform spectrometer. Spectra were recorded for sample densities ρ from 1 to 10 times that of an ideal gas under standard conditions (T = 273.15 K and P = 101.325 kPa) at temperatures of 253, 273, and 296 K for pure O2 and O2/N2 mixtures. After removing the contributions from the sharp lines of the υ = 0 ← 0 component of the O2 a1Δg ← X3∑g− band, which overlaps the continuum band, the integrated band strength per unit path length, S ≡ SO2−O2ρO22 + SO2−N2ρN2ρO2, has been determined for several values of the densities, ρO2 and ρN2, to give values for SO2−O2 and SO2−N2. At 296 K we find SO2−O2 = 4.847(22) × 10−43 cm−2 (molecule/cm3)−2 and SO2−N2 = 0.941(50) × 10−43 cm−2 (molecule/cm3)−2. Type A standard uncertainties are given, that is, ±1σ, from a least squares analysis of the integrated‐intensity‐versus‐density data. The SO2−O2 coefficient is in reasonable agreement with the previous measurements of Cho et al. [1963]; however, our value for SO2−N2is 2.6 times greater than their results. Our derived air coefficient SO2−air is 37% greater than the atmospheric value of Mlawer et al. [1998], after correcting their continuum value for an updated value for the absorption coefficients for the overlapping discrete structure of the O2a1Δg ← X3∑g− band.
Methyl bromide emissions from agricultural field fumigations in California
Authors: Williams Jody , Wang Nun‐Yii , Cicerone Ralph J.
Published: September 2002

Methyl bromide is the most abundant brominated hydrocarbon gas in the atmosphere and is significant as a source of stratospheric bromine radicals that destroy ozone. However, estimated sources and sinks of methyl bromide exhibit a deficit in sources of ∼70 Gg/yr (one Gg = 109 g), and the proportion of natural and anthropogenic sources is not known well. Known sources include agricultural fumigation (preplant and postplant), structural fumigation, biomass burning, gasoline additives, and oceans. The oceans, however, also act as a net sink for methyl bromide; that is, globally, consumption is greater than production. Early estimates of emissions of methyl bromide from fumigated agricultural fields from models were 30–60% of the amount applied. To test this estimate, we studied emissions from six field fumigations using chambers to measure the flux of methyl bromide, soil bromide analyses to measure degradation, and soil gas down to 90 cm or more to monitor methyl bromide with time in the soil profile. We found between 24–74% of applied methyl bromide was emitted. The average emission found in these experiments was 49 ± 19% based on chamber measurements and 52±20% based on the soil bromide measurements. Factors affecting emissions included the polyethylene film covering the soil, the injection method, the injection depth, and the chemical and physical properties of the soil. The main factors controlling the emissions in our studies are discussed.
A three‐dimensional modeling study of the correlations of 210Pb with HNO3 and peroxyacetylnitrate (PAN) at remote oceanic sites
Authors: Giannakopoulos C. , Chipperfield M. P. , Law K. S. , Plantevin P.‐H. , Pyle J. A. , Shallcross D. E.
Published: September 2002

We have used 210Pb, a tracer originating from the radioactive decay of 222Rn emitted from soils, to show that tracers not affected by complex chemical reactions can provide a strong indication of the origin of air masses in the remote oceanic atmosphere and can help us understand the behavior of species which are affected by chemistry. Using our three‐dimensional off‐line chemical transport model (CTM), TOMCAT, we show that 210Pb tends to covary with altitude with HNO3 arid peroxyacetylnitrate (PAN) at remote oceanic areas, suggesting the importance of transport for insoluble species (in our case 222Rn and NOx) that are able to escape deep convective scavenging and travel long distances before being transformed to soluble species (here 210Pb and HNO3). Near the continental coast, especially in the lower part of the troposphere, model HNO3 levels are large, evident of the continental influence. PAN and 210Pb levels are small. This indicates that 222Rn has not yet decayed to 210Pb and also PAN formation is not favored due to higher temperatures near the surface. Therefore, in these young air masses, only PAN and 210Pb correlate, both having low values. Higher up, in the middle to upper troposphere, our modeling study shows that HNO3 and 210Pb tend to correlate, since in these relatively older air masses there was sufficient time for 210Pb formation.
A new lumped structure photochemical mechanism for large‐scale applications
Authors: Zaveri Rahul A. , Peters Leonard K.
Published: September 2002

The lumped‐structure approach for condensing organic chemical mechanisms is attractive, since it yields fewer species and reactions and reduces computational costs. This paper leads through the development of a new lumped‐structure mechanism, largely based on the widely used Carbon Bond Mechanism (CBM‐IV) developed by Gery et al. [1989]. The new mechanism called CBM‐Z extends the original framework to function properly at larger spatial and longer timescales. The major modifications in the mechanism include revised inorganic chemistry; explicit treatment of the lesser reactive paraffins, methane and ethane; revised parameterizations of the reactive paraffin, olefin, and aromatic reactions; inclusion of alkyl and acyl peroxy radical interactions and their reactions with NO3; inclusion of organic nitrates and hydroperoxides; and refined isoprene chemistry based on the condensed one‐product mechanism of Carter [1996]. CBM‐Z was successfully evaluated along with the CBM‐IV, a partially revised CBM‐IV, and a revised Regional Acid Deposition Model (RADM2) mechanism [Stockwell et al., 1990; Kirchner and Stockwell, 1996] using the low NOx and volatile organic compound concentration smog chamber experiments of Simonaitis et al. [1997]. Box model versions of the four mechanisms were also evaluated under a variety of hypothetical urban and rural scenarios for a period of 30 days. Results from CBM‐Z and revised RADM2 were found to be within ±20% of each other, while CBM‐IV and revised CBM‐IV results deviated significantly by up to 50–95%. Sensitivity tests were performed to elucidate the effects of some of the new features added in CBM‐Z. Relative computational memory and time requirements of these mechanisms are also discussed.
Modeling of the transport and diffusion of a tracer in the Freiburg‐Schauinsland area
Authors: Fiedler F. , Bischoff‐Gauß I. , Kalthoff N. , Adrian G.
Published: September 2002

In June 1996, the Schaumsland Ozone Precursor Experiment (SLOPE) was performed in the area of Freiburg‐Schauinsland (Germany). A major objective of this experiment was to investigate the behavior of ozone and its precursors of the city plume of Freiburg on the way from Freiburg to Schauinsland [Volz‐Thomas et al., this issue]. Meteorological [Kalthoff et al., this issue] and chemical measurements [Pätz et al., this issue; Kolahgar et al., this issue] were carried out at several stations along the expected transport path between Freiburg and Schauinsland. In order to separate the contribution of transport and diffusion from that of chemical reaction, to calculate the transport time and dilution factor, the inert tracer SF6 was released at the beginning of the transport path [Kalthoff et al., this issue; M. Möllmann‐Coers et al., unpublished data, 1999 (hereinafter referred to as M99)]. The results from the model calculations were first compared with the observations at different measurement sites. Then the calculations were used to provide interpretation support with regard to the mesoscale meteorological phenomena observed. Finally, they delivered explanations for the observed temporal development and spatial distribution of the tracer concentrations between Freiburg and Schauinsland.
Measurements of trace gases and photolysis frequencies during SLOPE96 and a coarse estimate of the local OH concentration from HNO3 formation
Authors: Pätz Hans‐Werner , Corsmeier Uli , Glaser Konrad , Vogt Ulrich , Kalthoff Norbert , Klemp Dieter , Kolahgar Bita , Lerner Ansgar , Neininger Bruno , Schmitz Thomas , Schultz Martin G. , Slemr Jana , Volz‐Thomas Andreas
Published: September 2002

The Schauinsland Ozone Precursor Experiment (SLOPE96) campaign was conducted in June 1996 to study the physicochemical transformation of pollutants and the production of photooxidants during transport from the city of Freiburg to the Schauinsland mountain. For this purpose, chemical surface measurements were made at the entrance of the valley Großes Tal, and close to the Schauinsland summit, at 1200 m altitude on a saddle at the end of the valley. In addition, measurements of ozone, NO2, and meteorological parameters were made on two tethered balloons and aboard a small aircraft. This paper describes the experimental setup and the measurements of ozone, odd‐nitrogen compounds, carbonyl compounds, CO, and photolysis frequencies made during SLOPE96. The various instruments used on the different platforms were harmonized on the basis of intercomparison experiments in order to achieve a consistent picture. Large precursor concentrations from the nearby city of Freiburg are transported to Schauinsland in a valley wind system during stagnant high‐pressure conditions. These conditions occurred only on 2 days of the campaign, and only 1 day (June 5) was predictable enough to allow for deployment of the aircraft and the balloons. An OH concentration of 8 ‐ 10× 06 cm−3 is derived from the rate of change of HNO3 and NO2 on June 5 at Schauinsland (1.5–3 ppb NO2; JO1D ≈ 2 × 10−5 s−1), assuming quasi steady state and a homogeneous air mass. The ozone production rate as determined from the photostationary state of NOx at Schauinsland reached maximum daily values between 15 and 60 ppb h 1 around noontime. On average, P(O3) comprised about 30% of the photolysis rate of NO2. Similar to earlier observations at Schauinsland, a good correlation between P(O3) and the product of UV radiation and precursor concentrations was found.
A polar stratospheric cloud parameterization for the global modeling initiative three‐dimensional model and its response to stratospheric aircraft
Authors: Considine D. B. , Douglass A. R. , Connell P. S. , Kinnison D. E. , Rotman D. A.
Published: September 2002

We describe a new parameterization of polar stratospheric clouds (PSCs) which was written for and incorporated into the three‐dimensional (3‐D) chemistry and transport model (CTM) developed for NASA's Atmospheric Effects of Aviation Project (AEAP) by the Global Modeling Initiative (GMI). The parameterization was designed to respond to changes in NOy and H2O produced by high‐speed civilian transport (HSCT) emissions. The parameterization predicts surface area densities (SADs) of both Type 1 and Type 2 PSCs for use in heterogeneous chemistry calculations. Type 1 PSCs are assumed to have a supercooled ternary sulfate (STS) composition, and Type 2 PSCs are treated as water ice with a coexisting nitric acid trihydrate (NAT) phase. Sedimentation is treated by assuming that the PSC particles obey lognormal size distributions, resulting in a realistic mass flux of condensed phase H2O and HNO3. We examine a simulation of the Southern Hemisphere high‐latitude lower stratosphere winter and spring seasons driven by temperature and wind fields from a modified version of the National Center for Atmospheric Research (NCAR) Middle Atmosphere Community Climate Model Version 2 (MACCM2). Predicted PSC SADs and median radii for both Type 1 and Type 2 PSCs are consistent with observations. Gas phase HNO3 and H2O concentrations in the high‐latitude lower stratosphere qualitatively agree with Cryogenic Limb Array Etalon Spectrometer (CLAES) HNO3 and Microwave Limb Sounder (MLS) H2O observations. The residual denitrification and dehydration of the model polar vortex after polar winter compares well with atmospheric trace molecule spectroscopy (ATMOS) observations taken during November 1994. When the NOx and H2O emissions of a standard 500‐aircraft HSCT fleet with a NOx emission index of 5 are added, NOx and H2O concentrations in the Southern Hemisphere polar vortex before winter increase by up to 3%. This results in earlier onset of PSC formation, denitrification, and dehydration. Active Cly increases and produces small (∼1%) decreases in lower stratospheric vortex O3 concentrations during the spring relative to the HSCT‐free run.
Pollution from aircraft emissions in the North Atlantic flight corridor: Overview on the POLINAT projects
Authors: Schumann U. , Schlager H. , Arnold F. , Ovarlez J. , Kelder H. , Hov Ø. , Hayman G. , Isaksen I. S. A. , Staehelin J. , Whitefield P. D.
Published: September 2002

The Pollution From Aircraft Emissions in the North Atlantic Flight Corridor (POLINAT) projects were undertaken to investigate the impact of aircraft engine exhaust emissions on the state of the atmosphere in the North Atlantic flight corridor. Changes in the composition of the lower stratosphere and upper troposphere from aircraft emissions are identified from combined measurements and model analyses. Measurements were performed using the Deutsches Zentrum für Luft‐und Raumfahrt Falcon research aircraft and a Swissair B‐747 over the North Atlantic covering the altitude range 6 to 13 km in November 1994 and June/July 1995 and from August to November 1997. The measurements include those of nitrogen oxides, nitrous and nitric acids, sulfur dioxide, sulfuric acid, acetone, carbon dioxide, ozone, water vapor, carbon monoxide, aerosols, and meteorological parameters. The atmospheric composition was found to be highly variable, and emissions from sources at the surface or from lightning discharges also contribute strongly to the nitrogen oxides abundance and ozone formation. Contributions from aircraft emissions have been measured and identified in single and multiple plumes of several hours ages, and accumulation of such nitrogen oxides and particles emissions can be identified under certain conditions in and downstream of the flight corridor region. Acetone was found at high mixing ratios. The global and regional models predict ozone increases of 3 to 6% by current air traffic at the flight corridor altitude north of 30°N, in agreement with previous model analyses but too small to be measurable. In autumn, the upper troposphere is often humid with water vapor concentration far above ice saturation, providing conditions for persistent contrails.
Sensitivity of photochemical pollution using the adjoint of a simplified chemistry‐transport model
Authors: Menut L. , Vautard R. , Beekmann M. , Honoré C.
Published: September 2002

The nature of two summertime photooxidant pollution episodes over Paris is investigated by means of adjoint modeling. The first episode (July 12, 1994) is characteristic of a local production' episode, while the second (August 12, 1997) is mostly due to advection into the urban area of high concentrations of ozone. We calculate the sensitivities to emissions of individual primary species and to reaction rate coefficients using the adjoint of a simplified multibox model representing the urban and suburban areas of the city of Paris. Sensitivity to emissions demonstrates that the first episode is essentially sensitive to volatile organic compounds (VOC)/NOx emissions, while the second is sensitive to NOx emissions. These results also point out the two important emission activity categories: traffic and solvent use, the second one being more sensitive than the first one. Sensitivity to reaction rates indicates that oxidant production is only sensitive to a few reactions. The high sensitivity of photochemical pollutants peaks to particular chemical reactions points out the necessity to refine the knowledge of their reaction rates.
Implementation considerations of a conceptual precipitation model
Authors: Dolcine L. , Andrieu H. , French M. N. , Creutin J. D.
Published: September 2002

Some aspects of water management, such as flash flood analysis or sewerage management require spatially distributed rainfall estimates and forecasts over surface areas ranging from a few square kilometers to a few hundred square kilometers. Typically, these requirements cannot be satisfied by operational numerical weather prediction models. Faced with these constraints, an alternative solution consists of designing modeling tools consistent with observations routinely available for the survey of catchments, including ground meteorological data, voluminal radar data, satellite data, and operational numerical model output fields. This research headline is inspired by Georgakakos and Bras [1984a] who proposed a simplified dynamical approach considering an atmospheric column as a reservoir of liquid water to describe rainfall evolution. Initially, based on ground meteorological data, this approach was later adapted to voluminal radar data to model the evolution of vertically integrated rainwater content (VIL) in the atmospheric column. In the present work, the forecast lead time is extended through a proposed solution consisting of implementing a simplified precipitation model explicitly accounting for the cloud water content state. This paper demonstrates the potential interest of taking into account the cloud water state through a feasibility study. The first part of the paper presents the model formulation introducing a reservoir representing the cloud water state. The second part of the paper evaluates the potential improvement gained by introducing this component, and the influence of cloud and rainwater uncertainties on model performance. This evaluation utilizes rainwater content, cloud water content, and related meteorological variables produced by a meteorological microphysical monodimensional model. Results of modeling and forecast experiments are included to demonstrate the value of introducing the cloud water state. The experiments show improved forecast performance using the model accounting for cloud water compared with the simple extrapolation method and a related precipitation model dealing only with the rainwater content state.
Methods for cosine correction of broadband UV data and their effect on the relation between UV irradiance and cloudiness
Authors: Landelius T. , Josefsson W.
Published: September 2002

Irradiance measurements on a horizontal surface often deviate from theory where the irradiance is supposed to be proportional to the cosine of the angle of incidence. This discrepancy is known as the cosine error. In this paper, three different methods for cosine error correction are investigated. The simplest method is based on the assumption of an isotropic sky radiance distribution, regardless of sky conditions, and the irradiance is treated as a single component. In the second method the irradiance is divided into one direct solar and one diffuse sky component, where the latter is assumed to have an isotropic distribution. Finally, a third method also divides the irradiance into two components but under the assumption of an anisotropic sky radiance distribution. Irradiances under general sky conditions are found by interpolation between clear and overcast cases on the basis of sunshine duration or cloud cover. The three methods are applied to data from a Robertson‐Berger sunburning meter located in Norrköping, Sweden. Both methods, where the irradiance is divided into two components, produce acceptable and similar results, while the isotropic one‐component method does not.
Relationships between condensation nuclei number concentration, tides, and standard meteorological variables at Mace Head, Ireland
Authors: O'Brien Enda W. , Jennings S. Gerard , Geever Michael , Kleefeld Christoph
Published: September 2002

The set of hourly averaged condensation nuclei (CN) data collected at Mace Head during 1991–1994 was examined for relationships that might exist between CN number concentrations and the more commonly measured meteorological variables, including tides. CN number concentrations at Mace Head can be characterized by typically low “background” levels (less than about 700 particles cm−3) when the wind is from the west, somewhat higher “background” levels (1000–4000 particles cm−3) when the wind is from the east, with sporadic bursts of short‐lived discrete “events” of more than 10,000 cm−3for several hours. These events occur typically during early afternoon and are normally associated with slack winds and anomalously warm, dry air. They appear to be independent of pressure, wind direction and precipitation. They can occur any time during the year, although the strongest events tend to occur during spring and autumn. Large‐amplitude low tides also occur predominantly in the early afternoon during this observing period. We present evidence that large CN concentration events occur preferentially after exceptionally low tides during daylight. A neural network was employed to train the standard meteorological variables to predict CN concentrations. Baseline forecasts of CN counts for the final 180 days of the observing period were made using lagged values of all other variables. Further forecasts were made with some variables removed from the predictor set. The best correlation between the predicted values and the verifying data over the 180 days was 0.67, which was obtained from a 1‐hour forecast using knowledge of all variables except temperature. Other variables whose removal improved the forecast (or whose presence degraded it) were pressure and wind speed. The best predictors of CN values were wind direction, relative humidity, and time of day. An elementary “nearest neighbor,” or “historical analogue” approach to predicting the same set of CN values generated lower correlations with the verifying data but generated a much more accurate probability distribution function.
Temporal evolution of chlorine monoxide in the middle stratosphere
Authors: Ricaud Philippe , Chipperfield Martyn P. , Waters Joe W. , Russell James M. , Roche Aidan E.
Published: September 2002

The temporal evolution of stratospheric chlorine monoxide (ClO) at northern midlatitudes is studied over different scales: diurnal and seasonal variations. Data sets include temperature profiles, and ClO, HCl, ClONO2, NO2, O3, H2O, and CH4 mixing ratios as measured from 10 to 0.46 hPa (i.e., from ∼30 to ∼55 km) by the Microwave Limb Sounder (MLS), by the Halogen Occultation Experiment, and by the Cryogenic Limb Array Etalon Spectrometer instruments aboard the UARS satellite from at most September 1991 to June 1997 within the band 40°–50°N. The time evolution of these species is interpreted by comparison with results from a “zero‐dimensional” (0‐D) purely photochemical model and from the SLIMCAT three‐dimensional (3‐D) chemical transport model over the Plateau de Bure station (45°N, 10°E) from September 1991 to March 1998. A maximum confidence value for the yield in the reaction ClO + OH → HCl + O2 is deduced from the analysis to be in the range 0.05–0.10±0.03, which is consistent with recent laboratory data, suggesting a value of ∼0.05–0.06±0.02. Comparisons between the ClO diurnal variations measured by MLS and calculated by the 0‐D model agree to within 10% around the maximum of ClO (∼40 km) and within 5% elsewhere. The ClO diurnal variation is induced by variations in the partitioning with HOCl and ClONO2 below 50 km and by variations in the partitioning within the ClOx (=Cl+ClO) family above. The agreement between measured and modeled seasonal variations of ClO implies an evolution above 30 km essentially dictated by the variation in the partitioning with HCl, together with the partitioning within the ClOx family above 40 km. The differences between measured and modeled ClO seasonal variations above 50 km are attributed to uncertainties in the relative rates of the sources of HCl (reactions of Cl with CH4 and HO2).
Partitioning tropical oceanic convective and stratiform rains by draft strength
Authors: Atlas David , Ulbrich Carlton W. , Marks Frank D. , Black Robert A. , Amitai Eyal , Willis Paul T. , Samsury Christopher E.
Published: September 2002

The discrimination of convective from stratiform tropical oceanic rains by conventional radar‐based textural methods is problematic because of the small size and modest horizontal reflectivity gradients of the oceanic convective cells. In this work the vertical air motion measured by an aircraft gust probe is used as a discriminator which is independent of the textural methods. A threshold draft magnitude of ≈1 m s−1 separates the two rain types. Simultaneous airborne in situ observations of drop size distributions (DSD) made during the Tropical Ocean‐Global Atmosphere Coupled Ocean‐Atmosphere Response Experiment (TOGA COARE) were used to compute Z, R, and other integral parameters. The data were quality controlled to minimize misclassifications. The convective and stratiform rains, observed just below the melting level but adjusted to surface air density, are characterized by power law Z‐R relations (Z = 129R1.38 (convective) and 224R1.28 (stratiform)). However, at R < 10 mm h−1, the convective population is essentially coincident with the small‐drop size, small‐Z portion of the stratiform population. Tokay and Short [1996] found a similar result when their algorithm did not separate the rain types unambiguously at R < 10 mm h−1. The physical reasons for the wide variability of the drop size spectra and Z‐R points in stratiform rain and their overlap with that of convective rain are proposed. The subtle distinctions in the microphysical properties and the Z‐R relations by rain type could not be found by Yuter and Houze (YH) using the same airborne DSD data set as that in this work and a radar‐based textural classification algorithm.
Ozone production efficiency and loss of NOx in power plant plumes: Photochemical model and interpretation of measurements in Tennessee
Authors: Sillman Sanford
Published: September 2002

A model for photochemical evolution in power plants has been developed and used in combination with measurements to investigate ozone production efficiency (OPE) per NOx and the rate of photochemical removal of NOx. The model is a two‐dimensional (2‐D) Lagrangian model with 1 km horizontal resolution and vertical resolution ranging from 25 m to 300 m, nested within a larger 3‐D regional model. These results are compared with measured O3, Nox, and SO2 along aircraft transects through power plant plumes (Ryerson et al., 1998). Measured flux of NOx and SO2 in plume transects is 33%–50% lower than plume emission rates, suggesting that a fraction of plume emissions remained above the top of the convective mixed layer. The measured loss rate of SO2 is greater than expected from photochemistry and surface deposition, suggesting the possibility of cumulus venting of the boundary layer. If model parameters are adjusted to reflect this hypothesized transport of plume air above the boundary layer, then the model NOx removal rate agrees with measurements. OPE is derived from measured fluxes of O3, NOx and SO2 in the plume. The resulting OPE (1.2–2.5) is somewhat higher than the previous estimate by Ryerson et al. OPE in models is slightly higher than measurements (2–3). Higher OPE (3–4) is predicted for power plant plumes 18 hours downwind of the emission source. OPE for these far downwind plumes is comparable to OPE for other emission sources of NOx. OPE and NOx lifetime are both correlated with plume NOx concentrations. Model results suggest that OPE inferred from statistical correlations between O3 and tracers such as SO2 underestimate the true OPE in situations where the correlation between O3 and SO2 is nonlinear.
Meteorological controls on ozone at an elevated eastern United States regional background monitoring site
Authors: Cooper O. R. , Moody J. L.
Published: September 2002

To determine synoptic‐ and regional‐scale meteorological controls on ozone upwind of the North Atlantic Ocean, we developed an ozone climatology for Big Meadows, Virginia. Three methodologies were employed to analyze the 6‐year ozone data set (1989–1994) from this elevated, regional, background monitoring site. (1)A springtime case study showed that repeated dynamic processes associated with three consecutive cold‐front passages were related to a cyclic pattern in ozone variation. Back‐trajectory analysis suggests a stratospheric as well as anthropogenic influence on the enhanced ozone events. (2) Analyses of the meteorology and back trajectories associated with daytime ozone events above the 90th percentile and below the 10th percentile revealed strong contrasts in transport history. Enhanced events were strongly associated with dry high‐pressure conditions and half were associated with descent through surface anticyclones. Conversely, the depleted‐ozone trajectories were typically associated with low‐pressure systems and were more likely to be associated with ascending or low‐level flow than descending flow. (3) Back trajectories were grouped according to similar transport paths to try to explain ozone variance by airmass transport. In a previous study, segregation of ozone values by transport path explained a relatively large amount of the ozone variance at Bermuda. However, in our study, this approach explained only a small portion of the ozone variance. We attribute the differences in explained variance at the two sites to complex interactions between transport and photochemistry over the continent and a simplified transport regime over the western North Atlantic Ocean.
Influence of natural hydrocarbons on ozone formation in an isolated power plant plume
Authors: Luria M. , Tanner R. L. , Imhoff R. E. , Valente R. J. , Bailey E. M. , Mueller S. F.
Published: September 2002

On 4 days during the 1995 Southern Oxidant Study (SOS), air samples were taken in the plume of the Cumberland Power Plant in Tennessee using an instrumented helicopter. On these days a notable difference in excess ozone in the plumes was observed. Excess ozone varied from 20 ppb on July 7, 1995, up to 55 ppb on July 16. While the total amount of non‐methane VOC was quite similar, significant differences were observed in the levels of reactive hydrocarbons, mostly isoprene. This study examines the parameters that govern both emission rates of isoprene and its dispersion. These include temperature and wind speed on the surface and aloft, total solar radiation, and the height of the mixed layer. The results revealed and computer model simulations confirmed that although differences were not very large, the combinations of all of these parameters favored lower ambient isoprene levels and, consequently, lower ozone production on July 7 and higher production on the 3 other days.