bluuebunny/crossref_metadata_2025 huggingface dataset:
Factors influencing the stable carbon isotopic signature of methane from combustion and biomass burning
Authors: Chanton Jeffrey P. , Rutkowski Christine M. , Schwartz Candace C. , Ward Darold E. , Boring Lindsay
Published: September 2002

Factors controlling the δ13C of methane released by combustion include the combustion efficiency of the fire and the δ13C of the fuel. Smoldering fires produced13C‐depleted methane relative to hot, flaming fires in controlled forest and grassland burns and within a wood stove. Pine forest burns in the southeastern United States produced methane which ranged from −21 to −30‰, while African grassland burns varied from −17 to −26‰, depending upon combustion phase. African woodland burns produced methane at −30‰. In forest burns in the southeastern United States, the δ13C of methane released with smoldering was significantly13C depleted relative to methane released under hot flaming conditions. Methane released with smoldering was depleted by 2–3‰ relative to the fuel δ13C, but this difference was not significant. The δ13C of methane produced in a variety of wood stove conditions varied from −9 to −25‰ and also depended upon combustion efficiency. Similar results were found for methane produced by gasoline automobile engines, where the δ13C of methane varied from −9 to −22‰. For combustion occurring within the confining chamber of a wood stove or engine the δ13C of methane was clearly13C enriched relative to the δ13C of the fuel, possibly because of preferential combustion of12CH4in the gas phase. Significant quantities of ethylene (up to 25 to 50% of methane concentrations) were produced in southeastern U.S. forest fires, which may have consequences for physiological and reproductive responses of plants in the ecosystem. Methane production in these fires varied from 0.2 to 8.5% of the carbon dioxide production.
Sensitivity of mean age and long‐lived tracers to transport parameters in a two‐dimensional model
Authors: Li Shuhua , Waugh Darryn W.
Published: September 2002

Recent comparisons of modeled and observed stratospheric mean age show large differences between model predictions and data as well as between individual models, indicating large variations (and deficiencies) in model transport. We explore here the sensitivity of the mean age to different components of the transport by examining the effect of varying the transport parameters within a two‐dimensional model. The mean age is shown to be sensitive to changes in advective circulation and diffusion coefficients, with the sensitivity being largest for changes in the circulation strength. In most cases the magnitudes, but not the orientation, of the mean age isopleths change. However, if the horizontal mixing is made very small within middle latitudes or large within low latitudes, large changes occur in the orientation of mean age isopleths. The effects of these transport changes on chemically active long‐lived tracers are also examined. It is found that the lower stratospheric concentrations are relatively insensitive to the transport changes if these changes do not alter the general shape of mean age isopleths. However, significant changes occur when the transport parameters are modified so as to change the orientation of the mean age (and long‐lived tracer) isopleths.
Impact of NOx emissions from subsonic aircraft: Inclusion of plume processes in a three‐dimensional model covering Europe, North America, and the North Atlantic
Authors: Kraabøl A. G. , Flatøy F. , Stordal F.
Published: September 2002

A three‐dimensional (3‐D) regional chemistry transport model covering Europe, North America, and the North Atlantic Flight Corridor (NAFC) has been used to study the impact of NOx emissions from subsonic aircraft when plume processes were taken into account. An aircraft plume model has been used to quantify the chemical conversion of NOx to reservoir species. With the turbulent conditions used, the plume was spread to scales resolved by the 3‐D model after 15 hours. The conversion of NOx was calculated as a function of time of emission, latitude, and background concentration of ozone and NOx under summer conditions. The conversion of NOx in the plume showed a strong variation with time of emissions. In some cases, more than 50% of the emitted NOx was converted to reservoir species after 15 hours at midlatitudes. The results from the plume model were used to modify the aircraft emissions used as inputs to the 3‐D regional model. When the aircraft NOx emissions were instantaneously mixed over the model grid area, a standard procedure in regional and global models, monthly averaged NOx increases of up to 70 parts per trillion (ppt) were calculated over the midwest United States and over England in July 1998. The highest ozone increase was calculated northeast of Scandinavia (2.7 parts per billion (ppb)). When plume processes were taken into account, the corresponding monthly averaged NOx contribution from aircraft was reduced by ∼40% or less. Ozone was lowered by up to ∼30% within the NAFC, while the peak over Scandinavia was reduced by ∼20%.
AlGaN Photodiodes For Monitoring Solar UV Radiation
Authors: Muñoz E. , Monroy E. , Calle F. , Omnès F. , Gibart P.
Published: September 2002

AlGaN‐based Schottky barrier photodiodes, aimed to monitor the solar UV radiation, have been fabricated and characterized. AlGaN semiconductor layers were grown by metal‐organic vapor phase epitaxy on sapphire substrates, and the Al mole fraction was varied between zero and 0.35. The evolution of the characteristics of these UV detectors with the Al content is presented. Schottky barrier AlxGal−xN photodetectors show a very fast response that is independent of the optical power, and their visible rejection ratio is higher than 103. Al0.2Ga0.8N Schottky barriers are very good candidates for monitoring the UV‐B band. It is also reported that by using the proper Al mole fraction, the erythema‐weighted action of the solar UV radiation can be directly determined by AlGaN photodiodes, without any filter, for the first time.
Removal of SO2 from the marine boundary layer over the Atlantic Ocean: A case study on the kinetics of the heterogeneous S(IV) oxidation on marine aerosols
Authors: Krischke Udo , Staubes Regina , Brauers Theo , Gautrois Michael , Burkert Jan , Stöbener Dirk , Jaeschke Wolfgang
Published: September 2002

Measurements of SO2 and NSS‐SO42− were made over the Atlantic Ocean on board the RV Polarstern from October 9 to November 2, 1996, as part of the ALBATROSS campaign. The measurements were performed between 66.7°N and 37.8°S with a mean longitude of approximately 30°W. The most frequent background values for SO2 were found to be 13 parts per trillion by volume (pptv) (0.54 nmol m−3 at standard ambient temperature and pressure (SATP)) in the Southern Hemisphere, and 15 pptv (0.62 nmol m−3 SATP) in the Northern Hemisphere. The mean values for total NSS‐SO42− in particles with a d>0.2 μm were (5.99±2.93) nmol m−3 (SATP) in the Southern Hemisphere, and (8.93±5.29) nmol m−3 (SATP) in the Northern Hemisphere. An analysis of the size‐fractionated aerosol samples (d >1 μm and 0.2 μm < d < 1 μm) of NSS‐SO42− shows that (34±13)% of the total NSS‐SO42− exists in coarse mode particles with d>1 μm. The main fraction of this NSS‐SO42− is most likely produced by the oxidation of dissolved SO2 via heterogeneous reactions occurring in the aqueous phase of coarse mode marine aerosols. A case study on the kinetics of this oxidation pathway was conducted during ALBATROSS. October 12, 1996, the ship sailed in the plume of a volcano on Iceland during its eruption from September 30 to October 13, 1996, as indicated by trajectory analysis and by the measurements of NSS‐SO42−, SO2, CO, and Hg. An empirical physicochemical approach considering the atmosphere as a natural flow reactor is used for the presented case study. The determined pseudo‐first‐order reaction rate constant for the oxidation of SO2 on marine aerosols is 3.31×10−4 s−1 at 25°C. Assuming that the occurrence of coarse mode marine aerosols is the rate‐limiting variable of the reaction, the second‐order reaction rate constant is found to be 1.32×10−6 cm3 s−1 particle−1 at 25°C. These values are in good agreement with results of previous field experiments as well as with the results of model studies.
SAGE (version 5.96) ozone trends in the lower stratosphere
Authors: Cunnold D. M. , Wang H. J. , Thomason L. W. , Zawodny J. M. , Logan J. A. , Megretskaia I. A.
Published: September 2002

Ozone retrievals from Stratospheric Aerosol and Gas Experiment (SAGE) II version 5.96 (v5.96) below ∼25 km altitude are discussed. This version of the algorithm includes improved constraints on the wavelength dependence of aerosol extinctions based on the ensemble of aerosol size distribution measurements. This results in a reduction of SAGE ozone errors in the 2 years after the Mount Pinatubo eruption. However, SAGE ozone concentrations are still ∼10% larger than ozonesonde and Halogen Occultation Experiment (HALOE) measurements below 20 km altitude under nonvolcanic conditions (and by more than this in the tropics). The analysis by Steele and Turco [1997] suggests that the SAGE ozone overpredictions are in the wrong direction to be explained by aerosol extinction extrapolation errors. Moreover, preliminary SAGE II v6.0a retrievals suggest that they are partially accounted for by geometric difficulties at low altitudes in v5.96 and prior retrievals. SAGE ozone trends for the 1979–1996 and 1984–1996 periods are calculated and compared, and the sources of trend errors are discussed. These calculations are made after filtering out ozone data during periods of high, local aerosol extinctions. In the lower stratosphere, below ∼28 km altitude, there is shown to be excellent agreement in the altitudinal structure of ozone decreases at 45°N between SAGE and ozonesondes with the largest decrease in both between 1979 and 1996 having occurred below 20 km altitude, amounting to 0.9±0.7% yr−1 (2σ) at 16 km altitude. However, in contrast to the fairly steady decreases at 45°N, both SAGE measurements and Lauder ozonesondes show ozone increases at 45°S over the period from the mid‐1980s to 1996 of 0.2±0.5% yr−1 (2σ) from 15 to 20 km altitude. The SAGE data suggest that this increase is a wintertime phenomenon which occurs in the 15–20 km height range. Changes in dynamics are suggested as the most likely cause of this increase. These hemispheric differences in ozone trends are supported by ozone column measurements by the Total Ozone Mapping Spectrometer (TOMS).
Ball lightning as a self‐organization phenomenon
Authors: Sanduloviciu M. , Lozneanu E.
Published: September 2002

The genesis and characteristics of ball lightning are explained in the frame of a new self‐organization physical scenario suggested by laboratory investigations of formation and stability of self‐consistent extended macroscopic space charge configurations. These are known as fireballs in dc gas discharges and as plasmoids in gas discharges sustained by a radio frequency electric field. We justify the proposed explanation with a test experiment able to simulate step by step, under controllable laboratory conditions, the succession of physical processes whose final product is a gaseous stable flaming globe revealing characteristics usually attributed to ball lightning. Although involving energies much lower than that developed in the Earth's atmosphere during thunderstorms, the described experimental simulation evidences that self‐organization is, very probably, the most suitable natural phenomenon able to explain the ball lightning appearance.
FORTE observations of simultaneous VHF and optical emissions from lightning: Basic phenomenology
Authors: Suszcynsky D. M. , Kirkland M. W. , Jacobson A. R. , Franz R. C. , Knox S. O. , Guillen J. L. L. , Green J. L.
Published: September 2002

Preliminary observations of simultaneous VHF and optical emissions from lightning as seen by the Fast on‐Orbit Recording of Transient Events (FORTE) spacecraft are presented. VHF/optical waveform pairs are routinely collected both as individual lightning events and as sequences of events associated with cloud‐to‐ground (CG) and intracloud (IC) flashes. CG pulses can be distinguished from IC pulses on the basis of the properties of the VHF and optical waveforms but mostly on the basis of the associated VHF spectrograms. The VHF spectrograms are very similar to previous ground‐based HF and VHF observations of lightning and show signatures associated with return strokes, stepped and dart leaders, attachment processes, and intracloud activity. For a typical IC flash, the FORTE‐detected VHF is generally characterized by impulsive broadband bursts of emission, and the associated optical emissions are often highly structured. For a typical initial return stroke, the FORTE‐detected VHF is generated by the stepped leader, the attachment process, and the actual return stroke. For a typical subsequent return stroke, the FORTE‐detected VHF is mainly generated by dart leader processes. The detected optical signal in both return stroke cases is primarily produced by the in‐cloud portion of the discharge and lags the arrival of the corresponding VHF emissions at the satellite by a mean value of 243 μs. This delay is composed of a transit time delay (mean of 105 μs) as the return stroke current propagates from the attachment point up into the region of in‐cloud activity plus an additional delay due to the scattering of light during its traversal through the clouds. The broadening of the light pulse during its propagation through the clouds is measured and used to infer a mean of this scattering delay of about 138 μs (41 km additional path length) for CG light. This value for the mean scattering delay is consistent with the Thomason and Krider [1982] model for light propagation through clouds.
An examination of the inorganic chlorine budget in the lower stratosphere
Authors: Bonne G. P. , Stimpfle R. M. , Cohen R. C. , Voss P. B. , Perkins K. K. , Anderson J. G. , Salawitch R. J. , Elkins J. W. , Dutton G. S. , Jucks K. W. , Toon G. C.
Published: September 2002

We use the first simultaneous in situ measurements of ClONO2, ClO, and HCl acquired using the NASA ER‐2 aircraft during the Photochemistry of Ozone Loss in the Arctic Region in Summer (POLARIS) mission to test whether these three compounds quantitatively account for total inorganic chlorine (Cly) in the lower stratosphere in 1997. We find (ClO + ClONO2 + HCl)/Cly = 0.92±0.10, where Cly is inferred from in situ measurements of organic chlorine source gases. These observations are consistent with our current understanding of the budget and partitioning of Cly in the lower stratosphere. We find no evidence in support of missing inorganic chlorine species that compose a significant fraction of Cly. We apply the analysis to earlier ER‐2 observations dating from 1991 to investigate possible causes of previously observed discrepancies in the inorganic chlorine budget. Using space shuttle, satellite, balloon, and aircraft measurements in combination with ER‐2 data, we find that the discrepancy is unlikely to have been caused by missing chlorine species or an error in the photolysis rate of chlorine nitrate. We also find that HCl/Cly is not significantly controlled by aerosol surface area density in the lower stratosphere.
Analysis of the processing of Nashville urban emissions on July 3 and July 18, 1995
Authors: Daum P. H. , Kleinman L. , Imre D. G. , Nunnermacker L. J. , Lee Y.‐N. , Springston S. R. , Newman L. , Weinstein‐Lloyd J.
Published: September 2002

This paper analyzes data obtained on July 3 and 18, 1995, during the summer 1995 Southern Oxidant Study (SOS) field campaign. In a previous paper [Nunnermacker et al., 1998] we analyzed measurements of key species that contribute to formation of O3 in the Nashville urban plume and presented a semiquantitative picture of O3 production in the plume from the point of emission to locations where no net O3 was being formed. In this paper we use a box model constrained by observed concentrations of stable species to obtain a detailed mechanistic description of the instantaneous processing of urban emissions at various times in the chemical evolution of the urban plume. Instantaneous ozone production rates and efficiencies with respect to NOx and to primary radical production are examined. At high NOx concentrations in the fresh urban plume the O3 production rate was found to be directly proportional to the hydrocarbon to NOx reactivity ratio. At lower NOx concentrations, corresponding to the mature urban plume and the background atmosphere, the O3 production rate was found to be directly proportional to the NOx concentration and independent of the hydrocarbon reactivity. NOx was found to be most efficiently used for ozone production at low NOx concentrations. In contrast, the efficiency with which the system uses primary radicals was found to be very low at low NOx concentrations and to peak at a NOx concentration of approximately 4 ppbv. A sensitivity study of the instantaneous O3 production rates to changes in NOx or hydrocarbon concentrations showed that the instantaneous O3 production rate at the center of the urban plume, when half of the urban NOx emissions had been processed, is hydrocarbon sensitive. However, O3 production becomes NOx sensitive as the plume matures.
Perturbation dynamics in atmospheric chemistry
Authors: Farrell Brian F. , Ioannou Petros J.
Published: September 2002

Current understanding of how chemical sources and sinks in the atmosphere interact with the physical processes of advection and diffusion to produce local and global distributions of constituents is based primarily on analysis of chemical models. One example of an application of chemical models which has important implications for global change is to the problem of determining sensitivity of chemical equilibria to changes in natural and anthropogenic sources. This sensitivity to perturbation is often summarized by quantities such as a mean lifetime of a chemical species estimated from reservoir turnover time or the decay rate of the least damped normal mode of the species obtained from eigenanalysis of the linear perturbation equations. However, the decay rate of the least damped normal mode or a mean lifetime does not comprehensively reveal the response of a system to perturbation. In this work, sensitivity to perturbations of chemical equilibria is assessed in a comprehensive manner through analysis of the system propagator. When chemical perturbations are measured using the proper linear norms, it is found that the greatest disturbance to chemical equilibrium is achieved by introducing a single chemical species at a single location, and that this optimal perturbation can be easily found by a single integration of the transpose of the dynamical system. Among other results are determination of species distributions produced by impulsive, constant, and stochastic forcing; release sites producing the greatest and least perturbation in a chosen constituent at another chosen site; and a critical assessment of chemical lifetime measures. These results are general and apply to any perturbation chemical model, including three‐dimensional global models, provided the perturbations are sufficiently small that the perturbation dynamics are linear.
Mountain reference technique: Use of mountain returns to calibrate weather radars operating at attenuating wavelengths
Authors: Serrar Soumia , Delrieu Guy , Creutin Jean‐Dominique , Uijlenhoet Remko
Published: September 2002

The Mountain Reference Technique (MRT) was proposed as a means to perform a self‐calibration of a weather radar system operating at an attenuating wavelength in a mountainous environment. Two convective rain events observed during the Grenoble 97–98 Experiment are selected here for an illustration and a further verification of the method at X band: the June 16, 1997, event is a medium event with maximum path‐integrated attenuations (PIAs) of about 15 dB over a 9‐km path, while the July 3, 1998, event is quite extraordinary with (1) a maximum PIA of 50 dB over the same distance and (2) the temporary presence of hail. An improved scheme is proposed for the MRT parameter estimation procedure with a more satisfactory treatment of such high‐attenuation effects. It is shown that the optimal calibration factors obtained for the two rain events are almost equal to each other, a comforting result with respect to the radar equipment stability during the corresponding 1‐year period. Although the MRT is based on reflectivity and attenuation measurements only, validation of the rain rate retrieval algorithms with respect to rain gage data for the June 16, 1997, rain event showed that this technique is relevant in terms of rain rate estimation. In particular, the MRT‐calibrated Hitschfeld‐Bordan algorithm provides satisfactory results for this medium‐attenuation event. However, the July 3 case clearly demonstrates that this algorithm cannot correct for such high‐attenuation effects because of its inherent instability. For both rain events the Marzoug‐Amayenc algorithm, originally proposed for spaceborne configurations, is found to be stable and efficient in terms of rain rate estimation. These interesting features are counterbalanced by the fact that the algorithm implementation is limited to directions for which PIA measurements are actually available.
Surface submicron aerosol chemical composition: What fraction is not sulfate?
Authors: Quinn P. K. , Bates T. S. , Miller T. L. , Coffman D. J. , Johnson J. E. , Harris J. M. , Ogren J. A. , Forbes G. , Anderson T. L. , Covert D. S. , Rood M. J.
Published: September 2002

Measurements of submicron aerosol mass and the mass of major ionic components have been made over the past 5 years on cruises in the Pacific and Southern Oceans and at monitoring stations across North America (Barrow, Alaska; Cheeka Peak, Washington; Bondville, Illinois; and Sable Island, Nova Scotia). Reported here are submicron concentrations of aerosol mass, nonsea salt (nss) sulfate, sea salt, methanesulfonate, other nss inorganic ions, and residual, or chemically unanalyzed, mass. Residual mass concentrations are based on the difference between simultaneously measured aerosol mass and the mass of the major ionic components. A standardized sampling protocol was used for all measurements making the data from each location directly comparable. For the Pacific and Southern Oceans, concentrations of the chemical components are presented in zonally averaged 20° latitude bins. For the monitoring stations, mean concentrations are presented for distinct air mass types (marine, clean continental, and polluted based on air mass back trajectories). In addition, percentile information for each chemical component is given to indicate the variability in the measured concentrations. Mean nss sulfate submicron aerosol mass fractions for the different latitude bins of the Pacific ranged from 0.14±0.01 to 0.34±0.03 (arithmetic mean±absolute uncertainty at the 95% confidence level). The lowest average value occurred in the 40°–60°S latitude band where nss sulfate concentrations were low due to the remoteness from continental sources and sea salt concentrations were relatively high. Mean nss sulfate aerosol mass fractions were more variable at the monitoring stations ranging from 0.13±0.004 to 0.65±0.02. Highest values occurred in polluted air masses at Bondville and Sable Island. Sea salt mean mass fractions ranged between 0.20±0.02 and 0.53±0.03 at all latitude bands of the Pacific (except 20°–40°N where the residual mass fraction was relatively high) and at Barrow. The concentration of residual mass was significant at the 95% confidence level at all stations and all Pacific latitude bands (assuming that all errors were random and normally distributed and contamination of the samples did not occur beyond that accounted for by storage and transport uncertainties). Mean residual mass fractions ranged from 0.09±0.07 to 0.74±0.04.
Retrieving the vertical structure of the effective aerosol complex index of refraction from a combination of aerosol in situ and remote sensing measurements during TARFOX
Authors: Redemann J. , Turco R. P. , Liou K. N. , Russell P. B. , Bergstrom R. W. , Schmid B. , Livingston J. M. , Hobbs P. V. , Hartley W. S. , Ismail S. , Ferrare R. A. , Browell E. V.
Published: September 2002

The largest uncertainty in estimates of the effects of atmospheric aerosols on climate stems from uncertainties in the determination of their microphysical properties, including the aerosol complex index of refraction, which in turn determines their optical properties. A novel technique is used to estimate the aerosol complex index of refraction in distinct vertical layers from a combination of aerosol in situ size distribution and remote sensing measurements during the Tropospheric Aerosol Radiative Forcing Observational Experiment (TARFOX). In particular, aerosol backscatter measurements using the NASA Langley LASE (Lidar Atmospheric Sensing Experiment) instrument and in situ aerosol size distribution data are utilized to derive vertical profiles of the “effective” aerosol complex index of refraction at 815 nm (i.e., the refractive index that would provide the same backscatter signal in a forward calculation on the basis of the measured in situ particle size distributions for homogeneous, spherical aerosols). A sensitivity study shows that this method yields small errors in the retrieved aerosol refractive indices, provided the errors in the lidar‐derived aerosol backscatter are less than 30% and random in nature. Absolute errors in the estimated aerosol refractive indices are generally less than 0.04 for the real part and can be as much as 0.042 for the imaginary part in the case of a 30% error in the lidar‐derived aerosol backscatter. The measurements of aerosol optical depth from the NASA Ames Airborne Tracking Sunphotometer (AATS‐6) are successfully incorporated into the new technique and help constrain the retrieved aerosol refractive indices. An application of the technique to two TARFOX case studies yields the occurrence of vertical layers of distinct aerosol refractive indices. Values of the estimated complex aerosol refractive index range from 1.33 to 1.45 for the real part and 0.001 to 0.008 for the imaginary part. The methodology devised in this study provides, for the first time, a complete set of vertically resolved aerosol size distribution and refractive index data, yielding the vertical distribution of aerosol optical properties required for the determination of aerosol‐induced radiative flux changes.
On the budget of hydroxyl radicals at Schauinsland during the Schauinsland Ozone Precursor Experiment (SLOPE96)
Authors: Volz‐Thomas Andreas , Kolahgar Bita
Published: September 2002

The concentration of hydroxyl radicals is estimated from the degradation of NOx and selected volatile organic compounds (VOCs) during the transport of polluted air masses from the city of Freiburg to the Schauinsland mountain through a steep valley called “Großes Tal.” The approach is based upon chemical and meteorological measurements made during the Schauinsland Ozone Precursor Experiment (SLOPE96) at two ground‐based sites and aboard a small aircraft. Separation of chemistry and transport is achieved through the degradation of chemical compounds with significantly different reactivity towards OH. The transport time of the air between the two measurements (90±5 min) and the influence of mixing with background air on the calculated OH concentration is quantified with the help of a dispersion experiment with SF6 and from airborne chemical measurements. The OH concentration (7– 0 × 106 cm−3) is almost a factor of 2 larger than what is calculated with a chemical box model constrained by the measured trace gas concentrations and photolysis rates. The radical budget can be closed within the experimental uncertainties, when an upper limit is adopted for the photolysis of nitrous acid, in addition to the radical production from photolysis of ozone, H2O2, and carbonyl compounds as well as ozonolysis of unsaturated VOCs. Biogenic VOCs (i.e., isoprene, terpenes, and a number of oxidated compounds) comprise about half of the total VOC reactivity in the transported plume. The results from SLOPE96 confirm the assumptions made in the analysis of an earlier experiment conducted in 1992, when noontime OH concentrations of 6 ‐ 8×106 cm−3 were derived in the presence of NOx mixing ratios between 70 ppb at the entrance of the valley and 15 ppb at Schauinsland. Comparison with direct measurements from different studies qualitatively reveals the expected dependence of [OH] on the NO2 mixing ratio with a maximum around 1–2 ppb of NO2.
Parameterization of cold‐season processes in the MAPS land‐surface scheme
Authors: Smirnova Tatiana G. , Brown John M. , Benjamin Stanley G. , Kim Dongsoo
Published: September 2002

A coupled atmospheric/land‐surface model covering the conterminous United States with an associated 1‐hour atmospheric data assimilation cycle, the Mesoscale Analysis and Prediction System (MAPS), has been improved to include a snow accumulation/melting scheme and also parameterization of processes in frozen soil. The new aspects of the land‐surface model are described in this paper, along with detailed one‐dimensional (1‐D) tests using an 18‐year observation data set from Valday, Russia. These tests show that the MAPS 1‐D soil/vegetation/snow model is capable of providing accurate simulations over multiyear periods at locations with significant snow cover and frozen soil. A statistical analysis of the tests shows the expected improvement in snow depth, skin temperature, and especially in runoff from inclusion of these additional surface processes during the spring melting season. This performance in 1‐D tests is a necessary prerequisite for robust long‐term behavior of soil temperature and moisture fields and other components of the hydrological cycle in the 3‐D MAPS coupled assimilation cycle.
Measurements of nitrogen oxides at the tropopause: Attribution to convection and correlation with lightning
Authors: Jeker Dominique P. , Pfister Leonhard , Thompson Anne M. , Brunner Dominik , Boccippio Dennis J. , Pickering Kenneth E. , Wernli Heini , Kondo Yutaka , Staehelin Johannes
Published: September 2002

NOx (NO and NO2) and ozone were measured on 98 flights during August to November 1997 in the framework of the projects Pollution From Aircraft Emissions in the North Atlantic Flight Corridor (POLINAT 2) and Subsonic Assessment Ozone and Nitrogen Oxide Experiment (SONEX). The fully automated measurement system Nitrogen Oxides and Ozone Along Air Routes (NOXAR) was permanently installed aboard an inservice Swissair B‐747 airliner operating in the North Atlantic Flight Corridor. Below the tropopause, predominantly over the U.S. east coast, the patchy occurrence of NOx enhancements up to 3000 parts per trillion by volume (pptv) was observed frequently and led to a lognormal probability density function of NOx. These plumes extend over several hundred kilometers. In three case studies the origin of such plumes was investigated using back trajectories, satellite infrared images, and lightning observations from the U.S. National Lightning Detection Network (NLDN) and the Optical Transient Detector (OTD) satellite instrument. In the case of frontal activity above the continental United States, the location of NOx plumes was explained with maps of convective influence. In another case, NOx seems to have been produced by lightning in a marine thunderstorm over the eastern Atlantic. Lightning activity triggered over the warm Gulf Stream is found to be an important source for the regional upper tropospheric NOx budget, at least for the time period considered. With a method that we call “lightning tracing” we show for the first time that (in some cases) the number of lightning flashes, accumulated along back trajectories, was proportional to the NOx concentrations observed several hundred kilometers downwind of the anvil outflows. We suggest that mixing processes in convective clouds reduce the initially highly heterogeneous NOx field rapidly, but that following this phase, the structure of large‐scale plumes remains stable over relatively long periods of time (as they decay).
Photochemistry of the African troposphere: Influence of biomass‐burning emissions
Authors: Marufu L. , Dentener F. , Lelieveld J. , Andreae M. O. , Helas G.
Published: September 2002

The relative importance of biomass‐burning (pyrogenic) emissions from savannas, deforestation, agricultural waste burning, and biofuel consumption to tropospheric ozone abundance over Africa has been estimated for the year 1993, on the basis of global model calculations. We also calculated the importance of this emission source to tropospheric ozone in other regions of the world and compared it to different sources on the African regional and global scales. The estimated annual average total tropospheric ozone abundance over Africa for the reference year is 26 Tg. Pyrogenic, industrial, biogenic, and lightning emissions account for 16, 19, 12, and 27%, respectively, while stratospheric ozone input accounts for 26%. In the planetary boundary layer over Africa, the contribution by biomass burning is ∼24%. A large fraction of the African biomass‐burning‐related ozone is transported away from the continent. On a global scale, biomass burning contributes ∼9% to tropospheric ozone. Our model calculations suggest that Africa is the single most important region for biomass‐burning‐related tropospheric ozone, accounting for ∼35% of the global annual pyrogenic ozone enhancement of 29 Tg in 1993.
Laboratory study on heterogeneous degradation of methyl chloroform (CH3CCl3) on aluminosilica clay minerals as its potential tropospheric sink
Authors: Kutsuna Shuzo , Takeuchi Koji , Ibusuki Takashi
Published: September 2002

Heterogeneous reactions of methyl chloroform (1,1,1‐trichloroethane, CH3CCl3) with alminosilica clay particles were examined between 288 and 313 K as a potential sink. Allophane and halloysite particles exhibited the activity to transform CH3CCl3 to 1,1‐dichloroethene (CH2 = CCl2). The dependence of the reaction rate on the pretreatment, temperature, and relative humidity suggested that the reaction could proceed under environmental conditions. Illumination of light with wavelength longer than 300 nm did not affect CH3CCl3 decay but caused heterogeneous degradation of CH2 = CCl2 on clay particles. The lower limit of overall sticking coefficient for fresh allophane and halloysite particles was estimated to be 6×10−9 and 1.1×10−8, respectively. Heterogeneous degradation of CH3CCl3 on mineral aerosols and/or soils is worth taking into consideration in deriving tropospheric OH concentrations from global budget concentrations of CH3CCl3.
Temperature dependence of the absorption cross sections of formaldehyde between 223 and 323 K in the wavelength range 225–375 nm
Authors: Meller Richard , Moortgat Geert K.
Published: September 2002

UV absorption cross sections of formaldehyde (HCHO) have been measured with a spectral resolution of 0.025 nm in the wavelength range 225–375 nm at 298 K using a diode array detector. At selected temperatures ranging from 223 to 323 K, measurements have been conducted to obtain temperature gradients in the wavelength range 250–356 nm. Error limits for the reported absorption cross sections are ±5% but at least ±3×10−22 cm2 molecule−1. For the temperature gradients, uncertainties are <8%. Spectra and temperature gradients are compared with earlier measurements.
Global gridded emission inventories of α‐hexachlorocyclohexane
Authors: Li Y. F. , Scholtz M. T. , van Heyst B. J.
Published: September 2002

Emission factors of α‐hexachlorocyclohexane, the major isomer of technical hexachlorocyclohexane (HCH) for spray events and tilling events, are distributed on a 1°×1° longitude and latitude grid system. Estimations of global gridded α‐HCH emissions in 1980 and 1990 due to 15 consecutive years of application of technical HCH are presented. The total global usage of α‐HCH was estimated to be around 290 kt in 1980 and 59 kt in 1990. Total global α‐HCH emissions in 1980 were 184 kt, 92.5% of which was contributed by the current use of α‐HCH in 1980 and 7.5%, by the residues due to the use of technical HCH since 1966. Total global α‐HCH emissions in 1990 were 44 kt, 93% of which was contributed by the current use of α‐HCH in 1990 and 7%, by the residues due to the use of technical HCH since 1976. In 1980 approximately 74% of the global α‐HCH emissions originated in the Northern Hemisphere midlatitudes, followed by around 19% in the Northern Hemisphere tropics, while in 1990 approximately 54% of the global α‐HCH emissions originated in the Northern Hemisphere tropics, followed by around 37% in the Northern Hemisphere midlatitudes. Emissions of α‐HCH were strongly localized in Asia. Among total global α‐HCH emissions, 85% and 75% originated in Asia in 1980 and 1990, respectively. Study of trends of α‐HCH residue shows that α‐HCH can remain in the soil for more than 10 years after its ban in countries such as China and Japan. The trends of α‐HCH concentration in the soils in the Kitakyushu District, Japan, and Taihu Lake basin, China, estimated from our model fit the monitoring data in the same areas quite well. Qualitative uncertainty estimates have also been assigned on a regional basis.
Importance of vegetation feedbacks in doubled‐CO2 climate experiments
Authors: Douville H. , Planton S. , Royer J.‐F. , Stephenson D. B. , Tyteca S. , Kergoat L. , Lafont S. , Betts R. A.
Published: September 2002

The rising atmospheric concentration of carbon dioxide resulting from the burning of fossil fuels and deforestation is likely to provoke significant climate perturbations, while having far‐reaching consequences for the terrestrial biosphere. Some plants could maintain the same intake of CO2 for photosynthesis by reducing their stomatal openings, thus limiting the transpiration and providing a positive feedback to the projected surface warming. Other plants could benefit from the higher CO2 level and the warmer climate to increase their productivity, which would on the contrary promote the transpiration. The relevance of these feedbacks has been investigated with the Météo‐France atmospheric general circulation model. The model has been run at the T31 spectral truncation with 19 vertical levels and is forced with sea surface temperature and sea ice anomalies provided by a transient simulation performed with the Hadley Centre coupled ocean‐atmosphere model. Besides a reference doubled‐CO2 experiment with no modification of the vegetation properties, two other experiments have been performed to explore the impact of changes in the physiology (stomatal resistance) and structure (leaf area index) of plants. Globally and annually averaged, the radiative impact of the CO2 doubling leads to a 2°C surface warming and a 6% precipitation increase, in keeping with previous similar experiments. The vegetation feedbacks do not greatly modify the model response on the global scale. The increase in stomatal resistance does not systematically lead to higher near‐surface temperatures due to changes in the soil wetness annual cycle and the atmospheric circulation. However, both physiological and structural vegetation feedbacks are evident on the regional scale. They are liable to modify the CO2 impact on the hydrological cycle, as illustrated for the case of the European summertime climate and the Asian summer monsoon. The strong sensitivity of the climate in these areas emphasizes the large uncertainties of climate change predictions for some of the most populated regions of the world and argues for the need to include more interactive land surface processes in current generation climate models.
Characterization of late glacial continental dust in the Greenland Ice Core Project ice core
Authors: Svensson Anders , Biscaye Pierre E. , Grousset Francis E.
Published: September 2002

Twelve glacial dust samples extracted from the Greenland Ice Core Project ice core have been characterized in terms of mineralogy, Sr and Nd isotopic composition, and rare earth element concentrations. The ice samples are taken from the Younger Dry as, the Bølling, the Last Glacial Maximum, and both cold and mild glacial periods back to 44 kyr B.P. A comparison with samples from possible dust source areas determines eastern Asia as being the main source area at all times, hereby confirming and extending earlier results (Biscaye et al., 1997). This finding is partly in agreement with recent atmospheric general circulation model simulations of glacial atmospheric dust transport (Andersen et al., 1998; Mahowald et al., 1999). A low intersample variability in tracer characteristics is discussed in the context of a volcanogenic influence, grain size dependence, and variability in the continental dust source areas. The clay mineralogy of the ice core dust shows a weak climatic dependence, while the isotopic composition of Sr and Nd does not correlate with climate. This is interpreted as a geographical variation of source areas on a regional scale within Asia. Two ice dust samples were size‐fractionated at 2 μm, and the grain size dependence on tracer characteristics is in accordance with the literature.
Influence of the latitudinal temperature gradient on soil dust concentration and deposition in Greenland
Authors: Tegen Ina , Rind David
Published: September 2002

To investigate the effects of changes in the latitudinal temperature gradient and the global mean temperature on dust concentration in the Northern Hemisphere, experiments with the GISS GCM are performed. The dust concentration over Greenland is calculated from sources in central and eastern Asia, which are integrated on‐line in the model. The results show that an increase in the latitudinal temperature gradient increases both the Asian dust source strength and the concentration over Greenland. The source increase is the result of increased surface winds, and to a minor extent, the increase in Greenland dust is also associated with increased northward transport. Cooling the climate in addition to this increased gradient leads to a decrease in precipitation scavenging, which helps produce a further (slight) increase in Greenland dust in this experiment. Reducing the latitudinal gradient reduces the surface wind and hence the dust source, with a subsequent reduction in Greenland dust concentrations. Warming the climate in addition to this reduced gradient leads to a further reduction in Greenland dust due to enhanced precipitation scavenging. These results can be used to evaluate the relationship of Greenland ice core temperature changes to changes in the latitudinal and global temperatures.
Influences of the clearness index for the whole spectrum and of the relative optical air mass on UV solar irradiance for two locations in the Mediterranean area, Valencia and Cordoba
Authors: Cañada J. , Pedrós G. , López A. , Boscá J. V.
Published: September 2002

Ultraviolet solar irradiance (290–385 nm) was analyzed in Valencia and Cordoba, Spain, during 1996–1997. Its relation to the instantaneous atmospheric clearness index kt, the relative optical mass mr, the time of the year, and the total or global irradiance on a horizontal surface was established. The maximum values of UV irradiance for each optical mass exponentially diminished with the optical mass, thus for Cordoba and Valencia, Guv = 62.23 mr−1.34 and Guv = 52.84 mr−1.30, respectively. The UV irradiance in Cordoba represented 4.2% of the total irradiance while in Valencia this percentage was 4.9%. In the case of cloudy days (kt<0.4), these percentages ranged between 5.6% and 6.8% in Valencia and between 5.1% and 5.5% in Cordoba.
The leading variability mode of the coupled troposphere‐stratosphere winter circulation in different climate regimes
Authors: Perlwitz Judith , Graf Hans‐F. , Voss Reinhard
Published: September 2002

The leading variability mode of the coupled troposphere‐stratosphere winter circulation in the Northern Hemisphere (NH) describes a close relationship between the strength of the stratospheric cyclonic vortex and the index of a tropospheric wave‐like pattern covering the North Atlantic‐Eurasian region. This mode can be determined by applying singular value decomposition analysis between the time series of winter mean NH 50‐ and 500‐hPa geopotential heights. We compared the features of the leading coupled variability mode between two climate regimes, determined from a 1900‐year integration with the coupled atmosphere‐ocean climate model ECHAM3‐LSG. The two regimes differ on the interdecadal timescale in the strength of the stratospheric polar vortex and therefore in the transmission‐refraction properties of vertically propagating tropospheric waves. The spatial structures of the leading coupled variability mode of observational data better match the corresponding structures of the model's weak polar vortex regime (PVR) than those of the strong one. Because of the more effective tropospheric trapping of stationary wave energy of zonal wave number (ZWN) 2 at midlatitudes, the zonal variability structure of this wave is changed by barotropic effects in the troposphere as well as in the stratosphere. The coupled troposphere‐stratosphere mode and the response of winter circulation were studied in a climate‐change experiment carried out with the same model. We could show that under increased greenhouse gas forcing, both the response and the coupled variability mode between tropospheric and stratospheric circulation itself has a high similarity to the leading coupled mode in the strong PVR.
Impacts of biomass burning on tropospheric CO, NOx, and O3
Authors: Galanter Meredith , Levy Hiram , Carmichael Gregory R.
Published: September 2002

This study utilizes the National Oceanic and Atmospheric Administration Geophysical Fluid Dynamics Laboratory three‐dimensional global chemical transport model to quantify the impacts of biomass burning on tropospheric concentrations of carbon monoxide (CO), nitrogen oxides (NOx), and ozone (O3). We construct updated global sources that emit 748 Tg CO/yr and 7.8 Tg N/yr in the surface layer. Both sources include six types of biomass: forest, savanna, fuelwood, agricultural residues, domestic crop residues (burned in the home for cooking and/or heating), and dried animal waste. Timing for the burning of forest, savanna, and agricultural residues is based upon regional cultural use of fire, vegetation type, local climate, and information gathered from satellite observations, while emissions from the burning of fuelwood, domestic crop residues, and dried animal waste are constant throughout the year. Based on agreement with observations, particularly of CO, we conclude that the collective uncertainty in our biomass burning sources is much less than the factor of two suggested by previous estimates of biomass burned in the tropics annually. Overall, biomass burning is a major source of CO and NOxin the northern high latitudes during the summer and fall and in the tropics throughout most of the year. While it contributes more than 50% of both the NOxand CO in the boundary layer over major source regions, it has a much larger global impact on the CO distribution in comparison to either NOxor O3, contributing 15 to 30% of the entire tropospheric CO background. The only significant biomass burning contribution to NOxat 500 mbar, due to the short lifetime of NOxin the lower troposphere, is a plume occurring July through October in the Southern Hemisphere subtropical free troposphere, stretching from South America to the western Pacific. The largest impacts on O3are limited to those regions where NOximpacts are large as well. Near the surface, biomass burning indirectly contributes less than half of the total O3concentrations over major tropical source regions, up to 15% throughout the year in the tropics, and 10 to 20% throughout the Southern Hemisphere during September through November. At 500 mbar, the largest contribution to O3(20–30%) is correlated with the NOxplume during July through November. Biomass burning contributes less than 15% of either NOxor O3in the upper troposphere.