bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of O3 formation during a stagnation episode in central Tennessee in summer 1995
Authors: Daum P. H. , Kleinman L. I. , Imre D. , Nunnermacker L. J. , Lee Y.‐N. , Springston S. R. , Newman L. , Weinstein‐Lloyd J. , Valente R. J. , Imhoff R. E. , Tanner R. L. , Meagher J. F.
Published: September 2002

O3 production in the Nashville urban plume during the O3 episode that occurred on July 11–July 13 1995, is examined to characterize the factors that control the ozone production rate and efficiency, and to examine the relative importance of natural and anthropogenic sources of hydrocarbons to ozone production in the urban center and outlying areas. The analysis focuses on data collected during aircraft flights on July 11 when the Nashville area was sampled more or less continuously from about 1000 to 1800 LT. The instantaneous ozone production rate P(O3) in the downtown area from late morning through midafternoon on July 11 ranged between 10 and greater than 30 ppbv/h depending on location. After 1700 local time, production rates dropped to a few ppbv/h owing to the diminished solar intensity. Instantaneous production efficiencies with respect to NOx in the downtown area ranged between 2.5 and 8, linearly depending on the ratio of the hydrocarbon to NOx, OH reactivity. Integral O3 production efficiencies corrected for NOz losses ranged between 1.5 and 4. The lowest efficiency was observed in the downtown area in the morning where NOx concentrations were high and hydrocarbon to NOx reactivity ratios were the lowest. Throughout the day, P(O3) in the downtown area was limited by the availability of hydrocarbons. Anthropogenic hydrocarbons and CO contributed about 66% of the total hydrocarbon OH reactivity in the downtown area. In the mature urban plume downwind of Nashville, P(O3) dropped to 6–9 ppbv/h at midafternoon and was controlled by the availability of NOx. Integral O3 production efficiencies in the mature urban plume ranged between 3.5 and 4. When present in large quantities (1–3 ppbv), isoprene significantly increased both the rate and efficiency of ozone production as long as the photochemical system was not strongly NOx‐limited.
Activation of Br2 and BrCl via uptake of HOBr onto aqueous salt solutions
Authors: Fickert Stefan , Adams Jonathan W. , Crowley John N.
Published: September 2002

The reactive uptake of HOBr onto aqueous solutions containing Cl− and Br− has been studied using a wetted‐wall flow tube reactor. The uptake was found to be limited by gas phase transport, enabling the measurement of the diffusion coefficient of HOBr in He (319±48 torr cm2 s−1) and N2 (84±7 torr cm2 s−1) at 274 K (errors are 2 σ). The same experiments allowed a lower limit to the accommodation coefficient of α > 1×10−2 to be calculated. Both Br2 and BrCl products were observed in the gas phase, the relative yield of which was dependent on the ratio of Cl− to Br− in the aqueous phase. At [Cl−] = 1M, and [Br−] = 10−3 M, >90% of HOBr taken up by the film was released into the gas phase as Br2. At low Br− concentrations, BrCl was the dominant product. The role of pH in the efficiency of bromine release from the aqueous phase was examined by carrying out HOBr‐uptake experiments with 1 M Cl−, 10−3 MBr−, and pH between 4 and 10. At a pH of less than 6.5 at least 90% of the HOBr taken up onto the aqueous Cl− / Br− solution was released into the gas phase as Br2. Bromine was not released following HOBr uptake onto non‐acidified solution. These experiments confirm the efficient activation of bromine predicted by recent models of halogen chemistry in the marine boundary layer.
Composition and distribution of aerosols over the North Atlantic during the Subsonic Assessment Ozone and Nitrogen Oxide Experiment (SONEX)
Authors: Dibb Jack E. , Talbot Robert W. , Scheuer Eric M.
Published: September 2002

We report the mixing ratios of aerosol‐associated soluble ions (focusing on SO4= and NO3−) and HNO3 over the North Atlantic during NASA's Subsonic Assessment Ozone and Nitrogen Oxide Experiment (SONEX). The SONEX campaign was designed to quantify the impacts of jet emissions in the North Atlantic Flight Corridor (NAFC) by sampling both directly within and far removed from the organized track system. Beryllium‐7 activities were also measured to assess the magnitude of stratospheric influence in the SONEX study region. Mixing ratios of aerosol‐associated SO4= and NO3− above 8 km during SONEX were lower than recent measurements over the central United States during the Subsonic Aircraft Contrail and Cloud Effects Special Study (SUCCESS) and the same as those over the remote South Pacific during the Pacific Exploratory Mission‐Tropics (PEM‐Tropics), suggesting that aircraft emissions cannot yet be a major source of these ions. Furthermore, mean SO4= mixing ratios at high altitudes were 65% higher in regions away from the NAFC than they were directly in the track system just a few hours after peak traffic. Nitric acid mixing ratios at the highest DC‐8 sampling altitudes were elevated during SONEX compared to PEM‐Tropics, but there was no clear signal of enhancement by jet exhaust. Strong correlations with 7Be indicate that a large fraction of HNO3 and aerosol‐associated SO4= measured at high altitudes during SONEX were derived from a stratospheric source.
Airborne measurements of isoprene, CO, and anthropogenic hydrocarbons and their implications
Authors: Goldan P. D. , Parrish D. D. , Kuster W. C. , Trainer M. , McKeen S. A. , Holloway J. , Jobson B. T. , Sueper D. T. , Fehsenfeld F. C.
Published: September 2002

Measurements of the mixing ratios of light hydrocarbons (≥C6) were made aboard the National Oceanic and Atmospheric Administration Lockheed Orion WP‐3 aircraft during June and July of 1994 and 1995 during a series of flights over the region around Nashville, Tennessee. The measurements were carried out as part of the Nashville/Middle Tennessee Study of the Southern Oxidant Study (SOS) whose purpose was to describe the sources, variation, and distribution of ozone and its precursors in the southeastern United States during the summer season. The spatial (altitude and latitude) distribution of isoprene and anthropogenic nonmethane hydrocarbons (NMHCs) is described. The isoprene distribution measured within the planetary boundary layer over the region is compared to the recent inventories. The correlations between the various anthropogenic hydrocarbons are used to demonstrate the combined influence of OH photochemistry and dilution on their concentrations. Finally, the distributions of those NMHCs that were measured are compared to those of CO and methane and discussed in terms their implications for odd hydrogen photochemistry and our understanding of regional ozone production. In the boundary layer, OH reactions are dominated by isoprene in the southern part of the region explored and by CO and methane in the northern part. The other measured NMHCs are seen to play only a minor role in ozone production in the nonurban atmosphere.
Photochemistry and budget of ozone during the Mauna Loa Observatory Photochemistry Experiment (MLOPEX 2)
Authors: Hauglustaine D. A. , Madronich S. , Ridley B. A. , Flocke S. J. , Cantrell C. A. , Eisele F. L. , Shetter R. E. , Tanner D. J. , Ginoux P. , Atlas E. L.
Published: September 2002

During the Mauna Loa Observatory Photochemistry Experiment (MLOPEX 2), simultaneous measurements of a large number of photochemical species were measured during different seasons at Mauna Loa Observatory (MLO), Hawaii. In this study, these measurements are used to constrain a detailed photochemical box model and evaluate our understanding of the tropospheric photochemistry in this region of the Pacific. The simulations generally reproduce satisfactorily the NO/NO2 photostationary state, which controls the ozone production rate. However, the model fails in simulating the concentration of peroxy radicals (PO2) during all seasons and of hydroxyl radical (OH) during summer. Several hypotheses are considered to assess this discrepancy, including the removal of radicals by unidentified mechanisms and the potential impact of biogenic organic compounds. None of the tested hypotheses give satisfactorily results in terms of OH, PO2 and NO/NO2 simultaneously. Although experimental uncertainties are large for radicals, this issue constitutes a major inconsistency between measurements and model results during MLOPEX. Another disagreement arises from the simulation of peroxides for free tropospheric conditions. The model tends to overestimate H2O2 and CH3OOH by a factor of 1.5–2.5. On the other hand, a fair agreement is achieved in simulating formaldehyde when CH3OOH is constrained in the model. Finally, we find that the gross ozone production and destruction rates are nearly in balance in this region of the Pacific troposphere. The net production is slightly negative, ranging from nearly 0 in winter to about −1.4 ppbv/d during summer. In contrast, the NOx budget shows a severe imbalance. Our results indicate that an additional source of NOx ranging from 18 to 48 pptv/d (in winter and summer, respectively) would be required to sustain the 30 pptv of NOx measured on average at the site during free tropospheric conditions. Acetone has little effect on the budget of HOx at the altitude of MLO (3.4 km). However, including this species in the model induces an even larger imbalance in the NOx budget through the production of peroxyacetylnitrate.
The climate of the Last Glacial Maximum: Results from a coupled atmosphere‐ocean general circulation model
Authors: Bush Andrew B. G. , Philander S. George H.
Published: September 2002

Results from a coupled atmosphere‐ocean general circulation model simulation of the Last Glacial Maximum reveal annual mean continental cooling between 4° and 7°C over tropical landmasses, up to 26° of cooling over the Laurentide ice sheet, and a global mean temperature depression of 4.3°C. The simulation incorporates glacial ice sheets, glacial land surface, reduced sea level, 21 ka orbital parameters, and decreased atmospheric CO2. Glacial winds, in addition to exhibiting anticyclonic circulations over the ice sheets themselves, show a strong cyclonic circulation over the northwest Atlantic basin, enhanced easterly flow over the tropical Pacific, and enhanced westerly flow over the Indian Ocean. Changes in equatorial winds are congruous with a westward shift in tropical convection, which leaves the western Pacific much drier than today but the Indonesian archipelago much wetter. Global mean specific humidity in the glacial climate is 10% less than today. Stronger Pacific easterlies increase the tilt of the tropical thermocline, increase the speed of the Equatorial Undercurrent, and increase the westward extent of the cold tongue, thereby depressing glacial sea surface temperatures in the western tropical Pacific by ∼5°–6°C.
Greenhouse gases and climatic states of minimum entropy production
Authors: Pujol Toni , Llebot Josep Enric , Fort Joaquim
Published: September 2002

The hypothesis of minimum entropy production is applied to a simple one‐dimensional energy balance model and is analyzed for different values of the radiative forcing due to greenhouse gases. The extremum principle is used to determine the planetary “conductivity” and to avoid the “diffusive” approximation, which is commonly assumed in this type of model. For present conditions the result at minimum radiative entropy production is similar to that obtained by applying the classical model. Other climatic scenarios show visible differences, with better behavior for the extremal case.
Pacific Exploratory Mission‐Tropics carbon monoxide measurements in historical context
Authors: Pougatchev N. S. , Sachse G. W. , Fuelberg H. E. , Rinsland C. P. , Chatfield R. B. , Connors V. S. , Jones N. B. , Notholt J. , Novelli P. C. , Reichle H. G.
Published: September 2002

The three‐dimensional (3‐D) distribution of carbon monoxide (CO) over the southern Pacific during the NASA Global Tropospheric Experiment Pacific Exploratory Mission‐Tropics (PEM‐T) (August‐October 1996) has been analyzed in comparison to other CO measurements. The following data sets have been used in the study: National Oceanic and Atmospheric Administration Climate Monitoring and Diagnostic Laboratory surface level sampling; Commonwealth Scientific and Industrial Research Organization aircraft measurements over Cape Grim, Tasmania; solar spectroscopic measurements at Lauder, New Zealand; and data from two spaceborne Measurement of Air Pollution From Satellite experiments. For the PEM‐T mission back trajectories analysis and 3‐D modeling of the CO transport have been performed. It has been demonstrated that CO measurements obtained by different in situ and remote techniques can be used to build the picture of the CO climatology over the large geographical area. The structure of the CO distribution over the western part of the southern Pacific during the austral spring is mainly controlled by emission from biomass burning in Australia and Africa and subsequent long‐range transport. The prevailing westerly transport occurs in the middle and upper troposphere, whereas the marine boundary layer remains relatively clean and uniform. Barriers in the form of the Intertropical Convergence Zone and South Pacific Convergence Zone protect the equatorial area (equator to 10°S) from direct impact of biomass burning plumes from north and southwest. Consistency between the measurements taken in different years and modeling results indicates that the observed feature is a stable phenomenon. Outside the equatorial area the CO vertical distribution has a broad distinctive maximum at the altitude range 5–8 km and latitudes between 20°S and 30°S. This maximum is a stable feature, and its location indicates the area where the most intensive westerly transport occurs.
Stratospheric effects of 27‐day solar ultraviolet variations: The column ozone response and comparisons of solar cycles 21 and 22
Authors: Hood L. L. , Zhou S.
Published: September 2002

Two unresolved observational issues concerning the response of stratospheric ozone to 27‐day solar ultraviolet variations are as follows: (1) the amplitude of the column ozone response and whether it is consistent with the predictions of current two‐dimensional stratospheric models and (2) whether the ozone profile response in the upper stratosphere differed appreciably during the solar cycle 22 maximum period (around 1990) as compared with the solar cycle 21 maximum period (around 1980). To investigate these issues, two separate 4‐year intervals (1979–1982 and 1989–1992) of daily zonal mean Nimbus 7 Total Ozone Mapping Spectrometer, Nimbus 7 solar backscattered ultraviolet (SBUV), and/or NOAA 11 SBUV/2 data for tropical latitudes (30°S to 30°N) are analyzed using cross correlation and cross‐spectral and regression methods. The Mg II core‐to‐wing ratio is employed as a measure of solar UV variations near 200 nm. Results show that the mean tropical column ozone sensitivity (percent change of ozone for a 1% change in solar flux) is 0.09±0.01 at a lag of 4–6 days during both intervals and is approximately consistent with model predictions. Ozone profile sensitivities and phase lags are also in agreement between the two 4‐year intervals when statistical uncertainties and differences in data processing algorithms are considered.
Comparison between global chemistry transport model results and Measurement of Ozone and Water Vapor by Airbus In‐Service Aircraft (MOZAIC) data
Authors: Law K. S. , Plantevin P.‐H. , Thouret V. , Marenco A. , Asman W. A. H. , Lawrence M. , Crutzen P. J. , Muller J.‐F. , Hauglustaine D. A. , Kanakidou M.
Published: September 2002

Ozone distributions from state‐of‐the‐art global three‐dimensional chemistry transport models are compared to O3 data collected on Airbus A340 passenger aircraft as part of the Measurement of Ozone and Water Vapor by Airbus In‐Service Aircraft (MOZAIC) project. The model results are compared to monthly averaged data at cruise altitudes in the upper troposphere and lower stratosphere and monthly averaged vertical profiles collected over particular cities during takeoff and landing. The models generally show good agreement with the data in regions which have previously been well documented and where the meteorology is well understood/captured by meteorological models (e.g., over Europe). However, in the upper troposphere and lower stratosphere, models often fail to capture sharp gradients across the tropopause and from the subtropics to the tropics. In some models, this is related to deficiencies in model transport schemes and upper boundary conditions. Also, regions of the globe where our understanding of meteorology is poorer and emissions are less well known (e.g., tropics, continental Africa, Asia, and South America) are not simulated as well by all models. At particular measurement locations, it is apparent that emission inventories used by some global models underestimate emissions in certain regions (e.g., over southern Asia) or have incorrect seasonal variations (e.g., biomass burning over South America). Deficiencies in chemical schemes may also explain differences between models and the data.
Comparison of solar UV measurements performed with spectroradiometer and moderate bandwidth multichannel radiometer for different cloud conditions
Authors: Thorseth Trond Morten , Kjeldstad Berit , Johnsen Bjørn
Published: September 2002

A method to control spectral global irradiance data using moderate bandwidth multichannel radiometer data was analyzed. The multichannel instrument sampled at both 1 min averages and a high frequency of approximately 0.5 Hz simultaneously with the spectral data. Deviations between multichannel radiometer and spectroradiometer, caused by different angular response (cosine and azimuth), were investigated. Uncertainties due to separate sampling systems and nonideal timing were quantified and removed before data intercomparison. It is shown that high‐frequency multichannel measurements, ideal synchronized to spectral measurements can be used to identify short‐term unexpected errors in spectral measurements down to a level of 5%, limited by the relative angular response error between the instrument during variable cloud conditions.
Observations of the spectral clear‐sky aerosol forcing over the tropical Indian Ocean
Authors: Meywerk Jens , Ramanathan V.
Published: September 2002

During the first field phase (FFP) of the Indian Ocean Experiment (INDOEX) in February and March, 1998, the spectral global and direct beam irradiance have been measured between 350 and 1050 nm wavelengths using a 512‐channel, fixed grating, photodiode array spectroradiometer. A detailed analysis of the instrument's reliability, the absolute calibration, and the corrections for deviation from the ideal cosine response are presented. For most of the spectral region the total uncertainty is shown to be <2%. The spectral optical depth, the spectral aerosol forcing, and the aerosol forcing for the photosynthetically active radiation have been derived from direct beam measurements and global irradiance measurements. The optical depth at 500 nm wavelength decreases from ∼0.5 in the northern Arabian Sea to as low as 0.05 south of the Intertropical Convergence Zone (ITCZ) near ∼15°S latitude. The surface aerosol forcing efficiency is defined as the rate of change of net irradiance at the surface due to an increase by 1 in optical depth at 500 nm. The normalization procedure we adopt to determine the aerosol forcing efficiency with respect to a reference pristine day in the Southern Hemisphere eliminates most of the radiometric calibration uncertainties. The continental aerosol south of the ITCZ shifts the peak in the direct solar radiation from 470 nm (for pristine conditions) to ∼580 nm for the polluted region. The spectral aerosol forcing efficiency peaks around 460 nm, with −1.2, −0.6, and +0.6 W m−2 nm−1 for the direct, global, and diffuse irradiance, dropping for the lower and higher wavelengths to about −0.3, −0.25, and 0.05 W m−2 nm−1 at 350 nm and −0.3, −0.1, and +0.2 at 1050 nm. Integrated over 400–700 nm, the aerosols decrease the noontime solar flux by as much as −38 W m−2 in the Arabian Sea to as little as −2 W m−2 south of the ITCZ. This introduces a strong north to south gradient in the climate forcing of the ocean. In addition, the strong aerosol modulation of the photosynthetically active radiation (400–700 nm) and its north to south gradient have important implications for biomass production of the ocean.
Effect of the tropospheric trend on the stratospheric tracer‐tracer correlations: Methyl chloroform
Authors: Romashkin P. A. , Hurst D. F. , Elkins J. W. , Dutton G. S. , Wamsley P. R.
Published: September 2002

In situ measurements in the lower stratosphere in 1997 produced distinct intersecting correlations between methyl chloroform (CH3CCl3) and chlorofluorocarbon‐11 (CFC‐11) for air parcels sampled during spring and summer in the same physical space. The disagreement between spring and summer correlations in the stratosphere below 225 ppt of CFC‐11 is in the opposite direction than is expected from the documented tropospheric trend of −15 ppt yr−1. Summertime air parcels were enriched in CH3CCl3 compared to spring parcels. Mean ages based on sulfur hexafluoride (SF6) for CH3CCl3‐rich air masses observed during summer were older by about a year than mean ages of CH3CCl3‐depleted air parcels sampled during spring. The ages of stratospheric air masses and the documented history of methyl chloroform mixing ratios in the troposphere were used to normalize the stratospheric input of methyl chloroform, as if it had no tropospheric trend. The normalized correlations with and without parameterization for phyotoylic loss on the age distribution are more compact and revealed hidden anomalous mixing lines between polar vortex and midlatitude air. Higher mixing ratios of CH3CCl3, which the older air had at the time of the stratospheric entry, caused the summer correlation to be elevated on the tracer‐tracer plot below 225 ppt of CFC‐11. The ongoing tropospheric decrease of CH3CCl3 caused an inflection point and crossing of spring and summer correlations at 225 ppt of CFC‐11. These results suggest that the tropospheric history is especially important for correlations of species that were increasing in the 1980s and are now decreasing (some CFCs, CCl4, and CH3CCl3). Distinct correlations between CH3CCl3 and CFC‐11 observed for spring and summer 1997 measurements are the result of the 1991 tropospheric maximum of CH3CCl3 [Prinn et al, 1995] that has propagated into the stratosphere, where air parcels with high CH3CCl3 were sampled at 20 km altitude and 60°–90°N.
Mesospheric constituent variations during electron precipitation events
Authors: Aikin A. C. , Smith H. J. P.
Published: September 2002

The response of mesospheric constituents to energetic electron deposition events is modeled on a diurnal scale for two precipitation scenarios. In the first example, upper limit electron fluxes representative of diffuse aurora are employed. The other case considers the 10‐day precipitation event of May 1992 observed by the Upper Atmosphere Research satellite Particle Environment Monitor (UARS/PEM). Since the UARS Halogen Occultation Experiment (UARS/HALOE) water vapor measurements indicate large variability from day to day as well as at different longitudes on the same day, water is used as a parameter in studying the diurnal response of different species to particle precipitation. Water amount affects the diurnal variation of ozone by changing the concentration of hydrogen radicals, creating a water‐dependent temporal response of the depletion of ozone by precipitating ionizing energetic electrons and protons. For constant particle fluxes, ozone depletion at a given altitude varies throughout the day at variance with model results where the Sun is assumed to have an average solar zenith angle throughout the day. At night, ozone depletion remains nearly constant and different from daylight values. Nighttime and twilight OH and HO2 are significantly enhanced during electron precipitation, Since precipitation often occurs between L = 3 and L = 6, where L is the distance in earth radii from the center of the Earth dipole to the equatorial crossing of the field line in question, as far south as 35°N in the North American longitude zone, particle precipitation is one of the factors determining OH and HO2 concentrations within this latitude range, particularly when the magnetic index Ap is enhanced. Because of the large diurnal changes associated with the amount of particle‐related ozone depletion, fixed microwave sites measuring ozone and water will be better able to determine the atmospheric effects of particle precipitation than satellite measurements of ozone. Diurnally averaged models are inadequate for predicting the detailed ozone response to charged particle precipitation.
NOy lifetimes and O3 production efficiencies in urban and power plant plumes: Analysis of field data
Authors: Nunnermacker L. J. , Kleinman L. I. , Imre D. , Daum P. H. , Lee Y.‐N. , Lee J. H. , Springston S. R. , Newman L. , Gillani N.
Published: September 2002

In an effort to describe and characterize power plant plumes in the Nashville region, emissions from a small power plant (Gallatin) and a large power plant (Paradise) were examined using data obtained on the Department of Energy G‐1 airborne sampling platform. Observations made on July 3, 7, 15, 17, and 18, 1995, were compiled, and a kinetic analysis of the chemical evolution of the power plant plumes was performed. Analysis of the power plant plume data revealed a very active photochemistry, as had been determined previously for the urban plume. Ozone production efficiencies (OPE), defined as the number of molecules of O3 formed per NOx molecule consumed, were found to be 3 for Gallatin and 2 for Paradise. Lifetimes for NOx (2.8 and 4.2 hours) and NOy (7.0 and 7.7 hours) were determined for Gallatin and Paradise, respectively. These NOx and NOy lifetimes imply rapid loss of NOz (NOz is assumed to be primarily HNO3). Lifetimes for NOz are calculated to be 3 and 2.5 hours for Gallatin and Paradise, respectively. A sensitivity analysis indicates that the Gallatin NOz lifetime could be as long as 5 hours, bringing it into agreement with the value determined for the Nashville urban plume. It is unlikely that the Paradise NOz lifetime is as long as 4 hours. If NOz loss is attributed to dry deposition, a 3 hour lifetime implies a deposition velocity greater than 10 cm s−1, which is much faster than expected based on accepted theory. Possible reasons for this discrepancy are discussed.
Three‐dimensional model study of the influence of stratosphere‐troposphere exchange and its distribution on tropospheric chemistry
Authors: Lamarque J.‐F. , Hess P. G. , Tie X. X.
Published: September 2002

A three‐dimensional global chemistry transport model is used to examine the impact of stratosphere to troposphere fluxes of ozone (O3) and nitric acid (HNO3) on tropospheric chemistry. The stratospheric fluxes are parameterized as a tropospheric source of O3 and HNO3. The accuracy of the resulting model simulation is compared with measurements. The tropospheric impact of the stratospheric fluxes is examined through a parallel simulation that includes no stratospheric fluxes of O3 and HNO3. Stratosphere‐troposphere exchange (STE) increases the global average tropospheric ozone column by only 11.5%, increasing it in the Northern Hemisphere by 10.5% and in the Southern Hemisphere by 13%. STE shifts the springtime ozone maximum ∼1 month earlier in the Northern Hemisphere. The portion of the O3 distribution of stratospheric origin in the troposphere increases with altitude, from a maximum of 10–20% in the lower troposphere to 40–50% in the upper troposphere. The sensitivity of the tropospheric response to the spatiotemporal distribution of STE is also examined. On a hemispheric and annual scale the tropospheric composition is particularly sensitive to the temporal distribution of STE. The separate roles of stratospheric fluxes of O3 and HNO3 are also identified.
Diurnal variation of lightning characteristics around Java Island
Authors: Hidayat Syarif , Ishii Masaru
Published: September 2002

The diurnal variation of lightning activity on and around Java Island, Indonesia, is examined by using the observation results from a magnetic direction finder network. The magnetic direction finder network has four direction finders on Java Island and has been operating since 1994. Lightning is active during the rainy season, usually from October to May. The highest ground flash density on Java Island was 16 flashes per km2 per year. The diurnal variation of the lightning activity over land shows its peak at around 1500 LT. There is a small peak in the early morning around 0300–0500 LT over the sea, several hours prior to the reported peak times of the cold cloudiness, an indicator of deep convection observed from meteorological satellites. Existence of close sea‐land interaction related to the activity of deep convection in this area is suggested from the diurnal variations in the lightning activity. The diurnal variation is also found in the peak currents of negative first return strokes over land, medians from 25 kA around noon to 30 kA around midnight. The lightning activity over the ocean does not show such diurnal variation and delivers currents of higher amplitudes with a median of 36 kA.
Radiative forcing due to stratospheric ozone changes 1979–1997, using updated trend estimates
Authors: de F. Forster Piers M.
Published: September 2002

Recent estimates of stratospheric ozone changes since 1979, both from satellites and ground‐based instruments, show a smaller rate of ozone loss than previous measurements indicated. This paper calculates the radiative forcing resulting from these ozone changes. The trends are derived from a combination of Stratospheric Aerosol and Gas Experiment (SAGE), Total Ozone Mapping Spectrometer (TOMS), and ground‐based data. By combining these data in a variety of ways, several problems of determining an accurate forcing from available data are highlighted. Using only statistically significant changes, a “best guess” radiative forcing of −0.10±0.02 W m−2 is estimated for the 1979–1997 period which is about 50% less negative than previous estimates of this forcing, but provides an offset of about 10% to the well‐mixed greenhouse gas forcing over the same period.
Climatologies of lower stratospheric NOy and O3 and correlations with N2O based on in situ observations
Authors: Strahan S. E.
Published: September 2002

This paper presents NOy and O3 seasonal mean distributions as a function of equivalent latitude and height from more than 140 ER‐2 flights. The observations span a height range of 360–530 K (∼150‐45 hPa) and have nearly pole‐to‐pole coverage in most seasons. These climatologies are intended to support efforts to evaluate the chemistry and dynamics of assessment models. Reasonable model representations of NOy, O3, and their seasonal variations are necessary to assess the effects of aircraft exhaust on the stratosphere. ER‐2 measurements of N2O are combined with the NOy data to examine their lower stratospheric relationship and to identify regions of denitrification. Measurements of these species above ER‐2 altitudes in the Arctic vortex support the interpretation of some of the ER‐2 NOy‐N2O data, which suggest that transport rather than chemical denitrification causes deviations from the normally linear relationship. This places constraints on the use of a linear relationship to calculate denitrification. The observed relationship between N2O and O3 is also presented. The spatial gradients in lower stratospheric O3 photochemistry are used to explain observed variations in the N2O‐O3 relationship. The N2O‐O3 relationship above ER‐2 altitudes in the Arctic vortex, much like the case of NOy‐N2O, also differs in slope from lower altitudes. This points to the difficulties in using tracer correlations to infer O3 values in the vortex prior to polar stratospheric cloud processing. It is necessary to understand the photochemical and transport history of the air that descends into the lower stratospheric vortex in order to correctly quantify O3 depletion.
On the influence of diffusion upon the nonlinear behavior of the photochemistry of the mesopause region
Authors: Sonnemann G. R. , Feigin A. M. , Mol'kov Y. I.
Published: September 2002

The photochemical system of the mesopause region is a nonlinear driven oscillator enforced by the diurnal‐periodic solar radiation. Under idealized conditions this oscillator can display nonlinear effects such as period doubling cascades or chaos. We investigate what happens if this system is subjected to atmospheric diffusion. A high‐resolution one‐dimensional chemical system of the mesopause region has been established in order to answer this question. Strong diffusion destroys nonlinear effects, but for the lower values of the diffusion coefficient which are still of the order of magnitude of real values, different nonlinear effects occur. The most important effect consisted of the creation of a 2‐day subharmonic oscillation. Such a 2‐day oscillation of the concentration of chemical active species entails a corresponding oscillation of the chemical heating rates which feeds back to the dynamics of this region. The zonal wind influences the period of the oscillation so that the periods differ from the exact 48‐hour value by a few hours depending on the wind velocity and its direction. We call this phenomenon the photochemical Doppler effect.
Ozone fluxes obtained with the NOAA Twin Otter during the Southern Oxidants Study
Authors: McMillen Robert T. , Gunter R. Laureen , Luke Winston T. , Watson Thomas B.
Published: September 2002

During June and July of 1995, as part of the Southern Oxidants Study (SOS), the National Oceanic and Atmospheric Administration (NOAA) instrumented Twin Otter research aircraft made meteorological and chemical measurements to characterize atmospheric conditions in and around the Nashville, Tennessee, area. In addition to these characterization studies, the aircraft measured the vertical fluxes of ozone, water vapor, heat, and momentum in the study area, at altitudes between 100 and 2500 m above ground level (agl) along transects a few kilometers downwind of the urban area, and extending crosswind well outside of the urban plume. During all low‐level transects, fluxes were measured over short length scales in order to assess their spatial variability. Several powerplant plumes impacted the local region, creating a complex scenario for analysis of ozone production and deposition processes. Deposition velocities derived from aircraft observations near the ground were found to be in reasonable agreement with values estimated by a deposition velocity model applied along the transects. The results are difficult to reconcile with expectations unless it is assumed that the area of the measurements was susceptible to considerable advection and/or effects of plume chemistry and spatial heterogeneity. Additional studies of this kind are now planned, in situations that are less complex.
Sensitivity of photolysis rates and ozone production in the troposphere to aerosol properties
Authors: He Shan , Carmichael Gregory R.
Published: September 2002

Aerosol impacts on NO2 photolysis rates and ozone production in the troposphere are studied by applying a modern sensitivity analysis technique “ADIFOR” on a coupled transport/chemistry/radiative transfer model. Four representative types of tropospheric aerosol (rural, urban, maritime, and desert) are evaluated in terms of loading strength and radiative characteristics. The effects of relative humidity (RH), aerosol vertical loading profile, and NOx (NO + NO2) emission are also studied. The presence of absorbing aerosols in the boundary layer is found to inhibit near‐ground ozone formation and to reduce ground level ozone by up to 70% in polluted environments. The presence of strongly scattering aerosols may increase ozone concentration in the lower boundary layer, but their effects vary with season, NOx, nonmethane hydrocarbon emission (NMHC), and temperature. Ozone production in the upper troposphere can be either enhanced or weakened, depending on the scattering and absorbing ability of aerosol particles and availability of NOx. In the lower troposphere, NO2 photolysis and ozone production rates are most sensitive to urban aerosol, followed by rural, then desert, and finally, maritime aerosol. As expected, NMHC, and NOx emissions also are found to have a large influence on O3 formation.
Global climatology of abundance and solar absorption of oxygen collision complexes
Authors: Zender Charles S.
Published: September 2002

To improve our understanding of the absorption of solar radiation in the atmosphere we have characterized the spectral absorption, the spatial and temporal abundance, and the radiative forcing of the oxygen collision pairs O2·O2 and O2·N2 (O2·X ≡ O2·O2 + O2·N2). The regional, vertical, seasonal, and annual patterns of O2·X abundance and radiative forcing are obtained from a general circulation model. We estimate the mean absorption by O2·X, heretofore neglected in large scale atmospheric models, is 0.75–1.2 W m−2, or 1–2% of total atmospheric solar absorption. O2·X absorption reduces surface insolation by 0.48–0.78 W m−2 and increases the net radiative flux at the tropopause by 0.32–0.52 W m−2. These ranges bracket the uncertainties due to spectral absorption cross sections, O2·N2 efficiency, O2·X abundance, and cloud distribution. Globally averaged, O2·X enhances absorption equally in clear and in cloudy skies. We create a global climatology of well‐mixed collision complex abundances by scaling O2·X abundance to other complexes such as N2·N2 and O2·Ar. Collision complex abundance depends quadratically on the concentrations of the constituents. This dependence causes a 20% increase in O2·X abundance in the Arctic relative to the Tropics for the same sea level pressure. The variations in zonal mean O2·X abundance due to surface elevation, the annual mean meridional temperature gradient, and to seasonal temperature variations are 40, 15, and 10%, respectively. O2·X heating obeys the weakly absorbing, linear limit so it peaks at the surface in clear skies, but clouds shift this peak up by 200–300 mb on seasonal timescales. Surface albedo and clouds strongly modulate the solar forcing efficiency of O2·X (forcing per unit abundance) by altering the mean photon path length. These factors produce annual mean forcing maxima in the subtropics over bright deserts and regions of marine stratus. Inclusion of O2·X in models is likely to reduce cold biases in the summertime polar atmosphere, where O2·X contributes 2–4% of total solar heating.
On the maintenance of high tropical cirrus
Authors: Boehm Matthew T. , Verlinde Johannes , Ackerman Thomas P.
Published: September 2002

Observations reveal that cirrus clouds are ubiquitous in the tropics and therefore significantly impact the radiation budget in this region. Here numerical studies are conducted using a two‐dimensional cloud‐resolving model with explicit microphysics to study the processes that lead to the maintenance of tropical cirrus. It is found that despite significant differences in the cloud dynamics among the simulations performed, the model is unable to maintain a cloud against the processes of sedimentation and evaporation under the assumed environmental conditions. It is hypothesized that a source of large‐scale upward motion must be present to maintain tropical cirrus.
Airborne aerosols over central Africa during the Experiment for Regional Sources and Sinks of Oxidants (EXPRESSO)
Authors: Ruellan Stéphane , Cachier Hélène , Gaudichet Annie , Masclet Pierre , Lacaux Jean‐Pierre
Published: September 2002

As part of the Experiment for Regional Sources and Sinks of Oxidants (EXPRESSO) conducted over central Africa in November 1996, 24 airborne aerosol samples were obtained and further analyzed for black and organic carbon (BC and OC), water‐soluble organic carbon (WSOC), polycyclic aromatic hydrocarbons (PAHs), soluble ions, elemental composition, and morphology. Particles were collected in the different atmospheric layers either above the tropical forest or the savanna of central Africa near the Intertropical Convergence Zone. Particle number concentrations (10–14,000 nm diameter) were found to be high in all atmospheric layers (3100±2060 cm−3,n= 24). Soil‐derived particles were less abundant than expected (20±18 μg m−3,n= 21), and their presence was assessed mainly to reentrainment by fires. On the other hand, pyrogenic particles were abundant, and high levels of black carbon (BC) concentrations were found either in the forest boundary layer (3.8±2.3 μg m−3,n= 6), the savanna boundary layer (9.8±3.9 μg m−3,n= 6), or in the Harmattan layer (8.7±1.6 μg m−3,n= 3). Other fire tracers (such as K, oxalate, or PAHs) confirmed the overwhelming impact of savanna fires in the regional troposphere. Another result is the possible occurrence of vertical and horizontal exchanges between the different layers and through the ITCZ. WSOC was measured in our samples representing on average 46±9% (n= 11) of the total particulate organic carbon. High values were found in the Harmattan layer, where on average WSOC accounts for 85±18%, (n= 3) of the total particulate organic carbon, pointing out the potential of biomass burning particles to act as cloud condensation nuclei (CCN). Different chemical indicators were used, which produce convergent information on the aging of biomass burning particles. Among these indicators, the ratio WSOC/OC was found to increase by a factor of 2 to 3 from the ground to the Harmattan layer. A product of this work is also the presence of high concentrations of organic acids (formate, acetate, and also oxalate) in the forest boundary layer suggesting a strong biogenic source for these compounds. Finally, during the EXPRESSO experiment, which took place at the beginning of the dry season, savanna fires were prevailing at a regional scale, whereas dust inputs by Harmattan airflow were still low. Our results suggest that in these conditions nitrate primarily remains in the gaseous phase, and thus the translocation of nitrogen nutrients is confined to the region.
Inverse modeling of the global CO cycle: 1. Inversion of CO mixing ratios
Authors: Bergamaschi Peter , Hein Ralf , Heimann Martin , Crutzen Paul J.
Published: September 2002

A three‐dimensional modeling study on atmospheric carbon monoxide is presented, based on the TM2 model. A Bayesian inverse technique is applied to optimize the agreement between model and observational data, including a priori source information as regularization term. Using the National Oceanic and Atmospheric Administration Climate Monitoring and Diagnostics Laboratory data set for CO mixing ratios at 31 globally distributed sites, a posteriori CO budgets can be derived, which allow the model to reproduce the observations at most sites within two standard deviations of monthly mean values. Use of different spatiotemporal emission distributions for terpenes (Global Emissions Inventory Activity, ∼80% of emissions in the tropics; Hough [1991], ∼70% of emissions in the extratropical Northern Hemisphere) showed a large impact on calculated a posteriori source strengths and on the modeled partitioning among individual CO sources. In order to reproduce the interhemispheric gradient of observed CO mixing ratios, a ratio between total sources in the Northern Hemisphere and those in the Southern Hemisphere of ∼1.8 is required. While it is obvious that this asymmetry is mainly due to CO emissions from technological sources, the inversion results suggest that either (1) the global technological CO source strength is higher (∼800 Tg CO/yr) than present inventory based estimates or (2) CO from terpenes or vegetation (or additional sources with dominant emissions in the Northern Hemisphere) have a significant impact on the northern hemispheric mixing ratios. Further sensitivity studies showed that a posteriori results slightly depend on biomass burning seasonality (shifted by 1 month), but they are virtually identical for the two different OH fields (CH4‐nonmethanehydrocarbons chemistry vs. CH4‐Only chemistry). Inversion results, however, were sensitive to model wind fields used (based on meteorological observations of 1987 and 1986, respectively), mainly due to stations near source regions. Use of a reduced set of stations resulted in virtually identical a posteriori source strengths for both model wind fields. The analysis is extended in the companion paper which considers the additional information on the CO budget provided by measurements of the stable isotope ratios (13C/12C, 18O/16O).
European greenhouse gas emissions estimated from continuous atmospheric measurements and radon 222 at Mace Head, Ireland
Authors: Biraud Sébastien , Ciais Philippe , Ramonet Michel , Simmonds Peter , Kazan Victor , Monfray Patrick , O'Doherty Simon , Spain T. Gerard , Jennings S. Gerard
Published: September 2002

Flux estimates of CO2, CH4, N2O, and CFCs over western Europe have been inferred from continuous atmospheric records of these species at the atmospheric research station of Mace Head, Ireland. We use radon (222Rn) which has a fairly uniform source over continents as a reference compound to estimate unknown sources of other species. The correlation between each species and 222Rn is calculated for a suite of synoptic events that have been selected in the Mace Head record over the period 1996/97. In the following, we describe the method and its uncertainties, and we establish data selection criteria that minimize the influence of local sources over Ireland, in the vicinity of the station, in order to select synoptic events originating from western Europe. We estimate western European flux densities of 45–30 103 kg C km−2 month−1 during wintertime for CO2, of 4.8–3.5 103 kg CH4 km−2 yr−1, 475–330 kg N2O km−2 yr−1, 2.5–1.8 kg CFC‐11 km−2 yr−1 for CFC‐11, and 4.2–2.9 kg CFC‐12 km−2 yr−1 for CFC‐12. Our estimates are independent, although in good agreement with those produced by inventories, except for CFC‐11 where our estimate is much lower than the inventory.
Wintertime roll and cell convection over Greenland and Barents Sea regions: A climatology
Authors: Brümmer Burghard , Pohlmann Sophie
Published: September 2002

Wintertime cold‐air outbreaks from the polar ice and land surfaces over the open sea lead to organized convective patterns (OCP) in the atmosphere, visible as cloud streets and cellular cloud structures on satellite images. Large amounts of energy are transferred from the ocean to the atmosphere and convective organized flows contribute substantially to the vertical fluxes of heat, moisture and momentum in the boundary layer. However, little is known about the frequency of OCP occurrence. The paper is aimed to fill this gap and presents a climatology of OCP occurrence over the Greenland Sea and Barents Sea. The study is based on daily NOAA satellite images of 10 winters (November till March) for the years from 1985/1986 to 1994/1995. It covers the area from 70°N to 82.5°N and from 20°W to 60°E and is subdivided into 40 subareas with a grid size of 10 degrees in longitude and 2.5 degrees in latitude. OCP occur in more than 50% of the time averaged over the 10 winters. Complete absence of OCP is observed in less than 5% of the time. OCP occur most frequently over the Westspitsbergen current and around the border between the Greenland Sea and the Barents Sea. Cloud streets are the dominating OCP mode close to the ice edge, whereas cellular structures dominate at farther distances. Variability of OCP occurrence may be large on all timescales. A relation between ice extent and frequency of OCP occurrence is present occasionally.