bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of plumes from biomass burning on atmospheric chemistry over the equatorial and tropical South Atlantic during CITE 3
Authors: Andreae M. O. , Anderson B. E. , Blake D. R. , Bradshaw J. D. , Collins J. E. , Gregory G. L. , Sachse G. W. , Shipham M. C.
Published: February 2004

During all eight flights conducted over the equatorial and tropical South Atlantic (27°–35°W, 2°N–11°S; September 9–22, 1989) in the course of the Chemical Instrumentation Test and Evaluation (CITE 3) experiment, we observed haze layers with elevated concentrations of aerosols, O3, CO, and other trace gases related to biomass burning emissions. They occurred at altitudes between 1000 and 5200 m and were usually only some 100–300 m thick. These layers extended horizontally over several 100 km and were marked by the presence of visible brownish haze. These layers strongly influenced the chemical characteristics of the atmosphere over this remote oceanic region. Air mass trajectories indicate that these layers originate in the biomass burning regions of Africa and South America and typically have aged at least 10 days since the time of emission. In the haze layers, O3and CO concentrations up to 90 and 210 ppb were observed, respectively. The two species were highly correlated. The ratio ΔO3/ΔCO (Δ, concentrations in plume minus background concentrations) is typically in the range 0.2–0.7, much higher than the ratios in the less aged plumes investigated previously in Amazonia. In most cases, aerosol (0.12–3 μm diameter) number concentrations were also elevated by up to 400 cm−3in the layers; aerosol enrichments were also strongly correlated with elevated CO levels. Clear correlations between CO and NOxenrichments were not apparent due to the age of the plumes, in which most NOxwould have already reacted away within 1–2 days. Only in some of the plumes could clear correlations between NOyand CO be identified; the absence of a general correlation between NOyand CO may be due to instrumental limitations and to variable sinks for NOy. The average enrichment of ΔNOy/ΔCO was quite high, consistent with the efficient production of ozone observed in the plumes. The chemical characteristics of the haze layers, together with remote sensing information and trajectory calculations, suggest that fire emissions (in Africa and/or South America) are the primary source of the haze layer components.
Energy released by recombination of atomic oxygen and related species at mesopause heights
Authors: Riese M. , Offermann D. , Brasseur G.
Published: February 2004

This paper studies the total chemical energy release of seven exothermic reactions involving odd oxygen and odd hydrogen species at mesopause heights. Monthly and zonally averaged heating rates are calculated on the basis of atomic oxygen and atomic hydrogen densities as inferred from the SME satellite measurements in the altitude regime from 80 to 93 km. Trace constituents not available from SME were determined by means of a photochemical model. The resulting heating rates are found to be fairly high at all seasons, altitudes, and latitudes accessible to SME satellite measurements. Very large heating rates occur at high latitudes in early winter, reaching a maximum value of approximately 28 K per day. Consequently, chemical heating appears to play an important role in the energy budget and the dynamics of the upper mesosphere and lower thermosphere.
Interdecadal changes of surface temperature since the late nineteenth century
Authors: Parker D. E. , Jones P. D. , Folland C. K. , Bevan A.
Published: February 2004

We present global fields of decadal annual surface temperature anomalies, referred to the period 1951–1980, for each decade from 1881–1890 to 1981–1990 and for 1984–1993. In addition, we show decadal calendar‐seasonal anomaly fields for the warm decades 1936–1945 and 1981–1990. The fields are based on sea surface temperature (SST) and land surface air temperature data. The SSTs are corrected for the pre‐World War II use of uninsulated sea temperature buckets and incorporate adjusted satellite‐based SSTs from 1982 onward. Our results extend those published in the 1990 Intergovernmental Panel on Climate Change Scientific Assessment and its 1992 supplement. We assess the impact of various sources of error in the fields. Despite poor data coverage initially and around the two World Wars the generally cold end of the nineteenth century and start to the twentieth century are confirmed, together with the substantial warming between about 1920 and 1940. Slight cooling of the northern hemisphere took place between the 1950s and the mid‐1970s, although slight warming continued south of the equator. Recent warmth has been most marked over the northern continents in winter and spring, but the 1980s were warm almost everywhere apart from Greenland, the northwestern Atlantic and the midlatitude North Pacific. Parts of the middle‐ to high‐latitude southern ocean may also have been cool in the 1980s, but in this area the 1951–1980 climatology is unreliable. The impact of the satellite data is reduced because the record of blended satellite and in situ SST is still too short to yield a climatology from which to calculate representative anomalies reflecting climatic change in the southern ocean. However, we propose a method of using existing satellite data in a step toward this target. The maps are condensed into global and hemispheric decadal surface temperature anomalies. We show the sensitivity of these estimated anomalies to alternative methods of compositing the spatially incomplete fields. Running decadal zonal means and annual global and hemispheric time series are also shown. Finally, we discuss some salient features in terms of observed atmospheric circulation changes and of the results of climate model integrations with increasing atmospheric greenhouse gases.
Monitoring of the nocturnal mixed layer by means of participate radon progeny measurement
Authors: Allegrini I. , Febo A. , Pasini A. , Schiarini S.
Published: February 2004

Meteorological and radon concentration data referring to two measurement campaigns carried out in Milan, Italy, are reported and discussed. An urban mixing height (UMH) is defined through radio sounding data and an equivalent mixing height (EMH) is obtained through application of a simple box model obtained with radon measurements, especially in the meteorological situations found during the campaigns which were characterized by negligible advection. It is shown that the meteorological and the radon‐model estimations of the mixed layer height are highly correlated. It is concluded that a simple ß counter for particulate radon progeny can be regarded as a useful instrument for estimating urban mixing heights in situations dominated by weak thermally induced turbulence which are also responsible for intense photochemical activity and pollution episodes.
Seasonal variability of vertical eddy diffusivity in the middle atmosphere: 1. Three‐year observations by the middle and upper atmosphere radar
Authors: Fukao Shoichiro , Yamanaka Manabu D. , Ao Naoki , Hocking Wayne K. , Sato Toru , Yamamoto Mamoru , Nakamura Takuji , Tsuda Toshitaka , Kato Susumu
Published: February 2004

The vertical eddy diffusivity K due to atmospheric turbulence with spatial scales of 100–102 m has been computed from the echo power spectral width observed by the middle and upper atmosphere radar for almost every month from January 1986 to December 1988. The method of analysis follows Lilly et al. [1974], Sato and Woodman [1982], and Hocking [1983a, 1985, 1988], and the contamination due to beam broadening, vertical shear, and transience has been removed. Although observations for horizontal wind speeds larger than approximately 40 m/s, such as occur near the tropopause jet stream in winter, have been omitted because of excessive beam broadening, sufficient numbers of observations have been accumulated to produce a reasonable climatology for the upper troposphere and lower stratosphere (6–20 km altitude) and for the mesosphere (60–82 km altitude). The monthly median of K shows a local maximum near the tropopause jet stream altitude. It becomes larger in the mesosphere, increasing gradually with height. Maxima of K are observed in winter near the tropopause and in summer in the mesosphere, and the seasonal variability of K reaches approximately an order of magnitude. A semiannual variability is apparent in the mesosphere with minima in the equinoctial seasons.
Measurement and numerical modeling of radio sounding reflection from a lightning channel
Authors: Dubovoy E. I. , Mikhailov M. S. , Ogonkov A. L. , Pryazhinsky V. I.
Published: February 2004

Electric field impulses and radar echo signal from lightning were measured synchronously. The measured electric field was used to calculate currents in return strokes which were used in numerical modeling of lightning discharge. On the basis of this simulation the radiowave reflection from a lightning channel was calculated. From the comparison of measured and computed radar echo signals the validity of the lightning discharge and the radiowave reflection numerical model was stated. Also, a continuous current was found between the return strokes.
Simulating fluxes from heterogeneous land surfaces: Explicit subgrid method employing the biosphere‐atmosphere transfer scheme (BATS)
Authors: Seth Anji , Giorgi Filippo , Dickinson Robert E.
Published: February 2004

A vectorized version of the biosphere‐atmosphere transfer scheme (VBATS) is used to study moisture, energy, and momentum fluxes from heterogeneous land surfaces at the scale of an atmospheric model (AM) grid cell. To incorporate subgrid scale inhomogeneity, VBATS includes two important features: (1) characterization of the land surface (vegetation and soil parameters) at N subgrid points within an AM grid cell and (2) explicit distribution of climatic forcing (precipitation, clouds, etc.) over the subgrid. In this study, VBATS is used in stand‐alone mode to simulate a single AM grid cell and to evaluate the effects of subgrid scale vegetation and climate specification on the surface fluxes and hydrology. It is found that the partitioning of energy can be affected by up to 30%, runoff by 50%, and surface stress in excess of 60%. Distributing climate forcing over the AM grid cell increases the Bowen ratio, as a result of enhanced sensible heat flux and reduced latent heat flux. The combined effect of heterogeneous vegetation and distribution of climate is found to be dependent on the dominant vegetation class in the AM grid cell. Development of this method is part of a larger program to explore the importance of subgrid scale processes in regional and global climate simulations.
Satellite remote sensing of H2SO4 aerosol using the 8‐ to 12‐μm window region: Application to Mount Pinatubo
Authors: Ackerman Steven A. , Strabala Kathleen I.
Published: February 2004

Monitoring stratospheric aerosols containing H2SO4 using the brightness temperature (BT) difference between 11 and 8.3 μm (BT8–BT11) spectral channels is demonstrated using theoretical calculations and satellite observations. Assuming an aqueous solution of 50% and 75% sulfuric acid, radiative transfer calculations indicate that over oceans an increase in the optical depth of the stratospheric aerosol results in an increase in BT8–BT11. Theoretical simulations suggest that the technique is sensitive to visible optical depths greater than approximately 0.15. The simulations also demonstrate a lack of sensitivity to the particle size distribution. Changes in pre‐ and post‐Pinatubo observations by the HIRS2 on board the NOAA 10 are consistent with observed optical depth measurements and confirm the sensitivity of these channels to the presence of the aerosol. The technique is also applied to cold tropical convective clouds and desert regions where the signal, though evident, is less conclusive. Time series analysis is applied to the NOAA 10 and NOAA 12 combined BT8–BT11 observations to detect the periodicity of the spread of the volcanic aerosol. Over a region of the southern Pacific a 18‐ to 26‐day period is present. Model simulations were conducted to demonstrate a trispectral technique with observations near 8, 11, and 12 μm. The trispectral approach has high potential in that the spectral signature of cirrus, water vapor, and H2SO4 aerosols are different. Observations from NOAA 10 and NOAA 11 are combined to demonstrate the capabilities of these infrared wavelengths of detecting the aerosol. The signal is clearly evident when a region of the South Atlantic is compared for pre‐ and post‐Pinatubo conditions.
OH radical‐ initiated photooxidation of isoprene: An estimate of global CO production
Authors: Miyoshi Akira , Hatakeyama Shiro , Washida Nobuaki
Published: February 2004

The OH radical‐ initiated photooxidation of isoprene has been investigated experimentally by a 6‐m3 photochemical reaction chamber equipped with a long path length Fourier transform infrared spectrometer. In the presence of NOx, the major primary reaction products were methyl vinyl ketone, methacrolein, and formaldehyde. Their yields were in quantitative agreement with previous measurements. In the absence of NOx, the reaction mechanism was found to be quite different from that in the presence of NOx, and major reaction products observed in the infrared spectra were attributed to organic hydroperoxides. Based on the model experiments, the ultimate yield of CO was evaluated to be 60% on the carbon number basis in the presence of NOx and 23% in the absence of NOx. The CO yield in the real atmosphere was evaluated as 30% on the carbon number basis, and global annual CO production from isoprene was estimated to be 105 Tg C yr−1. Together with a previous estimate of the CO production from terpenes, global CO production from natural hydrocarbons was evaluated to be 200±60 Tg C yr−1.
Solute effects on the evaporation of ice particles
Authors: Chen Jen‐Ping , Crutzen Paul J.
Published: February 2004

The possible influence of trace chemicals, in particular sulfate, nitrate, and ammonia, on the growth and lifetime of ice crystals is studied theoretically, based on the concept of a transition layer on the ice surface. Solutes, which are produced in the gas phase or on the particle surface, can be incorporated into the bulk of the ice crystals during condensational growth and released from the bulk during evaporation. The solute accumulated on the surface of ice particles during evaporation tends to form a layer of concentrated solution, which alters the equilibrium vapor pressure and thus affects the evaporation of ice particles. Our analysis indicates that the evaporation of ice crystals can be retarded significantly by solutes, especially in polluted environments and for low ice particle number concentrations. It is also shown that ice particles in subsaturated air may survive without complete evaporation when the environmental ice‐saturation ratio is above a temperature‐dependent critical value that can be as low as 91%. Experimental and observational studies are necessary for verification. We also briefly speculate about other conditions in which atmospheric chemical processes may affect surface properties of ice particles.
Aircraft electric field measurements: Calibration and ambient field retrieval
Authors: Koshak William J. , Bailey Jeff , Christian Hugh J. , Mach Douglas M.
Published: February 2004

An aircraft locally distorts the ambient thundercloud electric field. In order to determine the field in the absence of the aircraft, an aircraft calibration is required. In this work a matrix inversion method is introduced for calibrating an aircraft equipped with four or more electric field sensors and a high‐voltage corona point that is capable of charging the aircraft. An analytic, closed form solution for the estimate of a (3×3) aircraft calibration matrix is derived, and an absolute calibration experiment is used to improve the relative magnitudes of the elements of this matrix. To demonstrate the calibration procedure, we analyze actual calibration data derived from a Lear jet 28/29 that was equipped with five shutter‐type field mill sensors (each with sensitivities of better than 1 V/m) located on the top, bottom, port, starboard, and aft positions. As a test of the calibration method, we analyze computer‐simulated calibration data (derived from known aircraft and ambient fields) and explicitly determine the errors involved in deriving the variety of calibration matrices. We extend our formalism to arrive at an analytic solution for the ambient field, and again carry all errors explicitly.
Evolution of the concentrations of trace species in an aircraft plume: Trajectory study
Authors: Danilin Michael Y. , Ebel Adolf , Elbern Hendrik , Petry Heribert
Published: February 2004

Permanent increase of the subsonic aviation flights and attempts to develop high‐speed civil transport (HSCT) necessitate an assessment of their possible environmental impacts. To evaluate global aviation effects, it is important to know the role of the chemical transformations inside an aircraft plume taking into account heterogeneous reactions. The goal of this work is to model the principal physical and chemical processes occurring inside an aircraft exhaust plume. A new box model which calculates 41 relevant Ox, HOx, NOx, ClOx, BrOx, SOx, and HC species and includes the possible heterogeneous reactions on the combustion aerosol and ice contrail particles is proposed. The simplified descriptions of the aircraft plume dilution and ice contrail formation are described. The transformations inside the aircraft wake are presented for the trajectories of the exhaust product motions at the levels of 200 and 100 mbar calculated for the particular atmospheric conditions on April 25, 1986. The following problems are discussed: the ozone response at these altitudes, the oxidation rate of NOx and SO2, the role of the heterogeneous reactions on the combustion aerosol and contrail particles, and the possibility of ice and nitric acid trihydrate (NAT or HNO2•3H2O) particle formation inside the wake. The model results are in agreement with available experimental data for NO, NO2, HNO3, HNO2, and SO2. Analytical expressions are proposed to evaluate the oxidation rates of NOx, and SO2 in the aircraft wake. The local ozone response is small (between 0.6% at 200 mb and −0.1% at 100 mb). Possible future investigations are proposed.
Evolution of negative small ions at enhanced ionization
Authors: Luts Aare
Published: February 2004

The paper deals with the modeling of the evolution (chemical kinetics) of tropospheric small ions for the case where the rate of ion generation is substantially above normal. Such types of situations can be found in the regions where because of either natural or artificial conditions the rate of ion generation is increased. This model would be applicable to the results of the measurements performed a few years ago in Chernobyl and also to the lab instruments, where enhanced ionization is used. This paper deals only with the effects which are caused by the evolution of negative ions. The concentrations of positive ions have been calculated for the natural concentrations of neutral gases and henceforth are considered constant. The model considers only ion‐molecular reactions; the reactions between neutral compounds have not been taken into account. The model describing the kinetics of positive ions contains 1048 reactions, 199 ions, and 131 neutral compounds; the negative ion model includes 474 reactions, 143 ions, and 106 neutral compounds. The results show that if the ionization rate is substantially increased, the concentrations of neutral gases will change. Many of these changes can be estimated. The estimated concentrations are (in cubic centimeters): [NO] = 2.0×1010; [NO2] = 3.5×107; [N2O] = 8.0×1013; [HNO3] = 1.0×107; [SO2] = 3.0×108. Next, the concentrations of OH, O, N, H, HNO2, HO2, and CH3 increase nearly independently of the concentrations of neutral gases. The extent of the change in the concentrations of OH, O, N, H, HNO2, HO2, and CH3 cannot be estimated, as the feedback processes through ion‐molecular reactions are practically absent. The chemical kinetics of ions at a given gas composition is significantly different from the kinetics at the normal gas concentrations, i.e., because of both the changed concentrations of neutral gases and the shortened lifetimes of ions. In the steady state the ions O2−(H2O)k become dominant, whereas the ions CO3−(H2O)k hold the second place.
Modeling of mineral dust in the atmosphere: Sources, transport, and optical thickness
Authors: Tegen Ina , Fung Inez
Published: February 2004

A global three‐dimensional model of the atmospheric mineral dust cycle is developed for the study of its impact on the radiative balance of the atmosphere. The model includes four size classes of mineral dust, whose source distributions are based on the distributions of vegetation, soil texture and soil moisture. Uplift and deposition are parameterized using analyzed winds and rainfall statistics that resolve high‐frequency events. Dust transport in the atmosphere is simulated with the tracer transport model of the Goddard Institute for Space Studies. The simulated seasonal variations of dust concentrations show general reasonable agreement with the observed distributions, as do the size distributions at several observing sites. The discrepancies between the simulated and the observed dust concentrations point to regions of significant land surface modification. Monthly distribution of aerosol optical depths are calculated from the distribution of dust particle sizes. The maximum optical depth due to dust is 0.4–0.5 in the seasonal mean. The main uncertainties, about a factor of 3–5, in calculating optical thicknesses arise from the crude resolution of soil particle sizes, from insufficient constraint by the total dust loading in the atmosphere, and from our ignorance about adhesion, agglomeration, uplift, and size distributions of fine dust particles (<1 μm).
Structure of the atmosphere in an urban planetary boundary layer from lidar and radiosonde observations
Authors: Cooper D. I. , Eichinger W. E.
Published: February 2004

The planetary boundary layer (PBL) over Mexico City was probed with a scanning backscatter lidar to characterize and evaluate the multidimensional structure of the atmosphere. Comparisons were made between radiosonde and lidar‐derived PBL heights which showed the two techniques to be in close agreement. The spatial properties of the free atmosphere‐PBL interface were found to be approximately the same size as the entrainment zone thickness. Below the interface the lidar observed spatially resolved structures, such as thermal plumes, convective eddies, low‐level jets, and entrainment into the PBL. These structures were spatially correlated with the local diabatic condition and wind stress. One highly unstable atmosphere contains a lidar‐visualized convective structure rising to a height of 0.45 the inversion base, which was predicted from earlier turbulence models. Other features, such as low‐level jets, were found to be associated with neutral atmospheres in the mixing layer. The analysis indicates that the transport of pollutants is not a continuous and gradient‐driven process, but low frequency and spatially discontinuous. The high spatial and temporal resolution afforded by the scanning lidar depicts surface‐atmosphere interactions which are neither spatially homogeneous nor horizontally uniform.
Kinetics of the reactions of HBr with O3 and HO2: The yield of HBr from HO2 + BrO
Authors: Mellouki Abdelwahid , Talukdar Ranajit K. , Howard Carleton J.
Published: February 2004

An upper limit on the yield of HBr from reaction (R1) (HO2 + BrO → products) has been determined by measuring an upper limit for the rate coefficient of the reverse reaction (R1′) (HBr + O3 → HO2 + BrO). The limits measured at 300 and 441 K were extrapolated to low temperatures to determine that the yield of HBr from reaction (R1) is negligible throughout the stratosphere (<0.01% of k1). An upper limit for the rate coefficient of the reaction of HO2 with HBr was also determined to be very low ≤3×10−17 cm3 molecule−1 s−1 at 300 K and ≤3×10−16 cm3 molecule−1 s−1 at 400 K. The implications of these results to stratospheric chemistry are discussed.
Total ozone measurements made with the Brewer ozone spectrophotometer during STOIC 1989
Authors: Kerr J. B. , McElroy C. T.
Published: February 2004

The Canadian Atmospheric Environment Service participated in the Stratospheric Ozone Intercomparison Campaign (STOIC) by operating a Brewer ozone spectrophotometer at the Table Mountain Observatory from July 19 to August 2, 1989. Frequent direct Sun measurements of total column ozone were made throughout most days during the 2 weeks of the intercomparison. Results of the Brewer instrument total ozone measurements are given. They show that there is a diurnal variation of total ozone with values increasing on average by 6.6±2.4 Dobson units between early morning and late afternoon. Comparing the total ozone measurements with ozone concentration measurements made at ground level suggests that the daytime increase is a result of a buildup of surface ozone during the day. The total ozone measurements made by the Brewer instrument during STOIC are compared with total ozone measurements made by the National Oceanic and Atmospheric Administration (NOAA) Dobson instrument, the NASA/Wallops electrochemical concentration cell ozonesondes and the total ozone mapping spectrometer satellite instrument.
Method of measuring the mobility spectrum versus agening of atmospheric ions
Authors: Knudsen E. , Israelsson S.
Published: February 2004

A new principle of studying the mobility spectrum versus agening of atmospheric ions has been developed. By exposing generated ions to an airstream and a counteracting adjustable electric field, the level when the force of the electric field will be greater than the mechanical (represented by the airstream) can be stated. By measuring the ion current versus the electric field at a fixed air stream, the mobility spectrum can be deduced. By selecting different values for air speed, electric field and traveling distance for the ions, the mobility spectrum versus agening of the ions can be deduced. Examples of recordings together with analysis are given.
Evaluation of monthly rainfall estimates derived from the special sensor microwave/imager (SSM/I) over the tropical Pacific
Authors: Berg Wesley , Avery Susan K.
Published: February 2004

Estimates of monthly rainfall have been computed over the tropical Pacific using passive microwave satellite observations from the special sensor microwave/imager (SSM/I) for the period from July 1987 through December 1990. These monthly estimates are calibrated using data from a network of Pacific atoll rain gauges in order to account for systematic biases and are then compared with several visible and infrared satellite‐based rainfall estimation techniques for the purpose of evaluating the performance of the microwave‐based estimates. Although several key differences among the various techniques are observed, the general features of the monthly rainfall time series agree very well. Finally, the significant error sources contributing to uncertainties in the monthly estimates are examined and an estimate of the total error is produced. The sampling error characteristics are investigated using data from two SSM/I sensors and a detailed analysis of the characteristics of the diurnal cycle of rainfall over the oceans and its contribution to sampling errors in the monthly SSM/I estimates is made using geosynchronous satellite data. Based on the analysis of the sampling and other error sources the total error was estimated to be of the order of 30 to 50% of the monthly rainfall for estimates averaged over 2.5°×2.5° latitude/longitude boxes, with a contribution due to diurnal variability of the order of 10%.
Radiative‐photochemical modeling of the annually averaged composition and temperature of the global atmosphere during the last glacial and interglacial periods
Authors: Karol I. L. , Frolkis V. A. , Kiselev A. A.
Published: February 2004

Recent measurements of CO2, CH4, and N2O content in Antarctic and Greenland ice core air allow the use of an one‐dimensional radiative‐photochemical model to reconstruct the annual global mean vertical distributions of trace gas concentrations for four periods: the contemporary period of 1985, the preindustrial period of 1850, the last glacial period of 18 ka B. P., and the interglacial period before the latter of 120–130 ka B. P. In this model reconstruction, the changes in surface air temperature and tropospheric relative humidity are prescribed, and both dry adiabatic and moist adiabatic lapse rates are used together with several other external estimates of radiative and photochemical parameters for these periods. The considerable reduction of greenhouse gas content in the atmosphere of both glacial and interglacial periods, including about a 50% reduction of stratospheric moisture in the glacial, leads to the warming of the middle and upper stratosphere by about 11 K and 4 K, in the glacial and interglacial periods, respectively. Stratospheric composition is found to be little sensitive to possible large variations of CO and NOx surface sources. The ozone mixing ratio drops to 10–12 ppbv in the lower troposphere and increases to a maximum 6.0–7.5 ppmv in 40 to 46‐km layer, but remains almost the same as in preindustrial and in 1985 periods in the 20 to 30‐km layer. This results in the approximate conservation of total ozone for all four periods considered.
Spectroscopic study of the seasonal variation of carbon monoxide vertical distribution above Kitt Peak
Authors: Pougatchev N. S. , Rinsland C. P.
Published: February 2004

A method to retrieve elements of the carbon monoxide (CO) vertical distribution from ground‐based high‐resolution infrared solar spectra has been developed. The method is based on the fact that the total column amount retrieved by nonlinear least squares spectral fitting techniques depends on the shape of the assumed a priori profile and this dependence is a function of the absorption line intensity and the lower state energy of the transition. Four CO lines between 2057 and 2159 cm−1 have been selected and the method has been tested on synthetic spectra. The CO total column content and average concentrations in two atmospheric layers (surface to 400 mbar and 400 mbar to the top of the atmosphere) can be retrieved with precisions of about 1% and less than 10%, respectively. Solar spectra recorded at Kitt Peak from 1982 to 1993 have been analyzed. The CO total column and the average concentration in the two layers show an asymmetrical seasonal cycle with extreme values of (1.1–2.1) × 1018 molecules cm−2, (50–80) parts per billion by volume (ppbv) in the top layer and (80–160) ppbv in the bottom layer, and precisions of 1, 3, and 6%, respectively; a spring maximum and late summer minimum are observed.
Toward optimizing Brewer zenith sky total ozone measurements at the Italian stations of Rome and Ispra
Authors: Muthama Nzioka John , Scimia Ugo , Siani Anna Maria , Palmieri Sabino
Published: February 2004

A “sky chart” program for optimizing Brewer zenith sky total ozone measurements at Rome Station is developed. It is applied to total ozone data at the Rome station, obtained by both direct Sun and zenith sky methods for the period May 1991 to March 1993, to compute new polynomial coefficients used in the calculation of the zenith sky total ozone values. These new coefficients are then utilized by the program to compute new zenith sky total ozone values. The percentage differences between (1) the zenith sky measurements computed using the old coefficients and direct Sun ozone data and (2) the direct Sun and the zenith sky total ozone values obtained using the new coefficients are presented. The new coefficients are also applied to some zenith sky (ZS) ozone data of Ispra. The results of the comparison between new ZS and old ZS values with respect to the corresponding DS measurements are presented. The new coefficients give more optimized zenith sky total ozone values than the old ones.
Comparison between SAGE II and ISCCP high‐level clouds: 2. Locating cloud tops
Authors: Liao Xiaohan , Rossow William B. , Rind David
Published: February 2004

A comparison is made of the vertical distribution of high‐level cloud tops derived from the Stratospheric Aerosol and Gas Experiment II (SAGE II) occultation measurements and from the International Satellite Cloud Climatology Project (ISCCP) for all Julys and Januarys in 1985 to 1990. The results suggest that ISCCP overestimates the pressure of high‐level clouds by up to 50–150 mbar, particularly at low latitudes. This is caused by the frequent presence of clouds with diffuse tops (>50% time when cloudy events are observed). The averaged vertical extent of the diffuse top is about 1.5 km. At midlatitudes where the SAGE II and ISCCP cloud top pressure agree best, clouds with distinct tops reach a maximum relative proportion of the total level cloud amount (about 30–40%), and diffuse‐topped clouds are reduced to their minimum (30–40%). The ISCCP‐defined cloud top pressure should be regarded not as the material physical height of the clouds but as the level which emits the same infrared radiance as observed. SAGE II and ISCCP cloud top pressures agree for clouds with distinct tops. There is also an indication that the cloud top pressures of optically thin clouds not overlying thicker clouds are poorly estimated by ISCCP at middle latitudes. The average vertical extent of these thin clouds is about 2.5 km.
On the evaluation of halocarbon radiative forcing and global warming potentials
Authors: Daniel John S. , Solomon Susan , Albritton Daniel L.
Published: February 2004

Net global warming potentials and instantaneous radiative forcing values that include the cooling from halocarbon‐induced ozone destruction have been calculated for 14 of the most significant halocarbons. These calculations were performed by incorporating knowledge of direct global warming potentials with an evaluation of the relationship between tropospheric cooling from stratospheric ozone loss and tropospheric halocarbon mixing ratios. The indirect cooling effect is strongly dependent upon the effectiveness of each halocarbon for ozone destruction. Strong net cooling is ascribed to additions of bromocarbon gases, while methyl chloroform and carbon tetrachloride are more nearly climate‐neutral, and the CFCs and HCFCs display strong net warming. Consideration of indirect cooling also has important implications for the expected future net halocarbon forcing of the climate system: in the next 20 years, halocarbon radiative forcing is not predicted to decrease as mixing ratios of strongly ozone‐depleting gases decline because of faster decreases in radiative cooling than in radiative warming. Furthermore, continuing production of HFCs as substitutes for CFCs could result in sharply increasing halocarbon radiative heating in the latter part of the 21st century because of the increasing atmospheric burden of these compounds.
Present OH measurement limits and associated uncertainties
Authors: Tanner D. J. , Eisele F. L.
Published: February 2004

The first ion‐assisted OH measurement instrument was developed and field tested in 1989. Since that time both instrument and technique have evolved substantially and several potential measurement interferences have been investigated. Included among these are reactions that could compete with the H2O/SO3 reaction, the effect Of H2O on the NO3− · HNO3/H2SO4 reaction, and potential wall losses. These investigations have also provided data of relevance to atmospheric ion and neutral chemistry for the two reactions listed above, as well as for the OH measurement itself. Measurements made at Mauna Loa Observatory in Hawaii show for the first time a diurnal variation in tropospheric OH which spans more than 2 orders of magnitude. Nighttime measurements revealed hydroxyl radicals in the 104 molecules cm−3 concentration range well after dark.
Surface temperature retrieval in a temperate grassland with multiresolution sensors
Authors: Goetz S. J. , Halthore R. N. , Hall F. G. , Markham B. L.
Published: February 2004

Radiometric surface temperatures retrieved at various spatial resolutions from aircraft and satellite measurements at the FIFE site in eastern Kansas were compared with near‐surface temperature measurements to determine the accuracy of the retrieval techniques and consistency between the various sensors. Atmospheric characterizations based on local radiosonde profiles of temperature, pressure, and water vapor were used with the LOWTRAN‐7 and MODTRAN atmospheric radiance models to correct measured thermal radiances of water and grassland targets for atmospheric attenuation. Comparison of retrieved surface temperatures from a helicopter‐mounted modular multispectral radiometer (MMR) (∼5‐m “pixel”), C‐130 mounted thematic mapper simulator (TMS) (NS001, ∼20‐m pixel), and the Landsat 5 thematic mapper (TM) (120‐m pixel) was done. Differences between atmospherically corrected radiative temperatures and near‐surface measurements ranged from less than 1°C to more than 8°C. Corrected temperatures from helicopter‐MMR and NS001‐TMS were in general agreement with near‐surface infrared radiative thermometer (IRT) measurements collected from automated meteorological stations, with mean differences of 3.2°C and 1.7°C for grassland targets. Much better agreement (within 1°C) was found between the retrieved aircraft surface temperatures and near‐surface measurements acquired with a hand‐held mast equipped with a MMR and IRT. The NS001‐TMS was also in good agreement with near‐surface temperatures acquired over water targets. In contrast, the Landsat 5 TM systematically overestimated surface temperature in all cases. This result has been noted previously but not consistently. On the basis of the results reported here, surface measurements were used to provide a calibration of the TM thermal channel. Further evaluation of the in‐flight radiometric calibration of the TM thermal channel is recommended.
Phase equilibria of H2SO4, HNO3, and HCl hydrates and the composition of polar stratospheric clouds
Authors: Wooldridge Paul J. , Zhang Renyi , Molina Mario J.
Published: February 2004

Thermodynamic properties and phase equilibria behavior for the hydrates and coexisting pairs of hydrates of common acids which exist in the stratosphere are assembled from new laboratory measurements and standard literature data. The analysis focuses upon solid‐vapor and solid‐solid‐vapor equilibria at temperatures around 200 K and includes new calorimetric and vapor pressure data. Calculated partial pressures versus 1/T slopes for the hydrates and coexisting hydrates agree well with experimental data where available.
Trajectory modeling of emissions from lower stratospheric aircraft
Authors: Sparling Lynn C. , Schoeberl Mark R. , Douglass Anne R. , Weaver Clark J. , Newman Paul A. , Lait Leslie R.
Published: February 2004

A series of isentropic trajectory calculations has been performed for emissions by stratospheric aircraft moving across the northern midlatitude oceanic flight corridors. Emission of exhaust is simulated by the daily initialization of air parcels along a flight path on the 500 K isentropic surface. Parcels are tracked during the first three weeks of each January from 1980 to 1994 in order to determine the interannual variability in the spatial distribution of the exhaust and the likelihood of exposure to cold temperatures. Few parcels emitted along these flight paths at this time of year were found to have experienced nitric acid trihydrate (NAT) formation temperatures, except for the particularly cold Januarys 1986, 1987, and 1992. We also find that large zonal fluctuations in the distribution of the emissions are typical for this time of year and are strongly dependent on flight path. An extended 6‐month (January–June) run in which parcels were released daily along the New York–London route shows that emissions in the flight corridor increase at a time‐averaged rate which is nearly twice the rate at which the zonal average increases. In addition, local fluctuations of pollutant density can be several times higher than the zonal average and can persist for several weeks. A study of seasonal variability also shows a rapid buildup of emissions during the summer months. These elevated emission levels must be considered in the interpretation of environmental impact assessments based on two‐dimensional transport models.
A search for the seasonal variability on the depositional fluxes of 7Be and 210Pb
Authors: Baskaran M.
Published: February 2004

Investigations of the atmospheric fallout of 7Be and 210Pb in many places around the globe indicate that there are seasonal variations on the depositional fluxes of these nuclides: high in winter in a few places, while in most places the high occurs in spring. However, these earlier studies did not address quantitatively the corresponding seasonal variations of the amount of precipitation during these periods. Data on the depositional fluxes of 7Be and 210Pb in Galveston, Texas, during the years 1989–1991 indicate that the seasonal variation is not uniform from year to year, and the amount of precipitation primarily controls the depositional fluxes. All the recently published data on the depositional fluxes of these radionuclides to date are synthesized. Also, the seasonal variations of the depositional fluxes of 7Be and 210Pb due to the variations in the amounts of precipitation during these seasons are discussed. This study clearly shows that the depositional fluxes of 7Be and 210Pb during fall were minimum, and most of the time the fallout maxima were confined to either spring and/or summer. Interseasonal variations of the depositional fluxes of these nuclides do not remain the same. The data presented in this paper in conjunction with earlier published data seem to indicate that the observed seasonal increase in the depositional fluxes of 7Be during spring is not due to the troposphere‐stratosphere exchange of air masses during that season. The 7Be/ 210Pb activity ratio values remain the highest in summer and this is attributed to the increased rate of vertical transport of 7Be (from the upper troposphere to the middle and lower troposphere) and 210Pb (from the lower troposphere to upper troposphere) due to decreased stability of the troposphere during summer months.
Entrainment of free tropospheric aerosols as a regulating mechanism for cloud condensation nuclei in the remote marine boundary layer
Authors: Raes Frank
Published: February 2004

A box model has been developed to study the formation of cloud condensation nuclei from DMS, in the unpolluted marine boundary layer (MBL). Chemical and microphysical processes include gas phase chemistry of DMS and SO2, formation and growth of H2SO4‐H2O aerosols, in‐cloud SO2 oxidation, and scavenging of SO2 and H2SO4 molecules by sea salt, cloud drops, and precipitation. Meteorological processes include exchange between the MBL and the overlying free troposphere (FT) and horizontal mixing after particle removal by precipitation. The description of the FT aerosol is based on the notion of new particle production in the upper troposphere (for which there is experimental evidence) and the notion that these particles evolve into a self‐preserving aerosol (for which there is no clear experimental evidence yet). We argue that FT aerosols are expected to be self‐preserving in areas of large‐scale subsidence such as the subtropics. The model results are in reasonable agreement with summer observations of DMS, SO2, non‐sea‐salt (nss) SO4, CN, and CCN at Cape Grim. They show that entrainment of FT aerosols in the MBL quenches new particle formation within the MBL. A sensitivity/uncertainty analysis shows that most of the variation in the number concentration of MBL aerosols is due to the variation in parameters linked to the FT aerosol, whereas most of the variations in the MBL nss‐sulphate mass is due to variations in the DMS flux. We conclude that FT‐MBL exchange is likely to be an important mechanism that can explain both the observed levels of CN and CCN (active in stratiform clouds) in the MBL and their lack of short‐term variability.
Uncertainties in the global source distribution of nitrous oxide
Authors: Bouwman A. F. , Van der Hoek K. W. , Olivier J. G. J.
Published: February 2004

Inventories with 1°×1° resolution were compiled of nitrous oxide (N2O) emissions from fertilized arable land, animal excreta, postclearing effects on soil emissions, fossil fuel and fuelwood combustion, and industrial N2O sources. For other sources of N2O, including soils under natural vegetation, oceans, and biomass burning, published inventories were used. From these inventories the annual N2O emission was calculated for four broad latitudinal zones covering the globe. Uncertainties were assessed by comparing variants of inventories with source estimates inferred from inverse modeling techniques. Major uncertainties occur in the tropics, where small errors in both soil and oceanic emission estimates may have large repercussions for the zonal distributions. Although there may still be many poorly known and unidentified N2O sources, the analysis has resulted in improved understanding of some sources, i.e., (1) the oceanic N2O emission may be more important than assumed in recent global N2O budgets, with a major portion stemming from the 30°–90°S zone; (2) the N2O emission from animal excreta forms a significant global source; (3) most of the N2O from arable lands and grasslands, including effects of synthetic fertilizers and animal excreta, comes from the northern hemisphere; accounting for only the synthetic‐fertilizer effect on N2O emission leads to an underestimation of the emission from arable lands; (4) fossil fuel combustion and industrial N2O sources are dominant in the 30°–90°N zone, while N2O from fuelwood combustion is mainly produced in the 0°–30°N zone; (5) the estimation of enhanced N2O soil emission following tropical forest clearing that has accounted for gradually declining N2O fluxes, along with aging of the clearing leads to a global emission that is significant but lower than previous estimates; (6) most of the N2O from coastal marine and freshwater systems and soil N2O emission resulting from N deposition probably comes from the northern hemisphere.
Estimating release of carbon from 1990 and 1991 forest fires in Alaska
Authors: Kasischke Eric S. , French Nancy H. F. , Bourgeau‐Chavez Laura L. , Christensen N. L.
Published: February 2004

An improved method to estimate the amounts of carbon released during fires in the boreal forest zone of Alaska in 1990 and 1991 is described. This method divides the state into 64 distinct physiographic regions and estimates areal extent of five different land covers: two forest types, peat land, tundra, and nonvegetated. The areal extent of each cover type was estimated from a review of topographic maps of each region and observations on the distribution of forest types within the state. Using previous observations and theoretical models for the two forest types found in interior Alaska, models of biomass accumulation as a function of stand age were developed. Stand age distributions for each region were determined using a statistical distribution based on fire frequency, which was from available long‐term historical records. Estimates of the degree of biomass combusted were based on recent field observations as well as research reported in the literature. The location and areal extent of fires in this region for 1990 and 1991 were based on both field observations and analysis of satellite (advanced very high resolution radiometer (AVHRR)) data sets. Estimates of average carbon release for the two study years ranged between 2.54 and 3.00 kg m−2, which are 2.2 to 2.6 times greater than estimates used in other studies of carbon release through biomass burning in boreal forests. Total average annual carbon release for the two years ranged between 0.012 and 0.018 Pg C yr−1, with the lower value resulting from the AVHRR estimates of fire location and area.