bluuebunny/crossref_metadata_2025 huggingface dataset:
Bioalteration of basaltic glass in the oceanic crust
Authors: Furnes Harald , Staudigel Hubert , Thorseth Ingunn H. , Torsvik Terje , Muehlenbachs Karlis , Tumyr Ole
Published: February 2004

Bioalteration of Quaternary to Early Cretaceous basaltic glass from pillow lavas of the upper oceanic crust can be documented in Deep Sea Drilling Project/Ocean Drilling Program (DSDP/ODP) samples from shallow to deep drill holes from the north to central Atlantic Ocean, Lau Basin, and Costa Rica Rift, a wide range of marine settings. Biogenerated textures are rooted in fractures and occur as two main types, a granular type and a tubular type. The granular type, common at all depths within the volcanic pile, appears as solid bands, semicircles or irregular patches of individual and/or coalesced spherical bodies, mostly 0.2–0.6 μm in diameter, with irregular protrusions into the fresh glass. The tubular type is more common at deeper levels in the crust and consists of thin tubes, sometime branching bodies, mostly 20–30 μm long and are more common at deeper levels. The upper crust displays a large variability in the relative importance of biotic to abiotic alteration, and the degree of bioalteration appears to decrease with depth. Thus the fraction of bioalteration of the total alteration of the glass ranges from 20–90% in the upper 300 m down to a maximum of 10% at about 500 m depth. This might be due to a natural variability in the abundance of bioaltered glass or to biased sampling from low drilling recovery of relatively young crust. The proportion of bioaltered to abiotically altered glass does not show any systematic variations with age of the crust. Thus bioalteration lasts as long as abiotic alteration, i.e., for as long as water is available to the hydration of the oceanic crust. Evidence from heat flow measurements suggests that hydrothermal circulation lasts until at least ∼70 Ma, and thus the deep biosphere is likely to expand at least into crust of this age.
The University of Illinois, Urbana‐Champaign three‐dimensional stratosphere‐troposphere general circulation model with interactive ozone photochemistry: Fifteen‐year control run climatology
Authors: Rozanov E. V. , Schlesinger M. E. , Zubov V. A.
Published: February 2004

A new University of Illinois at Urbana‐Champaign 24‐layer troposphere‐stratosphere general circulation model with interactive photochemistry is presented. We document here the results of a 15‐year‐long control run of the model and an evaluation of its performance. The ability of the model to simulate the Northern Hemisphere polar vortex has been improved because of the modification of the gravity wave drag parameterization. The extension and update of the chemical routine improved the simulated species distributions. As a result, the agreement of the simulated fields with observations is within 20% for total ozone and other species, 5 K for temperature, and 10 m s−1 for zonal wind over most of the atmosphere. The model simulates well the appearance of polar stratospheric clouds and the “ozone hole” over Antarctica. However, in some particular points the model results are unrealistic. These are (1) a cold bias (∼25 K) in the Southern Hemisphere lower stratosphere during austral summer, (2) a warm bias (∼20 K) in the middle stratosphere during austral winter, (3) a warm bias (∼10 K) near the stratopause in the tropics, and (4) a persistent cold bias of up to 8 K in the lowermost stratosphere almost everywhere over the globe. These problems may be due to the lack of a nonorographic gravity wave drag parameterization in the model, the influence of the top boundary conditions, and/or some problems with model treatment of the zonal wind‐planetary wave interaction in the stratosphere. Despite these few shortcomings, the model is now ready to be applied to several climate‐chemistry issues such as future ozone layer changes due to increasing greenhouse gas concentrations, the atmospheric influence of volcanic eruptions, and sun‐climate relations.
European pollution outbreaks during ACE 2: Lofted aerosol plumes observed with Raman lidar at the Portuguese coast
Authors: Ansmann Albert , Wagner Frank , Althausen Dietrich , Müller Detlef , Herber Andreas , Wandinger Ulla
Published: February 2004

During the Second Aerosol Characterization Experiment (ACE 2) in the summer of 1997, four pollution outbreaks from the European continent were monitored at Sagres (37°N, 9°W), Portugal, by applying the Raman lidar technique at a wavelength of 532 nm. The findings are presented in terms of vertical profiles of the volume extinction coefficient of the particles, the backscatter coefficient, the extinction‐to‐backscatter ratio (lidar ratio), the relative humidity, and the geometrical and optical depths of the marine boundary layer and the continental aerosol layers aloft. The lidar‐derived optical depths are compared with results of simultaneously conducted star photometer observations. During all outbreaks, similar aerosol profiles were observed. Above the cold marine boundary layer the warm continental pollution plume extended from about 500 to a maximum height of 3500 m. Strong temperature inversions prohibited mixing of the two layers. The ACE 2 mean optical depths of the marine boundary layer and the aerosol layers aloft were about 0.05 and 0.1, respectively. Maximum values of the optical depth in the pollution plumes were close to 0.25 at 532 nm. On average, the free‐tropospheric layers contributed about 60% to the total optical depth at the coast. Volume extinction coefficients were mainly between 30 and 70 Mm−1, and the lidar ratios ranged from 30 to 80 sr in the polluted continental air.
Volcanic layers in Antarctic (Vostok) ice cores: Source identification and atmospheric implications
Authors: Basile Isabelle , Petit Jean Robert , Touron Stéphanie , Grousset Francis E. , Barkov Nartsiss
Published: February 2004

Fifteen visible volcanic ash layers (tephra) from Vostok ice cores have been analyzed for major elements, trace elements, and Sr and Nd isotope composition. Comparison of their geochemical signatures to lava composition from the inventory of Antarctic and subantarctic volcanoes, which have been active over the last 0.5 million years, indicates that nine layers originate from activity of the South Sandwich volcanic arc, three from southern South America, one from the Antarctic Peninsula (Bransfield Strait), and one from West Antarctica (Marie Byrd Land province). The large size of the tephra (up to 50 μm) requires rapid atmospheric transfer from the volcanic centers to East Antarctica. Rapid tropospheric transport from the southwestern Atlantic, penetrating East Antarctica, therefore predominates during the period studied, whether in glacial or interglacial climatic mode. In spite of the low frequency of occurrence of visible tephra layers in Vostok core (one event every 20 kyr), the overall atmospheric pathway of these ash events appears consistent with the almost continuous advection of continental dust from South America.
Chamber measurements of CI depletion in cloud‐processed sea‐salt aerosol
Authors: Caffrey Peter , Hoppel William , Frick Glendon , Fitzgerald James , Shantz Nicole , Leaitch W. Richard , Pasternack Louise , Albrechcinski Tom , Ambrusko John
Published: February 2004

Cl− depletion in sea‐salt CCN was measured in chamber experiments after cloud formation in the presence of SO2 and O3. In each experiment, two successive clouds were formed on a sea‐salt aerosol generated from the nebulization of filtered seawater, while chamber SO2 (g) and O3 (g) concentrations ranged from 4.8–8.3 ppb and 69–75 ppb. Particle growth from cloud processing reactions was measured with a differential mobility analyzer (DMA) immediately after cloud dissipation, and particles activated from dry radii of 0.02–0.03 μm showed growth to 0.08 and 0.12 μm, with total aerosol mass increases of 7.0 and 2.4 μg m−3 (assuming a particle density of 2.4 g cm−3). Particle growth was greater than that predicted by standard SO2‐O3 oxidation kinetics and cannot be accounted for by the buffering capacity of the sea‐salt CCN. Micro‐orifice impactor (MOI) measurements of inorganic ions in the postcloud aerosol size distributions show, within analytical error, a 1:1 displacement of Cl− with nss ‐ SO42−, until the SO42− is in excess and the Cl− is completely depleted at the smaller CCN sizes. Calculations of Cl− depletion, based upon the input size distribution and assuming particle growth via sulfate addition, show greater Cl− depletion on smaller size particles than the measured values. However, there is agreement within the uncertainty of the measured values.
Measurements of enhanced H2SO4 and 3–4 nm particles near a frontal cloud during the First Aerosol Characterization Experiment (ACE 1)
Authors: Weber R. J. , Chen G. , Davis D. D. , Mauldin R. L. , Tanner D. J. , Eisele F. L. , Clarke A. D. , Thornton D. C. , Bandy A. R.
Published: February 2004

Observations of new particle production recorded near a frontal cloud at ∼6 km above sea level in a remote marine region are reported. Two distinct locations situated near the cloud were found to have enhanced concentrations of sulfuric acid vapor (H2SO4) and freshly formed 3–4 nm particles. Both were in droplet‐free air situated above cloudy regions. No evidence for enhanced H2SO4 or nucleation was observed in clear air far from the cloud. In the nucleating region the aerosol size distribution from 3 nm to 600 μm was observed to be trimodal, with a prominent ultrafine mode, and was qualitatively similar to surface‐based measurements recorded in regions of postfrontal subsidence. The measurements support the notion that new particle production in the free troposphere occurs preferentially in clear air near clouds via enhanced photochemical production of nucleation precursor gases and that H2SO4 participates. A model simulation suggested that a doubling of ultraviolet intensities above the cloud due to cloud enhanced up‐welling radiation or reasonable enhancements in sulfur dioxide concentrations could account for the higher H2SO4 concentration observed near the cloud. In the nucleation regions, H2SO4 and water vapor concentrations were too low for binary nucleation of sulfuric acid and water, according to current nucleation models. The mechanisms of particle formation and growth remain uncertain. The measurements were part of the first Aerosol Characterization Experiment (ACE 1) conducted in the remote South Pacific Ocean (153°E, 47°S) on November 27, 1995.
A robust retrieval of water vapor column in dry Arctic conditions using the rotating shadowband spectroradiometer
Authors: Kiedron P. , Michalsky J. , Schmid B. , Slater D. , Berndt J. , Harrison L. , Racette P. , Westwater E. , Han Y.
Published: February 2004

A method to retrieve water vapor column using the 940‐nm water vapor absorption band in dry Arctic conditions is presented. The retrievals with this method are stable with respect to uncertainties in instrument radiometric calibration, air pressure, solar source function, and aerosols. The water vapor column was retrieved with this method using spectra obtained with the rotating shadowband spectroradiometer (RSS) that was deployed during an intensive observation period near Barrow, Alaska, in March 1999. A line‐by‐line radiative transfer model was used to compute water vapor transmittance. The retrievals with this method are compared with retrievals obtained from three independent measurements with microwave radiometers. All four measurements show the same pattern of temporal variations. The RSS results agree most closely with retrievals obtained with the millimeter‐wave imaging radiometer (MIR) at its 183 GHz±7 double‐side band channel. Their correlation over a period of 7 days when water vapor column varied between 0.75 mm and 3.6 mm (according to RSS) is 0.968 with MIR readings 0.12 mm higher on average.
Raman lidar measurements of the aerosol extinction‐to‐backscatter ratio over the Southern Great Plains
Authors: Ferrare Richard A. , Turner David D. , Brasseur Lorraine Heilman , Feltz Wayne F. , Dubovik Oleg , Tooman Tim P.
Published: February 2004

We derive profiles of the aerosol extinction‐to‐backscatter ratio, Sa, at 355 nm using aerosol extinction and backscatter profiles measured during 1998 and 1999 by the operational Raman lidar at the Department of Energy Atmospheric Radiation Measurement Program Southern Great Plains site in north central Oklahoma. Data from this Raman/Rayleigh‐Mie lidar, which measures Raman scattering from nitrogen as well as the combined molecular (Rayleigh) and aerosol (Mie) scattering at the laser wavelength, are used to derive aerosol extinction and backscattering independently as a function of altitude. Because this lidar operates at 355 nm, where molecular backscattering is comparable to aerosol backscattering, Sa retrievals are generally limited to conditions where aerosol extinction at 355 nm is >0.03 km−1. The mean value of Sa at 355 nm derived for this period was 68 sr with a standard deviation of 12 sr. Sa was generally about 5–10 sr higher during high aerosol optical thickness (AOT) (>0.3) conditions than during low AOT (<0.1). A similar increase in Sa was found when the relative humidity increased from 30 to 80%. Large (>15%) variations in the vertical profile of Sa occurred about 30% of the time, which implies that significant variability in the vertical distribution of the aerosol size distribution, shape, and/or composition often occurs. The Raman lidar measurements of Sa were compared with estimates of particle size and refractive index derived from an algorithm that uses ground‐based Sun photometer measurements of Sun and sky radiance. For 17 cases of coincident Raman lidar and Sun and sky radiance measurements, Sa was linearly correlated with the aerosol fine mode effective radius and the volume ratio of fine/coarse particles.
Kinetic model for reaction of ClONO2 with H2O and HCl and HOCl with HCl in sulfuric acid solutions
Authors: Shi Q. , Jayne J. T. , Kolb C. E. , Worsnop D. R. , Davidovits P.
Published: February 2004

The heterogeneous reactions ClONO2 + H2O → HOCl + HNO3 (1), ClONO2 + HCl → Cl2 + HNO3 (2), and HOCl + HCl → Cl2 + H2O (3) on stratospheric aerosols convert ClONO2 and HCl to photo‐labile species, producing reactive Cl and ClO which are responsible for catalyzing ozone destruction in the lower stratosphere. The extent of the resulting ozone loss mirrors the steep negative temperature dependence of these reactions, which strongly depend on the solubility of ClONO2, HCl, and HOCl, and on the activity of H2O. Predicting the effect of these heterogeneous processes throughout the stratosphere requires detailed modeling of liquid phase solubility, diffusion, and reaction kinetics. A series of recent experiments from a number of laboratories have refined measurements of liquid diffusion coefficients, HCl and HOCl solubilities, and the reactivity of ClONO2 + H2O, ClONO2 + HCl and HCl + HOCl on liquid films, droplets, and aerosols. On the basis of those measurements we present a phenomenological uptake model in which parameterizations of ClONO2, HCl, and HOCl heterogeneous kinetics appropriate for stratospheric H2SO4/H2O aerosols are addressed. In this model we suggest that under high acid concentration conditions both HOCl and ClONO2 are protonated before they react with HCl. Data for all three reactions in concentrated H2SO4 solution indicate an acid‐catalyzed reaction channel, which had previously been inferred for ClONO2 hydrolysis. This updated parameterization is most significant at relatively high temperatures above 205 K which produce H2SO4 aerosols of >60 acid wt%, where the acid‐catalyzed reaction channels dominate. The comparisons between our new formulation and other recent formulations are presented.
Response of middle atmosphere chemistry and dynamics to volcanically elevated sulfate aerosol: Three‐dimensional coupled model simulations
Authors: Al‐Saadi Jassim A. , Pierce R. Bradley , Fairlie T. Duncan , Kleb Mary M. , Eckman Richard S. , Grose William L. , Natarajan Murali , Olson Jennifer R.
Published: February 2004

The NASA Langley Research Center Interactive Modeling Project for Atmospheric Chemistry and Transport (IMPACT) model has been used to examine the response of the middle atmosphere to a large tropical stratospheric injection of sulfate aerosol, such as that following the June 1991 eruption of Mount Pinatubo. The influence of elevated aerosol on heterogeneous chemical processing was simulated using a three‐dimensional climatology of surface area density (SAD)developed using observations made from the Halogen Occultation Experiment, Stratospheric Aerosol and Gas Experiment II, and Stratospheric Aerosol Measurement satellite instruments beginning in June 1991. Radiative effects of the elevated aerosol were represented by monthly mean zonally averaged heating perturbations obtained from a study conducted with the European Center/Hamburg (ECHAM4) general circulation model combined with an observationally derived set of aerosol parameters. Two elevated‐aerosol simulations were integrated for 31/2 years following the volcanic injection. One simulation included only the aerosol radiative perturbation, and one simulation included both the radiative perturbation and the elevated SAD. These perturbation simulations are compared with multiple‐year control simulations to isolate relative contributions of transport and heterogeneous chemical processing. Significance of modeled responses is assessed through comparison with interannual variability. Dynamical and photochemical contributions to ozone decreases are of comparable magnitude. Important stratospheric chemical/dynamical feedback effects are shown, as ozone reductions modulate aerosol‐induced heating by up to 10% in the lower stratosphere and 25% in the middle stratosphere. Dynamically induced changes in chemical constituents which propagate into the upper stratosphere are still pronounced at the end of the simulations.
Optical observations of terrestrial lightning by the FORTE satellite photodiode detector
Authors: Kirkland M. W. , Suszcynsky D. M. , Guillen J. L. L. , Green J. L.
Published: February 2004

We review data from observations of terrestrial lightning obtained by the FORTE satellite between September 1997 and January 2000. A silicon photodiode detector (PDD) records the intensity‐time history of transient optical events occurring within its 80° circular field of view. This field of view corresponds to a circle on the Earth's surface having an approximate diameter of 1200 km. We describe the instrument, present examples of the data, explain how the data are screened for false triggers, and review, within the context of previous measurements, the general statistics of peak irradiance, pulse width, and energy associated with the data. We compare the FORTE data with National Lightning Detection Network (NLDN) reported cloud‐to‐ground (CG) strokes and find that the PDD detection efficiency for these CG strokes is ∼6%. Moreover, we infer that FORTE preferentially detects the in‐cloud portion of optical lightning signals. Events having inferred peak powers between 108 and 1012 W and optical energy outputs between 103 and 109 J are observed. From a population of nearly 700,000 events we find that the median peak power and median detected optical energy at the source are estimated to be ∼1×109 W and 4.5×105 J, respectively. These values of source peak power and energy are comparable to previous space‐based measurements and consistent with aircraft‐based and ground‐based measurements. The observed median effective pulse width is about 590 microseconds. Further, the pulse widths for CG strokes, reported by NLDN, are inversely proportional to pulse peak power.
NOx production by lightning over the continental United States
Authors: Bond Donald W. , Zhang Renyi , Tie Xuexi , Brasseur Guy , Huffines Gary , Orville Richard E. , Boccippio Dennis J.
Published: February 2004

The production of NOx by lightning over the contiguous United States has been evaluated by using combined ground‐based and satellite lightning measurements. The lightning data from the National Lightning Detection Network (NLDN) over the period of 1995–1999, along with a ratio of intracloud (IC) to cloud‐to‐ground (CG) flashes derived in conjunction with satellite lightning measurements from the Optical Transient Detector (OTD), are analyzed to obtain the number of CG and IC flashes. The average annual lightning counts over the 5‐year period are about 23 million for CG flashes and 55 million for IC flashes. The resulting lightning distributions are employed to calculate the production of NOx, assuming a NO production rate of 6.7 × 1026 molecules for each CG flash and 6.7 × 1025 molecules for each IC flash. NOx production by lightning varies seasonally in accordance with the lightning distribution, with the maximum production occurring in the summer (June, July, and August) and in the Southeast. CG flashes produce more NOA than IC flashes despite fewer CG flashes by a factor of 2 or more. The geographical and seasonal production of NOx by lightning is compared to NOx emissions from other sources (i.e., from anthropogenic, soil, and biomass‐burning emissions). The results indicate that regional emissions of NOx by lightning can be significant in the summertime and may play a critical role in ozone formation in the free troposphere. Our estimate of NOx emission by lightning over the United States would decrease by an order of magnitude if we use the production rates from a recent laboratory study [Wang et al., 1998] that are significantly lower than previous estimates.
Downward propagation of zonal mean zonal wind anomalies from the stratosphere to the troposphere: Model and reanalysis
Authors: Christiansen Bo
Published: February 2004

The connection between the Arctic Oscillation and the stratosphere is investigated on intra‐annual timescales. Both the National Centers for Environmental Prediction reanalysis data and a general circulation model simulation are used. In the winter half year November–April the dominant variability in the stratosphere in middle and high latitudes has the form of downward propagation of zonal mean zonal wind anomalies. The strength of the anomalies decays below 10 hPa, but often the anomalies reach the surface. The time for the propagation from 10 hPa to the surface is ∼15 days. When positive anomalies reach the surface, the phase of the Arctic Oscillation tends to be positive. The stratospheric variability and the downward propagation is found to be driven by the vertical component of the Eliassen‐Palm flux. This flux propagates from the lower troposphere to the tropopause on a timescale of 5 days. Model and reanalysis compare well in the structure of the stratospheric variability and the connection between the stratosphere and troposphere. However, the strength of the stratospheric variability is ∼25% weaker in the model.
Interannual variability in the global carbon cycle
Authors: Houghton R. A.
Published: February 2004

The annual growth rate of atmospheric CO2 has varied between 1 and 5 Pg C yr−1 over the last decades. Most of this variation is associated with terrestrial and oceanic exchanges of carbon which seem to vary independently. Three processes contribute to the annual flux of carbon from terrestrial ecosystems: changes in land use, natural disturbances, and metabolic changes caused by variations in climate. Because rates of land‐use change are often not available on an annual basis, estimates of the flux of carbon attributable to land use change may underestimate year‐to‐year variability. Limited data reviewed here suggest that the interannual variability of this flux is generally small for two reasons. First, although rates of land use change may vary substantially from year to year at a local scale, variability is generally less at regional and global scales because high rates of deforestation in one area do not necessarily coincide with high rates in other areas. Second, less than 50% of the carbon lost to the atmosphere as a result of land use change is lost in the year of disturbance; the rest is released in subsequent years. The interannual variability of the flux of carbon from land use change is thus less variable than rates of land use change and probably accounts, globally, for less than 5–10% of the observed variation in the annual growth rate of CO2 in the atmosphere. Natural disturbances are estimated to account for a similar fraction of the variation. The most important contributor appears to be the effect of short‐term changes in climate (temperature and precipitation) on terrestrial metabolism. Over the period 1980–1995, year‐to‐year differences in the flux of carbon from terrestrial metabolism have almost been as large as variations in the growth rate of atmospheric CO2.
Detecting the recovery of total column ozone
Authors: Weatherhead Elizabeth C. , Reinsel Gregory C. , Tiao George C. , Jackman Charles H. , Bishop Lane , Frith Stacey M. Hollandsworth , DeLuisi John , Keller Teddie , Oltmans Samuel J. , Fleming Eric L. , Wuebbles Donald J. , Kerr James B. , Miller Alvin J. , Herman Jay , McPeters Richard , Nagatani Ronald M. , Frederick John E.
Published: February 2004

International agreements for the limitation of ozone‐depleting substances have already resulted in decreases in concentrations of some of these chemicals in the troposphere. Full compliance and understanding of all factors contributing to ozone depletion are still uncertain; however, reasonable expectations are for a gradual recovery of the ozone layer over the next 50 years. Because of the complexity of the processes involved in ozone depletion, it is crucial to detect not just a decrease in ozone‐depleting substances but also a recovery in the ozone layer. The recovery is likely to be detected in some areas sooner than others because of natural variability in ozone concentrations. On the basis of both the magnitude and autocorrelation of the noise from Nimbus 7 Total Ozone Mapping Spectrometer ozone measurements, estimates of the time required to detect a fixed trend in ozone at various locations around the world are presented. Predictions from the Goddard Space Flight Center (GSFC) two‐dimensional chemical model are used to estimate the time required to detect predicted trends in different areas of the world. The analysis is based on our current understanding of ozone chemistry, full compliance with the Montreal Protocol and its amendments, and no intervening factors, such as major volcanic eruptions or enhanced stratospheric cooling. The results indicate that recovery of total column ozone is likely to be detected earliest in the Southern Hemisphere near New Zealand, southern Africa, and southern South America and that the range of time expected to detect recovery for most regions of the world is between 15 and 45 years. Should the recovery be slower than predicted by the GSFC model, owing, for instance, to the effect of greenhouse gas emissions, or should measurement sites be perturbed, even longer times would be needed for detection.
Vertical aerosol fluxes measured by the eddy covariance method and deposition of nucleation mode particles above a Scots pine forest in southern Finland
Authors: Buzorius G. , Rannik Ü. , Mäkelä J. M. , Keronen P. , Vesala T. , Kulmala M.
Published: February 2004

Particle number fluxes were measured by the eddy covariance method above a Scots pine forest in southern Finland. The observed number fluxes included particles with sizes down to 10 nm in diameter. The errors of measured particle number fluxes resulting from the technical limitations of particle counter and atmospheric fluctuations of water content are estimated. Simultaneous aerosol size distribution measurements were used to obtain information on particle sizes contributing to the flux. During new particle formation events the particle fluxes were dominated by nucleation mode particles, allowing the deduction of the deposition velocities characteristic to those particles. The corresponding deposition velocities were within a range from 5 to 40 mm s−1.
Improvements to the correlated‐k radiative transfer method: Application to satellite infrared sounding
Authors: Edwards D. P. , Francis G. L.
Published: February 2004

This paper presents a new radiative transfer model based on the correlated‐k technique that is particularly suitable for applications associated with broadband infrared satellite remote sounding of the atmosphere. We describe new developments to the approach which improve the accuracy of correlated‐k distribution radiative transfer calculations. These include methods to model an instrument response function, spectral line overlap for multiple gases, and the spectral variation of solar and thermal source functions. We also describe an approach to improving vertical spectral correlation along ray paths through a nonhomogeneous atmosphere. For a radiative transfer model to be efficient as the forward model of a retrieval scheme, the calculation of analytical Jacobians is particularly important. This is implemented in the model using a variation on the correlated‐k approach. The application of the new model, RADCKD, is demonstrated with example calculations for the EOS Terra satellite Measurements of Pollution in the Troposphere (MOPITT) instrument.
Validation of 3 years of ozone measurements over Network for the Detection of Stratospheric Change station Lauder, New Zealand
Authors: Brinksma E. J. , Bergwerff J. B. , Bodeker G. E. , Boersma K. F. , Boyd I. S. , Connor B. J. , de Haan J. F. , Hogervorst W. , Hovenier J. W. , Parrish A. , Tsou J. J. , Zawodny J. M. , Swart D. P. J.
Published: February 2004

A large number of ozone profiles measured by using various methods (lidar, ozonesondes, microwave radiometer, and Stratospheric Aerosol and Gas Experiment II) over Lauder, New Zealand, between late 1994 and early 1998 are intercompared. These profiles are also used to validate a collocated Dobson spectrophotometer. Between March 1996 (August 1996 for sonde measurements) and January 1998, all instruments were operational and no instrument changes took place. The ozone number densities averaged over this period agreed within 5% in the 20‐ to 35‐km range. Between 12 and 20 km, lidar and sonde results deviated by less than 8%, and lidar and SAGE II results deviated by less than 15%. The ozone column densities measured by the Dobson spectrophotometer agreed within 3% with the integrated ozone profiles. The various methods are discussed, and modifications are proposed. They comprise a decrease of the reported sonde altitudes of about 125 m (±50 m) to correct for the response time of the sonde's chemical solution, the use of more accurate molecular parameter values in the lidar algorithm, and a 2.5% decrease in SAGE II ozone densities. Improved agreement between the average ozone profiles to within 1.5% for lidar and sondes (20–35 km) and within 2.5% for lidar and SAGE II (20–35 km) is achieved. The Dobson results are found to be influenced by the annual cycle of the temperature profile through the altitude‐averaged ozone absorption cross section, which has been assumed to be constant in the presented data but actually varies with an amplitude of 2% over Lauder.
Determination of radiative forcing of Saharan dust using combined TOMS and ERBE data
Authors: Hsu N. Christina , Herman Jay R. , Weaver Clark
Published: February 2004

We determine the direct radiative forcing of Saharan dust aerosols by combining aerosol information derived from Nimbus‐7 TOMS with radiation measurements observed at the top of atmosphere (TOA) by NOAA‐9 ERBE made during February‐July 1985. Cloud parameters and precipitable water derived from NOAA‐9 HIRS2 were used to aid in screening for clouds and water vapor in the analyses. Our results indicate that under “cloud‐free” and “dry” conditions there is a good correlation between the ERBE TOA outgoing longwave fluxes and the TOMS aerosol index measurements over both land and ocean in areas under the influence of airborne Saharan dust. The ERBE TOA outgoing shortwave fluxes were also found to correlate well with the dust loading derived from TOMS over ocean. However, the calculated shortwave forcing of Saharan dust aerosols is very weak and noisy over land for the range of solar zenith angle viewed by the NOAA‐9 ERBE in 1985. Sensitivity factors of the TOA outgoing fluxes to changes in aerosol index were estimated using a linear regression fit to the ERBE and TOMS measurements. The ratio of the shortwave‐to‐longwave response to changes in dust loading over the ocean is found to be roughly 2 to 3 but opposite in sign. The monthly averaged “clear‐sky” TOA direct forcing of airborne Saharan dust was also calculated by multiplying these sensitivity factors by the TOMS monthly averaged “clear‐sky” aerosol index. Both the observational and theoretical analyses indicate that the underlying surface properties, dust layer height, ambient moisture content, and the presence of cloud all play important roles in determining the TOA direct radiative forcing due to mineral aerosols.
Intraseasonal variations of water vapor in the tropical upper troposphere and tropopause region
Authors: Mote Philip W. , Clark Hannah L. , Dunkerton Timothy J. , Harwood Robert S. , Pumphrey Hugh C.
Published: February 2004

We show the signature of the tropical intraseasonal oscillation (TIO) in upper tropospheric moisture and dynamical fields, roughly between 200 and 100 hPa. Relationships among these fields are examined using lag‐correlation analysis and using multivariate extended empirical orthogonal functions (MEEOFs), which maximize the shared explained variance among several fields for both spatial and temporal variations. The MEEOFs show that all of the fields respond to the TIO and that the TIO is the dominant factor influencing each of the fields on these timescales. Convection associated with the TIO moistens the upper troposphere up to about 150 hPa, as expected; the behavior at 100 hPa is more complex. Over the longitude range where the TIO is associated with convection, roughly 60°–180°E, 100‐hPa temperature and water vapor tend to be reduced above convection on TIO timescales. East of 180°, though, the temperature and water vapor variations at 100 hPa become decoupled. The water vapor variations, like those of 200‐hPa velocity potential, appear to speed up at about 180°E.
Regional simulation of the low‐level monsoon winds over the Gulf of California and southwestern United States
Authors: Anderson Bruce T. , Roads John O. , Chen Shyh‐Chin , Juang Hann‐Ming H.
Published: February 2004

Using a fine‐scale (10–20 km) nested regional modeling system, synoptic variations in climatological summertime low‐level wind fields over the Gulf of California and the southwestern United States are described. Under appropriate synoptic conditions, strong surge events can develop. These are characterized by low‐level southerly flow over the entire Gulf of California with southerly winds extending into Arizona, California, and southern Nevada. Vertically, these southerly winds are present through the bottom 1–2 km of the atmosphere. Southerly flow is persistent throughout the day with some local diurnal cycling over the foothills of the Sierra Madre Occidental and northwestern Mexico. Under nonsurge conditions the simulated low‐level winds have a significantly different geographic structure. Nighttime southerly flow is limited to the northeastern Gulf and small portions of southwestern Arizona. Flow over the central and southern Gulf is northerly with weak, variable winds over the foothills of the Sierra Madre Occidental. During the day, southerly winds are present over the central and northern Gulf of California, extending into southwestern Arizona; however, this southerly wind pattern does not support continuous flow from the mouth of the Gulf into northwestern Mexico. Instead, there is a westerly component associated with predominantly upslope flow over the foothills of the Sierra Madre Occidental and the Sonora Desert.
Observed climate variability and change of relevance to the biosphere
Authors: Easterling David R. , Karl Thomas R. , Gallo Kevin P. , Robinson David A. , Trenberth Kevin E. , Dai Aiguo
Published: February 2004

In this paper we review the current instrumental evidence regarding climate variations and change during the 20th century emphasizing those changes that are likely to have direct interactions with the biosphere. Three basic questions are addressed: (1) Is the climate getting warmer, (2) is the hydrologic cycle changing, and (3) is the climate becoming more extreme. Based on global near‐surface temperature measurements for the 20th century, it is clear that a warming of ∼0.5°C has occurred. More importantly for biospheric systems, however, are the observed asymmetric changes in daily maximum and minimum temperature, with the minimum temperatures increasing at a rate approximately twice that of the maximum temperature. Other temperature‐sensitive measures, such as glacial and snow cover extent, reinforce the observed temperature trends. Examination of the hydrologic cycle indicates that changes also appear to be occurring, although less confidence can be placed on these analyses than those for temperature. Recent studies suggest that precipitation has increased in higher latitudes, particularly in the Northern Hemisphere. Increases in cloudiness, atmospheric water vapor, and changes in stream flow also suggest that changes to a more vigorous hydrologic cycle are taking place. The final question regarding climate extremes is much more difficult to assess due to a lack of high temporal resolution climate databases. Of the few studies that have been performed, however, there is evidence that precipitation extremes, particularly heavy rainfall events, are increasing in the United States and Australia, also suggesting an enhanced hydrologic cycle as the planet warms.
Effect of coarse biogenic aerosol on downwelling infrared flux at the surface
Authors: Spänkuch D. , Döhler W. , Güldner J.
Published: February 2004

The effect of coarse biogenic aerosol on the downwelling infrared flux at the surface was estimated from the enhancement of spectral IR zenith radiances measured by the ground‐based Fourier transform spectrometer Emission‐Infrared‐Spectrometer for Atmospheric Research (EISAR) at Potsdam, Germany. The enhancement in IR downwelling flux was found to 10.40 W m−2 for a pine pollen concentration of ∼2000 pollens per m3 per day, which is ∼8 times the monthly mean at the site in May where pine pollens are present in the air. The enhancement is ∼2 times larger than caused by a 10% change in precipitable water vapor (PWV) at midlatitudes in summer and also roughly 2 times the amount that would be caused by conventional aerosol models at 5 km visibility. The enhancement at average pine pollen abundance is estimated to ∼1–2 W m−2 and is not negligible if the effect found is not pine pollen specific. The effect of pollens on the downwelling radiance is a spectrally smooth curve with a maximum of 11 mW (m2 sr cm−1)−1 at 1000 cm −1. A broad dip in the radiance enhancement was found between 850 and 1000 cm−1 that could not be assigned to known atmospheric absorbers. It is thus most likely pollen specific and is probably caused by pollen exines. The spectral enhancement in IR zenith radiance caused by the pollens was compared with changes induced by PWV variations and the abundance of aerosol types. A distinct radiance enhancement by pine pollens of up to 80% in maximum and 20% on average was found around the 4.67 μm CO fundamental band used for remote sounding of CO from ground and satellites.
Modeling of carbonaceous particles emitted by boreal and temperate wildfires at northern latitudes
Authors: Lavoué David , Liousse Catherine , Cachier Hélène , Stocks Brian J. , Goldammer Johann G.
Published: February 2004

For the first time, a spatial and monthly inventory has been constructed for carbonaceous particles emitted by boreal and temperate wildfires in forests, shrublands, and grasslands, with burned area data statistics, fuel load maps, fire characteristics, and particle emission factors. The time period considered is 1960–1997, and an important year‐to‐year variability was observed. On average, boreal and temperate vegetation fires represent 4% of global biomass burning, but during extreme years, their contribution may reach 12%, producing 9% and 20% of black carbon (BC) and particulate organic matter (POM), respectively, emitted by worldwide fires. The North American component of the boreal forest fires (Canada and Alaska) represents 4 to 122 Gg C yr‐1 of BC and 0.07 to 2.4 Tg yr‐1 of POM emitted, whereas the Eurasiatic component (Russia and northern Mongolia) may vary in the 16 to 474 Gg C yr‐1 range for BC and between 0.3 and 9.4 Tg yr‐1 for POM, with however great uncertainty. Temperate forests in conterminous United States and Europe have a much lower contribution with an average of 11 Gg C yr‐1 of BC and 0.2 Tg yr‐1 of POM. Grassland fires in Mongolia represent significant BC and POM sources which may reach 62 Gg C and 0.4 Tg, respectively. Finally, an annual average of BC emissions for shrubland fires in both the Mediterranean region and California is 20 Gg C yr‐1, with average POM emissions of 0.1 Tg yr‐1. These source maps obtained with a high spatial resolution (lox lo) can now be added to previous ones developed for other global carbonaceous aerosol sources (fossil fuel combustion, tropical biomass burning, agricultural and domestic fires) in order to provide global maps of particulate carbon emissions. Taking into account particle injection height in relation with each type of fire, our source map is a useful tool for studying the atmospheric transport and the impact of carbonaceous aerosols in three‐dimensional transport and climate models.
Simulation of preindustrial atmospheric methane to constrain the global source strength of natural wetlands
Authors: Houweling Sander , Dentener Frank , Lelieveld Jos
Published: February 2004

Previous attempts to quantify the global source strength of CH4 from natural wetlands have resulted in a range of 90–260 Tg(CH4) yr−1. This relatively uncertain estimate significantly limits our understanding of atmospheric methane. In this study we reduce this uncertainty by simulating preindustrial CH4 with a three‐dimensional chemistry‐transport model. Methane mixing ratios and δ13C‐CH4, as deduced from ice cores, and estimates of other preindustrial sources and sinks, are used as constraints. This yields an average preindustrial natural wetland source strength of 163 Tg(CH4) yr−1, with an estimated ±2σ uncertainty range of 130–194 Tg(CH4) yr−1. The present natural wetland source may be ∼10% smaller, owing to drainage and cultivation of wetland area since 1800 A.D. The simulated pole‐to‐pole concentration difference is found to be rather insensitive to the assumed relative contributions of important preindustrial sources and sinks, and therefore imposes only a limited constraint on the estimate of natural wetland emissions. In contrast, δ13C‐CH4 could provide robust constraints, but, unfortunately, at present reliable measurements are absent. Estimates of the historic development of anthropogenic CH4 sources, in combination with our model calculations, can largely explain the increase of methane mixing ratios during the nineteenth century. Results for the twentieth century indicate that these historical emission inventories underestimate anthropogenic emissions by at least 10%. Simulations of preindustrial and present‐day isotopic ratios show that the growth of anthropogenic sources since 1800 A.D. may have increased δ13C‐CH4 by 3‰.
Variability‐lifetime relationship for organic trace gases: A novel aid to compound identification and estimation of HO concentrations
Authors: Williams J. , Fischer H. , Harris G. W. , Crutzen P. J. , Hoor P. , Hansel A. , Holzinger R. , Warneke C. , Lindinger W. , Scheeren B. , Lelieveld J.
Published: February 2004

In this study we report aircraft‐borne measurements of organic species made during March 1998 in Surinam, an unpolluted region on the northeast coast of South America Measurements included the following: CO by tunable diode laser; a wide variety of organics including acetone, acetonitrile, and isoprene by proton transfer mass spectrometry (PTR‐MS); and nonmethane hydrocarbon measurements by gas chromatography‐flame ionization detection. Here we compare the standard deviation of the natural logarithm of the mixing ratio (Sigma_lnX) to the estimated lifetime of these species. This relationship has been used to support identification of masses measured by the PTR‐MS; ascertain the consistency and quality of hydrocarbon measurement data; and to provide information concerning sinks of important trace species. A selection of the data is used to indirectly determine an average HO concentration of 2.0×105 molecules cm−3 along the back trajectory for air encountered during the Large‐Scale Biosphere‐Atmosphere Experiment in Amazonia‐Cooperative LBA Airborne Regional Experiment (LBA‐CLAIRE) measurement campaign between 0–1 km over the tropical rain forest. The lower than expected HO concentration derived could have been caused by significant atmospheric or oceanic photochemical production of acetone and MEK along the back trajectory.
Rainfall chemistry composition in two ecosystems in the northeastern Brazilian Amazon (Amapá State)
Authors: Forti M. Cristina , Melfi Adolpho J. , Astolfo Rosana , Fostier Anne‐Hélène
Published: February 2004

The rainfall chemical composition in two Amazonian ecosystems, a “terra firme” forest (dense tropical rain forest) and the “cerrado” (savanna) are presented. Both areas are located in the northeast Brazilian Amazon (Amapá State). This study evaluated the statistical differences in the rainfall chemistry, as well as the deposition through rainfall, for each ecosystem. The chemical species evaluated in the rainwater were Na+, K+, Mg2+, Ca2+, NH4+, Cl−, NO3−, SO42−, Fe3+, Al3+, Zn2+, and Mn2+ for both ecosystems. Factor analysis for the terra firme ecosystem indicated that there is a significant difference between the dry and wet periods in the rainfall chemical composition, indicating a biomass‐burning signature (K+ in association with Zn2+). High deposition of solutes, except for Mn2+ and Cl−, was also observed during the dry period. Comparison between the terra firme and cerrado rainfall chemistry showed statistical differences in concentration for the marine species (Na+ and Cl−) and for the soil dust species (Al3+, Fe3+, and Mn2+). The sea‐salt and biogenic sources of chemical species in terra firme forest rainwater are equally important. The site nearer to the sea (cerrado) has rainfall chemistry dominated by species having marine origins. The terra firme forest also has rainfall chemistry dominated by marine origin species, although the biogenic and soil dust origin species are highly significant at this site. Also in the terra firme a biomass‐burning signature was observed. The amount of sea salt deposited was more than 50% larger in the cerrado owing to its proximity to the shore.