bluuebunny/crossref_metadata_2025 huggingface dataset:
Sensitivity analysis of a chemical mechanism for aqueous‐phase atmospheric chemistry
Authors: Pandis Spyros N. , Seinfeld John H.
Published: February 2008

The sensitivity analysis of a comprehensive chemical mechanism for aqueous‐phase atmospheric chemistry is performed. The main aqueous‐phase reaction pathways for the system are the oxidation of S(IV) by H2O2, OH, O2 (catalyzed by Fe3+ and Mn2+), O3 and HSO5−. The HO2(aq) and OH(aq) radicals contribute indirectly to this process by producing and consuming H2O2(aq), respectively. The dominant pathway for HNO3(aq) acidity is scavenging of nitric acid from the gas phase. HCOOH is produced because of the reaction of HCHO(aq) with OH(aq). The gas‐phase concentrations of SO2, H2O2, HO2, OH, O3, HCHO, NH3, HNO3, and HCl are of primary importance. An increase in the liquid water content of the cloud results in a decrease of the sulfate concentration but an increase of the total sulfate amount in the aqueous phase. A condensed mechanism is derived from the analysis.
Surface drag over the snow surface of the Antarctic Plateau: 1. Factors controlling surface drag over the katabatic wind region
Authors: Inoue Jiro
Published: February 2008

The drag coefficient of the snow surface over the Antarctic Plateau is evaluated through direct measurement of Reynolds stress on the Mizuho Plateau, East Antarctica, in the austral summer. The estimated roughness height (Z0) varies from 10−l to 10−4 cm, even under near‐neutral conditions. Large shear stress appears in light wind, followed by increased turbulent intensity. In the katabatic wind region of the plateau, Z0 shows symmetric changes with wind direction. The average value of Z0 in the smoothest direction is 0.0004 cm, which is the minimum value previously reported, and it increases to 0.015 cm for 40° rotation of wind direction toward the roughest direction. The directional dependence of Z0 is similar at three stations located nearly 100 km apart. Unlike the results of Jackson and Carroll at the south pole, the smoothest direction deviates 20° from the mean sastrugi axes and agrees with the direction of the prevailing high wind. The 4‐m neutral drag coefficient is estimated to be 0.8 × 10−3 for the smoothest direction and 1.5 × 10−3 for the roughest direction. The effect of snow drift is unimportant. A generalized discussion of the results is given in a companion paper.
Infrared line intensity measurements in the v = 0–1 band of the ClO radical
Authors: Burkholder James B. , Hammer Philip D. , Howard Carleton J. , Goldman Aaron
Published: February 2008

Line intensities of the ClO radical in the fundamental vibrational band, v = 0–1, have been measured using a high‐resolution Fourier transform spectrometer coupled to a long path length absorption cell. The ClO infrared absorption spectra were recorded at 0.004 cm−1 unapodized resolution in 50 coadded scans at total pressures less than or equal to 0.4 torr, He buffer gas. Spectra were recorded at calibrated [ClO] over the range 4 × 1012 to 1.4 × 1013 molecule cm−3, using two different chemical sources of ClO: Cl + O3 and NO + OClO. The band intensity was measured as S = 9.68 ± 1.45 cm−2 atm−1 (95% confidence level) at 296 K, which is in agreement with a recent ClO band intensity determination using the concentration independent Herman‐Wallis method of band intensity analysis (Burkholder et al, 1987a). This value of the ClO band intensity is a factor of 2 greater than the value recently reported by Kostiuk et al. (1986). A N2 collisional broadening coefficient of γ0 = 0.093 ± 0.018 cm−1 atm−1 (95% confidence level) was determined from spectra recorded with 10 torr N2 added. A source of systematic error in the use of the Cl + O3 reaction as a quantitative source of ClO radicals is discussed.
Physical retrieval of rainfall rates over the ocean by multispectral microwave radiometry: Application to tropical cyclones
Authors: Olson William S.
Published: February 2008

A computationally efficient numerical model has been developed to study the transfer of microwave radiation through a horizontally finite cloud of hydrometeors. Although drop‐scattering effects are only approximated in this model, it yields radiances which agree well with more rigorous model computations. Model parameters characteristic of tropical cyclone rain cells over the ocean are specified, and the resulting microwave intensities emerging from the cloud tops at the Scanning Multichannel Microwave Radiometer (SMMR) frequencies (6.6–37 GHz) are calculated. SMMR antenna spatial response functions are estimated, based upon sensor specifications. The finite cloud model and antenna response functions serve as the basis for a rainfall rate retrieval method in which relevant model input parameters, such as the rainfall rate and rain area, are perturbed until the mean square error between model output brightness temperatures and SMMR‐measured temperatures is minimized. Synthetic retrieval tests indicate a significant reduction in retrieval error (50%) when information from the lower‐frequency SMMR channels is added to data from the highest‐resolution 37‐GHz channels. Upon application of this retrieval method to SMMR imagery of three hurricanes, a mean retrieval error of 57% is achieved with respect to rainfall rates derived from digitized Weather Surveillance Radar, model 57 (WSR‐57) data.
Theoretical algorithms for satellite‐derived sea surface temperatures
Authors: Barton I. J. , Zavody A. M. , O'Brien D. M. , Cutten D. R. , Saunders R. W. , Llewellyn‐Jones D. T.
Published: February 2008

Reliable climate forecasting using numerical models of the ocean‐atmosphere system requires accurate data sets of sea surface temperature (SST) and surface wind stress. Global sets of these data will be supplied by the instruments to fly on the ERS 1 satellite in 1990. One of these instruments, the Along‐Track Scanning Radiometer (ATSR), has been specifically designed to provide SST in cloud‐free areas with an accuracy of 0.3 K. The expected capabilities of the ATSR can be assessed using transmission models of infrared radiative transfer through the atmosphere. The performances of several different models are compared by estimating the infrared brightness temperatures measured by the NOAA 9 AVHRR for three standard atmospheres. Of these, a computationally quick spectral band model is used to derive typical AVHRR and ATSR SST algorithms in the form of linear equations. These algorithms show that a low‐noise 3.7‐μm channel is required to give the best satellite‐derived SST and that the design accuracy of the ATSR is likely to be achievable. The inclusion of extra water vapor information in the analysis did not improve the accuracy of multiwavelength SST algorithms, but some improvement was noted with the multiangle technique. Further modeling is required with atmospheric data that include both aerosol variations and abnormal vertical profiles of water vapor and temperature.
Study of the atmospheric general circulation as an initial value problem with the NCAR community climate model
Authors: Chen Tsing‐Chang , Branstator Grant W.
Published: February 2008

The NCAR Community Climate Model is used to examine the spinup of a model atmosphere from two extremely different initial isothermal rest states: a cold (240 K) state and a warm (310 K) state. Several interesting findings regarding the spinup of the model atmosphere are obtained: (1) The model equilibrium state is independent of the initial condition. (2) The spinup from the cold initial condition is faster than that from the warm initial condition. The former spinup also exhibits an overshooting in the thermal field. (3) The thermal field and baroclinic flow spinup simultaneously. (4) The spinup of the barotropic flow lags behind that of the baroclinic flow and the thermal field. (5) The model tropics spinup faster than the mid‐latitudes, and the stratosphere spins up slower than the troposphere. Synoptic and energetics analyses are performed to illustrate these findings and to explain possible mechanisms involved in the model spin up. Emphasis is placed on the adjustment of the model atmosphere by the secondary circulation.
Radon as a tracer of biogenic gas equilibration and transport from methane‐saturated sediments
Authors: Martens Christopher S. , Chanton Jeffrey P.
Published: February 2008

Radon 222 activity measurements in sediment gas bubbles can provide key information about in situ bubble equilibration with dissolved gases in pore waters and rates of dissolved gas stripping and transport via ebullition. Activities of the noble gas radon in bubbles will reflect gains or losses resulting only from physical processes and radioactive decay. Gas bubbles in the sediments of Cape Lookout Bight, a small coastal lagoon on the Outer Banks of North Carolina, are at equilibrium with respect to dissolved radon and methane present at concentrations of 1.6 ± 0.3 × 10−15 and 1.5 to over 2.5 mM, respectively. In situ radon activities in sediment gas bubbles at 1.8‐atm pressure range seasonally from 257 to 700 disintegrations per minute per liter of gas (dpm Lg−1), whereas methane concentrations range from 86.6 to 91.3%. During summer months, bubble ebullition strips and transports 1.9–4.8% day−1 of the standing crop of radon in surface sediments to the troposphere. The ebullitive mode of gas transport represents an effective mechanism for bypassing oxidizing environments and delivering biogenic gases produced in anoxic sedimentary environments directly to the atmosphere.
Airborne sampling of selected trace chemicals above the central United States
Authors: Boatman J. F. , Wellman D. L. , Van Valin C. C. , Gunter R. L. , Ray J. D. , Sievering H. , Kim Y. , Wilkison S. W. , Luria M.
Published: February 2008

Field observations during a series of 24 atmospheric sampling flights in winter, spring, summer, and fall of 1987 provided a preliminary climatology of selected trace chemicals above the central United States. Flights were along the 91.5°W meridian between 29° and 41°N latitude. The data set includes continuous measurements of trace gases (O3, SO2, H2O2, and NO/NOy), aerosol number and size distributions, meteorological variables, and position. Filter samples produced SO42−, NO3−, SO2, and trace metal data. Flask air samples yielded methane, hydrocarbon (C2‐C5), and CO concentrations. Mean concentrations of the measured species at 2450±150 m and 1450±150 m represent each season. These data are discussed as functions of season, location, and air mass origin. Solar energy (821–991 w m−2), temperature (18°–11.6°C) and water vapor mixing ratio (13.5–10.1 g kg−1) peaked during summer at low and high altitude. Carbon monoxide levels 88–160 parts per billion by volume (ppbv) peaked in spring and were characteristic of the planetary boundary layer during both spring and summer. Methane concentrations were maximized during spring (1770–1744 ppbv) and fall (1774–1733 ppbv) and minimized during winter (1747–1730 ppbv) and summer (1736–1705 ppbv) at low and high altitude. Spring had the highest (21.3–21.4 ppbv) and summer the lowest (7.1–5.3 ppbv) hydrocarbon concentrations at low and high altitude. Sulfur dioxide concentrations were highest in summer (1.0–2.3 ppbv) and winter (0.9–1.6 ppbv) at low altitude. SO2 concentrations at high altitude had no seasonal trend and averaged less than 0.9 ppbv. Sulfate concentrations were highest in summer (3.2–1.7 μg m−3) at low and high altitude. The average hydrogen peroxide concentration varied by a factor of 16 (0.3–4.8 ppbv) between winter and summer. Ozone concentrations were between 49 and 70 ppbv and were highest in spring and summer. The ratio of sulfate to sulfur dioxide increased slightly with altitude during winter, spring, and summer. This is probably due to SO2 oxidation in clouds. The ratio of H2O2 to SO2 is >1 during spring and summer and <1 during winter. This indicates that the conversion of sulfur dioxide to sulfate by reaction with hydrogen peroxide is not oxidant‐limited during spring and summer.
Transport of radon in a three‐dimensional, subhemispheric model
Authors: Brost Richard A. , Chatfield Robert B.
Published: February 2008

We study transport in a three‐dimensional, Eulerian tracer model that uses a subhemispheric domain. Because radon decays radioactively, with an e‐folding time of 5.5 days, it provides a test of transport away from its surface, continental source. In particular, we evaluate the importance of two vertical transport processes: (1) parameterizations of cloud transport based on precipitation and based on relative humidity and (2) vertical advection resolved by winds with a horizontal scale of 190 km and a temporal scale of 6 hours. We compare simulated and observed concentrations and distributions of concentration, as well as results from different model versions, such as those using the finite difference advection schemes of Smolarkiewicz (1983) and of Prather (1986). Meteorological variability, which affects the ratio of the standard deviation of concentration σ to the mean concentration , determines the number of independent events that must be sampled to observe or simulate a statistically significant . We did not allow lateral import of radon into our domain, but our simulations could be corrected to estimate the effect of a realistic input by multiplying the simulated by α and dividing σ/ by , with α ≈ 1.04 in the planetary boundary layer (PBL) and 1.5 in the upper free troposphere (FT). The best simulations over the United States suggest that less than 10% of the radon above 2 km and up to 30% of the radon above 5.5 km may come from Asia. The importance of imported radon and the statistical significance of our simulations limit the reliability of comparisons in the upper FT. The observed and the modeled , using a 15‐day simulation period, may only be accurate to about a factor of 2. Unfortunately, the parameterization of cloud transport that gives the best simulations in the upper FT over the United States does not give the best results in the remote marine PBL. Nonetheless, above 6–8 km, cloud transport is probably more important than both the mean vertical advection and the finite difference advection scheme in determining the average radon concentration over the United States.
Effect of superposition on measurements of atmospheric gravity waves: A cautionary note and some reinterpretations
Authors: Eckermann Stephen D. , Hocking Wayne K.
Published: February 2008

Recent studies of gravity waves in the upper stratosphere have produced some interesting, but as yet unexplained, results. The observation and analysis of apparently “monochromatic” waves is not at first sight consistent with the current conception that the wave motions at these heights are due to a spectrum of superposed waves with a wide range of frequencies. Recent studies have suggested that regardless of season or location, inertia gravity waves with intrinsic frequencies around 3 times the inertial frequency appear to dominate the wave field. We address these issues using both digital simulation and analytical analysis, first showing how seemingly “monochromatic” waves can arise naturally from a broad spectrum of waves. Critical reappraisal of the analysis technique used to infer the peak in wave activity near 3 times the inertial frequency shows that this result is not definitive. This peak is demonstrated to be a statistical manifestation of wave superposition. These results in fact indicate azimuthal directionality in wave propagation, an important measurement of a little‐known quantity. Strong directionality in winter and at the equator is revealed. The equatorial results suggest a deficiency in inertia gravity waves and a preponderance of Kelvin wave and/or mixed Rossby‐gravity wave motions.
Altitude distribution of stratospheric NO3: 1. Observations of NO3 and related species
Authors: Naudet Jean‐Pierre , Rigaud Pierre , Pirre Michel , Huguenin Daniel
Published: February 2008

Five balloon‐borne observations of the vertical profile of stratospheric NO3 and ozone were performed between 1981 and 1985 by using the star and planet occultation technique at 662 nm. During the last two flights, NO2 was also measured by the same technique at 440 nm. The latest available laboratory determination of the 662‐nm absorption cross section of NO3 has been used for the data analysis. This gives NO3 concentrations that are about a factor of 2 lower than those previously reported. The concentration of NO3 increases with altitude, from about 1×107 molecules cm−3 around 22 km, to 2×107 molecules cm−3 at 38 km in September. A maximum value of 4×107 molecules cm−3 was observed at 38 km in May 1982. Ozone and NO2 results obtained from the same flights as NO3 are also presented. A companion paper provides details on the comparison between observed and modeled NO3 vertical profiles.
The ultraviolet radiation environment of Antarctica: McMurdo Station during September‐October 1987
Authors: Lubin Dan , Frederick John E. , Krueger Arlin J.
Published: February 2008

The large depletions in column ozone observed over Antarctica during spring imply enhanced levels of solar ultraviolet radiation at the Earth's surface. Daily data from the Nimbus 7 Total Ozone Mapping Spectrometer were combined with a model of atmospheric radiative transfer to compute the time evolution of ultraviolet irradiance, at wavelengths from 290 to 350 nm, incident on McMurdo Station during September‐October 1987. Large changes in column ozone occur as the polar vortex moves over the site. This is accompanied by correspondingly large variations in ultraviolet radiation at the Earth's surface. At a wavelength near 305 nm, the irradiance in early October exceeds values appropriate to an unperturbed ozone layer by a factor of 5–6. As December 21 approaches, the noontime ultraviolet irradiance increases, irrespective of changes in ozone. Any lengthening of the period of ozone depletion toward summer solstice will have a substantial impact on the ultraviolet irradiance received by the Antarctic surface.
Optical and microphysical properties of a cold cirrus cloud: Evidence for regions of small ice particles
Authors: Platt C. M. R. , Spinhirne J. D. , Hart W. D.
Published: February 2008

Airborne lidar and scanning radiometer observations were made in 1984 on a cold cirrus cloud from an ER‐2 aircraft flying at 20‐km altitude. At the same time, in situ microphysical observations were made at two altitudes within the cloud. Optical properties calculated from observed particle size spectra were compared with optical properties determined from the ER‐2 lidar‐radiometer observations. When the two aircraft were approximately coincident in the vertical, cirrus cells with enhanced particle counts were sampled by the in situ aircraft. At an altitude where the temperature was −62.7°C, no particles with sizes greater than 70 μm were sampled by the two‐dimensional instrument, and the Forward Scattering Spectrometer Probe (FSSP) instrument sampled sizes only smaller than 10 μm. At the second altitude where the temperature was −47.3°C, larger particles were sampled up to sizes of 600 μm, and 95% of the extinction occurred for particles with dimensions greater than 30 μm. Measurements of lidar depolarization ratio indicated that the clouds were composed predominantly of ice crystals. At the first altitude, the lidar and radiometer analysis gave values of backscatter to extinction ratio k and the visible extinction to infrared absorption ratio α of 0.0324 sr−1 and 2.3, respectively, using a value for multiple‐scattering factor η equal to 0.76 calculated from the FSSP spectra. This compared with a value of α equal to 3.77 calculated from cloud microphysics. The value of k did not agree with values obtained in previous ground‐based experiments at an equivalent temperature. The discrepancies were attributed to undersizing of particles by the FSSP. At the second altitude, using a value of η equal to 0.4 estimated from the two‐dimensional spectra, values of 3.5 and 0.0112 sr−1 were measured for α and k, respectively, compared with a value of α of 2.0 calculated from cloud microphysics and 0.0127 sr−1 for k measured by previous workers. The discrepancy in α was observed in previous experimental data, where a value of 3.5 was also obtained. Direct and remote measurements were in basic agreement for the lower layer. A much less favorable comparison in the upper layer is considered to be due to limitations in the in situ observations for small crystals.
Visible and near‐ultraviolet spectroscopy at McMurdo Station, Antarctica: 4. Overview and daily measurements of NO2, O3, and OClO during 1987
Authors: Sanders R. W. , Solomon S. , Carroll M. A. , Schmeltekopf A. L.
Published: February 2008

Near‐ultraviolet absorption spectroscopy in the wavelength range from 330 to 370 nm was used to measure O3, NO2, OClO, and BrO at McMurdo Station (78°S) during 1987. Visible absorption measurements of O3, NO2, and OClO were also obtained using the wavelength range from about 403 to 453 nm. These data are described and compared to observations obtained in 1986. It is shown that comparisons of observations in the two wavelength ranges provide a sensitive measure of the altitude where the bulk of atmospheric absorption takes place. The measurements indicate that the bulk of the NO2 column abundance is located near 30 km, while those of OClO and O3 are near 20 km. The measurements of NO2 display a systematic increase during the month of September, probably reflecting the release of odd nitrogen from reservoirs formed earlier in the winter season. The measurements of OClO display a strong diurnal variation, with considerably higher values being obtained in the evening than those measured in the morning. The evening twilight OClO column abundances obtained in 1987 were notably larger than those in 1986, perhaps because stratospheric temperatures were colder, and associated heterogeneous chemistry may have been more intense. This in turn implies a faster rate of ozone destruction in 1987 than in 1986 by halogen chemistry. These observations provide important constraints on the coupled nitrogen‐halogen chemistry of Antarctic spring and its influence on the springtime Antarctic ozone depletion.
Potential vorticity and mixing in the south polar vortex during spring
Authors: Hartmann D. L. , Chan K. R. , Gary B. L. , Schoeberl M. R. , Newman P. A. , Martin R. L. , Loewenstein M. , Podolske J. R. , Strahan S. E.
Published: February 2008

A central part of the explanation of the Antarctic ozone hole is the dynamical isolation provided by the intense vortex present over the south polar region until late in the spring. In this paper some fluid dynamical aspects of the Antarctic ozone hole phenomena are investigated, using data collected by the ER‐2 aircraft during the Airborne Antarctic Ozone Experiment (AAOE). Analysis of high‐resolution potential vorticity and nitrous oxide sections determined from the aircraft data show relatively little evidence of irreversible lateral mixing associated with large‐scale disturbances. Less than 10% of the flight legs show evidence of reversed meridional gradients of potential vorticity and nitrous oxide for spatial scales of more than a few degrees of latitude. Correlation studies show that small‐scale static stability variations are correlated positively with wind speed and not with relative vorticity, which strongly suggests that these are gravity wave signatures. Smaller‐scale variations in nitrous oxide and wind velocity are thus believed to be associated with gravity waves and not to represent lateral mixing which would constitute a significant breach of the dynamical isolation implied by the large‐scale potential vorticity gradient. Compositing of wind, potential vorticity, and nitrous oxide relative to the edge of the chemically perturbed region shows an enhancement of the meridional gradient of potential vorticity and nitrous oxide near this boundary at the 450 K potential temperature level. It is argued that this may be caused by the developing ozone concentration gradient producing a strong gradient in solar heating, which in turn drives a steepened potential vorticity gradient, although the temporal sampling provided by the AAOE measurements is not sufficient to prove this hypothesis. Another possible explanation of the enhanced gradients would be gradient steepening through erosion, by lateral mixing on the inner edge of the region of the strong meridional gradients of conserved quantities that define the vortex.
Mesospheric water vapor measurements from Penn State: Monthly mean observations (1984–1987)
Authors: Bevilacqua Richard M. , Olivero John J. , Croskey Charles L.
Published: February 2008

Measurements of mesospheric water vapor, by ground‐based microwave spectroscopy, have been made over the period March 1984 to the present at Pennsylvania State University (Penn State) (41°N). In this study we address the measurements made within the period November 1984 to July 1987; the data for March‐May 1984 have been presented previously (Tsou et al., 1988). This is by far the longest record of mesospheric water vapor measurements yet obtained. We discuss the fundamentals of the technique and provide an extensive error analysis. We show monthly mean water vapor profiles for the altitude range 65–80 km and establish both annual and interannual variability. The observations consistently indicate that the seasonal variation of water vapor in the upper mesosphere is dominated by an annual component with low mixing ratios in winter and high mixing ratios in summer. The measurements are shown to generally compare favorably, in both the magnitude and seasonal variation of the mixing ratios, with similar measurements made at the Jet Propulsion Laboratory (JPL) (34°N). However, at 80 km the Penn State measurements are nearly 1 ppmv lower than the JPL results in the winter and early spring, which may be indicative of a large meridional gradient (or zonal asymmetry) during those seasons. The Penn State measurements are also shown to be in good general agreement with infrared solar occultation measurements made with the Spacelab 1 GRILLE and Spacelab 3 ATMOS experiments.
An energy balance climate model study of radiative forcing and temperature response at 18 ka
Authors: Harvey L. D. Danny
Published: February 2008

An energy balance climate model is used to study climatic sensitivity to surface boundary conditions and to hypothetical atmospheric properties of the Last Glacial Maximum (LGM) of 18 ka. Imposition of Climate: Long‐Range Investigation, Mapping, and Prediction (CLIMAP) sea and land ice and CLIMAP sea surface temperatures (SSTs) gives a global mean atmospheric cooling of 3.4°C, while imposition of land glacier ice alone with freely predicted SSTs, sea ice, and seasonal land snow cover causes global mean cooling of 3.2°C, northern hemisphere sea ice extent close to the CLIMAP amounts, but relatively little response in the southern hemisphere. Reducing atmospheric CO2 from 280 to 200 parts per million by volume (ppmv), applying the base case LGM aerosol increase scenario of L. D. D. Harvey (1988a), or decreasing the effective cloud droplet radius over oceans by 4% with constant liquid water content (LWC), as suggested by data from polar ice cores, gives global mean atmospheric coolings of 1.5°C, 2.2°C, and 0.9°C, respectively. When any one of these atmospheric changes is combined with imposed CLIMAP land glacier ice, the global mean cooling ranges from 4.0°C to 4.7°C and sea ice extent close to the CLIMAP 18‐ka amounts occurs in both hemispheres. If all three of the above atmospheric changes are combined with CLIMAP 18‐ka land ice, then unrealistically large cooling and sea ice extent occurs. This can be used to constrain estimates of the increase of atmospheric aerosols and of the increase in cloud reflectivity due to changes in cloud droplet radius during the LGM, or may indicate that a stabilizing negative feedback is needed. One possible feedback is a temperature‐LWC feedback. This feedback is characterized by the parameter f ≡ (1/L)∂L/∂T, where L = LWC. Values of 0.03 to 0.05 K−1 are required to give realistic LGM simulations in the presence of the combined CO2, aerosol, and cloud optics forcings, whereas no cloud optics feedback is needed if the aerosol and cloud optics forcings were much smaller than assumed here. Applying the same model to CO2 doubling (320 to 640 ppmv) withf ranging from 0 to 0.05 K−1 gives a global mean surface air temperature response of 2.2–3.0°C.
H2O2 and O3 in the atmosphere of Los Angeles and its vicinity: Factors controlling their formation and their role as oxidants of SO2
Authors: Sakugawa Hiroshi , Kaplan Isaac R.
Published: February 2008

Factors regulating the formation of gaseous H2O2 and O3, which are considered to be dominant oxidants for SO2 in the atmosphere, were studied in Los Angeles and its vicinity. The concentration of gaseous H2O2, as well as O3, was highest in the early afternoon at all the sites studied when the sky was clear or partially cloudy, whereas when it was hazy and foggy, H2O2 concentrations were substantially lower than those under clear or partially cloudy conditions. To study the seasonal variation of gaseous H2O2, its concentration was measured in west Los Angeles in the early afternoon (1200–1600 LT) during August 1985 to September 1988 as well as at other southern California sites. The observed total range of gaseous H2O2 concentration was 0.03–1.35 (n = 150), 0.20–2.04 (n = 16), and 0.43–1.72 (n = 13) ppb at Los Angeles, the Mojave Desert, and the San Bernardino Mountains, respectively. The mean seasonal H2O2 concentrations at Westwood, Los Angeles, were 1 ppb in summer and approximately 0.2 ppb in winter. The O3 concentration during each H2O2 measurement period ranged from 10 to 230, 48 to 95, and 120 to 160 ppb for the same sampling locations, and seasonal variation was not as pronounced as for H2O2. Statistical analysis indicated that (1) H2O2 was most correlated with solar radiation, whereas O3 was most correlated with temperature, the height of inversion layer, and the concentration of NOx; and (2) H2O2 concentration was inversely correlated with SO2 during warm months of 1987–1988, when haze events were frequently observed. From our observations we deduce that in Los Angeles air (1) the production rate of sulfuric acid from SO2 is significantly lower in winter than summer due to lack of sufficient amounts of oxidants, and (2) thus the reduction of SO2 emission from anthropogenic sources, which has been accomplished by electric utilities, has not resulted in the equivalent reduction in sulfuric acid in rainwater, where rain events principally occur in winter.
Chemistry of a polluted cloudy boundary layer
Authors: Jacob Daniel J. , Gottlieb Elaine W. , Prather Michael J.
Published: February 2008

A one‐dimensional photochemical model for cloud‐topped boundary layers is developed which includes detailed descriptions of gas‐phase and aqueous‐phase chemistry, and of the radiation field in and below cloud. The model is used to interpret the accumulation of pollutants observed over Bakersfield, California, during a wintertime stagnation episode with low stratus. The main features of the observations are well simulated; in particular, sulfate accumulates progressively over the course of the episode due to sustained aqueous‐phase oxidation of SO2in the stratus cloud. The major source of sulfate is the reaction S(IV) + Fe(III), provided that this reaction proceeds by a non radical mechanism in which Fe(III) is not reduced. A radical mechanism with SO3−and Fe(II) as immediate products would quench sulfate production because of depletion of Fe(III). The model results suggest that the non radical mechanism is more consistent with observations, although this result follows from the absence of a rapid Fe(II) oxidation pathway in the model. Even with the non‐radical mechanism, most of the soluble iron is present as Fe(II) because Fe(III) is rapidly reduced by O2−. The S(IV) + Fe(III) reaction provides the principal source of H2O2in the model; photochemical production of H2O2from HO2or O2(−I) is slow because HO2is depleted by high levels of NOx. The aqueous‐phase reaction S(IV) + OH initiates a radical‐assisted S(IV) oxidation chain but we find that the chain is not propagated due to efficient termination by SO4−+ Cl−followed by Cl + H2O. A major uncertainty attached to that result is that the reactivities of S(IV)‐carbonyl adducts with radical oxidants are unknown. The chain could be efficiently propagated, with high sulfate yields, if the S(IV)‐carbonyl adducts were involved in chain propagation. A remarkable feature of the observations, which is well reproduced by the model, is the close balance between total atmospheric concentrations of acids and bases. We argue that this balance reflects the control of sulfate production by NH3, which follows from thepH dependence of the S(IV) + Fe(III) reaction. Such a balance should be a general characteristic of polluted environments where aqueous‐phase oxidation of SO2is the main source of acidity. At night, the acidity of the cloud approaches a steady state between NH3emissions and H2SO4production by the S(IV) + Fe(III) reaction. A steady state analysis suggests that [H+] at night should be proportional to (ESO2/ENH3)1/2where ESO2and ENH3are emission rates of SO2and NH3, respectively. From this analysis it appears that cloud waterpH values below 3 are unlikely to occur in the Bakersfield atmosphere during the nighttime hours. Very high acidities could, however, be achieved in the daytime because of photochemical acid production by the gas‐phase reactions NO2+ OH and SO2+ OH.
Electrical measurements over thunderstorms
Authors: Blakeslee Richard J. , Christian Hugh J. , Vonnegut Bernard
Published: February 2008

During the summer of 1986, the air conductivity and the vertical electric field were measured over thunderstorms from a high‐altitude U‐2 airplane. The conductivity near 20 km was found to be relatively steady above storms with variations less than ±15%. In addition, the positive and negative conductivities were at all times approximately equal and displayed a very similar temporal/spatial behavior. While traversing thunderstorms, sustained upward directed electric fields were maintained along the flight path over distances of 20 to 40 km, and electric fields in excess of 5 kV/m were often observed while passing over very intense storm centers. Estimates of the storm generator current and the Wilson conduction current were obtained for 15 storm over‐flights using the current densities derived from the conductivity and field measurements and integrated over area. Area‐integrated Maxwell currents of 0.09 to 5.9 A were observed with an average of 2.2 A. The U‐2 data show that this measure of storm current varies linearly with flash rate, which suggest that the average charge transfer per discharge is independent of storm development or activity. The Wilson conduction current, which contributes to the global circuit, varied between 0.09 and 3.7 A above storms with an average of 1.7 A. The conduction current was not found to be linearly related to the total flash rate but, instead, leveled off with increasing flash rate. This result may indicate that the relative efficiency of a thunderstorm to supply current to the global electric circuit has an inverse relationship to the strength of the cloud electrical generator.
Recent observations of lightning discharges from the top of a thundercloud into the clear air above
Authors: Vaughan O. H. , Vonnegut B.
Published: February 2008

A note of inquiry published in a magazine read by airplane pilots has elicited 15 new observations of a rare form of lightning that comes out of the cloud top, goes up vertically, and terminates in the clear air above. These confirm previous observations showing that this phenomenon usually occurs above very large and energetic thunderclouds. However, small clouds with tops at 15,000 ft mean sea level (5000 m) have been observed to exhibit this rare form of lightning also. One of the more spectacular observations was made over the severe storm system that produced the devastating tornadoes of April 11, 1965.
Comparison of fast electric field changes from subsequent return strokes of natural and triggered lightning
Authors: Le Vine D. M. , Willett J. C. , Bailey J. C.
Published: February 2008

Fast electric field changes from subsequent return strokes of natural and triggered lightning with propagation paths almost entirely over water are compared. Data were collected at the Kennedy Space Center, Florida, during the summer of 1987. Comparisons have been made of the average shape, the risetime, and the spectrum of the electric field changes. To a first approximation, the waveforms are very similar; however, the electric field changes from the triggered flashes tend to rise to peak faster and decay faster than do their counterparts in natural cloud‐to‐ground flashes.
Corona envelopes and lightning currents
Authors: Heckman S. J. , Williams E. R.
Published: February 2008

Laboratory results on coronas and considerations of fundamental electrostatics are used to study the corona envelope around the lightning channel. Calculations predict that immediately after a return stroke, a corona current of the order 2 kA flows for less than a millisecond, that between steps of a stepped leader corona draws a current of about 3 kA, and that at all other times the current governed by the velocity of radial charge motion is less than 1 A. Observed currents in all phases of the lightning discharge are accounted for by longitudinal channel extension, not radial expansion. A speculative picture of the roles of the corona envelope and of channel extension in discrete strokes of lightning is presented.
The thermal response of the tropical atmosphere to variations in equatorial Pacific sea surface temperature
Authors: Reid George C. , Gage Kenneth S. , McAfee John R.
Published: February 2008

For the period 1966–1982, monthly mean temperature anomalies were determined for 30 pressure levels from 1000 mbar (0 km altitude) to 15 mbar (28 km) at five tropical radiosonde stations, four in the western Pacific Ocean (Yap, Majuro, Wake Island, and Pago Pago) and one in the Caribbean (Curacao). Long‐term trends in the data were removed, and the detrended time series were cross correlated with an index of nonseasonal Pacific sea surface temperature (SST) anomalies with lags ranging up to ±30 months. At each station the correlation diagrams show a clear division of the atmosphere into four distinct regions, each having a different response to SST variations. In the main troposphere (850–150 mbar; 2–14 km) the correlation is positive, with a maximum at a lag of 1–4 months, in general agreement with earlier studies. In the lower stratosphere (100–40 mbar; 16–22 km) the correlation is negative, with a similar delay, while the surface layer (1000–850 mbar; 0–2 km) and the upper troposphere (150–100 mbar; 14–16 km) show responses that vary from station to station. The correlation drops essentially to zero above 40 mbar (22 km). Examination of the lags at the different stations indicate that the tropospheric inphase and stratospheric out‐of‐phase responses appear to propagate zonally from an apparent point of origin in the east central equatorial Pacific with a speed of the order of 1 m s−1. The possible mechanisms underlying this propagation are discussed, and it is concluded that simple advection of air from centers of convective activity is unlikely to explain both the tropospheric and the stratospheric responses. An alternative explanation involving variations in the rate of tropospheric subsidence and stratospheric upwelling accompanying variations in convective activity is suggested. The long‐term trends in atmospheric temperature are shown to have a variation with height that parallels the variation in the SST correlation. This may indicate that the atmosphere is responding to a corresponding long‐term trend in Pacific sea surface temperatures.
Tropospheric and dissolved N2O of the west Pacific and east Indian Oceans during the El Niño Southern Oscillation event of 1987
Authors: Butler James H. , Elkins James W. , Thompson Thayne M. , Egan Keith B.
Published: February 2008

Over 2000 measurements of N2O in the surface water and marine troposphere along with 650 measurements of N2O from depths of up to 6000 m were obtained from the W. Pacific and E. Indian oceans during the late spring and early summer of 1987. The precision (1 standard deviation) for tropospheric, surface water, and deep‐water measurements was 0.2%, 1%, and 2%. The results show a latitudinally weighted, mean interhemispheric difference of 0.97 ppb, which suggests that 2/3 of the global flux of N2O into the atmosphere derives from sources in the northern hemisphere. The mean surface water saturation anomaly was only 2.5% during this study, which included subtropical gyres, current confluences and divergences, and some shelf waters. Supersaturations of dissolved N2O that might normally be associated with equatorial upwelling in the W. Pacific were depressed along with other upwelling indicators. Our surface water flux estimates suggest that the oceanic flux of N2O during an El Niño year may be less than 50 Gmol yr−1 (about 10% of the mean annual flux of N2O into the troposphere). Deep‐water N2O concentrations, which could be predicted with reasonable certainty from salinity, temperature, dissolved O2, and pressure, were highest in N. Pacific waters and lowest in the higher latitudes of S. Pacific and E. Indian oceans.
A three–dimensional model of chemically active trace species in the middle atmosphere during disturbed winter conditions
Authors: Rose Klaus , Brasseur Guy
Published: February 2008

Trace gases in the middle atmosphere are subject to chemical transformations as well as to transport. A study of these processes occurring simultaneously in the atmosphere is performed using a three–dimensional hemispheric model based on the primitive equations to which a chemical scheme is added. The model results exhibit the gross features seen in the real atmosphere during a simulated wave number 1 warming, including the transport of chemically active trace species such as ozone, nitric acid, and nitrogen oxides. The model simulation suggests that the polar vortex behaves as a material entity during the planetary wave disturbance. At the same time, poleward transport is accomplished through tongues of tracers originating in the subtropics. Finally, scale interaction leads to mixing into even smaller scales, flattening gradients of tracer mixing ratios at mid‐latitudes, while steepening them at the edge of the vortex. The relative influences of chemistry and dynamics on the distribution of these gases are investigated. The effect of nonlinearity on the transport is addressed.
Ozone profile measurements at McMurdo Station, Antarctica, during the spring of 1987
Authors: Hofmann D. J. , Harder J. W. , Rosen J. M. , Hereford J. V. , Carpenter J. R.
Published: February 2008

Ozone and temperature profiles were measured in 50 balloon flights at McMurdo Station (78°S) during the spring of 1987. Compared to similar data obtained in 1986, stratospheric temperatures were lower and the springtime Antarctic ozone reduction was greater in magnitude, extended to higher altitude, and proceeded at a higher rate in 1987. Ozone partial pressures reached values as low as 3 nbar (as compared to about 10 nbar in 1986) in the 16‐ to 18‐km region in early and late October, down from about 150 nbar in late August. These low values suggest essentially complete removal of ozone in this region. The upper boundary of the depletion region was observed to be 2–3 km higher than in 1986, extending to altitudes as high as 24 km in mid‐September. When averaged over September, the ozone mixing ratio at 18 km decayed with a half‐life of only 12.4 days, as compared to about 28 days in 1986. Adiabatic vertical motions over 1‐ to 2‐km intervals between 12 and 20 km with consequent ozone reductions were observed in association with the formation of nacreous clouds, indicating these to be rare events on a local scale probably associated with mountain lee waves.
Nitrogen and chlorine species in the spring Antarctic stratosphere: Comparison of models With Airborne Antarctic Ozone Experiment observations
Authors: Rodriguez J. M. , Ko M. K. W. , Sze N. D. , Pierce S. D. , Anderson J. G. , Fahey D. W. , Kelly K. , Farmer C. B. , Toon G. C. , Coffey M. T. , Heidt L. E. , Mankin W. G. , Chan K. R. , Starr W. L. , Vedder J. F. , McCormick M. P.
Published: February 2008

The Atmospheric and Environmental Research, Inc., photochemical model has been used to simulate the concentrations and time development of key trace gases in the Antarctic stratosphere before, during, and after the Airborne Antarctic Ozone Experiment (AAOE). The model includes complete gas phase photochemistry and heterogeneous reactions of ClNO3 (g) and N2O5 (g) with HCl (s) and H2O (s). Observations of long‐lived species by the AAOE instruments have been used to constrain the initial conditions in our calculations. We present results from four cases illustrating the evolution of the trace gases for a range of possible initial conditions and duration of heterogeneous activity. The amount of ClO produced by heterogeneous conversion of HCl is determined not only by the initial concentrations of NOx (NO + NO2 + NO3), N2O5, and ClNO3 during winter, but also by the rate at which NOx is resupplied by photolysis of N2O5 and HNO3, or by transport. Results from the four cases presented bracket column measurements of HCl, ClNO3, and HNO3 by the Jet Propulsion Laboratory and National Center for Atmospheric Research infrared spectrometers onboard the NASA DC‐8, and in situ measurements of ClO and NOy by instruments aboard the NASA ER‐2. Comparison of results and measurements of HCl and ClO suggests that heterogeneous chemistry was maintained throughout the month of September in 1987. We suggest field observations and kinetic data which would further constrain the photochemistry of the spring Antarctic stratosphere. The behavior of ozone is discussed in a companion paper (Ko et al., this issue).