bluuebunny/crossref_metadata_2025 huggingface dataset:
First mass spectrometric measurements of atmospheric ions at ground level
Authors: Perkins Mark D. , Eisele Fred L.
Published: February 2008

Naturally occurring positive and negative ions in the troposphere have been mass identified at Sapelo Island, Georgia, and Mt. Evans, Colorado. These measurements were made at ground level under a variety of weather conditions. Over the course of the experiment, positive ions were seen at masses 54, 60, 80, and 94 AMU. Mass 54 AMU is believed to be NH4 + · 2(H2O). In the negative spectrum, ions were observed at masses 62 and 125 AMU and are believed to be NO3− and NO3− · (HNO3). Several ions that appear to be H2O clusters of the above ions were also observed. These are the first measurements of the mass identity (1‐AMU resolution) of naturally occurring ions in the troposphere with the exception of a previous measurement made in 1982 over a limited mass range in an urban environment (Eisele, 1983). Ions that were artificially produced were also studied and compared to the much longer lived natural ions.
Seasonal variability of CO in the terrestrial mesosphere
Authors: Clancy R. T. , Muhleman D. O. , Allen M.
Published: February 2008

We measured the J = 1 → 2 rotational transition of terrestrial mesospheric CO both in emission and in absorption against the moon on January 25–26, 1982. A CO mixing profile was obtained from the high signal‐to‐noise ratio emission spectrum. With the inclusion of these most recent spectra and spectra measured by Kunzi and Carlson (1982) we find further evidence suggesting seasonal variation of mesospheric CO as originally reported by Clancy et al. (1982). This seasonal variation may be the consequence of hemispheric circulation in the upper atmosphere.
On the distributions of long‐lived tracers and chlorine species in the middle atmosphere
Authors: Solomon Susan , Garcia Rolando R.
Published: February 2008

A numerical model employing the residual Eulerian formulation and small eddy diffusivity coefficients is used to calculate the distributions of chemical tracers and chlorine species. The predicted densities of nitrous oxide, methane, and chlorocarbons are shown to be in good agreement with available observations and to exhibit strong latitude gradients. Computed spatial variations in methane produce large variations in the HCl and ClO densities. In particular, a pronounced local minimum in HCl is obtained near 40 km for certain latitudes and seasons, with a corresponding maximum in ClO, primarily as a result of transport of atmospheric methane. It is suggested that spatial and short‐term temporal variability in methane has potentially important consequences for the HCl and ClO distributions in the atmosphere, and their variability, and for the chlorine‐catalyzed destruction of stratospheric ozone.
An observational estimate of gravity wave drag from the momentum balance in the middle atmosphere
Authors: Smith Anne K. , Lyjak Lawrence V.
Published: February 2008

The zonal average momentum budget in the middle atmosphere (up to 0.1 mbar) is computed for 7 months of satellite observations in order to determine the forcing needed to obtain a balance. This momentum residual includes forcing by waves with small zonal scales, such as gravity waves. The results indicate that the forcing needed in the lower mesosphere reaches peak values of about 20 m s−1 d−1, which is large compared to the Rayleigh friction used in that part of the atmosphere in numerical models, such as that of Holton and Wehrbein (1980a). The seasonal change follows that of Rayleigh friction; the northern hemisphere momentum deficit is large easterly in winter, decreases in the spring, and becomes small westerly in late spring. However, the largest momentum deficits are in middle and high latitudes (50°–80°N) in winter, whereas the largest Rayleigh frictional damping is in the vicinity of the jet (30°–50°N). The observations were also compared with the parameterized acceleration of the mean flow by gravity waves (Lindzen, 1981; Holton, 1983). The observations of the wintertime momentum residual are similar to the values used in the circulation model of Holton (1983). Derivation of the parameterization constant from the satellite observations results in an equivalent zonal wave number for gravity waves that is substantially smaller than that used by Holton (1983) in his model. Possible reasons for this difference are that many of the gravity waves break at levels above the region where data are available and that gravity waves with nonzero phase speeds may be present.
The sensitivity of a thermodynamic sea ice model to changes in surface albedo parameterization
Authors: Shine K. P. , Henderson‐Sellers A.
Published: February 2008

The sensitivity of a thermodynamic sea ice model to changes in surface energy fluxes in the Arctic is investigated. The main emphasis of the paper is on the testing of the model sensitivity to changes in surface albedo parameterization. Climatologies of turbulent and long‐wave fluxes in the Arctic are scarce, and those that exist are shown to generate significant differences in the predicted ice thickness. There is considerable disagreement in the literature on albedo values, and in particular, proposed albedos of bare, puddled ice range from 0.4 to 0.66. The differences among published model simulations are shown to be potentially explicable in terms of this range in bare ice albedo. A new ice albedo parameterization is proposed, and its sensitivity is tested. It is shown that the increase in surface albedo with cloud cover can cause a doubling of the ice thickness, and the need to include melting snow as an albedo class distinct from dry snow is demonstrated. The value of bare‐ice albedo is shown to be important in determining whether the ice is in a multiyear or a seasonal ice zone, and the need for more observational data on the extent and role of melt puddles is emphasized.
Biogenic hydrocarbon emissions from deciduous and coniferous trees in the United States
Authors: Lamb Brian , Westberg Hal , Allwine Gene , Quarles Tim
Published: February 2008

Measurements of natural hydrocarbon emission fluxes are reported for a northeastern U.S. deciduous forest, for a northwestern U.S. coniferous forest, and for dominant tree species in the Atlanta, Georgia, region. The emission data were obtained by using a vegetation enclosure procedure and a micro‐meteorological gradient technique. Isoprene fluxes determined by the gradient method in the deciduous forest varied from 2500 μg/m2/h at 20°C to 8000 μg/m2/h at 30°C. Corresponding fluxes obtained with the vegetation enclosure method ranged from 890 to 7300 μg/m2/h. Isoprene fluxes determined by both methods increased exponentially with increasing temperature. Emission rates from isoprene‐emitting trees in the Atlanta area were similar to those observed in Pennsylvania. Alpha‐pinene fluxes measured in a Douglas fir (Pseudotsuga menziesii) forest ranged from 9 to 1320 μg/m2/h. Relative humidity appeared to directly influence the alpha‐pinene emission rate. The reasonable agreement between hydrocarbon fluxes obtained with two independent techniques is significant evidence of the general validity of current biogenic hydrocarbon emission rates.
Atmospheric trace elements at Enewetak Atoll: 2. Transport to the ocean by wet and dry deposition
Authors: Arimoto R. , Duce R. A. , Ray B. J. , Unni C. K.
Published: February 2008

The concentrations of trace elements in precipitation and dry deposition are presented for samples collected at Enewetak Atoll (11°N, 162° E) during SEAREX experiments in 1979. The concentrations of Al, Sc, Mn, Fe, Co, and Th in rain are dominated by crustal material, and for these elements, wet deposition evidently exceeds dry deposition. For most of these elements the present rates of atmospheric deposition at Enewetak are similar to their mean rate of accumulation in sediments over the past 5–10,000 years, suggesting that the air‐to‐sea exchange of particles is closely tied to the sedimentary cycle of the mid‐Pacific. Noncrustal sources govern the concentrations of Pb, Zn, Cu, Se, and Cd in wet and dry deposition samples. Analyses of dry deposition collected from a flat plastic plate indicate that the amount of material recycled from the sea surface varies markedly between samples, and even though these estimates do not necessarily reflect the dry deposition to the ocean surface, the results suggest that recycled sea spray often amounts to more than 50% of the total dry deposition of the enriched elements. Recycled sea spray also makes up a significant fraction of the total wet deposition of the enriched elements. The net deposition rates of elements such as Cu and Zn are greater than or equal to their inputs from vertical mixing, but the net deposition of Pb clearly exceeds the input from upwelling. The current net deposition rates of the enriched elements are also similar to their rates of removal to sediments. These results indicate that air‐sea exchange processes may significantly affect the chemistry of trace metals in the open ocean.
A laboratory and field study of the equilibrium N2O5 ⇌ NO3 + NO2
Authors: Perner D. , Schmeltekopf A. , Winkler R. H. , Johnston H. S. , Calvert J. G. , Cantrell C. A. , Stockwell W. R.
Published: February 2008

Laboratory and field studies have been carried out to determine the equilibrium constant for the system, N2O5⇌NO3 + NO2. In the laboratory studies a 170‐m multiple‐pass cell was used to study the equilibrium with the reactants at the ppm level in 700 torrs N2/O2 near 298 K. A Fourier transform infrared spectrometer was employed to follow N2O5, and an ultraviolet/visible differential optical absorption spectrometer to determine NO3 and NO2. The laboratory results for the Keq for temperature near 298 K are in good accord with the less direct estimates published by Graham and Johnston, but they are significantly different than some other recent direct measurements. Through measurements of [NO3], [NO2], [O3], and temperature in a 10.25‐km path in the remote troposphere of Colorado, indirect determinations of the Keq have been made for the temperature range 269–281 K. The estimates of Keq at the lower temperatures of the atmosphere, although somewhat higher than expected from the extrapolation of published data from higher temperatures, are also in accord with the Graham and Johnston data within our large experimental error of the field measurements.
Influence of temperature, moisture, and organic carbon on the flux of H2 and CO between soil and atmosphere: Field studies in subtropical regions
Authors: Conrad Ralf , Seiler Wolfgang
Published: February 2008

Production and deposition rates of atmospheric hydrogen and carbon monoxide were studied during field measurements in subtropical regions, i.e., Transvaal (South Africa), Andalusia (Spain), and the Karoo (South Africa). Measurements were carried out by applying static and equilibrium box techniques. The equilibrium technique has been introduced as a novel method to measure production and destruction rates simultaneously even when soil conditions (e.g., temperature) change during the course of the measurements. Deposition velocities of H2 and CO were virtually independent of the soil temperature measured in 3‐ to 10‐mm depths and agreed with those measured in the temperate regions. The deposition velocities were inhibited or stimulated by irrigation water depending on the conditions of the individual field sites. H2 production by soil was not observed. By contrast, CO was produced by soil in a dark chemical reaction. Production rates increased exponentially with soil temperatures, giving activation energies of 57–110 kJ mol−1 and increased linearly with soil organic carbon content. CO production rates followed a diel rhythm parallel to soil surface temperatures. Production generally exceeded CO deposition during the hot hours of the day, so that arid subtropical soils act as a net source of atmospheric CO during this time. On a global basis, CO production by soil may reach source strengths of 30 Tg yr−1, which is considerably less than the global deposition of CO estimated to be 190–580 Tg yr−1. Global H2 deposition rates were estimated to 70–110 Tg yr−1.
Secular variations in cyclone frequencies near the Drake Passage, southwest Atlantic
Authors: Mayes P. R.
Published: February 2008

Analysis of a 22‐year sequence of summer and winter cyclone frequencies for the Drake Passage‐Weddell Sea area produces important differences from previous short term studies. Two principal cyclone tracks are shown to occur in both seasons at around 55° and 65°S. Principal components analysis suggests that the minor cyclone track was more variable than the major track in both seasons. Variations in cyclone frequency at high latitudes appear to be directly linked to the strength of the westerly circulation actively enhancing lee cyclogenesis near the Antarctic Peninsula. Investigation of the relationship between the predominant cyclone track and the inferred movement of the Weddell Sea pack ice does not support the hypothesis that cyclonic activity is determined by the position of the pack ice boundary. Furthermore, there is an observed, but not statistically proven, link between cyclone movement and the mean annual position of the Oceanic Polar Front.
Ions and cluster ions: Experimental studies and atmospheric observations
Authors: Keesee R. G. , Castleman A. W.
Published: February 2008

The investigation of ion chemistry and the properties of ions and cluster ions is essential for a fundamental understanding of factors that affect atmospheric electrical conductivity. Recent mass spectrometeric observations of ambient stratospheric and tropospheric ions and recent laboratory studies of these ions are reviewed, and our present knowledge of the chemical nature of ions below 50 km is assessed. Some organic species, namely, trimethylamine, pyridine, and methylpyridines, are suggested to participate in the tropospheric positive ion chemistry.
Aircraft measurements of the atmospheric electrical global circuit during the period 1971–1984
Authors: Markson Ralph
Published: February 2008

This report will update an investigation of the global circuit conducted over the last 14 years through aircraft measurements of the variation of ionospheric potential and associated parameters. The data base included electric field, conductivity, and air‐earth current density profiles from the tropics (25°N) to the Arctic (79°N). Almost all of the data have been obtained over the ocean to reduce noise associated with local generators, aerosols, and convection. Recently, two aircraft have been utilized to obtain, for the first time, quasi‐periodic sets of simultaneous ionospheric potential (VI) soundings at remoted locations and extending over time spans sufficiently long so that the universal time diurnal variation (Carnegie curve) could be observed. In addition, these measurements provided the first detection of the modulation of electric fields in the troposphere caused by the double vortex ionospheric convection pattern. Beside summarizing these measurements and comparing them to similar data obtained by other groups, this report will discuss meteorological sources of error and criteria for determining if the global circuit is being measured rather than variations caused by local meteorological processes.
Charge separation in thunderstorms: Small scale processes
Authors: Illingworth A. J.
Published: February 2008

An analysis is presented of the many possible processes acting within a thunderstorm that can result in the separation of electric charge, and it is concluded that only those involving collisions between ice crystals and small hail pellets can account for the observed high fields and lightning. The fundamental physical processes causing the charge transfer when the ice particles interact remain to be identified, but it appears that differences in contact potential of ice formed in different ways in the atmosphere may be important.
The production of lightning‐associated infrasonic acoustic sources in thunderclouds
Authors: Few A. A.
Published: February 2008

Electrostatic production of low frequency (∼1 Hz) acoustic pulses associated with electrical discharges in thunderclouds has been theoretically described [e.g., Wilson, 1920; Dessler, 1973] and experimentally observed [e.g., Bohannon et al., 1977; Balachandran, 1983]. The measured waveforms differ consistently with the theories in that the observed wave has an initial positive (or condensation) pulse followed by a negative (or rarefaction) pulse; whereas theories predicted only a negative pulse. The electrical heating of the air by positive streamer systems during the discharge is computed in this theoretical paper. This rapid (supersonic) electrical heating, although small (∼10−6 T0), produces a positive pressure perturbation (∼10−1 Pa), which when added to the negative electrostatic pressure perturbation generates an acoustic wave consistent with measured signals. A positive pulse always precedes the negative pulse in this model, and the positive pulse is always smaller in amplitude than the negative. The durations of the positive and negative pulses are similar. When more realistic models are employed, the observed signal can be related through theory to physical parameters in the thundercloud.
Secular variations in thunder‐day frequencies in the twentieth century
Authors: Changnon Stanley A.
Published: February 2008

Data for thunder days during the 1901–1980 period from 227 stations around the globe were collected, evaluated, and then examined for temporal fluctuations. The densest and highest quality data were for North America, which was the focal point of the study. After three data quality tests, data for four North American stations were rejected, leaving 86 stations in the United States and Canada for study. A 14% increase in thunder days occurred from 1901 to 1945 in North America, followed by an 8% decrease through 1980 with an anomalous high during 1971–1975. The temporal behavior is similar to the annual temperature trends of North America and relates well to historical cyclone frequencies. Major regional differences existed in the temporal distributions of thunder days and their variability for North America. North of 45°N, a general increase existed from 1901–1980 along with decreasing interannual variability; the southeastern United States had a general decrease in thunderstorms with increasing variability from 1930 to 1980; and the western third of the continental United States had a downtrend in both thunderstorm frequencies and their interannual variability from 1901 to 1980. Statistically significant periodicities of greater than 15 years were found throughout the United States, with shorter periodicities, less than 7 years, also present in the western third of the United States. Moderate length periodicities of 7 up to 15 years were found in the northern United States and Canada. Thunder‐day trends at the 86 stations were used to delineate 14 areas that were consistent with standard climatic zones. There is a suggestion that inadvertent human influences may also relate to the decrease in thunder activity in the eastern United States. Discrete regions of uptrends or downtrends were found in the data of most stations in the other continents, but station density was too poor to allow definitive delineation of regions as in North America. However, all northern hemisphere stations above 50°N exhibited uptrends in thunder from 1901 through 1980. The quality data are available to interested scientists.
Measurements of the RF characteristics of Earth lightning with the Galileo probe lightning experiment
Authors: Rinnert K. , Lanzerotti L. J. , Dehmel G. , Gliem F. O. , Krider E. P. , Uman M. A.
Published: February 2008

We present the results of some measurements of Earth lightning made with the functional unit of the Galileo probe RF lightning experiment. The frequency range used is ∼100 Hz to 100 kHz. The measurements were carried out in conjunction with simultaneous studies of lightning sources made by the University of Florida lightning research group. We find that the typical RF pulse duration times are <30 μs, independent of lighting source distance <250 km. We also find that the time between successive pulses is either quite short (<64 μs), corresponding to the time between intracloud pulses and to the time between bipolar pulses, or occur around 100 ms, corresponding to the time between return strokes in ground discharges. The RF spectra are found to become less steep (relatively more power at the higher frequencies) during an interval of intense, nearby (<150 km) storms.
The concentration of atmospheric carbon dioxide at ocean weather station P from 1969 to 1981
Authors: Keeling Charles D. , Whorf Timothy P. , Wong Chi Shing , Bellagay Ronald D.
Published: February 2008

From May 1959 to June 1981 the concentration of atmospheric carbon dioxide was measured in 2419 samples of air collected on a weather ship situated at 50°N and 145°W in the North Pacific Ocean. Three principal characteristics of the variation in concentration of atmospheric CO2 are revealed by these data: an annual variation that repeats with nearly the same pattern each year, an interannual variation that correlates with the large‐scale circulation of the atmosphere, and a long‐term increase that is nearly proportional to the global input of CO2 from the combustion of fossil fuels. The peak‐to‐trough amplitude of the smoothed annual signal increased from 13.3 ppm in 1969 to 14.5 ppm in 1981. The phasing of the annual CO2 cycle suggests a close relation to the activity of land plants in the broad region of the northern hemisphere where plants grow mainly during the summer. The increasing amplitude suggests a heightening plant activity. The interannual variation and its first derivative correlate with the Southern Oscillation. A lag of 6 months in the derivative suggests a distant oceanic or terrestrial source‐sink in the tropics or southern hemisphere. The seasonally adjusted CO2 concentration increased from 324.9 ppm in May 1969 to 340.8 ppm in June 1981. This increase is 60% of the increase that would have occurred if all the CO2 from fossil fuel combustion had remained in the atmosphere and had been uniformly distributed there. The seasonally adjusted concentration, when averaged from 1975 to 1981, is 0.8 ppm lower than that found at Point Barrow, Alaska, at 71°N and 0.9 ppm higher than that found at Mauna Loa Observatory, Hawaii, at 19°N, suggesting a steadily decreasing concentration in CO2 from north to south in the broad band from 70°N to 20°N.
Operational overview of Wallops Island instrument intercomparison: Carbon monoxide, nitric oxide, and hydroxyl instrumentation
Authors: Gregory Gerald L. , Hoell James M. , Beck Sherwin M. , McDougal David S. , Meyers Jerome A. , Bruton Dempsey B.
Published: February 2008

The Wallops Island Instrument Intercomparison Workshop represented the first comprehensive intercomparison of techniques to measure ambient, free‐tropospheric levels of carbon monoxide, nitric oxide, and hydroxyl. The workshop was conducted as part of the National Aeronautics and Space Administration's Global Tropospheric Experiment. A summary of workshop operations and the results from the “exchange of standards” portion of the workshop are presented. The intercomparison results from the ambient measurement portions of the workshop are discussed in other papers in this issue of the journal.
A 2‐λ laser‐induced fluorescence field instrument for ground‐based and airborne measurements of atmospheric OH
Authors: Rodgers M. O. , Bradshaw J. D. , Sandholm S. T. , KeSheng S. , Davis D. D.
Published: February 2008

A modified laser‐induced fluorescence (LIF) technique for measuring tropospheric levels of OH is discussed. Although this system is still of the single‐photon laser‐induced fluorescence type (SP‐LIF), it has undergone major design changes. These changes have overcome several of the major problems encountered in first generation SP‐LIF sensors. Two of the more important of these are (1) the generation of high artificial levels of OH from the laser photolysis of atmospheric O3 and (2) the degradation in detection sensitivity resulting from temporal fluctuations in the nonresonant fluorescence background. In the 2‐λ LIF approach, two nearly identical laser systems are employed such that both “on” line OH signal monitoring and “off” line background levels are measured almost simultaneously (e.g., within 500 μs). This approach, in effect, freezes the atmosphere for purposes of comparing “on” versus “off” line signal measurements. Concerning the problem of laser‐generated OH, two approaches have been explored: the use of very short laser pulses and the use of reduced laser energies. The OH field measuring system reported on in this work used only the reduced energy scheme. Numerous tests have shown that the 2‐λ SP‐LIF system displays no measurable detection bias and, under typical operating conditions, displays shot‐noise‐limited extraction of weak signals. In addition, this in situ sampling system has lent itself to direct in‐flight OH calibrations. Tests also have been developed that quantitatively establish the magnitude of the O3/H2O/OH interference signal (which in nearly all cases was ≤20% of the total OH signal). Finally, the question of OH losses in the sampling manifold has been addressed, and the evidence strongly suggests that this loss is negligibly small. Null experiments, laboratory and in‐flight calibration exercises, and O3/H2O interference tests, as well as ground‐based OH measurements, are reported on. Collectively, these results indicate that the 2‐λ LIF OH system can provide reliable OH measurements down to the fundamental limits of its sensitivity, e.g., typically 1×106 molecules/cm3 for a 30‐min integration time at mid free‐tropospheric altitudes. The detection limit of this system at ground level as well as at mid‐latitudes should be adequate to address many interesting questions in tropospheric chemistry; however, further improvements will be required for routine high‐resolution OH measurements on aircraft sampling platforms.
Retrieval of cloud cover from satellite imagery data: A statistical approach
Authors: Molnar G. , Coakley J. A.
Published: February 2008

In order to retrieve reliable estimates of the fractional cloud cover for two‐layered cloud systems, the spatial coherence method generally requires imagery data containing observations of thermal emission at widely separated wavelengths. As the observations of thermal emission in the currently available imagery data are at 3.7 and 11 μm and as solar reflection contaminates the observations at 3.7 μm during the day, spatial coherence retrievals for two‐layered systems are in general limited to data taken at night. Here, we develop a retrieval scheme that uses only 11‐μm radiances to obtain the cloud cover for single‐ and two‐layered systems and therefore provides similar results for daytime and nighttime observations. To develop this retrieval method, we collect observations for an ensemble of single‐ and two‐layered cloud systems for which the spatial coherence method provides reliable retrievals of the cloud cover. We use this ensemble to study the relationship between the number of cloud‐free pixels, the number of completely cloud‐covered pixels, and the fractional cloud cover for (250 km)2 regions. We discover that when the cloud cover is extensive within (250 km)2 regions, pixels which are partially cloud covered are generally heavily covered. Likewise, when (250 km)2 regions are largely cloud‐free, pixels which are partially covered generally have little cover. Evidently, for the ensemble of cloud systems studied here the factors governing the large‐scale cloud cover also govern the cloud cover on scales approaching the resolution of the observations (8 km)2. We use this observation to construct a retrieval method which, though it may fail to provide reliable retrievals in individual cases, will provide reliable statistics of the cloud cover for ensembles of cases. Although this statistical retrieval is applied to single‐ and two‐layered systems here, the principles on which it is based seem to warrant more general usage.
Trends in Dobson total ozone: An update through 1983
Authors: Oehlert Gary W.
Published: February 2008

We estimate the trends in Dobson total ozone records from 1970 through 1983, using ozone data from 1964 through 1983. These estimates range from −0.31%/decade ± 0.49%/decade (1σ) for unadjusted data to −1.10%/decade ± 0.47%/decade for data adjusted for instrument interventions and the solar cycle. The negative trends are primarily the result of abnormally low total ozone values in the northern hemisphere during early 1983.
The relationship between marine aerosol particles and satellite‐detected radiance
Authors: Durkee P. A. , Jensen D. R. , Hindman E. E. , Haar T. H. Vonder
Published: February 2008

An experiment is described which investigated the relationship between marine aerosol particles and satellite‐detected radiance. The experiment resulted in a near‐simultaneous set of visible and near‐infrared satellite images and aircraft aerosol particle and state variable measurements. These data demonstrated that satellite‐detected radiance at red‐visible and near‐infrared wavelengths is positively correlated with aerosol optical depth. Further, the data show that relative humidity changes account for variations in aerosol particle size which in turn lead to variations in satellite‐detected upwelling radiance. Therefore it appears possible to use satellite imagery to investigate variations of marine boundary layer aerosol particles and relative humidity.
Speciation, photosensitivity, and reactions of transition metal ions in atmospheric droplets
Authors: Weschler C. J. , Mandich M. L. , Graedel T. E.
Published: February 2008

Dissolved transition metal ions (TMI) are common constituents of atmospheric droplets. They are known to catalyze sulfur oxidation in droplets and are suspected of being involved in other chemical processes as well. We have reviewed the relevant equilibrium constants and chemical reactions of the major TMI (iron, manganese, copper, and nickel), their ability to form complexes in aqueous solution, and their potential involvement in photochemical processes in atmospheric droplets. Among the results are the following: (1) The major Fe(III) species in atmospheric water droplets are [Fe(OH)(H2O)5]2+, [Fe(OH)2(H2O)4]+, and [Fe(SO3)(H2O)5]+; the partitioning among these complexes is a function of pH. In contrast, Cu(II), Mn(II), and Ni(II) exist almost entirely in the droplets as hexaquo complexes. (2) Within the tropospheric solar spectrum, some of the complexes of Fe(III) have large absorption cross‐sections. In this work we report cross‐section data for several of the complexes. Absorption of solar photons by such complexes is generally followed by cleavage, which in the same process reduces the iron (III) atom and produces a reactive free radical. This mechanism has the potential to be a significant and heretofore unappreciated source of free radicals in atmospheric droplets. (3) TMI participate in redox reactions with H2O2 and its associated species HO2· and O2−. These reactions furnish the potential for catalytic cycles involving TMI in atmospheric droplets under a variety of illumination and acidity conditions. (4) A number of organic processes in atmospheric droplets may involve TMI. Among these processes are the production and destruction of alkylhydroperoxides, the chemical chains linking RO2· radicals to stable alcohols and acids, and the oxidation of aliphatic aldehydes to organic acids.
Measurements of HNO3 and NO3− particulates at a rural site in the Colorado mountains
Authors: Parrish D. D. , Norton R. B. , Bollinger M. J. , Liu S. C. , Murphy P. C. , Albritton D. L. , Fehsenfeld F. C. , Huebert B. J.
Published: February 2008

The concentrations of HNO3 and NO3− particulates have been measured simultaneously with NO and NO2 concentrations at a nonurban field site in the Colorado mountains during a 5‐year period. Seasonal and diurnal trends of these species are presented. Correlations of HNO3 and NO3− levels with each other and with NOx (NO + NO2) levels elucidate atmospheric chemical processes. Generally, the measurements agree with the widely accepted views of odd nitrogen chemical cycles in the atmosphere, with the exception that fast surface deposition of nitric acid replaces rain out as the primary loss mechanism. Local anthropogenic sources of odd nitrogen are primarily responsible for the airborne nitrate in the air samples at this rural mountain site.
Detection of changes in the global troposphere temperature field induced by greenhouse gases
Authors: Barnett T. P.
Published: February 2008

Several approaches to detecting the existence of a theoretically predicted CO2‐induced signal in the global temperature field are investigated. It appears that a relatively thin network of observing stations can, when properly analyzed, provide a first‐order estimate of global‐scale temperature change and that this measurement is not necessarily the “global average” temperature. Using these stations, it is possible to estimate the strength of an a priori CO2 signal in the three dimensional tropospheric temperature field. This signal is derived from two different general circulation model simulations, both with some form of interactive oceans. The observed signal strength over 1960–1980 is roughly 0.5–1.0 times that expected “theoretically.” The observed signal demonstrated a trend that is marginally significant.
Variability of turbulence, 4–20 km, in Colorado and Alaska from MST radar observations
Authors: Nastrom G. D. , Gage K. S. , Ecklund W. L.
Published: February 2008

The variability of small‐scale atmospheric turbulence on time scales from a few minutes to the annual scale and at altitudes from about 4 to 20 km is studied using clear air Doppler radar data from Poker Flat, Alaska, and Platteville, Colorado. The variable used for this study is the refractivity turbulence structure constant Cn2. The frequency distribution of Cn2 is found to be lognormal during all seasons at all altitudes. Using data at 4‐min intervals, it is found that the autocorrelation function of Cn2 can be modeled as the sum of a first‐order autoregressive process and a random process. The associated integral time scale decreases with altitude from 25 to 45 min in the troposphere to about 18 min in the stratosphere. The power spectrum of log Cn2 follows a power law relation with frequency; at periods greater than about 2 hours the spectral slope is near −5/3 and at periods less than 2 hours the slope is near −1. Monthly mean values of log Cn2 are largest in the winter and show a secondary maximum in summer. The winter peak is apparently related to increased jet stream and baroclinic storm activity, and the summer peak is believed to be due to convective activity. The correlation of 3‐hour values of Cn2 with wind speed over month‐long periods ranges as high as 0.8 and has a median value near 0.3. During certain periods, Cn2 also depends on other variables such as boundary layer inversions and gravity wave activity. Monthly mean values of Cn2 correlate more closely with an indicator of the intensity of gravity wave activity than with wind speed or the coarse‐scale wind shear. The meteorological significance of these results is discussed briefly.
Identification of tropospheric ions
Authors: Eisele F. L.
Published: February 2008

Mass spectrometric measurements of naturally occurring atmospheric ions were performed near ground level at Sapelo Island, Georgia. The sampled ions were then passed through a chamber in which they could be dissociated by multiple collisions with a buffer gas. At low‐collision energies, H2O clusters were removed, allowing positive core ions to be identified at masses 18, 60, 80, 94, and 108. At high‐collision energies, positive core ions were dissociated, and the mass of their fragments was used to help determine their identity. Mass 18 is believed to be NH4+. Methylpyridine and dimethylpyridine were tentatively identified as the parent neutral species responsible for the core ions observed at mass 94 and 108.
A nonisothermal emissivity and absorptivity formulation for water vapor
Authors: Ramanathan V. , Downey P.
Published: February 2008

This study introduces nonisothermal H2O emissivity (E) and absorptivity (A) formulations for the troposphere and the stratosphere. The nonisothermal effects arise from the wavelength integration of the Planck function, evaluated at the emitting level temperature (Te), with the monochromatic absorption evaluated at the temperature of the absorbing path (Tp). In general, Te and Tp can differ by as much as 20–50 K in the atmosphere. Most of the published emissivities are essentially isothermal emissivities. We formulate a nonisothermal emissivity that satisfies the constraints posed by the monochromatic form of the transfer equation for a nonisothermal atmosphere. The new formulations employ continuous analytical expressions for E and A that retain the following H2O radiative properties: the asymptotic properties at small (≈0) and large (∞) pathlengths; temperature dependence of line parameters; nonisothermal effects; the e‐ and p‐type continuum in the 500–1200 cm−1 region; and the overlap of the e‐type continuum with the H2O line absorption. The E and A expressions are derived from a set of reference 5 cm−1 narrow‐band calculations for homogeneous atmospheres. When applied to the inhomogeneous atmosphere, including arctic, mid‐latitude, tropics, and antarctic atmospheres, the cooling rates from 0 to 40 km computed from the emissivity approach agree within 3% of those from the narrow‐band calculations; the surface downflux and the upflux at 50 km agree within 1.5%. A major fraction (>½) of these small errors are due to the strong‐line approximation employed in the emissivity model for the 0–800 cm−1 and the 1200–2200 cm−1 regions, and the emissivity approach itself introduces less than a 1% error in the fluxes. The excellent agreement with the narrow‐band calculations essentially verifies the nonisothermal emissivity approach proposed here. We also show that emissivities, fluxes, and cooling rates computed by narrow‐band models depend very strongly on the spectral resolution adopted in the model for computing transmittances. Thus the spectral resolution in the narrow‐band model is an arbitrary parameter. Furthermore, by comparing the narrow‐band model fluxes with line‐by‐line (LBL) calculations we conclude that the 5 cm−1 resolution model underestimates atmospheric opacity due to inadequate treatment of the far wing opacity of lines. We employ a simple continuum‐type opacity in our emissivity scheme to bring the present nonisothermal emissivity scheme into excellent agreement with available state‐of‐the‐art LBL calculations.
Molecular oxygen absorption continua at 195–300 nm and O2 radiative lifetimes
Authors: Saxon R. P. , Slanger T. G.
Published: February 2008

With the aid of new calculations on the transition moments between the six lowest states of O2, absorption cross sections have been calculated for several oxygen continua, including the A2Σu+ ← X3Σg− and A′3Δu ← a1Δg systems. Reasonable agreement is achieved with recent experimental results, the comparison indicating an overestimation of the theoretical transition moment for the A‐X system of 20–25%. With this adjustment, the calculated radiative lifetime for the O2(A) state is 150 ms, in close agreement with the currently used value. The A′ ← a and A ← X continua cross sections are of similar magnitude, indicating that absorption by O2(a) cannot be a significant atmospheric process.
Photochemical formation of peroxides in the boundary layer
Authors: Kleinman Lawrence I.
Published: February 2008

Boundary layer gas phase concentrations of H2O2 and CH3OOH are calculated using a multilevel Lagrangian photochemical model. A range of emission conditions and resultant pollutant levels are considered, such as occur in the northeastern United States during summer months. The dependence of peroxide concentrations on chemical rate constants and meteorological variables is analyzed in terms of a budget equation for the formation and removal of radicals in the atmosphere. For representative summer conditions (solar intensity, humidity, and ambient O3 level) the production of radicals, primarily from photolysis of O3, occurs significantly faster than the average NOx emission rate in the northeastern United States. A necessary condition of this imbalance is that only a fraction of the radicals introduced into the atmosphere can be removed by reactions with NO and NO2. The remaining radicals are removed primarily by recombination reactions forming peroxides. Variations in radical production, such as might reasonably be caused by changes in precursor concentration, latitude, season, cloud cover and/or humidity, can reverse the sense of the inequality between NOx emissions and radical production and lead to an order of magnitude decrease in the amount of peroxides formed.
Effects of radioactive fallout from a nuclear power plant accident on electrical parameters
Authors: Israelsson S. , Knudsen E.
Published: February 2008

Continuous recordings of atmospheric electric parameters were carried out in Uppsala, Sweden. Because of the accident in the nuclear power plant in Chernobyl, USSR, a rainfall on April 27, 1986, caused a considerable increase of the radioactive background radiation in the surroundings of the recording station. A pronounced influence on the atmospheric electric field, the conductivity of the air, and the space charge density is reported.
The charges that are deposited by cloud‐to‐ground lightning in Florida
Authors: Maier Launa M. , Krider E. Philip
Published: February 2008

Data from a network of electric field mills at the NASA Kennedy Space Center have been computer analyzed to determine the parameters of a charge model that describes the locations and magnitudes of the net changes in the cloud charge distribution that are caused by cloud‐to‐ground lightning. The results are limited to relatively large events that can be described by a point‐charge model, i.e., discharges that produced field changes of at least 1 kV m−1 at three or more sites and that have enough spatial symmetry to fit the model. The focus of effort has been to determine how the altitudes and magnitudes of different but comparable events vary from flash to flash, throughout the evolution of a storm, and from storm to storm. The results for seven small to medium thunderstorms in 1976, 1977, and 1978 indicate that the X, Y locations tend to cluster in cells with an overall dimension of 5 km or less and that the altitudes are surprisingly constant from flash to flash and throughout the day. Different storm days produced mean altitudes that range from 6.9 km (−14°C) to 8.8 km (−26°C), and the standard deviations are usually less than 20% of the mean. The average values of the charges that are deposited on different days range from 11 C to 44 C, and the standard deviations are typically 50% of the mean. The charges in two small storms exhibited 5‐min running means that increased by 80% or more and peaked as the lightning rate was decreasing. Errors in the charge parameters that might be caused by a nonspherical charge geometry fitting the point‐charge model were simulated by assuming that the lightning deposited a flat and horizontal disc of charge at various locations over the network. For disc radii of 5 km or less the standard deviation of the X‐Y position error at different disc locations was less than 2 km. The errors in the disc charge values and altitudes at different locations had standard deviations that were less than 20% and 10% of the means, respectively; but there was a systematic increase in the charge and a lowering of the height when the disc moved off the network.
Storm structure during aircraft lightning strike events
Authors: Bohne Alan R. , Chmela Albert C.
Published: February 2008

A small set of in‐situ aircraft and ground‐based radar data acquired during the 1981 and 1982 Joint Agency Turbulence Experiment is used to study the relationship of aircraft lightning strikes to storm precipitation, turbulence severity, and wind shear. The strikes were found to be strongly correlated with vertical drafts, predominantly downdrafts. Strikes were also well correlated with regions of strong turbulence. However, since most strong turbulence episodes encountered by the aircraft were not associated with lightning, use of lightning location methods to map hazardous turbulence within storms is considered unreliable. The strikes occurred in storm regions having a radar reflectivity factor between 25 and 35 dBZ (dBZ represents 10 log Z, where Z is the reflectivity factor). These regions were generally on the boundaries of the dominant storm precipitation cores. Storm wind shear was frequently high in regions near aircraft strikes.
Analysis of atmospheric photooxidation mechanisms for organosulfur compounds
Authors: Yin Fangdong , Grosjean Daniel , Seinfeld John H.
Published: February 2008

Reaction mechanisms are formulated for the atmospheric photooxidation of the organosulfur compounds, dimethyl sulfide, CH3SCH3, methanethiol, CH3SH, and diethyl sulfide, C2H5SC2H5. Predictions of the mechanisms are compared with available data on laboratory photooxidations of these three species to identify critical uncertainties in chemical pathways and reaction rate constants. The sensitivity of product yields to these uncertainties is investigated.
Trend analysis sensitivity studies of Dobson total ozone data through 1984
Authors: Hill William J. , Oehlert Gary W. , Reinsel Gregory C.
Published: February 2008

Dobson total ozone data have been analyzed using two different statistical methods, time series analysis using time domain (TD) methods and frequency domain (FD) methods. The trend estimates from these two methods using a network of 36 Dobson stations have differed from between 0.5% and 1% per decade over the past few years as new data have become available in the 1980's. The reasons for the differences are found to be largely due to a combination of (1) the shorter length data record used in the FD analysis, (2) the different sensitivity of each method to the low 1982–1983 winter ozone values, (3) the different methods of seasonal weighting, and (4) the varying sensitivities to a solar adjustment. Between 1970 and 1984 the total ozone trend estimates are −0.26 ± 0.92% per decade and −0.70 ± 0.82% per decade based on the TD and FD methods, respectively. Although different by nearly 0.5% per decade, neither trend estimate is statistically significant.
Variability of chromospheric and photospheric lines in solar cycle 21
Authors: White O. R. , Livingston W. C. , Wallace L.
Published: February 2008

A program to measure the variability of solar spectrum lines in the visible wavelengths began in 1974 at Kitt Peak Observatory and continues as we approach the minimum between solar cycles 21 and 22. Both photospheric and chromospheric lines are measured on a monthly basis using an optical system that permits observation of the irradiance from the full solar disk as well as a smaller region near the center of the sun's disk. The full disk measurements of the Ca II K line quantify the increase and subsequent decrease in line flux with the change in solar activity. However, spectra of quiet regions at disk center show little if any variation throughout the cycle. Photospheric lines separate into two classes according to their variability: low‐excitation lines of neutral metals resemble the K line in the shape of their solar cycle variability curve, but weaker lines formed deeper in the photosphere show no variation from 1974 to 1986. All of these findings point to solar activity as the source of the observed spectral variations, but the largest radiometric effects occur in chromospheric lines, with little or no evidence of variability in lines formed deep in the photosphere.