bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurements of atmospheric hydrocarbons and biogenic emission fluxes in the Amazon Boundary layer
Authors: Zimmerman P. R. , Greenberg J. P. , Westberg C. E.
Published: February 2008

Tropospheric mixing ratios of methane, C2–C10 hydrocarbons, and carbon monoxide were measured over the Amazon tropical forest near Manaus, Amazonas, Brazil, in July and August 1985. The measurements, consisting mostly of altitude profiles of these gases, were all made within the atmospheric boundary layer up to an altitude of 1000 m above ground level. Data characterize the diurnal hydrocarbon composition of the boundary layer in this tropical forest area. Biogenic emissions of isoprene control hydroxyl radical concentrations over the forest. Biogenic emission fluxes of isoprene and terpenes are estimated to be 25,000 μg m−2 d−1 and 5600 μm m−2 d−1, respectively. This isoprene emission is equivalent to 2% of the net primary productivity of the tropical forest. Atmospheric oxidation of biogenic isoprene and terpenes emissions from the Amazon forest may account for daily increases of 8–13 ppb for carbon monoxide in the planetary boundary layer.
Methane flux from the central Amazonian floodplain
Authors: Bartlett Karen B. , Crill Patrick M. , Sebacher Daniel I. , Harriss Robert C. , Wilson John O. , Melack John M.
Published: February 2008

A total of 186 methane measurements from the three primary Amazon floodplain environments of open water lakes, flooded forests, and floating grass mats were made over the period from July 18 through September 2, 1985. These data indicate that emissions were lowest over open water lakes, where flux averaged 27 plus or minus a standard error of 4.7 mg CH4 m−2 d−1(n = 41). Flux from flooded forests and grass mats was significantly higher. Emissions from flooded forests averaged 192±26.8 mg CH4 m−2 d−1(n = 90), while those from floating grass mats averaged 230±72.2 mg CH4 m−2 d−1 (n = 55). At least three transport processes contribute to tropospheric emissions: ebullition from sediments, diffusion along the concentration gradient from sediment to overlying water to air, and transport through the roots and stems of aquatic plants. Measurements indicate that the first two of these processes are most significant. Diffusive flux from flooded forests averaged 50.5±11.0 mg CH4 m−2 d−1, while that from floating mats averaged 43.7±11.8 mg CH4 m−2 d−1. Diffusive flux from open waters averaged 8.3±1.9 mg CH4 m−2 d−1. Emissions through bubbling were 168±32.2 (flooded forest), 346±128 mg CH4 m−2 d−1 (floating grasses), and 17.3±5.2 (open water). We estimate that on the average, bubbling makes up 49% of the flux from open water, 54% of that from flooded forests, and 64% of that from floating mats. If we apply our measurements to the entire Amazonian floodplain, we calculate that the region could supply up to 12% of the estimated global natural sources of methane.
The budget of biologically active ultraviolet radiation in the Earth‐atmosphere system
Authors: Frederick John E. , Lubin Dan
Published: February 2008

This study applies the concept of a budget to describe the interaction of solar ultraviolet (UV) radiation with the Earth‐atmosphere system. The wavelength ranges of interest are the biologically relevant UV‐B between 280 and 320 nm and the UV‐A from 320 to 400 nm. The Nimbus 7 solar backscattered ultraviolet (SBUV) instrument provides measurements of total column ozone and information concerning cloud cover which, in combination with a simple model of radiation transfer, define the fractions of incident solar irradiance absorbed in the atmosphere, reflected to space, and absorbed at the ground. Results for the month of July quantify the contribution of fractional cloud cover and cloud optical thickness to the radiation budget's three components. Scattering within a thick cloud layer makes the downward radiation field at the cloud base more isotropic than is the case for clear skies. For small solar zenith angles, typical of summer midday conditions, the effective path length of this diffuse irradiance through tropospheric ozone is greater than that under clear‐sky conditions. The result is an enhanced absorption of UV‐B radiation in the troposphere during cloud‐covered conditions. Major changes in global cloud cover or cloud optical thicknesses could alter the ultraviolet radiation received by the biosphere by an amount comparable to that predicted for long‐term trends in ozone.
Study of variability of mesospheric H2O during spring 1984 by ground‐based microwave radiometric observations
Authors: Tsou Jung‐Jung , Olivero John J. , Croskey Charles L.
Published: February 2008

Mesospheric water vapor profiles have been derived from ground‐based microwave radiative measurements at the 22.235‐GHz H2O spectral line. The measurements were made in the atmospheric thermal emission mode in spring 1984 at Pennsylvania State University (41°N, 78°W). The spectral data obtained were integrated and averaged over three different time scales: the total observational period, the monthly period, and the 12‐hour (day/night) period. The Phillips‐Twomey constrained inversion technique was modified for and then used in this study to improve the retrieval of H2O profiles. The inversion results of the total period averaged spectra suggest a mesospheric H2O mixing ratio decreasing with altitude. Values found were from 4 to 5 parts per million by volume (ppmv) at 65 km to less than 1 ppmv at 80 km, which is in basic agreement with most other observations reported. In addition, the monthly H2O retrievals showed a tendency of increasing H2O content toward the latter part of spring. This is consistent with the predictions from recent dynamic‐chemical models that include the effects of gravity wave breaking. On the other hand, the results of the study of the daily variability of mesospheric H2O support the presence of planetary wave activity in the middle mesosphere.
Large intraseasonal variations in wind stress over the tropical Pacific
Authors: Madden Roland A.
Published: February 2008

Time‐varying factional torques, due primarily to changing wind stress over the tropical Pacific associated with the 40‐ to 50‐day tropical oscillation, are computed for the northern summer of 1979. It is shown that they were large enough to cause variations in atmospheric angular momentum equal to one tenth of the annual average atmospheric angular momentum. Further, they are shown to be large enough to explain a considerable fraction of the observed 40‐ to 50‐day variations in atmospheric angular momentum and length of day.
A methodology for understanding and intercomparing atmospheric climate feedback processes in general circulation models
Authors: Cess Robert D. , Potter Gerald L.
Published: February 2008

Based upon the need to understand differences between general circulation model projections of climatic change due to increasing atmospheric carbon dioxide, the present study first categorizes reasons for these differences and presents suggestions for the design of future climate model simulations, so that these specific categories may directly be addressed and understood. Following this, and based upon tutorial use of a radiative‐convective model, it is suggested that sea surface temperature perturbations may be used, in conjunction with separation of clear and overcast regions within a model, as a surrogate climatic change for the purpose of understanding and intercomparing atmospheric climate feedback processes. This approach is illustrated through use of the Oregon State University/Lawrence Livermore National Laboratory general circulation model, with particular attention being paid to interpreting cloud/climate interactions within the model.
A global‐scale Lagrangian trace species model of transport, transformation, and removal processes
Authors: Walton John J. , MacCracken Michael C. , Ghan Steven J.
Published: February 2008

A Lagrangian model has been developed to treat the global‐scale transport, transformation, and removal of trace species in the atmosphere. The model uses prescribed velocity fields (either from observations or from Eulerian dynamical models) to advect constant‐mass parcels of air. These constant‐mass air parcels can contain varying amounts of aerosols, such as dust and smoke, or varying amounts of trace gases, such as ozone, methane, or nitrogen dioxide. Because advection operates on the air parcels, rather than on the trace species, the computational efficiency of the approach improves, in contrast to Eulerian approaches, as the number of trace species increases. Numerical diffusion is also much less than in typical Eulerian models, permitting a wide range of spatial distributions of species to be advected with minimal dispersion. The Lagrangian method is particularly well suited to species that are chemically active because deviations from chemical equilibrium associated with advection are greatly reduced. Additional processes presently represented in the model include precipitation scavenging, dry deposition, aerosol coagulation, gravitational settling, local mixing with nearby parcels, vertical mixing by moist convection, and horizontal and vertical mixing associated with eddy mixing on scales finer than the prescribed velocity field grid. The model can operate in either a passive or an interactive mode. In the passive mode the meteorological flow is assumed to be unaffected by the trace species. In this mode a wide variety of sensitivity experiments using the same meteorology can readily be conducted. In this paper we consider several such experiments using submicron and supermicron aerosol particles, including an assessment of the relative importance of convective versus dynamical mixing, an assessment of the relative importance of various removal mechanisms, and a sample application to investigate the deposition to the surface of locally injected radionuclides. Use of this model in the interactive mode is considered in a companion paper (Ghan et al., this issue).
Cloud droplets: Solute concentration is size dependent
Authors: Noone Kevin J. , Charlson Robert J. , Covert David S. , Ogren John A. , Heintzenberg Jost
Published: February 2008

An experiment is described in which cloud droplets are sampled as a function of their size using a counterflow virtual impactor, thereby revealing the degree to which the different sized droplets in a cloud are chemically different. The chief result is that the larger droplets sampled from a marine stratus cloud had a solute mass concentration that was a factor of 3 greater than in the smaller droplets.
Theory of fluorescent irradiance fields in natural waters
Authors: Preisendorfer Rudolph W. , Mobley Curtis D.
Published: February 2008

The theory of heterochromatic irradiance fields is developed from the fundamental principles of radiative transfer. The irradiance field in natural waters that have fluorescing stratified layers of chlorophyll and other organic material is determined. This is the direct solution of the irradiance field and assumes knowledge of the depth distribution of the inherent optical properties, in particular the spectral absorption and scattering functions. Conversely, these optical properties are determined from in situ irradiance measurements by inverting the direct solution for the irradiance field. This is the inverse solution of the irradiance field. These direct and inverse solutions provide the mathematical framework for optical assays of fluorescing matter in lakes and seas, using measurements of the irradiance field within such media. In particular, the concentrations of the various fluorescing substances within the water are determined from in situ spectral irradiance measurements.
Global atmospheric mass, surface pressure, and water vapor variations
Authors: Trenberth Kevin E. , Christy John R. , Olson Jerry G.
Published: February 2008

Variations in the hydrological cycle and the water vapor content of the atmosphere form a vital part of the “greenhouse” feedback mechanism that can substantially enhance perturbations in the atmosphere arising from changes in forcing, such as those associated with increases in the carbon dioxide content of the atmosphere. An analysis is therefore made of the mean annual cycle interannual variability and trends in global‐scale water vapor content of the atmosphere for December 1978 through December 1985, using global analyses from the European Centre for Medium Range Weather Forecasts. Since the variations in total atmospheric mass are almost entirely due to water vapor, two entirely independent global measures of the water vapor content can be compared. These are the total surface pressure due to water vapor from humidity analyses and the total surface pressure itself. For the mean annual cycle these show excellent agreement, and the analyses are therefore compatible with the constraint that the total mass of dry air is conserved. However, it appears that both the interannual variability and trends in water vapor are sufficiently small that they are lost in the noise level of the data, A new estimate of the total mass of the atmosphere is 5.1361×1018 kg for the annual mean, corresponding to a mean surface pressure of 984.43 mbar. It ranges from 5.1352×1018 kg in January to 5.1371×1018 kg in July, owing to the annual cycle in global water vapor which has an amplitude of 1.0×1015 kg (0.2 mbar). The total mass of dry air is estimated to be 5.123×1018 kg (or 981.9 mbar). Also presented is the partitioning of the mass for both the total and the water vapor into the contributions from each hemisphere and as a function of latitude. Mean annual surface pressures in the northern and southern hemispheres are found to be 981.92 and 986.93 mbar, respectively. Monthly mean hemispheric fluctuations in surface pressures of ±1 mbar are not uncommon and tend to be reflected by opposite anomalies in the other hemisphere (consistent with conservation of mass), but the residual in the global monthly mean is of the order of 0.1 mbar. Since this is greater than the magnitude of the possible signal in water vapor surface pressure, the available evidence indicates that the analyzed global monthly anomalies are mostly noise.
Principal oscillation pattern analysis of the 30‐ to 60‐day oscillation in general circulation model equatorial troposphere
Authors: von Storch Hans , Bruns Thomas , Fischer‐Bruns Irene , Hasselmann Klaus
Published: February 2008

A new technique is described for identifying time‐dependent patterns (i.e., “principal oscillation patterns,” or POPs) in a set of geophysical time series. POPs are defined as the normal modes of a linear dynamical representation of the data in terms of a first‐order autoregressive vector process with residual noise forcing. POPs associated with real eigenvalues represent nonpropagating, nonoscillatory patterns which decay exponentially. POPs associated with complex eigenvalues occur in complex conjugate pairs and can represent standing wave structures (if one pattern is much stronger than the other), propagating waves (if both patterns are periodic and have the same structure except for a quarter‐wavelength shift) or, in general, an arbitrary amphidromal oscillation. After the POPs have been defined for a selected set of primary variables, associated correlation or composite patterns may be derived for additional secondary fields to gain further insight into the structure of the interaction mechanisms. The method is illustrated by analyzing the tropical variability structure of a 10‐year numerical simulation with the T21 general circulation model (GCM) of the European Centre for Medium Range Weather Forecasts, Reading, England. The POP analysis is applied to the 200‐hPa horizontal divergence field along the equator for time scales shorter than 10 weeks. The associated patterns are determined for a number of additional fields in the tropical belt between 30°S and 30°N. One dominant POP pair is found. Its spatial scale corresponds to zonal wave number 1. The patterns travel eastward, with an average period of 24 days and an e‐folding decay time of 10 days. The maximum variance occurs in the area with maximum tropical precipitation, between 100°E and the dateline. These features correspond rather closely to the characteristics of the observed tropical “30‐ to 60‐day wave,” except for the smaller period. A frequency–wave number analysis confirms that this 30‐ to 60‐day wave is the most dominant regular oscillation in the tropical GCM troposphere. The associated patterns of sea level pressure, precipitation, and other quantities exhibit a number of intriguing aspects, namely, (1) the phase velocity of the 30‐ to 60‐day wave varies with longitude from 6 m s−1 in the Indonesian area to more than 30 m s−1 over the eastern Pacific, small phase speeds being associated with large amplitudes and high phase speeds with small amplitudes; (2) in the high‐amplitude regions, rainfall and upper air velocity potential are in phase, while in the low‐amplitude regions, rainfall and velocity potential appear uncorrelated; (3) at the surface a pattern strongly resembling Gill's theoretical response to an equatorial heating source is found, with a trough to the east and two off‐equatorial cyclones to the west of the heating. The lack of meridional winds is probably related to the disregard of the seasonal asymmetries.
Dynamical component of seasonal and year‐to‐year changes in Antarctic and global ozone
Authors: Tung Ka Kit , Yang Hu
Published: February 2008

Using a zonally averaged model in which all transport fields are fixed by input temperature data, we study dynamical aspects of the Antarctic ozone hole problem as a response to the observed year‐to‐year temperature change in August, September, October, and November. For the period studied, from 1979 to 1985, October column ozone density averaged over longitude is observed to decrease by 125 DU at 85°S. Our model produces 100 DU of decline from temperature change alone. At 60°S the model ozone decreases from 375 DU in 1979 to 325 DU in 1985, while the observed zonal mean column ozone declined from 410 DU in 1979 to 325 DU in 1985. The quasi‐biennial signal in the year‐to‐year variations in column ozone is well‐produced by the model with low (high) ozone correlating with westerly (easterly) phase of the tropical quasi‐biennial oscillation (QBO). It is estimated that our small underprediction of 25 DU of polar ozone decline for the period 1979–1985 is uncertain by a factor of 2 and that if the effect on temperature cooling by reduced ozone heating in later years is taken into account, our model underprediction may increase to 50 DU. The underprediction of the October mean for 1985 by the model appears to be caused by the underprediction of the seasonal decline in September in the present model without heterogeneous chemistry. However, the seasonal declines during the earlier years are well simulated. With dynamics accounting for between 60 to 80% of the Antarctic October mean, zonal mean ozone decline for the period 1979–1985, we infer, subject to uncertainties in the model and data inputs, that dynamics should play a more important role in the phenomenon than merely providing a special condition for heterogeneous chemical destruction of ozone. However, chemical depletion of ozone may have become more important after 1984. Because heterogeneous chemistry is not incorporated in the present model, the model may have overestimated the magnitude of upwelling after 1984. It is possible that the reduced springtime radiative heating due to chemically reduced ozone amount may have suppressed vertical motion in September and early October in the later years.
Radiative properties of desert aerosols by optical ground‐based measurements at solar wavelengths
Authors: Tanré D. , Devaux C. , Herman M. , Santer R. , Gac J. Y.
Published: February 2008

Radiation measurements were made during April and May 1986 at M'bour (16.9°W, 14.3°N), 80 km south of Dakar, Sénégal. The goal was to derive the optical properties of desert aerosols from ground‐based measurements in order to validate satellite monitoring of these aerosols. We present here the results of a ground truth experiment. The measurements were performed during 15 nonconsecutive days in April and May 1986. Weather conditions varied during the experiment, as did the aerosol optical thickness (0.4–2 at 550 nm). The results are consistent with previous studies, notably Shettle's (1984) desert aerosol models; the aerosol characteristics were observed to depend upon the dust conditions, i.e., background or dust storm conditions.
Multibeam radar observations of winds in the mesosphere
Authors: Franke S. J. , Liu C. H. , Fu I. J. , Rüster R. , Czechowsky P. , Schmidt G.
Published: February 2008

We present the results of a statistical analysis of mesospheric wind fluctuations with periods in the range 5 min to 8 hours. The data were collected with the SOUSY VHF radar by observing line‐of‐sight Doppler velocities sequentially in three directions. The temporal spectrum is computed for the vertical fluctuations as well as for line‐of‐sight fluctuations on two oblique beams at 3.6° zenith angle separated by 90° in azimuth. The observed spectra are shown to be mutually consistent if interpreted in terms of a field of propagating gravity waves. Using the three‐beam data, the temporal spectrum for the underlying gravity waves is obtained; the height dependence of the line‐of‐sight component of the mean square wave amplitudes is also studied.
Spatial and temporal variability of dust production caused by wind erosion in the United States
Authors: Gillette Dale A. , Hanson Kirby J.
Published: February 2008

Variability of model dust emissions by wind erosion was tested for sensitivity to variations of wind speed in the United States for a 31‐year period (1948–1978) and for a wide range of threshold velocities that arise from differing precipitation scenarios, from drought to abundant rainfall. Results showed that dust production increased about an order of magnitude when threshold velocities were changed from those appropriate for abundant rainfall to those appropriate for drought. About the same range of variability for dust production was seen in the model results when soil conditions and land use were held constant and U.S. wind data for 1948–1978 were used. Maximum dust production for the United States occurs in the spring, and minimum dust production occurs in the summer. Maximum model dust production for a 1‐year period occurred in the early 1950's and early 1970's, when a U.S. wind record for 1948–1978 was used. The location of maximum dust production is the area including the panhandles of Texas and Oklahoma and some surrounding areas.
Non‐sea‐salt sulfate and nitrate in trade wind aerosols at Barbados: Evidence for long‐range transport
Authors: Savoie Dennis L. , Prospero Joseph M. , Saltzman Eric S.
Published: February 2008

From mid‐May 1984 through December 1987, more than 1100 daily high‐volume bulk aerosol samples were collected during onshore trade winds at Barbados, West Indies. All of these have been analyzed to determine the concentrations of particulate non‐sea‐salt (nss) sulfate, nitrate, and Saharan dust; 91 of the samples were also analyzed for methanesulfonate (MSA). The mean concentrations (in μg m−3) during the period were nitrate, 0.509 (s = 0.389); nss sulfate, 0.751 (s = 0.602); mineral dust, 16.0 (s = 21.1); and MSA, 0.0207 (s = 0.0093). The concentrations of both nitrate and nss sulfate are significantly correlated with those of Saharan dust, indicating that substantial fractions of both are transported across the tropical North Atlantic in association with the dust. This transport accounts for about 60% of the mean total concentration of each of the anions at Barbados. Our data, combined with those from previous studies, indicate that these dust‐related fractions are probably not derived from the Sahara soil material; they are more likely derived from anthropogenic sources. The nitrate‐to‐nss sulfate ratio in this dust‐related fraction changes markedly from the summer to the winter. During the summer the general meteorology and nitrate‐to‐nss sulfate mass ratio (0.36) are consistent with Europe being the major source region; during the winter the ratio increases by a factor of 4 to 1.44, which may be consistent with a source region over southern West Africa. The ratio of the mean MSA concentration to that of the nss sulfate that is not related to dust transport is 0.066, a value similar to the ratio of MSA to total nss sulfate at relatively pristine stations in the Pacific: Fanning Island and American Samoa. The similarity suggests that this fraction of the nss sulfate at Barbados may be derived predominantly from oxidation of reduced sulfur compounds emitted from the ocean. The mean concentration of nitrate that is not related to dust transport is 0.22 μg m−3, about double the total mean concentration over the tropical South Pacific (0.11 μg m−3) and 40% higher than that over the equatorial Pacific (0.16 μg m−3). The major source (or sources) of this nondust‐related nitrate is still very uncertain.
Project Airstream: COS measurements in the stratosphere and troposphere
Authors: Leifer Robert
Published: February 2008

Stratospheric and tropospheric gas samples were collected and subsequently analyzed for COS under the Department of Energy's High‐Altitude Sampling Program (HASP) during the years 1980–1983. The northern hemisphere stratospheric inventories during these years ranged from 0.24 to 0.29 Tg. Coefficients for a least squares exponential fit were obtained for seasonal and latitudinal data subsets and showed profiles similar to previously published models. The HASP data base, when compared to these models, supports the concept of a low OH concentration profile in the lower stratosphere. Summer mixing ratios were elevated at all altitudes, indicating the need for model refinements to account for the seasonal difference. The results of the tropospheric samples analyzed suggest a decreasing COS mixing ratio with altitude.
OH A2Σ–X2π(0,0) band rotational line emission rate factors
Authors: Fennelly J. A. , Torr D. G. , Torr M. R.
Published: February 2008

The hydroxyl radical (OH) is an important species in the study of the Earth's ozone layer, because it moderates the catalytic destruction of ozone by odd halogens and odd nitrogen. The atmospheric distribution of OH can be deduced from measurements of the ultraviolet fluorescence emission of the (0,0) band of the OH (A2Σ–X2π) system. The fluorescence emission is proportional to the product of a g factor and the OH density. Since synthetic spectral fitting of the rotational lines of the OH bands constitutes an important aspect of the measurement process used by some experimenters, accurate knowledge of the g factors for the discrete rotational lines is essential for an accurate retrieval of the OH concentration from observed spectra. We present here, for the temperatures 200.0, 240.0, 296.0, 300.0, and 500.0 K, (1) the g factor for the entire OH (A2Σ–X2π)(0,0) band and (2) the individual g factors of each rotational line for the band. The derived g factor at 240 K for the entire band is (5.5±1.1)×10−4 photon s−1.
Lead 210 in surface air and soils from California: Implications for the behavior of trace constituents in the planetary boundary layer
Authors: Monaghan Marc C.
Published: February 2008

Measurements are reported of 210Pb activities in aerosols collected during the winter of 1985–1986 at Davis, located in California's Central Valley, and of 210Pb and 137Cs inventories in soils collected from the nearby Sierra Nevada mountains and Sierra Nevada‐Central Valley foothills. The results show that Central Valley surface air 210Pb activities increase (up to 98 disintegrations per min (dpm) 1000 m−3 STP) while high‐pressure systems are stationed over the western United States. During these periods the processes that control 210Pb activities in the boundary layer are the emanation of 222Rn from soils and, most likely, the exchange of air between the Central Valley boundary layer and the free troposphere. Model calculations indicate that the mean residence time of air in the Central Valley boundary layer during these periods ranges from 1 day to 4.5 days, depending upon the intensity of the regional high. Furthermore, because 210Pb is not removed efficiently from the boundary layer by other processes, these results indicate that as much as 90% of the 210Pb produced as a result of the decay of 222Rn emanating from Central Valley soils eventually escapes from the Central Valley to be deposited elsewhere, even though the boundary layer is relatively stagnant. Thus it is expected that a similar percentage of other species characterized by gas‐to‐particle conversion rates of about 3 days or longer (e.g., SO4 = from SO2) will also eventually escape from the Central Valley boundary layer to be deposited elsewhere. During the passage of cold fronts, surface air 210Pb activities decrease dramatically (to as low as 6 dpm 1000 m−3 STP). The study of 210Pb and 137Cs inventories in Central Valley‐Sierra Nevada foothill soils and in coastal soils indicates that this decrease is a result of marine air displacing the stagnant air in the Central Valley boundary layer and not a result of local washout of 210Pb. In the Sierra Nevada the ratio of the soil inventories of atmospherically derived 210Pb to 137Cs increases with elevation. This increase indicates that 210Pb derived recently from the continental boundary layer is preferentially deposited at higher elevations in the Sierra Nevada. A simple mass balance calculation indicates that between 28 and 53% of the 210Pb deposited in the Sierra Nevada is derived recently from the continental boundary layer. Together, the surface air and soil studies suggest that a large fraction of this 210Pb was transported from the Central Valley boundary layer during the passage of precipitating fronts.
Light‐absorbing material extracted from cloud droplets and its effect on cloud albedo
Authors: Twohy C. H. , Clarke A. D. , Warren S. G. , Radke L. F. , Charlson R. J.
Published: February 2008

Using the counterflow virtual impactor, a new instrument for sampling cloud droplets, measurable levels of light‐absorbing material were found to exist inside droplets in stratocumulus clouds off the coast of southern California. Eighty percent of the samples of droplet residue material had light absorption coefficients ranging from 6 to 20 × 10−8 m−1 (where m−1 means per meter of distance in the cloud, not in the cloud droplet nor in the dried bulk aerosol material). Calculated soot concentrations were between 23 and 79 ng soot g−1 of cloud water. These values are in general agreement with aerosol, rainwater, and snow measurements from other experiments and suggest that the coastal clouds were influenced by continental air. Aircraft measurements determined that the sampled clouds had average liquid water contents of 0.24–0.31 g m−3, effective droplet radii of 5.0–7.8 μm, and optical thicknesses of 14–28. Radiative transfer calculations indicate that even at the most sensitive wavelength, the maximum amount of light‐absorbing material from cloud air and inside cloud droplets in this experiment would not significantly alter the albedos of the clouds that were measured. The same amount could possibly affect the albedo of much thicker clouds or of snowpacks (which have relatively large particles and optical thicknesses).
The mixing ratio of the stratospheric hydroxyl radical from far infrared emission measurements
Authors: Carli Bruno , Carlotti Massimo , Dinelli Bianca M. , Mencaraglia Francesco , Park Jae H.
Published: February 2008

Far infrared emission spectra of the stratosphere, measured with a 0.0033‐cm−1 resolution Fourier transform spectrometer using a limb scanning method, are analyzed in order to retrieve the vertical distribution of the hydroxyl radical (OH). The observations cover a time interval between 1300 and 2300 hours, showing a pronounced time decrease of the OH signals. Vertical profiles are obtained for the afternoon and sunset periods. An upper limit is derived from the small signals present in the night measurements. Three different methods of analysis have been applied to the same data set, and the results provided the basis for a critical discussion of the error sources. The results are compared with theoretical predictions and with the results of other experiments.
The effect on Earth's surface temperature from variations in rotation rate, continent formation, solar luminosity, and carbon dioxide
Authors: Kuhn William R. , Walker J. C. G. , Marshall Hal G.
Published: February 2008

Proposed evolutionary histories of solar luminosity, atmospheric carbon dioxide amounts, Earth rotation rate, and continent formation have been used to generate a time evolution of Earth's surface temperature. While speculative because of uncertainties in the input parameters, such a study does help to prioritize the areas of most concern to paleoclimatic research while illustrating the relationships and mutual dependencies. The mean temperature averages about 5 K higher than today over most of geologic time; the overall variation is less than 15 K. The evolution of Earth's rotation rate makes a significant contribution to the surface temperature distribution as late as 0.5 b.y. ago. While there is little change in equatorial temperatures, polar temperatures decrease, being some 15 K lower 3.5 b.y. ago than with present day rotation. The effect of continent growth on albedo is of secondary importance.
Balloon‐borne measurements of aerosol, condensation nuclei, and cloud particles in the stratosphere at McMurdo Station, Antarctica, during the spring of 1987
Authors: Hofmann D. J. , Rosen J. M. , Harder J. W. , Hereford J. V.
Published: February 2008

Measurements of the vertical profile of particles with condensation nuclei counters and eight channel aerosol detectors at McMurdo Station, Antarctica, in 1987 verified observations made in 1986 concerning the absence of upwelling in the polar vortex and the presence of a condensation nuclei layer in conjunction with the ozone hole region. New observations of a bimodal aerosol size distribution, consisting of a large‐particle (≈1 μm) mode mixed in with the small‐particle sulfate mode, at temperatures below −79°C are consistent with the presence of nitric acid‐water particles at low concentrations. Higher concentrations of large particles were observed in association with nacreous clouds. An unusual particle layer which contained enhanced concentrations of both the small‐particle (sulfate) mode and the large‐particle (nitric acid) mode was detected at temperatures below −85°C, suggesting simultaneous nucleation and growth phenomena. The vortex condensation nuclei layer was observed to form at the same time as the ozone hole, indicating that formation of the layer is triggered by photochemical processes and may be important in controlling ozone depletion above 22 km.
Quasi‐biennial modulation of the Antarctic ozone depletion
Authors: Lait Leslie R. , Schoeberl Mark R. , Newman Paul A.
Published: February 2008

The quasi‐biennial oscillation (QBO) in total ozone and temperature has been extracted from 9 years of Total Ozone Mapping Spectrometer (TOMS) observations and National Meteorological Center (NMC) analyses. Years in which QBO‐related variations in the total ozone and temperature are positive are found to correspond to years with smaller September Antarctic total ozone hole decline rates and vice versa. The QBO appears to be responsible for September decline rate deviations up to 0.4 Dobson units (DU) per day. Also, the QBO at mid‐latitudes appears to be better correlated with the 30‐mbar tropical QBO winds than with those at 50 mbar. Possible mechanisms that would explain these phenomena are discussed.
The effect of nonerodible particles on wind erosion of erodible surfaces
Authors: Gillette Dale A. , Stockton Paul H.
Published: February 2008

Nonerodible elements on erodible surfaces have the effect of absorbing part of the wind momentum flux (stress) and thus protect the erodible surface to a degree, depending on the geometry of the mixture. Experiments measuring the effect of nonerodible elements show that these elements increase the apparent threshold velocity of erosion and that the functional form of the mass flux (of erodible sand particles) in terms of friction velocity follows an Owen function. The partitioning of momentum flux by the nonerodible elements is smaller in our experiments than measured in the experiments of Marshall; however, in those measurements for which nonerodible geometry is similar, our results are roughly consistent with the experimental results of Lyles et al. The disagreement with the Marshall results is tentatively explained by differences in scale and in the wind stress measuring systems.
The Atlas/Centaur lightning strike incident
Authors: Christian H. J. , Mazur V. , Fisher B. D. , Ruhnke L. H. , Crouch K. , Perala R. P.
Published: February 2008

On March 26, 1987, an Atlas/Centaur 67 vehicle carrying a naval communication satellite was launched at 1622:00.768 EST from pad 36B of the Cape Canaveral Air Force Station, Florida. The meteorological conditions at the time were typical of wintertime storms with heavy overcast, moderate rain, and occasional scattered lightning activity. The NASA Investigation Board determined that, at approximately 48 s into the flight, the vehicle was struck by a triggered, cloud‐to‐ground lightning flash, comprised of at least four return strokes. The resulting lightning current apparently coupled a transient signal into the wiring of the Centaur digital computer unit (DCU), which caused a change in one memory location. The altered memory was associated with the computation of the Atlas engine yaw commands and caused the DCU to issue a hardover engine gimbal command. This resulted in an excessive angle of attack, large dynamic loads, and the breakup of the Atlas/Centaur 67 vehicle. The paper represents a case study of meteorological conditions at the time of launch and of the lightning flash triggered by the Atlas/Centaur 67 vehicle. This is based on comprehensive analyses of the cause of the incident by the NASA Investigation Board.
Lightning spectra in the 850‐ to 1400‐nm near‐infrared region
Authors: Weidman C. , Boye A. , Crowell L.
Published: February 2008

Lightning spectra in the 850‐ to 1400‐nm near‐infrared region have been recorded with 200‐ to 300‐ms time resolution using a slitless spectrometer with a lead sulfide detector. Except for the wire portion of triggered discharge channels, rocket triggered and natural return stroke spectra are very similar. The following neutral atomic nitrogen (NI) and oxygen (OI) multiplet emissions have been identified (the wavelength, in nanometers, of the brightest line in each group is shown in parentheses): NI(2) (821.6), OI(4) (844.6), NI(1) (868.0), NI(15) (906.1), OI(8) (926.6), NI(7) (939.3), NI(19) (986.2), NI(18) (1011.3), NI(28) (1053.9), and NI(36) (1246.8). Continuum emissions with peak intensities at least an order of magnitude less than the strongest line emissions were detected. A laboratory arc simulation of a return stroke discharge produced a near‐IR spectrum containing all the features emitted by lightning. Additional NI radiation peaks at 1131.4 nm (NI(17)) and 1358.1 nm on the arc spectra overlapped water vapor absorption bands and were not visible on lightning spectra recorded at 2.2‐km range. A time‐averaged lightning channel temperature of about 16,000°K was calculated from the ratio of relative intensities of the NI(1) and NI(18) multiplets.
Utilization of a mobile laboratory for storm electricity measurements
Authors: Rust W. David
Published: February 2008

Since 1978, we have been developing and using a mobile laboratory to make observations of storms. With our mobile lab, we record electric field, slow and fast electric field changes from lightning, optical transients, return stroke velocity, temperature, pressure, dew point, wind speed and direction, lab position, and video images of clouds and lightning. The mobile lab idea has been key in obtaining new information on several phenomena, e.g., field changes to compare with high‐altitude airplane measurements, electrical aspects of tornadic storms, and positive ground flashes. Mobile lab data were critical in an evaluation of the two ground strike location networks that provide scientific and operational data in the United States. We have documented that storms often are more dominated by intracloud (IC) lightning than previously reported. Observations on two tornadic storms show the IC flashes averaged ≥80% and 95% of the total lightning, respectively. Mobile lab and polarization radar data of storms producing wet microbursts in Alabama suggest that high percentages of IC flashes (95%) occur when a larger percentage of the total storm mass is convected above the freezing level. With the recent addition of mobile balloon launch and tracking, we also make soundings of the electric field and meteorological parameters within storms.
African dust observed over Canary Islands: Source‐regions identification and transport pattern for some summer situations
Authors: Bergametti Gilles , Gomes Laurent , Coudé‐Gaussen Genevieve , Rognon Pierre , Le Coustumer Michelle‐Noelle
Published: February 2008

Bulk filtration samples of dust were collected on Fuerteventura (Canary Islands) in July 1985 in order to investigate African dust transport over this region during summer. Air mass trajectories and elemental and mineralogical analyses allowed us to distinguish between oceanic and continental influences: three African dust transport cases occured during this period. Geochemical and mineralogical tracers, combined with air mass trajectories, indicate that two different source regions of dust (Sahelian and Moroccan ones) are involved. Each of these exhibits specific Si/Al and Fe/Al ratios that can be considered as tracers of dust origin. A meteorological study, based on satellite imagery, meteorological maps, and air mass trajectories, confirms the previous identification of the source region. It is also possible to describe the meteorological situation controlling the atmospheric pathway of the dusts from the source regions up to the Canary Islands. This study suggests that some source regions (especially the Sahelian one) of dust affecting the Canary Islands during summer are rather different from the Moroccan ones observed in a spring situation by Coudé‐Gaussen et al. (1987).
Hydrogen and deuterium loss from the terrestrial atmosphere: A quantitative assessment of nonthermal escape fluxes
Authors: Yung Yuk L. , Wen Jun‐Shan , Moses Julianne I. , Landry Bridget M. , Allen Mark , Hsu Kuang‐Jung
Published: February 2008

A comprehensive one‐dimensional photochemical model extending from the middle atmosphere (50 km) to the exobase (432 km) has been used to study the escape of hydrogen and deuterium from the Earth's atmosphere. The model incorporates recent advances in chemical kinetics as well as atmospheric observations by satellites, especially the Atmosphere Explorer C satellite. The results suggest: (1) the escape fluxes of both H and D are limited by the upward transport of total hydrogen and total deuterium at the homopause (this result is known as Hunten's limiting flux theorem); (2) about one fourth of total hydrogen escape is thermal, the rest being nonthermal; (3) escape of D is nonthermal; and (4) charge exchange and polar wind are important mechanisms for the nonthermal escape of H and D, but other nonthermal mechanisms may be required. The efficiency to escape from the terrestrial atmosphere for D is 0.74 of the efficiency for H. If the difference between the D/H ratio measured in deep‐sea tholeiite glass and that of standard sea water, δD = −77‰, were caused by the escape of H and D, we estimate that as much water as the equivalent of 36% of the present ocean might have been lost in the past.
Atmospheric NO3: 2. Observations in polar regions
Authors: Solomon S. , Sanders R. W. , Mount G. H. , Carroll M. A. , Jakoubek R. O. , Schmeltekopf A. L.
Published: February 2008

Stratospheric NO3 is expected to depend strongly upon two major factors: solar illumination and temperature. This paper presents observations in the polar regions that confirm the influence of both of these on the NO3 column abundance. Measurements of the absorption of incoming lunar radiation near 662 nm as the sun rises exhibit large changes that apparently reflect the rapid photolysis of NO3. The increase in upper stratospheric temperature that occurs in early spring in polar regions should also affect the seasonal changes in stratospheric NO3 abundances. Observations of stratospheric NO3 at 76.5°N in early February are contrasted with those obtained at 77.8°S in late August and September. Large seasonal differences in stratospheric temperatures between these two locations and times are shown to be in excellent agreement with the observed NO3 column amounts, providing further support for current understanding of the factors controlling the stratospheric NO3 abundance and its variability. These findings provide further evidence against a stratospheric “scavenger” for NO3, even in polar latitudes, where the scavenging effect was believed to be most pronounced.
Remote sensing observations of daytime column NO2 during the Airborne Antarctic Ozone Experiment, August 22 to October 2, 1987
Authors: Wahner A. , Jakoubek R. O. , Mount G. H. , Ravishankara A. R. , Schmeltekopf A. L.
Published: February 2008

A sensitive absorption spectrograph was flown on the NASA DC‐8 aircraft as part of the 1987 Airborne Antarctic Ozone Experiment to measure column abundances of O3, NO2, OClO, and BrO inside the Antarctic polar vortex. The instrument functioned successfully on all flights. Slant column NO2 measurements were made every 300 s whenever light levels permitted observation with an absolute accuracy better than 20% and with a detection limit of 3.4×1015 cm−2 slant column. These measurements are presented and compared with TOMS total ozone along the flight track.
In situ observations of ClO in the Antarctic: ER‐2 aircraft results from 54°S to 72°S latitude
Authors: Brune W. H. , Anderson J. G. , Chan K. R.
Published: February 2008

Results from a series of 12 ER‐2 aircraft flights into the Antarctic polar vortex are summarized. These in situ data define the spatial and temporal distribution of ClO as the aircraft flew at an altitude of ∼18 km from Punta Arenas (54°S latitude, 7O°W longitude) to the base of the Palmer Peninsula (72°S latitude, 75°W longitude) and back. At the southern extremity of the flight trajectory the aircraft descended to ∼13 km, turned north, and ascended to 18 km. A general pattern in the ClO distribution is reported: mixing ratios of approximately 10 parts per trillion by volume (pptv) are found at cruise altitude in the vicinity of 55°S increasing to 50 pptv at 6O°S. In the vicinity of 65°S latitude a steep gradient in the ClO mixing ratio is observed. At a fixed potential temperature, the ClO mixing ratio increases by an order of magnitude within a very few degrees of latitude through this sharp transition, thus defining the edge of a “chemically perturbed region.” From the edge of that region to the southern extension of the flights, 72°S, a dome of slowly increasing ClO best describes the distribution. Peak mixing ratios at 18 km at the southern extension of the flight track increased from 800 pptv on August 23 to 1100 pptv in early September and then increased slowly to 1200 pptv by the end of the mission on September 22.