bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of air pollution and wind on the large‐ion concentration in the air above Athens
Authors: Retalis D. , Retalis A.
Published: February 2004

The influences of air pollution (due to smoke and sulfur dioxide) and wind speed on large‐ion concentration (LIC) for the period from 1969 to 1980 are examined. In addition, the variations of LIC during sea breeze and etesians days for the same time period are presented. It was shown that wind speed and LIC are anticorrelated, while LIC is significantly lower during Etesian winds in comparison with that during sea breeze. The effects of ozone and nitrogen dioxide on LIC for the period 1982–1984 are also examined. It was shown that increase of smoke and/or sulfur dioxide leads to increase of LIC. while LIC and ozone, nitrogen dioxide are anticorrelated.
Methane and carbon dioxide exchanges between the atmosphere and northern boreal forest soils
Authors: Savage K. , Moore T. R. , Crill P. M.
Published: February 2004

CH4and CO2fluxes were measured in upland boreal forest soils near Thompson, Manitoba, from May 16 to September 16, 1994. Most sites consumed atmospheric CH4, fluxes ranging from +0.6 to −2.6 mg CH4m−2d−1, and emitted CO2at rates between 0.2 and 26.8 g CO2m−2d−1. There was some evidence of episodic CH4emissions after heavy rainfall from soils which normally consumed CH4. There were two distinct groups: sites in which both CO2and CH4exchange was strong (mean 5.2 g CO2m−2d−1, −1.0 mg CH4m−2d−1); and those which had a weak exchange of both gases (mean 2.5 g CO2m−2d−1, −0.2 mg CH4m−2d−1). The presence of black spruce trees, aSphagnumspp. ground cover and a thick organic layer (20–50 cm) characterized the weak exchange group. These characteristics were indicative of colder, wetter conditions with slower N cycling and longer path lengths to the zone of CH4oxidation. The strong exchange group had either aspen, jack pine, or birch trees; a vascular plant cover; and a thin organic layer (1–5 cm). These characteristics were indicative of warmer, drier conditions with faster N cycling and shorter path lengths to the zone of CH4oxidation. The seasonal average of both CO2and CH4flux from 11 sites could be predicted by regressions involving the amount of soil organic matter (0–5 cm depth) and seasonal temperature at a depth of 20 cm (r2=0.69 and 0.82, respectively). Using these vegetation characteristics and a Landsat image of the Boreal Ecosystem‐Atmosphere Study (BOREAS) northern study area for areal weighting, net gas fluxes were calculated for the upland soils, estimated to be −0.4 mg CH4m−2d−1and 4 g CO2m−2d−1.
Homogeneous nucleation of supercooled water: Results from a new equation of state
Authors: Jeffery C. A. , Austin P. H.
Published: February 2004

A series of laboratory and aircraft measurements have indicated that supercooled liquid water exists to temperatures as low as −70°C. These measurements also show that classical nucleation theory, using standard values for the thermodynamic properties of supercooled water, underestimates the nucleation rate of ice in liquid water at large supercoolings. New theoretical estimates for this homogeneous nucleation rate are presented, based on a new analytic equation of state for liquid water. The new equation of state, which is accurate over a pressure range of 3000 atmospheres and a temperature range of 1200K, is used to infer the latent heat of melting, liquid water density, and ice‐water surface energy of supercooled water. Predictions of the nucleation rate and the homogeneous freezing temperature made by this equation of state are in agreement with observations at temperatures as cold as −70°C and at pressures as high as 2000 atmospheres. These results indicate that it is not necessary to invoke a phase transition at −45°C to explain aircraft and laboratory observations of homogeneous ice nucleation in supercooled water clouds.
Relation of vertical flux of particles smaller than 10 μm to total aeolian horizontal mass flux at Owens Lake
Authors: Gillette Dale A. , Fryrear D. W. , Gill Thomas E. , Ley Trevor , Cahill Thomas A. , Gearhart Elizabeth A.
Published: February 2004

The vertical flux of particles smaller than 10 μm for a saline playa surface, the particle size composition of which was classified as loam‐textured, was estimated for a highly wind‐erodible site on the playa of Owens (dry) Lake in California. The ratio of this vertical flux to the horizontal flux of total airborne material through a surface perpendicular to the soil and to the wind, Fa/qtot, is 2.75×10−4 m−1. This is consistent with that ratio for sand‐textured soils and suggests that the binding energy and size of saltating particles for the tested surface material at Owens Lake is of the same order as that for sandier soils. The horizontal mass flux of saltating grains, q, in the reported wind erosion event is 51.3% of the total horizontal mass flux qtot. Therefore the ratio of Fa/q is 5.4×10−4 m−1.
Cloud chemistry varies with drop size
Authors: Bator Aaron , Collett Jeffrey L.
Published: February 2004

Samples of fog and cloud drops were collected by drop size from several locations around the United States. Sites were selected to represent a variety of cloud types (coastal stratus clouds, frontal clouds, and radiation fog) as well as both clean and polluted environments. A size‐fractionating version of the Caltech Active Strand Cloudwater Collector (sf‐CASCC) and a two‐stage Eidgenössische Technische Hochschule (ETH) cloud impactor were each used to simultaneously collect small and large cloud drop fractions. The sf‐CASCC is designed to collect drops >23 μm in diameter in the large fraction and drops between 4 and 23 μm in the small fraction, while the ETH impactor is typically configured to collect drops >10 μm in diameter and drops between 3 and 10 μm in diameter in its two size fractions. Concentrations of sulfate and ammonium were typically observed to be enriched in small cloud drops. A similar pattern was observed for nitrate at several locations. Coarse mode aerosol species were often observed to be enriched in large cloud drops. These findings suggest that the size‐dependent chemical signature of the precursor aerosol particle size distribution is at least partially maintained in the cloud drop size spectrum. The observed size dependence of the cloud drop composition can enhance rates of aqueous phase sulfate production relative to expectations based on average cloud drop composition, bias efficiencies with which individual chemical species are incorporated into precipitation within clouds, and affect patterns of chemical deposition to plant canopies or within the respiratory tract.
Soil water balance in a boreal forest
Authors: Cuenca Richard H. , Stangel David E. , Kelly Shaun F.
Published: February 2004

Measurements of root zone soil water content and soil hydraulic properties at the flux tower sites were conducted during the course of the Boreal Ecosystem‐Atmosphere Study (BOREAS) experiment. Instrumentation included neutron probe, time domain reflectometry (TDR), and tension infiltrometer. Several methods of data visualization were employed to demonstrate fluctuations in soil water content with depth and time during the intensive field campaigns (IFCs). These methods started with two‐dimensional plots of soil water content as a function of time and depth and evolved into the construction of three‐dimensional soil water prisms. The prisms were constructed by using cubic‐spline (vertical z‐direction) and linear (horizontal x‐direction) interpolations for soil water content and linear interpolations along the time (y direction) axis. The prisms allow for animation along any plane or combination of planes to demonstrate the evolution of soil water conditions due to evapotranspiration, drainage, and precipitation. Soil hydraulic properties were determined at the flux tower sites based on analysis of in situ tension infiltrometer tests and soil water retention data from laboratory analysis of soil cores. Results from this analysis are saturated hydraulic conductivity and fitting parameters for the van Genuchten soil water retention function and Mualem hydraulic conductivity function at each flux tower site. These functions are required for physically based simulation models of soil water dynamics, soil water balance, and the interaction of the soil profile with the atmospheric boundary layer. Examples of cumulative evapotranspiration and drainage calculated from the soil water balance are presented and compared with flux tower measurements.
Anomalous behavior of Schumann resonances during the transition between 1995 and 1996
Authors: Sátori Gabriella , Zieger Bertalan
Published: February 2004

Anomalous behavior of Schumann resonance (SR) parameters is presented in interannual relations for the first time. The mean daily intensity of the first three SR modes measured in the vertical electric component at the Nagycenk Observatory (47.6°N, 16.7°E), Central Europe, was significantly higher in December 1995 and January 1996 than in the same months 1 year before. The largest relative SR intensity deviations occurred in the third part of December 1995 and in the evening hours (2000–2200 UT), when the lightning activity of the South American thunderstorm region is the most intense. In January 1996 the largest relative SR intensity deviations appeared in the early morning hours (0000–0030 UT), when the worldwide thunderstorm activity is at a minimum. This result suggests that a lightning activity in the Pacific region was not as sparse in January 1996 as it was in January 1995. The time variation of the maxima of the SR intensity ratios indicates a westward propagation with trade wind speeds of about 2 to 8 m s−1 from the end of December 1995 about to the end of January 1996. The anomalous SR intensity in December 1995 is attributed to a small increase in the surface air temperature (about 0.2°C) and to the extension of the thunderstorm region indicated by the SR frequency range variation. It is also suggested that this warmer air mass was advected by easterlies from the end of December 1995 over the cooler Pacific in January 1996 causing more intense lightning activity there.
Seasonal change in understory reflectance of boreal forests and influence on canopy vegetation indices
Authors: Miller John R. , White H. Peter , Chen Jing M. , Peddle Derek R. , McDermid Greg , Fournier Richard A. , Shepherd Paul , Rubinstein Irene , Freemantle Jim , Soffer Raymond , LeDrew Ellsworth
Published: February 2004

One objective of the Boreal Ecosystem‐Atmospheric Study (BOREAS) is to increase our understanding of the nature of canopy spectral bidirectional reflectance in the visible/near‐infrared regimes for open canopies typical of boreal forest stands. For such stands, the need to characterize the reflectance of the sunlit and shaded vegetated understory is critical. These variables are subject to temporal variability due to differences in species phenology and foliar display as well as diurnal and seasonal changes in solar illumination through a seasonally varying upper canopy foliar area. To provide for this need, a multiteam field effort was mounted to measure the nadir midday understory reflectance for the flux tower sites during 1994 BOREAS field campaigns between February and October, specifically during the winter focused field campaign (FFC‐W), the spring thaw focused field campaign (FFC‐T), and the three intensive field campaigns (IFC‐1, IFC‐2, and IFC‐3) between June and September, which sample vegetation phenological change. This was accomplished by measuring at near‐solar noon the sunlit and shaded nadir reflectance of the understory along a surveyed leaf area index (LAI) transect line at each flux tower site. Site‐to‐site comparisons of understory reflectance spectra reveal stand differences that become more significant as the season progresses. Mean midday understory reflectance spectra were observed to be remarkably consistent over the season for young jack pine stands, followed by somewhat increased variability for mature jack pine, and significant seasonal variability for black spruce stands. Derived vegetation indices for understories are generally consistent with extrapolations of previous relationships of canopy spectral vegetation indices (VIs) versus leaf area index to zero LAI. Inclusion of these “zeroLAI” understory‐derived indices significantly enhance the correlation in the linear VI‐LAI relationships.
Validation of an off‐line three‐dimensional chemical transport model using observed radon profiles: 2. Model results
Authors: Stockwell D. Zoe , Kritz Mark A. , Chipperfield Martyn P. , Pyle John A.
Published: February 2004

We parameterize radon emissions in the TOMCAT global off‐line three‐dimensional chemical transport model (CTM) and compare modeled radon profiles with spatially and temporally matched observations obtained near Moffett Field, California, in June 1994. The CTM was forced using European Centre for Medium‐Range Weather Forecasts analyses for April‐August 1994. To identify the origin of modeled radon, we divided the radon sources into three regions. We performed CTM sensitivity experiments at horizontal resolutions of 2.8° × 2.8° (latitude × longitude) and 7.5° × 7.5°, and with and without moist convection and/or vertical diffusion. At the higher resolution the full CTM (i.e., including convection and vertical diffusion) generally agrees well with the observations in the free troposphere. The observations exhibit free‐tropospheric radon peaks at altitudes where zonal wind speeds in the Pacific jet stream are greatest (generally at ≥7 km). In this region the modeled radon originates from Asia, and the observed variability in the radon concentration is reproduced. Thus, the model reproduces the position and strength of the jet. We identify observed radon peaks that may originate from convective lifting, as they do in the model results. If these observed peaks do originate from convection, then the full CTM captures the correct temporal variability in convection over Asia and the Pacific for the observation period. Quantitative comparison shows that the model‐data agreement is degraded if we decrease the model resolution to 7.5° × 7.5°, or remove the parameterizations of convection and/or vertical diffusion. This suggests a resolution of near 2.8° × 2.8° is needed in global models for realistic simulations of short‐lived species. We have identified certain shortcomings with TOMCAT: the model underestimates the amount of convective cloud, the convective cloud top height, and the amount of vertical diffusion. We identify improvements to ameliorate these problems.
An analysis of the structure and forcing of the equatorial semiannual oscillation in zonal wind
Authors: Ray Eric A. , Alexander M. Joan , Holton James R.
Published: February 2004

The low‐frequency variability in the equatorial middle atmosphere is dominated by the semiannual oscillation (SAO) and quasi‐biennial (QBO) oscillation. Although the general characteristics and forcing mechanisms of these oscillations are thought to be known, these oscillations are still not well reproduced in modeling experiments of the middle atmosphere. The relatively long period (1992–1996) of Upper Atmosphere Research Satellite (UARS) measurements and U.K. Meteorological Office (UKMO) assimilated model data have been used to examine the zonal wind SAO in the upper stratosphere. The SAO in zonal wind is found to be latitudinally asymmetric about the equator with strongest amplitudes in the southern hemisphere subtropics. The latitudinal asymmetry is diagnosed by using the TEM momentum equation and UKMO data. The asymmetry is mostly due to the different phasing of the peak advective forcing by the mean meridional circulation in each hemisphere. The contribution of gravity waves to the zonal wind SAO are also explored by using the forcing from a linear gravity wave model. Gravity waves are found to be the primary source of westerly momentum in each hemisphere during fall and contribute to the latitudinal asymmetry of the SAO by having more easterly forcing in the southern hemisphere during summer compared to in the northern hemisphere during summer.
Polar stratospheric cloud threshold temperatures in the 1995–1996 arctic vortex
Authors: Rosen James M. , Kjome Norman T. , Larsen Niels , Knudsen Bjørn M. , Kyrö Esko , Kivi Rigel , Karhu Juha , Neuber Roland , Beninga Ingo
Published: February 2004

Balloon‐borne backscattersondes have been used to study the relationship between particle scattering and ambient temperature near the vertical edge of arctic polar stratospheric clouds (PSCs) as well as to delineate the cloud type occurrence probability as a function of temperature. The observed typical threshold temperatures as a function of altitude are about1°K warmer than the temperature TSTS expected for rapid growth of supercooled ternary solution aerosols. A more descriptive analysis shows that the threshold temperatures occur over a definable range of temperatures and tend to cluster near, but somewhat warmer than, TSTS. Considering the experimental and theoretical uncertainties, this difference may not be significant. The probability of type Ib PSC occurrence shows a dramatic increase at TSTS±1°K, while for type Ia PSCs the probability is roughly constant at 10% for temperatures below the formation point of nitric acid trihydrate (TNAT).
Estimation of water cloud properties from satellite microwave, infrared and visible measurements in oceanic environments: 2. Results
Authors: Lin Bing , Minnis Patrick , Wielicki Bruce , Doelling David R. , Palikonda Rabindra , Young David F. , Uttal Taneil
Published: February 2004

A microwave (MW) method for deriving cloud liquid water path (LWP) and cloud water temperature (Tw) is validated by using soundings and results from a visible (VIS) and infrared (IR) retrieval method. The two retrieval methods are combined into a single technique, MVI (microwave, visible, and infrared), to estimate the frequency of multilayered clouds and the effective droplet radius re in water clouds. These techniques were applied to Meteosat and special sensor microwave/imager (SSM/I) data taken during June 1–28, 1992, over the Atlantic Stratocumulus Transition Experiment (ASTEX) region. For low clouds, as identified with the VIS‐IR method, Tw on average is nearly the same as the VIS‐IR cloud‐top temperatures (Tc). A negative correlation between LWP and Tc was found for the clouds. For midlevel clouds, Tw is about 8 K warmer than Tc because of either large cloud thicknesses or multilayered clouds. When high clouds are found by the VIS‐IR method, Tc is ∼30 K colder than Tw, indicating that lower‐level liquid‐water clouds may be detected by the MW method. On the basis of the matched Tw and Tc obsevations, the estimated frequencies of multilayered high, middle, and low clouds are about 36%, 19%, and 0%, respectively, values that are similar to cloud radar measurements. Matched satellite and ground‐based radar data show that the MVI technique can separate cloud layers when high ice clouds overlap lower liquid water clouds. The distributions of re for water clouds are about the same for low, middle, and broken clouds with mean and standard deviations of ∼12 and 10 μm, respectively. The frequency of large droplets (re>16 μm) suggests that drizzle occurs in ∼30% of the matched Meteosat‐SSM/I cloudy conditions.
Theoretical estimate of NOx production in lightning corona
Authors: Coppens F. , Berton R. , Bondiou‐Clergerie A. , Gallimberti I.
Published: February 2004

A theoretical estimate of the quantity of nitrogen oxides NO and NO2 produced by the corona phase of a lightning flash has been carried out. The procedure makes use of physical simulations of positive leader and streamer propagation, coupled to a chemical kinetics model including 35 species such as ions, radicals, and neutral molecules. The effects of molecular and turbulent diffusion in thunderstorms are also modeled. A parametric study with various values of pressure and temperature leads to the conclusion that the effect of the corona phase on NOx production is negligible compared to that of the return stroke of the flash.
Stratospheric effects of 27‐day solar ultraviolet variations: An analysis of UARS MLS ozone and temperature data
Authors: Hood L. L. , Zhou S.
Published: February 2004

The characteristics of upper stratospheric ozone and temperature responses at low latitudes to short‐term solar ultraviolet variations are studied by using 1000 days of UARS microwave limb sounder (MLS) and solar stellar irradiance comparison experiment data. Consistent with previous analyses of Nimbus 7 solar backscattered ultraviolet (SBUV) data, the high‐pass‐filtered solar flux in the 200‐to 205‐nm interval is most strongly correlated with MLS ozone measurements at tropical latitudes near 4 hPa with a sensitivity of about 0.4% for each 1% change in the solar flux. Reproducibility tests, power spectral, and coherency estimates support the reality of the observed ozone response at this level. The MLS solar UV/ozone response is significantly reduced at levels above ∼2 hPa as compared to earlier results based on SBUV data. This reduction appears to be a consequence of the ozone diurnal cycle at high altitudes combined with the necessary inclusion of nighttime records in calculating the MLS ozone zonal averages. Some evidence is obtained for an MLS solar UV/temperature response near the stratopause, but coherency tests are negative. Future analyses of independent data records having similar local time coverage as that of Nimbus 7 SBUV are needed to establish more definitively whether any significant change in the upper stratospheric UV response has occurred.
Comparison of calculated and measured peroxide data collected in marine air to investigate prominent features of the annual cycle of ozone in the troposphere
Authors: Penkett S. A. , Reeves C. E. , Bandy B. J. , Kent J. M. , Richer H. R.
Published: February 2004

Large amounts of data on the concentration of peroxides have been collected in vertical profiles over the North Atlantic Ocean by a Hercules aircraft. The measured peroxide concentrations have been compared with concentrations calculated by a simple algorithm derived assuming that the standing peroxide concentration is in equilibrium with its production and loss processes. In clean air where the peroxide and ozone concentrations are anticorrelated throughout the profile measured and calculated peroxide concentrations coincide, whereas in layers of polluted air within the profile, as determined from positive ozone peroxide correlations, calculated peroxide concentrations are greatly in excess of measured values. Using the degree of correlation between measured and calculated peroxide concentrations as a diagnostic, it is possible to show that many aspects of the seasonal cycle of ozone are caused by in situ tropospheric chemistry. Thus the summer minimum in the seasonal cycle of ozone, observed at clean marine ground‐based sites such as Mace Head, is due to photochemical destruction, and elevated levels of ozone are associated with the transport of polluted air, on occasion over thousands of kilometers. Of particular interest if our analysis is correct, the broad maximum of ozone occurring between March and May at ground‐based sites has a large contribution from ozone formed by tropospheric as well as stratospheric chemistry.
Incorporation of physical optics effects and computation of the Legendre expansion for ray‐tracing phase functions involving δ‐function transmission
Authors: Mishchenko Michael I. , Macke Andreas
Published: February 2004

The standard geometric optics (GO) technique predicts that the phase function for large nonspherical particles with parallel plane facets (e.g., hexagonal ice crystals) should have an infinitesimally narrow δ‐function transmission peak caused by rays twice transmitted (refracted) in exactly the forward scattering direction. However, exact T‐matrix computations and physical considerations based on the Kirchhoff approximation suggest that this peak is an artifact of GO completely ignoring physical optics effects and must be convolved with the Fraunhofer pattern, thereby producing a phase function component with an angular profile similar to the standard diffraction component. This convolution can be performed with a simple procedure which supplements the standard ray‐tracing code and makes the computation of the phase function and its Legendre expansion both more physically realistic and more accurate.
Potential retrieval of dominating crystal habit and size using radiance data from a dual‐view and multiwavelength instrument: A tropical cirrus anvil case
Authors: Baran A. J. , Watts P. D. , Foot J. S.
Published: February 2004

The potential to retrieve dominating crystal habit, size and bulk optical depth for tropical anvil cirrus using radiance measurements from a dual‐view and multiwavelength instrument is demonstrated. The radiance measurements are taken from the along‐track scanning radiometer (ATSR‐2) instrument at wavelengths of 0.87 and 1.6 μm. The ATSR‐2 has a dual‐view capability being able to make radiance measurements at near nadir and at a forward view of 55° of the same cloud. The dual‐view radiance measurements at 0.87 μm are best fitted by a polycrystal phase function and estimates of crystal size (crystal size in this paper is defined in terms of the crystal maximum dimension) using the 1.6 μm channel vary between 25 and 100 μm. Two other tropical cirrus anvil cases are used to show qualitatively the variation of crystal size with anvil maturity. Quantitative comparisons are made with observations taken from the Central Equatorial Pacific Experiment with regard to dominating habit and cloud‐top crystal size.
Some characteristics of cloud‐to‐ground lightning in mesoscale convective systems
Authors: MacGorman Donald R. , Morgenstern Carolyn D.
Published: February 2004

Selected characteristics of cloud‐to‐ground lightning were analyzed for twenty‐five mesoscale convective systems (MCSs) that occurred within the range of the National Severe Storm Laboratory direction‐finder network during the warm season of 1986. Positive ground flashes comprised 6% of ground flashes in MCSs versus 4% in warm‐season thunderstorms overall. For negative ground flashes the distribution of estimated peak currents from MCSs appeared almost identical to the distribution from all thunderstorms. The distribution of estimated peak currents varied more from MCS to MCS for positive ground flashes than for negative ground flashes, and the distributions for positive ground flashes in MCSs usually appeared much different from those for storms overall. We divided the spectrum of peak current distributions for positive ground flashes of individual MCSs into three categories: (1) the small‐amplitude category (mode of 9–13 kA; few flashes with >40 kA), (2) the middle‐amplitude category (mode of 13–17 kA; many flashes with >40 kA), and (3) the large‐amplitude category (mode of 51–56 kA). MCSs in the large‐amplitude category occurred throughout the warm season; those in the small‐amplitude category, primarily during April, May, and September; and those in the middle‐amplitude category, during June‐August. The maximum total ground flash rate per 30‐min period in each MCS tended to be smallest in the large‐amplitude category. Median peak currents for all 30‐min periods of MCSs in our analysis converged on a relatively narrow range of values when flash rates of a given ground flash polarity increased to large values. For negative ground flashes the median peak currents converged on 25–30 kA in all MCSs. For positive ground flashes the median peak currents converged on one of two narrow ranges: roughly 10 kA for the small‐amplitude category and 60 kA for the large‐ and middle‐amplitude categories.
BOREAS in 1997: Experiment overview, scientific results, and future directions
Authors: Sellers Piers J. , Hall Forrest G. , Kelly Robert D. , Black Andrew , Baldocchi Dennis , Berry Joe , Ryan Michael , Ranson K. Jon , Crill Patrick M. , Lettenmaier Dennis P. , Margolis Hank , Cihlar Josef , Newcomer Jeffrey , Fitzjarrald David , Jarvis Paul G. , Gower Stith T. , Halliwell David , Williams Darrel , Goodison Barry , Wickland Diane E. , Guertin Florian E.
Published: February 2004

The goal of the Boreal Ecosystem‐Atmosphere Study (BOREAS) is to improve our understanding of the interactions between the boreal forest biome and the atmosphere in order to clarify their roles in global change. This overview paper describes the science background and motivations for BOREAS and the experimental design and operations of the BOREAS 1994 and BOREAS 1996 field years. The findings of the 83 papers in this journal special issue are reviewed. In section 7, important scientific results of the project to date are summarized and future research directions are identified.
An ion‐molecule mechanism for the formation of neutral sporadic Na layers
Authors: Cox Rachel M. , Plane John M. C.
Published: February 2004

This paper describes a laboratory study into the chemical pathways by which Na+ is converted to Na in the upper atmosphere. The termolecular clustering reactions of Na+ with N2, O2, and CO2 were studied in a low‐temperature fast flow reactor coupled to a quadrupole mass spectrometer. This yielded k(Na+ + N2 + He, 93–255 K) = (1.20±0.13) × 10−30 (T/ 200 K)−(2.20±0.09), k(Na+ + O2 + He, 93–130 K) = (5.20±2.62) × 10−31 (T/ 200 K)−(2.64±0.74), k(Na+ + CO2 + He, 158–300 K) = (9.05±1.38) × 10−30 (T/ 200 K)−(2.84±0.48), where are cm6 molecule−2 s−1 and the stated errors are a combination of the 2σ standard errors in the kinetic data and the systematic errors in the temperature, pressure, and flow rates. It was then shown that atomic O will ligand switch with Na. N2+ but not with Na.CO2+, and that the former reaction proceeds essentially at the Langevin collision frequency. The neutralization of Na+ in the upper atmosphere is therefore rather complex. The first step is formation of the Na.N2+ ion from the recombination of Na+ with N2. This cluster ion can then either switch with O2, which leads to a stable cluster ion that will undergo dissociative electron recombination to form Na; or switch with atomic O, which reforms Na+. The result of this is that the lifetime of Na+ changes very rapidly from more than a day above 100 km to just a few minutes at 90 km. Furthermore, the rate of neutralization is largely independent of the electron concentration. A simple model describing the conversion of Na+ to atomic Na in a descending sporadic E layer demonstrates that this ion‐molecule mechanism appears to fulfil many of the major criteria for producing sporadic sodium layers.
A comparison of atmospheric tides inferred from observations at the mesopause during ALOHA‐93 with the model predictions of the TIME‐GCM
Authors: Hecht J. H. , Walterscheid R. L. , Roble R. G. , Lieberman R. S. , Talaat E. R. , Howat S. K. Ramsay , Lowe R. P. , Turnbull D. N. , Gardner C. S. , States R. , Dao P. D.
Published: February 2004

Observations made during the Airborne Lidar and Observations of Hawaiian Airglow (ALOHA‐93) campaign during October 1993 revealed the presence of persistent large perturbations of the temperature and density in the 80 to 100 km mesopause region. These perturbations, seen both by passive airglow and active lidar techniques, were identified as due to the presence of diurnal and semidiurnal tides. These results were compared with the predictions of the thermosphere/ionosphere/mesosphere electrodynamics general circulation model (TIME‐GCM). This model was recently tuned to agree with the observations from the Upper Atmosphere Research Satellite (UARS) with respect to mesosphere/lower thermosphere winds (60–200 km). It is found that although the TIME‐GCM agrees with UARS winds, it underpredicts the diurnal, and possibly the semidiurnal, tidal temperature perturbations seen during ALOHA‐93. Since the TIME‐GCM only includes migrating tides, this comparison suggests that nonmigrating tides may have had a significant amplitude during the ALOHA‐93 campaign period. UARS observations of the major nonmigrating diurnal mode were made just before and after the ALOHA‐93 period. It is found that the zonally symmetric nonmigrating tide can account for the discrepancy between the ALOHA‐93 results and the TIME‐GCM predictions only for a few periods and only at an altitude around 88 km. If the zonally symmetric nonmigrating tide is to account for the discrepancies between the model and the data, than it has to be highly variable.
Interpretation of gravity waves observed in the mesopause region at Starfire Optical Range, New Mexico: Strong evidence for nonseparable intrinsic (m, ω) spectra
Authors: Gardner Chester S. , Franke Steven J. , Yang Weimin , Tao Xin , Yu J. R.
Published: February 2004

Sixty‐five hours of Na lidar observations of vertical and horizontal winds, temperature, and Na density were obtained during eight different nights in 1994 and 1995 at the Starfire Optical Range, New Mexico, using a 3.5 m diameter telescope. The high‐resolution data are used to study the spectra of gravity wave perturbations in the mesopause region. Wave activity was strong during the observations. The average variances of temperature, relative atmospheric density, horizontal wind, and vertical wind were 80 K2, 28 (%)2, 1100 m2/s2, and 4.3 m2/s2, respectively. The temperature, relative density, and horizontal wind spectra are generally consistent with the large body of published measurements and with the predictions of gravity wave theory. The observed temporal frequency (ω0) and vertical wave number (m) spectra of vertical winds are both very shallow. The indices of the ω0 spectra vary between −0.59±0.13 and −1.2±0.09, and the mean value is −0.76. The indices of the m spectra vary between −0.83±0.04 and −1.48±0.03, and the mean value is −1.1. In contrast, the indices of the horizontal wind m spectra vary between −2.8±0.10 and −3.2±0.13 with a mean of −3.0. These large differences imply that the underlying intrinsic spectra are not separable. However, the observed vertical wind m spectra are not consistent with the nonseparable theories which predict index values near +1. By using mathematical and numerical models, we show that the observed m spectra are distorted by Doppler and critical layer effects associated with the height‐varying mean wind field. This distortion is greatest at high values of m and leads to observed vertical wind m spectra which are steeper than the underlying intrinsic spectra. Although the intrinsic spectra are definitely shallower (i.e., indices more positive) than the observations, it is not possible to determine if the measurements are entirely consistent with any of the nonseparable wave dissipation theories.
Measurements of reactive nitrogen and ozone to 5‐km altitude in June 1990 over the southeastern United States
Authors: Ridley B. A. , Walega J. G. , Lamarque J.‐F. , Grahek F. E. , Trainer M. , Hübler G. , Lin X. , Fehsenfeld F. C.
Published: February 2004

Aircraft flights made in June 1990 substantiate the expected variability of ozone and reactive nitrogen constituents in the lower atmosphere over Mississippi and Alabama due to the variety and proximity of sources and the photochemical production and loss of ozone. Urban, biomass burn, electrical power plant, and paper mill plumes are examples of sources encountered during these flights, and some of their characteristics are described. For example, in the urban plume from Mobile, Alabama, an upper limit to the ozone production efficiency was 6–7 parts per billion by volume (ppbv) of O3 per ppbv of NOx oxidized. Emissions from several biomass fires had lower efficiencies of 2–4 ppbv ppbv−1, but the average rate of production of ozone was as high as 58 ppbv hr−1 for one fire where the plume was isolated from mixing to the surface. Close encounters with paper mill and power plant emissions showed chemical consumption of O3, while far‐field encounters with power plant plumes showed enhanced O3 due to photochemical production. Observations made in early morning, below a nocturnal inversion provide indirect evidence of significant nighttime oxidation of freshly emitted NOx to reservoir constituents. Although statistics for the region covered by these flights clearly depend on precisely where the aircraft flew, the mean and median temporal and vertical behaviors of constituent mixing ratios are summarized.
Environmental variables regulating soil carbon dioxide efflux following clear‐cutting of a Pinus radiata D. Don plantation
Authors: Arneth A. , Kelliher F. M. , Gower S. T. , Scott N. A. , Byers J. N. , McSeveny T. M.
Published: February 2004

The regulation of soil surface CO2 efflux (Fs) from a dryland Pinus radiata clear‐cut in New Zealand (658‐mm annual rainfall, 50‐mm soil water storage over 0.5‐m depth of soil) was quantified using a multiplicative, soil moisture and temperature constraint model. Model parameters were determined from measurements of Fs by eddy covariance and by two portable CO2 analyzers equipped with soil chambers during 8 consecutive days in November 1995. Fs from the two chamber systems agreed consistently, but agreement between chamber and eddy covariance measurements was confined to a very small flux‐range (1.5–2.5 μmol m−2 s−1). When the soil surface was wet and wind speed (u, a surrogate for static pressure fluctuations) was high, eddy covariance fluxes were >3 μmol m−2 s−1 (maximum 5.0 m−2 s−1), significantly higher than the chamber values. Including u as a third constraint in the model facilitated good predictions of Fs over the entire range of environmental conditions. Daily Fs during the study period ranged from 0.8 to 2.9 g C m−2. Driven by weather data from the forest fire station and subroutines for soil water balance and temperature, modeled Fs for the year ending in June 1996 was 0.37 kg C m−2. This year had below average (547 mm) rainfall. For a year with 640‐mm rainfall, a significant increase of annual Fs (0.44 kg C m−2) demonstrated the severe restriction of soil microbial activity by moisture deficit at dryland sites. Moreover, when the soil was adequately watered, Fs was frequently restricted by low wind speed.
Evaluation of optimization of lidar temperature analysis algorithms using simulated data
Authors: Leblanc Thierry , McDermid I. Stuart , Hauchecorne Alain , Keckhut Philippe
Published: February 2004

Temperature lidar data have been simulated in order to test the Jet Propulsion Laboratory (JPL) SO3ANL version 3.2 and Service d'Aeronomie du Centre National de la Recherche Scientifique (CNRS/SA) TEMPER version 2.1 lidar temperature analysis software. Assuming known atmospheric temperature‐pressure‐density profiles, theoretical raw‐photons lidar profiles have been calculated using the actual characteristics of two JPL lidar instruments, located at the Table Mountain Facility (TMF) in California and the Mauna Loa Observatory (MLO), Hawaii, and the CNRS/SA Rayleigh lidar, located at the Observatoire de Haute‐Provence (OHP) in France. The simulations were performed for an initial climatological profile taken from the CIRA‐86 model and for various profiles derived from this model including realistic atmospheric disturbances. Comparisons between the original and retrieved temperature profiles revealed errors of several kelvins for both the JPL and the CNRS/SA programs. By varying parameters in the simulation, it was possible to determine both the source and the magnitude of these errors. Once identified, the errors were corrected, and the analysis programs were optimized, leading to new operational versions of these programs (SO3ANL version 3.6 and TEMPER version 2.2). An accurate accounting of the temperature lidar analysis errors, before and after this work, is presented.
Electrical structure in thunderstorm convective regions: 1. Mesoscale convective systems
Authors: Stolzenburg Maribeth , Rust W. David , Smull Bradley F. , Marshall Thomas C.
Published: February 2004

Electric field (E) soundings through convective regions of mesoscale convective systems (MCSs) are examined in this paper. Ten E soundings through updrafts in MCS convective regions and five soundings in MCS convective regions outside updrafts are used to show that a typical electrical structure exists in this region. These 15 E soundings plus one other previously published sounding, which is included in this analysis, comprise all known soundings in the convective region of MCSs. The basic charge structure identified in MCS updrafts consists of four charge regions, alternating in polarity, with the lowest region positive and the highest region negative. The basic charge structure outside updrafts in MCS convective regions has six charge regions, alternating in polarity, with a positive charge region lowest. Maximum E magnitudes of both polarities are larger and are located at lower heights in soundings outside updrafts compared to those within updrafts. Excepting the upper positive charge, inferred charge regions are shallower and have larger charge densities outside updrafts. The center of the main negative charge is lower and warmer outside updrafts (5.5 km, −6.2°C) than within updrafts (6.9 km, −15.7°C). These features inside and outside updrafts are incorporated in a new conceptual model of MCS convective region charge structure. Also, an expanded conceptual model is developed, using previously published data from other parts of MCSs. This more complete conceptual model shows the typical electrical charge, airflow, and reflectivity features in the stratiform region, the transition zone, and the convective region of midlatitude mesoscale convective systems.
The impact of nonmethane hydrocarbon compounds on tropospheric photochemistry
Authors: Houweling Sander , Dentener Frank , Lelieveld Jos
Published: February 2004

Nonmethane hydrocarbons (NMHC) play an important role in global scale tropospheric photochemistry. The representation of NMHC chemistry in three‐dimensional tropospheric chemistry transport models requires a highly parameterized description of only the most important processes, as the number of reactions and compounds involved is very large. In this paper a chemical scheme is presented, based on the Carbon Bond Mechanism 4 (CBM‐4), modified for use in the global Tracer Model 3 (TM3). The original scheme has been extended with reactions important under background conditions, and reaction rates and product distributions have been updated. Box model tests show that the modified CBM‐4 and a detailed reference mechanism agree well for a broad range of chemical conditions. Results of TM3 runs with and without NMHC chemistry are compared with observations, illustrating the effects of NMHC on key compounds of tropospheric photochemistry, such as ozone, the hydroxyl radical, carbon monoxide, and NOx. In particular, the simulation of ozone over polluted regions improves when NMHC chemistry is accounted for. Globally, the contribution of NMHC to net photochemical ozone production is estimated at about 40%, leading to a 17% increase of the tropospheric ozone column. OH is depleted over the continents owing to reactions with NMHC, which is most evident in regions with strong biogenic emissions. Although NMHC significantly influence the global OH distribution, their effect on its total tropospheric content appears to be marginal. Results of sensitivity runs with and without organic peroxy nitrates show that this N reservoir may significantly change the global NOx distribution, leading to a NOx increase over the oceans of the order of 50%. This increase improves the agreement between simulated and observed nitrate levels at remote stations, although large discrepancies remain. In general, the present treatment of NMHC reproduces the main features of tropospheric chemistry.
Photolysis and radiolysis of water ice on outer solar system bodies
Authors: Johnson R. E. , Quickenden T. I.
Published: February 2004

In this paper the available laboratory data on photolysis and radiolysis of water ice are summarized for the purpose of interpreting remote sensing data for the icy satellites. The relevance of these data to the objects in the outer solar system is then discussed. It is pointed out that the dominant species seen in laboratory spectra can differ from that seen on icy objects in space because of the low ion and UV fluxes and the relatively long annealing times in space. In the absence of contaminants, O2 is a relatively stable, photoresistant product which forms more efficiently with increasing temperature. O2 can accumulate in voids in which O3 is then formed by photolysis. In regions with temperatures always <100 K the absorption band seen in laboratory spectra at 0.28 μm, associated with trapped OH, as well as bands (<0.25 μm) associated with HO2 and H2O2 can produce a general reddening below ∼0.4 μm. This will contribute to the icy satellite reflectance spectra, as well as the reflectance spectra of more distant solar system objects. The stability of these species (O2, H2O2, HO2, OH) is enhanced by the preferential loss of H2, which also affects the D/H ratio in the surface. It is also shown that the luminescence produced by plasma bombardment might be observable by spacecraft on the nightside of certain satellites.
Lunar thermal emission and remote determination of surface properties
Authors: Urquhart Mary L. , Jakosky Bruce M.
Published: February 2004

Grain size, bulk density (or porosity), thermal conductivity, and rock abundance all play an important role in the thermal behavior of the lunar surface. Direct investigation of these properties of the lunar surface layer is not presently possible, with the exception of the samples returned from the Apollo landing sites. An indirect measurement of lunar surface properties may be possible using remote thermal infrared observations. In order to better understand the interplay between these properties, a diurnal thermal model for the lunar surface and near subsurface with temperature‐dependent specific heat and thermal conductivity was developed. The inclusion of the temperature dependence of thermal conductivity and specific heat was found to be essential when attempting to derive regolith properties of the Moon due to the large difference in surface temperatures between day and night. Although particle size, bulk density, and thermal conductivity cannot be investigated completely independently, a clear relationship between these parameters, and their effects on lunar surface temperatures, is determined. An increase in the bulk density of the regolith is found to correspond to an increase in the nighttime temperature of the surface. Similarly an increase in the rock fraction also raises the predicted nighttime temperatures. Increasing grain sizes correspond to decreasing nighttime temperatures. No unique set of surface properties can be determined from thermal remote sensing measurements alone. Grain size is the most difficult regolith property to determine remotely, and rock abundance is by far the strongest contributor to the derived thermal inertia of the bulk surface.
A simplified three‐dimensional model for Martian climate studies
Authors: Haberle Robert M. , Houben Howard , Barnes Jeffrey R. , Young Richard E.
Published: February 2004

We describe a simplified physics approach to generating time‐varying global wind and temperature fields suitable for conducting transport studies on Mars. The goal is to develop a computationally fast algorithm that will enable long‐term simulations of the planet's climate system. Thus we use a three‐dimensional log‐pressure global spectral model forced with a simplified physics package based on Newtonian cooling and Rayleigh friction. We examine the model's performance at northern winter solstice for clear and dusty conditions and find that the simulated mean meridional circulation and transient eddies compare well with a more sophisticated general circulation model by tuning a single parameter: the thermal damping time. Best results are obtained for a thermal damping time of 2 days for clear conditions and 1 day for dusty conditions.