bluuebunny/crossref_metadata_2025 huggingface dataset:
A numerical modeling study of a Montana thunderstorm: 1. Model results versus observations involving nonelectrical aspects
Authors: Helsdon John H. , Farley Richard D.
Published: February 2008

A recently developed Storm Electrification Model (SEM) has been used to simulate the July 19, 1981, Cooperative Convective Precipitation Experiment (CCOPE) case study cloud. This part of the investigation examines the comparison between the model results and the observations of the actual cloud with respect to its nonelectrical aspects. A timing equivalence is established between the simulation and observations based on an explosive growth phase which was both observed and modeled. This timing equivalence is used as a basis upon which the comparisons are made. The model appears to do a good job of reproducing (in both space and time) many of the observed characteristics of the cloud. These include: (1) the general cloud appearance; (2) cloud size; (3) cloud top rise rate; (4) rapid growth phase; (5) updraft structure; (6) first graupel appearance; (7) first radar echo; (8) qualitative radar range‐height indicator evolution; (9) cloud decay; and (10) the location of hydrometers with respect to the updraft/‐downdraft structure. Some features that are not accurately modeled are the cloud base height, the maximum liquid water content, and the time from first formation of precipitation until it reaches the ground. While the simulation is not perfect, the faithfulness of the model results to the observations is sufficient to give us confidence that the microphysical processes active in this storm are adequately represented in the model physics. Areas where model improvement is indicated are also discussed.
Atmospheric input of trace metals to the western Mediterranean Sea: 1. Factors controlling the variability of atmospheric concentrations
Authors: Dulac F. , Buat‐Ménard P. , Arnold M. , Ezat U. , Martin D.
Published: February 2008

The factors controlling the variability of atmospheric trace metal concentrations over the western Mediterranean Sea have been investigated using a combination of geochemical and meteorological approaches. Al, Br, Cd, Na, Pb and 210Po concentrations from bulk filters and cascade impactor samples collected during five cruises (1980–1983) have been used to characterize the aerosol sources: the marine source (Na), the aeolian soil mobilization (Al), the anthropic sources (Cd, Pb), and the volcanic source (210Po). It has been confirmed that Cd and Pb directly derive from anthropic sources. As shown by three‐dimensional air mass trajectory analyses, the variability of daily atmospheric concentrations reflects both changes in continental source strengths and in airflow patterns. Atmospheric concentrations appear to be higher during episodes of short‐range transport of continental material from riparian countries. It is suggested that such source regions can be precisely identified by a careful examination of both geochemical data and three‐dimensional trajectories. From our data set, southwestern Europe would be responsible for the largest Pb and Cd inputs to the western Mediterranean atmosphere (30–40%), but the inputs from North Africa are also likely to be significant (20–25%). However, it cannot be ascertained whether this conclusion is valid on a yearly time scale. Indeed, whereas our sample set is representative of the yearly airflow climatology, it has not been possible to assess the effect of seasonal (for Pb) or sporadic (for Al) changes in source strengths. This points out that over such a marine environment, continuous sampling programs are needed to assess the respective contributions of individual source regions to the atmospheric burden of particulate trace elements.
Thermodynamic constraint on the cloud liquid water feedback in climate models
Authors: Betts Alan K. , Harshvardhan
Published: February 2008

The cloud liquid water feedback in climate models consists of the increase (decrease) in optical depth of clouds resulting from higher (lower) liquid water contents that might accompany tropospheric warming (cooling). The change in cloud liquid water with temperature is shown to depend on the rate of change of the slope of the moist adiabat with respect to temperature, and it is a strong function of temperature. The value of this rate of change in the tropics is about half that in mid and high latitudes and is much less than the value obtained by assuming that liquid water scales with the saturation mixing ratio.
Physical modeling and analysis of rain and clouds by anisotropic scaling multiplicative processes
Authors: Schertzer Daniel , Lovejoy Shaun
Published: February 2008

We argue that the basic properties of rain and cloud fields (particularly their scaling and intermittency) are best understood in terms of coupled (anisotropic and scaling) cascade processes. We show how such cascades provide a framework not only for theoretically and empirically investigating these fields, but also for constructing physically based stochastic models. This physical basis is provided by cascade scaling and intermittency, which is of broadly the same sort as that specified by the dynamical (nonlinear, partial differential) equations. Theoretically, we clarify the links between the divergence of high‐order statistical moments, the multiple scaling and dimensions of the fields, and the multiplicative and anisotropic nature of the cascade processes themselves. We show how such fields can be modeled by fractional integration of the product of appropriate powers of conserved but highly intermittent fluxes. We also empirically test these ideas by exploiting high‐resolution radar rain reflectivities. The divergence of moments is established by direct use of probability distributions, whereas the multiple scaling and dimensions required the development of new empirical techniques. The first of these estimates the “trace moments” of rain reflectivities, which are used to determine a moment‐dependent exponent governing the variation of the various statistical moments with scale. This exponent function in turn is used to estimate the dimension function of the moments. A second technique called “functional box counting,” is a generalization of a method first developed for investigating strange sets and permits the direct evaluation of another dimension function, this time associated with the increasingly intense regions. We further show how the different intensities are related to singularities of different orders in the field. This technique provides the basis for another new technique, called “elliptical dimensional sampling,” which permits the elliptical dimension rain (describing its stratification) to be directly estimated: it yields del = 2.22 ± 0.07, which is less than that of an isotropic rain field (del = 3), but significantly greater than that of a completely flat (stratified) two‐dimensional field (del = 2).
On the prolonged lifetime of the El Chichón sulfuric acid aerosol cloud
Authors: Hofmann D. J. , Rosen J. M.
Published: February 2008

The observed decay of the aerosol mixing ratio following the eruption of El Chichón appears to have been 20–30% slower than that following the eruption of Fuego in 197M, even though the sulfuric acid droplets were observed to grow to considerably larger sizes after El Chichón. This suggests the possible presence of a condensation nuclei and sulfuric acid vapor source and continued growth phenomena occurring well after the El Chichón eruption. It is proposed that the source of these nuclei and the associated vapor may be derived from annual evaporation and condensation of aerosol in the high polar regions during stratospheric warming events, with subsequent spreading to lower latitudes.
An analytical solution to obtain the optimum source location using multiple direction finders on a spherical surface
Authors: Orville Richard E.
Published: February 2008

An analytical solution is presented for determining the optimum location of a radiating source on the surface of a sphere, given multiple bearings. The bearings are assumed to have small errors of the order of 0°–10°. The optimum location is found by minimizing the sum of the squares of the perpendicular great‐circle distances from the source to the bearing lines. This is achieved analytically through an eigenvalue approach, rather than the usual iterative, numerical approach. Bearings of different weight are taken into account by approximating the distance from each direction finder to the source. The result is general and may have wide application. Since it is simple and nearly as fast as the triangulation technique for source location, it is now used in the SUNY‐Albany East Coast Lightning Detection Network to compute the optimum location for lightning in real time. The solution is also used off‐line to evaluate the systematic errors in the network direction finders.
Concentrations of ethane (C2H6) in the lower stratosphere and upper troposphere and acetylene (C2H2) in the upper troposphere deduced from atmospheric trace molecule spectroscopy/Spacelab 3 spectra
Authors: Rinsland C. P. , Zander R. , Farmer C. B. , Norton R. H. , Russell J. M.
Published: February 2008

Volume mixing ratio profiles of ethane (C2H6) in the lower stratosphere and upper troposphere and acetylene (C2H2) in the upper troposphere have been deduced from analysis of 0.01‐cm−1‐resolution infrared solar absorption spectra recorded between 25°N and 31°N latitude. The spectral data were obtained by the ATMOS (Atmospheric Trace Molecule Spectroscopy) Fourier transform spectrometer during the Spacelab 3 shuttle mission on April 30 to May 1, 1985. The investigation was based on nonlinear least squares curve fitting of the ν7; band PQ3 subbranch near 2976.8 cm−1 and the ν9 band RQ0 subbranch near 822.3 cm−1 for C2H6 and of the ν5 band R10 and R19 lines of C2H2 at 755.0056 and 776.0818 cm−1, respectively. Improvements in the spectroscopic data base for the regions containing these absorption features are reported. The C2H6 results indicate a nearly constant volume mixing ratio of 0.97 parts per billion by volume (ppbv) between 6 and 12 km and a decline to 0.1–0.2 ppbv at 18 km altitude. Measured C2H2 mixing ratios are 0.070–0.092 ppbv between 7.7 and 12.6 km and 0.02 ppbv at 15.1 km. An upper limit of 0.02 ppbv is obtained for the average C2H2 mixing ratio above 16.6 km. The retrieved profiles are compared with previous measurements and model calculations.
Biogenic sulfur emissions from the Subantarctic and Antarctic Oceans
Authors: Berresheim Harald
Published: February 2008

Measurements of the atmospheric distributions of dimethylsulfide (DMS), sulfur dioxide (SO2), methanesulfonate (MSA), non‐seasalt sulfate (nss‐SO42−), and methylmercaptan (MeSH) were made over the Drake Passage and the coastal and inshore waters west of the Antarctic Peninsula during the 1986 austral fall season. DMS concentrations were also measured in the surface ocean, and vertical profiles were obtained at several locations in the inshore water areas. Surface seawater concentrations of DMS were on the order of 2 nmol L−1, similar to values observed in temperate latitudes. The vertical profiles showed maximum values at depths between 5–40 m. DMS concentrations in the atmosphere were near 4 nmol m−3(96 parts per trillion by volume, (pptv)), close to the global average for remote oceanic regions. The sea‐to‐air flux of DMS ranged between 1–5 μmol m−2d−1, with the highest values found in the open ocean areas. The total sea‐to‐air flux of DMS from the Southern Ocean is estimated to be 0.2 Tmol yr−1. MeSH was detected occasionally at concentrations up to 0.15 nmol m−3(3.6 pptv). The average aerosol MSA concentration (0.27 nmol m−3) was surprisingly high relative to the level of nss‐SO42−(0.31 nmol m−3). Both compounds were found predominantly in fine particles. The nss‐SO42−values were extremely low, comparable to winter values reported for the South Pole. SO2concentrations were also very low (0.45 nmol m−3(11 pptv)), consistent with the low levels of nss‐SO42−. The residence time of DMS in the Antarctic marine atmosphere is estimated to be about 2–3 days during clear weather and about 6–7 days during overcast conditions. Photooxidation of DMS in the Southern Ocean atmosphere may lead to a higher yield of MSA and a lower yield of SO2compared to other world ocean areas.
A three‐dimensional Eulerian acid deposition model: Physical concepts and formulation
Authors: Chang J. S. , Brost R. A. , Isaksen I. S. A. , Madronich S. , Middleton P. , Stockwell W. R. , Walcek C. J.
Published: February 2008

We have developed a three‐dimensional Eulerian regional acid deposition model to calculate episodic chemical concentrations and dry and wet deposition of acids in North America. This transport, transformation, and deposition modeling system subdivides the troposphere over the eastern United States, southeastern Canada, and the western Atlantic Ocean into a six‐level, 30 by 30 horizontal grid with a horizontal grid size of 80 × 80 km2. Transport and vertical diffusion of 24 trace gases and particles are calculated using temporally and spatially varying meteorology, provided by a mesoscale meteorological model. A gas phase chemical reaction mechanism is used to simulate concentrations and chemical conversion rates for 36 species, including 14 stable organics and 11 short‐lived radicals. Altitude‐, latitude‐, and season‐dependent photolysis rates for nine reactions in the chemical mechanism are specified using a delta‐Eddington radiative transfer model which includes O2 and O3 absorption, scattering and absorption by clouds and aerosols, Rayleigh scattering, and ground reflections. Subgrid scale vertical transport, aqueous chemical conversions, and trace gas and particle scavenging by clouds are parameterized using a one‐dimensional dynamical and microphysical cloud model and a box aqueous chemistry and scavenging submodel. The aqueous phase chemistry model includes sulfur oxidation by H2O2, O3, trace metals, and two organic peroxides, with numerous equilibria between all soluble trace species. Dry deposition rates for 13 compounds are computed using species‐specific deposition velocities that depend on the local meteorology, season, land type, insolation, and surface wetness conditions. Emissions of SO2, SO4=, NO, NO2, CO, NH3, and 10 classes of volatile organic compounds are included in the model. Trace gases are emitted into different vertical levels of the model according to a plume rise submodel. Hourly emissions are adjusted according to season and weekday or weekend activities. This model provides a framework to examine the relative importance and sensitivity of numerous physical and chemical processes responsible for the formation and deposition of tropospheric acidity.
Size distributions of sea‐source aerosol particles: A physical explanation of observed nearshore versus open‐sea differences
Authors: Sievering H. , Boatman J. , Gunter L. , Horvath H. , Wellman D. , Wilkison S.
Published: February 2008

Lognormal size distribution fits to aerosol probe data collected by the National Oceanic and Atmospheric Administration's King Air aircraft were obtained by a new computer fitting routine. The average fit to western Atlantic nearshore data (about 100 km off Newport News, Virginia) and open‐sea data (upwind of Bermuda) showed a marked difference in the volume geometric median diameter (VGMD) of the coarse‐particle (diameter range from 1 to 44 μm) sea‐salt mode. Analysis of seven separate near‐shore flights during offshore flow showed the average VGMD to be 8.1 μm, with a geometric median standard deviation (σg) of 2.1. Six separate open‐sea flights showed the average VGMD to be 5.6 μm, with a σg of 1.7. It is shown that atmospheric state conditions, nearshore versus open sea, could not have caused the significant difference (at 99.6% confidence) between the nearshore and open‐sea VGMD values. Use of in situ aircraft sampling and lognormal fitting, plus sampling during offshore flow conditions, gave rise to the ability to observe this difference. It is demonstrated, by considering both the developing wave under offshore flow conditions and the shoreline disturbed wave (i.e., wave age) condition, that sea‐derived aerosol size distributions nearshore may often be expected to have more large aerosol particles present than sea‐derived aerosol distributions over the open sea.
The behavior of cloud droplets in an acoustic field: A numerical investigation
Authors: Foster M. P. , Pflaum J. C.
Published: February 2008

This article reviews the basic properties of sound waves and the nature of their interactions with cloud droplets. It is demonstrated through the use of a numerical model that a single‐frequency, high‐intensity sound wave can apparently alter the characteristics of a droplet population, leading to a more rapid development of precipitation in some cases. A consideration of the sound properties of thunder suggests that atmospheric effects are probably minor, however further research is recommended.
The Amazon Boundary Layer Experiment (ABLE 2A): dry season 1985
Authors: Harriss R. C. , Wofsy S. C. , Garstang M. , Browell E. V. , Molion L. C. B. , McNeal R. J. , Hoell J. M. , Bendura R. J. , Beck S. M. , Navarro R. L. , Riley J. T. , Snell R. L.
Published: February 2008

The Amazon Boundary Layer Experiment (ABLE 2A) used data from aircraft, ground‐based, and satellite platforms to characterize the chemistry and dynamics of the lower atmosphere over the Amazon Basin during the early‐to‐middle dry season, July and August 1985. This paper reports the conceptual framework and experimental approach used in ABLE 2A and serves as an introduction to the detailed papers which follow in this issue. The results of ABLE 2A demonstrate that isoprene, methane, carbon dioxide, nitric oxide, dimethylsulfide, and organic aerosol emissions from soils and vegetation play a major role in determining the chemical composition of the atmospheric mixed layer over undisturbed forest and wetland environments. As the dry season progresses, emissions from both local and distant biomass burning become an important source of carbon monoxide, nitric oxide and ozone in the atmosphere over the central Amazon Basin.
Nitrous oxide flux and nitrogen transformations across a landscape gradient in Amazonia
Authors: Livingston Gerald P. , Vitousek Peter M. , Matson Pamela A.
Published: February 2008

Nitrous oxide flux and nitrogen turnover were measured in three types of Amazonian forest ecosystems within Reserva Florestal Ducke near Manaus, Brazil. Nitrogen mineralization and nitrate production measured during 10‐day laboratory incubations were 3–4 times higher in clay soils associated with “terra firme” forests on ridge‐top and slope positions than in “campinarana” forests on bottomland sand soils. In contrast, nitrous oxide fluxes did not differ significantly among sites, but were highly variable in space and time. The observed frequency distribution of flux was positively skewed, with a mean over all sites and all sampling times of 1.3 ng N2O‐N cm−2h−1. Overall, our flux estimates were comparable to or greater than those of temperate forests, but less than others reported for Amazonia. Results from a field fertilization experiment suggest that most nitrous oxide flux was associated with denitrification of soil nitrate.
Theory of the optical properties of lake ice
Authors: Mullen Peter C. , Warren Stephen G.
Published: February 2008

A radiative transfer model is developed to illustrate the processes which determine the spectral albedo and transmission of lake ice. The calculated spectral albedo is dominated by specular reflection from the ice surface in the near infrared, whereas multiple scattering by bubbles below the surface dominates the visible albedo. Adding a snow cover to lake ice will normally increase the visible albedo, but may reduce the albedo in some regions of the near infrared if the sun is low, by reducing the specular reflection. In a preliminary test of the model, spectral albedo was measured on the natural ice cover of a frozen lake. The measurements are explained using the radiative transfer model applied to the air bubble size distribution measured in the same ice. The uncertainty in measurement of bubble size distribution leads to uncertainty in the theoretical albedo which is much larger than the error due to approximations used in derivation of the model.
Average properties of the sodium density distribution as observed at 69°N latitude in winter
Authors: Tilgner C. , von Zahn U.
Published: February 2008

During 19 nights in the period from the end of November 1985 until mid‐March 1986, measurements of the sodium layer were performed with a lidar system located at Andøya (69°N, 16°E). Under these conditions we find the following average properties of the sodium layer: a Na column density of 5.6×109 cm−2, a Na density of 6100 cm−3 at the layer peak, an altitude of 89.2 km for the layer peak and a layer width (FWHM) of 9.0 km. At Andøya no significant seasonal trend in the Na layer parameters is apparent during the winter period. These results are compared with those obtained at several different latitudes by other researchers. We present the mean sodium density profile for the winter period over Andøya and the Na number density scale height distributions. A statistical analysis reveals averages of −0.4 km sodium density scale height at the layer bottom and 2.5 km at 100 km altitude, the latter continuously decreasing with increasing altitude. From the mean Na scale heights obtained for altitudes below 90 km we can derive that in the range from 80 to about 86 km the density of sodium grows almost quadratically with altitude. From the mean Na scale heights obtained for altitudes above 95 km altitude, vertical eddy coefficients and the vertical Na flux can be calculated.
Measurement of soil NOx emissions in central Pennsylvania
Authors: Williams E. J. , Parrish D. D. , Buhr M. P. , Fehsenfeld F. C. , Fall R.
Published: February 2008

Soil emissions of NO and NO2 were measured at forest and agricultural sites in Pennsylvania. The strong dependence of NO emissions on soil temperature observed in earlier studies was also found in these measurements. The large variation in the measured NO flux at these sites indicated that variables other than soil temperature play an important role. In the present study the strong correlation between the NO flux and the soil nitrate level suggests that the level of available nitrate in the soils may affect NO emission. In this connection it should be noted that the application of chemical pesticides, as well as nitrate‐containing fertilizer, may influence these results. In these studies, NO2 accounted for a minor fraction (6%) of the nitrogen oxide emissions. Laboratory studies designed to investigate the influence of certain environmental and experimental factors on NO emissions under controlled conditions were also conducted. These results also indicate that temperature has a large effect on soil NO emissions, while flush gas humidity and carbon dioxide level exert little, if any, effect.
Modeling dust emission caused by wind erosion
Authors: Gillette Dale A. , Passi Ranjit
Published: February 2008

A model for the estimation of total dust production for the United States is discussed. Its primary use will be in the inventory of alkaline elements for use in acid/base balance studies of atmospheric precipitation by the National Acid Precipitation Assessment Program (NAPAP). The model is a summation of the expected dust production caused by wind erosion for individual sampling units of the detailed soil and land use inventory of the National Resources Inventory, compiled by the U.S. Department of Agriculture. The model is based on a dust emission function derived theoretically and verified by experiment. An extremely important parameter is the threshold velocity for dust production; this parameter is dependent on effects of vegetative residue, roughness of the soil, live standing plants, soil texture and the effect of atmospheric precipitation. Experimentation has supplied values of this parameter for the calculation. Wind data used in the model were obtained from the Wind Energy Resource Information System (WERIS). The model was calibrated with dust emission data for the area, including the panhandles of Texas and Oklahoma.
An intercomparison of results from ferrous sulphate and photolytic converter techniques for measurements of NOx made during the NASA GTE/CITE 1 aircraft program
Authors: Ridley B. A. , Carroll M. A. , Torres A. L. , Condon E. P. , Sachse G. W. , Hill G. F. , Gregory G. L.
Published: February 2008

Two techniques designed for measurements of NOx (NO + NO2) were intercompared during aircraft flights made in the spring of 1984 in the middle free troposphere over the eastern Pacific Ocean and southwestern United States. One NO chemiluminescence instrument was equipped with a ferrous sulphate converter, another with a photolytic converter. The ferrous sulphate‐equipped instrument was apparently much less specific for NO2. It registered levels about 3 times larger than the photolytic converter and gave NO2/NO ratios that were much larger than photochemical calculations would indicate as reasonable. Additionally, the results imply that active NOx was only 10–20% of total odd nitrogen in the middle free troposphere.
On the nonlinearity of the tropospheric ozone production
Authors: Lin X. , Trainer M. , Liu S. C.
Published: February 2008

The relationship of photochemical ozone production versus photochemical loss of an ozone precursor, that is, either NOx or nonmethane hydrocarbons (NMHCs), is studied by using a box model with particular emphasis on the nonlinearity problem of the relationship with respect to the concentration of the precursor. Model calculations indicate that the composition of NMHCs, the ratio of NMHCs to NOx, and the background concentrations of natural hydrocarbons, CO, and CH4 all play important roles in determining the nonlinearity of O3 production with respect to the loss of NOx. In addition, influences on the nonlinearity due to radical loss via reactions of HO2 with RO2, exchanges between PAN and NO2, and inclusion of nighttime NOx loss processes are also investigated. Mechanisms that contribute to the nonlinearity are discussed. The nonlinear property of O3 production versus loss of hydrocarbons and CO is different from that of NOx. When the sum of CO and all hydrocarbons, including CH4, natural NMHCs, and anthropogenic NMHCs, is used as the reference O3 precursor, the nonlinearity is much less pronounced for ambient conditions usually found in rural air.
A tenfold increase in the abundance of large solid particles in the stratosphere, as measured over the period 1976–1984
Authors: Zolensky Michael E. , McKay David S. , Kaczor Laurel A.
Published: February 2008

Representative chemical, structural, and morphological analyses of the large (>1‐μm diameter) solid particles from three impaction collection surfaces have been performed. These collections sampled the stratosphere at approximately 17–19 km in altitude during 1976, 1981, and 1984. For these sampling periods the stratospheric solid‐particle number densities have been determined to be 0.089, 0.16, and 1.7 particles m−3 of air, respectively, for particles of >1‐μm diameter. This rise in solid‐particle number density for the stratosphere over the collection period is likely due to the influx of solid rocket exhaust and rocket and satellite debris into the atmosphere in increasingly larger amounts with time. Some of this material is shed from spacecraft during ascent through the atmosphere, but the majority is probably provided during the descent of material from Earth's growing belt of debris in low‐Earth orbit.
Ozone destruction through heterogeneous chemistry following the eruption of El Chichón
Authors: Hofmann David J. , Solomon Susan
Published: February 2008

It is now well established that heterogeneous reactions provide an important mechanism for Antarctic ozone depletion. Recent laboratory studies suggest that the same reactions that occur on HNO3/H2O ice clouds in the cold Antarctic stratosphere can also take place on sulfuric acid particles (e.g., volcanic and background aerosols) typical of lower latitudes, albeit at slower rates. The reduction in stratospheric ozone observed at northern mid‐latitudes in late 1982 through 1983 following the volcanic eruption of El Chichón is investigated in terms of ozone loss through heterogeneous chemistry on the aerosol which formed in the stratosphere. The rates of the relevant heterogeneous reactions are believed to be critically dependent on (1) the aerosol surface area density and (2) the percent by weight sulfuric acid in the liquid particles. Direct measurements of both of these important quantities for El Chichón aerosol are described and used as a basis for model calculations of their possible effects on ozone and other trace species. The observed volcanic particle surface area reached a maximum at mid‐latitudes of about 50 μm2cm−3(above a typical background value of about 0.75) at an altitude of 18–20 km in early 1983. This enhancement of surface area is about the same as that encountered in stratospheric clouds in the Antarctic, suggesting a possible basis for ozone depletion through heterogeneous chemistry. Observations of NO2and HNO3also suggest that heterogeneous reactions on both background and volcanic aerosol play a significant role in partitioning reactive nitrogen species in middle and high latitudes in winter. It is shown that heterogeneous reactions similar to those occurring in Antarctica may have been responsible for at least a portion of the anomalous ozone reduction observed at mid‐latitudes in early 1983.
Principal modes of intraseasonal variations in atmospheric angular momentum and tropical convection
Authors: Lau K.‐M. , Kang In‐Sik , Sheu P. J.
Published: February 2008

The seasonal and intraseasonal variation of angular momentum and its relationship with tropical convection is studied using 5‐day mean wind and outgoing longwave radiation (OLR). It was found that the zonally averaged u component and OLR both show pronounced periodicities around 30–60 days in the tropics. The globally averaged zonal wind at 250 mbar exhibits a very pronounced peak at 50 days, with strong seasonal and intraseasonal variations that are linked to the expansion and contraction of the lower level easterlies and the equatorward and poleward migration of the subtropical jet streams at upper levels. In the 30‐ to 60‐day time scale, three basic meridional modes of angular momentum are found. First, the tropical modes have Gaussianlike meridional structures, which decay rapidly away from the equator. These modes are related to both symmetric and antisymmetric tropical heating about the equator. Second, the tropical‐subtropical modes feature a strong amplitude in angular momentum in the tropics and subtropics. They are likely to be related to the seasonal and intraseasonal fluctuations of tropical heating, subtropical jet streams, and transfer of angular momentum through localized meridional circulations. Finally, the extratropical modes have a large amplitude poleward of 30° latitude. They appear to have some relationship with tropical convection, but it is not very strong. Most importantly, they do not seem to contribute significantly to the global angular momentum fluctuations in the 30‐ to 60‐day time scale. Our results indicate that angular momentum generated within the tropics and subtropics contributes to a large part of the observed global angular momentum changes in the intraseasonal and interannual time scales. In these time scales, angular momentum inside the tropics is exported outside the tropics (poleward of 20°N) via jet stream variations associated with regional atmospheric teleconnections.
Assessment of surface turbulent fluxes using geostationary satellite surface skin temperatures and a mixed layer planetary boundary layer scheme
Authors: Diak George R. , Stewart Tod R.
Published: February 2008

A method is presented for evaluating the fluxes of sensible and latent heating at the land surface, using satellite‐measured surface temperature changes in a composite surface layer‐mixed layer representation of the planetary boundary layer. The basic prognostic model is tested by comparison with synoptic station information at sites where surface evaporation climatology is well known. The remote sensing version of the model, using satellite‐measured surface temperature changes, is then used to quantify the sharp spatial gradient in surface heating/evaporation across the central United States. An error analysis indicates that perhaps five levels of evaporation are recognizable by these methods and that the chief cause of error is the interaction of errors in the measurement of surface temperature change with errors in the assignment of surface roughness character. Finally, two new potential methods for remote sensing of the land‐surface energy balance are suggested which will rely on space‐borne instrumentation planned for the 1990's.
Ozone in rural areas of the United States
Authors: Logan Jennifer A.
Published: February 2008

I present the results of an analysis of ozone data from rural locations in the United States. Ozone concentrations above 80 ppb are common in the east in spring and summer, but they are unusual in the west, and ozone shows considerably more day‐to‐day variability in the east. Variations in ozone levels are highly correlated over distances of several hundred kilometers in the east, indicating that high values are associated with episodes of large spatial scale, >600,000 km2. There were 10 and seven such episodes in 1978 and 1979 respectively, between the months of April and September; they persisted for 3–4 days, on average, with a range of 2–8 days, and were most common in June. Daily maximum ozone values exceeded 90 ppb at over half the sites during these episodes and were often greater than 120 ppb at one or more sites. An analysis of the meteorology for each episode shows that they occurred preferentially in the presence of weak, slow‐moving, and persistent high‐pressure systems. Two episodes that occurred outside the summer half of the year were associated with unseasonably warm weather; only one episode, in March 1978, appeared to reflect a major stratospheric intrusion. Concentrations of NOx at rural locations in the east are frequently high enough (>1 ppb) to permit significant photochemical formation of ozone. It is clear that rural ozone in the east in spring and summer is severely impacted by anthropogenic emissions of NOx and hydrocarbons, and that ozone episodes occur when the weather is particularly conducive to photochemical formation of ozone. Ozone episodes were present on 23% of days in May‐August in the east in 1978–1979. The effect of these pollution episodes on vegetation cannot be assessed with current information on dose‐response characteristics, which is based primarily on exposure of crops to a given level of ozone for 7 hours a day. The results presented here may be used to design studies that account for the periodic exposure of vegetation to high values of ozone for several consecutive days.
Atmospheric carbon dioxide at Mauna Loa Observatory: 2. Analysis of the NOAA GMCC data, 1974–1985
Authors: Thoning Kirk W. , Tans Pieter P. , Komhyr Walter D.
Published: February 2008

The first 12 years (1974–1985) of continuous atmospheric CO2 measurements from the NOAA GMCC program at the Mauna Loa Observatory in Hawaii are analyzed. Hourly and daily variations in the concentration of CO2 due to local sources and sinks are described, with subsequent selection of data representing background concentrations. A digital filtering technique using the fast Fourier transform and low‐pass filters was used to smooth the selected data and to separate the seasonal cycle from the long‐term increase in CO2. The amplitude of the seasonal cycle was found to be increasing at a rate of 0.05±0.02 ppm yr−1. The average growth rate of CO2 was 1.42±0.02 ppm yr−1, and the fraction of CO2 remaining in the atmosphere from fossil fuel combustion was 59%. A comparison between the Mauna Loa continuous CO2 data and the CO2 flask sample data from the sea level site at Cape Kumukahi, Hawaii, showed that the amplitude of the seasonal cycle at Cape Kumukahi was 23% larger than at Mauna Loa, with the phase of the cycle at Mauna Loa lagging the cycle at Cape Kumukahi by about 1–2 weeks.
Atomic and ionic calcium in the Earth's upper atmosphere
Authors: Granier C. , Jegou J. P. , Megie G.
Published: February 2008

Resonant lidar measurements of calcium and sodium atoms and calcium ions have been made from 1982 to 1987 at the Observatoire de Haute Provence. An average value of the column atomic calcium abundance of 2.7×107 cm−2 has been measured, and it is 120 times lower than the corresponding sodium abundance. No systematic seasonal variation of the atomic calcium abundance can be deduced from the measurements. Average density profiles of these two species are also compared for each season. For the calcium ions, two different types of profiles have been identified. Diffuse Ca+ layers are centered around 94 km and constitute the background ionic calcium layer. Denser and narrower layers, presenting strong short time scale variations, are centered in the 95‐ to 115–km altitude range. Comparisons are made between Ca and Ca+ density profiles determined by lidar measurements and through other techniques, such as mass spectrometry. Finally, the relative abundance in the atmosphere and in meteorites of these two metallic species, Ca and Na, are briefly discussed.
Diurnal variations of mesospheric ozone obtained by ground‐based microwave radiometry
Authors: Zommerfelds W. C. , Kunzi K. F. , Summers M. E. , Bevilacqua R. M. , Strobel D. F. , Allen M. , Sawchuck W. J.
Published: February 2008

From December 1986 until April 1987 ground‐based microwave observations of the diurnal variation of mesospheric ozone were made over Bern, Switzerland. These data were of sufficient quality to define the characteristic diurnal behavior of the ozone mixing ratio during winter and equinoctial conditions. The observed diurnal variation of ozone peaks at ∼74 km, where its amplitude is about a factor of 6. At 65 km the observed diurnal variation is a factor of 3, whereas at 55 km it is only a factor of 1.4. One‐dimensional model calculations accurately reproduce the relative diurnal variation of ozone at equinox, suggesting that the model value of the ozone photolysis rate coefficient is accurate to better than 10%. For winter conditions, however, the model underpredicts the observed relative diurnal variation by a factor of 2; a major part of this discrepancy is due to an observed postmidnight increase in ozone. Various suggested changes in model parameters to better reproduce the ozone abundance vertical profile result in only small differences in the relative diurnal variation, indicating that these observations do not provide a sensitive test of the mesopheric chemistry controlling the abundance of odd oxygen.
The tripole structure of thunderstorms
Authors: Williams Earle R.
Published: February 2008

Evidence for the tripole structure of electrified clouds is summarized. The observed structure is quantitatively consistent with the results of laboratory simulations and suggests that collision between ice crystals and rimed graupel particles is the dominant mechanism for charge separation in thunderstorms. The physical basis for this mechanism is poorly understood.
The relationship between lightning type and convective state of thunderclouds
Authors: Williams E. R. , Weber M. E. , Orville R. E.
Published: February 2008

Thunderstorm case studies and earlier observations are described which illuminate the relationship between cloud vertical development and the prevalence of intracloud (IC) and cloud‐to‐ground (CG) lightning. A consistent temporal evolution starting with peak IC activity changing to predominant CG activity and concluding with strong outflow (microburst) suggests that ice is responsible for both the electrical (i.e., lightning) and dynamical (i.e., microburst) phenomena. The IC activity is attributed to the updraft‐driven accumulation of graupel particles in the central dipole region, and the subsequent CG activity to the descent of ice particles beneath the height of the main negative charge. The subsequent descent and melting of ice particles beneath the height of the 0°C isotherm are associated with the acceleration of the downdraft and outflow. The IC lightning precursor can provide a valuable short‐term (5–10 min) warning for microburst hazard at ground level.
Submicrosecond intercomparison of radiation fields and currents in triggered lightning return strokes based on the transmission‐line model
Authors: Willett J. C. , Bailey J. C. , Idone V. P. , Eybert‐Berard A. , Barret L.
Published: February 2008

The “transmission‐line model” of return‐stroke radiation, proposed by Uman and McLain (1970), has been tested on rocket‐triggered lightning. Simultaneous measurements are reported of electric radiation field, current at the channel base, and stroke‐propagation velocity. Agreement between model and measurements is generally good during the first few microseconds, although several anomalies are pointed out. Truncation of the sharp initial peak in many of the field waveforms, motivated by the hypothesis that the return stroke begins a short distance above the ground, leads to an average apparent velocity (derived from the ratio of peak field to peak current) of (1.51±0.17) × 108m/s for 28 strokes, in excellent agreement with the average, photographically measured two‐dimensional velocity of (1.52±0.17) × 108m/s for 18 of these same strokes. Although the correlation between apparent and photographic velocities for these 18 strokes is poor, the uncertainty in the photographic velocity determinations could explain most of the scatter. The best formula for estimating peak currents (ip) in subsequent return strokes from remotely measured, truncated peak electric fields (E′p) at rangeDappears to beip= −3.9 × 10−2DE′p− 2.7 × 103, where all variables are in MKS units and the electric field polarity of return strokes lowering negative charge is considered negative.
A 3‐year continuous record on the influence of daytime, season, and fertilizer treatment on methane emission rates from an Italian rice paddy
Authors: Schütz H. , Holzapfel‐Pschorn A. , Conrad R. , Rennenberg H. , Seiler W.
Published: February 2008

CH4 emission rates have been measured in an Italian rice paddy between 1984 and 1986, covering three vegetation periods. For these measurements a fully automated, computerized sampling and analyzing system was developed which allowed the simultaneous determination of CH4 emission rates at 16 different field plots. CH4 emission rates showed strong diurnal and seasonal variations. Diurnal changes correlated with changes in soil temperature. During the season, CH4 emission rates showed a first maximum in May–June before tillering and a second maximum in July during the reproductive stage of the rice plants. In 1985 and 1986 two maxima were observed during summer in addition to the first maximum in the rate of CH4 emission during spring. Application of mineral and/or organic fertilizer strongly influenced the CH4 emission rates, depending on the type, rate, and mode of fertilizer application. Thus the rates decreased by at most 40% and 60% after fertilization by deep incorporation with 200 kg N/ha urea and 200 kg N/ha ammonium sulfate, respectively. Application of 200 kg N/ha calcium cyanamide led to a reduction of the first maximum of CH4 emission but caused the second maximum to increase, the overall result being that the seasonally averaged CH4 emission rate was comparable to that observed in unfertilized fields. Application of rice straw at a rate of 12 t/ha enhanced the rate of CH4 emission by a factor of 2 compared with the control. Higher application rates of rice straw did not cause a further increase in CH4 emission. The complete records of CH4 emissions over three vegetation periods indicate an average seasonal CH4 emission rate from unfertilized fields of 0.28 g CH4/m2 d, with a range of 0.16–0.38 g CH4/m2 d. Based on this value and applying the observed temperature dependence of the CH4 emission rates, the global annual CH4 emission from rice paddies is estimated to be in the range of 50–150 Tg, with a likely average of 100 Tg. This figure represents between 19% and 25% of the global CH4 emission, indicating that rice paddies are one of the most important individual sources of atmospheric CH4.
Correlation of N2O and ozone in the southern polar vortex during the Airborne Antarctic Ozone Experiment
Authors: Strahan S. E. , Loewenstein M. , Podolske J. R. , Starr W. L. , Chan K. R. , Proffitt M. H. , Kelly K. K.
Published: February 2008

N2O mixing ratios, measured in situ by an airborne laser spectrometer (ATLAS), have been used along with in situ ozone measurements to determine the correlation of N2O and ozone in the Antarctic stratosphere during the late austral winter. N2O and ozone measurements on five transit flights between Ames Research Center, California (37°N), and Punta Arenas, Chile (53°S), were used to determine the correlation of N2O and ozone between 13 and 20 km in the mid‐latitudes. The mid‐latitude correlation is negative (≤−0.5). However, poleward of 53°S, N2O and ozone often show a strong positive correlation which approximately coincides with the wind speed maximum surrounding the Antarctic vortex. Strong zonal winds appearing between 60°S and 70°S are colocated with strong potential vorticity gradients, indicating that the wind speed maximum is a good marker for the vortex boundary. Flight tracks penetrating well beyond the wind maximum show a return to negative correlation. With few exceptions, regions in the vortex with positive N2O and O3 correlation are colocated with total water mixing ratios of greater than 2.9 ppmv, and negatively correlated regions with water mixing ratios of less than 2.9 ppmv. The driest regions appear to be colocated with the greatest ozone loss. Because positive correlation between N2O and O3 cannot be explained by horizontal or vertical transport (below 35 km), positive N2O/O3 correlations appear to be a sensitive indicator of chemical loss of ozone.
Formation of isolated vortices in a rotating convecting fluid
Authors: Chen R. , Fernando H. J. S. , Boyer D. L.
Published: February 2008

The results of an experimental study designed to investigate the properties of isolated intense vortices that are formed during rotating turbulent thermal convection are presented. The vortices were generated by uniform heating of the base of a laboratory tank rotating about its vertical axis. Concentrated vortices were found to emerge sporadically, abide for some time and then fade away. Measurements included the spatial frequency of occurrence of vortices and their physical dimensions and characteristic velocities. Theoretical arguments are advanced to explain the observations. Possible geophysical applications of the results are also discussed.