bluuebunny/crossref_metadata_2025 huggingface dataset:
Electric field measurements within a severe thunderstorm anvil
Authors: Byrne G. J. , Few A. A. , Stewart M. F.
Published: February 2008

The anvil cloud of a supercell severe storm in central Oklahoma was penetrated by two free balloons carrying corona probes to measure electric fields. The two balloons passed through the portion of the anvil upstream of the precipitation core and provided information on the charge concentrations and vertical thicknesses of the electric charge regions within the cloud. The trajectories of the balloons relative to the storm were horizontally separated by approximately 35 km, providing information on the horizontal extent of the charge regions. Contrary to the general assumption that anvil interiors are positively charged, the results of the two flights indicate that extensive regions of both net positive and negative charge were present in the interior of the anvil. Net positive charge was observed in both balloon flights in the lower portion of the anvil interior. The vertical thickness of the positive charge region was measured in each flight to be 1.6 and 2.3 km, respectively. A charge concentration of +0.2 nC m−3 was estimated from one of the flights. Net negative charge was observed by both balloons in the upper portion of the anvil interior. The vertical thickness and charge concentration of the negative charge region were estimated from one flight to be 3.2 km and −0.1 nC m−3, respectively. Screening charge layers were identified at the upper and lower boundaries of the anvil, with a typical thickness of a few hundred meters, which is an order of magnitude greater than that calculated in a previous model. We propose a conceptual model of the development of anvil charge regions based on our balloon measurements and previous observations of anvil dynamics. In this model we suggest that the thicknesses of the anvil screening layers increase with distance from the precipitation core of the storm owing to turbulent mixing near the cloud boundaries and differences in the sedimentation rates of the cloud particles. Negative charge in the upper portion of the anvil interior results from the expansion of the upper negative screening layer into lower levels of the anvil cloud.
SAGE II aerosol data validation and initial data use: An introduction and overview
Authors: Russell P. B. , McCormick M. P.
Published: February 2008

Correlative sensors used in the SAGE II aerosol data validation program included two‐ and six‐channel dustsondes; ground‐based and airborne multiwavelength lidars; wire, ribbon, and related impactors; laser spectrometers; filter collectors; spectral polarimeters; and spectral limb cameras. Measurement campaigns were conducted in the northern, southern, eastern, and western hemispheres, and in low, middle, and high latitudes. Measurement conditions were often strongly perturbed by El Chichón and other volcanic eruptions, which posed new challenges because of (1) multimodal size distributions, (2) spatiotemporal inhomogeneity, and (3) large extinction values. New experimental and analytical approaches were developed to meet these challenges. Several of the analytical approaches use SAGE II four‐wavelength aerosol extinction values to derive or check particle size distributions. Extensive comparisons between SAM II and SAGE II were also conducted. The validation results are detailed in the following six papers. They show that when correlative measurements are nearly coincident with the SAGE II measurements in space and time, the SAGE II and correlative values are consistent within their respective uncertainties. This is especially so of the SAGE II 1.02‐μm extinction profiles, for which numerous instances of good coincidence show agreement from heights near the tropopause to ∼28 km. For the shorter wavelengths (0.525, 0.453, and 0.385 μm), several comparisons show agreement within mutual error bars at heights between ∼15 and 26 km. However, above ∼24 km, correlative observations are scarce and the data is of poorer quality because of low aerosol content and relatively strong Rayleigh, NO2, and ozone contributions. Thus for the short wavelengths, especially above ∼24 km, further correlative measurements would be desirable to provide a conclusive validation. Initial data use investigations demonstrate methods for inferring aerosol physical and optical properties from the SAGE II four‐wavelength extinction data. The methods yield values and uncertainties for particle volume, area, effective size, distribution width, model size distribution parameters, number larger than specified sizes, and backscatter coefficient. In many cases, SAGE II‐derived values are compared to measurements by dustsonde and lidar. Results vary, but they are usually consistent within mutual error bars.
Presentation of the European correlative experiment program for SAGE II
Authors: Lenoble J.
Published: February 2008

A coordinated program has been organized in Europe for the validation of SAGE II data. During four campaigns in 1984–1985, aerosol, ozone, and nitrogen dioxide measurements were performed at various stations, when SAGE II was observing over Europe.
Comparative studies of aerosol extinction measurements made by the SAM II and SAGE II satellite experiments
Authors: Yue Glenn K. , McCormick M. P. , Chu W. P. , Wang P. , Osborn M. T.
Published: February 2008

Stratospheric Aerosol Measurement (SAM) II and Stratospheric Aerosol and Gas Experiment (SAGE) II are two currently operating satellite systems designed to measure stratospheric aerosol extinction coefficients using the technique of solar occultation or limb extinction. Although each sensor is mounted aboard a different satellite, there are occasions when their measurement locations are nearly coincident in time and space, thereby providing opportunities for a measurement comparison. This paper presents results of comparative study, which demonstrates that SAM II and SAGE II are producing similar aerosol extinction profiles at 1.0 μm within their measurement errors. Since SAM II has been validated, these results show the validity of the SAGE II aerosol extinction measurements at longer wavelengths. In addition, there are occasions when locations of sunrise and sunset aerosol extinction measurements by SAGE II are nearly coincident in space and about 12 hours apart, thereby providing opportunities for a test of the consistency of SAGE II profiles. Comparisons of sunrise and sunset aerosol extinction data at four different wavelengths for some of these occasions are presented and discussed.
The electrification of New Mexico thunderstorms: 1. Relationship between precipitation development and the onset of electrification
Authors: Dye J. E. , Winn W. P. , Jones J. J. , Breed D. W.
Published: February 2008

Aircraft, radar, and surface observations were used to study the relationship between precipitation development and the onset of electrification in thunderstorms which formed near or over the Magdalena Mountains of New Mexico. The study included storms which were electrically active as well as ones in which no electrical enhancement was observed. Electric fields inside these clouds showed negligible enhancement and did not exceed 1 kV m−1 until reflectivities at 6 km above mean sea level (msl) (about −10°C) exceeded approximately 40 dBZ and cloud tops exceeded 8 km. The onset of electrification occurred during or immediately after convective growth within the cloud.
Remote sensing observations of nighttime OClO column during the Airborne Antarctic Ozone Experiment, September 8, 1987
Authors: Wahner A. , Jakoubek R. O. , Mount G. H. , Ravishankara A. R. , Schmeltekopf A. L.
Published: February 2008

The daytime and nighttime slant column abundances of OClO were measured by near‐UV absorption spectroscopy between 64° and 76°S latitude and 62° and 84°W longitude during the DC‐8 flight on days 251 and 252 (UT) 1987 as a part of the Airborne Antarctic Ozone Experiment (AAOE). Daytime and nighttime measurements used the scattered sunlight and the Moon as the light sources, respectively. The measured OClO column abundance during the nighttime was found to be 10 times larger than that measured during the day.
A field investigation of sulfate fluxes to a deciduous forest
Authors: Hicks B. B. , Matt D. R. , McMillen R. T. , Womack J. D. , Wesely M. L. , Hart R. L. , Cook D. R. , Lindberg S. E. , de Pena R. G. , Thomson D. W.
Published: February 2008

An intensive investigation of particulate sulfur fluxes to a deciduous forest was conducted at Oak Ridge, Tennessee, during May 1983, as part of a multilaboratory program to study the dry deposition of airborne trace gases and aerosols to vegetated surfaces. At this time, the leaf area was approximately 50% of the maximum and was rapidly increasing. Eddy correlation methods were used to measure fluxes of submicron particulate sulfur (presumably sulfate), of submicron particles in three different size ranges, and of ozone above the forest canopy. The measured deposition velocities (vd) of particulate sulfur peaked at about 1 cm s−1 in daytime, but dropped to near zero at night, with a long‐term average of about 0.6 cm s−1. When scaled with friction velocity, these values of vd are consistent with similar measurements taken previously over different surfaces. Measurements and analyses indicate that the flux divergence of particulate sulfur should have caused an error no greater than ±0.05 cm s−1 in vd estimates. For very small particles (less than 0.1 μm diameter), measured values of vd were similar to those for particulate sulfate, but deposition velocities for particles in the accumulation size range decreased as particle size increased, and upward components of fluxes were found in daytime convective conditions. During this study, measurements were also made of sulfur deposition to polycarbonate petri dishes placed in the forest canopy, and to the bucket of a standard wet‐dry collector in a forest clearing. These surrogate surface studies produced much smaller values of vd for sulfate than those derived from eddy correlation, when no scaling as a function of leaf area relative to ground area was applied.
Intensity measurements in the 720.8‐cm−1 Q branch of 12C16O2
Authors: Varanasi Prasad , Chudamani Sury
Published: February 2008

Absolute intensities in the 1000‐0l10 band of 12C16O2 at 720.8 cm−1 have been measured at 295 K using the Doppler‐limited spectral resolution (∼10−4 cm−1) of a tunable diode laser. Our highly accurate measurements differ significantly from previously published and cataloged data.
Ion chemistry of the cold summer mesopause region
Authors: Reid George C.
Published: February 2008

Ions form important constituents of the cold summer mesopause region, since their tendency to form heavy clusters makes them a strong candidate for the nucleation cores of the ice particles that make up noctilucent and polar mesospheric clouds and since their chemical composition can yield important information about the thermal structure and the minor neutral composition of the mesopause region itself. The sources of mesospheric ionization at high latitudes and the outlines of the chemical reaction chains that determine the steady state positive ion composition are discussed. A one‐dimensional model is used to calculate the steady state composition, and the main features are discussed, with emphasis on the altitude distribution of the proton hydrates and their dependence on such atmospheric variables as the temperature, the ionization rate, and the concentrations of water vapor and atomic oxygen. The model predictions are compared with mass spectrometer measurements made at high latitudes in summer, and the main discrepancies are pointed out. The possible role of negative ions is discussed briefly.
Time‐averaged transport coefficients in photochemical modeling: A conjecture
Authors: Weinstock J.
Published: February 2008

It has been pointed out by several authors that constituent diffusivities associated with breaking gravity waves vary dramatically with the wave saturation amplitude. This variation introduces an uncertainty for the value to be used for diffusivity. In principle, this particular uncertainty may be avoided if an appropriate time average is used and the corresponding wave statistics are known. A simple hypothesis is put forward regarding what average is appropriate. A limitation is that turbulence scales be less than constituent scales.
Evidence From the Limb Infrared Monitor of the Stratosphere for nonlocal thermodynamic equilibrium in the v2 mode of mesospheric water vapour and the ν3 mode of stratospheric nitrogen dioxide
Authors: Kerridge Brian J. , Remsberg Ellis E.
Published: February 2008

The Nimbus 7 Limb Infrared Monitor of the Stratosphere (LIMS) included channels centred at 6.9 μm (1370 cm−1 to 1560 cm−1) and 6.2 μm (1560 cm−1 to 1630 cm−1) to measure H2O and NO2, respectively. Since the photochemical lifetime of H2O is several months, no diurnal variation was expected, but retrieved concentrations at mid and low latitudes were larger in the daytime than in the nighttime (by 20–30% at 1 mbar). This is attributed to departure from local thermodynamic equilibrium of daytime emission which had not been accounted for in retrievals. It is shown that excess radiance in the lower mesosphere may be due to emission from the H2O(020) → (010) hot band and that in the stratosphere pumping of high vibrational states of NO2(ν3) by chemical reaction NO + O3 → NO2 + O2 and by absorption of visible and near‐IR sunlight may be the cause. This nonthermal emission from NO2 is shown to also significantly affect retrieval of H2O in the polar night mesosphere and NO2 in the daytime stratosphere at low latitudes. LIMS nighttime measurements of H2O and NO2 in regions other than the high latitude winter mesosphere should not be affected.
Thunderstorm related variations in stratospheric conductivity measurements
Authors: Hu Hua , Holzworth Robert H. , Li Ya Qi
Published: February 2008

The vector electric field and polar conductivities were measured by zero‐pressure balloon‐borne payloads launched from Wallops Island, Virginia, during the summers of 1987 and 1988. Data were collected over thunderstorms (or electrified clouds) during 6‐hour flights at altitudes near 30 km. The vector electric field measurements were made with the double Langmuir probe high‐impedance method, and the direct conductivity measurements were obtained with the relaxation technique. We show evidence for conductivity variations over thunderstorms (or electrified clouds). We find that both positive and negative polar conductivity data do show variations of up to a factor of 2 from ambient values associated with the disturbed periods. Some ideas for possible physical mechanisms which may be responsible for the conductivity variations over thunderstorms are also discussed in this paper.
Concentrations and size distributions of Antarctic stratospheric aerosols
Authors: Ferry G. V. , Neish E. , Schultz M. , Pueschel R. F.
Published: February 2008

Particle Measuring Systems laser particle spectrometer (ASAS‐X and FSSP) probes were used to measure aerosol particle concentrations and size distributions during 11 out of 12 ER‐2 flights between Punta Arenas (53°S) and Antarctica (up to 72°S) from August 17 to September 22, 1987. The time resolution was 10 s, corresponding to a spatial resolution of 2 km. The data were divided into two size classes (0.05–0.25 and 0.53–5.5 μm radius) to separate the small particle from the coarse particle populations. Results show that the small particle concentrations are typical for a background aerosol during volcanic quiescence. This concentration is generally constant along a flight track; in only one instance did we measure a depletion of small particles during a polar stratospheric cloud (PSC) encounter, suggesting a nucleation of type I PSC particles on background aerosols. Temporary increases of the coarse particle concentrations indicated the presence of tenuous polar stratospheric clouds that were encountered most frequently at the southernmost portion of a flight track and when the aircraft descended to lower altitudes. During “particle events,” particle modes were found at 0.6 μm radius, corresponding to type I PSCs, and occasionally, a second mode at 2.0 μm radius, corresponding to type II PSCs.
13C/12C of atmospheric CO2 in the Amazon Basin: Forest and river sources
Authors: Quay Paul , King Stagg , Wilbur Dave , Wofsy Steven , Rickey Jeffrey
Published: February 2008

Concentrations and the δ13C of CO2 were measured on air in the lower portion of the atmospheric boundary layer in the Amazon basin. Three major trends were observed: (1) a diurnal cycle with an amplitude of 70 to 150 ppm for concentration and 3 to 6‰ for δ13C, (2) a vertical gradient of CO2 and δ13C in forest air, and (3) different 13C composition for CO2 in air over the river and in the forest. The diurnal changes in CO2 concentration and δ13C of the CO2 resulted from diurnal cycles in boundary layer mixing and photosynthetic uptake of CO2. Photosynthetic uptake of CO2 increased the δ13C to levels up to ∼0.6‰ higher than tropospheric values in forest air samples collected during the afternoon at heights >7 m. An observed 5‰ decrease in δ13C of CO2 in forest air between canopy height and ground level indicates that photosynthetic uptake of biogenic CO2 is an important factor in determining the δ13C of plants growing in the Amazonian rain forest. The observed nighttime increase in CO2 concentration and δ13C decrease differed for air within the forest canopy versus air over the river. The δ13C values of the CO2 sources for air in the forest and over the river were −28‰ and −22‰, respectively. The results indicate that soil and plant respiration were the primary sources of CO2 input to air in the forest, whereas degassing of CO2 from the Amazon River is the likely source of CO2 input to air over the river.
Sensitivity study of advection and diffusion coefficients in a two‐dimensional stratospheric model using excess carbon 14 data
Authors: Shia Run‐Lie , Yung Yuk L. , Allen Mark , Zurek Richard W. , Crisp David
Published: February 2008

Using the California Institute of Technology/Jet Propulsion Laboratory two‐dimensional transport model, with transport coefficients taken from Yang and Tung (1989), we study the time evolution of excess carbon 14 in the stratosphere and the troposphere from October 1963 to December 1966. The model provides a satisfactory simulation of the observed data. Due to the impulsive nature of its source, initial distributions of excess carbon 14 exhibit large spatial gradients. This permits important constraints on the range of transport coefficients in the lower stratosphere to be derived. The standard model uses the circulation and eddy diffusivity of the year 1980. Large deviations (by factor of 2) from this standard transport are ruled out by our model. A self‐consistently derived Kyy which is small (∼109 cm2 s−1) in tropical regions, but is larger (∼1010 cm2 s−1) at higher latitudes is preferred. A Kzz as large as 1×104 cm2 s−1 would be inconsistent with the data. Excess carbon 14 is removed from the atmosphere with surface deposition velocities vS = 3 × 10−3 cm s−1 and vN = 5 × 10−3 cm s−1 in the southern and northern hemispheres, respectively. The last result is contrary to the current understanding that the oceans are the dominant sink for excess 14C.
Evaluation of excess carbon 14 and strontium 90 data for suitability to test two‐dimensional stratospheric models
Authors: Johnston Harold
Published: February 2008

From reports by the Atomic Energy Commission concerning the atmospheric distribution of radionucleides following the nuclear bomb tests of 1958–1959 and 1961–1962, excess carbon 14 data from the period 1959–1970 and strontium 90 data from 1963–1967 are reviewed for possible use as inert tracers to test two‐dimensional stratospheric‐tropospheric models. Contrary to some views expressed in the literature, it is concluded that the carbon 14 data are suitable to test (1) the altitude (at 4 latitudes) of the transition region between troposphere and stratosphere with respect to transport of an inert tracer, (2) some aspects of transport between the northern and southern hemispheres, (3) horizontal and vertical transport as the vertical profile between 4.5 and 33 km and at 31°N evolves from a skewed Gaussian in 1963 to an almost stair‐step profile in 1966, and (4) the long‐term one‐dimensional aspect of a two‐dimensional model over the period 1966–1970. More tentatively, it is concluded that the strontium 90 data may be used as a model for the distribution and gross settling rate of the natural stratospheric aerosol layer between 15 and 25 km. Data from difficultly obtained laboratory reports and suggested initial conditions and boundary conditions are included as a microfiche supplement to this paper.
In search of regularities in extreme rainstorms
Authors: Foufoula‐Georgiou Efi , Wilson Larry L.
Published: February 2008

Extreme rainstorms play an important role in the hydrologic design and operation of water resource systems. Due to the lack of complete knowledge of the complex meteorological mechanisms that produce and sustain extreme storms, statistical and correlation analyses are a valuable and complementary tool in identifying regularities of extreme rainfall characteristics. In this paper we have studied the statistical properties of several characteristics of extreme midwestern storms. In particular, we have analyzed the storm occurrence process in space and time, storm shape and orientation, total storm center depth, storm duration, storm areal extent, and depth‐area relationships. Our analysis is based on the data base of extreme storms published by the U.S. Army Corps of Engineers. Several trends and regularities among extreme midwestern storms have been identified and are expected to prove useful in developing and/or evaluating empirical and physically based models of extreme rainfall.
The distribution of lead between sea salt dust, and lead‐rich aerosols in the mid South Pacific easterlies at American Samoa
Authors: Rosman Kevin J. R. , Patterson Clair C. , Settle Dorothy M.
Published: February 2008

Aerosols in the South Pacific Easterlies have been sampled at American Samoa with a cascade impactor and analysed for Pb, Ba, K, Ca, Sr, and Rb by isotope dilution mass spectrometry using ultraclean procedures. Some 84% of the Pb was found in fine (≤ 0.5 μm) aerosols which were collected on the backup filter with an efficiency of only 33%. Sea salt and eroded terrestrial material (dust) containing 6% and <1% respectively, of the Pb (sea salt indexed by the metals K, Ca, Sr, and Rb and dust indexed by Ba) were collected on early stages of the impactor, although 65% of the dust, because of its larger size, was lost to surfaces of the rain shelter before reaching the impactor. The remaining 10% of the Pb was associated with plant leaf waxes of continental origin which produced Pb and Ba peaks on stage 4 (0.5 μ) of the impactor.
A case study of the Thunderstorm Research International Project storm of July 11, 1978: 1. Analysis of the data base
Authors: Nisbet John S. , Barnard Theresa A. , Forbes Gregory S. , Krider E. Philip , Lhermitte Roger , Lennon Carl L.
Published: February 2008

A coordinated analysis of the Thunderstorm Research International Project storm of July 11, 1978, from 1900 to 2000 UT at the Kennedy Space Center is presented using data from three Doppler radars, a lightning detection and ranging system and a network of 25 electric field mills, and rain gages. This storm produced two cells for which the center of the updraft remained within range of the observational network. Electric field measurements were used to analyze the charge moments transferred by lightning flashes. An attempt was made to analyze as large a percentage as possible of the flashes so that the measurements would be usable to study the charge moment transferred by lightning in the storm. These data were fitted to Weibull distributions which were used to estimate statistical parameters of the lightning for both intracloud and cloud‐to‐ground flashes and to estimate the fraction of the flashes which were below the observation threshold for the two cells studied. The displacement and conduction current densities were calculated throughout the storm from electric field measurements between flashes, and data are presented of values at 5‐min intervals throughout the storm. These values were used to derive the magnitudes and locations of dipole and monopole generators by least squares fitting the measured Maxwell current densities to the displacement‐dominated equations. Constrained fitting was used to examine the uniqueness of the solutions.
Earth‐atmosphere exchange of angular momentum simulated in a general circulation model and implications for the length of day
Authors: Boer G. J.
Published: February 2008

The angular momentum of the Earth‐atmosphere system is conserved to good approximation because external torques are small. Variations in the angular momentum of the atmosphere must therefore be accompanied by and directly connected with variations in the angular momentum of the Earth and hence with variations in the length of day (lod). The atmospheric angular momentum budget simulated in the Canadian Climate Centre general circulation model is investigated in order to assess the fidelity of the model to the atmosphere but, more importantly, to investigate the nature of the simulated interaction between the atmosphere and the underlying surface and the implications for variations in the length of day. These interaction terms are difficult to obtain based on observations. The general circulation model successfully reproduces many of the observed aspects of the angular momentum budget, including the partition of the angular momentum between hemispheres, the dominance of the seasonal cycle and, as well as may be determined, the climatological distribution of the mountain torque and stress torque interaction terms. As to the simulated interaction between atmosphere and underlying surface on shorter time scales, it is found that on time scales of days the mountain and stress torque terms contribute to the rate of change of angular momentum (and by implication the lod) in the ratio of 60–40%, while at weekly and longer time scales the stress torque dominates by increasing amounts. The notable contemporaneity of changes in the length of day and of atmospheric angular momentum suggests that much of the interaction occurs directly with the solid Earth and that the oceans, despite their large area, play a lesser role. This is verified in the simulation where the sum of the stress and mountain torque over land contributes of the order of 85–90% to the variation in angular momentum for time scales of days to months.
Solar radiation (190–230 nm) in the stratosphere: Implications for photoelectric emissions from instrumentation at balloon altitudes
Authors: Byrne G. J. , Benbrook J. R. , Bering E. A. , Oró D. M.
Published: February 2008

Photoelectric contamination of conductivity measurements using the relaxation time method and electric field measurements using double‐probe systems have been observed well below maximum balloon altitudes. The solar wavelengths responsible for the photoemissions are primarily those in the 190–230 nm range. At these wavelengths, the atmosphere is partially transparent, allowing a large fraction of the incident solar photons to penetrate deep into the stratosphere. The effects of photoemissions on the electrical measurements have been observed at altitudes as low as 25 km, even for low solar angles. In the relaxation time measurements the photoelectric effects are manifested by a large perturbation of the positive conductivity measurement as a function of altitude and solar angle, with a ratio of the measured positive and negative conductivities greater than 1 above 25 km. We employ a photocurrent model to investigate the contamination of the relaxation time measurements. The model result shows that the solar flux in the range of 190–230 nm is more than sufficient to account for our conductivity observations. In the double‐probe measurements of electric fields, the photoelectric effects appear as perturbations to the probe potentials. As a result of the large flux of energetic solar photons in the stratosphere, many of the requirements for satellite double‐probe systems to reduce photoelectric contamination of electric field measurements are also applicable to balloon‐borne systems. On the basis of our analysis, we recommend that the surfaces of double‐probe instruments in the stratosphere be coated with a material of highly uniform work function in the optimum range of 4.6–5.4 eV. Our observations demonstrate the presence of a large flux of ultraviolet radiation in the stratosphere which is capable of photoemissions from aluminum surfaces and surfaces coated with high work function materials. As a consequence, many types of electrical or chemical measurements made in the sunlit stratosphere may suffer contamination by photoemissions.
Heterodyne spectrophotometry of ozone in the 9.6‐μm band using a tunable diode laser
Authors: McElroy C. T. , Goldman A. , Fogal P. F. , Murcray D. G.
Published: February 2008

Tunable diode laser heterodyne spectrophotometry (TDLHS) has been used to make extremely high resolution (0.0003 cm−1) solar spectra in the 9.6‐μm ozone band. Observations have shown that a signal‐to‐noise ratio of 120:1 (∼30% of theoretical) for an integration time of 1/8 s can be achieved at a resolution of 0.0013 wave numbers. The spectral data have been inverted to yield a total column amount of ozone, in good agreement with that measured at the nearby National Oceanic and Atmospheric Administration (NOAA) ozone monitoring facility in Boulder, Colorado. Line positions for several ozone lines in the spectral region 996–997 cm−1 are reported. Recent improvements have produced a signal‐to‐noise ratio of 95∶1 (∼40% of theoretical) at 0.0003 cm−1 and extended the range of wavelengths which can be observed.
Polar twilight UV‐visible radiation field: Perturbations due to multiple scattering, ozone depletion, stratospheric clouds, and surface albedo
Authors: Anderson Donald E. , Lloyd Steven A.
Published: February 2008

The polar twilight atmosphere is different from that at mid‐latitude in several ways which lead to significant changes in the wavelength‐dependent radiation field. Ozone depletion in the stratosphere leads to increased scattering below 340 nm. Polar stratospheric clouds produce changes in the radiation field which depend on cloud height and thickness. A surface albedo near unity produces a large increase in scattering. Multiple scattering becomes a larger percentage of the radiation field as solar zenith angle increases. These perturbations on the radiation field lead to enhanced ozone destruction in the stratosphere, increased surface irradiance, and a significant wavelength‐dependent increase in nadir radiance.
A statistical trend analysis of revised Dobson total ozone data over the northern hemisphere
Authors: Bojkov R. , Bishop L. , Hill W. J. , Reinsel G. C. , Tiao G. C.
Published: February 2008

A seasonal trend analysis of Dobson total ozone data that have been critically reevaluated and revised is performed for 29 northern hemisphere stations located between 19°N and 64°N latitude using data through 1986. The trend model considered for these data allows for a different linear trend for each month of the year, so that the seasonal as well as the latitudinal and regional nature of the total ozone trend behavior can be examined. The trend model also incorporates the 10.7‐cm solar flux series and the 50‐hPa equatorial zonal wind series as additional explanatory factors for solar and quasi‐biennial oscillation induced ozone variations. Regression random effects models are then used for the individual station seasonal trend estimates to obtain trend estimates as a function of latitude for different seasons of the year. The results of this seasonal trend analysis indicate significantly more negative trends during the winter months (December‐March) than during the summer months (May–August), notably at higher latitudes, with the trends in winter becoming more negative with increasing latitude. The trends in the winter are estimated to be of the order of −1.2%, −2.1%, and −3.0% per decade for latitudes 35°N, 45°N, and 55°N, respectively, while trends during the summer are of the order of −0.6% per decade with no distinct pattern as a function of latitude. The year‐round or annual trend over all latitudes is estimated to be about −0.84±0.82% per decade. The trends are found to display some regional variation, with trends in Japan being considerably less negative than those in North America and Europe. Sensitivity studies are also performed to investigate the effects on ozone trend estimates due to certain factors such as abnormal ozone behavior in 1983 and 1985, the use of ozone data prior to 1965, and nuclear weapons testing in the early 1960s. The seasonal trend analysis is also performed using published (unrevised) Dobson data. Trend results based on published data are on average less negative than trends from revised Dobson data for European stations, by about 1.0% per decade across all seasons, with only small average differences for stations in North America and Japan.
An intercomparison of airborne PAN measurements
Authors: Gregory Gerald L. , Hoell James M. , Ridley Brian A. , Singh Hanwant B. , Gandrud Bruce , Salas Louis J. , Shetter James
Published: February 2008

As part of the NASA Tropospheric Chemistry Program a series of field intercomparisons have been initiated to evaluate state‐of‐the‐art capability for measuring key tropospheric species. These intercomparisons, designated as Chemical Instrumentation Test and Evaluation (CITE), are conducted as part of NASA's Global Tropospheric Experiment. The objectives of the second series of instrument tests, CITE 2, were to evaluate instrumentation for measuring NO2, HNO3, and peroxyacetyl nitrate (PAN) and to determine for various tropospheric environments the relative abundances and partitioning among the major nitrogen species. This paper summarizes the results from the PAN instrument intercomparisons. Other results are addressed in companion papers. Both PAN instruments use the same detection principle of electron capture gas chromatography of a cryogenically enriched sample of ambient air. NASA Ames Research Center and the National Center for Atmospheric Research were responsible for the respective instruments. The intercomparisons included three exchanges of standards and 13 intercomparison flights in which a variety of types of air masses were sampled. Nine flights were based from Ames Research Center, California, and the remaining four were ferry flights between Ames and Wallops Flight Center, Virginia (aircraft home base). Flight altitudes ranged from 150 to 5000 m above ground level. All flights but one were during daylight hours. PAN mixing ratios during the flight intercomparison periods were generally <300 parts per trillion by volume (pptv), and about 40% of the results for mixing ratios were <100 pptv. At mixing ratios of <100 pptv the two instruments agreed on the average to about 17 pptv with a 95% confidence interval of ±9 pptv. Instrument agreement at PAN levels of 100–300 pptv was of the order of 25% with a confidence interval of ±6%. These levels of agreement are within expected limits based on the stated accuracy and precision of the two instruments. However, it is noted that for some of the individual intercomparison data periods, agreement was outside expected levels.
Thunderstorms, cosmic rays, and solar‐lunar influences
Authors: Lethbridge Mae Devoe
Published: February 2008

A study of cosmic rays and thunderstorm frequency has shown a decrease in thunderstorms at the time of high cosmic rays and an increase in thunderstorms 2–4 days later. This was done by superposed epoch analysis of thunderstorms over the eastern two thirds of the United States for 1957–1976. When data for spring and fall months were used, the minimum deepened. When high cosmic rays near full and new moon for these months were key days, the minimum deepened again and was significant at less than the 0.01% level. It is believed that when the Sun, Earth, and Moon are aligned, particulate matter in the lower stratosphere is modulated and acted upon by cosmic rays, bringing about an immediate decrease in thunderstorms.
The coarse particle aerosols in the free troposphere around Japan
Authors: Hayasaka Tadahiro , Nakajima Teruyuki , Tanaka Masayuki
Published: February 2008

Airborne measurements of solar aureole intensities were carried out around Japan with a spectral scanning radiometer. Horizontal and vertical stratifications and volume spectra of tropospheric aerosols were retrieved from the measured solar aureole intensities. The results show that bimodal volume spectra of aerosols with a saddle point radius around 0.5 μm are generally observed in the troposphere, both within and above the planetary boundary layer. A submicrometer particle mode of the spectra, known as the accumulation mode, dominates the coarse particle mode within the planetary boundary layer, especially in summer, whereas coarse particles were observed frequently in the free troposphere. Synoptic analyses with air mass trajectories, isentropic surfaces, and weather charts suggest that the windblown dust particles injected into the atmosphere in arid regions of eastern Asia are the origin of the coarse particles observed in the free troposphere around Japan. Windblown dust particles are elevated to the free troposphere by ascending air motion in a warm front and then transported by the westerlies. The arid regions to the east of the Tibetan Plateau, where disturbances due to the frontogenesis occur frequently, are capable of supplying coarse particles to the free troposphere over the northwestern Pacific Ocean throughout the year.
Carbon monoxide over the Amazon Basin during the wet season
Authors: Harriss R. C. , Sachse G. W. , Hill G. F. , Wade L. O. , Gregory G. L.
Published: February 2008

Measurements of carbon monoxide (CO) were made over the Amazon Basin of Brazil during the 1987 wet season as part of the NASA Global Tropospheric Experiment/Amazon Boundary Layer Experiment (ABLE 2B). The distribution of CO over the altitude range sampled (0.15–4.5 km) was influenced by surface emissions from biological sources, long‐range transport of pollutants from northern hemisphere sources, and by transport processes associated with local convective mixing. Surface sources are indicated by a qualitative interpretation of the typical pattern of decreasing concentrations with increasing altitude and increasing concentrations of CO at 0.15‐km altitude during a transect from the Atlantic coast to the central basin. Atmospheric convective activity produced irregular patterns of variability at time scales of less than 1 hour over a localized area. The disruption of mixed layer growth and decay processes has a particularly important influence on CO concentrations in the daytime lower troposphere. Intrusions of northern hemisphere air into the central Amazon resulted in increased CO concentrations in the lower and midtroposphere. The correlation of CO with O3 was positive under conditions interpreted as being influenced by northern hemisphere air, and negative during all other meterological conditions experienced in ABLE 2B.
Convection links biomass burning to increased tropical ozone: However, models will tend to overpredict O3
Authors: Chatfield Robert B. , Delany Anthony C.
Published: February 2008

Biomass burning throughout the inhabited portions of the tropics generates precursors which lead to significant local atmospheric ozone pollution. Several simulations show how this smog could be only an easily observed, local manifestation of a much broader increase in tropospheric ozone. We illustrate basic processes with a one‐dimensional time‐dependent model that is closer to true meteorological motions than commonly used eddy diffusion models. Its application to a representative region of South America gives reasonable simulations of the local pollutants measured there. Three illustrative simulations indicate the importance of dilution, principally due to vertical transport, in increasing the efficiency of ozone production, possibly enough for high ozone to be apparent on a very large, intercontinental scale. In the first, cook‐then‐mix, simulation the nitrogen oxides and other burning‐produced pollutants are confined to a persistently subsident fair weather boundary layer for several days, and the resultant ozone is found to have only a transient influence on the whole column of tropospheric ozone. In the second, mix‐then‐cook, simulation the effect of typical cumulonimbus convection, which vents an actively polluted boundary layer, is to make a persistent increase in the tropical ozone column. Such a broadly increased ozone column is observed over the the populated “continental” portion of the tropics. A third simulation averages all emission, transport, and deposition parameters, representing one column in a global tropospheric model that does not simulate individual weather events. This “oversmoothing” simulation produces 60% more ozone than observed or otherwise modeled. Qualitatively similar overprediction is suggested for all models which average significantly in time or space, as all need do. Clearly, simulating these O3 levels will depend sensitively on knowledge of the timing of emissions and transport.
Precipitation type transition regions in winter storms over southern Ontario
Authors: Stewart Ronald E. , King Patrick
Published: February 2008

Two winter storms passed through the Toronto area during November and December 1987. Information from radar, rawinsonde, and surface observations was analyzed in order to determine the kinematic flow fields and thermodynamic environment in the vicinity of the transition at the surface between snow and rain. This region was also linked to heavy precipitation and thunder. Updrafts preferentially occurred over the snow region, and deep near‐0°C layers occurred in the transition region. Observations are consistent with a mesoscale circulation initiated by melting snow and possibly with the occurrence of symmetric instability. It is further suggested that large, possibly wet, snowflakes being formed within such deep near‐0°C layers would contribute to the radar detection of precipitation bands near the precipitation transition region.
Late Pleistocene time series of atmospheric and oceanic variables recorded in sediments from the Subarctic Pacific
Authors: Morley Joseph J. , Pisias Nicklas G. , Leinen Margaret
Published: February 2008

Time series analyses of atmospheric and oceanic variables in a late Pleistocene record from the northwest Pacific show the complex relationship of the response of various segments of the climate system to changes in the earth's orbit. Most variance spectra of time series from this subarctic record contain frequency peaks with periods corresponding to at least one of the major orbital components of eccentricity, obliquity, or precession. Although the radiolarian faunal (water mass) assemblages have prominent spectral peaks with 41,000‐year periods which are coherent with obliquity at this frequency, only the Transitional faunal assemblage contains variance focused at a frequency corresponding to the 100,000‐year period of eccentricity. Three of these faunal time series also show variance concentrated at a frequency with a 20,000‐year period. These three time series are not coherent at a 20,000‐year frequency with either of the dominant spectral peaks of precession. They are coherent, however, with variations in the second harmonic of the obliquity cycle. Changes in obliquity apparently affect siliceous faunal abundances in the northwest Pacific region of this high‐latitude site more than variations in eccentricity or precession. Maxima in the time series of quartz abundance occur during low values of eccentricity and high glacial ice volume. Because atmospheric winds serve as the major source of supply of quartz to the sediments at this site, these high quartz values reflect increased aridity at the source region. Except for short periods during interglacials, the characteristics of the surface waters in this region of the subarctic Pacific during much of the last 460,000 years were similar to those which exist today in the Sea of Okhotsk. The spectrum of winter sea surface temperature estimates, derived from siliceous microfaunal abundances, contains dominant frequency peaks at periods of 100,000, 41,000, and 23,000 years which are coherent with eccentricity, obliquity, and precession, respectively. Based upon the relationship of the Subarctic Front with the dominance of specific faunal asemblages, the front was positioned south of its present‐day location throughout much of the late Pleistocene.
Late Eocene perturbations: Foraminiferal biofacies and evolutionary overturn, southern Australia
Authors: McGowran Brian
Published: February 2008

Abundance patterns of planktonic and benthic foraminifera in profiles of neritic successions at high southern paleolatitudes show evidence that they represent systemic stratigraphic signals from the global ocean. In an interval correlated with upper Zone P15 and Zone P16, long‐distance correlations can be made on benthic Sphaeroidina and the aragonitic Robertinacea. Among the plankton, increased numbers of Globigerinatheka alternate with high abundances of Chiloguembelina and increased numbers of Pseudohastigerina, especially during an Hantkenina ingression. Those alternations indicate environmental fluctuations in the upper part of the water column, just as alternations in Cibicididae/Uvigerinidae ratios give similar signals from the benthic communities. The fluctuations are considered to be directly or indirectly linked to available oxygen. Several local neritic events can be correlated with oceanic events, and on the basis of those correlations the suggestion of a stratified ocean during Zone P16 is supported. Near the end of Zone P16 there is a major benthic species overturn and disappearance or weakening of signals of water column stratification and restricted bottom water circulation. I conclude that local events such as species overturn, biofacies spikes, and a brief regression (the Chinaman Gully regression at about the end of Zone P16) are of global significance as part of the stepwise configuration of the Terminal Eocene Event.
The Eurasian Ice Sheet Formation and collapse resulting from natural atmospheric CO2 concentration variations
Authors: Lindstrom Dean R.
Published: February 2008

Finite element model simulations of ice sheet dynamics are conducted to investigate the role of natural atmospheric CO2 variations (obtained from ice core bubbles) in creating climatic conditions necessary to glaciate the Eurasian Arctic. Effects of CO2 variations are sufficient to support extensive marine ice sheet and ice shelf development at the last glacial maximum and to deglaciate the region during the Holocene (from approximately 14 ka to 9 ka). The ice sheet coverage simulated for the last glacial maximum agrees with evidence for extensive ice sheet grounding over the shallow continental shelves of the Barents, Kara, Laptev, and East Siberian seas. An ice shelf also forms over the Arctic Ocean and Greenland and Norwegian seas.