bluuebunny/crossref_metadata_2025 huggingface dataset:
Radar imaging of submarine sand waves in tidal channels
Authors: Hennings Ingo
Published: February 2008

The simple theoretical model of Alpers and Hennings describing the radar imaging of submarine bottom topography in coastal waters with strong unidirectional tidal currents is analytically extended to show the influence of advection. The theory applies for L band radar, where second‐order terms in the hydrodynamic interaction can be neglected as a first approximation. If future imaging radars from satellites and space platforms as the ERS‐I (First European Remote Sensing Satellite), the JERS‐I (First Japanese Earth Remote Sensing Satellite), and the EOS (Earth Observing System) are to be used for cartographic applications, it is necessary to include the effect of advection to improve accuracy. This extension of the model simulates the position of the radar cross‐section modulation relative to coastal geomorphological bedforms. By application of that theory it is possible to map features such as the crests of sandbanks and sand waves.
Dissipation estimates for stratified turbulence
Authors: Yamazaki Hidekatsu , Osborn Thomas
Published: February 2008

There is concern about the appropriateness of the isotropic formula for calculating the dissipation rate of turbulent kinetic energy in a stratified fluid, such as turbulence in the thermocline. An alternative approach, given that stratification acts directly on the vertical component of the motion, is the axisymmetric theory of Batchelor (1946). Under the assumption that 〈(∂u2/∂x3)2〉 ≈ 〈(∂u2/∂x1)2〉, which is consistent with our measurements, we derive an upper and lower bound for dissipation in axisymmetric turbulence. For a value of ε/νN2 > 20 the dissipation estimate is comparable to the isotropic formula (based on the gradient of a horizontal velocity component). For decreasing values of ε/νN2 the error increases but is limited to less than 35%. Interestingly enough, in an axisymmetric turbulence the correct dissipation rate may be larger or smaller than an appropriate isotropic estimation. The important result is that the isotropic formula based on the shear of a horizontal velocity component is a good estimate of the dissipation, given the uncertainty in the current oceanographic technique. Both vertical and horizontal sampling are appropriate to estimate the dissipation rate from the isotropic formula as long as one uses a horizontal component of the velocity.
Southern ocean winter mixed layer
Authors: Gordon Arnold L. , Huber Bruce A.
Published: February 2008

Austral winter 1986 observations from the Polarstern along the Greenwich meridian from the ice edge to the Antarctic margin show the mixed layer beneath the winter sea ice cover to be significantly depressed in oxygen saturation. Incorporation of Weddell Deep Water (WDW) into the winter mixed layer, responsible for this undersaturation, also introduces heat and salinity into the surface layer which strongly influences the mixed layer, sea‐air exchanges and sea ice formation processes. The total WDW transfer into the mixed layer averages 45 myr−1, implying a residence time for the surface water of 2.5 years. The associated winter heat flux is 41 W m−2, which limits ice thickness to about 0.55 m, agreeing quite well with observations. The air temperatures during the cruise are just sufficient to remove the WDW heat input in the presence of observed ice thickness and concentration. This suggests that the sea ice cover and WDW heat input into the mixed layer are in approximate balance by midwinter. The annual heat flux from WDW to the surface layer, and hence into the atmosphere, is estimated as 16 W m−2. Extrapolation of the Greenwich meridian WDW entrainment value to the full circumpolar 60°–70°S belt yields total up welling of 24×106 m3 s−1. Similar extrapolation of the heat flux value gives a circumpolar total of 2.8 × 1014 W. As a consequence of circulation/topography interaction, the Maud Rise water column stands out as an anomaly relative to the surrounding region, with a significantly more saline and dense mixed layer. Below the mixed layer the water column over the crest of the rise is identical to that over the flanks if the latter water column is upwelled by 400 m. This uplifting is believed to be a response of the upstream flow encountering the rise. Increased upstream flow would be expected to increase Maud Rise upwelling and the dependent salinity (density) of the mixed layer. Slight increases in the mixed layer density could trigger a convective mode and generation of a polynya. It is hypothesized that spin‐up of the Weddell Gyre's barotropic circulation induced by an increase of the regional wind stress curl would enhance the probability of polynya development over Maud Rise.
Estimation of sea ice type and concentration by linear unmixing of Geosat altimeter waveforms
Authors: Chase Juanita R. , Holyer Ronald J.
Published: February 2008

The Geosat (geodetic satellite) altimeter transmits a radar pulse toward Earth, then measures Earth‐reflected energy in a number of time gates. The signal amplitudes in successive gates create a “waveform,” the shape of which is determined by the reflectance characteristics of the Earth's surface. This study shows that over the polar ice cap, the type and concentration of sea ice can be related to Geosat return waveform shapes. Because it is known that an altimeter waveform may be a mixture of returns from two or more ice types within the footprint, linear unmixing theory is chosen as the framework for analysis of waveform data. The mixing model assumes that data samples are linear combinations of a limited number of end members. Unmixing analysis therefore consists of identifying the number and nature of the end members, followed by an interpretation of the data set in terms of combinations of these end members. Estimates of ice type and concentration obtained by linear unmixing of waveforms are compared with “ground truth” derived from visual interpretation of passive microwave imagery and aerial photography, which were collected coincident with Geosat overpasses during the 1987 Marginal Ice Zone Experiment. Generally good agreement is observed between waveform‐based ice information and the corresponding imagery ground truth. This analysis has revealed some deficiencies in a current parameterization of waveform shape called the Geosat ice index. A new ice index formulation is proposed.
The current and sea level variability in the Chesapeake and Delaware Canal
Authors: Wong Kuo‐Chuin
Published: February 2008

Current and sea level observations in the Chesapeake and Delaware (C&D) Canal are used to examine the frequency‐dependent spatial distributions of tidal and subtidal variability along the canal. To first order of approximation, the C&D Canal is shown to be a linear system. A linearized, frequency‐dependent analytical model is developed to examine details in the tidal and subtidal variability along the canal, and results agree well with observations. The principal semidiurnal tides (M2) at the two ends of the canal are roughly in phase but differ substantially in amplitude. The amplitude of the M2 tide increases monotonically from the Chesapeake end of the canal toward the Delaware end. The amplitude of the M2 current is of the order 60 cm s−1, and it is higher in the western part of the canal than in the eastern part of the canal. The amplitudes of the principal diurnal tides (K1) at the two ends of the canal are much smaller than those for M2, but the K1 tides at the ends are nearly 180° out of phase with each other. The amplitude of the K1 tide decreases toward the interior of the canal from both ends. Relatively strong K1 current of the order 20 cm s−1 exists in the canal, and its amplitude shows only slight variation along the canal. There are substantial differences in the subtidal sea level fluctuations along the canal, resulting in strong subtidal currents which may exceed 70 cm s−1. The importance of the C&D Canal on the upper Delaware Bay is assessed by comparing the volume flux through the canal relative to that in the upper Delaware. It is shown that the influence of the canal on the Delaware depends strongly on the time scales involved. It appears that the C&D Canal is not important to the overall tidal response in upper Delaware Bay, but the subtidal volume flux through the canal must be included for a proper assessment of the dynamics of upper Delaware Bay at subtidal frequencies.
Numerical solution of the linearized three‐dimensional tidal equations using eddy viscosity eigenfunctions
Authors: Lardner R. W.
Published: February 2008

A modification of the spectral method of solving the linearized three‐dimensional tidal equations is described. The resulting expansions, using a basis of eddy viscosity eigenfunctions, are more rapidly convergent than are those that have been previously developed by this method. For a test problem involving a rectangular sea subject to a steady wind stress, an expansion with four eigenfunctions produces errors of not more than about 1% in the computed velocities, including the surface component parallel to the wind. This rate of convergence is comparable to that obtained previously using a basis of Chebychev polynomials or B‐splines, and has the advantage of uncoupling the differential equations for the modal amplitudes. It is also shown that when the bottom drag is zero, the fluid velocities can be obtained in closed form for arbitrary eddy viscosity, apart from the depth‐averaged components. This analytical solution is used to verify the accuracy of the numerical algorithm.
A measurement of stratospheric HO2 by ground‐based millimeter‐wave spectroscopy
Authors: De Zafra R. L. , Parrish A. , Solomon P. M. , Barrett J. W.
Published: February 2008

We have measured stratospheric perhydroxyl (HO2) by using a sensitive mm‐wave receiver to obtain spectroscopic line profiles of three rotational emission lines in the vicinity of 265.8 GHz. The observations were carried out over four days in September–October 1982 at Mauna Kea, Hawaii (19.5 N latitude) and yield good agreement with the column density and vertical distribution predicted above ∼35 km by three representative two‐dimensional photochemical models employing JPL 82‐57 reaction rates and chemistry; predictions from the same models using WMO/NASA chemistry yield poor agreement with our observations. Contrasts between current theoretical predictions and previous observations by Anderson et al. are pointed out for HO2 in the 28 to 37‐km range, along with the difficulty of joining the latter with our own measurements through a monotonically varying vertical profile for HO2. A possible explanation involving strong temporal and spatial variation in stratospheric water vapor content is suggested.
Nitrous oxide production by lightning
Authors: Hill R. D. , Rinker R. G. , Coucouvinos A.
Published: February 2008

Problems in accounting for the production of nitrous oxide by electrical discharges and lightning are discussed. A model of nitrous oxide production by corona discharge in lightning appears able to quantitatively account for both storm cloud and laboratory observations of nitrous oxide enhancements if the N2O yield from collisions between N2(A3 Σ) and O2 molecules is, as found by Zipf, large. Global estimates of nitrous oxide production by lightning and by point discharges beneath thunderclouds are only of the order of thousands of tons of nitrous oxide per year; however, estimates of global production of N2O by electrical, high voltage, power line coronas are from 1 to 2 orders of magnitude larger than by lightning.
Acidic and related constituents in liquid water stratiform clouds
Authors: Daum P. H. , Schwartz S. E. , Newman L.
Published: February 2008

Composition of cloud liquid water and interstitial air is reported for aircraft measurements near Charleston, South Carolina, in February 1982. Cloud water was collected by means of a slotted‐rod impactor. Cloud‐free interstitial air was obtained by a centrifugal separator. Principal ionic species in cloud water were H+, SO4=, NO3−, and NH4+. The relative acidity of cloud water, as measured by the ratio of H+ to NH4+, was much greater than that of the interstitial aerosol or of clear‐air aerosol samples. Gaseous O3, NOx (i.e., NO+NO2), and SO2 were present in interstitial air within clouds, whereas HNO3 and NH3 were below limit of detection (0.4 ppb for both species). Comparison of relative aciditiy of cloud water samples with that of clear‐air samples suggests that clear‐air aerosol and HNO3 are incapable of providing the levels of acidity observed in cloud water. Such acidity would be consistent with in‐cloud conversion of prevailing concentrations of SO2 or SO2+NOx to aqueous strong acid, although other hypotheses cannot be excluded. Comparison of absolute concentrations of cloudwater constituents to concentrations in clear‐air measurements gives no indication of accumulation of sulfur and nitrogen species by clouds.
Transport of ozone by turbulence and clouds in an urban boundary layer
Authors: Greenhut Gary K. , Ching Jason K. S. , Pearson Richard , Repoff Thomas P.
Published: February 2008

The turbulent fluxes of ozone and latent and sensible heat are computed from fast‐response measurements made aboard a National Oceanic and Atmospheric Administration aircraft over downtown Philadelphia and the surrounding suburbs during the afternoon and evening of August 22, 1979. In the afternoon the ozone flux at a height of 200 m is downward throughout the region with the largest magnitude (−2 (ppb) m s−1) occurring over the urban center. During the afternoon at both 200 m and a few hundred meters below cloud base, the horizontal profile of mean ozone concentration peaks at 130 ppb over the urban core with values of the order of 90 ppb to the southeast and northwest. The urban ozone concentration at 200 m decreases to 35 ppb by early evening. The normalized variances and spectra of vertical velocity, temperature, and ozone show little change with height or location in the urban center and northwest suburbs during the afternoon in good agreement with normalized statistics obtained over rural terrain (Kaimal et al., 1976; Lenschow et al., 1980). Data from a cloud penetration by the aircraft is used to estimate a mean updraft velocity of 4 m s−1 and an updraft area of approximately 1 km2. The flux of ozone due to the mean motion in the updraft is 2 orders of magnitude larger than the turbulent eddy fluxes within the cloud.
Nonmethane hydrocarbons in remote tropical, continental, and marine atmospheres
Authors: Greenberg J. P. , Zimmerman P. R.
Published: February 2008

Atmospheric hydrocarbon measurements from remote areas are presented and analyzed to determine sources of ambient mixing ratios. Biomass burning appears to make major contributions to free tropospheric hydrocarbon burden over tropical forests and grasslands. Biogenic emissions constitute a large percentage of atmospheric hydrocarbon volume in continental areas of significant productivity. In marine areas studied, ambient hydrocarbons may include contributions from evaporation of dissolved hydrocarbons transported by ocean currents from areas of coastal upwellings or marine pollution. In all cases, hydrocarbons from local sources are major components of the atmospheric hydrocarbon composition.
Large‐scale analysis and forecast experiments with wind data from the Seasat A scatterometer
Authors: Baker W. E. , Atlas R. , Kalnay E. , Halem M. , Woiceshyn P. M. , Peteherych S. , Edelmann D.
Published: February 2008

A series of data assimilation experiments is performed to assess the impact of Seasat A satellite scatterometer (SASS) wind data on Goddard Laboratory for Atmospheric Sciences (GLAS) model forecasts. The SASS data are dealiased as part of an objective analysis system utilizing a three‐pass procedure. The impact of the SASS data is evaluated with and without temperature soundings from the NOAA 4 Vertical Temperature Profile Radiometer (VTPR) instrument in order to study possible redundancy between surface wind data and upper air temperature data. In the northern hemisphere the SASS data are generally found to have a negligible effect on the forecasts. In the southern hemisphere the forecast impact from SASS data is somewhat larger and primarily beneficial in the absence of VTPR data. However, the inclusion of VTPR data effectively eliminates the positive impact over Australia and South America. This indicates that SASS data can be beneficial for numerical weather prediction in regions with large data gaps, but in the presence of satellite soundings the usefulness of SASS data is significantly reduced.
A numerical model for sulfur chemistry in warm‐frontal rainbands
Authors: Hegg Dean A. , Rutledge Steven A. , Hobbs Peter V.
Published: February 2008

A two‐dimensional kinematic model of warm‐frontal precipitation has been employed to model the sulfur chemistry of warm‐frontal rainbands. Analysis of the model results indicates that nucleation scavenging, in‐solution oxidation of SO2, and impaction of particulate sulfate by hydrometeors all contribute significantly to wet sulfate deposition, with nucleation scavenging generally the most important process. The model results also indicate that, in general, sulfate deposition will be a nonlinear function of the initial amount of sulfur species. Model predictions of sulfate concentrations in rain from warm‐frontal rainbands and the variability of these concentrations within individual rain events are in accord with observations.
Photodissociation of 16O18O in the atmosphere
Authors: Blake A. J. , Gibson S. T. , McCoy D. G.
Published: February 2008

Although 16O18O is a minor constituent of the atmosphere, a recent estimate vindicated that its photodissociation rate may be significant because of selective absorption in the region of the Schumann‐Runge bands as a result of isotope effects in the spectrum. We have calculated the 16O18O dissociation rate coefficient (J34) using a line‐by‐line model of the cross section in the band system and have found that at altitudes between 50 km and 80 km it is of the order of 10 times the dissociation rate coefficient for 16O2 (J32).The total 16O18O dissociation rate contributes a maximum of 3% of the O2 photodissociation, an order of magnitude less than the previous estimate. Theoretical values of the spectroscopic constants for 16O18O are given.
Measurements of stratospheric NO2 from the solar mesosphere explorer satellite: 2. General morphology of observed NO2 and derived N2O5
Authors: Solomon S. , Mount G. H. , Zawodny J. M.
Published: February 2008

Observations of NO2 densities from 28 to 40 km as measured by the Solar Mesosphere Explorer (SME) satellite are compared to model calculations for the month of January. Low densities are obtained in the tropics and in high latitude winter, with much larger values in the summer middle and high latitude regions in both the observations and the model. The reasons for areas of agreement and disagreement between the model and the observations are explored. The observed NO2 distribution is also used to infer the N2O5 distribution based on presently accepted chemistry and suggests that very large amounts of N2O5 are present in high latitude winter.
Lightning phenomenology in the Tampa Bay area
Authors: Peckham David W. , Uman Martin A. , Wilcox Chester E.
Published: February 2008

A lightning locating system employing two wideband, gated magnetic direction finders was used to study the negative cloud‐to‐ground lightning in 111 storms that occurred on 8 days during August 1979 in the Tampa Bay area of Florida. The storms were classified as (1) single‐peak storms—spatially isolated groupings of lightning whose cloud‐to‐ground flashing rate vs. time curves exhibited a single peak; (2) multiple‐peak storms—spatially isolated groupings of lightning with multiple‐peak flashing rates; and (3) storm systems—two or more related single‐peak and/or multiple‐peak storms. The following parameters are given for single‐peak storms, multiple‐peak storms, and storm systems: duration, area, number of ground flashes, mean ground flash density, mean ground flashing rate, and maximum ground flashing rate averaged over a 5‐min interval. Ground flash counts are corrected for the location system detection efficiency, which varied from about 75% at close range to about 55% at 100 to 150 km. The mean duration of single‐peak storms, multiple‐peak storms, and storm systems was 41, 77, and 130 min, respectively; the mean area 103, 256, and 900 km2, respectively; and the mean number of lightning flashes to ground 73, 270, and 887, respectively. The mean ground flash density for single‐peak storms, multiple‐peak storms, and storm systems was 18×10−3, 15×10−3, and 9.7×10−3 km−2 min−1, respectively; and the mean ground flashing rate 1.7, 3.4, and 6.8 min−1, respectively. The highest maximum ground flashing rate averaged over a 5‐min interval for all single‐peak storms, multiple‐peak storms, and storm systems was 17, 22, and 32 min−1, respectively, while the mean of the maximum flashing rates was 3.7, 7.3, and 14 min−1, respectively. The relation between storm duration D in minutes and number of ground flashes Ng for single‐ and multiple‐peak storms can be described by log10 Ng = 0.014D + 1.2.
The “rain gush”, lightning, and the lower positive charge center in thunderstorms
Authors: Jayaratne E. R. , Saunders C. P. R.
Published: February 2008

Laboratory studies of charge transfer, when vapor‐grown ice crystals bounce off a hailstone in simulated thunderstorm conditions, have shown that the sign and magnitude of the charge separated is a sensitive function of the cloud and cloud particle properties. In general, at temperatures colder than −20°C, hail becomes negatively charged, but at warmer temperatures it becomes positively charged. The formation of the lower positive charge center in thunderstorms and the initiation of a lightning flash which precedes the commonly observed gush of rain on the ground may be explained in terms of this charging process.
Eddy correlation measurements of atmospheric fluxes of ozone, sulphur, and particulates during the Champaign Intercomparison Study
Authors: Neumann H. H. , Den Hartog G.
Published: February 2008

Atmospheric fluxes of momentum, sensible heat, water vapor, ozone, and sulphur were measured on 10 days during the intercomparison study. Computed mean daytime (average z/L = −0.33) deposition velocities were 0.47 cm/s for ozone and 0.33 cm/s for sulphur, while for measurements during the early evening (average z/L = 0.27), the mean deposition velocities decreased to 0.35 and 0.21 cms, respectively. These deposition velocities have been corrected to account for the slow time response (time constant near 1.1 s) of the pollutant analyzers. The corrections were based on computed effects of a similar time response on temperature‐vertical velocity cospectra. These were found to be stability dependent and ranged from about an additional 20% in unstable atmospheres to factors of 2–3 for stable conditions. Eddy correlation measurements were also attempted for particulates using a laser particle spectrometer. Subsequent analysis revealed that for our combinations of sample flow rate and the ambient concentrations, deposition velocities were too small to be distinguished from the inherent Poisson uncertainty in particle counting. This implied that for particles of diameters 0.1–0.5 μm deposition velocities were less than 0.05 cm/s, assuming no source for particles below our measuring height.
A coupled one‐dimensional radiative‐convective, chemistry‐transport model of the atmosphere: 1. Model structure and steady state perturbation calculations
Authors: Owens A. J. , Hales C. H. , Filkin D. L. , Miller C. , Steed J. M. , Jesson J. P.
Published: February 2008

An atmosphere model composed of a narrow band radiative‐convective (RC) code coupled with a one‐dimensional chemistry and transport code is described. The RC model, formulated in log‐pressure coordinates, includes accurate solar absorption calculations for O3, O2, H2O, and CO2. Infrared heating and cooling by CO2, O3, and H2O are calculated with a narrow band formulation, while broader band formulations are used for CH4, N2O, CFC 11, and CFC 12. The atmospheric chemistry and transport model uses photochemical reaction rate data from Jet Propulsion Laboratory publication 82–57. The calculated steady state atmospheric response to several potential perturbations is discussed. Doubling the atmospheric CO2 level yields a change in total ozone of +2.9% and a surface temperature increase of 1.7 K. The continued release of chlorofluorocarbons (CFC's) alone at nominal rates gives a calculated column ozone change of −5.7% at steady state, while for a combined 2×CO2+CFC perturbation the result is −3.5%. Ozone perturbations due to increases in N2O, CH4, and aircraft are also discussed. Two coupled scenarios including projected changes that may occur in about 100 years due to all these identified man‐made perturbations are discussed. The calculated ozone column changes are −4.5% and +1.5%, assuming fixed and doubled methane source strengths, respectively.
Seasonal contributions to the climatic variations recorded in tree ring deuterium/hydrogen data
Authors: Yapp Crayton J. , Epstein Samuel
Published: February 2008

Tree ring δD records do not always reflect variations in the average annual δD values of local precipitation, but may instead record changes in the δD values of seasonal components of precipitation. The δD values measured for tree ring sequences from the three trees in this study are correlated with variations in summer climatic conditions at each of the sites. The D/H ratios in an aspen from Fairbanks, Alaska, correlate with summer temperatures in Fairbanks. An aspen which grew near Anchorage, Alaska, and a pine located near Seeley Lake, British Columbia, contain δD records which correlate with the amount of summer precipitation at their respective sites. The δD variations of the two Alaskan aspens are correlated for the five 5‐year sample intervals which they have in common. It is emphasized that a correlation between tree ring δD variations and a local seasonal climatic parameter for a given tree does not imply that all trees in that area will exhibit similar correlations. The site and growth conditions of individual trees will probably determine what climatic signal is contained in the D/H records of each.
Characteristics of the radiation fields from lightning in Sri Lanka in the tropics
Authors: Cooray Vernon , Lundquist Stig
Published: February 2008

Characteristics of the radiation fields from (1) stepped leader, (2) return strokes, and (3) cloud flashes in the tropics are presented. The separation between the successive leader pulses immediately preceding the return strokes are distributed over the range of 4–40 μs with a mean value of 12 μs. The ratio of the amplitude of the last leader pulse to that of the return stroke is log‐normally distributed with mean and standard deviation of 0.1 and 0.03, respectively. A correlation between the amplitude of the last leader pulse and the return stroke radiation field peak is observed. Consequences of this correlation are interpreted using the transmission line return stroke model. The initial peak of the return stroke radiation field is followed by several subsequent peaks. The time intervals between the successive peaks and their amplitudes are studied and compared with those observed in Florida. The zero crossing time of the first stroke radiation fields are distributed over the range of 40–160 μs, with a mean and standard deviation of 95 μs and 30 μs, respectively. The corresponding values for the subsequent strokes are 15–75 μs, 42 μs, and 14 μs, respectively. The separation between the subsequent strokes are distributed log normally with a mean and standard deviation of 91 ms and 62 ms, respectively. The average number of strokes per flash is 3.2. Characteristics of a particular type of radiation field pulses from cloud flashes are presented. Initial polarity of these pulses is opposite to that of the return strokes. The amplitudes of these pulses are about 0.2–0.5 of the return stroke amplitudes. Total duration of these pulses is about 70 μs, with initial half‐cycle duration of about 10 μs.
Photographic verification of continuing current in positive cloud‐to‐ground flashes
Authors: Rust W. David , MacGorman Donald R. , Taylor William L.
Published: February 2008

Earlier studies based on electric field change data have presented evidence for the frequent occurrence of continuing current in positive cloud‐to‐ground (+CG) lightning. We present photographic verification of continuing current from four +CG flashes. The polarity of these flashes was determined from coincidence of fast electric field waveforms with the return stroke image from streak‐film photographs and television recordings. Luminosity from continuing current is usually apparent during the initial slow field change after the return stroke but is absent during later stages of this field change.
Electron waves in the electrical breakdown of gases, with application to the dart leader in lightning
Authors: Jurenka H. , Barreto E.
Published: February 2008

The fluid dynamical analysis of an electron gas has been recently reviewed and applied to the final stages of an electrical breakdown in gases at atmospheric pressure. In particular, it has been used to describe the wavelike propagation of luminous pulses (ionizing waves) that move with speeds of 106–107 m/s. Because of the complexity of the fluid equations, the usual attempts to find shocklike solutions use numerical methods. In an attempt to find analytical solutions, we have reduced the original system of electron fluid equations (continuity, momentum, and energy conservation) and Maxwell's equations to single nonlinear differential equations. These model equations were solved analytically. Here, this analysis is improved by including a source of electrons due to collisional ionization, as well as the term that takes into account the changes in the cross‐sectional area of an ionized channel. In order to be consistent with the concept of a weakly ionized gas, the source term has to be small. The dominant force term that controls the wave motion (in or against the externally applied electrical field, as observed experimentally) is still the electron pressure gradient. The formation, propagation, and damping of electron waves in electrical breakdown of gases are discussed. The results obtained are used to describe the properties and propagation characteristics of a dart leader in lightning. In the fluid dynamical approach, the dart leader is regarded as a compressional wave in an electron fluid component, produced by a rapid charge accumulation at the top of a lightning channel. It moves toward the earth along a decaying channel, formed by a return stroke, with speeds of 106 to 3×107 m/s. The speed is shown to be linearly proportional to the electron number density gradient, and inversely proportional to the number density of neutral molecules. Dart leader propagates without significant damping as long as the electron pressure gradient is externally maintained by continuous current flow. The observed luminous extent of a dart leader (on average ∼50 m) does not represent its true length. It is interpreted as the result of a collisional ionization in the wake of a dart leader, due to the electron temperature increase at its wave front.
Lightning on other planets
Authors: Rinnert K.
Published: February 2008

The necessary conditions for producing lightning discharges, the experimental possibilities for investigating extraterrestrial lightning, and the scientific objectives of planetary lightning research are briefly discussed. Present knowledge on the composition, structure, and dynamics of the atmospheres for the extraterrestrial planets and the satellites Io and Titan are reviewed in terms of their importance for the production of lightning. From the knowledge on planetary atmospheres, intensive lightning activity can be expected to exist in the Jupiter and Saturn cloud systems; this is less conclusive for Venus and unlikely for the other bodies. Electrical activity is not completely ruled out for Martian dust storms. Optical and RF wave measurements from spacecraft have yielded evidence of possible lightning activity on Venus, Jupiter, and Saturn. These observations are reviewed and discussed. The conclusion that the optical and/or RF emissions are definitely from lightning is not unambiguous and based on poor data bases. There are no coincidence measurements of optical and RF pulses, and there is no information on the characteristics of individual pulses, which would help to clarify the source.
Measurements of peroxides in cloudwater and rain
Authors: Kelly Thomas J. , Daum Peter H. , Schwartz Stephen E.
Published: February 2008

Measurements of total peroxide content are reported for 190 cloud water samples from nonsupercooled stratiform clouds, and for 54 rain samples, collected at several nonurban sites in the eastern United States. Observed aqueous peroxide concentrations ranged from less than 0.1 μM to over 100 μM, with rain samples, precipitating cloudwater samples, and nonprecipitating cloudwater samples all exhibiting median values of less than 10 μM and similar concentration distributions. Specific analyses for H2O2 on 48 of the samples showed that in the majority of samples tested, H2O2 was the sole contributor to the total peroxide concentration, but in some samples, substantial signal was observed after selective destruction of H2O2, possibly indicating the presence of organic peroxides. Calculation of the total potential partial pressure of H2O2 for the samples collected in nonprecipitating clouds, using the measured aqueous concentrations and cloud liquid water content values, indicates a median potential partial pressure of H2O2 of 0.1 ppbv, and a maximum value of approximately 1 ppbv, Gaseous SO2 and aqueous peroxide were rarely simultaneously present in substantial concentrations; generally one reactant was present in great excess over the other, consistent with the occurrence of the aqueous phase reaction of peroxide with S(IV) in which one or the other species is the limiting reagent. Evaluation of the rates of S(IV) oxidation by peroxide and ozone, under conditions representative of the clouds sampled in this study, indicates that the former reaction, but not the latter, can produce substantial acidification in such clouds.
Particle size distribution of lipids in aerosols off the coast of Peru
Authors: Schneider Jürg K. , Gagosian Robert B.
Published: February 2008

Lipid components in aerosols were characterized as a function of particle size from samples collected in spring 1981 off the coast of Peru as part of the Sea‐Air Exchange Program. The investigation was designed to determine (1) the particle size distributions for different terrestrial and marine source marker organic compounds close to their source, (2) the importance of the atmosphere as an input source to the sea for terrestrial compounds, and (3) the significance of recycling of the terrestrial components of these compound classes from seawater back into the atmosphere. The terrestrially derived components of three compound classes (fatty alcohols, wax esters, and n‐alkanes) were found to have similar particle size distributions. They are relatively evenly distributed over the whole particle size range, suggesting (1) little modification of the wide spectrum of plant‐ and soil‐derived particles by short‐range transport offshore and (2) insignificant gas‐particle partitioning for these materials. On the other hand, the terrestrially derived fatty acid salts show a different particle size distribution probably due to their very different physicochemical properties. The atmospheric flux to the sea surface via both wet and dry deposition is not significant in relation to the flux through the euphotic zone of the water column for two lipids of terrestrial origin, octacosanoic acid and 24‐ethylcholest‐5‐en‐3β‐ol. No significant recycling from the sea surface back into the atmosphere was observed for lipid compounds of terrestrial origin. Marine‐derived sterols, fatty alcohols, and fatty acid salts were found in high concentrations in surface microlayer samples. The enrichment of these compound classes is about 2–4 orders of magnitude relative to bulk seawater.
Tentative identification of the 780‐cm−1 ν4 band Q branch of chlorine nitrate in high‐resolution solar absorption spectra of the stratosphere
Authors: Rinsland C. P. , Goldman A. , Murcray D. G. , Murcray F. J. , Bonomo F. S. , Blatherwick R. D. , Devi V. Malathy , Smith M. A. H. , Rinsland P. L.
Published: February 2008

Absorption by the Q branch of the ν4 band Of CIONO2 at 780.2 cm−1 has been tentatively identified in a series of 0.02‐cm−1‐resolution balloon‐borne solar absorption spectra of the stratosphere. The spectral data were recorded at sunset from a float altitude of 33.5 km during a balloon flight from Holloman Air Force Base (32.8°N, 106.0°W) near Alamogordo, New Mexico, on March 23, 1981. A preliminary CIONO2 vertical profile has been determined from the stratospheric spectra by using the technique of nonlinear least squares spectral curve fitting and new spectroscopic parameters deduced from high‐resolution laboratory spectra of CIONO2 and O3.
Contribution of stratospheric winds to annual and semiannual fluctuations in atmospheric angular momentum and the length of day
Authors: Rosen Richard D. , Salstein David A.
Published: February 2008

Stratospheric zonal wind values are used in conjunction with operationally produced tropospheric data and contemporaneous earth rotation data to study the angular momentum budget of the global atmosphere‐earth system on seasonal time scales. Previous imbalances found in this budget at the semiannual period are considerably reduced with the inclusion of the stratospheric data. At the annual period the momentum contained in stratospheric winds also appears large enough to account for the previous discrepancies, although there is more uncertainty at this period because of the sizeable disagreements that exist between the tropospheric time series. Despite this and the limitation of our study to a 2‐year sample, our results nevertheless suggest that tropospheric plus stratospheric winds can fully account for seasonal, nontidal changes in the length of day without invoking other geophysical processes. The amplitude and phase of the seasonal components of momentum fluctuations within the stratosphere resemble those which can be inferred from some earlier studies. Annual variations in the stratosphere's globally integrated momentum result from opposing contributions by the two hemispheres. Semiannual variations in this quantity result mainly from behavior in the tropics.
Particulate sulfate and nitrate in the boundary layer over the North Pacific Ocean
Authors: Prospero J. M. , Savoie D. L. , Nees R. T. , Duce R. A. , Merrill J.
Published: February 2008

Concentrations of aerosol NO3− and non‐sea‐salt (nss) SO4= have been measured in samples collected weekly between January 1981 and March 1982 at seven stations in the Sea‐Air Exchange Program Asian Dust Network in the North Pacific between 4°N and 53°N. Mean NO3− concentrations were relatively uniform, ranging between 0.18 and 0.35 μg/m3 STP; mean nss SO4= ranged from 0.37 to 1.20 μg/m3 STP. At most stations there was no consistent correlation between NO3− and nss SO4=or between these species and mineral aerosol. At Midway these species did covary in a clear and consistent manner; this correlation appears to be forced by large‐scale meteorological factors. In some cases, high nss SO4= concentrations were associated with high mineral aerosol concentrations; this suggests that the SO4= in these episodes was transported from the continents. A particularly impressive event occurred in May 1981, when much of the North Pacific region was affected by extremely high nss SO4= concentrations; evidence suggests that the SO4= was not derived from the soil material itself. At Fanning Island, NO3− concentrations showed a strong seasonal variation; there is evidence that the high NO3− concentrations are attributable to transport from the continents. In contrast, nss SO4= concentrations at Fanning were relatively constant throughout the year, and they were consistent with recent estimates of the oceanic emission rates of sulfur as dimethyl sulfide. The NO3− data from the tropics suggest that there is a relatively uniform background concentration of about 0.10 μg/m3 STP; this concentration is close to that recently predicted by models that assume only lightning and the stratosphere as sources for NOx.
The H2SO4‐HNO3‐NH3 system at high humidities and in fogs: 1. Spatial and temporal patterns in the San Joaquin Valley of California
Authors: Jacob Daniel J. , Munger J. William , Waldman Jed M. , Hoffmann Michael R.
Published: February 2008

A systematic characterization of the atmospheric H2SO4‐HNO3‐NH3 system was conducted in the fog water, the aerosol, and the gas phase at a network of sites in the San Joaquin Valley of California. Spatial patterns of concentrations were established that reflect the distribution of SO2, NOx, and NH3 emissions within the valley. The concept of atmospheric alkalinity was introduced to interpret these concentrations in terms of the buffering capacity of the atmosphere with respect to inputs of strong acids. Regions of predominantly acidic and alkaline fog water were identified. Fog water was found to be alkaline in most of the valley, but small changes in emission budgets could lead to widespread acid fog. An extended stagnation episode was studied in detail: progressive accumulation of H2SO4‐HNO3‐NH3 species was documented over the course of the episode and interpreted in terms of production and removal mechanisms. Secondary production of strong acids H2SO4 and HNO3 under stagnant conditions resulted in a complete titration of available alkalinity at the sites farthest from NH3 sources. A steady SO2 conversion rate of 0.4–1.1% h−1 was estimated in the stagnant mixed layer under overcast conditions and was attributed to nonphotochemical heterogeneous processes. Removal of SO2 was enhanced in fog, compared to nonfoggy conditions. Conversion of NOx to HNO3 slowed down during the stagnation episode because of reduced photochemical activity; fog did not appear to enhance conversion of NOx. Decreases in total HNO3 concentrations were observed upon acidification of the atmosphere and were attributed to displacement of NO3− by H2SO4 in the aerosol, followed by rapid deposition of HNO3(g). The occurrence of fog was associated with general decreases of aerosol concentrations due to enhanced removal by deposition.
The H2SO4‐HNO3‐NH3 system at high humidities and in fogs: 2. Comparison of field data with thermodynamic calculations
Authors: Jacob Daniel J. , Waldman Jed M. , Munger J. William , Hoffmann Michael R.
Published: February 2008

Concentrations of HNO3(g) and NH3(g) determined in the field were compared to predictions from aerosol equilibrium models. The products of HNO3(g) and NH3(g) concentrations measured under cool and humid nonfoggy conditions agreed in magnitude with predictions from a comprehensive thermodynamic model for the atmospheric H2SO4‐HNO3‐NH3‐H2O system. Observed concentrations of NH3(g) in fogs were generally consistent with those predicted at equilibrium with fog water, but important discrepancies were noted in some cases. These discrepancies may be due to fluctuations in fog water composition over the course of sample collection or to the sampling of nonfoggy pockets of air present within the fog. Detectable concentrations of HNO3(g) (up to 23 neq m−3) were often found in fogs with pH < 5 and were attributed to the sampling of nonfoggy air or to the slow rate of HNO3(g) diffusion to fog droplets. Concentrations of HNO3(g) in fogs with pH > 5 were below the detection limit of 4–8 neq m−3.
Stratospheric photochemical studies using Nimbus 7 data: 2. Development of inferred trace specie distributions
Authors: Callis Linwood B. , Natarajan Murali , Boughner Robert E. , Russell James M. , Lambeth James D.
Published: February 2008

The limb infrared monitor of the stratosphere, stratospheric and mesospheric sounder, and solar backscatter ultraviolet satellite measurements of stratospheric T, O3, NO2, HNO3, H2O, CH4, and solar flux are used in conjunction with a zero‐dimensional, stratospheric, photochemical model to infer distributions of other constituents. For periods in October and December 1978 and in March and May 1979, latitude‐altitude distributions of O(3P), O(1D), OH, HO2, H2O2, NO, NO3, N2O5, HNO4, HCℓ, Cℓ, CℓO, CℓNO3, HOCℓ, total odd nitrogen, and total odd hydrogen are derived and presented. Results are presented for altitudes from 20.5 km to 53.5 km and for latitudes from 60°S to 80°N with some variation depending upon season. The techniques used are described. They require the specification of the distribution of the total odd chlorine due to the absence of satellite measurements of chlorine species. Two‐dimensional model results for odd chlorine, scaled to provide the required level of total odd chlorine for the 1978–1979 time period, were used. Sensitivity of results to input values of CH4 (for which some extrapolation was required) and odd chlorine is presented and discussed. Uncertainties in the inferred species due to uncertain chemical rates, cross sections, and measurement errors are presented. Results provide a useful climatology of these infrequently measured species for the four time periods. Of particular interest are maximum odd nitrogen (≡NO + NO2 + NO3 + HNO3 + HNO4 + CℓNO3 + 2 × N2O5) levels which range between 24 and 27 ppbv, significantly higher than predicted by most contemporary models.
On the consequence of a tropospheric CH4 increase to the exospheric density
Authors: Ehhalt D. H.
Published: February 2008

It is argued that the past increase in tropospheric CH4 of about 1 ppm should have caused an increase in the exospheric H atom concentration by about 30%, with a corresponding increase in the total density in the hydrogen‐dominated part of the exosphere.
Lightning: A possible source of stratospheric odd nitrogen
Authors: Ko Malcolm K. W. , McElroy Michael B. , Weisenstein Debra K. , Sze Nien Dak
Published: February 2008

It is argued on the basis of a two‐dimensional stratospheric model that upward transport of oxides of nitrogen produced by lightning in the tropical troposphere can significantly enhance the concentrations of NOY, the composite of all forms of odd nitrogen, in the lower stratosphere. The impact can be as large as a factor of 10 at 22 km near the equator, dropping to less than 50% above 30 km. Inclusion of the lightning source of NOY in the model results in improved agreement with available satellite data for the sum of NO2 and HNO3. Lightning is important even if only 5% of the nitrogen oxides produced enters the stratosphere. This amounts to ∼2 × 105 t N yr−1 and is equivalent to about one third of the global production from in situ photochemical reaction of N2O with O(1D).
Short‐term variability of nitrogen dioxide in the winter stratosphere
Authors: Zawodny Joseph M.
Published: February 2008

Measurements of limb radiance from the Solar Mesosphere Explorer (SME) satellite are used to infer the NO2 density at the 10‐ and 16‐mbar pressure levels from January 1 to March 31 of 1982. A photochemical‐dynamical model is developed using the presently accepted chemistry of the NOx family. The dynamical model produces isentropic trajectories which simulate the history of air parcels. From the trajectories the photochemical model calculates NO2 densities, which are compared to those observed by SME. Although the model generally reproduces the spatial and temporal variations rather well, some disagreement was noted for conditions of exceptionally low temperatures. Further analysis indicates that the temperature sensitivity of the N2O5 photolysis cross sections may be overestimated at low temperatures.