bluuebunny/crossref_metadata_2025 huggingface dataset:
In situ stratospheric measurements of HNO3 and HCl Near 30 km using the balloon‐borne laser in situ sensor tunable diode laser spectrometer
Authors: May R. D. , Webster C. R.
Published: February 2008

In situ stratospheric measurements of the concentrations of the reservoir species HNO3 and HCl made during two flights of the high‐resolution (0.0005 cm−1) balloon‐borne laser in situ sensor (BLISS) instrument from Palestine, Texas, are reported. A measured HNO3 volume mixing ratio of 4.3 parts per billion by volume (ppbv) at 31 km altitude is about 1 ppbv larger than previously reported measurements at 32°N. An HCl mixing ratio of 1.6 ppbv at 29 km is in agreement with values obtained from earlier remote sensing techniques within the experimental uncertainties. Upper limits at 31 km of 0.4 ppbv for H2O2 and 0.2 ppbv for HOCl are also derived from analyses of spectra recorded near 1252 cm−1.
Lagrangian photochemical modeling studies of the 1987 Antarctic spring vortex: 2. Seasonal trends in ozone
Authors: Austin J. , Jones R. L. , McKenna D. S. , Buckland A. T. , Anderson J. G. , Fahey D. W. , Farmer C. B. , Heidt L. E. , Proffitt M. H. , Tuck A. F. , Vedder J. F.
Published: February 2008

A photochemical model consisting of 40 species and 107 reactions is integrated along 80 day air parcel trajectories calculated in the lower stratosphere for the springtime Antarctic. For the trajectory starting at 58°S, which may be regarded as outside the circumpolar vortex, only a small change in O3 occurs in the model. In contrast, for the air parcel starting in the vortex at 74°S, the O3 concentration is reduced by 93% during the 80 days from the beginning of August to late October. The model results for several species are compared with measurements from the Airborne Antarctic Ozone Experiment and, in general, good agreement is obtained. In the model, the denitrification of the air parcels in polar stratospheric clouds increases the amount of chlorine present in active form. Heterogeneous reactions maintain high active chlorine which destroys O3 via the formation of the ClO dimer. Results of calculations with reduced concentrations of inorganic chlorine show considerably reduced O3 destruction rates and compare favorably with the behavior of total O3 since the late 1970s. The remaining major uncertainties in the photochemical aspects of the Antarctic ozone hole are highlighted.
Reconstruction of the constituent distribution and trends in the Antarctic polar vortex from ER‐2 flight observations
Authors: Schoeberl Mark R. , Lait Leslie R. , Newman Paul A. , Martin Russell L. , Proffitt Michael H. , Hartmann Dennis L. , Loewenstein Max , Podolske James , Strahan Susan E. , Anderson James , Chan K. Roland , Gary Bruce
Published: February 2008

During the Airborne Antarctic Ozone Experiment, the high‐altitude ER‐2 aircraft measured ozone, chlorine monoxide, and nitrous oxide concentrations in the south polar region. These measurements have been analyzed using conservative coordinate transformations to potential temperature‐N2O and potential temperature‐potential vorticity space. The latter transformation is equivalent to interpreting trace species observations within the modified Lagrangian mean (MLM) coordinate system. With certain assumptions about zonal symmetry, this transformation allows for the interpretation of chemical changes of constituents independent of meteorological variability. The method also allows for a reasonable reconstruction of constituent distributions outside the aircraft flight track. Our analysis shows that the MLM transformed ozone concentration decreases at about 0.06 ppmv (parts per million by volume) per day between 20 and 16 km altitude inside the polar vortex during the mid‐August to mid‐September period. These ozone changes must be chemical in origin; they are also collocated with the region of high ClO. Outside the CPR (chemically perturbed region) at the highest aircraft altitudes, ozone systematically increases, suggesting a diabatic cooling of the order of 0.3–0.6 K/d. Within the CPR the cooling rate appears to be less than 0.2 K/d. The MLM analysis technique creates a picture of the general chemical structure of the Austral polar vortex which shows that air deep within the chemically perturbed region has subsided substantially in relation to the air outside. However, there is also a tongue of high ozone air which extends from mid‐latitudes downward along the stratospheric jet at 65°W and 6O°S. An examination of the last three flight days, September 20–22, 1987, shows that during this period the polar vortex shifts systematically equatorward along the Antarctic Peninsula. Apparent changes in the constituents measured over this period result from sampling air progressively further into the vortex.
Forcing of late Cenozoic northern hemisphere climate by plateau uplift in southern Asia and the American west
Authors: Ruddiman W. F. , Kutzbach J. E.
Published: February 2008

Geologic evidence indicates that net vertical uplift occurred on a large (kilometer) scale and at accelerating rates during the middle and late Cenozoic in plateaus of southern Asia and the American west. Based on this evidence, General Circulation Model sensitivity tests were run to isolate the unique effects of plateau uplift on climate. The experiments simulated significant climatic changes in many places, some far from the uplifted regions. The basic direction of most of these simulated responses to progressive uplift is borne out by changes found in the geologic record: winter cooling of North America, northern Europe, northern Asia, and the Arctic Ocean; summer drying of the North American west coast, the Eurasian interior, and the Mediterranean; winter drying of the North American northern plains and the interior of Asia; and changes over the North Atlantic Ocean conducive to increased formation of deep water. The modeled changes result from increased orographic diversion of westerly winds, from cyclonic and anticyclonic surface flow induced by summer heating and winter cooling of the uplifted plateaus, and from the intensification of vertical circulation cells in the atmosphere caused by exchanges of mass between the summer‐heated (and winter‐cooled) plateaus and the mid‐latitude oceans. Disagreements between the geologic record and the model simulations in Alaska and the Southern Rockies and plains may be related mainly to the lack of narrow mountain barriers in the model orography. Taken together, the observed regional trends comprise much of the pattern of “late Cenozoic climatic deterioration” in the northern hemisphere that culminated in the Plio‐Pleistocene ice ages. The success of the uplift sensitivity experiment in simulating the correct pattern and sign of most of the observed regional climatic trends points to uplift as an important forcing function of late Cenozoic climatic change in the northern hemisphere at time scales longer than orbital variations; however, the modest amplitude of the uplift‐induced cooling simulated at high latitudes indicates a probable need for additional climatic forcing.
El Chichon volcanic aerosols: Impact of radiative, thermal, and chemical perturbations
Authors: Michelangeli Diane V. , Allen Mark , Yung Yuk L.
Published: February 2008

We examine the consequences of the eruption of the El Chichon volcano on the Earth's stratospheric chemistry. Formed after the eruption, the volcanic aerosol cloud, with a peak particle density at 27 km, was very efficient at altering the radiation field. The results of a one‐dimensional radiative transfer model show that the total radiation increased by 8% within the aerosol layer longward of 3000 Å. At certain altitudes and wavelengths below 3000 Å, the total radiation decreased by 15%. Consequently, there are changes in the photolysis rates obtained with a one‐dimensional photochemical model: for example, O2 photodissociation rate constants decrease by 10%, while O3 photodissociation rate constants increase by a comparable amount. A combination of this radiation change and the effect of a temperature variation of a few degrees causes the abundance of O3 to decrease by 7% at 24 km, in good agreement with the Solar Backscattered Ultraviolet experiment (SBUV) measurements of a 5–10% decrease. The combined radiative and thermal perturbations on the concentrations of O, O(1D), OH, HO2, H2O2, NO, NO2, NO3, N2O5, HNO3, HO2NO2, Cl, ClO, ClO2, HOCl, ClNO3, and HCl are computed and presented in detail. However, these changes as calculated are insufficient to explain the observations of significant decreases in NO and NO2 and increases in HCl. A heterogeneous reaction catalyzed by aerosol surfaces which transforms ClNO3 into HCl provides a pathway for sequestering NOx, and at the same time reduces ClNO3 in favor of HCl. The inclusion of this reaction in the model leads to a satisfactory single‐step explanation of the otherwise puzzling observations of NO, NO2, and HCl. The observed lack of change in HNO3 cannot be explained by this hypothesis. The effects of a number of heterogenous reactions, some believed to be important for the Antarctic stratosphere, have been assessed with our model. We also examine the hypothesis of direct injection of gases from the volcano into the stratosphere. Only an unrealistically large injection (60% column increase above 12 km) results in an HCl increase in agreement with observations. An equally large water injection decreases HCl, and decreases the NO and NO2 by as much as 20%, but still does not simulate the observed NOx decrease.
Current and electric field derivatives in triggered lightning return strokes
Authors: Leteinturier C. , Weidman C. , Hamelin J.
Published: February 2008

Forty simultaneous, submicrosecond time‐resolved measurements of triggered lightning returnstroke current (I), current derivative (dI/dt), and electric field derivative (dE/dt) were made in Florida and France in 1985 and 1986. Peak currents ranged from about 5 to 50 kA, peak dI/dt amplitudes from 60 to 260 kA/μs in 1985 and from 20 to 140 kA/μs in 1986. The mean peak dI/dt values, 111 kA/μs (1985) and 68 kA/μs (1986), are 2–3 times higher than data from instrumented towers, and peak I and dI/dt appear to be positively correlated. The dE/dt and dI/dt waveform pairs have similar shapes, and the peak amplitudes are linearly proportional. Return‐stroke velocity, computed from the ratio of peak dE/dt and dI/dt signal amplitudes using an expression derived from the radiation field term of the transmission line model (TLM), averaged 2.9×108 m/s and 3.0×108 m/s in 1985 and 1986, respectively, which is about 2 times higher than most optical measurements. The TLM velocity may be erroneous because (1) the dE/dt measurement was made only 50 m from the lightning channel, where fields other than the radiation field component, that is near fields, may contribute to the total dE/dt and (2) fine structure on the measured E fields was not consistent with a single upwardly propagating return‐stroke current wave assumed by the TLM (two waves are more consistent).
A two‐dimensional stochastic‐dynamical quantitative precipitation forecasting model
Authors: Lee T. H. , Georgakakos K. P.
Published: February 2008

Presented is a two‐dimensional model for quantitative precipitation forecasting at spatial and temporal scales relevant to hydrologic forecasting. The model uses as input operational forecasts of surface air temperature, pressure and dew‐point temperature, and wind speed and direction at midtropospheric levels. Such forecasts are expected to be available at the spatial scales of the large‐scale numerical weather prediction models. The two‐dimensional precipitation model produces as an output mean areal precipitation at scales down to 100 km2 in space and 1 hour in time. Thermodynamics and microphysics are used to determine the source and sink terms in the conservation equation for the mass of condensed liquid water equivalent utilized by the model. A state estimator has been designed to update precipitation model states from observations of precipitation in real time and to produce estimates of the variance of the precipitation forecasts. Preliminary tests of the model with hourly data from Oklahoma appear encouraging. The model developed offers a link in the operational environment between the prediction scales of the operational weather prediction models and the hydrologic prediction scales.
Variability of summer Florida rainfall and its significance for the estimation of rainfall by gages, radar, and satellite
Authors: Seed A. , Austin G. L.
Published: February 2008

Simulations based on a month of radar data from the Patrick Air Force Base radar in Florida give the following results for the estimation of daily rainfall amounts over the 124,000 km2 area covered by the radar: (1) 30‐min sampling by a perfect satellite sensor will increase the rainfall measurement error by 7% compared with 5‐min radar sampling, (2) if the instrument is only able to determine the raining area and a good climatological rainfall rate is available, then the measurement error is increased to 35%, and (3) exceptionally dense gage networks are needed to estimate daily convective rainfall (for example, a network with 625 km2 per gage would be required to equal a minute rain‐area‐only technique.) For monthly areal mean rainfall, the proposed Tropical Rain Measuring Mission (TRMM) sampling strategy with a perfect satellite sensor gives errors of the order of 22%. A 30‐min rain‐area‐only technique combined with a good climatological rainfall rate yields an error of at least 32%. It would seem therefore that the main contribution of TRMM could be to provide good estimates of the mean climatological rainfall rate (given that it is raining), which could then be used with the geostationary weather satellite to provide the required monthly area rainfall estimates.
Origins and variations of nitrate in south polar precipitation
Authors: Legrand Michel R. , Kirchner Séverine
Published: February 2008

South polar firn cores spanning the last millennium have been analyzed to determine the nitrate background level of high‐latitude precipitation and its temporal variations. The resulting data reveal no evidence of a positive correlation between solar activity (11‐year solar cycle, low solar activity time periods, and solar proton events) and the NO3 content of south polar snow. These data therefore suggest that NOx production in the upper stratosphere, mesosphere, and thermosphere does not contribute significantly to the antarctic NO3 budget. This study of the NO3 content of high latitude precipitation suggests a major contribution by lightning (from a third to a half of the total) and by NOx produced in the lower stratosphere (approximately a third from N2O oxidation and to a lesser extent galactic cosmic rays) to the NO3 budget of this background atmosphere, the remaining portion being related to the present NOx surface sources of the southern hemisphere. For the first time, our data point to a decrease of NO3 content when very large amounts of sulfuric acid are present in South Pole snow layers. This observation suggests a possible interaction (via the hydroxyl radical) between S‐ and N‐derived species when large quantities of SO2 are injected by volcanic eruptions. Although the deposition mechanism of HNO3 in South Pole snow layers is far from well understood, our data suggest that only a minor amount of this compound is deposited directly on surface snow layers. Finally, the role played by particles (volcanic ash, terrestrial impurities, or ice particles) to enhance the uptake of odd nitrogen from the atmosphere by heteregeneous processes is discussed. In particular, it is suggested that in late winter, under certain meteorological conditions leading to ice particle formation, a significant uptake of HNO3 from the lower stratosphere can occur.
Laboratory studies on the stratospheric NOx production rate
Authors: Greenblatt Gary D. , Ravishankara A. R.
Published: February 2008

The chemistry of the production of NO in the stratosphere was examined in a two part study. First, the absolute quantum yield for the production of NO(2Π) + N(4S) from N2O photolysis at 193 run was measured to be less than 8×10−3. Second, in a new type of experiment, the yields of NO from the photolysis of N2O at 193 nm in N2O/O2/N2 and the photolysis of O3 at 248 nm in O3/N2O/O2/N2 mixtures were measured. The measured yields showed excellent agreement with NO yields predicted from a model using previously measured rate parameters. The results of this “integrated” experiment reduced the most probable uncertainty in the yield of NO from near 80% (calculated from the uncertainties in each individual step) to less than 30%.
Infrared spectroscopic detection of sulfur hexafluoride (sf6) in the lower stratosphere and upper troposphere
Authors: Rinsland C. P. , Brown L. R. , Farmer C. B.
Published: February 2008

Absorption by sulfur hexafluoride (SF6) has been detected in high‐resolution infrared solar spectra of the lower stratosphere and upper troposphere. The identification is based on measurements of the intense, unresolvedν3bandQbranch at 947.9 cm−1in solar occultation spectra recorded near 31°N and 47°S latitude by the Atmospheric Trace Molecule Spectroscopy (ATMOS) Fourier transform spectrometer on April 30 to May 1, 1985, during the Spacelab 3 shuttle mission. Vertical SF6volume mixing ratio profiles have been retrieved using an onion‐peeling nonlinear least squares spectral fitting procedure with SF6line‐by‐line Spectroscopic parameters generated recently by Bobin and coworkers from their analysis of the SF6ν3band. Between 12 and 18 km altitude, the region over which the retrievals are most accurate (about ±26% one sigma), the SF6volume mixing ratio is independent of altitude with an average measured value of 1.42 parts per trillion by volume (pptv) at 31°N latitude. There is evidence for a decline in the SF6volume mixing ratio with increasing altitude between 18 and 22 km, but the results are not conclusive because of the weakness of the absorption. Absorption by the SF6Qbranch is below the noise level of the spectra at tangent heights above ∼22 km. The measurements are compared with previously reported values and discussed in terms of the atmospheric lifetime of SF6, the long‐term trend of atmospheric SF6, and the possible role of SF6as an atmospheric greenhouse gas.
Two‐dimensional atmospheric transport and chemistry model: Numerical experiments with a new advection algorithm
Authors: Shia Run‐Lie , Ha Yuk Lung , Wen Jun‐Shan , Yung Yuk L.
Published: February 2008

Extensive testing of the advective scheme, proposed by Prather (1986), has been carried out in support of the California Institute of Technology–Jet Propulsion Laboratory two‐dimensional model of the middle atmosphere. We generalize the original scheme to include higher‐order moments. In addition, we show how well the scheme works in the presence of chemistry as well as eddy diffusion. Six types of numerical experiments including simple clock motion and pure advection in two dimensions have been investigated in detail. By comparison with analytic solutions it is shown that the new algorithm can faithfully preserve concentration profiles, has essentially no numerical diffusion, and is superior to a typical fourth‐order finite difference scheme.
The distribution of middle tropospheric carbon monoxide during early October 1984
Authors: Reichle Henry G. , Connors Vickie S. , Holland J. Alvin , Sherrill Robert T. , Wallio H. Andrew , Casas Joseph C. , Condon Estelle P. , Gormsen Barbara B. , Seiler Wolfgang
Published: February 2008

The Measurement of Air Pollution from Satellite (MAPS) experiment measured the distribution of middle tropospheric carbon monoxide (CO) from the space shuttle during October 1984. The data represent average mixing ratios in the middle troposphere between 57°N and 57°S. Approximately 75,000 individual CO measurements were obtained during the 9‐day mission. The data are presented in maps that show the CO mixing ratios averaged over 5° latitude by 5° longitude areas for 6 days of the mission. Comparisons with concurrent, direct measurements taken aboard aircraft show that the inferred concentrations are systematically low by 20–40% depending upon which direct measurement calibration standard is used. The data show that there are very large CO sources resulting from biomass burning over South America and southern Africa. Measured mixing ratios were high over northeast Asia and were highly variable over Europe.
Measurements of tropospheric nitric acid over the western United States and northeastern Pacific Ocean
Authors: LeBel P. J. , Huebert B. J. , Schiff H. I. , Vay S. A. , VanBramer S. E. , Hastie D. R.
Published: February 2008

During the August–September 1986 GTE/CITE 2 aircraft mission, more than 240 measurements of nitric acid (HNO3) were made in the free troposphere as well as in the boundary layer over the northeastern Pacific Ocean and western continental United States. Marine HNO3 measurement results were strikingly similar to results from GAMETAG and other past atmospheric field experiments. The marine boundary layer HNO3 average, 62 parts per trillion by volume (pptv), was one third lower than the marine free tropospheric average, 108 pptv, suggesting that the boundary layer is a sink for tropospheric nitric acid, probably by dry deposition. Nitric acid measurements on a nighttime continental flight gave a free tropospheric average of 218 pptv, substantially greater than the daytime continental free tropospheric five‐flight average of 61 pptv. However, the nighttime results may have been influenced by highly convective conditions that existed from thunderstorms in the vicinity during that night flight. Our continental boundary layer HNO3 average of 767 pptv is an order of magnitude greater than the free tropospheric average, indicating that the boundary layer is a source of free tropospheric HNO3. The distribution of continental boundary layer HNO3 data, from averages of 123 pptv over rural Nevada and Utah to 1057 pptv in the polluted San Joaquin Valley of California suggests a close tie between boundary layer HNO3 and anthropogenic activity.
Evidence of inertial oscillations of the surface wind at Marcus Island
Authors: Mori Yukihiro
Published: February 2008

Near‐inertial oscillations of the surface wind were observed at Marcus Island (24°N, 154°E) in the subtropical Pacific area. Kinetic energy spectra of the surface wind show a peak at a period of 1.1 days in the clockwise component spectrum. This period is slightly (6%) shorter than the local inertial period (1.2 days). The peak period varies slightly during the record analyzed, but tends to remain below the local inertial period. Complex demodulation with a filter shows that the large inertial amplitudes occur intermittently and decay rapidly. Most of the occurrences of large inertial events seem to be related to passing cold frontal systems or migrating low‐pressure systems.
Two‐dimensional modeling of the northern hemisphere high latitude lower stratosphere
Authors: Chipperfield M. P. , Pyle J. A.
Published: February 2008

The importance of chemical processes on polar stratospheric clouds (PSCs) has been investigated in the context of the reported ozone depletion in middle and high northern latitudes. Using a variety of PSC frequencies during the polar winter and early spring the observed ozone depletion can be reproduced in a two‐dimensional model of the atmosphere. Support for the mechanism is provided by the behavior of other model variables. For example, a ClO mixing ratio of more than 600pptv is predicted within the polar vortex; the ClONO2 column peaks around the edge, or ‘collar’, of the vortex. These and other results resemble the findings of recent Antarctic expeditions. In runs with low levels of chlorine, the presence of PSCs leads to ozone production due to the inhibition of the classical NOx catalytic destruction cycle. This could have implications for strategies to control chlorine‐containing compounds.
The behavior of some organic nitrates at Boulder and Niwot Ridge, Colorado
Authors: Ridley B. A. , Shetter J. D. , Walega J. G. , Madronich S. , Elsworth C. M. , Grahek F. E. , Fehsenfeld F. C. , Norton R. B. , Parrish D. D. , Hübler G. , Buhr M. , Williams E. J. , Allwine E. J. , Westberg H. H.
Published: February 2008

Observations show that the ratio of peroxypropionyl nitrate (PPN) to peroxyacetyl nitrate (PAN) increases to a maximum in the afternoon period at Boulder and at Niwot Ridge. In Boulder air and in easterly flow reaching Niwot Ridge, maximum average PPN/PAN ratios were near 15%, while in westerly flow or more remote continental air, the ratio was much smaller and averaged 4%. Relative to the PAN‐mixing ratios, methyl nitrate (MN) was less than 0.2% in the afternoon and less than 0.9% at night in Boulder air masses. The sum of ambient n‐propyl nitrate (NPN) and 2‐butyl nitrate (2BN) mixing ratios was also small, the diurnal average at Niwot Ridge being about 2% of the PAN‐mixing ratio. The diurnal average contribution of MN + PPN + (NPN+2BN) to the total odd nitrogen budget at Niwot Ridge was at most 4%, leaving a 21–27% shortfall between the sum of individual measurements of odd nitrogen species and the total odd nitrogen (NOy) measurement.
Atomic hydrogen and atomic oxygen density in the mesopause region: Global and seasonal variations deduced from Solar Mesosphere Explorer near‐infrared emissions
Authors: Thomas Ronald J.
Published: February 2008

Atomic oxygen and atomic hydrogen have been inferred from the hydroxyl airglow measurements on Solar Mesosphere Explorer (SME) spacecraft between 0.01 and 0.0013 mbar (80–93 km). This constitutes the first measurements of the seasonal and latitudinal variations of these atomic species, in the mesopause region. At night, atomic oxygen is directly proportional to the Meinel band emission of OH. During the day the emission is proportional to the product of ozone and hydrogen. Since daytime ozone is inferred from the O2(1Δg) emission, daytime hydrogen can be inferred. Daytime atomic oxygen is then inferred from the measured hydrogen and ozone. At levels where atomic oxygen is found by both methods (at 0.0032–0.0013 mbar or 88–93 km) the day and night atomic oxygen display the same relative seasonal variations. Very large annual and semiannual changes are found in the atomic hydrogen density between 80 and 93 km. At 40°N the summer‐to‐spring ratio of atomic hydrogen exceeds a factor of 4 at 0.01 mbar (80 km). Between 80 and 90 km the odd oxygen family is found to be almost entirely atomic oxygen. Its behavior is characterized by annual variations at 40° north and south and semiannual changes at the equator; in both cases the changes are a doubling from minimum to maximum. At least part of the mid‐latitude semiannual variation in ozone is found to be due to the product of two annually varying functions. The atomic oxygen is annual and maximizes in the winter while the ozone‐oxygen partitioning, controlled mostly by temperature, maximizes in the summer due to temperature changes.
Daytime turbulent exchange between the Amazon forest and the atmosphere
Authors: Fitzjarrald David R. , Moore Kathleen E. , Cabral Osvaldo M. R. , Scolar José , Manzi Antônio O. , de Abreu Sá Leonardo D.
Published: February 2008

Detailed observations of turbulence just above and below the crown of the Amazon rain forest during the wet season are presented. The forest canopy is shown to remove high‐frequency turbulent fluctuations while passing lower frequencies. Filter characteristics of turbulent transfer into the Amazon rain forest canopy are quantified. In spite of the ubiquitous presence of clouds and frequent rain during this season, the average horizontal wind speed spectrum and the relationship between the horizontal wind speed and its standard deviation are well described by dry convective boundary layer similarity hypotheses originally found to apply in flat terrain. Diurnal changes in the sign of the vertical velocity skewness observed above and inside the canopy are shown to be plausibly explained by considering the skewness budget. Simple empirical formulas that relate observed turbulent heat fluxes to horizontal wind speed and variance are presented. Changes in the amount of turbulent coupling between the forest and the boundary layer associated with deep convective clouds are presented in three case studies. Even small raining clouds are capable of evacuating the canopy of substances normally trapped by persistent static stability near the forest floor. Recovery from these events can take more than an hour, even during midday.
Aerosol chemistry during the wet season in central Amazonia: The influence of long‐range transport
Authors: Talbot R. W. , Andreae M. O. , Berresheim H. , Artaxo P. , Garstang M. , Harriss R. C. , Beecher K. M. , Li S. M.
Published: February 2008

The distribution and chemistry of the atmospheric aerosol over the Amazon Basin during the April‐May segment of the 1987 wet season are described using ground‐ and aircraft‐based data. Wet season aerosol concentrations and composition are variable in contrast to the remarkably uniform distribution and composition of the predominantly biogenic aerosol that we observed during the 1985 dry season. Four distinct intervals of enhanced aerosol concentration coincided with 3‐ to 5‐day periods of extensive rainfall over central Amazonia. It is hypothesized that a major source of aerosols to the basin was the direct input of northern hemispheric air laden with variable mixtures of Saharan dust, marine aerosol, and possibly biomass combustion products. The enhanced aerosol concentrations over Amazonia were reduced in 1–3 days to 5–10% of their peak levels by large‐scale changes in the circulation field with subsequent decoupling from the source region, frequent precipitation, and intermixing of northern and southern hemispheric air masses. The intrusion of northern hemispheric air into the Amazon Basin is linked to the establishment and persistence of the West African Subtropical High (WASH) in a limited region over west Africa. Marine aerosols may be intermixed with the soil dust during transit across the Atlantic or within the sea breeze regime along the northeast coast of South America. It is proposed that a principal source of NO3− and SO42− associated with the dust is biomass burning south of the Sahara in western Africa.
The smog‐fog‐smog cycle and acid deposition
Authors: Pandis Spyros N. , Seinfeld John H. , Pilinis Christodoulos
Published: February 2008

A model including descriptions of aerosol and droplet microphysics, gas and aqueous‐phase chemistry, and deposition is used to study the transformation of aerosol to fog droplets and back to aerosol in an urban environment. Fogs in polluted environments have the potential to increase aerosol sulfate concentrations but at the same time to cause reductions in the aerosol concentration of nitrate, chloride, ammonium and sodium and well as in the total aerosol mass concentration. The sulfate produced during fog episodes favors the aerosol particles that have access to most of the fog liquid water which are usually the large particles. Aerosol scavenging efficiencies of around 80 percent are calculated for urban fogs. Sampling and subsequent mixing of fog droplets of different sizes may result in measured concentrations that are not fully representative of the fogwater chemical composition and can introduce errors in the reported values of the ionic species deposition velocities. Differences in the major ionic species deposition velocities can be explained by their distribution over the droplet size spectrum and can be correlated with the species average diameter. Two different expressions are derived for use in fog models for the calculation of the liquid water deposition velocity during fog growth and dissipation stages.
The effects of variation of current amplitude, current risetime, and return stroke velocity along the return stroke channel on the electromagnetic fields generated by return strokes
Authors: Cooray Vernon , Orville R. E.
Published: February 2008

Calculations are presented to show how the return stroke electromagnetic fields are influenced by the variation of amplitude of the current waveform, the variation of risetime of the current waveform, and the variation of return stroke velocity along the return stroke channel. Calculations clearly show that these parameters play a dominant role in determining the characteristics of the return stroke electromagnetic fields. The narrow initial peak observed in first and subsequent stroke electromagnetic fields can be produced either by a narrow initial peak present in the current waveform, a rapid decrease in the return stroke current amplitude during the first hundred meters, a rapid decrease in the velocity of the return stroke over the first few hundred meters, or the variation of return stroke current risetime with height. The subsequent peak often observed in return stroke radiation fields can be generated either by a similar feature in the return stroke current waveform or by the variation of return stroke current risetime with height. The rate of decay of the radiation field after the initial peak depends on the rate of decay of the current waveform after the initial peak, the variation of the amplitude of the current waveform with height, and the variation of return stroke velocity with height. Calculations are also presented to show how the risetime of the current waveform affects the radiation field generated by a tortuous return stroke channel. These calculations provide an explanation for the lack of fine structure in the subsequent return stroke radiation fields though the subsequent return stroke channel is tortuous. The calculations presented in this paper demonstrate the importance of including the variation of return stroke current amplitude, variation of return stroke velocity with height, and variation of risetime of the current waveform with height in the return stroke models which are used to derive the return stroke current parameters from the return stroke electromagnetic fields.
On the Master, Uman, Lin, Standler and the Modified Transmission Line Lightning return stroke current models
Authors: Rachidi F. , Nucci C. A.
Published: February 2008

We show that the lightning return stroke model by Master, Uman, Lin, and Standler (MULS), a modification of the Lin, Uman, Standler (LUS) model, can be viewed mathematically as having a specified channel‐base current, although in the original formulation it was the channel current sources that were specified. The specification of the MULS channel‐base current is independent of the time dependence of the corona current sources which characterize the MULS model. Further, we show that, when starting from the same channel‐base current, the MULS return stroke model, except for the uniform current component, is mathematically equivalent to the Modified Transmission Line (MTL) model. For both the MULS and the MTL models we present a single analytical expression relating the far fields and the channel‐base current. This formulation provides for a simpler procedure to infer MULS channel‐base currents from remote electric and magnetic field measurements than was previously available and hence to test experimentally the MULS model.
Theoretical study of the cloud physics of Mei‐Yu
Authors: Lo K. Kenneth , Liu Chung‐Ming
Published: February 2008

The paper theoretically explains some of the microphysical phenomena observed in Mei‐Yu. In the melting layer the theory shows that most of the changes from the top to the bottom of the melting layer in the particle number density and the particle size distribution slope can be explained by assuming a constant precipitation rate and increasing particle fall speed due to melting. However, the theory implies that some aggregation is going on during melting. In the warm‐rain region, binary interaction of coalescence and breakup are the prominent microphysical processes. In general, coalescence dominates over breakup. But in these cases the two processes will approximately arrive at equilibrium when the precipitation reaches the Earth's surface.
On the biogenic origin of dimethylsulfide: Relation between chlorophyll, ATP, organismic DMSP, phytoplankton species, and DMS distribution in Atlantic surface water and atmosphere
Authors: Bürgermeister S. , Zimmermann R. L. , Georgii H.‐W. , Bingemer H. G. , Kirst G. O. , Janssen M. , Ernst W.
Published: February 2008

During a cruise over the Atlantic from 40°S to 50°N in March–April 1987 the concentrations of dimethylsulfide (DMS) in the ocean and atmosphere were measured as well as the distribution of its precursor, dimethylsulfoniopropionate (DMSP), and of several biological parameters such as chlorophyll, phytoplankton species, and adenosine‐5‐triphosphate (ATP) in the surface water. The DMS concentration varied in the range 0.2–2 nmol DMS L−1 (surface water) and 0.05–3 nmol DMS m−3 (atmosphere) in the region of the remote tropical and subtropical Atlantic and increased to 2–10 nmol DMS L−1 (surface water) and 1–8 nmol DMS m−3 (atmosphere) north of 40°N and in the English Channel. Based on these results the mean flux of DMS from the Atlantic to the atmosphere is estimated to be 4–4.65 nmol DMS m−2 min−1. A moderate diurnal variation of atmospheric DMS was found with a minimum during daytime. The DMS concentration in seawater correlated well with the concentration of DMSP and showed a similar trend to ATP, chlorophyll, and some phytoplankton species.
Trends in surface ozone at Hohenpeissenberg and Arkona
Authors: Low P. S. , Davies T. D. , Kelly P. M. , Farmer G.
Published: February 2008

Variations in the 18‐year (1971–1988) Hohenpeissenberg (Federal Republic of Germany) and the 33‐year (1956–1988) Arkona (German Democratic Republic) surface ozone data sets are analyzed. Over the full period of the records (as made available to us), both stations, which are about 800 km apart, show a positive long‐term trend of about 1.0% per year (strongest in winter at Hohenpeissenberg and in spring at Arkona). There are, however, marked differences in the fluctuations over various subperiods at the two locations. For example, the Hohenpeissenberg data show a larger increase in mean surface ozone concentration in the 1970s (about 2.1% per year, strongest in winter) compared with that in the 1980s (about 0.5% per year, strongest in summer). The Arkona data show a significant linear increase from 1956 to 1979 (about 2.4% per year, strongest in winter in the 1960s and in summer in the 1970s) but a linear decrease in the 1980s (about −2.4% per year, strongest in winter) and over the period 1971–1988 (about −1.2% per year, strongest in autumn and weakest in spring). The decrease is caused by the considerably lower concentrations in the 1980–1985 period when concentrations declined at about −10% per year. Over the same period 1971–1988, the seasonal cycle at Hohenpeissenberg exhibits a summer maximum in July (with a broad peak), while that at Arkona displays a spring maximum in May (with a sharp peak). The causes of these differences are likely to be complex: a combination of photochemistry (which depends on the distribution of precursors, particularly NOx), differences in surface deposition, local departures in the atmospheric circulation and, possibly, data quality. The pre‐1976 Hohenpeissenberg data and the pre‐1972 Arkona data (before filters were used to remove SO2) and the post‐1982 Arkona data (after a new measuring instrument was installed) may need to be further scrutinized to ensure consistency in data quality.
Tectonic cycles and the history of the Earth's biogeochemical and paleoceanographic record
Authors: Worsley Thomas R. , Nance R. Damian , Moody Judith B.
Published: February 2008

An integrated approach to earth history for the last 2.5 b.y. reveals the strong interdependence of all geologic variables. Three earth history components are identified and interrelated: secular trends as the earth ages, recurring events of a previously proposed supercontinent megacycle (Worsley et al., 1984, 1985), and nonrecurring environmental shifts. Declining secular trends are endogenic heat production, atmospheric carbon dioxide levels, and surface temperatures. Continental differentiation, enzyme efficiency, atmospheric oxygen levels, and solar luminosity are increasing secular trends. Four phases of a supercontinent cycle (supercontinent fragmentation, maximum continent dispersal, continental assembly, and supercontinental stasis) recur with a ∼0.5‐b.y. period and are correlated with tectonism, cratonic sediment preservation, atmospheric and hydrospheric evolution, and the distribution of marine platform stable isotopes. These correlations reflect coupling among the various oceanic and continental constituents during consecutive supercontinent assemblies and fragmentations. Nonrecurring shifts are unique and irreversible events in earth history (e.g., development of photosynthesis, occurrence of banded iron formations, and deposition of detrital uraninite) that represent periods of rapid geochemical adjustment to biospheric evolution. Earth's tectonobiogeochemical history is then synthesized by integrating secular trends and nonrecurring events with the supercontinent cycle, emphasizing the preferentially preserved periods of fragmentation and continental dispersal. Paleoceanographic consequences of the megacycle are considered to reflect the stepwise coupling of secular trends and nonrecurring events to a biotically controlled, phosphorus‐organic carbon‐climate linkage required to maintain earth's post‐Archean surface temperature.
Paleoceanography of Silurian Seaways in the Midwestern Basins and Arches Region
Authors: Droste J. B. , Shaver R. H.
Published: February 2008

Prima facie isotopic, salinity, and other geochemical data of the kind normally cited as evidence for a set of stated oceanographic parameters scarcely exist for the mostly highly dolomitized rocks of the Silurian System in the midwestern basins and arches region. This lack requires that Silurian paleoceanographic reconstructions be highly generalized as projections from a recently published integrative stratigraphy and from prior proposals of regional cyclicity in sedimentation, bathymetry, and salinity. We propose that midwestern Silurian sea level fluctuated only in modest amounts from late Early to middle Late Silurian time. Further, bathymetric differentiation among some of the basins and arches was modest. These bathymetric generalities for three selected time slices are representative of a complex history of Silurian cyclicity: mid‐Wenlockian time, 50 to more than 75 m in the basins, about 30 m on the intervening platforms, and less than 15 m in parts of major carbonate bank and reef areas; latest Wenlockian, about 100 m in the Illinois Basin, about 20 m to supratidal on the carbonate shelves, and 10 m and, at times, less in the Appalachian and Michigan evaporite basins; and mid‐Ludlovian, only a modest 10–15 m deeper than that of latest Wenlockian time. The mid‐Ludlovian deepening was sufficient, however, to restore circulation and salinity to normal on the interbasin platforms and to near normal in the evaporite basins. Near the evaporite basins, net current flow was toward and into the basins through belts of increasing evaporation. Such currents became increasingly enriched in Mg ions and effected early dolomitization of Silurian carbonate, including reef sediments. Biotas ranged from normal marine, high‐diversity communities, which were most widespread during mid‐Wenlockian time, to variably restricted, algae‐dominated communities and were even nonexistent in the evaporite basins during latest Wenlockian time. Generally, shallow depth may have been more important in effecting all these gradients than were latitudinally related climatic differences. As an explanation for the pattern of cyclicity proposed here, global controls of sea level are invoked, but these are not well understood, and localized structural and biologic controls within the North American craton accounted for some details of the paleoceanographic gradients.
The radiocarbon record in varved sediments of Carmen Basin, Gulf of California: A measure of upwelling intensity variation during the past several hundred years
Authors: DeMaster David J. , Turekian Karl K.
Published: February 2008

The decrease in 14C/12C with depth in a varved sediment core raised from the eastern flank of Carmen Basin, Gulf of California, is greater than expected from varve and 210Pb chronology. The discrepancy is ascribed to a virtually monotonic decrease in upwelling intensity from several hundred years ago to the present. This radiochemical study presents an approach, independent of previously used biostratigraphic techniques, for evaluating temporal variations in upwelling intensity in the Gulf of California.
Glacial‐interglacial changes in global deepwater circulation
Authors: Kellogg Thomas B.
Published: February 2008

Variations in the areal extent of the cryosphere appear to exert an important control over glacial‐interglacial changes in the mode of formation and source areas for deepwater and bottom water masses. During interglacials, when ice extents are minimal, these water masses form by mechanisms which are well documented for the present interglacial. Climatically related advances and retreats of sea ice in the northern hemisphere during glacials probably resulted in shifting loci of formation for each of the three types of North Atlantic Deep Water (NADW). Probable glacial advances of grounded ice sheets to the continental shelf margins in Antarctica precluded formation of Antarctic Bottom Water (AABW) at the presently active continental shelf sites. Because these shifts in source areas for AABW and NADW probably involved source waters with salinity, temperature, oxygen content, and nutrient levels that differed from modern values, deep and bottom waters are likely to have had different characteristics in glacials than they do during interglacials.
Changes in deep‐ocean water δ18O and temperature from the Last Glacial Maximum to the present
Authors: Birchfield G. Edward
Published: February 2008

Estimates are made of changes of the oxygen isotope anomaly of deep‐ocean water and of deep‐ocean temperature for the Atlantic, Indian, and Pacific oceans from the time of the last glacial maximum to the present. Several independent sources of data, including oxygen isotope records of planktic and benthic foraminifera at selected core sites (primarily in the equatorial oceans), Climate: Long‐Range Investigation, Mapping, and Prediction sea surface temperatures estimates, and GEOSECS δ18O data for the present ocean water, are utilized together with the paleotemperature equation of Epstein et al. (1953). Glacial to interglacial change in oxygen isotope composition of the global deep‐ocean water is found to be −1.41 per mil compared with a global average change of −1.75 per mil for benthic foraminifera. The former value implies a sea level change between 128 and 141 m, depending on the choice of the isotope sea level conversion constant. A global deep ocean warming of 1.4°C from glacial maximum to the present is found from the above isotopic difference of 0.34 per mil. The consistency of the results in this paper with those of Chappell and Shackleton (1986) suggest that there is no significant contribution from isotopically light floating ice shelves surrounding Antarctica as proposed by Johnson and Andrews (1986), at least for the change from glacial maximum to the present. The ocean transition from glacial to interglacial episodes was accompanied by an estimated warming of 2.0°C in the Atlantic, 1.4°C in the Indian, and 1.1°C in the Pacific oceans. The glacial Pacific was colder than the Atlantic Ocean, but the difference between the two oceans was smaller than today.