bluuebunny/crossref_metadata_2025 huggingface dataset:
SAGE observations of stratospheric nitrogen dioxide
Authors: Chu W. P. , McCormick M. P.
Published: February 2008

The global distribution of nitrogen dioxide in the middle to upper stratosphere (25–45 km altitude) for the period Feburary 1979 to November 1981 has been determined from observations of attenuated solar radiation in the visible region 0.385–0.45 μm by the Stratospheric Aerosol and Gas Experiment (SAGE) satellite instrument. The SAGE‐derived NO2 vertical profiles compare well with observations by balloon and aircraft‐borne sensors. The global SAGE NO2 distributions generally show a maximum in mixing ratio of 8 parts per billion by volume at about 35 km altitude near the equatorial latitudes at local sunset. The location of the mixing ratio peak moves synchronously with the overhead sun for the four different seasons. High‐latitude NO2 column content shows strong seasonal variation, with a maximum in local summer and a minimum in local winter. Selected data at high‐latitude winter seasons are presented, suggesting that the large variation shown could be explained by the coupling of both dynamics and photochemistry of the NOx species. Finally, profiles of the ratio of sunset to sunrise NO2 mixing ratios, peaking at about a factor of 2 at 30 km, are shown.
Meridional eddy diffusion model of the transport of atmospheric carbon dioxide: 2. Mean annual carbon cycle
Authors: Keeling Charles D. , Heimann Martin
Published: February 2008

In the second of two papers interpreting atmospheric CO2 observations obtained during the First Global Geophysical Experiment (FGGE) Hawaii to Tahiti Shuttle expedition of 1979–1980, we consider features of the atmospheric CO2 cycle revealed by the mean annual component of the CO2 concentration field. For this purpose the FGGE data, after decomposition into seasonal, secular, and north‐south varying components, were extended to 71°N and to the south pole by included smoothed mean annual data based on CO2 observations at seven land stations. The resulting mean annual north‐south profile was referred to a datum of January 1, 1980. An additional profile for January 1, 1962 was derived from observations at five land stations, at an Arctic ice floe station, and from ships during the period 1960–1963. Both profiles have been examined using a one‐dimensional meridional diffusive transport model of the atmospheric circulation in which the latitudinal dependence of the eddy diffusion coefficient between 14.5°N and 14.5°S has been determined from seasonal variations in atmospheric CO2, and its mean value estimated from halocarbon and 85Kr data. The difference between the two CO2 concentration profiles is explained as being due almost entirely to the combustion of fossil fuels, which caused 2.7 × 1015 g more carbon to be injected into the air in 1980 than in 1962, predominantly north of 14.5°N. A residual profile was obtained by subtracting the predicted effect of the injection of fossil fuel CO2 from the 1980 profile. This residual profile has a peak concentration near the equator which, according to the model, is a result of the release of 5.0 × 1015 g yr−1 of carbon to the atmosphere between 14.5°N and 14.5°S, balanced by an equal removal from the atmosphere poleward of these latitudes. The source‐sink couple inferred to produce this CO2 exchange is consistent with the distribution of CO2 partial pressure in the equatorial ocean surface water, as observed on the FGGE Shuttle Expedition, provided that the air‐sea exchange rate of CO2 there is 30 mol m−2 yr−1. This exaggerated rate probably reflects the lack of vertical resolution in the model, such that the CO2 concentration near the sea surface is assumed to apply to the entire air column. The residual profile also shows a higher average concentration in the southern hemisphere than in the northern. The cause of this difference, of the order of 1 ppm, could not be resolved by the model owing to lack of information on the character of sources and sinks and transport behavior poleward of 14.5°N and 14.5°S; it may be owing to either oceanic or land biospheric CO2 exchange with the air or even to time dependent atmospheric transport.
A novel method to identify the radiation fields produced by positive return strokes and their submicrosecond structure
Authors: Cooray Vernon
Published: February 2008

The submicrosecond structure of the positive return stroke radiation fields, together with the temporal behavior of HF at 3 MHz measured simultaneously with the electric fields, are presented. It is shown that (1) positive return strokes in the range of 25–100 km over land can be identified by studying the temporal behavior of the HF radiation, (2) the positive return stroke from its very beginning is a strong source of HF radiation, and (3) radiation fields from positive return strokes exhibit large submicrosecond components, which in turn suggest that currents in positive return strokes also contain a large submicrosecond component.
The effects of atmospheric parameters on a corona probe used in measuring thunderstorm electric fields
Authors: Byrne G. J. , Few A. A. , Stewart M. F.
Published: February 2008

The effects of atmospheric parameters (pressure, temperature, relative humidity, and wind) on the induced corona current through a corona probe are evaluated through a laboratory investigation. The corona probe has a high series resistance, which tends to linearize the relationship between the induced corona current and the electric field. From a best fit of the data, the slope of the linear relationship for corona currents greater than 1.5 μA varies with air density D as (DO/D)0.15. For lower currents the slope varies as (DO/D)0.33. The onset electric field required to initiate corona varies slightly with air density; this relationship is (D/DO)0.15. The high series resistance significantly reduces the effects of variations in the relative humidity and in low wind velocities across the corona point. When balloon borne, the probe can reliably measure thunderstorm electric fields.
Theory and observations of the short‐period normal mode oscillations of the atmosphere
Authors: Hamilton Kevin , Garcia Rolando R.
Published: February 2008

Virtually all previous work on the subject of atmospheric normal modes has concentrated on the relatively long‐period Rossby modes, such as the familiar “5‐day” and “16‐day” waves. However, theory does predict the existence of shorter‐period Rossby‐gravity, Kelvin, and gravity modes. In the present investigation, long time series of hourly and 3‐hourly barometric observations from several tropical stations were employed in a search for these high‐frequency modes. Evidence was found for several spectral peaks that can be identified with various Rossby‐gravity, Kelvin, and gravity wave normal modes. Particularly prominent is the zonal wave number 1 Kelvin normal mode with a period of about 33 hours. This mode was found to undergo systematic seasonal and interannual variations. The theory of short‐period normal modes in the Martian atmosphere is also briefly examined. Such modes might be detectable in the surface pressure time series obtained in the Viking missions to Mars.
Radiation from lightning return strokes over a finitely conducting Earth
Authors: Le Vine D. M. , Gesell L. , Kao Michael
Published: February 2008

The effects of the conductivity of the earth on radiation from lightning return strokes are examined theoretically, using a piecewise linear transmission line model for the return stroke. First, calculations are made of the electric field radiated during the return stroke, and then this electric field is used to compute the response of conventional AM radio receivers and electric field change systems during the return stroke. The calculations apply to the entire transient waveform (they are not restricted to the initial portions of the return stroke) and yield fast field changes and RF radiation in agreement with measurements made during real lightning. This research was motivated by measurements indicating that a time delay exists between the time of arrival of the fast electric field change and the RF radiation from first return strokes. The time delay is on the order of 20 μs for frequencies in the HF‐UHF range for lightning in Florida. The time delay is obtained theoretically in this paper. It occurs when both the effects of attenuation due to the conductivity of the earth and the finite velocity of propagation of the current pulse up the return stroke channel are taken into account in the model.
Active region influences upon the solar constant
Authors: Schatten Kenneth H. , Mayr Hans G. , Omidvar Kazem
Published: February 2008

In this paper we discuss the influence that active regions have upon the solar constant. Sunspots appear to lower the solar constant for the few days in which they are located near central meridian. This raises the possibility that an 11‐year, solar‐cycle‐related depression in the solar constant may occur. Recent findings concerning the physics of active regions suggest that sunspots and faculae are largely surface features. Within that surface faculae reradiate, within a few weeks, the “missing energy” associated with sunspots. This is consistent with the observations showing that the solar constant does not have an 11‐year cycle‐related depression that some authors predicted. However, there is a secular variation in the solar constant, whose explanation is not completely understood.
Response of middle atmosphere to short‐term solar ultraviolet variations: 2. Theory
Authors: Brasseur G. , De Rudder A. , Keating G. M. , Pitts M. C.
Published: February 2008

Ozone and temperature responses to solar variability, based on satellite data, have been reported in a companion paper (Keating et al., this issue). The present paper is intended to present a theoretical interpretation of this analysis with the purpose of better understanding the chemical behavior of the stratosphere and the coupling between temperature and ozone concentration, when a periodic forcing is applied to the solar ultraviolet (UV) flux. The response of the temperature and of the trace species concentrations, including ozone, to short‐term variations in the solar UV irradiance is calculated by a one‐dimensional chemical‐radiative time‐dependent model. The applied solar variability is assumed to be sinusoidal with a period of 27 days (in accordance with the rotation period of the sun) or 13.5 days (when two active regions are on opposite sides of the sun). The amplitude varies with wavelength, which is consistent with observations made by the Nimbus 7 solar backscattered ultraviolet (SBUV) experiment. The maximum ozone sensitivity in the stratosphere appears to be located near 3 mbar. The calculated amplitude and phase of the ozone response are significantly modified when the feedback between ozone and temperature is taken into account. The ozone/temperature coupling tends to modify the ozone phase lag such that, in the upper stratosphere and in the mesosphere, the ozone peak occurs a few days before the UV peak. Comparison of the model results with the observed ozone and temperature responses, based on satellite data, shows that the theory is consistent in many respects with observations. The calculated time lag of the temperature response, however, is approximately a factor of 2–4 smaller than the time lags derived from the measurements, suggesting evidence for some additional process not included in the model calculation. Large negative ozone sensitivities and positive temperature responses are predicted in the mesosphere as a result of the absorption by O2 of the solar irradiance at the Lyman α wavelength. The model also shows that the expected variation in the stratospheric nitric acid mixing ratio is a factor 2 larger than the corresponding opposite variation in the ozone concentration.
H2O2, O3 and SO2 measurements in the lower troposphere over the eastern United States during fall
Authors: Heikes Brian G. , Kok Gregory L. , Walega James G. , Lazrus Allan L.
Published: February 2008

We report gas phase measurements of hydrogen peroxide, sulfur dioxide and ozone in the lower troposphere over the eastern United States in October and November 1984. A series of flights based at Springfield, Ohio, extending from the Gulf of Mexico to upstate New York, and from the surface to 3.5 km, were flown in air having a predominantly southerly origin. Occasionally, air of northwesterly origin and of local stagnation was sampled. Flights occurred between 0800 and 2000 EST on 10 different days. Gas phase H2O2 concentrations ranged from between the detection limit (nominally 0.2 ppbv at S/N = 3) to 4.1 ppbv. In general, air near the surface contained substantially less H2O2 than air aloft. Maximum H2O2 concentrations were observed just above cloud tops. A latitudinal H2O2 gradient existed in air near the surface and in air above cloud top with higher concentrations in the south. This gradient was absent at higher altitudes (>3.0 km). SO2 concentrations ranged from the detection limit (nominally 1 ppbv at S/N = 3) to 50 ppbv, were typically between 5 and 10 ppbv in surface air and were less than 2 ppbv aloft. Ozone concentrations were typically 35±10 ppbv, ranged from 11 to 57 ppbv and showed no trend with altitude. The H2O2 measurements were the first of their kind above the surface and have several implications for acid deposition and tropospheric chemistry research. We observed an inverse relationship between H2O2 and SO2, evidence for the long‐range transport of H2O2 from southern latitudes, and no discernable relationship between O3 and H2O2 concentrations. Observation near cloud suggested that mixing of H2O2 from above with SO2 from below could be the controlling process in converting SO2 to SO42− in cloud.
In situ measurements and radar observations of a severe storm: Electricity, kinematics, and precipitation
Authors: Byrne G. J. , Few A. A. , Stewart M. F. , Conrad A. C. , Torczon R. L.
Published: February 2008

Electric field measurements have been acquired inside an electrically active cell of a multicelled severe storm in Oklahoma with a free balloon‐borne instrument. The electrical measurements are analyzed in conjunction with standard weather radar and Doppler radar observations and standard meteorological measurements of the radiosonde in order to relate the inferred electrical structure with the precipitation and kinematic features of the cell. The precipitation and kinematic characteristics of the storm are consistent with those of the general model for a “typical” multicelled severe storm in a mature stage. The cell exhibited a bipolar charge structure with negative charge below positive charge, which was distributed throughout the upper portion of the cloud. The average charge concentrations of the two regions were estimated to be −1.2 and 0.15 nC m−3 respectively. The upper positive charge was approximately 6 km in vertical extent, nonuniformly distributed, and was coincident with generally upward moving air. The lower negative charge was less than 1 km in vertical extent, centered near the −9°C atmospheric temperature level, and coincident with downdraft air in moderate precipitation. Near the top of the negative region, concentrated charge of approximately 17 nC m−3 was measured with a vertical extent of at least 40 m. A screening layer of negative charge was detected at the upper boundary of the cloud. The layer was 200–250 m thick with an average charge concentration of −1.5 nC m−3.
Correlations between ozone and carbon monoxide in the lower stratosphere, folded tropopause, and maritime troposphere
Authors: Hipskind R. Stephen , Gregory Gerald L. , Sachse Glen W. , Hill G. F. , Danielsen Edwin F.
Published: February 2008

The variations of ozone and carbon monoxide with respect to the atmospheric flow structure are investigated for two aircraft flights: one in the upper troposphere/lower stratosphere over the continental United States on April 20, 1984, and the other in the marine troposphere over the eastern Pacific on April 26, 1984. The high frequency (1 Hz) and precision of the measurements allow detailed analysis of the species distribution down to length scales of the order of 1 km. Correlations between the two species are made on large, medium, and small scales of motion, and the results are interpreted. In general, the correlations are negative with some regions of positive correlation. The interpretation of these results is discussed.
Deforestation in the tropics: New measurements in the Amazon Basin using Landsat and NOAA Advanced Very High Resolution Radiometer imagery
Authors: Woodwell G. M. , Houghton R. A. , Stone T. A. , Nelson R. F. , Kovalick W.
Published: February 2008

Objective measurements of rates of deforestation, especially in the tropics, have been elusive. We report the development and use of a series of techniques for use of existing satellite imagery for measurement of rates of deforestation in the tropics. The techniques have been applied in the Brazilian state of Rondonia in the southwestern Amazon Basin, the site of a large Brazilian resettlement project, started in the early 1970s. Application of special techniques for detecting change using Landsat imagery showed that between 1976–1978 and 1978–1981 the rate of deforestation increased by a factor of 2 from 620 km2 yr−1 to 1270 km2 yr−1 in the 109,000‐km2 section of Rondonia studied with Landsat imagery. A combination of the Landsat and NOAA 7 advanced very high resolution radiometer imagery was used to provide an estimate of the total extent of deforestation in Rondonia by 1982. The area was 11,400 km2 or 43% of the total area of the project and 6% of the state. The techniques are highly promising and, with further development, can be used to estimate the extent and rates of deforestation globally.
Measurement of nitrogen oxide fluxes from soils: Intercomparison of enclosure and gradient measurement techniques
Authors: Parrish D. D. , Williams E. J. , Fahey D. W. , Liu S. C. , Fehsenfeld F. C.
Published: February 2008

The present estimates of emissions of NOx from soils to the atmosphere are based on field studies that used enclosure techniques. While this technique is direct, convenient and precise, the technique may perturb the biogenic soil processes under study. In addition, the limited sample size may produce nonrepresentative results. In order to address these concerns, NO flux measurements made using an enclosure technique are intercompared with NO flux determinations made using a gradient technique. The measurements were made during the nighttime hours from August to October, 1985, at an unfertilized, uncultivated grassland site in Colorado, United States. The NO flux measured during this period ranged between 0.08 ng N m−2 s−1 and 21 ng N m−2 s−1. The flux measurements made by the two techniques, which are based on very different approaches as described herein, agree very well.
Sulfur scavenging in a mesoscale model with quasi‐spectral microphysics: Two‐dimensional results for continental and maritime clouds
Authors: Chaumerliac N. , Richard E. , Pinty J.‐P. , Nickerson E. C.
Published: February 2008

A three‐dimensional mesoscale numerical model (Nickerson et al., 1986) with quasi‐spectral microphysics has been extended to include gas and aerosol removal by cloud droplets and raindrops. Combining meteorological predictions and pollutant scavenging parameterizations, two‐dimensional sensitivity tests have been carried out for continental and maritime clouds over an idealized topography. Nucleation scavenging is the most efficient in‐cloud removal mechanism; however, differences in cloud droplet spectra between continental and maritime clouds lead to differences in their scavenging efficiencies for gases and aerosols, thereby emphasizing the need for the simultaneous treatment of meteorological and physicochemical processes.
Large‐scale distribution of peroxyacetylnitrate results from the STRATOZ III flights
Authors: Rudolph J. , Vierkorn‐Rudolph B. , Meixner F. X.
Published: February 2008

During the STRATOZ III flights in June 1984, approximately 160 measurements of peroxyacetylnitrate (PAN) were made with a specially designed gas chromatograph on board the Caravelle 116 airplane. The measurements cover a latitude range from 70°N to 60°S and altitudes up to 12 km. The results show that PAN is present throughout the troposphere at low but measurable levels. Southern hemispheric data from clean marine air masses show levels of 7–10 ppt, with little variability up to about 10 km altitude. In the southern uppermost troposphere and lowest stratosphere a significant increase in PAN can be seen, indicating substantial in situ formation of PAN at these altitudes. The situation at lower latitudes in the northern hemisphere is similar as long as the air masses are free of anthropogenic influence. At mid and high northern latitudes, considerably higher PAN mixing ratios (sometimes more than 100 ppt) are found even outside continental areas. These data also show a rather high variability. This can be ascribed to the influence of North America and Europe as source areas for PAN and PAN precursors.
Visible spectroscopy at McMurdo Station, Antarctica: 1. Overview and daily variations of NO2 and O3, Austral Spring, 1986
Authors: Mount G. H. , Sanders R. W. , Schmeltekopf A. L. , Solomon S.
Published: February 2008

Observations of the visible spectra of the sun and moon were obtained at McMurdo Station, Antarctica, during austral spring in 1986. The data coverage and observing conditions are described. Daily variations of ozone suggest that the bulk of the springtime ozone depletion (or the Antarctic ozone “hole”) occurs rapidly during early September. Total NO2 abundances were less than about 1×1015 cm−2 during August and September inside the polar vortex and displayed a near‐absence of diurnal variation from morning to evening twilight. The total NO2 column abundance was closely correlated to 50‐mbar temperatures.
Simultaneous measurement of stratospheric O3, H2O, CH4, and N2O profiles from infrared limb thermal emissions
Authors: Abbas M. M. , Glenn M. J. , Kunde V. G. , Brasunas J. , Conrath B. J. , Maguire W. C. , Herman J. R.
Published: February 2008

Thermal emission measurements of the earth's stratospheric limb were made with a cryogenically cooled high‐resolution Michelson interferometer on a balloon flight launched from Palestine, Texas, on November 6, 1984. Infrared spectra for complete limb sequences were obtained over portions of the 700–1940 cm−1 range with an unapodized spectral resolution of 0.03 cm−1 for tangent heights varying from 13 to 39 km. The observed data from 1125 to 1425 cm−1 have been analyzed for simultaneous measurement of O3, H2O, CH4, and N2O profiles. The analysis employs line‐by‐line and layer‐by‐layer radiative transfer calculations, including curvature and refraction effects. The optimum use of geometric and spectral effects is made to obtain sharply peaked weighting functions. Contributions from stratospheric aerosol are included by measuring the light extinction within the window regions of the observed spectra. The retrieved constituent profiles are compared with measurements made with a variety of techniques by other groups. The comparison shows good agreement with the published data for all gases, indicating the capability of retrieving trace gas profiles from high‐resolution thermal emission limb measurements.
Aerosol optical depth and planetary albedo in the visible from the Solar Mesosphere Explorer
Authors: Naudet J. P. , Thomas G. E.
Published: February 2008

The Solar Mesosphere Explorer (SME) satellite has observed the visible sunlight scattered at the earth's limb since early 1982. By using a radiative transfer model including multiple scattering and albedo effects, observations at 20°N latitude have been interpreted in terms of aerosol optical depth. The ratio of aerosol extinction to Rayleigh extinction at 431.8 nm shows a large increase after the eruption of El Chichon. A maximum ratio of 5 at 36 km and larger than 11 at 30 km occurs in the summer of 1982 followed by a decrease through 1983 and 1984. Aspects of the aerosol time evolution appear to be consistent with other observations and model predictions. Quantitative differences exist between inferred SME and lidar extinction coefficients, possibly due to the different wavelengths of the measurements and to the different scattering phase functions used in the two analyses. It is also shown that visible limb radiances provide information on the planetary albedo, which shows an increase from the equator to the poles with a maximum in the winter hemisphere and a minimum in the summer hemisphere.
Relationships between changes in the length of day and the 40‐ to 50‐ day oscillation in the tropics
Authors: Madden Roland A.
Published: February 2008

Attempts are made to link observed variations of the length‐of‐day with a period near 50 days to the atmospheric 40‐ to 50‐day oscillation in the tropics. Because the earth‐atmosphere system maintains constant angular momentum a longer length of day (slower rotation rate of the earth) goes with higher momentum of the atmosphere. It is shown that the longest length of day and greatest atmospheric momentum occurs when tropical convection associated with the 40‐ to 50‐day oscillation is beginning to weaken near or east of the date line. We present some evidence suggesting that, over a broad period range bridging 40–50 days, a strengthening of the easterlies east of the convection increases wind stress and frictional torques, and serves as an important mechanism for exchange of momentum from earth to atmosphere.
A ground‐based intercomparison of NO, NOx, and NOy measurement techniques
Authors: Fehsenfeld F. C. , Dickerson R. R. , Hübler G. , Luke W. T. , Nunnermacker L. J. , Williams E. J. , Roberts J. M. , Calvert J. G. , Curran C. M. , Delany A. C. , Eubank C. S. , Fahey D. W. , Fried A. , Gandrud B. W. , Langford A. O. , Murphy P. C. , Norton R. B. , Pickering K. E. , Ridley B. A.
Published: February 2008

At a site near Boulder, Colorado, simultaneous atmospheric measurements were made of NO, NOx, and NOy in a field intercomparison of instruments involving two currently employed techniques of NOx and NOy measurement. Both NOy instruments depended upon the reduction of the NOy species to NO with detection by chemiluminescence, but different catalysts were employed for the reduction: (1) a gold catalyst (with addition of 0.3% CO) at 300°C, or (2) a molybdenum catalyst at 400°C. The two systems of NOx detection involved (1) photolysis of NO2, and (2) reduction of NO2 by solid ferrous sulfate. Several times during the intercomparison the response to calibrated samples of reference compounds NO, NO2, PAN, HNO3, n‐propyl nitrate (NPN), and NH3 was measured. From the results the following conclusions were made: (1) The two NO instruments agreed on NO mixing ratios that were measured during the daytime hours over a range from the limits of detection to 35 parts per billion by volume (ppbv), (2) the two NOy instruments gave similar estimates of NOy in ambient air over a wide range of mixing ratios (0.4–10 ppbv), and (3) the ferrous sulfate converter used for NOx detection showed a significant interference from NPN and PAN.
Atmospheric infrared emission of ClONO2 observed by a balloon‐borne Fourier spectrometer
Authors: Massie S. T. , Davidson J. A. , Cantrell C. A. , McDaniel A. H. , Gille J. C. , Kunde V. G. , Brasunas J. C. , Conrath B. J. , Maguire W. C. , Goldman A. , Abbas M. M.
Published: February 2008

ClONO2 was observed in high‐resolution infrared emission spectra obtained on November 6, 1984, by a balloon‐borne Fourier spectrometer. The observations took place near 0300 LT at a latitude of 35°N. Spectral simulations are used to determine the mixing ratios of ClONO2. This analysis incorporates line by line calculations and new ClONO2 cross sections measured in the laboratory at 223 K. The inferred mixing ratios of ClONO2 are 1.3±0.45 ppb and 0.98±0.35 ppb at 14 and 34 mbar. One‐dimensional photochemical model predictions are compared to the observations. The ClONO2 mixing ratio at 34 mbar appears to be larger than theory, while there is agreement at 14 mbar.
The electric field alignment of ice particles in thunderstorms
Authors: Weinheimer Andrew J. , Few Arthur A.
Published: February 2008

Electrical and aerodynamic torques on atmospheric ice particles are calculated in order to assess the degree of alignment of these particles with the electric fields in thunderstorms. In such clouds fields of many tens of kilovolts per meter are commonly measured, and values of 100 to 200 kV/m are not rare. For E = 100 kV/m the calculations indicate that electric field alignment occurs for crystals with major dimensions up to maximum values in the range from 200 μ to 1 mm, depending upon crystal type. Columns are aligned more easily than platelike crystals, except for dendrites which, by virtue of their smaller assumed density, have smaller fall velocities thereby experiencing weaker aerodynamic torques. Thus a substantial degree of alignment is expected for E = 100 kV/m. For E = 10 kV/m only much smaller crystals will be aligned, probably only ones with major dimensions of less than 50 μ or so.
Chemical consequences of mixing atmospheric droplets of varied pH
Authors: Perdue E. Michael , Beck Kevin C.
Published: February 2008

The mixing of droplets of different pH and acid‐neutralizing capacity that occurs when bulk samples of cloud, fog, and rainwater are collected yields solutions that are not in equilibrium with the atmosphere in which the droplets originally equilibrated. In most instances, bulk solutions are expected to outgas volatile solutes to reestablish equilibrium with the atmosphere, with concomitant changes in solution pH. This mixing‐induced gas exchange complicates equilibrium and kinetic modeling of pH‐dependent atmospheric processes and limits the use of bulk samples for estimation of atmospheric fluxes of volatile weak acids and bases (SO2(g), NH3(g), etc.). Calculations that attempt to interrelate bulk solution pH, bulk solution S(IV) concentration, and atmospheric SO2(g) partial pressure are shown to be fundamentally incorrect, unless the bulk sample has completely reequilibrated with the same atmosphere in which its component droplets were formed. A theoretical proof and several numerical examples are presented to show that droplet mixing at constant atmospheric partial pressures of soluble gases cannot occur without gas exchange.
First tandem mass spectrometric measurement of tropospheric ions
Authors: Eisele F. L.
Published: February 2008

Tandem mass spectrometric measurements of naturally occurring tropospheric ions have identified pyridine, methylpyridine, and ethylpyridine as the parent neutral species responsible for ions observed at mass 80, 94, and 108, respectively. High‐resolution mass spectra of natural ions observed over an extended mass range are also shown for two field study locations. At one site (Sapelo Island, Georgia), pyridine and its homologues dominated the positive spectrum. At Mount Evans, Colorado, the second site, pyridine along with a large number of more massive and presumably very alkali species were observed to dominate the positive spectrum. In addition, X ray‐produced ion spectra were also measured and used to make rough estimates of the pyridine concentrations at the Sapelo site (∼10 ppt) and the total concentration of alkali compounds, excluding NH3, at Mount Evans (∼0.5 ppb).
Trace gas exchanges and convective transports over the Amazonian rain forest
Authors: Garstang Michael , Scala John , Greco Steve , Harriss Robert , Beck Sherwin , Browell Edward , Sachse Glen , Gregory Gerald , Hill Gerald , Simpson Joanne , Tao Wei‐Kuo , Torres Arnold
Published: February 2008

The NASA Amazon Boundary Layer Experiment (ABLE 2A) based in Manaus, Brazil, in July and August, 1985, is used to examine meteorological processes responsible for the vertical and horizontal transport of biogenic and anthropogenic trace gases generated over the Amazon basin. Direct sampling of the surrounding environment of deep convective clouds shows marked changes in the vertical distribution of the lower and midtroposphere concentration of O3 and such surface‐derived species as CO, CO2, and NO. Thermodynamic observations, together with two‐dimensional cloud model simulations, confirm vertical transports within the convection and provide a basis to estimate the magnitude and efficiency of cloud upward and downward exchanges. A distinction is drawn between local changes due to convective updrafts and downdrafts and convective overturning as a net result of the storm processes. Marked variability is seen in trace gas concentrations along horizontal flight paths in the vicinity of the convection. Interpretation of simultaneously measured thermodynamic quantities and trace gas concentrations provide the information to infer the presence and direction of atmospheric transports and/or the presence of anthropogenic influences. The level of convective activity and the closely coupled Hadley and Walker circulations over the Amazon basin and its associated trace chemistry suggest the importance of this region to the global atmosphere.
Methane emissions to the troposphere from the Amazon floodplain
Authors: Devol Allan H. , Richey Jeffrey E. , Clark Wayne A. , King Stagg L. , Martinelli Luiz A.
Published: February 2008

Methane emissions to the troposphere from the Amazon River floodplain have been determined. In total, 94 individual flux measurements were made along a 1,700‐km stretch of the river during the early falling water period of the flood cycle (July–August 1985). The overall average rate of CH4 emission from wetlands was 390 mg CH4 m−2 d−1. Water surfaces covered by aquatic macrophytes had the highest emissions, 590 mg CH4 m−2 d−1, while emissions from flooded forests were 110 mg CH4 m−2 d−1 and open lake areas averaged 120 mg CH4 m−2 d−1. Ebullition was the dominant mechanism of emission, accounting for 85% of the total. Surface water dissolved oxygen was always undersaturated, while dissolved CO2 concentrations were significantly supersaturated with respect to atmospheric equilibrium. Surface water CH4 concentrations were highly supersaturated, averaging 6.4 μM. The δ13C of the CH4 varied from −42‰ to −73‰ with an apparent trend toward heavier values downstream. Extrapolation to the entire Amazon floodplain results in estimated annual emissions in the troposphere of 10 Tg yr−1 and indicates the importance of the area in the global atmospheric CH4 cycle.
Atmospheric geochemistry of formic and acetic acids at a mid‐latitude temperate site
Authors: Talbot R. W. , Beecher K. M. , Harriss R. C. , Cofer W. R.
Published: February 2008

We have determined the atmospheric concentrations of formic and acetic acid in gas and particulate phases and in precipitation over a 15‐month time period at a site in eastern Virginia. These atmospheric species occurred principally in the gas phase (≥98%), with a marked annual seasonality. Atmospheric concentrations of formic and acetic acid in the gas phase averaged 1890±1235 and 1310±910 ppt during the growing season, compared to 695±405 and 700±375 ppt over the nongrowing season, respectively. Our data support the hypothesis that biogenic emissions from vegetation are important sources of atmospheric formic and acetic acid during the local growing season. The same general time series trends were also evident in precipitation, but the seasonality was not defined nearly as well as in the gas phase. Atmospheric concentrations of aerosol formate and acetate showed substantial temporal variability and generally remained in the 5‐ to 25‐ppt range throughout the year. Our measurements indicate that the near‐surface (≤10 m altitude) diurnal behavior of formic and acetic acids in the gas phase is as follows: the concentrations are lowest prior to sunrise, increase steadily thereafter, and begin to decline by late afternoon, again reaching very low levels in the early morning hours. We have observed a diurnal variation with an amplitude of up to tenfold in atmospheric concentration for formic acid. This pronounced diurnal variation is presumably related to mixed layer dynamics, in addition to daytime biogenic and photochemical source inputs and gaseous dry deposition at nighttime. The removal of organic acids from the nocturnal boundary layer may be facilitated by uptake of their vapors into dew. A striking feature of our data is the distinct differences in both gas phase and precipitation ratios of formic‐to‐acetic acid between the growing and nongrowing seasons. In the gas phase this ratio had a mean value of 1.33 during the growing season, decreasing to 0.90 in the nongrowing season. Likewise, the ratio averaged 1.43 and 1.09 in precipitation at this site during the growing and nongrowing season, respectively. Our measurements indicated that direct emissions from motor vehicles and biomass combustion processes are important sources of atmospheric acetic acid and that these sources have formic‐to‐acetic ratios much less than 1.0. We hypothesize that the seasonal variability in formic‐to‐acetic acid ratios in ambient air is due to a shift in the relative dominance of biogenic versus anthropogenic sources. During the nongrowing season, anthropogenic inputs appear to be the principal source of acetic acid to the atmosphere. However, it remains unclear as to what the major source of formic acid is to the wintertime atmosphere.
An analysis of the 7‐year record of SBUV satellite ozone data: Global profile features and trends in total ozone
Authors: Reinsel Gregory C. , Tiao George C. , Ahn Sung K. , Pugh Marian , Basu Sabyasachi , DeLuisi John J. , Mateer Carl L. , Miller Alvin J. , Connell Peter S. , Wuebbles Donald J.
Published: February 2008

An analysis of Nimbus 7 solar backscattered ultraviolet (SBUV) monthly average total ozone data for changes over the 7‐year period from November 1978 through September 1985 is considered. Regression‐time series models, which include seasonal components, a linear trend term, an F10.7 solar flux term, and an autocorrelated autoregressive noise term to account for variations in total ozone, are estimated for both latitudinal zonal averages and a global series over this time period. The resulting linear trend and solar flux coefficient estimates are examined. A comparison between SBUV monthly average total ozone data near Dobson ground station locations and the corresponding Dobson station total ozone data is performed for a network of 35 Dobson stations. Linear drifts are estimated for the differences between SBUV and Dobson total ozone data at each station. The results show an average negative linear drift in SBUV data relative to Dobson data of about −0.4% per year. A linear trend estimate for the global SBUV series of (−0.74±0.26)% per year is obtained for the model which takes into account the association of ozone changes with solar flux variations. When this linear trend estimate for the global SBUV series is “corrected” for the negative drift between SBUV and Dobson data, the 95% confidence interval estimate of the linear trend component in the global SBUV series, exclusive of trend variations associated with solar flux variations, over this 7‐year period is (−0.35±0.28)% per year. The global estimate of the relation between total ozone and solar flux variations is (0.97±0.61)% per 100 solar flux units, which represents a change in total ozone over this 7‐year period associated with solar flux variations of about (−0.20±0.13)% per year. Comparisons are also performed which indicate that trends obtained from SBUV data at the Dobson station network of locations over this 7‐year period are quite similar to trend estimates obtained from the global SBUV series. When comparing the above SBUV data global trend estimate for the 7‐year period with a linear trend estimate of (−0.04±0.07)% per year obtained from a network of Dobson station data over the longer period 1970–1985, we find that the trend estimate for the recent 7‐year period is considerably more negative but with a much larger standard error. In recognition of the rather unusual natural atmospheric fluctuations which occurred during the period 1982–1985, no firm conclusions can be drawn in terms of interpretation of the negative trend finding over the relatively short 7‐year time period. Such interpretations require a detailed understanding of the atmospheric dynamical and chemical mechanisms related to ozone variations during this period.
The sensitivity to input parameters of atmospheric concentrations simulated by a regional chemical model
Authors: Brost Richard A.
Published: February 2008

I study the sensitivity of three‐dimensional Eulerian simulations of the evolution of 26 trace chemical species. The region simulated is 2,400 by 2,400 km horizontally and from the surface to about 15 km vertically. The uncertainty in simulated concentration is from perturbations or errors in input parameters and physical parameterizations: chemistry, emissions, meteorology, and initial and boundary conditions. I vary each input parameter p and calculate the root‐mean‐square (rms) change in concentration σ between the sensitivity run and the base run. The sensitivity parameter, S = ∂σ/∂p, is defined for each species and input parameter. For three scenarios I assign errors to each input parameter. For each species the total error in simulated concentration, σt, is the rms sum of the contributions by errors in each input parameter. I describe this error as the uncertainty, un = σt/cb, where cb is the horizontal mean concentration in the base run, and as the normalized uncertainty, nu = σt/σb, where σb is the standard deviation of fluctuations horizontally about cb. The uncertainty suggests that O3 is well simulated, but the normalized uncertainty shows it is poorly simulated. I prefer nu because it is more nearly constant for different species, but nu increases with height, implying that the simulations are poorer aloft. If the input parameters have 25% errors, then, averaged for all species, un = 0.53 ± 0.43 and nu = 0.45 ± 0.24. Often, σt is largely from errors in meteorology and in initial and boundary conditions. Chemical errors dominate steady state species. Initial and boundary conditions must have errors less than 25% before the errors in emissions begin to be important.
A growth‐sedimentation model of polar mesospheric clouds: Comparison with SME measurements
Authors: Jensen Eric , Thomas Gary E.
Published: February 2008

A numerical model for the brightness of polar mesospheric clouds (PMC) is described, and is compared with measurements from the Solar mesosphere Explorer (SME) satellite. These clouds occur during the summer months at polar latitudes where temperatures are known to fall below 140 K. We calculate the optical properties of a cloud by simulating the growth and sedimentation of ice particles at the cold supersaturated mesopause. Time‐dependent trajectories of ice particles are calculated from their origin at the temperature minimum region to their demise at the cloud base through evaporation. We consider the effects of the removal of atmospheric water vapor by the growing particles and its restoration by ice evaporation at the cloud base. This “freeze‐drying” effect is crucial in limiting the maximum size of the particles and therefore the maximum brightness of the cloud. Assuming spherical particles, Mie‐scattering calculations of the directional albedo of a cloud are performed using a range of possible values for the atmospheric variables (water vapor mixing ratio, temperature, upward wind speed, atmospheric pressure, and eddy diffusion coefficient). We find that for a nominal atmospheric case the model predicts a moderately weak cloud at 265 nm, the wavelength of the SME measurements. An extreme model (cold and moist with high vertical wind and eddy transport) is needed to account for the brightest cloud observed. We estimate an upper limit for the water vapor to be of the order of 5 parts per million by volume. Higher values would imply the existence of clouds which exceed in brightness every cloud observed by the satellite over the time period 1981–1986. SME observations of greater cloud height in the northern hemisphere, despite their greater brightness, possibly imply an excess (by a factor of 2) of northern hemisphere water vapor. This holds if the other atmospheric variables (and cloud particle numbers) are the same in both north and south. Dependence of model cloud brightness on atmospheric pressure (∼P4.4), water vapor mixing ratio (∼w2.8), thickness of the cloud saturation region (∼d4) and advective wind speed (∼υ) are determined. These scalings are shown to result from a calculated proportionality of the cloud brightness to R6 (R is the maximum particle radius), and from simple considerations of ice layer growth, particle sedimentation, and the mass budget of water. Mie scattering calculations for a wavelength of 550 nm show that SME and OGO‐6 data on PMC brightnesses are consistent.
Winter cloud water and air composition in central Ontario
Authors: Strapp J. W. , Leaitch W. R. , Anlauf K. G. , Bottenheim J. W. , Joe P. , Schemenauer R. S. , Wiebe H. A. , Isaac G. A. , Kelly T. J. , Daum P. H.
Published: February 2008

Time histories of surface air composition and cloud water composition in winter in Central Ontario are compared in order to establish a winter data set for this region, and to identify dominant processes responsible for the incorporation of sulfate, nitrate, and acidity into cloud water. Cloud water comparisons are restricted to low‐level collections (median altitude 625 m above ground) within the boundary layer. Surface level measurements during the 6‐week period show a variety of conditions, including several episodes of elevated concentrations of SO2, NO3−, HNO3, aerosol SO4=, and occasionally aerosol NO3−. Nitric acid comprised the majority of soluble acidity at ground level more than half the time, and was relatively more important during the periods of elevated SO4 = and NO3− concentrations. Examination of cloud water composition indicated that HNO3 was also the dominant contributor to cloud water acidity on the majority of days sampled. Comparisons of air and cloud water absolute concentrations and concentration ratios suggest that aqueous SO2 oxidation was of minor importance in determining cloud composition. The conclusion is supported by measurements of hydrogen peroxide in cloud water samples. Cloud water NO3−/SO4 = ratios were found to exceed (HNO3 + aerosol NO3−)/SO4= ratios in air at the surface in most cases, and in a few instances cloud water NO3− concentrations were higher than expected based on the surface air composition data; several possible causes for this observation are discussed. It is concluded that in this region in winter, the composition of low‐level clouds can be estimated to within a factor of 2 by measurements of air composition at the surface, and that dissolution of soluble aerosol and gaseous species is primarily responsible for cloud composition. In‐cloud SO2 oxidation is found to be of minor significance, but the data may indicate in‐cloud production of HNO3 in some cases.