bluuebunny/crossref_metadata_2025 huggingface dataset:
The CH3CHO‐NO3 reaction and possible nighttime PAN generation
Authors: Cantrell Christopher A. , Davidson James A. , Busarow Kerry L. , Calvert Jack G.
Published: February 2008

Kinetic studies have been made of the CH3CHO‐NO3 reaction in dilute mixtures of CH3CHO, NO2, and N2O5 in synthetic air at 700 torr and room temperature. During the course of the reaction, reactant and product analyses were made in situ, using long path length Fourier transform infrared spectroscopy. The major products of the reaction for these conditions are HONO2 and CH3COO2NO2. All evidence suggests that the first step in the reaction sequence, NO3 + CH3CHO → HONO2 + CH3CO, proceeds with a rate constant,k = (2.1 ± 0.4) × 10−15 cm3 molecule−1 s−1 at 299 ± 1 K. These results, combined with other reaction rate data pertinent to tropospheric chemistry, are used to computer simulate the homogeneous chemistry of the polluted troposphere and to evaluate theoretically the nature of the nighttime chemistry.
Measurements of the NOx‐O3 photostationary state at Niwot Ridge, Colorado
Authors: Parrish D. D. , Trainer M. , Williams E. J. , Fahey D. W. , Hübler G. , Eubank C. S. , Liu S. C. , Murphy P. C. , Albritton D. L. , Fehsenfeld F. C.
Published: February 2008

The photostationary state (PSS) involving NO, NO2, and O3 has been studied at a site located in the Colorado mountains. During the daytime in summer the concentration of NO2 relative to the concentration of NO is greater than expected from the PSS. These results indicate that an additional oxidant OX other than O3 is converting NO to NO2. The level of OX depends on season, NOx (NO + NO2) concentration, and solar UV intensity. The maximum OX levels occur for an NOx mixing ratio of about 0.4 parts per billion by volume (ppbv). For NOx mixing ratios below 0.1 ppbv, no substantial imbalance in the PSS is observed. For NOx concentrations between 0.25 and 1.0 ppbv, the OX level depends linearly on solar UV intensity. In the winter the level of OX is much lower than in the summer for all NOx concentrations and solar UV intensities. The nature of OX, as indicated from the NOx‐catalyzed formation of O3, is examined.
Measurement of gas phase hydrogen peroxide in air by tunable diode laser absorption spectroscopy
Authors: Slemr F. , Harris G. W. , Hastie D. R. , Mackay G. I. , Schiff H. I.
Published: February 2008

Tunable diode laser absorption spectroscopy has been applied to the determination of gas phase hydrogen peroxide in ambient air with sub‐ppbv (parts per billion by volume) detection limits for measurement times of the order of minutes. The methods for calibrating the instrument and for assuring the absence of spectroscopic and sampling interferences at the level of our present detection limits are described. Ambient air monitoring with our system indicates that the hydrogen peroxide mixing ratio is often < 0.3 ppbv. Five‐minute average mixing ratios of up to 2.9 ppbv have been measured at sites in southwestern Ontario, Canada, during the summer months of 1984 and 1985, while the highest 1‐hour average value observed was 2.1 ppbv.
Simultaneous measurements of stratospheric NO and NO2 and their comparison with model predictions
Authors: Roscoe H. K. , Kerridge B. J. , Gray L. J. , Wells R. J. , Pyle J. A.
Published: February 2008

Measurements of stratospheric NO and NO2 from the last four flights of the Oxford radiometer are compared with predictions by a diurnal photochemical model. The rapid sunrise and sunset changes predicted by the model and detected on previous flights are confirmed. The observations suggest agreement with model predictions of the night time decay of NO2 associated with N2O5 production but do not fully verify them. For three of the flights this is due to insufficient measurement precision and short flight duration, and in the other flight it is due to disruption of the diurnal cycle by viewing parts of the stratosphere of different composition. The 1982 flight showed both NO and NO2 to be greatly reduced between 30 and 35 km. We attribute this to the eruption of the El Chichon volcano. Possible mechanisms for this reduction are discussed.
Numerical advection by conservation of second‐order moments
Authors: Prather Michael J.
Published: February 2008

A new, accurate, and nondiffusive method for three‐dimensional advection of trace species is presented. The method preserves tracer structures by conserving the second‐order moments of the spatial distribution of tracer during advection. Tracer concentrations are represented by separate, second‐order polynomials within each grid box. This second‐order moments method has been shown, in typical tests for advective schemes, to be equal or superior to presently available methods in terms of absolute accuracy, numerical diffusion, and computational cost.
Response of ozone to short‐term variations in the solar ultraviolet irradiance: 2. Observations and interpretation
Authors: Eckman Richard S.
Published: February 2008

An analysis of the response of middle atmospheric ozone to short‐term variations in the solar ultraviolet irradiance is presented. Measurements of ozone from the Solar Mesosphere Explorer (SME) ultraviolet spectrometer (UVS) are compared to calculations of a one‐dimensional, radiative‐photochemical model of the upper stratosphere and lower mesosphere. SME UVS measurements in the 0.1‐ to 1‐mbar range suggest that tropical ozone responds to solar rotational variation when analyzed using both frequency and time domain techniques. Three periods during 1982 and 1983 were selected for the analysis. The solar irradiance during each period exhibited different spectral characteristics. A significant 27‐day variation in the solar irradiance at 205 nm was measured during mid‐1982, with an amplitude of 2.5%. Observations of ozone near the stratopause during this period showed a corresponding variation, with a 1.3% amplitude. Analysis of ozone variations at extratropical latitudes revealed different periodicities that were not correlated with solar variations. The amplitude of the measured response is, in all cases, systematically larger than theoretical calculations but is nonetheless in agreement when uncertainties in the analysis are considered. However, the observed phase lag of ozone with respect to the solar UV variations is generally not in accord with model predictions.
Horizontal mixing coefficients for two‐dimensional chemical models calculated from National Meteorological Center data
Authors: Newman Paul A. , Schoeberl Mark R. , Plumb R. Alan
Published: February 2008

Calculations of the two‐dimensional species‐independent mixing coefficients for two‐dimensional chemical models for the troposphere and stratosphere are performed using quasi‐geostrophic potential vorticity fluxes and gradients from 4 years of National Meteorological Center data for the four seasons in both hemispheres. Results show that Kyy values for the winter lower stratosphere are broadly consistent with those currently employed in two‐dimensional models, but Kyy values in the northern winter upper stratosphere are much larger than those usually used.
The antarctic ozone minimum: Relationship to odd nitrogen, odd chlorine, the final warming, and the 11‐year solar cycle
Authors: Callis Linwood B. , Natarajan Murali
Published: February 2008

Photochemical calculations along “diabatic trajectories” in the meridional plane are used to search for the cause of the dramatic springtime minimum in Antarctic column ozone. Results indicate that the minimum is principally due to catalytic destruction of ozone by high levels of total odd nitrogen which are in accord with column sum observations of NO2(between 20 and 35 km) made in the Antarctic. Calculations suggest that these levels of odd nitrogen are transported to the lower stratosphere from the mid to upper stratosphere and lower mesosphere. This transport occurs within the polar vortex and during the polar night. The possibility that these odd nitrogen levels are related to the 11‐year solar cycle and are increased by enhanced formation in the thermosphere and mesosphere during solar maximum conditions is discussed. Analysis of satellite data (LIMS, SME, SAGE, SAGE II) establishes significantly increased levels of stratospheric total odd nitrogen for the 1979–1984 time period, particularly at the midsouthern latitudes. Calculations suggest that these mid‐latitude increases in odd nitrogen contribute significantly to the recently reported mid‐latitude ozone decreases. The persistent reoccurrence of the Antarctic ozone minima into the mid‐1980s is related to this growth of odd nitrogen. Transient planetary wave activity near the onset of the final warming is found to significantly moderate the formation of the minimum in column ozone. Chlorine species at double the present atmospheric levels are shown to have an insignificant effect if only homogeneous processes are considered. If heterogeneous chlorine reactions are considered, the catalytic destruction of ozone by the odd nitrogen is slightly inhibited between 20 and 30 km. Below 20 km the catalytic destruction of ozone due to an odd hydrogen and odd chlorine cycle may be fostered by the heterogeneous reactions but this cycle contributes only modestly to the calculated ozone column sum destruction.
Southern hemisphere medium‐scale waves and total ozone disturbances in a spectral general circulation model
Authors: Cariolle D. , Déqué M.
Published: February 2008

The ozone distribution and its variability is simulated with a general circulation model (GCM), which includes self‐consistent representation of the physical processes and an accurate parameterization of the ozone photochemical sources and sinks. Emphasis is placed on analysis of the action of atmospheric waves on the O3 distribution. In particular, the model generates the medium‐scale waves which are often observed in the southern hemisphere. These waves tend to form quasi‐regular O3 patterns with zonal wave numbers 4, 5, and 6, in fairly good agreement with the observations. Baroclinic instability generates the waves in the lower troposphere, but it is their equivalent barotropic structure in the upper troposphere‐lower stratosphere which produces the signal on the total ozone column, since O3 disturbances are nearly in phase in this altitude range. Episodes of large amplitude of the medium‐scale waves occur when the transient waves interact with a stationary wave. This standing wave has a zonal wave number close to 4 and appears to result from the large convective activity within the South Pacific Convergence Zone and its southward extension at mid‐latitudes. This study gives a good illustration of the important role played by GCMs in understanding the interactions between dynamical and physical processes in the troposphere and wave activity and O3 distribution in the lower stratosphere.
Chemical and microphysical studies of nonprecipitating summer cloud in Ontario, Canada
Authors: Leaitch W. R. , Strapp J. W. , Wiebe H. A. , Anlauf K. G. , Isaac G. A.
Published: February 2008

During the fall of 1981 and the summer of 1982, airborne and ground‐level field studies were conducted in southern and central Ontario to investigate the processes leading to cloud water acidification. Aircraft measurements were made of aerosol particles, cloud droplets, and cloud liquid water content. Cloud water samples were collected in nonprecipitating cumulus and stratocumulus clouds and analyzed for the concentrations of SO4=, NO3−, Cl−, Na+, NH4+, Ca++, Mg++, and H+. Aerosol composition was studied at a rural location on the ground. The ground‐level aerosol composition was compared with the cloud water composition. Observations of the vertical variation of the aerosol particle size distribution were used to justify this procedure, but it was also assumed that the relative fraction of submicron aerosol SO4= did not vary between the ground and cloud base during individual flights. In this way the cloud water SO4= was explained by the nucleation of water droplets on sulphate aerosol particles in at least nine of 11 cases studied. In several of the cases the concentration of NO3− measured in cloud water samples was much higher than could be accounted for by the measurement of below‐cloud aerosol NO3− plus gaseous HNO3. Similarly, concentrations of Ca++ found in the cloud water far exceeded concentrations measured in the aerosol.
Nonmethane hydrocarbons in the troposphere: Impact on the odd hydrogen and odd nitrogen chemistry
Authors: Kasting James F. , Singh Hanwant B.
Published: February 2008

The chemistry of light nonmethane hydrocarbons (NMHCs), including C2H6, C3H8, n‐C4H10, C2H4, and C3H6, was incorporated into a seasonally varying, one‐dimensional model of the mid‐latitude troposphere (45°N). Simulations were performed for both marine and continental atmospheres. Where possible, these simulations have been compared with surface and aircraft measurements of test molecules, such as C2H6, C3H8, CO, peroxyacetyl nitrate (PAN), and peroxypropionyl nitrate (PPN). Model calculations predict that NMHC oxidation produces acetaldehyde and acetone in concentrations that can exceed that of formaldehyde. Organic peroxides were found to be present in concentrations that, considered collectively, are comparable to that of hydrogen peroxide. Peroxyacetyl nitrate is the dominant odd nitrogen (NOx) compound in wintertime and is surpassed only by HNO3 during the summer. The inclusion of NMHC‐PAN chemistry has little effect on summertime odd hydrogen/odd nitrogen photochemistry, but is shown to have a substantial impact in wintertime, particularly over the continents, where NOx concentrations are high and temperatures are low. Under these circumstances, oxidation of NMHC compounds can enhance ground‐level OH and HO2 concentrations by factors of 5–50, respectively. Formation of PAN during the wintertime can reduce upper tropospheric NOx concentrations by a factor of 2–3 over the oceans and a factor of 20–30 over the continents. Significant changes also occur in the predicted concentrations of HNO3 and HO2NO2. The effects of NMHCs on wintertime photochemistry might be moderated by seasonal variations in NMHC source strengths or by horizontal transport of trace gases from the continents to the oceans and from high latitudes toward the equator. Nonetheless, it seems likely that models of the troposphere must include NMHC‐PAN chemistry in order to correctly predict the seasonal behavior of trace chemicals.
Considerations regarding sources for formic and acetic acids in the troposphere
Authors: Keene William C. , Galloway James N.
Published: February 2008

HCOOH and CH3COOH are important chemical constituents of cloud water and precipitation, but sources for these compounds in the atmosphere are at present unknown. The question of source identification was addressed through the analysis of 465 samples of precipitation collected at 14 continental and marine locations around the world. Continental precipitation during growing seasons contained, relative to marine precipitation and to continental precipitation during nongrowing seasons, higher absolute concentrations of organic acids and higher ratios of HCOOT (HCOOHaq + HCOO−) to CH3COOT (CH3COOHaq + CH3COO−). The concentrations of HCOOT and CH3COOT in precipitation at most locations were also highly correlated. These results support the hypothesis that organic acidity in precipitation may originate with two major sources, volatile vegetative constituents over continents and a second weaker source in both continental and marine regions. Relative to the similar ratios of HCOOT to CH3COOT in the aqueous phase, differences in precipitation pH resulted in large regional differences in calculated equilibrium vapor phase concentrations. The mechanism(s) by which proportionate concentrations of HCOOT and CH3COOT are maintained in the aqueous phase remains an open question. Comparisons between precipitation in impacted and remote regions indicate that although possibly important near large population and industrial centers, anthropogenic emissions are probably not major sources for organic acids in precipitation over broad geographic regions.
Solar EUV induced variations in the thermosphere
Authors: Hedin A. E. , Mayr H. G.
Published: February 2008

The effects of solar activity on the thermosphere are reviewed. The neutral total density, temperature, and electron density increase with solar activity, and their variations are fairly well correlated with variations in solar 10.7‐cm flux. The electron temperature, by contrast, has a complex behavior with solar activity, depending on altitude and season, as increased heat input is balanced by increased cooling provided by the enhanced electron density. Also, individual neutral species do not all increase in step but are influenced by dissociation and dynamical processes. The inceased ion drag at higher solar activities inhibits the neutral wind from increasing in the same proportion as the neutral temperatures and densities.
Net ozone photochemical production over the eastern and central North Pacific as inferred from GTE/CITE 1 observations during fall 1983
Authors: Chameides W. L. , Davis D. D. , Rodgers M. O. , Bradshaw J. , Sandholm S. , Sachse G. , Hill G. , Gregory G. , Rasmussen R.
Published: February 2008

Simultaneous measurements of O3, NO, CO, H2O vapor, and temperature over the eastern and central North Pacific Ocean are analyzed to infer the role of photochemistry in the budget of tropospheric ozone. A statistical analysis of the data reveals a close correlation between ozone and nitric oxide levels and an anticorrelation between these two constituents and water vapor, thus implying the existence of a major ozone source associated with NO‐rich air parcels from the upper troposphere and/or lower stratosphere. The NO in these parcels is believed to have originated from the stratosphere, from air detrained from active thunderclouds, or from some combination thereof. The statistical analysis also indicates the existence of an additional source of secondary importance associated with CO‐rich air parcels, possibly of continental origin. Photochemical simulations of ozone photochemistry for the conditions encountered during the flights indicates, on average, a net photochemical source of ozone in the free troposphere and a net sink in the boundary layer. The free tropospheric, photochemical source of ozone is found to be strongly correlated with NO, implying that regions of enhanced NO are also regions of enhanced ozone production. A similar statistical correlation between ozone photochemical production and CO levels was not found. It is estimated that on average, during the period of the fall operation, photochemistry provided a net source of ozone to the free troposphere overlying the eastern and central North Pacific Ocean of about 5×1010 molecules cm−2 s−1 and a net sink of ozone to the boundary layer overlying this region of about 3×1010 molecules cm−2 s−1.
A two‐dimensional numerical investigation of the dynamics and microphysics of Saharan dust storms
Authors: Westphal Douglas L. , Toon Owen B. , Carlson Toby N.
Published: February 2008

Two‐dimensional numerical simulations of the spatial and temporal distributions of Saharan dust size distributions over the desert and the eastern Atlantic Ocean are presented. The simulations show that during mobilization the soil size distribution is modified by either a size‐dependent lifting mechanism or by mixing of local soil with aged aerosols or with aerosols originating from nearby soils which have different size distributions. The highest number concentrations encountered were not high enough for coagulation to have a significant effect over the time scales considered here. When the source region is near the coast, as opposed to the central Sahara, the highest mass concentration achieved at Sal Island is more than doubled. However, in the two‐dimensional simulations the central Saharan storms seem to be equally as important as coastal sources in terms of the optical properties of an outbreak, since the total surface area of the suspended dust at the end of the coastal and inland source simulations are nearly the same. A background mineral aerosol or increased vertical turbulent diffusion across the marine layer inversion is required for the simulated marine layer size distributions to match the observed distributions at particle sizes under 8 μm. Sedimentation prohibits the direct advection of ultragiant particles very far from the coast, suggesting that the ultragiant particles observed over the ocean are locally generated, perhaps in water clouds.
Model ozone photochemistry on the basis of Solar Mesosphere Explorer mesospheric observations
Authors: Clancy R. T. , Rusch D. W. , Thomas R. J. , Allen M. , Eckman R. S.
Published: February 2008

Morning and afternoon mesospheric ozone profiles (50–90 km) measured by the Solar Mesosphere Explorer (SME) satellite are analyzed with one‐dimensional photochemical models. The observed ozone abundances are 40% and 100% greater than the model ozone abundances at 50 and 80 km, respectively, assuming standard chemistry and rate coefficients. A Monte Carlo analysis for model ozone abundances that includes uncertainties in kinetic rate coefficients indicates that the model‐data disagreement exceeds 2 standard deviations. The majority of the disagreement must be due to errors in the rate of odd‐hydrogen catalytic destruction of ozone, unless the rate coefficient for O + O2 + M → O3 + M is significantly (>50%) in error. Diurnal model calculations are compared with SME observations of ozone profiles at ∼0400 and 1400 LT for high northern summer latitudes. Analysis of the ratios of these early morning and midafternoon ozone profiles provides the additional constraint that larger odd‐oxygen production rates are required if lower odd‐hydrogen activity is invoked to increase model O3 abundances. The increase in odd‐oxygen production must be solar zenith angle independent in the mesosphere, ruling out significant changes in the Schumann‐Runge band O2 opacities from Allen and Frederick (1982). However, an increase in three‐body formation of O3 is also consistent with the observed morning/afternoon ratios. Any of the above changes are consistent with an improvement in model ozone comparisons with stratospheric observations. Finally, we find evidence for diurnal variations in mesospheric ozone above 80‐km altitude, which are likely related to diurnal variations in vertical transport.
Components of the ice age circulation
Authors: Rind D.
Published: February 2008

Four general climate model (GCM) simulations are compared to investigate the influence of ice age boundary conditions on atmospheric dynamics and regional climate patterns. Starting with a simulation of the current climate, the ice age distributions of (1) sea surface temperatures; (2) 10‐m‐thick land ice in locations of ice age ice sheets; and (3) ice sheets elevated to their proper altitude were added sequentially. The results show that these different boundary conditions often impart conflicting influences, with the full ice age simulation representing a compromise between different tendencies inherent in the different boundary components. In particular, the ice age sea surface temperatures stablize the atmosphere over the oceans, increase the frequency of storms tracking through central North America, and amplify transient eddy energy without increasing baroclinic generation. Low‐elevation ice generates low pressure over eastern North America and southern Europe in winter, while increasing cloud cover and cooling the land in summer. Elevation of the ice sheets cools the land in winter, further intensifies storms off northeastern North America, induces subsidence warming downstream of the European ice sheets in summer, and increases both transient and stationary eddy energy through increased baroclinicity. In all of the experiments the atmosphere is transporting a similar amount of energy poleward, consistent with the similarity in sea surface temperature gradients, but the eddy characteristics employed in the process vary with the longitudinal distribution of the boundary conditions. Other results show that the Broad raised ice sheets have both a topographic and a thermal effect (due to the reduced optical thickness above) which occur simultaneously and lead to a greater stationary eddy forcing of the zonal mean flow. The stationary wave change in the northern hemisphere is accompanied by a similar change in the southern hemisphere, implying a dynamical interhemispheric connection. The Walker circulation and the July Hadley circulation weaken as a result of the altered sea surface temperature patterns, but the poleward extent of the Hadley cell and the zonally averaged jet stream show little difference from current climate values. The results are compared with two‐dimensional model expectations, paleoclimate evidence, and previous ice age simulations.
Reflectivity of Earth's surface and clouds in ultraviolet from satellite observations
Authors: Eck T. F. , Bhartia P. K. , Hwang P. H. , Stowe L. L.
Published: February 2008

The Total Ozone Mapping Spectrometer (TOMS) on board Nimbus 7 is used to infer the ultraviolet (UV) surface and cloud reflectance at 370 nm. Cloudless surface reflectivity was analyzed on a global basis for all surface types for several months. The UV surface reflectivity varies from 2% for some forest and grassland regions to 14% for some sandy desert areas. A notable exception is the large salt flats of Bolivia, which have a reflectivity of ∼60%. Cloud reflectivity was also analyzed for clouds located at three levels in the atmosphere, as determined by the 11.5‐μm channel of the Temperature Humidity Infrared Radiometer. Average cloud reflectivity at 370 nm ranges from 52% for low clouds (tops <2 km) to 76% for high clouds (tops > 7 km at the equator, decreasing to >4 km at poles).
Polar stratospheric optical depth observed between 1978 and 1985
Authors: McCormick M. P. , Trepte C. R.
Published: February 2008

Observations of the stratospheric optical depth at 1.0 μm obtained for high latitudes are presented for a 7‐year period. Weekly averaged data determined from measurements made by the Stratospheric Aerosol Measurement (SAM) II experiment from October 1978 to October 1985 show that the overall yearly values in both polar regions are controlled by volcanic perturbations, with most volcanic effects being experienced in Arctic latitudes. The largest values over this period were observed after the eruption of El Chichon in 1982. Conservatively, peak values found in the Antarctic region were approximately 2.0×10−2and in the Arctic region about 5.5×10−2. We estimate probable values for these regions to be 2.6×10−2and 0.11, respectively. The Arctic values are almost 40 times greater than values observed during the first several months after the instrument was launched. The weekly averaged data also show the seasonal fluctuations due to microphysical and dynamical processes. Comparison of the optical depth record with a weekly averaged 50‐mbar temperature record indicates that polar stratospheric clouds are present in the southern high latitudes each year near this level from early June to early September. A depression observed in the optical depth record each austral spring season is believed to be the result of the downward displacement of particles caused by subsidence and sedimentation during the course of winter. Following the breakup of the vortex, optical depth values increase as aerosol is transported poleward. These features are noted to be present in the Arctic region as well, but on a smaller scale because of the satellite sampling methodology and the averaging scheme employed.
Atomic oxygen in the lower thermosphere
Authors: Lin Florence J. , Chance Kelly V. , Traub Wesley A.
Published: February 2008

We measured in thermal emission the 63‐μm line due to thermospheric atomic oxygen O(3P), using a far‐infrared spectrometer on a balloon platform at 37 km altitude over Palestine, Texas (32°N), on June 20, 1983. From measurements of the equivalent width of this line at two elevation angles, we find a weak angular dependence: the equivalent width increases by a factor of 1.5 ±0.3 as the angle decreases from +30° to +1°. Since the optical depth of the O(3P) line is large, we cannot directly convert the measured line intensity to a column abundance. Instead, we interpret the measurements in terms of radiative transfer through a 16‐layer atmosphere extending to 200 km. We use a model atmosphere for summer at 30°N, with an exospheric temperature of 1300 K, including (1) an assumed daytime atomic oxygen abundance profile constructed from recent chemical and dynamical models and (2) a water vapor abundance profile constructed from recent experimental and model results. For this assumed O(3P) vertical profile shape we determine from our spectra at two elevation angles a multiplicative scaling factor of 0.8, with an altitude‐dependent uncertainty. In the best‐determined layer the uncertainty in the multiplier is ±0.2 at 119 km. The model‐dependent peak atomic oxygen density is 3.6 (±1.9) × 1011 cm−3 at an altitude of about 101 km.
The interannual variation in the seasonal cycle of carbon dioxide concentration at Mauna Loa
Authors: Enting I. G.
Published: February 2008

A band‐pass filter is used to obtain an estimate of the seasonal CO2 cycle at Mauna Loa from monthly mean concentration data. The signal that is extracted shows interannual variations in the amplitude with, as has frequently been noted, a preponderance of larger amplitudes in recent years. An interesting feature of the signal is that abnormally small amplitude peaks in the (northern) spring are almost always followed by small‐amplitude troughs in the following fall but that there is no similar correlation between the amplitudes of peaks in fall and the following spring. This suggests that the amplitude variations reflect changes in individual northern growth seasons.
An investigation of cloud/radiation interactions using three‐dimensional nephanalysis and earth radiation budget data bases
Authors: Koenig George , Liou Kuo‐Nan , Griffin Michael
Published: February 2008

The cloud climatology data obtained from the analysis of the Air Force three‐dimensional nephanalysis (3DNEPH) cloud data base and the broadband radiation budget data derived from the Nimbus 7 earth radiation budget (ERB) measurements, are compared on regional, zonally averaged, and hemispheric scales for January and July 1979. The analyzed cloud climatologies are also compared with existing cloud climatologies and general circulation features. In addition, they are used as input to an IR parameterization model to calculate the emitted IR flux at the top of the atmosphere. These model fluxes are subsequently compared with the ERB flux climatologies. An investigation of the sensitivity, at 1200 and 2400 local time, of the reflected solar, emitted IR, and net radiation to changes in cloud amount on a regional, zonal, and hemispherical basis is then carried out employing the 3DNEPH and ERB data. The daily net radiation sensitivity factors for the northern hemisphere for January and July, with values of −8.1 and −50.9 W m−2, respectively, compare reasonably well with those obtained by other investigators.
Measurements of mesospheric water vapor in 1984 and 1985: Results and implications for middle atmospheric transport
Authors: Bevilacqua Richard M. , Wilson William J. , Schwartz Philip R.
Published: February 2008

We present the detailed results of ground‐based mesospheric water vapor measurements obtained by microwave spectroscopy at the Jet Propulsion Laboratory (JPL) from December 1984 to April 1985 (JPL 1984/85), and an overview of results obtained the previous year from April to June 1984 (published by Bevilacqua et al., 1985). The JPL 1984/85 spectral data appeared to contain an instrumental baseline curvature which we were able to bracket and remove. In general, the JPL 1984/85 results are in good agreement with those of our previous measurements. They indicate water vapor mixing ratios between 6 and 8 ppmv at 60 or 65 km and falling off steeply with height above this point to values of less than 2 ppmv at 80 km. In addition, there is a large amount of day‐to‐day variability indicated in the data. A major result of the study is that we find that both the observed vertical gradient of water vapor mixing ratio and its seasonal variation are consistent with the hypothesis that vertical transport time scales are smaller, perhaps by an order of magnitude, than values currently used in both one‐ and two‐dimensional photochemical/dynamical models.
Mesoscale convective complexes in the Americas
Authors: Velasco Ines , Fritsch J. Michael
Published: February 2008

Enhanced infrared satellite imagery and conventional surface and sounding data are used to document the existence and climatological characteristics of mesoscale convective complexes (MCCs) over midlatitude South America (south of 20°S) and in the tropical region (20°N to 20°S) between North and South America. The implications of the results, with regard to the structure and dynamics of MCCs, are discussed. It is found that MCCs occur with approximately the same frequency in mid‐latitude South America as they do in mid‐latitude North America. For the most part the characteristics of mid‐latitude South American MCCs are similar to those of MCCs in the United States. The most notable difference between North and South American MCCs is that the South American systems are, on the average, about 60% larger than MCCs in the United States. In addition to the large population of mid‐latitude South American MCCs, an even larger number of low‐latitude (tropical) systems were found. In general, both the mid‐latitude and tropical populations of MCCs are nocturnal and continental; i.e., the great majority of systems occur at night over land. Of the systems that do occur over water, a significant fraction develop into tropical storms. Large populations of MCCs occur in each of the physiographically similar mid‐latitude areas of North and South America where low‐level nocturnal jets frequently develop. Very few MCCs occur over the Amazon River Basin or over the southeastern United States, even though both of these areas exhibit large amounts of deep convective activity. All of the various MCC population centers occur in latitudinal zones of westerlies or easterlies and are concentrated immediately downwind of major mountain ranges. One of the 2 years of data that was investigated was an El Niño year. During the El Niño period the number of mid‐latitude South American systems was more than double the number in the non‐El Niño year. Moreover, several MCCs formed over the anomalously warm water that appeared along the Peruvian coast. Thus on the basis of this very small sample, there may be a direct connection between MCC activity and El Niño.
Saharan dust on Fuerteventura Island (Canaries): Chemical and mineralogical characteristics, air mass trajectories, and probable sources
Authors: Coude‐Gaussen G. , Rognon P. , Bergametti G. , Gomes L. , Strauss B. , Gros J. M. , Le Coustumer M. N.
Published: February 2008

From April 12 to 19, 1984, dust was collected by cascade impactor on Fuerteventura Island, 100 km from the Saharan coast. The samples were analyzed by X ray fluorescence spectrometry (elemental composition), by X ray diffraction (mineral constituents), and by scanning electron microscope (SEM) and energy dispersive X ray analyzer (EDXA) examination (shape, surface features, and mineralogy of particles), with the aim of determining the possible source areas of the dust. On the scale of dust clouds, another method allowed us to define the displacements of the dust: using remote sensing (METEOSAT II, National Oceanic and Atmospheric Administration (NOAA)) and computing trajectories for any starting or ending point at any time. These various methods gave complementary results and pointed out two successive episodes of dust with two different continental origins. The first originated from a nearby source in the Souss plain (southern Morocco) and was characterized by very fine quartz particles. The second drifted above more remote calcareous regions. This study allows us to show how different methods can be used to characterize dust and to find the source areas. The results suggest some general questions about the occurrence of coarse particles in the atmosphere and their role in the atmospheric deposition flux budget.
Absolute infrared absorption cross sections for ClONO2 at 296 and 223 K
Authors: Davidson J. A. , Cantrell C. A. , Shetter R. E. , McDaniel A. H. , Calvert J. G.
Published: February 2008

The infrared absorption spectrum of chlorine nitrate has been measured at 296 K and at 223 K, a temperature typical of the stratosphere. Absorption cross sections are reported for all the strong features of the absorption spectrum between 450 and 2000 cm−1. These cross sections may be used in determining stratospheric ClONO2 concentrations. The ν4, ν3, and ν2 transitions near 780, 809, and 1292 have been studied in detail, and some significant temperature dependencies in the cross sections have been found. The most dramatic of these is the 34% increase in the Q branch at 780.2 cm−1 between 296 K and 223 K.
Chemistry of precipitation from a remote, terrestrial site in Australia
Authors: Likens Gene E. , Keene William C. , Miller John M. , Galloway James N.
Published: February 2008

Wet‐only rain samples were collected and chemically analyzed during 1980–1984 at Katherine, Australia, as part of the Global Precipitation Chemistry Project. Rainfall averaged 104 cm/yr and ranged from 74.6 cm in 1982–1983 to 135.7 cm in 1983–1984. Total cation concentration was about 29 μeq/L. The volume‐weighted mean H+ concentration expressed as pH was 4.73, 64% of the free acidity was due to organic acids (formic and acetic). The pH due to strong mineral acids only was 5.08. Air mass trajectories during the wet season were predominantly from the northeast (51%), and this trajectory was most important in terms of deposition. Although there is a high frequency of lightning during the wet season, no evidence was found that it contributed significantly to the nitrate concentration in rain. Because concentrations decreased markedly with amount of precipitation, the total deposition of dissolved substances was not correlated directly with the amount of rain. Comparisons were made between the chemistry of rain at Katherine and with other remote areas and with the eastern United States.
Infrared measurements of several nitrogen species above the South Pole in December 1980 and November‐December 1986
Authors: Murcray F. J. , Murcray F. H. , Goldman A. , Murcray D. G. , Rinsland C. P.
Published: February 2008

Ground‐based high‐resolution infrared solar absorption spectra recorded from the Amundsen‐Scott south pole station have been analyzed to determine total vertical column amounts of HNO3 in December 1980 and November 1986, and NO, NO2, in November–December 1986.
Deposition rate of particulate and dissolved aluminum derived from saharan dust in precipitation at Miami, Florida
Authors: Prospero Joseph M. , Nees Ruby T. , Uematsu Mitsuo
Published: February 2008

Precipitation was collected for a 1‐year period in Miami, Florida. The deposition rate of Al in samples containing Saharan dust was 10.1 μg/cm2, this flux is equivalent to a mineral deposition rate of 126 μg/cm2 per year, a value comparable to the mineral accumulation rate in sediments of the tropical North Atlantic. Mineral deposition rates in rain were highly variable, with 22% of the total occurring in 1 day and 68% occurring in 4 days in two separate dust episodes. The volume‐weighted average concentration of dissolved Al in dust‐related rain events was 9.8 μg/L; if normalized to the total volume of rain that fell that year, the average would have a minimum value of 3.0 μg/L. The dissolved Al fraction (defined as all Al that passes through a 0.45‐μm filter) ranged from 0.5 to 48%, with a volume‐weighted mean of 5%; solubility tended to increase with decreasing rain pH and decreasing mineral concentration. If the 5% solubility applies to all Saharan dust deposited in the tropical Atlantic, then the annual deposition rate of soluble Al in this region would be 2–8×1011 g, a rate commensurate with that carried by the Amazon; on a global basis the annual input to the oceans of soluble Al in dust would be 20–40×1011 g, a rate comparable to that carried by rivers. These atmospheric input rates of dissolved Al are sufficient to account for many of the distribution features of Al in the oceans.
Stratospheric electric field and conductivity measurements over electrified convective clouds in the South American region
Authors: Pinto I. R. C. A. , Pinto O. , Gonzalez W. D. , Dutra S. L. G. , Wygant J. , Mozer F. S.
Published: February 2008

In this work, stratospheric dc electric fields and conductivity measurements, associated with electrified convective clouds identified by satellite infrared imagery, are presented. These measurements were obtained at an altitude of 26 km by a balloon‐borne double‐probe detector, launched from Cachoeira Paulista (geographic coordinates 23°40′S, 45°W) on April 2, 1980. The electric fields are found to correspond to electrified convective clouds with charges of the order of a few coulombs. The conductivity measurements show variations by over a factor of 2 around the average value of 4 × 10−12 mho/m. Such variations, which merit more investigation, did not show an apparent relation with the simultaneous electric field measurements. Using the vertical electric field and conductivity measurements, a current density is also estimated. Furthermore, a detailed original discussion on conductivity measurements in the atmosphere as well as a suggestion for estimating distances from the detector to the cloud, using the ratio between the magnitudes of the measured vertical and horizontal electric fields, is included.
An improved atmospheric buoyancy wave spectrum model
Authors: Sidi C. , Lefrere J. , Dalaudier F. , Barat J.
Published: February 2008

A Garrett‐Munk‐type spectrum, describing in the frequency–wave number space the energy per unit mass distribution of the atmospheric buoyancy wave field, is derived from experimental spectra of the field variables, within the following constraints: (1) the spectral modeling must refer only to kz spectra, in order to minimize the spectral contributions of the possibly coexisting quasi‐two‐dimensional turbulence and; (2) the resulting model must correspond to a saturated wave field in its high wave number limit. A spectral dependence on intrinsic frequencies is estimated from the ratios of experimental temperature and vertical velocity kz spectra, obtained by balloon‐borne instrumentation. These results and previously published horizontal velocity kz spectra allow determination of the model spectrum parameters, which differ substantially from those proposed by VanZandt (1982). This resulting model spectrum is characterized by a nearly universal high wave number limit (with a −3 spectral slope) and a total energy that varies, mainly with altitude. Two typical atmospheric conditions, characterized by high or low vertical velocity variances, are, however, much better represented using two slightly different parameter sets. Then, the model spectra account for most experimental mesoscale range kz, kH, and frequency spectra. As a tentative interpretation, it is suggested that these two conditions are associated with the presence or absence of a turbulent buoyancy subrange, while, in both cases, the energy levels within the saturated subrange imply strongly interacting wave fields.
The cycle of biogenic sulfur compounds over the Amazon Basin: 1. Dry season
Authors: Andreae M. O. , Andreae T. W.
Published: February 2008

We determined the concentrations of gaseous and participate sulfur species over the Amazon Basin during July/August 1985. The concentration of dimethylsulfide (DMS) in the mixed layer was near 10 parts per trillion (ppt); methylmercaptan (MeSH) levels were about 1 order of magnitude lower. Above 1000 m, DMS levels decreased rapidly with altitude to about 1–2 ppt at 5 km. At ground level within the forest canopy, concentrations up to 40 ppt were observed. The distribution and diurnal behavior of DMS, MeSH, and hydrogen sulfide in the rain forest canopy and measurements by a flux chamber suggest that both the soil and the tree canopy contribute to the emissions of these gases. The SO2 levels measured over central Amazonia were relatively low: averages were 27 and 18 ppt in the boundary layer and the free troposphere, respectively. Together with the concentrations of aerosol sulfate and methanesulfonate (boundary layer averages: 129 and 6 ppt, respectively), these data suggest that the flux of biogenic sulfur from tropical forests (at least in the Amazon Basin) is lower than has been estimated previously. This is further supported by relatively low concentrations of sulfate in rain collected near Manaus. The sulfur flux from the Amazon rain forests is of the order of 3–8 nmol m−2 min−1; per unit area, it appears to be comparable to the flux from the ocean surface (about 6 nmol m−2 min−1). However, comparison of atmospheric and riverine fluxes of sulfur in the Amazon region suggests that biogenic sulfur cycling through the atmosphere may have considerable geochemical and ecological significance.
Absolute absorption coefficients of ClONO2 infrared bands at stratospheric temperatures
Authors: Ballard J. , Johnston W. B. , Gunson M. R. , Wassell P. T.
Published: February 2008

Fourier‐transform absorption spectroscopy has been used in the laboratory to obtain absolute absorption coefficients σ(ν) in infrared bands of ClONO2 in the 700–1800 cm−1 spectral region. These data have been obtained over a temperature range (213–296 K) corresponding to stratospheric temperatures. The results are therefore applicable to retrievals of stratospheric ClONO2 from remote‐sensing observations. Room temperature absorption coefficients are some 25% larger than previously reported values, and large temperature dependences in the absorption coefficients have been observed. The ν1 and ν2 bands behave as simple fundamentals of a system which has low‐energy vibrational or torsional modes, with little contribution from hot bands over the temperature range used. The intensity in the ν2 Q branch increased by 53% over the temperature range 296–213 K. A similar increase was observed for the ν4 Q branch, and significant hot‐band features were seen in the ν3, ν4 spectral region. The ν4 Q branch and the ν2 Q branch were observed to obey the Beer‐Lambert law over the range of pressure, temperature, absorber amount, and resolution employed. The absorption coefficients in the ν4 Q branch and in the ν2 band were modeled by equispaced absorption lines, each characterized by a central frequency, strength, lower‐state energy, and pressure‐broadened width.