bluuebunny/crossref_metadata_2025 huggingface dataset:
Free tropospheric and boundary layer measurements of NO over the central and eastern North Pacific Ocean
Authors: Davis D. D. , Bradshaw J. D. , Rodgers M. O. , Sandholm S. T. , KeSheng S.
Published: February 2008

Reported in this paper are the Georgia Institute of Technology NO results from the fall 1983 NASA GTE/CITE 1 Airborne Field Sampling Program. These data were predominantly collected over a geographical area defined by the eastern and central North Pacific Ocean, spanning the latitude range of 15°–42°N. These NO measurements were taken using the two‐photon laser‐induced fluorescence technique. The data show a general trend of increasing levels of NO from the boundary layer up to altitudes of nearly 10 km. The average midday value of No at altitudes of ≤1.8 km was 4 parts per trillion by volume (pptv), and at ∼6 km, 20 pptv, whereas that at ∼9 km was 25–35 pptv, the higher value reflecting the inclusion of NO data collected from the outflow region of two electrically active cumulonimbus clouds. The high‐altitude NO data strongly suggest that at least during the time of the GTE flight operation, the major sources of NO for remote regions of the Pacific Ocean were those resulting from lightning and the downward transport of stratospheric air.
Determination of nitrogen oxide emissions from soils: Results from a grassland site in Colorado, United States
Authors: Williams E. J. , Parrish D. D. , Fehsenfeld F. C.
Published: February 2008

The fluxes of NO and NO2 have been measured at a grassland site in Colorado, United States. The measurements were made using an enclosure technique during the period between Aug. 16, 1985, and Nov. 15, 1985. The fluxes ranged between 0.028 and 65 ng N m−2 s−1 with an average value for all measurements of 3.0 ng N m−2 s−1. The NO flux was found to increase rapidly with increasing temperature. Large variations of NO flux with soil moisture were also observed. Under dry soil conditions, NO2 was present in the effluent from the sampling enclosure but was not present when the soil and/or vegetation covering the soil was moist. Overall, the NO2 totalled approximately 10% of the NO emissions. The results are compared with NOx soil emission measurements carried out elsewhere.
A cloud type classification with NOAA 7 split‐window measurements
Authors: Inoue Toshiro
Published: February 2008

A simple objective cloud type classification method has been developed, based on split‐window measurements of the Advanced Very High Resolution Radiometer on board the NOAA 7 satellite. Brightness temperature difference between the split‐window data is a good parameter for the detection of cirrus and blackbody clouds. Two‐dimensional histograms of brightness temperature of the 11‐μm channel and the brightness temperature difference between the split‐window data over (64 km)2 subareas are constructed. By selecting appropriate thresholds in the two‐dimensional histogram, cirrus, dense cirrus, cumulonimbus, and cumulus clouds are classified over the tropical ocean. Cloud type classification maps were generated by this method for the western Pacific Ocean and were compared with the nephanalysis chart constructed at the Japan Meteorological Satellite Center from GMS data collected within 1 hour of the NOAA 7 observations. The comparison shows reasonable agreement. Fractional cloud cover for cirrus over each (64 km)2 subarea is calculated as the ratio of the number of samples which belong to the cirrus cloud type in the two‐dimensional histogram to the number of total samples in the subarea. Fractional cloud cover estimations for cumulonimbus and low‐level cumulus are also presented.
Solar radiation transmitted to the ground through cloud in relation to surface albedo
Authors: Gardiner Brian G.
Published: February 2008

The global solar radiation received at the earth's surface in the presence of cloud depends not only on the optical depth of the cloud and its other physical properties, but also on the albedo of the underlying surface. Multiple reflection of radiation between the cloud and a snow‐covered surface, mainly in the visible spectrum, can increase the measured global solar radiation by a factor of 2 or more in overcast conditions. A quantitative account of this effect is required, applicable to any cloud conditions, if climatological records of solar radiation at high latitudes are to provide adequate figures, even for monthly means, at locations where the surface albedo differs appreciably from that of the observing station. Measurements made at an Antarctic offshore station (65°S, 64°W) are compared during two periods of extreme surface albedo (open water and fast ice surrounding the island station) and demonstrate that the effect increases, in amplitude and variability, with increasing cloud cover. The extreme cases are reconciled by a relatively simple numerical model, of general applicability, in which partial cloud cover is parameterized by sunshine duration. Absorption in the cloud and the effect of local land surfaces are taken into account. The model is applied predictively to sunshine and visual sea ice data throughout a 2‐year period and successfully simulates the measured values of global solar radiation over a wide range of cloud and sea ice cover, enabling the irradiance for any value of surface albedo to be inferred.
Mesospheric motions observed by simultaneous medium‐frequency interferometer and spaced antenna experiments
Authors: Meek C. E. , Manson A. H.
Published: February 2008

Doppler sorting and angle of arrival have been used in an attempt to identify localized scattering features in the mesosphere. These might be caused by isolated perturbations in electron density carried along by the neutral wind or by some focusing mechanism in which a stable horizontally stratified scattering layer is perturbed by a wave motion, creating a moving “glint.” Discrepancies were found between interferometer and “true” (spaced antenna drift analysis) speeds using T = 3.2‐min record lengths and averaging over 1 hour. These records have good frequency resolution (1/T), but the length combined with normal wind speeds present means that single scatterers will be spread over several Doppler bins, and it is always possible that echoes from different locations combine to give a false angle of arrival. Consequently, series of shorter records (72 s) were examined in the hope of tracking echo location. Two examples have been found. Both occurred during signal strength “bursts” near 85 km, and their appearance suggests “glints” from 5‐min period waves, one traveling with and the other traveling ∼60° away from the background wind direction. The signal bursts themselves are of interest, having a regular repetition rate (30–40 min) and being very common at these heights in the summer. It is possible that these bursts are due to focusing or turbulence created by long‐period waves.
Atmospheric measurements of pyruvic and formic acid
Authors: Andreae Meinrat O. , Talbot Robert W. , Li Shao‐Meng
Published: February 2008

Pyruvic acid, a product of the atmospheric oxidation of cresols and probably of isoprene, has been determined together with formic acid in atmospheric aerosols and rain as well as in the vapor phase. Both acids are present predominantly as vapor; only about 10–20% of the total atmospheric pyruvate and 1–2% of the total formate are in the particulate phase. The concentrations of pyruvic and formic acid are highly correlated, with typical formic‐to‐pyruvic ratios of 10–30 in the gas phase, 20–30 in rain, and 2–10 in aerosols. The gas‐phase and rain ratios are comparable to those predicted to result from isoprene oxidation. Pyruvic acid levels were similar in the eastern United States (during summer) and the Amazon Basin, suggesting that natural processes, particularly the photochemical oxidation of isoprene, could account for most of the pyruvic acid present in the atmosphere.
Stratospheric O3, H2O, and HDO distributions from balloon‐based far‐infrared observations
Authors: Abbas M. M. , Guo J. , Carli B. , Mencaraglia F. , Bonetti A. , Carlotti M. , Nolt I. G.
Published: February 2008

Limb thermal emission spectra of the earth's stratosphere in the far‐infrared spectral region, obtained as part of the Balloon Intercomparison Campaign (BIC), have been analyzed for retrieval of trace constituent distributions. The observations analyzed here were made with a balloon‐borne high‐resolution Michelson interferometer operating in the 20–100 cm−1 region, with an unapodized spectral resolution of 0.0033 cm−1. In this paper the vertical profiles of O3, H2O, and HDO retrieved from the observed spectra are presented and compared with the results from other BIC experiments. The retrieved profiles are found to be in good agreement with other measurements. The measurement of the HDO profile provides information about the sources of stratospheric water vapor. The variation of the D/H ratio of water vapor is derived from an analysis of HDO and H2O lines observed in the far‐infrared spectra and is compared with the available measurements in the literature.
A comparison of SAGE 1, SBUV, and Umkehr ozone profiles including a search for Umkehr aerosol effects
Authors: Newchurch M. J. , Grams G. W. , Cunnold D. M. , DeLuisi J. J.
Published: February 2008

Using a spatially weighted average of SAGE 1 measurements, we find 337 colocated SAGE 1 and Umkehr ozone profiles. The total column ozone above 250 mbar measured by SAGE 1 averages 5% higher than that measured by Umkehr. This difference is concentrated in the lower stratosphere and, for latitudes poleward of 30°N, the difference depends on both the total column ozone and the season. The difference, however, is insensitive to the stratospheric aerosol optical depth measured by SAGE 1. Intercomparison of SAGE 1, SBUV, and Umkehr ozone at stations north of 30° indicates that in layer six (approximately 10 mbar) Umkehr values are approximately 10% high, and in layer eight (approximately 3 mbar) SBUV ozone is approximately 10% high. In the upper stratosphere, the SAGE 1‐ Umkehr ozone differences are small for low stratospheric aerosol optical depth cases (less than 0.025 at 0.3 μm) but vary from −3% in layer six to −8% in layer nine for high optical depth cases (greater than 0.025). This tendency is opposite to that predicted by empirical studies, which included large amounts of volcanic aerosols, and by theoretical model studies.
Random processes with long‐range dependence and high variability
Authors: Taqqu Murad S.
Published: February 2008

A family of stochastic models which may be relevant to meteorology is described. The family can be characterized by the intensity of dependence, the heaviness of the probability tails, and the degree of nonlinearity. Two processes, the fractional stable motion and the spectral fractional stable motion, are introduced in some detail, and the range of values of their parameters is investigated. Both processes have scaling properties and display long‐range dependence and high variability.
Modeling the variability in measured atmospheric CO2 data
Authors: Surendran S. , Mulholland R. J.
Published: February 2008

A model representing the trends and variations in the Mauna Loa data is presented. The model uses an autoregressive process for low‐frequency variations, which enables the noise residuals to pass two tests for whiteness. The analysis of the noise residuals provides a measure of uncertainity for estimates of nonfossil fuel emission of CO2 to the atmosphere. Finally, an adaptive Kalman filter is used to estimate measurement errors contained in the Mauna Loa data. The results obtained agree with previous estimates of the precision and accuracy of the measuring instruments.
Increased occurrence of lightning flashes in Sweden during 1986
Authors: Israelsson S. , Schütte T. , Pisler E. , Lundquist S.
Published: February 2008

As a result of the accident in the nuclear power plant at Chernobyl, USSR, a considerable increase in radioactive background radiation was noted in some regions of Sweden. In areas with high radioactive fallout an increase in the amount of lightning flashes was observed during the 1986 thunderstorm season. A statistical test shows that there is a risk of less than 1% that the observed difference has occurred by mere chance.
Effects of El Chichón on stratospheric aerosols late 1982 to early 1984
Authors: Snetsinger K. G. , Ferry G. V. , Russell P. B. , Pueschel R. F. , Oberbeck V. R. , Hayes D. M. , Fong W.
Published: February 2008

Stratospheric aerosols collected over the western United States from late 1982 to early 1984 show the strong effects of El Chichón's eruption. Although mineral particles disappeared during this period, large (> 0.9‐μm diameter) acid droplets were still common. Because these have never been seen in prevolcanic, background‐level collections, they apparently result from increased droplet growth made possible by the unusual abundance of sulfate. Aerosol size distributions show a wide variety of multimodal curves due to mixing of air masses containing aerosols of various ages or histories. Toward the end of the study time there are fewer large aerosols because of gravitational settling and poleward transport. The result is a steady reduction in sulfate, as most aerosol mass is concentrated in a small number of large droplets. Even the later sulfate levels (0.3 μg m−3) are, however, 5 times typical prevolcanic background contents (about 0.06 μg m−3). Thus the influence of El Chichón on high‐altitude (15–21 km) air was still considerable 22 months after eruption.
Structure and growth of the mixing layer over the Amazonian rain forest
Authors: Martin Charles L. , Fitzjarrald David , Garstang Michael , Oliveira Amauri P. , Greco Steve , Browell Edward
Published: February 2008

Measurements carried out over the rain forest of central Amazonia during the NASA Amazon Boundary Layer Experiment (ABLE 2A) are used to examine the structure and growth of the atmospheric mixed layer. Fluxes of sensible and latent heat were measured at the top of the canopy, and measurements of temperature, moisture, and horizontal wind were made in and above the mixed layer by means of a tethered balloon, rawinsonde, and aircraft. The mixing layer grows rapidly at 5–8 cm s−1 soon after sunrise to a mean maximum height of 1200 m by 1300 local standard time (LST). Mixed layer heights above 1000 m between 1000 and 1600 LST are common during undisturbed conditions. Fossil mixed layers, well mixed but no longer mixing, were found to 2000 m and at all times of the day and night. Airborne lidar measurements provided an estimate of the depth of the mixed layer over large distances. No horizontal inhomogeneities in the mixed layer structure or depth were found over large distances, suggesting that point measurements under undisturbed conditions can be used to obtain estimates of mixed layer structure and fluxes over large areas of the Amazon basin. Budget calculations using the averaged mixed layer depths and surface fluxes are made, which provide estimates of the entrainment flux of moisture across the mixed layer top of the order of 600 W m−2. The simple jump model, when initialized with an early‐morning sounding and forced with observed buoyancy fluxes, is compared with the budget calculation and observations. The entrainment flux calculations agree favorably. Flux divergence in the mixed layer leads to significant drying, which is observed at the top of the canopy.
Isoprene over the Amazon Basin
Authors: Rasmussen R. A. , Khalil M. A. K.
Published: February 2008

Data obtained during the 1985 ABLE expedition to the Amazon are used to describe the diurnal and vertical variations of isoprene. Isoprene is a natural hydrocarbon emitted by many species of trees, particularly those in tropical forests. The concentrations of isoprene at lower levels in the atmosphere undergo large diurnal variations, with the highest concentrations during midday and the lowest during the night. At ground level, outside the forest, peak concentrations of about 3 parts per billion by volume (ppbv) of isoprene were observed around midday. Concentrations were nearly zero before sunrise, increased to their maximum values during the day, and declined after sunset. Concentrations of 1–2 ppbv of isoprene were observed up to 300 m. Near the canopy level, up to 8 ppbv of isoprene were observed. In the forest, concentrations are generally quite low below the canopy and are highest at the level of the canopy. Since the reaction of isoprene with OH radicals is extremely fast, its concentrations fall off rapidly with altitude, so that practically none of it was seen above the boundary layer. During nighttime, however, concentrations comparable to daytime values were observed at altitudes of 300 m and above.
Northeastern Pacific submicrometer aerosol and rainwater composition: A multivariate analysis
Authors: Vong Richard J. , Hansson Hans‐Christen , Ross Howard B. , Covert David S. , Charlson Robert J.
Published: February 2008

Simultaneous observations of aerosol and rainwater composition were performed at a remote, mid‐latitude, marine, land‐based site to characterize the chemistry of Northeastern Pacific cyclonic frontal air masses. The measured concentrations of both the major ions (SO4=, NO3−, H+) and trace metals (Pb, Cu, Cd, Mn, V, Cr, Ni, Zn) in the submicrometer aerosol and rainwater were very low and similar to other remote locations indicating that the Lake Ozette sampling site is not dominated by human activity during on‐shore air flow. Statistical analysis indicated that experimental uncertainty was not a significant source of variability and that rainwater solute has independent influences from sea salt and a component that included NH4+, H+, and SO4=. Further investigation of source relationships was performed using 850 mbar trajectories, principal component analysis, partial least squares regression, enrichment factors, and scavenging ratios. Using these methods we conclude that submicrometer aerosol is the main precursor of trace metals and excess sulfate in Northeastern Pacific rain.
Observations of the stratospheric conductivity and its variation at three latitudes
Authors: Byrne G. J. , Benbrook J. R. , Bering E. A. , Oró D. , Seubert C. O. , Sheldon W. R.
Published: February 2008

Measurements of the atmospheric conductivity from nine high‐altitude balloon flights are presented. The measurements were obtained between the altitudes of 10 and 30 km at three locations widely separated in latitude, providing the opportunity to investigate conductivity variations on local and global scales. The data contribute to the set of global conductivity measurements, which are generally lacking. The conductivity profiles exhibit a considerable variability from day to day which does not correlate with solar or cosmic ray activity. The variations are apparently dominated by local effects. The conductivity measurements provide evidence of stratospheric aerosol layers with number densities of the order of 1000 cm−3. The observed variation of the conductivity with latitude is much larger than that predicted by a latitudinal variation of cosmic ray ionization alone. A global background distribution of aerosols is estimated and parameterized. By including the effects of aerosols and latitudinal temperature variations, the agreement between the predicted variation of conductivity with latitude and the observed variation is significantly improved. The implication is that present global models of the conductivity, which employ latitudinal variations based on cosmic ray ionization alone, may be improved by including the effects of latitudinal variations of temperature and aerosols. The effects of photoelectric emissions on relaxation time conductivity measurements are discussed.
Vertical column abundance measurements of atmospheric hydroxyl From 26°, 40°, and 65°N
Authors: Burnett Clyde R. , Minschwaner Kenneth R. , Burnett Elizabeth B.
Published: February 2008

Hydroxyl (OH) vertical column abundances measured with Pepsios spectrometers from Fritz Peak, Colorado (40°N), Boca Raton, Florida (26.4°N), and Poker Flat, Alaska (65°N), are presented. The Colorado normalized abundances have remained nearly constant since 1980 at levels about 1.7 times the 1977 values. Theoretical models agree well with the pre‐1980 abundances, but recent data appear to require a significant change in the atmospheric photochemistry. The Colorado seasonal diurnal asymmetry and its correlation with total ozone are shown to persist. The Florida data show little seasonal variation and have diurnal asymmetry characteristics which differ considerably from those of the Colorado asymmetry. Large Florida OH abundance excursions with respect to Colorado levels are seen in the wintertime of 1980, 1984, and 1986, which suggests the possibility of a relationship with the quasi‐biennial oscillation in tropical stratospheric winds. Responses of the Florida OH column to the passage of a tropical storm (July 1985) and to a partial solar eclipse (October 1986) are also documented. An anomalous drop of 80% in OH column abundances on March 18, 1986, is discussed. Hydroxyl abundance values at Poker Flat (June–July 1983) are 40% higher than corresponding Colorado or Florida values.
Comparison of ground‐based and total ozone mapping spectrometer measurements used in assessing the performance of the global ozone observing system
Authors: Bojkov Rumen D. , Mateer Carlton L. , Hansson Anne L.
Published: February 2008

Uniformly reevaluated Nimbus 7 Total Ozone Mapping Spectrometer (TOMS) total ozone data (1978–1985) are compared with data from ground‐based stations during the daily overpasses of the satellite. Existence of a drift between the two systems is identified, showing the TOMS‐derived total ozone to be decreasing nonuniformly by an average of about 0.4% per year. After removing the individual monthly biases and using the satellite as a transfer standard, the differences between 92 currently operating stations of the Global Ozone Observing System (GO3OS) are analyzed. About two thirds of all Dobson stations show differences of less than 2%, while only half of the M‐83 filter stations fall into this good station category; close to 20% of the Dobson stations and nearly 30% of the filter stations show differences greater than 3%. Several examples of individual station discrepancies are discussed in order to encourage the complete reevaluation of the ground‐based ozone record and to forewarn potential users from taking the published ozone data at their face value.
The principal discriminant method of prediction: Theory and evaluation
Authors: Preisendorfer Rudolph W. , Mobley Curtis D. , Barnett Tim P.
Published: February 2008

The Principal Discriminant Method (PDM) of prediction employs a novel combination of principal component analysis and statistical discriminant analysis. Discriminant analysis is based on the construction of discrete category subsets of predictor values in a multidimensional predictor space. A category subset contains those predictor values which give rise to a predictand (or observation) in that particular category. A new predictor value is then assigned to a particular category (i.e., a forecast is made) through the use of probability distribution functions which have been fitted to the category subsets. The PDM uses principal component analysis to define the multidimensional probability distribution functions associated with the category subsets. Because of its underlying discriminant nature the PDM is also applicable to problems in data classification. The PDM is applied to prediction problems using both artificial and actual data sets. When applied to artificial data the PDM shows forecast skills which are comparable to those of standard forecast techniques, such as linear regression and classical discriminant analysis. When applied to actual data in a forecast of the 1982–1983 El Niño, the PDM performed poorly. However, in forecasting winter air temperatures over North America, the PDM proved superior to other forecast techniques, after suitably filtering or smoothing the raw data in order to improve the signal‐to‐noise ratio. It is expected that the PDM will show its greatest advantage over other forecast techniques when the relation between predictors and predictand is nonlinear.
A semianalytic radiance model of ocean color
Authors: Gordon Howard R. , Brown Otis B. , Evans Robert H. , Brown James W. , Smith Raymond C. , Baker Karen S. , Clark Dennis K.
Published: February 2008

A semianalytical radiance model is developed which predicts the upwelled spectral radiance at the sea surface as a function of the phytoplankton pigment concentration for Morel Case 1 waters. The model is in good agreement with experimental measurements carried out in waters which were not included in the data base used to derive it. It suggests that the observed variability in the radiance is due to variations in the backscattering of plankton and the associated detrital material. The model is extended to include other material in the water, such as dissolved organic material, referred to as yellow substances, and detached coccoliths from coccolithophorids, e.g., Emiliana huxleyi. Potential applications include an improved bio‐optical algorithm for the retrieval of pigment concentrations from satellite imagery in the presence of interference from detached coccoliths and an improved atmospheric correction for satellite imagery. The model also serves to identify and to interpret deviations from Case 1 waters.
The relationship between large‐scale vertical motion, highly reflective cloud, and sea surface temperature in the tropical Pacific region
Authors: Zimmermann Peter H. , Selkirk Henry B. , Newell Reginald E.
Published: February 2008

Vertical motion fields at 850 mbar over the tropical Pacific region are calculated from the 1963–1973 mean wind fields for 4 months of the year and for October 1972, the peak month in the 1972–1973 El Niño event. These vertical motion fields are derived using the projective separation technique, which has the unique property of separating vertical motion into components due to meridional wind convergence and zonal wind convergence. This separation permits investigation of the response of the Hadley and Walker circulations to annual and interannual variation of the sea surface temperature in the tropical Pacific. The large‐scale features of the computed vertical motion fields are in agreement with those of highly reflective clouds, which indicate the locations of deep convection. Examination of the annual cycle of the vertical motion and its components shows no strong variation of the Walker circulation with the east‐west gradient of sea surface temperature. On the other hand, a strong correlation is found between meridional overturning in the eastern Pacific and the local equatorial sea surface temperature: during El Niño events, the eastern and central Pacific contribution to the Hadley circulation tends to increase.
Threshold friction velocities for dust production for agricultural soils
Authors: Gillette Dale A.
Published: February 2008

Threshold velocities for agricultural soils were measured for a wide variety of conditions in order to quantify a model of dust emissions for the United States. These measurements supplement threshold velocities for arid and semiarid soils (Gillette, et al., 1980, Gillette, et al., 1982). The model will be used in precipitation acid/base balance studies. The soils were organized according to surface texture, organic matter content, and calcium carbonate composition. They were further organized by the physical surface states: smooth‐loose, cloddy, and crusted. Sandy soils were found to have the lowest threshold velocities and were the least affected by wetting (precipitation). Loamy soils were found to have the highest threshold velocities and were the most affected by precipitation wetting.
Chemistry and transport in a three‐dimensional stratospheric model: Chlorine species during a simulated stratospheric warming
Authors: Kaye Jack A. , Rood Richard B.
Published: February 2008

Calculations of coupled chemistry and transport for the stratosphere are carried out for a 6‐day period during the February 1979 stratospheric major warming, using winds derived from a spectral forecast model. All major families of stratospheric chemistry (odd oxygen, odd nitrogen, odd hydrogen, and odd chlorine), as well as longitudinally varying reaction rate coefficients and photolysis rates, are included in the model. Eight constituents and/or families are transported in the model; additional ones are held fixed or inferred by photochemical equilibrium approximations. Results presented include zonal mean fields, latitude‐longitude distributions (and their changes with time), vertical profiles, and time series of the mixing ratios of transported constituents and families as well as of their total stratospheric column amounts. The results obtained show the relative importance of chemistry and transport for the chlorine‐containing species ClO, ClONO2, HCl, and HOCl. Dynamical effects dominate the variability of HCl, while diurnal ones dominate that of ClONO2 and ClO. Diurnal chemistry and dynamical variability are of similar magnitude for HOCl. The effects of strong planetary wave activity may be seen as large longitudinal variability of the total HCl and ClONO2 columns in the stratosphere; in middle and high northern latitudes it is sufficiently large that it exceeds the diurnal variability of the column.
Natural and anthropogenic negative ions in the troposphere
Authors: Eisele F. L.
Published: February 2008

Negative ion species were identified and studied at three separate field sites. The first study was conducted under an operating high‐voltage direct current (HVDC) transmission line. The second was near a HVDC test line, and measurements were performed with the line in both an energized and de‐energized state. The third was far from any anthropogenic ionization sources. During clear, sunny days, HSO4−·H2SO4 was observed to be the dominant ion in the natural ion spectrum. At night, however, HSO4− core ions virtually disappeared and were replaced by NO3− and its first nitric acid cluster. Both spectra also typically contained lesser concentrations of the malonate ion and its nitric acid cluster. In contrast, the transmission line spectra were typically dominated by the NO3− core ions during both day and night, presumably because the much shorter lifetime of these ions did not permit sufficient time for reactions with H2SO4. The C3H3O4− and HSO4− ions were also observed in the HVDC line daytime spectra, but their relative concentrations dropped dramatically at night. It appeared that the primary difference between the ion species observed near the transmission line, as compared to the natural environment, was attributable to the shortening of the ion's reaction time, caused by it being driven to the ground or other conductor by strong transmission line electric fields. Additionally, the daytime gas phase concentration of H2SO4 was estimated to be ∼1 ppt from both transmission line and natural ion spectral measurements.
Atmospheric deposition of beryllium 7 in the Chesapeake Bay region
Authors: Dibb Jack E.
Published: February 2008

Bulk (combined wet and dry) atmospheric deposition of the cosmogenic isotope 7Be was monitored at Solomons, Maryland (38°19′N, 76°27′W), from March 1986 to November 1987. The observed deposition of 7Be supported an inventory ranging from 2 to 4 dpm (disintegrations per minute)/cm2. The supported inventory and monthly fluxes of 7Be showed maxima in late spring (March–May). The peak in 7Be deposition was very similar in 1986 and 1987 despite 1986 having a very dry spring. It thus appears that given even modest amounts of precipitation, there is strong seasonality in the atmospheric deposition of 7Be near 40°N. The timing and magnitude of the spring peak in 7Be deposition are in close agreement with estimates of the seasonal variation in the injection of stratospheric air into the troposphere, suggesting that on a monthly time scale the bulk deposition of 7Be closely reflects the tropospheric inventory of 7Be.
Pangaean climates: Megamonsoons of the megacontinent
Authors: Kutzbach J. E. , Gallimore R. G.
Published: February 2008

The climate for a highly idealized geographic representation of the megacontinent of Pangaea, corresponding to the period 250–200 m.y. ago, is explored using a low‐resolution atmospheric general circulation model that is coupled to a static mixed layer ocean of constant depth, with a provision for sea‐ice formation and decay. Soil moisture is included as a predicted variable on the continent. Because there are large uncertainties about key factors that might influence the Pangaean climate, sensitivity experiments are used to examine the climate for two different mean elevations (0 and 1000 m), two different snowcover prescriptions, and two different levels of implied greenhouse heating and solar luminosity (modern CO2 concentration and modern solar luminosity; fivefold increase in modern CO2 concentration and a 1% decrease in modern solar luminosity). In all of the experiments, the large bipolar land masses of Laurasia and Gondwanaland, joined near the equator in the west and separated by the Tethys Sea in the east, exhibit extreme continentality, with hot summers, cold winters, and large‐scale summer and winter monsoon circulations. Year‐round or seasonal aridity is simulated for all but the eastern coastal regions, the tropical western coast, and the regions poleward of 40° latitude. The simulated climate of the idealized Pangaean continent has many features that correspond qualitatively with geologic evidence for tropical warmth and aridity in the late Permian and Triassic. However, the model results serve mainly to indicate the importance of various climate‐forming factors (geography, topography, heating). Detailed comparisons will require new experiments, with better models and more accurate geologic boundary conditions.
Simple models of diabatically forced mesoscale circulations and a mechanism for amplification
Authors: Robichaud Alain , Lin Charles A.
Published: February 2008

A two‐dimensional, linear, Boussinesq, inviscid, hydrostatic model is used to simulate the flow over an elevated diabatic source and a surface diabatic source. The elevated source is identified as being due to cooling by melting, while the surface source is associated with land/sea temperature differences. Melting frequently produces near‐0°C isothermal layers. The atmosphere in this case tends to have strong static stability in the melting layer, capped by a much less stable layer aloft. This creates a strong change in the vertical wave number, which might lead to resonant amplification of mesoscale perturbations, just as in mountain wave theory. Comparison with sounding data suggests that this amplification mechanism is potentially important for precipitation enhancement due to melting.
NO2 observations at 45°S during the decreasing phase of solar cycle 21, from 1980 to 1987
Authors: Johnston P. V. , McKenzie R. L.
Published: February 2008

Monthly averaged NO2 columns obtained at twilight at 45°S over the period December 1980 to August 1987 are presented. Improvements to the retrieval technique used previously are discussed. The slant columns presented typically range from 3 to 12 × 1016 cm−2 which, because of the geometry at twilight, are approximately 20 times greater than the vertical columns. In addition to the expected diurnal and seasonal variations, the data also show variations on longer time scales. The identification of any long‐term trends is masked by the effects of the El Chichón eruption, which was probably responsible for a decrease in the column of 1.5×1016 cm−2 in 1983. After allowing for this, there remains a small but significant long‐term trend. This trend may be due to a cooling in the stratosphere that has taken place over the observation period. Alternatively, there may be a correlation with solar activity. The observation period is too short to be able to establish a definite link, but the trend is consistent with a decrease of 0.5×1016 cm−2 in the NO2 column from solar maximum to solar minimum. The self‐consistency from year to year does not support the theory that the “Antarctic ozone hole” is caused by variations in solar activity which change the production of the nitrogen oxides responsible for the catalytic destruction of ozone. Both the El Chichón eruption and the long‐term trend discussed earlier produce additive rather than multiplicative effects, with similar column reductions occurring in the summer and winter as well as in the morning and evening measurements.
Continuing current in negative cloud‐to‐ground lightning
Authors: Shindo T. , Uman M. A.
Published: February 2008

Simultaneous single‐station electric field and multiple‐station TV measurements on 90 negative cloud‐to‐ground lightning flashes that occurred on 3 days in July 1979 near Tampa, Florida, have been analyzed for the following characteristics of electric field changes indicative of continuing current: frequency of occurrence, duration, duration of interstroke interval preceding, duration of interstroke interval containing, current and charge transferred, and magnitude of initiating return‐stroke electric field peak. Of the 90 flashes, 22 contained a long (greater than 40 ms) continuing current and 11 contained a short (10–40 ms) continuing current. Only one of 19 single‐stroke flashes was followed by a long continuing current, and none were followed by a short continuing current; none of the first strokes of 71 multiple‐stroke flashes were followed by either long or short continuing current. The geometric mean duration of long continuing current was 115 ms and that of short continuing current was 23 ms. Long and short continuing current average amplitudes were primarily in the range 30–200 A. There is an inverse relation between the duration of the interstroke interval just preceding the interval containing continuing current and the duration of the continuing current. Twenty‐two interstroke intervals just preceding interstroke intervals containing long continuing current have a geometric mean duration of 28 ms, and 16 intervals preceding interstroke intervals containing short continuing current have a geometric mean duration of 53 ms; however, the geometric mean duration of 161 interstroke intervals neither containing continuing current nor preceding it is 64 ms and the geometric mean duration of all 258 interstroke intervals in the 90 ground flashes is 65 ms. On average, the return strokes that precede continuing current have smaller initial peak electric fields, and hence smaller peak currents, than do other return strokes. Sixteen electric field peaks associated with return strokes preceding long continuing current have a geometric mean, normalized to 100 km, of 2.6 V/m, and 15 field peaks initiating short continuing current have a geometric mean of 2.4 V/m, whereas 199 field peaks associated with strokes not initiating continuing current have a geometric mean of 3.5 V/m.
Altitude distribution of stratospheric NO3: 2. Comparison of observations with model
Authors: Pirre Michel , Ramaroson Radiela , Naudet Jean‐Pierre , Rigaud Pierre
Published: February 2008

The theoretical calculations of the altitude distribution of |NO3|, made with a time‐dependent zero‐dimensional model taking into account the accepted photochemistry of the stratosphere, are compared with the measurements presented in a companion paper. The concentration of |NO3| is shown to be strongly dependent on the ozone concentration and temperature. These parameters were measured and used as fixed data in the model. The results show excellent consistency between theory and measurements.
Retrieval of aerosol size distribution moments from multiwavelength particulate extinction measurements
Authors: Livingston John M. , Russell Philip B.
Published: February 2008

Two methods for inferring aerosol size distribution moments (for example, particle area and volume) from multiwavelength particulate extinction measurements have been investigated. The first is an analytic, or eigenvalue, technique that approximates an appropriate moment‐weighting function by a linear combination of kernel functions (Mie extinction cross sections). It then uses the same linear combination of the measured particulate extinction coefficients to infer the size distribution moment. The second technique is a conversion ratio approach that uses the ratio of the particulate extinction measurements at two wavelengths to choose a model moment‐to‐extinction conversion ratio. For each method, expressions are derived that estimate the uncertainty in retrieved moments. The eigenvalue technique has been tested by application to synthetic particulate extinction measurements calculated at wavelengths corresponding to those of the satellite‐borne Stratospheric Aerosol and Gas Experiment (SAGE) II Sun photometer. The synthetic measurements were calculated from model stratospheric aerosol size distributions and from stratospheric aerosol size distributions measured by a wire impactor before and after the eruption of El Chichón. Moments have been derived for two‐ and three‐wavelength retrievals. In general, it was found that retrieved moments agreed well with the analytical model values, when random experimental uncertainties of a few percent or less were included in the synthetic extinction measurements. Typical retrieval errors were between 10 and 20%, with a few exceptions. When random measurement uncertainties with a rms mean value of 5% were included in the synthetic extinction coefficients, retrieval errors increased somewhat, but they rarely exceeded 40%. When applied to synthetic particulate extinction measurements that were calculated from the wire impactor‐measured stratospheric aerosol size distributions and which included 30% rms random experimental uncertainties, the eigenvalue retrieval technique successfully reproduced the large changes in particle volume, effective radius, and distribution width that followed the eruption of El Chichón. Both the eigenvalue and conversion ratio moment retrieval methods have been used to infer the third moment, or volume, of the aerosol size distribution from actual particulate extinction measurements taken by SAGE II during an April 1985 correlative measurement experiment in Brazil. Corresponding inferences are found to be in good agreement with each other.
Least independent variables method for simulation of tropospheric ozone
Authors: Jacob D. J. , Sillman S. , Logan J. A. , Wofsy S. C.
Published: February 2008

We describe a method for simulating photochemical production of O3 in a continental‐scale tropospheric model with only six independent chemical variables representing tracers transported in the model. The tracers are two primary hydrocarbon families, CO, NOx, peroxyacylnitrates, and odd oxygen (Ox). A chemical module is developed to compute the production and loss rates of tracers over a model time step of 4 hours, using only information on the tracer concentrations input to the module at the beginning of the time step. Test simulations for summertime conditions at mid‐latitudes indicate little loss in accuracy compared to detailed model simulations of chemistry with high time resolution. Minimization of the number of tracers and use of a long time step reduces computer time and storage requirements. In addition, parameterization of the chemical computation is facilitated, allowing further savings in computer time.
Ozone budgets from the dynamics and chemistry of marine stratocumulus experiment
Authors: Kawa S. R. , Pearson R.
Published: February 2008

Measurements from the Dynamics and Chemistry of Marine Stratocumulus experiment have been used to study components of the regional ozone budget. The surface destruction rate is determined by eddy correlation of ozone and vertical velocity measured by a low‐flying aircraft. Significant variability is found in the measured surface resistance; it is partially correlated with friction velocity but appears to have other controlling influences as well. The mean resistance is 4190 s m−1 which is higher (slower destruction) than most previous estimates for seawater. Flux and mean measurements throughout the marine boundary layer are used to estimate the net rate of in situ photochemical production/destruction of ozone. Averaged over the flights, ozone concentration is found to be near steady state, and a net photochemical destruction of 0.02–0.07 ng m−3 s−1 is diagnosed. This is an important confirmation of photochemical model results for the remote marine boundary layer. These results should generally be applicable to remote marine regions over the globe although the observed variations give large uncertainties. Ozone vertical distributions above the boundary layer show a strongly layered structure with very sharp gradients. These distributions are possibly related to the stratospheric ozone source, but the processes creating and maintaining them are not clearly discernable.
Dobson spectrophotometer 83: A standard for total ozone measurements, 1962–1987
Authors: Komhyr W. D. , Grass R. D. , Leonard R. K.
Published: February 2008

Dobson spectrophotometer 83 was established in 1962 as a standard for total ozone measurements in the United States. In 1980 the instrument was designated by the World Meteorological Organization (WMO) as the primary standard Dobson spectrophotometer for the world. Since the early 1960s, virtually all (∼90) Dobson instruments in the global Dobson instrument network have been calibrated several times, either directly or indirectly, relative to instrument 83. Calibrations of instrument 83 by the Langley method were performed in 1962 at Sterling, Virginia, and during 1972–1987 at Mauna Loa Observatory (MLO), Hawaii. A detailed analysis of these calibration data, as well as calibration data based on standard lamp measurements made since 1962, indicates that the long‐term (25‐year) ozone measurement precision for the instrument is known to within an uncertainty of ±0.5%. On an absolute scale, the ozone measurements made at MLO with instrument 83 are estimated to be too low by about 2.4%, as a result of errors in the A and D wavelength ozone absorption coefficients used with the instrument and their temperature dependence. Cumulative other biases most likely do not exceed ±1%. This documentation of the calibration history of instrument 83 lends credence to the accuracy with which other Dobson instruments have been calibrated in the past and to Dobson and satellite instrument ozone measurement comparisons, thereby increasing confidence in ozone trends determined by these ozone measurement systems in recent years.
On the use of surface equivalent potential temperature in isolating the influence of local as opposed to transported sources on aerosol concentrations
Authors: Obremski J. S. , Samson J. A. , Dutkiewicz V. A. , Husain Liaquat
Published: February 2008

An atmospheric aerosol transport hypothesis is presented. An analytical technique, based on an analysis of surface equivalent potential temperature, is used to isolate meteorological conditions that encourage an introduction of transported (advected) aerosols into the surface layer. The difference between the equivalent potential temperature at the surface and 700‐ mbars and the identification of periods of precipitation, are used to define the stability characterstics of the lower troposphere. It is suggested that these three meteorological parameters provide an excellent indication of the horizontal and vertical exchange occurring in the lower troposphere. These parameters, calculated for six upper air sounding stations in North America, are used to isolate those time periods when aerosol populations are most likely influenced by local as opposed to advected sources. Sources of particulate SO4, Al, Se, and crustal corrected V measured at sampling sites in New York State are evaluated with this technique.