bluuebunny/crossref_metadata_2025 huggingface dataset:
A contribution toward understanding the biospherical significance of Antarctic ozone depletion
Authors: Lubin Dan , Mitchell B. Greg , Frederick John E. , Alberts Amy D. , Booth C. R. , Lucas Timothy , Neuschuler David
Published: February 2012

Measurements of biologically active UV radiation made by the National Science Foundation (NSF) scanning spectroradiometer (UV‐monitor) at Palmer Station, Antarctica, during the Austral springs of 1988, 1989, and 1990 are presented and compared. Column ozone abundance above Palmer Station is computed from these measurements using a multiple wavelength algorithm. Two contrasting action spectra (biological weighting functions) are used to estimate the biologically relevant dose from the spectral measurements: a standard weighting function for damage to DNA, and a new action spectrum representing the potential for photosynthesis inhibition in Antarctic phytoplankton. The former weights only UV‐B wavelengths (280–320 nm) and gives the most weight to wavelengths shorter than 300 nm, while the latter includes large contributions out to 355 nm. The latter is the result of recent Antarctic field work and is relevant in that phytoplankton constitute the base of the Antarctic food web. The modest ozone hole of 1988, in which the ozone abundance above Palmer Station never fell below 200 Dobson units (DU), brought about summerlike doses of DNA‐effective UV radiation 2 months early, but UV doses which could inhibit photosynthesis in phytoplankton did not exceed a clear‐sky “maximum normal” dose for that time of year. The severe ozone holes of 1989 and 1990, in which the ozone abundance regularly fell below 200 DU, brought about increases in UV surface irradiance weighted by either action spectrum. Ozone abundances and dose‐weighted irradiances provided by the NSF UV‐monitor are used to derive the radiation amplification factors (RAFs) for both DNA‐effective irradiance and phytoplankton‐effective irradiance. The RAF for DNA‐effective irradiance is nonlinear in ozone abundance and is in excess of the popular “two for one” rule, while the RAF for phytoplankton‐effective irradiance approximately follows a “one for one” rule.
Partitioning and budget of NOy species during the Mauna Loa Observatory Photochemistry Experiment
Authors: Atlas E. L. , Ridley B. A. , Hubler G. , Walega J. G. , Carroll M. A. , Montzka D. D. , Huebert B. J. , Norton R. B. , Grahek F. E. , Schauffler S.
Published: February 2012

During the Mauna Loa Observatory Photochemistry Experiment (MLOPEX), measurements were made of total odd nitrogen (NOy) and the known individual daytime odd‐nitrogen species. The individual species measured were NO, NO2, HNO3, paniculate NO3−, peroxyacetyl nitrate (PAN), peroxypropionyl nitrate (PPN), methyl nitrate, and >C3 alkyl nitrates. The most abundant component of NOy was nitric acid; its median contribution to NOy in free tropospheric samples was 43%. The large fraction of HNO3 is consistent with the long transport times and photochemical processing of air masses reaching the mid‐Pacific site as well as possible stratospheric input of NOy. The median contribution of NOx to NOy in the free troposphere near 3.4 km was ≈14%. PAN and other measured organic nitrates contributed < 7% to NOy. The median sum of the individually measured species was 102% of NOy in upslope periods which consist of a mixture of island‐modified marine boundary layer and free tropospheric air. This total was 75% of NOy during downslope periods representative of the free troposphere. This shortfall in the odd‐nitrogen budget in the free troposphere corresponds to 72 pptv of reactive nitrogen, which is over 2 times median NOx. The NOy shortfall and the composition of NOy appeared to have a regular variation in the free troposphere during the experiment which was related to air mass origin, recycling of odd nitrogen, and loss processes during transport. The presence of an odd‐nitrogen deficit in the remote free troposphere suggests that our understanding of the NOy system is incomplete. Unidentified odd‐nitrogen species, such as organic nitrates, may be present, but sampling limitations and analytical uncertainties in NOy and individual (NOy)i measurements still restrict our ability to accurately define an NOy budget, especially in remote regions.
The influence of atmospheric moisture transport on the fresh water balance of the Atlantic drainage basin: General circulation model simulations and observations
Authors: Zaucker Fritz , Broecker Wallace S.
Published: February 2012

An attempt has been made to evaluate the reliability of water vapor transport estimates from atmospheric general circulation models (GCMs) by comparing the vapor export from the Atlantic basin obtained using the GISS 4° × 5° grid GCM with that obtained from observations of wind velocity and humidity [Oort, 1983]. We find substantial differences. The model gives an export of 0.13 Sverdrups (Sv) from the Atlantic basin compared to 0.32 Sv from the Oort data set. We note that the GCM produces far stronger easterly winds and correspondingly larger tropical vapor transports. Further, because of the model's low orography, steering of the winds and drying of air masses by mountain chains are not adequately represented. This leads to a dramatic overestimation of water vapor transport across mountain ranges. In an additional model experiment, we calculated the water vapor transports in a double‐CO2 scenario. We find that atmospheric freshwater loss from the Atlantic basin is increased to 0.30 Sv compared to 0.13 Sv in the control run. Because of the deficiencies of the model mentioned above, however, we conclude that estimates of vapor transport for future greenhouse conditions and past glacial conditions made using GCMs have to be taken with great caution until models with more realistic flow patterns, especially around mountain ranges, are available.
Seasonal variations in Antarctic NOx chemistry
Authors: Solomon Susan , Keys J. Gordon
Published: February 2012

Observations of the NO2 column and its diurnal variation provide an important test of aspects of stratospheric chemistry. Measurements of NO2 from two sites in the Antarctic are compared with model calculations that include a detailed treatment of diurnal NOx: chemistry for fall, winter, and spring. Observed slant column amounts in spring provide strong evidence for important heterogeneous effects, probably through polar stratospheric cloud chemistry. It is shown that the slow growth of NO2 column observed during September is consitent with release of NO2 from N2O5 formed above the altitudes where polar stratospheric clouds occur. The observed early fall column amounts are in good agreement with model calculations, and the sharp onset of diurnal variation in column NO2 obtained near day 57 is well stimulated. Following this period, gas‐phase model calculations suggest that N2O5 will rapidly accumulate during the Antarctic fall as nights become longer. It is suggested that the high latitude fall period during which N2O5 grows rapidly represents an optimum time to search for evidence of possible heterogeneous chemistry on background aerosols.
Bayesian relative information measure: A tool for analyzing the outputs of general circulation models
Authors: Moss Marshall E.
Published: February 2012

Mathematical models that generate scenarios containing no temporal correspondence to time series of actual occurrences are difficult to evaluate. One such class of models consists of atmospheric General Circulation Models (GCM), which have an additional drawback that the temporal and spatial scales of their outputs do not match those of the actual observations of the simulated phenomena. The problem of disparate scales can be ameliorated by aggregating both the model output and the observed data to commensurate scales. However, this approach does not permit quantitative testing at scales less than the least common level of aggregation. The lack of paired observations in the aggregated time series makes standard statistical methods either invalid or ineffective in testing the validity of a GCM. One approach to resolving this quandary is the use of a relative information measure, which is based on the uncertainties contained in the histograms of the aggregations of both the model output and the data base. Each interval of each histogram is analyzed, from a Bayesian perspective, as a binomial probability. For the data‐based histogram, the reciprocal of the sum of the variances of the posterior distributions of probability in each interval is denoted as its information content. For the model‐based histogram, the reciprocal of the sum of the expected mean squared errors of the posterior distributions in each interval likewise is its information content. The expected mean squared error, which accounts for potential biases in the GCM, is computed as the expectation of the squared differences between the data‐based and the model‐based posterior distributions for each interval. The ratio of the information content of the model‐based histogram to that of the data‐based histogram is the relative information of the model. A 5‐year monthly precipitation time series for January at a single node of the current version of the Community Climate Model including the Biosphere Atmosphere Transfer Scheme contains 7.5 % of the information in the most recent 30 years of data in the Climatological Data Set assembled by the National Climate Data Center (NCDC). If the 5‐year simulation were extended, its relative information content could be expected to approach 11.5 %. For July monthly precipitation, the 5‐year simulation contained 13.7 % of the information of the NCDC data base and had a limit of 39.3 % for extremely long simulations. Aggregation of two adjacent cells at the same latitude showed some improvements in relative information, but longitudinal aggregation with two additional adjacent cells showed improvement for January precipitation, but degraded information for July precipitation.
The Arctic polar stratospheric cloud aerosol: Aircraft measurements of reactive nitrogen, total water, and particles
Authors: Kawa S. R. , Fahey D. W. , Kelly K. K. , Dye J. E. , Baumgardner D. , Gandrud B. W. , Loewenstein M. , Ferry G. V. , Chan K. R.
Published: February 2012

The reactive nitrogen (NOy), total water, and particle components of the polar stratospheric cloud (PSC) aerosol in the Arctic are studied using in situ aircraft measurements in the lower stratosphere. The results are compared to findings from the Antarctic derived using similar measurements and interpretive techniques. The Arctic data show that particle volume well above background values is present at temperatures above the frostpoint, confirming the result from the Antarctic that the observed PSC's are not water ice particles. NOy measurements inside a PSC are enhanced above ambient values consistent with anisokinetic sampling of particles containing NOy. Furthermore, relative changes in the measured particle volume along a flight track are well correlated with changes in the amount of NOy estimated to be in the particle phase. With the exception of data from one flight, assuming that the composition of the PSC particles is nitric acid trihydrate (NAT), the HNO3 content of the measured particle volume is consistent with the amount of HNO3 predicted to be available for condensation. To this extent, the Arctic observations are consistent with NAT as the composition of PSC particles, in agreement with the Antarctic findings. In the Arctic data over long segments of several flights, calculations show saturation with respect to NAT without significant PSC particle growth above background. PSCs in the Arctic are not observed in situ until the apparent saturation ratio of HNO3 with respect to NAT is greater than 10, in marked contrast to the Antarctic, where PSCs are observed in conditions of apparent HNO3 saturation of 1 and above. This difference cannot be resolved by known measurement uncertainties. Also, a discrepancy is noted in the comparison of the amount of condensed HNO3 derived from the particle distribution measurements with that derived from the NOy measurements, assuming a NAT composition for the particles. Although the relative variations in the derived quantities are similar, as in the Antarctic, the mean values consistently disagree by about a factor of 2. The differences suggest that there may be systematic errors in the data and/or physical assumptions used in the analysis. Several possibilities are discussed.
The vertical distribution of atmospheric H2O2: A case study
Authors: Ray John D. , Van Valin Charles C. , Boatman Joe F.
Published: February 2012

Vertical profiles of H2O2 mixing ratios were obtained for each season from a site in central Arkansas during 1988. Aircraft‐based measurements indicated that H2O2 mixing ratios followed an annual cycle, peaking during the summer at >6 parts per billion by volume (ppbv). The minimum occurred in winter when mixing ratios for H2O2 averaged about 0.2 ppbv. The H2O2 mixing ratio generally peaked at an altitude of about 800 mbar (2 km), although there may have been some seasonal dependence. The annual cycle followed variations in solar intensity, water mixing ratio, and temperature. Within a season, strong variations could be related to meteorological events. A daily cycle was inferred in which the H2O2 mixing ratio varied by a factor of 2 to 3; the peak observed values were at night. H2O2 mixing ratios at altitudes higher than 0.7 km were generally greater than local SO2 values above 0.7 km during all but the winter season.
Global ozone depletion and the Antarctic ozone hole
Authors: Pitari Giovanni , Visconti Guido , Verdecchia Marco
Published: February 2012

The secular trend of the Antarctic ozone hole has been studied with a two‐dimensional model which can simulate formation of polar stratospheric clouds and includes heterogeneous chemical reactions. Results from the numerical simulation have been validated by comparison with available experimental data. Trends up to the year 2010 using standard (i.e., homogeneous) and heterogeneous chemistry have been compared and show that global ozone depletion reached 5–6% in the last 30 years and will average 8% for the next 20 years. Subtracting a 2% loss due to standard chemistry in the presence of trace gas increase in the last 30 years, we find a 3–4% global ozone loss due to heterogeneous chemistry. The depletion is evident even outside the southern hemisphere spring season and at mid‐latitudes, pointing to an increase in global ozone sink.
The structure of the polar vortex
Authors: Schoeberl Mark R. , Lait Leslie R. , Newman Paul A. , Rosenfield Joan E.
Published: February 2012

Reconstruction of the Airborne Antarctic Ozone Experiment and Airborne Arctic Stratosphere Expedition aircraft constituent observations, radiative heating rate computations, and trajectory calculations are used to generate comparative pictures of the 1987 southern hemisphere (SH) late winter and 1989 northern hemisphere (NH) mid‐winter, lower stratospheric, polar vortices. Overall, both polar vortices define a region of highly isolated air, where the exchange of trace gases occurs principally at the vortex edge through erosional wave activity. Aircraft measurement showed that (1) between 50 and 100 mbar, horizontally stratified long‐lived tracers such as N2O are displaced downward 2–3 km on the cyclonic (poleward) side of the jet with the meridional tracer gradient sharpest at the jet core. (2) Eddy mixing rates, computed using parcel ensemble statistics, are an order of magnitude or more lower on the cyclonic side of the jet compared to those on the anticyclonic side. (3) Poleward zonal mean meridional flow on the anticyclonic side of the jet terminates in a descent zone at the jet core. Despite the similarities between the SH and NH winter vortices, there are important differences. During the aircraft campaign periods, the SH vortex jet core was located roughly 8°–10° equatorward of its NH counterpart after pole centering. As a result of the larger size of the SH vortex, the dynamical heating associated with the jet core descent zone is displaced further from the pole. The SH polar vortex can therefore approach radiative equilibrium temperatures over a comparatively larger area than the NH vortex. The subsequent widespread formation of polar stratospheric clouds within the much colder SH vortex core gives rise to the interhemispheric differences in the reconstructed H2O, NOy, ClO, and O3, species which are affected by polar stratospheric clouds.
The modulation of sea surface temperature and rainfall associations over southern Africa with solar activity and the quasi‐biennial oscillation
Authors: Mason S. J. , Tyson P. D.
Published: February 2012

Correlations between solar activity and southern African rainfall, stratified according to the phase of the Quasi‐Biennial Oscillation (QBO), reveal significant zero and 3‐month lag associations in both the summer and the winter rainfall regions. The solar‐rainfall associations are significant for in‐season rainfall only when the QBO is in its easterly phase, while for out‐of‐season rainfall, significant associations are evident when the QBO is in its westerly phase. When the QBO is in its easterly phase, an increase (decrease) in early season solar activity (October‐December in the summer rainfall region, April‐June in the winter region) produces a synchronous increase (decrease) in rainfall over both the summer and the winter rainfall regions. The same increase (decrease) in solar activity produces a significant decrease (increase) in rainfall over the regions in the second half of the same rainfall season, 3 months later. When the QBO is in its westerly phase, out‐of‐season changes occur with both the winter precipitation of the summer rainfall region and the summer precipitation of the winter rainfall region, showing a tendency to become somewhat higher (lower) following an increase (decrease) in solar activity. During the early and late summer seasons, when the QBO is in its easterly phase, anomalous rainfall receipts over the summer rainfall region are the result of anomalies in the tropical atmospheric circulation of the region, which can in part be understood by reference to the sea surface temperature departures of the southwest Indian Ocean. In contrast, the rainfall anomalies observed in the southwest Cape Province during its peak rainfall season in winter can be related to anomalies in the temperate atmospheric circulation and sea surface temperature anomalies in the South Atlantic Ocean. Out‐of‐season associations between solar activity and southern African rainfall are evident for the summer rainfall region when the QBO is in its westerly phase and can be explained by reference to sea surface temperature anomalies in both the South Atlantic and the southwest Indian oceans. The phase of the QBO appears to modulate the association between solar activity and rainfall and also between solar activity and sea surface temperatures.
Observations of peroxyacetyl nitrate, peroxypropionyl nitrate, methyl nitrate and ozone during the Mauna Loa Observatory photochemistry experiment
Authors: Walega J. G. , Ridley B. A. , Madronich S. , Grahek F. E. , Shetter J. D. , Sauvain T. D. , Hahn C. J. , Merill J. T. , Bodhaine B. A. , Robinson E.
Published: February 2012

Measurements of the title species were made during the Mauna Loa Observatory Photochemistry Experiment (MLOPEX) conducted between May 1 and June 4, 1988, at the Geophysical Monitoring for Climatic Change (GMCC) station at 3.4‐km elevation on the Island of Hawaii. Diurnal changes in the organic nitrates primarily resulted from the transition between downslope flow (usually free tropospheric air) and upslope flow (marine boundary layer or a mix of marine boundary layer and free tropospheric air, both influenced by island sources of precursors) characteristic of the site. Longer term trends in the mixing ratios reflected changes in air mass origins from mid‐latitudes to more tropical latitudes. The average mixing ratios in free tropospheric samples were peroxyacetyl nitrate (PAN, 17 pptv), peroxypropionyl nitrate (PPN, 0.3 pptv), methyl nitrate (MN, 4 pptv), and O3 (43 ppbv). The organic nitrates (PAN, PPN, MN) represent minor components of the total odd nitrogen budget at the site. In free tropospheric samples, PAN, PPN, and MN constituted average percentages of 7%, <1%, and 2% of total odd nitrogen. In more tropical air masses, MN could constitute as much as 10% of total odd nitrogen. A photochemical model is used to investigate the sensitivity of free tropospheric PAN to local precursor concentrations. The observed mixing ratios of PAN are also contrasted with measurements made at continental surface sites and during aircraft programs.
Assessment of the African airborne dust mass over the western Mediterranean Sea using Meteosat data
Authors: Dulac François , Tanré Didier , Bergametti Gilles , Buat‐Ménard Patrick , Desbois Michel , Sutton David
Published: February 2012

The mass of African dust present over the western Mediterranean during a transport episode from northwestern Africa, which occurred in early July 1985, is estimated using a desert aerosol model, an Earth‐atmosphere radiative transfer model and Meteosat visible channel data from 4 days running. Dust pixels are selected from Meteosat images, and their aerosol optical thickness is retrieved. A proportionality factor between aerosol optical thickness and atmospheric columnar aerosol loading is computed and applied to the dust pixels. The total mass of atmospheric particles over the basin is obtained by interpolation and spatial integration. The maximum aerosol optical thickness is 1.8. The maximum aerosol columnar loading is evaluated to be 2.3 g m−2. The integrated mass of particles present at a given time is estimated to raise up to about 0.6 × 1012 g at the maximum and the total mass of dust exported from Africa to be of the order of 1012 g. The method is carefully evaluated and uncertainties are discussed, with particular emphasis on the relationship between atmospheric dust mass and aerosol optical depth. The overall uncertainty on the total mass is roughly a factor ±3. In the absence of clouds it appears that the major uncertainty results from the lack of knowledge of the actual mass‐size distribution of suspended dust particles, pointing out the lack of relevant data on particles larger than 10 μm in diameter. A simple calculation based on results from both computations and simultaneous field measurements yields a net transfer velocity of particles from the dust layer of approximately 1 cm s−1.
SAGE II stratospheric density and temperature retrieval experiment
Authors: Wang Pi‐Huan , McCormick M. P. , Chu W. P. , Lenoble J. , Nagatani R. M. , Chanin M. L. , Barnes R. A. , Schmidlin F. , Rowland M.
Published: February 2012

This paper describes a stratospheric density and temperature retrieval experiment based on the solar occultation measurement of the Stratospheric Aerosol and Gas Experiment (SAGE II). The entire retrieval analysis involves two inversion steps: the vertical structure inversion, which derives the profile of local atmospheric extinction from SAGE II limb optical depth data, and the species inversion, which inverts the concentration of air molecules, aerosols, ozone, and nitrogen dioxide from the derived atmospheric extinction at five SAGE II short wavelengths (0.385, 0.448, 0.453, 0,525, and 0.600 μm). The inversion schemes for these steps are Twomey's (1975) modification of Chahine's nonlinear inversion algorithm and the Levenberg‐Marquardt nonlinear least squares method, respectively. The derived density profile is then used to infer the temperature distribution, assuming that the atmosphere is in hydrostatic equilibrium and obeys the ideal gas law. The retrieval analysis is illustrated in detail by using a SAGE II measurement event that occurred on September 15, 1987 (43.6°N, 4.1°W). An estimate of the error associated with the retrieved molecular density and temperature profiles based on the propagation of the instrument measurement error, the reference altitude error, and an assigned 10% error to the pressure at the top measurement level is also provided. The temperature profiles retrieved from the SAGE II observations are compared with near‐coincident, in both time and space, French Rayleigh lidar and NASA Wallops Flight Facility rocket datasonde soundings as well as the National Meteorological Center (NMC) data analyses. The results indicate that the mean SAGE II temperature agrees with the mean lidar measurement to within 2°C at altitudes from 30.5 to 52.5 km. The SAGE II and datasonde observations agree to within about 4°C in approximately the same altitude region. The mean temperature difference between the SAGE II and NMC analyses are, on average, about 1°, 4°, 2°, and 3°C at the standard pressure levels of 10, 5, 2, and 1 mbar, respectively.
Meteorological overview of the Arctic Boundary Layer Expedition (ABLE 3A) flight series
Authors: Shipham Mark C. , Bachmeier A. Scott , Cahoon Donald R. , Browell Edward V.
Published: February 2012

A meteorological overview of the Arctic Boundary Layer Expedition (ABLE 3A) flight series is presented. Synoptic analyses of mid‐tropospheric circulation patterns are combined with isentropic back trajectory calculations to describe the long‐range (400–3000 km) atmospheric transport mechanisms and pathways of air masses to the Arctic and sub‐Arctic regions of North America during July and August 1988. Siberia and the northern Pacific Ocean were found to be the two most likely source areas for 3‐day transport to the study areas in Alaska. Transport to the Barrow region was frequently influenced by polar vortices and associated short‐wave troughs over the Arctic Ocean, while the Bethel area was most often affected by lows migrating across the Bering Sea and the Gulf of Alaska, as well as ridges of high pressure which built into interior Alaska. July 1988 was warmer and dryer than normal over much of Alaska. As a result, the 1988 Alaska fire season was one of the most active of the past decade. Airborne lidar measurements verified the presence of biomass burning plumes on many flights, often trapped in thin subsidence layer temperature inversions. Several cases of stratosphere/troposphere exchange were noted, based upon potential vorticity analyses and aircraft lidar data, especially in the Barrow region and during transit flights to and from Alaska.
Surface ozone levels at the end of the nineteenth century in South America
Authors: Sandroni S. , Anfossi D. , Viarengo S.
Published: February 2012

Records of surface ozone data collected twice a day by means of the Schönbein method at Villa Colon, Montevideo, Uruguay, during the years 1883–1885 and at Cordoba, Argentina, during the years 1886–1892 have been converted to present‐day concentrations. Most of the uncertainties suffered from the original technique are removed by a two‐step procedure, in particular a conversion algorithm for humidity and a linear regression constructed by simultaneous readings of Schönbein and a quantitative method. The relative error of this procedure, previously applied to the Moncalieri data series, is 33%. Within these limitations we can state that one century ago the surface ozone levels at that latitude of the southern hemisphere were comparable to those of Moncalieri and Montsouris. Furthermore, the recent levels observed in remote areas at that latitude are approximately twice as large as a century ago.
Deposition of ozone to tundra
Authors: Jacob D. J. , Fan S.‐M. , Wofsy S. C. , Spiro P. A. , Bakwin P. S. , Ritter J. A. , Browell E. V. , Gregory G. L. , Fitzjarrald D. R. , Moore K. E.
Published: February 2012

Vertical turbulent fluxes of O3 were measured by eddy correlation from a 12‐m high tower erected over mixed tundra terrain (dry upland tundra, wet meadow tundra, and small lakes) in western Alaska during the Arctic Boundary Layer Expedition (ABLE 3A). The measurements were made continuously for 30 days in July‐August 1988. The mean O3 deposition flux was 1.3 × 1011 molecules cm−2 s−1. The mean O3 deposition velocity was 0.24 cm s−1 in the daytime and 0.12 cm s−1 at night. The day‐to‐night difference in deposition velocity was driven by both atmospheric stability and surface reactivity. The mean surface resistance to O3 deposition was 2.6 s cm−1 in the daytime and 3.4 s cm−1 at night. The relatively low surface resistance at night is attributed to light‐insensitive uptake of O3 at dry upland tundra surfaces (mosses, lichens). The small day‐to‐night difference in surface resistance is attributed to additional stomatal uptake by wet meadow tundra plants in the daytime. Flux measurements from the ABLE 3A aircraft flying over the tower are in agreement with the tower data. The mean O3 deposition flux to the world north of 60°N in July–August is estimated at 8.2 × 1010 molecules cm−2 s−1, comparable in magnitude to the O3 photochemical loss rate in the region derived from the ABLE 3A aircraft data. Suppression of photochemical loss by small anthropogenic inputs of nitrogen oxides could have a major effect on O3 concentrations in the summertime Arctic troposphere.
Interpretation of measurements made by the forward scattering spectrometer probe (FSSP‐300) during the Airborne Arctic Stratospheric Expedition
Authors: Baumgardner Darrel , Dye James E. , Gandrud Bruce W. , Knollenberg Robert G.
Published: February 2012

An improved forward scattering spectrometer probe, the FSSP‐300, was developed for the Airborne Arctic Stratospheric Expedition. The 300 measures particles in the size range 0.3 μm to 20 μm and has a greater sensitivity and faster time response than its predecessor, the FSSP‐100X. An intensive characterization of this probe's operating characteristics has been made and its limitations evaluated. Measurements from this probe are affected by Mie scattering ambiguities and index of refraction uncertainties, nonuniform laser intensity, uncertainties in sample volume definition, and time response roll‐off. Correction algorithms have been developed to account for some of the probe limitations. After applying these corrections, the uncertainties in number and mass concentration are on the order of 25% and 60%, respectively.
Particle size distributions in Arctic polar stratospheric clouds, growth and freezing of sulfuric acid droplets, and implications for cloud formation
Authors: Dye J. E. , Baumgardner D. , Gandrud B. W. , Kawa S. R. , Kelly K. K. , Loewenstein M. , Ferry G. V. , Chan K. R. , Gary B. L.
Published: February 2012

Particle size and volume measurements obtained with the forward scattering spectrometer probe (FSSP), model 300 during January and February 1989 in the Airborne Arctic Stratospheric Experiment are presented and used to study processes important in the formation and growth of polar stratospheric cloud (PSC) particles. Comparisons of the observations with expected sulfuric acid droplet deliquescence suggest that in the Arctic a major fraction of the sulfuric acid droplets remain liquid until temperatures at least as low as 193 K. Arguments are presented to suggest that homogeneous freezing of the sulfuric acid droplets might occur near 190 K and might play a role in the formation of PSCs. The first suggestion of nitric acid trihydrate (NAT) particles appears near saturation ratios of HNO3 with respect to NAT of 1 (about 195 K) as an enhancement, of the large particles on the tail of the sulfuric acid droplet size distribution. The major increases in number and volume indicative of the main body of the NAT cloud are not seen in these Arctic investigations until 191 to 192 K, which corresponds to an apparent saturation ratio of HNO3 with respect to NAT of about 10, unlike the Antarctic where clouds were encountered at saturation ratios near 1. A decrease in the number of particles was observed in regions in which the airmass was denitrified, i.e. NOy, the sum of all reactive nitrogen species, was reduced. This was especially true for the larger particles on the upper tail of the sulfate size distribution. The loss of these largest particles supports the idea that denitrification may be the result of the preferential nucleation and growth of NAT on only the largest sulfate particles, which then sediment out of the airmass.
Geographical distribution and seasonal variation of surface emissions and deposition velocities of atmospheric trace gases
Authors: Müller Jean‐François
Published: February 2012

The geographical distributions on the global scale of trace gas surface emission and deposition are established on the basis of a variety of technical, geographic, and climatic data. The 5° × 5° resolution maps of the sources and deposition velocities are constructed, which can be used as surface boundary conditions in a three‐dimensional chemical/transport model of the troposphere. Special attention is devoted to emissions of CO, NOx, and several nonmethane hydrocarbons (NMHC) and to the fossil fuel emissions of methane. Anthropogenic sources, i.e., the emissions produced or controlled by human activities, represent about 75% or more of the total surface emissions of CO, CH4, SOx and NOx and about two thirds of the total production of atmospheric CO (from surface sources and atmospheric oxidation of hydrocarbons). The possibility arises that methane releases from natural gas exploitation in the USSR are substantially larger than accounted for in previous studies, implying possible important consequences for the methane budget.
Comment on the transmission‐line model for computing radiation from lightning
Authors: Le Vine D. M. , Willett J. C.
Published: February 2012

The “transmission‐line” model is an approximation that is frequently used to relate the electric and magnetic fields radiated during lightning discharges to the currents that produce those fields. A principal prediction of this model is that the distant (radiation) fields are directly proportional to the current propagating along the lightning channel, multiplied by the velocity of propagation. This paper examines the derivation of this relationship and its implications in some detail. We show that the formulas commonly used to describe the transmission‐line model cannot be correctly applied to many lightning processes. A correction factor is required that is significant when the channel is not oriented perpendicular to the line of sight to the observer, unless the propagation velocity is only a small fraction of the speed of light. An important implication of this more general version of the model is that the current and velocity decouple so that they could be separately determined by suitable, multistation measurements.
Atmosphere‐surface exchange of mercury in a forest: Results of modeling and gradient approaches
Authors: Lindberg S. E. , Meyers T. P. , Taylor G. E. , Turner R. R. , Schroeder W. H.
Published: February 2012

We have modified recently published dry deposition models to estimate deposition velocities (Vd) for Hg in both fine aerosol and vapor form to forest canopy surfaces. Aerosol and total vapor phase Hg concentrations in air previously measured at Walker Branch Watershed in Tennessee have been used with model results to estimate dry deposition to a deciduous forest. The concentration data confirm that airborne Hg is dominated by vapor forms at this site and exhibits concentrations moderately above continental background levels. The modeled Vd values reflect published data which suggest that dry deposition of Hg vapor is strongly controlled by surface transport processes, notably stomatal and mesophyll resistances, the latter dominating. Weekly mean Vd values ranged from 0.006 (winter) to 0.12 (summer) cm s−1. We have also measured concentration gradients of Hg vapor in air above this forest to estimate air‐surface exchange during short‐term experiments. While the model results indicate that the canopy is a sink for Hg vapor, the concentration profiles suggest that the forest soils are a source during some periods, the combined effect of which is net Hg fluxes in the upward direction. Application of a detailed canopy turbulence model yielded soil emission rates of the order of 50 ng Hg m−2 h−1, ∼10% of which is deposited in the canopy. Our modeled dry deposition estimates plus limited measurements of wet deposition in this area suggest that dry and wet deposition may be comparable in magnitude.
Ozone precursor relationships in the ambient atmosphere
Authors: Chameides W. L. , Fehsenfeld F. , Rodgers M. O. , Cardelino C. , Martinez J. , Parrish D. , Lonneman W. , Lawson D. R. , Rasmussen R. A. , Zimmerman P. , Greenberg J. , Mlddleton P. , Wang T.
Published: February 2012

The concentrations of ozone, nitrogen oxides, and nonmethane hydrocarbons measured near the surface in a variety of urban, suburban, rural, and remote locations are analyzed and compared in order to elucidate the relationships between ozone, its photochemical precursors, and the sources of these precursors. While a large gradient is found among remote, rural, and urban/suburban nitrogen oxide concentrations, the total hydrocarbon reactivity in all continental locations is found to be comparable. Apportionment of the observed hydrocarbon species to mobile and stationary anthropogenic sources and biogenic sources suggests that present‐day emission inventories for the United States underestimate the size of mobile emissions. The analysis also suggests a significant role for biogenic hydrocarbon emissions in many urban/suburban locations and a dominant role for these sources in rural areas of the eastern United States. As one moves from remote locations to rural locations and then from rural to urban/suburban locations, ozone and nitrogen oxide concentrations tend to increase in a consistent manner while total hydrocarbon reactivity does not.
An intercomparison of surface energy flux measurement systems used during FIFE 1987
Authors: Nie D. , Kanemasu E. T. , Fritschen L. J. , Weaver H. L. , Smith E. A. , Verma S. B. , Field R. T. , Kustas W. P. , Stewart J. B.
Published: February 2012

During FIFE 1987, surface energy fluxes were measured at 22 flux sites by nine groups of scientists using different measuring systems. A rover Bowen ratio station was taken to 20 of the flux stations to serve as a reference for estimating the instrument‐related differences. The rover system was installed within a few meters from the host instrument of a site. Using linear regression analysis, net radiation, Bowen ratio, and latent heat fluxes were compared between the rover measurements and the host measurements. The average differences in net radiation, Bowen ratio, and latent heat flux from different types of instruments can be up to 10, 30, and 20%, respectively. The Didcot net radiometer gave higher net radiation while the Swissteco type showed lower values, as compared to the corrected radiation energy balance system (REBS) model. The four‐way components method and the Thornthwaite type give similar values to the REBS. The surface energy radiation balance systems type Bowen ratio systems exhibit slightly lower Bowen ratios and thus higher latent heat fluxes, compared to the arid zone evapotranspiration systems. Eddy correlation systems showed slightly lower latent heat flux in comparison to the Bowen ratio systems. It is recommended that users of the flux data take these differences into account.
Estimation of surface heat and moisture fluxes over a prairie grassland: 1. In situ energy budget measurements incorporating a cooled mirror dew point hygrometer
Authors: Smith Eric A. , Crosson William L. , Tanner Bertrand D.
Published: February 2012

This paper focuses on in situ measurements obtained during the First ISLSCP Field Experiment (FIFE) needed to support the development and validation of a biosphere model. Seasonal time series of surface flux measurements obtained from two surface radiation and energy budget stations (SREBS) used to support the FIFE surface flux measurement subprogram are analyzed. Data collection and processing procedures are presented along with the measurement analysis for the entire 1987 experimental period. The two Florida State University (FSU) stations, which were part of a 22‐station surface flux network, used a cooled mirror dew point hygrometer to measure surface layer moisture gradients. Evapotranspiration was determined using the Bowen ratio method. A case study of FIFE Golden Day 2 illustrates the capabilities of a SREBS system. Sensible and latent heat fluxes are compared among themselves and against the 22‐site domain means. The FSU site intercomparison demonstrates clear evidence of site‐to‐site differences, but a lengthy time series is required to interpret them correctly. Consistent relationships are observed between the SREBS fluxes and the all‐site means on the FIFE Golden Days. The 1987 surface flux data show variations on annual, intraseasonal, synoptic, and diurnal time scales. The annual time scale, arising from a continually changing solar declination, is evident in the available heating although cloudiness variability serves to disguise the signal until late summer. The intraseasonal time scale is observed to be a response to the large scale rainfall pattern of 1987 (alternating wet and dry conditions during the summer months resulted in daytime daily mean Bowen ratios ranging from 0.1 to 0.7, with highest values occurring during plant senescence in October). Fluxes are also modulated on a synoptic time scale (5–7 days) resulting mostly from cloudiness perturbations which have a direct impact on surface available heating. The diurnal time scale, which results from the continually changing solar zenith angle, is modulated by a variety of soil moisture and plant physiology factors but is most sensitive to the intermittent behavior of cloudiness. These characteristics of the surface fluxes emphasize the strong feedback cloud and precipitation have on virtually all aspects of the atmospheric and surface energy budgets.
Estimation of surface heat and moisture fluxes over a prairie grassland: 2. Two‐dimensional time filtering and site variability
Authors: Crosson William L. , Smith Eric A.
Published: February 2012

The behavior of in situ measurements of surface fluxes obtained during FIFE 1987 is examined by using correlative and spectral techniques in order to assess the significance of fluctuations on various time scales, from subdiurnal up to synoptic, intraseasonal, and annual scales. The objectives of this analysis are (1) to determine which temporal scales have a significant impact on areal averaged fluxes and (2) to design a procedure for filtering an extended flux time series that preserves the basic diurnal features and longer time scales while removing high frequency noise that cannot be attributed to site‐induced variation. These objectives are accomplished through the use of a two‐dimensional cross‐time Fourier transform, which serves to separate processes inherently related to diurnal and subdiurnal variability from those which impact flux variations on the longer time scales. A filtering procedure is desirable before the measurements are utilized as input with an experimental biosphere model, to insure that model based intercomparisons at multiple sites are uncontaminated by input variance not related to true site behavior. Analysis of the spectral decomposition indicates that subdiurnal time scales having periods shorter than 6 hours have little site‐to‐site consistency and therefore little impact on areal integrated fluxes. The spectral filter has thus been designed to remove these modes. Application of the filter to the 143‐day FIFE 1987 flux records results in time series that retain at least 90% of the original variance and preserve the slower diurnal and longer time scales.
The interrelationship between temperature changes in the free atmosphere and sea surface temperature changes
Authors: Newell Reginald E. , Wu Zhong‐Xiang
Published: February 2012

Fields of sea surface temperature anomalies from the Global Ocean Surface Temperature Atlas (GOSTA) and microwave sounding measurements (MSU) of temperature in the troposphere are examined separately and together for the 1979–1988 period. Global correlation patterns of both sets of fields are investigated at a range of leads and lags up to 6 months and exhibit a wide range of correlation structure. There are regions, such as the tropical eastern Pacific, where sea surface temperature anomalies persist for several months and are associated with local air temperature anomalies; in this particular example, about 0.7°C air temperature change is associated with a 1.0°C sea temperature change. By contrast, some ocean regions and many atmospheric regions, mostly in middle and high latitude, show only local spatial correlations that disappear completely in a month or two. The most persistent and extensive spatial correlation patterns are quite different for the sea and the air. In the sea the “butterfly” pattern of the Pacific is the most important and reverses sign between the eastern equatorial Pacific and the western Pacific and subtropics. In the warm phase the temperature anomalies associated with this pattern are similar to the correlation pattern. For the atmosphere the main correlation pattern is an equatorial belt with no sign changes in the tropics; this pattern is linked to the oceanic El Niño mode. In the warm phase the temperature anomalies show peak values on both sides of the equator in the eastern and central Pacific. Based mainly on the results from the spatial patterns, certain regions are selected for intercomparison of time series. In the tropical eastern Pacific the sea leads the air by about a month while in the Gulf Stream and Kuroshio regions the sequence is reversed.
A method to delineate extreme structures within airborne flux traces over the FIFE site
Authors: Duncan M. R. , Schuepp P. H.
Published: February 2012

Conditional sampling techniques are used to create a method for examining the structure within airborne flux samples collected over the FIFE site. Isolating individual structures, linked to physical transport phenomena such as eddies or thermals, reveal that a few structures within each trace are responsible for most of the flux. A statistic given the name ψ was developed to classify the “extremeness” of the contribution to the flux fraction of these structures. An examination of the gamma intermittency parameter was also conducted using these techniques. It was concluded that if the objective of the gamma parameter is to measure the percentage of a flux trace occupied by a thermal, then a more restrictive definition of a thermal must be used. The establishment of such a definition is aided by quadrant analysis techniques.
Stratospheric clouds at South Pole during 1988 2. Their evolution in relation to atmospheric structure and composition
Authors: Fuà Daniele , Cacciani Marco , Di Girolamo Paolo , Fiocco Giorgio , Di Sarra Alcide
Published: February 2012

A lidar was installed at the Amundsen‐Scott South Pole Station in the austral summer 1987–1988: aerosol layers, generically identified as polar stratospheric clouds, were frequently observed in the period May–October 1988 through the altitude range 8–20 km. On the basis of previous work (Fiocco et al., 1991) the behavior of the aerosol backscattering cross section Ba has been related to the temperature T through linear fits between the two variables (Fiocco et al., this issue). The resulting coefficients, namely the slope b = dBa/dT and Tf, the temperature at which the onset of condensation occurs, help to classify these clouds as Type I or II, in view of the thermodynamic properties of the condensing species. A strong dependence of Ba on T, represented by a large value of b, is interpreted as evidence of ice condensation and leads us to identify the cloud as Type II, while a lower value of b, characteristic of diffuse structures, is taken as evidence for Type I clouds, composed of nitric acid trihydrate. The evolution of these features is reported. Type II clouds, appearing as sharp layers of moderate vertical extent, are almost always present in the interval from June to early September. The temperature at the base of the lowest layer spans an initial value around 198 K to a final value in September around 196 K, with a corresponding height value from around 13.5 km to 10.5 km. Layers that we identify as Type I clouds appeared at higher temperatures with an onset at the beginning of the season around 200 K to a final value at mid‐October around 203 K.